NASA Astrophysics Data System (ADS)
Haas, Fernando
2016-11-01
A didactic and systematic derivation of Noether point symmetries and conserved currents is put forward in special relativistic field theories, without a priori assumptions about the transformation laws. Given the Lagrangian density, the invariance condition develops as a set of partial differential equations determining the symmetry transformation. The solution is provided in the case of real scalar, complex scalar, free electromagnetic, and charged electromagnetic fields. Besides the usual conservation laws, a less popular symmetry is analyzed: the symmetry associated with the linear superposition of solutions, whenever applicable. The role of gauge invariance is emphasized. The case of the charged scalar particle under external electromagnetic fields is considered, and the accompanying Noether point symmetries determined. Noether point symmetries for a dynamical system in extended gravity cosmology are also deduced.
Relativistic gravity gradiometry
NASA Astrophysics Data System (ADS)
Bini, Donato; Mashhoon, Bahram
2016-12-01
In general relativity, relativistic gravity gradiometry involves the measurement of the relativistic tidal matrix, which is theoretically obtained from the projection of the Riemann curvature tensor onto the orthonormal tetrad frame of an observer. The observer's 4-velocity vector defines its local temporal axis and its local spatial frame is defined by a set of three orthonormal nonrotating gyro directions. The general tidal matrix for the timelike geodesics of Kerr spacetime has been calculated by Marck [Proc. R. Soc. A 385, 431 (1983)]. We are interested in the measured components of the curvature tensor along the inclined "circular" geodesic orbit of a test mass about a slowly rotating astronomical object of mass M and angular momentum J . Therefore, we specialize Marck's results to such a "circular" orbit that is tilted with respect to the equatorial plane of the Kerr source. To linear order in J , we recover the gravitomagnetic beating phenomenon [B. Mashhoon and D. S. Theiss, Phys. Rev. Lett. 49, 1542 (1982)], where the beat frequency is the frequency of geodetic precession. The beat effect shows up as a special long-period gravitomagnetic part of the relativistic tidal matrix; moreover, the effect's short-term manifestations are contained in certain post-Newtonian secular terms. The physical interpretation of this effect is briefly discussed.
NASA Astrophysics Data System (ADS)
Parker, Edward
2017-08-01
A nonrelativistic particle released from rest at the edge of a ball of uniform charge density or mass density oscillates with simple harmonic motion. We consider the relativistic generalizations of these situations where the particle can attain speeds arbitrarily close to the speed of light; generalizing the electrostatic and gravitational cases requires special and general relativity, respectively. We find exact closed-form relations between the position, proper time, and coordinate time in both cases, and find that they are no longer harmonic, with oscillation periods that depend on the amplitude. In the highly relativistic limit of both cases, the particle spends almost all of its proper time near the turning points, but almost all of the coordinate time moving through the bulk of the ball. Buchdahl's theorem imposes nontrivial constraints on the general-relativistic case, as a ball of given density can only attain a finite maximum radius before collapsing into a black hole. This article is intended to be pedagogical, and should be accessible to those who have taken an undergraduate course in general relativity.
Non-relativistic Limit of Dirac Equations in Gravitational Field and Quantum Effects of Gravity
NASA Astrophysics Data System (ADS)
Wu, Ning
2006-03-01
Based on unified theory of electromagnetic interactions and gravitational interactions, the non-relativistic limit of the equation of motion of a charged Dirac particle in gravitational field is studied. From the Schrödinger equation obtained from this non-relativistic limit, we can see that the classical Newtonian gravitational potential appears as a part of the potential in the Schrödinger equation, which can explain the gravitational phase effects found in COW experiments. And because of this Newtonian gravitational potential, a quantum particle in the earth's gravitational field may form a gravitationally bound quantized state, which has already been detected in experiments. Three different kinds of phase effects related to gravitational interactions are studied in this paper, and these phase effects should be observable in some astrophysical processes. Besides, there exists direct coupling between gravitomagnetic field and quantum spin, and radiation caused by this coupling can be used to directly determine the gravitomagnetic field on the surface of a star.
Compact objects in relativistic theories of gravity
NASA Astrophysics Data System (ADS)
Okada da Silva, Hector
2017-05-01
In this dissertation we discuss several aspects of compact objects, i.e. neutron stars and black holes, in relativistic theories of gravity. We start by studying the role of nuclear physics (encoded in the so-called equation of state) in determining the properties of neutron stars in general relativity. We show that low-mass neutron stars are potentially useful astrophysical laboratories that can be used to constrain the properties of the equation of state. More specifically, we show that various bulk properties of these objects, such as their quadrupole moment and tidal deformability, are tightly correlated. Next, we develop a formalism that aims to capture how generic modifications from general relativity affect the structure of neutron stars, as predicted by a broad class of gravity theories, in the spirit of the parametrized post-Newtonian formalism (PPN). Our "post-Tolman-Oppenheimer-Volkoff" formalism provides a toolbox to study both stellar structure and the interior/exterior geometries of static, spherically symmetric relativistic stars. We also apply the formalism to parametrize deviations from general relativity in various astrophysical observables related with neutron stars, including surface redshift, apparent radius, Eddington luminosity. We then turn our attention to what is arguably the most well-motivated and well-investigated generalization of general relativity: scalar-tensor theory. We start by considering theories where gravity is mediated by a single extra scalar degree of freedom (in addition to the metric tensor). An interesting class of scalar-tensor theories passes all experimental tests in the weak-field regime of gravity, yet considerably deviates from general relativity in the strong-field regime in the presence of matter. A common assumption in modeling neutron stars is that the pressure within these object is spatially isotropic. We relax this assumption and examine how pressure anisotropy affects the mass, radius and moment of inertia
NASA Astrophysics Data System (ADS)
Pucacco, Giuseppe; Lucchesi, David; Anselmo, Luciano; Bassan, Massimo; Magnafico, Carmelo; Pardini, Carmen; Peron, Roberto; Stanga, Ruggero; Visco, Massimo
2017-04-01
The importance of General Relativity (GR) for space geodesy — and for geodesy in general — is well known since several decades and it has been confirmed by a number of very significant results. For instance, GR plays a fundamental role for the following very notable techniques: Satellite-and-Lunar Laser Ranging (SLR/LLR), Very Long Baseline Interferometry (VLBI), Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS), and Global Navigation Satellite Systems (GNSS). Each of these techniques is intimately and closely related with both GR and geodesy, i.e. they are linked in a loop where benefits in one field provide positive improvements in the other ones. A common ingredient for a suitable and reliable use of each of these techniques is represented by the knowledge of the Earth's gravitational field, both in its static and temporal dependence. Spaceborne gravimetry, with the inclusion of accelerometers and gradiometers on board dedicated satellites, together with microwave links between satellites and GPS measurements, have allowed a huge improvement in the determination of the Earth's geopotential during the last 15 years. In the near future, further improvements are expected in this knowledge thanks to the inclusion of laser inter-satellite link and the possibility to compare frequency and atomic standards by a direct use of atomic clocks, both on the Earth's surface and in space. Such results will be also important for the possibility to further improve the GR tests and measurements in the field of the Earth with laser-ranged satellites in order to compare the predictions of Einstein's theory with those of other (proposed) relativistic theories for the interpretation of the gravitational interaction. Within the present paper we describe the state of the art of such measurements with geodetic satellites, as the two LAGEOS and LARES, and we discuss the effective impact of the systematic errors of gravitational origin on the measurement of
Feeling Gravity's Pull: Gravity Modeling. The Gravity Field of Mars
NASA Technical Reports Server (NTRS)
Lemoine, Frank; Smith, David; Rowlands, David; Zuber, Maria; Neumann, G.; Chinn, Douglas; Pavlis, D.
2000-01-01
Most people take the constant presence of gravitys pull for granted. However, the Earth's gravitational strength actually varies from location to location. This variation occurs because mass, which influences an object's gravitational pull, is not evenly distributed within the planet. Changes in topography, such as glacial movement, an earthquake, or a rise in the ocean level, can subtly affect the gravity field. An accurate measurement of the Earth's gravity field helps us understand the distribution of mass beneath the surface. This insight can assist us in locating petroleum, mineral deposits, ground water, and other valuable substances. Gravity mapping can also help notice or verify changes in sea surface height and other ocean characteristics. Such changes may indicate climate change from polar ice melting and other phenomena. In addition, gravity mapping can indicate how land moves under the surface after earthquakes and other plate tectonic processes. Finally, changes in the Earth's gravity field might indicate a shift in water distribution that could affect agriculture, water supplies for population centers, and long-term weather prediction. Scientists can map out the Earth's gravity field by watching satellite orbits. When a satellite shifts in vertical position, it might be passing over an area where gravity changes in strength. Gravity is only one factor that may shape a satellite's orbital path. To derive a gravity measurement from satellite movement, scientists must remove other factors that might affect a satellite's position: 1. Drag from atmospheric friction. 2. Pressure from solar radiation as it heads toward Earth and. as it is reflected off the surface of the Earth 3. Gravitational pull from the Sun, the Moon, and other planets in the Solar System. 4. The effect of tides. 5. Relativistic effects. Scientists must also correct for the satellite tracking process. For example, the tracking signal must be corrected for refraction through the
(abstract) Venus Gravity Field
NASA Technical Reports Server (NTRS)
Konopliv, A. S.; Sjogren, W. L.
1995-01-01
A global gravity field model of Venus to degree and order 75 (5772 spherical harmonic coefficients) has been estimated from Doppler radio tracking of the orbiting spacecraft Pioneer Venus Orbiter (1979-1992) and Magellan (1990-1994). After the successful aerobraking of Magellan, a near circular polar orbit was attained and relatively uniform gravity field resolution (approximately 200 km) was obtained with formal uncertainties of a few milligals. Detailed gravity for several highland features are displayed as gravity contours overlaying colored topography. The positive correlation of typography with gravity is very high being unlike that of the Earth, Moon, and Mars. The amplitudes are Earth-like, but have significantly different gravity-topography ratios for different features. Global gravity, geoid, and isostatic anomaly maps as well as the admittance function are displayed.
Testing relativistic theories of gravity with spacecraft-Doppler gravity-wave detection
NASA Technical Reports Server (NTRS)
Hellings, R. W.
1978-01-01
The response of a spacecraft Doppler-tracking system to the passage of a weak plane gravity wave of the most general polarization is calculated. Results show that the simultaneous tracking of several spacecraft could provide an unambiguous determination of the gravity-wave polarization, a much needed result in the continuing experimental testing of relativistic theories of gravity.
Rotating black hole solutions in relativistic analogue gravity
NASA Astrophysics Data System (ADS)
Giacomelli, Luca; Liberati, Stefano
2017-09-01
Simulation and experimental realization of acoustic black holes in analogue gravity systems have lead to a novel understanding of relevant phenomena such as Hawking radiation or superradiance. We explore here the possibility of using relativistic systems for simulating rotating black hole solutions and possibly get an acoustic analogue of a Kerr black hole. In doing so, we demonstrate a precise relation between nonrelativistic and relativistic solutions and provide a new class of vortex solutions for relativistic systems. Such solutions might be used in the future as a test bed in numerical simulations as well as concrete experiments.
Existence of relativistic stars in f(R) gravity
Upadhye, Amol; Hu, Wayne
2009-09-15
We refute recent claims in the literature that stars with relativistically deep potentials cannot exist in f(R) gravity. Numerical examples of stable stars, including relativistic (GM{sub *}/r{sub *}{approx}0.1), constant density stars, are studied. As a star is made larger, nonlinear 'chameleon' effects screen much of the star's mass, stabilizing gravity at the stellar center. Furthermore, we show that the onset of this chameleon screening is unrelated to strong gravity. At large central pressures P>{rho}/3, f(R) gravity, like general relativity, does have a maximum gravitational potential, but at a slightly smaller value: GM{sub *}/r{sub *}|{sub max}=0.345<4/9 for constant density and one choice of parameters. This difference is associated with negative central curvature R under general relativity not being accessed in the f(R) model, but does not apply to any known astrophysical object.
NASA Astrophysics Data System (ADS)
Burla, Santoshkumar; Mueller, Vitali; Flury, Jakob; Jovanovic, Nemanja
2016-04-01
CHAMP, GRACE and GOCE missions have been successful in the field of satellite geodesy (especially to improve Earth's gravity field models) and have established the necessity towards the next generation gravity field missions. Especially, GRACE has shown its capabilities beyond any other gravity field missions. GRACE Follow-On mission is going to continue GRACE's legacy which is almost identical to GRACE mission with addition of laser interferometry. But these missions are not only quite expensive but also takes quite an effort to plan and to execute. Still there are few drawbacks such as under-sampling and incapability of exploring new ideas within a single mission (ex: to perform different orbit configurations with multi satellite mission(s) at different altitudes). The budget is the major limiting factor to build multi satellite mission(s). Here, we offer a solution to overcome these drawbacks using cubesat/ nanosatellite mission. Cubesats are widely used in research because they are cheaper, smaller in size and building them is easy and faster than bigger satellites. Here, we design a 3D model of GRACE like mission with available sensors and explain how the Attitude and Orbit Control System (AOCS) works. The expected accuracies on final results of gravity field are also explained here.
Momentum and charge transport in non-relativistic holographic fluids from Hořava gravity
NASA Astrophysics Data System (ADS)
Davison, Richard A.; Grozdanov, Sašo; Janiszewski, Stefan; Kaminski, Matthias
2016-11-01
We study the linearized transport of transverse momentum and charge in a conjectured field theory dual to a black brane solution of Hořava gravity with Lifshitz exponent z = 1. As expected from general hydrodynamic reasoning, we find that both of these quantities are diffusive over distance and time scales larger than the inverse temperature. We compute the diffusion constants and conductivities of transverse momentum and charge, as well the ratio of shear viscosity to entropy density, and find that they differ from their relativistic counterparts. To derive these results, we propose how the holographic dictionary should be modified to deal with the multiple horizons and differing propagation speeds of bulk excitations in Hořava gravity. When possible, as a check on our methods and results, we use the covariant Einstein-Aether formulation of Hořava gravity, along with field redefinitions, to re-derive our results from a relativistic bulk theory.
Test of Relativistic Gravity for Propulsion at the Large Hadron Collider
NASA Astrophysics Data System (ADS)
Felber, Franklin
2010-01-01
A design is presented of a laboratory experiment that could test the suitability of relativistic gravity for propulsion of spacecraft to relativistic speeds. An exact time-dependent solution of Einstein's gravitational field equation confirms that even the weak field of a mass moving at relativistic speeds could serve as a driver to accelerate a much lighter payload from rest to a good fraction of the speed of light. The time-dependent field of ultrarelativistic particles in a collider ring is calculated. An experiment is proposed as the first test of the predictions of general relativity in the ultrarelativistic limit by measuring the repulsive gravitational field of bunches of protons in the Large Hadron Collider (LHC). The estimated `antigravity beam' signal strength at a resonant detector of each proton bunch is 3 nm/s2 for 2 ns during each revolution of the LHC. This experiment can be performed off-line, without interfering with the normal operations of the LHC.
Vector-tensor nature of Bekenstein's relativistic theory of modified gravity
Zlosnik, T. G.; Ferreira, P. G.; Starkman, Glenn D.
2006-08-15
Bekenstein's theory of relativistic gravity is conventionally written as a bimetric theory. The two metrics are related by a disformal transformation defined by a dynamical vector field and a scalar field. In this paper we show that the theory can be rewritten as vector-tensor theory akin to Einstein-Aether theories with noncanonical kinetic terms. We discuss some of the implications of this equivalence.
MOND as the weak field limit of an extended metric theory of gravity with torsion
NASA Astrophysics Data System (ADS)
Barrientos, E.; Mendoza, S.
2017-08-01
In this article we construct a relativistic extended metric theory of gravity, for which its weak field limit reduces to the non-relativistic MOdified Newtonian Dynamics regime of gravity. The theory is fully covariant and local. The way to achieve this is by introducing torsion in the description of gravity as well as with the addition of a particular function of the matter Lagrangian into the gravitational action.
Group field theory for quantum gravity minimally coupled to a scalar field
NASA Astrophysics Data System (ADS)
Li, Yang; Oriti, Daniele; Zhang, Mingyi
2017-10-01
We construct a group field theory model for quantum gravity minimally coupled to relativistic scalar fields, defining as well a corresponding discrete gravity path integral (and, implicitly, a coupled spin foam model) in its Feynman expansion. We also analyze a number of variations of the same model, the corresponding discrete gravity path integrals, its generalization to the coupling of multiple scalar fields and discuss its possible applications to the extraction of effective cosmological dynamics from the full quantum gravity formalism, in the context of group field theory condensate cosmology.
Gauging the Carroll algebra and ultra-relativistic gravity
NASA Astrophysics Data System (ADS)
Hartong, Jelle
2015-08-01
It is well known that the geometrical framework of Riemannian geometry that underlies general relativity and its torsionful extension to Riemann-Cartan geometry can be obtained from a procedure known as gauging the Poincaré algebra. Recently it has been shown that gauging the centrally extended Galilei algebra, known as the Bargmann algebra, leads to a geometrical framework that when made dynamical gives rise to Hořava-Lifshitz gravity. Here we consider the case where we contract the Poincaré algebra by sending the speed of light to zero leading to the Carroll algebra. We show how this algebra can be gauged and we construct the most general affine connection leading to the geometry of so-called Carrollian space-times. Carrollian space-times appear for example as the geometry on null hypersurfaces in a Lorentzian space-time of one dimension higher. We also construct theories of ultra-relativistic (Carrollian) gravity in 2+1 dimensions with dynamical exponent z < 1 including cases that have anisotropic Weyl invariance for z = 0.
Weak-field general relativistic dynamics and the Newtonian limit
NASA Astrophysics Data System (ADS)
Cooperstock, F. I.
2016-01-01
We show that the generally held view that the gravity of weak-field nonrelativistic-velocity sources being invariably almost equivalent to Newtonian gravity (NG) (the “Newtonian limit” approach) is in some instances misleading and in other cases incorrect. A particularly transparent example is provided by comparing the Newtonian and general relativistic analyses of a simple variant of van Stockum’s infinite rotating dust cylinder. We show that some very recent criticisms of our work that had been motivated by the Newtonian limit approach were incorrect and note that no specific errors in our work were found in the critique. In the process, we underline some problems that arise from inappropriate coordinate transformations. As further support for our methodology, we note that our weak-field general relativistic treatment of a model galaxy was vindicated recently by the observations of Xu et al. regarding our prediction that the Milky Way was 19-21 kpc in radius as opposed to the commonly held view that the radius was 15 kpc.
Lucchesi, David M; Peron, Roberto
2010-12-03
The pericenter shift of a binary system represents a suitable observable to test for possible deviations from the newtonian inverse-square law in favor of new weak interactions between macroscopic objects. We analyzed 13 years of tracking data of the LAGEOS satellites with GEODYN II software but with no models for general relativity. From the fit of LAGEOS II pericenter residuals we have been able to obtain a 99.8% agreement with the predictions of Einstein's theory. This result may be considered as a 99.8% measurement in the field of the Earth of the combination of the γ and β parameters of general relativity, and it may be used to constrain possible deviations from the inverse-square law in favor of new weak interactions parametrized by a Yukawa-like potential with strength α and range λ. We obtained |α| ≲ 1 × 10(-11), a huge improvement at a range of about 1 Earth radius.
Relativistic electron in curved magnetic fields
NASA Technical Reports Server (NTRS)
An, S.
1985-01-01
Making use of the perturbation method based on the nonlinear differential equation theory, the author investigates the classical motion of a relativistic electron in a class of curved magnetic fields which may be written as B=B(O,B sub phi, O) in cylindrical coordinates (R. phi, Z). Under general astrophysical conditions the author derives the analytical expressions of the motion orbit, pitch angle, etc., of the electron in their dependence upon parameters characterizing the magnetic field and electron. The effects of non-zero curvature of magnetic field lines on the motion of electrons and applicabilities of these results to astrophysics are also discussed.
PREFACE: 2nd International Symposium on the Modern Physics of Compact Stars and Relativistic Gravity
NASA Astrophysics Data System (ADS)
Edvard Chubaryan, Professor; Aram Saharian, Professor; Armen Sedrakian, Professor
2014-03-01
The international conference ''The Modern Physics of Compact Stars and Relativistic Gravity'' took place in Yerevan, Armenia, from 18-21 September 2013. This was the second in a series of conferences which aim to bring together people working in astrophysics of compact stars, physics of dense matter, gravitation and cosmology, observations of pulsars and binary neutron stars and related fields. The conference was held on the occasion of 100th birthday of the founder of the Theoretical Physics Chair at the Department of Physics of Yerevan State University and prominent Armenian scientist Academician Gurgen S Sahakyan. The field of compact stars has seen extraordinary development since the discovery of pulsars in 1967. Even before this discovery, pioneering work of a number of theoretical groups had laid the foundation for this development. A pioneer of this effort was Professor G S Sahakyan who, together with Professor Victor Ambartsumyan and a group of young scientists, started in the early sixties their fundamental work on the properties of superdense matter and on the relativistic structure of compact stellar objects. This conference explored the vast diversity of the manifestations of compact stars, including the modern aspects of the equation of state of superdense matter, its magnetic and thermal properties, rotational dynamics, superfluidity and superconductivity, phase transition from hadronic to quark matter, etc. The articles on these subjects collected in this volume are evidence of liveliness of the field and of the continuous feedback between theory and the experiment. A part of this volume is devoted to the cosmology and the theories of gravity — the subfields of astrophysics that are of fundamental importance to our understanding of the universe. The reader will find here articles touching on the most diverse aspects of these fields such as modern problems in Einstein's classical theory of gravity and its alternatives, string theory motivated
NASA Astrophysics Data System (ADS)
Goon, Garrett
2017-01-01
We study the effects of heavy fields on 4D spacetimes with flat, de Sitter and anti-de Sitter asymptotics. At low energies, matter generates specific, calculable higher derivative corrections to the GR action which perturbatively alter the Schwarzschild-( A) dS family of solutions. The effects of massive scalars, Dirac spinors and gauge fields are each considered. The six-derivative operators they produce, such as ˜ R 3 terms, generate the leading corrections. The induced changes to horizon radii, Hawking temperatures and entropies are found. Modifications to the energy of large AdS black holes are derived by imposing the first law. An explicit demonstration of the replica trick is provided, as it is used to derive black hole and cosmological horizon entropies. Considering entropy bounds, it's found that scalars and fermions increase the entropy one can store inside a region bounded by a sphere of fixed size, but vectors lead to a decrease, oddly. We also demonstrate, however, that many of the corrections fall below the resolving power of the effective field theory and are therefore untrustworthy. Defining properties of black holes, such as the horizon area and Hawking temperature, prove to be remarkably robust against higher derivative gravitational corrections.
Relativistic thermal plasmas - Effects of magnetic fields
NASA Technical Reports Server (NTRS)
Araki, S.; Lightman, A. P.
1983-01-01
Processes and equilibria in finite, relativistic, thermal plasmas are investigated, taking into account electron-positron creation and annihilation, photon production by internal processes, and photon production by a magnetic field. Inclusion of the latter extends previous work on such plasmas. The basic relations for thermal, Comptonized synchrotron emission are analyzed, including emission and absorption without Comptonization, Comptonized thermal synchrotron emission, and the Comptonized synchrotron and bremsstrahlung luminosities. Pair equilibria are calculated, including approximations and dimensionless parameters, the pair balance equation, maximum temperatures and field strengths, and individual models and cooling curves.
Progress in the Determination of the Earth's Gravity Field
NASA Technical Reports Server (NTRS)
Rapp, Richard H. (Editor)
1989-01-01
Topics addressed include: global gravity model development; methods for approximation of the gravity field; gravity field measuring techniques; global gravity field applications and requirements in geophysics and oceanography; and future gravity missions.
Years of Testing Relativistic Gravity: Where Do We Go from Here?
NASA Astrophysics Data System (ADS)
Turyshev, Slava G.; Williams, James G.; Nordtvedt, Kenneth Jr.; Shao, Michael; Murphy, Thomas W. Jr.
This paper addresses the motivation, technology and recent results in the tests of the general theory of relativity in the solar system. We specifically discuss Lunar Laser Ranging (LLR), the only technique available to test the Strong Equivalence Principle (SEP) and presently the most accurate method to test for the constancy of the gravitational constant G. After almost 35 years since beginning of the experiment, LLR is poised to take a dramatic step forward by proceeding from cm to mm range accuracies enabled by the new Apache Point Observatory Lunar Laser-ranging Operation (APOLLO) currently under development in New Mexico. This facility will enable tests of the Weak and Strong Equivalence Principles with a sensitivity approaching 10 14, translating to a test of the SEP violation parameter, , to a precision of ~ 3× 10 5. In addition, the v2/c2 general relativistic effects would be tested to better than 0.1%, and measurements of the relative change in the gravitational constant, , would be ~0.1% the inverse age of the universe.
Chameleon scalar fields in relativistic gravitational backgrounds
Tsujikawa, Shinji; Tamaki, Takashi; Tavakol, Reza E-mail: tamaki@gravity.phys.waseda.ac.jp
2009-05-15
We study the field profile of a scalar field {phi} that couples to a matter fluid (dubbed a chameleon field) in the relativistic gravitational background of a spherically symmetric spacetime. Employing a linear expansion in terms of the gravitational potential {Phi}{sub c} at the surface of a compact object with a constant density, we derive the thin-shell field profile both inside and outside the object, as well as the resulting effective coupling with matter, analytically. We also carry out numerical simulations for the class of inverse power-law potentials V({phi}) = M{sup 4+n}{phi}{sup -n} by employing the information provided by our analytical solutions to set the boundary conditions around the centre of the object and show that thin-shell solutions in fact exist if the gravitational potential {Phi}{sub c} is smaller than 0.3, which marginally covers the case of neutron stars. Thus the chameleon mechanism is present in the relativistic gravitational backgrounds, capable of reducing the effective coupling. Since thin-shell solutions are sensitive to the choice of boundary conditions, our analytic field profile is very helpful to provide appropriate boundary conditions for {Phi}{sub c}{approx}
General Relativistic Theory of the VLBI Time Delay in the Gravitational Field of Moving Bodies
NASA Technical Reports Server (NTRS)
Kopeikin, Sergei
2003-01-01
The general relativistic theory of the gravitational VLBI experiment conducted on September 8, 2002 by Fomalont and Kopeikin is explained. Equations of radio waves (light) propagating from the quasar to the observer are integrated in the time-dependent gravitational field of the solar system by making use of either retarded or advanced solutions of the Einstein field equations. This mathematical technique separates explicitly the effects associated with the propagation of gravity from those associated with light in the integral expression for the relativistic VLBI time delay of light. We prove that the relativistic correction to the Shapiro time delay, discovered by Kopeikin (ApJ, 556, L1, 2001), changes sign if one retains direction of the light propagation but replaces the retarded for the advanced solution of the Einstein equations. Hence, this correction is associated with the propagation of gravity. The VLBI observation measured its speed, and that the retarded solution is the correct one.
Gravity field information from Gravity Probe-B
NASA Technical Reports Server (NTRS)
Smith, D. E.; Lerch, F. J.; Colombo, O. L.; Everitt, C. W. F.
1989-01-01
The Gravity Probe-B Mission will carry the Stanford Gyroscope relativity experiment into orbit in the mid 1990's, as well as a Global Positioning System (GPS) receiver whose tracking data will be used to study the earth gravity field. Estimates of the likely quality of a gravity field model to be derived from the GPS data are presented, and the significance of this experiment to geodesy and geophysics are discussed.
Magnetic Field Structure in Relativistic Jets
NASA Astrophysics Data System (ADS)
Jermak, Helen; Mundell, Carole; Steele, Iain; Harrison, Richard; Kobayashi, Shiho; Lindfors, Elina; Nilsson, Kari; Barres de Almeida, Ulisses
2013-12-01
Relativistic jets are ubiquitous when considering an accreting black hole. Two of the most extreme examples of these systems are blazars and gamma-ray bursts (GRBs), the jets of which are thought to be threaded with a magnetic field of unknown structure. The systems are made up of a black hole accreting matter and producing, as a result, relativistic jets of plasma from the poles of the black hole. Both systems are viewed as point sources from Earth, making it impossible to spatially resolve the jet. In order to explore the structure of the magnetic field within the jet we take polarisation measurements with the RINGO polarimeters on the world's largest fully autonomous, robotic optical telescope: The Liverpool Telescope. Using the polarisation degree and angle measured by the RINGO polarimeters it is possible to distinguish between global magnetic fields created in the central engine and random tangled magnetic fields produced locally in shocks. We also monitor blazar sources regularly during quiescence with periods of flaring monitored more intensively. Reported here are the early polarisation results for GRBs 060418 and 090102, along with future prospects for the Liverpool Telescope and the RINGO polarimeters.
The facets of relativistic quantum field theory
NASA Astrophysics Data System (ADS)
Dosch, H. G.; Müller, V. F.
2011-04-01
Relativistic quantum field theory is generally recognized to form the adequate theoretical frame for subatomic physics, with the Standard Model of Particle Physics as a major achievement. We point out that quantum field theory in its present form is not a monolithic theory, but rather consists of distinct facets, which aim at a common ideal goal. We give a short overview of the strengths and limitations of these facets. We emphasize the theory-dependent relation between the quantum fields, and the basic objects in the empirical domain, the particles. Given the marked conceptual differences between the facets, we argue to view these, and therefore also the Standard Model, as symbolic constructions. We finally note that this view of physical theories originated in the 19th century and is related to the emergence of the classical field as an autonomous concept.
Relativistic mean field description of cluster radioactivity
NASA Astrophysics Data System (ADS)
Bhagwat, A.; Gambhir, Y. K.
2005-01-01
Comprehensive investigations of the observed cluster radioactivity are carried out. First, the relativistic mean field (RMF) theory is employed for the calculations of the ground-state properties of relevant nuclei. The calculations reproduce the experiment well. The calculated RMF point densities are folded with the density-dependent M3Y nucleon-nucleon interaction to obtain the cluster-daughter interaction potential. This, along with the calculated and experimental Q values, is used in the WKB approximation for estimating the half-lives of the parent nuclei against cluster decay. The calculations qualitatively agree with the experiment. Sensitive dependence of the half-lives on Q values is explicitly demonstrated.
Gravity quantized: Loop quantum gravity with a scalar field
Domagala, Marcin; Kaminski, Wojciech; Giesel, Kristina; Lewandowski, Jerzy
2010-11-15
...''but we do not have quantum gravity.'' This phrase is often used when analysis of a physical problem enters the regime in which quantum gravity effects should be taken into account. In fact, there are several models of the gravitational field coupled to (scalar) fields for which the quantization procedure can be completed using loop quantum gravity techniques. The model we present in this paper consists of the gravitational field coupled to a scalar field. The result has similar structure to the loop quantum cosmology models, except that it involves all the local degrees of freedom of the gravitational field because no symmetry reduction has been performed at the classical level.
Relativistic Lagrangian displacement field and tensor perturbations
NASA Astrophysics Data System (ADS)
Rampf, Cornelius; Wiegand, Alexander
2014-12-01
We investigate the purely spatial Lagrangian coordinate transformation from the Lagrangian to the basic Eulerian frame. We demonstrate three techniques for extracting the relativistic displacement field from a given solution in the Lagrangian frame. These techniques are (a) from defining a local set of Eulerian coordinates embedded into the Lagrangian frame; (b) from performing a specific gauge transformation; and (c) from a fully nonperturbative approach based on the Arnowitt-Deser-Misner (ADM) split. The latter approach shows that this decomposition is not tied to a specific perturbative formulation for the solution of the Einstein equations. Rather, it can be defined at the level of the nonperturbative coordinate change from the Lagrangian to the Eulerian description. Studying such different techniques is useful because it allows us to compare and develop further the various approximation techniques available in the Lagrangian formulation. We find that one has to solve the gravitational wave equation in the relativistic analysis, otherwise the corresponding Newtonian limit will necessarily contain spurious nonpropagating tensor artifacts at second order in the Eulerian frame. We also derive the magnetic part of the Weyl tensor in the Lagrangian frame, and find that it is not only excited by gravitational waves but also by tensor perturbations which are induced through the nonlinear frame dragging. We apply our findings to calculate for the first time the relativistic displacement field, up to second order, for a Λ CDM Universe in the presence of a local primordial non-Gaussian component. Finally, we also comment on recent claims about whether mass conservation in the Lagrangian frame is violated.
Interplanetary Magnetic Field Guiding Relativistic Particles
NASA Technical Reports Server (NTRS)
Masson, S.; Demoulin, P.; Dasso, S.; Klein, K. L.
2011-01-01
The origin and the propagation of relativistic solar particles (0.5 to few Ge V) in the interplanetary medium remains a debated topic. These relativistic particles, detected at the Earth by neutron monitors have been previously accelerated close to the Sun and are guided by the interplanetary magnetic field (IMF) lines, connecting the acceleration site and the Earth. Usually, the nominal Parker spiral is considered for ensuring the magnetic connection to the Earth. However, in most GLEs the IMF is highly disturbed, and the active regions associated to the GLEs are not always located close to the solar footprint of the nominal Parker spiral. A possible explanation is that relativistic particles are propagating in transient magnetic structures, such as Interplanetary Coronal Mass Ejections (ICMEs). In order to check this interpretation, we studied in detail the interplanetary medium where the particles propagate for 10 GLEs of the last solar cycle. Using the magnetic field and the plasma parameter measurements (ACE/MAG and ACE/SWEPAM), we found widely different IMF configurations. In an independent approach we develop and apply an improved method of the velocity dispersion analysis to energetic protons measured by SoHO/ERNE. We determined the effective path length and the solar release time of protons from these data and also combined them with the neutron monitor data. We found that in most of the GLEs, protons propagate in transient magnetic structures. Moreover, the comparison between the interplanetary magnetic structure and the interplanetary length suggest that the timing of particle arrival at Earth is dominantly determined by the type of IMF in which high energetic particles are propagating. Finally we find that these energetic protons are not significantly scattered during their transport to Earth.
RELATIVISTIC TWO-FLUID SIMULATIONS OF GUIDE FIELD MAGNETIC RECONNECTION
Zenitani, Seiji; Hesse, Michael; Klimas, Alex
2009-11-01
The nonlinear evolution of relativistic magnetic reconnection in sheared magnetic configuration (with a guide field) is investigated by using two-dimensional relativistic two-fluid simulations. Relativistic guide field reconnection features the charge separation and the guide field compression in and around the outflow channel. As the guide field increases, the composition of the outgoing energy changes from enthalpy-dominated to Poynting-dominated. The inertial effects of the two-fluid model play an important role to sustain magnetic reconnection. Implications for the single-fluid magnetohydrodynamic approach and the physics models of relativistic reconnection are briefly addressed.
Magnetic Fields In Relativistic Collisionless Shocks
NASA Astrophysics Data System (ADS)
Santana, Rodolfo; Barniol Duran, R.; Kumar, P.
2013-01-01
We present a systematic study on magnetic fields in Gamma-Ray Burst (GRB) relativistic shocks by making use of X-ray and optical afterglow observations, mostly coming from the Swift satellite. We use two methods to constrain the afterglow parameter epsilon_B (the fraction of energy in the magnetic field in the shocked plasma): 1. For the X-ray sample, the observed flux at the end of the X-ray steep decline is larger than or equal to the flux from the external-forward shock. 2. The observed optical afterglow flux arises from the external-forward shock emission. From the method for our X-ray sample (60 GRBs), we determine an upper limit on epsilon_B and from the method for our optical sample (35 GRBs), we determine a measurement for epsilon_B. Combining our X-ray and optical results, the median value we found for epsilon_B is ~ 10^-5. The distributions of epsilon_B from our X-ray and optical samples showed a wide distribution, with epsilon_B ranging from ~ 10^-7 - 10^-3. To characterize how much magnetic field amplification is needed, beyond shock compression of the seed magnetic field, we expressed our results for epsilon_B in terms of an amplification factor, AF. For both our X-ray and optical samples, the median value we found is AF ˜ 50-70. The distributions of AF from our X-ray and optical samples also showed a wide distribution, with AF ranging from ~ 1-1000. These results for epsilon_B and AF suggest that a weak amplification, in addition to shock compression, is needed to explain the afterglow observations. Our main conclusion is that shock compression and weak amplification of the magnetic field in GRB relativistic external shocks is sufficient to explain the afterglow data.
Relativistic nonlinear plasma waves in a magnetic field
NASA Technical Reports Server (NTRS)
Kennel, C. F.; Pellat, R.
1975-01-01
Five relativistic plane nonlinear waves were investigated: circularly polarized waves and electrostatic plasma oscillations propagating parallel to the magnetic field, relativistic Alfven waves, linearly polarized transverse waves propagating in zero magnetic field, and the relativistic analog of the extraordinary mode propagating at an arbitrary angle to the magnetic field. When the ions are driven relativistic, they behave like electrons, and the assumption of an 'electron-positron' plasma leads to equations which have the form of a one-dimensional potential well. The solutions indicate that a large-amplitude superluminous wave determines the average plasma properties.
Global marine gravity field map
NASA Astrophysics Data System (ADS)
Sloss, Peter W.
A color relief image of the marine gravity field from SEASAT altimeter measurements of the topography of the ocean surface is now available through the National Geophysical Data Center (NGDC) of the National Oceanic and Atmospheric Administration. This image, prepared by William F. Haxby (Lamont-Doherty Geological Observatory of Columbia University, Palisades, N.Y.), has been published by NGDC for the Office of Naval Research, which was the principal sponsor of the effort leading to the development of the image. The U.S. Geological Survey, National Mapping Division, printed the map.
Gravitational-wave observations as a tool for testing relativistic gravity
NASA Technical Reports Server (NTRS)
Eardley, D. M.; Lee, D. L.; Lightman, A. P.; Wagoner, R. V.; Will, C. M.
1973-01-01
Approaches regarding the role of gravitational wave observations in the investigation of relativistic theories of gravity are treated as providing greater potential in the prediction of wave propagation speed and the polarization properties of gravitational waves. The invariant classes of waves discussed have the same post-Newtonian limit as general relativity for a reasonable choice of cosmological models.
Gravity Control Propulsion - Towards a General Relativistic Approach
NASA Astrophysics Data System (ADS)
Bertolami, O.; Pedro, F. G.
Evaluation of gravity control concepts should be examined with respect to currently known physical theories. In this work we study the hypothetical conversion of gravitational potential energy into kinetic energy using the formalism of general relativity. We show that the energy involved in the process greatly exceeds the Newtonian estimate, given the nature of general relativity. We conclude that the impact of any gravity manipulation for propulsion greatly depends fundamentally on its exact definition.
Theoretical frameworks for testing relativistic gravity: A review
NASA Technical Reports Server (NTRS)
Thorne, K. S.; Will, C. M.; Ni, W.
1971-01-01
Metric theories of gravity are presented, including the definition of metric theory, evidence for its existence, and response of matter to gravity with test body trajectories, gravitational red shift, and stressed matter responses. Parametrized post-Newtonian framework and interpretations are reviewed. Gamma, beta and gamma, and varied other parameters were measured. Deflection of electromagnetic waves, radar time delay, geodetic gyroscope precession, perihelion shifts, and periodic effects in orbits are among various studies carried out for metric theory experimentation.
Dirac fields in loop quantum gravity and big bang nucleosynthesis
NASA Astrophysics Data System (ADS)
Bojowald, Martin; Das, Rupam; Scherrer, Robert J.
2008-04-01
Big bang nucleosynthesis requires a fine balance between equations of state for photons and relativistic fermions. Several corrections to equation of state parameters arise from classical and quantum physics, which are derived here from a canonical perspective. In particular, loop quantum gravity allows one to compute quantum gravity corrections for Maxwell and Dirac fields. Although the classical actions are very different, quantum corrections to the equation of state are remarkably similar. To lowest order, these corrections take the form of an overall expansion-dependent multiplicative factor in the total density. We use these results, along with the predictions of big bang nucleosynthesis, to place bounds on these corrections and especially the patch size of discrete quantum gravity states.
Dirac fields in loop quantum gravity and big bang nucleosynthesis
Bojowald, Martin; Das, Rupam; Scherrer, Robert J.
2008-04-15
Big bang nucleosynthesis requires a fine balance between equations of state for photons and relativistic fermions. Several corrections to equation of state parameters arise from classical and quantum physics, which are derived here from a canonical perspective. In particular, loop quantum gravity allows one to compute quantum gravity corrections for Maxwell and Dirac fields. Although the classical actions are very different, quantum corrections to the equation of state are remarkably similar. To lowest order, these corrections take the form of an overall expansion-dependent multiplicative factor in the total density. We use these results, along with the predictions of big bang nucleosynthesis, to place bounds on these corrections and especially the patch size of discrete quantum gravity states.
Electron-Ion collisions in relativistically strong laser fields
Balakin, A. A.
2008-04-15
Electron-ion collisions in relativistically strong electromagnetic fields are considered. Analytical and numerical analyses both show that all qualitative effects characteristic of collisions in nonrelativistic strong fields [1-3] occur at relativistic intensities of an electromagnetic wave as well. Expressions for Joule plasma heating and for the energy distributions of fast particles are derived from simple analytic considerations and are confirmed by numerical simulations. It is found, in particular, that, due to the relativistic increase in the mass of a scattered electron, Joule heating in ultrarelativistic fields becomes more intense as the field amplitude grows.
Exact general relativistic disks with magnetic fields
NASA Astrophysics Data System (ADS)
Letelier, Patricio S.
1999-11-01
The well-known ``displace, cut, and reflect'' method used to generate cold disks from given solutions of Einstein equations is extended to solutions of Einstein-Maxwell equations. Four exact solutions of the these last equations are used to construct models of hot disks with surface density, azimuthal pressure, and azimuthal current. The solutions are closely related to Kerr, Taub-NUT, Lynden-Bell-Pinault, and to a one-soliton solution. We find that the presence of the magnetic field can change in a nontrivial way the different properties of the disks. In particular, the pure general relativistic instability studied by Bic̆ák, Lynden-Bell, and Katz [Phys. Rev. D 47, 4334 (1993)] can be enhanced or cured by different distributions of currents inside the disk. These currents, outside the disk, generate a variety of axial symmetric magnetic fields. As far as we know these are the first models of hot disks studied in the context of general relativity.
Gravity Field Characterization around Small Bodies
NASA Astrophysics Data System (ADS)
Takahashi, Yu
A small body rendezvous mission requires accurate gravity field characterization for safe, accurate navigation purposes. However, the current techniques of gravity field modeling around small bodies are not achieved to the level of satisfaction. This thesis will address how the process of current gravity field characterization can be made more robust for future small body missions. First we perform the covariance analysis around small bodies via multiple slow flybys. Flyby characterization requires less laborious scheduling than its orbit counterpart, simultaneously reducing the risk of impact into the asteroid's surface. It will be shown that the level of initial characterization that can occur with this approach is no less than the orbit approach. Next, we apply the same technique of gravity field characterization to estimate the spin state of 4179 Touatis, which is a near-Earth asteroid in close to 4:1 resonance with the Earth. The data accumulated from 1992-2008 are processed in a least-squares filter to predict Toutatis' orientation during the 2012 apparition. The center-of-mass offset and the moments of inertia estimated thereof can be used to constrain the internal density distribution within the body. Then, the spin state estimation is developed to a generalized method to estimate the internal density distribution within a small body. The density distribution is estimated from the orbit determination solution of the gravitational coefficients. It will be shown that the surface gravity field reconstructed from the estimated density distribution yields higher accuracy than the conventional gravity field models. Finally, we will investigate two types of relatively unknown gravity fields, namely the interior gravity field and interior spherical Bessel gravity field, in order to investigate how accurately the surface gravity field can be mapped out for proximity operations purposes. It will be shown that these formulations compute the surface gravity field with
NASA Technical Reports Server (NTRS)
Kahn, W. D.
1984-01-01
The spaceborne gravity gradiometer is a potential sensor for mapping the fine structure of the Earth's gravity field. Error analyses were performed to investigate the accuracy of the determination of the Earth's gravity field from a gravity field satellite mission. The orbital height of the spacecraft is the dominating parameter as far as gravity field resolution and accuracies are concerned.
Relativistic Feedback Rates in the Presence of the Geomagnetic Field
NASA Astrophysics Data System (ADS)
Lucia, R. J.; Dwyer, J. R.; Liu, N.; Rassoul, H.
2013-12-01
It has been shown that relativistic feedback allows runaway electron avalanche discharges in the atmosphere to become self-sustaining. Since relativistic feedback is also capable of increasing the flux of runaway electrons and x-rays by a factor of 10^13 under certain thunderstorm conditions, it provides a plausible mechanism for the generation of terrestrial gamma-ray flashes (TGFs). Relativistic feedback has been previously investigated without the presence of a geomagnetic field. However, for altitudes near the tops of thunderclouds and above, the effects of the magnetic field on the feedback rates can be important in some cases. We use detailed three-dimensional Monte Carlo simulations of runaway electron avalanches in the presence of the earth's magnetic field to investigate the field's impact on relativistic feedback. In particular, we shall present results for fundamental parameters such as avalanche lengths, feedback factors, and the feedback threshold, above which an electric field is unstable.
Gravity field of the Western Weddell Sea: Comparison of airborne gravity and Geosat derived gravity
NASA Technical Reports Server (NTRS)
Bell, R. E.; Brozena, J. M.; Haxby, W. F.; Labrecque, J. L.
1989-01-01
Marine gravity surveying in polar regions was typically difficult and costly, requiring expensive long range research vessels and ice-breakers. Satellite altimetry can recover the gravity field in these regions where it is feasible to survey with a surface vessel. Unfortunately, the data collected by the first global altimetry mission, Seasat, was collected only during the austral winter, producing a very poor quality gravitational filed for the southern oceans, particularly in the circum-Antarctic regions. The advent of high quality airborne gravity (Brozena, 1984; Brozena and Peters, 1988; Bell, 1988) and the availability of satellite altimetry data during the austral summer (Sandwell and McAdoo, 1988) has allowed the recovery of a free air gravity field for most of the Weddell Sea. The derivation of the gravity field from both aircraft and satellite measurements are briefly reviewed, before presenting along track comparisons and shaded relief maps of the Weddell Sea gravity field based on these two data sets.
Relativistic mean-field mass models
NASA Astrophysics Data System (ADS)
Peña-Arteaga, D.; Goriely, S.; Chamel, N.
2016-10-01
We present a new effort to develop viable mass models within the relativistic mean-field approach with density-dependent meson couplings, separable pairing and microscopic estimations for the translational and rotational correction energies. Two interactions, DD-MEB1 and DD-MEB2, are fitted to essentially all experimental masses, and also to charge radii and infinite nuclear matter properties as determined by microscopic models using realistic interactions. While DD-MEB1 includes the σ, ω and ρ meson fields, DD-MEB2 also considers the δ meson. Both mass models describe the 2353 experimental masses with a root mean square deviation of about 1.1 MeV and the 882 measured charge radii with a root mean square deviation of 0.029 fm. In addition, we show that the Pb isotopic shifts and moments of inertia are rather well reproduced, and the equation of state in pure neutron matter as well as symmetric nuclear matter are in relatively good agreement with existing realistic calculations. Both models predict a maximum neutron-star mass of more than 2.6 solar masses, and thus are able to accommodate the heaviest neutron stars observed so far. However, the new Lagrangians, like all previously determined RMF models, present the drawback of being characterized by a low effective mass, which leads to strong shell effects due to the strong coupling between the spin-orbit splitting and the effective mass. Complete mass tables have been generated and a comparison with other mass models is presented.
Tunnelling of relativistic particles from new type black hole in new massive gravity
Gecim, Ganim; Sucu, Yusuf E-mail: ysucu@akdeniz.edu.tr
2013-02-01
In the framework of the three dimensional New Massive Gravity theory introduced by Bergshoeff, Hohm and Townsend, we analyze the behavior of relativistic spin-1/2 and spin-0 particles in the New-type Black Hole backgroud, solution of the New Massive Gravity.We solve Dirac equation for spin-1/2 and Klein-Gordon equation for spin-0. Using Hamilton-Jacobi method, we discuss tunnelling probability and Hawking temperature of the spin-1/2 and spin-0 particles for the black hole. We observe that the tunnelling probability and Hawking temperature are same for the spin-1/2 and spin-0.
Gravity-darkening exponents for neutron and non-relativistic stars
NASA Astrophysics Data System (ADS)
Claret, A.
2015-05-01
Context. Rotation affects various aspects of the stellar structure and evolution. For example, it distorts the star and causes the energy flow to be dependent on the local gravity (von Zeipel effect). Recent advances in the semi-empirical derivation of the gravity-darkening exponents in eclipsing binaries and very fast rotators require new theoretical calculations so that the results can be compared with these observations. Aims: Using an analytical alternative method, we studied how the temperature is distributed over distorted neutron star (NS) surfaces through the gravity-darkening exponent (GDE). We also extended these investigations to non-relativistic stars. Methods: The envelopes of NS, whose properties are necessary to derive the GDE, were computed using routines of the code mesa. The non-relativistic stellar models were computed following the code granada. Results: We use a perturbation theory to derive an equation for the GDE for neutron and non-relativistic stars as a function of the rotation law, of the colatitude, and of the logarithmic derivatives of the opacity. Significant deviations from the von Zeipel's theorem were found for differentially rotating NS as well as for non-relativistic stars. This equation is also capable of predicting the transition zone in the GDE around log Teff = 3.9 for non-relativistic stars, in good agreement with observational data. We use this equation to explore the effects of differential rotation to explain the anomalous values of semi-empirical GDE found in some early-type eclipsing binaries. We also analysed the role of convection and of the change of the main thermonuclear energy source in the GDE calculations for late-type stars.
Dipole magnetic field of neutron stars in f(R) gravity
NASA Astrophysics Data System (ADS)
Bakirova, Elizat; Folomeev, Vladimir
2016-10-01
The structure of an interior dipole magnetic field of neutron stars in f( R) gravity is considered. For this purpose, the perturbative approaches are used when both the deviations from general relativity and the deformations of spherically symmetric configurations associated with the presence of the magnetic field are assumed to be small. Solutions are constructed which describe relativistic, spherically symmetric configurations consisting of a gravitating magnetized perfect fluid modeled by a realistic equation of state. Comparing configurations from general relativity and modified gravity, we reveal possible differences in the structure of the magnetic field which occur in considering neutron stars in modified gravity.
Gravity field determination and error assessment techniques
NASA Technical Reports Server (NTRS)
Yuan, D. N.; Shum, C. K.; Tapley, B. D.
1989-01-01
Linear estimation theory, along with a new technique to compute relative data weights, was applied to the determination of the Earth's geopotential field and other geophysical model parameters using a combination of satellite ground-based tracking data, satellite altimetry data, and the surface gravimetry data. The relative data weights for the inhomogeneous data sets are estimated simultaneously with the gravity field and other geophysical and orbit parameters in a least squares approach to produce the University of Texas gravity field models. New techniques to perform calibration of the formal covariance matrix for the geopotential solution were developed to obtain a reliable gravity field error estimate. Different techniques, which include orbit residual analysis, surface gravity anomaly residual analysis, subset gravity solution comparisons and consider covariance analysis, were applied to investigate the reliability of the calibration.
NASA Astrophysics Data System (ADS)
Varjú, Katalin; Ryder, Lewis H.
2000-05-01
In the Colella-Overhauser-Werner (COW) experiment a gravity-induced phase shift of spin 1/2 particles was detected. The experimental results were explained by using the Newtonian theory of gravity. The explanation can be easily given using general relativistic arguments and the highest order term reproduces the result of Colella, Overhauser, and Werner together with additional, lower order corrections. The derivation can be considered as an interesting exercise for students with basic knowledge of the field of general relativity.
Janiszewski, Stefan; Karch, Andreas
2013-02-22
We argue that generic nonrelativistic quantum field theories with a holographic description are dual to Hořava gravity. We construct explicit examples of this duality embedded in string theory by starting with relativistic dual pairs and taking a nonrelativistic scaling limit.
Brane structure from a scalar field in general covariant Horava-Lifshitz gravity
NASA Astrophysics Data System (ADS)
Bazeia, D.; Brito, F. A.; Costa, F. G.
2015-02-01
In this paper we have considered the structure of the nonprojectable Horava-Melby-Thompson gravity to find braneworld scenarios. A relativistic scalar field is considered in the matter sector and we have shown how to reduce the equations of motion to first-order differential equations. In particular, we have studied thick brane solutions of both the dilatonic and Randall-Sundrum types.
Limits of Strong Field Rescattering in the Relativistic Regime
NASA Astrophysics Data System (ADS)
Klaiber, M.; Hatsagortsyan, K. Z.; Wu, J.; Luo, S. S.; Grugan, P.; Walker, B. C.
2017-03-01
Recollision for a laser driven atomic system is investigated in the relativistic regime via a strong field quantum description and Monte Carlo semiclassical approach. We find the relativistic recollision energy cutoff is independent of the ponderomotive potential Up , in contrast to the well-known 3.2 Up scaling. The relativistic recollision energy cutoff is determined by the ionization potential of the atomic system and achievable with non-negligible recollision flux before entering a "rescattering free" interaction. The ultimate energy cutoff is limited by the available intensities of short wavelength lasers and cannot exceed a few thousand Hartree, setting a boundary for recollision based attosecond physics.
Electric fields in micro-gravity can replace gravity
NASA Astrophysics Data System (ADS)
Gorgolewski, S.
The influence of the world-wide atmospheric electric field on the growth of plants seems to have been neglected. The confirmation of the existence of electrotropism shows effects on some plants similar to gravity. I propose space ex eriments withp plants that grow in microgravity but are exposed to different electric field configurations with various field strengths and polarity. The electric field in terrestrial environment shows strong effects on some plants that can be regarded as due to phototropism. In microgravity we have full control of light and electric field, and thus we can practically eliminate the effects of gravity and we can study to what degree the electric field can replace the gravitational effects on plants. In this way we can create a new habitat for some plants and study its role in the rate of growth as well as in the sensing of free space for growth of plants in absence of gravity. By varying the strength and direction of illumination of plants we can also study the relative role of phototropism and electrotropism on different plants. This should enable us to select the most suitable plants for Advanced Life Support systems (ALS) for long-duration missions in microgravity environment. Some simple space experiments for verification of these assumptions are described that should answer the basic questions how should we design the ALS for the future high performance space stations and long duration manned space flights. The selection of the suitable plants for such ALS may go along two approaches: the self supporting electrotropic plants using the optimal electric field strength and its range of variation, non electrotropic plants that creep along the "ground" or other supporting plants or special structures. Ground based fitotron experiments have shown that several kV/m electric fields overwhelm the gravity better than clinostats can do. It happens in case of electrotropic plants but also after several days for non-electrotropic plants
NASA Technical Reports Server (NTRS)
Gottlieb, Robert G.
1993-01-01
Derivation of first and second partials of the gravitational potential is given in both normalized and unnormalized form. Two different recursion formulas are considered. Derivation of a general gravity gradient torque algorithm which uses the second partial of the gravitational potential is given. Derivation of the geomagnetic field vector is given in a form that closely mimics the gravitational algorithm. Ada code for all algorithms that precomputes all possible data is given. Test cases comparing the new algorithms with previous data are given, as well as speed comparisons showing the relative efficiencies of the new algorithms.
Toward a gauge field theory of gravity.
NASA Astrophysics Data System (ADS)
Yilmaz, H.
Joint use of two differential identities (Bianchi and Freud) permits a gauge field theory of gravity in which the gravitational energy is localizable. The theory is compatible with quantum mechanics and is experimentally viable.
NASA Astrophysics Data System (ADS)
Renk, Janina; Zumalacárregui, Miguel; Montanari, Francesco
2016-07-01
We address the impact of consistent modifications of gravity on the largest observable scales, focusing on relativistic effects in galaxy number counts and the cross-correlation between the matter large scale structure (LSS) distribution and the cosmic microwave background (CMB). Our analysis applies to a very broad class of general scalar-tensor theories encoded in the Horndeski Lagrangian and is fully consistent on linear scales, retaining the full dynamics of the scalar field and not assuming quasi-static evolution. As particular examples we consider self-accelerating Covariant Galileons, Brans-Dicke theory and parameterizations based on the effective field theory of dark energy, using the hi class code to address the impact of these models on relativistic corrections to LSS observables. We find that especially effects which involve integrals along the line of sight (lensing convergence, time delay and the integrated Sachs-Wolfe effect—ISW) can be considerably modified, and even lead to O(1000%) deviations from General Relativity in the case of the ISW effect for Galileon models, for which standard probes such as the growth function only vary by O(10%). These effects become dominant when correlating galaxy number counts at different redshifts and can lead to ~ 50% deviations in the total signal that might be observable by future LSS surveys. Because of their integrated nature, these deep-redshift cross-correlations are sensitive to modifications of gravity even when probing eras much before dark energy domination. We further isolate the ISW effect using the cross-correlation between LSS and CMB temperature anisotropies and use current data to further constrain Horndeski models. Forthcoming large-volume galaxy surveys using multiple-tracers will search for all these effects, opening a new window to probe gravity and cosmic acceleration at the largest scales available in our universe.
Dual geometric-gauge field aspects of gravity
Huei Peng; Wang, K.
1992-07-01
We propose that the geometric and standard gauge field aspects of gravity are equally essential for a complete description of gravity and can be reconciled. We show that this dualism of gravity resolves the dimensional Newtonian constant problem in both quantum gravity and unification schemes involving gravity (i.e., the Newtonian constant is no longer the coupling constant in the gauge aspect of gravity) and reveals the profound similarity between gravity and other fields. 23 refs., 3 tabs.
A comprehensive study of relativistic gravity using PSR B1534+12
Fonseca, Emmanuel; Stairs, Ingrid H.; Thorsett, Stephen E. E-mail: stairs@astro.ubc.ca
2014-05-20
We present updated analyses of pulse profiles and their arrival times from PSR B1534+12, a 37.9 ms radio pulsar in orbit with another neutron star. A high-precision timing model is derived from 22 yr of timing data and accounts for all astrophysical processes that systematically affect pulse arrival times. Five 'post-Keplerian' parameters are measured that represent relativistic corrections to the standard Keplerian quantities of the pulsar's binary orbit. These relativistic parameters are then used to test general relativity by comparing the measurements with their predicted values. We conclude that relativity theory is confirmed to within 0.17% of its predictions. Furthermore, we derive the following astrophysical results from our timing analysis: a distance of d {sub GR} = 1.051 ± 0.005 kpc to the pulsar-binary system, by relating the 'excess' orbital decay to Galactic parameters; evidence for pulse 'jitter' in PSR B1534+12 due to short-term magnetospheric activity; and evolution in pulse-dispersion properties. As a secondary study, we also present several analyses on pulse-structure evolution and its connection to relativistic precession of the pulsar's spin axis. The precession-rate measurement yields a value of Ω{sub 1}{sup spin}=0.59{sub −0.08}{sup +0.12}° yr{sup –1} (68% confidence) that is consistent with expectations and represents an additional test of relativistic gravity.
Relativistic Quantum Mechanics and Introduction to Field Theory
NASA Astrophysics Data System (ADS)
Yndurain, Francisco J.
This is an advanced textbook meant as a primer in quantum theory for graduate students. A full relativistic treatment of particle dynamics needs to be based on quantum field theory. However, there exists a variety of processes that can be discussed with concepts like potentials, classical current distributions, prescribed external fields dealt with in the framework of relativistic quantum mechanics. Then, in an introduction to field theory the author emphasizes the deduction of the said potentials or currents. The unique feature of this book is the modern presentation of the subject together with many exercises and furthermore the underlying concept to combine a reference book on relativistic quantum mechanics with an introduction into quantum field theory.
NASA Astrophysics Data System (ADS)
Rezzolla, Luciano; Ahmedov, Bobomurat J.
2016-07-01
An important issue in the asteroseismology of compact and magnetized stars is the determination of the dissipation mechanism which is most efficient in damping the oscillations when these are produced. In a linear regime and for low-multipolarity modes, these mechanisms are confined to either gravitational-wave or electromagnetic losses. We here consider the latter and compute the energy losses in the form of Poynting fluxes, Joule heating and Ohmic dissipation in a relativistic oscillating spherical star with a dipolar magnetic field in vacuum. While this approach is not particularly realistic for rapidly rotating stars, it has the advantage that it is fully analytic and that it provides expressions for the electric and magnetic fields produced by the most common modes of oscillation both in the vicinity of the star and far away from it. In this way, we revisit and extend to a relativistic context the classical estimates of McDermott et al. Overall, we find that general-relativistic corrections lead to electromagnetic damping time-scales that are at least one order of magnitude smaller than in Newtonian gravity. Furthermore, with the only exception of g (gravity) modes, we find that f (fundamental), p (pressure), i (interface) and s (shear) modes are suppressed more efficiently by gravitational losses than by electromagnetic ones.
Solutions of relativistic Newton's equations for nonconstant fields
NASA Astrophysics Data System (ADS)
Wooten, R. E.; Macek, J. H.
2004-08-01
Newton's second law can be readily solved for many forces, but few situations can be solved for the relativistic form of Newton's second law. The only problems directly solvable are those involving charged particles in constant electromagnetic fields. If the external field represents a light pulse, Dirac's relativistic equation can be solved, as done by Volkov in 1935. Classical solutions based on Volkov's work employ the Hamilton-Jacobi equations. We discuss the solution of this problem using Newton's equations, thereby making the solution more accessible.
Post-Minkowskian Gravity: Dark matter as a relativistic inertial effect?
NASA Astrophysics Data System (ADS)
Lusanna, Luca
2010-04-01
Talk at the 1st Mediterranean Conference in Classical and Quantum Gravity, held in the Orthodox Academy of Crete in Kolymbari (Greece) from Monday, September 14th to Friday, September 18th, 2009. A review is given of the theory of non-inertial frames (with the associated inertial effects and the study of the non-relativistic limit) in Minkowski space-time, of parametrized Minkowski theories and of the rest-frame instant form of dynamics for isolated systems admitting a Lagrangian description. The relevance and gauge equivalence of the clock synchronization conventions for the identification of the instantaneous 3-spaces (Euclidean only in inertial frames) are described. Then this formalism is applied to tetrad gravity in globally hyperbolic, asymptotically Minkowskian space-times without super-translations, where the equivalence principle implies the absence of global inertial frames. The recently discovered York canonical basis, diagonalizing the York-Lichnerowicz approach, allows to identify the gauge variables (inertial effects in general relativity) and the tidal ones (the gravitational waves of the linearized theory) and to clarify the meaning of the Hamilton equations. The role of the gauge variable 3K, the trace of the extrinsic curvature of the non-Euclidean 3-space (the York time not existing in Newton theory), as a source of inertial effects is emphasized. After the presentation of preliminary results on the linearization of tetrad gravity in the family of non-harmonic 3-orthogonal gauges with a free value of 3K, we define post-Minkowskian gravitational waves (without post-Newtonian approximations on the matter sources) propagating in a non-Euclidean 3-space, emphasizing the non-graviton-like aspects of gravity. It is conjectured that dark matter may be explained as a relativistic inertial effect induced by 3K: it would simulate the need to choose a privileged gauge connected with the observational conventions for the description of matter.
On the usefulness of relativistic space-times for the description of the Earth's gravitational field
NASA Astrophysics Data System (ADS)
Soffel, Michael; Frutos, Francisco
2016-12-01
The usefulness of relativistic space-times for the description of the Earth's gravitational field is investigated. A variety of exact vacuum solutions of Einstein's field equations (Schwarzschild, Erez and Rosen, Gutsunayev and Manko, Hernández-Pastora and Martín, Kerr, Quevedo, and Mashhoon) are investigated in that respect. It is argued that because of their multipole structure and influences from external bodies, all these exact solutions are not really useful for the central problem. Then, approximate space-times resulting from an MPM or post-Newtonian approximation are considered. Only in the DSX formalism that is of the first post-Newtonian order, all aspects of the problem can be tackled: a relativistic description (a) of the Earth's gravity field in a well-defined geocentric reference system (GCRS), (b) of the motion of solar system bodies in a barycentric reference system (BCRS), and (c) of inertial and tidal terms in the geocentric metric describing the external gravitational field. A relativistic SLR theory is also discussed with respect to our central problem. Orders of magnitude of many effects related to the Earth's gravitational field and SLR are given. It is argued that a formalism with accuracies better than of the first post-Newtonian order is not yet available.
Relativistic effects in photon-induced near field electron microscopy.
Park, Sang Tae; Zewail, Ahmed H
2012-11-26
Electrons and photons, when interacting via a nanostructure, produce a new way of imaging in space and time, termed photon-induced near field electron microscopy or PINEM [Barwick et al. Nature 2009, 462, 902]. The phenomenon was described by considering the evanescent field produced by the nanostructure, but quantification of the experimental results was achieved by solving the Schrödinger equation for the interaction of the three bodies. The question remained, is the nonrelativistic formulation sufficient for this description? Here, relativistic and nonrelativistic quantum mechanical formulations are compared for electron-photon interaction mediated by nanostructures, and it is shown that there is an exact equivalence for the two formulations. The nonrelativistic formulation was found to be valid in the relativistic regime when using in the former formulation the relativistically corrected velocity (and the corresponding values of momentum and energy). In the PINEM experiment, 200 keV electrons were utilized, giving the experimental (relativistically corrected) velocity to be 0.7c(v without relativistic correction is 0.885c). When this value (0.7c), together with those of the corresponding momentum (p(c) = mv) and energy (E(c) = (1/2)mv(2)), is used in the first order solution of the Schrödinger formulation, an exact equivalence is obtained.
Global Lunar Gravity Field Recovery from SELENE
NASA Technical Reports Server (NTRS)
Matsumoto, Koji; Heki, Kosuke; Hanada, Hideo
2002-01-01
Results of numerical simulation are presented to examine the global gravity field recovery capability of the Japanese lunar exploration project SELENE (Selenological and Engineering Explorer) which will be launched in 2005. New characteristics of the SELENE lunar gravimetry include four-way satellite-to-satellite Doppler tracking of main orbiter and differential VLBI tracking of two small free-flier satellites. It is shown that planned satellites configuration will improve lunar gravity field in wide range of wavelength as well as far-side selenoid.
The earth's gravity field and ocean dynamics
NASA Technical Reports Server (NTRS)
Mather, R. S.
1978-01-01
An analysis of the signal-to-noise ratio of the best gravity field available shows that a basis exists for the recovery of the dominant parameters of the quasi-stationary sea surface topography. Results obtained from the analysis of GEOS-3 show that it is feasible to recover the quasi-stationary dynamic sea surface topography as a function of wavelength. The gravity field models required for synoptic ocean circulation modeling are less exacting in that constituents affecting radial components of orbital position need not be known through shorter wavelengths.
Using Clocks and Atomic Interferometry for Gravity Field Observations
NASA Astrophysics Data System (ADS)
Müller, Jürgen
2016-07-01
New technology developed in the frame of fundamental physics may lead to enhanced capabilities for geodetic applications such as refined observations of the Earth's gravity field. Here, we will present new sensor measurement concepts that apply atomic interferometry for gravimetry and clock measurements for observing potential values. In the first case, gravity anomalies can be determined by observing free-falling atoms (quantum gravimetry). In the second case, highly precise optical clocks can be used to measure differences of the gravity potential over long distances (relativistic geodesy). Principally, also inter-satellite ranging between test masses in space with nanometer accuracy belongs to these novel developments. We will show, how the new measurement concepts are connected to classical geodetic concepts, e.g. geopotential numbers and clock readings. We will illustrate the application of these new methods and their benefit for geodesy, where local and global mass variations can be observed with unforeseen accuracy and resolution, mass variations that reflect processes in the Earth system. We will present a few examples where geodesy will potentially benefit from these developments. Thus, the novel technologies might be applied for defining and realizing height systems in a new way, but also for fast local gravimetric surveys and exploration.
On the impact of airborne gravity data to fused gravity field models
NASA Astrophysics Data System (ADS)
Bolkas, Dimitrios; Fotopoulos, Georgia; Braun, Alexander
2016-06-01
In gravity field modeling, fused models that utilize satellite, airborne and terrestrial gravity observations are often employed to deal with erroneous terrestrially derived gravity datasets. These terrestrial datasets may suffer from long-wavelength systematic errors and inhomogeneous data coverage, which are not prevalent in airborne and satellite datasets. Airborne gravity acquisition plays an essential role in gravity field modeling, providing valuable information of the Earth's gravity field at medium and short wavelengths. Thus, assessing the impact of airborne gravity data to fused gravity field models is important for identifying problematic regions. Six study regions that represent different gravity field variability and terrestrial data point-density characteristics are investigated to quantify the impact of airborne gravity data to fused gravity field models. The numerical assessments of these representative regions resulted in predictions of airborne gravity impact for individual states and provinces in the USA and Canada, respectively. Prediction results indicate that, depending on the terrestrial data point-density and gravity field variability, the expected impact of airborne gravity can reach up to 3mGal (in terms of standard deviation) in Canada and Alaska (over areas of 1° × 1°). However, in the mainland US region, small changes are expected (0.2-0.4 mGal over areas of 1° × 1°) due to the availability of high spatial resolution terrestrial data. These results can serve as a guideline for setting airborne gravity data acquisition priorities and for improving future planning of airborne gravity surveys.
Relativistic Particle in Electromagnetic Fields with a Generalized Uncertainty Principle
NASA Astrophysics Data System (ADS)
Merad, M.; Zeroual, F.; Falek, M.
2012-05-01
In this paper, we propose to solve the relativistic Klein-Gordon and Dirac equations subjected to the action of a uniform electromagnetic field with a generalized uncertainty principle in the momentum space. In both cases, the energy eigenvalues and their corresponding eigenfunctions are obtained. The limit case is then deduced for a small parameter of deformation.
Relativistic mean field calculations in neutron-rich nuclei
Gangopadhyay, G.; Bhattacharya, Madhubrata; Roy, Subinit
2014-08-14
Relativistic mean field calculations have been employed to study neutron rich nuclei. The Lagrange's equations have been solved in the co-ordinate space. The effect of the continuum has been effectively taken into account through the method of resonant continuum. It is found that BCS approximation performs as well as a more involved Relativistic Continuum Hartree Bogoliubov approach. Calculations reveal the possibility of modification of magic numbers in neutron rich nuclei. Calculation for low energy proton scattering cross sections shows that the present approach reproduces the density in very light neutron rich nuclei.
Radiation from Relativistic Shocks with Turbulent Magnetic Fields
NASA Technical Reports Server (NTRS)
Nishkawa, K.; Medvedev, M.; Zhang, B.; Hardee, P.; Niemiec, J.; Mizuno, A.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Oka, M.; Fishman, J.
2009-01-01
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs at shocked region. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the shock. The "jitter" radiation from deflected electrons in turbulent magnetic fields has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. New recent calculation of spectra with various different Lorentz factors of jets (two electrons) and initial magnetic fields. New spectra based on small simulations will be presented.
The weak gravity conjecture and scalar fields
NASA Astrophysics Data System (ADS)
Palti, Eran
2017-08-01
We propose a generalisation of the Weak Gravity Conjecture in the presence of scalar fields. The proposal is guided by properties of extremal black holes in N=2 supergravity, but can be understood more generally in terms of forbidding towers of stable gravitationally bound states. It amounts to the statement that there must exist a particle on which the gauge force acts more strongly than gravity and the scalar forces combined. We also propose that the scalar force itself should act on this particle stronger than gravity. This implies that generically the mass of this particle decreases exponentially as a function of the scalar field expectation value for super-Planckian variations, which is behaviour predicted by the Refined Swampland Conjecture. In the context of N=2 supergravity the Weak Gravity Conjecture bound can be tied to bounds on scalar field distances in field space. Guided by this, we present a general proof that for any linear combination of moduli in any Calabi-Yau compactification of string theory the proper field distance grows at best logarithmically with the moduli values for super-Planckian distances.
Estimation of gravity field by mobile gravimetry
NASA Astrophysics Data System (ADS)
Li, Q.; Verdun, J.; Cali, J.; Diament, M.; Maia, M. A.; Panet, I.
2011-12-01
In geophysics and geodesy, it is important to know the gravity field for determining of gravity anomaly maps and high-resolution geoid models. These data and model help to understand the structure and dynamics of our planet. Actual measurement techniques of the gravity field, from space to surface observations, cover a wide range of spatial resolutions of the Earth gravity field. Nevertheless, spatial and spectral extends of gravity measurements are not homogeneous on Earth's surface and for some isolated areas, measurements are missing. Furthermore, the intermediate spatial resolutions (10-100 km) are still badly covered by the terrestrial and space gravimetry. To face with the problem, an autonomous mobile gravimetry system (Limog) to be embarked on terrestrial vehicles, boats or planes has been developed, to compensate for the lack of current gravimetry techniques. The system is composed of three high resolution accelerometers mounted on a triad in order to have their sensitive axes non coplanar, to measure the components of the specific force. The determination of the movement of the vehicle and its attitude is obtained respectively with a dual frequencies GPS receiver and a 4 antenna GPS receiver. Also, this system is far less expensive than classical gravimetric apparatus and has no equivalent. An original treatment method based on a Kalman filter combining accelerometers and GPS data has been developed and tested using semi-synthetic data based on real data acquired from an experimental survey in the Mediterranean Sea. Here, we show an application of the method to gravity field determination in the East Pacific RiDe (EPR) between 15°22'N and 16°15'N from the Cruise PARISUB ("PAnache - RIde par SUBmersible", or Plume - Ridge by Submersible). An implicit least-square method of data processing has also been developed, and compared with the Kalman filter. The results of our analysis will be shown in the presentation.
Electromagnetic field and cylindrical compact objects in modified gravity
NASA Astrophysics Data System (ADS)
Yousaf, Z.; Bhatti, M. Zaeem ul Haq
2016-05-01
In this paper, we have investigated the role of different fluid parameters particularly electromagnetic field and f(R) corrections on the evolution of cylindrical compact object. We have explored the modified field equations, kinematical quantities and dynamical equations. An expression for the mass function has been found in comparison with the Misner-Sharp formalism in modified gravity, after which different mass-radius diagrams are drawn. The coupled dynamical transport equation have been formulated to discuss the role of thermoinertial effects on the inertial mass density of the cylindrical relativistic interior. Finally, we have presented a framework, according to which all possible solutions of the metric f(R)-Maxwell field equations coupled with static fluid can be written through set of scalar functions. It is found that modified gravity induced by Lagrangians f(R) = αR2, f(R) = αR2 - βR and f(R)=α R^2-β R/1+γ R are likely to host more massive cylindrical compact objects with smaller radii as compared to general relativity.
Particle Acceleration, Magnetic Field Generation and Emission from Relativistic Jets
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Hardee, P.; Hededal, C.; Mizuno, Yosuke; Fishman, G. Jerry; Hartmann, D. H.
2006-01-01
Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), supernova remnants, and Galactic microquasar systems usually have power-law emission spectra. Fermi acceleration is the mechanism usually assumed for the acceleration of particles in astrophysical environments. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that particle acceleration occurs within the downstream jet, rather than by the scattering of particles back and forth across the shock as in Fermi acceleration. Shock acceleration' is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different spectral properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. We will review recent PIC simulations of relativistic jets and try to make a connection with observations.
GRAIL Gravity Field of the Moon
2012-12-05
This map shows the gravity field of the moon as measured by NASA GRAIL mission. The viewing perspective, known as a Mercator projection, shows the far side of the moon in the center and the nearside as viewed from Earth at either side.
Moon Gravity Field Using Prospector Data
2012-12-05
This map shows the gravity field of the moon from the Lunar Prospector mission. The viewing perspective, known as a Mercator projection, shows the far side of the moon in the center and the nearside as viewed from Earth at either side.
Gravitational-wave observations as a tool for testing relativistic gravity
NASA Technical Reports Server (NTRS)
Eardley, D. M.; Lee, D. L.; Lightman, A. P.
1973-01-01
Gravitational radiation in the far field was examined using a formalism that encompassed all metric theories of gravity. There are six possible modes of polarization, which can be completely resolved by feasible experiments. A theoretical framework is set forth for classification of waves and theories, based on the Lorentz transformation properties of the six modes. Also shown in detail is how the six modes may be experimentally identified and to what extent such information limits the correct theory of gravity.
Non-perturbative methods in relativistic field theory
Franz Gross
2013-03-01
This talk reviews relativistic methods used to compute bound and low energy scattering states in field theory, with emphasis on approaches that John Tjon and I discussed (and argued about) together. I compare the Bethe–Salpeter and Covariant Spectator equations, show some applications, and then report on some of the things we have learned from the beautiful Feynman–Schwinger technique for calculating the exact sum of all ladder and crossed ladder diagrams in field theory.
NASA Astrophysics Data System (ADS)
Deng, X. M.
2011-09-01
With the development of the unprecedented techniques for observation and the improvement of the advanced methods for measurement, it is time for astrometry to unfold a new era indubitably. Presently, the satellite laser ranging like LAser GEOdynamics Satellite (LAGEOS) has achieved a precision of 0.5 mas for orbit determination, the precision of Lunar Laser Ranging (LLR) has approached one millimeter, and Very Long Baseline Interferometry (VLBI) has attained the precision of 0.1 mas or even better. Beyond the current thresholds, astrometric observation will be able to attain the precision of a few μas or higher for some astrometric missions in the near future, such as Global Astrometric Interferometer for Astrophysics (GAIA) and Space Interferometry Mission (SIM). With the modern continuous improvement of the observational accuracy, we realize that Newtonian mechanics has already deviated from the high-precision astronomical observation. A relativistic model for data processing of high-precision astrometry needs to be established. On the other hand, the continued failure in merging gravity with quantum mechanics and recent cosmological observations indicate that Einstein's general relativity needs some modifications. Thus, we are motivated by testing alternative gravity theories and parameterizing relativistic model. We mainly try to research these deeply. Firstly, it is shown that the parameterized post-Newtonian parameter γ≠1 for Moffat's STVG by using Chandrasekhar's approach, and the theory is then ruled out by the experiments in the solar system. Then we propose a modified theory, MSTVG, to solve this problem. Besides, we use binary pulsar data to constrain two parameters in MSTVG. Secondly, a parameterized 2PN framework for light propagation is developed based on the previous works in our research. By considering the non-static gravitational field of the solar system, the influences of all kinds of relativistic terms with different physical origins on
Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, Ken-IchiI.; Hededal, C.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G.
2004-01-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (m) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient parallel magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. New simulations with an ambient perpendicular magnetic field show the strong interaction between the relativistic jet and the magnetic fields. The magnetic fields are piled up by the jet and the jet electrons are bent, which creates currents and displacement currents. At the nonlinear stage, the magnetic fields are reversed by the current and the reconnection may take place. Due to these dynamics the jet and ambient electron are strongly accelerated in both parallel and perpendicular directions.
Particle Acceleration, Magnetic Field Generation in Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, Ken-Ichi; Hardee, P.; Hededal, C. B.; Richardson, G.; Sol, H.; Preece, R.; Fishman, G. J.
2005-01-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient parallel magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. New simulations with an ambient perpendicular magnetic field show the strong interaction between the relativistic jet and the magnetic fields. The magnetic fields are piled up by the jet and the jet electrons are bent, which creates currents and displacement currents. At the nonlinear stage, the magnetic fields are reversed by the current and the reconnection may take place. Due to these dynamics the jet and ambient electron are strongly accelerated in both parallel and perpendicular directions.
Gravity anomaly map of Mars and Moon and analysis of Venus gravity field: New analysis procedures
NASA Technical Reports Server (NTRS)
1984-01-01
The technique of harmonic splines allows direct estimation of a complete planetary gravity field (geoid, gravity, and gravity gradients) everywhere over the planet's surface. Harmonic spline results of Venus are presented as a series of maps at spacecraft and constant altitudes. Global (except for polar regions) and local relations of gravity to topography are described.
Quantum field theory and gravity in causal sets
NASA Astrophysics Data System (ADS)
Sverdlov, Roman M.
Causal set is a model of space time that allows to reconcile discreteness and manifest relativistic invariance. This is done by viewing space time as finite, partially ordered set. The elements of the set are viewed as points of space time, or events; the partial ordering between them is viewed as causal relations. It has been shown that, in discrete scenario, the information about causal relations between events can, indeed, approximate the metric. The goal of this thesis is to introduce matter fields and their Lagrangians into causal set context. This is a two step process. The first step is to re-define gauge fields, gravity, and distances in such a way that no reference to Lorentz index is made. This is done by defining gauge fields as two-point real valued functions, and gravitational field as causal structure itself. Once the above is done, Lagrangians have to be defined in a way that they don't refer to Lorentzian indices either. This is done by introducing a notion of type 1 and type 2 Lagrangian generators, coupled with respective machinery that "translates" each generator into corresponding Lagrangian. The fields that are subject to these generators are, respectively, defined as type 1 and type 2. The main difference between two kinds of fields is the prediction of different behavior in different dimensions of type 2 fields. However, despite our inability to travel to different dimensions, gravity was shown to be type 2 based on the erroneous predictions of its 4-dimensional behavior if it was viewed as type 1. However, no erroneous predictions are made if non-gravitational fields are viewed as either type 1 or type 2, thus the nature of the latter is still an open question. Finally, an attempt was made to provide interpretation of quantum mechanics that would allow to limit fluctuations of causal structure to allow some topological background. However, due to its controversial nature, it is placed in the Appendix.
Radiation from Relativistic Jets in Turbulent Magnetic Fields
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Mizuno, Y.; Medvedev, M.; Zhang, B.; Hardee, P.; Niemiec, J.; Nordlund, A.; Frederiksen, J.; Mizuno, Y.; Sol, H.; Fishman, G. J.
2008-01-01
Using our new 3-D relativistic electromagnetic particle (REMP) code parallelized with MPI, we have investigated long-term particle acceleration associated with an relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. The simulations have been performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. The acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value. Behind the bow shock in the jet shock strong electromagnetic fields are generated. These fields may lead to the afterglow emission. We have calculated the time evolution of the spectrum from two electrons propagating in a uniform parallel magnetic field to verify the technique.
NASA Astrophysics Data System (ADS)
Barrientos, E.; Mendoza, S.
2016-10-01
We construct a relativistic metric description of MOND using the Palatini formalism following the f(χ) = χb description of T. Bernal et al. (Eur. Phys. J. C 71, 1794 (2011)). We show that in order to recover the non-relativistic MOND regime where, for circular orbits the Tully-Fisher law replaces Kepler's third law, the value of the parameter b = 3/2, which is coincident with the value found using the pure metric formalism of T. Bernal et al. Unlike this pure metric formalism, which yields fourth-order field equations, the Palatini approach yields second-order field equations, which is a desirable requirement from a theoretical perspective. Thus, the phenomenology associated to astrophysical phenomena with Tully-Fisher scalings can be accounted for using this proposal, without the need to introduce any non-baryonic dark matter particles.
Weak gravity conjecture and effective field theory
NASA Astrophysics Data System (ADS)
Saraswat, Prashant
2017-01-01
The weak gravity conjecture (WGC) is a proposed constraint on theories with gauge fields and gravity, requiring the existence of light charged particles and/or imposing an upper bound on the field theory cutoff Λ . If taken as a consistency requirement for effective field theories (EFTs), it rules out possibilities for model building including some models of inflation. I demonstrate simple models which satisfy all forms of the WGC, but which through Higgsing of the original gauge fields produce low-energy EFTs with gauge forces that badly violate the WGC. These models illustrate specific loopholes in arguments that motivate the WGC from a bottom-up perspective; for example the arguments based on magnetic monopoles are evaded when the magnetic confinement that occurs in a Higgs phase is accounted for. This indicates that the WGC should not be taken as a veto on EFTs, even if it turns out to be a robust property of UV quantum gravity theories. However, if the latter is true, then parametric violation of the WGC at low energy comes at the cost of nonminimal field content in the UV. I propose that only a very weak constraint is applicable to EFTs, Λ ≲(log 1/g )-1 /2Mpl , where g is the gauge coupling, motivated by entropy bounds. Remarkably, EFTs produced by Higgsing a theory that satisfies the WGC can saturate but not violate this bound.
The relativistic Boltzmann equation on a spherically symmetric gravitational field
NASA Astrophysics Data System (ADS)
Takou, Etienne; Ciake Ciake, Fidèle L.
2017-10-01
In this paper, we consider the Cauchy problem for the relativistic Boltzmann equation with near vacuum initial data where the distribution function depends on the time, the position and the impulsion. We consider this equation on a spherically symmetric gravitational field spacetime. The collision kernel considered here is for the hard potentials case. We prove the existence of a unique global (in time) mild solution in a suitable weighted space.
Relativistic electron vortex beams in a constant magnetic field
NASA Astrophysics Data System (ADS)
Rajabi, Ahmad; Berakdar, Jamal
2017-06-01
We present solutions for the Dirac equation in the form of Bessel or Laguerre-Gaussian beams for, respectively, a free electron or an electron subject to a longitudinal constant magnetic field. We calculate the probability and the current distributions and find a strong dependence on the spin angular momentum and the orbital angular momentum of the relativistic electron beam. The role of the intrinsic spin-orbital coupling is investigated.
Magnetic Fields in Relativistic Collisionless Shocks
NASA Astrophysics Data System (ADS)
Santana, Rodolfo; Barniol Duran, Rodolfo; Kumar, Pawan
2014-04-01
We present a systematic study on magnetic fields in gamma-ray burst (GRB) external forward shocks (FSs). There are 60 (35) GRBs in our X-ray (optical) sample, mostly from Swift. We use two methods to study epsilon B (fraction of energy in magnetic field in the FS): (1) for the X-ray sample, we use the constraint that the observed flux at the end of the steep decline is >= X-ray FS flux; (2) for the optical sample, we use the condition that the observed flux arises from the FS (optical sample light curves decline as ~t -1, as expected for the FS). Making a reasonable assumption on E (jet isotropic equivalent kinetic energy), we converted these conditions into an upper limit (measurement) on epsilon B n 2/(p + 1) for our X-ray (optical) sample, where n is the circumburst density and p is the electron index. Taking n = 1 cm-3, the distribution of epsilon B measurements (upper limits) for our optical (X-ray) sample has a range of ~10-8-10-3 (~10-6-10-3) and median of ~few × 10-5 (~few × 10-5). To characterize how much amplification is needed, beyond shock compression of a seed magnetic field ~10 μG, we expressed our results in terms of an amplification factor, AF, which is very weakly dependent on n (AFvpropn 0.21). The range of AF measurements (upper limits) for our optical (X-ray) sample is ~1-1000 (~10-300) with a median of ~50 (~50). These results suggest that some amplification, in addition to shock compression, is needed to explain the afterglow observations.
Magnetic fields in relativistic collisionless shocks
Santana, Rodolfo; Kumar, Pawan; Barniol Duran, Rodolfo E-mail: pk@astro.as.utexas.edu
2014-04-10
We present a systematic study on magnetic fields in gamma-ray burst (GRB) external forward shocks (FSs). There are 60 (35) GRBs in our X-ray (optical) sample, mostly from Swift. We use two methods to study ε {sub B} (fraction of energy in magnetic field in the FS): (1) for the X-ray sample, we use the constraint that the observed flux at the end of the steep decline is ≥ X-ray FS flux; (2) for the optical sample, we use the condition that the observed flux arises from the FS (optical sample light curves decline as ∼t {sup –1}, as expected for the FS). Making a reasonable assumption on E (jet isotropic equivalent kinetic energy), we converted these conditions into an upper limit (measurement) on ε {sub B} n {sup 2/(p+1)} for our X-ray (optical) sample, where n is the circumburst density and p is the electron index. Taking n = 1 cm{sup –3}, the distribution of ε {sub B} measurements (upper limits) for our optical (X-ray) sample has a range of ∼10{sup –8}-10{sup –3} (∼10{sup –6}-10{sup –3}) and median of ∼few × 10{sup –5} (∼few × 10{sup –5}). To characterize how much amplification is needed, beyond shock compression of a seed magnetic field ∼10 μG, we expressed our results in terms of an amplification factor, AF, which is very weakly dependent on n (AF∝n {sup 0.21}). The range of AF measurements (upper limits) for our optical (X-ray) sample is ∼1-1000 (∼10-300) with a median of ∼50 (∼50). These results suggest that some amplification, in addition to shock compression, is needed to explain the afterglow observations.
Relativistic mean field approximation to baryons
Dmitri Diakonov
2005-02-01
We stress the importance of the spontaneous chiral symmetry breaking for understanding the low-energy structure of baryons. The Mean Field Approximation to baryons is formulated, which solves several outstanding paradoxes of the naive quark models, and which allows to compute parton distributions at low virtuality in a consistent way. We explain why this approach to baryons leads to the prediction of relatively light exotic pentaquark baryons, in contrast to the constituent models which do not take seriously the importance of chiral symmetry breaking. We briefly discuss why, to our mind, it is easier to produce exotic pentaquarks at low than at high energies.
Field Theories from the Relativistic Law of Motion
NASA Astrophysics Data System (ADS)
Singh, Parampreet; Dadhich, Naresh
From the relativistic law of motion we attempt to deduce the field theories corresponding to the force law being linear and quadratic in four-velocity of the particle. The linear law leads to the vector gauge theory which could be the Abelian Maxwell electrodynamics or the non-Abelian Yang-Mills theory. On the other hand, the quadratic law demands space-time metric as its potential which is equivalent to demanding the principle of equivalence. It leads to the tensor theory of gravitational field - general relativity. It is remarkable that a purely dynamical property of the force law leads uniquely to the corresponding field theories.
Classical gluon fields of relativistic color charges
NASA Astrophysics Data System (ADS)
Zadora, A. S.
2016-09-01
The objective of the present study is to consider in more detail the exotic color-charge-glow effect discovered recently and to analyze its possible physical manifestations associated with the treatment of ensembles of color-charged particles at a classical level. The ways in which this effect may appear in arbitrary systems consisting of pointlike massive particles and admitting the partition into elementary configurations like color charges and color dipoles are studied. The possible influence of this effect on particle dynamics (in particular, on gluon distributions) is also examined. Particle collisions at a given impact parameters are considered for a natural regularization of emerging expressions. It is shown that, in the case of reasonable impact-parameter values, collisions may proceed in the electrodynamic mode, in which case the charge-glow contribution to field strengths is suppressed in relation to what we have in the electrodynamic picture. From an analysis of the color-echo situation, it follows that the above conclusion remains valid for more complicated particle configurations as well, since hard gluon fields may arise only owing to a direct collision rather than owing to any echo-like effects.
Classical gluon fields of relativistic color charges
Zadora, A. S.
2016-09-15
The objective of the present study is to consider in more detail the exotic color-charge-glow effect discovered recently and to analyze its possible physical manifestations associated with the treatment of ensembles of color-charged particles at a classical level. The ways in which this effect may appear in arbitrary systems consisting of pointlike massive particles and admitting the partition into elementary configurations like color charges and color dipoles are studied. The possible influence of this effect on particle dynamics (in particular, on gluon distributions) is also examined. Particle collisions at a given impact parameters are considered for a natural regularization of emerging expressions. It is shown that, in the case of reasonable impact-parameter values, collisions may proceed in the electrodynamic mode, in which case the charge-glow contribution to field strengths is suppressed in relation to what we have in the electrodynamic picture. From an analysis of the color-echo situation, it follows that the above conclusion remains valid for more complicated particle configurations as well, since hard gluon fields may arise only owing to a direct collision rather than owing to any echo-like effects.
Noncommutative Scalar Field Minimally Coupled to Gravity
NASA Astrophysics Data System (ADS)
Bertolami, Orfeu
A model for noncommutative scalar fields coupled to gravity based on the generalization of the Moyal product is proposed. Solutions compatible with homogeneous and isotropic flat Robertson-Walker spaces to first non-trivial order in the perturbation of the star-product are presented. It is shown that in the context of a typical chaotic inflationary scenario, at least in the slow-roll regime, noncommutativity yields no observable effect.
NASA Astrophysics Data System (ADS)
Flury, J.
2016-06-01
Quantum metrology enables new applications in geodesy, including relativistic geodesy. The recent progress in optical atomic clocks and in long-distance frequency transfer by optical fiber together pave the way for using measurements of the gravitational frequency redshift for geodesy. The remote comparison of frequencies generated by calibrated clocks will allow for a purely relativistic determination of differences in gravitational potential and height between stations on Earth surface (chronometric leveling). The long-term perspective is to tie potential and height differences to atomic standards in order to overcome the weaknesses and inhomogeneity of height systems determined by classical spirit leveling. Complementarily, gravity measurements with atom interferometric setups, and satellite gravimetry with space borne laser interferometers allow for new sensitivities in the measurement of the Earth's gravity field.
Finite- to zero-range relativistic mean-field interactions
Niksic, T.; Vretenar, D.; Lalazissis, G. A.; Ring, P.
2008-03-15
We study the relation between the finite-range (meson-exchange) and zero-range (point-coupling) representations of effective nuclear interactions in the relativistic mean-field framework. Starting from the phenomenological interaction DD-ME2 with density-dependent meson-nucleon couplings, we construct a family of point-coupling effective interactions for different values of the strength parameter of the isoscalar-scalar derivative term. In the meson-exchange picture this corresponds to different values of the {sigma}-meson mass. The parameters of the isoscalar-scalar and isovector-vector channels of the point-coupling interactions are adjusted to nuclear matter and ground-state properties of finite nuclei. By comparing results for infinite and semi-infinite nuclear matter, ground-state masses, charge radii, and collective excitations, we discuss constraints on the parameters of phenomenological point-coupling relativistic effective interaction.
Electric field replaces gravity in laboratory
NASA Astrophysics Data System (ADS)
Gorgolewski, S.
For several years experiments in physical laboratories and in the fitotron have shown that one can replace gravitational field with electrical fields for plants. First obvious experiments in strong electrical fields in the MV/m regi on show that any materials and living plants respond immediately to Coulomb forces. Such fields are found in nature during thunderstorms. One has to be very careful in handling such strong fields for safety reasons. The fair weather global electrical field is about 20,000 times weaker. The coulomb forces are proportional to the square of the field strength and are thus 400 milion times weaker for a field of the order of 100 V/m.Yet it was found that some plants respond to such "weak" fields. We must remember that the electrical field is a factor of 10 38 times stronger than gravitational interaction. In plants we have dissociated in water mineral salts and the ions are subject to such ernormous forces. It was shown and published that the positive charges in the air in fields of the order of 3kV/m enhance lettuce growth by a factor of four relative to fields about 30 times weaker (100V/m). Reversal of the field polarity reverses the direction of plant growth and retards the plant's growth. Such fields overpower the gravitropism in the laboratory. More so horizontal electrical field is othogonal to gravity, now the fields do not see each other. Lettuce now growth horizontally ignoring the gravitational field. We can thus select the plants whose electrotropism even in the laboratory overwhelms gravity. This is important for the long space flights that we must grow vegetarian food for the crew. The successful harvesting of wheat in orbit does not contradict our experimental findings because wheat is not electrotropic like all plants from the grass family. The results of fitotron experiments with kV/m electrical fields are richly illustrated with colour digital photographs. We also subjected the candle flame to very strong horizontal
Studies of GRACE Gravity Field Inversion Techniques
NASA Astrophysics Data System (ADS)
Wang, L.; Shum, C.; Duan, J.; Schmidt, M.; Yuan, D.; Watkins, M. M.
2008-12-01
The geophysical inverse problem using satellite observations, such as GRACE, to estimate gravity change and mass variations at the Earth's surface is a well-known ill-posed problem. Different methods using different basis function (representing the gravity field) for different purposes (global or regional inversion) have been employed to obtain a stable solution, such as Bayesian estimation with prior information, the repro-BIQUUE of variance components and iterative least-squares estimation with simultaneous updating of a prior covariance, and to achieve enhanced spatial resolutions. The gravity field representation methods include spherical harmonics, regional gridded data (including mascons), and various wavelet representations (Poisson wavelets, Blackman band-limited regional wavelets with global representation). Finally, the use of data types (KBR range, range-rate, range-rate-rate) and data-generation methods (e.g., nonlinear orbit determination and geophysical inverse approach, energy conservation principle, etc) could also reflect relative inversion accuracy and the content of signal spectra in the resulting solution. In this contribution, we present results of a simulation experiment, which used various solution techniques and data types to attempt to quantify the relative advantage and disadvantage of each of the techniques.
Subduction dynamics: Constraints from gravity field observations
NASA Technical Reports Server (NTRS)
Mcadoo, D. C.
1985-01-01
Satellite systems do the best job of resolving the long wavelength components of the Earth's gravity field. Over the oceans, satellite-borne radar altimeters such as SEASAT provide the best resolution observations of the intermediate wavelength components. Satellite observations of gravity contributed to the understanding of the dynamics of subduction. Large, long wavelength geoidal highs generally occur over subduction zones. These highs are attributed to the superposition of two effects of subduction: (1) the positive mass anomalies of subducting slabs themselves; and (2) the surface deformations such as the trenches convectively inducted by these slabs as they sink into the mantle. Models of this subduction process suggest that the mantle behaves as a nonNewtonian fluid, its effective viscosity increases significantly with depth, and that large positive mass anomalies may occur beneath the seismically defined Benioff zones.
GRAIL gravity field determination using the Celestial Mechanics Approach
NASA Astrophysics Data System (ADS)
Arnold, Daniel; Bertone, Stefano; Jäggi, Adrian; Beutler, Gerhard; Mervart, Leos
2015-11-01
The NASA mission GRAIL (Gravity Recovery and Interior Laboratory) inherited its concept from the GRACE (Gravity Recovery and Climate Experiment) mission to determine the gravity field of the Moon. We present lunar gravity fields based on the data of GRAIL's primary mission phase. Gravity field recovery is realized in the framework of the Celestial Mechanics Approach, using a development version of the Bernese GNSS Software along with Ka-band range-rate data series as observations and the GNI1B positions provided by NASA JPL as pseudo-observations. By comparing our results with the official level-2 GRAIL gravity field models we show that the lunar gravity field can be recovered with a high quality by adapting the Celestial Mechanics Approach, even when using pre-GRAIL gravity field models as a priori fields and when replacing sophisticated models of non-gravitational accelerations by appropriately spaced pseudo-stochastic pulses (i.e., instantaneous velocity changes). We present and evaluate two lunar gravity field solutions up to degree and order 200 - AIUB-GRL200A and AIUB-GRL200B. While the first solution uses no gravity field information beyond degree 200, the second is obtained by using the official GRAIL field GRGM900C up to degree and order 660 as a priori information. This reduces the omission errors and demonstrates the potential quality of our solution if we resolved the gravity field to higher degree.
A framework for modelling kinematic measurements in gravity field applications
NASA Technical Reports Server (NTRS)
Schwarz, K. P.; Wei, M.
1989-01-01
To assess the resolution of the local gravity field from kinematic measurements, a state model for motion in the gravity field of the earth is formulated. The resulting set of equations can accommodate gravity gradients, specific force, acceleration, velocity and position as input data and can take into account approximation errors as well as sensor errors.
Quantum gravity model with fundamental spinor fields
NASA Astrophysics Data System (ADS)
Obukhov, Yu. N.; Hehl, F. W.
2014-01-01
We discuss the possibility that gravitational potentials (metric, coframe and connection) may emerge as composite fields from more fundamental spinor constituents. We use the formalism of Poincaré gauge gravity as an appropriate theoretical scheme for the rigorous development of such an approach. We postulate the constitutive relations of an elastic Cosserat type continuum that models spacetime. These generalized Hooke and MacCullagh type laws consistently take into account the translational and Lorentz rotational deformations, respectively. The resulting theory extends the recently proposed Diakonov model. An intriguing feature of our theory is that in the lowest approximation it reproduces Heisenberg's nonlinear spinor model.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-09
We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed.
An approach to adjustment of relativistic mean field model parameters
NASA Astrophysics Data System (ADS)
Bayram, Tuncay; Akkoyun, Serkan
2017-09-01
The Relativistic Mean Field (RMF) model with a small number of adjusted parameters is powerful tool for correct predictions of various ground-state nuclear properties of nuclei. Its success for describing nuclear properties of nuclei is directly related with adjustment of its parameters by using experimental data. In the present study, the Artificial Neural Network (ANN) method which mimics brain functionality has been employed for improvement of the RMF model parameters. In particular, the understanding capability of the ANN method for relations between the RMF model parameters and their predictions for binding energies (BEs) of 58Ni and 208Pb have been found in agreement with the literature values.
Systematic study of bubble nuclei in relativistic mean field model
Shukla, A.; Åberg, S.; Bajpeyi, A.
2016-01-15
We have theoretically studied potential bubble nuclei ({sup 20,22}O, {sup 34,36}Si, and {sup 46}Ar), which are experimentally accessible and have attracted several studies in the recent past. Relativistic mean field is employed in conjunction with the NL–SH parameter set. Our results show that among the possible candidates, {sup 22}Oand {sup 34}Si may be the most prominent candidates, showing significant depletion of density at the center, which could be verified experimentally in the near future with some of the experiments underway.
Bose-Einstein condensation of relativistic Scalar Field Dark Matter
Urena-Lopez, L. Arturo
2009-01-15
Standard thermodynamical results of ideal Bose gases are used to study the possible formation of a cosmological Bose-Einstein condensate in Scalar Field Dark Matter models; the main hypothesis is that the boson particles were in thermal equilibrium in the early Universe. It is then shown that the only relevant case needs the presence of both particles and anti-particles, and that it corresponds to models in which the bosonic particle is very light. Contrary to common wisdom, the condensate should be a relativistic phenomenon. Some cosmological implications are discussed in turn.
Relativistic Killingbeck energy states under external magnetic fields
NASA Astrophysics Data System (ADS)
Eshghi, M.; Mehraban, H.; Ikhdair, S. M.
2016-07-01
We address the behavior of the Dirac equation with the Killingbeck radial potential including the external magnetic and Aharonov-Bohm (AB) flux fields. The spin and pseudo-spin symmetries are considered. The correct bound state spectra and their corresponding wave functions are obtained. We seek such a solution using the biconfluent Heun's differential equation method. Further, we give some of our results at the end of this study. Our final results can be reduced to their non-relativistic forms by simply using some appropriate transformations. The spectra, in the spin and pseudo-spin symmetries, are very similar with a slight difference in energy spacing between different states.
Critical parameters of consistent relativistic mean-field models
NASA Astrophysics Data System (ADS)
Lourenço, O.; Dutra, M.; Menezes, D. P.
2017-06-01
In the present work, the critical temperature, critical pressure, and critical density, known as the critical parameters related to the liquid-gas phase transition are calculated for 34 relativistic mean-field models, which were shown to satisfy nuclear matter constraints in a comprehensive study involving 263 models. The compressibility factor was calculated and all 34 models present values lower than the one obtained with the van der Waals equation of state. The critical temperatures were compared with experimental data and just two classes of models can reach values close to them. A correlation between the critical parameters and the incompressibility was obtained.
The realistic models of relativistic stars in f (R) = R + αR 2 gravity
NASA Astrophysics Data System (ADS)
Astashenok, Artyom V.; Odintsov, Sergei D.; de la Cruz-Dombriz, Álvaro
2017-10-01
In the context of f(R)=R+α R2 gravity, we study the existence of neutron and quark stars for various α with no intermediate approximation in the system of equations. Analysis shows that for positive α the scalar curvature does not drop to zero at the star surface (as in general relativity) but exponentially decreases with distance. Also the stellar mass bounded by star surface decreases when the value α increases. Nonetheless distant observers would observe a gravitational mass due to appearance of a so-called gravitational sphere around the star. The non-zero curvature contribution to the gravitational mass eventually is shown to compensate the stellar mass decrease for growing α’s. We perform our analysis for several equations of state including purely hadronic configurations as well as hyperons and quark stars. In all cases, we assess that the relation between the parameter α and the gravitational mass weakly depends upon the chosen equation of state. Another interesting feature is the increase of the star radius in comparison with general relativity for stars with masses close to maximal, whereas for intermediate masses 1.4 –1.6 M_ȯ the radius of star depends upon α very weakly. Also the decrease in the mass bounded by star surface may cause the surface redshift to decrease in R 2-gravity when compared to Einsteinian predictions. This effect is shown to hardly depend upon the observed gravitational mass. Finally, for negative values of α our analysis shows that outside the star the scalar curvature has damped oscillations but the contribution of the gravitational sphere into the gravitational mass increases indefinitely with radial distance putting into question the very existence of such relativistic stars.
Regional gravity field modelling from GOCE observables
NASA Astrophysics Data System (ADS)
Pitoňák, Martin; Šprlák, Michal; Novák, Pavel; Tenzer, Robert
2017-01-01
In this article we discuss a regional recovery of gravity disturbances at the mean geocentric sphere approximating the Earth over the area of Central Europe from satellite gravitational gradients. For this purpose, we derive integral formulas which allow converting the gravity disturbances onto the disturbing gravitational gradients in the local north-oriented frame (LNOF). The derived formulas are free of singularities in case of r ≠ R . We then investigate three numerical approaches for solving their inverses. In the initial approach, the integral formulas are firstly modified for solving individually the near- and distant-zone contributions. While the effect of the near-zone gravitational gradients is solved as an inverse problem, the effect of the distant-zone gravitational gradients is computed by numerical integration from the global gravitational model (GGM) TIM-r4. In the second approach, we further elaborate the first scenario by reducing measured gravitational gradients for gravitational effects of topographic masses. In the third approach, we apply additional modification by reducing gravitational gradients for the reference GGM. In all approaches we determine the gravity disturbances from each of the four accurately measured gravitational gradients separately as well as from their combination. Our regional gravitational field solutions are based on the GOCE EGG_TRF_2 gravitational gradients collected within the period from November 1 2009 until January 11 2010. Obtained results are compared with EGM2008, DIR-r1, TIM-r1 and SPW-r1. The best fit, in terms of RMS (2.9 mGal), is achieved for EGM2008 while using the third approach which combine all four well-measured gravitational gradients. This is explained by the fact that a-priori information about the Earth's gravitational field up to the degree and order 180 was used.
The Gravity Fields of the Saturnian Satellites
NASA Astrophysics Data System (ADS)
Iess, L.
2011-12-01
In its tour of the Saturnian system, begun on July 1st, 2004, the Cassini spacecraft had many close flybys of Saturn's main satellites. However, due to impossibility to carry out simultaneously remote sensing observations and microwave tracking from ground, only a small fraction of those flybys could be exploited for gravity measurements. So far, the quadrupole field has been mapped only for Titan, Rhea and Enceladus, while for Hyperion and Iapetus the mass was the only accessible parameter. For Titan and Enceladus, the only satellites targeted more than once for gravity observations, also a rough geoid to degree and order 3 has been determined. Satellite gravity investigations rely upon accurate measurements of the spacecraft range rate, enabled by coherent, two-way radio links at X and Ka band (8.4 and 32.5 GHz). The use of hydrogen masers frequency standards at the ground station and the consid-erable suppression of plasma noise at X and Ka band frequen-cies provide range rate accuracies of 10-30 micron/s at integra-tion times of 60 s. Thanks to the higher frequency of the radio link, these measurement accuracies are in the average a factor of 10 better than those attained by Galileo in its tour of the Jovian system. However, in order to attain a reliable determination of the low degree field, good measurements must be combined with appropriate flyby geometries and adequate sampling, a condition that necessarily requires multiple flybys. We review the main results obtained so far by Cassini for Titan, Rhea and Enceladus, and discuss the methods of analysis used by the Radio Science Team.
NASA Technical Reports Server (NTRS)
Ni, W.-T.
1972-01-01
Metric theories of gravity are compiled and classified according to the types of gravitational fields they contain, and the modes of interaction among those fields. The gravitation theories considered are classified as (1) general relativity, (2) scalar-tensor theories, (3) conformally flat theories, and (4) stratified theories with conformally flat space slices. The post-Newtonian limit of each theory is constructed and its Parametrized Post-Newtonian (PPN) values are obtained by comparing it with Will's version of the formalism. Results obtained here, when combined with experimental data and with recent work by Nordtvedt and Will and by Ni, show that, of all theories thus far examined by our group, the only currently viable ones are general relativity, the Bergmann-Wagoner scalar-tensor theory and its special cases (Nordtvedt; Brans-Dicke-Jordan), and a recent, new vector-tensor theory by Nordtvedt, Hellings, and Will.
NASA Technical Reports Server (NTRS)
Ni, W.-T.
1972-01-01
Metric theories of gravity are compiled and classified according to the types of gravitational fields they contain, and the modes of interaction among those fields. The gravitation theories considered are classified as (1) general relativity, (2) scalar-tensor theories, (3) conformally flat theories, and (4) stratified theories with conformally flat space slices. The post-Newtonian limit of each theory is constructed and its Parametrized Post-Newtonian (PPN) values are obtained by comparing it with Will's version of the formalism. Results obtained here, when combined with experimental data and with recent work by Nordtvedt and Will and by Ni, show that, of all theories thus far examined by our group, the only currently viable ones are general relativity, the Bergmann-Wagoner scalar-tensor theory and its special cases (Nordtvedt; Brans-Dicke-Jordan), and a recent, new vector-tensor theory by Nordtvedt, Hellings, and Will.
Magnetic field modification to the relativistic runaway electron avalanche length
NASA Astrophysics Data System (ADS)
Cramer, E. S.; Dwyer, J. R.; Rassoul, H. K.
2016-11-01
This paper explores the impact of the geomagnetic field on the relativistic runaway electron avalanche length, λe-. Coleman and Dwyer (2006) developed an analytical fit to Monte Carlo simulations using the Runaway Electron Avalanche Model. In this work, we repeat this process but with the addition of the geomagnetic field in the range of [100,900]/n μT, where n is the ratio of the density of air at altitude to the sea level density. As the ambient electric field approaches the runaway threshold field (Eth≈284 kV/m sea level equivalent), it is shown that the magnetic field has an impact on the orientation of the resulting electron beam. The runaway electrons initially follow the vertically oriented electric field but then are deflected in the v × B direction, and as such, the electrons experience more dynamic friction due to the increase in path length. This will be shown to result in a difference in the avalanche length from the case where B = 0. It will also be shown that the average energy of the runaway electrons will decrease while the required electric field to produce runaway electrons increases. This study is also important in understanding the physics of terrestrial gamma ray flashes (TGFs). Not only will this work impact relativistic feedback rates determined from simulations, it may also be useful in studying spectroscopy of TGFs observed from balloon and aircraft measurements. These models may also be used in determining beaming properties of TGFs originating in the tropical regions seen from orbiting spacecraft.
Propagation peculiarities of mean field massive gravity
Deser, S.; Waldron, A.; Zahariade, G.
2015-07-28
Massive gravity (mGR) describes a dynamical “metric” on a fiducial, background one. We investigate fluctuations of the dynamics about mGR solutions, that is about its “mean field theory”. Analyzing mean field massive gravity (m¯GR) propagation characteristics is not only equivalent to studying those of the full non-linear theory, but also in direct correspondence with earlier analyses of charged higher spin systems, the oldest example being the charged, massive spin 3/2 Rarita–Schwinger (RS) theory. The fiducial and mGR mean field background metrics in the m¯GR model correspond to the RS Minkowski metric and external EM field. The common implications in bothmore » systems are that hyperbolicity holds only in a weak background-mean-field limit, immediately ruling both theories out as fundamental theories; a situation in stark contrast with general relativity (GR) which is at least a consistent classical theory. Moreover, even though both m¯GR and RS theories can still in principle be considered as predictive effective models in the weak regime, their lower helicities then exhibit superluminal behavior: lower helicity gravitons are superluminal as compared to photons propagating on either the fiducial or background metric. Thus our approach has uncovered a novel, dispersive, “crystal-like” phenomenon of differing helicities having differing propagation speeds. As a result, this applies both to m¯GR and mGR, and is a peculiar feature that is also problematic for consistent coupling to matter.« less
Global gravity field recovery from the ARISTOTELES satellite mission
NASA Astrophysics Data System (ADS)
Visser, P. N. A. M.; Wakker, K. F.; Ambrosius, B. A. C.
1994-02-01
One of the primary objectives of the future ARISTOTELES satellite mission is to map Earth's gravity field with high resolution and accuracy. In order to achieve this objective, the ARISTOTELES satellite will be equipped with a gravity gradiometer and a Global Positioning System (GPS) receiver. Global gravity field error analyses have been performed for several combinations of gradiometer and GPS observations. These analyses indicated that the bandwidth limitation of the gradiometer prevents a stable high-accuracy, high-resolution gravity solution if no additional information is available. However, with the addition of high-accuracy GPS observations, a stable gravity field solution can be obtained. A combination of the measurements acquired by the high-quality GPS receiver and the bandwidth-limited gradiometer on board ARISTOTELES will yield a global gravity field model with a resolution of less than 100 km and with an accuracy of better than 5 mGal for gravity anomalies and 10 cm for geoid undulations.
LISA sensitivities to gravitational waves from relativistic metric theories of gravity
NASA Astrophysics Data System (ADS)
Tinto, Massimo; Alves, Márcio Eduardo Da Silva
2010-12-01
The direct observation of gravitational waves will provide a unique tool for probing the dynamical properties of highly compact astrophysical objects, mapping ultrarelativistic regions of space-time, and testing Einstein’s general theory of relativity. LISA (Laser Interferometer Space Antenna), a joint National Aeronautics and Space Administration and European Space Agency mission to be launched in the next decade, will perform these scientific tasks by detecting and studying low-frequency cosmic gravitational waves through their influence on the phases of six modulated laser beams exchanged between three remote spacecraft. By directly measuring the polarization components of the waves LISA will detect, we will be able to test Einstein’s theory of relativity with good sensitivity. Since a gravitational wave signal predicted by the most general relativistic metric theory of gravity accounts for six polarization modes (the usual two Einstein’s tensor polarizations as well as two vector and two scalar wave components), we have derived the LISA time-delay interferometric responses and estimated their sensitivities to vector- and scalar-type waves. We find that (i) at frequencies larger than roughly the inverse of the one-way light time (≈6×10-2Hz), LISA is more than ten times sensitive to scalar-longitudinal and vector signals than to tensor and scalar-transverse waves, and (ii) in the low part of its frequency band is equally sensitive to tensor and vector waves and somewhat less sensitive to scalar signals.
Gravity fields of the solar system
NASA Technical Reports Server (NTRS)
Zendell, A.; Brown, R. D.; Vincent, S.
1975-01-01
The most frequently used formulations of the gravitational field are discussed and a standard set of models for the gravity fields of the earth, moon, sun, and other massive bodies in the solar system are defined. The formulas are presented in standard forms, some with instructions for conversion. A point-source or inverse-square model, which represents the external potential of a spherically symmetrical mass distribution by a mathematical point mass without physical dimensions, is considered. An oblate spheroid model is presented, accompanied by an introduction to zonal harmonics. This spheroid model is generalized and forms the basis for a number of the spherical harmonic models which were developed for the earth and moon. The triaxial ellipsoid model is also presented. These models and their application to space missions are discussed.
Gravity duals for nonrelativistic conformal field theories.
Balasubramanian, Koushik; McGreevy, John
2008-08-08
We attempt to generalize the anti-de Sitter/conformal field theory correspondence to nonrelativistic conformal field theories which are invariant under Galilean transformations. Such systems govern ultracold atoms at unitarity, nucleon scattering in some channels, and, more generally, a family of universality classes of quantum critical behavior. We construct a family of metrics which realize these symmetries as isometries. They are solutions of gravity with a negative cosmological constant coupled to pressureless dust. We discuss realizations of the dust, which include a bulk superconductor. We develop the holographic dictionary and find two-point correlators of the correct form. A strange aspect of the correspondence is that the bulk geometry has two extra noncompact dimensions.
Estimate of the maximum induced magnetic field in relativistic shocks
NASA Astrophysics Data System (ADS)
Ghorbanalilu, M.; Sadegzadeh, S.
2017-01-01
The proton-driven Weibel instability is a crucial process for amplifying the generated magnetic fields in gamma-ray bursts. An expression for the saturation level of magnetic fields is estimated in a relativistic shock consisting of electron-proton plasmas. Within the shock transition layer, the plasma is modelled with the waterbag and Maxwell-Jüttner distribution functions for asymmetric counter-propagating proton beams and isotropic background electrons, respectively. The proton-driven Weibel-type instability in the linear phase is investigated thoroughly and then the instability conditions and the stabilization mechanisms are considered in details just after the shutdown of the electron Weibel instability. The growth rate of the instability and the saturated magnetic field strength are obtained in terms of the effective proton beam Mach number, asymmetry parameter, and the background electron temperature. In this paper, fully relativistic kinetic treatment is used to formulate the dispersion relation for the proton Weibel-type instability. Then, by using the magnetic trapping criteria, the saturated magnetic field strength is computed. In the present scenario, the instability includes two stages: in the first stage the electron Weibel instability evolves very rapidly, but in the second one because of the free energy stored in the slow counter-propagating proton beams, the instability is further amplified in the context of electrons with an isotropic distribution function. Increment of the growth rate and saturated magnetic field by increasing (decreasing) the effective proton beam Mach number (the asymmetry parameter) is deduced from the results. It is shown that at the temperatures around 108 K a maximum magnetic field up to around 56 G can be detected by this mechanism after the saturation time.
Beyond the relativistic mean-field approximation -- collective correlations
NASA Astrophysics Data System (ADS)
Li, Zhipan; Nikšić, Tamara; Vretenar, Dario; Yao, Jiangming
Semi-empirical relativistic energy density functionals (EDFs) or effective interactions implicitly comprise short-range correlations related to the repulsive core of the inter-nucleon interaction, and long-range correlations mediated by nuclear resonance modes. To model spectroscopic properties of finite nuclei, the self-consistent mean-field method must be extended to include collective correlations that arise from restoration of broken symmetries and fluctuations in collective coordinates. These correlations are sensitive to shell effects, vary with particle number, and cannot be included in a universal EDF. We review and compare recent advances in "beyond mean-field" methods based on relativistic EDFs: the angular-momentum and particle-number projected triaxial generator coordinate method, the five-dimensional quadrupole collective Hamiltonian and the axial quadrupole-octupole collective Hamiltonian models. Illustrative applications include low-energy collective excitation spectra and electromagnetic transition rates of nuclei characterised by quadrupole and/or octupole deformations: 24Mg, 76Kr, 240Pu and 224Ra, in comparison with available data.
DeDeo, Simon; Psaltis, Dimitrios
2003-04-11
In contrast to gravity in the weak-field regime, which has been subject to numerous experimental tests, gravity in the strong-field regime is largely unconstrained by observations. We show that gravity theories that pass solar system tests, but that diverge from general relativity in the strong-field regime, predict neutron stars with significantly different properties than their general relativistic counterparts. The range of redshfits of surface atomic lines predicted by such theories is significantly wider than the uncertainty introduced by our lack of knowledge of the equation of state of ultradense matter. Measurements of such lines with x-ray observatories can thus put new constraints on strong-field gravity.
Gravity Field Mapping of Mars with MGS
NASA Technical Reports Server (NTRS)
Smith, David E.; Zuber, Maria T.; Lemoine, Frank G.
1998-01-01
Tracking of the MGS spacecraft in orbit at Mars by the Deep Space Network since last September has provided doppler and range measurements that are being used to improve the model of the Mars gravity field. During most of October 1997, April 1998, and June thru August 1998 high quality tracking data were obtained while the periapse was in the northern hemisphere at altitudes in the 170 to 190 km range. The eccentric orbit had a period of about 11.5 hrs and an inclination of about 96.2 degrees so that low altitude tracking was obtained over most of the northern hemisphere, including the north polar icecap. Data from the earlier Mariner 9 and Viking missions have been added to the MGS data and a series of experimental gravity models developed from the combined datasets. These models have generally been of degree and order 70 and are a significant improvement over earlier models that did not include the MGS data. Gravity anomalies over the north polar cap region of Mars are generally less than 50 to 100 mgals and show no obvious correlation with the topography. Successive MGS orbits derived using these new models are showing agreement at the 100 meter level, and this has been confirmed with the laser altimeter (MOLA) on MGS These comparisons are expected to improve significantly as more tracking data get included in the solution and the MGS orbit becomes more circular giving a more balanced geographical distribution of data at low altitude. This will happen early in 1999 as the orbit approaches the mapping configuration of a circular orbit at about 400 Km.
Applications of satellite technology to gravity field determination
NASA Technical Reports Server (NTRS)
Argentiero, P.; Lowrey, B. E.
1975-01-01
Various techniques for using satellite technology to determine the earth's gravity field are analyzed and compared. A high-low configuration satellite to satellite tracking mission is recommended for the determination of the long wavelength portion of the gravity field. Satellite altimetry and satellite gradiometry experiments are recommended for determination of the short wavelength portion of the gravity field. The recently developed least squares collocation method for estimating the gravity field from satellite derived data is analyzed and its equivalence to conventional methods is demonstrated.
Relativistic particle acceleration by obliquely propagating electromagnetic fields
NASA Astrophysics Data System (ADS)
Villalón, Elena; Burke, William J.
1987-12-01
The relativistic equations of motion are analyzed for charged particles in a magnetized plasma and externally imposed electromagnetic fields (ω, k), which have wave vectors k that are at arbitrary angles. The particle energy is obtained from a set of nonlinear differential equations, as a function of time, initial conditions, and cyclotron harmonic numbers. For a given cyclotron resonance, the energy oscillates in time within the limits of a potential well; stochastic acceleration occurs if the widths of different Hamiltonian potentials overlap. The net energy gain for a given harmonic increase with the angle of propagation, and decreases as the magnitude of the wave magnetic field increases. Potential applications of these results to the acceleration of ionsopheric electrons are presented.
Aspects of nonlocality in quantum field theory, quantum gravity and cosmology
NASA Astrophysics Data System (ADS)
Barvinsky, A. O.
2015-02-01
This paper contains a collection of essays on nonlocal phenomena in quantum field theory, gravity and cosmology. Mechanisms of nonlocal contributions to the quantum effective action are discussed within the covariant perturbation expansion in field strengths and spacetime curvatures. Euclidean version of the Schwinger-Keldysh technique for quantum expectation values is presented as a special rule of obtaining the nonlocal effective equations of motion for the mean quantum field from the Euclidean effective action. This rule is applied to a new model of ghost free nonlocal cosmology which can generate the de Sitter (dS) cosmological evolution at an arbitrary value of Λ — a model of dark energy with the dynamical scale selected by a kind of a scaling symmetry breaking mechanism. This model is shown to interpolate between the superhorizon phase of a scalar mediated gravity and the short distance general relativistic limit in a special metric frame related by a nonlocal conformal transformation to the original metric.
Global gravity field models and their use for geophysical modelling
NASA Astrophysics Data System (ADS)
Pail, R.
2015-12-01
During the last decade, the successful operation of the dedicated satellite missions GOCE and GRACE have revolutionized our picture of the Earth's gravity field. They delivered static global gravity field maps with high and homogeneous accuracy for spatial length-scales down to 70-80 km. The current satellite-only models of the fifth generation including GOCE data have reached accuracies of about 2 cm in geoid height and less than 0.7 mGal in gravity anomalies at 100 km spatial half-wavelength. However, the spatial resolution of gravity models derived from satellite data is limited. Since precise knowledge of the Earth's gravity field structure with very high resolution is essential in solid Earth applications such as lithospheric modelling, geological interpretation and exploration geophysics, satellite-only models are complemented by combined gravity field models, which contain very high-resolution gravity field information obtained by terrestrial gravity measurements over continents, and satellite altimetry over the oceans. To further increase the spatial resolution beyond 10-20 km, measured terrestrial and satellite data can also be augmented by high-resolution gravity field signals synthesized from topographic models. In this contribution an overview of the construction of satellite-only and combined global gravity field models is given. The specific characteristics of the individual input data and the resulting models will be assessed, and their impact for geophysical modelling will be discussed. On the basis of selected case studies, commission and omission errors and thus the contribution and impact of satellite gravity data on gravity field applications will be quantified, and the benefit of current satellite gravity data shall be investigated and demonstrated. Future gravity field missions beyond GRACE Follow-On will provide global gravity field information with further increased accuracy, spatial and temporal resolution. In an international initiative
Global gravity field modeling based on GOCE and complementary gravity data
NASA Astrophysics Data System (ADS)
Fecher, Thomas; Pail, Roland; Gruber, Thomas
2015-03-01
A combined high-resolution global gravity field model up to degree/order (d/o) 720, including error estimates in terms of a full variance-covariance matrix, is determined from GOCE (Gravity field and steady-state Ocean Circulation Explorer) and complementary gravity field data. GOCE observations, highly accurate in the low to medium wavelength part (∼d/o 40-220), are supplemented by GRACE (Gravity Recovery and Climate Experiment) with high accuracy in the low wavelength part (∼d/o 2-150), and altimetric and terrestrial gravity field observations to enhance the spectral resolution of the combined gravity field model. The theory of combining different data sets by least-squares techniques, applying optimum weighting strategies, is illustrated. Full normal equation systems are used to enable stochastic modeling of all individual observations. High performance computing techniques are applied in order to handle normal equations of enormous size (about 2 TB). The quality of the resulting gravity field solution is analyzed by comparisons with independent gravity field models and GPS/leveling observations, and also in the frame of the computation of a mean dynamic topography. The validation shows that the new combined model TUM2013C achieves the quality level of established high-resolution models. Compared to EGM2008, the improvements due to the inclusion of GOCE are clearly visible.
Rotating and binary relativistic stars with magnetic field
NASA Astrophysics Data System (ADS)
Markakis, Charalampos
We develop a geometrical treatment of general relativistic magnetohydrodynamics for perfectly conducting fluids in Einstein--Maxwell--Euler spacetimes. The theory is applied to describe a neutron star that is rotating or is orbiting a black hole or another neutron star. Under the hypotheses of stationarity and axisymmetry, we obtain the equations governing magnetohydrodynamic equilibria of rotating neutron stars with poloidal, toroidal or mixed magnetic fields. Under the hypothesis of an approximate helical symmetry, we obtain the first law of thermodynamics governing magnetized equilibria of double neutron star or black hole - neutron star systems in close circular orbits. The first law is written as a relation between the change in the asymptotic Noether charge deltaQ and the changes in the area and electric charge of black holes, and in the vorticity, baryon rest mass, entropy, charge and magnetic flux of the magnetofluid. In an attempt to provide a better theoretical understanding of the methods used to construct models of isolated rotating stars and corotating or irrotational binaries and their unexplained convergence properties, we analytically examine the behavior of different iterative schemes near a static solution. We find the spectrum of the linearized iteration operator and show for self-consistent field methods that iterative instability corresponds to unstable modes of this operator. On the other hand, we show that the success of iteratively stable methods is due to (quasi-)nilpotency of this operator. Finally, we examine the integrability of motion of test particles in a stationary axisymmetric gravitational field. We use a direct approach to seek nontrivial constants of motion polynomial in the momenta---in addition to energy and angular momentum about the symmetry axis. We establish the existence and uniqueness of quadratic constants and the nonexistence of quartic constants for stationary axisymmetric Newtonian potentials with equatorial symmetry
Quantum reduced loop gravity: Extension to gauge vector field
NASA Astrophysics Data System (ADS)
Bilski, Jakub; Alesci, Emanuele; Cianfrani, Francesco; Donà, Pietro; Marcianò, Antonino
2017-05-01
Within the framework of quantum reduced loop gravity, we quantize the Hamiltonian for a gauge vector field. The regularization can be performed using tools analogous to the ones adopted in full loop quantum gravity, while the matrix elements of the resulting operator between basis states are analytic coefficients. This analysis is the first step toward deriving the full quantum gravity corrections to the vector field semiclassical dynamics.
Braneworld gravity: influence of the moduli fields
NASA Astrophysics Data System (ADS)
Barceló, Carlos; Visser, Matt
2000-10-01
We consider the case of a generic braneworld geometry in the presence of one or more moduli fields (e.g. the dilaton) that vary throughout the bulk spacetime. Working in an arbitrary conformal frame, using the generalized junction conditions of gr-qc/0008008 and the Gauss-Codazzi equations, we derive the effective ``induced'' on-brane gravitational equations. As usual in braneworld scenarios, these equations do not form a closed system in that the bulk can exchange both information and stress-energy with the braneworld. We work with an arbitrary number of moduli fields described by an arbitrary sigma model, with arbitrary curvature couplings, arbitrary self interactions, and arbitrary dimension for the bulk. (The braneworld is always codimension one.) Among the novelties we encounter are modifications of the on-brane stress-energy conservation law, anomalous couplings between on-brane gravity and the trace of the on-brane stress-energy tensor, and additional possibilities for modifying the on-brane effective cosmological constant. After obtaining the general stress-energy ``conservation'' law and the ``induced Einstein equations'' we particularize the discussion to two particularly attractive cases: for a (n-2)-brane in ([n-1] + 1) dimensions we discuss both the effect of (1) generic variable moduli fields in the Einstein frame, and (2) the effect of a varying dilaton in the string frame.
Magnetic Field Generation and Particle Energization in Relativistic Shear Flows
NASA Astrophysics Data System (ADS)
Liang, Edison; Boettcher, Markus; Smith, Ian
2012-10-01
We present Particle-in-Cell simulation results of magnetic field generation by relativistic shear flows in collisionless electron-ion (e-ion) and electron-positron (e+e-) plasmas. In the e+e- case, small current filaments are first generated at the shear interface due to streaming instabilities of the interpenetrating particles from boundary perturbations. Such current filaments create transverse magnetic fields which coalesce into larger and larger flux tubes with alternating polarity, eventually forming ordered flux ropes across the entire shear boundary layer. Particles are accelerated across field lines to form power-law tails by semi-coherent electric fields sustained by oblique Langmuir waves. In the e-ion case, a single laminar slab of transverse flux rope is formed at the shear boundary, sustained by thin current sheets on both sides due to different drift velocities of electrons and ions. The magnetic field has a single polarity for the entire boundary layer. Electrons are heated to a fraction of the ion energy, but there is no evidence of power-law tail forming in this case.
Strong versus weak wave-turbulence in relativistic field theory
NASA Astrophysics Data System (ADS)
Berges, Jürgen; Sexty, Dénes
2011-04-01
Nonthermal scaling phenomena can exhibit a characteristic dependence on the dimensionality d of space. For d=3 and 4 we simulate a relativistic scalar field theory on a lattice and compute turbulent scaling exponents. We recover Kolmogorov or weak wave-turbulence in the perturbative high-momentum regime, where it exhibits the scaling exponent κw=d-3/2. In the nonperturbative infrared regime, we find a different scaling exponent κs=4(5) for d=3(4), which is in agreement with the recently predicted anomalously large values κs=d+1 of strong turbulence. We show how the latter can be seen to characterize stationary transport of a conserved effective particle number.
Relativistic mean field models for finite nuclei and neutron stars
NASA Astrophysics Data System (ADS)
Chen, Wei-Chia
In this dissertation we have created theoretical models for finite nuclei, nuclear matter, and neutron stars within the framework of relativistic mean field (RMF) theory, and we have used these models to investigate the elusive isovector sector and related physics, in particular, the neutron-skin thickness of heavy nuclei, the nuclear symmetry energy, and the properties of neutron stars. To build RMF models that incorporate collective excitations in finite nuclei in addition to their ground-state properties, we have extended the non-relativistic sum rule approach to the relativistic domain. This allows an efficient estimate of giant monopole energies. Moreover, we have combined an exact shell-model-like approach with the mean-field calculation to describe pairing correlations in open-shell nuclei. All the ingredients were then put together to establish the calibration scheme. We have also extended the transformation between model parameters and pseudo data of nuclear matter within the RMF context. Performing calibration in this pseudo data space can not only facilitate the searching algorithm but also make the pseudo data genuine model predictions. This calibration scheme is also supplemented by a covariance analysis enabling us to extract the information content of a model, including theoretical uncertainties and correlation coefficients. A series of RMF models subject to the same isoscalar constraints but one differing isovector assumption were then created using this calibration scheme. By comparing their predictions of the nuclear matter equation of state to both experimental and theoretical constraints, we found that a small neutron skin of about 0.16 fm in Pb208 is favored, indicating that the symmetry energy should be soft. To obtain stronger evidence, we proceeded to examine the evolution of the isotopic chains in both oxygen and calcium. Again, it was found that the model with such small neutron skin and soft symmetry energy can best describe both isotopic
I.Y. Dodin; N.J. Fisch; G.M. Fraiman
2003-02-06
The Lagrangian and Hamiltonian functions describing average motion of a relativistic particle under the action of intensive high-frequency electromagnetic radiation are obtained. In weak, low-frequency background fields, such a particle on average drifts with an effective, relativistically invariant mass, which depends on the intensity of the electromagnetic field.
Altimeter measurements for the determination of the Earth's gravity field
NASA Technical Reports Server (NTRS)
Tapley, B. D.; Schutz, B. E.; Shum, C. K.
1986-01-01
Progress in the following areas is described: refining altimeter and altimeter crossover measurement models for precise orbit determination and for the solution of the earth's gravity field; performing experiments using altimeter data for the improvement of precise satellite ephemerides; and analyzing an optimal relative data weighting algorithm to combine various data types in the solution of the gravity field.
NASA Astrophysics Data System (ADS)
Zhao, Qile; Guo, Jing; Hu, Zhigang; Shi, Chuang; Liu, Jingnan; Cai, Hua; Liu, Xianglin
2011-05-01
The GRACE (Gravity Recovery And Climate Experiment) monthly gravity models have been independently produced and published by several research institutions, such as Center for Space Research (CSR), GeoForschungsZentrum (GFZ), Jet Propulsion Laboratory (JPL), Centre National d’Etudes Spatiales (CNES) and Delft Institute of Earth Observation and Space Systems (DEOS). According to their processing standards, above institutions use the traditional variational approach except that the DEOS exploits the acceleration approach. The background force models employed are rather similar. The produced gravity field models generally agree with one another in the spatial pattern. However, there are some discrepancies in the gravity signal amplitude between solutions produced by different institutions. In particular, 10%-30% signal amplitude differences in some river basins can be observed. In this paper, we implemented a variant of the traditional variational approach and computed two sets of monthly gravity field solutions using the data from January 2005 to December 2006. The input data are K-band range-rates (KBRR) and kinematic orbits of GRACE satellites. The main difference in the production of our two types of models is how to deal with nuisance parameters. This type of parameters is necessary to absorb low-frequency errors in the data, which are mainly the aliasing and instrument errors. One way is to remove the nuisance parameters before estimating the geopotential coefficients, called NPARB approach in the paper. The other way is to estimate the nuisance parameters and geopotential coefficients simultaneously, called NPESS approach. These two types of solutions mainly differ in geopotential coefficients from degree 2 to 5. This can be explained by the fact that the nuisance parameters and the gravity field coefficients are highly correlated, particularly at low degrees. We compare these solutions with the official and published ones by means of spectral analysis. It is
Relativistic mean-field models and nuclear matter constraints
Dutra, M.; Lourenco, O.; Carlson, B. V.; Delfino, A.; Menezes, D. P.; Avancini, S. S.; Stone, J. R.; Providencia, C.; Typel, S.
2013-05-06
This work presents a preliminary study of 147 relativistic mean-field (RMF) hadronic models used in the literature, regarding their behavior in the nuclear matter regime. We analyze here different kinds of such models, namely: (i) linear models, (ii) nonlinear {sigma}{sup 3}+{sigma}{sup 4} models, (iii) {sigma}{sup 3}+{sigma}{sup 4}+{omega}{sup 4} models, (iv) models containing mixing terms in the fields {sigma} and {omega}, (v) density dependent models, and (vi) point-coupling ones. In the finite range models, the attractive (repulsive) interaction is described in the Lagrangian density by the {sigma} ({omega}) field. The isospin dependence of the interaction is modeled by the {rho} meson field. We submit these sets of RMF models to eleven macroscopic (experimental and empirical) constraints, used in a recent study in which 240 Skyrme parametrizations were analyzed. Such constraints cover a wide range of properties related to symmetric nuclear matter (SNM), pure neutron matter (PNM), and both SNM and PNM.
Relativistic charge currents in oblique electric and magnetic fields
NASA Astrophysics Data System (ADS)
Melia, Fulvio; Fatuzzo, Marco
1991-06-01
Runaway processes on neutron stars leading to the sudden release of large quantities of energy (up to of order 1040 erg) on time scales as short as a fraction of a second involve plasma heating and particle acceleration in superstrong magnetic fields H (of order 1012 G). These transient events are interesting from a theoretical standpoint because they require knowledge of particle transport properties in low-density plasmas (ɛe 1025 cm-3) threaded by both electric (E) and magnetic fields. The evaluation of matrix elements involving solutions to the Dirac equation for such a field configuration is often difficult and sometimes impossible, since no completely normalized wave function has yet been found. Here it is shown that, in the special case of E/H 10-4, a simplification of the overlap integrals permits an analytical integration that yields explicit expressions for the relativistic charge currents needed in the computation of the anisotropic conductivity tensor when E.H ≠ 0. The application of these results to the evaluation of the conductivity is briefly discussed. Among other things, this work is relevant to a theory of resistive magnetic tearing instabilities in a quantizing field.
Retrieving hydrological signals from current and future gravity field missions
NASA Astrophysics Data System (ADS)
Pail, Roland; Horvath, Alexander
2017-04-01
The Global Geodetic Observing System is formed by three pillars: Changes in Earth's shape, gravity field and rotation. Dedicated satellite missions are crucial in the determination and monitoring of the Earth's gravity field. Monitoring the gravity field and studying mass transport phenomena, responsible for the temporal variability of the gravity field, are of high interest. Especially the hydrology is of importance since the mechanisms of water redistribution and unexpected events like floods and droughts can have significant socio-economic impact. The presented study investigates in the possibilities and limits of current space geodetic missions like GRACE to observe such effects. The main target of the study is to determine the potential gain in accuracy as well as spatial and temporal resolution of target signals like hydrological events, whilst operating future mission scenarios. The results from a series of comprehensive simulation runs are presented to demonstrate the benefits to society operating dedicated future space geodetic gravity field missions.
Some exact solutions for a scalar field in the relativistic theory of gravitation
Sveshnikov, K.A.; Silaev, P.K. )
1989-03-01
The problem of finding exact solutions for matter fields in the relativistic theory of gravitation is of great interest. Particularly important is the question of the existence of particle-like solutions with finite sizes. As matter field it is natural to take a scalar field as the simplest. Moreover, study of this case can also be helpful for the study of other fields. Static spherically symmetric solutions for a scalar field in the relativistic theory of gravitation are found.
Bhuyan, M.; Panda, R. N.; Routray, T. R.; Patra, S. K.
2010-12-15
In the framework of relativistic mean field (RMF) theory, we have calculated the density distribution of protons and neutrons for {sup 40,42,44,48}Ca with NL3 and G2 parameter sets. The microscopic proton-nucleus optical potentials for p+{sup 40,42,44,48}Ca systems are evaluated from the Dirac nucleon-nucleon scattering amplitude and the density of the target nucleus using relativistic-Love-Franey and McNeil-Ray-Wallace parametrizations. We have estimated the scattering observables, such as the elastic differential scattering cross section, analyzing power and the spin observables with the relativistic impulse approximation (RIA). The results have been compared with the experimental data for a few selective cases and we find that the use of density as well as the scattering matrix parametrizations are crucial for the theoretical prediction.
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Mizuno, Y.; Hardee, P.; Hededal, C. B.; Fishman, G. J.
2006-01-01
Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets into ambient plasmas show that acceleration occurs in relativistic shocks. The Weibel instability created in shocks is responsible for particle acceleration, and generation and amplification of highly inhomogeneous, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection in relativistic jets. The "jitter" radiation from deflected electrons has different properties than the synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understand the complex time evolution and spectral structure in relativistic jets and gamma-ray bursts. We will present recent PIC simulations which show particle acceleration and magnetic field generation. We will also calculate associated self-consistent emission from relativistic shocks.
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Mizuno, Y.; Hardee, P.; Hededal, C. B.; Fishman, G. J.
2006-01-01
Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets into ambient plasmas show that acceleration occurs in relativistic shocks. The Weibel instability created in shocks is responsible for particle acceleration, and generation and amplification of highly inhomogeneous, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection in relativistic jets. The "jitter" radiation from deflected electrons has different properties than the synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understand the complex time evolution and spectral structure in relativistic jets and gamma-ray bursts. We will present recent PIC simulations which show particle acceleration and magnetic field generation. We will also calculate associated self-consistent emission from relativistic shocks.
The Impact of Geological Structures On The Gravity Field
NASA Astrophysics Data System (ADS)
Marti, U.
In general, a uniform standard density value is used for the calculation of topographic effects for gravity field modelling in Switzerland. Only a limited number of promi- nent mass anomalies is treated with an individual density. In some regions this causes problems in predicting the surface gravity or the deflections of the vertical. An actual example is the construction of a new 57 km railway tunnel, where accurate deflec- tions of the vertical are needed for the orientation of gyroscope measurements. It was rather doubtful if our standard national gravity field model would fulfil the accuracy demands. Therefore, a refinement of the gravity field model was performed by digi- tising all the relevant geological structures in the vicinity of the planned tunnel. This lead to a 3D density model of irregularly shaped polyhedrons. Their influence on the gravity field (potential, gravity, deflections of the vertical and their first derivatives) are calculated rigorously. First results of this study are now available and reveal that the influences of the geological structures on the deflections of the vertical and on gravity are rather small (1 - 2 arcsec, 3 - 5 mgal) in the investigated region and they are at the limit of significance for the technical applications of levelling or gyroscope mea- surements. The largest effects are caused by quaternary sediments with a large density contrast and by some gneiss structures, which show only a small density contrast but their total mass can cause considerable anomalies in the gravity field.
NASA Astrophysics Data System (ADS)
Talvik, Silja; Oja, Tõnis; Ellmann, Artu; Jürgenson, Harli
2014-05-01
Gravity field models in a regional scale are needed for a number of applications, for example national geoid computation, processing of precise levelling data and geological modelling. Thus the methods applied for modelling the gravity field from surveyed gravimetric information need to be considered carefully. The influence of using different gridding methods, the inclusion of unit or realistic weights and indirect gridding of free air anomalies (FAA) are investigated in the study. Known gridding methods such as kriging (KRIG), least squares collocation (LSCO), continuous curvature (CCUR) and optimal Delaunay triangulation (ODET) are used for production of gridded gravity field surfaces. As the quality of data collected varies considerably depending on the methods and instruments available or used in surveying it is important to somehow weigh the input data. This puts additional demands on data maintenance as accuracy information needs to be available for each data point participating in the modelling which is complicated by older gravity datasets where the uncertainties of not only gravity values but also supplementary information such as survey point position are not always known very accurately. A number of gravity field applications (e.g. geoid computation) demand foran FAA model, the acquisition of which is also investigated. Instead of direct gridding it could be more appropriate to proceed with indirect FAA modelling using a Bouguer anomaly grid to reduce the effect of topography on the resulting FAA model (e.g. near terraced landforms). The inclusion of different gridding methods, weights and indirect FAA modelling helps to improve gravity field modelling methods. It becomes possible to estimate the impact of varying methodical approaches on the gravity field modelling as statistical output is compared. Such knowledge helps assess the accuracy of gravity field models and their effect on the aforementioned applications.
Relativistic thermodynamics, a Lagrangian field theory for general flows including rotation
NASA Astrophysics Data System (ADS)
Frønsdal, Christian
Any theory that is based on an action principle has a much greater predictive power than one that does not have such a formulation. The formulation of a dynamical theory of General Relativity, including matter, is here viewed as a problem of coupling Einstein’s theory of pure gravity to an independently chosen and well-defined field theory of matter. It is well known that this is accomplished in a most natural way when both theories are formulated as relativistic, Lagrangian field theories, as is the case with Einstein-Maxwell theory. Special matter models of this type have been available; here a more general thermodynamical model that allows for vortex flows is presented. In a wider context, the problem of subjecting hydrodynamics and thermodynamics to an action principle is one that has been pursued for at least 150 years. A solution to this problem has been known for some time, but only under the strong restriction to potential flows. A variational principle for general flows has become available. It represents a development of the Navier-Stokes-Fourier approach to fluid dynamics. The principal innovation is the recognition that two kinds of flow velocity fields are needed, one the gradient of a scalar field and the other the time derivative of a vector field, the latter closely associated with vorticity. In the relativistic theory that is presented here, the latter is the Hodge dual of an exact 3-form, well known as the notoph field of Ogievetskij and Palubarinov, the B-field of Kalb and Ramond and the vorticity field of Lund and Regge. The total number of degrees of freedom of a unary system, including the density and the two velocity fields is 4, as expected — as in classical hydrodynamics. In this paper, we do not reduce Einstein’s dynamical equation for the metric to phenomenology, which would have denied the relevance of any intrinsic dynamics for the matter sector, nor do we abandon the equation of continuity - the very soul of hydrodynamics.
Gravity Fields and Interiors of the Saturnian Satellites
NASA Technical Reports Server (NTRS)
Rappaport, N. J.; Armstrong, J. W.; Asmar, Sami W.; Iess, L.; Tortora, P.; Somenzi, L.; Zingoni, F.
2006-01-01
This viewgraph presentation reviews the Gravity Science Objectives and accomplishments of the Cassini Radio Science Team: (1) Mass and density of icy satellites (2) Quadrupole field of Titan and Rhea (3) Dynamic Love number of Titan (4) Moment of inertia of Titan (in collaboration with the Radar Team) (5) Gravity field of Saturn. The proposed measurements for the extended tour are: (1) Quadrupole field of Enceladus (2) More accurate measurement of Titan k2 (3) Local gravity/topography correlations for Iapetus (4) Verification/disproof of "Pioneer anomaly".
Gravity Fields and Interiors of the Saturnian Satellites
NASA Technical Reports Server (NTRS)
Rappaport, N. J.; Armstrong, J. W.; Asmar, Sami W.; Iess, L.; Tortora, P.; Somenzi, L.; Zingoni, F.
2006-01-01
This viewgraph presentation reviews the Gravity Science Objectives and accomplishments of the Cassini Radio Science Team: (1) Mass and density of icy satellites (2) Quadrupole field of Titan and Rhea (3) Dynamic Love number of Titan (4) Moment of inertia of Titan (in collaboration with the Radar Team) (5) Gravity field of Saturn. The proposed measurements for the extended tour are: (1) Quadrupole field of Enceladus (2) More accurate measurement of Titan k2 (3) Local gravity/topography correlations for Iapetus (4) Verification/disproof of "Pioneer anomaly".
Gravitational collapse of massless scalar field in f (R ) gravity
NASA Astrophysics Data System (ADS)
Zhang, Cheng-Yong; Tang, Zi-Yu; Wang, Bin
2016-11-01
We study the spherically symmetric gravitational collapse of massless scalar matter field in asymptotic flat spacetime in the Starobinsky R2 gravity, one specific model in the f (R ) gravity. In the Einstein frame of f (R ) gravity, an additional scalar field arises due to the conformal transformation. We find that in addition to the usual competition between gravitational energy and kinetic energy in the process of gravitational collapse, the new scalar field brought by the conformal transformation adds one more competing force in the dynamical system. The dynamical competition can be controlled by tuning the amplitudes of the initial perturbations of the new scalar field and the matter field. To understand the physical reasons behind these phenomena, we analyze the gravitational potential behavior and calculate the Ricci scalar at center with the change of initial amplitudes of perturbations. We find rich physics on the formation of black holes through gravitational collapse in f (R ) gravity.
Green's function relativistic mean field theory for Λ hypernuclei
NASA Astrophysics Data System (ADS)
Ren, S.-H.; Sun, T.-T.; Zhang, W.
2017-05-01
The relativistic mean field theory with the Green's function method is extended to study Λ hypernuclei. Taking the hypernucleus Ca61Λ as an example, the single-particle resonant states for Λ hyperons are investigated by analyzing the density of states, and the corresponding energies and widths are given. Different behaviors are observed for the resonant states, i.e., the distributions of the very narrow 1 f5 /2 and 1 f7 /2 states are very similar to bound states while those of the wide 1 g7 /2 and 1 g9 /2 states are like scattering states. Besides, the impurity effect of Λ hyperons on the single-neutron resonant states is investigated. For most of the resonant states, both the energies and widths decrease with adding more Λ hyperons due to the attractive Λ N interaction. Finally, the energy level structure of Λ hyperons in the Ca hypernucleus isotopes with mass number A =53 -73 are studied; obvious shell structure and small spin-orbit splitting are found for the single-Λ spectrum.
Gravity field models derived from Swarm GPS data
NASA Astrophysics Data System (ADS)
Teixeira da Encarnação, João; Arnold, Daniel; Bezděk, Aleš; Dahle, Christoph; Doornbos, Eelco; van den IJssel, Jose; Jäggi, Adrian; Mayer-Gürr, Torsten; Sebera, Josef; Visser, Pieter; Zehentner, Norbert
2016-07-01
It is of great interest to numerous geophysical studies that the time series of global gravity field models derived from Gravity Recovery and Climate Experiment (GRACE) data remains uninterrupted after the end of this mission. With this in mind, some institutes have been spending efforts to estimate gravity field models from alternative sources of gravimetric data. This study focuses on the gravity field solutions estimated from Swarm global positioning system (GPS) data, produced by the Astronomical Institute of the University of Bern, the Astronomical Institute (ASU, Czech Academy of Sciences) and Institute of Geodesy (IfG, Graz University of Technology). The three sets of solutions are based on different approaches, namely the celestial mechanics approach, the acceleration approach and the short-arc approach, respectively. We derive the maximum spatial resolution of the time-varying gravity signal in the Swarm gravity field models to be degree 12, in comparison with the more accurate models obtained from K-band ranging data of GRACE. We demonstrate that the combination of the GPS-driven models produced with the three different approaches improves the accuracy in all analysed monthly solutions, with respect to any of them. In other words, the combined gravity field model consistently benefits from the individual strengths of each separate solution. The improved accuracy of the combined model is expected to bring benefits to the geophysical studies during the period when no dedicated gravimetric mission is operational.
Developments in Lunar Gravity Field Recovery Within the Project GRAZIL
NASA Astrophysics Data System (ADS)
Wirnsberger, Harald; Klinger, Beate; Krauss, Sandro; Mayer-Gürr, Torsten
2016-10-01
The project GRAZIL addresses the highly accurate recovery of the lunar gravity field using intersatellite Ka-band ranging (KBR) measurements collected by the Lunar Gravity Ranging System (LGRS) of the Gravity Recovery And Interior Laboratory (GRAIL) mission. Dynamic precise orbit determination is an indispensable task in order to recover the lunar gravity field based on LGRS measurements. The concept of variational equations is adopted to determine the orbit of the two GRAIL satellites based on radio science data. In this contribution we focus on the S-band two-way Doppler data collected by the Deep Space Network.As far as lunar gravity field recovery is concerned, we apply an integral equation approach using short orbital arcs. In this contribution we demonstrate the progress of Graz lunar gravity field models (GrazLGM) from the beginning, till the end of the projet GRAZIL. For the latest GrazLGM version special attention is given to the refinement of our processing strategy in conjunction with an increase of the spectral resolution. Furthermore, we present the first GrazLGM based on KBR observations during the primary and the extended mission phase. Our results are validated against state of the art lunar gravity field models computed at NASA-GSFC and NASA-JPL.
The gravity field of topography buried by sediments
NASA Technical Reports Server (NTRS)
Sandwell, D. T.; Liu, C. S.
1985-01-01
The gravity field over topography in the northern Indian Ocean that was completely buried by sediments of the Bengal Fan was investigated to understand the effect of sedimentation on the continental gravity field. An isopach map made from the seismic reflection and refraction in the Bay of Bengal shows two prominent N-S trending features in the basement topography. The northernmost portion of the Ninetyeast Ridge is totally buried by sediments north of 10 deg N. The other buried ridge trends roughly N-S for 1400 km at 85 deg E to the latitude of Sri Lanka and then curves toward the west. It has basement relief up to 6 km. Two free air gravity anomaly profiles across the region show a strong gravity low over the 85 deg E ridge, while the Ninetyeast Ridge shows a gravity high.
BF gravity with Immirzi parameter and matter fields
NASA Astrophysics Data System (ADS)
Montesinos, Merced; Velázquez, Mercedes
2012-03-01
We perform the coupling of the scalar, Maxwell, and Yang-Mills fields as well as the cosmological constant to BF gravity with Immirzi parameter. The proposed action principles employ auxiliary fields in order to keep a polynomial dependence on the B fields. By handling the equations of motion for the B field and for the auxiliary fields, these latter can be expressed in terms of the physical fields and by substituting these expressions into the original action principles we recover the first-order (Holst) and second-order actions for gravity coupled to the physical matter fields. We consider these results a relevant step towards the understanding of the coupling of matter fields to gravity in the theoretical framework of BF theory.
Multi-scale gravity field modeling in space and time
NASA Astrophysics Data System (ADS)
Wang, Shuo; Panet, Isabelle; Ramillien, Guillaume; Guilloux, Frédéric
2016-04-01
The Earth constantly deforms as it undergoes dynamic phenomena, such as earthquakes, post-glacial rebound and water displacement in its fluid envelopes. These processes have different spatial and temporal scales and are accompanied by mass displacements, which create temporal variations of the gravity field. Since 2002, the GRACE satellite missions provide an unprecedented view of the gravity field spatial and temporal variations. Gravity models built from these satellite data are essential to study the Earth's dynamic processes (Tapley et al., 2004). Up to present, time variations of the gravity field are often modelled using spatial spherical harmonics functions averaged over a fixed period, as 10 days or 1 month. This approach is well suited for modeling global phenomena. To better estimate gravity related to local and/or transient processes, such as earthquakes or floods, and adapt the temporal resolution of the model to its spatial resolution, we propose to model the gravity field using localized functions in space and time. For that, we build a model of the gravity field in space and time with a four-dimensional wavelet basis, well localized in space and time. First we design the 4D basis, then, we study the inverse problem to model the gravity field from the potential differences between the twin GRACE satellites, and its regularization using prior knowledge on the water cycle. Our demonstration of surface water mass signals decomposition in time and space is based on the use of synthetic along-track gravitational potential data. We test the developed approach on one year of 4D gravity modeling and compare the reconstructed water heights to those of the input hydrological model. Perspectives of this work is to apply the approach on real GRACE data, addressing the challenge of a realistic noise, to better describe and understand physical processus with high temporal resolution/low spatial resolution or the contrary.
Valkenburg, Wessel; Hu, Bin E-mail: hu@lorentz.leidenuniv.nl
2015-09-01
We present a description for setting initial particle displacements and field values for simulations of arbitrary metric theories of gravity, for perfect and imperfect fluids with arbitrary characteristics. We extend the Zel'dovich Approximation to nontrivial theories of gravity, and show how scale dependence implies curved particle paths, even in the entirely linear regime of perturbations. For a viable choice of Effective Field Theory of Modified Gravity, initial conditions set at high redshifts are affected at the level of up to 5% at Mpc scales, which exemplifies the importance of going beyond Λ-Cold Dark Matter initial conditions for modifications of gravity outside of the quasi-static approximation. In addition, we show initial conditions for a simulation where a scalar modification of gravity is modelled in a Lagrangian particle-like description. Our description paves the way for simulations and mock galaxy catalogs under theories of gravity beyond the standard model, crucial for progress towards precision tests of gravity and cosmology.
Torus Approach in Gravity Field Determination from Simulated GOCE Gravity Gradients
NASA Astrophysics Data System (ADS)
Liu, Huanling; Wen, Hanjiang; Xu, Xinyu; Zhu, Guangbin
2016-08-01
In Torus approach, observations are projected to the nominal orbits with constant radius and inclination, lumped coefficients provides a linear relationship between observations and spherical harmonic coefficients. Based on the relationship, two-dimensional FFT and block-diagonal least-squares adjustment are used to recover Earth's gravity field model. The Earth's gravity field model complete to degree and order 200 is recovered using simulated satellite gravity gradients on a torus grid, and the degree median error is smaller than 10-18, which shows the effectiveness of Torus approach. EGM2008 is employed as a reference model and the gravity field model is resolved using the simulated observations without noise given on GOCE orbits of 61 days. The error from reduction and interpolation can be mitigated by iterations. Due to polar gap, the precision of low-order coefficients is lower. Without considering these coefficients the maximum geoid degree error and cumulative error are 0.022mm and 0.099mm, respectively. The Earth's gravity field model is also recovered from simulated observations with white noise 5mE/Hz1/2, which is compared to that from direct method. In conclusion, it is demonstrated that Torus approach is a valid method for processing massive amount of GOCE gravity gradients.
Evaluation of recent Earth's global gravity field models with terrestrial gravity data
NASA Astrophysics Data System (ADS)
Karpik, Alexander P.; Kanushin, Vadim F.; Ganagina, Irina G.; Goldobin, Denis N.; Kosarev, Nikolay S.; Kosareva, Alexandra M.
2016-03-01
In the context of the rapid development of environmental research technologies and techniques to solve scientific and practical problems in different fields of knowledge including geosciences, the study of Earth's gravity field models is still important today. The results of gravity anomaly modelling calculated by the current geopotential models data were compared with the independent terrestrial gravity data for the two territories located in West Siberia and Kazakhstan. Statistical characteristics of comparison results for the models under study were obtained. The results of investigations show that about 70% of the differences between the gravity anomaly values calculated by recent global geopotential models and those observed at the points in flat areas are within ±10 mGal, in mountainous areas are within ±20 mGal.
Computational Relativistic Astrophysics Using the Flow Field-Dependent Variation Theory
NASA Technical Reports Server (NTRS)
Richardson, G. A.; Chung, T. J.
2002-01-01
We present our method for solving general relativistic nonideal hydrodynamics. Relativistic effects become pronounced in such cases as jet formation from black hole magnetized accretion disks which may lead to the study of gamma-ray bursts. Nonideal flows are present where radiation, magnetic forces, viscosities, and turbulence play an important role. Our concern in this paper is to reexamine existing numerical simulation tools as to the accuracy and efficiency of computations and introduce a new approach known as the flow field-dependent variation (FDV) method. The main feature of the FDV method consists of accommodating discontinuities of shock waves and high gradients of flow variables such as occur in turbulence and unstable motions. In this paper, the physics involved in the solution of relativistic hydrodynamics and solution strategies of the FDV theory are elaborated. The general relativistic astrophysical flow and shock solver (GRAFSS) is introduced, and some simple example problems for computational relativistic astrophysics (CRA) are demonstrated.
Quantum Gravity Effects in Scalar, Vector and Tensor Field Propagation
NASA Astrophysics Data System (ADS)
Dutta, Anindita
Quantum theory of gravity deals with the physics of the gravitational field at Planck length scale (10-35 m). Even though it is experimentally hard to reach the Planck length scale, on can look for evidence of quantum gravity that is detectable in astrophysics. In this thesis, we try to find effects of loop quantum gravity corrections on observable phenomena. We show that the quantum fluctuation strain for LIGO data would be 10 -125 on the Earth. Th correction is, however, substantial near the black hole horizon. We discuss the effect of this for scalar field propagation followed by vector and tensor fields. For the scalar field, the correction introduces a new asymmetry; for the vector field, we found a new perturbation solution and for the tensor field, we found the corrected Einstein equations which are yet to solve. These will affect phenomena like Hawking radiation, black hole entropy and gravitational waves.
Particlelike distributions of the Higgs field nonminimally coupled to gravity.
Füzfa, André; Rinaldi, Massimiliano; Schlögel, Sandrine
2013-09-20
When the Higgs field is nonminimally coupled to gravity, there exists a family of spherically symmetric particlelike solutions to the field equations. These monopoles are the only globally regular and asymptotically flat distributions with finite energy of the Higgs field around compact objects. Moreover, spontaneous scalarization is strongly amplified for specific values of their mass and compactness.
Geometry, topology, field theory and two-dimensional quantum gravity
Wong, E.C.M.
1992-01-01
This dissertation presents geometrically a simplified theory of two-dimensional quantum gravity called topological gravity. The motivation for such a simplification is to shed light on the complicated problem of real quantum gravity. The author introduces new supermanifolds called semirigid super Riemann surfaces on which two-dimensional quantum field theories of topological (super) gravity are defined. It is shown that semirigid surfaces are integrable reductions from ordinary complex supermanifolds. Unlike other supergeometries, the semirigid moduli space of topological gravity is as well understood as that of ordinary Riemann surface. The author applies in semirigid gravity the operator formalism to construct correlation functions of observables in two-dimensional spacetime of arbitrarily complicated topology. A one-to-one correspondence is established between the equivalent BRST cohomology of the states in the Hilbert space and the deRham cohomology on the ordinary moduli space. Moreover, the couplings between the observables are topological, coming only through contact interactions. Two recursion relations of observables are derived in the semirigid framework. One involves in particular an observable associated to the two-dimensional cosmological constant and the other the string coupling constant. These are the same recursion relations that partially characterized the [open quotes]one matrix model,[close quotes] a discretized approach to quantum gravity, at its topological critical point. This lends strong support to the hypothesis that semirigid gravity and the one matrix model at the topological critical point are equivalent.
NASA Astrophysics Data System (ADS)
Freire, Paulo C. C.; Wex, Norbert; Esposito-Farèse, Gilles; Verbiest, Joris P. W.; Bailes, Matthew; Jacoby, Bryan A.; Kramer, Michael; Stairs, Ingrid H.; Antoniadis, John; Janssen, Gemma H.
2012-07-01
We report the results of a 10-year timing campaign on PSR J1738+0333, a 5.85-ms pulsar in a low-eccentricity 8.5-h orbit with a low-mass white dwarf companion. We obtained 17 376 pulse times of arrival with a stated uncertainty smaller than ?s and weighted residual rms of ?s. The large number and precision of these measurements allow highly significant estimates of the proper motion μα, δ= (+7.037 ± 0.005, +5.073 ± 0.012) mas yr-1, parallax πx = (0.68 ± 0.05) mas and a measurement of the apparent orbital decay, ? (all 1σ uncertainties). The measurements of μα, δ and πx allow for a precise subtraction of the kinematic contribution to the observed orbital decay; this results in a significant measurement of the intrinsic orbital decay: ?. This is consistent with the orbital decay from the emission of gravitational waves predicted by general relativity, ?, i.e. general relativity passes the test represented by the orbital decay of this system. This agreement introduces a tight upper limit on dipolar gravitational wave emission, a prediction of most alternative theories of gravity for asymmetric binary systems such as this. We use this limit to derive the most stringent constraints ever on a wide class of gravity theories, where gravity involves a scalar-field contribution. When considering general scalar-tensor theories of gravity, our new bounds are more stringent than the best current Solar system limits over most of the parameter space, and constrain the matter-scalar coupling constant ? to be below the 10-5 level. For the special case of the Jordan-Fierz-Brans-Dicke, we obtain the 1σ bound ?, which is within a factor of 2 of the Cassini limit. We also use our limit on dipolar gravitational wave emission to constrain a wide class of theories of gravity which are based on a generalization of Bekenstein's Tensor-Vector-Scalar gravity, a relativistic formulation of modified Newtonian dynamics.
Key techniques of the high precision gravity field system
NASA Astrophysics Data System (ADS)
Xu, Weimin; Chen, Shi; Lu, Hongyan; Shi, Lei
2017-04-01
Ground-based gravity time series provide a direct method to monitor all sources of mass changes from local to global scale. But the effectively infinite spatial sensitivity of gravity measurements make it difficult to isolate the signal of interest. The high precision gravity field system is an alternative approach of modeling mass changes under-ground. The field system, consists of absolute gravity, gravity and gravity gradient, GNSS, leveling and climate hydrology measurements, can improve the signal-to-noise ratio for many applications by removing contributions of unwanted signal from elevation changes, air pressure changes, local hydrology, and others. The networks of field system combination, such as field-profile in more than 100 kilometers, can be used in critical zone with high seismic risk for monitoring earth dynamics, volcanic and seismic phenomena. The system is constituted by 9 typical observation stations in 3*3 array (or 4 in 2*2 array) in 60 square meters field, each station is designed for integrated measurements, including absolute gravity, gravity gradient, elevation changes, air pressure and hydrology. Time-lapse gravity changes resulting from absolute gravimeter (FG5 or A10) with standard deviation less than 2 μGal, without the contributions of Earth tides, loading and polar motion. Additional measurements such as air pressure change, local hydrology and soil moisture are indispensable. The elevation changes resulting from GNSS (on the base station) and leveling (between stations) with precision less than 10 mm. The gravity gradient is the significant measurement for delimiting the location of the related mass changes underground the station, which is measured by Scintrex CG-5 gravimeters in different height (80cm in the test field), with precision less than 10 E. It is necessary to improve the precision of gravity gradient measurements by certain method in field experiment for the high precision measurement system. Acknowledgment: This
A comparison of satellite systems for gravity field measurements
NASA Technical Reports Server (NTRS)
Argentiero, P. D.; Lowrey, B. E.
1977-01-01
A detailed and accurate earth gravity field model is important to the understanding of the structure and composition of the earth's crust and upper mantle. Various satellite-based techniques for providing more accurate models of the gravity field are analyzed and compared. A high-low configuration satellite-to-satellite tracking mission is recommended for the determination of both the long wavelength and short wavelength portions of the field. Satellite altimetry and satellite gradiometry missions are recommended for determination of the short wavelength portion of the field.
Incorporating SMART-1 Tracking Data into Lunar Gravity Field Determination
NASA Astrophysics Data System (ADS)
Goossens, S.; Matsumoto, K.; Kikuchi, F.; Sasaki, S.; Ping, J.
In the near future, a number of satellite missions are planned to be launched to the Moon. These missions include initiatives by China, India, the USA, as well as the Japanese SELENE mission. These missions will gather a wealth of lunar data which will improve the knowledge of the Moon. One of the main topics to be addressed will be the lunar gravity field. Especially SELENE will contribute to improving the knowledge of the gravity field, by applying 4-way Doppler tracking between the main satellite and a relay satellite, and by applying a separate differential VLBI experiment. These will improve the determination of the global gravity field, especially over the far side and at the lower degrees. This also implies an improvement for the precision of the determination of orbits around the Moon. This work focuses on the determination of the lunar gravity field from all available tracking data to this date. In preparation to SELENE, analysis using Lunar Prospector tracking data, as well as Clementine data and historical data from the Apollo and Lunar Orbiter projects is being conducted at NAOJ. The goal is to combine the existing good-quality data set with the tracking data from SELENE in order to derive a new lunar gravity field model. To this extent, SMART-1 tracking data, kindly provided by ESA, are also included. Due to many manoeuvres on the satellite, relatively short- arcs need to be used so the signal is not contaminated with spurious information. Good quality data fits can be obtained for these arcs, at the level of few tenths of mm/s for the Doppler data. Including SMART-1 data from the high-altitude part of the mission improves the gravity field only little. However, low-altitude tracking data prior to SMART-1's crash into the Moon are expected to contribute to the improvement of the high-frequency part of the gravity field model.
A spaceborne superconducting gravity gradiometer for mapping the earth's gravity field
NASA Technical Reports Server (NTRS)
Paik, H. J.
1981-01-01
The principles of a satellite gravity gradiometer system which measures all five independent components of the gravity gradient tensor with a sensitivity of 0.001 E/Hz to the 1/2 power or better, are analyzed, and the status of development of the system is reviewed. The superconducting gravity gradiometer uses sensitive superconducting accelerometers, each of which are composed of a weakly suspended superconducting proof mass, a superconducting magnetic transducer, and a low-noise superconducting magnetometer. The magnetic field produced by the transducer coils is modulated by the motion of the proof mass and detected by the magnetometer. A combination of two or four of such accelerometers with proper relative orientation of sensitive axes results in an in-line or a cross component gravity gradiometer.
Equilibrium and stability of relativistic stars in extended theories of gravity
NASA Astrophysics Data System (ADS)
Wojnar, Aneta; Velten, Hermano
2016-12-01
We study static, spherically symmetric equilibrium configurations in extended theories of gravity (ETG) following the notation introduced by Capozziello et al. We calculate the differential equations for the stellar structure in such theories in a very generic form i.e., the Tolman-Oppenheimer-Volkoff generalization for any ETG is introduced. Stability analysis is also investigated with special focus on the particular example of scalar-tensor gravity.
Fields and fluids on curved non-relativistic spacetimes
NASA Astrophysics Data System (ADS)
Geracie, Michael; Prabhu, Kartik; Roberts, Matthew M.
2015-08-01
We consider non-relativistic curved geometries and argue that the background structure should be generalized from that considered in previous works. In this approach the derivative operator is defined by a Galilean spin connection valued in the Lie algebra of the Galilean group. This includes the usual spin connection plus an additional "boost connection" which parameterizes the freedom in the derivative operator not fixed by torsion or metric compatibility. As an example we write down the most general theory of dissipative fluids consistent with the second law in curved non-relativistic geometries and find significant differences in the allowed transport coefficients from those found previously. Kubo formulas for all response coefficients are presented. Our approach also immediately generalizes to systems with independent mass and charge currents as would arise in multicomponent fluids. Along the way we also discuss how to write general locally Galilean invariant non-relativistic actions for multiple particle species at any order in derivatives. A detailed review of the geometry and its relation to non-relativistic limits may be found in a companion paper.
Gravity Effects of Solar Eclipse and Inducted Gravitational Field
NASA Astrophysics Data System (ADS)
Tang, K.; Wang, Q.; Zhang, H.; Hua, C.; Peng, F.; Hu, K.
2003-12-01
During solar eclipses in recent decades, gravity anomalies were observed and difficult to be explained by Newton's gravitational theory. During the solar eclipse of 1995, India scientists Mishra et al. recorded a gravity valley in amplitude of 12 μ Gal; they interpreted that qualitatively as atmospheric effects. During the total solar eclipse of March 1997, we conducted a comprehensive geophysical observation at Mohe geophysical observatory of China (with latitude of 53.490 N and longitude of 122.340 E. From the data we recorded, we found two valleys about 5 to 7 μ Gal. Unnikrishnan et al. inferred this gravity anomaly was caused by the environment changes. We know that the observation had been conducting in a room inside a small building with a stable coal heating system; the temperature variation inside the experimental room was less 10C during the eclipse. Moreover, the measured atmospheric pressure change was less 1hPa during the eclipse. It is reasonable to believe that surrounding environment of the observatory excluded the significant gravity variations caused by temperature, pressure variation and local moving of persons and vehicles. To further study the gravity effects related to solar eclipses, our scientific team took more observations during Zambia total solar eclipse of June 2001 and Australia total solar eclipse of December 2002. After data corrections, we found respectively two gravity anomalies, with 3 to 4μ Gal for Zambia eclipse and 1.5μ Gal for Australia eclipse. As many scientists have pointed out that pressure-gravity factor is lower than 0.3μ Gal/hPa, it means that any gravity anomaly great than 0.5μ Gal could not be inferred as the results of atmospheric pressure change. The two more gravity anomalies recorded during the solar eclipses provided us strong evidences that some gravity anomalies could not simply be inferred as atmospheric pressure change. We have tried to explain those anomalies by the induced gravitational field.
Gravity field models derived from Swarm GPS data
NASA Astrophysics Data System (ADS)
de Teixeira da Encarnação, João; Arnold, Daniel; Bezděk, Aleš; Dahle, Christoph; Doornbos, Eelco; van den IJssel, Jose; Jäggi, Adrian; Mayer-Gürr, Torsten; Sebera, Josef; Visser, Pieter; Zehentner, Norbert
2016-04-01
The GPS instruments on-board the three Earth's Magnetic Field and Environment Explorer (Swarm) satellites provide the opportunity to measure the gravity field model at basin-wide spatial scales. In spite of being a geo-magnetic satellite mission, Swarm's GPS receiver collects highly accurate hl-SST data (van den IJssel et al., 2015), which has been exploited to produce gravity field models at a number of institutes, namely at the Astronomical Institute (ASU) of the Czech Academy of Sciences (Bezděk et al., 2014), the Astronomical Institute of the University of Bern (AIUB, Jäggi et al., 2015) and the Institute of Geodesy (IfG) of the Graz University of Technology (Zehentner et al., 2015). With the help of GRACE gravity field models, which are derived from much more accurate ll-SST data, we investigate the best combination strategy for producing a superior model on the basis of the solutions produced by the three institutes, similarly to the approach taken by the European Gravity Service for Improved Emergency Management project (http://egsiem.eu). We demonstrate that the Swarm-derived gravity field models are able to resolve monthly solutions with 1666km spatial resolutions (roughly up to degree 12). We illustrate how these monthly solutions correlate with GRACE-derived monthly solutions, for the period of 2014 - 2015, as well as indicate which geographical areas are measured more or less accurately.
Interior Models and Gravity Field of Jupiter's Moon Amalthea
NASA Astrophysics Data System (ADS)
Weinwurm, G.; Weber, R.
2003-12-01
Before its final plunge into Jupiter in September 2003, GALILEO made a last visit to Jupiters moon Amalthea. This final flyby of the spacecrafts successful mission occurred on November 5, 2002. In order to analyse the spacecraft data with respect to Amaltheas gravity field, interior models of the moon had to be provided. The method used for this approach is based on the numerical integration of infinitesimal volume elements, which are calculated by the scale factors of a three-axial ellipsoid (elliptic coordinates). To derive the gravity field coefficients of the body, the second method of Neumann was applied. Based on the spacecraft trajectory data provided by the Jet Propulsion Laboratory, GALILEOs velocity perturbations at closest approach could be calculated. We have derived the harmonic coefficients of Amaltheas gravity field up to degree and order six, for both homogeneous and reasonable heterogeneous cases. Based on these numbers we calculated the impact on the trajectory of GALILEO and compared it to existing Doppler data. Although no two-way Doppler-data was available during the flyby and the harmonic coefficients of the gravity field are buried in the one-way Doppler-noise, the calculated gravity field models of Amalthea can be a basis for further exploration of the Jupiter system. Furthermore, the model approach can be used for any planetary body.
Super-Planckian spatial field variations and quantum gravity
NASA Astrophysics Data System (ADS)
Klaewer, Daniel; Palti, Eran
2017-01-01
We study scenarios where a scalar field has a spatially varying vacuum expectation value such that the total field variation is super-Planckian. We focus on the case where the scalar field controls the coupling of a U(1) gauge field, which allows us to apply the Weak Gravity Conjecture to such configurations. We show that this leads to evidence for a conjectured property of quantum gravity that as a scalar field variation in field space asymptotes to infinity there must exist an infinite tower of states whose mass decreases as an exponential function of the scalar field variation. We determine the rate at which the mass of the states reaches this exponential behaviour showing that it occurs quickly after the field variation passes the Planck scale.
Cartan gravity, matter fields, and the gauge principle
Westman, Hans F.; Zlosnik, Tom G.
2013-07-15
Gravity is commonly thought of as one of the four force fields in nature. However, in standard formulations its mathematical structure is rather different from the Yang–Mills fields of particle physics that govern the electromagnetic, weak, and strong interactions. This paper explores this dissonance with particular focus on how gravity couples to matter from the perspective of the Cartan-geometric formulation of gravity. There the gravitational field is represented by a pair of variables: (1) a ‘contact vector’ V{sup A} which is geometrically visualized as the contact point between the spacetime manifold and a model spacetime being ‘rolled’ on top of it, and (2) a gauge connection A{sub μ}{sup AB}, here taken to be valued in the Lie algebra of SO(2,3) or SO(1,4), which mathematically determines how much the model spacetime is rotated when rolled. By insisting on two principles, the gauge principle and polynomial simplicity, we shall show how one can reformulate matter field actions in a way that is harmonious with Cartan’s geometric construction. This yields a formulation of all matter fields in terms of first order partial differential equations. We show in detail how the standard second order formulation can be recovered. In particular, the Hodge dual, which characterizes the structure of bosonic field equations, pops up automatically. Furthermore, the energy–momentum and spin-density three-forms are naturally combined into a single object here denoted the spin-energy–momentum three-form. Finally, we highlight a peculiarity in the mathematical structure of our first-order formulation of Yang–Mills fields. This suggests a way to unify a U(1) gauge field with gravity into a SO(1,5)-valued gauge field using a natural generalization of Cartan geometry in which the larger symmetry group is spontaneously broken down to SO(1,3)×U(1). The coupling of this unified theory to matter fields and possible extensions to non-Abelian gauge fields are left as
3D quantum gravity and effective noncommutative quantum field theory.
Freidel, Laurent; Livine, Etera R
2006-06-09
We show that the effective dynamics of matter fields coupled to 3D quantum gravity is described after integration over the gravitational degrees of freedom by a braided noncommutative quantum field theory symmetric under a kappa deformation of the Poincaré group.
Magnetic field induced by strong transverse plasmons in ultra-relativistic electron-positron plasmas
NASA Astrophysics Data System (ADS)
Liu, Y.; Li, X. Q.; Liu, S. Q.
2012-08-01
Context. We investigated the generation of localized magnetic fields in an ultra-relativistic non-isothermal electron-positron plasma by strong electromagnetic plasmons. Aims: The results obtained can be used to explain the origin of small-scale magnetic fields in the internal shock region of gamma-ray bursts with ultra-relativistic electron positron plasmas. Methods: The generation of magnetic fields was investigated with kinetic Vlasov Maxwell equations. Results: The self-generated magnetic field will collapse for modulation instability, leading to spatially highly intermittent magnetic fluxes, whose characteristic scale is much larger than relativistic plasma skin depth, which in turn is conducive to the generation of the long-life small-scale magnetic fields in the internal shock region of gamma-ray bursts.
Finite field-dependent symmetries in perturbative quantum gravity
Upadhyay, Sudhaker
2014-01-15
In this paper we discuss the absolutely anticommuting nilpotent symmetries for perturbative quantum gravity in general curved spacetime in linear and non-linear gauges. Further, we analyze the finite field-dependent BRST (FFBRST) transformation for perturbative quantum gravity in general curved spacetime. The FFBRST transformation changes the gauge-fixing and ghost parts of the perturbative quantum gravity within functional integration. However, the operation of such symmetry transformation on the generating functional of perturbative quantum gravity does not affect the theory on physical ground. The FFBRST transformation with appropriate choices of finite BRST parameter connects non-linear Curci–Ferrari and Landau gauges of perturbative quantum gravity. The validity of the results is also established at quantum level using Batalin–Vilkovisky (BV) formulation. -- Highlights: •The perturbative quantum gravity is treated as gauge theory. •BRST and anti-BRST transformations are developed in linear and non-linear gauges. •BRST transformation is generalized by making it finite and field dependent. •Connection between linear and non-linear gauges is established. •Using BV formulation the results are established at quantum level also.
Shear waves in inhomogeneous, compressible fluids in a gravity field.
Godin, Oleg A
2014-03-01
While elastic solids support compressional and shear waves, waves in ideal compressible fluids are usually thought of as compressional waves. Here, a class of acoustic-gravity waves is studied in which the dilatation is identically zero, and the pressure and density remain constant in each fluid particle. These shear waves are described by an exact analytic solution of linearized hydrodynamics equations in inhomogeneous, quiescent, inviscid, compressible fluids with piecewise continuous parameters in a uniform gravity field. It is demonstrated that the shear acoustic-gravity waves also can be supported by moving fluids as well as quiescent, viscous fluids with and without thermal conductivity. Excitation of a shear-wave normal mode by a point source and the normal mode distortion in realistic environmental models are considered. The shear acoustic-gravity waves are likely to play a significant role in coupling wave processes in the ocean and atmosphere.
An improved model for the Earth's gravity field
NASA Technical Reports Server (NTRS)
Tapley, B. D.; Shum, C. K.; Yuan, D. N.; Ries, J. C.; Schutz, B. E.
1989-01-01
An improved model for the Earth's gravity field, TEG-1, was determined using data sets from fourteen satellites, spanning the inclination ranges from 15 to 115 deg, and global surface gravity anomaly data. The satellite measurements include laser ranging data, Doppler range-rate data, and satellite-to-ocean radar altimeter data measurements, which include the direct height measurement and the differenced measurements at ground track crossings (crossover measurements). Also determined was another gravity field model, TEG-1S, which included all the data sets in TEG-1 with the exception of direct altimeter data. The effort has included an intense scrutiny of the gravity field solution methodology. The estimated parameters included geopotential coefficients complete to degree and order 50 with selected higher order coefficients, ocean and solid Earth tide parameters, Doppler tracking station coordinates and the quasi-stationary sea surface topography. Extensive error analysis and calibration of the formal covariance matrix indicate that the gravity field model is a significant improvement over previous models and can be used for general applications in geodesy.
Validation of the EGSIEM combined monthly GRACE gravity fields
NASA Astrophysics Data System (ADS)
Li, Zhao; van Dam, Tonie; Chen, Qiang; Weigelt, Matthias; Güntner, Andreas; Jäggi, Adrian; Meyer, Ulrich; Jean, Yoomin; Altamimi, Zuheir; Rebischung, Paul
2016-04-01
Observations indicate that global warming is affecting the water cycle. Here in Europe predictions are for more frequent high precipitation events, wetter winters, and longer and dryer summers. The consequences of these changes include the decreasing availability of fresh water resources in some regions as well as flooding and erosion of coastal and low-lying areas in other regions. These weather related effects impose heavy costs on society and the economy. We cannot stop the immediate effects global warming on the water cycle. But there may be measures that we can take to mitigate the costs to society. The Horizon2020 supported project, European Gravity Service for Improved Emergency Management (EGSIEM), will add value to EO observations of variations in the Earth's gravity field. In particular, the EGSIEM project will interpret the observations of gravity field changes in terms of changes in continental water storage. The project team will develop tools to alert the public water storage conditions could indicate the onset of regional flooding or drought. As part of the EGSIEM project, a combined GRACE gravity product is generated, using various monthly GRACE solutions from associated processing centers (ACs). Since each AC follows a set of common processing standards but applies its own independent analysis method, the quality, robustness, and reliability of the monthly combined gravity fields should be significantly improved as compared to any individual solution. In this study, we present detailed and updated comparisons of the combined EGSIEM GRACE gravity product with GPS position time series, hydrological models, and existing GRACE gravity fields. The GPS residuals are latest REPRO2 station position residuals, obtained by rigorously stacking the IGS Repro 2 , daily solutions, estimating, and then restoring the annual and semi-annual signals.
High-resolution regional gravity field modelling in a mountainous area from terrestrial gravity data
NASA Astrophysics Data System (ADS)
Bucha, Blažej; Janák, Juraj; Papčo, Juraj; Bezděk, Aleš
2016-11-01
We develop a high-resolution regional gravity field model by a combination of spherical harmonics, band-limited spherical radial basis functions (SRBFs) and the residual terrain model (RTM) technique. As the main input data set, we employ a dense terrestrial gravity database (3-6 stations km-2), which enables gravity field modelling up to very short spatial scales. The approach is based on the remove-compute-restore methodology in which all the parts of the signal that can be modelled are removed prior to the least-squares adjustment in order to smooth the input gravity data. To this end, we utilize degree-2159 spherical harmonic models and the RTM technique using topographic models at 2 arcsec resolution. The residual short-scale gravity signal is modelled via the band-limited Shannon SRBF expanded up to degree 21 600, which corresponds to a spatial resolution of 30 arcsec. The combined model is validated against GNSS/levelling-based height anomalies, independent surface gravity data, deflections of the vertical and terrestrial vertical gravity gradients achieving an accuracy of 2.7 cm, 0.53 mGal, 0.39 arcsec and 279 E in terms of the RMS error, respectively. A key aspect of the combined approach, especially in mountainous areas, is the quality of the RTM. We therefore compare the performance of two RTM techniques within the innermost zone, the tesseroids and the polyhedron. It is shown that the polyhedron-based approach should be preferred in rugged terrain if a high-quality RTM is required. In addition, we deal with the RTM computations at points located below the reference surface of the residual terrain which is known to be a rather delicate issue.
High-Resolution Gravity and Time-Varying Gravity Field Recovery using GRACE and CHAMP
NASA Technical Reports Server (NTRS)
Shum, C. K.
2002-01-01
This progress report summarizes the research work conducted under NASA's Solid Earth and Natural Hazards Program 1998 (SENH98) entitled High Resolution Gravity and Time Varying Gravity Field Recovery Using GRACE (Gravity Recovery and Climate Experiment) and CHAMP (Challenging Mini-satellite Package for Geophysical Research and Applications), which included a no-cost extension time period. The investigation has conducted pilot studies to use the simulated GRACE and CHAMP data and other in situ and space geodetic observable, satellite altimeter data, and ocean mass variation data to study the dynamic processes of the Earth which affect climate change. Results from this investigation include: (1) a new method to use the energy approach for expressing gravity mission data as in situ measurements with the possibility to enhance the spatial resolution of the gravity signal; (2) the method was tested using CHAMP and validated with the development of a mean gravity field model using CHAMP data, (3) elaborate simulation to quantify errors of tides and atmosphere and to recover hydrological and oceanic signals using GRACE, results show that there are significant aliasing effect and errors being amplified in the GRACE resonant geopotential and it is not trivial to remove these errors, and (4) quantification of oceanic and ice sheet mass changes in a geophysical constraint study to assess their contributions to global sea level change, while the results improved significant over the use of previous studies using only the SLR (Satellite Laser Ranging)-determined zonal gravity change data, the constraint could be further improved with additional information on mantle rheology, PGR (Post-Glacial Rebound) and ice loading history. A list of relevant presentations and publications is attached, along with a summary of the SENH investigation generated in 2000.
Status of Next Generation GRACE Gravity Field Data Products
NASA Astrophysics Data System (ADS)
Bettadpur, S.; Team, L.
2006-12-01
The Gravity Recovery And Climate Experiment was launched on Mar 17, 2002 in order to measure mass flux within the Earth system through its effects on Earth's gravity field. Since that time, using the inter-satellite tracking data between the twin GRACE satellites, monthly gravity field estimates for more than 4 years have been delivered to the user community, and these fields have shown clear evidence of hydrological, oceanographic & glaciological phenomena. The GRACE Science Data System is in the midst of a re-processing activity, focusing on improvements to the background models and processing methodology. This paper describes the status of the new results from the re-processing, including changes to the background models, improvement in the processing, and the resulting error characteristics.
Gradio - Earth gravity field measurement on Aristoteles
NASA Astrophysics Data System (ADS)
Pawlak, D.; Meyer, Ph.; Bernard, A.; Touboul, P.
1991-10-01
The design and operation of Gradio, the instrument that was specifically designed for precise gradiometry measurements during the Aristoteles mission, are described. The Gradio is based on simultaneous measurements by four three-axis ultrasensitive accelerometers performed in several locations on a rigid stable structure, called gradio plate, which are then used to compute g gradients. The operational phase of Gradio will last 6 months; the orbit will be circular, near polar, and heliosynchronous, at an altitude of 200 km. It is estimated that Gradio will measure the two main components T(yy) and T(zz) of the gravity gradient tensor in the (0.005, 0.125) Hz frequency bandwidth with an accuracy of 0.01 E.U.
Phobos interior structure from its gravity field
NASA Astrophysics Data System (ADS)
Le Maistre, S.; Rosenblatt, P.; Rivoldini, A.
2015-10-01
Phobos origin remains mysterious. It could be a captured asteroid, or an in-situ object co-accreted with Mars or formed by accretion from a disk of impact ejecta.Although it is not straightforward to relate its interior properties to its origin, it is easy to agree that the interior properties of any body has to be accounted for to explain its life's history. What event could explain such an internal structure? Where should this object formed to present such interior characteristics and composition? We perform here numerical simulations to assess the ability of a gravity experiment to constrain the interior structure of the martian moon Phobos, which could in turn allow distinguishing among the competing scenarios for the moon's origin.
Relativistic mean-field hadronic models under nuclear matter constraints
NASA Astrophysics Data System (ADS)
Dutra, M.; Lourenço, O.; Avancini, S. S.; Carlson, B. V.; Delfino, A.; Menezes, D. P.; Providência, C.; Typel, S.; Stone, J. R.
2014-11-01
Background: The microscopic composition and properties of infinite hadronic matter at a wide range of densities and temperatures have been subjects of intense investigation for decades. The equation of state (EoS) relating pressure, energy density, and temperature at a given particle number density is essential for modeling compact astrophysical objects such as neutron stars, core-collapse supernovae, and related phenomena, including the creation of chemical elements in the universe. The EoS depends not only on the particles present in the matter, but, more importantly, also on the forces acting among them. Because a realistic and quantitative description of infinite hadronic matter and nuclei from first principles in not available at present, a large variety of phenomenological models has been developed in the past several decades, but the scarcity of experimental and observational data does not allow a unique determination of the adjustable parameters. Purpose: It is essential for further development of the field to determine the most realistic parameter sets and to use them consistently. Recently, a set of constraints on properties of nuclear matter was formed and the performance of 240 nonrelativistic Skyrme parametrizations was assessed [M. Dutra et al., Phys. Rev. C 85, 035201 (2012), 10.1103/PhysRevC.85.035201] in describing nuclear matter up to about three times nuclear saturation density. In the present work we examine 263 relativistic-mean-field (RMF) models in a comparable approach. These models have been widely used because of several important aspects not always present in nonrelativistic models, such as intrinsic Lorentz covariance, automatic inclusion of spin, appropriate saturation mechanism for nuclear matter, causality, and, therefore, no problems related to superluminal speed of sound in medium. Method: Three different sets of constraints related to symmetric nuclear matter, pure neutron matter, symmetry energy, and its derivatives were used. The
NASA Technical Reports Server (NTRS)
Pavlis, Erricos C.
1992-01-01
Accurate knowledge of the gravity field is a firm requirement in any study of Planet Earth. Space techniques have so far demonstrated their superiority in the global mapping of the gravity field based on ground tracking and altimeter data mostly. Numerical and analytical simulation studies of the upcoming geophysically relevant missions that will most likely carry GPS receivers, indicate significant improvements in the accuracy as well as the resolution of the gravity field. TOPEX will improve by some two orders of magnitude the long wavelength part (to degree about 20), while GP-B will contribute in the long as well as medium wavelength part of the spectrum (up to degree about 60). The gradiometer measurements on ARISTOTELES will contribute in the medium and short wavelength regions (from degree 30 up); GPS tracking of the spacecraft though will provide additional information for the long wavelength gravity and will help resolve it to accuracies comparable to those obtained from GP-B. With the mean rms coefficient error per degree kept below 10 exp -10, geophysical signals such as the post-glacial rebound, tidal variations, and secular and periodic variations of the zonal field rise above the noise level and become readily observable processes.
NASA Astrophysics Data System (ADS)
Pavlis, Erricos C.
Accurate knowledge of the gravity field is a firm requirement in any study of Planet Earth. Space techniques have so far demonstrated their superiority in the global mapping of the gravity field based on ground tracking and altimeter data mostly. Numerical and analytical simulation studies of the upcoming geophysically relevant missions that will most likely carry GPS receivers, indicate significant improvements in the accuracy as well as the resolution of the gravity field. TOPEX will improve by some two orders of magnitude the long wavelength part (to degree about 20), while GP-B will contribute in the long as well as medium wavelength part of the spectrum (up to degree about 60). The gradiometer measurements on ARISTOTELES will contribute in the medium and short wavelength regions (from degree 30 up); GPS tracking of the spacecraft though will provide additional information for the long wavelength gravity and will help resolve it to accuracies comparable to those obtained from GP-B. With the mean rms coefficient error per degree kept below 10 exp -10, geophysical signals such as the post-glacial rebound, tidal variations, and secular and periodic variations of the zonal field rise above the noise level and become readily observable processes.
NASA Technical Reports Server (NTRS)
Pavlis, Erricos C.
1992-01-01
Accurate knowledge of the gravity field is a firm requirement in any study of Planet Earth. Space techniques have so far demonstrated their superiority in the global mapping of the gravity field based on ground tracking and altimeter data mostly. Numerical and analytical simulation studies of the upcoming geophysically relevant missions that will most likely carry GPS receivers, indicate significant improvements in the accuracy as well as the resolution of the gravity field. TOPEX will improve by some two orders of magnitude the long wavelength part (to degree about 20), while GP-B will contribute in the long as well as medium wavelength part of the spectrum (up to degree about 60). The gradiometer measurements on ARISTOTELES will contribute in the medium and short wavelength regions (from degree 30 up); GPS tracking of the spacecraft though will provide additional information for the long wavelength gravity and will help resolve it to accuracies comparable to those obtained from GP-B. With the mean rms coefficient error per degree kept below 10 exp -10, geophysical signals such as the post-glacial rebound, tidal variations, and secular and periodic variations of the zonal field rise above the noise level and become readily observable processes.
Dark energy cosmology with tachyon field in teleparallel gravity
Motavalli, H. Akbarieh, A. Rezaei; Nasiry, M.
2016-07-15
We construct a tachyon teleparallel dark energy model for a homogeneous and isotropic flat universe in which a tachyon as a non-canonical scalar field is non-minimally coupled to gravity in the framework of teleparallel gravity. The explicit form of potential and coupling functions are obtained under the assumption that the Lagrangian admits the Noether symmetry approach. The dynamical behavior of the basic cosmological observables is compared to recent observational data, which implies that the tachyon field may serve as a candidate for dark energy.
Dark energy cosmology with tachyon field in teleparallel gravity
NASA Astrophysics Data System (ADS)
Motavalli, H.; Akbarieh, A. Rezaei; Nasiry, M.
2016-07-01
We construct a tachyon teleparallel dark energy model for a homogeneous and isotropic flat universe in which a tachyon as a non-canonical scalar field is non-minimally coupled to gravity in the framework of teleparallel gravity. The explicit form of potential and coupling functions are obtained under the assumption that the Lagrangian admits the Noether symmetry approach. The dynamical behavior of the basic cosmological observables is compared to recent observational data, which implies that the tachyon field may serve as a candidate for dark energy.
New Views of Earth's Gravity Field from GRACE
NASA Technical Reports Server (NTRS)
2003-01-01
[figure removed for brevity, see original site] [figure removed for brevity, see original site] Map 1Map 2
Gravity and the Earth's Shape Gravity is the force that is responsible for the weight of an object and is determined by how the material that makes up the Earth is distributed throughout the Earth. Because gravity changes over the surface of the Earth, the weight of an object changes along with it. One can define standard gravity as the value of gravity for an perfectly smooth 'idealized' Earth, and the gravity 'anomaly' is a measure of how actual gravity deviates from this standard. Gravity reflects the Earth's surface topography to a high degree and is associated with features that most people are familiar with such as large mountains and deep ocean trenches.
Progress in Measuring the Earth's Gravity Field Through GRACE Prior to GRACE, the Earth's gravity field was determined using measurements of varying quality from different satellites and of incomplete coverage. Consequently the accuracy and resolution of the gravity field were limited. As is shown in Figure 1, the long wavelength components of the gravity field determined from satellite tracking were limited to a resolution of approximately 700 km. At shorter wavelengths, the errors were too large to be useful. Only broad geophysical features of the Earth's structure could be detected (see map 1).
In contrast, GRACE, by itself, has provided accurate gravity information with a resolution of 200 km. Now, much more detail is clearly evident in the Earth's geophysical features (see map 2). High resolution features detected by GRACE that are representative of geophysical phenomena include the Tonga/Kermadec region (a zone where one tectonic plate slides under another), the Himalayan/Tibetan Plateau region (an area of uplift due to colliding plates), and the mid-Atlantic ridge (an active spreading center in the middle of the Atlantic ocean where new crust is being created). Future GRACE gravity
Hydrogen atom in a strong magnetic field. II. Relativistic corrections for low-lying excited states
NASA Astrophysics Data System (ADS)
Poszwa, A.; Rutkowski, A.
2004-02-01
The highly accurate solution of the Schrödinger equation in the form of common Landau exponential factor multiplied by a power series in two variables, the sine of the cone angle and radial variable is completed by the first-order relativistic correction calculated within the framework of the relativistic direct perturbation theory (DPT). It is found that in contrast to behavior of relativistic corrections for the ground state and 2p-1(ms=-1/2) excited state, which change sign from negative to positive near B≈1011 G and B≈1010 G, respectively [Z. Chen and S. P. Goldman, Phys. Rev A 45, 1722 (1992)], the relativistic corrections for 2s0(ms=-1/2) and 2p0(ms=-1/2) excited states are negative for the magnetic field varying in range 0relativistic correction significantly mix nonrelativistic states the near-degenerate version of DPT is used. The avoided crossings of relativistic levels with μ=-1/2 and π=-1, evolving from field-free states with principal quantum numbers n=2,3,4 are presented.
Vlasov, A.A.; Logunov, A.A.
1986-01-01
It is shown that the external gravitational field of a nonstatic spherically symmetric body is static in the relativistic theory of gravitation. In the general theory of relativity it is shown that the graviational field exterior to a nonstatic spherically symmetric body reduces to a static gravitational field given by the Schwarzschild metric (Birkhoff's theorem). However, the Schwarzschild solution does not satisfy the equations of the relativistic theory of gravitation, and it is therefore necessary to prove the analogous theorem in the latter theory.
Was Newton right? A search for non-Newtonian behavior of weak-field gravity
NASA Astrophysics Data System (ADS)
Boynton, Paul; Moore, Michael; Newman, Riley; Berg, Eric; Bonicalzi, Ricco; McKenney, Keven
2014-06-01
Empirical tests of Einstein's metric theory of gravitation, even in the non-relativistic, weak-field limit, could play an important role in judging theory-driven extensions of the current Standard Model of fundamental interactions. Guided by Galileo's work and his own experiments, Newton formulated a theory of gravity in which the force of attraction between two bodies is independent of composition and proportional to the inertia of each, thereby transparently satisfying Galileo's empirically informed conjecture regarding the Universality of Free Fall. Similarly, Einstein honored the manifest success of Newton's theory by assuring that the linearized equations of GTR matched the Newtonian formalism under "classical" conditions. Each of these steps, however, was explicitly an approximation raised to the status of principle. Perhaps, at some level, Newtonian gravity does not accurately describe the physical interaction between uncharged, unmagnetized, macroscopic bits of ordinary matter. What if Newton were wrong? Detecting any significant deviation from Newtonian behavior, no matter how small, could provide new insights and possibly reveal new physics. In the context of physics as an empirical science, for us this yet unanswered question constitutes sufficient motivation to attempt precision measurements of the kind described here. In this paper we report the current status of a project to search for violation of the Newtonian inverse square law of gravity.
Earth's gravity field mapping requirements and concept. [using a supercooled gravity gradiometer
NASA Technical Reports Server (NTRS)
Vonbun, F. O.; Kahn, W. D.
1981-01-01
A future sensor is considered for mapping the Earth's gravity field to meet future scientific and practical requirements for earth and oceanic dynamics. These are approximately + or - 0.1 to 10 mgal over a block size of about 50 km and over land and an ocean geoid to 1 to 2 cm over a distance of about 50 km. To achieve these values requires a gravity gradiometer with a sensitivity of approximately 10 to the -4 power EU in a circular polar orbiting spacecraft with an orbital altitude ranging 160 km to 180 km.
Field-theoretical formulation of Regge–Teitelboim gravity
Sheykin, A. A. Paston, S. A.
2016-12-15
Theory of gravity is considered in the Regge–Teitelboim approach in which the pseudo-Rimannian space is treated as a surface isometrically embedded in an ambient Minkowski space of higher dimension. This approach is formulated in terms of a field theory in which the original pseudo-Rimannian space is defined by the field constant-value surfaces. The symmetry properties of the proposed theory are investigated, and possible structure of the field-theoretical Lagrangian is discussed.
Higher derivative gravity: Field equation as the equation of state
NASA Astrophysics Data System (ADS)
Dey, Ramit; Liberati, Stefano; Mohd, Arif
2016-08-01
One of the striking features of general relativity is that the Einstein equation is implied by the Clausius relation imposed on a small patch of locally constructed causal horizon. The extension of this thermodynamic derivation of the field equation to more general theories of gravity has been attempted many times in the last two decades. In particular, equations of motion for minimally coupled higher-curvature theories of gravity, but without the derivatives of curvature, have previously been derived using a thermodynamic reasoning. In that derivation the horizon slices were endowed with an entropy density whose form resembles that of the Noether charge for diffeomorphisms, and was dubbed the Noetheresque entropy. In this paper, we propose a new entropy density, closely related to the Noetheresque form, such that the field equation of any diffeomorphism-invariant metric theory of gravity can be derived by imposing the Clausius relation on a small patch of local causal horizon.
Alternative methods to smooth the Earth's gravity field
NASA Technical Reports Server (NTRS)
Jekeli, C.
1981-01-01
Convolutions on the sphere with corresponding convolution theorems are developed for one and two dimensional functions. Some of these results are used in a study of isotropic smoothing operators or filters. Well known filters in Fourier spectral analysis, such as the rectangular, Gaussian, and Hanning filters, are adapted for data on a sphere. The low-pass filter most often used on gravity data is the rectangular (or Pellinen) filter. However, its spectrum has relatively large sidelobes; and therefore, this filter passes a considerable part of the upper end of the gravity spectrum. The spherical adaptations of the Gaussian and Hanning filters are more efficient in suppressing the high-frequency components of the gravity field since their frequency response functions are strongly field since their frequency response functions are strongly tapered at the high frequencies with no, or small, sidelobes. Formulas are given for practical implementation of these new filters.
Gravity field and internal structure of Mercury from MESSENGER.
Smith, David E; Zuber, Maria T; Phillips, Roger J; Solomon, Sean C; Hauck, Steven A; Lemoine, Frank G; Mazarico, Erwan; Neumann, Gregory A; Peale, Stanton J; Margot, Jean-Luc; Johnson, Catherine L; Torrence, Mark H; Perry, Mark E; Rowlands, David D; Goossens, Sander; Head, James W; Taylor, Anthony H
2012-04-13
Radio tracking of the MESSENGER spacecraft has provided a model of Mercury's gravity field. In the northern hemisphere, several large gravity anomalies, including candidate mass concentrations (mascons), exceed 100 milli-Galileos (mgal). Mercury's northern hemisphere crust is thicker at low latitudes and thinner in the polar region and shows evidence for thinning beneath some impact basins. The low-degree gravity field, combined with planetary spin parameters, yields the moment of inertia C/MR(2) = 0.353 ± 0.017, where M and R are Mercury's mass and radius, and a ratio of the moment of inertia of Mercury's solid outer shell to that of the planet of C(m)/C = 0.452 ± 0.035. A model for Mercury's radial density distribution consistent with these results includes a solid silicate crust and mantle overlying a solid iron-sulfide layer and an iron-rich liquid outer core and perhaps a solid inner core.
A dynamic model of Venus's gravity field
NASA Technical Reports Server (NTRS)
Kiefer, W. S.; Richards, M. A.; Hager, B. H.; Bills, B. G.
1984-01-01
Unlike Earth, long wavelength gravity anomalies and topography correlate well on Venus. Venus's admittance curve from spherical harmonic degree 2 to 18 is inconsistent with either Airy or Pratt isostasy, but is consistent with dynamic support from mantle convection. A model using whole mantle flow and a high viscosity near surface layer overlying a constant viscosity mantle reproduces this admittance curve. On Earth, the effective viscosity deduced from geoid modeling increases by a factor of 300 from the asthenosphere to the lower mantle. These viscosity estimates may be biased by the neglect of lateral variations in mantle viscosity associated with hot plumes and cold subducted slabs. The different effective viscosity profiles for Earth and Venus may reflect their convective styles, with tectonism and mantle heat transport dominated by hot plumes on Venus and by subducted slabs on Earth. Convection at degree 2 appears much stronger on Earth than on Venus. A degree 2 convective structure may be unstable on Venus, but may have been stabilized on Earth by the insulating effects of the Pangean supercontinental assemblage.
Gravity field fine structure estimation techniques for a spaceborne gravity gradiometer
NASA Technical Reports Server (NTRS)
Kahn, W. D.; Englar, T. S., Jr.
1987-01-01
Use of standard estimation techniques to recover geopotential fine structure from gradiometer data requires the adjustment of small subsets of parameters while constraining others to their a priori values in order to minimize the computational load. Here, gravitational anomalies are selected as a parametrization of the gravity field which permits such an approach. Techniques coupled with numerical results for a spaceborne gravity gradiometer mission simulation are described which demonstrate that if a satellite is in a polar/circular orbit at an altitude of 160 km, 1 deg mean free air gravity anomalies can be recovered to an accuracy of 0.4 mgal, where 1 mgal = 0.001 cm/sq s.
Barbero-Immirzi parameter as a scalar field: K-inflation from loop quantum gravity?
NASA Astrophysics Data System (ADS)
Taveras, Victor; Yunes, Nicolás
2008-09-01
We consider a loop-quantum gravity inspired modification of general relativity, where the Holst action is generalized by making the Barbero-Immirzi (BI) parameter a scalar field, whose value could be dynamically determined. The modified theory leads to a nonzero torsion tensor that corrects the field equations through quadratic first derivatives of the BI field. Such a correction is equivalent to general relativity in the presence of a scalar field with nontrivial kinetic energy. This stress energy of this field is automatically covariantly conserved by its own dynamical equations of motion, thus satisfying the strong equivalence principle. Every general relativistic solution remains a solution to the modified theory for any constant value of the BI field. For arbitrary time-varying BI fields, a study of cosmological solutions reduces the scalar-field stress energy to that of a pressureless perfect fluid in a comoving reference frame, forcing the scale-factor dynamics to be equivalent to those of a stiff equation of state. Upon ultraviolet completion, this model could provide a natural mechanism for k inflation, where the role of the inflaton is played by the BI field and inflation is driven by its nontrivial kinetic energy instead of a potential.
Visualizing Special Relativity: The Field of An Electric Dipole Moving at Relativistic Speed
ERIC Educational Resources Information Center
Smith, Glenn S.
2011-01-01
The electromagnetic field is determined for a time-varying electric dipole moving with a constant velocity that is parallel to its moment. Graphics are used to visualize this field in the rest frame of the dipole and in the laboratory frame when the dipole is moving at relativistic speed. Various phenomena from special relativity are clearly…
Visualizing Special Relativity: The Field of An Electric Dipole Moving at Relativistic Speed
ERIC Educational Resources Information Center
Smith, Glenn S.
2011-01-01
The electromagnetic field is determined for a time-varying electric dipole moving with a constant velocity that is parallel to its moment. Graphics are used to visualize this field in the rest frame of the dipole and in the laboratory frame when the dipole is moving at relativistic speed. Various phenomena from special relativity are clearly…
New parameterization of the effective field theory motivated relativistic mean field model
NASA Astrophysics Data System (ADS)
Kumar, Bharat; Singh, S. K.; Agrawal, B. K.; Patra, S. K.
2017-10-01
A new parameter set is generated for finite and infinite nuclear system within the effective field theory motivated relativistic mean field (ERMF) formalism. The isovector part of the ERMF model employed in the present study includes the coupling of nucleons to the δ and ρ mesons and the cross-coupling of ρ mesons to the σ and ω mesons. The results for the finite and infinite nuclear systems obtained using our parameter set are in harmony with the available experimental data. We find the maximum mass of the neutron star to be 2.03M⊙ and yet a relatively smaller radius at the canonical mass, 12.69 km, as required by the available data.
Collapse of charged scalar field in dilaton gravity
Borkowska, Anna; Rogatko, Marek; Moderski, Rafal
2011-04-15
We elaborated the gravitational collapse of a self-gravitating complex charged scalar field in the context of the low-energy limit of the string theory, the so-called dilaton gravity. We begin with the regular spacetime and follow the evolution through the formation of an apparent horizon and the final central singularity.
Arctic Ocean Gravity Field Derived From ERS-1 Satellite Altimetry.
Laxon, S; McAdoo, D
1994-07-29
The derivation of a marine gravity field from satellite altimetry over permanently ice-covered regions of the Arctic Ocean provides much new geophysical information about the structure and development of the Arctic sea floor. The Arctic Ocean, because of its remote location and perpetual ice cover, remains from a tectonic point of view the most poorly understood ocean basin on Earth. A gravity field has been derived with data from the ERS-1 radar altimeter, including permanently ice-covered regions. The gravity field described here clearly delineates sections of the Arctic Basin margin along with the tips of the Lomonosov and Arctic mid-ocean ridges. Several important tectonic features of the Amerasia Basin are clearly expressed in this gravity field. These include the Mendeleev Ridge; the Northwind Ridge; details of the Chukchi Borderland; and a north-south trending, linear feature in the middle of the Canada Basin that apparently represents an extinct spreading center that "died" in the Mesozoic. Some tectonic models of the Canada Basin have proposed such a failed spreading center, but its actual existence and location were heretofore unknown.
Gravity field models derived from Swarm GPS data
NASA Astrophysics Data System (ADS)
Teixeira da Encarnação, João; Arnold, Daniel; Bezděk, Aleš; Dahle, Christoph; Doornbos, Eelco; van den IJssel, Jose; Jäggi, Adrian; Mayer-Gürr, Torsten; Sebera, Josef; Visser, Pieter; Zehentner, Norbert
2017-04-01
The Swarm satellites, with primary mission to measure Earth's Magnetic Field, continue to provide high-quality hl-SST data. We use these data to derive the time-varying gravity field of the Earth up to Spherical Harmonic degree and order 12, on a monthly basis since December 2013. We combine the gravity field solutions computed with the data of all three satellites, as provided by a number of institutes, namely at the Astronomical Institute (ASU) of the Czech Academy of Sciences (Bezděk et al., 2016), the Astronomical Institute of the University of Bern (AIUB, Jäggi et al., 2016) and the Institute of Geodesy (IfG) of the Graz University of Technology (Zehentner et al., 2015) and demonstrate that this uninterrupted time series of gravity field models are in good agreement with the temporal variations observed by the GRACE satellites. Therefore, these data can be used to study large-scale mass changes globally, e.g. i) in the context of low-latency applications, such as the European Gravity Service for Improved Emergency Management project (http://egsiem.eu), ii) in those months where GRACE solutions are not available, and iii) as an important source of independent information for mitigating the GRACE/GRACE Follow-On gap.
The Estimation of the Earth’s Gravity Field.
1986-06-01
technique of the satellite-to-satellite tracking for direct measurement of the earth’s gravity field originated in the Apollo program. Muller and Sjogren ...recovery of 5" mean gravity anomales in local areas from ATS-6/GEOS-3 satellite to satellite range rate observations. J. Geophys. Res. Vol., 84, No. B12 ...and OSU/DGSS Report No. 352 (full report). AFGL-TR-84-0042 AD-A145799. Muller, P.M. and W.L. Sjogren (1968). Mascons: lunar mass concentrations
Spontaneous growth of vector fields in gravity
NASA Astrophysics Data System (ADS)
Ramazanoǧlu, Fethi M.
2017-09-01
We show that the spontaneous scalarization scenario in scalar-tensor theories is a specific case of a more general phenomenon. The key fact is that the instability causing the spontaneous growth in scalars is due to the nonminimal coupling in the theory, and not related to the nature of the scalar. Another field with the same form of coupling undergoes spontaneous growth as well. We explicitly demonstrate this idea for vectors, naming it "spontaneous vectorization", and study spherically symmetric neutron stars in such a theory. We also comment on other tensor fields the idea can be applied, naming the general mechanism "spontaneous tensorization."
Rhea gravity field and interior modeling from Cassini data analysis
NASA Astrophysics Data System (ADS)
Tortora, Paolo; Zannoni, Marco; Hemingway, Doug; Nimmo, Francis; Jacobson, Robert A.; Iess, Luciano; Parisi, Marzia
2016-01-01
During its tour of the Saturn system, Cassini performed two close flybys of Rhea dedicated to gravity investigations, the first in November 2005 and the second in March 2013. This paper presents an estimation of Rhea's fully unconstrained quadrupole gravity field obtained from a joint multi-arc analysis of the two Cassini flybys. Our best estimates of the main gravity quadrupole unnormalized coefficients are J2 × 106 = 946.0 ± 13.9, C22 × 106 = 242.1 ± 4.0 (uncertainties are 1-σ). Their resulting ratio is J2/C22 = 3.91 ± 0.10, statistically not compatible (at a 5-σ level) with the theoretical value of 10/3, predicted for a hydrostatic satellite in slow, synchronous rotation around a planet. Therefore, it is not possible to infer the moment of inertia factor directly using the Radau-Darwin approximation. The observed excess J2 (gravity oblateness) was investigated using a combined analysis of gravity and topography, under different plausible geophysical assumptions. The observed gravity is consistent with that generated by the observed shape for an undifferentiated (uniform density) body. However, because the surface is more likely to be water ice, a two-layer model may be a better approximation. In this case, and assuming a mantle density of 920 kg/m3, some 1-3 km of excess core oblateness is consistent with the observed gravity. A wide range of moments of inertia is allowed, but models with low moments of inertia (i.e., more differentiation) require greater magnitudes of excess core topography to satisfy the observations.
GRACE gravity field recovery using refined acceleration approach
NASA Astrophysics Data System (ADS)
Li, Zhao; van Dam, Tonie; Weigelt, Matthias
2017-04-01
Since 2002, the GRACE mission has yielded monthly gravity field solutions with such a high level of quality that we have been able to observe so many changes to the Earth mass system. Based on GRACE L1B observations, a number of official monthly gravity field models have been developed and published using different methods, e.g. the CSR RL05, JPL RL05, and GFZ RL05 are being computed by a dynamic approach, the ITSG and Tongji GRACE are generated using what is known as the short-arc approach, the AIUB models are computed using celestial mechanics approach, and the DMT-1 model is calculated by means of an acceleration approach. Different from the DMT-1 model, which links the gravity field parameters directly to the bias-corrected range measurements at three adjacent epochs, in this work we present an alternative acceleration approach which connects range accelerations and velocity differences to the gradient of the gravitational potential. Due to the fact that GPS derived velocity difference is provided at a lower precision, we must reduce this approach to residual quantities using an a priori gravity field which allows us to subsequently neglect the residual velocity difference term. We find that this assumption would cause a problem in the low-degree gravity field coefficient, particularly for degree 2 and also from degree 16 to 26. To solve this problem, we present a new way of handling the residual velocity difference term, that is to treat this residual velocity difference term as unknown but estimable quantity, as it depends on the unknown residual gravity field parameters and initial conditions. In other word, we regard the kinematic orbit position vectors as pseudo observations, and the corrections of orbits are estimated together with both the geopotential coefficients and the accelerometer scale/bias by using a weighted least square adjustment. The new approach is therefore a refinement of the existing approach but offers a better approximation to reality
On the gravity field processing of next generation satellite gravity missions
NASA Astrophysics Data System (ADS)
Daras, Ilias; Pail, Roland
2016-04-01
Dedicated gravity field missions delivering observations for a period longer than 16 years have drastically contributed in improving our knowledge of mass transport processes in the Earth system. At the same time, they have left a precious heritage for the design of next generation satellite gravity missions to be launched in the mid-term future. Main subject of this study is the gravity field processing of future Low-Low Satellite-to-Satellite Tracking (LL-SST) missions. We perform assessment of the contribution of all error sources and develop methods for reducing their effect at the level of gravity field processing. Advances in metrology of sensors such as the inter-satellite ranging instrument, may raise the demands for processing accuracy. We show that gravity field processing with double precision may be a limiting factor for exploiting the nm-level accuracy of a laser interferometer that future missions are expected to carry. An enhanced numerical precision processing scheme is proposed instead, where double and quadruple precision is used in different parts of the processing chain. It is demonstrated that processing with enhanced precision can efficiently handle laser measurements and take full advantage of their accuracy, while keeping the computational times within reasonable levels (Daras, 2015). However, error sources of considerably larger impact are expected to affect future missions, with the accelerometer instrument noise and temporal aliasing effects being the most significant ones. The effect of time-correlated noise such as the one present in accelerometer measurements can be efficiently handled by frequency dependent data weighting. Residual time series that contain the effect of system errors and propagated accelerometer and laser noise, is considered as a noise realization with stationary stochastic properties. The weight matrix is constructed from the auto-correlation functions of these residuals. Applying the weight matrix to a noise case
Perturbative quantum gravity in double field theory
NASA Astrophysics Data System (ADS)
Boels, Rutger H.; Horst, Christoph
2016-04-01
We study perturbative general relativity with a two-form and a dilaton using the double field theory formulation which features explicit index factorisation at the Lagrangian level. Explicit checks to known tree level results are performed. In a natural covariant gauge a ghost-like scalar which contributes even at tree level is shown to decouple consistently as required by perturbative unitarity. In addition, a lightcone gauge is explored which bypasses the problem altogether. Using this gauge to study BCFW on-shell recursion, we can show that most of the D-dimensional tree level S-matrix of the theory, including all pure graviton scattering amplitudes, is reproduced by the double field theory. More generally, we argue that the integrand may be reconstructed from its single cuts and provide limited evidence for off-shell cancellations in the Feynman graphs. As a straightforward application of the developed technology double field theory-like expressions for four field string corrections are derived.
Relativistic Runaway Electron Avalanches in the Presence of an External Magnetic Field
NASA Astrophysics Data System (ADS)
Cramer, E. S.; Dwyer, J. R.; Liu, N.; Rassoul, H.; Briggs, M. S.
2015-12-01
Relativistic runaway electron avalanches are known to be produced inside the high electric field regions of thunderstorms. In this work, we include the effects of an external static magnetic field. Previous studies have shown that the magnetic field has a great influence on the electron motion at higher altitudes, e.g. Lehtinen et al., 1997, and Gurevich et al., 1996. This result proves important when studying phenomena such as Terrestrial Gamma-ray Flashes, and their effects on the upper atmosphere. Therefore, electron avalanche rates, feedback rates, and electron energy distribution functions will be analyzed and compared to the results of previous studies that did not include a magnetic field. The runaway electron avalanche model (REAM) is a Monte Carlo code that simulates the generation, interactions, and propagation of relativistic runaway electrons in air [Dwyer, 2003, 2004, 2007]. We use this simulation for varying strengths and angles between the electric and magnetic fields to calculate avalanche lengths and angular distribution functions of the relativistic runaway electrons. We will also show electron distribution functions in momentum space. Finally, we will discuss the important regimes for which the magnetic field becomes significant in studying the properties of runaway electron avalanches and relativistic feedback.
Barbero-Immirzi field in canonical formalism of pure gravity
NASA Astrophysics Data System (ADS)
Calcagni, Gianluca; Mercuri, Simone
2009-04-01
The Barbero-Immirzi (BI) parameter is promoted to a field and a canonical analysis is performed when it is coupled with a Nieh-Yan topological invariant. It is shown that, in the effective theory, the BI field is a canonical pseudoscalar minimally coupled with gravity. This framework is argued to be more natural than the one of the usual Holst action. Potential consequences in relation with inflation and the quantum theory are briefly discussed.
Mizuno, Yosuke; Nishikawa, Ken-Ichi; Pohl, Martin; Niemiec, Jacek; Zhang, Bing; Hardee, Philip E.
2011-01-10
We perform two-dimensional relativistic magnetohydrodynamic simulations of a mildly relativistic shock propagating through an inhomogeneous medium. We show that the postshock region becomes turbulent owing to preshock density inhomogeneity, and the magnetic field is strongly amplified due to the stretching and folding of field lines in the turbulent velocity field. The amplified magnetic field evolves into a filamentary structure in two-dimensional simulations. The magnetic energy spectrum is flatter than the Kolmogorov spectrum and indicates that a so-called small-scale dynamo is occurring in the postshock region. We also find that the amount of magnetic-field amplification depends on the direction of the mean preshock magnetic field, and the timescale of magnetic-field growth depends on the shock strength.
Zenitani, S; Hoshino, M
2005-08-26
The linear and nonlinear evolution of a relativistic current sheet of pair (e(+/-)) plasmas is investigated by three-dimensional particle-in-cell simulations. In a Harris configuration, it is obtained that the magnetic energy is fast dissipated by the relativistic drift kink instability (RDKI). However, when a current-aligned magnetic field (the so-called "guide field") is introduced, the RDKI is stabilized by the magnetic tension force and it separates into two obliquely propagating modes, which we call the relativistic drift-kink-tearing instability. These two waves deform the current sheet so that they trigger relativistic magnetic reconnection at a crossover thinning point. Since relativistic reconnection produces a lot of nonthermal particles, the guide field is of critical importance to study the energetics of a relativistic current sheet.
The Martian: Examining Human Physical Judgments across Virtual Gravity Fields.
Ye, Tian; Qi, Siyuan; Kubricht, James; Zhu, Yixin; Lu, Hongjing; Zhu, Song-Chun
2017-04-01
This paper examines how humans adapt to novel physical situations with unknown gravitational acceleration in immersive virtual environments. We designed four virtual reality experiments with different tasks for participants to complete: strike a ball to hit a target, trigger a ball to hit a target, predict the landing location of a projectile, and estimate the flight duration of a projectile. The first two experiments compared human behavior in the virtual environment with real-world performance reported in the literature. The last two experiments aimed to test the human ability to adapt to novel gravity fields by measuring their performance in trajectory prediction and time estimation tasks. The experiment results show that: 1) based on brief observation of a projectile's initial trajectory, humans are accurate at predicting the landing location even under novel gravity fields, and 2) humans' time estimation in a familiar earth environment fluctuates around the ground truth flight duration, although the time estimation in unknown gravity fields indicates a bias toward earth's gravity.
The gravity field observations and products at IGFS
NASA Astrophysics Data System (ADS)
Barzaghi, Riccardo; Vergos, George; Bonvalot, Sylvain; Barthelmes, Franz; Reguzzoni, Mirko; Wziontek, Hartmut; Kelly, Kevin
2017-04-01
The International Gravity Field Service (IGFS) is a service of the International Association of Geodesy (IAG) that was established in 2003 at the IAG/IUGG General Assembly in Sapporo (Japan). This service aims at coordinating the actions of the IAG services related to the Earth gravity field, i.e. the Bureau Gravimétrique International (BGI), the International Service for the Geoid (ISG), the International Geodynamics and Earth Tides Service (IGETS), the International Center for Global Earth Models (ICGEM) and the International Digital Elevation Model Service (IDEMS). Also, via its Central Bureau hosted at the Aristotle University of Thessaloniki (Greece), IGFS provides a link to the Global Geodetic Observing System (GGOS) bureaus in order to communicate their requirements and recommendations to the IGFS-Centers. In this work, a presentation is given on the recent activities of the service, namely those related to the contributions to the implementation of: the International Height Reference System/Frame; the Global Geodetic Reference System/Frame; the new Global Absolute Gravity Reference System/Frame. Particularly, the impact that these activities have in improving the estimation of the Earth's gravity field, either at global and local scale, is highlighted also in the framework of GGOS.
Properties of the gravity fields of terrestrial planets
NASA Technical Reports Server (NTRS)
Kaula, William M.
1992-01-01
The properties of the gravity fields of the earth, Mars, and Venus, as expressed by spherical harmonic coefficients, are examined, using the harmonic expansions of the respective planetary topographies reported by Balmino et al. (1973), Bills and Ferrari (1978), and Bills and Kobrick (1985). The items examined include the spectral magnitudes and slopes of the gravity coefficients; the correlations between gravity and topography; and the correlations among different gravity harmonics, expressed by axiality and angularity. It was found that Venus differs from the other two planets in its great apparent depths of compensation, indicating a tectonics dominated by a stiff upper mantle. In addition, Venus has less activity deep in the mantle than do earth or Mars. Mars is marked by large gravity irregularities, as well as by their axial symmetry on a global scale. Although earth is probably the most peculiar planet, spherical harmonics do not bring out its varied characteristics. It is clearly a more active planet than Venus, with activity deep in the mantle. The lower magnitude of its higher harmonics is considered to be due to water recycled to the upper mantle.
The negative gravity field over the 85 deg E ridge
NASA Technical Reports Server (NTRS)
Liu, C.-S.; Curray, J. R.; Sandwell, D. T.
1982-01-01
Two north-south ridges in the basement topography of the Bay of Bengal may be observed on an isopach map at 85 and at 90 deg E. Free-air gravity anomaly profiles across the region show a strong gravity low (about -60 mGal) over the 85 deg E ridge, and a gravity high over the other. Using a simple two-stage loading model, the negative gravity anomaly over the 85 deg E ridge is explained as a direct consequence of sediment loading, and the flexural rigidity of the lithosphere when the ridge was formed is estimated to have been about 180 times less than the flexural rigidity during the sediment loading. An approximate relationship between flexural rigidity and crustal age shows that the 85 deg E ridge was formed on relatively young lithosphere, 5-15 million years old, and that it was buried when the lithosphere was 40-80 million years old. The alteration of the gravity field by a thick layer of sediments may occur in other large sedimentary basins or along continental margins.
Classifying linearly shielded modified gravity models in effective field theory.
Lombriser, Lucas; Taylor, Andy
2015-01-23
We study the model space generated by the time-dependent operator coefficients in the effective field theory of the cosmological background evolution and perturbations of modified gravity and dark energy models. We identify three classes of modified gravity models that reduce to Newtonian gravity on the small scales of linear theory. These general classes contain enough freedom to simultaneously admit a matching of the concordance model background expansion history. In particular, there exists a large model space that mimics the concordance model on all linear quasistatic subhorizon scales as well as in the background evolution. Such models also exist when restricting the theory space to operators introduced in Horndeski scalar-tensor gravity. We emphasize that whereas the partially shielded scenarios might be of interest to study in connection with tensions between large and small scale data, with conventional cosmological probes, the ability to distinguish the fully shielded scenarios from the concordance model on near-horizon scales will remain limited by cosmic variance. Novel tests of the large-scale structure remedying this deficiency and accounting for the full covariant nature of the alternative gravitational theories, however, might yield further insights on gravity in this regime.
Gravitational constant in multiple field gravity
Abedi, Habib; Abbassi, Amir M. E-mail: amabasi@khayam.ut.ac.ir
2015-05-01
In the present study, we consider general form of the Lagrangian f(R, φ{sup I}, X) , that is a function of the Ricci scalar, multiple scalar fields and non-canonical kinetic terms. We obtain the effective Newton's constant deep inside the Hubble radius. We use Jordan and Einstein frames, and study the conservation of energy-momentum tensor.
New isostatic model of the lithosphere and gravity field
NASA Astrophysics Data System (ADS)
Kaban, M. K.; Schwintzer, P.; Reigber, Ch.
2003-04-01
A new global model of the isostatic gravity field based on the up-to-date data sets is computed in terms of gravity and geoid. The initial gravity field model is improved using the new CHAMP data. For a construction of the isostatic model of the lithosphere we use the latest compilation of crustal data. Globally this is the CRUST2.0 model, which is supplemented by detailed original data for large parts of North America and North Eurasia. The long-wavelengths of the computed isostatic anomalies up to spherical harmonic degree 20 reflect deep density heterogeneities and the influence of mantle convection through the dynamic topography. The signal contribution of the isostatically balanced lithosphere to the observed gravity or geoid is still significant also for the long-wavelengths: -30- +60 mGal and -15- +40 m peak-to-peak, respectively. Generally the long-wavelength isostaticaly reduced gravity field has much less correlation with the lithosphere patterns than the observed field. This demonstrates that the long-wavelength isostatic gravity field is more appropriate for a modelling of mantle convection than the observed one. The smaller scale isostatic anomalies (wavelengths less than 2000 km) on the other hand are highly sensitive to the quality of the input data used for their computation. To a large extent they reflect internal crustal density inhomogeneities, not included in the isostatic compensation scheme, and uncertainties in the initial crustal data. Thus, small-scale isostatic anomalies may not be always interpreted as a measure of the disturbances of isostatic balance of the lithosphere. Instead we suggest to compute for the smaller scale spectral part the non-isostatic residual topography. The initial crust - upper mantle density model is corrected by gravity inversion in a least squares adjustment. Then, the residual (unbalanced) topography computed with the corrected density distribution represents the isostatic state of the lithosphere. The maximum
The Mercury Gravity Field after the MESSENGER Low-Altitude Gravity Campaign
NASA Astrophysics Data System (ADS)
Mazarico, E.; Genova, A.; Goossens, S. J.; Lemoine, F. G.; Neumann, G. A.; Smith, D. E.; Zuber, M. T.; Solomon, S. C.
2014-12-01
NASA's MESSENGER spacecraft has collected more than 3.5 years of X-band radio tracking data in orbit around the planet Mercury. During its one-year primary mission, which started in March 2011, MESSENGER was in an eccentric, near-polar orbit of 12-hour period, and the periapsis altitude was actively maintained between 200 and 500 km. For its extended mission, the orbit period was reduced to 8 hours. As the orbit naturally evolved, in large part due to the third-body gravitational perturbation of the Sun, the periapsis altitude reached a maximum of ~450 km in March 2013 and then began to decrease. An ambitious end of mission was designed to use the remaining fuel to delay impact and to observe the northern hemisphere for nearly a year at periapsis altitudes lower than 200 km, including four intervals of exceptionally low altitude (25-100 km). Periapsis passages are visible from Earth only for two of these intervals, in August and October 2014. These new data, the lowest-altitude radio tracking measurements to be acquired by MESSENGER, prompt an updated solution for the gravity field of Mercury. In preparation for acquisition of the low-altitude (<100 km) data, we have reprocessed tracking data through 14 July 2014. These data already provide good coverage below 200 km over most longitudes. A preliminary gravity solution to degree and order 50 shows stronger gravity anomalies near the periapsis latitudes than in the most recent global solution, HgM005. To best capture the shorter-wavelength signals expected from the lowest-altitude passes, we are estimating a large number of local surface anomalies (arranged on a 1°x1° grid) in addition to a harmonic field. We are also using the resulting gravity anomalies to update crustal thickness models and to explore the implications for gravity anomalies over basins and topographic rises and the modes of compensation of these features.
Gravity Field of the Orientale Basin from the Gravity Recovery and Interior Laboratory Mission
NASA Technical Reports Server (NTRS)
Zuber, Maria T.; Smith, David E.; Neumann, Gregory A.; Goossens, Sander; Andrews-Hanna, Jeffrey C.; Head, James W.; Kiefer, Walter S.; Asmar, Sami W.; Konopliv, Alexander S.; Lemoine, Frank G.; Matsuyama, Isamu; Melosh, H. Jay; McGovern, Patrick J.; Nimmo, Francis; Phillips, Roger J.; Solomon, Sean C.; Taylor, G. Jeffrey; Watkins, Michael M.; Wieczorek, Mark A.; Williams, James G.; Jansen, Johanna C.; Johnson, Brandon C.; Keane, James T.; Mazarico, Erwan; Miljkovic, Katarina; Park, Ryan S.; Soderblom, Jason M.; Yuan, Dah-Ning
2016-01-01
The Orientale basin is the youngest and best-preserved major impact structure on the Moon. We used the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft to investigate the gravitational field of Orientale at 3- to 5-kilometer (km) horizontal resolution. A volume of at least (3.4 +/- 0.2) × 10(exp 6) cu km of crustal material was removed and redistributed during basin formation. There is no preserved evidence of the transient crater that would reveal the basin's maximum volume, but its diameter may now be inferred to be between 320 and 460 km. The gravity field resolves distinctive structures of Orientale's three rings and suggests the presence of faults associated with the outer two that penetrate to the mantle. The crustal structure of Orientale provides constraints on the formation of multiring basins.
Gravity field of the Orientale basin from the Gravity Recovery and Interior Laboratory Mission.
Zuber, Maria T; Smith, David E; Neumann, Gregory A; Goossens, Sander; Andrews-Hanna, Jeffrey C; Head, James W; Kiefer, Walter S; Asmar, Sami W; Konopliv, Alexander S; Lemoine, Frank G; Matsuyama, Isamu; Melosh, H Jay; McGovern, Patrick J; Nimmo, Francis; Phillips, Roger J; Solomon, Sean C; Taylor, G Jeffrey; Watkins, Michael M; Wieczorek, Mark A; Williams, James G; Jansen, Johanna C; Johnson, Brandon C; Keane, James T; Mazarico, Erwan; Miljković, Katarina; Park, Ryan S; Soderblom, Jason M; Yuan, Dah-Ning
2016-10-28
The Orientale basin is the youngest and best-preserved major impact structure on the Moon. We used the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft to investigate the gravitational field of Orientale at 3- to 5-kilometer (km) horizontal resolution. A volume of at least (3.4 ± 0.2) × 10(6) km(3) of crustal material was removed and redistributed during basin formation. There is no preserved evidence of the transient crater that would reveal the basin's maximum volume, but its diameter may now be inferred to be between 320 and 460 km. The gravity field resolves distinctive structures of Orientale's three rings and suggests the presence of faults associated with the outer two that penetrate to the mantle. The crustal structure of Orientale provides constraints on the formation of multiring basins.
Gravity Field of the Orientale Basin from the Gravity Recovery and Interior Laboratory Mission
NASA Technical Reports Server (NTRS)
Zuber, Maria T.; Smith, David E.; Neumann, Gregory A.; Goossens, Sander; Andrews-Hanna, Jeffrey C.; Head, James W.; Kiefer, Walter S.; Asmar, Sami W.; Konopliv, Alexander S.; Lemoine, Frank G.;
2016-01-01
The Orientale basin is the youngest and best-preserved major impact structure on the Moon. We used the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft to investigate the gravitational field of Orientale at 3- to 5-kilometer (km) horizontal resolution. A volume of at least (3.4 +/- 0.2) × 10(exp 6) cu km of crustal material was removed and redistributed during basin formation. There is no preserved evidence of the transient crater that would reveal the basin's maximum volume, but its diameter may now be inferred to be between 320 and 460 km. The gravity field resolves distinctive structures of Orientale's three rings and suggests the presence of faults associated with the outer two that penetrate to the mantle. The crustal structure of Orientale provides constraints on the formation of multiring basins.
Gravity field of the Orientale basin from the Gravity Recovery and Interior Laboratory Mission
NASA Astrophysics Data System (ADS)
Zuber, Maria T.; Smith, David E.; Neumann, Gregory A.; Goossens, Sander; Andrews-Hanna, Jeffrey C.; Head, James W.; Kiefer, Walter S.; Asmar, Sami W.; Konopliv, Alexander S.; Lemoine, Frank G.; Matsuyama, Isamu; Melosh, H. Jay; McGovern, Patrick J.; Nimmo, Francis; Phillips, Roger J.; Solomon, Sean C.; Taylor, G. Jeffrey; Watkins, Michael M.; Wieczorek, Mark A.; Williams, James G.; Jansen, Johanna C.; Johnson, Brandon C.; Keane, James T.; Mazarico, Erwan; Miljković, Katarina; Park, Ryan S.; Soderblom, Jason M.; Yuan, Dah-Ning
2016-10-01
The Orientale basin is the youngest and best-preserved major impact structure on the Moon. We used the Gravity Recovery and Interior Laboratory (GRAIL) spacecraft to investigate the gravitational field of Orientale at 3- to 5-kilometer (km) horizontal resolution. A volume of at least (3.4 ± 0.2) × 106 km3 of crustal material was removed and redistributed during basin formation. There is no preserved evidence of the transient crater that would reveal the basin’s maximum volume, but its diameter may now be inferred to be between 320 and 460 km. The gravity field resolves distinctive structures of Orientale’s three rings and suggests the presence of faults associated with the outer two that penetrate to the mantle. The crustal structure of Orientale provides constraints on the formation of multiring basins.
Effects of the imposed magnetic field on the production and transport of relativistic electron beams
NASA Astrophysics Data System (ADS)
Cai, Hong-bo; Zhu, Shao-ping; He, X. T.
2013-07-01
The effects of the imposed uniform magnetic field, ranging from 1 MG up to 50 MG, on the production and transport of relativistic electron beams (REBs) in overdense plasmas irradiated by ultraintense laser pulse are investigated with two-dimensional particle-in-cell numerical simulations. This study gives clear evidence that the imposed magnetic field is capable of effectively confining the relativistic electrons in space even when the source is highly divergent since it forces the electrons moving helically. In comparison, the spontaneous magnetic fields, generated by the helically moving electrons interplaying with the current filamentation instability, are dominant in scattering the relativistic electrons. As the imposed magnetic field was increased from 1 MG to 50 MG, overall coupling from laser to the relativistic electrons which have the potential to heat the compressed core in fast ignition was found to increase from 6.9% to 21.3% while the divergence of the REB increases significantly from 64° to 90°. The simulations show that imposed magnetic field of the value of 3-30 MG could be more suitable to fast-ignition inertial fusion.
Rapid 3-D forward modeling of gravity and gravity gradient tensor fields
NASA Astrophysics Data System (ADS)
Longwei, C.; Dai, S.; Zhang, Q.
2014-12-01
Three-dimensional inversion are the key process in gravity exploration. In the commonly used scheme of inversion, the subsurface of the earth is usually divided into many small prism blocks (or grids) with variable density values. A key task in gravity inversion is to calculate the composite fields (gravity and gravity gradient tensor) generated by all these grids, this is known as forward modeling. In general forward modeling is memory-demanding and time-consuming. One scheme to rapidly calculate the fields is to implement it in Fourier domain and use fast Fourier transform algorithm. The advantage of the Fourier domain method is, obviously, much faster. However, the intrinsic edge effect of the Fourier domain method degrades the precision of the calculated fields. We have developed an innovative scheme to directly calculate the fields in spatial domain. There are two key points in this scheme. One key point is spatial discretization. Spatial convolution formula is discretized using an approach similar to normal difference method. A key idea during discretization is to use the analytical formula of a cubic prism, and this makes the resultant discrete formula have clear physical meaning: it embodies the superposition principle of the fields and is the exact formula to calculate the fields generated by all grids. The discretization only requires the grids have the same dimension in horizontal directions, and grids in different layers may have different dimension in vertical direction, and this offers more flexibility for inversion. Another key point is discrete convolution calculation. We invoke a high efficient two-dimensional discrete convolution algorithm, and it guarantees both time-saving and memory-saving. Its memory cost has the same order as the number of grids. Numerical test result shows that for a model with a dimension of 1000x1000x201 grids, it takes about 300s to calculate the fields on 1000x1000 field points in a personal computer with 3.4-GHz CPU
NASA Technical Reports Server (NTRS)
Griggs, C. E.; Paik, H. J.; Moody, M. V.; Han, S.-C.; Rowlands, D. D.; Lemoine, F. G.; Shirron, P. J.
2015-01-01
We are developing a compact tensor superconducting gravity gradiometer (SGG) for obtaining gravimetric measurements from planetary orbits. A new and innovative design gives a potential sensitivity of approximately 10(sup -4) E Hz(sup - 1/2)( 1 E = 10(sup -9 S(sup -2) in the measurement band up to 0.1 Hz (suitale for short wavelength static gravity) and of approximately 10(sup -4) E Hz(sup - 1/2) in the frequency band less than 1 mHz (for long wavelength time-variable gravity) from the same device with a baseline just over 10 cm. The measurement band and sensitiy can be optimally tuned in-flight during the mission by changing resonance frequencies, which allows meaurements of both static and time-variable gravity fields from the same mission. Significant advances in the technologies needed for space-based cryogenic instruments have been made in the last decade. In particular, the use of cryocoolers will alleviate the previously severe constraint on mission lifetime imposed by the use of liquid helium, enabling mission durations in the 5 - 10 year range.
Satellite laser ranging and gravity field modeling accuracy
NASA Technical Reports Server (NTRS)
Rosborough, George W.
1990-01-01
Gravitational field mismodeling procedures errors in the estimated orbital motion of near Earth satellites. This effect is studied using a linear perturbation approach following the analysis of Kaula. The perturbations in the orbital position as defined by either orbital elements or Cartesian components are determined. From these perturbations it is possible to ascertain the expected signal due to gravitational mismodeling that would be present in station-to-satellite laser ranging measurements. This expected signal has been estimated for the case of the Lageos satellite and using the predicted uncertainties of the GEM-T1 and GEM-T2 gravity field models. The results indicate that observable signal still exists in the laser range residuals given the current accuracy of the range measurements and the accuracy of the gravity field models.
Time-variable gravity fields from satellite tracking
NASA Astrophysics Data System (ADS)
Bettadpur, Srinivas; Cheng, Minkang; Ries, John
2014-05-01
At the University of Texas Center for Space Research (CSR), we routinely deliver time-series of Earth's gravity field variations, some of it spanning more than two decades. These time-series are derived - in a consistent manner - from satellite laser ranging (SLR) data, from low-Earth orbiters tracked using GPS, and from low-low satellite to satellite tracking data from GRACE. In this paper, we review the information content in the gravity field time-series derived from each of these methods. We provide a comparison of the time-series at the decadal and annual time-scales, and identify the spatial modes of variability that are well or poorly estimated by each of the observing systems. The results have important bearing on the prospects of extending GRACE time-variable gravity time-series in the event of gaps between dedicated gravity missions, and for extending the time-series into the past. Support for this research from joint NASA/DLR GRACE mission, the NASA MEASURs program, and the NASA ROSES/GRACE Science Team is gratefully acknowledged.
DiPerna-Lions Flow for Relativistic Particles in an Electromagnetic Field
NASA Astrophysics Data System (ADS)
Jabin, P.-E.; Masmoudi, N.
2015-09-01
We show the existence and uniqueness of a DiPerna-Lions flow for relativistic particles subject to a Lorentz force in an electromagnetic field. The electric and magnetic fields solve the linear Maxwell system in the vacuum but for singular initial conditions which are only in the physical energy space. As the corresponding force field is only in L 2, we have to perform a careful analysis of the cancellations over a trajectory.
Theoretical frameworks for testing relativistic gravity. V - Post-Newtonian limit of Rosen's theory
NASA Technical Reports Server (NTRS)
Lee, D. L.; Ni, W.-T.; Caves, C. M.; Will, C. M.
1976-01-01
The post-Newtonian limit of Rosen's theory of gravity is evaluated and is shown to be identical to that of general relativity, except for the post-Newtonian parameter alpha sub 2 (which is related to the difference in propagation speeds for gravitational and electromagnetic waves). Both the value of alpha sub 2 and the value of the Newtonian gravitational constant depend on the present cosmological structure of the Universe. If the cosmological structure has a specific (but presumably special) form, the Newtonian gravitational constant assumes its current value, alpha sub 2 is zero, the post-Newtonian limit of Rosen's theory is identical to that of general relativity - and standard solar system experiments cannot distinguish between the two theories.
Theoretical frameworks for testing relativistic gravity. 5: Post-Newtonian limit of Rosen's theory
NASA Technical Reports Server (NTRS)
Lee, D. L.; Caves, C. M.
1974-01-01
The post-Newtonian limit of Rosen's theory of gravity is evaluated and is shown to be identical to that of general relativity, except for the PPN parameter alpha sub 2, which is related to the difference in propagation speeds for gravitational and electromagnetic waves. Both the value of alpha sub 2 and the value of the Newtonian gravitational constant depend on the present cosmological structure of the Universe. If the cosmological structure has a specific but presumably special form, the Newtonian gravitational constant assumes its current value, alpha sub 2 is zero, the post-Newtonian limit of Rosen's theory is identical to that of general relativity--and standard solar system experiments cannot distinguish between the two theories.
Theoretical frameworks for testing relativistic gravity. V - Post-Newtonian limit of Rosen's theory
NASA Technical Reports Server (NTRS)
Lee, D. L.; Ni, W.-T.; Caves, C. M.; Will, C. M.
1976-01-01
The post-Newtonian limit of Rosen's theory of gravity is evaluated and is shown to be identical to that of general relativity, except for the post-Newtonian parameter alpha sub 2 (which is related to the difference in propagation speeds for gravitational and electromagnetic waves). Both the value of alpha sub 2 and the value of the Newtonian gravitational constant depend on the present cosmological structure of the Universe. If the cosmological structure has a specific (but presumably special) form, the Newtonian gravitational constant assumes its current value, alpha sub 2 is zero, the post-Newtonian limit of Rosen's theory is identical to that of general relativity - and standard solar system experiments cannot distinguish between the two theories.
Examination of Biological Effects of Magnetic Field Concealed by Gravity
NASA Astrophysics Data System (ADS)
Yamashita, M.; Tomita-Yokotani, K.; Hashimoto, H.; Nakamura, T.
Response of biological systems against combined environment of zero-gravity and zero-magnetic field should be examined as the baseline to investigate biological effects of magnetic field that might be concealed by gravity. Space offers unique opportunities to conduct such study because long term microgravity is available for the scientific use. However, magnetic environment has been neither well controlled nor documented both in space and ground based experiments. Biological specimen is exposed to the various magnetic field of Earth during the revolutions in orbit. The profile of magnetic field varying in time depends on the orbital parameters and attitude of the space platform. Furthermore, the onboard 1 G control group is subjected to centrifugation spinning where magnetic field varies differently from the microgravity experiment group. It can not be accepted as the 1 G control in terms of magnetic environment. We propose experiment set up to shield exotic magnetic field experienced in orbiting space experiment platform. Thin film of amorphous metal or alloys has shielding capability, and is feasible to implement for space experimentation. In order to simulate zero-gravity and zero-magnetic field on ground, we developed a 3D- clinostat that equips a magnetic shielding layer for specimen. In order to evaluate effects of normal magnetic field of Earth, steady magnetic field is induced at the site of specimen inside the shield layer either in orbit or on 3D-clinostat. To fill the matrix of experimental design, 1 G control under the magnetic shielded condition, and 1 G control that is exposed to the normal field should be taken. Degree of magnetic shielding magnitude required for plant studies and other issues were examined by the preliminary experiments using a 3D-clinostat for the studies of etiolated seedlings.
The Gravity Field of Enceladus from the three Cassini Flybys
NASA Astrophysics Data System (ADS)
Iess, L.; Parisi, M.; Ducci, M.; Jacobson, R. A.; Armstrong, J. W.; Asmar, S. W.; Lunine, J. I.; Stevenson, D. J.; Tortora, P.
2013-12-01
The Cassini spacecraft carried out gravity measurements of the small Saturnian moon Enceladus during three close flybys on April 28, 2010, November 30, 2010 and May 2, 2012 (designated E9, E12 and E19), at the low altitudes of 100, 48 and 70 km to maximize the accelerations exerted by the moon on the spacecraft. The goals of these observations were the determination of the gravitational quadrupole and the search for a North-South asymmetry in the gravity field, controlled primarily by the spherical harmonic coefficient C30. The estimation of Enceladus' gravity field is especially complex because of the small surface gravity (0.11 m/s2), the short duration of the gravitational interaction and the small number of available flybys. In addition to the gravitational accelerations, the spacecraft was also subject to small but non-negligible drag when it flew through the plume emitted from the south pole of the satellite. This effect occurred during the two south polar flybys E9 and E19. The inclusion of these non-gravitational accelerations proved to be crucial to attain a stable solution for the gravity field. Our estimation relied entirely on precise range rate measurements enabled by a coherent, two-way, microwave link at X-band (7.2-8.4 GHz). Measurement accuracies of 10 micron/s at 60 s integration times were attained under favorable conditions, thanks also to an advanced tropospheric calibration system. The data were fitted using the MONTE orbit determination code, recently developed by JPL for deep space navigation. In addition to the satellite degree 2 gravity field and C30, the solution included the state vector of the spacecraft (one for each flyby) and corrections to the mass and the initial orbital elements of Enceladus. The effect of the drag in E9 and E19 was modeled either as an unknown, impulsive, vectorial delta-V at closest approach, or by using density profiles from models of the plume and solving for the aerodynamic coefficient of the spacecraft. Both
NASA Technical Reports Server (NTRS)
Niemiec, J.; Nishikawa, K.-I.; Hardee, P.; Pohl, M.; Medvedev, M.; Mizuno, Y.; Zhang, B.; Oka, M.; Sol, H.; Hartmann, D.
2009-01-01
Using 3D and 2D particle-in-cell simulations we investigate a shock structure, magnetic field generation, and particle acceleration associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized pair plasma. The simulations use long computational grids which allow to study the formation and dynamics of the system in a spatial and temporal way. We find for the first time a relativistic shock system comparable to a predicted magnetohydrodynamic shock structure consisting of leading and trailing shocks separated by a contact discontinuity. Strong electromagnetic fields resulting from the Weibel two-stream instability are generated in the trailing shock where jet matter is thermalized and decelerated. We analyze the formation and nonlinear development through saturation and dissipation of those fields and associated particle acceleration. In the AGN context the trailing shock corresponds to the jet shock at the head of a relativistic astrophysical jet. In the GRB context this trailing shock can be identified with the bow shock driven by relativistic ejecta. The strong electromagnetic field region in the trailing shock provides the emission site for the hot spot at the leading edge of AGN jets and for afterglow emission from GRBs.
Particle acceleration magnetic field generation, and emission in Relativistic pair jets
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C.; Kouveliotou, C.; Fishman, G. J.
2005-01-01
Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) are responsible for particle acceleration in relativistic pair jets. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic pair jet propagating through a pair plasma. Simulations show that the Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. Simulation results show that this instability generates and amplifies highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The "jitter' I radiation from deflected electrons can have different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. The growth rate of the Weibel instability and the resulting particle acceleration depend on the magnetic field strength and orientation, and on the initial particle distribution function. In this presentation we explore some of the dependencies of the Weibel instability and resulting particle acceleration on the magnetic field strength and orientation, and the particle distribution function.
B. Julia-Diaz, H. Kamano, T.-S. H. Lee, A. Matsuyama, T. Sato, N. Suzuki
2009-04-01
Within the relativistic quantum field theory, we analyze the differences between the $\\pi N$ reaction models constructed from using (1) three-dimensional reductions of Bethe-Salpeter Equation, (2) method of unitary transformation, and (3) time-ordered perturbation theory. Their relations with the approach based on the dispersion relations of S-matrix theory are dicusssed.
Objective realism and freedom of choice in relativistic quantum field theory
NASA Astrophysics Data System (ADS)
Bednorz, Adam
2016-10-01
Traditional Bell's argument shows that freedom of choice is inconsistent with quantum realism if lack of signaling and sufficiently fast choices and readouts are assumed. While no-signaling alone is a consequence of special relativity, this is not the case of spacetime location of choice and readout. Here we attempt to incorporate freedom of choice into quantum objective realism relying solely on relativistic quantum field theory. We conclude that this is impossible without breaking relativistic invariance and put forward the possibility of signaling faster than light, which cannot be excluded if an ultimate theory violates relativity.
Plasma waves in a relativistic, strongly anisotropic plasma propagated along a strong magnetic field
NASA Technical Reports Server (NTRS)
Onishchenko, O. G.
1980-01-01
The dispersion properties of plasma waves in a relativistic homogeneous plasma propagated along a strong magnetic field are studied. It is shown that the non-damping plasma waves exist in the frequency range omega sub p or = omega or = omega sub L. The values of omega sub p and omega sub L are calculated for an arbitrary homogeneous relativistic function of the particle distribution. In the case of a power ultrarelativistic distribution, it is shown that, if the ultrarelativistic tail of the distribution drops very rapidly, slightly damping plasma waves are possible with the phase velocity (omega/K)c.
Is nonrelativistic gravity possible?
Kocharyan, A. A.
2009-07-15
We study nonrelativistic gravity using the Hamiltonian formalism. For the dynamics of general relativity (relativistic gravity) the formalism is well known and called the Arnowitt-Deser-Misner (ADM) formalism. We show that if the lapse function is constrained correctly, then nonrelativistic gravity is described by a consistent Hamiltonian system. Surprisingly, nonrelativistic gravity can have solutions identical to relativistic gravity ones. In particular, (anti-)de Sitter black holes of Einstein gravity and IR limit of Horava gravity are locally identical.
NASA Technical Reports Server (NTRS)
Colombo, Oscar L. (Editor)
1992-01-01
This symposium on space and airborne techniques for measuring gravity fields, and related theory, contains papers on gravity modeling of Mars and Venus at NASA/GSFC, an integrated laser Doppler method for measuring planetary gravity fields, observed temporal variations in the earth's gravity field from 16-year Starlette orbit analysis, high-resolution gravity models combining terrestrial and satellite data, the effect of water vapor corrections for satellite altimeter measurements of the geoid, and laboratory demonstrations of superconducting gravity and inertial sensors for space and airborne gravity measurements. Other papers are on airborne gravity measurements over the Kelvin Seamount; the accuracy of GPS-derived acceleration from moving platform tests; airborne gravimetry, altimetry, and GPS navigation errors; controlling common mode stabilization errors in airborne gravity gradiometry, GPS/INS gravity measurements in space and on a balloon, and Walsh-Fourier series expansion of the earth's gravitational potential.
Electric Field Effect on Bubble Detachment in Variable Gravity Environment
NASA Technical Reports Server (NTRS)
Iacona, Estelle; Herman, Cila; Chang, Shinan
2003-01-01
The subject of the present study, the process of bubble detachment from an orifice in a plane surface, shows some resemblance to bubble departure in boiling. Because of the high heat transfer coefficients associated with phase change processes, boiling is utilized in many industrial operations and is an attractive solution to cooling problems in aerospace engineering. In terrestrial conditions, buoyancy is responsible for bubble removal from the surface. In space, the gravity level being orders of magnitude smaller than on earth, bubbles formed during boiling remain attached at the surface. As a result, the amount of heat removed from the heated surface can decrease considerably. The use of electric fields is proposed to control bubble behavior and help bubble removal from the surface on which they form. The objective of the study is to investigate the behavior of individual air bubbles injected through an orifice into an electrically insulating liquid under the influence of a static electric field. Bubble cycle life were visualized in terrestrial conditions and for several reduced gravity levels. Bubble volume, dimensions and contact angle at detachment were measured and analyzed for different parameters as gravity level and electric field magnitude. Situations were considered with uniform or non-uni form electric field. Results show that these parameters significantly affect bubble behavior, shape, volume and dimensions.
Investigating High Field Gravity using Astrophysical Techniques
Bloom, Elliott D.; /SLAC
2008-02-01
The purpose of these lectures is to introduce particle physicists to astrophysical techniques. These techniques can help us understand certain phenomena important to particle physics that are currently impossible to address using standard particle physics experimental techniques. As the subject matter is vast, compromises are necessary in order to convey the central ideas to the reader. Many general references are included for those who want to learn more. The paragraphs below elaborate on the structure of these lectures. I hope this discussion will clarify my motivation and make the lectures easier to follow. The lectures begin with a brief review of more theoretical ideas. First, elements of general relativity are reviewed, concentrating on those aspects that are needed to understand compact stellar objects (white dwarf stars, neutron stars, and black holes). I then review the equations of state of these objects, concentrating on the simplest standard models from astrophysics. After these mathematical preliminaries, Sec. 2(c) discusses 'The End State of Stars'. Most of this section also uses the simplest standard models. However, as these lectures are for particle physicists, I also discuss some of the more recent approaches to the equation of state of very dense compact objects. These particle-physics-motivated equations of state can dramatically change how we view the formation of black holes. Section 3 focuses on the properties of the objects that we want to characterize and measure. X-ray binary systems and Active Galactic Nuclei (AGN) are stressed because the lectures center on understanding very dense stellar objects, black hole candidates (BHCs), and their accompanying high gravitational fields. The use of x-ray timing and gamma-ray experiments is also introduced in this section. Sections 4 and 5 review information from x-ray and gamma-ray experiments. These sections also discuss the current state of the art in x-ray and gamma-ray satellite experiments and
Nonuniform Currents and Spins of Relativistic Electron Vortices in a Magnetic Field
NASA Astrophysics Data System (ADS)
van Kruining, Koen; Hayrapetyan, Armen G.; Götte, Jörg B.
2017-07-01
We present a relativistic description of electron vortex beams in a homogeneous magnetic field. Including spin from the beginning reveals that spin-polarized electron vortex beams have a complicated azimuthal current structure, containing small rings of counterrotating current between rings of stronger corotating current. Contrary to many other problems in relativistic quantum mechanics, there exists a set of vortex beams with exactly zero spin-orbit mixing in the highly relativistic and nonparaxial regime. The well-defined phase structure of these beams is analogous to simpler scalar vortex beams, owing to the protection by the Zeeman effect. For states that do show spin-orbit mixing, the spin polarization across the beam is nonuniform rendering the spin and orbital degrees of freedom inherently inseparable.
Studies of Entanglement Entropy, and Relativistic Fluids for Thermal Field Theories
NASA Astrophysics Data System (ADS)
Spillane, Michael
In this dissertation we consider physical consequences of adding a finite temperature to quantum field theories. At small length scales entanglement is a critically important feature. It is therefore unsurprising that entanglement entropy and Renyi entropy are useful tools in studying quantum phase transition, and quantum information. In this thesis we consider the corrections to entanglement and Renyi entropies due to addition of a finite temperature. More specifically, we investigate the entanglement entropy of a massive scalar field in 1+1 dimensions at nonzero temperature. In the small mass ( m) and temperature (T) limit, we put upper and lower bounds on the two largest eigenvalues of the covariance matrix used to compute the entanglement entropy. We argue that the entanglement entropy has e-m/T scaling in the limit T << m.. Additionally, we calculate thermal corrections to Renyi entropies for free massless fermions on R x S d-1. By expanding the density matrix in a Boltzmann sum, the problem of finding the Renyi entropies can be mapped to the problem of calculating a two point function on an n-sheeted cover of the sphere. We map the problem on the sphere to a conical region in Euclidean space. By using the method of images, we calculate the two point function and recover the Renyi entropies. At large length scales hydrodynamics is a useful way to study quantum field theories. We review recent interest in the Riemann problem as a method for generating a non-equilibrium steady state. The initial conditions consist of a planar interface between two halves of a system held at different temperatures in a hydrodynamic regime. The resulting fluid flow contains a fixed temperature region with a nonzero flux. We briefly discuss the effects of a conserved charge. Next we discuss deforming the relativistic equations with a nonlinear term and how that deformation affects the temperature and velocity in the region connecting the asymptotic fluids. Finally, we study
Gravity field of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) mission.
Zuber, Maria T; Smith, David E; Watkins, Michael M; Asmar, Sami W; Konopliv, Alexander S; Lemoine, Frank G; Melosh, H Jay; Neumann, Gregory A; Phillips, Roger J; Solomon, Sean C; Wieczorek, Mark A; Williams, James G; Goossens, Sander J; Kruizinga, Gerhard; Mazarico, Erwan; Park, Ryan S; Yuan, Dah-Ning
2013-02-08
Spacecraft-to-spacecraft tracking observations from the Gravity Recovery and Interior Laboratory (GRAIL) have been used to construct a gravitational field of the Moon to spherical harmonic degree and order 420. The GRAIL field reveals features not previously resolved, including tectonic structures, volcanic landforms, basin rings, crater central peaks, and numerous simple craters. From degrees 80 through 300, over 98% of the gravitational signature is associated with topography, a result that reflects the preservation of crater relief in highly fractured crust. The remaining 2% represents fine details of subsurface structure not previously resolved. GRAIL elucidates the role of impact bombardment in homogenizing the distribution of shallow density anomalies on terrestrial planetary bodies.
Aristoteles - An ESA mission to study the earth's gravity field
NASA Astrophysics Data System (ADS)
Lambeck, K.
In preparing for its first Solid-Earth Program, ESA has studied a satellite concept for a mission dedicated to the precise determination of the earth's geopotential (gravitational and magnetic) fields. Data from such a mission are expected to make substantial contributions to a number of research and applications fields in solid-earth geophysics, oceanography and global-change monitoring. The impact of a high-resolution gravity-field mission on studies of the various earth-science problems is assessed. The current state of our knowledge in this area is discussed and the ability of low-orbit satellite gradiometry to contribute to their solution is demonstrated.
Jupiter gravity field estimated from the first two Juno orbits
NASA Astrophysics Data System (ADS)
Folkner, W. M.; Iess, L.; Anderson, J. D.; Asmar, S. W.; Buccino, D. R.; Durante, D.; Feldman, M.; Gomez Casajus, L.; Gregnanin, M.; Milani, A.; Parisi, M.; Park, R. S.; Serra, D.; Tommei, G.; Tortora, P.; Zannoni, M.; Bolton, S. J.; Connerney, J. E. P.; Levin, S. M.
2017-05-01
The combination of the Doppler data from the first two Juno science orbits provides an improved estimate of the gravity field of Jupiter, crucial for interior modeling of giant planets. The low-degree spherical harmonic coefficients, especially J4 and J6, are determined with accuracies better than previously published by a factor of 5 or more. In addition, the independent estimates of the Jovian gravity field, obtained by the orbits separately, agree within uncertainties, pointing to a good stability of the solution. The degree 2 sectoral and tesseral coefficients, C2,1, S2,1, C2,2, and S2,2, were determined to be statistically zero as expected for a fluid planet in equilibrium.
The power of weak-field GR gravity
NASA Astrophysics Data System (ADS)
Cooperstock, F. I.
2016-10-01
While general relativity (GR) is our premier theory of gravity, galactic dynamics from the outset has been studied with Newtonian gravity (NG), guided by the long-held belief in the idea of the “Newtonian-limit” of GR. This maintains that when the gravitational field is weak and the velocities are nonrelativistic, NG is the appropriate theory, apart from small corrections at best (such as in GPS tracking). However, there are simple examples of phenomena where there is no NG counterpart. We present a particularly simple new example of the stark difference that NG and weak-field GR exhibit for a modified van Stockum source, which speaks to the flat galactic rotation curve problem. We note that the linear GR compatibility equation in the literature is incomplete. Its completion is vital for our case, leading to a stark contrast between GR and NG for totally flat van Stockum rotation curves.
Domain decomposition methods in FVM approach to gravity field modelling.
NASA Astrophysics Data System (ADS)
Macák, Marek
2017-04-01
The finite volume method (FVM) as a numerical method can be straightforwardly implemented for global or local gravity field modelling. This discretization method solves the geodetic boundary value problems in a space domain. In order to obtain precise numerical solutions, it usually requires very refined discretization leading to large-scale parallel computations. To optimize such computations, we present a special class of numerical techniques that are based on a physical decomposition of the global solution domain. The domain decomposition (DD) methods like the Multiplicative Schwarz Method and Additive Schwarz Method are very efficient methods for solving partial differential equations. We briefly present their mathematical formulations and we test their efficiency. Presented numerical experiments are dealing with gravity field modelling. Since there is no need to solve special interface problems between neighbouring subdomains, in our applications we use the overlapping DD methods.
Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Pair Jets
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C.; Mizuno, Y.
2005-01-01
Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created by relativistic pair jets are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet propagating through an ambient plasma with and without initial magnetic fields. The growth rates of the Weibel instability depends on the distribution of pair jets. Simulations show that the Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Pair Jets
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C.; Mizuno, Y.
2005-01-01
Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created by relativistic pair jets are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet propagating through an ambient plasma with and without initial magnetic fields. The growth rates of the Weibel instability depends on the distribution of pair jets. Simulations show that the Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
Particle acceleration, magnetic field generation, and emission in relativistic pair jets
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Ramirez-Ruiz, E.; Hardee, P.; Hededal, C.; Kouveliotou, C.; Fishman, G. J.; Mizuno, Y.
2005-01-01
Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Recent simulations show that the Weibel instability created by relativistic pair jets is responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet propagating through an ambient plasma with and without initial magnetic fields. The growth rates of the Weibel instability depends on the distribution of pair jets. The Weibel instability created in the collisionless shock accelerates particles perpendicular and parallel to the jet propagation direction. This instability is also responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron s transverse deflection behind the jet head. The jitter radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
Chaos in Non-Abelian Gauge Fields, Gravity and Cosmology
NASA Astrophysics Data System (ADS)
Matinyan, S. G.
2002-12-01
This talk describes the evolution of studies of chaos in Yang-Mills fields, gravity, and cosmology. The main subject is a BKL regime near the singularity t = 0 and its survival in higher dimensions and in string theory. We also describe the recent progress in the search for particle-like solutions of the Einstein-Yang-Mills system (monopoles and dyons), colored black holes and the problem of their stability.
Computation of the gravity field and its gradient: Some applications
NASA Astrophysics Data System (ADS)
Dubey, C. P.; Tiwari, V. M.
2016-03-01
New measuring instruments of Earth's gravity gradient tensors (GGT) have offered a fresh impetus to gravimetry and its application in subsurface exploration. Several efforts have been made to provide a thorough understanding of the complex properties of the gravity gradient tensor and its mathematical formulations to compute GGT. However, there is not much open source software available. Understanding of the tensor properties leads to important guidelines in the development of real three dimensional geological models. We present a MATLAB computational algorithm to calculate the gravity field and full gravity gradient tensor for an undulated surface followed by regular geometries like an infinite horizontal slab, a vertical sheet, a solid sphere, a vertical cylinder, a normal fault model and a rectangular lamina or conglomerations of such bodies and the results are compared with responses using professional software based on different computational schemes. Real subsurface geometries of complex geological structures of interest are approximated through arrangements of vertical rectangular laminas. The geological application of this algorithm is demonstrated over a horst-type structure of Oklahoma Aulacogen, USA and Vredefort Dome, South Africa, where measured GGT data are available.
High-resolution gravity field modeling using GRAIL mission data
NASA Astrophysics Data System (ADS)
Lemoine, F. G.; Goossens, S. J.; Sabaka, T. J.; Nicholas, J. B.; Mazarico, E.; Rowlands, D. D.; Neumann, G. A.; Loomis, B.; Chinn, D. S.; Smith, D. E.; Zuber, M. T.
2015-12-01
The Gravity Recovery and Interior Laboratory (GRAIL) spacecraft were designed to map the structure of the Moon through high-precision global gravity mapping. The mission consisted of two spacecraft with Ka-band inter-satellite tracking complemented by tracking from Earth. The mission had two phases: a primary mapping mission from March 1 until May 29, 2012 at an average altitude of 50 km, and an extended mission from August 30 until December 14, 2012, with an average altitude of 23 km before November 18, and 20 and 11 km after. High-resolution gravity field models using both these data sets have been estimated, with the current resolution being degree and order 1080 in spherical harmonics. Here, we focus on aspects of the analysis of the GRAIL data: we investigate eclipse modeling, the influence of empirical accelerations on the results, and we discuss the inversion of large-scale systems. In addition to global models we also estimated local gravity adjustments in areas of particular interest such as Mare Orientale, the south pole area, and the farside. We investigate the use of Ka-band Range Rate (KBRR) data versus numerical derivatives of KBRR data, and show that the latter have the capability to locally improve correlations with topography.
Testing relativistic gravity theories using radio tracking data from planetary orbiting spacecraft.
NASA Technical Reports Server (NTRS)
Jordan, J. F.; Melbourne, W. G.; Anderson, J. D.
1972-01-01
We present a thorough analysis of a computational method for determining the numerical values of the relativity and other related dynamical parameters using two-way Doppler and ranging data from planetary orbiting spacecraft. The computational method consists of two parts. From Doppler data we first determine the earth-planet components of the position of the orbiting spacecraft relative to the center of gravity of the planet to high accuracy; adding the observed spacecraft range yields a range value to the center of the planet. These constructed earth-planet range data, referred to as normal points, are then treated as raw data in a regression analysis combined with planetary radar delay and meridian circle measurements to solve for the significant solar system dynamical parameters. The major errors sources in the planetary orbiter process are enumerated and their individual effects on the overall accuracy of the normal point accuracies are presented. The accuracies of the parameter estimates as a function of time, data sampling, and a priori assumptions are illustrated.
Noncommutative Gravity and Quantum Field Theory on Noncommutative Curved Spacetimes
NASA Astrophysics Data System (ADS)
Schenkel, Alexander
2012-10-01
The focus of this PhD thesis is on applications, new developments and extensions of the noncommutative gravity theory proposed by Julius Wess and his group. In part one we propose an extension of the usual symmetry reduction procedure to noncommutative gravity. We classify in the case of abelian Drinfel'd twists all consistent deformations of spatially flat Friedmann-Robertson-Walker cosmologies and of the Schwarzschild black hole. The deformed symmetry structure allows us to obtain exact solutions of the noncommutative Einstein equations in many of our models. In part two we develop a new formalism for quantum field theory on noncommutative curved spacetimes by combining methods from the algebraic approach to quantum field theory with noncommutative differential geometry. We also study explicit examples of deformed wave operators and find that there can be noncommutative corrections even on the level of free field theories. The convergent deformation of simple toy models is investigated and it is found that these theories have an improved behaviour at short distances, i.e. in the ultraviolet. In part three we study homomorphisms between and connections on noncommutative vector bundles. We prove that all homomorphisms and connections of the deformed theory can be obtained by applying a quantization isomorphism to undeformed homomorphisms and connections. The extension of homomorphisms and connections to tensor products of bimodules is clarified. As a nontrivial application of the new mathematical formalism we extend our studies of exact noncommutative gravity solutions to more general deformations.
Planetary Gravity Fields and Their Impact on a Spacecraft Trajectory
NASA Technical Reports Server (NTRS)
Weinwurm, G.; Weber, R.
2005-01-01
The present work touches an interdisciplinary aspect of space exploration: the improvement of spacecraft navigation by means of enhanced planetary interior model derivation. The better the bodies in our solar system are known and modelled, the more accurately (and safely) a spacecraft can be navigated. In addition, the information about the internal structure of a planet, moon or any other planetary body can be used in arguments for different theories of solar system evolution. The focus of the work lies in a new approach for modelling the gravity field of small planetary bodies: the implementation of complex ellipsoidal coordinates (figure 1, [4]) for irregularly shaped bodies that cannot be represented well by a straightforward spheroidal approach. In order to carry out the required calculations the computer programme GRASP (Gravity Field of a Planetary Body and its Influence on a Spacecraft Trajectory) has been developed [5]. The programme furthermore allows deriving the impact of the body s gravity field on a spacecraft trajectory and thus permits predictions for future space mission flybys.
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Hartmann, D. H.; Hardee, P.; Hededal, C.; Mizunno, Y.; Fishman, G. J.
2006-01-01
We performed numerical simulations of particle acceleration, magnetic field generation, and emission from shocks in order to understand the observed emission from relativistic jets and supernova remnants. The investigation involves the study of collisionless shocks, where the Weibel instability is responsible for particle acceleration as well as magnetic field generation. A 3-D relativistic particle-in-cell (RPIC) code has been used to investigate the shock processes in electron-positron plasmas. The evolution of theWeibe1 instability and its associated magnetic field generation and particle acceleration are studied with two different jet velocities (0 = 2,5 - slow, fast) corresponding to either outflows in supernova remnants or relativistic jets, such as those found in AGNs and microquasars. Slow jets have intrinsically different structures in both the generated magnetic fields and the accelerated particle spectrum. In particular, the jet head has a very weak magnetic field and the ambient electrons are strongly accelerated and dragged by the jet particles. The simulation results exhibit jitter radiation from inhomogeneous magnetic fields, generated by the Weibel instability, which has different spectral properties than standard synchrotron emission in a homogeneous magnetic field.
Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Mizuno, Y.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, G. J.
2010-01-01
Recent PIC simulations of relativistic electron-positron (electron-ion) jets injected into a stationary medium show that particle acceleration occurs at shocked regions. Simulations show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields and particle acceleration. These magnetic fields contribute to the electron's transverse deflection behind the shock. The jitter'' radiation from deflected electrons in turbulent magnetic fields has different properties than synchrotron radiation, which is calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets in general, and supernova remnants. We will present detailed spectra for conditions relevant of various astrophysical sites of shock formation via the Weibel instability. In particular we will discuss the application to GRBs and SNRs
Particle-in-cell Simulations of Global Relativistic Jets with Helical Magnetic Fields
NASA Astrophysics Data System (ADS)
Duţan, Ioana; Nishikawa, Ken-Ichi; Mizuno, Yosuke; Niemiec, Jacek; Kobzar, Oleh; Pohl, Martin; Gómez, Jose L.; Pe'er, Asaf; Frederiksen, Jacob T.; Nordlund, Åke; Meli, Athina; Sol, Helene; Hardee, Philip E.; Hartmann, Dieter H.
We study the interaction of relativistic jets with their environment, using 3-dimen- sional relativistic particle-in-cell simulations for two cases of jet composition: (i) electron-proton (e - - p +) and (ii) electron-positron (e +/-) plasmas containing helical magnetic fields. We have performed simulations of ``global'' jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability and the Mushroom instability. We have found that these kinetic instabilities are suppressed and new types of instabilities can grow. For the e - - p + jet, a recollimation-like instability occurs and jet electrons are strongly perturbed, whereas for the e +/- jet, a recollimation-like instability occurs at early times followed by kinetic instability and the general structure is similar to a simulation without a helical magnetic field. We plan to perform further simulations using much larger systems to confirm these new findings.
The gravity field of the Saturnian satellites Enceladus and Dione
NASA Astrophysics Data System (ADS)
Iess, L.; Jacobson, R.; Ducci, M.; Stevenson, D. J.; Lunine, J. I.; Armstrong, J. W.; Asmar, S.; Racioppa, P.; Rappaport, N. J.; Tortora, P.
2012-12-01
Enceladus and Dione are the innermost moons of the Saturnian system visited by the spacecraft Cassini for gravity investigations. The small surface gravity (0.11 and 0.23 m/s2 respectively for Enceladus and Dione), the short duration of the gravitational interaction and the small number of available flybys (three for Enceladus and just one for Dione) make the determination of their gravity field particularly challenging. In spite of these limitations, we have measured the low degree gravity field of both satellites with sufficient accuracy to draw preliminary geophysical conclusions. The estimation relied primarily on precise range rate data, whose accuracy reached 10 micron/s at 60 s integration times under favorable conditions. In order to disentangle the effects of the spacecraft orbit, the satellite orbit and the satellite gravity, tracking coverage is required not only across closest approach, but also days before and after the flyby. The dynamical model used for the fits includes all relevant gravitational perturbations and the main non-gravitational accelerations (Cassini RTG's anisotropic thermal emission, solar radiation pressure). In addition to the gravity field coefficients a correction to the orbit of the spacecraft and the satellites was also estimated. The first and so far only Dione's flyby with tracking at closest approach occurred on December 12, 2011, at an altitude of 99 km. (A second gravity flyby is scheduled in 2015.) Although the low solar elongation angle caused a significant increase of the plasma noise in Doppler data, the low spacecraft altitude at closest approach and the otherwise favorable geometry allowed an estimation of the harmonic coefficients J2 and C22 to a relative accuracy below 2%. We have produced, in addition to an unconstrained estimate, a second solution where the quadrupole field is constrained by the requirement of hydrostaticity. Doppler residuals are unbiased and consistent with the expected noise in both cases. When
Hainzl, Christian; Lewin, Mathieu; Sere, Eric; Solovej, Jan Philip
2007-11-15
We study a mean-field relativistic model which is able to describe both the behavior of finitely many spin-1/2 particles such as electrons and of the Dirac sea which is self-consistently polarized in the presence of the real particles. The model is derived from the QED Hamiltonian in Coulomb gauge neglecting the photon field. All our results are nonperturbative and mathematically rigorous.
Twisting space-time: relativistic origin of seed magnetic field and vorticity.
Mahajan, S M; Yoshida, Z
2010-08-27
We demonstrate that a purely ideal mechanism, originating in the space-time distortion caused by the demands of special relativity, can break the topological constraint (leading to helicity conservation) that would forbid the emergence of a magnetic field (a generalized vorticity) in an ideal nonrelativistic dynamics. The new mechanism, arising from the interaction between the inhomogeneous flow fields and inhomogeneous entropy, is universal and can provide a finite seed even for mildly relativistic flows.
NASA Astrophysics Data System (ADS)
Blair, D. G.; Buckingham, M. J.
Contents: Part A. 1. Rigorous and exact. Classical general relativity: highly non-linear behaviour. Spin, geometry and topology. Approximation methods. Exact solutions. Black hole physics. Alternative theories and torsion. 2. Quantum gravity. Critical accelerations. Quantum gravity. String theories. Cosmic strings, superstrings and supergravity. Quantum cosmology: wavefunction of the universe. Quantum cosmology. 3. Cosmology. Early cosmology and quantum field theory. Supersymmetry, multidimensional cosmology and Kaluza-Klein theory. Theoretical cosmology. Large-scale structure of the universe. Dark matter. Part B. 4. Mathematical astrophysics. Algebraic computing. Numerical relativity. Astrophysics of collapsed objects. Self gravitating systems. History of general relativity. 5. Observational astrophysics. Sources of gravitational radiation. Relativistic astrophysics. Supernovae. Observation of collapsed objects. Cosmic background. 5. Precision experiments. The fifth force. Measuring the gravitational interaction in precision space experiments. Resonant bar antennas. Laser interferometer antennas. Detection of gravitational radiation. Quantum technology for gravitational radiation detection. Precision clocks in general relativity.
Combination of monthly gravity field solutions from different processing centers
NASA Astrophysics Data System (ADS)
Jean, Yoomin; Meyer, Ulrich; Jäggi, Adrian
2015-04-01
Currently, the official GRACE Science Data System (SDS) monthly gravity field solutions are generated independently by the Centre for Space Research (CSR) and the German Research Centre for Geosciences (GFZ). Additional GRACE SDS monthly fields are provided by the Jet Propulsion Laboratory (JPL) for validation and outside the SDS by a number of other institutions worldwide. Although the adopted background models and processing standards have been harmonized more and more by the various processing centers during the past years, notable differences still exist and the users are more or less left alone with a decision which model to choose for their individual applications. Combinations are well-established in the area of other space geodetic techniques, such as the Global Navigation Satellite Systems (GNSS), Satellite Laser Ranging (SLR), and Very Long Baseline Interferometry (VLBI), where regular comparisons and combinations of space-geodetic products have tremendously increased the usefulness of the products in a wide range of disciplines and scientific applications. In the frame of the recently started Horizon 2020 project European Gravity Service for Improved Emergency Management (EGSIEM), a scientific combination service shall therefore be established to deliver the best gravity products for applications in Earth and environmental science research based on the unified knowledge of the European GRACE community. In a first step the large variety of available monthly GRACE gravity field solutions shall be mutually compared spatially and spectrally. We assess the noise of the raw as well as filtered solutions and compare the secular and seasonal periodic variations fitted to the monthly solutions. In a second step we will explore ways to generate combined solutions, e.g., based on a weighted average of the individual solutions using empirical weights derived from pair-wise comparisons. We will also assess the quality of such a combined solution and discuss the
Consolidated science requirements for a next generation gravity field mission
NASA Astrophysics Data System (ADS)
Pail, Roland; Bingham, Rory; Braitenberg, Carla; Eicker, Annette; Floberghagen, Rune; Haagmans, Roger; Horwath, Martin; LaBrecque, John; Longuevergne, Laurent; Panet, Isabelle; Rolstad-Denby, Cecile; Wouters, Bert
2014-05-01
As a joint initiative of the IAG (International Association of Geodesy) Sub-Commissions 2.3 and 2.6, the GGOS (Global Geodetic Observing System) Working Group on Satellite Missions, and the IUGG (International Union of Geodesy and Geophysics), science requirements for a next generation gravity field mission (beyond GRACE-FO) shall be defined and consolidated. A consolidation of the user requirements is required, because several future gravity field studies have resulted in quite different performance numbers as a target for a future gravity mission (2025+). For this purpose, the science requirements shall be accorded by the different user groups, i.e. hydrology, ocean, cryosphere, solid Earth and atmosphere, under the boundary condition of the technical feasibility of the mission concepts and before the background of double- and multi-pair formations. This initiative shall mainly concentrate on the consolidation of the science requirements, and should result in a document that can be used as a solid basis for further programmatic and technological developments. Based on limited number of realistic mission scenarios, a consolidated view on the science requirements within the international user communities shall be derived, research fields that could not be tackled by current gravity missions shall be identified, and the added value (qualitatively and quantitatively) of these scenarios with respect to science return shall be evaluated. The final science requirements shall be agreed upon during a workshop which will be held in September 2014. In this contribution, the mission scenarios will be discussed and first results of the consolidation process will be presented.
Wormholes, emergent gauge fields, and the weak gravity conjecture
Harlow, Daniel
2016-01-20
This paper revisits the question of reconstructing bulk gauge fields as boundary operators in AdS/CFT. In the presence of the ormhole dual to the thermo field double state of two CFTs, the existence of bulk gauge fields is in some tension with the microscopic tensor factorization of the Hilbert space. Here, I explain how this tension can be resolved by splitting the gauge field into charged constituents, and I argue that this leads to a new argument for the "principle of completeness", which states that the charge lattice of a gauge theory coupled to gravity must be fully populated. I also claim that it leads to a new motivation for (and a clarification of) the "weak gravity conjecture", which I interpret as a strengthening of this principle. This setup gives a simple example of a situation where describing low-energy bulk physics in CFT language requires knowledge of high-energy bulk physics. Furthermore, this contradicts to some extent the notion of "effective conformal field theory", but in fact is an expected feature of the resolution of the black hole information problem. An analogous factorization issue exists also for the gravitational field, and I comment on several of its implications for reconstructing black hole interiors and the emergence of spacetime more generally.
Wormholes, emergent gauge fields, and the weak gravity conjecture
Harlow, Daniel
2016-01-20
This paper revisits the question of reconstructing bulk gauge fields as boundary operators in AdS/CFT. In the presence of the ormhole dual to the thermo field double state of two CFTs, the existence of bulk gauge fields is in some tension with the microscopic tensor factorization of the Hilbert space. Here, I explain how this tension can be resolved by splitting the gauge field into charged constituents, and I argue that this leads to a new argument for the "principle of completeness", which states that the charge lattice of a gauge theory coupled to gravity must be fully populated. Imore » also claim that it leads to a new motivation for (and a clarification of) the "weak gravity conjecture", which I interpret as a strengthening of this principle. This setup gives a simple example of a situation where describing low-energy bulk physics in CFT language requires knowledge of high-energy bulk physics. Furthermore, this contradicts to some extent the notion of "effective conformal field theory", but in fact is an expected feature of the resolution of the black hole information problem. An analogous factorization issue exists also for the gravitational field, and I comment on several of its implications for reconstructing black hole interiors and the emergence of spacetime more generally.« less
Particle Acceleration, Magnetic Field Generation, and Emission in Relativistic Pair Jets
NASA Technical Reports Server (NTRS)
Nishikawa, K. I.; Hardee, P.; Hededal, C. B.; Richardson, G.; Sol, H.; Preece, R.; Fishman, G. J.
2004-01-01
Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating into an ambient plasma. We find that the growth times depend on the Lorenz factors of jets. The jets with larger Lorenz factors grow slower. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The small scale magnetic field structure generated by the Weibel instability is appropriate to the generation of "jitter" radiation from deflected electrons (positrons) as opposed to synchrotron radiation. The jitter radiation resulting from small scale magnetic field structures may be important for understanding the complex time structure and spectral evolution observed in gamma-ray bursts or other astrophysical sources containing relativistic jets and relativistic collisionless shocks.
NASA Astrophysics Data System (ADS)
Higuera, A. V.; Cary, J. R.
2017-05-01
Time-centered, hence second-order, methods for integrating the relativistic momentum of charged particles in an electromagnetic field are derived. A new method is found by averaging the momentum before use in the magnetic rotation term, and an implementation is presented that differs from the relativistic Boris Push only in the method for calculating the Lorentz factor. This is shown to have the same second-order accuracy in time as that found by splitting the electric acceleration and magnetic rotation (Boris Push) and that found by averaging the velocity in the magnetic rotation term (Vay's method) [J.-L. Vay, Phys. Plasmas 15, 056701 (2008)]. All three methods are shown to conserve energy when there is no electric field. The Boris Push and the current method are shown to be volume-preserving, while Vay's method and the current method preserve the E →×B → velocity. Thus, of these second-order relativistic momentum integrations, only the integrator introduced here both preserves volume and gives the correct E →×B → velocity. While all methods have error that is second-order in time, they deviate from each other by terms that increase as the motion becomes relativistic. Numerical results show that Vay's method develops energy errors near resonant orbits of a test problem that neither volume-preserving integrator does.
The Gravity Field of Titan From Four Cassini Flybys
NASA Astrophysics Data System (ADS)
Rappaport, N. J.; Jacobson, R. A.; Iess, L.; Racioppa, P.; Armstrong, J. W.; Asmar, S. W.; Stevenson, D. J.; Tortora, P.; di Benedetto, M.; Graziani, A.; Meriggiola, R.
2008-12-01
Doppler tracking of the Cassini spacecraft across four flybys has been used for a preliminary determination of Titan's gravity field. The flybys occurred on February 27, 2006, December 28, 2006, June 29, 2007 and July 31, 2008, with closest approach altitudes between 1300 and 2100 km. X- and Ka-band Doppler data from each flyby have been combined in a multi-arc solution for the Stokes coefficients up to degree-3. The dynamical models employed in the data fit were limited to the static component of the gravity field and did not include eccentricity tides. Tidal variations of the quadrupole coefficients are expected at a level of a few percents if the surface hides an internal ocean, and are therefore accessible to Cassini measurements. As the flybys were evenly distributed about pericenter and apocenter of Titan's orbit, the current analysis provides a good representation of the static component of the quadrupole field. In one setup, Titan's ephemerides were also updated, leading to improved determination of the satellite's orbit and gravitational parameter (GM). The measured gravity field is dominated by a large, nearly hydrostatic, quadrupole component, consistent with an equilibrium response to the perturbations due to rotation and Saturn gravity gradient. The magnitude of the degree-3 coefficients accounts for about 1-3% of the overall field, with significant gravity disturbances (at a level of 2-5 mgal) over broad regions of the surface. The corresponding peak-to-peak geoid height variations amount to a few tens of meters. The ellipsoidal reference surface shows variations among the axes of a few hundred meters. The near hydrostaticity of Titan justifies the application of Radau-Darwin equilibrium theory, which provides the fluid Love number and the average moment of inertia. The latter is consistent with a partial, but not full, differentiation of the interior. This work was partly conducted at the Jet Propulsion Laboratory, California Institute of Technology
The symmetric tensor field in the relativistic theory of gravitation
NASA Astrophysics Data System (ADS)
Grigoryan, A. Sh.; Gottlöber, S.
1995-07-01
The system of a self-gravitating scalar field is frequently used in inflationary cosmological models. In the present paper we study a more complicated system containing an extra linear tensor field ψik=ψki with minimal coupling. We determine five of the six free parameters that occur in the most general expression for the actionS ψ of this field. In doing so we assume that in flat space-time the field ψik must be invariant under gauge transformations. In a special case theS ψ found becomes a known expression for the action of a massless tensor field ψik. We compute the metric energy-momentum tensor that determines the contribution of ψik to the Einstein equations. We also exhibit the equations of motion of ψik in curved space-time.
Mars gravity field based on a short-arc technique
NASA Technical Reports Server (NTRS)
Sjogren, W. L.; Lorell, J.; Wong, L.; Downs, W.
1975-01-01
The magnitudes of 92 surface mass points at designated locations were estimated from the radio tracking data of the Mariner Mars 1971 (M9) orbiter. This result is the first mass point model of a global field. The derived surface mass distribution correlates positively with the visible topography. The Hellas basin contains a mass deficiency, in contrast to some of the lunar basins which contain mass excesses. The Mars gravity field represented by the four parameters of an optimally located mass point (superimposed on an oblate spheroid) has third- and fourth-degree harmonics comparable to those of the complete model.
Noncommutative scalar field minimally coupled to nonsymmetric gravity
Kouadik, S.; Sefai, D.
2012-06-27
We construct a non-commutative non symmetric gravity minimally coupled model (the star product only couples matter). We introduce the action for the system considered namely a non-commutative scalar field propagating in a nontrivial gravitational background. We expand the action in powers of the anti-symmetric field and the graviton to second order adopting the assumption that the scalar is weekly coupled to the graviton. We compute the one loop radiative corrections to the self-energy of a scalar particle.
Gravity Field and Internal Structure of Mercury from MESSENGER
NASA Technical Reports Server (NTRS)
Smith, David E.; Zuber, Maria T.; Phillips, Roger J.; Solomon, Sean C.; Hauck, Steven A., II; Lemoine, Frank G.; Mazarico, Erwan; Neumann, Gregory A.; Peale, Stanton J.; Margot, Jean-Luc;
2012-01-01
Radio tracking of the MESSENGER spacecraft has provided a model of Mercury's gravity field. In the northern hemisphere, several large gravity anomalies, including candidate mass concentrations (mascons), exceed 100 milli-Galileos (mgal). Mercury's northern hemisphere crust is thicker at low latitudes and thinner in the polar region and shows evidence for thinning beneath some impact basins. The low-degree gravity field, combined with planetary spin parameters, yields the moment of inertia C/M(R(exp 2) = 0.353 +/- 0.017, where M and R are Mercury's mass and radius, and a ratio of the moment of inertia of Mercury's solid outer shell to that of the planet of C(sub m)/C = 0.452 +/- 0.035. A model for Mercury s radial density distribution consistent with these results includes a solid silicate crust and mantle overlying a solid iron-sulfide layer and an iron-rich liquid outer core and perhaps a solid inner core.
Gravity Field and Internal Structure of Mercury from MESSENGER
NASA Technical Reports Server (NTRS)
Smith, David E.; Zuber, Maria T.; Phillips, Roger J.; Solomon, Sean C.; Hauck, Steven A., II; Lemoine, Frank G.; Mazarico, Erwan; Neumann, Gregory A.; Peale, Stanton J.; Margot, Jean-Luc; Johnson, Catherine L.; Torrence, Mark H.; Perry, Mark E.; Rowlands, David D.; Goossens, Sander; Head, James W.; Taylor, Anthony H.
2012-01-01
Radio tracking of the MESSENGER spacecraft has provided a model of Mercury's gravity field. In the northern hemisphere, several large gravity anomalies, including candidate mass concentrations (mascons), exceed 100 milli-Galileos (mgal). Mercury's northern hemisphere crust is thicker at low latitudes and thinner in the polar region and shows evidence for thinning beneath some impact basins. The low-degree gravity field, combined with planetary spin parameters, yields the moment of inertia C/M(R(exp 2) = 0.353 +/- 0.017, where M and R are Mercury's mass and radius, and a ratio of the moment of inertia of Mercury's solid outer shell to that of the planet of C(sub m)/C = 0.452 +/- 0.035. A model for Mercury s radial density distribution consistent with these results includes a solid silicate crust and mantle overlying a solid iron-sulfide layer and an iron-rich liquid outer core and perhaps a solid inner core.
Estimates on Functional Integrals of Quantum Mechanics and Non-relativistic Quantum Field Theory
NASA Astrophysics Data System (ADS)
Bley, Gonzalo A.; Thomas, Lawrence E.
2017-01-01
We provide a unified method for obtaining upper bounds for certain functional integrals appearing in quantum mechanics and non-relativistic quantum field theory, functionals of the form {E[{exp}(A_T)]} , the (effective) action {A_T} being a function of particle trajectories up to time T. The estimates in turn yield rigorous lower bounds for ground state energies, via the Feynman-Kac formula. The upper bounds are obtained by writing the action for these functional integrals in terms of stochastic integrals. The method is illustrated in familiar quantum mechanical settings: for the hydrogen atom, for a Schrödinger operator with {1/|x|^2} potential with small coupling, and, with a modest adaptation of the method, for the harmonic oscillator. We then present our principal applications of the method, in the settings of non-relativistic quantum field theories for particles moving in a quantized Bose field, including the optical polaron and Nelson models.
Magnetic Field Generation and Electron Acceleration in Relativistic Laser Channel
I.Yu. Kostyukov; G. Shvets; N.J. Fisch; J.M. Rax
2001-12-12
The interaction between energetic electrons and a circularly polarized laser pulse inside an ion channel is studied. Laser radiation can be resonantly absorbed by electrons executing betatron oscillations in the ion channel and absorbing angular momentum from the laser. The absorbed angular momentum manifests itself as a strong axial magnetic field (inverse Faraday effect). The magnitude of this magnetic field is calculated and related to the amount of the absorbed energy. Absorbed energy and generated magnetic field are estimated for the small and large energy gain regimes. Qualitative comparisons with recent experiments are also made.
Cold atom simulation of interacting relativistic quantum field theories.
Cirac, J Ignacio; Maraner, Paolo; Pachos, Jiannis K
2010-11-05
We demonstrate that Dirac fermions self-interacting or coupled to dynamic scalar fields can emerge in the low energy sector of designed bosonic and fermionic cold atom systems. We illustrate this with two examples defined in two spacetime dimensions. The first one is the self-interacting Thirring model. The second one is a model of Dirac fermions coupled to a dynamic scalar field that gives rise to the Gross-Neveu model. The proposed cold atom experiments can be used to probe spectral or correlation properties of interacting quantum field theories thereby presenting an alternative to lattice gauge theory simulations.
The gravity field of Mars: results from Mars Global Surveyor.
Smith, D E; Sjogren, W L; Tyler, G L; Balmino, G; Lemoine, F G; Konopliv, A S
1999-10-01
Observations of the gravity field of Mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes. The rough, elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near-isostatic compensation, whereas the smooth, low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south. The northern hemisphere shows evidence for buried impact basins, although none large enough to explain the hemispheric elevation difference. The gravitational potential signature of Tharsis is approximately axisymmetric and contains the Tharsis Montes but not the Olympus Mons or Alba Patera volcanoes. The gravity signature of Valles Marineris extends into Chryse and provides an estimate of material removed by early fluvial activity.
Inversion of Gravity and Magnetic Field Data for Tyrrhena Patera
NASA Technical Reports Server (NTRS)
Milbury, C.; Schubert, G.; Raymond, C. A.; Smrekar, S. E.
2011-01-01
Tyrrhena Patera is located to the southeast/northeast of the Isidis/Hellas impact basin. It was geologically active into the Late Amazonian, although the main edifice was formed in the Noachian(approximately 3.7-4.0 Ga). Tyrrhena Patera and the surrounding area contain gravity and magnetic anomalies that appear to be correlated. The results presented here are for the anomalies 1a and 1b (closest to Tyrrhena Patera), however other anomalies in this region have been modeled and will be presented at the conference.The Mars Global Surveyor (MGS) free-air gravity signature of Tyrrhena Patera has been studied by Kiefer, who inferred the existence of an extinct magma chamber below it. The magnetic signature has been mapped by Lillis R. J. et al., who compared electron reflectometer data, analogous to the total magnetic field, for Syrtis Major and Tyrrhena Patera and argued for demagnetization of both volcanoes.
Inversion of Gravity and Magnetic Field Data for Tyrrhena Patera
NASA Technical Reports Server (NTRS)
Milbury, C.; Schubert, G.; Raymond, C. A.; Smrekar, S. E.
2011-01-01
Tyrrhena Patera is located to the southeast/northeast of the Isidis/Hellas impact basin. It was geologically active into the Late Amazonian, although the main edifice was formed in the Noachian(approximately 3.7-4.0 Ga). Tyrrhena Patera and the surrounding area contain gravity and magnetic anomalies that appear to be correlated. The results presented here are for the anomalies 1a and 1b (closest to Tyrrhena Patera), however other anomalies in this region have been modeled and will be presented at the conference.The Mars Global Surveyor (MGS) free-air gravity signature of Tyrrhena Patera has been studied by Kiefer, who inferred the existence of an extinct magma chamber below it. The magnetic signature has been mapped by Lillis R. J. et al., who compared electron reflectometer data, analogous to the total magnetic field, for Syrtis Major and Tyrrhena Patera and argued for demagnetization of both volcanoes.
Action and entanglement in gravity and field theory.
Neiman, Yasha
2013-12-27
In nongravitational quantum field theory, the entanglement entropy across a surface depends on the short-distance regularization. Quantum gravity should not require such regularization, and it has been conjectured that the entanglement entropy there is always given by the black hole entropy formula evaluated on the entangling surface. We show that these statements have precise classical counterparts at the level of the action. Specifically, we point out that the action can have a nonadditive imaginary part. In gravity, the latter is fixed by the black hole entropy formula, while in nongravitating theories it is arbitrary. From these classical facts, the entanglement entropy conjecture follows by heuristically applying the relation between actions and wave functions.
Gravitomagnetic effects in quadratic gravity with a scalar field
NASA Astrophysics Data System (ADS)
Finch, Andrew; Said, Jackson Levi
2016-10-01
The two gravitomagnetic effects which influence bodies orbiting around a gravitational source are the geodetic effect and the Lense-Thirring effect. The former describes the precession angle of the axis of a spinning gyroscope while in orbit around a nonrotating gravitational source whereas the latter provides a correction for this angle in the case of a spinning source. In this paper we derive the relevant equations in quadratic gravity and relate them to their equivalents in general relativity. Starting with an investigation into Kepler's third law in quadratic gravity with a scalar field, the effects of an axisymmetric and rotating gravitational source on an orbiting body in a circular, equatorial orbit are introduced.
Wormholes, emergent gauge fields, and the weak gravity conjecture
NASA Astrophysics Data System (ADS)
Harlow, Daniel
2016-01-01
This paper revisits the question of reconstructing bulk gauge fields as boundary operators in AdS/CFT. In the presence of the wormhole dual to the thermofield double state of two CFTs, the existence of bulk gauge fields is in some tension with the microscopic tensor factorization of the Hilbert space. I explain how this tension can be resolved by splitting the gauge field into charged constituents, and I argue that this leads to a new argument for the "principle of completeness", which states that the charge lattice of a gauge theory coupled to gravity must be fully populated. I also claim that it leads to a new motivation for (and a clarification of) the "weak gravity conjecture", which I interpret as a strengthening of this principle. This setup gives a simple example of a situation where describing low-energy bulk physics in CFT language requires knowledge of high-energy bulk physics. This contradicts to some extent the notion of "effective conformal field theory", but in fact is an expected feature of the resolution of the black hole information problem. An analogous factorization issue exists also for the gravitational field, and I comment on several of its implications for reconstructing black hole interiors and the emergence of spacetime more generally.
NASA Astrophysics Data System (ADS)
Rothacher, M.; Reigber, C.; Schmidt, R.; Foerste, C.; Koenig, R.; Flechtner, F.; Meyer, U.; Stubenvoll, R.; Barthelmes, F.; Neumayer, K. H.; Biancale, R.; Bruinsma, S.; Lemoine, J.
2005-12-01
High-resolution global mean gravity field models can be derived from the combination of satellite tracking and surface data. With the CHAMP and GRACE satellite missions, a new generation of such global gravity field models became available. Here the latest results of the processing of GRACE, CHAMP and SLR satellite tracking are presented and compared with outcomes of former analyses. The gravity field parameters obtained are the result of a substantial satellite data reprocessing, based on recently improved processing standards and models. On the other hand, surface gravity data derived from altimetry and gravimetry are globally available, providing a higher resolution than pure satellite data but lacking the high precision in the long-wavelength part. In an optimal approach the satellite-based data are combined with latest, partially newly processed surface gravity data sets to derive a global high-resolution gravity field model combining the high precision and homogeneity in the long- to medium-wavelength part from the satellite data with the short-wavelength resolution of the surface data. The obtained Earth gravity field model is an update of former EIGEN models of a resolution corresponding to a wavelength of 100 km and degree/order 360, respectively.
Amplification of Relativistic Electron Bunches by Acceleration in Laser Fields
NASA Astrophysics Data System (ADS)
Braenzel, J.; Andreev, A. A.; Abicht, F.; Ehrentraut, L.; Platonov, K.; Schnürer, M.
2017-01-01
Direct acceleration of electrons in a coherent, intense light field is revealed by a remarkable increase of the electron number in the MeV energy range. Laser irradiation of thin polymer foils with a peak intensity of ˜1 ×1020 W /cm2 releases electron bunches along the laser propagation direction that are postaccelerated in the partly transmitted laser field. They are decoupled from the laser field at high kinetic energies, when a second foil target at an appropriate distance prevents their subsequent deceleration in the declining laser field. The scheme is established with laser pulses of high temporal contrast (1010 peak to background ratio) and two ultrathin polymer foils at a distance of 500 μ m . 2D particle in cell simulations and an analytical model confirm a significant change of the electron spectral distribution due to the double foil setup, which leads to an amplification of about 3 times of the electron number around a peak at 1 MeV electron energy. The result verifies a theoretical concept of direct electron bunch acceleration in a laser field that is scalable to extreme acceleration potential gradients. This method can be used to enhance the density and energy spread of electron bunches injected into postaccelerator stages of laser driven radiation sources.
NASA Astrophysics Data System (ADS)
Lin, Fu-Jun; Chen, Zong-Hua; Li, Xiao-Qing; Liao, Jing-Jing; Zhu, Yun
2017-02-01
A GigaGauss quasi-steady magnetic field can be generated in astrophysical plasmas and laser-produced plasmas with high-frequency electromagnetic radiation through wave-wave and wave-particle interactions. A set of governing equations for this field are obtained in the plasma consisting of ultra-relativistic electrons following q-nonextensive distribution. The numerical results show that the initial field is unstable and can collapse to generate various spatially intermittent magnetic flux tubes. It can also be found that the behavior of the magnetic field is greatly dependent on the nonextensive index q, which may be helpful in understanding the magnetic turbulence.
NASA Astrophysics Data System (ADS)
Ruchin, Vyacheslav; Vacaru, Olivia; Vacaru, Sergiu I.
2017-03-01
Using double 2+2 and 3+1 nonholonomic fibrations on Lorentz manifolds, we extend the concept of W-entropy for gravitational fields in general relativity (GR). Such F- and W-functionals were introduced in the Ricci flow theory of three dimensional (3-d) Riemannian metrics by Perelman (the entropy formula for the Ricci flow and its geometric applications. arXiv:math.DG/0211159). Non-relativistic 3-d Ricci flows are characterized by associated statistical thermodynamical values determined by W-entropy. Generalizations for geometric flows of 4-d pseudo-Riemannian metrics are considered for models with local thermodynamical equilibrium and separation of dissipative and non-dissipative processes in relativistic hydrodynamics. The approach is elaborated in the framework of classical field theories (relativistic continuum and hydrodynamic models) without an underlying kinetic description, which will be elaborated in other work. The 3+1 splitting allows us to provide a general relativistic definition of gravitational entropy in the Lyapunov-Perelman sense. It increases monotonically as structure forms in the Universe. We can formulate a thermodynamic description of exact solutions in GR depending, in general, on all spacetime coordinates. A corresponding 2+2 splitting with nonholonomic deformation of linear connection and frame structures is necessary for generating in very general form various classes of exact solutions of the Einstein and general relativistic geometric flow equations. Finally, we speculate on physical macrostates and microstate interpretations of the W-entropy in GR, geometric flow theories and possible connections to string theory (a second unsolved problem also contained in Perelman's work) in Polyakov's approach.
Report of the panel on geopotential fields: Gravity field, section 8
NASA Technical Reports Server (NTRS)
Anderson, Allen Joel; Kaula, William M.; Lazarewics, Andrew R.; Lefebvre, Michel; Phillips, Roger J.; Rapp, Richard H.; Rummel, Reinhard F.; Smith, David E.; Tapley, Byron D.; Zlotnick, Victor
1991-01-01
The objective of the Geopotential Panel was to develop a program of data acquisition and model development for the Earth's gravity and magnetic fields that meet the basic science requirements of the solid Earth and ocean studies. Presented here are the requirements for gravity information and models through the end of the century, the present status of our knowledge, data acquisition techniques, and an outline of a program to meet the requirements.
Gravity, Topography, and Magnetic Field of Mercury from Messenger
NASA Technical Reports Server (NTRS)
Neumann, Gregory A.; Solomon, Sean C.; Zuber, Maria T.; Phillips, Roger J.; Barnouin, Olivier; Ernst, Carolyn; Goosens, Sander; Hauck, Steven A., II; Head, James W., III; Johnson, Catherine L.;
2012-01-01
On 18 March 2011, the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft was inserted into a 12-hour, near-polar orbit around Mercury, with an initial periapsis altitude of 200 km, initial periapse latitude of 60 deg N, and apoapsis at approximately 15,200 km altitude in the southern hemisphere. This orbit has permitted the mapping of regional gravitational structure in the northern hemisphere, and laser altimetry from the MESSENGER spacecraft has yielded a geodetically controlled elevation model for the same hemisphere. The shape of a planet combined with gravity provides fundamental information regarding its internal structure and geologic and thermal evolution. Elevations in the northern hemisphere exhibit a unimodal distribution with a dynamic range of 9.63 km, less than that of the Moon (19.9 km), but consistent with Mercury's higher surface gravitational acceleration. After one Earth-year in orbit, refined models of gravity and topography have revealed several large positive gravity anomalies that coincide with major impact basins. These candidate mascons have anomalies that exceed 100 mGal and indicate substantial crustal thinning and superisostatic uplift of underlying mantle. An additional uncompensated 1000-km-diameter gravity and topographic high at 68 deg N, 33 deg E lies within Mercury's northern volcanic plains. Mercury's northern hemisphere crust is generally thicker at low latitudes than in the polar region. The low-degree gravity field, combined with planetary spin parameters, yields the moment of inertia C/MR2 = 0.353 +/- 0.017, where M=3.30 x 10(exp 23) kg and R=2440 km are Mercury's mass and radius, and a ratio of the moment of inertia of Mercury's solid outer shell to that of the planet of Cm/C = 0.452 +/- 0.035. One proposed model for Mercury's radial density distribution consistent with these results includes silicate crust and mantle layers overlying a dense solid (possibly Fe-S) layer, a liquid Fe
The role of topography in geodetic gravity field modelling
NASA Technical Reports Server (NTRS)
Forsberg, R.; Sideris, M. G.
1989-01-01
Masses associated with the topography, bathymetry, and its isostatic compensation are a dominant source of gravity field variations, especially at shorter wavelengths. On global scales the topographic/isostatic effects are also significant, except for the lowest harmonics. In practice, though, global effects need not be taken into account as such effects are included in the coefficients of the geopotential reference fields. On local scales, the short-wavelength gravity variations due to the topography may, in rugged terrain, be an order of magnitude larger than other effects. In such cases, explicit or implicit terrain reduction procedures are mandatory in order to obtain good prediction results. Such effects may be computed by space-domain integration or by fast Fourier transformation (FFT) methods. Numerical examples are given for areas of the Canadian Rockies. In principle, good knowledge of the topographic densities is required to produce the smoothest residual field. Densities may be determined from sample measurements or by gravimetric means, but both are somewhat troublesome methods in practice. The use of a standard density, e.g., 2.67 g/cu cm, may often yield satisfactory results and may be put within a consistent theoretical framework. The independence of density assumptions is the key point of the classical Molodensky approach to the geodetic boundary value problem. The Molodensky solutions take into account that land gravity field observations are done on a non-level surface. Molodensky's problem may be solved by integral expansions or more effective FFT methods, but the solution should not be intermixed with the use of terrain reductions. The methods are actually complimentary and may both be required in order to obtain the smoothest possible signal, least prone to aliasing and other effects coming from sparse data coverage, typical of rugged topography.
NASA Astrophysics Data System (ADS)
Wu, Yihao; Zhou, Hao; Zhong, Bo; Luo, Zhicai
2017-08-01
A regional approach using Poisson wavelets is applied for gravity field recovery using the GOCE (Gravity Field and Steady-State Ocean Circulation Explorer) gravity gradient tensor, heterogeneous gravimetry data, and altimetry measurements. The added value to the regional model introduced by GOCE data is validated and quantified. The performances of the solutions modeled with different diagonal components of GOCE data and their combinations are investigated. Numerical experiments in a region in Europe show that the effects introduced by GOCE data demonstrate long-wavelength patterns on the centimeter scale in terms of quasi-geoid heights, which may allow reducing the remaining long-wavelength errors in ground-based data, and improve the regional model. The accuracy of the gravimetric quasi-geoid computed with a combination of three diagonal components is improved by 0.6 cm (0.5 cm) in the Netherlands (Belgium) compared to that derived from gravimetry and altimetry data alone, when GOCO05s is used as the reference model. Moreover, the added value from GOCE data reduces the mean values of the misfit between the gravimetric solution and GPS/leveling data. Performances of different components and their combinations are not identical, and the solution with vertical gradients is best when a single component is used. The incorporation of multiple components shows further improvements, and the combination of three components best fits the local GPS/leveling data. Further comparison shows that our solution is the highest quality and may be substituted for existing models for engineering purposes and geophysical investigations over the target area.
NASA Technical Reports Server (NTRS)
Nishikawa, K.; Hardee, P. E.; Richardson, G. A.; Preece, R. D.; Sol, H.; Fishman, G. J.
2003-01-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic jet front propagating through an ambient plasma with and without initial magnetic fields. We find only small differences in the results between no ambient and weak ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates particles perpendicular and parallel to the jet propagation direction. While some Fermi acceleration may occur at the jet front, the majority of electron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that this instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields, which contribute to the electron s transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
Detailed balance condition and ultraviolet stability of scalar field in Horava-Lifshitz gravity
NASA Astrophysics Data System (ADS)
Borzou, Ahmad; Lin, Kai; Wang, Anzhong
2011-05-01
Detailed balance and projectability conditions are two main assumptions when Horava recently formulated his theory of quantum gravity - the Horava-Lifshitz (HL) theory. While the latter represents an important ingredient, the former often believed needs to be abandoned, in order to obtain an ultraviolet stable scalar field, among other things. In this paper, because of several attractive features of this condition, we revisit it, and show that the scalar field can be stabilized, if the detailed balance condition is allowed to be softly broken. Although this is done explicitly in the non-relativistic general covariant setup of Horava-Melby-Thompson with an arbitrary coupling constant λ, generalized lately by da Silva, it is also true in other versions of the HL theory. With the detailed balance condition softly breaking, the number of independent coupling constants can be still significantly reduced. It is remarkable to note that, unlike other setups, in this da Silva generalization, there exists a master equation for the linear perturbations of the scalar field in the flat Friedmann-Robertson-Walker background.
Raffai, Peter; Szeifert, Gabor; Matone, Luca; Bartos, Imre; Marka, Zsuzsa; Aso, Yoichi; Ricci, Fulvio; Marka, Szabolcs
2011-10-15
We present an experimental opportunity for the future to measure possible violations to Newton's 1/r{sup 2} law in the 0.1-10 m range using dynamic gravity field generators (DFG) and taking advantage of the exceptional sensitivity of modern interferometric techniques. The placement of a DFG in proximity to one of the interferometer's suspended test masses generates a change in the local gravitational field that can be measured at a high signal to noise ratio. The use of multiple DFGs in a null-experiment configuration allows us to test composition-independent non-Newtonian gravity significantly beyond the present limits. Advanced and third-generation gravitational-wave detectors are representing the state-of-the-art in interferometric distance measurement today, therefore, we illustrate the method through their sensitivity to emphasize the possible scientific reach. Nevertheless, it is expected that due to the technical details of gravitational-wave detectors, DFGs shall likely require dedicated custom-configured interferometry. However, the sensitivity measure we derive is a solid baseline indicating that it is feasible to consider probing orders of magnitude into the pristine parameter well beyond the present experimental limits significantly cutting into the theoretical parameter space.
NASA Astrophysics Data System (ADS)
Li, Shucai; Wang, Lu; Chen, Zhongyong; Huang, Duwei; Tong, Ruihai
2016-10-01
The dynamics of relativistic electrons are analyzed using the relativistic Fokker-Planck equation including deceleration due to synchrotron radiation (SR) and radial diffusion loss caused by magnetic fluctuation (MF). Threshold electric field for avalanche growth is enhanced, and the growth rate is reduced by the combined effect of MF and SR as compared to the case with only SR. The threshold electric field is determined by the time scales balance between momentum evolution and radial diffusion loss induced by MF, and increased with level of MF. More importantly, the hysteresis behavior of runaway pointed out by does not exist anymore. This is because the ``seed electrons'' cannot be sustained as a result of diffusion loss. This work was supported by NSFC Grant No. 11305071, and the Ministry of Science and technology of China, under Contract Nos. 2013GB112002, 2015GB111002 and 2015GB111001.
Systematic nuclear structure studies using relativistic mean field theory in mass region A ˜ 130
NASA Astrophysics Data System (ADS)
Shukla, A.; Åberg, Sven; Bajpeyi, Awanish
2017-02-01
Nuclear structure studies for even-even nuclei in the mass region \\backsim 130, have been performed, with a special focus around N or Z = 64. On the onset of deformation and lying between two closed shell, these nuclei have attracted attention in a number of studies. A revisit to these experimentally accessible nuclei has been made via the relativistic mean field. The role of pairing and density depletion in the interior has been specially investigated. Qualitative analysis between two versions of relativistic mean field suggests that there is no significant difference between the two approaches. Moreover, the role of the filling {{{s}}}1/2 orbital in density depletion towards the centre has been found to be consistent with our earlier work on the subject Shukla and Åberg (2014 Phys. Rev. C 89 014329).
NASA Astrophysics Data System (ADS)
Flechtner, Frank; Neumayer, Karl Hans; Kusche, Jürgen; Schäfer, Wolfgang; Sohl, Frank
2008-10-01
A simulation study has been performed at GFZ Potsdam, which shows the anticipated improvement of the lunar gravity field model with respect to current (LP150Q model) or near-future (SELENE) knowledge in the framework of the planned German Lunar Explorations Orbiter (LEO) mission, based on PRARE-L (Precise Range And Range-rate Equipment - Lunar version) Satellite-to-Satellite (SST) and Satellite-Earth-Satellite (SEST) tracking observations. It is shown that the global mean error of the lunar gravity field can be reduced to less than 0.1 mGal at a spatial resolution of 50 km. In the spectral domain, this means a factor of 10 (long wavelengths) and some 100 (mid to short wavelengths) improvement as compared to predictions for SELENE or a factor of 1000 with respect to LP150Q. Furthermore, a higher spatial resolution of up to 28 km seems feasible and would correspond to a factor of 2-3 improvement of SELENE results. Moreover, PRARE-L is expected to derive the low-degree coefficients of the lunar gravity field with unprecedented accuracy. Considering long mission duration (at least 1 year is planned) this would allow for the first time a precise direct determination of the low-degree tidal Love numbers of the Moon and, in combination with high precision SEST, would provide an experimental basis to study relativistic effects such as the periselenium advance in the Earth-Moon system.
Gravity Field, Topography, and Interior Structure of Amalthea
NASA Astrophysics Data System (ADS)
Anderson, J. D.; Anabtawi, A.; Jacobson, R. A.; Johnson, T. V.; Lau, E. L.; Moore, W. B.; Schubert, G.; Taylor, A. H.; Thomas, P. C.; Weinwurm, G.
2002-12-01
A close Galileo flyby of Jupiter's inner moon Amalthea (JV) occurred on 5 November 2002. The final aimpoint was selected by the Galileo Radio Science Team on 5 July 2002. The closest approach distance for the selected aimpoint was 221 km from the center of mass, the latitude was - 45.23 Deg and the west longitude was 266.41 Deg (IAU/IAG/COSPAR cartographic coordinate system). In order to achieve an acceptable impact probability (0.15%), and yet fly close to Amalthea, the trajectory was selected from a class of trajectories running parallel to Amalthea's long axis. The Deep Space Network (DSN) had the capability to generate continuous coherent radio Doppler data during the flyby. Such data can be inverted to obtain information on Amalthea's gravity field. Amalthea is irregular and neither a triaxial ellipsoid nor an equilibrium body. It has a volume of about 2.4 x 106 km3, and its best-fit ellipsoid has dimensions 131x73x67 km. Its mass can be determined from the 2002 flyby, and in combination with the volume, a density can be obtained accurate to about 5%, where the error is dominated by the volume uncertainty. Similarly, gravity coefficients (Cnm Snm) can be detected up to fourth degree and order, and the second degree field (quadrupole) can be measured. Topography data are available from Voyager imaging and from images taken with Galileo's solid state imaging system at various times between February and June 1997. By combining the gravity and topography data, new information can be obtained on Amalthea's interior. For example if the gravity coefficients agree with those calculated from the topography, assuming constant density, we can conclude that Amalthea is homogeneous. On the other hand, if the gravity coefficients are smaller than predicted from topography, we can conclude that there is a concentration of mass toward Amalthea's center. We are presenting preliminary pre-publication results at the Fall meeting. This work was sponsored by the Galileo Project
On parasupersymmetric oscillators and relativistic vector mesons in constant magnetic fields
NASA Technical Reports Server (NTRS)
Debergh, Nathalie; Beckers, Jules
1995-01-01
Johnson-Lippmann considerations on oscillators and their connection with the minimal coupling schemes are visited in order to introduce a new Sakata-Taketani equation describing vector mesons in interaction with a constant magnetic field. This new proposal, based on a specific parasupersymmetric oscillator-like system, is characterized by real energies as opposed to previously pointed out relativistic equations corresponding to this interacting context.
Aspects of ultra-relativistic field theories via flat-space holography
NASA Astrophysics Data System (ADS)
Fareghbal, Reza; Naseh, Ali; Rouhani, Shahin
2017-08-01
Recently it was proposed that asymptotically flat spacetimes have a holographic dual which is an ultra-relativistic conformal field theory. In this paper, we obtain the conformal anomaly for such a theory via the flat-space holography technique. Furthermore, using flat-space holography we obtain a C-function for this theory which is monotonically decreasing from the UV to the IR by employing the null energy condition in the bulk.
The determination of Dione's gravity field after four Cassini flybys
NASA Astrophysics Data System (ADS)
Zannoni, Marco; Tortora, Paolo; Iess, Luciano; Jacobson, Robert A.; Armstrong, John W.; Asmar, Sami W.
2015-04-01
We present the expected accuracy in the determination of Dione's gravity field obtained through numerical simulations of all radio science flybys currently planned in the entire Cassini mission. During its tour of the Saturn system, Cassini already performed two flybys of Dione dedicated to the determination of its mass and gravity field, in October 2005 and December 2011, respectively. Two additional radio science flybys are planned in June 2015 and August 2015. The analysis of the Doppler data acquired during the closest approach of the second flyby allowed the first estimation of Dione's J2 and C22 but, given the limited amount of data, their estimation has a large correlation and cannot be considered fully reliable. Here we infer the expected final accuracy in the determination of Dione's J2 and C22 by combining the available results from the already performed experiments with numerical simulations of future flybys. The main observables considered in the analysis are two-way and three-way Doppler data obtained from the frequency shift of a highly stable microwave carrier between the spacecraft and the stations of NASA's Deep Space Network. White Gaussian noise was added to the simulated data, with a constant standard deviation for each tracking pass, obtained from an accurate noise budget of the Cassini mission. For the two flybys to be carried out in 2015, we consider a continuous coverage during +/-18 hours around the closest approach, plus one tracking pass 36 hours before and after it. The data analysis is carried out using a global, multi-arc fit, and comparing the independent solutions obtained from each flyby and different multi-arc solutions. The analysis of all four flybys is expected to provide the best, unconstrained, reliable estimation of the full quadrupole gravity field of Dione.
Pu, Hung-Yi; Nakamura, Masanori; Hirotani, Kouichi; Asada, Keiichi; Wu, Kinwah
2015-03-01
General relativistic magnetohydrodynamic (GRMHD) flows along magnetic fields threading a black hole can be divided into inflow and outflow parts, according to the result of the competition between the black hole gravity and magneto-centrifugal forces along the field line. Here we present the first self-consistent, semi-analytical solution for a cold, Poynting flux–dominated (PFD) GRMHD flow, which passes all four critical (inner and outer, Alfvén, and fast magnetosonic) points along a parabolic streamline. By assuming that the dominating (electromagnetic) component of the energy flux per flux tube is conserved at the surface where the inflow and outflow are separated, the outflow part of the solution can be constrained by the inflow part. The semi-analytical method can provide fiducial and complementary solutions for GRMHD simulations around the rotating black hole, given that the black hole spin, global streamline, and magnetizaion (i.e., a mass loading at the inflow/outflow separation) are prescribed. For reference, we demonstrate a self-consistent result with the work by McKinney in a quantitative level.
Paramagnetic Liquid Bridge in a Gravity-Compensating Magnetic Field
NASA Technical Reports Server (NTRS)
Mahajan, Milind P.; Tsige, Mesfin; Taylor, P. L.; Rosenblatt, Charles
1999-01-01
Magnetic levitation was used to stabilize cylindrical columns of a paramagnetic liquid in air between two solid supports. The maximum achievable length to diameter ratio R(sub max) was approx. (3.10 +/- 0.07), very close to the Rayleigh-Plateau limit of pi. For smaller R, the stability of the column was measured as a function of the Bond number, which could be continuously varied by adjusting the strength of the magnetic field. Liquid bridges supported by two solid surfaces have been attracting scientific attention since the time of Rayleigh and Plateau. For a cylindrical bridge of length L and diameter d, it was shown theoretically that in zero gravity the maximum slenderness ratio R (identically = L/d) is pi. The stability and ultimate collapse of such bridges is of interest because of their importance in a number of industrial processes and their potential for low gravity applications. In the presence of gravity, however, the cylindrical shape of an axisymmetric bridge tends to deform, limiting its stability and decreasing the maximum achievable value of R. Theoretical studies have discussed the stability and possible shapes of axisymmetric bridges. Experiments typically are performed in either a Plateau tank, in which the bridge is surrounded by a density-matched immiscible fluid, or in a space-borne microgravity environment. It has been shown, for example, that the stability limit R can be pushed beyond pi by using flow stabilization, by acoustic radiation pressure, or by forming columns in the presence of an axial electric field. In this work, magnetic levitation was used to simulate a low gravity environment and create quasi-cylindrical liquid columns in air. Use of a magnetic field permits us to continuously vary the Bond number B identically equal to (g)(rho)d(exp 2)/4(sigma), where g is the gravitational acceleration, rho is the density of the liquid, and sigma is the surface tension of the liquid in air. The dimensionless Bond number represents the
Gravity field data products from the ARISTOTELES mission.
NASA Astrophysics Data System (ADS)
Balmino, G.
1991-12-01
The ARISTOTELES mission will bring a wealth of homogeneous information about the Earth gravity field enabling new direct and inverse modeling of geophysical structures at various scales, yielding a reference geoid surface of great quality for oceanographic studies, leading to global models of high resolution for versatile applications and in particular precise orbit determination of artificial satellites. The author's purpose is to review the different types of measurements involved in these investigations, the various levels of processing and how they can be phased with the scientific activities, and the expected products. Also, some general schemes are proposed along which the different tasks can be undertaken.
Mercury's Gravity Field from BepiColombo MORE experiment
NASA Astrophysics Data System (ADS)
Marabucci, M.; Genova, A.; Iess, L.
2012-04-01
The Mercury Orbiter Radioscience Experiment (MORE) is one of the main instruments on board the BepiColombo Mercury Planetary Orbiter (MPO), designed to provide an accurate estimation of Mercury's gravity field by means of highly stable, multi-frequency radio links in X and Ka band. The state-of-the-art microwave equipment enables simultaneous two-way links in X/X (7.2 GHz uplink/8.4 GHz downlink), X/Ka (7.2/32.5 GHz) and Ka/Ka band (34/32.5 GHz), providing range rate accuracies of 3 micron/s (at 1000 s integration time) at nearly all elongation angles. Range observables accurate to 20 cm (two-way) will be attained using a novel, wideband (24 Mcps) ranging system, based upon a pseudo-noise modulation scheme. The multifrequency link, adopted for the first time by the Cassini mission to Saturn [1,2], allows a nearly complete cancellation of the plasma noise both in Doppler and range measurements and hence an accurate determination of Mercury's gravity field and ephemerides. The orbit determination of spacecraft in deep space is generally carried out by means of batch filters, for recovering the trajectory and the model parameters (i.e. gravity field coefficients). The complexity of Mercury's environment penalizes strongly the accuracy of the orbit determination because of the non-gravitational perturbations, such as the solar radiation pressure. Although the non-gravitational accelerations of the MPO will be measured by a highly sensitive accelerometer (the Italian Spring Accelerometer, ISA), a classical, global batch filter proved to be inadequate for precise orbit propagation due to numerical instabilities. Therefore, a different approach has been devised, where the information accumulated previously is exploited in a batch-sequential filter. This paper reports on a new set of numerical simulations carried out with this strategy. The simulation setup takes into account the latest changes in the spacecraft design, the mission profile and the tracking system. We
Quantum theory of fields and origin of gravity
Gliner, E.B.
1986-05-01
The unification of the quantum theory of fields and general relativity is supposed possible on the basis of Sakharov's hypothesis that gravity results from variations in vacuum fluctuations. It is shown that under very general conditions this hypothesis leads to Riemannian geometry of the world-lines of free particle motion. The origin of causal spacetime relations is discussed as the problem complementary to that of the source of geometry. This involves an interpretation of the EPR experiment and supports the idea that spacetime relations in microphysics result from adjusting quantum processes to the causality of macroscopic participators.
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.
2007-01-01
Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron)jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.
2006-01-01
Nonthermal radiation observed from astrophysical systems containing (relativistic) jets and shocks, e.g., supernova remnants, active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Fermi acceleration is the mechanism usually assumed for the acceleration of particles in astrophysical environments. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet, rather than by the scattering of particles back and forth across the shock as in Fermi acceleration. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the .shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. We will review recent PIC simulations which show particle acceleration in jets.
NASA Technical Reports Server (NTRS)
Nishikawa, K. I.; Ramirez-Ruiz, E.; Hardee, P.; Mizuno, Y.; Fishman. G. J.
2007-01-01
Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.
2006-01-01
Nonthermal radiation observed from astrophysical systems containing (relativistic) jets and shocks, e.g., supernova remnants, active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Fermi acceleration is the mechanism usually assumed for the acceleration of particles in astrophysical environments. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet, rather than by the scattering of particles back and forth across the shock as in Fermi acceleration. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the .shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. We will review recent PIC simulations which show particle acceleration in jets.
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.
2007-01-01
Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron)jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
NASA Technical Reports Server (NTRS)
Nishikawa, K. I.; Ramirez-Ruiz, E.; Hardee, P.; Mizuno, Y.; Fishman. G. J.
2007-01-01
Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The "jitter" radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants.
Lee, H. C.; Jiang, T. F.
2010-11-15
We analytically solve the relativistic equation of motion for an electron in ion plasma channels and calculate the corresponding trajectory as well as the synchrotron radiation. The relativistic effect on a trajectory is strong, i.e., many high-order harmonic terms in the trajectory, when the ratio of the initial transverse velocity (v{sub x0}) to the longitudinal velocity (v{sub z0}) of the electron injected to ion plasma channels is high. Interestingly, these high-order harmonic terms result in a quite broad and intense radiation spectrum, especially at an oblique angle, in contrast to an earlier understanding. As the initial velocity ratio (v{sub x0}:v{sub z0}) decreases, the relativistic effect becomes weak; only the first and second harmonic terms remain in the transverse and longitudinal trajectories, respectively, which coincides with the result of Esarey et al. [Phys. Rev. E 65, 056505 (2002)]. Our formalism also allows the description of electron's trajectory in the presence of an applied magnetic field. Critical magnetic fields for cyclotron motions are figured out and compared with semiclassical results. The cyclotron motion leads to more high-order harmonic terms than the trajectory without magnetic fields and causes an immensely broad spectrum with vastly large radiation amplitude for high initial velocity ratios (v{sub x0}:v{sub z0}). The radiation from hard x-ray to gamma-ray regions can be generated with a broad radiation angle, thus available for applications.
Electro-optic measurement of the wake fields of a relativistic electron beam.
Fitch, M J; Melissinos, A C; Colestock, P L; Carneiro, J P; Edwards, H T; Hartung, W H
2001-07-16
When a relativistic electron bunch traverses a structure, strong electromagnetic fields are induced in its wake. For a 12 nC bunch of duration 4.2 ps FWHM, the peak field is measured >0.5 MV/m. Time resolution of approximately 5 ps is achieved using electro-optic sampling with a lithium tantalate (LiTaO3) crystal and a short-pulse infrared laser synchronized to the beam. We present measurements for both the longitudinal and radial components of the field and relate them to the wall impedance.
NASA Astrophysics Data System (ADS)
Gattamraju, Ravindra Kumar; Shaikh, Moniruzzaman; Lad, Amit; Sarkar, Deep; Jana, Kamalesh; Dey, Indranuj
2016-10-01
Intense,femtosecond laser pulses generate relativistic electron pulses,important for many applications. In this paper, we present a femtosecond time-resolved and micrometer space resolved giant magnetic fields generated by 1019 W cm-2, 800 nm, 30 fs, high intensity contrast laser pulses in using pump-probe Cotton Mouton polarimetry. The space and time resolved maps of the magnetic fields at the front and rear of targets reveal turbulence in the magnetic fields. We also present data from shadowgraphy and Cherenkov emission along with model calculations to build up a picture of the transport process. GRK thanks J C Bose Fellowship Grant JCB-37/2010 for partial support.
Linear connections with a propagating spin-3 field in gravity
Baekler, Peter; Boulanger, Nicolas; Hehl, Friedrich W.
2006-12-15
We show that Fronsdal's Lagrangian for a free massless spin-3 gauge field in Minkowski spacetime is contained in a general Yang-Mills-like Lagrangian of metric-affine gravity (MAG), the gauge theory of the general affine group in the presence of a metric. Because of the geometric character of MAG, this can best be seen by using Vasiliev's frame formalism for higher-spin gauge fields in which the spin-3 frame is identified with the tracefree nonmetricity one-form associated with the shear generators of GL(n,R). Furthermore, for specific gravitational gauge models in the framework of full nonlinear MAG, exact solutions are constructed, featuring propagating massless and massive spin-3 fields.
Fugacity and concentration gradients in a gravity field
NASA Technical Reports Server (NTRS)
May, C. E.
1986-01-01
Equations are reviewed which show that at equilibrium fugacity and concentration gradients can exist in gravitational fields. At equilibrium, the logarithm of the ratio of the fugacities of a species at two different locations in a gravitational field is proportional to the difference in the heights of the two locations and the molecular weight of the species. An analogous relation holds for the concentration ratios in a multicomponent system. The ratio is calculated for a variety of examples. The kinetics for the general process are derived, and the time required to approach equilibrium is calculated for several systems. The following special topics are discussed: ionic solutions, polymers, multiphase systems, hydrostatic pressure, osmotic pressure, and solubility gradients in a gravity field.
Fugacity and concentration gradients in a gravity field
NASA Astrophysics Data System (ADS)
May, C. E.
1986-07-01
Equations are reviewed which show that at equilibrium fugacity and concentration gradients can exist in gravitational fields. At equilibrium, the logarithm of the ratio of the fugacities of a species at two different locations in a gravitational field is proportional to the difference in the heights of the two locations and the molecular weight of the species. An analogous relation holds for the concentration ratios in a multicomponent system. The ratio is calculated for a variety of examples. The kinetics for the general process are derived, and the time required to approach equilibrium is calculated for several systems. The following special topics are discussed: ionic solutions, polymers, multiphase systems, hydrostatic pressure, osmotic pressure, and solubility gradients in a gravity field.
Relativistic quantum channel of communication through field quanta
Cliche, M.; Kempf, A.
2010-01-15
Setups in which a system Alice emits field quanta that a system Bob receives are prototypical for wireless communication and have been extensively studied. In the most basic setup, Alice and Bob are modeled as Unruh-DeWitt detectors for scalar quanta, and the only noise in their communication is due to quantum fluctuations. For this basic setup, we construct the corresponding information-theoretic quantum channel. We calculate the classical channel capacity as a function of the spacetime separation, and we confirm that the classical as well as the quantum channel capacity are strictly zero for spacelike separations. We show that this channel can be used to entangle Alice and Bob instantaneously. Alice and Bob are shown to extract this entanglement from the vacuum through a Casimir-Polder effect.
Relativistic Particle Population and Magnetic Fields in Clusters of Galaxies
NASA Astrophysics Data System (ADS)
Kushnir, Doron
2011-08-01
We derive constrains on the cosmic ray (CR) population and magnetic fields (MF) in clusters of galaxies, based on: 1. The correlation between the radio and the X-ray luminosities: the former emitted by synchrotron of secondary electrons in a strong MF, >˜3 muG; In the core, the CR energy is ˜10^{-3} of the thermal energy; The source of CR is the accretion shock (AS), which accelerate CR with efficiency >˜1%. 2. The HXR luminosity: emitted by IC of CMB photons by electrons accelerated in AS with efficiency >˜1%. The constrains imply that gamma-ray emission from secondaries will be difficult to detect with existing/planned instruments. However, the extended emission from primary electrons might be detected by future HXR (NuStar, Simbol-X) and gamma-ray observations (Fermi, HESS, VERITAS).
General relativistic simulations of black-hole-neutron-star mergers: Effects of magnetic fields
NASA Astrophysics Data System (ADS)
Etienne, Zachariah B.; Liu, Yuk Tung; Paschalidis, Vasileios; Shapiro, Stuart L.
2012-03-01
As a neutron star (NS) is tidally disrupted by a black hole (BH) companion at the end of a black-hole-neutron-star (BHNS) binary inspiral, its magnetic fields will be stretched and amplified. If sufficiently strong, these magnetic fields may impact the gravitational waveforms, merger evolution and mass of the remnant disk. Formation of highly-collimated magnetic field lines in the disk+spinning BH remnant may launch relativistic jets, providing the engine for a short-hard GRB. We analyze this scenario through fully general relativistic, magnetohydrodynamic BHNS simulations from inspiral through merger and disk formation. Different initial magnetic field configurations and strengths are chosen for the NS interior for both nonspinning and moderately spinning (aBH/MBH=0.75) BHs aligned with the orbital angular momentum. Only strong interior (Bmax˜1017G) initial magnetic fields in the NS significantly influence merger dynamics, enhancing the remnant disk mass by 100% and 40% in the nonspinning and spinning BH cases, respectively. However, detecting the imprint of even a strong magnetic field may be challenging for Advanced LIGO. Though there is no evidence of mass outflows or magnetic field collimation during the preliminary simulations we have performed, higher resolution, coupled with longer disk evolutions and different initial magnetic field configurations, may be required to definitively assess the possibility of BHNS binaries as short-hard gamma-ray burst progenitors.
Determination of Enceladus' gravity field from Cassini radio science data
NASA Astrophysics Data System (ADS)
Parisi, Marzia; Iess, Luciano; Ducci, Marco
2014-05-01
In May 2012 the Cassini spacecraft completed its last gravity flyby of Saturn's moon Enceladus (identified as E19 in the sequence), following E9 in April 2010 and E12 in November 2010. The multiarc analysis of the gravity data collected during these low-altitude encounters has produced a stable solution for the gravity field of Enceladus, leading to compelling inferences and implications on the interior structure, but also raising new questions on the evolution of this small but yet fascinating icy body. The gravitational signature of the satellite was detected by means of precise Doppler tracking of the Cassini spacecraft around closest approach (±3h) of the three flybys. Cassini tracking system exploits both X/X and X/Ka links, with accuracies that range between 0.02 - 0.09 mm/s at 60 s integration time. Range-rate measurements were processed into a multi-arc least square filter so as to attain a solution for the quadrupole field of Enceladus and its degree-3 zonal harmonic J3, the most important indication of hemispherical asymmetries. In addition to these crucial parameters, corrections to the estimated orbits of Cassini and Enceladus were applied. The inclusion in the dynamical model of the neutral particle drag exerted by Enceladus south polar plumes (1) is essential for a satisfactory orbital fit. The results of the analysis show that Enceladus is indeed characterized by a predominant quadrupole term, with its J2/C22 ratio being that of a body not in hydrostatic equilibrium. The estimate of tesseral degree-2 coefficients (C21, S21 and C22), being statistically close to 0 (at a 3-σ level), imply that the adopted rotational model for the satellite is consistent with the observed gravity field. Furthermore, the estimated value for J3 turned out to be statistically significant (although only about 1/50 of J2) and pointing at a significant hemispherical asymmetry that is consistent with the presence of a regional sea at depth. References (1) C.C. Porco et al
Hot and dense matter beyond relativistic mean field theory
NASA Astrophysics Data System (ADS)
Zhang, Xilin; Prakash, Madappa
2016-05-01
Properties of hot and dense matter are calculated in the framework of quantum hadrodynamics by including contributions from two-loop (TL) diagrams arising from the exchange of isoscalar and isovector mesons between nucleons. Our extension of mean field theory (MFT) employs the same five density-independent coupling strengths which are calibrated using the empirical properties at the equilibrium density of isospin-symmetric matter. Results of calculations from the MFT and TL approximations are compared for conditions of density, temperature, and proton fraction encountered in the study of core-collapse supernovae, young and old neutron stars, and mergers of compact binary stars. The TL results for the equation of state (EOS) of cold pure neutron matter at sub- and near-nuclear densities agree well with those of modern quantum Monte Carlo and effective field-theoretical approaches. Although the high-density EOS in the TL approximation for cold and β -equilibrated neutron-star matter is substantially softer than its MFT counterpart, it is able to support a 2 M⊙ neutron star required by recent precise determinations. In addition, radii of 1.4 M⊙ stars are smaller by ˜1 km than those obtained in MFT and lie in the range indicated by analysis of astronomical data. In contrast to MFT, the TL results also give a better account of the single-particle or optical potentials extracted from analyses of medium-energy proton-nucleus and heavy-ion experiments. In degenerate conditions, the thermal variables are well reproduced by results of Landau's Fermi-liquid theory in which density-dependent effective masses feature prominently. The ratio of the thermal components of pressure and energy density expressed as Γth=1 +(Pth/ɛth) , often used in astrophysical simulations, exhibits a stronger dependence on density than on proton fraction and temperature in both MFT and TL calculations. The prominent peak of Γth at supranuclear density found in MFT is, however, suppressed in
NASA Astrophysics Data System (ADS)
Horwitz, Lawrence; Hu, Bei-Lok; Lee, Da-Shin; Gill, Tepper; Land, Martin
2011-12-01
relativity. The opening session of IARD 2010 was held jointly with the closing seesion of the RQI-N workshop on relativistic quantum information that took place from 28-30 May. This joint meeting emphasized the importance of including dynamical models in relativistic quantum information theory, and of utilizing the perspective of quantum information in extracting results with strong implications for application in relativistic dynamics. Topics discussed at the conference and reported in this volume included investigations into problems in general relativity, relations between quantum field theory, cosmology and, in its statistical aspects, to the extraction of classical attributes of macroscopic quantum systems. There was also a very fundamental study by David R Finkelstein, of the stucture of spacetime itself, posing the possibility that the spacetime manifold emerges from an underlying quantum complex, composed of simplices with spin 1/2 and Fermi statistics, resulting in the regularization of the Standard Model and perhaps a regularized structure for quantum gravity. H T Cho and B L Hu study the vacuum expectation value of the stress energy tensor of a minimally coupled massless scalar field and its role as a source in the Einstein-Langevin equations of quantum gravity, governing the induced metric of fluctuations above the mean field dynamics of the semiclassical theory. C H Chou, B L Hu and Y Subasi study macroscopic quantum phenomena from the point of view of correlations, coupling and criticality, and explain how a macroscopic quantum system may, in this way, acquire classical attributes but still retain some quantum features. S Y Lin discusses a connection with quantum information science as one of the consequences of his work on local projective measurements on relativistic fields. In the field of cosmology, F H Ho and J M Nester study Poincaré gauge theory with a metric compatible connection to an independent dynamics associated with torsion and curvature. They
The inteplanetary magnetic field associated to the propagation of solar relativistic particles
NASA Astrophysics Data System (ADS)
Masson, Sophie; Dasso, Sergio; Démoulin, Pasal; Klein, Karl-Ludwig
2010-05-01
The origin and the propagation of high energetic solar particles (450 MeV- few GeV) in the interplanetary medium remains a complex topic. These relativistic solar particles, detected at the Earth by neutron monitors (called Ground level enhancement, GLE), have been previously accelerated close to the Sun. In order to be detected at the Earth, these relativistic particles have to travel along an interplanetary magnetic field (IMF) connecting the acceleration site and the Earth. Generally, the nominal Parker spiral (SP), is considered for ensuring the magnetic connection to the Earth. However, in most of GLEs the IMF is highly disturbed, and the active regions (ARs) associated to the GLEs are not always located close to the footprint of the nominal Parker spiral. If the AR is not connected to the Earth by the nominal Parker spiral, which is the IMF connecting the acceleration site and the Earth during the GLEs? A possible explanation of relativistic particles propagation under these circumstances are transient magnetic structures, travelling in the IMF as Interplanetary coronal mass ejections (ICMEs). In order to check this interpretation, we studied in detail the magnetic connection for 10 GLEs of the last solar cycle. Using the magnetic field and the plasma parameter measurements (ACE/MAG and ACE/SWEPAM), we find that relativistic particles associated to ARs located close to the footprint of the nominal Parker spiral tend to propagate along this nominal Parker spiral (2 clear cases) or in a solar wind disturbed by a previous magnetic perturbation (3 cases). Instead, the GLEs associated to ARs which is clearly not-well connected tend to propagate in an interplanetary coronal mass ejection or in the back of a previous ICME. More specifically on the 3 not-well connected cases, two propagate in the back of an ICME and one of them propagates in the ICME. Depending in which IMF particles propagate, the path length can display significant differences. Using the velocity
Altimeter measurements for the determination of the Earth's gravity field
NASA Technical Reports Server (NTRS)
Tapley, B. D.; Schutz, B. E.; Shum, C. K.
1987-01-01
The ability of satellite-borne radar altimeter data to measure the global ocean surface with high precision and dense spatial coverage provides a unique tool for the mapping of the Earth's gravity field and its geoid. The altimeter crossover measurements, created by differencing direct altimeter measurements at the subsatellite points where the orbit ground tracks intersect, have the distinct advantage of eliminating geoid error and other nontemporal or long period oceanographic features. In the 1990's, the joint U.S./French TOPEX/POSEIDON mission and the European Space Agency's ERS-1 mission will carry radar altimeter instruments capable of global ocean mapping with high precision. This investigation aims at the development and application of dynamically consistent direct altimeter and altimeter crossover measurement models to the simultaneous mapping of the Earth's gravity field and its geoid, the ocean tides and the quasi-stationary component of the dynamic sea surface topography. Altimeter data collected by SEASAT, GEOS-3, and GEOSAT are used for the investigation.
A Revolution in Mars Topography and Gravity and Magnetic Fields
NASA Technical Reports Server (NTRS)
Smith, David E.
2002-01-01
Since the arrival of the Mars Global Surveyor (MGS) at Mars in September 1997 and the subsequent beginning of observations of the planet there has been a constant stream of surprises and puzzling observations that have kept scientists looking at new 'out of the box' explanations. Observations of the shape and topography have shown a planet with one hemisphere, the southern, several kilometers higher than the north and a northern hemisphere that is so flat and smooth in places that it's difficult to imagine it was not once the bottom of an ocean. And yet the ocean idea presents some enormous difficulties. The measurements of gravity derived from the tracking of MGS have shown that several Mars volcanoes are enormous positive gravity anomalies much larger than we see on Earth and revealed small errors in the orbit of Mars and or Earth. And the magnetic field is found to be composed of a number of extremely large crustal anomalies; but as far as can be ascertained there is no main dipole field such as we have on Earth. Understanding these diverse observations and placing them in the sequence of the evolution of the planet will be a long, challenging but rewarding task.
A Revolution in Mars Topography and Gravity and Magnetic Fields
NASA Technical Reports Server (NTRS)
Smith, David E.
2002-01-01
Since the arrival of the Mars Global Surveyor (MGS) at Mars in September 1997 and the subsequent beginning of observations of the planet there has been a constant stream of surprises and puzzling observations that have kept scientists looking at new 'out of the box' explanations. Observations of the shape and topography have shown a planet with one hemisphere, the southern, several kilometers higher than the north and a northern hemisphere that is so flat and smooth in places that it's difficult to imagine it was not once the bottom of an ocean. And yet the ocean idea presents some enormous difficulties. The measurements of gravity derived from the tracking of MGS have shown that several Mars volcanoes are enormous positive gravity anomalies much larger than we see on Earth and revealed small errors in the orbit of Mars and or Earth. And the magnetic field is found to be composed of a number of extremely large crustal anomalies; but as far as can be ascertained there is no main dipole field such as we have on Earth. Understanding these diverse observations and placing them in the sequence of the evolution of the planet will be a long, challenging but rewarding task.
High field terahertz emission from relativistic laser-driven plasma wakefields
Chen, Zi-Yu; Pukhov, Alexander
2015-10-15
We propose a method to generate high field terahertz (THz) radiation with peak strength of GV/cm level in the THz frequency gap range of 1–10 THz using a relativistic laser interaction with a gaseous plasma target. Due to the effect of local pump depletion, an initially Gaussian laser pulse undergoes leading edge erosion and eventually evolves to a state with leading edge being step function. Interacting with such a pulse, electrons gain transverse residual momentum and excite net transverse currents modulated by the relativistic plasma frequency. These currents give rise to the low frequency THz emission. We demonstrate this process with one and two dimensional particle-in-cell simulations.
NASA Astrophysics Data System (ADS)
Eliasson, B.; Papadopoulos, K.
2017-10-01
A theoretical study of the propagation of left-hand polarized shear Alfvén waves in spatially decreasing magnetic field geometries near the EMIC resonance, including the spectrum and amplitude of the mode converted EMIC waves and the pitch angle scattering of relativistic electrons transiting the resonant region, is presented. The objective of the paper is to motivate an experimental study of the subject using the UCLA LAPD chamber. The results are relevant in exploring the possibility that shear Alfvén waves strategically injected into the radiation belts using either ionospheric heating from ground based RF transmitters or injected by transmitters based on space platforms can enhance the precipitation rate of trapped relativistic electrons. Effects of multi-ionic composition are also investigated.
The use of high-resolution terrain data in gravity field prediction
NASA Technical Reports Server (NTRS)
Groten, E.; Becker, M.; Euler, H.-J.; Hausch, W.; Kling, TH.
1989-01-01
Different types of gravity prediction methods for local and regional gravity evaluation are developed, tested, and compared. Four different test areas were particularly selected in view of different prediction requirements. Also different parts of the spectrum of the gravity field were considered.
Entropy of Egypt's virtual water trade gravity field
NASA Astrophysics Data System (ADS)
Karakatsanis, Georgios; Bierbach, Sandra
2016-04-01
's 20 trading partner countries, for a time frame from 1995 to 2013. The calculations -implemented for each country and each crop- display a network that illustrates the gravity of virtual water trade. It is then possible for us to model the entropy of Egypt's virtual water trade gravity field, via the statistical examination of its spatial fragmentation or continuity for each traded crop and for each water footprint type. Hence, with the distribution's entropy we may conduct a targeted analysis on the comparative advantages of the Egyptian agriculture. Keywords: entropy, virtual water trade, gravity model, agricultural trade, water footprint, water subsidies, comparative advantage References 1. Antonelli, Marta and Martina Sartori (2014), Unfolding the potential of the Virtual Water concept. What is still under debate?, MPRA Paper No. 60501, http://mpra.ub.uni-muenchen.de/60501/ 2. Fracasso, Andrea (2014), A gravity model of virtual water trade, Ecological Economics, Vol. 108, p. 215-228 3. Fracasso, Andrea; Martina Sartori and Stefano Schiavo (2014), Determinants of virtual water flows in the Mediterranean, MPRA Paper No. 60500, https://mpra.ub.uni-muenchen.de/60500/ 4. Yang, H. et al. (2006), Virtual water trade: An assessment of water use efficiency in the international food trade, Hydrology and Earth System Sciences 10, p. 443-454
Barceló, Carlos; Liberati, Stefano; Visser, Matt
2011-01-01
Analogue gravity is a research programme which investigates analogues of general relativistic gravitational fields within other physical systems, typically but not exclusively condensed matter systems, with the aim of gaining new insights into their corresponding problems. Analogue models of (and for) gravity have a long and distinguished history dating back to the earliest years of general relativity. In this review article we will discuss the history, aims, results, and future prospects for the various analogue models. We start the discussion by presenting a particularly simple example of an analogue model, before exploring the rich history and complex tapestry of models discussed in the literature. The last decade in particular has seen a remarkable and sustained development of analogue gravity ideas, leading to some hundreds of published articles, a workshop, two books, and this review article. Future prospects for the analogue gravity programme also look promising, both on the experimental front (where technology is rapidly advancing) and on the theoretical front (where variants of analogue models can be used as a springboard for radical attacks on the problem of quantum gravity).
Vector field models of modified gravity and the dark sector
Zuntz, J.; Ferreira, P. G.; Zlosnik, T. G; Bourliot, F.; Starkman, G. D.
2010-05-15
We present a comprehensive investigation of cosmological constraints on the class of vector field formulations of modified gravity called generalized Einstein-aether models. Using linear perturbation theory we generate cosmic microwave background and large-scale structure spectra for general parameters of the theory, and then constrain them in various ways. We investigate two parameter regimes: a dark matter candidate where the vector field sources structure formation, and a dark energy candidate where it causes late-time acceleration. We find that the dark matter candidate does not fit the data, and identify five physical problems that can restrict this and other theories of dark matter. The dark energy candidate does fit the data, and we constrain its fundamental parameters; most notably we find that the theory's kinetic index parameter n{sub ae} can differ significantly from its {Lambda}CDM value.
Modified f( R, T) gravity theory and scalar field cosmology
NASA Astrophysics Data System (ADS)
Singh, Vijay; Singh, C. P.
2015-03-01
In this paper, we explore the behaviors of scalar field in modified f( R, T) gravity theory within the framework of a flat Friedmann-Robertson-Walker cosmological model. The universe is assumed to be filled with two non-interacting matter sources, scalar field (normal or phantom) with scalar potential and matter contribution due to f( R, T) action. We first explore a model where the potential is a constant, and the universe evolves as a de Sitter type. This model is compatible with phantom scalar field only which gives fine tuning with the recent observations. The model exhibits a wide variety of early time physical phenomena that eventually behaves like a cosmological constant at late times. The model shows transition from decelerated to accelerated expansion of the universe. We also explore a model where the scalar field potential and the scale factor evolve exponentially as a scalar field. This model is compatible with normal scalar field only and describes transition from inflationary to the decelerated phase at early times and quintessence to phantom phase at late times. We constraint our results with the recent observational data and find that some values of parameters are consistent with SNe Ia and H( z)+SNe Ia data to describe accelerated expansion only whereas some one give decelerated and accelerated expansions with H( z), WMAP7 and WMAP7+BAO+ H( z) observational data.
Liang, Edison; Smith, Ian; Boettcher, Markus E-mail: iansmith@rice.edu
2013-04-01
Using particle-in-cell simulations, we study the kinetic physics of relativistic shear flow in collisionless electron-positron (e+e-) plasmas. We find efficient magnetic field generation and particle energization at the shear boundary, driven by streaming instabilities across the shear interface and sustained by the shear flow. Nonthermal, anisotropic high-energy particles are accelerated across field lines to produce a power-law tail turning over just below the shear Lorentz factor. These results have important implications for the dissipation and radiation of jets in blazars and gamma-ray bursts.
Magnetic-Field-Induced Relativistic Properties in Type-I and Type-II Weyl Semimetals
NASA Astrophysics Data System (ADS)
Tchoumakov, Serguei; Civelli, Marcello; Goerbig, Mark O.
2016-08-01
We investigate Weyl semimetals with tilted conical bands in a magnetic field. Even when the cones are overtilted (type-II Weyl semimetal), Landau-level quantization can be possible as long as the magnetic field is oriented close to the tilt direction. Most saliently, the tilt can be described within the relativistic framework of Lorentz transformations that give rise to a rich spectrum, displaying new transitions beyond the usual dipolar ones in the optical conductivity. We identify particular features in the latter that allow one to distinguish between semimetals of different types.
Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Nordlund, A.; Frederiksen, J.; Mizuno, Y.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, G. J.
2011-01-01
Using our new 3-D relativistic particle-in-cell (PIC) code, we investigated long-term particle acceleration associated with a relativistic electron-positron jet propagating in an unmagnetized ambient electron-positron plasma. The simulations were performed using a much longer simulation system than our previous simulations in order to investigate the full nonlinear stage of the Weibel instability and its particle acceleration mechanism. Cold jet electrons are thermalized and ambient electrons are accelerated in the resulting shocks. Acceleration of ambient electrons leads to a maximum ambient electron density three times larger than the original value as predicted by hydrodynamic compression. Behind the bow shock, in the jet shock, strong electromagnetic fields are generated. These fields may lead to time dependent afterglow emission. In order to go beyond the standard synchrotron model used in astrophysical objects we have used PIC simulations and calculated radiation based on first principles. We calculated radiation from electrons propagating in a uniform parallel magnetic field to verify the technique. We also used the technique to calculate emission from electrons based on simulations with a small system. We obtain spectra which are consistent with those generated from electrons propagating in turbulent magnetic fields. This turbulent magnetic field is similar to the magnetic field generated at an early nonlinear stage of the Weibel instability. A fully developed shock within a larger system may generate a jitter/synchrotron spectrum.
NASA Astrophysics Data System (ADS)
Rocha da Silva, G.; Falceta-Gonçalves, D.; Kowal, G.; de Gouveia Dal Pino, E. M.
2015-01-01
Strong downstream magnetic fields of the order of ˜1 G, with large correlation lengths, are believed to cause the large synchrotron emission at the afterglow phase of gamma-ray bursts (GRBs). Despite the recent theoretical efforts, models have failed to fully explain the amplification of the magnetic field, particularly in a matter-dominated scenario. We revisit the problem by considering the synchrotron emission to occur at the expanding shock front of a weakly magnetized relativistic jet over a magnetized surrounding medium. Analytical estimates and a number of high-resolution 2D relativistic magnetohydrodynamical (RMHD) simulations are provided. Jet opening angles of θ = 0°-20°, and ambient to jet density ratios of 10-4-102 were considered. We found that most of the amplification is due to compression of the ambient magnetic field at the contact discontinuity between the reverse and forward shocks at the jet head, with substantial pile-up of the magnetic field lines as the jet propagates sweeping the ambient field lines. The pile-up is maximum for θ → 0, decreasing with θ, but larger than in the spherical blast problem. Values obtained for certain models are able to explain the observed intensities. The maximum correlation lengths found for such strong fields is of lcorr ≤ 1014 cm, 2-6 orders of magnitude larger than the found in previous works.
Antarctic marine gravity field from high-density satellite altimetry
NASA Technical Reports Server (NTRS)
Sandwell, David T.
1992-01-01
High-density (about 2-km profile spacing) Geosat/GM altimetry profiles were obtained for Antarctic waters (6-deg S to 72 deg S) and converted to vertical gravity gradient, using Laplace's equation to directly calculate gravity gradient from vertical deflection grids and Fourier analysis to construct gravity anomalies from two vertical deflection grids. The resultant gravity grids have resolution and accuracy comparable to shipboard gravity profiles. The obtained gravity maps display many interesting and previously uncharted features, such as a propagating rift wake and a large 'leaky transform' along the Pacific-Antarctic Rise.
NASA Technical Reports Server (NTRS)
Uemaatsu, Hirohiko; Parkinson, Bradford W.; Lockhart, James M.; Muhlfelder, Barry
1993-01-01
Gravity Probe B (GP-B) is a relatively gyroscope experiment begun at Stanford University in 1960 and supported by NASA since 1963. This experiment will check, for the first time, the relativistic precession of an Earth-orbiting gyroscope that was predicted by Einstein's General Theory of Relativity, to an accuracy of 1 milliarcsecond per year or better. A drag-free satellite will carry four gyroscopes in a polar orbit to observe their relativistic precession. The primary sensor for measuring the direction of gyroscope spin axis is the SQUID (superconducting quantum interference device) magnetometer. The data reduction scheme designed for the GP-B program processes the signal from the SQUID magnetometer and estimates the relativistic precession rates. We formulated the data reduction scheme and designed the Niobium bird experiment to verify the performance of the data reduction scheme experimentally with an actual SQUID magnetometer within the test loop. This paper reports the results from the first phase of the Niobium bird experiment, which used a commercially available SQUID magnetometer as its primary sensor, and adresses the issues they raised. The first phase resulted in a large, temperature-dependent bias drift in the insensitive design and a temperature regulation scheme.
Singular boundary method for global gravity field modelling
NASA Astrophysics Data System (ADS)
Cunderlik, Robert
2014-05-01
The singular boundary method (SBM) and method of fundamental solutions (MFS) are meshless boundary collocation techniques that use the fundamental solution of a governing partial differential equation (e.g. the Laplace equation) as their basis functions. They have been developed to avoid singular numerical integration as well as mesh generation in the traditional boundary element method (BEM). SBM have been proposed to overcome a main drawback of MFS - its controversial fictitious boundary outside the domain. The key idea of SBM is to introduce a concept of the origin intensity factors that isolate singularities of the fundamental solution and its derivatives using some appropriate regularization techniques. Consequently, the source points can be placed directly on the real boundary and coincide with the collocation nodes. In this study we deal with SBM applied for high-resolution global gravity field modelling. The first numerical experiment presents a numerical solution to the fixed gravimetric boundary value problem. The achieved results are compared with the numerical solutions obtained by MFS or the direct BEM indicating efficiency of all methods. In the second numerical experiments, SBM is used to derive the geopotential and its first derivatives from the Tzz components of the gravity disturbing tensor observed by the GOCE satellite mission. A determination of the origin intensity factors allows to evaluate the disturbing potential and gravity disturbances directly on the Earth's surface where the source points are located. To achieve high-resolution numerical solutions, the large-scale parallel computations are performed on the cluster with 1TB of the distributed memory and an iterative elimination of far zones' contributions is applied.
Cardiopulmonary Resuscitation in Lunar and Martian Gravity Fields
NASA Technical Reports Server (NTRS)
Sarkar, Subhajit
2004-01-01
Cardiopulmonary resuscitation is required training for all astronauts. No studies thus far have investigated how chest compressions may be affected in lunar and Martian gravities. Therefore a theoretical quantitative study was performed. The maximum downward force an unrestrained person can apply is mg N (g(sub Earth) = 9.78 ms(sup -2), g(sub moon) = 1.63 ms(sup -2), g(sub Mars) = 3.69 ms(sup -2). Tsitlik et a1 (Critical Care Medicine, 1983) described the human sternal elastic force-displacement relationship (compliance) by: F = betaD(sub s) + gammaD(sub s)(sup 2) (beta = 54.9 plus or minus 29.4 Ncm(sup -1) and gamma = 10.8 plus or minus 4.1 Ncm(sup -2)). Maximum forces in the 3 gravitational fields produced by 76 kg (US population mean), 41 kg and 93 kg (masses derived from the limits for astronaut height), produced solutions for compression depth using Tsitlik equations for chests of: mean compliance (beta = 54.9, gamma = 10.8), low compliance (beta = 84.3, gamma = 14.9) and high compliance (beta = 25.5, gamma = 6.7). The mass for minimum adequate adult compression, 3.8 cm (AHA guidelines), was also calculated. 76 kg compresses the mean compliance chest by: Earth, 6.1 cm, Mars, 3.2 cm, Moon, 1.7 cm. In lunar gravity, the high compliance chest is compressed only 3.2 cm by 93 kg, 120 kg being required for 3.8 cm. In Martian gravity, on the mean chest, 93 kg compresses 3.6 cm; 99 kg is required for 3.8 cm. On Mars, the high compliance chest is compressed 4.8 cm with 76 kg, 5.5 cm with 93 kg, with 52 kg required for 3.8 cm.
GRAIL - A Microwave Ranging Instrument to Map Out the Lunar Gravity Field
NASA Technical Reports Server (NTRS)
Enzer, Daphna G.; Wang, Rabi T.; Klipstein, William M.
2010-01-01
Gravity Recovery and Interior Laboratory, or GRAIL, is a NASA mission to map out the gravity field of the moon to an unprecedented level of detail. The instrument for this mission is based on GRACE (Gravity Recovery and Climate Experiment), an earth-orbiting mission currently mapping out the gravity field of the earth. This paper will describe the similarities and differences between these two instruments with a focus on the microwave ranging measurements used to determine the gravity parameters and the testbed built at Jet Propulsion Laboratory to demonstrate micron level ranging capability. The onboard ultrastable oscillator and RF instruments will be described and noise contributions discussed.
Cold Atom Interferometers Used in Space (CAIUS) for Measuring the Earth's Gravity Field
NASA Astrophysics Data System (ADS)
Carraz, Olivier; Siemes, Christian; Massotti, Luca; Haagmans, Roger; Silvestrin, Pierluigi
2016-08-01
The scope of the paper is to propose different concepts for future space gravity missions using Cold Atom Interferometers (CAI) for measuring the diagonal elements of the gravity gradient tensor, the spacecraft angular velocity and the spacecraft acceleration. The aim is to achieve better performance than previous space gravity missions due to a very low white noise spectral behaviour of the CAI instrument and a very high common mode rejection, with the ultimate goals of determining the fine structures of the gravity field with higher accuracy than GOCE and detecting time-variable signals in the gravity field.
GRAIL - A Microwave Ranging Instrument to Map Out the Lunar Gravity Field
NASA Technical Reports Server (NTRS)
Enzer, Daphna G.; Wang, Rabi T.; Klipstein, William M.
2010-01-01
Gravity Recovery and Interior Laboratory, or GRAIL, is a NASA mission to map out the gravity field of the moon to an unprecedented level of detail. The instrument for this mission is based on GRACE (Gravity Recovery and Climate Experiment), an earth-orbiting mission currently mapping out the gravity field of the earth. This paper will describe the similarities and differences between these two instruments with a focus on the microwave ranging measurements used to determine the gravity parameters and the testbed built at Jet Propulsion Laboratory to demonstrate micron level ranging capability. The onboard ultrastable oscillator and RF instruments will be described and noise contributions discussed.
NASA Astrophysics Data System (ADS)
Hegelich, B. Manuel
2011-10-01
A steady increase of on-target laser intensity with also increasing pulse contrast is leading to light-matter interactions of extreme laser fields with matter in new physics regimes which in turn enable a host of applications. A first example is the realization of interactions in the transperent-overdense regime (TOR), which is reached by interacting a highly relativistic (a0 >10), ultra high contrast laser pulse [1] with a solid density target, turning it transparent to the laser by the relativistic mass increase of the electrons. Thus, the interactions becomes volumetric, increasing the energy coupling from laser to plasma, facilitating a range of effects, including relativistic optics and pulse shaping, mono-energetic electron acceleration [3], highly efficient ion acceleration in the break-out afterburner regime [4], and the generation of relativistic and forward directed surface harmonics. Experiments at the LANL 130TW Trident laser facility successfully reached the TOR, and show relativistic pulse shaping beyond the Fourier limit, the acceleration of mono-energetic ~40 MeV electron bunches from solid targets, forward directed coherent relativistic high harmonic generation >1 keV Break-Out Afterburner (BOA) ion acceleration of Carbon to >1 GeV and Protons to >100 MeV. Carbon ions were accelerated with a conversion efficiency of >10% for ions >20 MeV and monoenergetic carbon ions with an energy spread of <20%, have been accelerated at up to ~500 MeV, demonstrating 3 out of 4 for key requirements for ion fast ignition. The shown results now approach or exceed the limits set by many applications from ICF diagnostics over ion fast ignition to medical physics. Furthermore, TOR targets traverse a wide range of HEDP parameter space during the interaction ranging from WDM conditions (e.g. brown dwarfs) to energy densities of ~1011 J/cm3 at peak, then dropping back to the underdense but extremely hot parameter range of gamma-ray bursts. Whereas today this regime can
Notes on Translational and Rotational Properties of Tensor Fields in Relativistic Quantum Mechanics
NASA Astrophysics Data System (ADS)
Dvoeglazov, V. V.
Recently, several discussions on the possible observability of 4-vector fields have been published in literature. Furthermore, several authors recently claimed existence of the helicity=0 fundamental field. We re-examine the theory of antisymmetric tensor fields and 4-vector potentials. We study the massless limits. In fact, a theoretical motivation for this venture is the old papers of Ogievetskiĭ and Polubarinov, Hayashi, and Kalb and Ramond. Ogievetskiĭ and Polubarinov proposed the concept of the notoph, whose helicity properties are complementary to those of the photon. We analyze the quantum field theory with taking into account mass dimensions of the notoph and the photon. It appears to be possible to describe both photon and notoph degrees of freedom on the basis of the modified Bargmann-Wigner formalism for the symmetric second-rank spinor. Next, we proceed to derive equations for the symmetric tensor of the second rank on the basis of the Bargmann-Wigner formalism in a straightforward way. The symmetric multispinor of the fourth rank is used. Due to serious problems with the interpretation of the results obtained on using the standard procedure we generalize it and obtain the spin-2 relativistic equations, which are consistent with the general relativity. Thus, in fact we deduced the gravitational field equations from relativistic quantum mechanics. The relations of this theory with the scalar-tensor theories of gravitation and f(R) are discussed. Particular attention has been paid to the correct definitions of the energy-momentum tensor and other Nöther currents in the electromagnetic theory, the relativistic theory of gravitation, the general relativity, and their generalizations. We estimate possible interactions, fermion-notoph, graviton-notoph, photon-notoph, and we conclude that they can probably be seen in experiments in the next few years.
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, K.-L.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.
2004-01-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at the comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. Additionally, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportional to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform: small-scale magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.
2004-01-01
Shock acceleration is an ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a 3-D relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. Simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. The non-linear fluctuation amplitudes of densities, currents, electric, and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. Additionally, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by the Weibel instability scale proportional to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields which contribute to the electron's (positron's) transverse deflection behind the jet head. This small scale magnetic field structure is appropriate to the generation
Particle Acceleration and Magnetic Field Generation in Electron-Positron Relativistic Shocks
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Hardee, P.; Richardson, G.; Preece, R.; Sol, H.; Fishman, G. J.
2005-01-01
Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., Buneman, Weibel, and other two-stream instabilities) created in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a three-dimensional relativistic electromagnetic particle (REMP) code, we have investigated particle acceleration associated with a relativistic electron-positron jet front propagating into an ambient electron-positron plasma with and without initial magnetic fields. We find small differences in the results for no ambient and modest ambient magnetic fields. New simulations show that the Weibel instability created in the collisionless shock front accelerates jet and ambient particles both perpendicular and parallel to the jet propagation direction. Furthermore, the nonlinear fluctuation amplitudes of densities, currents, and electric and magnetic fields in the electron-positron shock are larger than those found in the electron-ion shock studied in a previous paper at a comparable simulation time. This comes from the fact that both electrons and positrons contribute to generation of the Weibel instability. In addition, we have performed simulations with different electron skin depths. We find that growth times scale inversely with the plasma frequency, and the sizes of structures created by tine Weibel instability scale proportionally to the electron skin depth. This is the expected result and indicates that the simulations have sufficient grid resolution. While some Fermi acceleration may occur at the jet front, the majority of electron and positron acceleration takes place behind the jet front and cannot be characterized as Fermi acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying nonuniform, small-scale magnetic fields, which contribute to the electron s (positron s) transverse deflection behind the jet head. This
Next Generation Gravity Mission: a Step Forward in the Earth's Gravity Field Determination
NASA Astrophysics Data System (ADS)
Silvestrin, P.; Aguirre, M.; Massotti, L.; Cesare, S.
2009-04-01
This paper concerns with the "System Support to Laser Interferometry Tracking Technology Development for Gravity Field Monitoring" study of the European Space Agency, a mission study for monitoring the variations of Earth's gravity field at high resolution (up to harmonic degree 200) over a long time period (>5 years). The mission exploits the use of a heterodyne laser interferometer for the high-resolution measurement of the displacement between two satellites flying at low altitude (around 325 km). More in details, employing a formation of two co-orbiting satellites at 10 km relative distance, a resolution of about 1 nm rms is needed in the inter-satellite distance measurement, and the non gravitational accelerations must be measured with a resolution of about 10-10 m/s2 rms to achieve geoid height variation rate error equal to 0.1 mm/year at degree 200. Starting from the geophysical phenomena to be investigated, a detailed derivation of the mission requirements on the orbit, satellite formation and control, measurement instruments (laser interferometer and accelerometer) was performed using analytical models and numerical simulations, and the satellite GNC (Guidance, Navigation & Control) was approached through different techniques. A possible solution for the optical metrology suitable for the realization of a Next-Generation Gravimetric Mission has been identified, designed, breadboarded and tested to a level of detail sufficient to assess its feasibility. The main elements of this optical metrology are: 1) a Michelson-type heterodyne laser interferometer for measuring the distance variation between the retro-reflectors installed on two satellites. The innovative feature of the interferometer consists in chopping the laser beam with a frequency related to the satellite distance. This enables its proper functioning with a retro-reflector placed at large distances (around 10 km) from the source; 2) an optical device consisting of three small telescopes endowed
Geometric scalar theory of gravity
Novello, M.; Bittencourt, E.; Goulart, E.; Salim, J.M.; Toniato, J.D.; Moschella, U. E-mail: eduhsb@cbpf.br E-mail: egoulart@cbpf.br E-mail: toniato@cbpf.br
2013-06-01
We present a geometric scalar theory of gravity. Our proposal will be described using the ''background field method'' introduced by Gupta, Feynman, Deser and others as a field theory formulation of general relativity. We analyze previous criticisms against scalar gravity and show how the present proposal avoids these difficulties. This concerns not only the theoretical complaints but also those related to observations. In particular, we show that the widespread belief of the conjecture that the source of scalar gravity must be the trace of the energy-momentum tensor — which is one of the main difficulties to couple gravity with electromagnetic phenomenon in previous models — does not apply to our geometric scalar theory. From the very beginning this is not a special relativistic scalar gravity. The adjective ''geometric'' pinpoints its similarity with general relativity: this is a metric theory of gravity. Some consequences of this new scalar theory are explored.
NASA Astrophysics Data System (ADS)
Ivanov, A. N.; Wellenzohn, M.
2016-02-01
We analyze a spin precession of slow neutrons in the Einstein-Cartan gravity with torsion, chameleon and magnetic field. For the derivation of the Heisenberg equation of motion of the neutron spin we use the effective low-energy potential, derived by Ivanov and Wellenzohn [Phys. Rev. D 92, 125004 (2015)] for slow neutrons, coupled to gravitational, chameleon, and torsion fields to order 1 /m , where m is the neutron mass. In addition to these low-energy interactions we switch on the interaction of slow neutrons with a magnetic field. We show that to linear order approximation with respect to gravitational, chameleon, and torsion fields the Dirac Hamilton operator for fermions (neutrons), moving in spacetimes created by rotating coordinate systems, contains the anti-Hermitian operators of torsion-fermion (neutron) interactions, caused by torsion scalar and tensor space-space-time and time-space-space degrees of freedom. Such anti-Hermitian operators violate C P and T invariance. In the low-energy approximation the C P and T violating torsion-fermion (neutron) interactions appear only to order O (1 /m ). One may assume that in the rotating Universe and galaxies the obtained anti-Hermitian torsion-fermion interactions might be an origin of (i) violation of C P and T invariance in the Universe and (ii) of baryon asymmetry. We show that anti-Hermitian torsion-fermion interactions of relativistic fermions, violating C P and T invariance, (i) cannot be removed by nonunitary transformations of the Dirac fermion wave functions and (ii) are conformal invariant. According to general requirements of conformal invariance of massive particle theories in gravitational fields [see R. H. Dicke, Phys. Rev. 125, 2163 (1962) and A. J. Silenko, Phys. Rev. D 91, 065012 (2015)], conformal invariance of anti-Hermitian torsion-fermion interactions is valid only if the fermion mass is changed by a conformal factor.
Generation of magnetic fields in Einstein-aether gravity
NASA Astrophysics Data System (ADS)
Saga, Shohei; Shiraishi, Maresuke; Ichiki, Kiyotomo; Sugiyama, Naoshi
2013-05-01
Recently the lower bounds of the intergalactic magnetic fields 10-16˜10-20G are set by gamma-ray observations while it is unlikely to generate such large scale magnetic fields through astrophysical processes. It is known that large scale magnetic fields could be generated if there exist cosmological vector-mode perturbations in the primordial plasma. The vector mode, however, has only a decaying solution in general relativity if the plasma consists of perfect fluids. In order to investigate a possible mechanism of magnetogenesis in the primordial plasma, here we consider cosmological perturbations in the Einstein-aether gravity model, in which the aether field can act as a new source of vector metric perturbations. The vector metric perturbations induce the velocity difference between baryons and photons which then generate magnetic fields. This velocity difference arises from effects at the second order in the tight-coupling approximation. We estimate the angular power spectra of temperature and B-mode polarization of the cosmic microwave background anisotropies in this model and put a rough constraint on the aether field parameters from latest observations. We then estimate the power spectrum of associated magnetic fields around the recombination epoch within this limit. It is found that the spectrum has a characteristic peak at k=0.1hMpc-1, and at that scale the amplitude can be as large as B˜10-22G where the upper bound comes from cosmic microwave background temperature anisotropies. The magnetic fields with this amplitude can be seeds of large scale magnetic fields observed today if the sufficient dynamo mechanism takes place. Analytic interpretation for the power spectra is also given.
Self-accelerating massive gravity: Time for field fluctuations
NASA Astrophysics Data System (ADS)
Wyman, Mark; Hu, Wayne; Gratia, Pierre
2013-04-01
The ghost-free theory of massive gravity has exact solutions where the effective stress energy generated by the graviton mass term is a cosmological constant for any isotropic metric. Since they are exact, these solutions mimic a cosmological constant in the presence of any matter-induced isotropic metric perturbation. In the Stückelberg formulation, this stress energy is carried entirely by the spatial Stückelberg field. We show that any stress energy carried by fluctuations in the spatial field away from the exact solution always decays away in an expanding universe. However, the dynamics of the spatial Stückelberg field perturbation depend on the background temporal Stückelberg field, which is equivalent to the unitary gauge time coordinate. This dependence resolves an apparent conflict in the existing literature by showing that there is a special unitary time choice for which the field dynamics and energy density perturbations vanish identically. In general, the isotropic system has a single dynamical degree of freedom requiring two sets of initial data; however, only one of these initial data choices will affect the observable metric. Finally, we construct cosmological solutions with a well-defined perturbative initial value formulation and comment on alternate solutions that evolve to singularities.
Grassi, A; Grech, M; Amiranoff, F; Pegoraro, F; Macchi, A; Riconda, C
2017-02-01
The Weibel instability driven by two symmetric counterstreaming relativistic electron plasmas, also referred to as current-filamentation instability, is studied in a constant and uniform external magnetic field aligned with the plasma flows. Both the linear and nonlinear stages of the instability are investigated using analytical modeling and particle-in-cell simulations. While previous studies have already described the stabilizing effect of the magnetic field, we show here that the saturation stage is only weakly affected. The different mechanisms responsible for the saturation are discussed in detail in the relativistic cold fluid framework considering a single unstable mode. The application of an external field leads to a slight increase of the saturation level for large wavelengths, while it does not affect the small wavelengths. Multimode and temperature effects are then investigated. While at high temperature the saturation level is independent of the external magnetic field, at low but finite temperature the competition between different modes in the presence of an external magnetic field leads to a saturation level lower with respect to the unmagnetized case.
NASA Astrophysics Data System (ADS)
Grassi, A.; Grech, M.; Amiranoff, F.; Pegoraro, F.; Macchi, A.; Riconda, C.
2017-02-01
The Weibel instability driven by two symmetric counterstreaming relativistic electron plasmas, also referred to as current-filamentation instability, is studied in a constant and uniform external magnetic field aligned with the plasma flows. Both the linear and nonlinear stages of the instability are investigated using analytical modeling and particle-in-cell simulations. While previous studies have already described the stabilizing effect of the magnetic field, we show here that the saturation stage is only weakly affected. The different mechanisms responsible for the saturation are discussed in detail in the relativistic cold fluid framework considering a single unstable mode. The application of an external field leads to a slight increase of the saturation level for large wavelengths, while it does not affect the small wavelengths. Multimode and temperature effects are then investigated. While at high temperature the saturation level is independent of the external magnetic field, at low but finite temperature the competition between different modes in the presence of an external magnetic field leads to a saturation level lower with respect to the unmagnetized case.
Entropy production for a relativistic simple fluid in a weak electromagnetic field
NASA Astrophysics Data System (ADS)
García-Perciante, A. L.; Sandoval-Villalbazo, A.; Brun-Battistini, D.
2016-11-01
Thermal dissipation in plasmas includes a variety of effects, most of them arising from the fact that these gases are usually composed of at least two species. In the case of a mild temperature single component charged fluid kinetic theory indicates that the temperature gradient is the only source of vector-type dissipation. However, if the temperature increases to a point in which the molecule's velocities approach the speed of light, electrothermal dissipation is possible even for the single component charged gas. The modification to the structure of the entropy production introduced by this effect is established in order to address the second law of thermodynamics for such a system. The entropy balance equation is obtained from the relativistic Boltzmann equation and the vector contribution to the entropy production is calculated in terms of the thermodynamic forces and the electromagnetic field using Chapman-Enskog's expansion. It is shown that the structure is consistent with the constitutive equation previously reported, in which a thermoelectric effect was found for a single component relativistic fluid. This effect does not have a non-relativistic counterpart and presents no ambiguity regarding the frame chosen as the comoving frame, which is an issue in the mixture case.
Dark energy or modified gravity? An effective field theory approach
Bloomfield, Jolyon; Flanagan, Éanna É.; Park, Minjoon; Watson, Scott E-mail: eef3@cornell.edu E-mail: gswatson@syr.edu
2013-08-01
We take an Effective Field Theory (EFT) approach to unifying existing proposals for the origin of cosmic acceleration and its connection to cosmological observations. Building on earlier work where EFT methods were used with observations to constrain the background evolution, we extend this program to the level of the EFT of the cosmological perturbations — following the example from the EFT of Inflation. Within this framework, we construct the general theory around an assumed background which will typically be chosen to mimic ΛCDM, and identify the parameters of interest for constraining dark energy and modified gravity models with observations. We discuss the similarities to the EFT of Inflation, but we also identify a number of subtleties including the relationship between the scalar perturbations and the Goldstone boson of the spontaneously broken time translations. We present formulae that relate the parameters of the fundamental Lagrangian to the speed of sound, anisotropic shear stress, effective Newtonian constant, and Caldwell's varpi parameter, emphasizing the connection to observations. It is anticipated that this framework will be of use in constraining individual models, as well as for placing model-independent constraints on dark energy and modified gravity model building.
Performance of FFT methods in local gravity field modelling
NASA Technical Reports Server (NTRS)
Forsberg, Rene; Solheim, Dag
1989-01-01
Fast Fourier transform (FFT) methods provide a fast and efficient means of processing large amounts of gravity or geoid data in local gravity field modelling. The FFT methods, however, has a number of theoretical and practical limitations, especially the use of flat-earth approximation, and the requirements for gridded data. In spite of this the method often yields excellent results in practice when compared to other more rigorous (and computationally expensive) methods, such as least-squares collocation. The good performance of the FFT methods illustrate that the theoretical approximations are offset by the capability of taking into account more data in larger areas, especially important for geoid predictions. For best results good data gridding algorithms are essential. In practice truncated collocation approaches may be used. For large areas at high latitudes the gridding must be done using suitable map projections such as UTM, to avoid trivial errors caused by the meridian convergence. The FFT methods are compared to ground truth data in New Mexico (xi, eta from delta g), Scandinavia (N from delta g, the geoid fits to 15 cm over 2000 km), and areas of the Atlantic (delta g from satellite altimetry using Wiener filtering). In all cases the FFT methods yields results comparable or superior to other methods.
The Effect of Gravity Fields on Cellular Gene Expression
NASA Technical Reports Server (NTRS)
Hughes-Fulford, Millie
1999-01-01
Early theoretical analysis predicted that microgravity effects on the isolated cell would be minuscule at the subcellular level; however, these speculations have not proven true in the real world. Astronauts experience a significant bone and muscle loss in as little as 2 weeks of spaceflight and changes are seen at the cellular level soon after exposure to microgravity. Changes in biological systems may be primarily due to the lack of gravity and the resulting loss of mechanical stress on tissues and cells. Recent ground and flight studies examining the effects of gravity or mechanical stress on cells demonstrate marked changes in gene expression when relatively small changes in mechanical forces or gravity fields were made. Several immediate early genes (IEG) like c-fos and c-myc are induced by mechanical stimulation within minutes. In contrast, several investigators report that the absence of mechanical forces during space flight result in decreased sera response element (SRE) activity and attenuation of expression of IEGs such as c-fos, c-jun and cox-2 mRNAs. Clearly, these early changes in gene expression may have long term consequences on mechanically sensitive cells. In our early studies on STS-56, we reported four major changes in the osteoblast; 1) prostaglandin synthesis in flight, 2) changes in cellular morphology, 3) altered actin cytoskeleton and 4) reduced osteoblast growth after four days exposure to microgravity. Initially, it was believed that changes in fibronectin (FN) RNA, FN protein synthesis or subsequent FN matrix formation might account for the changes in cytoskeleton and/ or reduction of growth. However our recent studies on Biorack (STS-76, STS-81 and STS-84), using ground and in-flight 1-G controls, demonstrated that fibronectin synthesis and matrix formation were normal in microgravity. In addition, in our most recent Biorack paper, our laboratory has documented that relative protein synthesis and mRNA synthesis are not changed after 24
The Effect of Gravity Fields on Cellular Gene Expression
NASA Technical Reports Server (NTRS)
Hughes-Fulford, Millie
1999-01-01
Early theoretical analysis predicted that microgravity effects on the isolated cell would be minuscule at the subcellular level; however, these speculations have not proven true in the real world. Astronauts experience a significant bone and muscle loss in as little as 2 weeks of spaceflight and changes are seen at the cellular level soon after exposure to microgravity. Changes in biological systems may be primarily due to the lack of gravity and the resulting loss of mechanical stress on tissues and cells. Recent ground and flight studies examining the effects of gravity or mechanical stress on cells demonstrate marked changes in gene expression when relatively small changes in mechanical forces or gravity fields were made. Several immediate early genes (IEG) like c-fos and c-myc are induced by mechanical stimulation within minutes. In contrast, several investigators report that the absence of mechanical forces during space flight result in decreased sera response element (SRE) activity and attenuation of expression of IEGs such as c-fos, c-jun and cox-2 mRNAs. Clearly, these early changes in gene expression may have long term consequences on mechanically sensitive cells. In our early studies on STS-56, we reported four major changes in the osteoblast; 1) prostaglandin synthesis in flight, 2) changes in cellular morphology, 3) altered actin cytoskeleton and 4) reduced osteoblast growth after four days exposure to microgravity. Initially, it was believed that changes in fibronectin (FN) RNA, FN protein synthesis or subsequent FN matrix formation might account for the changes in cytoskeleton and/ or reduction of growth. However our recent studies on Biorack (STS-76, STS-81 and STS-84), using ground and in-flight 1-G controls, demonstrated that fibronectin synthesis and matrix formation were normal in microgravity. In addition, in our most recent Biorack paper, our laboratory has documented that relative protein synthesis and mRNA synthesis are not changed after 24
NASA Astrophysics Data System (ADS)
Gienko, Elena; Kanushin, Vadim; Tolstikov, Alexander; Karpik, Alexander; Kosarev, Nikolay; Ganagina, Irina
2016-04-01
In 2015 in the research on the grant of the Russian science Foundation No. 14-27-00068 was experimentally confirmed the possibility of measuring the gravity potential difference on relativistic frequency shift of the mobile hydrogen standard CH1-1006 (relative frequency instability of the order 10E-14). Hydrogen frequency standard CH1-1006 was calibrated in the system of secondary standard WET 1-19 (SNIIM, Novosibirsk, Russia) and transported to the place of experiment (a distance of 550 km, the Russian Federation, Republic of Altai), where it moved between the measured points at a distance of 35 km with a height difference of 850 meters. To synchronize spatially separated standard CH1-1006 and secondary standard WET 1-19 was applied the method "CommonView", based on the processing results of pseudorange phase GNSS measurements at the point of placement hours. Changing the frequency standard CH1-1006, measured in the system of secondary standard WET 1-19 and associated with his movement between points and the change of gravitational potential, was equal to 7.98•10E-14. Evaluation of root-mean-square two-sample frequency deviation of the standard at the time interval of the experiment was equal to the value of 7.27•10E-15. To control the results of the frequency determination of the gravity potential difference between the points were made high precision gravimetric measurements with an error of 6 MkGal and GNSS measurements for the coordinate determinations in ITRF2008 with an accuracy of 2-5 cm. The difference between the results of the frequency determination of the gravity potential difference with control data from GNSS and gravimetric measurements was estimated 16% of the total value that corresponds to the error of frequency measurement in the experiment. The possibility of using a single moveable frequency standard to determine the gravity potential difference at spaced points using the method of "CommonView", without the use of optical communications
NASA Astrophysics Data System (ADS)
Li, Wei; Liu, Yong-gui
2011-02-01
A modified magnetic field distribution in relativistic magnetron with diffraction output (MDO) for compact operation is proposed in this paper. The principle of how the modified magnetic field confines electrons drifting out of the interaction space is analyzed. The results of the particle-in-cell (PIC) simulations of the MDO with the modified magnetic field distribution show that the output power of the MDO is improved, and the long cylindrical waveguide used for collecting the drifting electrons can be omitted. The latter measure allows the horn antenna of the MDO to produce more focused energy with better directivity in the far field than it does with the long cylindrical waveguide. The MDO with the modified magnetic field distribution promises to be the real most compact narrow band high power microwave source.
Higher-Order Nonlocal Effects of a Relativistic Ponderomotive Force in High-Intensity Laser Fields
NASA Astrophysics Data System (ADS)
Iwata, Natsumi; Kishimoto, Yasuaki
2014-01-01
We have developed a new formula for a relativistic ponderomotive force of transversely localized laser fields based on the noncanonical Lie perturbation method by finding proper coordinates and gauges in the variational principle. The formula involves new terms represented by second and third spatial derivatives of the field amplitude, so that the ponderomotive force depends not only on the local field gradient, but also on the curvature and its variation. The formula is then applicable to a regime in which the conventional formula is hardly applied such that nonlocal and/or global extent of the field profile becomes important. The result can provide a theoretical basis for describing nonlinear laser-plasma interaction including such nonlocal effects, which is examined via particle-in-cell simulation of laser propagation in a plasma with a super Gaussian transverse field profile.
NASA Astrophysics Data System (ADS)
East, William E.
2017-07-01
We study the superradiant instability of massive vector fields, i.e. Proca fields, around spinning black holes in the test field limit. This is motivated by the possibility that observations of astrophysical black holes can probe the existence of ultralight bosons subject to this mechanism. By making use of time-domain simulations, we characterize the growth rate, frequency, spatial distribution, and other properties of the unstable modes, including in the regime where the black hole is rapidly spinning and the Compton wavelength of the Proca field is comparable to the black hole radius. We find that relativistic effects in this regime increase the range of Proca masses that are unstable, as well as the maximum instability rate. We also study the gravitational waves that can be sourced by such an instability, finding that they can be significantly stronger than in the massive scalar field case.
Pressure of Degenerate and Relativistic Electrons in a Superhigh Magnetic Field
NASA Astrophysics Data System (ADS)
Gao, Zhi Fu; Wang, Na; Peng, Qiu He; Li, Xiang Dong; Du, Yuan Jie
2013-11-01
Based on our previous work, we deduce a general formula for pressure of degenerate and relativistic electrons, Pe, which is suitable for superhigh magnetic fields, discuss the quantization of Landau levels of electrons, and consider the quantum electrodynamic (QED) effects on the equations of states (EOSs) for different matter systems. The main conclusions are as follows: Pe is related to the magnetic field B, matter density ρ, and electron fraction Ye; the stronger the magnetic field, the higher the electron pressure becomes; the high electron pressure could be caused by high Fermi energy of electrons in a superhigh magnetic field; compared with a common radio pulsar, a magnetar could be a more compact oblate spheroid-like deformed neutron star (NS) due to the anisotropic total pressure; and an increase in the maximum mass of a magnetar is expected because of the positive contribution of the magnetic field energy to the EOS of the star.
The interplanetary magnetic field associated with the propagation of solar relativistic particles
NASA Astrophysics Data System (ADS)
Masson, Sophie; Dasso, Sergio; Demoulin, Pascal
The origin and the propagation of relativistic solar particles (450 MeV-few GeV) in the inter-planetary medium remains a complex topic. These particles, detected at the Earth by neutron monitors (called Ground level enhancement, GLE), have been previously accelerated close to the Sun. Before being detected at the Earth, these relativistic particles have to travel along an interplanetary magnetic field (IMF) connecting the acceleration site and the Earth. Generally, the nominal Parker spiral (SP), is considered for ensuring the magnetic connection to the Earth. However, in most GLEs the IMF is highly disturbed, and the active regions (ARs) associated to the GLEs are not always located close to the footprint of the nominal Parker spiral. If it is not the nominal Parker spiral, which IMF connects the acceleration site and the Earth during the GLEs? A possible explanation of relativistic particles propagation under these circumstances are transient magnetic structures, travelling in the IMF as Interplanetary coronal mass ejections (ICMEs). In order to check this interpretation, we studied in detail the interplanetary medium in which 10 GLEs of the last solar cycle propagate. Using the magnetic field and the plasma parameter measurements (ACE/MAG and ACE/SWEPAM), we found widely different IMF configurations. Those included obvious cases of propagation in an ICME, as well as some cases consistent with a Parker Spiral. But, we also found cases correponding to the propagation of relativistic particles in a highly disturbed Parker like IMF. In an independant approach we applied the velocity dispersion method (VDA) to energetic protons measured by SoHO/ERNE and relativistic particles measured by the neutron monitor network. We determined the path length travelled by energetic particles. These lengths are fully consistent with the IMF shape determined previously. Thus, the length associated to particles propagating along the nominal Parker spiral is of the order of 1-1.2 AU
Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields
NASA Technical Reports Server (NTRS)
Nishikawa, K.-I.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Mizuno, Y.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; Hartmann, D. H.; Fishman, J. F.
2009-01-01
Plasma instabilities excited in collisionless shocks are responsible for particle acceleration. We have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic-like shock structure. In the leading shock, electron density increases by a factor of about 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. These magnetic fields contribute to the electron's transverse deflection behind the shock. The jitter'' radiation from deflected electrons in turbulent magnetic fields has different properties than synchrotron radiation, which is calculated in a uniform magnetic field. This jitter radiation may be important for understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets in general, and supernova remnants. New spectra based on simulations will be presented.
Greenwald, Jared; Satheeshkumar, V.H.; Wang, Anzhong E-mail: VHSatheeshkumar@baylor.edu
2010-12-01
We study spherically symmetric static spacetimes generally filled with an anisotropic fluid in the nonrelativistic general covariant theory of gravity. In particular, we find that the vacuum solutions are not unique, and can be expressed in terms of the U(1) gauge field A. When solar system tests are considered, severe constraints on A are obtained, which seemingly pick up the Schwarzschild solution uniquely. In contrast to other versions of the Horava-Lifshitz theory, non-singular static stars made of a perfect fluid without heat flow can be constructed, due to the coupling of the fluid with the gauge field. These include the solutions with a constant pressure. We also study the general junction conditions across the surface of a star. In general, the conditions allow the existence of a thin matter shell on the surface. When applying these conditions to the perfect fluid solutions with the vacuum ones as describing their external spacetimes, we find explicitly the matching conditions in terms of the parameters appearing in the solutions. Such matching is possible even without the presence of a thin matter shell.
Cosmology from group field theory formalism for quantum gravity.
Gielen, Steffen; Oriti, Daniele; Sindoni, Lorenzo
2013-07-19
We identify a class of condensate states in the group field theory (GFT) formulation of quantum gravity that can be interpreted as macroscopic homogeneous spatial geometries. We then extract the dynamics of such condensate states directly from the fundamental quantum GFT dynamics, following the procedure used in ordinary quantum fluids. The effective dynamics is a nonlinear and nonlocal extension of quantum cosmology. We also show that any GFT model with a kinetic term of Laplacian type gives rise, in a semiclassical (WKB) approximation and in the isotropic case, to a modified Friedmann equation. This is the first concrete, general procedure for extracting an effective cosmological dynamics directly from a fundamental theory of quantum geometry.
New space missions for mapping the Earth's gravity field
NASA Astrophysics Data System (ADS)
Balmino, Georges
The knowledge of the gravity field of the Earth and of an associated reference surface of altitudes (the geoid) is necessary for geodesy, for improving theories of the physics of the planet interior and for modeling the ocean circulation in absolute. This knowledge comes from several observing techniques but, although it benefited from the artificial satellite approach, it remains incomplete and erroneous in places. Within a reasonable future, a substantial improvement can only come from new space techniques. Thanks to the intense lobbying by the concerned geoscientists, the coming decade will see the advent of three techniques already proposed in the seventies and to be implemented by different space agencies; these are the CHAMP, GRACE and GOCE missions.
Gravity field, shape, and moment of inertia of Titan.
Iess, Luciano; Rappaport, Nicole J; Jacobson, Robert A; Racioppa, Paolo; Stevenson, David J; Tortora, Paolo; Armstrong, John W; Asmar, Sami W
2010-03-12
Precise radio tracking of the spacecraft Cassini has provided a determination of Titan's mass and gravity harmonics to degree 3. The quadrupole field is consistent with a hydrostatically relaxed body shaped by tidal and rotational effects. The inferred moment of inertia factor is about 0.34, implying incomplete differentiation, either in the sense of imperfect separation of rock from ice or a core in which a large amount of water remains chemically bound in silicates. The equilibrium figure is a triaxial ellipsoid whose semi-axes a, b, and c differ by 410 meters (a-c) and 103 meters (b-c). The nonhydrostatic geoid height variations (up to 19 meters) are small compared to the observed topographic anomalies of hundreds of meters, suggesting a high degree of compensation appropriate to a body that has warm ice at depth.
Mars Gravity Field: Combined Viking and Mariner 9 Results
NASA Technical Reports Server (NTRS)
Gapcynski, J. P.; Tolson, R. H.; Michael, W. H., Jr.
1977-01-01
A Martian gravity field of sixth degree and order has been determined from an analysis of a combination of Viking and Mariner 9 spacecraft Doppler tracking data. A short-arc technique utilizing approximately 4 hours of data centered at periapsis was used, and the data covered 16 arcs from Mariner 9 and 17 arcs from the Viking orbiters. The data were selected so as to obtain a uniform distribution of periapsis longitudes over the surface of Mars, and both S band and X band data were used where possible to eliminate charged particle effects. Inclusion of the Viking data arcs altered the Martian geoid features, as defined by previous short-arc analysis techniques of Mariner 9 data, by about 80 m in the southern hemisphere and about 140 m in the northern hemisphere.
NASA Astrophysics Data System (ADS)
Klaiber, Michael; Yakaboylu, Enderalp; Hatsagortsyan, Karen Z.
2013-02-01
We develop a relativistic Coulomb-corrected strong-field approximation (SFA) for the investigation of spin effects at above-threshold ionization in relativistically strong laser fields with highly charged hydrogenlike ions. The Coulomb-corrected SFA is based on the relativistic eikonal-Volkov wave function describing the ionized electron laser-driven continuum dynamics disturbed by the Coulomb field of the ionic core. The SFA in different partitions of the total Hamiltonian is considered. The formalism is applied for direct ionization of a hydrogenlike system in a strong linearly polarized laser field. The differential and total ionization rates are calculated analytically. The relativistic analog of the Perelomov-Popov-Terent'ev ionization rate is retrieved within the SFA technique. The physical relevance of the SFA in different partitions is discussed.
Observation of Self-Sustaining Relativistic Ionization Wave Launched by a Sheath Field
NASA Astrophysics Data System (ADS)
McCormick, M.; Arefiev, A. V.; Quevedo, H. J.; Bengtson, R. D.; Ditmire, T.
2014-01-01
We present experimental evidence supported by simulations of a relativistic ionization wave launched into a surrounding gas by the sheath field of a plasma filament with high energy electrons. Such a filament is created by irradiating a clustering gas jet with a short pulse laser (115 fs) at a peak intensity of 5×1017 W/cm2. We observe an ionization wave propagating radially through the gas for about 2 ps at 0.2-0.5 c after the laser has passed, doubling the initial radius of the filament. The gas is ionized by the sheath field, while the longevity of the wave is explained by a moving field structure that traps the high energy electrons near the boundary, maintaining a strong sheath field despite the significant expansion of the plasma.
Visualizing special relativity: the field of an electric dipole moving at relativistic speed
NASA Astrophysics Data System (ADS)
Smith, Glenn S.
2011-05-01
The electromagnetic field is determined for a time-varying electric dipole moving with a constant velocity that is parallel to its moment. Graphics are used to visualize this field in the rest frame of the dipole and in the laboratory frame when the dipole is moving at relativistic speed. Various phenomena from special relativity are clearly illustrated by these graphics and explained with simple calculations; these include the constancy of the speed of light in inertial frames, the Doppler effect, the headlight effect, and the concentration of field lines. In addition, the energy and linear momentum of the radiated field are determined and shown to satisfy the transformation and invariance required by special relativity.
Tidal deformability of neutron and hyperon stars within relativistic mean field equations of state
NASA Astrophysics Data System (ADS)
Kumar, Bharat; Biswal, S. K.; Patra, S. K.
2017-01-01
We systematically study the tidal deformability for neutron and hyperon stars using relativistic mean field equations of state (EOSs). The tidal effect plays an important role during the early part of the evolution of compact binaries. Although, the deformability associated with the EOSs has a small correction, it gives a clean gravitational wave signature in binary inspiral. These are characterized by various Love numbers kl(l =2 ,3 ,4 ), that depend on the EOS of a star for a given mass and radius. The tidal effect of star could be efficiently measured through an advanced LIGO detector from the final stages of an inspiraling binary neutron star merger.
Refractive and Relativistic Effects on ITER Low Field Side Reflectometer Design
Wang, G.; Rhodes, T. L.; Peebles, W. A.; Harvey, R. W.; Budny, R. V.
2010-06-01
The ITER low field side reflectometer faces some unique design challenges, among which are included the effect of relativistic electron temperatures and refraction of probing waves. This paper utilizes GENRAY, a 3- D ray tracing code, to investigate these effects. Using a simulated ITER operating scenario, characteristics of the reflected RF waves returning to the launch plane are quantified as a function of a range of design parameters, including antenna height, antenna size, and antenna radial position. Results for edge/SOL measurement with both O- and X-modes using proposed antennas are reported.
Giant halos in medium nuclei within modified relativistic mean field (MRMF) model
Nugraha, A. M. Sulaksono, A.; Sumaryada, T.
2016-04-19
The large number of neutrons in a region beyond a closed shell core indicates the presence of giant halos in nuclei. In this work, by using the Rotival method within a modified relativistic mean field (MRMF) model, we predict theoretically the formation of giant halos in Cr and Zr isotopes. The MRMF model is a modification of standard RMF model augmented with isoscalar and isovector tensor terms, isovector-isoscalar vector cross coupling term and electromagnetic exchange term for Coulomb interaction in local density approximation (LDA).
Antikaons in the extended relativistic mean-field models for neutron star
Gupta, Neha; Arumugam, P.
2012-10-20
We review the role of antikaons in recent versions of relativistic mean field models and focus on the interactions in which all parameters are obtained by fitting finite nuclear data and successfully applied to reproduce a variety of nuclear and neutron star (NS) properties. We show that the recently observed 1.97 solar mass NS can be explained in three ways: (i) A stiffer EoS with both antikaons (K{sup -}, K-bar {sup 0}), (ii) a relatively softer EoS with K{sup -} and (iii) a softer EoS with nucleon phase only.
Hadronic matter at finite temperature and density within an effective relativistic mean-field model
NASA Astrophysics Data System (ADS)
Lavagno, A.
2012-10-01
We study hot and dense hadronic matter by means of an effective relativistic mean-field model with the inclusion of the full octet of baryons, the Δ-isobar degrees of freedom and the lightest pseudoscalar and vector mesons. These last particles are considered by taking into account an effective chemical potential and an effective mass depending on the self-consistent interaction between baryons. The analysis is performed by requiring the Gibbs conditions on the global conservation of baryon number, electric charge fraction and zero net strangeness.
Evidence for creation of strong electromagnetic fields in relativistic heavy-ion collisions
NASA Astrophysics Data System (ADS)
Toneev, V.; Rogachevsky, O.; Voronyuk, V.
2016-08-01
It is proposed to identify the strong electric field created during relativistic collisions of asymmetric nuclei via observation of pseudorapidity and transverse-momentum distributions of hadrons with the same mass but opposite charges. The detailed calculation results for the directed flow within the Parton-Hadron String Dynamics model are given for Cu-Au interactions at the NICA collision energies of √{s_{NN}} = 9 and 5 GeV. The separation effect is observable at 9GeV as clearly as at 200 GeV.
Kalman Filtered Daily GRACE Gravity Field Solutions in Near Real-Time- First Steps
NASA Astrophysics Data System (ADS)
Kvas, Andreas; Mayer-Gurr, Torsten
2016-08-01
As part of the EGSIEM (European Gravity Service for Improved Emergency Management) project, a technology demonstrator for a near real-time (NRT) gravity field service will be established. In preparation of the operational phase, several aspects of the daily gravity field processing chain at Graz University of Technology have been inspected in order to improve the gravity field solutions and move towards NRT. The effect of these adaptions is investigated by comparison with post-processing and forward-only filtered solutions and evaluated using in-situ data.
Gravity field improvement using GPS data from Topex/Poseidon - A covariance analysis
NASA Technical Reports Server (NTRS)
Bertiger, Willy I.; Wu, J. T.; Wu, Sien C.
1990-01-01
A covariance analysis is performed using a realistic scenario for processing 10 days of GPS data, to obtain the expected improvement to the GEM-T2 gravity field. The gravity bin technique has been refined to compute the covariance matrix associated with the spherical harmonic gravity field. It is shown that the GPS data from one ten-day arc of Topex/Poseidon with no a priori can improve medium degree and order (3-26) sigmas for the parameters in the GEM-T2 gravity field by more than an order of magnitude.
Propagation of acoustic pulses in random gravity wave fields
NASA Astrophysics Data System (ADS)
Millet, Christophe; de La Camara, Alvaro; Lott, François
2015-11-01
A linear solution modeling the interaction between an incoming acoustic wave and a randomly perturbed atmosphere is developed, using the normal mode method. The wave mode structure is determined by a sound speed profile that is confining. The environmental uncertainty is described by a stochastic field obtained with a multiwave stochastic parameterization of gravity waves (GW). Using the propagating modes of the unperturbed atmosphere, the wave propagation problem is reduced to solving a system of ordinary differential equations. We focus on the asymptotic behavior of the transmitted waves in the weakly heterogeneous regime. In this regime, the coupling between the acoustic pulse and the randomly perturbed waveguides is weak and the propagation distance must be large enough for the wave to experience significant scattering. A general expression for the pressure far-field is derived in terms of saddle-point contributions. The saddle-points are obtained from a WKB approximation of the vertical eigenvalue problem. We present preliminary results that show how statistics of the transmitted signal are related to some eigenvalues and how an ``optimal'' GW field can trigger large deviations in the acoustic signals. The present model is used to explain the variability of infrasound signals.
Simulation of Relativistic Shocks and Associated Radiation from Turbulent Magnetic Fields
NASA Technical Reports Server (NTRS)
Nishikawa, K.; Niemiec, J.; Medvedev, M.; Zhang, B.; Hardee, P.; Mizuno, Y.; Nordlund, A.; Frederiksen, J.; Sol, H.; Pohl, M.; Oka, M.; Hartmann, D. H.; Fishman, J. F.
2009-01-01
Plasma instabilities (e.g., Buneman, Weibel and other two-stream instabilities) excited in collisionless shocks are responsible for particle (electron, positron, and ion) acceleration. Using a new 3-D relativistic particle-in-cell code, we have investigated the particle acceleration and shock structure associated with an unmagnetized relativistic electron-positron jet propagating into an unmagnetized electron-positron plasma. The simulation has been performed using a long simulation system in order to study the nonlinear stages of the Weibel instability, the particle acceleration mechanism, and the shock structure. Cold jet electrons are thermalized and slowed while the ambient electrons are swept up to create a partially developed hydrodynamic (HD) like shock structure. In the leading shock, electron density increases by a factor of <_ 3.5 in the simulation frame. Strong electromagnetic fields are generated in the trailing shock and provide an emission site. We discuss the possible implication of our simulation results within the AGN and GRB context. We have calculated the time evolution of the spectrum from two electrons propagating in a uniform parallel magnetic field to verify the technique. The same technique will be used to calculate radiation from accelerated electrons (positrons) in turbulent magnetic fields generated by Weibel instability.
Quantum speed limit for a relativistic electron in a uniform magnetic field
NASA Astrophysics Data System (ADS)
Villamizar, D. V.; Duzzioni, E. I.
2015-10-01
We analyze the influence of relativistic effects on the minimum evolution time between two orthogonal states of a quantum system. Defining the initial state as a homogeneous superposition between two Hamiltonian eigenstates of an electron in a uniform magnetic field, we obtain a relation between the minimum evolution time and the displacement of the mean radial position of the electron wave packet. The quantum speed limit time is calculated for an electron dynamics described by Dirac and Schrödinger-Pauli equations considering different parameters, such as the strength of magnetic field and the linear momentum of the electron in the axial direction. We highlight that when the electron undergoes a region with extremely strong magnetic field the relativistic and nonrelativistic dynamics differ substantially, so that the description given by the Schrödinger-Pauli equation enables the electron to travel faster than c , which is prohibited by Einstein's theory of relativity. This approach allows a connection between the abstract Hilbert space and the space-time coordinates, besides the identification of the most appropriate quantum dynamics used to describe the electron motion.
Certified randomness from a two-level system in a relativistic quantum field
NASA Astrophysics Data System (ADS)
Thinh, Le Phuc; Bancal, Jean-Daniel; Martín-Martínez, Eduardo
2016-08-01
Randomness is an indispensable resource in modern science and information technology. Fortunately, an experimentally simple procedure exists to generate randomness with well-characterized devices: measuring a quantum system in a basis complementary to its preparation. Towards realizing this goal one may consider using atoms or superconducting qubits, promising candidates for quantum information processing. However, their unavoidable interaction with the electromagnetic field affects their dynamics. At large time scales, this can result in decoherence. Smaller time scales in principle avoid this problem, but may not be well analyzed under the usual rotating wave and single mode approximation (RWA and SMA) which break the relativistic nature of quantum field theory. Here, we use a fully relativistic analysis to quantify the information that an adversary with access to the field could get on the result of an atomic measurement. Surprisingly, we find that the adversary's guessing probability is not minimized for atoms initially prepared in the ground state (an intuition derived from the RWA and SMA model).
Cremaschini, Claudio Stuchlík, Zdeněk; Tessarotto, Massimo
2014-03-15
The kinetic description of relativistic plasmas in the presence of time-varying and spatially non-uniform electromagnetic (EM) fields is a fundamental theoretical issue both in astrophysics and plasma physics. This refers, in particular, to the treatment of collisionless and strongly-magnetized plasmas in the presence of intense radiation sources. In this paper, the problem is investigated in the framework of a covariant gyrokinetic treatment for Vlasov–Maxwell equilibria. The existence of a new class of kinetic equilibria is pointed out, which occur for spatially-symmetric systems. These equilibria are shown to exist in the presence of non-uniform background EM fields and curved space-time. In the non-relativistic limit, this feature permits the determination of kinetic equilibria even for plasmas in which particle energy is not conserved due to the occurrence of explicitly time-dependent EM fields. Finally, absolute stability criteria are established which apply in the case of infinitesimal symmetric perturbations that can be either externally or internally produced.
Effects of magnetic field on plasma evolution in relativistic heavy-ion collisions
NASA Astrophysics Data System (ADS)
Das, Arpan; Dave, Shreyansh S.; Saumia, P. S.; Srivastava, Ajit M.
2017-09-01
Very strong magnetic fields can arise in noncentral heavy-ion collisions at ultrarelativistic energies, and may not decay quickly in a conducting plasma. We carry out relativistic magnetohydrodynamics (RMHD) simulations to study the effects of this magnetic field on the evolution of the plasma and on resulting flow fluctuations in the ideal RMHD limit. Our results show that the magnetic field leads to enhancement in elliptic flow for small impact parameters while it suppresses it for large impact parameters (which may provide a signal for the initial stage magnetic field). Interestingly, we find that magnetic field in localized regions can temporarily increase in time as evolving plasma energy density fluctuations lead to reorganization of magnetic flux. This can have important effects on the chiral magnetic effect. The magnetic field has nontrivial effects on the power spectrum of flow fluctuations. For the very strong magnetic field case, one sees a pattern of even-odd difference in the power spectrum of flow coefficients arising from reflection symmetry about the magnetic field direction if initial state fluctuations are not dominant. We discuss the situation of nontrivial magnetic field configurations arising from collision of deformed nuclei and show that it can lead to anomalous elliptic flow. Special (crossed body-body) configurations of deformed nuclei collisions can lead to the presence of a quadrupolar magnetic field, which can have very important effects on the rapidity dependence of transverse expansion (similar to beam focusing from quadrupole fields in accelerators).
Relativistic Two and Three-Particle Bound States in Scalar Quantum Field Theory.
NASA Astrophysics Data System (ADS)
di Leo, Leo
This thesis is concerned with the application of the variational method, within the Hamiltonian formalism of quantum field theory (QFT), to describe relativistic two and three particle states in scalar field theories. Two models are considered: scalar particles interacting through the exchange of scalar quanta, and the Higgs sector of the Minimal Standard Model. We derive relativistic particle-antiparticle wave equations for scalar particles, phi and |phi, interacting via a massive or massless scalar field, chi (the Wick-Cutkosky model), using simple Fock space ansatze. The variational method, within the Hamiltonian formalism of QFT, is used to derive equations with and without coupling of this quasi-bound phi|phi system to the chichi decay channel. The equations are then approximately decoupled to yield a relativistic momentum-space (Schrodinger-like) wave equation from which we determine bound-state energies numerically, perturbatively or variationally for various strengths of the coupling. Bound-state energies in the massless case are compared to the known ladder Bethe-Salpeter and light-cone solutions of this model. In the case of coupling to the decay channel, which is easily accomplished in the present formalism by expanding our Fock-space ansatz, the quasi-bound phi|phi states are seen to arise as resonances in the chichi scattering cross section. Numerical results are presented for the massive and massless chi case for various coupling strengths. The same variational method can be easily extended to derive relativistic three-particle wave equations for scalar particles phi,phi and |phi, interacting via a massive or massless scalar field, chi. In this case, the equations are obtained using a simple |phiphi|phi > +| phiphi|{phi}chi > ansatz. Approximate variational solutions (using product-type hydrogenic wave functions) of these equations are presented for various strengths of the coupling. The magnitude of the relativistic effects in the three
The use of satellites in gravity field determination and model adjustment
NASA Astrophysics Data System (ADS)
Visser, Petrus Nicolaas Anna Maria
1992-06-01
Methods to improve gravity field models of the Earth with available data from satellite observations are proposed and discussed. In principle, all types of satellite observations mentioned give information of the satellite orbit perturbations and in conjunction the Earth's gravity field, because the satellite orbits are affected most by the Earth's gravity field. Therefore, two subjects are addressed: representation forms of the gravity field of the Earth and the theory of satellite orbit perturbations. An analytical orbit perturbation theory is presented and shown to be sufficiently accurate for describing satellite orbit perturbations if certain conditions are fulfilled. Gravity field adjustment experiments using the analytical orbit perturbation theory are discussed using real satellite observations. These observations consisted of Seasat laser range measurements and crossover differences, and of Geosat altimeter measurements and crossover differences. A look into the future, particularly relating to the ARISTOTELES (Applications and Research Involving Space Techniques for the Observation of the Earth's field from Low Earth Orbit Spacecraft) mission, is given.
Three dimensional gravity field modelling of the Chicxulub impact crater
NASA Astrophysics Data System (ADS)
Hildebrand, A.; Millar, J.; Pilkington, M.; Lawton, D.
2003-04-01
Three dimensional gravity field modeling of the Chicxulub crater’s gravity field has refined our working structural model [e.g. 1, 2], and differs somewhat from the results of [3]. The 3D gravity model establishes that the central uplift is within reach of scientific drilling. The 3D gravity modeling method employed is that of [4]. Modelling results particularly reveal the crater’s central structures. The central uplift is a twin peaked structural high with vergence towards the southwest as previously indicated by 2D models [1] and consistent with seismic refraction results [5]. An arm extends towards the northeast, in contrast to the steep gradients that bound the central uplift to the southwest. The width of the uplift at 4 km depth is ~45 km broadening to ~60 km at 5 km depth consistent with 2D modeling. The central uplift rises into the melt sheet to ~2 km depth in contrast to the results of [4] where a top of ~4 km was obtained. However, as refraction results [5] independently constrain the central uplift width and the central uplift density contrast is limited (+0.11gcm-3 here), this is probably a realistic result. The shape of the modeled central uplift is radically different from that advocated by [6] who, based on seismic refraction results, proposed a cup-shaped central uplift (concave top) with a top at ~3 km depth, but of similar width. This interpretation requires substantial departure from density velocity proportionality, and we doubt that the central uplift has an annular top. The filling of the CDC, which we interpret as melt, is revealed as a body slightly elongated in a NE-SW sense with a size consistent with previous 2D model results. With the density contrast measured from the top of the melt sheet, its base lies near ~4 km is obtained consistent with the result of [4]. This depth is dependent upon the density contrast used (-0.15 g/cc), however, and all the mass deficiency need not be melt. The derived melt volume is 1.5 X 104 km3
Towards strong field tests of beyond Horndeski gravity theories
NASA Astrophysics Data System (ADS)
Sakstein, Jeremy; Babichev, Eugeny; Koyama, Kazuya; Langlois, David; Saito, Ryo
2017-03-01
Theories of gravity in the beyond Horndeski class encompass a wide range of scalar-tensor theories that will be tested on cosmological scales over the coming decade. In this work, we investigate the possibility of testing them in the strong field regime by looking at the properties of compact objects—neutron, hyperon, and quark stars—embedded in an asymptotically de Sitter space-time, for a specific subclass of theories. We extend previous works to include slow rotation and find a relation between the dimensionless moment of inertia (I ¯ =I c2/GNM3 ) and the compactness C =GNM /R c2 (an I ¯-C relation), independent of the equation of state, that is reminiscent of but distinct from the general relativity prediction. Several of our equations of state contain hyperons and free quarks, allowing us to revisit the hyperon puzzle. We find that the maximum mass of hyperon stars can be larger than 2 M⊙ for small values of the beyond Horndeski parameter, thus providing a resolution of the hyperon puzzle based on modified gravity. Moreover, stable quark stars exist when hyperonic stars are unstable, which means that the phase transition from hyperon to quark stars is predicted just as in general relativity (GR), albeit with larger quark star masses. Two important and potentially observable consequences of some of the theories we consider are the existence of neutron stars in a range of masses significantly higher than in GR and I ¯-C relations that differ from their GR counterparts. In the former case, we find objects that, if observed, could not be accounted for in GR because they violate the usual GR causality condition. We end by discussing several difficult technical issues that remain to be addressed in order to reach more realistic predictions that may be tested using gravitational wave searches or neutron star observations.
An Exact Solution of Einstein-Maxwell Gravity Coupled to a Scalar Field
NASA Technical Reports Server (NTRS)
Turyshev, S. G.
1995-01-01
The general solution to low-energy string theory representing static spherically symmetric solution of the Einstein-Maxwell gravity with a massless scalar field has been found. Some of the partial cases appear to coincide with known solutions to black holes, naked singularities, and gravity and electromagnetic fields.
An Exact Solution of Einstein-Maxwell Gravity Coupled to a Scalar Field
NASA Technical Reports Server (NTRS)
Turyshev, S. G.
1995-01-01
The general solution to low-energy string theory representing static spherically symmetric solution of the Einstein-Maxwell gravity with a massless scalar field has been found. Some of the partial cases appear to coincide with known solutions to black holes, naked singularities, and gravity and electromagnetic fields.
NASA Technical Reports Server (NTRS)
Nelson, Robert W.; Wasserman, Ira
1991-01-01
A rigorous discussion is presented of the classical motion of a relativistic electron in a magnetic field and the resulting electromagnetic radiation when radiation reaction is important. In particular, for an electron injected with initial energy gamma(0), a systematic perturbative solution to the Lorentz-Dirac equation of motion is developed for field strengths satisfying gamma(0) B much less than 6 x 10 to the 15th G. A particularly accurate solution to the electron orbital motion in this regime is found and it is demonstrated how lowest-order corrections can be calculated. It is shown that the total energy-loss rate corresponds to what would be found using the exact Larmor power formula without including radiation reaction. Provided that the particle energy and field strength satisfy the same contraint, it is explicitly demonstrated that the intuitive prescription for calculating the time-integrated radiation spectrum described above is correct.
Relativistic mean-field model with energy dependent self-energies
Antic, S.; Typel, S.
2015-02-24
Conventional relativistic mean-field theory is extended with the introduction of higher-order derivative couplings of nucleons with the meson fields. The Euler-Lagrange equations follow from the principle of stationary action. From invariance principles of the Lagrangian density the most general expressions for the conserved current and energy-momentum tensor are derived. The nucleon self-energies show the explicit dependence on the meson fields. They contain additional regulator functions which describe the energy dependence. The density dependence of meson-nucleon couplings causes the apperance of additional rearrangement contributions in the self-energies. The equation of state of infinite nuclear matter is obtained and the thermodynamical consistency of the model is demonstrated. This model is applied to the description of spherical, non-rotating stars in β-equilibrium. Stellar structure is calculated by solving the Tolman-Oppenheimer-Volkov (TOV) equations. The results for neutron stars are shown in terms of mass-radius relations.
Mars gravity field via the short data arcs
NASA Technical Reports Server (NTRS)
Sjogren, W. L.; Lorell, J.; Reinbold, S. J.; Wimberly, R. N.
1973-01-01
Short arc reduction of satellite Mars tracking data shows that: (1) There is one large gravity high covering the region of Nix Olympica and the three peaks to the east (about 110 deg longitude). It has an amplitude of 50 milligals at 2200-km altitude and implies a surface mass anomaly times greater than any on earth; (2) there are no large negative gravity anomalies comparable to the positive; and (3) the large 3000-km canyon seems to originate in a gravity high and end in a gravity low.
Ensemble prediction and intercomparison analysis of GRACE time-variable gravity field models
NASA Astrophysics Data System (ADS)
Sakumura, C.; Bettadpur, S.; Bruinsma, S.
2014-03-01
Precise measurements of the Earth's time-varying gravitational field from the NASA/Deutsches Zentrum für Luft- und Raumfahrt Gravity Recovery and Climate Experiment (GRACE) mission allow unprecedented tracking of the transport of mass across and underneath the surface of the Earth and give insight into secular, seasonal, and subseasonal variations in the global water supply. Several groups produce these estimates, and while the various gravity fields are similar, differences in processing strategies and tuning parameters result in solutions with regionally specific variations and error patterns. This study examined the spatial, temporal, and spectral variations between the different gravity field products and developed an ensemble gravity field solution from the products of four such analysis centers. The solutions were found to lie within a certain analysis scatter regardless of the local relative water height variation, and the ensemble model is clearly seen to reduce the noise in the gravity field solutions within the available scatter of the solutions.
Unification of gravity and quantum field theory from extended noncommutative geometry
NASA Astrophysics Data System (ADS)
Yu, Hefu; Ma, Bo-Qiang
2017-02-01
We make biframe and quaternion extensions on the noncommutative geometry, and construct the biframe spacetime for the unification of gravity and quantum field theory (QFT). The extended geometry distinguishes between the ordinary spacetime based on the frame bundle and an extra non-coordinate spacetime based on the biframe bundle constructed by our extensions. The ordinary spacetime frame is globally flat and plays the role as the spacetime frame in which the fields of the Standard Model are defined. The non-coordinate frame is locally flat and is the gravity spacetime frame. The field defined in both frames of such “flat” biframe spacetime can be quantized and plays the role as the gravity field which couples with all the fields to connect the gravity effect with the Standard Model. Thus, we provide a geometric paradigm in which gravity and QFT can be unified.
The delineation and interpretation of the earth's gravity field
NASA Technical Reports Server (NTRS)
Marsh, Bruce D.
1988-01-01
A series of fluid dynamical experiments in variable viscosity fluid have been made and are in progress to study: (1) the onset of small scale convection relative to lithosphere growth rate; (2) the influence of paired fracture zones in modulating the horizontal scale of small scale convection; (3) the influence of the mantle vertical viscosity structure on determing the mode of small scale convection; and (4) the 3-D and temporal evolution of flows beneath a high viscosity lid. These experiments extend and amplify the present experimental work that has produced small scale convection beneath a downward-moving solidification front. Rapid growth of a high viscosity lid stifles the early onset of convection such that convection only begins once the lithosphere is older than a certain minimum age. The interplay of this convection with both the structure of the lithosphere and mantle provide a fertile field of investigation into the origin of geoid, gravity, and topographic anomalies in the central Pacific. These highly correlated fields of intermediate wavelength (approximately 200 to 2000 km), but not the larger wavelengths. It is the ultimate, dynamic origin of this class of anomalies that is sought in this investigation.
Gravity capillary waves in fluid layers under normal electric fields.
Papageorgiou, Demetrios T; Petropoulos, Peter G; Vanden-Broeck, Jean-Marc
2005-11-01
We study the formation and dynamics of interfacial waves on a perfect dielectric ideal fluid layer of finite depth, wetting a solid wall, when the region above the fluid is hydrodynamically passive but has constant permittivity, for example, air. The wall is held at a constant electric potential and a second electrode having a different potential is placed parallel to the wall and infinitely far from it. In the unperturbed state the interface is flat and the normal horizontally uniform electric field is piecewise constant in the liquid and air. We derive a system of long wave nonlinear evolution equations valid for interfacial amplitudes as large as the unperturbed layer depth and which retain gravity, surface tension and electric field effects. It is shown that for given physical parameters there exists a critical value of the voltage potential difference between electrodes, below which the system is dispersive and above which a band of unstable waves is possible centered around a finite wavenumber. In the former case nonlinear traveling waves are calculated and their stability is studied, while in the latter case the instability leads to thinning of the layer with the interface touching down in finite time. A similarity solution of the second kind is found to be dominant near the singularity, and the scaling exponents are determined using analysis and computations.
Testing strong-field gravity with tidal Love numbers
NASA Astrophysics Data System (ADS)
Cardoso, Vitor; Franzin, Edgardo; Maselli, Andrea; Pani, Paolo; Raposo, Guilherme
2017-04-01
The tidal Love numbers (TLNs) encode the deformability of a self-gravitating object immersed in a tidal environment and depend significantly both on the object's internal structure and on the dynamics of the gravitational field. An intriguing result in classical general relativity is the vanishing of the TLNs of black holes. We extend this result in three ways, aiming at testing the nature of compact objects: (i) we compute the TLNs of exotic compact objects, including different families of boson stars, gravastars, wormholes, and other toy models for quantum corrections at the horizon scale. In the black-hole limit, we find a universal logarithmic dependence of the TLNs on the location of the surface. (ii) We compute the TLNs of black holes beyond vacuum general relativity, including Einstein-Maxwell, Brans-Dicke, and Chern-Simons gravity. (iii) We assess the ability of present and future gravitational-wave detectors to measure the TLNs of these objects, including the first analysis of TLNs with LISA. Both LIGO, ET, and LISA can impose interesting constraints on boson stars, while LISA is able to probe even extremely compact objects. We argue that the TLNs provide a smoking gun of new physics at the horizon scale and that future gravitational-wave measurements of the TLNs in a binary inspiral provide a novel way to test black holes and general relativity in the strong-field regime.
The Weak Field Limit of Higher Order Gravity
NASA Astrophysics Data System (ADS)
Stabile, Arturo
2008-09-01
The Higher Order Theories of Gravity - f(R, R_{alphabeta}R(alphabeta) ) - theory, where R is the Ricci scalar, R_{alphabeta} is the Ricci tensor and f is any analytic function - have recently attracted a lot of interest as alternative candidates to explain the observed cosmic acceleration, the flatness of the rotation curves of spiral galaxies and other relevant astrophysical phenomena. It is a crucial point testing these alternative theories in the so called weak field and newtonian limit of a f(R, R_{alphabeta}R(alphabeta) ) - theory. With this "perturbation technique" it is possible to find spherically symmetric solutions and compare them with the ones of General Relativity. On both approaches we found a modification of General Relativity: the behaviour of gravitational potential presents a modification Yukawa - like in the newtonian case and a massive propagation in the weak field case. When the modification of the theory is removed (i.e. f(R, R_{alphabeta}R(alphabeta) ) = R, Hilbert - Einstein lagrangian) we find the usual outcomes of General Relativity. Also the Noether symmetries technique has been investigated to find some time independent spherically symmetric solutions.
Relativistic ponderomotive Hamiltonian of a Dirac particle in a vacuum laser field
Ruiz, D. E.; Ellison, C. L.; Dodin, I. Y.
2015-12-16
Here, we report a point-particle ponderomotive model of a Dirac electron oscillating in a high-frequency field. Starting from the Dirac Lagrangian density, we derive a reduced phase-space Lagrangian that describes the relativistic time-averaged dynamics of such a particle in a geometrical-optics laser pulse propagating in vacuum. The pulse is allowed to have an arbitrarily large amplitude provided that radiation damping and pair production are negligible. The model captures the Bargmann-Michel-Telegdi (BMT) spin dynamics, the Stern-Gerlach spin-orbital coupling, the conventional ponderomotive forces, and the interaction with large-scale background fields (if any). Agreement with the BMT spin precession equation is shown numerically.more » The commonly known theory in which ponderomotive effects are incorporated in the particle effective mass is reproduced as a special case when the spin-orbital coupling is negligible. This model could be useful for studying laser-plasma interactions in relativistic spin-1/2 plasmas.« less
Relativistic ponderomotive Hamiltonian of a Dirac particle in a vacuum laser field
Ruiz, D. E.; Ellison, C. L.; Dodin, I. Y.
2015-12-16
Here, we report a point-particle ponderomotive model of a Dirac electron oscillating in a high-frequency field. Starting from the Dirac Lagrangian density, we derive a reduced phase-space Lagrangian that describes the relativistic time-averaged dynamics of such a particle in a geometrical-optics laser pulse propagating in vacuum. The pulse is allowed to have an arbitrarily large amplitude provided that radiation damping and pair production are negligible. The model captures the Bargmann-Michel-Telegdi (BMT) spin dynamics, the Stern-Gerlach spin-orbital coupling, the conventional ponderomotive forces, and the interaction with large-scale background fields (if any). Agreement with the BMT spin precession equation is shown numerically. The commonly known theory in which ponderomotive effects are incorporated in the particle effective mass is reproduced as a special case when the spin-orbital coupling is negligible. This model could be useful for studying laser-plasma interactions in relativistic spin-1/2 plasmas.
Clear and Measurable Signature of Modified Gravity in the Galaxy Velocity Field
NASA Astrophysics Data System (ADS)
Hellwing, Wojciech A.; Barreira, Alexandre; Frenk, Carlos S.; Li, Baojiu; Cole, Shaun
2014-06-01
The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution v12 are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion σ12(r) is very sensitive to the presence of modified gravity. Using a set of high-resolution N-body simulations, we compute the pairwise velocity distribution and its projected line-of-sight dispersion for a class of modified gravity theories: the chameleon f(R) gravity and Galileon gravity (cubic and quartic). The velocities of dark matter halos with a wide range of masses would exhibit deviations from general relativity at the (5-10)σ level. We examine strategies for detecting these deviations in galaxy redshift and peculiar velocity surveys. If detected, this signature would be a "smoking gun" for modified gravity.
Clear and measurable signature of modified gravity in the galaxy velocity field.
Hellwing, Wojciech A; Barreira, Alexandre; Frenk, Carlos S; Li, Baojiu; Cole, Shaun
2014-06-06
The velocity field of dark matter and galaxies reflects the continued action of gravity throughout cosmic history. We show that the low-order moments of the pairwise velocity distribution v_{12} are a powerful diagnostic of the laws of gravity on cosmological scales. In particular, the projected line-of-sight galaxy pairwise velocity dispersion σ_{12}(r) is very sensitive to the presence of modified gravity. Using a set of high-resolution N-body simulations, we compute the pairwise velocity distribution and its projected line-of-sight dispersion for a class of modified gravity theories: the chameleon f(R) gravity and Galileon gravity (cubic and quartic). The velocities of dark matter halos with a wide range of masses would exhibit deviations from general relativity at the (5-10)σ level. We examine strategies for detecting these deviations in galaxy redshift and peculiar velocity surveys. If detected, this signature would be a "smoking gun" for modified gravity.
Relativistic weak lensing from a fully non-linear cosmological density field
Thomas, D.B.; Bruni, M.; Wands, D. E-mail: marco.bruni@port.ac.uk
2015-09-01
In this paper we examine cosmological weak lensing on non-linear scales and show that there are Newtonian and relativistic contributions and that the latter can also be extracted from standard Newtonian simulations. We use the post-Friedmann formalism, a post-Newtonian type framework for cosmology, to derive the full weak-lensing deflection angle valid on non-linear scales for any metric theory of gravity. We show that the only contributing term that is quadratic in the first order deflection is the expected Born correction and lens-lens coupling term. We use this deflection angle to analyse the vector and tensor contributions to the E- and B- mode cosmic shear power spectra. In our approach, once the gravitational theory has been specified, the metric components are related to the matter content in a well-defined manner. Specifying General Relativity, we write down a complete set of equations for a GR+ΛCDM universe for computing all of the possible lensing terms from Newtonian N-body simulations. We illustrate this with the vector potential and show that, in a GR+ΛCDM universe, its contribution to the E-mode is negligible with respect to that of the conventional Newtonian scalar potential, even on non-linear scales. Thus, under the standard assumption that Newtonian N-body simulations give a good approximation of the matter dynamics, we show that the standard ray tracing approach gives a good description for a ΛCDM cosmology.
Moon Exploration from "apollo" Magnetic and Gravity Field Data
NASA Astrophysics Data System (ADS)
Kharitonov, Andrey
Recently, the great value is given to various researches of the Moon, as nearest nature satellite of the Earth, because there is preparation for forthcoming starts on the Moon of the American, European, Russian, Chinese, Indian new Orbiters and Landers. Designing of International Lu-nar bases is planned also. Therefore, in the near future the series of the questions connected with placing of International Lunar bases which coordinates substantially should to be connected with heterogeneity of the internal structure of the Moon can become especially interesting. If in the Moon it will be possible to find large congestions of water ice and those chemical elements which stocks in the Earth are limited this area of the Moon can become perspective for Inter-national Lunar bases. To solve a question of research of the deep structure of the Moon in the locations of International Lunar bases, competently, without excessive expenses for start new various under the form of the Lunar orbit of automatic space vehicles (polar, equatorial, inclined to the rotation axis) and their altitude of flight, which also not always were connected with investigation programs of measured fields (video observation, radio-frequency sounding, mag-netic, gravity), is possible if already from the available information of space vehicles APOLLO, SMART1, KAGUYA, LCROSS, LRO, CHANDRAYAAN-1, CHANG'E-1 it will be possible to analyse simultaneously some various fields, at different altitudes of measuring over the surface (20-300 km) of the Moon. The experimental data of the radial component magnetic field and gravity field the Moon measured at different altitudes, in its equatorial part have been analysed for the research of the deep structure of the Moon. This data has been received as a result of start of space vehicles -APOLLO-15 and APOLLO-16 (USA), and also the Russian space vehicles "LUNOHOD". Authors had been used the data of a magnetic field of the Moon at flight altitude 160, 100, 75, 30, 0 km
NASA Astrophysics Data System (ADS)
Bering, E. A.; Kokorowski, M.; Holzworth, R. H.; Sample, J. G.; McCarthy, M. P.; Smith, D. M.; Parks, G. K.; Millan, R. M.; Woodger, L.; Reddell, B. D.; Lay, E.; Bale, S. D.; Pulupa, M.; O'Brien, T. P.; Blake, J. B.; Lin, R. P.; Moraal, H.; Stoker, P.; Hughes, A. R.; Collier, A. B.
2005-05-01
The MINIS balloon campaign was successfully conducted in January 2005 to investigate relativistic electron loss mechanisms. Quantifying and understanding losses is an integral part of understanding the variability of relativistic electrons in the radiation belts. Balloon-based experiments directly measure precipitation and thus provide a method for quantifying losses, while the nearly stationary platform allows for the separation of temporal and spatial variations. A new class of precipitation event, characterized by extremely hard spectra, short durations, and complex temporal structure, occurring in the evening to midnight sector, was discovered by the INTERBOA balloon in 1996 and studied further by the MAXIS balloon in 2000. The MINIS campaign provided the first opportunities for multi-point measurements of electron precipitation up to MeV energies, including simultaneous measurements at different longitudes and at near-conjugate locations. Two balloons, each carrying an X-ray spectrometer for measuring the bremsstrahlung produced as electrons precipitate into the atmosphere, were launched from Churchill, Manitoba at 0850 UT on 21 January 2005 and 0140 UT on 25 January 2005. Four balloons, each carrying an X-ray spectrometer, a Z-axis search coil magnetometer, and a 3-axis electric field instrument providing DC electric field and VLF measurements in 3 frequency bands, were launched from the South African Antarctic Station (SANAE IV). The Southern launches took place at 1400 UT on 17 January, 1309 UT on 19 January, 2115 UT on 20 January, and 0950 UT on 24 January 2005. In this paper, we present the preliminary results from the MINIS South electric field instrumentation. We have good DC and VLF electric field data from all payloads, and the payload rotation mechanism worked in all four as well. The campaign began with two large solar flares. In the post-flare environment, some very magnetospherically active periods are included in our data, with strong and
Relativistic electron loss process by pitch angle scattering due to field curvature
NASA Astrophysics Data System (ADS)
Lee, J. J.; Parks, G. K.; Lee, E.; McCarthy, M. P.; Min, K.; Kim, H.; Park, J.; Hwang, J.
2006-12-01
Relativistic electron dropout (RED) events are characterized by fast electron flux decrease at the geostationary orbit. It is known that the main loss process is non adiabatic and more effective for the high energy particles. RED events generally start to occur at midnight sector and propagate to noon sector and are correlated with magnetic field stretching. We discuss this kind of event can be caused from pitch angle diffusion induced when the gyro radius of the electrons is comparable to the radius of curvature of the magnetic field and the magnetic moment is not conserved any more. While this process has been studied theoretically, the question is whether electron precipitation could be explained with this process for the real field configuration. This paper will show that this process can successfully explain the precipitation that occurred on June 14, 2004 observed by the low-altitude (680 km) polar orbiting Korean satellite, STSAT-1. In this precipitation event, the energy dispersion showed higher energy electron precipitation occurred at lower L values. This feature is a good indicator that precipitation was caused by the magnetic moment scattering in the geomagnetic tail. This interpretation is supported by the geosynchronous satellite GOES observations that showed significant magnetic field distortion occurred on the night side accompanying the electron flux depletion. Tsyganenko-01 model also shows the magnetic moment scattering could occur under the geomagnetic conditions existing at that time. We suggest the pitch angle scattering by field curvature violating the first adiabatic invariant as a possible candidate for loss mechanism of relativistic electrons in radiation belt.
A Schrödinger approach to Newton-Cartan and Hořava-Lifshitz gravities
NASA Astrophysics Data System (ADS)
Afshar, Hamid R.; Bergshoeff, Eric A.; Mehra, Aditya; Parekh, Pulastya; Rollier, Blaise
2016-04-01
We define a `non-relativistic conformal method', based on a Schrödinger algebra with critical exponent z = 2, as the non-relativistic version of the relativistic conformal method. An important ingredient of this method is the occurrence of a complex compensating scalar field that transforms under both scale and central charge transformations. We apply this non-relativistic method to derive the curved space Newton-Cartan gravity equations of motion with twistless torsion. Moreover, we reproduce z = 2 Hořava-Lifshitz gravity by classifying all possible Schrödinger invariant scalar field theories of a complex scalar up to second order in time derivatives.
NASA Astrophysics Data System (ADS)
Bast, Radovan; Thorvaldsen, Andreas J.; Ringholm, Magnus; Ruud, Kenneth
2009-02-01
We present the first analytic calculations of the second hyperpolarizability in a relativistic framework. The calculations are made possible by our recent developments of a response theory built on a quasienergy formalism, in which the basis set may be both time and perturbation dependent. The approach is formulated for an arbitrary self-consistent field state in the atomic orbital basis. The implementation consists of a stand-alone code that only requires the unperturbed density in the atomic orbital basis as input, as well as a linear response solver by which we can determine the perturbed density matrices to different orders, at each new order solving equations that have the same structure as the linear response equation. Using these features of our formalism, we extend in this paper our approach to the relativistic domain, utilizing both two- and four-component relativistic wave functions. We apply the formalism to the calculation of the electronic and pure vibrational contributions to the second hyperpolarizability tensor for the hydrogen halides. Our results demonstrate that relativistic effects can be substantial for frequency-dependent second hyperpolarizabilities. Due to changes in the pole structure when going to the relativistic domain, the relativistic corrections to the hyperpolarizabilities are not transferable between different optical processes, except for very low frequencies.
Patra, S. K.; Panda, R. N.; Arumugam, P.; Gupta, Raj K.
2009-12-15
We have calculated the total nuclear reaction cross sections of exotic nuclei in the framework of the Glauber model, using as inputs the standard relativistic mean field (RMF) densities and the densities obtained from the more recently developed effective-field-theory-motivated RMF (the E-RMF). Both light and heavy nuclei are taken as the representative targets, and the light neutron-rich nuclei as projectiles. We found the total nuclear reaction cross section to increase as a function of the mass number, for both the target and projectile nuclei. The differential nuclear elastic scattering cross sections are evaluated for some selected systems at various incident energies. We found a large dependence of the differential elastic scattering cross section on incident energy. Finally, we have applied the same formalism to calculate both the total nuclear reaction cross section and the differential nuclear elastic scattering cross section for the recently discussed superheavy nucleus with atomic number Z=122.
On slow flows of a weakly stratified relativistic fluid in a static gravitational field
NASA Astrophysics Data System (ADS)
Ruban, V. P.
2014-04-01
Simplified equations for slow flows of a weakly stratified (in entropy) fluid inside or near a massive astrophysical object have been derived from the variational formulation of ideal general relativistic hydrodynamics under the conditions that the gravitational field in the leading order is centrosymmetric and static and that the effect of a magnetic field is negligibly small. Internal waves and vortices in such systems are soft modes as compared to sound. This circumstance allows the formulation of a "soundproof" Hamiltonian model. This model is an analog of nonrelativistic hydrodynamic anelastic models, which are widely used in studies of internal waves and/or convection in spatially inhomogeneous compressible media in atmospheric physics, geophysics, and astrophysics.
NASA Astrophysics Data System (ADS)
Zhong, Yang; Yang, Chun-Bin; Cai, Xu; Feng, Sheng-Qin
2016-08-01
It has been proposed that electric fields may lead to chiral separation in quark-gluon plasma (QGP). This is called the chiral electric separation effect. The strong electromagnetic field and the QCD vacuum can both be completely produced in off-central nuclear-nuclear collision. We use the Woods-Saxon nucleon distribution to calculate the electric field distributions of off-central collisions. The chiral electric field spatial distribution at Relativistic Heavy-Ion Collider (RHIC) and Large Hadron Collider (LHC) energy regions are systematically studied in this paper. The dependence of the electric field produced by the thermal quark in the central position with different impact parameters on the proper time with different collision energies in the RHIC and LHC energy regions are studied in this paper. Supported by National Natural Science Foundation of China (11375069, 11435054, 11075061, 11221504) and Key Laboratory Foundation of Quark and Lepton Physics (Hua-Zhong Normal University)(QLPL2014P01)
NASA Astrophysics Data System (ADS)
Lin, M. C.; Chang, P. C.; Lu, P. S.; Verboncoeur, J. P.
2011-10-01
Influence of ion effects on a space charge limited field emission flow has been studied systematically, by employing both analytical and numerical approaches. In our model, the field emission of electrons is described by the Fowler-Nordheim equation. The cathode plasma and surface properties are considered within the framework of an effective work function approximation. Ionization effects at the anode as well as electron space-charge effects are described by Poisson's equation coupled with the energy conservation equation including the relativistic effects. The calculations are carried out self-consistently to yield the steady states of the bipolar flow. The electric field on the cathode surface is found to be saturated due to space charge effects and is determined by the effective work function approximately. In addition, the upstream ion current bas been treated as a tuning parameter. It is found that the field emission currents in the presence of saturated ion currents can be enhanced to be nearly 1.8, 1.5, and 1.4 times of the cases with no upstream ion current in non-relativistic, intermediate, and ultra-relativistic regimes, respectively. The solutions have also been verified using 1D PIC simulations, as implemented in the OOPD1 code developed by PTSG of UC Berkeley. Work supported by the National Science Council, Taiwan, R.O.C. under Grant No. NSC 96-2112-M-030-004-MY3, National Center for Theoretical Sciences, and National Center for High-Performance Computing, Taiwan, ROC which provides the computing resources.
Killing vector fields in three dimensions: a method to solve massive gravity field equations
NASA Astrophysics Data System (ADS)
Gürses, Metin
2010-10-01
Killing vector fields in three dimensions play an important role in the construction of the related spacetime geometry. In this work we show that when a three-dimensional geometry admits a Killing vector field then the Ricci tensor of the geometry is determined in terms of the Killing vector field and its scalars. In this way we can generate all products and covariant derivatives at any order of the Ricci tensor. Using this property we give ways to solve the field equations of topologically massive gravity (TMG) and new massive gravity (NMG) introduced recently. In particular when the scalars of the Killing vector field (timelike, spacelike and null cases) are constants then all three-dimensional symmetric tensors of the geometry, the Ricci and Einstein tensors, their covariant derivatives at all orders, and their products of all orders are completely determined by the Killing vector field and the metric. Hence, the corresponding three-dimensional metrics are strong candidates for solving all higher derivative gravitational field equations in three dimensions.
Simulations of ion acceleration at non-relativistic shocks. II. Magnetic field amplification
Caprioli, D.; Spitkovsky, A.
2014-10-10
We use large hybrid simulations to study ion acceleration and generation of magnetic turbulence due to the streaming of particles that are self-consistently accelerated at non-relativistic shocks. When acceleration is efficient, we find that the upstream magnetic field is significantly amplified. The total amplification factor is larger than 10 for shocks with Alfvénic Mach number M = 100, and scales with the square root of M. The spectral energy density of excited magnetic turbulence is determined by the energy distribution of accelerated particles, and for moderately strong shocks (M ≲ 30) agrees well with the prediction of resonant streaming instability, in the framework of quasilinear theory of diffusive shock acceleration. For M ≳ 30, instead, Bell's non-resonant hybrid (NRH) instability is predicted and found to grow faster than resonant instability. NRH modes are excited far upstream by escaping particles, and initially grow without disrupting the current, their typical wavelengths being much shorter than the current ions' gyroradii. Then, in the nonlinear stage, most unstable modes migrate to larger and larger wavelengths, eventually becoming resonant in wavelength with the driving ions, which start diffuse. Ahead of strong shocks we distinguish two regions, separated by the free-escape boundary: the far upstream, where field amplification is provided by the current of escaping ions via NRH instability, and the shock precursor, where energetic particles are effectively magnetized, and field amplification is provided by the current in diffusing ions. The presented scalings of magnetic field amplification enable the inclusion of self-consistent microphysics into phenomenological models of ion acceleration at non-relativistic shocks.
On the theory of magnetic field generation by relativistically strong laser radiation
Berezhiani, V.I.; Shatashvili, N.L.; Mahajan, S.M. |
1996-07-01
The authors consider the interaction of subpicosecond relativistically strong short laser pulses with an underdense cold unmagnetized electron plasma. It is shown that the strong plasma inhomogeneity caused by laser pulses results in the generation of a low frequency (quasistatic) magnetic field. Since the electron density distribution is determined completely by the pump wave intensity, the generated magnetic field is negligibly small for nonrelativistic laser pulses but increases rapidly in the ultrarelativistic case. Due to the possibility of electron cavitation (complete expulsion of electrons from the central region) for narrow and intense beams, the increase in the generated magnetic field slows down as the beam intensity is increased. The structure of the magnetic field closely resembles that of the field produced by a solenoid; the field is maximum and uniform in the cavitation region, then it falls, changes polarity and vanishes. In extremely dense plasmas, highly intense laser pulses in the self-channeling regime can generate magnetic fields {approximately} 100 Mg and greater.
Recent results on modelling the spatial and temporal structure of the Earth's gravity field.
Moore, P; Zhang, Q; Alothman, A
2006-04-15
The Earth's gravity field plays a central role in sea-level change. In the simplest application a precise gravity field will enable oceanographers to capitalize fully on the altimetric datasets collected over the past decade or more by providing a geoid from which absolute sea-level topography can be recovered. However, the concept of a static gravity field is now redundant as we can observe temporal variability in the geoid due to mass redistribution in or on the total Earth system. Temporal variability, associated with interactions between the land, oceans and atmosphere, can be investigated through mass redistributions with, for example, flow of water from the land being balanced by an increase in ocean mass. Furthermore, as ocean transport is an important contributor to the mass redistribution the time varying gravity field can also be used to validate Global Ocean Circulation models. This paper will review the recent history of static and temporal gravity field recovery, from the 1980s to the present day. In particular, mention will be made of the role of satellite laser ranging and other space tracking techniques, satellite altimetry and in situ gravity which formed the basis of gravity field determination until the last few years. With the launch of Challenging Microsatellite Payload and Gravity and Circulation Experiment (GRACE) our knowledge of the spatial distribution of the Earth's gravity field is taking a leap forward. Furthermore, GRACE is now providing insight into temporal variability through 'monthly' gravity field solutions. Prior to this data we relied on satellite tracking, Global Positioning System and geophysical models to give us insight into the temporal variability. We will consider results from these methodologies and compare them to preliminary results from the GRACE mission.
Periodic orbits around areostationary points in the Martian gravity field
NASA Astrophysics Data System (ADS)
Liu, Xiao-Dong; Baoyin, Hexi; Ma, Xing-Rui
2012-05-01
This study investigates the problem of areostationary orbits around Mars in three-dimensional space. Areostationary orbits are expected to be used to establish a future telecommunication network for the exploration of Mars. However, no artificial satellites have been placed in these orbits thus far. The characteristics of the Martian gravity field are presented, and areostationary points and their linear stability are calculated. By taking linearized solutions in the planar case as the initial guesses and utilizing the Levenberg-Marquardt method, families of periodic orbits around areostationary points are shown to exist. Short-period orbits and long-period orbits are found around linearly stable areostationary points, but only short-period orbits are found around unstable areostationary points. Vertical periodic orbits around both linearly stable and unstable areostationary points are also examined. Satellites in these periodic orbits could depart from areostationary points by a few degrees in longitude, which would facilitate observation of the Martian topography. Based on the eigenvalues of the monodromy matrix, the evolution of the stability index of periodic orbits is determined. Finally, heteroclinic orbits connecting the two unstable areostationary points are found, providing the possibility for orbital transfer with minimal energy consumption.
The Gravity Field and Interior Structure of Enceladus
NASA Astrophysics Data System (ADS)
Iess, L.; Stevenson, D. J.; Parisi, M.; Hemingway, D.; Jacobson, R. A.; Lunine, J. I.; Nimmo, F.; Armstrong, J. W.; Asmar, S. W.; Ducci, M.; Tortora, P.
2014-04-01
The small and active Saturnian moon Enceladus is one of the primary targets of the Cassini mission. We determined the quadrupole gravity field of Enceladus and its hemispherical asymmetry using Doppler data from three spacecraft flybys. Our results indicate the presence of a negative mass anomaly in the south-polar region, largely compensated by a positive subsurface anomaly compatible with the presence of a regional subsurface sea at depths of 30 to 40 kilometers and extending up to south latitudes of about 50°. The estimated values for the largest quadrupole harmonic coefficients (106J2 = 5435.2 ± 34.9, 106C22 = 1549.8 ± 15.6, 1σ) and their ratio (J2/C22 = 3.51 ± 0.05) indicate that the body deviates mildly from hydrostatic equilibrium. The moment of inertia is around 0.335MR2, where M is the mass and R is the radius, suggesting a differentiated body with a low-density core.
The gravity field and interior structure of Enceladus.
Iess, L; Stevenson, D J; Parisi, M; Hemingway, D; Jacobson, R A; Lunine, J I; Nimmo, F; Armstrong, J W; Asmar, S W; Ducci, M; Tortora, P
2014-04-04
The small and active Saturnian moon Enceladus is one of the primary targets of the Cassini mission. We determined the quadrupole gravity field of Enceladus and its hemispherical asymmetry using Doppler data from three spacecraft flybys. Our results indicate the presence of a negative mass anomaly in the south-polar region, largely compensated by a positive subsurface anomaly compatible with the presence of a regional subsurface sea at depths of 30 to 40 kilometers and extending up to south latitudes of about 50°. The estimated values for the largest quadrupole harmonic coefficients (10(6)J2 = 5435.2 ± 34.9, 10(6)C22 = 1549.8 ± 15.6, 1σ) and their ratio (J2/C22 = 3.51 ± 0.05) indicate that the body deviates mildly from hydrostatic equilibrium. The moment of inertia is around 0.335MR(2), where M is the mass and R is the radius, suggesting a differentiated body with a low-density core.
NASA Astrophysics Data System (ADS)
Piñeiro Orioli, Asier; Boguslavski, Kirill; Berges, Jürgen
2015-07-01
We investigate universal behavior of isolated many-body systems far from equilibrium, which is relevant for a wide range of applications from ultracold quantum gases to high-energy particle physics. The universality is based on the existence of nonthermal fixed points, which represent nonequilibrium attractor solutions with self-similar scaling behavior. The corresponding dynamic universality classes turn out to be remarkably large, encompassing both relativistic as well as nonrelativistic quantum and classical systems. For the examples of nonrelativistic (Gross-Pitaevskii) and relativistic scalar field theory with quartic self-interactions, we demonstrate that infrared scaling exponents as well as scaling functions agree. We perform two independent nonperturbative calculations, first by using classical-statistical lattice simulation techniques and second by applying a vertex-resummed kinetic theory. The latter extends kinetic descriptions to the nonperturbative regime of overoccupied modes. Our results open new perspectives to learn from experiments with cold atoms aspects about the dynamics during the early stages of our universe.
Takahashi, Hiroyuki R.; Ohsuga, Ken
2013-08-01
We develop a numerical scheme for solving fully special relativistic, resistive radiation magnetohydrodynamics. Our code guarantees conservation of total mass, momentum, and energy. The radiation energy density and the radiation flux are consistently updated using the M-1 closure method, which can resolve an anisotropic radiation field, in contrast to the Eddington approximation, as well as the flux-limited diffusion approximation. For the resistive part, we adopt a simple form of Ohm's law. The advection terms are explicitly solved with an approximate Riemann solver, mainly the Harten-Lax-van Leer scheme; the HLLC and HLLD schemes are also solved for some tests. The source terms, which describe the gas-radiation interaction and the magnetic energy dissipation, are implicitly integrated, relaxing the Courant-Friedrichs-Lewy condition even in an optically thick regime or a large magnetic Reynolds number regime. Although we need to invert 4 Multiplication-Sign 4 matrices (for the gas-radiation interaction) and 3 Multiplication-Sign 3 matrices (for the magnetic energy dissipation) at each grid point for implicit integration, they are obtained analytically without preventing massive parallel computing. We show that our code gives reasonable outcomes in numerical tests for ideal magnetohydrodynamics, propagating radiation, and radiation hydrodynamics. We also applied our resistive code to the relativistic Petschek-type magnetic reconnection, revealing the reduction of the reconnection rate via radiation drag.
The delineation and interpretation of the earth's gravity field
NASA Technical Reports Server (NTRS)
Marsh, Bruce D.
1989-01-01
In an attempt to understand the mechanical interaction of a growing lithosphere containing fracture zones with small and large scale mantle convection, which gives rise to geoid anomalies in oceanic regions, a series of fluid dynamical experiments is in progress to investigate: (1) the influence of lithosphere structure, fluid depth and viscosity field on the onset, scale, and evolution of sublithospheric convection; (2) the role of this convection in determining the rate of growth of lithosphere, especially in light of the flattening of the lithosphere bathymetry and heat flow at late times; and (3) combining the results of both numerical and laboratory experiments to decide the dominate factors in producing geoid anomalies in oceanic regions through the thermo-mechanical interaction of the lithosphere and subjacent mantle. The clear existence of small scale convection associated with a downward propagating solidification front (i.e., the lithosphere) and a larger scale flow associated with a discontinuous upward heat flux (i.e., a fracture zone) has been shown. The flows exist simultaneously and each may have a significant role in deciding the thermal evolution of the lithosphere and in understanding the relation of shallow mantle convection to deep mantle convection. This overall process is reflected in the geoid, gravity, and topographic anomalies in the north-central Pacific. These highly correlated fields of intermediate wavelength (approx. 200 to 2000 km) show isostatic compensation by a thin lithosphere for shorter (less than or equal to approx. 500 km), but not the longer, wavelengths. The ultimate, dynamic origin of this class of anomalies is being investigated.
The mass, gravity field, and ephemeris of Mercury
NASA Technical Reports Server (NTRS)
Anderson, John D.; Esposito, Pasquale B.; Lau, Eunice L.; Trager, Gayle B.; Colombo, Giuseppe
1987-01-01
In the present gravity analysis of Mariner 10/Deep Space Network radio Doppler and range data for Mercury encounters in March 1974 and March 1975, a combined least-squares fit to the Doppler data has determined two second-degree gravity harmonics that are referred to a 2439-km equatorial radius. It is noted that the 1-sigma error limits on the gravity results encompass the possibility that harmonics other than J2 and C22 significantly differ from zero. The Deep Space Network radio range data obtained with Mariner 10 are primarily applicable to such improvements of Mercury's ephemeris as the more precise determination of perihelion precession.
Gravity Field Recovery from the Cartwheel Formation by the Semi-analytical Approach
NASA Astrophysics Data System (ADS)
Li, Huishu; Reubelt, Tilo; Antoni, Markus; Sneeuw, Nico; Zhong, Min; Zhou, Zebing
2016-04-01
Past and current gravimetric satellite missions have contributed drastically to our knowledge of the Earth's gravity field. Nevertheless, several geoscience disciplines push for even higher requirements on accuracy, homogeneity and time- and space-resolution of the Earth's gravity field. Apart from better instruments or new observables, alternative satellite formations could improve the signal and error structure. With respect to other methods, one significant advantage of the semi-analytical approach is its effective pre-mission error assessment for gravity field missions. The semi-analytical approach builds a linear analytical relationship between the Fourier spectrum of the observables and the spherical harmonic spectrum of the gravity field. The spectral link between observables and gravity field parameters is given by the transfer coefficients, which constitutes the observation model. In connection with a stochastic model, it can be used for pre-mission error assessment of gravity field mission. The cartwheel formation is formed by two satellites on elliptic orbits in the same plane. The time dependent ranging will be considered in the transfer coefficients via convolution including the series expansion of the eccentricity functions. The transfer coefficients are applied to assess the error patterns, which are caused by different orientation of the cartwheel for range-rate and range acceleration. This work will present the isotropy and magnitude of the formal errors of the gravity field coefficients, for different orientations of the cartwheel.
GRAIL gravity field determination using the Celestial Mechanics Approach - status report
NASA Astrophysics Data System (ADS)
Bertone, S.; Arnold, D.; Jäggi, A.; Beutler, G.; Mervart, L.
2015-10-01
The NASA mission GRAIL (Gravity Recovery And Interior Laboratory [1]) inherits its concept from the GRACE (Gravity Recovery And Climate Experiment)mission to determine the gravity field of the Moon. The use of inter-satellite Ka-band range-rate (KBRR) observations enables data aquisition even when the spacecraft are not tracked from the Earth [2]. The data allows for a highly accurate estimation of the lunar gravity field on both sides of the Moon, which is crucial to improve the understanding of its internal structure and thermal evolution. In this presentation we dis- cuss our latest GRAIL-based lunar gravity fields generated with the Celestial Mechanics Approach using the Bernese Software.
The Earth's gravity field from satellite geodesy - a 30 year adventure.
NASA Astrophysics Data System (ADS)
Rapp, R. H.
1991-12-01
The first information on the Earth's gravitational field from artificial satellite observations was published in 1958. The next years have seen a dramatic improvement in the resolution and accuracy of the series representation of the Earth's gravity field. The improvements have taken place slowly taking advantage of improved measurement accuracy and the increasing number of satellites. The proposed ARISTOTELES mission would provide the opportunity to take a significant leap in improving our knowledge of the Earth's gravity field.
Chiba, Takeshi; Yamaguchi, Masahide E-mail: gucci@phys.aoyama.ac.jp
2009-01-15
As an extension of our previous study, we derive slow-roll conditions for multiple scalar fields which are non-minimally coupled with gravity and for generalized gravity theories of the form f({phi}, R). We provide simple formulae of the spectral indices of scalar/tensor perturbations in terms of the slow-roll parameters.
Revision of geodetic parameters. [determination of earth's gravity field with laser data
NASA Technical Reports Server (NTRS)
Gaposchkin, E. M.; Williamson, M. R.
1975-01-01
Laser data from nine satellites and 12 stations are combined with surface-gravity data to obtain spherical harmonics representing the geopotential complete through degree and order 18. This laser-data-only solution provides a reasonable improvement to the gravity field.
A 10 km-resolution synthetic Venus gravity field model based on topography
NASA Astrophysics Data System (ADS)
Li, Fei; Yan, Jianguo; Xu, Luyuan; Jin, Shuanggen; Rodriguez, J. Alexis P.; Dohm, James H.
2015-02-01
A high resolution gravity field model is extremely important in the exploration of Venus. In this paper, we present a 3-dimensional Venus gravity field VGM2014 constructed by using the latest gravity and topography models, residual terrain model (RTM) and the Airy-Heiskanen isostatic compensation model. The VGM2014 is the first 10 km scale Venus gravity field model; the final results are representations of the 3-dimensional surface gravity accelerations and gravity disturbances for Venus. We found that the optimal global compensation depth of Venus is about 60 km, and the crustal density is potentially less than the commonly accepted value of 2700-2900 kg m-3. This model will be potentially beneficial for the precise orbit determination and landing navigation of spacecraft around Venus, and may be utilized as a priori model for Venus gravity field simulation and inversion studies. The VGM2014 does not incorporate direct gravity information beyond degree 70 and it is not recommended for small-scale geophysical interpretation.
Gravity fields of the terrestrial planets - Long-wavelength anomalies and tectonics
NASA Technical Reports Server (NTRS)
Phillips, R. J.; Lambeck, K.
1980-01-01
The paper discusses the gravity and topography data available for four terrestrial planets (earth, moon, Mars, and Venus), with particular emphasis on drawing inferences regarding the relationship of long-wavelength anomalies to tectonics. The discussion covers statistical analyses of global planetary gravity fields, relationship of gravity anomalies to elastic and viscoelastic models, relationship of gravity anomalies to convection models, finite strength, and isostasy (or the state of isostatic compensation). The cases of the earth and the moon are discussed in some detail. A summary of comparative planetology is presented.
Topographic/isostatic evaluation of new-generation GOCE gravity field models
NASA Astrophysics Data System (ADS)
Hirt, C.; Kuhn, M.; Featherstone, W. E.; GöTtl, F.
2012-05-01
We use gravity implied by the Earth's rock-equivalent topography (RET) and modeled isostatic compensation masses to evaluate the new global gravity field models (GGMs) from European Space Agency (ESA)'s Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite gravimetry mission. The topography is now reasonably well-known over most of the Earth's landmasses, and also where conventional GGM evaluation is prohibitive due to the lack (or unavailability) of ground-truth gravity data. We construct a spherical harmonic representation of Earth's RET to derive band-limited topography-implied gravity, and test the somewhat simplistic Airy/Heiskanen and Pratt/Hayford hypotheses of isostatic compensation, but which did not improve the agreement between gravity from the uncompensated RET and GOCE. The third-generation GOCE GGMs (based on 12 months of space gravimetry) resolve the Earth's gravity field effectively up to spherical harmonic degree ˜200-220 (˜90-100 km resolution). Such scales could not be resolved from satellites before GOCE. From the three different GOCE processing philosophies currently in use by ESA, the time-wise and direct approaches exhibit the highest sensitivity to short-scale gravity recovery, being better than the space-wise approach. Our topography-implied gravity comparisons bring evidence of improvements from GOCE to gravity field knowledge over the Himalayas, Africa, the Andes, Papua New Guinea and Antarctic regions. In attenuated form, GOCE captures topography-implied gravity signals up to degree ˜250 (˜80 km resolution), suggesting that other signals (originating, e.g., from the crust-mantle boundary and buried loads) are captured as well, which might now improve our knowledge on the Earth's lithosphere structure at previously unresolved spatial scales.
NASA Technical Reports Server (NTRS)
Barriot, J. P.; Balmino, G.
1992-01-01
A novel method is presented for mapping line-of-sight gravity data (LOSGD) joining planetary probes and observers during Doppler tracking operations, with a view to geodetic and geophysical applications. LOSGD are in this case mapped as gravity anomalies along a radial direction, at constant altitude, using an inversion procedure in conjunction with a Tikhonov-Arsenine regularization method. The application of different regularization-parameter choices to a synthetic case is followed by application to the real case of Pioneer-Venus orbiter data for Venus' Gula Mons.
NASA Astrophysics Data System (ADS)
Barriot, J. P.; Balmino, G.
1992-09-01
A novel method is presented for mapping line-of-sight gravity data (LOSGD) joining planetary probes and observers during Doppler tracking operations, with a view to geodetic and geophysical applications. LOSGD are in this case mapped as gravity anomalies along a radial direction, at constant altitude, using an inversion procedure in conjunction with a Tikhonov-Arsenine regularization method. The application of different regularization-parameter choices to a synthetic case is followed by application to the real case of Pioneer-Venus orbiter data for Venus' Gula Mons.
Bose-Einstein Condensation in Relativistic Field Theories Far from Equilibrium
NASA Astrophysics Data System (ADS)
Berges, Jürgen; Sexty, Dénes
2012-04-01
The formation of Bose condensates far from equilibrium can play an important role in our understanding of collision experiments of heavy nuclei or for the evolution of the early Universe. In the relativistic quantum world particle number changing processes can counteract Bose condensation, and there is a considerable debate about the relevance of this phenomenon in this context. We show that the involved question of Bose condensation from initial overpopulation can be answered for the example of scalar field theories. Condensate formation occurs as a consequence of an inverse particle cascade with a universal power-law spectrum. This particle transport towards low momenta is part of a dual cascade, in which energy is also transferred by weak wave turbulence towards higher momenta. To highlight the importance of number changing processes for the subsequent decay of the condensate, we also compare to nonrelativistic theories with exact number conservation. We discuss the relevance of these results for non-Abelian gauge theories.
Building Relativistic Mean-Field Models for Atomic Nuclei and Neutron Stars
NASA Astrophysics Data System (ADS)
Chen, Wei-Chia; Piekarewicz, Jorge
2014-03-01
Nuclear energy density functional (EDF) theory has been quite successful in describing nuclear systems such as atomic nuclei and nuclear matter. However, when building new models, attention is usually paid to the best-fit parameters only. In recent years, focus has been shifted to the neighborhood around the minimum of the chi-square function as well. This powerful covariance analysis is able to provide important information bridging experiments, observations, and theories. In this work, we attempt to build a specific type of nuclear EDFs, the relativistic mean-field models, which treat atomic nuclei, nuclear matter, and neutron stars on the same footing. The application of covariance analysis can reveal correlations between observables of interest. The purpose is to elucidate the alleged relations between the neutron skin of heavy nuclei and the size of neutron stars, and to develop insight into future investigations.
Relay transport of relativistic flows in extreme magnetic fields of stars
NASA Astrophysics Data System (ADS)
Yao, W. P.; Qiao, B.; Xu, Z.; Zhang, H.; Chang, H. X.; Zhou, C. T.; Zhu, S. P.; Wang, X. G.; He, X. T.
2017-08-01
We find that the transport of relativistic flows in extreme magnetic fields can be achieved in a relay manner by considering the quantum electromagnetic cascade process, where photons play a key role as a medium. During the transport, the flow emits particle energy into photons via quantum synchrotron radiation, and then gains particles back by magnetic pair creation, forming a "particle-photon-particle" relay. Particle-in-cell simulations demonstrate that forward transport of the flow density is realized by a self-replenishment process with photon-pair cascades, while that of the flow energy is accomplished due to a new coupling path through radiation of photons. This novel transport mechanism is closely associated with jet generation and disk accretion around the neutron star of X-Ray Binaries, offering a potential explanation for the powerful jets observed there.
Neutron driplines for Ca and Pb using modified relativistic mean field (MRMF) model
Diningrum, J. P. Sulaksono, A.
2016-04-19
The position of two neutron driplines for Ca and Pb nuclei are studied using four different parameter sets obtained from Modified Relativistic Mean Field (MRMF) model. The roles of isovector-isoscalar and electromagnetic exchange couplings to predict the position of two neutron driplines for Ca and Pb nuclei are also investigated. The prediction of the position of nuclei dripline is calculated using two different methods, i.e., by observing the separation energy of two neutrons in the corresponding isotopes chains and analyzing the corresponding single particle energies. Our results showed that the appearance of driplines for Ca and Pb nuclei are influenced by all these couplings that characterized by different position prediction on each parameter set.
Ground State Properties of Z=126 Isotopes within the Relativistic Mean Field Model
NASA Astrophysics Data System (ADS)
Yu, Qi-Xin; Li, Jun-Qing; Zhang, Hong-Fei
2017-01-01
The ground state properties of Z = 126 isotopes with neutron numbers N = 174-244 are calculated by the relativistic mean field (RMF) theory with effective interactions NL-Z2. In order to make a comprehensive understanding of the possible proton magic number Z = 126, we also perform the calculations in the vicinity of Z = 126, such as Z = 114,116,118,120,122,124,128 and 130 isotopic chains. The calculated results show there exist evident magicity for proton number Z = 120 and relatively weak magicity for proton number Z = 126. Supported by the National Natural Science Foundation of China under Grant Nos. 11675066, 11475050, 11265013, and the CAS Knowledge Innovation under Grant No. KJCX2-EW-N02
K--nucleus relativistic mean field potentials consistent with kaonic atoms
NASA Astrophysics Data System (ADS)
Friedman, E.; Gal, A.; Mareš, J.; Cieplý, A.
1999-08-01
K- atomic data are used to test several models of the K- nucleus interaction. The t(ρ)ρ optical potential, due to coupled channel models incorporating the Λ(1405) dynamics, fails to reproduce these data. A standard relativistic mean field (RMF) potential, disregarding the Λ(1405) dynamics at low densities, also fails. The only successful model is a hybrid of a theoretically motivated RMF approach in the nuclear interior and a completely phenomenological density dependent potential, which respects the low density theorem in the nuclear surface region. This best-fit K- optical potential is found to be strongly attractive, with a depth of 180+/-20 MeV at the nuclear interior, in agreement with previous phenomenological analyses.
Cluster decay in very heavy nuclei in a relativistic mean field model
NASA Astrophysics Data System (ADS)
Bhattacharya, Madhubrata; Gangopadhyay, G.
2008-02-01
Exotic cluster decay of very heavy nuclei was studied in the microscopic Super-Asymmetric Fission Model. The Relativistic Mean Field model with the force FSU Gold was employed to obtain the densities of the cluster and the daughter nuclei. The microscopic nuclear interaction DDM3Y1, which has an exponential density dependence, and the Coulomb interaction were used in the double folding model to obtain the potential between the cluster and the daughter. Half-life values were calculated in the WKB approximation and the spectroscopic factors were extracted. The latter values are seen to have a simple dependence of the mass of the cluster as has been observed earlier. Predictions were made for some possible decays.
Impact of tracking loop settings of the Swarm GPS receiver on gravity field recovery
NASA Astrophysics Data System (ADS)
Dahle, C.; Arnold, D.; Jäggi, A.
2017-06-01
The Swarm mission consists of three identical satellites equipped with GPS receivers and orbiting in near-polar low Earth orbits. Thus, they can be used to determine the Earth's gravity field by means of high-low satellite-to-satellite tracking (hl-SST). However, first results by several groups have revealed systematic errors both in precise science orbits and resulting gravity field solutions which are caused by ionospheric disturbances affecting the quality of Swarm GPS observations. Looking at gravity field solutions, the errors lead to systematic artefacts located in two bands north and south of the geomagnetic equator. In order to reduce these artefacts, erroneous GPS observations can be identified and rejected before orbit and gravity field processing, but this may also lead to slight degradations of orbit and low degree gravity field coefficient quality. Since the problems were believed to be receiver-specific, the GPS tracking loop bandwidths onboard Swarm have been widened several times starting in May 2015. The influence of these tracking loop updates on Swarm orbits and, particularly, gravity field solutions is investigated in this work. The main findings are that the first updates increasing the bandwidth from 0.25 Hz to 0.5 Hz help to significantly improve the quality of Swarm gravity fields and that the improvements are even larger than those achieved by GPS data rejection. It is also shown that these improvements are indeed due to an improved quality of GPS observations around the geomagnetic equator, and not due to missing observations in these regions. As the ionospheric activity is rather low in the most recent months, the effect of the tracking loop updates in summer 2016 cannot be properly assessed yet. Nevertheless, the quality of Swarm gravity field solutions has already improved after the first updates which is especially beneficial in view of filling the upcoming gap between the GRACE and GRACE Follow-on missions with hl-SST gravity products.
Bubble Detachment in Variable Gravity Under the Influence of Electric Fields
NASA Technical Reports Server (NTRS)
Herman, Cila; Chang, Shinan; Iacona, Estelle
2002-01-01
The objective of the research is to investigate the behavior of individual air bubbles injected through an orifice into an electrically insulating liquid under the influence of a static electric field. Situations were considered with both uniform and nonuniform electric fields. Bubble formation and detachment were visualized in terrestrial gravity as well as for several levels of reduced gravity (lunar, martian and microgravity) using a high-speed video camera. Bubble volume, dimensions and contact angles at detachment were measured. In addition to the experimental studies, a simple model, predicting bubble characteristics at detachment in an initially uniform electric field was developed. The model, based on thermodynamic considerations, accounts for the level of gravity as well as the magnitude of the uniform electric field. The results of the study indicate that the level of gravity and the electric field magnitude significantly affect bubble behavior as well as shape, volume and dimensions.
Bubble Detachment in Variable Gravity Under the Influence of Electric Fields
NASA Technical Reports Server (NTRS)
Herman, Cila; Chang, Shinan; Iacona, Estelle
2002-01-01
The objective of the research is to investigate the behavior of individual air bubbles injected through an orifice into an electrically insulating liquid under the influence of a static electric field. Situations were considered with both uniform and nonuniform electric fields. Bubble formation and detachment were visualized in terrestrial gravity as well as for several levels of reduced gravity (lunar, martian and microgravity) using a high-speed video camera. Bubble volume, dimensions and contact angles at detachment were measured. In addition to the experimental studies, a simple model, predicting bubble characteristics at detachment in an initially uniform electric field was developed. The model, based on thermodynamic considerations, accounts for the level of gravity as well as the magnitude of the uniform electric field. The results of the study indicate that the level of gravity and the electric field magnitude significantly affect bubble behavior as well as shape, volume and dimensions.
A Study of Multi-Λ Hypernuclei Within Spherical Relativistic Mean-Field Approach
NASA Astrophysics Data System (ADS)
Rather, Asloob A.; Ikram, M.; Usmani, A. A.; Kumar, B.; Patra, S. K.
2017-09-01
This research article is a follow up of an earlier work by M. Ikram et al., reported in Int. J. Mod. Phys. E 25, 1650103 (2016) where we searched for Λ magic numbers in experimentally confirmed doubly magic nucleonic cores in light to heavy mass region (i.e., 16 O-208 P b) by injecting Λ's into them. In the present manuscript, working within the state of the art relativistic mean field theory with the inclusion of ΛN and ΛΛ interaction in addition to nucleon-meson NL 3∗ effective force, we extend the search of lambda magic numbers in multi- Λ hypernuclei using the predicted doubly magic nucleonic cores 292120, 304120, 360132, 370132, 336138, 396138 of the elusive superheavy mass regime. In analogy to well established signatures of magicity in conventional nuclear theory, the prediction of hypernuclear magicities is made on the basis of one-, two- Λ separation energy (S Λ,S 2Λ) and two lambda shell gaps (δ 2Λ) in multi- Λ hypernuclei. The calculations suggest that the Λ numbers 92, 106, 126, 138, 184, 198, 240, and 258 might be the Λ shell closures after introducing the Λ's in the elusive superheavy nucleonic cores. The appearance of new lambda shell closures apart from the nucleonic ones predicted by various relativistic and non-relativistic theoretical investigations can be attributed to the relatively weak strength of the spin-orbit coupling in hypernuclei compared to normal nuclei. Further, the predictions made in multi- Λ hypernuclei under study resembles closely the magic numbers in conventional nuclear theory suggested by various relativistic and non-relativistic theoretical models. Moreover, in support of the Λ shell closure, the investigation of Λ pairing energy and effective Λ pairing gap has been made. We noticed a very close agreement of the predicted Λ shell closures with the survey made on the pretext of S Λ, S 2Λ, and δ 2Λ except for the appearance of magic numbers corresponding to Λ = 156 which manifest in Λ effective
Effective field theory of gravity for extended objects
Goldberger, Walter D.; Rothstein, Ira Z.
2006-05-15
Using effective field theory (EFT) methods we present a Lagrangian formalism which describes the dynamics of nonrelativistic extended objects coupled to gravity. The formalism is relevant to understanding the gravitational radiation power spectra emitted by binary star systems, an important class of candidate signals for gravitational wave observatories such as LIGO or VIRGO. The EFT allows for a clean separation of the three relevant scales: r{sub s}, the size of the compact objects, r, the orbital radius, and r/v, the wavelength of the physical radiation (where the velocity v is the expansion parameter). In the EFT, radiation is systematically included in the v expansion without the need to separate integrals into near zones and radiation zones. Using the EFT, we show that the renormalization of ultraviolet divergences which arise at v{sup 6} in post-Newtonian (PN) calculations requires the presence of two nonminimal worldline gravitational couplings linear in the Ricci curvature. However, these operators can be removed by a redefinition of the metric tensor, so that the divergences arising at v{sup 6} have no physically observable effect. Because in the EFT finite size features are encoded in the coefficients of nonminimal couplings, this implies a simple proof of the decoupling of internal structure for spinless objects to at least order v{sup 6}. Neglecting absorptive effects, we find that the power counting rules of the EFT indicate that the next set of short distance operators, which are quadratic in the curvature and are associated with tidal deformations, does not play a role until order v{sup 10}. These operators, which encapsulate finite size properties of the sources, have coefficients that can be fixed by a matching calculation. By including the most general set of such operators, the EFT allows one to work within a point-particle theory to arbitrary orders in v.
Particle drift in the field of internal gravity wave
NASA Astrophysics Data System (ADS)
Grinshpun, S. A.; Redcoborody, Yu. N.; Kravchuk, S. G.; Zadorozhnii, V. I.; Zhdanov, V. I.
2000-08-01
Similarly to an acoustic wave, an internal gravity wave (IGW) can cause the drift of a dispersed component in a two-component system, e.g. in a hydrosol or an aerosol. The IGW-caused particle drift may play a significance role in many natural processes occurring in very large water reservoirs or air volumes and thus is of interest for atmospheric and oceanic research. The analytical and numerical calculations of the IGW-caused particle drift motion were performed in this study for the following two sets of conditions: (i) propagating IGW in a horizontal infinite waveguide and (ii) standing IGW in a rectangular resonator. It was shown that particles concentrate in certain areas of an IGW field as a result of their migration. When IGW is propagating in an infinite waveguide, the particle drift causes the vertical stratification and horizontal unidirectional motion. The particle size affects the shape of the particle trajectories and the vertical component of the drift velocity in an infinite waveguide. In contrast, the shape of trajectories in the IGW rectangular resonator is not affected by the particle size and IGW intensity. The IGW-caused particle drift was shown to result in purification of a two-component system or in its "structurization" (the formation of purified areas of the fluid alternating with the areas loaded with particles). These effects were found to be low energy consuming: ∼10 J/m3 of liquid. However, the particle migration in the infinite waveguide and rectangular resonator is a very slow process, and the time needed for an efficient purification of a fluid increases quickly with the decrease of particle size. The particle coagulation is expected to significantly accelerate the fluid purification. Another way to reduce this characteristic time is proposed through utilizing the horizontal component of the particle drift in the semi-infinite IGW waveguide.
Costa, R. S.; Duarte, S. B.; Oliveira, J. C. T.; Chiapparini, M.
2010-05-21
We study the nuclear matter properties in the regime of high temperatures using a relativistic mean-field theory. Contrasting with the usual linear Walecka model, we include the sigma-omega meson coupling in order to investigate the role of this interaction in the nucleon effective mass behavior. Some numerical results are presented and discussed.
Mashhoon, B.; Paik, H. J.; Will, C. M.
1989-05-15
The angular momentum of the Earth produces gravitomagnetic components of the Riemann curvature tensor, which are of the order of 10/sup /minus/10/ of the Newtonian tidal terms arising from the mass of the Earth. These components could be detected in principle by sensitive superconducting gravity gradiometers currently under development. We lay out the theoretical principles of such an experiment by using the parametrized post-Newtonian formalism to derive the locally measured Riemann tensor in an orbiting proper reference frame, in a class of metric theories of gravity that includes general relativity. A gradiometer assembly consisting of three gradiometers with axes at mutually right angles measures three diagonal components of a 3/times/3 ''tidal tensor,'' related to the Riemann tensor. We find that, by choosing a particular assembly orientation relative to the orbit and taking a sum and difference of two of the three gradiometer outputs, one can isolate the gravitomagnetic relativistic effect from the large Newtonian background.
Wu, Ping; Sun, Jun; Cao, Yibing
2015-06-15
In O-type high power microwave (HPM) devices, the annular relativistic electron beam is constrained by a strong guiding magnetic field and propagates through an interaction region to generate HPM. Some papers believe that the E × B drift of electrons may lead to beam breakup. This paper simplifies the interaction region with a smooth cylindrical waveguide to research the radial motion of electrons under conditions of strong guiding magnetic field and TM{sub 01} mode HPM. The single-particle trajectory shows that the radial electron motion presents the characteristic of radial guiding-center drift carrying cyclotron motion. The radial guiding-center drift is spatially periodic and is dominated by the polarization drift, not the E × B drift. Furthermore, the self fields of the beam space charge can provide a radial force which may pull electrons outward to some extent but will not affect the radial polarization drift. Despite the radial drift, the strong guiding magnetic field limits the drift amplitude to a small value and prevents beam breakup from happening due to this cause.
Dynamics of perturbations in Double Field Theory & non-relativistic string theory
NASA Astrophysics Data System (ADS)
Ko, Sung Moon; Melby-Thompson, Charles M.; Meyer, René; Park, Jeong-Hyuck
2015-12-01
Double Field Theory provides a geometric framework capable of describing string theory backgrounds that cannot be understood purely in terms of Riemannian geometry — not only globally (`non-geometry'), but even locally (`non-Riemannian'). In this work, we show that the non-relativistic closed string theory of Gomis and Ooguri [1] arises precisely as such a non-Riemannian string background, and that the Gomis-Ooguri sigma model is equivalent to the Double Field Theory sigma model of [2] on this background. We further show that the target-space formulation of Double Field Theory on this non-Riemannian background correctly reproduces the appropriate sector of the Gomis-Ooguri string spectrum. To do this, we develop a general semi-covariant formalism describing perturbations in Double Field Theory. We derive compact expressions for the linearized equations of motion around a generic on-shell background, and construct the corresponding fluctuation Lagrangian in terms of novel completely covariant second order differential operators. We also present a new non-Riemannian solution featuring Schrödinger conformal symmetry.
Design of a high efficiency relativistic backward wave oscillator with low guiding magnetic field
Li, Xiaoze; Song, Wei; Tan, Weibing; Zhang, Ligang; Su, Jiancang; Zhu, Xiaoxin; Hu, Xianggang; Shen, Zhiyuan; Liang, Xu; Ning, Qi
2016-07-15
A high efficiency relativistic backward wave oscillator working at a low guiding magnetic field is designed and simulated. A trapezoidal resonant reflector is used to reduce the modulation field in the resonant reflector to avoid overmodulation of the electron beam which will lead to a large momentum spread and then low conversion efficiency. The envelope of the inner radius of the slow wave structure (SWS) increases stepwise to keep conformal to the trajectory of the electron beam which will alleviate the bombardment of the electron on the surface of the SWS. The length of period of the SWS is reduced gradually to make a better match between phase velocity and electron beam, which decelerates continually and improves the RF current distribution. Meanwhile the modulation field is reduced by the introduction of nonuniform SWS also. The particle in cell simulation results reveal that a microwave with a power of 1.8 GW and a frequency of 14.7 GHz is generated with an efficiency of 47% when the diode voltage is 620 kV, the beam current 6.1 kA, and the guiding magnetic field 0.95 T.
Experimental study of transport of relativistic electron beams in strong magnetic mirror field
NASA Astrophysics Data System (ADS)
Sakata, Shohei; Kondo, Kotaro; Bailly-Grandvaux, Mathiu; Bellei, Claudio; Santos, Joao; Firex Project Team
2015-11-01
Relativistic electron beams REB produced by ultra high intense laser pulses have generally a large divergence angle that results in degradation of energy coupling between the REB and a fuel core in the fast ignition scheme. Guiding and focusing of the REB by a strong external magnetic field was proposed to achieve high efficiency. We investigated REB transport through 50 μm or 250 μm thick plastic foils CuI doped under external magnetic fields, in magnetic mirror configurations of 1.2 or 4 mirror ratio. The experiment was carried out at the GEKKO XII and LFEX laser facility. Spatial pattern of the REB was measured by coherent transition radiation and/or Cu Ka x ray emission from the rear surface of the foil targets. Strong collimation of the REB by the external magnetic field was observed with 50 μm thick plastic targets, while the REB scattered in 250 μm thick targets. The experimental results are compared with computer simulations to understand the physical mechanisms of the REB transport in the external magnetic field. This work is supported by NIFS (Japan), MEXT/JSPS KAKENHI (Japan), JSPS Fellowship (Japan), ANR (France) and COST (Europe).
NASA Astrophysics Data System (ADS)
Fendt, C.
1997-07-01
Highly collimated jets are observed in various astronomical objects, as active galactic nuclei, galactic high energy sources, and also young stellar objects. There is observational indication that these jets originate in accretion disks, and that magnetic fields play an important role for the jet collimation and plasma acceleration. The rapid disk rotation close to the central object leads to relativistic rotational velocities of the magnetic field lines. The structure of these axisymmetric magnetic flux surfaces follows from the trans-field force-balance described by the Grad-Schlueter-Shafranov equation. In this paper, we investigate the asymptotic field structure of differentially rotating magnetic jets, widening the study by Appl & Camenzind (1993A&A...270...71A, 1993A&A...274..699A). In general, our results show that, with the same current distribution, differentially rotating jets are collimated to smaller jet radii as compared with jets with rigidly rotating field. Differentially rotating jets need a stronger net poloidal current in order to collimate to the same asymptotic radius. Current-free solutions are not possible for differentially rotating disk-jet magnetospheres with cylindrical asymptotics. We present a simple analytical relation between the poloidal current distribution and magnetic field rotation law. A general relation is derived for the current strength for jets with maximum differential rotation and minimum differential rotation. Analytical solutions are also given in the case of a field rotation leading to a degeneration of the light cylinder. By linking the asymptotic solution to a Keplerian accretion disk, 'total expansion rates' for the jets, and also the flux distribution at the foot points of the flux surfaces are derived. Large poloidal currents imply a strong opening of flux surfaces, a stronger gradient of field rotation leads to smaller expansion rates. There is indication that AGN jet expansion rates are less than in the case of
On the existence of neutral directions of the normal gravity field
NASA Astrophysics Data System (ADS)
Manoussakis, Gerassimos; Milas, Paraskevas
2014-03-01
A neutral direction of a gravity field is a direction along which the components of the gravity vector remain locally unchanged. A neutral point is a point at which there exists a neutral direction. This research will focus on the neutral directions for the normal gravity vector. The necessary condition for the existence of neutral directions at an arbitrary point P above the ellipsoid is that the determinant of the E¨otv¨os matrix must be equal to zero. The slopes of these directions depend on the value of the principal curvatures and the curvature of the plumbline. In all cases the neutral directions lie on the meridian plane at point P. An interesting case is when the vertical gradient of normal gravity is equal to zero. Finally in the last two paragraphs we show that neutral points are not isolated in the three dimensional space and give a numerical example for the case of a spherical gravity field.
Milant'ev, V. P. Castillo, A. J.
2013-04-15
Averaged relativistic equations of motion of a charged particle in the field of intense electromagnetic radiation have been obtained in the geometrical optics approximation using the Bogoliubov method. Constraints are determined under which these equations are valid. Oscillating additions to the smoothed dynamical variables of the particle have been found; they are reduced to known expressions in the case of the circularly and linearly polarized plane waves. It has been shown that the expressions for the averaged relativistic force in both cases contain new additional small terms weakening its action. The known difference between the expressions for the ponderomotive force in the cases of circularly and linearly polarized waves has been confirmed.
NASA Astrophysics Data System (ADS)
Iess, L.; Finocchiaro, S.; Racioppa, P.
2013-12-01
be estimated to about 0.2 mGal for Jupiter (at latitudes between 10N and 30N) and 0.05 mGal for Saturn (between 10S and 10N). As a consequence of the large eccentricity of the orbits, the estimates degrade rapidly at latitudes outside these intervals. Tighter regularization constraints on the tesseral harmonics improve the overall estimate, calling for better theoretical upper limits on the non-zonal field. Both Juno and Cassini will be sensitive also to the time variable gravity field, controlled mostly by the Love number k2. Its expected uncertainty is about 0.002 for Juno, and an order of magnitude worse for Cassini. In addition to classical gravity perturbations, Juno measurements will be sensitive also to the relativistic Lense-Thirring (LT) precession. This effect, due to the massive and rapidly rotating Jupiter, results in an out of plane acceleration of the spacecraft that is proportional to the angular momentum of the planet. Assuming that general relativity is correct, the LT acceleration can be used to determine the unknown specific angular momentum of Jupiter (J/M), with a relative accuracy of about 2%. This measurement is not accessible to Cassini, due to the lower mass of the Saturn, the nearly edge-on orientation of the spacecraft orbital plane and the lower range rate accuracies.
Bubble Formation and Detachment in Reduced Gravity Under the Influence of Electric Fields
NASA Technical Reports Server (NTRS)
Herman, Cila; Iacona, Estelle; Chang, Shinan
2002-01-01
The objective of the study is to investigate the behavior of individual air bubbles injected through an orifice into an electrically insulating liquid under the influence of a static electric field. Both uniform and nonuniform electric field configurations were considered. Bubble formation and detachment were recorded and visualized in reduced gravity (corresponding to gravity levels on Mars, on the Moon as well as microgravity) using a high-speed video camera. Bubble volume, dimensions and contact angle at detachment were measured. In addition to the experimental studies, a simple model, predicting bubble characteristics at detachment was developed. The model, based on thermodynamic considerations, accounts for the level of gravity as well as the magnitude of the uniform electric field. Measured data and model predictions show good agreement and indicate that the level of gravity and the electric field magnitude significantly affect bubble shape, volume and dimensions.
An improved JPL Mars gravity field and orientation from Mars orbiter and lander tracking data
NASA Astrophysics Data System (ADS)
Konopliv, Alex S.; Park, Ryan S.; Folkner, William M.
2016-08-01
The Mars gravity field resolution is mostly determined by the lower altitude Mars Reconnaissance Orbiter (MRO) tracking data. With nearly four years of additional MRO and Mars Odyssey tracking data since the last JPL released gravity field MRO110C and lander tracking from the MER Opportunity Rover, the gravity field and orientation of Mars have been improved. The new field, MRO120D, extends the maximum spherical harmonic degree slightly to 120, improves the determination of the higher degree coefficients as demonstrated by improved correlation with topography and reduces the uncertainty in the corresponding Mars orientation parameters by up to a factor of two versus previously combined gravity and orientation solutions. The new precession solution is ψ˙ = - 7608.3 ± 2.1 mas / yr and is consistent with previous results but with a reduced uncertainty by 40%. The Love number solution, k2 = 0.169 ± 0.006, also shows a similar result to previous studies.
Bubble Formation and Detachment in Reduced Gravity Under the Influence of Electric Fields
NASA Technical Reports Server (NTRS)
Herman, Cila; Iacona, Estelle; Chang, Shinan
2002-01-01
The objective of the study is to investigate the behavior of individual air bubbles injected through an orifice into an electrically insulating liquid under the influence of a static electric field. Both uniform and nonuniform electric field configurations were considered. Bubble formation and detachment were recorded and visualized in reduced gravity (corresponding to gravity levels on Mars, on the Moon as well as microgravity) using a high-speed video camera. Bubble volume, dimensions and contact angle at detachment were measured. In addition to the experimental studies, a simple model, predicting bubble characteristics at detachment was developed. The model, based on thermodynamic considerations, accounts for the level of gravity as well as the magnitude of the uniform electric field. Measured data and model predictions show good agreement and indicate that the level of gravity and the electric field magnitude significantly affect bubble shape, volume and dimensions.
Popa, Alexandru
2011-08-15
We prove that the analytical expression of the intensity of the relativistic Thomson scattered field for a system composed of an electron interacting with a plane electromagnetic field can be written in the form of a composite periodic function of only one variable, that is, the phase of the incident field. This property is proved without using any approximation in the most general case in which the field is elliptically polarized, the initial phase of the incident field and the initial velocity of the electron are taken into consideration, and the direction in which the radiation is scattered is arbitrary. This property leads to an exact method for calculating the angular and spectral distributions of the scattered field, which reveals a series of physical details of these distributions, such as their dependence on the components of the initial electron velocity. Since the phase of the field is a relativistic invariant, it follows that the periodicity property is also valid when the analysis is made in the inertial system in which the initial velocity of the electron is zero in the case of interactions between very intense electromagnetic fields and relativistic electrons. Consequently, the calculation method can be used for the evaluation of properties of backscattered hard radiations generated by this type of interaction. The theoretical evaluations presented in this paper are in good agreement with the experimental data from literature.
Maruyama, Tomoyuki; Cheoun, Myung-Ki; Kajino, Toshitaka; ...
2016-03-26
We study pion production by proton synchrotron radiation in the presence of a strong magnetic field when the Landau numbers of the initial and final protons are n(i, f) similar to 10(4)-10(5). We find in our relativistic field theory calculations that the pion decay width depends only on the field strength parameter which previously was only conjectured based upon semi-classical arguments. Moreover, we also find new results that the decay width satisfies a robust scaling relation, and that the polar angular distribution of emitted pion momenta is very narrow and can be easily obtained. This scaling implies that one canmore » infer the decay width in more realistic magnetic fields of 10(15) G, where n(i, f) similar to 10(12)-10(13), from the results for n(i, f) similar to 10(4)-10(5). The resultant pion intensity and angular distributions for realistic magnetic field strengths are presented and their physical implications discussed. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).« less
Maruyama, Tomoyuki; Cheoun, Myung-Ki; Kajino, Toshitaka; Mathews, Grant J.
2016-03-26
We study pion production by proton synchrotron radiation in the presence of a strong magnetic field when the Landau numbers of the initial and final protons are n(i, f) similar to 10(4)-10(5). We find in our relativistic field theory calculations that the pion decay width depends only on the field strength parameter which previously was only conjectured based upon semi-classical arguments. Moreover, we also find new results that the decay width satisfies a robust scaling relation, and that the polar angular distribution of emitted pion momenta is very narrow and can be easily obtained. This scaling implies that one can infer the decay width in more realistic magnetic fields of 10(15) G, where n(i, f) similar to 10(12)-10(13), from the results for n(i, f) similar to 10(4)-10(5). The resultant pion intensity and angular distributions for realistic magnetic field strengths are presented and their physical implications discussed. (C) 2016 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/). Funded by SCOAP(3).
On axionic field ranges, loopholes and the weak gravity conjecture
Brown, Jon; Cottrell, William; Shiu, Gary; ...
2016-04-05
Here, we clarify some aspects of the impact that the Weak Gravity Conjecture has on models of (generalized) natural inflation. In particular we address certain technical and conceptual concerns recently raised regarding the stringent constraints and conclusions found in our previous work. We also point out the difficulties faced by attempts to evade these constraints. Furthermore, these new considerations improve the understanding of the quantum gravity constraints we found and further support the conclusion that it remains challenging for axions to drive natural inflation.
On axionic field ranges, loopholes and the weak gravity conjecture
Brown, Jon; Cottrell, William; Shiu, Gary; Soler, Pablo
2016-04-05
Here, we clarify some aspects of the impact that the Weak Gravity Conjecture has on models of (generalized) natural inflation. In particular we address certain technical and conceptual concerns recently raised regarding the stringent constraints and conclusions found in our previous work. We also point out the difficulties faced by attempts to evade these constraints. Furthermore, these new considerations improve the understanding of the quantum gravity constraints we found and further support the conclusion that it remains challenging for axions to drive natural inflation.
On the Helical Fields Guiding Near-Relativistic Electron Beams in the Heliosphere
NASA Astrophysics Data System (ADS)
Rust, David M.; Haggerty, D. K.; Georgoulis, M. K.; Stenborg, G.
2009-05-01
Wavelet processing of the LASCO images of the solar corona brings out many subtle details that are easily missed in the intensity images. Specifically, wavelet processing can enhance the edges on large and small scales making it easier to detect and define helical features. We used the processed LASCO images obtained during the period 1997 -2001 to study the structure and motions of nearly radial streamers extending from coronal holes adjacent to flaring active regions. Some of the streamers show outward-propagating twist. These helical fields extend into the heliosphere where they would reach 1 AU with a path length generally greater than the 1.2 AU of idealized fields following the Parker spiral. We focused on the regions from our earlier work (Rust et al., ApJ 687, 635, 2008) on flares associated with beams of near-relativistic electrons detected at 1 AU with the ACE spacecraft. Our study shows that the electron beam's typical delay of about 10 min in arriving at 1 AU may be due to their following a helical path from Sun to Earth. According to the reconnection jet model, the helical component may be introduced to open fields by earlier events involving reconnections with emerging, twisted flux ropes. Our study implies that the escaping electrons may be accelerated at the same time as the trapped electrons that produce X-ray flare emissions. NASA supported this work with grant NNG 05GM69G.
Notes on the relativistic movement of runaway electrons in parallel electric and magnetic fields
NASA Astrophysics Data System (ADS)
Delong, Vojtěch Adalbert; BeÅo, Radek; BřeÅ, David; Kulhánek, Petr
2016-09-01
Runaway electrons are a potential threat in many plasma devices. At high velocities, the plasma acceleration is not further offset by collisions in the plasma, as in the ohmic regime. The particles obtain relativistic velocity and considerable energy. A typical configuration includes parallel electric and magnetic fields, in which there are no drifts, and the movement of the charged particles is a combination of gyration motion with the acceleration in an electric field. It follows from the Lorentz equation of motion that the transverse velocity component (perpendicular to the fields) will be interconnected with the longitudinal component via the Lorentz factor. The increasing longitudinal velocity will therefore ultimately reduce the magnitude of the transverse velocity component, thereby decreasing the gyrofrequency. The corresponding change in Larmor radius will be offset by the increase in the particle mass and the Larmor radius of gyration therefore remains unchanged. We derive analytical relations for the temporal and spatial dependences of frequency, and longitudinal and transverse components of the velocity.
Motion of relativistic particles in axially symmetric and perturbed magnetic fields in a tokamak
de Rover, M.; Lopes Cardozo, N.J.; Montvai, A.
1996-12-01
An extensive comparison is given between an analytical theory for the computations of particle orbits of relativistic runaway electrons [M. de Rover {ital et} {ital al}., Phys. Plasmas {bold 3}, 4468 (1996)], and numerical simulations. A new numerical scheme is used for the computer simulations of guiding center orbits. Furthermore, simulations of the full particle motion, including the gyration are performed to check the guiding center approximation. The behavior of drift surfaces and particle orbits in axially symmetric magnetic fields, as predicted in the companion paper are confirmed. This includes the smaller minor radius of a drift surface compared to a magnetic flux surface with identical rotational transform, and the decrease of the minor radius of a drift surface with increasing particle energy. Magnetic islands and drift islands appear when the axial symmetry of the magnetic field is broken by harmonic perturbations. In the numerical simulations the amplitudes of the perturbations have been chosen to increase towards the plasma edge. The analytic theory gave predictions of the width of the drift islands that are in good agreement with the numerical simulations. When overlap of the magnetic perturbations introduces stochasticity, the Hamiltonian theory shows that drift islands can exist in the region of stochastic magnetic field lines, which is also confirmed by the numerical simulations. {copyright} {ital 1996 American Institute of Physics.}
Point-particle effective field theory III: relativistic fermions and the Dirac equation
NASA Astrophysics Data System (ADS)
Burgess, C. P.; Hayman, Peter; Rummel, Markus; Zalavári, László
2017-09-01
We formulate point-particle effective field theory (PPEFT) for relativistic spin-half fermions interacting with a massive, charged finite-sized source using a first-quantized effective field theory for the heavy compact object and a second-quantized language for the lighter fermion with which it interacts. This description shows how to determine the near-source boundary condition for the Dirac field in terms of the relevant physical properties of the source, and reduces to the standard choices in the limit of a point source. Using a first-quantized effective description is appropriate when the compact object is sufficiently heavy, and is simpler than (though equivalent to) the effective theory that treats the compact source in a second-quantized way. As an application we use the PPEFT to parameterize the leading energy shift for the bound energy levels due to finite-sized source effects in a model-independent way, allowing these effects to be fit in precision measurements. Besides capturing finite-source-size effects, the PPEFT treatment also efficiently captures how other short-distance source interactions can shift bound-state energy levels, such as due to vacuum polarization (through the Uehling potential) or strong interactions for Coulomb bound states of hadrons, or any hypothetical new short-range forces sourced by nuclei.
Effect of the plasma-generated magnetic field on relativistic electron transport.
Nicolaï, Ph; Feugeas, J-L; Regan, C; Olazabal-Loumé, M; Breil, J; Dubroca, B; Morreeuw, J-P; Tikhonchuk, V
2011-07-01
In the fast-ignition scheme, relativistic electrons transport energy from the laser deposition zone to the dense part of the target where the fusion reactions can be ignited. The magnetic fields and electron collisions play an important role in the collimation or defocusing of this electron beam. Detailed description of these effects requires large-scale kinetic calculations and is limited to short time intervals. In this paper, a reduced kinetic model of fast electron transport coupled to the radiation hydrodynamic code is presented. It opens the possibility to carry on hybrid simulations in a time scale of tens of picoseconds or more. It is shown with this code that plasma-generated magnetic fields induced by noncollinear temperature and density gradients may strongly modify electron transport in a time scale of a few picoseconds. These fields tend to defocus the electron beam, reducing the coupling efficiency to the target. This effect, that was not seen before in shorter time simulations, has to be accounted for in any ignition design using electrons as a driver.