Science.gov

Sample records for dark current carried

  1. Lorentz Contraction and Current-Carrying Wires

    ERIC Educational Resources Information Center

    van Kampen, Paul

    2008-01-01

    The force between two parallel current-carrying wires is investigated in the rest frames of the ions and the electrons. A straightforward Lorentz transformation shows that what appears as a purely magnetostatic force in the ion frame appears as a combined magnetostatic and electrostatic force in the electron frame. The derivation makes use of a…

  2. Current and future searches for dark matter

    SciTech Connect

    Bauer, Daniel A.; /Fermilab

    2005-07-01

    Recent experimental data confirms that approximately one quarter of the universe consists of cold dark matter. Particle theories provide natural candidates for this dark matter in the form of either Axions or Weakly Interacting Massive Particles (WIMPs). A growing body of experiments is aimed at direct or indirect detection of particle dark matter. I summarize the current status of these experiments and offer projections of their future sensitivity.

  3. Current-carrying capacity of composite superconductors

    SciTech Connect

    Andrianov, V.; Baeu, V.; Ivanov, S.; Mints, R.; Rakhmanov, A.

    1983-05-01

    The maximum transport current I /SUB m/ of the composite superconductors is investigated both theoretically and experimentally. It is shown that the high values of the transport current observed in these materials is due to the non-linear part of the current-voltage characteristic in the range of low electric fields (E less than or equal to 10/sup -6/ Vcm/sup -1/). The conductors of rather different structure with Nb-Ti superconducting filaments were tested in a wide range of the external parameters. It is shown that in the external magnetic fields B /SUB a/ greater than or equal to 1T the ratio I /SUB m/ /I /SUB c/ (where I /SUB c/ is the critical current) is the universal function of the single dimensionless parameter which depends on the sample properties and the external conditions. The theory and experiment are in a good agreement.

  4. LOWCAL Ground Receiver: PMT Dark Current Measurement

    NASA Technical Reports Server (NTRS)

    MacCannell, John

    2001-01-01

    This paper is part of a series of papers for a research project at New Mexico State University. The project is referred to as LOWCAL or Lightweight Optical Wavelength Communications without A Laser in space. While some of the material presented is specific to tile LOWCAL project, the general procedure for measuring the dark current of a photomultiplier tube is presented.

  5. Measuring the Magnetic Force on a Current-Carrying Conductor.

    ERIC Educational Resources Information Center

    Herreman, W.; Huysentruyt, R.

    1995-01-01

    Describes a fast and simple method for measuring the magnetic force acting on a current-carrying conductor using a digital balance. Discusses the influence of current intensity and wire length on the magnetic force on the conductor. (JRH)

  6. Dynamical dark energy: Current constraints and forecasts

    NASA Astrophysics Data System (ADS)

    Upadhye, Amol; Ishak, Mustapha; Steinhardt, Paul J.

    2005-09-01

    We consider how well the dark energy equation of state w as a function of redshift z will be measured using current and anticipated experiments. We use a procedure which takes fair account of the uncertainties in the functional dependence of w on z, as well as the parameter degeneracies, and avoids the use of strong prior constraints. We apply the procedure to current data from the Wilkinson Microwave Anisotropy Probe, Sloan Digital Sky Survey, and the supernova searches, and obtain results that are consistent with other analyses using different combinations of data sets. The effects of systematic experimental errors and variations in the analysis technique are discussed. Next, we use the same procedure to forecast the dark energy constraints achievable by the end of the decade, assuming 8 years of Wilkinson Microwave Anisotropy Probe data and realistic projections for ground-based measurements of supernovae and weak lensing. We find the 2σ constraints on the current value of w to be Δw0(2σ)=0.20, and on dw/dz (between z=0 and z=1) to be Δw1(2σ)=0.37. Finally, we compare these limits to other projections in the literature. Most show only a modest improvement; others show a more substantial improvement, but there are serious concerns about systematics. The remaining uncertainty still allows a significant span of competing dark energy models. Most likely, new kinds of measurements, or experiments more sophisticated than those currently planned, are needed to reveal the true nature of dark energy.

  7. Dark Current and Photocurrent in Retinal Rods

    PubMed Central

    Hagins, W. A.; Penn, R. D.; Yoshikami, S.

    1970-01-01

    The interstitial voltages, currents, and resistances of the receptor layer of the isolated rat retina have been investigated with arrays of micropipette electrodes inserted under direct visual observation by infrared microscopy. In darkness a steady current flows inward through the plasma membrane of the rod outer segments. It is balanced by equal outward current distributed along the remainder of each rod. Flashes of light produce a photocurrent which transiently reduces the dark current with a waveform resembling the PII and a-wave components of the electroretinogram. The photocurrent is produced by a local action of light within 12 μm of its point of absorption in the outer segments. The quantum current gain of the photocurrent is greater than 106. The electrical space constant of rat rods is greater than 25 μm, so that the electrical effects of the photocurrent are large enough at the rod synapses to permit single absorbed photons to be detected by the visual system. The photocurrent is apparently the primary sensory consequence of light absorption by rhodopsin. ImagesFigure 3Figure 8Figure 14 PMID:5439318

  8. Pipelike current-carrying vortices in two-component condensates

    SciTech Connect

    Chernodub, M. N.; Nedelin, A. S.

    2010-06-15

    We study straight vortices with global longitudinal currents in the Bogomolny limit of the Abelian Higgs model with two charged scalar fields. The model possesses global SU(2) and local electromagnetic U(1) symmetries spontaneously broken to a global U(1) group, and corresponds to a semilocal limit of the standard electroweak model. We show that the contribution of the global SU(2) current to the vortex energy is proportional to the total current squared. Locally, these vortices carry also longitudinal electromagnetic currents, while the total electromagnetic current flowing through a transverse section of the vortex is always zero. The vortices with high winding numbers have, in general, a nested pipelike structure. The magnetic field of the vortex is concentrated at a certain distance from the geometric center of the vortex, thus resembling a 'pipe'. This magnetic pipe is layered between two electrically charged pipes that carry longitudinal electric currents in opposite directions.

  9. Charges and Fields in a Current-Carrying Wire

    ERIC Educational Resources Information Center

    Redzic, Dragan V.

    2012-01-01

    Charges and fields in a straight, infinite, cylindrical wire carrying a steady current are determined in the rest frames of ions and electrons, starting from the standard assumption that the net charge per unit length is zero in the lattice frame and taking into account a self-induced pinch effect. The analysis presented illustrates the mutual…

  10. Bifurcations and chaos in a current-carrying ion sheath

    SciTech Connect

    Komori, A.; Kono, M.; Norimine, T.; Kawai, Y. )

    1992-11-01

    Cascading bifurcations to chaos are investigated experimentally and theoretically in a current-carrying stable plasma. A dc plasma current is required to produce an electron-depleted thick sheath on a grid, which obeys the Child--Langmuir law of space-charge-limited current in a diode. Bifurcation cascade and chaotic behavior are exhibited when an external periodic oscillation is applied to the grid, and are in good agreement for the first time with a theory, which describes ion dynamics in the Child--Langmuir sheath and is represented by the differential equation with three independent variables. A fractal dimension predicted by the theory is verified by the experiment.

  11. Lower-Dark-Current, Higher-Blue-Response CMOS Imagers

    NASA Technical Reports Server (NTRS)

    Pain, Bedabrata; Cunningham, Thomas; Hancock, Bruce

    2008-01-01

    Several improved designs for complementary metal oxide/semiconductor (CMOS) integrated-circuit image detectors have been developed, primarily to reduce dark currents (leakage currents) and secondarily to increase responses to blue light and increase signal-handling capacities, relative to those of prior CMOS imagers. The main conclusion that can be drawn from a study of the causes of dark currents in prior CMOS imagers is that dark currents could be reduced by relocating p/n junctions away from Si/SiO2 interfaces. In addition to reflecting this conclusion, the improved designs include several other features to counteract dark-current mechanisms and enhance performance.

  12. Dark current mechanism of terahertz quantum-well photodetectors

    SciTech Connect

    Jia, J. Y.; Gao, J. H.; Hao, M. R.; Wang, T. M.; Shen, W. Z.; Zhang, Y. H.; Cao, J. C.; Guo, X. G.; Schneider, H.

    2014-10-21

    Dark current mechanisms of terahertz quantum-well photodetectors (THz QWPs) are systematically investigated experimentally and theoretically by measuring two newly designed structures combined with samples reported previously. In contrast to previous investigations, scattering-assisted tunneling dark current is found to cause significant contributions to total dark current. A criterion is also proposed to determine the major dark current mechanism at different peak response frequencies. We further determine background limited performance (BLIP) temperatures, which decrease both experimentally and theoretically as the electric field increases. This work gives good description of dark current mechanism for QWPs in the THz region and is extended to determine the transition fields and BLIP temperatures with response peaks from 3 to 12 THz.

  13. A new method of CCD dark current correction via extracting the dark Information from scientific images

    NASA Astrophysics Data System (ADS)

    Ma, Bin; Shang, Zhaohui; Hu, Yi; Liu, Qiang; Wang, Lifan; Wei, Peng

    2014-07-01

    We have developed a new method to correct dark current at relatively high temperatures for Charge-Coupled Device (CCD) images when dark frames cannot be obtained on the telescope. For images taken with the Antarctic Survey Telescopes (AST3) in 2012, due to the low cooling efficiency, the median CCD temperature was -46°C, resulting in a high dark current level of about 3e-/pix/sec, even comparable to the sky brightness (10e-/pix/sec). If not corrected, the nonuniformity of the dark current could even overweight the photon noise of the sky background. However, dark frames could not be obtained during the observing season because the camera was operated in frame-transfer mode without a shutter, and the telescope was unattended in winter. Here we present an alternative, but simple and effective method to derive the dark current frame from the scientific images. Then we can scale this dark frame to the temperature at which the scientific images were taken, and apply the dark frame corrections to the scientific images. We have applied this method to the AST3 data, and demonstrated that it can reduce the noise to a level roughly as low as the photon noise of the sky brightness, solving the high noise problem and improving the photometric precision. This method will also be helpful for other projects that suffer from similar issues.

  14. Simulation of dark current and dark current-induced background photons in the Thomson scattering X-ray source

    NASA Astrophysics Data System (ADS)

    Zheng, Lianmin; Du, Yingchao; Huang, Wenhui; Tang, Chuanxiang

    2015-11-01

    A model of dark current generation in the photocathode radio-frequency (RF) gun is established in the Thomson scattering X-ray source, and dark current transport and losses along the beamline are simulated. A velocity bunching cavity is added between the RF gun and the first linac to achieve the longitudinal compression of the photoelectron bunches. Given the longitudinal acceleration and the transverse focusing of the bunching cavity, the dark current electrons with bunching are approximately three times more than those without bunching, and this condition aggravates the harm to the operation of the photoinjector. Numerous dark current electrons around the electron-laser interaction section hit against the pipe inner wall and two laser focusing mirrors, producing a large number of background photons. A simulation of the bremsstrahlung process using an MCNP code is presented, showing that the background photon yield is less than 2.1% of the scattering photon yield, which is acceptable for our application.

  15. The gravity of dark vortices: effective field theory for branes and strings carrying localized flux

    NASA Astrophysics Data System (ADS)

    Burgess, C. P.; Diener, R.; Williams, M.

    2015-11-01

    A Nielsen-Olesen vortex usually sits in an environment that expels the flux that is confined to the vortex, so flux is not present both inside and outside. We construct vortices for which this is not true, where the flux carried by the vortex also permeates the `bulk' far from the vortex. The idea is to mix the vortex's internal gauge flux with an external flux using off-diagonal kinetic mixing. Such `dark' vortices could play a phenomenological role in models with both cosmic strings and a dark gauge sector. When coupled to gravity they also provide explicit ultra-violet completions for codimension-two brane-localized flux, which arises in extra-dimensional models when the same flux that stabilizes extra-dimensional size is also localized on space-filling branes situated around the extra dimensions. We derive simple formulae for observables such as defect angle, tension, localized flux and on-vortex curvature when coupled to gravity, and show how all of these are insensitive to much of the microscopic details of the solutions, and are instead largely dictated by low-energy quantities. We derive the required effective description in terms of a world-sheet brane action, and derive the matching conditions for its couplings. We consider the case where the dimensions transverse to the bulk compactify, and determine how the on- and off-vortex curvatures and other bulk features depend on the vortex properties. We find that the brane-localized flux does not gravitate, but just renormalizes the tension in a magnetic-field independent way. The existence of an explicit UV completion puts the effective description of these models on a more precise footing, verifying that brane-localized flux can be consistent with sensible UV physics and resolving some apparent paradoxes that can arise with a naive (but commonly used) delta-function treatment of the brane's localization within the bulk.

  16. Pulsed currents carried by whistlers. II. Excitation by biased electrodes

    SciTech Connect

    Urrutia, J.M.; Stenzel, R.L.; Rousculp, C.L. )

    1994-05-01

    The transport of time-dependent current between electrodes in contact with a large laboratory magnetoplasma is examined experimentally. Single electrodes biased with respect to the chamber wall or pairs of electrically floating electrodes are used to produce pulsed currents ([omega][sub [ital ci

  17. Pulsed currents carried by whistlers. I - Excitation by magnetic antennas

    NASA Technical Reports Server (NTRS)

    Stenzel, R. L.; Urrutia, J. M.; Rousculp, C. L.

    1993-01-01

    Time-varying plasma currents associated with low-frequency whistlers have been investigated experimentally. Pulsed currents are induced in the uniform, boundary-free interior of a large laboratory plasma by means of insulated magnetic antennas. The time-varying magnetic field is measured in three dimensions, and the current density is calculated from del x B(r,t) = mu(0)J, where J includes the displacement current density. Typical fields B(r,t) and J(r,t) induced by a magnetic loop antenna show three-dimensional helices due to linked toroidal and solenoidal field topologies. Constant amplitude and phase surfaces assume conical shapes since the propagation speed along B0 is higher than oblique to B0. The electric field in the wave packet contains both inductive and space-charge contributions, the latter arising from the different dynamics of electrons and ions. The dominant electric field in a whistler packet is a radial space-charge field.

  18. Research on Field Emission and Dark Current in ILC Cavities

    SciTech Connect

    Liu, Kexin; Li, Yongming; Palczewski, Ari; Geng, Rongli

    2013-09-01

    Field emission and dark current are issues of concern for SRF cavity performance and SRF linac operation. Complete understanding and reliable control of the issue are still needed, especially in full-scale multi-cell cavities. Our work aims at developing a generic procedure for finding an active field emitter in a multi-cell cavity and benchmarking the procedure through cavity vertical test. Our ultimate goal is to provide feedback to cavity preparation and cavity string assembly in order to reduce or eliminate filed emission in SRF cavities. Systematic analysis of behaviors of field emitted electrons is obtained by ACE3P developed by SLAC. Experimental benchmark of the procedure was carried out in a 9-cell cavity vertical test at JLab. The energy spectrum of Bremsstrahlung X-rays is measured using a NaI(Tl) detector. The end-point energy in the X-ray energy spectrum is taken as the highest kinetic electron energy to predict longitudinal position of the active field emitter. Angular location of the field emitter is determined by an array of silicon diodes around irises of the cavity. High-resolution optical inspection was conducted at the predicted field emitter location.

  19. Evaluating plasmonic transport in current-carrying silver nanowires.

    PubMed

    Song, Mingxia; Stolz, Arnaud; Zhang, Douguo; Arocas, Juan; Markey, Laurent; Colas des Francs, Gérard; Dujardin, Erik; Bouhelier, Alexandre

    2013-01-01

    Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information support. In this context, metal nanowires are especially desirable for realizing dense routing networks. A prerequisite to operate such shared nanowire-based platform relies on our ability to electrically contact individual metal nanowires and efficiently excite surface plasmon polaritons in this information support. In this article, we describe a protocol to bring electrical terminals to chemically-synthesized silver nanowires randomly distributed on a glass substrate. The positions of the nanowire ends with respect to predefined landmarks are precisely located using standard optical transmission microscopy before encapsulation in an electron-sensitive resist. Trenches representing the electrode layout are subsequently designed by electron-beam lithography. Metal electrodes are then fabricated by thermally evaporating a Cr/Au layer followed by a chemical lift-off. The contacted silver nanowires are finally transferred to a leakage radiation microscope for surface plasmon excitation and characterization. Surface plasmons are launched in the nanowires by focusing a near infrared laser beam on a diffraction-limited spot overlapping one nanowire extremity. For sufficiently large nanowires, the surface plasmon mode leaks into the glass substrate. This leakage radiation is readily detected, imaged, and analyzed in the different conjugate planes in leakage radiation microscopy. The electrical terminals do not affect the plasmon propagation. However, a current-induced morphological deterioration of the nanowire drastically degrades the flow of surface plasmons. The combination of surface plasmon leakage radiation microscopy with a simultaneous analysis of the nanowire electrical transport characteristics reveals the intrinsic limitations of such plasmonic circuitry. PMID:24378340

  20. Evaluating plasmonic transport in current-carrying silver nanowires.

    PubMed

    Song, Mingxia; Stolz, Arnaud; Zhang, Douguo; Arocas, Juan; Markey, Laurent; Colas des Francs, Gérard; Dujardin, Erik; Bouhelier, Alexandre

    2013-12-11

    Plasmonics is an emerging technology capable of simultaneously transporting a plasmonic signal and an electronic signal on the same information support. In this context, metal nanowires are especially desirable for realizing dense routing networks. A prerequisite to operate such shared nanowire-based platform relies on our ability to electrically contact individual metal nanowires and efficiently excite surface plasmon polaritons in this information support. In this article, we describe a protocol to bring electrical terminals to chemically-synthesized silver nanowires randomly distributed on a glass substrate. The positions of the nanowire ends with respect to predefined landmarks are precisely located using standard optical transmission microscopy before encapsulation in an electron-sensitive resist. Trenches representing the electrode layout are subsequently designed by electron-beam lithography. Metal electrodes are then fabricated by thermally evaporating a Cr/Au layer followed by a chemical lift-off. The contacted silver nanowires are finally transferred to a leakage radiation microscope for surface plasmon excitation and characterization. Surface plasmons are launched in the nanowires by focusing a near infrared laser beam on a diffraction-limited spot overlapping one nanowire extremity. For sufficiently large nanowires, the surface plasmon mode leaks into the glass substrate. This leakage radiation is readily detected, imaged, and analyzed in the different conjugate planes in leakage radiation microscopy. The electrical terminals do not affect the plasmon propagation. However, a current-induced morphological deterioration of the nanowire drastically degrades the flow of surface plasmons. The combination of surface plasmon leakage radiation microscopy with a simultaneous analysis of the nanowire electrical transport characteristics reveals the intrinsic limitations of such plasmonic circuitry.

  1. WFC3/UVIS Dark Current Calibration and Detector Characteristics

    NASA Astrophysics Data System (ADS)

    Bourque, Matthew; Biretta, John A.; Baggett, Sylvia M.; Anderson, Jay; MacKenty, John W.; WFC3 Team

    2015-01-01

    The Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) is a fourth-generation imaging instrument that was installed during Servicing Mission 4 in May 2009. The WFC3/UVIS detector, comprised of two e2v CCDs, exhibits an inherent dark current (in the absence of any illumination) presently measured at ~6 e-/hr. In addition, detector degradation due to on-orbit radiation damage generates a continuously increasing though small population of hot pixels (dark current exceeding 54 e-/hr, ~4% of each chip) as well as 'sink' pixels (pixels which contain a large number of charge traps). We present the procedures and results of the WFC3/UVIS dark calibration, which provides calibration files used as a correction for these detector characteristics. We discuss the impacts that Charge Transfer Efficiency (CTE) losses and detector post-flashing have on the hot pixel population and overall calibration, as well as the plans for flagging the 'sink' pixels in the calibration pipeline. Finally, we discuss various improvements to the calibration procedure that will increase the accuracy of dark current and hot pixel measurements.

  2. S-NPP VIIRS DNB Dark Offset and Detector Dark Current Trending Study

    NASA Astrophysics Data System (ADS)

    Sun, Z.; Chen, W.; DeLuccia, F.; Moy, G.

    2015-12-01

    The Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band (DNB) is a panchromatic band in the VisNIR spectral range from 0.5 to 0.9 μm with a dynamic range from 3x10-9 to about 0.02 W cm-2 sr-1. DNB achieves this large dynamic range by having three gain stages: low gain (LGS), mid gain (MGS), and high gain (HGS). HGS is the average of two redundant detector arrays, HGA and HGB. The HGS offset determination is critically important to improve the imagery capability and calibration accuracy and stability at novel low radiances. Currently, the dark offset is determined on a monthly basis by observing new moon data in the dark regions in the Pacific Ocean. The data is mainly comprised of detector dark current, electronic/clock offsets, artificial illumination sources, and nighttime airglow contamination. The first two are instrument phenomena/characterizations and the last two are scene contaminations.In this presentation, we discuss the long-term growth in offset with short-term fluctuations we have captured since the beginning of the mission. We associate the long-term growth with dark current increase. We show that the offset rate of change over time is proportional to the number of Charge Coupled Device (CCD) elements aggregated to comprise a DNB pixel. We compare offset growth rate from new moon data in the dark ocean and that from calibration sector data at the same time; which contain very limited scene contaminations. We associate the short-term variability in offset growth with airglow effects that survive the filtering process used to derive the offsets from dark ocean data. These spurious offset fluctuations are removed from the offset LUTs via long time scale smoothing of the offsets. The remaining persistent time average contribution due to airglow can be estimated by comparison of the pitch maneuver propagated offsets determined from deep space scans early in the mission and the offsets determined from the dark regions in the Pacific Ocean.

  3. Projecting EOL dark current distribution of proton irradiated CCDs

    NASA Astrophysics Data System (ADS)

    Flores, James S.

    2005-09-01

    Space instrument programs occasionally need an estimate of how dark current distribution of a silicon CCD changes versus proton radiation exposure and temperature. The task that is the subject of this article was started by adopting a relevant gamma distribution model produced by M.S. Robbins [1] and estimating its parameters, α and β, by using data acquired by Demara [2]. The fortuitous result was that α was found to depend solely on damage displacement dose and β was found to be practically equal to the native bulk dark current of silicon. These implications were tested with information from three published articles. In comparison with the published results, the model was found to be accurate within a factor of two.

  4. Trapping and dark current in plasma-based accelerators

    SciTech Connect

    Schroder, C.B.; Esarey, E.; Shadwick, B.A.; Leemans, W.P.

    2004-06-01

    The trapping of thermal electrons in a nonlinear plasma wave of arbitrary phase velocity is investigated. The threshold plasma wave amplitude for trapping plasma electrons is calculated, thereby determining the fraction trapped and the expected dark current in a plasma-based accelerator. It is shown that the presence of a laser field (e.g., trapping in the self-modulated regime of the laser wakefield accelerator) increases the trapping threshold. Implications for experimental and numerical laser-plasma studies are discussed.

  5. Proposed Dark Current Studies at the Argonne Wakefield Accelerator Facility

    SciTech Connect

    Antipov, S.P.; Conde, Manoel Eduardo; Gai, Wei; Power, John Gorham; Yusof, Z.M.; Spentzouris, L.K.; Dolgashev, V.A.; /SLAC

    2008-01-18

    A study of dark currents has been initiated at the Argonne Wakefield Accelerator Facility (AWA). Emission of dark current is closely related to a breakdown. Breakdown may include several factors such as local field enhancement, explosive electron emission, Ohmic heating, tensile stress produced by electric field, and others. The AWA is building a dedicated facility to test various models for breakdown mechanisms and to determine the roles of different factors in the breakdown. An imaging system is being put together to identify single emitters on the cathode surface. This will allow us to study dark current properties in the gun. We also plan to trigger breakdown events with a high-powered laser at various wavelengths (IR to UV). Another experimental idea follows from the recent work on a Schottky-enabled photoemission in an RF photoinjector that allows us to determine in situ the field enhancement factor on a cathode surface. Monitoring the field enhancement factor before and after can shed some light on a modification of metal surface after the breakdown.

  6. Probing dark energy dynamics from current and future cosmological observations

    SciTech Connect

    Zhao Gongbo; Zhang Xinmin

    2010-02-15

    We report the constraints on the dark energy equation-of-state w(z) using the latest 'Constitution' SNe sample combined with the WMAP5 and Sloan Digital Sky Survey data. Assuming a flat Universe, and utilizing the localized principal component analysis and the model selection criteria, we find that the {Lambda}CDM model is generally consistent with the current data, yet there exists a weak hint of the possible dynamics of dark energy. In particular, a model predicting w(z)<-1 at z is an element of [0.25,0.5) and w(z)>-1 at z is an element of [0.5,0.75), which means that w(z) crosses -1 in the range of z is an element of [0.25,0.75), is mildly favored at 95% confidence level. Given the best fit model for current data as a fiducial model, we make future forecast from the joint data sets of Joint Dark Energy Mission, Planck, and Large Synoptic Survey Telescope, and we find that the future surveys can reduce the error bars on the w bins by roughly a factor of 10 for a 5-w-bin model.

  7. Mechanisms of the passage of dark currents through Cd(Zn)Te semi-insulating crystals

    NASA Astrophysics Data System (ADS)

    Sklyarchuk, V.; Fochuk, P.; Rarenko, I.; Zakharuk, Z.; Sklyarchuk, O.; Nykoniuk, Ye.; Rybka, A.; Kutny, V.; Bolotnikov, A. E.; James, R. B.

    2014-09-01

    We investigated the passage of dark currents through semi-insulating crystals of Cd(Zn)Te with weak n-type conductivity that are used widely as detectors of ionizing radiation. The crystals were grown from a tellurium solution melt at 800 оС by the zone-melting method, in which a polycrystalline rod in a quartz ampoule was moved through a zone heater at a rate of 2 mm per day. The synthesis of the rod was carried out at ~1150 оС. We determined the important electro-physical parameters of this semiconductor, using techniques based on a parallel study of the temperature dependence of current-voltage characteristics in both the ohmic and the space-charge-limited current regions. We established in these crystals the relationship between the energy levels and the concentrations of deep-level impurity states, responsible for dark conductivity and their usefulness as detectors.

  8. Correcting magnetic probe perturbations on current density measurements of current carrying plasmas

    SciTech Connect

    Knoblauch, P.; Raspa, V.; Di Lorenzo, F.; Lazarte, A.; Moreno, C.; Clausse, A.

    2010-09-15

    A method to infer the current density distribution in the current sheath of a plasma focus discharge from a magnetic probe is formulated and then applied to experimental data obtained in a 1.1 kJ device. Distortions on the magnetic probe signal caused by current redistribution and by a time-dependent total discharge current are considered simultaneously, leading to an integral equation for the current density. Two distinct, easy to implement, numerical procedures are given to solve such equation. Experimental results show the coexistence of at least two maxima in the current density structure of a nitrogen sheath.

  9. A Failure Mode in Dense Infrared Detector Arrays Resulting in Increased Dark Current

    NASA Astrophysics Data System (ADS)

    Pinkie, Benjamin; Bellotti, Enrico

    2016-09-01

    In this paper, we investigate a failure mode that arises in dense infrared focal plane detector arrays as a consequence of the interactions of neighboring pixels through the minority carrier profiles in the common absorber layer. We consider the situation in which one pixel in a hexagonal array becomes de-biased relative to its neighbors and show that the dark current in the six neighboring pixels increases exponentially as a function of the difference between the nominal and anomalous biases. Moreover, we show that the current increase in the six nearest-neighbor pixels is in total larger than that by which the current in the affected pixel decreases, causing a net increase in the dark current. The physical origins of this effect are explained as being due to increased lateral diffusion currents that arise as a consequence of breaking the symmetry of the minority carrier profiles. We then perform a parametric study to quantify the magnitude of this effect for a number of detector geometric parameters, operating temperatures, and spectral bands. Particularly, numerical simulations are carried out for short-, mid-, and long-wavelength HgCdTe infrared detectors operating between 77 K and 210 K. We show that this effect is most prevalent in architectures for which the lateral diffusion current is the largest component of the total dark current—high operating temperature devices with narrow epitaxial absorber thicknesses and pitches small compared to the diffusion length of minority carriers. These results could prove significant particularly for short- and mid-wave infrared detectors, which are typically designed to fit these conditions.

  10. Dark Current Degradation of Near Infrared Avalanche Photodiodes from Proton Irradiation

    NASA Technical Reports Server (NTRS)

    Becker, Heidi N.; Johnston, Allan H.

    2004-01-01

    InGaAs and Ge avalanche photodiodes (APDs) are examined for the effects of 63-MeV protons on dark current. Dark current increases were large and similar to prior results for silicon APDs, despite the smaller size of InGaAs and Ge devices. Bulk dark current increases from displacement damage in the depletion regions appeared to be the dominant contributor to overall dark current degradation. Differences in displacement damage factors are discussed as they relate to structural and material differences between devices.

  11. Equilibrium configurations of Vlasov plasmas carrying a current component along an external magnetic field.

    NASA Technical Reports Server (NTRS)

    Kan, J. R.

    1972-01-01

    A model of equilibrium configurations of Vlasov plasmas is considered which represents a combination of the models of Harris (1962) and Nicholson (1963). These plasma configurations carry a current component along an external magnetic field. The considered slab model contains a diamagnetic current and a field-aligned current for an arbitrary ratio of particle pressure to magnetic pressure of the applied constant field. For a fixed pressure ratio and field-aligned current, the model admits a family of equilibrium solutions in which the diamagnetic currents range from zero to a maximum value. The amount of diamagnetic current flowing in a machine depends on the width of the machine, the field-aligned current and other plasma parameters.

  12. A Measurement of the Force between Two Current-Carrying Wires

    ERIC Educational Resources Information Center

    Straulino, S.; Cartacci, A.

    2014-01-01

    The measurement of the force acting between two parallel, current-carrying wires is known as Ampère's experiment. A mechanical balance was historically employed to measure that force. We report a simple experiment based on an electronic precision balance that is useful in clearly showing students the existence of this interaction and how to…

  13. Charged Particle Dynamics in the Magnetic Field of a Long Straight Current-Carrying Wire

    ERIC Educational Resources Information Center

    Prentice, A.; Fatuzzo, M.; Toepker, T.

    2015-01-01

    By describing the motion of a charged particle in the well-known nonuniform field of a current-carrying long straight wire, a variety of teaching/learning opportunities are described: 1) Brief review of a standard problem; 2) Vector analysis; 3) Dimensionless variables; 4) Coupled differential equations; 5) Numerical solutions.

  14. Magnetic Field Due to a Finite Length Current-Carrying Wire Using the Concept of Displacement Current

    NASA Astrophysics Data System (ADS)

    Buschauer, Robert

    2014-10-01

    In undergraduate E&M courses the magnetic field due to a finite length, current-carrying wire can be calculated using the Biot-Savart law.1 However, to the author's knowledge, no textbook presents the calculation of this field using the Ampere-Maxwell law: ∮B .dl=μ0[I +ɛ0dΦ/dt

  15. Experimental evidence of photoinduced vortex crossing in current carrying superconducting strips

    NASA Astrophysics Data System (ADS)

    Casaburi, A.; Heath, R. M.; Ejrnaes, M.; Nappi, C.; Cristiano, R.; Hadfield, R. H.

    2015-12-01

    We report an experimental investigation that shows how magnetic vortices are generated and cross a current carrying superconducting strip when illuminated by a bright (˜MeV) and fast (<500 ps duration) infrared light pulse. The work has been carried out using a strike-and-probe electro-optic technique on a device consisting of a parallel superconducting strip configuration, with wide spacing between the strips to allow the interaction of the photons with a single strip. We find that photons hitting one strip induce a collective current redistribution in the parallel strips, which we can quantitatively account for in the framework of the London model by including the effect of generated and trapped magnetic vortices in the superconducting loops formed by the two adjacent slots. The amount of trapped vorticity and its dependence on increasing current density flowing in the illuminated strip is in good agreement with the photon-assisted unbinding of vortex-antivortex pairs. This work allows us to gain a deeper understanding of the interaction between photons and current carrying superconducting strips.

  16. Holographic Ricci dark energy: Current observational constraints, quintom feature, and the reconstruction of scalar-field dark energy

    NASA Astrophysics Data System (ADS)

    Zhang, Xin

    2009-05-01

    In this work, we consider the cosmological constraints on the holographic Ricci dark energy proposed by Gao et al. [Phys. Rev. DPRVDAQ1550-7998 79, 043511 (2009)10.1103/PhysRevD.79.043511], by using the observational data currently available. The main characteristic of holographic Ricci dark energy is governed by a positive numerical parameter α in the model. When α<1/2, the holographic Ricci dark energy will exhibit a quintomlike behavior; i.e., its equation of state will evolve across the cosmological-constant boundary w=-1. The parameter α can be determined only by observations. Thus, in order to characterize the evolving feature of dark energy and to predict the fate of the Universe, it is of extraordinary importance to constrain the parameter α by using the observational data. In this paper, we derive constraints on the holographic Ricci dark energy model from the latest observational data including the Union sample of 307 type Ia supernovae, the shift parameter of the cosmic microwave background given by the five-year Wilkinson Microwave Anisotropy Probe observations, and the baryon acoustic oscillation measurement from the Sloan Digital Sky Survey. The joint analysis gives the best-fit results (with 1σ uncertainty): α=0.359-0.025+0.024 and Ωm0=0.318-0.024+0.026. That is to say, according to the observations, the holographic Ricci dark energy takes on the quintom feature. Finally, in light of the results of the cosmological constraints, we discuss the issue of the scalar-field dark energy reconstruction, based on the scenario of the holographic Ricci vacuum energy.

  17. Selective equilibration among the current-carrying states in the quantum Hall regime

    NASA Technical Reports Server (NTRS)

    Alphenaar, B. W.; Mceuen, P. L.; Wheeler, R. G.; Sacks, R. N.

    1990-01-01

    The Hall resistance of a two-dimensional electron gas is measured with gated probes to determine the extent of equilibration among the N current-carrying states in the quantum Hall regime. After traveling macroscopic distances, current injected into the first state is equilibrated among the N - 1 lowest states but equilibration into the highest state varies strongly across the Hall plateau. This is attributed to a change in the Nth state from being localized within a magnetic length of the edge to substantially extending into the sample.

  18. Magnetic Field Due to a Finite Length Current-Carrying Wire Using the Concept of Displacement Current

    ERIC Educational Resources Information Center

    Buschauer, Robert

    2014-01-01

    In undergraduate E&M courses the magnetic field due to a finite length, current-carrying wire can be calculated using the Biot-Savart law. However, to the author's knowledge, no textbook presents the calculation of this field using the Ampere-Maxwell law: ?B [multiplied by] dl = µ[subscript 0] (I + e[subscript 0] dF/dt) [multiplied by] 1

  19. Earth Observing-1 Advanced Land Imager: Dark Current and Noise Characterization and Anomalous Detectors

    NASA Technical Reports Server (NTRS)

    Mendenhall, J. A.

    2001-01-01

    The dark current and noise characteristics of the Earth Observing-1 Advanced Land Imager measured during ground calibration at MIT Lincoln Laboratory are presented. Data were collected for the nominal focal plane operating temperature of 220 K as well as supplemental operating temperatures (215 and 225 K). Dark current baseline values are provided, and noise characterization includes the evaluation of white, coherent, low frequency, and high frequency components. Finally, anomalous detectors, characterized by unusual dark current, noise, gain, or cross-talk properties are investigated.

  20. Sharp burnout failure observed in high current-carrying double-walled carbon nanotube fibers.

    PubMed

    Song, Li; Toth, Geza; Wei, Jinquan; Liu, Zheng; Gao, Wei; Ci, Lijie; Vajtai, Robert; Endo, Morinobu; Ajayan, Pulickel M

    2012-01-13

    We report on the current-carrying capability and the high-current-induced thermal burnout failure modes of 5-20 μm diameter double-walled carbon nanotube (DWNT) fibers made by an improved dry-spinning method. It is found that the electrical conductivity and maximum current-carrying capability for these DWNT fibers can reach up to 5.9 × 10(5) S m(-1) and over 1 × 10(5) A cm(-2) in air. In comparison, we observed that standard carbon fiber tended to be oxidized and burnt out into cheese-like morphology when the maximum current was reached, while DWNT fiber showed a much slower breakdown behavior due to the gradual burnout in individual nanotubes. The electron microscopy observations further confirmed that the failure process of DWNT fibers occurs at localized positions, and while the individual nanotubes burn they also get aligned due to local high temperature and electrostatic field. In addition a finite element model was constructed to gain better understanding of the failure behavior of DWNT fibers. PMID:22156276

  1. Sharp burnout failure observed in high current-carrying double-walled carbon nanotube fibers

    NASA Astrophysics Data System (ADS)

    Song, Li; Toth, Geza; Wei, Jinquan; Liu, Zheng; Gao, Wei; Ci, Lijie; Vajtai, Robert; Endo, Morinobu; Ajayan, Pulickel M.

    2012-01-01

    We report on the current-carrying capability and the high-current-induced thermal burnout failure modes of 5-20 µm diameter double-walled carbon nanotube (DWNT) fibers made by an improved dry-spinning method. It is found that the electrical conductivity and maximum current-carrying capability for these DWNT fibers can reach up to 5.9 × 105 S m - 1 and over 1 × 105 A cm - 2 in air. In comparison, we observed that standard carbon fiber tended to be oxidized and burnt out into cheese-like morphology when the maximum current was reached, while DWNT fiber showed a much slower breakdown behavior due to the gradual burnout in individual nanotubes. The electron microscopy observations further confirmed that the failure process of DWNT fibers occurs at localized positions, and while the individual nanotubes burn they also get aligned due to local high temperature and electrostatic field. In addition a finite element model was constructed to gain better understanding of the failure behavior of DWNT fibers.

  2. Column buckling of doubly parallel slender nanowires carrying electric current acted upon by a magnetic field

    NASA Astrophysics Data System (ADS)

    Kiani, Keivan

    2016-08-01

    Axial buckling of current-carrying double-nanowire-systems immersed in a longitudinal magnetic field is aimed to be explored. Each nanowire is affected by the magnetic forces resulted from the externally exerted magnetic field plus the magnetic field resulted from the passage of electric current through the adjacent nanowire. To study the problem, these forces are appropriately evaluated in terms of transverse displacements. Subsequently, the governing equations of the nanosystem are constructed using Euler-Bernoulli beam theory in conjunction with the surface elasticity theory of Gurtin and Murdoch. Using a meshless technique and assumed mode method, the critical compressive buckling load of the nanosystem is determined. In a special case, the obtained results by these two numerical methods are successfully checked. The roles of the slenderness ratio, electric current, magnetic field strength, and interwire distance on the axial buckling load and stability behavior of the nanosystem are displayed and discussed in some detail.

  3. Sausage Instabilities on top of Kinking Lengthening Current-Carrying Magnetic Flux Tubes

    NASA Astrophysics Data System (ADS)

    von der Linden, Jens; You, Setthivoine

    2015-11-01

    Observations indicate that the dynamics of magnetic flux tubes in our cosmos and terrestrial experiments involve fast topological change beyond MHD reconnection. Recent experiments suggest that hierarchies of instabilities coupling disparate plasma scales could be responsible for this fast topological change by accessing two-fluid and kinetic scales. This study will explore the possibility of sausage instabilities developing on top of a kink instability in lengthening current-carrying magnetic flux tubes. Current driven flux tubes evolve over a wide range of aspect ratios k and current to magnetic flux ratios λ . An analytical stability criterion and numerical investigations, based on applying Newcomb's variational approach to idealized magnetic flux tubes with core and skin currents, indicate a dependence of the stability boundaries on current profiles and overlapping kink and sausage unstable regions in the k - λ trajectory of the flux tubes. A triple electrode planar plasma gun (Mochi.LabJet) is designed to generate flux tubes with discrete core and skin currents. Measurements from a fast-framing camera and a high resolution magnetic probe are being assembled into stability maps of the k - λ space of flux tubes. This work was sponsored in part by the US DOE Grant DE-SC0010340.

  4. Dark current in multilayer stabilized amorphous selenium based photoconductive x-ray detectors

    SciTech Connect

    Frey, Joel B.; Belev, George; Kasap, Safa O.; Tousignant, Olivier; Mani, Habib; Laperriere, Luc

    2012-07-01

    We report on experimental results which show that the dark current in n-i-p structured, amorphous selenium films is independent of i-layer thickness in samples with consistently thick blocking layers. We have observed, however, a strong dependence on the n-layer thickness and positive contact metal chosen. These results indicate that the dominant source of the dark current is carrier injection from the contacts and any contribution from carriers thermally generated in the bulk of the photoconductive layer is negligible. This conclusion is supported by a description of the dark current transients at different applied fields by a model which assumes only carrier emission over a Schottky barrier. This model also predicts that while hole injection is initially dominant, some time after the application of the bias, electron injection may become the dominant source of dark current.

  5. One hundred fold increase in current carrying capacity in a carbon nanotube–copper composite

    PubMed Central

    Subramaniam, Chandramouli; Yamada, Takeo; Kobashi, Kazufumi; Sekiguchi, Atsuko; Futaba, Don N.; Yumura, Motoo; Hata, Kenji

    2013-01-01

    Increased portability, versatility and ubiquity of electronics devices are a result of their progressive miniaturization, requiring current flow through narrow channels. Present-day devices operate close to the maximum current-carrying-capacity (that is, ampacity) of conductors (such as copper and gold), leading to decreased lifetime and performance, creating demand for new conductors with higher ampacity. Ampacity represents the maximum current-carrying capacity of the object that depends both on the structure and material. Here we report a carbon nanotube–copper composite exhibiting similar conductivity (2.3–4.7 × 105 S cm−1) as copper (5.8 × 105 S cm−1), but with a 100-times higher ampacity (6 × 108 A cm−2). Vacuum experiments demonstrate that carbon nanotubes suppress the primary failure pathways in copper as observed by the increased copper diffusion activation energy (∼2.0 eV) in carbon nanotube–copper composite, explaining its higher ampacity. This is the only material with both high conductivity and high ampacity, making it uniquely suited for applications in microscale electronics and inverters. PMID:23877359

  6. Quantum Well Infrared Photodetectors (QWIPs) Optimization Based on Dark Current Models Evaluation

    NASA Astrophysics Data System (ADS)

    Favero, Priscila P.; Tanaka, Roberto Y.; Vieira, Gustavo S.; Muraro, Ademar; Abe, Nancy M.; Passaro, Angelo

    2011-12-01

    In this work we evaluate different dark current models applied in QWIPs. In order to avoid empirical parameters we calculate the sequential tunneling probability of the lowest energy state to reproduce the dark current properties. Using the same arguments, the photocurrent is replaced by the tunneling probability modulated by the optical matrix element. Considering the different tunneling models presented in literature we apply a genetic algorithm to evaluate the models role on the election of the optimized infrared sensor.

  7. Diffraction of Harmonic Flexural Waves in a Cracked Elastic Plate Carrying Electrical Current

    NASA Technical Reports Server (NTRS)

    Ambur, Damodar R.; Hasanyan, Davresh; Librescu, iviu; Qin, Zhanming

    2005-01-01

    The scattering effect of harmonic flexural waves at a through crack in an elastic plate carrying electrical current is investigated. In this context, the Kirchhoffean bending plate theory is extended as to include magnetoelastic interactions. An incident wave giving rise to bending moments symmetric about the longitudinal z-axis of the crack is applied. Fourier transform technique reduces the problem to dual integral equations, which are then cast to a system of two singular integral equations. Efficient numerical computation is implemented to get the bending moment intensity factor for arbitrary frequency of the incident wave and of arbitrary electrical current intensity. The asymptotic behaviour of the bending moment intensity factor is analysed and parametric studies are conducted.

  8. Extraction of activation energies from temperature dependence of dark currents of SiPM

    NASA Astrophysics Data System (ADS)

    Engelmann, E.; Vinogradov, S.; Popova, E.; Wiest, F.; Iskra, P.; Gebauer, W.; Loebner, S.; Ganka, T.; Dietzinger, C.; Fojt, R.; Hansch, W.

    2016-02-01

    Despite several advantages of Silicon Photomultipliers (SiPM) over Photomultiplier Tubes (PMT) like the increased photon detection efficiency (PDE), the compact design and the insensitivity to magnetic fields, the dark count rate (DCR) of SiPM is still a large drawback. Decreasing of the SiPM dark count rate has become a modern task, which could lead to an enormous enhancement of the application range of this promising photo-detector. The main goal of this work is to gain initial information on the dark generation and identify the dominating contributions to dark currents. The chosen approach to fulfill this task is to extract characteristic activation energies of the contributing mechanisms from temperature dependent investigations of dark currents and DCR. Since conventional methods are not suited for a precise analysis of activation energies, a new method has to be developed. In this paper, first steps towards the development of a reliable method for the analysis of dark currents and dark events are presented.

  9. Spatially resolved determination of the dark saturation current of silicon solar cells from electroluminescence images

    NASA Astrophysics Data System (ADS)

    Glatthaar, Markus; Giesecke, Johannes; Kasemann, Martin; Haunschild, Jonas; The, Manuel; Warta, Wilhem; Rein, Stefan

    2009-06-01

    We present a novel method to determine spatially resolved the dark saturation current of standard silicon solar cells. For this two electroluminescence images are taken at two different voltages. From these two images, first the spatial voltage distribution can be calculated. Second by applying the Laplacian to the voltage image from Ohm's law and the continuity equation, the current through the device at a certain position can be determined. Knowing the local current through the device, the local voltage, and the emitter sheet resistance allows to determine the local dark saturation current. The clue of this method is to cope with the noise by using an appropriate noise reduction algorithm. By simulating electroluminescence images with realistic noise and known dark saturation current we demonstrate the applicability of the method with our noise reduction algorithm. Experimentally we compare our method with spectral response light beam induced current on multicrystalline solar cell.

  10. Design Guidelines for Shielding Effectiveness, Current Carrying Capability, and the Enhancement of Conductivity of Composite Materials

    NASA Technical Reports Server (NTRS)

    Evans, R. W.

    1997-01-01

    These guidelines address the electrical properties of composite materials which may have an effect on electromagnetic compatibility (EMC). The main topics of the guidelines include the electrical shielding, fault current return, and lightning protection capabilities of graphite reinforced polymers, since they are somewhat conductive but may require enhancement to be adequate for EMC purposes. Shielding effectiveness depends heavily upon the conductivity of the material. Graphite epoxy can provide useful shielding against RF signals, but it is approximately 1,000 times more resistive than good conductive metals. The reduced shielding effectiveness is significant but is still useful in many cases. The primary concern is with gaps and seams in the material just as it is with metal. Current carrying capability of graphite epoxy is adequate for dissipation static charges, but fault currents through graphite epoxy may cause fire at the shorting contact and at joints. The effect of lightning on selected graphite epoxy material and mating surfaces is described, and protection methods are reviewed.

  11. The structure of fast sausage waves in current-carrying coronal loops

    NASA Astrophysics Data System (ADS)

    Bembitov, D. B.; Mikhalyaev, B. B.; Ruderman, M. S.

    2014-09-01

    We study fast sausage waves in a model coronal loop that consists of a cylindrical core with axial magnetic field and coaxial annulus with purely azimuthal magnetic field. The magnetic field is discontinuous at the tube and core boundaries, and there are surface currents with the opposite directions on these boundaries. The principal mode of fast sausage waves in which the magnetic pressure perturbation has no nodes in the radial direction can exist for arbitrary wavelength. The results for the fundamental radial mode of sausage waves are applied to the interpretation of observed periodic pulsations of microwave emission in flaring loops with periods of a few tens of seconds. Radial plasma motion has opposite directions at the tube and core boundaries. This leads to the periodic contraction and expansion of the annulus. We assume that the principal mode of fast sausage waves in the current-carrying coronal loops is able to produce a current sheet. However, the nonlinear analysis is needed to confirm this conjecture.

  12. Roebel assembled coated conductor cables (RACC): Ac-Losses and current carrying potential

    NASA Astrophysics Data System (ADS)

    Frank, A.; Heller, R.; Goldacker, W.; Kling, A.; Schmidt, C.

    2008-02-01

    Low ac-loss HTS cables for transport currents well above 1 kA are required for application in transformers and generators and are taken into consideration for future generations of fusion reactor coils. Coated conductors (CC) are suitable candidates for high field application at an operation temperature in the range 50-77 K. Ac-field applications require cables with low ac-losses and hence twisting of the individual strands. We solved this problem using the Roebel technique. Short lengths of Roebel bar cables were prepared from industrial DyBCO and YBCO-CC. Meander shaped tapes of 4 or 5 mm width with twist pitches of 123 or 127 mm were cut from the 10 or 12 mm wide CC tapes using a specially designed tool. Eleven or twelve of these strands were assembled to a cable. The electrical and mechanical connection of the tapes was achieved using a silver powder filled conductive epoxy resin. Ac-losses of a short sample in an external ac-field were measured as a function of frequency and field amplitude as well as the coupling current decay time constant. We discuss the results in terms of available theories and compare measured time constants in transverse field with measured coupling losses. Finally the potential of this cable type for ac-use is discussed with respect to ac-losses and current carrying capability.

  13. In Situ Observation of Dark Current Emission in a High Gradient rf Photocathode Gun.

    PubMed

    Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P; Baryshev, Sergey V; Chen, Huaibi; Conde, Manoel; Gai, Wei; Ha, Gwanghui; Jing, Chunguang; Wang, Faya; Wisniewski, Eric

    2016-08-19

    Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (∼100  μm) dark current imaging experiment has been performed in an L-band photocathode gun operating at ∼100  MV/m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. The postexaminations with scanning electron microscopy and white light interferometry reveal the origins of ∼75% strong emission areas overlap with the spots where rf breakdown has occurred. PMID:27588860

  14. In Situ Observation of Dark Current Emission in a High Gradient rf Photocathode Gun

    NASA Astrophysics Data System (ADS)

    Shao, Jiahang; Shi, Jiaru; Antipov, Sergey P.; Baryshev, Sergey V.; Chen, Huaibi; Conde, Manoel; Gai, Wei; Ha, Gwanghui; Jing, Chunguang; Wang, Faya; Wisniewski, Eric

    2016-08-01

    Undesirable electron field emission (also known as dark current) in high gradient rf photocathode guns deteriorates the quality of the photoemission current and limits the operational gradient. To improve the understanding of dark current emission, a high-resolution (˜100 μ m ) dark current imaging experiment has been performed in an L -band photocathode gun operating at ˜100 MV /m of surface gradient. Scattered strong emission areas with high current have been observed on the cathode. The field enhancement factor β of selected regions on the cathode has been measured. The postexaminations with scanning electron microscopy and white light interferometry reveal the origins of ˜75 % strong emission areas overlap with the spots where rf breakdown has occurred.

  15. Spatial and temporal evolution of filamentation instability in a current-carrying plasma

    SciTech Connect

    Mohammadhosseini, B.; Niknam, A. R.; Shokri, B.

    2010-12-15

    The spatial and temporal evolution of the electric and magnetic fields in a current-carrying plasma is investigated in the nonlinear regime. Using the magnetohydrodynamic equations, a nonlinear diffusion equation for the magnetic field in the plasma is obtained. This nonlinear equation is numerically solved and the spatiotemporal evolution of the electric and magnetic fields and the electron density distribution are plotted. It is shown that as the time passes, the profile of the electric and magnetic fields changes from a sinusoidal shape to a saw-tooth one and the electron density distribution becomes very steepened. Also, the mechanism of the filament formation is then discussed. Furthermore, the effects of the thermal motion, collisions, and ion mass on growth rate of filaments as well as the saturation time are argued. Finally, it is found that the energy dissipation is associated with the aforementioned effects and strong plasma density gradient.

  16. Suppression of vertical instability in elongated current-carrying plasmas by applying stellarator rotational transform

    SciTech Connect

    ArchMiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Knowlton, S. F.; Ma, X.; Maurer, D. A.; Pandya, M. D.; Traverso, P.

    2014-05-15

    The passive stability of vertically elongated current-carrying toroidal plasmas has been investigated in the Compact Toroidal Hybrid, a stellarator/tokamak hybrid device. In this experiment, the fractional transform f, defined as the ratio of the imposed external rotational transform from stellarator coils to the total rotational transform, was varied from 0.04 to 0.50, and the elongation κ was varied from 1.4 to 2.2. Plasmas that were vertically unstable were evidenced by motion of the plasma in the vertical direction. Vertical drifts are measured with a set of poloidal field pickup coils. A three chord horizontally viewing interferometer and a soft X-ray diode array confirmed the drifts. Plasmas with low fractional transform and high elongation are the most susceptible to vertical instability, consistent with analytic predictions that the vertical mode in elongated plasmas can be stabilized by the poloidal field of a relatively weak stellarator equilibrium.

  17. Suppression of vertical instability in elongated current-carrying plasmas by applying stellarator rotational transforma)

    NASA Astrophysics Data System (ADS)

    ArchMiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Knowlton, S. F.; Ma, X.; Maurer, D. A.; Pandya, M. D.; Traverso, P.

    2014-05-01

    The passive stability of vertically elongated current-carrying toroidal plasmas has been investigated in the Compact Toroidal Hybrid, a stellarator/tokamak hybrid device. In this experiment, the fractional transform f, defined as the ratio of the imposed external rotational transform from stellarator coils to the total rotational transform, was varied from 0.04 to 0.50, and the elongation κ was varied from 1.4 to 2.2. Plasmas that were vertically unstable were evidenced by motion of the plasma in the vertical direction. Vertical drifts are measured with a set of poloidal field pickup coils. A three chord horizontally viewing interferometer and a soft X-ray diode array confirmed the drifts. Plasmas with low fractional transform and high elongation are the most susceptible to vertical instability, consistent with analytic predictions that the vertical mode in elongated plasmas can be stabilized by the poloidal field of a relatively weak stellarator equilibrium.

  18. Dark current in GaAs/AlxGa1-xAs quantum well infrared detectors

    NASA Astrophysics Data System (ADS)

    Nathan, Vaidya

    2013-01-01

    It is not clear whether the tunneling current in QWIPs depends just on the energy corresponding to motion perpendicular to the plane of the quantum well or on the total energy. In order to get a quantitative assessment of the contribution of energy corresponding to motion in the plane of the quantum well to the dark current we use the following approach. We calculate the dark current in GaAs/AlxGa1-x s quantum well infrared detectors for both tunneling dependent only on Ez, and tunneling dependent on the total energy, and compare the results to experimental data. Comparison of theoretical results with experimental data at 40K shows that motion in the plane of the quantum well plays a significant role in determining the tunneling dark current. Corrections are made to Levine's original formula. Variation of the dark current with barrier width and doping density is systematically studied. It is shown that increasing the barrier width and/or decreasing the doping density in the well do not always reduce the dark current.

  19. Transient and steady-state dark current mechanisms in amorphous selenium avalanche radiation detectors

    SciTech Connect

    Kabir, M. Z.; Imam, Safayat-Al

    2013-04-15

    A theoretical model for describing bias-dependent transient and steady-state behaviors of dark current in amorphous selenium (a-Se) avalanche detector structures has been developed. The analytical model considers bulk thermal generation current from mid-gap sates, transient carrier depletion, and carrier injection from the electrodes incorporating avalanche multiplication. The proposed physics-based dark current model is compared with the published experimental results on three potential a-Se avalanche detector structures. The steady-state dark current is the minimum for the structures that have effective blocking layers for both holes and electrons. The transient decay time to reach a plateau decreases considerably with increasing electric field.

  20. Dynamics and instability of current-carrying microbeams in a longitudinal magnetic field

    NASA Astrophysics Data System (ADS)

    Wang, Lin; Liu, Wen-Bo; Dai, Hu-Liang

    2015-02-01

    The dynamics and instability of current-carrying slender microbeams immersed in a longitudinal magnetic field is investigated by considering the material length scale effect of the microbeam. On the basis of modified couple stress theory, a theoretical model considering the effect of Lorentz forces is developed to analyze the free vibration and possible instability of the microbeam. Using the differential quadrature method, the governing equations of motion are solved and the lowest three natural frequencies are determined. The obtained results reveal that the electric current and the longitudinal magnetic field tend to reduce the microbeam's flexural stiffness. It is therefore shown that the lowest natural frequencies would decrease with increasing magnetic field parameter. The mode shapes of the microbeam are found to be generally three-dimensional spatial in the presence of the longitudinal magnetic field. It is interesting that buckling instability would concurrently occur in the first mode or in the higher-order modes when the magnetic field parameter becomes sufficiently large.

  1. Spin Currents Carried by Spinons in XXZ Spin Chains: Signatures in Polarized Inelastic Neutron Scattering

    NASA Astrophysics Data System (ADS)

    English, Leonard Patrick; Braun, Hans-Benjamin; Kulda, Jiri

    2015-03-01

    Quantum spin chains serve as a paradigm for exploring truly quantum phenomena, with spinons being the elementary excitations. Motivated by compounds such as CsCoBr3 and CsCoCl3, we focus on the Ising-like antiferromagnetic Heisenberg XXZ model (spin-1/2). Here we present theoretical results for the total inelastic scattering cross section of spin-polarized neutrons in the presence of an external magnetic field, which is applied transverse to the Ising direction. In particular, we identify the spin current associated with spinons and their corresponding signatures in the neutron scattering cross section. The presence of a transverse magnetic field no longer allows for reliance on Stotz as a conserved quantity, which has traditionally been assumed in this context. As a striking consequence, we find that the spinons carry a non-vanishing spin current, even in the limit of infinitesimal fields. Our results are shown to be in good agreement with experimental neutron scattering data on CsCoBr3.

  2. Using dark current data to estimate AVIRIS noise covariance and improve spectral analyses

    NASA Technical Reports Server (NTRS)

    Boardman, Joseph W.

    1995-01-01

    Starting in 1994, all AVIRIS data distributions include a new product useful for quantification and modeling of the noise in the reported radiance data. The 'postcal' file contains approximately 100 lines of dark current data collected at the end of each data acquisition run. In essence this is a regular spectral-image cube, with 614 samples, 100 lines and 224 channels, collected with a closed shutter. Since there is no incident radiance signal, the recorded DN measure only the DC signal level and the noise in the system. Similar dark current measurements, made at the end of each line are used, with a 100 line moving average, to remove the DC signal offset. Therefore, the pixel-by-pixel fluctuations about the mean of this dark current image provide an excellent model for the additive noise that is present in AVIRIS reported radiance data. The 61,400 dark current spectra can be used to calculate the noise levels in each channel and the noise covariance matrix. Both of these noise parameters should be used to improve spectral processing techniques. Some processing techniques, such as spectral curve fitting, will benefit from a robust estimate of the channel-dependent noise levels. Other techniques, such as automated unmixing and classification, will be improved by the stable and scene-independence noise covariance estimate. Future imaging spectrometry systems should have a similar ability to record dark current data, permitting this noise characterization and modeling.

  3. The microscopic Z-pinch process of current-carrying rarefied deuterium plasma shell

    SciTech Connect

    Ning, Cheng; Xue, Chuang; Li, Baiwen; Feng, Zhixing

    2015-02-15

    For insight into the microscopic mechanism of Z-pinch dynamic processes, a code of two-dimensional particle-in-cell (PIC) simulation has been developed in cylindrical coordinates. In principle, the Z-pinch of current-carrying rarefied deuterium plasma shell has been simulated by means of this code. Many results related to the microscopic processes of the Z-pinch are obtained. They include the spatio-temporal distributions of electromagnetic field, current density, forces experienced by the ions and electrons, positions and energy distributions of particles, and trailing mass and current. In radial direction, the electric and magnetic forces exerted on the electrons are comparable in magnitude, while the forces exerted on the ions are mainly the electric forces. So in the Z-pinch process, the electrons are first accelerated in Z direction and get higher velocities; then, they are driven inwards to the axis at the same time by the radial magnetic forces (i.e., Lorentz forces) of them. That causes the separations between the electrons and ions because the ion mass is much larger than the electron's, and in turn a strong electrostatic field is produced. The produced electrostatic field attracts the ions to move towards the electrons. When the electrons are driven along the radial direction to arrive at the axis, they shortly move inversely due to the static repellency among them and their tiny mass, while the ions continue to move inertially inwards, and later get into stagnation, and finally scatter outwards. Near the stagnation, the energies of the deuterium ions mostly range from 0.3 to 6 keV, while the electron energies are mostly from 5 to 35 keV. The radial components, which can contribute to the pinched plasma temperature, of the most probable energies of electron and ion at the stagnation are comparable to the Bennett equilibrium temperature (about 1 keV), and also to the highest temperatures of electron and ion obtained in one dimensional radiation

  4. Low dark current LWIR HgCdTe focal plane arrays at AIM

    NASA Astrophysics Data System (ADS)

    Haiml, M.; Eich, D.; Fick, W.; Figgemeier, H.; Hanna, S.; Mahlein, M.; Schirmacher, W.; Thöt, R.

    2016-05-01

    Cryogenically cooled HgCdTe (MCT) quantum detectors are unequalled for applications requiring high imaging as well as high radiometric performance in the infrared spectral range. Compared with other technologies, they provide several advantages, such as the highest quantum efficiency, lower power dissipation compared to photoconductive devices, and fast response times, hence outperforming micro-bolometer arrays. AIM will present its latest results on n-on-p as well as p-on-n low dark current planar MCT photodiode focal plane detector arrays at cut-off wavelengths >11 μm at 80 K. Dark current densities below the Rule'07 have been demonstrated for n-on-p devices. Slightly higher dark current densities and excellent cosmetics with very low cluster and point defect densities have been demonstrated for p-on-n devices.

  5. Modeling of the quantum dot filling and the dark current of quantum dot infrared photodetectors

    SciTech Connect

    Ameen, Tarek A.; El-Batawy, Yasser M.; Abouelsaood, A. A.

    2014-02-14

    A generalized drift-diffusion model for the calculation of both the quantum dot filling profile and the dark current of quantum dot infrared photodetectors is proposed. The confined electrons inside the quantum dots produce a space-charge potential barrier between the two contacts, which controls the quantum dot filling and limits the dark current in the device. The results of the model reasonably agree with a published experimental work. It is found that increasing either the doping level or the temperature results in an exponential increase of the dark current. The quantum dot filling turns out to be nonuniform, with a dot near the contacts containing more electrons than one in the middle of the device where the dot occupation approximately equals the number of doping atoms per dot, which means that quantum dots away from contacts will be nearly unoccupied if the active region is undoped.

  6. Curvature and torsion effects in electric current-carrying twisted solar loops

    SciTech Connect

    Garcia de Andrade, L. C.

    2006-11-15

    Riemannian geometry of the electric current-carrying solar loops is obtained from a thin tube approximation of twisted magnetic flux tubes. The Frenet torsion and curvature affect the electron drift speed of the electrons of the current along the toroidal direction of the tube. The twist of the tube is computed and it is shown that twist is maximum at the surface of the tube and minimum at the tube axis. This acts as inertia effects to the electron drift. The higher the torsion of the tube axis the smaller is the velocity along the direction of the tube. This effect is similar to the one obtained by Tyspin et al. [Physics of Plasmas, 5, 3385 (1998)] in the case of toroidal devices with curvature and torsion. Here the simple geometrical effects are enough to slow down the currents and no viscosity in the fluid is taken into account. A slight compressibility of the plasma flow is due to the twist of the tube. As applications of these ideas, it is shown that torsion effects are not enough to accelerate electrons up to relativistic energies, and the torsion is computed in the case of the force-free loop. The value of torsion is used to compute the electron acceleration in two distinct cases. The first is the case when the Riemann loop suffers the action of a dc electric sub-Dreicer field, where the magnetic field is direct along the magnetic loop, and the loop moves along the orthogonal direction to the loop as in vortex filaments. In this case, the acceleration is shown to be of the order of 10{sup -17} cm s{sup -2} for a solar torsion of the order of 10{sup -4} cm{sup -1}. The second case is for the curvature drift contribution, where torsion is also present. In this case we show that torsion is not present in the velocity drift but just in the electron acceleration. Though these values are extremely low, they can be improved by considering small loops lowering the radius of the loop which, here, was taken as 600 km. Curvature drift acceleration is also estimated as

  7. Low dark current MCT-based focal plane detector arrays for the LWIR and VLWIR developed at AIM

    NASA Astrophysics Data System (ADS)

    Gassmann, Kai Uwe; Eich, Detlef; Fick, Wolfgang; Figgemeier, Heinrich; Hanna, Stefan; Thöt, Richard

    2015-10-01

    prerequisite for future scientific space and earth observation missions. Aiming, for example at exoplanet or earth atmospheric spectral analysis, significant improvement in LWIR / VLWIR detector material performance is mandatory. LDC material optimization can target different directions of impact: (i) reduction of dark current for a given operational temperature to increase SNR and reduce thermally induced signal offset variations. (ii) operation at elevated temperatures at a given dark current level to reduce mass and power budget of the required cryocooler and to reduce cryostat complexity. (iii) increase the accessible cut-off wavelength at constant detector temperature and dark current level. This paper presents AIM's latest results on n-on-p as well as p-on-n low dark current planar MCT photodiode focal plane detector arrays at cut-off wavelengths >11 μm at 80 K. Dark current densities below Tennant's `Rule07'1 have been demonstrated for n-on-p and p-on-n devices. This work has been carried out under ESA contract ESTEC 4000107414/13/NL/SFe².

  8. Comparison of Measured Dark Current Distributions with Calculated Damage Energy Distributions in HgCdTe

    NASA Technical Reports Server (NTRS)

    Marshall, C. J.; Marshall, P. W.; Howe, C. L.; Reed, R. A.; Weller, R. A.; Mendenhall, M.; Waczynski, A.; Ladbury, R.; Jordan, T. M.

    2007-01-01

    This paper presents a combined Monte Carlo and analytic approach to the calculation of the pixel-to-pixel distribution of proton-induced damage in a HgCdTe sensor array and compares the results to measured dark current distributions after damage by 63 MeV protons. The moments of the Coulombic, nuclear elastic and nuclear inelastic damage distributions were extracted from Monte Carlo simulations and combined to form a damage distribution using the analytic techniques first described in [1]. The calculations show that the high energy recoils from the nuclear inelastic reactions (calculated using the Monte Carlo code MCNPX [2]) produce a pronounced skewing of the damage energy distribution. While the nuclear elastic component (also calculated using the MCNPX) contributes only a small fraction of the total nonionizing damage energy, its inclusion in the shape of the damage across the array is significant. The Coulombic contribution was calculated using MRED [3-5], a Geant4 [4,6] application. The comparison with the dark current distribution strongly suggests that mechanisms which are not linearly correlated with nonionizing damage produced according to collision kinematics are responsible for the observed dark current increases. This has important implications for the process of predicting the on-orbit dark current response of the HgCdTe sensor array.

  9. Radiative dark current in optically thin III-V photovoltaic devices

    NASA Astrophysics Data System (ADS)

    Welser, Roger E.; Sood, Ashok K.; Tatavarti, Sudersena Rao; Wibowo, Andree; Wilt, David M.; Howard, Alex

    2015-03-01

    High-voltage InGaAs quantum well solar cells have been demonstrated in a thin-film format, utilizing structures that employ advanced band gap engineering to suppress non-radiative recombination and expose the limiting radiative component of the diode current. In particular, multiple InGaAs quantum well structures fabricated via epitaxial lift-off exhibit one-sun open circuit voltages as high as 1.05 V. The dark diode characteristics of these high-voltage III-V photovoltaic devices are compared to the radiative current calculated from the measured external quantum efficiency using a generalized detailed balance model specifically adapted for optically-thin absorber structures. The fitted n=1 component of the diode current is found to match the calculated radiative dark current when assuming negligible photon recycling, suggesting this thin-film multiple quantum well structure is operating close to the radiative limit.

  10. HIPS-GLAD core shell nanorod array photodetectors with enhanced photocurrent and reduced dark current

    NASA Astrophysics Data System (ADS)

    Keles, Filiz; Cansizoglu, Hilal; Badraddin, Emad O.; Brozak, Matthew P.; Watanabe, Fumiya; Karabacak, Tansel

    2016-10-01

    Vertically aligned core/shell nanorod array photodetectors were fabricated by high pressure sputter (HIPS) deposition of copper indium sulfide (CIS) films on glancing angle deposited (GLAD) indium sulfide (In2S3) nanorods. For comparison, we also studied nanorod photodetectors with conventional low pressure sputtered (LPS) CIS film coatings and counterpart thin film devices incorporating HIPS or LPS-CIS on In2S3 films. HIPS-GLAD core/shell photodetectors have shown a superior photocurrent density response along with lowest dark current density. Photoresponsivity defined with the photocurrent density/dark current density ratio γ = |J ph/J dark| was about ∼1820 for HIPS-GLAD nanorod devices, which is several orders of magnitude higher compared to those of LPS-CIS thin film (γ ∼ 2) and HIPS-CIS thin film (γ ∼ 9) devices, and also about four-fold higher than LPS-CIS nanorod devices (γ ∼ 490). Enhanced photoresponsivity is attributed to the porous microstructure and improved conformality of HIPS-CIS film around the In2S3 nanorods confirmed by SEM and EDS measurements. Due to randomization of the sputtered flux at higher working gas pressures, HIPS can provide a more conformal while at the same time a voidy low-density film around nanostructured surfaces. Reduced interelectrode distance and improved p–n junction interface due to the more uniform conformality of HIPS-CIS result in a higher photocurrent in our HIPS-GLAD devices. In addition, the voids in HIPS-CIS film as a result of its porous nature can behave as highly resistive spots that lower the dark current. Therefore, we have demonstrated that by utilizing a simple and low-temperature HIPS-GLAD method, high-photocurrent and low-dark-current photodetectors can be achieved by controlling the conformality and microstructure of a shell layer around nanorod arrays. HIPS shell coating method can be extended to almost any type of nanostructured substrate.

  11. Investigation of dark current mechanisms on type-II InAs/GaSb superlattice very long wavelength infrared detectors

    NASA Astrophysics Data System (ADS)

    Li, Xiaochao; Jiang, Dongwei; Zhang, Yong; Wang, Dongbo; Yu, Qingjiang; Liu, Tong; Ma, Honghu; Zhao, Liancheng

    2016-04-01

    An analytical approach to isolating the contribution of surface leakage current from bulk dark current by simulating the current-voltage characteristic of InAs/GaSb superlattice detectors is presented in this paper. It is found that for all the mesa sizes used, the dark current is dominated by the surface component under low reverse bias, and the proportion of surface leakage current to total dark current increases with decreasing mesa size. The limiting dark current mechanisms and main parameters of the InAs/GaSb T2SL detectors were analyzed using a theoretical model including the contribution of surface leakage. We found that surface leakage currents provide a significant contribution, while the ohmic shunt current originating from threading dislocations is not significant.

  12. Dark current in antimony-based mid-infrared interband cascade infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Tian, Z.-B.; Schuler-Sandy, T.; Krishna, S.

    2015-05-01

    The quantum-engineered interband cascade (IC) photodetector is a new type of infrared detectors with many unique and highly desirable features. The multi-stage design allows much flexibility in device optimization for different application environment, such as operation temperature, irradiance level, and possibly high-speed and fast frame-rate application scenarios. Many other distinctive features, such as excellent photo-carrier extraction and photovoltaic (zero-bias) operations, are also very attractive for high performance infrared imaging applications. In this paper, we report our experimental investigation on the dark current mechanisms in mid-wave infrared (MWIR) InAs/GaSb type-II superlattices based IC photodetectors. The electrical performance of MWIR IC detectors with several different designs are presented in detail. The dark current density in the MWIR IC detectors is as low as 4.26 × 10-8 A/cm2 (1.44 × 10-3 A/cm2) at -10 mV, with Johnson-limited D∗ of 9.11 × 1011 cm Hz1/2/W (1.58 × 109 cm Hz1/2/W) at 140 K (room temperature) and 3.6 μm. Our results indicate that the dominating dark current in IC detectors is from tunneling components at lower temperatures, and changes to diffusion current at higher operating temperatures. Furthermore, our effort also shows that the dark current performance in IC devices can be improved substantially by refining the device design and implementations.

  13. Uniform magnetic fields generated by circular current-carrying coils. [for spacecraft

    NASA Technical Reports Server (NTRS)

    Williams, V. L.; Cain, J. C.

    1975-01-01

    The study described was carried out to evaluate known systems of circular coils with a view toward their application on board the space probes Ranger 1, Ranger 2, and Explorer 10. Particular attention is given to a new method, developed during the investigation, for determining the constants of systems composed of 6 to 8 coils. Such systems were found to generate magnetic fields of very high uniformity. By using advanced computational techniques, it proved possible to evaluate the field uniformity of various systems without recourse to complex analytical methods. Means of evaluating the influence of coil dimensions on the uniformity of the field of any system are described.

  14. Suppression of dark current through barrier engineer for solution-processed colloidal quantum-dots infrared photodetectors

    SciTech Connect

    Jiang, Zhenyu E-mail: jianxu@engr.psu.edu; Liu, Yan; Mo, Chen; Wang, Li; Atalla, Mahmoud R. M.; Liu, Jie; Kurhade, Kandhar K.; Xu, Jian E-mail: jianxu@engr.psu.edu; Hu, Wenjia; Zhang, Wenjun; You, Guanjun; Zhang, Yu

    2015-08-31

    In an attempt to suppress the dark current, the barrier layer engineer for solution-processed PbSe colloidal quantum-dot (CQD) photodetectors has been investigated in the present study. It was found that the dark current can be significantly suppressed by implementing two types of carrier blocking layers, namely, hole blocking layer and electron blocking layer, sandwiched in between two active PbSe CQD layers. Meanwhile no adverse impact has been observed for the photo current. Our study suggests that this improvement resides on the transport pathway created via carrier recombination at intermediate layer, which provides wide implications for the suppression of dark current for infrared photodetectors.

  15. Dark-current characteristics of GaN-based UV avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Xu, Jintong; Chang, Chao; Li, Xiangyang

    2015-04-01

    For UV detecting, it needs high ratio of signal to noise, which means high responsibility and low noise. GaN-based avalanche photodiodes can provide a high internal photocurrent gain. In this paper, we report the testing and characterization of GaN based thin film materials, optimization design of device structure, the device etching and passivation technology, and the photoelectric characteristics of the devices. Also, uniformity of the device was obtained. The relationship between dark current and material quality or device processes was the focus of this study. GaN based material with high aluminum components have high density defects. Scanning electron microscope, cathodoluminescence spectra, X-ray double crystal diffraction and transmission spectroscopy testing were employed to evaluate the quality of GaN-based material. It shows that patterned sapphire substrate or thick AlN buffer layer is more effective to get high quality materials. GaN-based materials have larger hole ionization coefficient, so back incident structure were adopted to maximize the hole-derived multiplication course and it was helped to get a smaller multiplication noise. The device with separate absorption and multiplication regions is also prospective to reduce the avalanche noise. According to AlGaN based material characteristics and actual device fabrication, device structure was optimized further. Low physical damage inductively coupled plasma (ICP) etching method was used to etch mesa and wet etching method was employed to treat mesa damage. Silica is passivation material of device mesa. For solar-blind ultraviolet device, it is necessary to adopt a wider bandgap material than AlGaN material. The current-voltage characteristics under reverse bias were measured in darkness and under UV illumination. The distribution of dark current and response of different devices was obtained. In short, for GaN-based UV avalanche photodiode, dark current was related to high density dislocation of

  16. Nonequilibrium current-carrying steady states in the anisotropic XY spin chain.

    PubMed

    Lancaster, Jarrett L

    2016-05-01

    Out-of-equilibrium behavior is explored in the one-dimensional anisotropic XY model. Initially preparing the system in the isotropic XX model with a linearly varying magnetic field to create a domain-wall magnetization profile, dynamics is generated by rapidly changing the exchange interaction anisotropy and external magnetic field. Relaxation to a nonequilibrium steady state is studied analytically at the critical transverse Ising point, where correlation functions may be computed in closed form. For arbitrary values of anisotropy and external field, an effective generalized Gibbs' ensemble is shown to accurately describe observables in the long-time limit. Additionally, we find spatial oscillations in the exponentially decaying, transverse spin-spin correlation functions with wavelength set by the magnetization jump across the initial domain wall. This wavelength depends only weakly on anisotropy and magnetic field in contrast to the current, which is highly dependent on these parameters.

  17. Defect-controlled vortex generation in current-carrying narrow superconducting strips

    NASA Astrophysics Data System (ADS)

    Vodolazov, D. Yu; Ilin, K.; Merker, M.; Siegel, M.

    2016-02-01

    We experimentally study the effect of a single circular hole on the critical current I c of narrow superconducting strip with width W much smaller than Pearl penetration depth Λ. We found non-monotonous dependence of I c on the location of a hole across the strip and a weak dependence of I c on the radius of a hole in the case of a hole with ξ \\ll R\\ll W (ξ is a superconducting coherence length) which is placed in the center of strip. The observed effects are caused by competition of two mechanisms of destruction of superconductivity—the entrance of vortex via the edge of the strip and the nucleation of the vortex-antivortex pair near the hole. The mechanisms are clearly distinguishable by a difference in dependence of I c on weak magnetic field.

  18. CURRENT STATUS OF THE G0 PARITY VIOLATION EXPERIMENT CARRIED OUT AT JEFFERSON LABORATORY

    SciTech Connect

    Bimbot, L.

    2010-12-01

    Among experiments looking for strangeness in nuclear systems, electron scattering parity-violation type experiments aim mainly at measuring the strange quark contributions to the form factors of the proton. They can be accessed by measuring asymmetry in longitudinally polarized electron elastic scattering on hydrogen. The parity-violating asymmetry is measured at the ~ 10-7 level of accuracy, and when combined with the electromagnetic form factors of the proton, the strange form factors can be determined. The full separation of form factors according to quark flavour requires measurements at forward angle on hydrogen and at backward angle on proton and deuteron. The experimental setups used for the G0 experiment in the two different configurations will be described. The status of the analysis and the current results will be presented and discussed in relation with other experiments past and planned. The G0 forward angle measurement(2) detected the recoil proton with a segmented detector covering, for one incident energy, different Q2 bins ranging from 0.1 to 1.0 (GeV/c)2. This measurement provided a linear combination of strange magnetic and strange electric form factors for each Q2. In the backward angle configuration, electrons were detected and just one Q2 value was covered at a given incident energy. Due to time limitation, only two cases have been studied: Q2 ~ 0.63 and 0.23 (GeV/c)2. These values were chosen to be directly comparable with results from other experiments. By combining backward and forward configuration measurements it is possible to extract separately the electric and the magnetic strange form factors. The measurements are complete. The analysis, still in progress, will be described. A few comments will also be made regarding some other aspects of physics accessible in simultaneous measurements: neutral current in N transition parity violation in inclusive - production and 2 contribution to elastic scattering.

  19. Nonlinear Resonant Excitation of Fast Sausage Waves in Current-Carrying Coronal Loops

    NASA Astrophysics Data System (ADS)

    Mikhalyaev, B. B.; Bembitov, D. B.

    2014-11-01

    We consider a model of a coronal loop that is a cylindrical magnetic tube with two surface electric currents. Its principal sausage mode has no cut-off in the long-wavelength limit. For typical coronal conditions, the period of the mode is between one and a few minutes. The sausage mode of flaring loops could cause long-period pulsations observed in microwave and hard X-ray ranges. There are other examples of coronal oscillations: long-period pulsations of active-region quiet loops in the soft X-ray emission are observed. We assume that these can also be caused by sausage waves. The question arises of how the sausage waves are generated in quiet loops. We assume that they can be generated by torsional oscillations. This process can be described in the framework of the nonlinear three-wave interaction formalism. The periods of interacting torsional waves are similar to the periods of torsional oscillations observed in the solar atmosphere. The timescale of the sausage-wave excitation is not much longer than the periods of interacting waves, so that the sausage wave is excited before torsional waves are damped.

  20. Barrier lowering effect and dark current characteristics in asymmetric GaAs/AlGaAs multi quantum well structure

    NASA Astrophysics Data System (ADS)

    Altin, E.; Hostut, M.; Ergun, Y.

    2011-12-01

    In this study, we investigate dark current voltage characteristics of GaAs/AlGaAs staircase-like asymmetric multiquantum well structure at various temperatures experimentally. The activation energy is calculated by using Arrhenius plots at different voltages. It is found that the activation energy decreased with increasing electric field. This result is evaluated using a barrier lowering effect which is a combination of geometrical and Poole-Frenkel effects. Measured dark current density-voltage ( J- V) characteristics compared with the Levine model, 3D carrier drift model and the emission capture model. The best agreement with the experimental results of dark current densities is obtained by the Levine model.

  1. Neutrino physics with dark matter experiments and the signature of new baryonic neutral currents

    SciTech Connect

    Pospelov, Maxim

    2011-10-15

    New neutrino states {nu}{sub b}, sterile under the standard model interactions, can be coupled to baryons via the isoscalar vector currents that are much stronger than the standard model weak interactions. If some fraction of solar neutrinos oscillate into {nu}{sub b} on their way to Earth, the coherently enhanced elastic {nu}{sub b}-nucleus scattering can generate a strong signal in the dark matter detectors. For the interaction strength a few hundred times stronger than the weak force, the elastic {nu}{sub b}-nucleus scattering via new baryonic currents may account for the existing anomalies in the direct detection dark matter experiments at low recoil. We point out that for solar-neutrino energies, the baryon-current-induced inelastic scattering is suppressed, so that the possible enhancement of a new force is not in conflict with signals at dedicated neutrino detectors. We check this explicitly by calculating the {nu}{sub b}-induced deuteron breakup, and the excitation of a 4.4 MeV {gamma} line in {sup 12}C. A stronger-than-weak force coupled to the baryonic current implies the existence of a new Abelian gauge group U(1){sub B} with a relatively light gauge boson.

  2. Testing an e2v CCD230-42 sensor for dark current performance at ambient temperatures - Final Paper

    SciTech Connect

    Dungee, Ryan

    2015-08-20

    The design of the Guidance Focus and Alignment (GFA) system for the Dark Energy Spectroscopic Instrument (DESI) project calls for a set of charge-coupled devices (CCDs) which operate at ambient temperature. Here we assess the performance of these CCDs under such conditions. Data was collected from –21°C to 28°C and used to determine the effect of temperature on the effectiveness of dark current subtraction. Comparing the dark current uncertainty to our expected signal has shown that the DESI design specifications will be met without need for significant changes.

  3. Ultra compact 45 GHz CMOS compatible Germanium waveguide photodiode with low dark current.

    PubMed

    DeRose, Christopher T; Trotter, Douglas C; Zortman, William A; Starbuck, Andrew L; Fisher, Moz; Watts, Michael R; Davids, Paul S

    2011-12-01

    We present a compact 1.3 × 4 μm2 Germanium waveguide photodiode, integrated in a CMOS compatible silicon photonics process flow. This photodiode has a best-in-class 3 dB cutoff frequency of 45 GHz, responsivity of 0.8 A/W and dark current of 3 nA. The low intrinsic capacitance of this device may enable the elimination of transimpedance amplifiers in future optical data communication receivers, creating ultra low power consumption optical communications. PMID:22273883

  4. Limiting dark current mechanisms in antimony-based superlattice infrared detectors for the long-wavelength infrared regime

    NASA Astrophysics Data System (ADS)

    Rehm, Robert; Lemke, Florian; Schmitz, Johannes; Wauro, Matthias; Walther, Martin

    2015-06-01

    A detailed understanding of limiting dark current mechanisms in InAs/GaSb type-II superlattice (T2SL) infrared detectors is key to improve the electrooptical performance of these devices. We present a six-component dark current analysis which, for the first time, takes account of sidewall-related dark current contributions in mesa-etched T2SL photodiodes. In a wide temperature range from 30K to 130K, the paper compares limiting mechanisms in two homojunction T2SL photodiode wafers for the long-wavelength infrared regime. While the two epi wafers were fabricated with nominally the same frontside process they were grown on different molecular beam epitaxy systems. In the available literature a limitation by Shockley-Read-Hall processes in the space charge region giving rise to generation-recombination (GR) dark current is the prevailing verdict on the bulk dark current mechanism in T2SL homojunction photodiodes around 77K. In contrast, we find that investigated photodiode wafers are instead limited by the diffusion mechanism and the ohmic shunt component, respectively. Furthermore, our in-depth analysis of the various dark current components has led to an interesting observation on the temperature dependence of the shunt resistance in T2SL homojunction photodiodes. Our results indicate that the GR and the shunt mechanism share the same dependence on bandgap and temperature, i.e., a proportionality to exp(-Eg/2kT).

  5. Influence of wave and current flow on sediment-carrying capacity and sediment flux at the water-sediment interface.

    PubMed

    Zheng, Jun; Li, Ruijie; Yu, Yonghai; Suo, Anning

    2014-01-01

    In nearshore waters, spatial and temporal scales of waves, tidal currents, and circulation patterns vary greatly. It is, therefore, difficult to combine these factors' effects when trying to predict sediment transport processes. This paper proposes the concept of significant wave velocity, which combines the effects of waves, tides, and ocean currents using the horizontal kinetic energy superposition principle. Through a comparison of the relationship between shear stress at the water-sediment interface and sediment-carrying capacity, assuming equilibrium sediment flux, a new formula for sediment-carrying capacity, which incorporates the concept of significant wave velocities, is derived. Sediment-carrying capacity is a function of the critical velocity, which increases with water depth and decreases with increasing relative roughness of the sea bed. Finally, data from field observation stations and simulations are used to test the proposed formula. The results show that the new formula is in good agreement with both field and simulation data. This new formula for sediment-carrying capacity can be used to simulate nearshore sediment transport. PMID:25259499

  6. Analysis of non-ohmic electrical current-voltage characteristic of membranes carrying a single track-etched conical pore

    NASA Astrophysics Data System (ADS)

    Woermann, D.

    2002-10-01

    The model of the membrane with narrow pores is used to rationalise the existence of a non-ohmic current-voltage characteristic of membranes carrying a single narrow conical pore. The observation of this characteristic was reported recently by Apel et al. [Nucl. Instr. and Meth. B 184 (2001) 366]. The membranes used in that study were produced by an advanced track etch technique.

  7. Simulation of RF Cavity Dark Current In Presence of Helical Magnetic Field

    SciTech Connect

    Romanov, Gennady; Kashikhin, Vladimir; /Fermilab

    2012-05-01

    In order to produce muon beam of high enough quality to be used for a Muon Collider, its large phase space must be cooled several orders of magnitude. This task can be accomplished by ionization cooling. Ionization cooling consists of passing a high-emittance muon beam alternately through regions of low Z material, such as liquid hydrogen, and very high accelerating RF cavities within a multi-Tesla solenoidal focusing channel. But first high power tests of RF cavity with beryllium windows in solenoidal magnetic field showed a dramatic drop in accelerating gradient due to RF breakdowns. It has been concluded that external magnetic fields parallel to RF electric field significantly modifies the performance of RF cavities. However, magnetic field in Helical Cooling Channel has a strong dipole component in addition to solenoidal one. The dipole component essentially changes electron motion in a cavity compare to pure solenoidal case, making dark current less focused at field emission sites. The simulation of dark current dynamic in HCC performed with CST Studio Suit is presented in this paper.

  8. Ultra-Low Dark Current HgCdTe Detector in SWIR for Space Applications

    NASA Astrophysics Data System (ADS)

    Cervera, C.; Boulade, O.; Gravrand, O.; Lobre, C.; Guellec, F.; Sanson, E.; Ballet, P.; Santailler, J. L.; Moreau, V.; Zanatta, J. P.; Fieque, B.; Castelein, P.

    2016-09-01

    This paper presents recent developments at Commissariat à l'Energie atomique, Laboratoire d'Electronique et de Technologie de l'Information infrared laboratory on processing and characterization of p-on-n HgCdTe (MCT) planar infrared focal plane arrays (FPAs) in short-wave infrared (SWIR) spectral band for the astrophysics applications. These FPAs have been grown using both liquid phase epitaxy and molecular beam epitaxy on a lattice-matched CdZnTe substrate. This technology exhibits lower dark current and lower series resistance in comparison with n-on-p vacancy-doped architecture and is well adapted for low flux detection or high operating temperature. This architecture has been evaluated for space applications in long-wave infrared and very-long-wave infrared spectral bands with cut-off wavelengths from 10 μm up to 17 μm at 78 K and is now evaluated for the SWIR range. The metallurgical nature of the absorbing layer is also examined and both molecular beam epitaxy and liquid phase epitaxy have been investigated. Electro-optical characterizations have been performed on individual photodiodes from test arrays, whereas dark current investigation has been performed with a fully functional readout integrated circuit dedicated to low flux operations.

  9. Simulation of RF Cavity Dark Current in Presence of Helical Magnetic Field

    SciTech Connect

    Romanov, Gennady; Kashikhin, Vladimir; /Unlisted

    2010-09-01

    In order to produce muon beam of high enough quality to be used for a Muon Collider, its large phase space must be cooled several orders of magnitude. This task can be accomplished by ionization cooling. Ionization cooling consists of passing a high-emittance muon beam alternately through regions of low Z material, such as liquid hydrogen, and very high accelerating RF cavities within a multi-Tesla solenoidal focusing channel. But first high power tests of RF cavity with beryllium windows in solenoidal magnetic field showed a dramatic drop in accelerating gradient due to RF breakdowns. It has been concluded that external magnetic fields parallel to RF electric field significantly modifies the performance of RF cavities. However, magnetic field in Helical Cooling Channel has a strong dipole component in addition to solenoidal one. The dipole component essentially changes electron motion in a cavity compare to pure solenoidal case, making dark current less focused at field emission sites. The simulation of dark current dynamic in HCC performed with CST Studio Suit is presented in this paper.

  10. Effect of the magnetic material on AC losses in HTS conductors in AC magnetic field carrying AC transport current

    NASA Astrophysics Data System (ADS)

    Wan, Xing-Xing; Huang, Chen-Guang; Yong, Hua-Dong; Zhou, You-He

    2015-11-01

    This paper presents an investigation on the AC losses in several typical superconducting composite conductors using the H-formulation model. A single superconducting strip with ferromagnetic substrate or cores and a stack of coated conductors with ferromagnetic substrates are studied. We consider all the coated conductors carrying AC transport currents and simultaneously exposed to perpendicular AC magnetic fields. The influences of the amplitude, frequency, phase difference and ferromagnetic materials on the AC losses are investigated. The results show that the magnetization losses of single strip and stacked strips have similar characteristics. The ferromagnetic substrate can increase the magnetization loss at low magnetic field, and decrease the loss at high magnetic field. The ferromagnetic substrate can obviously increase the transport loss in stacked strips. The trends of total AC losses of single strip and stacked strips are similar when they are carrying current or exposed to a perpendicular magnetic field. The effect of the frequency on the total AC losses of single strip is related to the amplitude of magnetic field. The AC losses decrease with increasing frequency in low magnetic field region while increase in high magnetic field region. As the phase difference changes, there is a periodic variation for the AC losses. Moreover, when the strip is under only the transport current and magnetic field, the ferromagnetic cores will increase the AC losses for large transport current or field.

  11. Higher harmonics in voltage on superconductor carrying AC current due to non-linear I- V curve

    NASA Astrophysics Data System (ADS)

    Janíková, Edita; Gömöry, Fedor; Šouc, Ján

    2004-01-01

    When superconducting wire carries AC current with amplitude exceeding its critical current, additional losses appear due to non-zero resistivity. The voltage attributed to this mechanism will contain higher harmonics because of non-linear I- V curve of superconducting material. This curve can be derived using the following simple model: parallel combination of superconductor standing for the properties of all the filaments and the normal resistor representing the matrix. I- V relation is then characterized by three parameters: the critical current, I0, the n-exponent, n, and the ratio of the cross-section to the resistivity of metallic matrix. Expressions for Fourier coefficients have been calculated for this model. Extensive analysis of the influence that the model parameters exhibit on higher harmonics have revealed some useful features: 3rd harmonic could be nicely used to detect I0 and n, while from the maximum of 5th harmonic the value of matrix resistivity can be estimated.

  12. Linear optical response of current-carrying molecular junction: a nonequilibrium Green's function-time-dependent density functional theory approach.

    PubMed

    Galperin, Michael; Tretiak, Sergei

    2008-03-28

    We propose a scheme for calculation of linear optical response of current-carrying molecular junctions for the case when electronic tunneling through the junction is much faster than characteristic time of external laser field. We discuss relationships between nonequilibrium Green's function (NEGF) and time-dependent density functional theory (TDDFT) approaches and derive expressions for optical response and linear polarizability within NEGF-TDDFT scheme. Corresponding results for isolated molecule, derived within TDDFT approach previously, are reproduced when coupling to contacts is neglected. PMID:18376958

  13. The quantum-mechanical basis of an extended Landau-Lifshitz-Gilbert equation for a current-carrying ferromagnetic wire.

    PubMed

    Edwards, D M; Wessely, O

    2009-04-01

    An extended Landau-Lifshitz-Gilbert (LLG) equation is introduced to describe the dynamics of inhomogeneous magnetization in a current-carrying wire. The coefficients of all the terms in this equation are calculated quantum-mechanically for a simple model which includes impurity scattering. This is done by comparing the energies and lifetimes of a spin wave calculated from the LLG equation and from the explicit model. Two terms are of particular importance since they describe non-adiabatic spin-transfer torque and damping processes which do not rely on spin-orbit coupling. It is shown that these terms may have a significant influence on the velocity of a current-driven domain wall and they become dominant in the case of a narrow wall.

  14. Modeling the dark current histogram induced by gold contamination in complementary-metal-oxide-semiconductor image sensors

    NASA Astrophysics Data System (ADS)

    Domengie, F.; Morin, P.; Bauza, D.

    2015-07-01

    We propose a model for dark current induced by metallic contamination in a CMOS image sensor. Based on Shockley-Read-Hall kinetics, the expression of dark current proposed accounts for the electric field enhanced emission factor due to the Poole-Frenkel barrier lowering and phonon-assisted tunneling mechanisms. To that aim, we considered the distribution of the electric field magnitude and metal atoms in the depth of the pixel. Poisson statistics were used to estimate the random distribution of metal atoms in each pixel for a given contamination dose. Then, we performed a Monte-Carlo-based simulation for each pixel to set the number of metal atoms the pixel contained and the enhancement factor each atom underwent, and obtained a histogram of the number of pixels versus dark current for the full sensor. Excellent agreement with the dark current histogram measured on an ion-implanted gold-contaminated imager has been achieved, in particular, for the description of the distribution tails due to the pixel regions in which the contaminant atoms undergo a large electric field. The agreement remains very good when increasing the temperature by 15 °C. We demonstrated that the amplification of the dark current generated for the typical electric fields encountered in the CMOS image sensors, which depends on the nature of the metal contaminant, may become very large at high electric field. The electron and hole emissions and the resulting enhancement factor are described as a function of the trap characteristics, electric field, and temperature.

  15. Asymmetric MSM sub-bandgap all-silicon photodetector with low dark current.

    PubMed

    Casalino, M; Iodice, M; Sirleto, L; Rendina, I; Coppola, G

    2013-11-18

    Design, fabrication, and characterization of an asymmetric metal-semiconductor-metal photodetector, based on internal photoemission effect and integrated into a silicon-on-insulator waveguide, are reported. For this photodetector, a responsivity of 4.5 mA/W has been measured at 1550 nm, making it suitable for power monitoring applications. Because the absorbing metal is deposited strictly around the vertical output facet of the waveguide, a very small contact area of about 3 µm2 is obtained and a transit-time-limited bandwidth of about 1 GHz is demonstrated. Taking advantage of this small area and electrode asymmetry, a significant reduction in the dark current (2.2 nA at -21 V) is achieved. Interestingly, applying reverse voltage, the photodetector is able to tune its cut-off wavelength, extending its range of application into the MID infrared regime.

  16. Dark current and photocurrent analysis of plasmonic nano-antenna photodetector

    NASA Astrophysics Data System (ADS)

    Kemsri, Thitikorn

    Surface plasmonic resonance (SPR) plays important roles in performance enhancement in the Quantum Dot Infrared Photodetector. It can increase the photoresponse, SPR induced surface confinement and electromagnetic field enhancement. The angular dependence of the SPR enhancement effect has been fully investigated. In this thesis, the angular dependent effects of the two dimensional subwavelength hole array (2DSHA) and circular disk array (CDA) plasmonic structures are analyzed and compared with regular quantum dot photodetector. The photocurrent and dark current of both SPR structures are at different angles. The CDA plasmonic structure shows stronger angular dependence pattern than the 2DSHA plasmonic structure. The angular dependence is analyzed and agrees with the radiation pattern of a circular aperture antenna.

  17. Dark current and optical properties in asymmetric GaAs/AlGaAs staircase-like multiquantum well structure

    NASA Astrophysics Data System (ADS)

    Altin, E.; Hostut, M.; Ergun, Y.

    2013-05-01

    In this study, we investigate dark current voltage characteristics of GaAs/AlGaAs staircase-like asymmetric multiquantum well structure at various temperatures experimentally. Measured dark current density-voltage (Jd-V) characteristics are compared with the Levine Model. It is seen that the model fits well with the experimental dark current density. Ground state energy of electrons, heavy holes and light holes are calculated by Kronig-Penney Model. Optical properties of sample are characterized by photoluminescence and photoconductivity measurements. The temperature-dependent photoluminescence (PL) spectra of the GaAs/GaAlAs QWIP show that the peaks corresponding interband transition from the ground heavy-hole subband to the ground electronic subband (Ehh1 - Ee1) are dominantly observed and the peak positions corresponding to the interband transitions of the PL spectrum are dependent on the temperature. Photoconductivity measurement is performed for different negative polarities at 37 K.

  18. Low edge safety factor operation and passive disruption avoidance in current carrying plasmas by the addition of stellarator rotational transform

    NASA Astrophysics Data System (ADS)

    Pandya, M. D.; ArchMiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Knowlton, S. F.; Ma, X.; Massidda, S.; Maurer, D. A.; Roberds, N. A.; Traverso, P. J.

    2015-11-01

    Low edge safety factor operation at a value less than two ( q (a )=1 /ι̷tot(a )<2 ) is routine on the Compact Toroidal Hybrid device with the addition of sufficient external rotational transform. Presently, the operational space of this current carrying stellarator extends down to q (a )=1.2 without significant n = 1 kink mode activity after the initial plasma current rise phase of the discharge. The disruption dynamics of these low edge safety factor plasmas depend upon the fraction of helical field rotational transform from external stellarator coils to that generated by the plasma current. We observe that with approximately 10% of the total rotational transform supplied by the stellarator coils, low edge q disruptions are passively suppressed and avoided even though q(a) < 2. When the plasma does disrupt, the instability precursors measured and implicated as the cause are internal tearing modes with poloidal, m, and toroidal, n, helical mode numbers of m /n =3 /2 and 4/3 observed on external magnetic sensors and m /n =1 /1 activity observed on core soft x-ray emissivity measurements. Even though the edge safety factor passes through and becomes much less than q(a) < 2, external n = 1 kink mode activity does not appear to play a significant role in the disruption phenomenology observed.

  19. Dark current and light illumination effects on grating formation during periodic long-term operation in photorefractive polymers

    SciTech Connect

    Fujihara, T.; Mamiya, J.; Kawamoto, M.; Sassa, T.

    2014-01-14

    Photorefractive grating formation dynamics in long-timescale writing and the effects of periodic writing through the control of writing beam irradiation or electric field application were investigated using typical photorefractive polymers. Both dark current and writing beam irradiation affected grating formation dynamics. Dark current in polymers changed the effective trap density over time through deep trap filling and/or detrapping and thus affected grating formation considerably. The writing beam irradiation also affected grating development in the presence of an electric field owing to the accumulation of filled deep traps. However, grating development recovered after the elimination of the electric field freed up the filled deep traps.

  20. Asymmetrically contacted germanium photodiode using a metal-interlayer-semiconductor-metal structure for extremely large dark current suppression.

    PubMed

    Zang, Hwan-Jun; Kim, Gwang-Sik; Park, Gil-Jae; Choi, Yong-Soo; Yu, Hyun-Yong

    2016-08-15

    In this study, we proposed germanium (Ge) metal-interlayer-semiconductor-metal (MISM) photodiodes (PD), with an anode of a metal-interlayer-semiconductor (MIS) contact and a cathode of a metal-semiconductor (MS) contact, to efficiently suppress the dark current of Ge PD. We selected titanium dioxide (TiO2) as an interlayer material for the MIS contact, due to its large valence band offset and negative conduction band offset to Ge. We significantly suppress the dark current of Ge PD by introducing the MISM structure with a TiO2 interlayer, as this enhances the hole Schottky barrier height, and thus acts as a large barrier for holes. In addition, it collects photo-generated carriers without degradation, due to its negative conduction band offset to Ge. This reduces the dark current of Ge MISM PDs by ×8000 for 7-nm-thick TiO2 interlayer, while its photo current is still comparable to that of Ge metal-semiconductor-metal (MSM) PDs. Furthermore, the proposed Ge PD shows ×6,600 improvement of the normalized photo-to-dark-current ratio (NPDR) at a wavelength of 1.55 μm. The proposed Ge MISM PD shows considerable promise for low power and high sensitivity Ge-based optoelectronic applications. PMID:27519063

  1. Formation of a Micropinch and Generation of Multiply Charged Ions at the Front of a Current-Carrying Plasma Jet

    SciTech Connect

    Zverev, E.A.; Krasov, V.I.; Krinberg, I.A.; Papernyi, V.L.

    2005-10-15

    The formation of a neck in the cathode plasma jet in the initial stage of a low-voltage vacuum spark is investigated experimentally and theoretically. X-ray bursts corresponding to an electron temperature of 150-300 eV are detected. With the use of a pinhole camera, it is found that an emitting region less than 1 mm in size is located near the cathode. The free expansion of a current-carrying cathode plasma jet with a current growing in accordance with the experimentally observed time dependence is simulated using a hydrodynamic model. It is shown that the neck forms at the front of the plasma jet due to the plasma compression by the magnetic self-field. In the constriction region, the plasma is rapidly heated and multiply charged ions are generated. The calculated spatial and temporal variations in the electron temperature and average ion charge are close to the measured dependences over a wide range of the discharge parameters.

  2. Ion-cyclotron instability in current-carrying Lorentzian (kappa) and Maxwellian plasmas with anisotropic temperatures: A comparative study

    SciTech Connect

    Basu, B.; Grossbard, N. J.

    2011-09-15

    Current-driven electrostatic ion-cyclotron instability has so far been studied for Maxwellian plasma with isotropic and anisotropic temperatures. Since satellite-measured particle velocity distributions in space are often better modeled by the generalized Lorentzian (kappa) distributions and since temperature anisotropy is quite common in space plasmas, theoretical analysis of the current-driven, electrostatic ion-cyclotron instability is carried out in this paper for electron-proton plasma with anisotropic temperatures, where the particle parallel velocity distributions are modeled by kappa distributions and the perpendicular velocity distributions are modeled by Maxwellian distributions. Stability properties of the excited ion cyclotron modes and, in particular, their dependence on electron to ion temperature ratio and ion temperature anisotropy are presented in more detail. For comparison, the corresponding results for bi-Maxwellian plasma are also presented. Although the stability properties of the ion cyclotron modes in the two types of plasmas are qualitatively similar, significant quantitative differences can arise depending on the values of {kappa}{sub e} and {kappa}{sub i}. The comparative study is based on the numerical solutions of the respective linear dispersion relations. Quasilinear estimates of the resonant ion heating rates due to ion-cyclotron turbulence in the two types of plasma are also presented for comparison.

  3. Earth Observing-1 Advanced Imager Flight Performance Assessment: Investigating Dark Current Stability Over One-Half Orbit Period during the First 60 Days

    NASA Technical Reports Server (NTRS)

    Mendenhall, J. A.

    2001-01-01

    The stability of the EO-1 Advanced Land Imager dark current levels over the period of one-half orbit is investigated. A series of two-second dark current collections, over the course of 40 minutes, was performed during the first sixty days the instrument was in orbit. Analysis of this data indicates only two dark current reference periods, obtained entering and exiting eclipse, are required to remove ALI dark current offsets for 99.9% of the focal plane to within 1.5 digital numbers for any observation on the solar illuminated portion of the orbit.

  4. Pixel pitch and particle energy influence on the dark current distribution of neutron irradiated CMOS image sensors.

    PubMed

    Belloir, Jean-Marc; Goiffon, Vincent; Virmontois, Cédric; Raine, Mélanie; Paillet, Philippe; Duhamel, Olivier; Gaillardin, Marc; Molina, Romain; Magnan, Pierre; Gilard, Olivier

    2016-02-22

    The dark current produced by neutron irradiation in CMOS Image Sensors (CIS) is investigated. Several CIS with different photodiode types and pixel pitches are irradiated with various neutron energies and fluences to study the influence of each of these optical detector and irradiation parameters on the dark current distribution. An empirical model is tested on the experimental data and validated on all the irradiated optical imagers. This model is able to describe all the presented dark current distributions with no parameter variation for neutron energies of 14 MeV or higher, regardless of the optical detector and irradiation characteristics. For energies below 1 MeV, it is shown that a single parameter has to be adjusted because of the lower mean damage energy per nuclear interaction. This model and these conclusions can be transposed to any silicon based solid-state optical imagers such as CIS or Charged Coupled Devices (CCD). This work can also be used when designing an optical imager instrument, to anticipate the dark current increase or to choose a mitigation technique.

  5. Organic-inorganic hybrid inverted photodiode with planar heterojunction for achieving low dark current and high detectivity

    NASA Astrophysics Data System (ADS)

    Ha, JaeUn; Yoon, Seongwon; Lee, Jong-Soo; Chung, Dae Sung

    2016-03-01

    In this study, the strategy of using an organic-inorganic hybrid planar heterojunction consisting of polymeric semiconductors and inorganic nanocrystals is introduced to realize a high-performance hybrid photodiode (HPD) with low dark current and high detectivity. To prevent undesired charge injection under the reverse bias condition, which is the major dark current source of the photodiode, a well-defined planar heterojunction is strategically constructed via smart solution process techniques. The optimized HPD renders a low dark current of ˜10-5 mA cm-2 at -5 V and ˜10-6 mA cm-2 at -1 V, as well as a high detectivity ˜1012 Jones across the entire visible wavelength range. Furthermore, excellent photocurrent stability is demonstrated under continuous light exposure. We believe that the solution-processed planar heterojunction with inverted structure can be an attractive alternative diode structure for fabricating high-performance HPDs, which usually suffer from high dark current issues.

  6. Dark Current Characterization of SW HgCdTe IRFPAs Detectors on Si Substrate with Long Time Integration

    NASA Astrophysics Data System (ADS)

    Song, P. Y.; Ye, Z. H.; Huang, A. B.; Chen, H. L.; Hu, X. N.; Ding, R. J.; He, L.

    2016-09-01

    The dark currents of two short wave (SW) HgCdTe infrared focal plane arrays (IRFPA) detectors hybridized with direct injection (DI) readout and capacitance transimpedance amplifier (CTIA) with long time integration were investigated. The cutoff wavelength of the two SW IRFPAs is about 2.6 μm at 84 K. The dark current densities of DI and CTIA samples are approximately 8.0 × 10-12 A/cm2 and 7.2 × 10-10 A/cm2 at 110 K, respectively. The large divergence of the dark current density might arise from the injection efficiency difference of the two readouts. The low injection efficiency of the DI readout, compared with the high injection efficiency of the CTIA readout at low temperature, makes the dark current density of the DI sample much lower than that of the CTIA sample. The experimental value of injection efficiency of the DI sample was evaluated as 1.1% which is consistent with its theoretical value.

  7. Supernova and baryon acoustic oscillation constraints on (new) polynomial dark energy parametrizations: current results and forecasts

    NASA Astrophysics Data System (ADS)

    Sendra, Irene; Lazkoz, Ruth

    2012-05-01

    In this work we introduce two new polynomial parametrizations of dark energy and explore their correlation properties. The parameters to fit are the equation-of-state values at z= 0 and z= 0.5, which have naturally low correlation and have already been shown to improve the popular Chevallier-Polarski-Linder (CPL) parametrization. We test our models with low-redshift astronomical probes: type Ia supernovae and baryon acoustic oscillations (BAO), in the form of both current and synthetic data. Specifically, we present simulations of measurements of the radial and transversal BAO scales similar to those expected in a BAO high-precision spectroscopic redshift survey such as EUCLID. According to the Bayesian deviance information criterion (DIC), which penalizes large errors and correlations, we show that our models perform better than the CPL reparametrization proposed by Wang (in terms of z= 0 and z= 0.5). This is due to the combination of lower correlation and smaller relative errors. The same holds for a frequentist perspective: the figure-of-merit is larger for our parametrizations.

  8. Scalar dark matter search at the LHC through flavor-changing neutral current top decay

    SciTech Connect

    Li Tong; Shafi, Qaisar

    2011-05-01

    We discuss an extended standard model electroweak sector which contains a stable scalar dark matter particle, the D boson. To search for the D boson at the LHC we exploit the flavor-changing neutral current top quark decay, t{yields}cDD, mediated by the lightest standard model-like Higgs h{sup 0} in a two Higgs doublet model framework. The branching ratio for t{yields}cDD in this case can be as high as 10{sup -3}, after taking into account constraints arising from the D boson relic abundance. With an integrated luminosity of 10(100) fb{sup -1}, the 14 TeV LHC can explore values of this branching ratio that are one (two) order of magnitude smaller in tt production with tt{yields}cbl{sup -}(cbl{sup +})+Ee{sub T}. For a D boson mass < or approx. 60 GeV, m{sub h}{sup 0} < or approx. 2M{sub Z}, 10 fb{sup -1} luminosity and a branching ratio BR(t{yields}cDD){approx}10{sup -4}, the estimated number of signal events at the 14 TeV LHC is of order 80.

  9. IRAC test report. Gallium doped silicon band 2: Read noise and dark current

    NASA Technical Reports Server (NTRS)

    Lamb, Gerald; Shu, Peter; Mather, John; Ewin, Audrey; Bowser, Jeffrey

    1987-01-01

    A direct readout infrared detector array, a candidate for the Space Infrared Telescope Facility (SIRTF) Infrared Array Camera (IRAC), has been tested. The array has a detector surface of gallium doped silicon, bump bonded to a 58x62 pixel MOSFET multiplexer on a separate chip. Although this chip and system do not meet all the SIRTF requirements, the critically important read noise is within a factor of 3 of the requirement. Significant accomplishments of this study include: (1) development of a low noise correlated double sampling readout system with a readout noise of 127 to 164 electrons (based on the detector integrator capacitance of 0.1 pF); (2) measurement of the readout noise of the detector itself, ranging from 123 to 214 electrons with bias only (best to worst pixel), and 256 to 424 electrons with full clocking in normal operation at 5.4 K where dark current is small. Thirty percent smaller read noises are obtained at a temperature of 15K; (3) measurement of the detector response versus integration time, showing significant nonlinear behavior for large signals, well below the saturation level; and (4) development of a custom computer interface and suitable software for collection, analysis and display of data.

  10. Modeling the dark current histogram induced by gold contamination in complementary-metal-oxide-semiconductor image sensors

    SciTech Connect

    Domengie, F. Morin, P.; Bauza, D.

    2015-07-14

    We propose a model for dark current induced by metallic contamination in a CMOS image sensor. Based on Shockley-Read-Hall kinetics, the expression of dark current proposed accounts for the electric field enhanced emission factor due to the Poole-Frenkel barrier lowering and phonon-assisted tunneling mechanisms. To that aim, we considered the distribution of the electric field magnitude and metal atoms in the depth of the pixel. Poisson statistics were used to estimate the random distribution of metal atoms in each pixel for a given contamination dose. Then, we performed a Monte-Carlo-based simulation for each pixel to set the number of metal atoms the pixel contained and the enhancement factor each atom underwent, and obtained a histogram of the number of pixels versus dark current for the full sensor. Excellent agreement with the dark current histogram measured on an ion-implanted gold-contaminated imager has been achieved, in particular, for the description of the distribution tails due to the pixel regions in which the contaminant atoms undergo a large electric field. The agreement remains very good when increasing the temperature by 15 °C. We demonstrated that the amplification of the dark current generated for the typical electric fields encountered in the CMOS image sensors, which depends on the nature of the metal contaminant, may become very large at high electric field. The electron and hole emissions and the resulting enhancement factor are described as a function of the trap characteristics, electric field, and temperature.

  11. Turbulence in Toroidally Confined Plasma: Ion - - Gradient-Driven Turbulence; Dynamics of Magnetic Relaxation in Current-Carrying Plasma

    NASA Astrophysics Data System (ADS)

    Lee, Gyung Su.

    This thesis is devoted to two studies of low-frequency turbulence in toroidally confined plasma. Low-frequency turbulence is believed to play an important role in anomalous transport in toroidal confinement devices. The first study pertains the the development of an analytic theory of ion-temperature-gradient-driven turbulence in tokamaks. Energy-conserving, renormalized spectrum equations are derived and solved in order to obtain the spectra of stationary ion-temperature-gradient-driven turbulence. Corrections to mixing-length estimates are calculated explicitly. The resulting anomalous ion thermal diffusivity is derived and is found to be consistent with experimentally-deduced ion thermal diffusivities. The associated electron thermal diffusivity, particle and heat-pinch velocities are also calculated. The effects of impurity gradients on saturated ion-temperature-gradient-driven turbulence are discussed and a related explanation of density profile steepening during Z-mode operation is proposed. The second study is devoted to the role of multiple helicity nonlinear interactions of tearing modes and dynamics of magnetic relaxation in a high-temperature current-carrying plasma. To extend the resistive MHD theory of magnetic fluctuations and dynamo activity observed in the reversed field pinch, the fluid equations for high-temperature regime are derived and basic nonlinear interaction mechanism and the effects of diamagnetic corrections to the MHD turbulence theory are studied for the case of fully developed, densely packed turbulence. Modifications to the MHD dynamo theory and anomalous thermal transport and confinement scaling predictions are examined.

  12. The ghost of social environments past: dominance relationships include current interactions and experience carried over from previous groups.

    PubMed

    Tanner, Colby J; Salali, Gul Deniz; Jackson, Andrew L

    2011-12-23

    Dominance hierarchies pervade animal societies. Within a static social environment, in which group size and composition are unchanged, an individual's hierarchy rank results from intrinsic (e.g. body size) and extrinsic (e.g. previous experiences) factors. Little is known, however, about how dominance relationships are formed and maintained when group size and composition are dynamic. Using a fusion-fission protocol, we fused groups of previously isolated shore crabs (Carcinus maenas) into larger groups, and then restored groups to their original size and composition. Pre-fusion hierarchies formed independently of individuals' sizes, and were maintained within a static group via winner/loser effects. Post-fusion hierarchies differed from pre-fusion ones; losing fights during fusion led to a decline in an individual's rank between pre- and post-fusion conditions, while spending time being aggressive during fusion led to an improvement in rank. In post-fusion tanks, larger individuals achieved better ranks than smaller individuals. In conclusion, dominance hierarchies in crabs represent a complex combination of intrinsic and extrinsic factors, in which experiences from previous groups can carry over to affect current competitive interactions.

  13. Development of Analytical Solutions for Quasistationary Electromagnetic Fields for Conducting Spheroids in the Proximity of Current-Carrying Turns

    NASA Astrophysics Data System (ADS)

    Jayasekara, Nandaka

    Exact analytical solutions for the quasistationary electromagnetic fields in the presence of conducting objects require the field solutions both internal and external to the conductors. Such solutions are limited for certain canonically shaped objects but are useful in testing the accuracy of various approximate models and numerical methods developed to solve complex problems related to real world conducting objects and in calibrating instruments designed to measure various field quantities. Theoretical investigations of quasistationary electromagnetic fields also aid in improving the understanding of the physical phenomena of electromagnetic induction. This thesis presents rigorous analytical expressions derived as benchmark solutions for the quasistationary field quantities both inside and outside, Joule losses and the electromagnetic forces acting upon a conducting spheroid placed in the proximity of a non-uniform field produced by current-carrying turns. These expressions are used to generate numerous numerical results of specified accuracy and selected results are presented in a normalized form for extended ranges of the spheroid axial ratio, the ratio of the depth of penetration to the semi-minor axis and the position of the inducing turns relative to the spheroids. They are intended to constitute reference data to be employed for comprehensive comparisons of results from approximate numerical methods or from boundary impedance models used for real world conductors. Approximate boundary conditions such as the simpler perfect electric conductor model or the Leontovich surface impedance boundary condition model can be used to obtain approximate solutions by only analyzing the field external to the conducting object. The range of validity of these impedance boundary condition models for the analysis of axisymmetric eddy-current problems is thoroughly investigated. While the simpler PEC model can be employed only when the electromagnetic depth of penetration is

  14. Bayesian approach to estimation of the map of dark current in wavelet domain

    NASA Astrophysics Data System (ADS)

    Švihlík, J.; Řeřábek, M.; Páta, P.

    2008-07-01

    This paper deals with advanced methods for elimination of the thermally generated charge in the astronomical images, which were acquired by Charged Coupled Device (CCD) sensor. There exist a number of light images acquired by telescope, which were not corrected by dark frame. The reason is simple the dark frame doesn't exists, because it was not acquired. This situation may for instance come when sufficient memory space is not available. There will be discussed the correction method based on the modeling of the light and dark image in the wavelet domain. As the model for the dark frame image and for the light image the generalized Laplacian was chosen. The models parameters were estimated using moment method, whereas an extensive measurement on astronomical camera were proposed and done. This measurement simplifies estimation of the dark frame model parameters. Finally a set of the astronomical testing images were corrected and then the objective criteria for an image quality evaluation based on the aperture photometry were applied.

  15. SEMICONDUCTOR TECHNOLOGY: Influence of hydrogenation on the dark current mechanism of HgCdTe photovoltaic detectors

    NASA Astrophysics Data System (ADS)

    Hui, Qiao; Weida, Hu; Zhenhua, Ye; Xiangyang, Li; Haimei, Gong

    2010-03-01

    The influence of hydrogenation on the dark current mechanism of HgCdTe photovoltaic detectors is studied. The hydrogenation is achieved by exposing samples to a H2/Ar plasma atmosphere that was produced during a reactive ion etching process. A set of variable-area photomask was specially designed to evaluate the hydrogenation effect. It was found that the current-voltage characteristics were gradually improved when detectors were hydrogenated by different areas. The fitting results of experimental results at reverse bias conditions sustained that the improvement of current-voltage curves was due to the suppression of trap assisted tunneling current and the enhancement of minority lifetime in the depletion region. It was also found that the dominative forward current was gradually converted from a generation-recombination current to a diffusion current with the enlargement of the hydrogenation area, which was infered from the ideality factors by abstraction of forward resistance-voltage curves of different detectors.

  16. Dark current reduction of small molecule organic photodetectors by controlling gap states of molybdenum oxide buffer layers

    NASA Astrophysics Data System (ADS)

    Kim, Seong Heon; Heo, Sung; Yun, Dong-Jin; Satoh, Ryu-ichi; Park, Gyeongsu; Kim, Kyu-Sik

    2016-09-01

    The gap states of the molybdenum-oxide (MoO x ) hole-extraction layer (HEL) in an organic photodetector (OPD) device, which originate from oxygen-vacancy defects, are controlled by appropriate plasma treatments on the MoO x layer. The density of MoO x gap states, investigated using X-ray photoelectron spectroscopy (XPS), is enhanced and depressed with Ar- and O2-plasma treatments, respectively. The dark current of an OPD with a MoO x HEL is considerably reduced by controlling the MoO x gap states using the plasma-treatment method. The mechanism of dark-current reduction may be interpreted by reduced gap states and by a suitable energy level bending and alignment.

  17. MCT-Based LWIR and VLWIR 2D Focal Plane Detector Arrays for Low Dark Current Applications at AIM

    NASA Astrophysics Data System (ADS)

    Hanna, S.; Eich, D.; Mahlein, K.-M.; Fick, W.; Schirmacher, W.; Thöt, R.; Wendler, J.; Figgemeier, H.

    2016-09-01

    We present our latest results on n-on- p as well as on p-on- n low dark current planar mercury cadmium telluride (MCT) photodiode technology long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) two-dimensional focal plane arrays (FPAs) with quantum efficiency (QE) cut-off wavelength >11 μm at 80 K and a 512 × 640 pixel format FPA at 20 μm pitch stitched from two 512 × 320 pixel photodiode arrays. Significantly reduced dark currents as compared with Tennant's "Rule 07" are demonstrated in both polarities while retaining good detection efficiency ≥60% for operating temperatures between 30 K and 100 K. This allows for the same dark current performance at 20 K higher operating temperature than with previous AIM INFRAROT-MODULE GmbH (AIM) technology. For p-on- n LWIR MCT FPAs, broadband photoresponse nonuniformity of only about 1.2% is achieved at 55 K with low defective pixel numbers. For an n-on- p VLWIR MCT FPA with 13.6 μm cut-off at 55 K, excellent photoresponse nonuniformity of about 3.1% is achieved at moderate defective pixel numbers. This advancement in detector technology paves the way for outstanding signal-to-noise ratio performance infrared detection, enabling cutting-edge next-generation LWIR/VLWIR detectors for space instruments and devices with higher operating temperature and low size, weight, and power for field applications.

  18. Testing the interaction between dark energy and dark matter via the latest observations

    SciTech Connect

    He Jianhua; Wang Bin; Abdalla, Elcio

    2011-03-15

    Cosmological analyses based on currently available observations are unable to rule out a sizeable coupling between dark energy and dark matter. However, the signature of the coupling is not easy to grasp, since the coupling is degenerate with other cosmological parameters, such as the dark energy equation of state and the dark matter abundance. We discuss possible ways to break such degeneracy. Based on the perturbation formalism, we carry out the global fitting by using the latest observational data and get a tight constraint on the interaction between dark sectors. We find that the appropriate interaction can alleviate the coincidence problem.

  19. Confirmation of Auger-1 Minority-Carrier Lifetimes in Hg0.77Cd0.23Te and Prediction of Dark Current for Long-Wave Infrared Focal-Plane Arrays

    NASA Astrophysics Data System (ADS)

    Destefanis, V.; Kerlain, A.

    2016-09-01

    Minority-carrier lifetime measurements have been carried out on Hg0.77Cd0.23Te (111)B materials with gap suitable for detection in the Long-Wave Infrared (LWIR) band. The materials were grown on top of CdZnTe substrates using a liquid-phase epitaxy (LPE) process. From measurements done at 80 K, a clear difference in terms of minority-carrier lifetimes was obtained, as expected, between p-intrinsic (≤5 ns) and n-extrinsic doped samples (420 ns). Minority-carrier lifetimes were also measured as a function of temperature for the n-type samples. Auger-1-limited lifetimes were demonstrated over a wide temperature range (from 80 K to 300 K) with negligible Radiative or Shockley-Read-Hall lifetime contributions. Predictions of dark current densities are made from those lifetime measurements, assuming an Auger-1-limited lifetime. The agreement is very good between the predictions and dark current densities measured from p-on- n 640 × 512 pixels LWIR HgCdTe focal-plane arrays with 15- μm pitch from SOFRADIR, Agreement between predicted and measured dark currents and Rule'07 for LWIR is also demonstrated herein. Finally, minority-carrier lifetime measurements are demonstrated as a predictive method for focal-plane array performance. State-of-the-art dark currents from SOFRADIR p-on- n LWIR focal-plane arrays based upon high-quality HgCdTe materials are also illustrated.

  20. Quenched dynamics in interacting one-dimensional systems: Appearance of current carrying steady states from initial domain wall density profiles

    NASA Astrophysics Data System (ADS)

    Lancaster, Jarrett; Gull, Emanuel; Mitra, Aditi

    2011-03-01

    Dynamics arising after an interaction quench in the quantum sine-Gordon model is studied for the case of a system initially prepared in a spatially inhomogeneous domain wall state. The time-evolution of the density, current and equal time correlation functions are studied using the truncated Wigner approximation (TWA) to which quantum corrections are added in order to set the limits on its validity. For weak to moderate strengths of the back-scattering interaction, the domain wall is found to spread out ballistically with the system within the light cone reaching a non-equilibrium steady-state characterized by a net current flow. A steady state current is also found to exist for a quench at the exactly solvable Luther-Emery point. The magnitude of the current decreases with increasing strength of the back-scattering interaction. The two-point correlation function of the variable canonically conjugate to the density reaches a steady state which is spatially oscillating at a wavelength which is inversely related to the current. This was was supported by NSF-DMR (Award no. 1004589).

  1. Quintessence versus phantom dark energy: the arbitrating power of current and future observations

    SciTech Connect

    Novosyadlyj, B.; Sergijenko, O.; Durrer, R.; Pelykh, V. E-mail: olka@astro.franko.lviv.ua E-mail: pelykh@iapmm.lviv.ua

    2013-06-01

    We analyze the possibility to distinguish between quintessence and phantom scalar field models of dark energy using observations of luminosity distance moduli of SNe Ia, CMB anisotropies and polarization, matter density perturbations and baryon acoustic oscillations. Among the present observations only Planck data on CMB anisotropy and SDSS DR9 data on baryon acoustic oscillations may be able to decide between quintessence or phantom scalar field models, however for each model a set of best-fit parameters exists, which matches all data with similar goodness of fit. We compare the relative differences of best-fit model predictions with observational uncertainties for each type of data and we show that the accuracy of SNe Ia luminosity distance data is far from the one necessary to distinguish these types of dark energy models, while the CMB data (WMAP, ACT, SPT and especially Planck) are close to being able to reliably distinguish them. Also an improvement of the large-scale structure data (future releases of SDSS BOSS and e.g. Euclid or BigBOSS) will enable us to surely decide between quintessence and phantom dark energy.

  2. Dark Agouti rat model of chemotherapy-induced mucositis: Establishment and current state of the art

    PubMed Central

    Vanhoecke, Barbara; Bateman, Emma; Mayo, Bronwen; Vanlancker, Eline; Thorpe, Daniel; Keefe, Dorothy

    2015-01-01

    Mucositis is a major oncological problem. The entire gastrointestinal and genitourinary tract and also other mucosal surfaces can be affected in recipients of radiotherapy, and/or chemotherapy. Major progress has been made in recent years in understanding the mechanisms of oral and small intestinal mucositis, which appears to be more prominent than colonic damage. This progress is largely due to the development of representative laboratory animal models of mucositis. This review focuses on the development and establishment of the Dark Agouti rat mammary adenocarcinoma model by the Mucositis Research Group of the University of Adelaide over the past 20 years to characterize the mechanisms underlying methotrexate-, 5-fluorouracil-, and irinotecan-induced mucositis. It also aims to summarize the results from studies using different animal model systems to identify new molecular and cellular markers of mucositis. PMID:25966981

  3. Dark Agouti rat model of chemotherapy-induced mucositis: establishment and current state of the art.

    PubMed

    Vanhoecke, Barbara; Bateman, Emma; Mayo, Bronwen; Vanlancker, Eline; Stringer, Andrea; Thorpe, Daniel; Keefe, Dorothy

    2015-06-01

    Mucositis is a major oncological problem. The entire gastrointestinal and genitourinary tract and also other mucosal surfaces can be affected in recipients of radiotherapy, and/or chemotherapy. Major progress has been made in recent years in understanding the mechanisms of oral and small intestinal mucositis, which appears to be more prominent than colonic damage. This progress is largely due to the development of representative laboratory animal models of mucositis. This review focuses on the development and establishment of the Dark Agouti rat mammary adenocarcinoma model by the Mucositis Research Group of the University of Adelaide over the past 20 years to characterize the mechanisms underlying methotrexate-, 5-fluorouracil-, and irinotecan-induced mucositis. It also aims to summarize the results from studies using different animal model systems to identify new molecular and cellular markers of mucositis.

  4. Leaf respiration in darkness and in the light under pre-industrial, current and elevated atmospheric CO₂ concentrations.

    PubMed

    Ayub, Gohar; Zaragoza-Castells, Joana; Griffin, Kevin L; Atkin, Owen K

    2014-09-01

    Our study sought to understand how past, low atmospheric CO2 concentrations ([CO2]) impact respiration (R) of soybean (Glycine max), when compared to plants grown under current and future [CO2]s. Experiments were conducted using plants grown under 290, 400 and 700 ppm [CO2]. Leaf R was measured in both darkness (RD) and in the light (RL; using the Kok method), with short-term changes in measurement [CO2] and [O2] being used to explore the relationship between light inhibition of leaf R and photorespiration. Root R, photosynthesis (A), leaf [N] and biomass allocation traits were also quantified. In contrast to the inhibitory effect of low growth [CO2] on A, growth [CO2] had no significant effect on leaf RD or root R. Irrespective of growth [CO2], RL was always lower than RD, with light inhibiting leaf R by 17-47%. Importantly, the degree of light inhibition of leaf R was lowest in plants grown under low [CO2], with variations in RL being positively correlated with RD and photorespiration. Irrespective of whether leaf R was measured in the light or dark, a greater proportion of the carbon fixed by leaf photosynthesis was released by leaf R in plants grown under low [CO2] than under current/future [CO2]'s. Collectively, our results highlight the differential responses of A and R to growth of plants under low to elevated atmospheric [CO2].

  5. Tailored Electrospinning of WO₃ Nanobelts as Efficient Ultraviolet Photodetectors with Photo-Dark Current Ratios up to 1000.

    PubMed

    He, Zhiyang; Liu, Qiao; Hou, Huilin; Gao, Fengmei; Tang, Bin; Yang, Weiyou

    2015-05-27

    In this work, polycrystalline WO3 nanobelts were fabricated via an electrospinning process combined with subsequent air calcination. The resultant products were characterized by X-ray diffraction, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy in regard to the structures. It has been found that the applied voltage during the electrospinning process played the determined role in the formation of the WO3 nanobelts, allowing the controlled growth of the nanobelts. The ultraviolet (UV) photodetector assembled by an individual WO3 nanobelt exhibits a high sensitivity and a precise selectivity to the different wavelength lights, with a very low dark current and typical photo-dark current ratio up to 1000, which was the highest for any WO3 photodectectors ever reported. This work could not only push forward the facile preparation of WO3 nanobelts but also represent, for the first time, the possibility that the polycrystalline WO3 nanobelts could be a promising building block for the highly efficient UV photodetectors.

  6. Electrical modeling of InAs/GaSb superlattice mid-wavelength infrared pin photodiode to analyze experimental dark current characteristics

    SciTech Connect

    Delmas, Marie; Rodriguez, Jean-Baptiste; Christol, Philippe

    2014-09-21

    Dark current characteristics of 7 Monolayers (ML) InAs/ 4 ML GaSb SL pin photodiodes are simulated using ATLAS software. Using appropriate models and material parameters, we obtain good agreement between the simulated and the experimental dark current curves of photodiodes grown by molecular beam epitaxy. The n-type non-intentionally-doped (nid) SL samples exhibit a dependence of the lifetime with temperature following the T{sup -1/2} law, signature of Shockley-Read-Hall (SRH) Generation-Recombination current. We also studied the dependence of the dark current with the absorber doping level. It appears that the absorber doping level must not exceed a value of 2×10¹⁵cm⁻³, above this value the dark current is increasing with increased doping level. However for this doping value, a dark current as low as 5 × 10⁻⁹ A/cm², at 50 mV reverse bias at 77 K can be obtained.

  7. Minority carrier lifetime and dark current measurements in mid-wavelength infrared InAs0.91Sb0.09 alloy nBn photodetectors

    DOE PAGES

    Olson, B. V.; Kim, J. K.; Kadlec, E. A.; Klem, J. F.; Hawkins, S. D.; Leonhardt, D.; Coon, W. T.; Fortune, T. R.; Cavaliere, M. A.; Tauke-Pedretti, A.; et al

    2015-11-03

    Carrier lifetime and dark current measurements are reported for a mid-wavelength infrared InAs 0.91Sb0.09 alloy nBn photodetector. Minority carrier lifetimes are measured using a non-contact time-resolved microwave technique on unprocessed portions of the nBn wafer and the Auger recombination Bloch function parameter is determined to be |F1F2|=0.292. Moreover, the measured lifetimes are also used to calculate the expected diffusion dark current of the nBn devices and are compared with the experimental dark current measured in processed photodetector pixels from the same wafer. As a result, excellent agreement is found between the two, highlighting the important relationship between lifetimes and diffusionmore » currents in nBn photodetectors.« less

  8. SU-E-T-66: Characterization of Radiation Dose Associated with Dark Currents During Beam Hold for Respiratory-Gated Electron Therapy

    SciTech Connect

    Hessler, J; Gupta, N; Rong, Y; Weldon, M

    2014-06-01

    Purpose: The main objective of this study was to estimate the radiation dose contributed by dark currents associated with the respiratory-gated electron therapy during beam hold. The secondary aim was to determine clinical benefits of using respiratory-gated electron therapy for left-sided breast cancer patients with positive internal mammary nodes (IMN). Methods: Measurements of the dark current-induced dose in all electron modes were performed on multiple Siemens and Varian linear accelerators by manually simulating beam-hold during respiratory gating. Dose was quantified at the machine isocenter by comparing the collected charge to the known output for all energies ranging from 6 to 18 MeV for a 10cm × 10cm field at 100 SSD with appropriate solid-water buildup. Using the Eclipse treatment planning system, we compared the additional dose associated with dark current using gated electron fields to the dose uncertainties associated with matching gated photon fields and ungated electron fields. Dose uncertainties were seen as hot and cold spots along the match line of the fields. Results: The magnitude of the dose associated with dark current is highly correlated to the energy of the beam and the amount of time the beam is on hold. For lower energies (6–12 MeV), there was minimal dark current dose (0.1–1.3 cGy/min). Higher energies (15–18 MeV) showed measurable amount of doses. The dark current associated with the electron beam-hold varied between linear accelerator vendors and depended on dark current suppression and the age of the linear accelerator. Conclusion: For energies up to 12 MeV, the dose associated with the dark current for respiratorygated electron therapy was shown to be negligible, and therefore should be considered an option for treating IMN positive left-sided breast cancer patients. However, at higher energies the benefit of respiratory gating may be outweighed by dose due to the dark current.

  9. Axial buckling analysis of a slender current-carrying nanowire acted upon by a magnetic field using the surface energy approach

    NASA Astrophysics Data System (ADS)

    Kiani, Keivan

    2015-06-01

    The axial buckling behavior of magnetically affected current-carrying nanowires is studied accounting for the surface energy effect. Using Euler-Bernoulli beam theory, the Lorentz force on the nanowire is determined and the governing equations are established. By application of the Galerkin approach and assumed mode method, the critical axial compressive load of the nanostructure is evaluated in the cases of simply supported and fully clamped ends. The effects of surface energy, electric current, strength of the magnetic field, slenderness ratio, and nanowire’s radius on the axial buckling loads are comprehensively discussed. The obtained results reveal that both the electric current and exerted magnetic field endanger the axial stability of the nanowire. For high levels of electric current or magnetic field strength, the surface effect becomes significant in the axial buckling performance of the nanostructure.

  10. New design of InGaAs guided-mode resonance photodiode for SWIR low dark current imaging

    NASA Astrophysics Data System (ADS)

    Verdun, Michaël.; Portier, Benjamin; Jaworowicz, Katarzyna; Jaeck, Julien; Dupuis, Christophe; Haidar, Riad; Pardo, Fabrice; Pelouard, Jean-Luc

    2016-04-01

    We investigate a full-dielectric guided mode resonant photodiode. It has been designed to enhance the absorption by excitation of several resonances in the SWIR domain. The device consists of an InP/InGaAs/InP P-i-N heterojunction containing an active layer as thin as 90 nm on top of a subwavelength lamellar grating and a gold mirror. We successfully compared the electro-optical characterizations of individual pixels with electro-magnetic simulations. In particular, we observe near perfect collection of the photo-carriers and external quantum efficiency (EQE) of up to 71% around 1.55 μm. Moreover, compared with InGaAs resonator state-of-the-art detector, we show a broader spectral response in the 1.2-1.7 μm range, thus paving the way for SWIR low dark current imaging.

  11. Constraining the dark fluid

    SciTech Connect

    Kunz, Martin; Liddle, Andrew R.; Parkinson, David; Gao Changjun

    2009-10-15

    Cosmological observations are normally fit under the assumption that the dark sector can be decomposed into dark matter and dark energy components. However, as long as the probes remain purely gravitational, there is no unique decomposition and observations can only constrain a single dark fluid; this is known as the dark degeneracy. We use observations to directly constrain this dark fluid in a model-independent way, demonstrating, in particular, that the data cannot be fit by a dark fluid with a single constant equation of state. Parametrizing the dark fluid equation of state by a variety of polynomials in the scale factor a, we use current kinematical data to constrain the parameters. While the simplest interpretation of the dark fluid remains that it is comprised of separate dark matter and cosmological constant contributions, our results cover other model types including unified dark energy/matter scenarios.

  12. Nanocoating of particles for optimal doping and universal enhancement of current-carrying ability in ''organic''MgB{sub 2-x}C{sub x} superconductors

    SciTech Connect

    Shcherbakova, O. V.; Pan, A. V.; Dou, S. X.; Nigam, R.; Wexler, D.

    2010-05-15

    The universal approach of liquid mixing has been found to produce 'organic' MgB{sub 2-x}C{sub x} superconductors with structural and supercurrent-carrying properties unattainable by other techniques. We show by transmission electron microscopy combined with energy dispersive spectroscopy that these unique properties are enabled through coating of boron particles with a nanolayer of carbon. The subsequent reaction between carbon-encapsulated boron and magnesium results in enhanced carbon content x in the crystal lattice, as determined by x-ray diffraction pattern analysis. Among various carbon-containing compounds investigated, polycarbosilane has been found to be the optimal dopant for MgB{sub 2} superconductor, producing the largest critical current density due to the formation of wide range of nanodefects with pinning properties within the MgB{sub 2} crystal lattice, as well as due to minimal formation of current-blocking layers around the grains.

  13. Low Dark-Current, High Current-Gain of PVK/ZnO Nanoparticles Composite-Based UV Photodetector by PN-Heterojunction Control.

    PubMed

    Lee, Sang-Won; Cha, Seung-Hwan; Choi, Kyung-Jae; Kang, Byoung-Ho; Lee, Jae-Sung; Kim, Sae-Wan; Kim, Ju-Seong; Jeong, Hyun-Min; Gopalan, Sai-Anand; Kwon, Dae-Hyuk; Kang, Shin-Won

    2016-01-07

    We propose a solution-processable ultraviolet (UV) photodetector with a pn-heterojunction hybrid photoactive layer (HPL) that is composed of poly-n-vinylcarbazole (PVK) as a p-type polymer and ZnO nanoparticles (NPs) as an n-type metal oxide. To observe the effective photo-inducing ability of the UV photodetector, we analyzed the optical and electrical properties of HPL which is controlled by the doping concentration of n-type ZnO NPs in PVK matrix. Additionally, we confirmed that the optical properties of HPL dominantly depend on the ZnO NPs from the UV-vis absorption and the photoluminescence (PL) spectral measurements. This HPL can induce efficient charge transfer in the localized narrow pn-heterojunction domain and increases the photocurrent gain. It is essential that proper doping concentration of n-type ZnO NPs in polymer matrix is obtained to improve the performance of the UV photodetector. When the ZnO NPs are doped with the optimized concentration of 3.4 wt.%, the electrical properties of the photocurrent are significantly increased. The ratio of the photocurrent was approximately 10³ higher than that of the dark current.

  14. Current-carrying element based on second-generation high-temperature superconductor for the magnet system of a fusion neutron source

    SciTech Connect

    Novikov, M. S. Ivanov, D. P. E-mail: denis.ivanov30@mail.ru; Novikov, S. I. Shuvaev, S. A. E-mail: sergey.shuvaev@phystech.edu

    2015-12-15

    Application of current-carrying elements (CCEs) made of second-generation high-temperature superconductor (2G HTS) in magnet systems of a fusion neutron source (FNS) and other fusion devices will allow their magnetic field and thermodynamic stability to be increased substantially in comparison with those of low-temperature superconductor (LTS) magnets. For a toroidal magnet of the FNS, a design of a helical (partially transposed) CCE made of 2G HTS is under development with forced-flow cooling by helium gas, a current of 20–30 kA, an operating temperature of 10–20 K, and a magnetic field on the winding of 12–15 T (prospectively ∼20 T). Short-sized samples of the helical flexible heavy-current CCE are being fabricated and investigated; a pilot-line unit for production of long-sized CCE pieces is under construction. The applied fabrication technique allows the CCE to be produced which combines a high operating current, thermal and mechanical stability, manufacturability, and low losses in the alternating modes. The possibility of fabricating the CCE with the outer dimensions and values of the operating parameter required for the FNS (and with a significant margin) using already available serial 2G HTS tapes is substantiated. The maximum field of toroidal magnets with CCEs made of 2G HTS will be limited only by mechanical properties of the magnet’s casing and structure, while the thermal stability will be approximately two orders of magnitude higher than that of toroidal magnets with LTS-based CCEs. The helical CCE made of 2G HTS is very promising for fusion and hybrid electric power plants, and its design and technologies of production, as well as the prototype coils made of it for the FNS and other tokamaks, are worth developing now.

  15. Current-carrying element based on second-generation high-temperature superconductor for the magnet system of a fusion neutron source

    NASA Astrophysics Data System (ADS)

    Novikov, M. S.; Ivanov, D. P.; Novikov, S. I.; Shuvaev, S. A.

    2015-12-01

    Application of current-carrying elements (CCEs) made of second-generation high-temperature superconductor (2G HTS) in magnet systems of a fusion neutron source (FNS) and other fusion devices will allow their magnetic field and thermodynamic stability to be increased substantially in comparison with those of low-temperature superconductor (LTS) magnets. For a toroidal magnet of the FNS, a design of a helical (partially transposed) CCE made of 2G HTS is under development with forced-flow cooling by helium gas, a current of 20-30 kA, an operating temperature of 10-20 K, and a magnetic field on the winding of 12-15 T (prospectively ~20 T). Short-sized samples of the helical flexible heavy-current CCE are being fabricated and investigated; a pilot-line unit for production of long-sized CCE pieces is under construction. The applied fabrication technique allows the CCE to be produced which combines a high operating current, thermal and mechanical stability, manufacturability, and low losses in the alternating modes. The possibility of fabricating the CCE with the outer dimensions and values of the operating parameter required for the FNS (and with a significant margin) using already available serial 2G HTS tapes is substantiated. The maximum field of toroidal magnets with CCEs made of 2G HTS will be limited only by mechanical properties of the magnet's casing and structure, while the thermal stability will be approximately two orders of magnitude higher than that of toroidal magnets with LTS-based CCEs. The helical CCE made of 2G HTS is very promising for fusion and hybrid electric power plants, and its design and technologies of production, as well as the prototype coils made of it for the FNS and other tokamaks, are worth developing now.

  16. NUV Detector Dark Monitor

    NASA Astrophysics Data System (ADS)

    Zheng, Wei

    2010-09-01

    Perform routine monitoring of MAMA detector dark current. The main purpose isto look for evidence of a change in the dark rates, both to track on-orbit timedependence and to check for a detector problem developing. The spatial distribution of dark rates on the detector and the effect of SAA will also be studied.

  17. NUV Detector Dark Monitor

    NASA Astrophysics Data System (ADS)

    Ely, Justin

    2013-10-01

    Perform routine monitoring of MAMA detector dark current. The main purpose isto look for evidence of a change in the dark rates, both to track on-orbit timedependence and to check for a detector problem developing. The spatial distribution of dark rates on the detector and the effect of SAA will also be studied.

  18. NUV Detector Dark Monitor

    NASA Astrophysics Data System (ADS)

    Ely, Justin

    2012-10-01

    Perform routine monitoring of MAMA detector dark current. The main purpose isto look for evidence of a change in the dark rates, both to track on-orbit timedependence and to check for a detector problem developing. The spatial distribution of dark rates on the detector and the effect of SAA will also be studied.

  19. NUV Detector Dark Monitor

    NASA Astrophysics Data System (ADS)

    Cox, Colin

    2011-10-01

    Perform routine monitoring of MAMA detector dark current. The main purpose isto look for evidence of a change in the dark rates, both to track on-orbit timedependence and to check for a detector problem developing. The spatial distribution of dark rates on the detector and the effect of SAA will also be studied.

  20. Comparisons of the proton-induced dark current and charge transfer efficiency responses of n- and p-channel CCDs

    NASA Astrophysics Data System (ADS)

    Marshall, Cheryl J.; Marshall, Paul W.; Wacynski, Augustyn; Polidan, Elizabeth; Johnson, Scott D.; Campbell, Art

    2004-09-01

    The proton-induced charge transfer efficiency (CTE) behavior for the Lawrence Berkeley National Laboratory (LBNL) p-channel CCD [being developed for the Supernovae Acceleration Probe (SNAP)] is compared with the Hubble Space Telescope"s (HST) Wide Field Camera 3 (WFC3) n-channel CCDs CTE using 55Fe x-rays, first pixel edge response (FPR), and extended pixel edge response (EPER) techniques. The pre- and post-proton radiation performance parameters of p-channel CCDs designed by LBNL and fabricated at Dalsa Semiconductor, Inc. are compared with n-channel CCDs from E2V, Inc. LBNL p-channel CCDs both with and without notched parallel registers are compared with the E2V CCD43 [a notched, multi-phase pinned (MPP) device] and the E2V CCD44 (an un-notched, non-MPP device), using the same readout timing and measured over the same range of temperatures. The CTE performance of the p-channel CCD is about an order of magnitude better than similar n-channel CCDs for the conditions measured here after a 63 MeV proton fluence of 2.5 x 109 cm-2, which is equivalent to 2.5 years in the HST orbit behind shielding comparable to about 2.5 cm Al. Our measurements are compared with previous CTE measurements at 12 MeV by Bebek et al. The ~ 10 x CTE improvements relative to n-channel CCDs is seen at -83°C, a temperature which is optimized for n-channel CCD performance. Advantages from p-channel CCDs should be greater at other temperatures. Dark current measurements and hot pixel issues are also discussed.

  1. Dark current studies on a normal-conducting high-brightness very-high-frequency electron gun operating in continuous wave mode

    NASA Astrophysics Data System (ADS)

    Huang, R.; Filippetto, D.; Papadopoulos, C. F.; Qian, H.; Sannibale, F.; Zolotorev, M.

    2015-01-01

    We report on measurements and analysis of a field-emitted electron current in the very-high-frequency (VHF) gun, a room temperature rf gun operating at high field and continuous wave (CW) mode at the Lawrence Berkeley National Laboratory (LBNL). The VHF gun is the core of the Advanced Photo-injector Experiment (APEX) at LBNL, geared toward the development of an injector for driving the next generation of high average power x-ray free electron lasers. High accelerating fields at the cathode are necessary for the high-brightness performance of an electron gun. When coupled with CW operation, such fields can generate a significant amount of field-emitted electrons that can be transported downstream the accelerator forming the so-called "dark current." Elevated levels of a dark current can cause radiation damage, increase the heat load in the downstream cryogenic systems, and ultimately limit the overall performance and reliability of the facility. We performed systematic measurements that allowed us to characterize the field emission from the VHF gun, determine the location of the main emitters, and define an effective strategy to reduce and control the level of dark current at APEX. Furthermore, the energy spectra of isolated sources have been measured. A simple model for energy data analysis was developed that allows one to extract information on the emitter from a single energy distribution measurement.

  2. Contribution of generation-recombination processes at inner interface of MBE-grown Hg1-xCdxTe heterostucture to dark current of small active area photodiode

    NASA Astrophysics Data System (ADS)

    Chekanova, Galina V.; Drugova, Albina A.; Kholodnov, Viacheslav; Nikitin, Mikhail S.

    2009-09-01

    Multilayer heterostructures of Hg1-xCdxTe alloy grown by Molecular Beam Epitaxy (MBE) on large size alternative substrates Si, GaAs and Ge are considered as one of productive alternative materials for issue of large format photovoltaic (PV) infrared (IR) focal plane arrays. However reaching of ultimate performance of small-pitched photodiode's (PD) covering spectral range from 8 to 12 μm depends on electronic properties of both individual layers and heterostructure interfaces. Due to small thickness of heterostructure layers, interfaces are located close to active regions of p-n junction and hence generation-recombination processes at interfaces will contribute to value of current flowing through junction. As usual measured dark current value of small-sized PD is higher than estimated from calculation and cannot be explained by discrepancy between real and estimated charge carriers concentration in absorption layers where p-n junction is formed. Objective of the present work was to calculate the contribution of recombination of charge carriers via electronic states on nearby inner interface to dark current of Hg1-xCdxTe LWIR PD (λco equals to 9.5-10.3 μm at Top=77 K) and its variation with absorption layer parameters and compare it to measured data on small-pitched arrays. We have concluded previously that at high recombination rate dark current can grow in orders of value.

  3. Impact of field-enhanced band-traps-band tunneling on the dark current generation in germanium p-i-n photodetector

    NASA Astrophysics Data System (ADS)

    Ang, Kah-Wee; Ng, Joseph Weisheng; Lo, Guo-Qiang; Kwong, Dim-Lee

    2009-06-01

    This letter investigates the impact of field-enhanced band-traps-band tunneling on the dark current generation in germanium (Ge) p-i-n photodetector. We show that the existence of defect-induced traps within the forbidden gap forms the underlying leakage mechanism. Enhancing the electric field intensity is found to reduce the activation energy that governs the leakage generation rates. In the presence of enlarged band-bending, the dark current generation is further aggravated by the enhancement in electrons and holes tunneling from the resulting deep levels into the conduction and valence bands, respectively. Such field-enhanced band tunneling effect becomes increasingly prominent with a downsizing of the detector's depletion width, which imposes a design trade-off between leakage generation and bandwidth enhancement.

  4. [Correlation of fine structures of distributions of amplitudes of a photomultiplier dark current fluctuations with the Earth rotations about its axis].

    PubMed

    Fedorov, M V; Belousov, L V; Voeĭkov, V L; Zenchenko, K I; Zenchenko, T A; Konradov, A A; Shnol', S E

    2001-01-01

    The fine structures of distributions of photomultiplier dark current fluctuations measured in two laboratories 2000 km distant from other: in the international Institute of Biophysics (Neuss, Germany) and in the Moscow State University (Moscow, Russia) were compared. It is shown that similar forms of appropriate histograms are apparently more often realized at both locations at the same local time. This confirms the previous conclusion that the fine structure of distributions correlates with rotation of the Earth about its axis.

  5. Short-wavelength infrared imaging using low dark current InGaAs detector arrays and vertical-cavity surface-emitting laser illuminators

    NASA Astrophysics Data System (ADS)

    Macdougal, Michael; Geske, Jon; Wang, Chad; Follman, David

    2011-06-01

    We describe the factors that go into the component choices for a short wavelength IR (SWIR) imager, which include the SWIR sensor, the lens, and the illuminator. We have shown the factors for reducing dark current, and shown that we can achieve well below 1.5 nA/cm2 for 15 μm devices at 7 °C. In addition, we have mated our InGaAs detector arrays to 640×512 readout integrated integrated circuits to make focal plane arrays (FPAs). The resulting FPAs are capable of imaging photon fluxes with wavelengths between 1 and 1.6 μm at low light levels. The dark current associated with these FPAs is extremely low, exhibiting a mean dark current density of 0.26 nA/cm2 at 0 °C. Noise due to the readout can be reduced from 95 to 57 electrons by using off-chip correlated double sampling. In addition, Aerius has developed laser arrays that provide flat illumination in scenes that are normally light-starved. The illuminators have 40% wall-plug efficiency and provide low-speckle illumination, and provide artifact-free imagery versus conventional laser illuminators.

  6. Specific features of light current-voltage characteristics of p-i-n structures based on amorphous silicon in the case of the tunnel-drift mechanism of dark current transport

    SciTech Connect

    Andreev, A. A.

    2008-11-15

    Current-voltage (I-V) characteristics of p-i-n structures based on amorphous silicon ({alpha}-Si:H) with small hole diffusion lengths (shorter than the thickness of the i-layer of a p-i-n structure) have been experimentally studied with and without illumination. It is shown that forward I-V characteristics of structures of this kind can be described by a dependence inherent in diodes, with a diode ideality factor two-three times the maximum value of 2, theoretically predicted for generation-recombination currents in p-n junctions. The dark current is always substantially lower than the photocurrent in a cell biased with a voltage approximately equal to the opencircuit voltage of the photocell. Dark currents cannot contribute to the I-V characteristic under illumination. The photocurrent decreases with increasing photovoltage at a bias lower than the open-circuit voltage because of a decrease in the collection coefficient and the increasingly important role of back diffusion of electrons into the p-contact, rather than as a result of the dark injection. In the case of biases exceeding the open-circuit voltage, back diffusion becomes the predominant component of the current.

  7. Dark stars: a review.

    PubMed

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars. PMID:27214049

  8. Dark stars: a review

    NASA Astrophysics Data System (ADS)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (˜10 AU) and cool (surface temperatures  ˜10 000 K) objects. We follow the evolution of dark stars from their inception at  ˜1{{M}⊙} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >{{10}6}{{M}⊙} and luminosities  >{{10}10}{{L}⊙} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  9. Dark stars: a review

    NASA Astrophysics Data System (ADS)

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only ≲ 0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼1{{M}ȯ} as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >{{10}6}{{M}ȯ} and luminosities  >{{10}10}{{L}ȯ} , making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  10. Dark stars: a review.

    PubMed

    Freese, Katherine; Rindler-Daller, Tanja; Spolyar, Douglas; Valluri, Monica

    2016-06-01

    Dark stars are stellar objects made (almost entirely) of hydrogen and helium, but powered by the heat from dark matter annihilation, rather than by fusion. They are in hydrostatic and thermal equilibrium, but with an unusual power source. Weakly interacting massive particles (WIMPs), among the best candidates for dark matter, can be their own antimatter and can annihilate inside the star, thereby providing a heat source. Although dark matter constitutes only [Formula: see text]0.1% of the stellar mass, this amount is sufficient to power the star for millions to billions of years. Thus, the first phase of stellar evolution in the history of the Universe may have been dark stars. We review how dark stars come into existence, how they grow as long as dark matter fuel persists, and their stellar structure and evolution. The studies were done in two different ways, first assuming polytropic interiors and more recently using the MESA stellar evolution code; the basic results are the same. Dark stars are giant, puffy (∼10 AU) and cool (surface temperatures  ∼10 000 K) objects. We follow the evolution of dark stars from their inception at  ∼[Formula: see text] as they accrete mass from their surroundings to become supermassive stars, some even reaching masses  >[Formula: see text] and luminosities  >[Formula: see text], making them detectable with the upcoming James Webb Space Telescope. Once the dark matter runs out and the dark star dies, it may collapse to a black hole; thus dark stars may provide seeds for the supermassive black holes observed throughout the Universe and at early times. Other sites for dark star formation may exist in the Universe today in regions of high dark matter density such as the centers of galaxies. The current review briefly discusses dark stars existing today, but focuses on the early generation of dark stars.

  11. Pixel isolation of low dark-current large-format InAs/GaSb superlattice complementary barrier infrared detector focal plane arrays with high fill factor

    NASA Astrophysics Data System (ADS)

    Nguyen, Jean; Hill, Cory J.; Rafol, Don; Keo, Sam; Soibel, Alexander; Ting, David Z.-Y.; Mumolo, Jason; Liu, John; Gunapala, Sarath D.

    2011-01-01

    Low dark current and high fill factor are two crucial characteristics for the realization of the InAs/GaSb superlattice (SL) technology as third generation focal plane arrays (FPAs). Recent development proved high performance results for the complementary barrier infrared detector (CBIRD) design, and a high-quality etch technique is required to minimize surface leakage currents. We report on a n-CBIRD with 10.3 μm cutoff, exhibiting a responsivity of 1.7 A/W and dark current density of 1×10-5 A/cm2 at 77K under 0.2 V bias, without AR coating and without passivation. Results from four different mesa isolation techniques are compared on single element diodes: chemical wet etch using C4H6O6:H3PO4:H2O2:H2O, BCl3/Ar inductively coupled plasma (ICP), CH4/H2/Ar ICP, and CH4/H2/BCl3/Cl2/Ar ICP. The CH4/H2/BCl3/Cl2/Ar etched structures yielded more than 2.5 times improvement in dark current density and nearvertical sidewalls. Using this etching technique, we then implement a 1k x 1k p-CBIRD array with 11.5 μm cutoff and peak responsivity of 3 A/W. Operating at T = 80K, the array yielded a 81% fill factor with 98% operability and performance results of 21% quantum efficiency, 53 mK NE▵T, and NEI of 6.9×1013 photons/sec-cm2.

  12. Dark-disk universe.

    PubMed

    Fan, JiJi; Katz, Andrey; Randall, Lisa; Reece, Matthew

    2013-05-24

    We point out that current constraints on dark matter imply only that the majority of dark matter is cold and collisionless. A subdominant fraction of dark matter could have much stronger interactions. In particular, it could interact in a manner that dissipates energy, thereby cooling into a rotationally supported disk, much as baryons do. We call this proposed new dark matter component double-disk dark matter (DDDM). We argue that DDDM could constitute a fraction of all matter roughly as large as the fraction in baryons, and that it could be detected through its gravitational effects on the motion of stars in galaxies, for example. Furthermore, if DDDM can annihilate to gamma rays, it would give rise to an indirect detection signal distributed across the sky that differs dramatically from that predicted for ordinary dark matter. DDDM and more general partially interacting dark matter scenarios provide a large unexplored space of testable new physics ideas.

  13. Dark-disk universe.

    PubMed

    Fan, JiJi; Katz, Andrey; Randall, Lisa; Reece, Matthew

    2013-05-24

    We point out that current constraints on dark matter imply only that the majority of dark matter is cold and collisionless. A subdominant fraction of dark matter could have much stronger interactions. In particular, it could interact in a manner that dissipates energy, thereby cooling into a rotationally supported disk, much as baryons do. We call this proposed new dark matter component double-disk dark matter (DDDM). We argue that DDDM could constitute a fraction of all matter roughly as large as the fraction in baryons, and that it could be detected through its gravitational effects on the motion of stars in galaxies, for example. Furthermore, if DDDM can annihilate to gamma rays, it would give rise to an indirect detection signal distributed across the sky that differs dramatically from that predicted for ordinary dark matter. DDDM and more general partially interacting dark matter scenarios provide a large unexplored space of testable new physics ideas. PMID:23745856

  14. Effect of self assembled quantum dots on carrier mobility, with application to modeling the dark current in quantum dot infrared photodetectors

    NASA Astrophysics Data System (ADS)

    Youssef, Sarah; El-Batawy, Yasser M.; Abouelsaood, Ahmed A.

    2016-09-01

    A theoretical method for calculating the electron mobility in quantum dot infrared photodetectors is developed. The mobility calculation is based on a time-dependent, finite-difference solution of the Boltzmann transport equation in a bulk semiconductor material with randomly positioned conical quantum dots. The quantum dots act as scatterers of current carriers (conduction-band electrons in our case), resulting in limiting their mobility. In fact, carrier scattering by quantum dots is typically the dominant factor in determining the mobility in the active region of the quantum dot device. The calculated values of the mobility are used in a recently developed generalized drift-diffusion model for the dark current of the device [Ameen et al., J. Appl. Phys. 115, 063703 (2014)] in order to fix the overall current scale. The results of the model are verified by comparing the predicted dark current characteristics to those experimentally measured and reported for actual InAs/GaAs quantum dot infrared photodetectors. Finally, the effect of the several relevant device parameters, including the operating temperature and the quantum dot average density, is studied.

  15. Low dark current P-InAsSbP/n-InAs/N-InAsSbP/n+-InAs double heterostructure back-side illuminated photodiodes

    NASA Astrophysics Data System (ADS)

    Brunkov, P. N.; Il'inskaya, N. D.; Karandashev, S. A.; Karpukhina, N. G.; Lavrov, A. A.; Matveev, B. A.; Remennyi, M. A.; Stus', N. M.; Usikova, A. A.

    2016-05-01

    P-InAsSbP/n-InAs/N-InAsSbP/n+-InAs double heterostructure photodiodes with linear impurity distribution in the space charge region have been fabricated and studied. The photodiodes showed good perspectives for use in low temperature pyrometry as low dark current (8·10-6 A/cm2, Vbias = -0.5 V, 164 K) and background limited infrared photodetector (BLIP) regime starting from 150 K (2π field of view, D3.1μm ∗ = 1.4·1012 cm Hz1/2/W) have been demonstrated.

  16. Low dark current and high speed ZnO metal–semiconductor–metal photodetector on SiO{sub 2}/Si substrate

    SciTech Connect

    Çalışkan, Deniz; Bütün, Bayram; Çakır, M. Cihan; Özcan, Şadan; Özbay, Ekmel

    2014-10-20

    ZnO thin films are deposited by radio-frequency magnetron sputtering on thermally grown SiO{sub 2} on Si substrates. Pt/Au contacts are fabricated by standard photolithography and lift-off in order to form a metal-semiconductor-metal (MSM) photodetector. The dark current of the photodetector is measured as 1 pA at 100 V bias, corresponding to 100 pA/cm{sup 2} current density. Spectral photoresponse measurement showed the usual spectral behavior and 0.35 A/W responsivity at a 100 V bias. The rise and fall times for the photocurrent are measured as 22 ps and 8 ns, respectively, which are the lowest values to date. Scanning electron microscope image shows high aspect ratio and dense grains indicating high surface area. Low dark current density and high speed response are attributed to high number of recombination centers due to film morphology, deducing from photoluminescence measurements. These results show that as deposited ZnO thin film MSM photodetectors can be used for the applications needed for low light level detection and fast operation.

  17. Quenched dynamics in interacting one-dimensional systems: Appearance of current-carrying steady states from initial domain wall density profiles

    NASA Astrophysics Data System (ADS)

    Lancaster, Jarrett; Gull, Emanuel; Mitra, Aditi

    2010-12-01

    We investigate dynamics arising after an interaction quench in the quantum sine-Gordon model for a one-dimensional system initially prepared in a spatially inhomogeneous domain wall state. We study the time evolution of the density, current, and equal time correlation functions using the truncated Wigner approximation to which quantum corrections are added in order to set the limits on its validity. For weak to moderate strengths of the backscattering interaction, the domain wall spreads out ballistically with the system within the light cone reaching a nonequilibrium steady state characterized by a net current flow. A steady-state current exists for a quench at the exactly solvable Luther-Emery point. The magnitude of the current decreases with increasing strength of the backscattering interaction. The two-point correlation function of the variable canonically conjugate to the density reaches a spatially oscillating steady state at a wavelength inversely related to the current.

  18. Dark current reduction for 2.5 {micro}m wavelength, 2% mismatched InGaAs photodetectors, by changing bufferlayer structure and growth temperature

    SciTech Connect

    D`Hondt, M.; Moerman, I.; Demeester, P.

    1996-12-31

    Optical components with wavelengths ranging between 1.5 and 2.5{micro}m are becoming increasingly important. Applications include various earth observation missions, NIR spectroscopy and fiber-optic communications at 2.55{micro}m. A possible material candidate for devices at 2.5{micro}m wavelength is In{sub .82}Ga{sub .18}As with a lattice mismatch of {+-}2% with respect to the InP-substrate. To improve optical and electrical performances of a mismatched device an effective buffer layer structure is wanted: a good buffer layer prevents the generated dislocations to propagate towards the mismatched active layer. Especially the dark current, which needs to be very low for space applications (low noise), is strongly influenced by those dislocations which act as generation-recombination centers. The authors describe the influence of growth temperature, bufferlayer structure and substrate orientation on the dark current density of test devices. All growth runs were performed by means of low-pressure MOVPE, using a horizontal liner. The processing of these devices consisted of deposition of TiAu contacts, by using a removable Ni mask, with openings of different size and shape. These metal contacts were in turn used as a mask for the etching of the mesa. Afterwards a AuGe/Ni back contact was deposited.

  19. Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

    SciTech Connect

    Ma, X.; Maurer, D. A.; Knowlton, Stephen F.; ArchMiller, M. C.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; Roberts, N. A.; Traverso, P. J.; Cianciosa, M. R.

    2015-12-22

    Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. Lastly, the inversion radius of standard saw-teeth is used to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.

  20. Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

    DOE PAGES

    Ma, X.; Maurer, D. A.; Knowlton, Stephen F.; ArchMiller, M. C.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; et al

    2015-12-22

    Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. Lastly, the inversion radius of standard saw-teeth is usedmore » to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.« less

  1. Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

    SciTech Connect

    Ma, X. Maurer, D. A.; Knowlton, S. F.; ArchMiller, M. C.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; Roberds, N. A.; Traverso, P. J.; Cianciosa, M. R.

    2015-12-15

    Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. The inversion radius of standard sawteeth is used to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.

  2. Non-axisymmetric equilibrium reconstruction of a current-carrying stellarator using external magnetic and soft x-ray inversion radius measurements

    NASA Astrophysics Data System (ADS)

    Ma, X.; Maurer, D. A.; Knowlton, S. F.; ArchMiller, M. C.; Cianciosa, M. R.; Ennis, D. A.; Hanson, J. D.; Hartwell, G. J.; Hebert, J. D.; Herfindal, J. L.; Pandya, M. D.; Roberds, N. A.; Traverso, P. J.

    2015-12-01

    Non-axisymmetric free-boundary equilibrium reconstructions of stellarator plasmas are performed for discharges in which the magnetic configuration is strongly modified by ohmically driven plasma current. These studies were performed on the compact toroidal hybrid device using the V3FIT reconstruction code with a set of 50 magnetic diagnostics external to the plasma. With the assumption of closed magnetic flux surfaces, the reconstructions using external magnetic measurements allow accurate estimates of the net toroidal flux within the last closed flux surface, the edge safety factor, and the plasma shape of these highly non-axisymmetric plasmas. The inversion radius of standard sawteeth is used to infer the current profile near the magnetic axis; with external magnetic diagnostics alone, the current density profile is imprecisely reconstructed.

  3. Three dimensional equilibrium solutions for a current-carrying reversed-field pinch plasma with a close-fitting conducting shell

    NASA Astrophysics Data System (ADS)

    Koliner, J. J.; Cianciosa, M. R.; Boguski, J.; Anderson, J. K.; Hanson, J. D.; Chapman, B. E.; Brower, D. L.; Den Hartog, D. J.; Ding, W. X.; Duff, J. R.; Goetz, J. A.; McGarry, M.; Morton, L. A.; Parke, E.

    2016-03-01

    In order to characterize the Madison Symmetric Torus (MST) reversed-field pinch (RFP) plasmas that bifurcate to a helical equilibrium, the V3FIT equilibrium reconstruction code was modified to include a conducting boundary. RFP plasmas become helical at a high plasma current, which induces large eddy currents in MST's thick aluminum shell. The V3FIT conducting boundary accounts for the contribution from these eddy currents to external magnetic diagnostic coil signals. This implementation of V3FIT was benchmarked against MSTFit, a 2D Grad-Shafranov solver, for axisymmetric plasmas. The two codes both fit Bθ measurement loops around the plasma minor diameter with qualitative agreement between each other and the measured field. Fits in the 3D case converge well, with q-profile and plasma shape agreement between two distinct toroidal locking phases. Greater than 60% of the measured n = 5 component of Bθ at r = a is due to eddy currents in the shell, as calculated by the conducting boundary model.

  4. Three dimensional equilibrium solutions for a current-carrying reversed-field pinch plasma with a close-fitting conducting shell

    DOE PAGES

    Koliner, J. J.; Boguski, J.; Anderson, J. K.; Hanson, J. D.; Chapman, B. E.; Brower, D. L.; Den Hartog, D. J.; Ding, W. X.; Duff, J. R.; Goetz, J. A.; et al

    2016-03-25

    In order to characterize the Madison Symmetric Torus (MST) reversed-field pinch(RFP)plasmas that bifurcate to a helical equilibrium, the V3FIT equilibrium reconstruction code was modified to include a conducting boundary. RFPplasmas become helical at a high plasma current, which induces large eddy currents in MST's thick aluminum shell. The V3FIT conducting boundary accounts for the contribution from these eddy currents to external magnetic diagnostic coil signals. This implementation of V3FIT was benchmarked against MSTFit, a 2D Grad-Shafranov solver, for axisymmetric plasmas. The two codes both fit B measurement loops around the plasma minor diameter with qualitative agreement between each other andmore » the measured field. Fits in the 3D case converge well, with q-profile and plasma shape agreement between two distinct toroidal locking phases. Greater than 60% of the measured n = 5 component of B at r = a is due to eddy currents in the shell, as calculated by the conducting boundary model.« less

  5. The dark side of cosmology: dark matter and dark energy.

    PubMed

    Spergel, David N

    2015-03-01

    A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "dark energy," energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales.

  6. The dark side of cosmology: dark matter and dark energy.

    PubMed

    Spergel, David N

    2015-03-01

    A simple model with only six parameters (the age of the universe, the density of atoms, the density of matter, the amplitude of the initial fluctuations, the scale dependence of this amplitude, and the epoch of first star formation) fits all of our cosmological data . Although simple, this standard model is strange. The model implies that most of the matter in our Galaxy is in the form of "dark matter," a new type of particle not yet detected in the laboratory, and most of the energy in the universe is in the form of "dark energy," energy associated with empty space. Both dark matter and dark energy require extensions to our current understanding of particle physics or point toward a breakdown of general relativity on cosmological scales. PMID:25745164

  7. Coupling dark energy to dark matter inhomogeneities

    NASA Astrophysics Data System (ADS)

    Marra, Valerio

    2016-09-01

    We propose that dark energy in the form of a scalar field could effectively couple to dark matter inhomogeneities. Through this coupling energy could be transferred to/from the scalar field, which could possibly enter an accelerated regime. Though phenomenological, this scenario is interesting as it provides a natural trigger for the onset of the acceleration of the universe, since dark energy starts driving the expansion of the universe when matter inhomogeneities become sufficiently strong. Here we study a possible realization of this idea by coupling dark energy to dark matter via the linear growth function of matter perturbations. The numerical results show that it is indeed possible to obtain a viable cosmology with the expected series of radiation, matter and dark-energy dominated eras. In particular, the current density of dark energy is given by the value of the coupling parameters rather than by very special initial conditions for the scalar field. In other words, this model-unlike standard models of cosmic late acceleration-does not suffer from the so-called "coincidence problem" and its related fine tuning of initial conditions.

  8. Minority carrier lifetime and dark current measurements in mid-wavelength infrared InAs0.91Sb0.09 alloy nBn photodetectors

    SciTech Connect

    Olson, B. V.; Kim, J. K.; Kadlec, E. A.; Klem, J. F.; Hawkins, S. D.; Leonhardt, D.; Coon, W. T.; Fortune, T. R.; Cavaliere, M. A.; Tauke-Pedretti, A.; Shaner, E. A.

    2015-11-03

    Carrier lifetime and dark current measurements are reported for a mid-wavelength infrared InAs 0.91Sb0.09 alloy nBn photodetector. Minority carrier lifetimes are measured using a non-contact time-resolved microwave technique on unprocessed portions of the nBn wafer and the Auger recombination Bloch function parameter is determined to be |F1F2|=0.292. Moreover, the measured lifetimes are also used to calculate the expected diffusion dark current of the nBn devices and are compared with the experimental dark current measured in processed photodetector pixels from the same wafer. As a result, excellent agreement is found between the two, highlighting the important relationship between lifetimes and diffusion currents in nBn photodetectors.

  9. Identification of Defect Candidates and their Effects on Carrier Lifetimes and Dark Currents in InAs/InAsSb Strained-Layer Superlattices for Infrared Detectors

    NASA Astrophysics Data System (ADS)

    Kioussis, Nicholas

    The InAs/GaSb and InAs/InAsSb type-II strain-layer superlattices (T2SLS) are of great importance and show great promise for mid-wave and long-wave infrared (IR) detectors for a variety of civil and military applications. The T2SLS offer several advantages over present day detection technologies including suppressed Auger recombination relative to the bulk MCT material, high quantum efficiencies, and commercial availability of low defect density substrates. While the T2SLS detectors are approaching the empirical Rule-07 benchmark of MCT's performance level, the dark-current density is still significantly higher than that of bulk MCT detectors. One of the major origins of dark current is associated with the Shockley-Read- Hall (SRH) process in the depletion region of the detector. I will present results of ab initio electronic structure calculations of the stability of a wide range of point defects [As and In vacancies, In, As and Sb antisites, In interstitials, As interstitials, and Sb interstitials] in various charged states in bulk InAs, InSb, and InAsSb systems and T2SLS. I will also present results of the transition energy levels. The calculations reveal that compared to defects in bulk materials, the formation and defect properties in InAs/InAsSb T2SLS can be affected by various structural features, such as strain, interface, and local chemical environment. I will present examples where the effect of strain or local chemical environment shifts the transition energy levels of certain point defects either above or below the conduction band minimum, thus suppressing their contribution to the SRH recombination.

  10. Dark Matters

    ScienceCinema

    Joseph Silk

    2016-07-12

    One of the greatest mysteries in the cosmos is that it is mostly dark.  Astronomers and particle physicists today are seeking to unravel the nature of this mysterious, but pervasive dark matter which has profoundly influenced the formation of structure in the universe.  I will describe the complex interplay between galaxy formation and dark matter detectability and review recent attempts to measure particle dark matter by direct and indirect means.

  11. Dark Matters

    SciTech Connect

    Joseph Silk

    2009-09-23

    One of the greatest mysteries in the cosmos is that it is mostly dark.  Astronomers and particle physicists today are seeking to unravel the nature of this mysterious, but pervasive dark matter which has profoundly influenced the formation of structure in the universe.  I will describe the complex interplay between galaxy formation and dark matter detectability and review recent attempts to measure particle dark matter by direct and indirect means.

  12. Light's Darkness

    ScienceCinema

    Padgett, Miles [University of Glasgow, Glasgow, Scotland

    2016-07-12

    Optical vortices and orbital angular momentum are currently topical subjects in the optics literature. Although seemingly esoteric, they are, in fact, the generic state of light and arise whenever three or more plane waves interfere. To be observed by eye the light must be monochromatic. Laser speckle is one such example, where the optical energy circulates around each black spot, giving a local orbital angular momentum. This talk with report three on-going studies. First, when considering a volume of interfering waves, the laser specs map out threads of complete darkness embedded in the light. Do these threads form loops? Links? Or even knots? Second, when looking through a rapidly spinning window, the image of the world on the other side is rotated: true or false? Finally, the entanglement of orbital angular momentum states means measuring how the angular position of one photons sets the angular momentum of another: is this an angular version of the EPR (Einstein, Podolsky, and Rosen) paradox?

  13. Dark matters

    NASA Astrophysics Data System (ADS)

    Steigman, Gary

    The observational evidence for dark matter in the universe is reviewed. Constraints on the baryon density from primordial nucleosynthesis are presented and compared to the dynamical estimates of the mass on various scales. Baryons can account for the observed luminous mass as well as some, perhaps most, of the 'observed' dark mass. However if, as inflation/naturalness suggest, the total density of the universe is equal to the critical density, then nonbaryonic dark matter is required. The assets and liabilities of, as well as the candidates for, hot and cold dark matter are outlined. At present, there is no completely satisfactory candidate for nonbaryonic dark matter.

  14. Multi-Component Dark Matter

    SciTech Connect

    Zurek, Kathryn M.

    2008-11-01

    We explore multi-component dark matter models where the dark sector consists of multiple stable states with different mass scales, and dark forces coupling these states further enrich the dynamics. The multi-component nature of the dark matter naturally arises in supersymmetric models, where both R parity and an additional symmetry, such as a Z{sub 2}, is preserved. We focus on a particular model where the heavier component of dark matter carries lepton number and annihilates mostly to leptons. The heavier component, which is essentially a sterile neutrino, naturally explains the PAMELA, ATIC and synchrotron signals, without an excess in antiprotons which typically mars other models of weak scale dark matter. The lighter component, which may have a mass from a GeV to a TeV, may explain the DAMA signal, and may be visible in low threshold runs of CDMS and XENON, which search for light dark matter.

  15. Dynamics of dark energy with a coupling to dark matter

    SciTech Connect

    Boehmer, Christian G.; Caldera-Cabral, Gabriela; Maartens, Roy; Lazkoz, Ruth

    2008-07-15

    Dark energy and dark matter are the dominant sources in the evolution of the late universe. They are currently only indirectly detected via their gravitational effects, and there could be a coupling between them without violating observational constraints. We investigate the background dynamics when dark energy is modeled as exponential quintessence and is coupled to dark matter via simple models of energy exchange. We introduce a new form of dark sector coupling, which leads to a more complicated dynamical phase space and has a better physical motivation than previous mathematically similar couplings.

  16. Direct search for dark matter

    SciTech Connect

    Yoo, Jonghee; /Fermilab

    2009-12-01

    Dark matter is hypothetical matter which does not interact with electromagnetic radiation. The existence of dark matter is only inferred from gravitational effects of astrophysical observations to explain the missing mass component of the Universe. Weakly Interacting Massive Particles are currently the most popular candidate to explain the missing mass component. I review the current status of experimental searches of dark matter through direct detection using terrestrial detectors.

  17. Dilaton-assisted dark matter.

    PubMed

    Bai, Yang; Carena, Marcela; Lykken, Joseph

    2009-12-31

    A dilaton could be the dominant messenger between standard model fields and dark matter. The measured dark matter relic abundance relates the dark matter mass and spin to the conformal breaking scale. The dark matter-nucleon spin-independent cross section is predicted in terms of the dilaton mass. We compute the current constraints on the dilaton from LEP and Tevatron experiments, and the gamma-ray signal from dark matter annihilation to dilatons that could be observed by Fermi Large Area Telescope.

  18. Dilaton-Assisted Dark Matter

    SciTech Connect

    Bai Yang; Lykken, Joseph; Carena, Marcela

    2009-12-31

    A dilaton could be the dominant messenger between standard model fields and dark matter. The measured dark matter relic abundance relates the dark matter mass and spin to the conformal breaking scale. The dark matter-nucleon spin-independent cross section is predicted in terms of the dilaton mass. We compute the current constraints on the dilaton from LEP and Tevatron experiments, and the gamma-ray signal from dark matter annihilation to dilatons that could be observed by Fermi Large Area Telescope.

  19. High performance x-ray imaging detectors on foil using solution-processed organic photodiodes with extremely low dark leakage current (Presentation Recording)

    NASA Astrophysics Data System (ADS)

    Kumar, Abhishek; Moet, Date; van der Steen, Jan Laurens; van Breemen, Albert; Shanmugam, Santhosh; Gilot, Jan; Andriessen, Ronn; Simon, Matthias; Ruetten, Walter; Douglas, Alexander; Raaijmakers, Rob; Malinowski, Pawel E.; Myny, Kris; Gelinck, Gerwin

    2015-10-01

    High performance X-ray imaging detectors on foil using solution-processed organic photodiodes with extremely low dark leakage current Abhishek Kumara, Date Moeta, Albert van Breemena, Santhosh Shanmugama, Jan-Laurens van der Steena, Jan Gilota, Ronn Andriessena, Matthias Simonb, Walter Ruettenb, Alexander U. Douglasb, Rob Raaijmakersc, Pawel E. Malinowskid, Kris Mynyd and Gerwin H. Gelincka,e a. Holst Centre/TNO, High Tech Campus 31, Eindhoven 5656 AE, The Netherlands b. Philips Research, High Tech Campus 34, 5656 AE Eindhoven, The Netherlands c. Philips Healthcare, Veenpluis 6-8, 5684 PC Best, The Netherlands d. Department of Large Area Electronics, imec vzw, Kapeldreef 75, Leuven B3001, Belgium e. Applied Physics Department, TU Eindhoven, Eindhoven, The Netherlands We demonstrate high performance X-ray imaging detectors on foil suitable for medical grade X-ray imaging applications. The detectors are based on solution-processed organic photodiodes forming bulk-heterojunctions from photovoltaic donor and acceptor blend. The organic photodiodes are deposited using an industrially compatible slot die coating technique with end of line processing temperature below 100°C. These photodiodes have extremely low dark leakage current density of 10-7 mA/cm2 at -2V bias with very high yield and have peak absorption around 550 nm wavelength. We combine these organic photodiodes with high mobility metal oxide semiconductor based thin film transistor arrays with high pixel resolution of 200ppi on thin plastic substrate. When combined with a typical CsI(TI) scintillator material on top, they are well suited for low dose X-ray imaging applications. The optical crosstalk is insignificant upto resolution of 200 ppi despite the fact that the photodiode layer is one continuous layer and is non-pixelated. Low processing temperatures are another key advantage since they can be fabricated on plastic substrate. This implies that we can make X-ray detectors on flexible foil. Those

  20. Dark strings

    SciTech Connect

    Vachaspati, Tanmay

    2009-09-15

    Recent astrophysical observations have motivated novel theoretical models of the dark matter sector. A class of such models predicts the existence of GeV scale cosmic strings that communicate with the standard model sector by Aharonov-Bohm interactions with electrically charged particles. We discuss the cosmology of these 'dark strings' and investigate possible observational signatures. More elaborate dark sector models are argued to contain hybrid topological defects that may also have observational signatures.

  1. Supernovae and Dark Energy

    NASA Astrophysics Data System (ADS)

    Domínguez, I.; Bravo, E.; Piersanti, L.; Straniero, O.; Tornambé, A.

    2009-08-01

    A decade ago the observations of thermonuclear supernovae at high-redhifts showed that the expansion rate of the Universe is accelerating and since then, the evidence for cosmic acceleration has gotten stronger. This acceleration requires that the Universe is dominated by dark energy, an exotic component characterized by its negative pressure. Nowadays all the available astronomical data (i.e. thermonuclear supernovae, cosmic microwave background, barionic acoustic oscillations, large scale structure, etc.) agree that our Universe is made of about 70% of dark energy, 25% of cold dark matter and only 5% of known, familiar matter. This Universe is geometrically flat, older than previously thought, its destiny is no longer linked to its geometry but to dark energy, and we ignore about 95% of its components. To understand the nature of dark energy is probably the most fundamental problem in physics today. Current astronomical observations are compatible with dark energy being the vacuum energy. Supernovae have played a fundamental role in modern Cosmology and it is expected that they will contribute to unveil the dark energy. In order to do that it is mandatory to understand the limits of supernovae as cosmological distance indicators, improving their precision by a factor 10.

  2. On dark energy isocurvature perturbation

    SciTech Connect

    Liu, Jie; Zhang, Xinmin; Li, Mingzhe E-mail: limz@nju.edu.cn

    2011-06-01

    Determining the equation of state of dark energy with astronomical observations is crucially important to understand the nature of dark energy. In performing a likelihood analysis of the data, especially of the cosmic microwave background and large scale structure data the dark energy perturbations have to be taken into account both for theoretical consistency and for numerical accuracy. Usually, one assumes in the global fitting analysis that the dark energy perturbations are adiabatic. In this paper, we study the dark energy isocurvature perturbation analytically and discuss its implications for the cosmic microwave background radiation and large scale structure. Furthermore, with the current astronomical observational data and by employing Markov Chain Monte Carlo method, we perform a global analysis of cosmological parameters assuming general initial conditions for the dark energy perturbations. The results show that the dark energy isocurvature perturbations are very weakly constrained and that purely adiabatic initial conditions are consistent with the data.

  3. Temperature dependence of 1/f noise, defects, and dark current in small pitch MWIR and LWIR HDVIP® HgCdTe FPAs

    NASA Astrophysics Data System (ADS)

    Strong, Roger L.; Kinch, Michael A.; Armstrong, John M.

    2013-06-01

    Reducing an array's pixel pitch reduces the size and weight of the focal plane array (FPA) and its associated dewar, cooler and optics. Higher operating temperatures reduce cool-down time and cooler power, enabling reduced cooler size and weight. High operating temperature small pitch (<=15 um) infrared detectors are therefore highly desirable. We have characterized a large number of MWIR and LWIR FPAs as a function of temperature and cutoff wavelength to determine the impact of these parameters on the FPA's dark current, 1/f noise and defects. The 77K cutoff wavelength range for the MWIR arrays was 5.0-5.6 um, and 8.5-11 um for the LWIR arrays. DRS' HDVIP® FPAs are based on a front-side illuminated, via interconnected, cylindrical geometry, N+/N/P architecture. An FPA's 1/f noise is manifested as a tail in the FPA's rmsnoise distribution. We have found that the model-independent nonparametric skew [(mean-median)/standard deviation] of the rmsnoise distribution is a highly effective tool for quantifying the magnitude of an FPA's 1/f noise tail. In this paper we show that a standard FPA's 1/f noise varies as ni (the intrinsic carrier concentration), in agreement with models that treat dislocations as donor pipes located within the P-volume of the unit cell. Nonstandard FPAs have been observed with systemic 1/f noise which varies as ni2.

  4. Dark matter and dark radiation

    SciTech Connect

    Ackerman, Lotty; Buckley, Matthew R.; Carroll, Sean M.; Kamionkowski, Marc

    2009-01-15

    We explore the feasibility and astrophysical consequences of a new long-range U(1) gauge field ('dark electromagnetism') that couples only to dark matter, not to the standard model. The dark matter consists of an equal number of positive and negative charges under the new force, but annihilations are suppressed if the dark-matter mass is sufficiently high and the dark fine-structure constant {alpha}-circumflex is sufficiently small. The correct relic abundance can be obtained if the dark matter also couples to the conventional weak interactions, and we verify that this is consistent with particle-physics constraints. The primary limit on {alpha}-circumflex comes from the demand that the dark matter be effectively collisionless in galactic dynamics, which implies {alpha}-circumflex < or approx. 10{sup -3} for TeV-scale dark matter. These values are easily compatible with constraints from structure formation and primordial nucleosynthesis. We raise the prospect of interesting new plasma effects in dark-matter dynamics, which remain to be explored.

  5. Dark matter: Theoretical perspectives

    SciTech Connect

    Turner, M.S. . Enrico Fermi Inst. Fermi National Accelerator Lab., Batavia, IL )

    1993-01-01

    I both review and make the case for the current theoretical prejudice: a flat Universe whose dominant constituent is nonbaryonic dark matter, emphasizing that this is still a prejudice and not yet fact. The theoretical motivation for nonbaryonic dark matter is discussed in the context of current elementary-particle theory, stressing that: (1) there are no dark matter candidates within the standard model of particle physics; (2) there are several compelling candidates within attractive extensions of the standard model of particle physics; and (3) the motivation for these compelling candidates comes first and foremost from particle physics. The dark-matter problem is now a pressing issue in both cosmology and particle physics, and the detection of particle dark matter would provide evidence for new physics.'' The compelling candidates are: a very light axion ( 10[sup [minus]6] eV--10[sup [minus]4] eV); a light neutrino (20 eV--90 eV); and a heavy neutralino (10 GeV--2 TeV). The production of these particles in the early Universe and the prospects for their detection are also discussed. I briefly mention more exotic possibilities for the dark matter, including a nonzero cosmological constant, superheavy magnetic monopoles, and decaying neutrinos.

  6. Dark matter: Theoretical perspectives

    SciTech Connect

    Turner, M.S. |

    1993-01-01

    I both review and make the case for the current theoretical prejudice: a flat Universe whose dominant constituent is nonbaryonic dark matter, emphasizing that this is still a prejudice and not yet fact. The theoretical motivation for nonbaryonic dark matter is discussed in the context of current elementary-particle theory, stressing that: (1) there are no dark matter candidates within the standard model of particle physics; (2) there are several compelling candidates within attractive extensions of the standard model of particle physics; and (3) the motivation for these compelling candidates comes first and foremost from particle physics. The dark-matter problem is now a pressing issue in both cosmology and particle physics, and the detection of particle dark matter would provide evidence for ``new physics.`` The compelling candidates are: a very light axion ( 10{sup {minus}6} eV--10{sup {minus}4} eV); a light neutrino (20 eV--90 eV); and a heavy neutralino (10 GeV--2 TeV). The production of these particles in the early Universe and the prospects for their detection are also discussed. I briefly mention more exotic possibilities for the dark matter, including a nonzero cosmological constant, superheavy magnetic monopoles, and decaying neutrinos.

  7. Dark matter: theoretical perspectives.

    PubMed Central

    Turner, M S

    1993-01-01

    I both review and make the case for the current theoretical prejudice: a flat Universe whose dominant constituent is nonbaryonic dark matter, emphasizing that this is still a prejudice and not yet fact. The theoretical motivation for nonbaryonic dark matter is discussed in the context of current elementary-particle theory, stressing that (i) there are no dark-matter candidates within the "standard model" of particle physics, (ii) there are several compelling candidates within attractive extensions of the standard model of particle physics, and (iii) the motivation for these compelling candidates comes first and foremost from particle physics. The dark-matter problem is now a pressing issue in both cosmology and particle physics, and the detection of particle dark matter would provide evidence for "new physics." The compelling candidates are a very light axion (10(-6)-10(-4) eV), a light neutrino (20-90 eV), and a heavy neutralino (10 GeV-2 TeV). The production of these particles in the early Universe and the prospects for their detection are also discussed. I briefly mention more exotic possibilities for the dark matter, including a nonzero cosmological constant, superheavy magnetic monopoles, and decaying neutrinos. PMID:11607395

  8. Milli-interacting dark matter

    NASA Astrophysics Data System (ADS)

    Wallemacq, Quentin

    2013-09-01

    We present a dark matter model reproducing well the results from DAMA/LIBRA and CoGeNT and having no contradiction with the negative results from XENON100 and CDMS-II/Ge. Two new species of fermions F and G form hydrogenlike atoms with standard atomic size through a dark U(1) gauge interaction carried out by a dark massless photon. A Yukawa coupling between the nuclei F and neutral scalar particles S induces an attractive shorter-range interaction. This dark sector interacts with our standard particles because of the presence of two mixings, a kinetic photon-dark photon mixing, and a mass σ-S mixing. The dark atoms from the halo diffuse elastically in terrestrial matter until they thermalize and then reach underground detectors with thermal energies, where they form bound states with nuclei by radiative capture. This causes the emission of photons that produce the signals observed by direct-search experiments.

  9. Dark matter universe.

    PubMed

    Bahcall, Neta A

    2015-10-01

    Most of the mass in the universe is in the form of dark matter--a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations--from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is "cold" (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology--a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)--fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle.

  10. Dark matter universe

    PubMed Central

    Bahcall, Neta A.

    2015-01-01

    Most of the mass in the universe is in the form of dark matter—a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations—from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is “cold” (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology—a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)—fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle. PMID:26417091

  11. Dark matter universe.

    PubMed

    Bahcall, Neta A

    2015-10-01

    Most of the mass in the universe is in the form of dark matter--a new type of nonbaryonic particle not yet detected in the laboratory or in other detection experiments. The evidence for the existence of dark matter through its gravitational impact is clear in astronomical observations--from the early observations of the large motions of galaxies in clusters and the motions of stars and gas in galaxies, to observations of the large-scale structure in the universe, gravitational lensing, and the cosmic microwave background. The extensive data consistently show the dominance of dark matter and quantify its amount and distribution, assuming general relativity is valid. The data inform us that the dark matter is nonbaryonic, is "cold" (i.e., moves nonrelativistically in the early universe), and interacts only weakly with matter other than by gravity. The current Lambda cold dark matter cosmology--a simple (but strange) flat cold dark matter model dominated by a cosmological constant Lambda, with only six basic parameters (including the density of matter and of baryons, the initial mass fluctuations amplitude and its scale dependence, and the age of the universe and of the first stars)--fits remarkably well all the accumulated data. However, what is the dark matter? This is one of the most fundamental open questions in cosmology and particle physics. Its existence requires an extension of our current understanding of particle physics or otherwise point to a modification of gravity on cosmological scales. The exploration and ultimate detection of dark matter are led by experiments for direct and indirect detection of this yet mysterious particle. PMID:26417091

  12. GUTzilla dark matter

    NASA Astrophysics Data System (ADS)

    Harigaya, Keisuke; Lin, Tongyan; Lou, Hou Keong

    2016-09-01

    Motivated by gauge coupling unification and dark matter, we present an extension to the Standard Model where both are achieved by adding an extra new matter multiplet. Such considerations lead to a Grand Unified Theory with very heavy WIMPzilla dark matter, which has mass greater than ˜ 107 GeV and must be produced before reheating ends. Naturally, we refer to this scenario as GUTzilla dark matter. Here we present a minimal GUTzilla model, adding a vector-like quark multiplet to the Standard Model. Proton decay constraints require the new multiplet to be both color and electroweak charged, which prompts us to include a new confining SU(3) gauge group that binds the multiplet into a neutral composite dark matter candidate. Current direct detection constraints are evaded due to the large dark matter mass; meanwhile, next-generation direct detection and proton decay experiments will probe much of the parameter space. The relic abundance is strongly dependent on the dynamics of the hidden confining sector, and we show that dark matter production during the epoch of reheating can give the right abundance.

  13. Dark coupling

    SciTech Connect

    Gavela, M.B.; Hernández, D.; Honorez, L. Lopez; Mena, O.; Rigolin, S. E-mail: d.hernandez@uam.es E-mail: omena@ific.uv.es

    2009-07-01

    The two dark sectors of the universe—dark matter and dark energy—may interact with each other. Background and linear density perturbation evolution equations are developed for a generic coupling. We then establish the general conditions necessary to obtain models free from non-adiabatic instabilities. As an application, we consider a viable universe in which the interaction strength is proportional to the dark energy density. The scenario does not exhibit ''phantom crossing'' and is free from instabilities, including early ones. A sizeable interaction strength is compatible with combined WMAP, HST, SN, LSS and H(z) data. Neutrino mass and/or cosmic curvature are allowed to be larger than in non-interacting models. Our analysis sheds light as well on unstable scenarios previously proposed.

  14. Dark Matter

    ERIC Educational Resources Information Center

    Lincoln, Don

    2013-01-01

    It's a dark, dark universe out there, and I don't mean because the night sky is black. After all, once you leave the shadow of the Earth and get out into space, you're surrounded by countless lights glittering everywhere you look. But for all of Sagan's billions and billions of stars and galaxies, it's a jaw-dropping fact that the ordinary kind of…

  15. Dark GPC

    NASA Astrophysics Data System (ADS)

    Bañas, Andrew R.; Villangca, Mark J.; Palima, Darwin; Glückstad, Jesper

    2016-03-01

    Generalized Phase Contrast (GPC) is an efficient method for efficiently shaping light into speckle-free contiguous optical distributions useful in diverse applications such as static beam shaping, optical manipulation and recently, for excitation in two-photon optogenetics. GPC typically results in a 3x intensified user defined input mask shape against a dark background. In this work, we emphasize GPC's capability of optimal destructive interference, normally used to create the dark background surrounding the shaped light. We also study input parameters wherein the locations of light and darkness are interchanged with respect to typical GPC output, thus resulting to a well-defined structured darkness. The conditions that give destructive interference for the output are then applied to near-arbitrary shapes. Preliminary experimental results are presented using dynamic spatial light modulator to form scaled arbitrary darkness shapes. Supporting demonstrations that reverse the light and dark regions of amplitude-modulated input are also presented as a related case of structuring destructive interference. Our analysis and experimental demonstrations show a simplified approach in the generation of extended regions of destructive interference within coherent beams.

  16. History and modern applications of nano-composite materials carrying GA/cm2 current density due to a Bose-Einstein Condensate at room temperature produced by Focused Electron Beam Induced Processing for many extraordinary novel technical applications

    NASA Astrophysics Data System (ADS)

    Koops, Hans W. P.

    2015-12-01

    The discovery of Focused Electron Beam Induced Processing and early applications of this technology led to the possible use of a novel nanogranular material “Koops-GranMat®” using Pt/C and Au/C material. which carries at room temperature a current density > 50 times the current density which high TC superconductors can carry. The explanation for the characteristics of this novel material is given. This fact allows producing novel products for many applications using Dual Beam system having a gas supply and X.Y.T stream data programming and not using GDSII layout pattern control software. Novel products are possible for energy transportation. -distribution.-switching, photon-detection above 65 meV energy for very efficient energy harvesting, for bright field emission electron sources used for vacuum electronic devices like amplifiers for HF electronics, micro-tubes, 30 GHz to 6 THz switching amplifiers with signal to noise ratio >10(!), THz power sources up to 1 Watt, in combination with miniaturized vacuum pumps, vacuum gauges, IR to THz detectors, EUV- and X-Ray sources. Since focusing electron beam induced deposition works also at low energy, selfcloning multibeam-production machines for field emitter lamps, displays, multi-beam - lithography, - imaging, and - inspection, energy harvesting, and power distribution with switches controlling field-emitter arrays for KA of currents but with < 100 V switching voltage are possible. Finally the replacement of HTC superconductors and its applications by the Koops-GranMat® having Koops-Pairs at room temperature will allow the investigation devices similar to Josephson Junctions and its applications now called QUIDART (Quantum interference devices at Room Temperature). All these possibilities will support a revolution in the optical, electric, power, and electronic technology.

  17. Carrying Backpacks: Physical Effects

    ERIC Educational Resources Information Center

    Illinois State Board of Education, 2006

    2006-01-01

    It is estimated that more than 40 million U.S. youth carry school materials in backs, routinely carrying books, laptop computers, personal and other items used on a daily basis. The Consumer Product Safety Commission (CPSC) estimates that 7,277 emergency visits each year result from injuries related to backpacks. Injury can occur when a child…

  18. The DarkSide awakens

    NASA Astrophysics Data System (ADS)

    Davini, S.; Agnes, P.; Agostino, L.; Albuquerque, I. F. M.; Alexander, T.; Alton, A. K.; Arisaka, K.; Back, H. O.; Baldin, B.; Biery, K.; Bonfini, G.; Bossa, M.; Bottino, B.; Brigatti, A.; Brodsky, J.; Budano, F.; Bussino, S.; Cadeddu, M.; Cadonati, L.; Cadoni, M.; Calaprice, F.; Canci, N.; Candela, A.; Cao, H.; Cariello, M.; Carlini, M.; Catalanotti, S.; Cavalcante, P.; Chepurnov, A.; Cocco, A. G.; Covone, G.; D'Angelo, D.; D'Incecco, M.; De Cecco, S.; De Deo, M.; De Vincenzi, M.; Derbin, A.; Devoto, A.; Di Eusanio, F.; Di Pietro, G.; Edkins, E.; Empl, A.; Fan, A.; Fiorillo, G.; Fomenko, K.; Foster, G.; Franco, D.; Gabriele, F.; Galbiati, C.; Giganti, C.; Goretti, A. M.; Granato, F.; Grandi, L.; Gromov, M.; Guan, M.; Guardincerri, Y.; Hackett, B. R.; Herner, K. R.; Hungerford, E. V.; Ianni, Aldo; Ianni, Andrea; James, I.; Jollet, C.; Keeter, K.; Kendziora, C. L.; Kobychev, V.; Koh, G.; Korablev, D.; Korga, G.; Kubankin, A.; Li, X.; Lissia, M.; Lombardi, P.; Luitz, S.; Ma, Y.; Machulin, I. N.; Mandarano, A.; Mari, S. M.; Maricic, J.; Marini, L.; Martoff, C. J.; Meregaglia, A.; Meyers, P. D.; Miletic, T.; Milincic, R.; Montanari, D.; Monte, A.; Montuschi, M.; Monzani, M. E.; Mosteiro, P.; Mount, B. J.; Muratova, V. N.; Musico, P.; Napolitano, J.; Orsini, M.; Ortica, F.; Pagani, L.; Pallavicini, M.; Pantic, E.; Parmeggiano, S.; Pelczar, K.; Pelliccia, N.; Perasso, S.; Pocar, A.; Pordes, S.; Pugachev, D. A.; Qian, H.; Randle, K.; Ranucci, G.; Razeto, A.; Reinhold, B.; Renshaw, A. L.; Romani, A.; Rossi, B.; Rossi, N.; Rountree, S. D.; Sablone, D.; Saggese, P.; Saldanha, R.; Sands, W.; Sangiorgio, S.; Savarese, C.; Segreto, E.; Semenov, D. A.; Shields, E.; Singh, P. N.; Skorokhvatov, M. D.; Smirnov, O.; Sotnikov, A.; Stanford, C.; Suvorov, Y.; Tartaglia, R.; Tatarowicz, J.; Testera, G.; Tonazzo, A.; Trinchese, P.; Unzhakov, E. V.; Vishneva, A.; Vogelaar, B.; Wada, M.; Walker, S.; Wang, H.; Wang, Y.; Watson, A. W.; Westerdale, S.; Wilhelmi, J.; Wojcik, M. M.; Xiang, X.; Xu, J.; Yang, C.; Yoo, J.; Zavatarelli, S.; Zec, A.; Zhong, W.; Zhu, C.; Zuzel, G.

    2016-05-01

    The DarkSide program at LNGS aims to perform background-free WIMP searches using two phase liquid argon time projection chambers, with the ultimate goal of covering all parameters down to the so-called neutrino floor. One of the distinct features of the program is the use of underground argon with has a reduced content of the radioactive 39Ar compared to atmospheric argon. The DarkSide Collaboration is currently operating the DarkSide-50 experiment, the first such WIMP detector using underground argon. Operations with underground argon indicate a suppression of 39Ar by a factor (1.4 ± 0.2) × 103 relative to atmospheric argon. The new results obtained with DarkSide-50 and the plans for the next steps of the DarkSide program, the 20t fiducial mass DarkSide-20k detector and the 200 t fiducial Argo, are reviewed in this proceedings.

  19. MAMA Dark Monitor

    NASA Astrophysics Data System (ADS)

    Zheng, Wei

    2010-09-01

    This proposal monitors the behavior of the dark current in each of the MAMA detectors, to look for evidence of change in the dark rate, indicative of detector problems developing.The basic monitor takes two 1300s TIME-TAG darks bi-weekly with each detector. The pairs of exposures for each detector are linked so that they are taken at opposite ends of the same SAA free interval. This pairing of exposures will make it easier to separate long and short term temporal variability from temperature dependent changes.For both detectors, additional blocks of exposures are taken once a year. These are groups of three 1314 s TIME-TAG darks for each of the MAMA detectors, distributed over a single SAA free interval. This will give more information on the brightness of the FUV MAMA dark current as a function of the amount of time that the HV has been on, and for the NUV MAMA will give a better measure of the short term temperature dependence.

  20. MAMA Dark Monitor

    NASA Astrophysics Data System (ADS)

    Cox, Colin

    2011-10-01

    This proposal monitors the behavior of the dark current in each of the MAMA detectors, to look for evidence of change in the dark rate, indicative of detector problems developing.The basic monitor takes two 1300s TIME-TAG darks bi-weekly with each detector. The pairs of exposures for each detector are linked so that they are taken at opposite ends of the same SAA free interval. This pairing of exposures will make it easier to separate long and short term temporal variability from temperature dependent changes.For both detectors, additional blocks of exposures are taken once a year. These are groups of three 1314 s TIME-TAG darks for each of the MAMA detectors, distributed over a single SAA free interval. This will give more information on the brightness of the FUV MAMA dark current as a function of the amount of time that the HV has been on, and for the NUV MAMA will give a better measure of the short term temperature dependence.

  1. Proposed mechanism to represent the suppression of dark current density by four orders with low energy light ion (H{sup −}) implantation in quaternary alloy-capped InAs/GaAs quantum dot infrared photodetectors

    SciTech Connect

    Mandal, A.; Ghadi, H.; Mathur, K.L.; Basu, A.; Subrahmanyam, N.B.V.; Singh, P.; Chakrabarti, S.

    2013-08-01

    Graphical abstract: - Abstract: Here we propose a carrier transport mechanism for low energy H{sup −} ions implanted InAs/GaAs quantum dot infrared photodetectors supportive of the experimental results obtained. Dark current density suppression of up to four orders was observed in the implanted quantum dot infrared photodetectors, which further demonstrates that they are effectively operational. We concentrated on determining how defect-related material and structural changes attributed to implantation helped in dark current density reduction for InAs/GaAs quantum dot infrared photodetectors. This is the first study to report the electrical carrier transport mechanism of H{sup −} ion-implanted InAs/GaAs quantum dot infrared photodetectors.

  2. Characterisation of dark current in novel Hg 1- xCd xTe mid-wavelength infrared photovoltaic detectors based on n-on-p junctions formed by plasma-induced type conversion

    NASA Astrophysics Data System (ADS)

    Rais, M. H.; Musca, C. A.; Antoszewski, J.; Dell, J. M.; Nener, B. D.; Faraone, L.

    2000-06-01

    This paper reports initial characterisation results for planar mid-wavelength infrared (MWIR) photodiodes fabricated using a novel reactive ion plasma-induced n-on-p junction formation technology on vacancy-doped p-type HgCdTe grown by LPE on CdZnTe substrates. The junction is formed without the need for post-implant annealing typically required by ion implantation junction formation techniques to repair damage or to move the junction away from damaged regions. The dark current and dynamic resistance, Rd, of the fabricated photodiodes have been characterised as a function of temperature. At 80 K, the zero-bias dynamic resistance-junction area product ( R0A) of the diodes is 4.6×10 7 Ω cm 2, with the devices being diffusion limited down to ˜135 K. Dynamic resistance has been measured for temperatures between 80 and 195 K and biases between -200 and +150 mV. Modelling of the observed dark current has been undertaken using three distinct mechanisms, diffusion, generation-recombination, and trap-assisted tunnelling. The results show that the plasma-induced junction formation technique can produce high-performance planar HgCdTe photodiodes. The dark current mechanisms found in these devices are similar to those found in diodes formed using conventional ion implantation techniques.

  3. Dark matter assimilation into the baryon asymmetry

    SciTech Connect

    D'Eramo, Francesco; Fei, Lin; Thaler, Jesse E-mail: lfei@mit.edu

    2012-03-01

    Pure singlets are typically disfavored as dark matter candidates, since they generically have a thermal relic abundance larger than the observed value. In this paper, we propose a new dark matter mechanism called {sup a}ssimilation{sup ,} which takes advantage of the baryon asymmetry of the universe to generate the correct relic abundance of singlet dark matter. Through assimilation, dark matter itself is efficiently destroyed, but dark matter number is stored in new quasi-stable heavy states which carry the baryon asymmetry. The subsequent annihilation and late-time decay of these heavy states yields (symmetric) dark matter as well as (asymmetric) standard model baryons. We study in detail the case of pure bino dark matter by augmenting the minimal supersymmetric standard model with vector-like chiral multiplets. In the parameter range where this mechanism is effective, the LHC can discover long-lived charged particles which were responsible for assimilating dark matter.

  4. Big Mysteries: Dark Energy

    SciTech Connect

    Lincoln, Don

    2014-04-15

    Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up! That observation is just mind blowing, and yet it is true. In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.

  5. Big Mysteries: Dark Energy

    ScienceCinema

    Lincoln, Don

    2016-07-12

    Scientists were shocked in 1998 when the expansion of the universe wasn't slowing down as expected by our best understanding of gravity at the time; the expansion was speeding up! That observation is just mind blowing, and yet it is true. In order to explain the data, physicists had to resurrect an abandoned idea of Einstein's now called dark energy. In this video, Fermilab's Dr. Don Lincoln tells us a little about the observations that led to the hypothesis of dark energy and what is the status of current research on the subject.

  6. Will our Current Data Rescue, Curation and Preservation Practices bring us out of the Digital Dark Ages and into the Renaissance of Multi-Source Science? (Invited)

    NASA Astrophysics Data System (ADS)

    Wyborn, L. A.

    2013-12-01

    evolutions of both hardware and software. The move to data intensive science has driven the realisation that we need to put more effort and resources into rescuing, curating and preserving data and properly preserved data sets are now being use to resolve the real world issues of today. However, as the capacity of computational systems increases relentlessly we need to question if our current efforts in data curation and preservation will scale to these ever growing systems. For Earth and Space Sciences to come out of the digital dark ages and into the renaissance of multi-source science, it is time to take stock and question our current data rescue, curation and preservation initiatives. Will the data store I am using be around in 50 years' time? What measures is this data store taking to avoid bit-rot and/or deal with software and hardware obsolescence. Is my data self-describing? Have I paid enough attention to cross domain data standards so my data can be reused and repurposed for the current decadal challenges? More importantly, as the capacity of computational systems scale beyond exascale to zettascale and yottascale, will my data sets that I have rescued, curated and preserved in my lifetime, no matter whether they are small or large, be able to contribute to addressing the decadal challenges that are as yet undefined.

  7. Axion dark matter searches

    DOE PAGES

    Stern, Ian P.

    2014-01-01

    We report nearly all astrophysical and cosmological data point convincingly to a large component of cold dark matter in the Universe. The axion particle, first theorized as a solution to the strong charge-parity problem of quantum chromodynamics, has been established as a prominent CDM candidate. Cosmic observation and particle physics experiments have bracketed the unknown mass of the axion between approximately a μeV and a meV. The Axion Dark Matter eXperiement (ADMX) has successfully completed searches between 1.9 and 3.7 μeV down to the KSVZ photon-coupling limit. ADMX and the Axion Dark Matter eXperiement High-Frequency (ADMX-HF) will search for axionsmore » at weaker coupling and/or higher frequencies within the next few years. Status of the experiments, current research and development, and projected mass-coupling exclusion limits are presented.« less

  8. Dark matter candidates

    NASA Technical Reports Server (NTRS)

    Turner, Michael S.

    1989-01-01

    The types of particles which may provide the nonluminous mass required by big-bang cosmological models are listed and briefly characterized. The observational evidence for the existence of dark matter (outweighing the luminous component by at least a factor of 10) is reviewed; the theoretical arguments favoring mainly nonbaryonic dark matter are summarized; and particular attention is given to weakly interacting massive particles (WIMPs) remaining as relics from the early universe. The WIMPs are classified as thermal relics (heavy stable neutrinos and lighter neutralinos), asymmetric relics (including baryons), nonthermal relics (superheavy magnetic monopoles, axions, and soliton stars), and truly exotic relics (relativistic debris or vacuum energy). Explanations for the current apparent baryon/exotica ratio of about 0.1 in different theoretical scenarios are considered, and the problems of experimental and/or observational dark-matter detection are examined.

  9. Axion dark matter searches

    SciTech Connect

    Stern, Ian P.; Collaboration: ADMX Collaboration; ADMX-HF Collaboration

    2014-06-24

    Nearly all astrophysical and cosmological data point convincingly to a large component of cold dark matter in the Universe. The axion particle, first theorized as a solution to the strong charge-parity problem of quantum chromodynamics, has been established as a prominent CDM candidate. Cosmic observation and particle physics experiments have bracketed the unknown mass of the axion between approximately a μeV and a meV. The Axion Dark Matter eXperiement (ADMX) has successfully completed searches between 1.9 and 3.7 μeV down to the KSVZ photon-coupling limit. ADMX and the Axion Dark Matter eXperiement High-Frequency (ADMX-HF) will search for axions at weaker coupling and/or higher frequencies within the next few years. Status of the experiments, current research and development, and projected mass-coupling exclusion limits are presented.

  10. Dark Energy. What the ...?

    SciTech Connect

    Wechsler, Risa

    2007-10-30

    What is the Universe made of? This question has been asked as long as humans have been questioning, and astronomers and physicists are finally converging on an answer. The picture which has emerged from numerous complementary observations over the past decade is a surprising one: most of the matter in the Universe isn't visible, and most of the Universe isn't even made of matter. In this talk, I will explain what the rest of this stuff, known as 'Dark Energy' is, how it is related to the so-called 'Dark Matter', how it impacts the evolution of the Universe, and how we can study the dark universe using observations of light from current and future telescopes.

  11. Axion dark matter searches

    SciTech Connect

    Stern, Ian P.

    2014-01-01

    We report nearly all astrophysical and cosmological data point convincingly to a large component of cold dark matter in the Universe. The axion particle, first theorized as a solution to the strong charge-parity problem of quantum chromodynamics, has been established as a prominent CDM candidate. Cosmic observation and particle physics experiments have bracketed the unknown mass of the axion between approximately a μeV and a meV. The Axion Dark Matter eXperiement (ADMX) has successfully completed searches between 1.9 and 3.7 μeV down to the KSVZ photon-coupling limit. ADMX and the Axion Dark Matter eXperiement High-Frequency (ADMX-HF) will search for axions at weaker coupling and/or higher frequencies within the next few years. Status of the experiments, current research and development, and projected mass-coupling exclusion limits are presented.

  12. Inflation, Dark Matter, Dark Energy

    NASA Astrophysics Data System (ADS)

    Kolb, Edward W.

    2005-06-01

    Remarkable 20th-century cosmological discoveries and theoretical ideas led to the development of the present cosmological "standard model." In this lecture I will focus on one of the more recent ideas that may now be regarded as part of the framework of the standard big-bang model; namely, that structure in the universe results from the growth of small seed density fluctuations produced during the inflationary universe. In order to complete this picture, I will also discuss the idea that the present mass density is dominated by dark matter and that there is now a preponderance of dark energy.

  13. The search for dark matter

    NASA Astrophysics Data System (ADS)

    Cline, David B.

    2016-03-01

    We discuss the search for dark matter. We first review the data from LUX that excludes the low-mass WIMP region and slightly lowers the XENON100 limits. We provide a brief review of the problems with the claimed low-mass signals. We discuss the current expectations for SUSY-WIMP dark matter and show why very massive detectors like Darwin may be required. We discuss some theoretical predictions from the meeting. There was compelling evidence from events observed in the Galactic Center by Fermi-LAT of WIMP dark matter at the UCLA meeting. We recount the Richard Arnowitt Lectures at UCLA dark matter symposiums and his role in the development of the strategy to detect SUGRA dark matter. In Honor of Richard Arnowitt.

  14. Big Bang synthesis of nuclear dark matter

    NASA Astrophysics Data System (ADS)

    Hardy, Edward; Lasenby, Robert; March-Russell, John; West, Stephen M.

    2015-06-01

    We investigate the physics of dark matter models featuring composite bound states carrying a large conserved dark "nucleon" number. The properties of sufficiently large dark nuclei may obey simple scaling laws, and we find that this scaling can determine the number distribution of nuclei resulting from Big Bang Dark Nucleosynthesis. For plausible models of asymmetric dark matter, dark nuclei of large nucleon number, e.g. ≳ 108, may be synthesised, with the number distribution taking one of two characteristic forms. If small-nucleon-number fusions are sufficiently fast, the distribution of dark nuclei takes on a logarithmically-peaked, universal form, independent of many details of the initial conditions and small-number interactions. In the case of a substantial bottleneck to nucleosynthesis for small dark nuclei, we find the surprising result that even larger nuclei, with size ≫ 108, are often finally synthesised, again with a simple number distribution. We briefly discuss the constraints arising from the novel dark sector energetics, and the extended set of (often parametrically light) dark sector states that can occur in complete models of nuclear dark matter. The physics of the coherent enhancement of direct detection signals, the nature of the accompanying dark-sector form factors, and the possible modifications to astrophysical processes are discussed in detail in a companion paper.

  15. Baryon destruction by asymmetric dark matter

    SciTech Connect

    Davoudiasl, Hooman; Morrissey, David E.; Tulin, Sean; Sigurdson, Kris

    2011-11-01

    We investigate new and unusual signals that arise in theories where dark matter is asymmetric and carries a net antibaryon number, as may occur when the dark matter abundance is linked to the baryon abundance. Antibaryonic dark matter can cause induced nucleon decay by annihilating visible baryons through inelastic scattering. These processes lead to an effective nucleon lifetime of 10{sup 29}-10{sup 32} yrs in terrestrial nucleon decay experiments, if baryon number transfer between visible and dark sectors arises through new physics at the weak scale. The possibility of induced nucleon decay motivates a novel approach for direct detection of cosmic dark matter in nucleon decay experiments. Monojet searches (and related signatures) at hadron colliders also provide a complementary probe of weak-scale dark-matter-induced baryon number violation. Finally, we discuss the effects of baryon-destroying dark matter on stellar systems and show that it can be consistent with existing observations.

  16. Baryon destruction by asymmetric dark matter

    SciTech Connect

    Davoudiasl H.; Morrissey, D.; Sigurdson, K.; Tulin, S.

    2011-11-10

    We investigate new and unusual signals that arise in theories where dark matter is asymmetric and carries a net antibaryon number, as may occur when the dark matter abundance is linked to the baryon abundance. Antibaryonic dark matter can cause induced nucleon decay by annihilating visible baryons through inelastic scattering. These processes lead to an effective nucleon lifetime of 10{sup 29}-10{sup 32} yrs in terrestrial nucleon decay experiments, if baryon number transfer between visible and dark sectors arises through new physics at the weak scale. The possibility of induced nucleon decay motivates a novel approach for direct detection of cosmic dark matter in nucleon decay experiments. Monojet searches (and related signatures) at hadron colliders also provide a complementary probe of weak-scale dark-matter-induced baryon number violation. Finally, we discuss the effects of baryon-destroying dark matter on stellar systems and show that it can be consistent with existing observations.

  17. Cosmology with interaction in the dark sector

    SciTech Connect

    Costa, F. E. M.; Barboza, E. M. Jr.; Alcaniz, J. S.

    2009-06-15

    Unless some unknown symmetry in nature prevents or suppresses a nonminimal coupling in the dark sector, the dark energy field may interact with the pressureless component of dark matter. In this paper, we investigate some cosmological consequences of a general model of interacting dark matter-dark energy characterized by a dimensionless parameter {epsilon}. We derive a coupled scalar field version for this general class of scenarios and carry out a joint statistical analysis involving type Ia supernovae data (Legacy and Constitution sets), measurements of baryon acoustic oscillation peaks at z=0.20 (2dFGRS) and z=0.35 (SDSS), and measurements of the Hubble evolution H(z). For the specific case of vacuum decay (w=-1), we find that, although physically forbidden, a transfer of energy from dark matter to dark energy is favored by the data.

  18. Dark scenarios

    NASA Astrophysics Data System (ADS)

    Ahonen, Pasi; Alahuhta, Petteri; Daskala, Barbara; Delaitre, Sabine; Hert, Paul De; Lindner, Ralf; Maghiros, Ioannis; Moscibroda, Anna; Schreurs, Wim; Verlinden, Michiel

    In this chapter, we present four "dark scenarios" that highlight the key socio-economic, legal, technological and ethical risks to privacy, identity, trust, security and inclusiveness posed by new AmI technologies. We call them dark scenarios, because they show things that could go wrong in an AmI world, because they present visions of the future that we do not want to become reality. The scenarios expose threats and vulnerabilities as a way to inform policy-makers and planners about issues they need to take into account in developing new policies or updating existing legislation. Before presenting the four scenarios and our analysis of each, we describe the process of how we created the scenarios as well as the elements in our methodology for analysing the scenarios.

  19. Optimizing New Dark Energy Experiments

    SciTech Connect

    Tyson, J. Anthony

    2013-08-26

    Next generation “Stage IV” dark energy experiments under design during this grant, and now under construction, will enable the determination of the properties of dark energy and dark matter to unprecedented precision using multiple complementary probes. The most pressing challenge in these experiments is the characterization and understanding of the systematic errors present within any given experimental configuration and the resulting impact on the accuracy of our constraints on dark energy physics. The DETF and the P5 panel in their reports recommended “Expanded support for ancillary measurements required for the long-term program and for projects that will improve our understanding and reduction of the dominant systematic measurement errors.” Looking forward to the next generation Stage IV experiments we have developed a program to address the most important potential systematic errors within these experiments. Using data from current facilities it has been feasible and timely to undertake a detailed investigation of the systematic errors. In this DOE grant we studied of the source and impact of the dominant systematic effects in dark energy measurements, and developed new analysis tools and techniques to minimize their impact. Progress under this grant is briefly reviewed in this technical report. This work was a necessary precursor to the coming generations of wide-deep probes of the nature of dark energy and dark matter. The research has already had an impact on improving the efficiencies of all Stage III and IV dark energy experiments.

  20. Dark matter

    PubMed Central

    Peebles, P. James E.

    2015-01-01

    The evidence for the dark matter (DM) of the hot big bang cosmology is about as good as it gets in natural science. The exploration of its nature is now led by direct and indirect detection experiments, to be complemented by advances in the full range of cosmological tests, including judicious consideration of the rich phenomenology of galaxies. The results may confirm ideas about DM already under discussion. If we are lucky, we also will be surprised once again. PMID:24794526

  1. Dark matter.

    PubMed

    Peebles, P James E

    2015-10-01

    The evidence for the dark matter (DM) of the hot big bang cosmology is about as good as it gets in natural science. The exploration of its nature is now led by direct and indirect detection experiments, to be complemented by advances in the full range of cosmological tests, including judicious consideration of the rich phenomenology of galaxies. The results may confirm ideas about DM already under discussion. If we are lucky, we also will be surprised once again.

  2. Dark matter.

    PubMed

    Peebles, P James E

    2015-10-01

    The evidence for the dark matter (DM) of the hot big bang cosmology is about as good as it gets in natural science. The exploration of its nature is now led by direct and indirect detection experiments, to be complemented by advances in the full range of cosmological tests, including judicious consideration of the rich phenomenology of galaxies. The results may confirm ideas about DM already under discussion. If we are lucky, we also will be surprised once again. PMID:24794526

  3. STIS-20 NUV MAMA Dark Monitor

    NASA Astrophysics Data System (ADS)

    Proffitt, Charles

    2009-07-01

    The STIS NUV-MAMA dark current is dominated by a phosphorescent glow from the detector window. Meta-stable states in this window are populated by cosmic ray impacts, which, days later, can be thermally excited to an unstable state from which they decay, emitting a UV photon. The equilibrium population of these meta-stable states is larger at lower temperatures; so warming up the detector from its cold safing will lead to a large, but temporary, increase in the dark current. To monitor the decay of this glow, and to determine the equilibrium dark current for Cycle 17, four 1380s NUV-MAMA ACCUM mode darks should be taken each week during the SMOV period. Once the observed dark current has reached an approximate equilibrium with the mean detector temperature, the frequency of this monitor can be reduced to one pair of darks per week.

  4. Current trends in non-accelerator particle physics: 1, Neutrino mass and oscillation. 2, High energy neutrino astrophysics. 3, Detection of dark matter. 4, Search for strange quark matter. 5, Magnetic monopole searches

    SciTech Connect

    He, Yudong |

    1995-07-01

    This report is a compilation of papers reflecting current trends in non-accelerator particle physics, corresponding to talks that its author was invited to present at the Workshop on Tibet Cosmic Ray Experiment and Related Physics Topics held in Beijing, China, April 4--13, 1995. The papers are entitled `Neutrino Mass and Oscillation`, `High Energy Neutrino Astrophysics`, `Detection of Dark Matter`, `Search for Strange Quark Matter`, and `Magnetic Monopole Searches`. The report is introduced by a survey of the field and a brief description of each of the author`s papers.

  5. Dynamics of Dark Energy

    SciTech Connect

    Copeland, Edmund J.

    2007-11-20

    I briefly review attempts that have been made to model dark energy. These include models of a cosmological constant, dynamical models where a scalar field may be responsible for the observed late time acceleration through to the possibility that we are not fully in control of the gravity sector and the acceleration may be some manifestation of modified gravity. In all cases we will see some degree of fine tuning is required with the current models.

  6. Non-baryonic dark matter in cosmology

    NASA Astrophysics Data System (ADS)

    Del Popolo, A.

    2013-07-01

    This paper is based on lectures given at the IX Mexican School on Gravitation and Mathematical Physics. The lectures (as the paper) were a broad-band review of the current status of non-baryonic dark matter research. I start with a historical overview of the evidences of dark matter existence, then I discuss how dark matter is distributed from small scale to large scale, and I then verge the attention to dark matter nature: dark matter candidates and their detection. I finally discuss some of the limits of the ΛCDM model, with particular emphasis on the small scale problems of the paradigm.

  7. Analysis of dark matter and dark energy

    NASA Astrophysics Data System (ADS)

    Yongquan, Han

    2016-05-01

    As the law of unity of opposites of the Philosophy tells us, the bright material exists, the dark matter also exists. Dark matter and dark energy should allow the law of unity of opposites. The Common attributes of the matter is radiation, then common attributes of dark matter must be absorb radiation. Only the rotation speed is lower than the speed of light radiation, can the matter radiate, since the speed of the matter is lower than the speed of light, so the matter is radiate; The rotate speed of the dark matter is faster than the light , so the dark matter doesn't radiate, it absorbs radiation. The energy that the dark matter absorb radiation produced (affect the measurement of time and space distribution of variations) is dark energy, so the dark matter produce dark energy only when it absorbs radiation. Dark matter does not radiate, two dark matters does not exist inevitably forces, and also no dark energy. Called the space-time ripples, the gravitational wave is bent radiation, radiation particles should be graviton, graviton is mainly refers to the radiation particles whose wavelength is small. Dark matter, dark energy also confirms the existence of the law of symmetry.

  8. "Christian carrying goomies".

    PubMed

    1994-01-01

    Dr. Passingan Usurup tells critics of his pragmatic approach on condom promotion that he is a Christian carrying condoms for Christ. He is head of the University of Papua New Guinea Medical Center and is credited with developing an AIDS/HIV policy for the Papua New Guinea Defence Force. The condoms were named Goomy and promoted at launching in 1992 in a blue packet under the slogan "The bond that guards." Goomy was chosen as the name because it is pidgin for rubber, chewing gum, and anything associated with rubber. Blue packets were chosen over the calls of most soldiers for a camouflage design because of its universal appeal as the color of the sea and sky and because it was the preference of women in the airlines. Once firmly ensconced in his role at the University, Usurup plans to develop a policy for students and staff and help to conduct AIDS prevention and education activities on campus. He will encourage students to test for HIV rather than highlighting the gloom and doom of infection and disease.

  9. Skew-flavored dark matter

    DOE PAGES

    Agrawal, Prateek; Chacko, Zackaria; Fortes, Elaine C. F. S.; Kilic, Can

    2016-05-10

    We explore a novel flavor structure in the interactions of dark matter with the Standard Model. We consider theories in which both the dark matter candidate, and the particles that mediate its interactions with the Standard Model fields, carry flavor quantum numbers. The interactions are skewed in flavor space, so that a dark matter particle does not directly couple to the Standard Model matter fields of the same flavor, but only to the other two flavors. This framework respects minimal flavor violation and is, therefore, naturally consistent with flavor constraints. We study the phenomenology of a benchmark model in whichmore » dark matter couples to right-handed charged leptons. In large regions of parameter space, the dark matter can emerge as a thermal relic, while remaining consistent with the constraints from direct and indirect detection. The collider signatures of this scenario include events with multiple leptons and missing energy. In conclusion, these events exhibit a characteristic flavor pattern that may allow this class of models to be distinguished from other theories of dark matter.« less

  10. Current sensor

    DOEpatents

    Yakymyshyn, Christopher Paul; Brubaker, Michael Allen; Yakymyshyn, Pamela Jane

    2007-01-16

    A current sensor is described that uses a plurality of magnetic field sensors positioned around a current carrying conductor. The sensor can be hinged to allow clamping to a conductor. The current sensor provides high measurement accuracy for both DC and AC currents, and is substantially immune to the effects of temperature, conductor position, nearby current carrying conductors and aging.

  11. Dark matter and the equivalence principle

    NASA Technical Reports Server (NTRS)

    Frieman, Joshua A.; Gradwohl, Ben-Ami

    1993-01-01

    A survey is presented of the current understanding of dark matter invoked by astrophysical theory and cosmology. Einstein's equivalence principle asserts that local measurements cannot distinguish a system at rest in a gravitational field from one that is in uniform acceleration in empty space. Recent test-methods for the equivalence principle are presently discussed as bases for testing of dark matter scenarios involving the long-range forces between either baryonic or nonbaryonic dark matter and ordinary matter.

  12. TASI 2008 Lectures on Dark Matter

    SciTech Connect

    Hooper, Dan; /Fermilab /Chicago U., Astron. Astrophys. Ctr.

    2009-01-01

    Based on lectures given at the 2008 Theoretical Advanced Study Institute (TASI), I review here some aspects of the phenomenology of particle dark matter, including the process of thermal freeze-out in the early universe, and the direct and indirect detection of WIMPs. I also describe some of the most popular particle candidates for dark matter and summarize the current status of the quest to discover dark matter's particle identity.

  13. Dark Matter Jets at the LHC

    SciTech Connect

    Bai, Yang; Rajaraman, Arvind; /UC, Irvine

    2012-03-28

    We argue that dark matter particles which have strong interactions with the Standard Model particles are not excluded by current astrophysical constraints. These dark matter particles have unique signatures at colliders; instead of missing energy, the dark matter particles produce jets. We propose a new search strategy for such strongly interacting particles by looking for a signal of two trackless jets. We show that suitable cuts can plausibly allow us to find these signals at the LHC even in early data.

  14. Dark matter directional detection in non-relativistic effective theories

    SciTech Connect

    Catena, Riccardo

    2015-07-20

    We extend the formalism of dark matter directional detection to arbitrary one-body dark matter-nucleon interactions. The new theoretical framework generalizes the one currently used, which is based on 2 types of dark matter-nucleon interaction only. It includes 14 dark matter-nucleon interaction operators, 8 isotope-dependent nuclear response functions, and the Radon transform of the first 2 moments of the dark matter velocity distribution. We calculate the recoil energy spectra at dark matter directional detectors made of CF{sub 4}, CS{sub 2} and {sup 3}He for the 14 dark matter-nucleon interactions, using nuclear response functions recently obtained through numerical nuclear structure calculations. We highlight the new features of the proposed theoretical framework, and present our results for a spherical dark matter halo and for a stream of dark matter particles. This study lays the foundations for model independent analyses of dark matter directional detection experiments.

  15. Dark matter directional detection in non-relativistic effective theories

    SciTech Connect

    Catena, Riccardo

    2015-07-01

    We extend the formalism of dark matter directional detection to arbitrary one-body dark matter-nucleon interactions. The new theoretical framework generalizes the one currently used, which is based on 2 types of dark matter-nucleon interaction only. It includes 14 dark matter-nucleon interaction operators, 8 isotope-dependent nuclear response functions, and the Radon transform of the first 2 moments of the dark matter velocity distribution. We calculate the recoil energy spectra at dark matter directional detectors made of CF{sub 4}, CS{sub 2} and {sup 3}He for the 14 dark matter-nucleon interactions, using nuclear response functions recently obtained through numerical nuclear structure calculations. We highlight the new features of the proposed theoretical framework, and present our results for a spherical dark matter halo and for a stream of dark matter particles. This study lays the foundations for model independent analyses of dark matter directional detection experiments.

  16. Measuring Dark Energy with CHIME

    NASA Astrophysics Data System (ADS)

    Newburgh, Laura; Chime Collaboration

    2015-04-01

    The Canadian Hydrogen Intensity Mapping Experiment (CHIME) is a new radio transit interferometer currently being built at the Dominion Radio Astrophysical Observatory (DRAO) in Penticton, BC, Canada. We will use the 21 cm emission line of neutral hydrogen to map baryon acoustic oscillations between 400-800 MHz across 3/4 of the sky. These measurements will yield sensitive constraints on the dark energy equation of state between redshifts 0.8 - 2.5, a fascinating but poorly probed era corresponding to when dark energy began to impact the expansion history of the Universe. I will describe theCHIME instrument, the analysis challenges, the calibration requirements, and current status.

  17. Direct search for dark matter with DarkSide

    DOE PAGES

    Agnes, P.

    2015-11-16

    Here, the DarkSide experiment is designed for the direct detection of Dark Matter with a double phase liquid Argon TPC operating underground at Laboratori Nazionali del Gran Sasso. The TPC is placed inside a 30 tons liquid organic scintillator sphere, acting as a neutron veto, which is in turn installed inside a 1 kt water Cherenkov detector. The current detector is running since November 2013 with a 50 kg atmospheric Argon fill and we report here the first null results of a Dark Matter search for a (1422 ± 67) kg.d exposure. This result correspond to a 90% CL uppermore » limit on the WIMP-nucleon cross section of 6.1 × 10-44 cm2 (for a WIMP mass of 100 GeV/c2) and it's currently the most sensitive limit obtained with an Argon target.« less

  18. Direct search for dark matter with DarkSide

    SciTech Connect

    Agnes, P.

    2015-11-16

    Here, the DarkSide experiment is designed for the direct detection of Dark Matter with a double phase liquid Argon TPC operating underground at Laboratori Nazionali del Gran Sasso. The TPC is placed inside a 30 tons liquid organic scintillator sphere, acting as a neutron veto, which is in turn installed inside a 1 kt water Cherenkov detector. The current detector is running since November 2013 with a 50 kg atmospheric Argon fill and we report here the first null results of a Dark Matter search for a (1422 ± 67) kg.d exposure. This result correspond to a 90% CL upper limit on the WIMP-nucleon cross section of 6.1 × 10-44 cm2 (for a WIMP mass of 100 GeV/c2) and it's currently the most sensitive limit obtained with an Argon target.

  19. Dark matter beams at LBNF

    DOE PAGES

    Coloma, Pilar; Dobrescu, Bogdan A.; Frugiuele, Claudia; Harnik, Roni

    2016-04-08

    High-intensity neutrino beam facilities may produce a beam of light dark matter when protons strike the target. Searches for such a dark matter beam using its scattering in a nearby detector must overcome the large neutrino background. We characterize the spatial and energy distributions of the dark matter and neutrino beams, focusing on their differences to enhance the sensitivity to dark matter. We find that a dark matter beam produced by a Zmore » $$^{'}$$ boson in the GeV mass range is both broader and more energetic than the neutrino beam. The reach for dark matter is maximized for a detector sensitive to hard neutral-current scatterings, placed at a sizable angle off the neutrino beam axis. In the case of the Long-Baseline Neutrino Facility (LBNF), a detector placed at roughly 6 degrees off axis and at a distance of about 200 m from the target would be sensitive to Z$$^{'}$$ couplings as low as 0.05. This search can proceed symbiotically with neutrino measurements. We also show that the MiniBooNE and MicroBooNE detectors, which are on Fermilab’s Booster beamline, happen to be at an optimal angle from the NuMI beam and could perform searches with existing data. As a result, this illustrates potential synergies between LBNF and the short-baseline neutrino program if the detectors are positioned appropriately.« less

  20. Dark Energy and Termonuclear Supernovae

    NASA Astrophysics Data System (ADS)

    Domíngez, I.; Bravo, E.; Piersanti, L.; Tornambé, A.; Straniero, O.; Höflich, P.

    2008-12-01

    Nowadays it is widely accepted that the current Universe is dominated by dark energy and exotic matter, the so called StandardModel of Cosmoloy or CDM model. All the available data (Thermonuclear Supernovae, Cosmic Microwave Background, Baryon Acoustic Oscillations, Large Scale Structure, etc.) are compatible with a flat Universe made by ~70% of dark energy. Up to now observations agree that dark energy may be the vacuum energy (or cosmological constant) although improvements are needed to constrain further its equation of state. In this context, the cosmic destiny of the Universe is no longer linked to its geometry but to the nature of dark energy; it may be flat and expand forever or collapse. To understand the nature of dark energy is probably the most fundamental problem in physics today; it may open new roads of knowledge and led to unify gravity with the other fundamental interactions in nature. It is expected that astronomical data will continue to provide directions to theorists and experimental physicists. Type Ia supernovae (SNe Ia) have played a fundamental role, showing the acceleration of the expansion rate of the Universe a decade ago, and up to now they are the only astronomical observations that provide a direct evidence of the acceleration. However, in order to determine the source of the dark energy term it is mandatory to improve the precision of supernovae as distance indicators on cosmological scale.

  1. Dark sector shining through 750 GeV dark Higgs boson at the LHC

    NASA Astrophysics Data System (ADS)

    Ko, P.; Nomura, Takaaki

    2016-07-01

    We consider a dark sector with SU(3)C × U(1)Y × U(1)X and three families of dark fermions that are chiral under dark U(1)X gauge symmetry, whereas scalar dark matter X is the SM singlet. U(1)X dark symmetry is spontaneously broken by nonzero VEV of dark Higgs field < Φ >, generating the masses of dark fermions and dark photon Z‧. The resulting dark Higgs boson ϕ can be produced at the LHC by dark quark loop (involving 3 generations) and will decay into a pair of photon through charged dark fermion loop. Its decay width can be easily ∼ 45 GeV due to its possible decays into a pair of dark photon, which is not strongly constrained by the current LHC searches pp → ϕ →Z‧Z‧ followed by Z‧ decays into the SM fermion pairs. The scalar DM can achieve thermal relic density without conflict with direct detection bound or the invisible ϕ decay into a pair of DM.

  2. Simulation of dark current suppression in p-i-n InGaAs photodetector with In0.66Ga0.34As/InAs superlattice electron barrier

    NASA Astrophysics Data System (ADS)

    Lv, Jiabing; Chen, Jun

    2016-07-01

    An InGaAs-based photodetector with different periods of inserting strain-compensated In0.66Ga0.34As/InAs superlattice (SL) electron barrier in the In0.83Ga0.17As absorption layer has been investigated. The band diagram, electron concentration and electric field intensity of the structure were analyzed with numerical simulation. It was found that the period of SL has a remarkable influence on the properties of the photodetectors. With the decrease of the period of In0.66Ga0.34As/InAs SL, the dark current density is suppressed significantly, which is reduced to 2.46 × 10-3 A/cm2 at 300 K and a reverse bias voltage of 1 V when the period is 2.5 nm.

  3. Dark matter directionality revisited with a high pressure xenon gas detector

    DOE PAGES

    Mohlabeng, Gopolang; Kong, Kyoungchul; Li, Jin; Para, Adam; Yoo, Jonghee

    2015-07-20

    An observation of the anisotropy of dark matter interactions in a direction-sensitive detector would provide decisive evidence for the discovery of galactic dark matter. Directional information would also provide a crucial input to understanding its distribution in the local Universe. Most of the existing directional dark matter detectors utilize particle tracking methods in a low-pressure gas time projection chamber. These low pressure detectors require excessively large volumes in order to be competitive in the search for physics beyond the current limit. In order to avoid these volume limitations, we consider a novel proposal, which exploits a columnar recombination effect inmore » a high-pressure gas time projection chamber. The ratio of scintillation to ionization signals observed in the detector carries the angular information of the particle interactions. In this paper, we investigate the sensitivity of a future directional detector focused on the proposed high-pressure Xenon gas time projection chamber. We study the prospect of detecting an anisotropy in the dark matter velocity distribution. We find that tens of events are needed to exclude an isotropic distribution of dark matter interactions at 95% confidence level in the most optimistic case with head-to-tail information. However, one needs at least 10-20 times more events without head-to-tail information for light dark matter below ~50 GeV. For an intermediate mass range, we find it challenging to observe an anisotropy of the dark matter distribution. Our results also show that the directional information significantly improves precision measurements of dark matter mass and the elastic scattering cross section for a heavy dark matter.« less

  4. Dark matter directionality revisited with a high pressure xenon gas detector

    SciTech Connect

    Mohlabeng, Gopolang; Kong, Kyoungchul; Li, Jin; Para, Adam; Yoo, Jonghee

    2015-07-20

    An observation of the anisotropy of dark matter interactions in a direction-sensitive detector would provide decisive evidence for the discovery of galactic dark matter. Directional information would also provide a crucial input to understanding its distribution in the local Universe. Most of the existing directional dark matter detectors utilize particle tracking methods in a low-pressure gas time projection chamber. These low pressure detectors require excessively large volumes in order to be competitive in the search for physics beyond the current limit. In order to avoid these volume limitations, we consider a novel proposal, which exploits a columnar recombination effect in a high-pressure gas time projection chamber. The ratio of scintillation to ionization signals observed in the detector carries the angular information of the particle interactions. In this paper, we investigate the sensitivity of a future directional detector focused on the proposed high-pressure Xenon gas time projection chamber. We study the prospect of detecting an anisotropy in the dark matter velocity distribution. We find that tens of events are needed to exclude an isotropic distribution of dark matter interactions at 95% confidence level in the most optimistic case with head-to-tail information. However, one needs at least 10-20 times more events without head-to-tail information for light dark matter below ~50 GeV. For an intermediate mass range, we find it challenging to observe an anisotropy of the dark matter distribution. Our results also show that the directional information significantly improves precision measurements of dark matter mass and the elastic scattering cross section for a heavy dark matter.

  5. 35. CARRIE FURNACE No. 6 AND CAST HOUSE. THE CARRIE ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    35. CARRIE FURNACE No. 6 AND CAST HOUSE. THE CARRIE BOILER SHOP IS ON THE RIGHT, IN FRONT OF HOT BLAST STOVES. - U.S. Steel Homestead Works, Blast Furnace Plant, Along Monongahela River, Homestead, Allegheny County, PA

  6. Faces in the dark: interactive effects of darkness and anxiety on the memory for threatening faces.

    PubMed

    Nakashima, Satoshi F; Morimoto, Yuko; Takano, Yuji; Yoshikawa, Sakiko; Hugenberg, Kurt

    2014-01-01

    In the current research, we extend past work on the effects of ambient darkness and threat to the domain of memory for expressive faces. In one study, we examined the effects of ambient darkness and individual differences in state anxiety on memory of unfamiliar expressive faces. Here, participants were seated in either a dark or light room and encoded a set of unfamiliar faces with angry, happy, and neutral facial expressions. A subsequent recognition task revealed an interactive effect of ambient darkness, anxiety, and target expression. Highly anxious participants in ambient darkness had worse memory for angry faces than did low-anxiety participants. On the other hand, the recognition performance for happy faces was affected neither by the darkness nor state anxiety. The results suggest not only that ambient darkness has its strongest effect on anxious perceivers, but also that person × situation effects should be considered in face recognition research.

  7. Is Cold Dark Matter a Vacuum Effect?

    NASA Astrophysics Data System (ADS)

    Houlden, Michael A.

    Current theories about the Universe based on an FLRW model conclude that it is composed of ~4% normal matter, ~28 % dark matter and ~68% Dark Energy which is responsible for the well-established accelerated expansion: this model works extremely well. As the Universe expands the density of normal and dark matter decreases while the proportion of Dark Energy increases. This model assumes that the amount of dark matter, whose nature at present is totally unknown, has remained constant. This is a natural assumption if dark matter is a particle of some kind - WIMP, sterile neutrino, lightest supersysmmetric particle or axion, etc. - that must have emerged from the early high temperature phase of the Big Bang. This paper proposes that dark matter is not a particle such as these but a vacuum effect, and that the proportion of dark matter in the Universe is actually increasing with time. The idea that led to this suggestion was that a quantum process (possibly the Higgs mechanism) might operate in the nilpotent vacuum that Rowlands postulates is a dual space to the real space where Standard Model fundamental fermions (and we) reside. This could produce a vacuum quantum state that has mass, which interacts gravitationally, and such states would be `dark matter'. It is proposed that the rate of production of dark matter by this process might depend on local circumstances, such as the density of dark matter and/or normal matter. This proposal makes the testable prediction that the ratio of baryonic to dark matter varies with redshift and offers an explanation, within the framework of Rowlands' ideas, of the coincidence problem - why has cosmic acceleration started in the recent epoch at redshift z ~0.55 when the Dark Energy density first became equal to the matter density?. This process also offers a potential solution to the `missing baryon' problem.

  8. On fast carry select adders

    NASA Technical Reports Server (NTRS)

    Shamanna, M.; Whitaker, S.

    1992-01-01

    This paper presents an architecture for a high-speed carry select adder with very long bit lengths utilizing a conflict-free bypass scheme. The proposed scheme has almost half the number of transistors and is faster than a conventional carry select adder. A comparative study is also made between the proposed adder and a Manchester carry chain adder which shows that the proposed scheme has the same transistor count, without suffering any performance degradation, compared to the Manchester carry chain adder.

  9. Carrying Position Influences Infant Behavior.

    ERIC Educational Resources Information Center

    Field, Tiffany; And Others

    1996-01-01

    A total of 32 3-month-old infants were carried by their mothers in a soft infant carrier designed to place the infants facing either inward or outward. A within-subject comparison found that when infants were carried facing in, they spent significantly more time sleeping, while infants carried facing out were more active. (MDM)

  10. Cryogenic Dark Matter Search (CDMS): The Hunt for Dark Matter

    SciTech Connect

    Sadoulet, Bernard

    2006-03-06

    Deciphering the nature of dark matter has great scientific importance. A leading hypothesis is that dark matter is made of Weakly Interactive Massive Particles (WIMPs), which may result from supersymmetry or additional spatial dimensions. The underground search for elastic scattering of WIMPs on suitable targets (the so-called 'direct detection') is currently led by the Cryogenic Dark Matter Search II (CDMS II) experiment. Its sensitivity is ten times better than any other experiment and we hope to obtain another factor ten in the coming two years. After a brief recall of our recent results, I will describe the complementarity between direct detection experiments, the LHC and the ILC and I will outline the role that SLAC could play in this SuperCDMS program.

  11. The DAMIC Dark Matter Experiment

    SciTech Connect

    de Mello Neto, J. R.T.

    2015-10-07

    The DAMIC (DArk Matter In CCDs) experiment uses high-resistivity, scientific-grade CCDs to search for dark matter. The CCD’s low electronic noise allows an unprecedently low energy threshold of a few tens of eV; this characteristic makes it possible to detect silicon recoils resulting from interactions of low-mass WIMPs. In addition, the CCD’s high spatial resolution and the excellent energy response results in very effective background identification techniques. The experiment has a unique sensitivity to dark matter particles with masses below 10 GeV/c2. Previous results have motivated the construction of DAMIC100, a 100 grams silicon target detector currently being installed at SNOLAB. The mode of operation and unique imaging capabilities of the CCDs, and how they may be exploited to characterize and suppress backgrounds are discussed, as well as physics results after one year of data taking.

  12. Dark Energy Camera for Blanco

    SciTech Connect

    Binder, Gary A.; /Caltech /SLAC

    2010-08-25

    In order to make accurate measurements of dark energy, a system is needed to monitor the focus and alignment of the Dark Energy Camera (DECam) to be located on the Blanco 4m Telescope for the upcoming Dark Energy Survey. One new approach under development is to fit out-of-focus star images to a point spread function from which information about the focus and tilt of the camera can be obtained. As a first test of a new algorithm using this idea, simulated star images produced from a model of DECam in the optics software Zemax were fitted. Then, real images from the Mosaic II imager currently installed on the Blanco telescope were used to investigate the algorithm's capabilities. A number of problems with the algorithm were found, and more work is needed to understand its limitations and improve its capabilities so it can reliably predict camera alignment and focus.

  13. Dark matter from decaying topological defects

    SciTech Connect

    Hindmarsh, Mark; Kirk, Russell; West, Stephen M. E-mail: russell.kirk.2008@live.rhul.ac.uk

    2014-03-01

    We study dark matter production by decaying topological defects, in particular cosmic strings. In topological defect or ''top-down'' (TD) scenarios, the dark matter injection rate varies as a power law with time with exponent p−4. We find a formula in closed form for the yield for all p < 3/2, which accurately reproduces the solution of the Boltzmann equation. We investigate two scenarios (p = 1, p = 7/6) motivated by cosmic strings which decay into TeV-scale states with a high branching fraction into dark matter particles. For dark matter models annihilating either by s-wave or p-wave, we find the regions of parameter space where the TD model can account for the dark matter relic density as measured by Planck. We find that topological defects can be the principal source of dark matter, even when the standard freeze-out calculation under-predicts the relic density and hence can lead to potentially large ''boost factor'' enhancements in the dark matter annihilation rate. We examine dark matter model-independent limits on this scenario arising from unitarity and discuss example model-dependent limits coming from indirect dark matter search experiments. In the four cases studied, the upper bound on Gμ for strings with an appreciable channel into TeV-scale states is significantly more stringent than the current Cosmic Microwave Background limits.

  14. How clustering dark energy affects matter perturbations

    NASA Astrophysics Data System (ADS)

    Mehrabi, A.; Basilakos, S.; Pace, F.

    2015-09-01

    The rate of structure formation in the Universe is different in homogeneous and clustered dark energy models. The degree of dark energy clustering depends on the magnitude of its effective sound speed c2_eff and for c2_eff=0 dark energy clusters in a similar fashion to dark matter while for c2_eff=1 it stays (approximately) homogeneous. In this paper we consider two distinct equations of state for the dark energy component, wd = const and w_d=w_0+w_1(z/1+z) with c2_eff as a free parameter and we try to constrain the dark energy effective sound speed using current available data including Type Ia supernovae, baryon acoustic oscillation, cosmic microwave background shift parameter (Planck and WMAP), Hubble parameter, big bang nucleosynthesis and the growth rate of structures fσ8(z). At first we derive the most general form of the equations governing dark matter and dark energy clustering under the assumption that c2_eff=const. Finally, performing an overall likelihood analysis we find that the likelihood function peaks at c2_eff=0; however, the dark energy sound speed is degenerate with respect to the cosmological parameters, namely Ωm and wd.

  15. Z-portal dark matter

    SciTech Connect

    Arcadi, Giorgio; Mambrini, Yann; Richard, Francois

    2015-03-11

    We propose to generalize the extensions of the Standard Model where the Z boson serves as a mediator between the Standard Model sector and the dark sector χ. We show that, like in the Higgs portal case, the combined constraints from the recent direct searches restrict severely the nature of the coupling of the dark matter to the Z boson and set a limit m{sub χ}≳200 GeV (except in a very narrow region around the Z-pole region). Using complementarity between spin dependent, spin independent and FERMI limits, we predict the nature of this coupling, more specifically the axial/vectorial ratio that respects a thermal dark matter coupled through a Z-portal while not being excluded by the current observations. We also show that the next generation of experiments of the type LZ or XENON1T will test Z-portal scenario for dark matter mass up to 2 TeV. The condition of a thermal dark matter naturally predicts the spin-dependent scattering cross section on the neutron to be σ{sub χn}{sup SD}≃10{sup −40} cm{sup 2}, which then becomes a clear prediction of the model and a signature testable in the near future experiments.

  16. One dark matter mystery: halos in the cosmic web

    NASA Astrophysics Data System (ADS)

    Gaite, Jose

    2015-01-01

    The current cold dark matter cosmological model explains the large scale cosmic web structure but is challenged by the observation of a relatively smooth distribution of matter in galactic clusters. We consider various aspects of modeling the dark matter around galaxies as distributed in smooth halos and, especially, the smoothness of the dark matter halos seen in N-body cosmological simulations. We conclude that the problems of the cold dark matter cosmology on small scales are more serious than normally admitted.

  17. Reduction of the dark current in a P3HT-based organic photodiode with a ytterbium-fluoride buffer layer for electron transport

    NASA Astrophysics Data System (ADS)

    Lim, Seong Bin; Ji, Chan Hyuk; Kim, Kee Tae; Oh, Se Young

    2016-08-01

    Photodiodes are widely used to convert light into electrical signals. The conventional silicon (Si) based photodiodes boast high photoelectric conversion efficiency and detectivity. However, in general, inorganic-based photodiodes have low sensitivity at visible wavelengths due to their absorption of infrared wavelengths. Recently, electrical conducting polymer-based photodiodes have received significant attention due to their flexibility, low cost of production and high sensitivity at visible wavelength ranges. In the present work, we fabricated an organic photodiode (OPD) with a consisting of ITO/ NiO x / P3HT:PC60BM/ YbF3/Al structure. In the OPD, a yitterbium fluoride (YbF3) buffer layer was used as the electron transport layer. The OPD was analyzed by using optical-electrical measurements to determine its J-V, detectivity, and dynamic characteristics. We investigated the physical effects of the YbF3 buffer layer on the performance of OPD such as its carrier extraction, leakage current and ohmic characteristics.

  18. A Search for Dark Matter Annihilation from Dwarf Galaxies using VERITAS

    NASA Astrophysics Data System (ADS)

    Zitzer, Ben; VERITAS Collaboration

    2013-06-01

    Current cosmological models and data suggest the existence of a Cold Dark Matter (DM) component, however the nature of DM particles remains unknown. A favored candidate for DM is a Weakly Interacting Massive Particle (WIMP) in the mass range of 50 GeV to greater than 10 TeV. Nearby dwarf spheroidal galaxies (Dsph) are expected to contain a high density of Dark Matter with a low gamma-ray background, and are thus promising targets for the detection of secondary gamma rays at very high energies (VHE, E > 0.1 TeV) through the annihilation of WIMPs into standard model particles. The VERITAS array of Cherenkov Telescopes, sensitive to gamma rays in the 100GeV to 10 TeV range, carries out an extensive observation program of Dsphs. Presented here are results of the observations and new statistical techniques for constraining the dark matter physics from these objects.

  19. Constraining Dark Matter Through the Study of Merging Galaxy Clusters

    NASA Astrophysics Data System (ADS)

    Dawson, William Anthony

    2013-03-01

    matter offset measurement is dominated by random errors in each cluster. Thus measuring this offset in other dissociative mergers holds the promise of reducing our uncertainty and enabling us to: 1) state confidently whether dark matter self-interacts via a new dark sector force, or 2) constrain the dark matter cross-section to such a degree that SIDM cannot explain the aforementioned mysteries. To this end we have established the Merging Cluster Collaboration to observe and simulate an ensemble of dissociative merging clusters. We are currently in the process of analyzing six dissociative mergers with existing data, and carrying out multi-wavelength observations of a new sample of 15 radio relic identified dissociative mergers. (Abstract shortened by UMI.)

  20. THE DARK ENERGY CAMERA

    SciTech Connect

    Flaugher, B.; Diehl, H. T.; Alvarez, O.; Angstadt, R.; Annis, J. T.; Buckley-Geer, E. J.; Honscheid, K.; Abbott, T. M. C.; Bonati, M.; Antonik, M.; Brooks, D.; Ballester, O.; Cardiel-Sas, L.; Beaufore, L.; Bernstein, G. M.; Bernstein, R. A.; Bigelow, B.; Boprie, D.; Campa, J.; Castander, F. J.; Collaboration: DES Collaboration; and others

    2015-11-15

    The Dark Energy Camera is a new imager with a 2.°2 diameter field of view mounted at the prime focus of the Victor M. Blanco 4 m telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five-element optical corrector, seven filters, a shutter with a 60 cm aperture, and a charge-coupled device (CCD) focal plane of 250 μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 megapixel focal plane comprises 62 2k × 4k CCDs for imaging and 12 2k × 2k CCDs for guiding and focus. The CCDs have 15 μm × 15 μm pixels with a plate scale of 0.″263 pixel{sup −1}. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 s with 6–9 electron readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

  1. The Dark Energy Camera

    SciTech Connect

    Flaugher, B.

    2015-04-11

    The Dark Energy Camera is a new imager with a 2.2-degree diameter field of view mounted at the prime focus of the Victor M. Blanco 4-meter telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration, and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five element optical corrector, seven filters, a shutter with a 60 cm aperture, and a CCD focal plane of 250-μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 Mpixel focal plane comprises 62 2k x 4k CCDs for imaging and 12 2k x 2k CCDs for guiding and focus. The CCDs have 15μm x 15μm pixels with a plate scale of 0.263" per pixel. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 seconds with 6-9 electrons readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

  2. The Dark Energy Camera

    NASA Astrophysics Data System (ADS)

    Flaugher, B.; Diehl, H. T.; Honscheid, K.; Abbott, T. M. C.; Alvarez, O.; Angstadt, R.; Annis, J. T.; Antonik, M.; Ballester, O.; Beaufore, L.; Bernstein, G. M.; Bernstein, R. A.; Bigelow, B.; Bonati, M.; Boprie, D.; Brooks, D.; Buckley-Geer, E. J.; Campa, J.; Cardiel-Sas, L.; Castander, F. J.; Castilla, J.; Cease, H.; Cela-Ruiz, J. M.; Chappa, S.; Chi, E.; Cooper, C.; da Costa, L. N.; Dede, E.; Derylo, G.; DePoy, D. L.; de Vicente, J.; Doel, P.; Drlica-Wagner, A.; Eiting, J.; Elliott, A. E.; Emes, J.; Estrada, J.; Fausti Neto, A.; Finley, D. A.; Flores, R.; Frieman, J.; Gerdes, D.; Gladders, M. D.; Gregory, B.; Gutierrez, G. R.; Hao, J.; Holland, S. E.; Holm, S.; Huffman, D.; Jackson, C.; James, D. J.; Jonas, M.; Karcher, A.; Karliner, I.; Kent, S.; Kessler, R.; Kozlovsky, M.; Kron, R. G.; Kubik, D.; Kuehn, K.; Kuhlmann, S.; Kuk, K.; Lahav, O.; Lathrop, A.; Lee, J.; Levi, M. E.; Lewis, P.; Li, T. S.; Mandrichenko, I.; Marshall, J. L.; Martinez, G.; Merritt, K. W.; Miquel, R.; Muñoz, F.; Neilsen, E. H.; Nichol, R. C.; Nord, B.; Ogando, R.; Olsen, J.; Palaio, N.; Patton, K.; Peoples, J.; Plazas, A. A.; Rauch, J.; Reil, K.; Rheault, J.-P.; Roe, N. A.; Rogers, H.; Roodman, A.; Sanchez, E.; Scarpine, V.; Schindler, R. H.; Schmidt, R.; Schmitt, R.; Schubnell, M.; Schultz, K.; Schurter, P.; Scott, L.; Serrano, S.; Shaw, T. M.; Smith, R. C.; Soares-Santos, M.; Stefanik, A.; Stuermer, W.; Suchyta, E.; Sypniewski, A.; Tarle, G.; Thaler, J.; Tighe, R.; Tran, C.; Tucker, D.; Walker, A. R.; Wang, G.; Watson, M.; Weaverdyck, C.; Wester, W.; Woods, R.; Yanny, B.; DES Collaboration

    2015-11-01

    The Dark Energy Camera is a new imager with a 2.°2 diameter field of view mounted at the prime focus of the Victor M. Blanco 4 m telescope on Cerro Tololo near La Serena, Chile. The camera was designed and constructed by the Dark Energy Survey Collaboration and meets or exceeds the stringent requirements designed for the wide-field and supernova surveys for which the collaboration uses it. The camera consists of a five-element optical corrector, seven filters, a shutter with a 60 cm aperture, and a charge-coupled device (CCD) focal plane of 250 μm thick fully depleted CCDs cooled inside a vacuum Dewar. The 570 megapixel focal plane comprises 62 2k × 4k CCDs for imaging and 12 2k × 2k CCDs for guiding and focus. The CCDs have 15 μm × 15 μm pixels with a plate scale of 0.″263 pixel-1. A hexapod system provides state-of-the-art focus and alignment capability. The camera is read out in 20 s with 6-9 electron readout noise. This paper provides a technical description of the camera's engineering, construction, installation, and current status.

  3. Light chiral dark sector

    NASA Astrophysics Data System (ADS)

    Harigaya, Keisuke; Nomura, Yasunori

    2016-08-01

    An interesting possibility for dark matter is a scalar particle of mass of order 10 MeV-1 GeV, interacting with a U (1 ) gauge boson (dark photon) which mixes with the photon. We present a simple and natural model realizing this possibility. The dark matter arises as a composite pseudo-Nambu-Goldstone boson (dark pion) in a non-Abelian gauge sector, which also gives a mass to the dark photon. For a fixed non-Abelian gauge group, S U (N ) , and a U (1 ) charge of the constituent dark quarks, the model has only three free parameters: the dynamical scale of the non-Abelian gauge theory, the gauge coupling of the dark photon, and the mixing parameter between the dark and standard model photons. In particular, the gauge symmetry of the model does not allow any mass term for the dark quarks, and the stability of the dark pion is understood as a result of an accidental global symmetry. The model has a significant parameter space in which thermal relic dark pions comprise all of the dark matter, consistently with all experimental and cosmological constraints. In a corner of the parameter space, the discrepancy of the muon g -2 between experiments and the standard model prediction can also be ameliorated due to a loop contribution of the dark photon. Smoking-gun signatures of the model include a monophoton signal from the e+e- collision into a photon and a "dark rho meson." Observation of two processes in e+e- collision—the mode into the dark photon and that into the dark rho meson—would provide strong evidence for the model.

  4. Nonthermal Supermassive Dark Matter

    NASA Technical Reports Server (NTRS)

    Chung, Daniel J. H.; Kolb, Edward W.; Riotto, Antonio

    1999-01-01

    We discuss several cosmological production mechanisms for nonthermal supermassive dark matter and argue that dark matter may he elementary particles of mass much greater than the weak scale. Searches for dark matter should ma be limited to weakly interacting particles with mass of the order of the weak scale, but should extend into the supermassive range as well.

  5. The Dark Matter Problem

    NASA Astrophysics Data System (ADS)

    Sanders, Robert H.

    2014-02-01

    1. Introduction; 2. Early history of the dark matter hypothesis; 3. The stability of disk galaxies: the dark halo solutions; 4. Direct evidence: extended rotation curves of spiral galaxies; 5. The maximum disk: light traces mass; 6. Cosmology and the birth of astroparticle physics; 7. Clusters revisited: missing mass found; 8. CDM confronts galaxy rotation curves; 9. The new cosmology: dark matter is not enough; 10. An alternative to dark matter: Modified Newtonian Dynamics; 11. Seeing dark matter: the theory and practice of detection; 12. Reflections: a personal point of view; Appendix; References; Index.

  6. Present and future evidence for evolving dark energy

    SciTech Connect

    Liddle, Andrew R.; Mukherjee, Pia; Parkinson, David; Wang Yun

    2006-12-15

    We compute the Bayesian evidences for one- and two-parameter models of evolving dark energy, and compare them to the evidence for a cosmological constant, using current data from Type Ia supernova, baryon acoustic oscillations, and the cosmic microwave background. We use only distance information, ignoring dark energy perturbations. We find that, under various priors on the dark energy parameters, {lambda}CDM is currently favored as compared to the dark energy models. We consider the parameter constraints that arise under Bayesian model averaging, and discuss the implication of our results for future dark energy projects seeking to detect dark energy evolution. The model selection approach complements and extends the figure-of-merit approach of the Dark Energy Task Force in assessing future experiments, and suggests a significantly-modified interpretation of that statistic.

  7. Dark matter superfluid and DBI dark energy

    NASA Astrophysics Data System (ADS)

    Cai, Rong-Gen; Wang, Shao-Jiang

    2016-01-01

    It was shown recently that, without jeopardizing the success of the Λ cold dark matter model on cosmic scales, the modified Newtonian dynamics (MOND) can be derived as an emergent phenomenon when axionlike dark matter particles condense into superfluid on the galactic scales. We propose in this paper a Dirac-Born-Infeld (DBI) scalar field conformally coupled to the matter components. To maintain the success of MOND phenomenon of dark matter superfluid on the galactic scales, the fifth force introduced by the DBI scalar should be screened on the galactic scales. It turns out that the screening effect naturally leads to a simple explanation for a longstanding puzzle that the MOND critical acceleration coincides with present Hubble scale. This galactic coincidence problem is solved, provided that the screened DBI scalar also plays the role of dark energy on the cosmic scales.

  8. The darkness of spin-0 dark radiation

    SciTech Connect

    Marsh, M.C. David

    2015-01-01

    We show that the scattering of a general spin-0 sector of dark radiation off the pre-recombination thermal plasma results in undetectably small spectral distortions of the Cosmic Microwave Background.

  9. Dark Energy from Discrete Spacetime

    PubMed Central

    Trout, Aaron D.

    2013-01-01

    Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies. PMID:24312502

  10. Dark energy from discrete spacetime.

    PubMed

    Trout, Aaron D

    2013-01-01

    Dark energy accounts for most of the matter-energy content of our universe, yet current theories of its origin rely on radical physical assumptions such as the holographic principle or controversial anthropic arguments. We give a better motivated explanation for dark energy, claiming that it arises from a small negative scalar-curvature present even in empty spacetime. The vacuum has this curvature because spacetime is fundamentally discrete and there are more ways for a discrete geometry to have negative curvature than positive. We explicitly compute this effect using a variant of the well known dynamical-triangulations (DT) model for quantum gravity. Our model predicts a time-varying non-zero cosmological constant with a current value, [Formula: see text] in natural units, in agreement with observation. This calculation is made possible by a novel characterization of the possible DT action values combined with numerical evidence concerning their degeneracies.

  11. Dark Forces and Light Dark Matter

    SciTech Connect

    Hooper, Dan; Weiner, Neal; Xue, Wei

    2012-09-01

    We consider a simple class of models in which the dark matter, X, is coupled to a new gauge boson, phi, with a relatively low mass (m_phi \\sim 100 MeV-3 GeV). Neither the dark matter nor the new gauge boson have tree-level couplings to the Standard Model. The dark matter in this model annihilates to phi pairs, and for a coupling of g_X \\sim 0.06 (m_X/10 GeV)^1/2 yields a thermal relic abundance consistent with the cosmological density of dark matter. The phi's produced in such annihilations decay through a small degree of kinetic mixing with the photon to combinations of Standard Model leptons and mesons. For dark matter with a mass of \\sim10 GeV, the shape of the resulting gamma-ray spectrum provides a good fit to that observed from the Galactic Center, and can also provide the very hard electron spectrum required to account for the observed synchrotron emission from the Milky Way's radio filaments. For kinetic mixing near the level naively expected from loop-suppressed operators (epsilon \\sim 10^{-4}), the dark matter is predicted to scatter elastically with protons with a cross section consistent with that required to accommodate the signals reported by DAMA/LIBRA, CoGeNT and CRESST-II.

  12. Cosmic acceleration without dark energy: background tests and thermodynamic analysis

    SciTech Connect

    Lima, J.A.S.; Graef, L.L.; Pavón, D.; Basilakos, Spyros E-mail: leilagraef@usp.br E-mail: svasil@academyofathens.gr

    2014-10-01

    A cosmic scenario with gravitationally induced particle creation is proposed. In this model the Universe evolves from an early to a late time de Sitter era, with the recent accelerating phase driven only by the negative creation pressure associated with the cold dark matter component. The model can be interpreted as an attempt to reduce the so-called cosmic sector (dark matter plus dark energy) and relate the two cosmic accelerating phases (early and late time de Sitter expansions). A detailed thermodynamic analysis including possible quantum corrections is also carried out. For a very wide range of the free parameters, it is found that the model presents the expected behavior of an ordinary macroscopic system in the sense that it approaches thermodynamic equilibrium in the long run (i.e., as it nears the second de Sitter phase). Moreover, an upper bound is found for the Gibbons–Hawking temperature of the primordial de Sitter phase. Finally, when confronted with the recent observational data, the current 'quasi'-de Sitter era, as predicted by the model, is seen to pass very comfortably the cosmic background tests.

  13. The LZ Dark Matter Experiment

    NASA Astrophysics Data System (ADS)

    Gehman, Victor M.

    2012-10-01

    One of the most important open questions in physics is the fundamental nature of the dark matter. The direct detection of a dark matter particle in a terrestrial experiment would dramatically impact cosmology and particle physics, and would open a window on a new type of observational astrophysics. The LZ collaboration has proposed to construct a 7-ton liquid xenon dark matter detector at the 4850 level of the Sanford Underground Research Facility (SURF) in Lead, South Dakota. The LZ detector will be based upon the well-established liquid xenon TPC technology, and will capitalize upon the existing infrastructure of the LUX experiment to allow for a rapid turn-around after the conclusion of LUX data taking. With a ducial mass of more than 5 tons, the experiment will probe WIMP-nucleon cross sections down to 2x10-48 cm^2 in 3 years of operation. This represents an improvement of approximately 5000 times over current results, covering a substantial range of theoretically-motivated particle dark matter candidates.

  14. Dark Energy, Particle Physics and Cosmology

    NASA Astrophysics Data System (ADS)

    Turner, Michael S.

    2012-05-01

    Dark energy and cosmic acceleration is one of the three pillars of the current cosmological paradigm. Moreover, both raise fundamental issues in cosmology and particle physics. In particle physics, the dark energy problem is intimately related to the perplexing issue of why the quantum energy of the vacuum is so small. In cosmology, the nature of the dark energy is crucial to understanding the destiny of the Universe. I will discuss the status of current models for dark energy -- including vacuum energy and rolling scalar fields -- their implications for cosmology and for particle physics and how they can be tested by WFIRST. I will also address the status of the possibility that cosmic acceleration is explained by modifying or replacing general relativity.

  15. Dark matter and dark energy interactions: theoretical challenges, cosmological implications and observational signatures.

    PubMed

    Wang, B; Abdalla, E; Atrio-Barandela, F; Pavón, D

    2016-09-01

    Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.

  16. Dark matter and dark energy interactions: theoretical challenges, cosmological implications and observational signatures.

    PubMed

    Wang, B; Abdalla, E; Atrio-Barandela, F; Pavón, D

    2016-09-01

    Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector. PMID:27517328

  17. Dark matter and dark energy interactions: theoretical challenges, cosmological implications and observational signatures

    NASA Astrophysics Data System (ADS)

    Wang, B.; Abdalla, E.; Atrio-Barandela, F.; Pavón, D.

    2016-09-01

    Models where dark matter and dark energy interact with each other have been proposed to solve the coincidence problem. We review the motivations underlying the need to introduce such interaction, its influence on the background dynamics and how it modifies the evolution of linear perturbations. We test models using the most recent observational data and we find that the interaction is compatible with the current astronomical and cosmological data. Finally, we describe the forthcoming data sets from current and future facilities that are being constructed or designed that will allow a clearer understanding of the physics of the dark sector.

  18. Embrace the Dark Side: Advancing the Dark Energy Survey

    NASA Astrophysics Data System (ADS)

    Suchyta, Eric

    The Dark Energy Survey (DES) is an ongoing cosmological survey intended to study the properties of the accelerated expansion of the Universe. In this dissertation, I present work of mine that has advanced the progress of DES. First is an introduction, which explores the physics of the cosmos, as well as how DES intends to probe it. Attention is given to developing the theoretical framework cosmologists use to describe the Universe, and to explaining observational evidence which has furnished our current conception of the cosmos. Emphasis is placed on the dark sector - dark matter and dark energy - the content of the Universe not explained by the Standard Model of particle physics. As its name suggests, the Dark Energy Survey has been specially designed to measure the properties of dark energy. DES will use a combination of galaxy cluster, weak gravitational lensing, angular clustering, and supernovae measurements to derive its state of the art constraints, each of which is discussed in the text. The work described in this dissertation includes science measurements directly related to the first three of these probes. The dissertation presents my contributions to the readout and control system of the Dark Energy Camera (DECam); the name of this software is SISPI. SISPI uses client-server and publish-subscribe communication patterns to coordinate and command actions among the many hardware components of DECam - the survey instrument for DES, a 570 megapixel CCD camera, mounted at prime focus of the Blanco 4-m Telescope. The SISPI work I discuss includes coding applications for DECam's filter changer mechanism and hexapod, as well as developing the Scripts Editor, a GUI application for DECam users to edit and export observing sequence SISPI can load and execute. Next, the dissertation describes the processing of early DES data, which I contributed. This furnished the data products used in the first-completed DES science analysis, and contributed to improving the

  19. Neutrinos and dark matter

    SciTech Connect

    Ibarra, Alejandro

    2015-07-15

    Neutrinos could be key particles to unravel the nature of the dark matter of the Universe. On the one hand, sterile neutrinos in minimal extensions of the Standard Model are excellent dark matter candidates, producing potentially observable signals in the form of a line in the X-ray sky. On the other hand, the annihilation or the decay of dark matter particles produces, in many plausible dark matter scenarios, a neutrino flux that could be detected at neutrino telescopes, thus providing non-gravitational evidence for dark matter. More conservatively, the non-observation of a significant excess in the neutrino fluxes with respect to the expected astrophysical backgrounds can be used to constrain dark matter properties, such as the self-annihilation cross section, the scattering cross section with nucleons and the lifetime.

  20. To carry or not to carry--is this the question? Disentangling the carry effect in multi-digit addition.

    PubMed

    Klein, Elise; Moeller, Korbinian; Dressel, Katharina; Domahs, Frank; Wood, Guilherme; Willmes, Klaus; Nuerk, Hans-Christoph

    2010-09-01

    Recent research has suggested addition performance to be determined by both the need for a carry operation and problem size. Nevertheless, it has remained debatable, how these two factors are interrelated. In the current study, this question was pursued by orthogonally manipulating carry and problem size in two-digit addition verification. As the two factors interacted reliably, our results indicate that the carry effect is moderated by number magnitude processing rather than representing a purely procedural, asemantic sequence of processing steps. Moreover, it was found that the carry effect may not be a purely categorical effect but may be driven by continuous characteristics of the sum of the unit digits as well. Since the correct result of a carry problem can only be derived by integrating and updating the magnitudes of tens and units within the place-value structure of the Arabic number system, the present study provides evidence for the idea that decomposed processing of tens and units also transfers to mental arithmetic.

  1. Clumpy cold dark matter

    NASA Technical Reports Server (NTRS)

    Silk, Joseph; Stebbins, Albert

    1993-01-01

    A study is conducted of cold dark matter (CDM) models in which clumpiness will inhere, using cosmic strings and textures suited to galaxy formation. CDM clumps of 10 million solar mass/cu pc density are generated at about z(eq) redshift, with a sizable fraction surviving. Observable implications encompass dark matter cores in globular clusters and in galactic nuclei. Results from terrestrial dark matter detection experiments may be affected by clumpiness in the Galactic halo.

  2. Interacting warm dark matter

    SciTech Connect

    Cruz, Norman; Palma, Guillermo; Zambrano, David; Avelino, Arturo E-mail: guillermo.palma@usach.cl E-mail: avelino@fisica.ugto.mx

    2013-05-01

    We explore a cosmological model composed by a dark matter fluid interacting with a dark energy fluid. The interaction term has the non-linear λρ{sub m}{sup α}ρ{sub e}{sup β} form, where ρ{sub m} and ρ{sub e} are the energy densities of the dark matter and dark energy, respectively. The parameters α and β are in principle not constrained to take any particular values, and were estimated from observations. We perform an analytical study of the evolution equations, finding the fixed points and their stability properties in order to characterize suitable physical regions in the phase space of the dark matter and dark energy densities. The constants (λ,α,β) as well as w{sub m} and w{sub e} of the EoS of dark matter and dark energy respectively, were estimated using the cosmological observations of the type Ia supernovae and the Hubble expansion rate H(z) data sets. We find that the best estimated values for the free parameters of the model correspond to a warm dark matter interacting with a phantom dark energy component, with a well goodness-of-fit to data. However, using the Bayesian Information Criterion (BIC) we find that this model is overcame by a warm dark matter – phantom dark energy model without interaction, as well as by the ΛCDM model. We find also a large dispersion on the best estimated values of the (λ,α,β) parameters, so even if we are not able to set strong constraints on their values, given the goodness-of-fit to data of the model, we find that a large variety of theirs values are well compatible with the observational data used.

  3. On the capture of dark matter by neutron stars

    SciTech Connect

    Güver, Tolga; Erkoca, Arif Emre; Sarcevic, Ina; Reno, Mary Hall E-mail: aeerkoca@gmail.com E-mail: ina@physics.arizona.edu

    2014-05-01

    We calculate the number of dark matter particles that a neutron star accumulates over its lifetime as it rotates around the center of a galaxy, when the dark matter particle is a self-interacting boson but does not self-annihilate. We take into account dark matter interactions with baryonic matter and the time evolution of the dark matter sphere as it collapses within the neutron star. We show that dark matter self-interactions play an important role in the rapid accumulation of dark matter in the core of the neutron star. We consider the possibility of determining an exclusion region of the parameter space for dark matter mass and dark matter interaction cross section with the nucleons as well as dark matter self-interaction cross section, based on the observation of old neutron stars. We show that for a dark matter density of 10{sup 3} GeV/cm{sup 3}and dark matter mass m{sub χ} ∼< 10 GeV, there is a potential exclusion region for dark matter interactions with nucleons that is three orders of magnitude more stringent than without self-interactions. The potential exclusion region for dark matter self-interaction cross sections is many orders of magnitude stronger than the current Bullet Cluster limit. For example, for high dark matter density regions, we find that for m{sub χ} ∼ 10 GeV when the dark matter interaction cross section with the nucleons ranges from σ{sub χn} ∼ 10{sup −52} cm{sup 2} to σ{sub χn} ∼ 10{sup −57} cm{sup 2}, the dark matter self-interaction cross section limit is σ{sub χχ} ∼< 10{sup −33} cm{sup 2}, which is about ten orders of magnitude stronger than the Bullet Cluster limit.

  4. Dark matter and cosmology

    SciTech Connect

    Schramm, D.N.

    1992-03-01

    The cosmological dark matter problem is reviewed. The Big Bang Nucleosynthesis constraints on the baryon density are compared with the densities implied by visible matter, dark halos, dynamics of clusters, gravitational lenses, large-scale velocity flows, and the {Omega} = 1 flatness/inflation argument. It is shown that (1) the majority of baryons are dark; and (2) non-baryonic dark matter is probably required on large scales. It is also noted that halo dark matter could be either baryonic or non-baryonic. Descrimination between cold'' and hot'' non-baryonic candidates is shown to depend on the assumed seeds'' that stimulate structure formation. Gaussian density fluctuations, such as those induced by quantum fluctuations, favor cold dark matter, whereas topological defects such as strings, textures or domain walls may work equally or better with hot dark matter. A possible connection between cold dark matter, globular cluster ages and the Hubble constant is mentioned. Recent large-scale structure measurements, coupled with microwave anisotropy limits, are shown to raise some questions for the previously favored density fluctuation picture. Accelerator and underground limits on dark matter candidates are also reviewed.

  5. Searching for dark matter

    NASA Astrophysics Data System (ADS)

    Mateo, Mario

    1994-01-01

    Three teams of astronomers believe they have independently found evidence for dark matter in our galaxy. A brief history of the search for dark matter is presented. The use of microlensing-event observation for spotting dark matter is described. The equipment required to observe microlensing events and three groups working on dark matter detection are discussed. The three groups are the Massive Compact Halo Objects (MACHO) Project team, the Experience de Recherche d'Objets Sombres (EROS) team, and the Optical Gravitational Lensing Experiment (OGLE) team. The first apparent detections of microlensing events by the three teams are briefly reported.

  6. Dark U (1)

    NASA Astrophysics Data System (ADS)

    Chang, Chia-Feng; Ma, Ernest; Yuan, Tzu-Chiang

    2015-06-01

    In this talk we will explore the possibility of adding a local U(1) dark sector to the standard model with the Higgs boson as a portal connecting the visible standard model sector and the dark one. We will discuss existing experimental constraint on the model parameters from the invisible width of Higgs decay. Implications of such a dark U(1) sector on phenomenology at the Large Hardon Collider will be addressed. In particular, detailed results for the non-standard signals of multi-lepton-jets that arise from this simple dark sector will be presented.

  7. Dark matter in cosmology

    NASA Astrophysics Data System (ADS)

    Luković, Vladimir; Cabella, Paolo; Vittorio, Nicola

    2014-07-01

    In this paper we review the main theoretical and experimental achievements in the field of dark matter from the cosmological and astrophysical point of view. We revisit it from the very first surveys of local astrophysical matter, up to the stringent constraints on matter properties, coming from the last release of data on cosmological scales. To bring closer and justify the idea of dark matter, we will go across methods and tools for measuring dark matter characteristics, and in some cases a combination of methods that provide one of the greatest direct proofs for dark matter, such as Bullet cluster.

  8. Dark matter and cosmology

    SciTech Connect

    Schramm, D.N.

    1992-03-01

    The cosmological dark matter problem is reviewed. The Big Bang Nucleosynthesis constraints on the baryon density are compared with the densities implied by visible matter, dark halos, dynamics of clusters, gravitational lenses, large-scale velocity flows, and the {Omega} = 1 flatness/inflation argument. It is shown that (1) the majority of baryons are dark; and (2) non-baryonic dark matter is probably required on large scales. It is also noted that halo dark matter could be either baryonic or non-baryonic. Descrimination between ``cold`` and ``hot`` non-baryonic candidates is shown to depend on the assumed ``seeds`` that stimulate structure formation. Gaussian density fluctuations, such as those induced by quantum fluctuations, favor cold dark matter, whereas topological defects such as strings, textures or domain walls may work equally or better with hot dark matter. A possible connection between cold dark matter, globular cluster ages and the Hubble constant is mentioned. Recent large-scale structure measurements, coupled with microwave anisotropy limits, are shown to raise some questions for the previously favored density fluctuation picture. Accelerator and underground limits on dark matter candidates are also reviewed.

  9. Dark energy and extended dark matter halos

    NASA Astrophysics Data System (ADS)

    Chernin, A. D.; Teerikorpi, P.; Valtonen, M. J.; Dolgachev, V. P.; Domozhilova, L. M.; Byrd, G. G.

    2012-03-01

    The cosmological mean matter (dark and baryonic) density measured in the units of the critical density is Ωm = 0.27. Independently, the local mean density is estimated to be Ωloc = 0.08-0.23 from recent data on galaxy groups at redshifts up to z = 0.01-0.03 (as published by Crook et al. 2007, ApJ, 655, 790 and Makarov & Karachentsev 2011, MNRAS, 412, 2498). If the lower values of Ωloc are reliable, as Makarov & Karachentsev and some other observers prefer, does this mean that the Local Universe of 100-300 Mpc across is an underdensity in the cosmic matter distribution? Or could it nevertheless be representative of the mean cosmic density or even be an overdensity due to the Local Supercluster therein. We focus on dark matter halos of groups of galaxies and check how much dark mass the invisible outer layers of the halos are able to host. The outer layers are usually devoid of bright galaxies and cannot be seen at large distances. The key factor which bounds the size of an isolated halo is the local antigravity produced by the omnipresent background of dark energy. A gravitationally bound halo does not extend beyond the zero-gravity surface where the gravity of matter and the antigravity of dark energy balance, thus defining a natural upper size of a system. We use our theory of local dynamical effects of dark energy to estimate the maximal sizes and masses of the extended dark halos. Using data from three recent catalogs of galaxy groups, we show that the calculated mass bounds conform with the assumption that a significant amount of dark matter is located in the invisible outer parts of the extended halos, sufficient to fill the gap between the observed and expected local matter density. Nearby groups of galaxies and the Virgo cluster have dark halos which seem to extend up to their zero-gravity surfaces. If the extended halo is a common feature of gravitationally bound systems on scales of galaxy groups and clusters, the Local Universe could be typical or even

  10. Asymmetric Dark Matter and Dark Radiation

    SciTech Connect

    Blennow, Mattias; Martinez, Enrique Fernandez; Mena, Olga; Redondo, Javier; Serra, Paolo E-mail: enfmarti@cern.ch E-mail: redondo@mppmu.mpg.de

    2012-07-01

    Asymmetric Dark Matter (ADM) models invoke a particle-antiparticle asymmetry, similar to the one observed in the Baryon sector, to account for the Dark Matter (DM) abundance. Both asymmetries are usually generated by the same mechanism and generally related, thus predicting DM masses around 5 GeV in order to obtain the correct density. The main challenge for successful models is to ensure efficient annihilation of the thermally produced symmetric component of such a light DM candidate without violating constraints from collider or direct searches. A common way to overcome this involves a light mediator, into which DM can efficiently annihilate and which subsequently decays into Standard Model particles. Here we explore the scenario where the light mediator decays instead into lighter degrees of freedom in the dark sector that act as radiation in the early Universe. While this assumption makes indirect DM searches challenging, it leads to signals of extra radiation at BBN and CMB. Under certain conditions, precise measurements of the number of relativistic species, such as those expected from the Planck satellite, can provide information on the structure of the dark sector. We also discuss the constraints of the interactions between DM and Dark Radiation from their imprint in the matter power spectrum.

  11. 4. DARK CANYON SIPHON VIEW ACROSS DARK CANYON AT ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. DARK CANYON SIPHON - VIEW ACROSS DARK CANYON AT LOCATION OF SIPHON. VIEW TO NORTHWEST - Carlsbad Irrigation District, Dark Canyon Siphon, On Main Canal, 1 mile South of Carlsbad, Carlsbad, Eddy County, NM

  12. The local dark matter density

    NASA Astrophysics Data System (ADS)

    Read, J. I.

    2014-06-01

    I review current efforts to measure the mean density of dark matter near the Sun. This encodes valuable dynamical information about our Galaxy and is also of great importance for ‘direct detection’ dark matter experiments. I discuss theoretical expectations in our current cosmology; the theory behind mass modelling of the Galaxy; and I show how combining local and global measures probes the shape of the Milky Way dark matter halo and the possible presence of a ‘dark disc’. I stress the strengths and weaknesses of different methodologies and highlight the continuing need for detailed tests on mock data—particularly in the light of recently discovered evidence for disequilibria in the Milky Way disc. I collate the latest measurements of ρdm and show that, once the baryonic surface density contribution Σb is normalized across different groups, there is remarkably good agreement. Compiling data from the literature, I estimate Σb = 54.2 ± 4.9 M⊙pc-2, where the dominant source of uncertainty is in the H i gas contribution. Assuming this contribution from the baryons, I highlight several recent measurements of ρdm in order of increasing data complexity and prior, and, correspondingly, decreasing formal error bars. Comparing these measurements with spherical extrapolations from the Milky Way’s rotation curve, I show that the Milky Way is consistent with having a spherical dark matter halo at R0 ˜ 8 kpc. The very latest measures of ρdm based on ˜10 000 stars from the Sloan Digital Sky Survey appear to favour little halo flattening at R0, suggesting that the Galaxy has a rather weak dark matter disc, with a correspondingly quiescent merger history. I caution, however, that this result hinges on there being no large systematics that remain to be uncovered in the SDSS data, and on the local baryonic surface density being Σb ˜ 55 M⊙pc-2. I conclude by discussing how the new Gaia satellite will be transformative. We will obtain much tighter

  13. No evidence of dark matter in the solar neighborhood

    NASA Astrophysics Data System (ADS)

    Moni Bidin, C.; Carraro, G.; Méndez, R. A.; Smith, R.

    We measured the surface mass density of the Galactic disk at the solar posi- tion, up to 4 kpc from the plane, by means of the kinematics of 400 thick disk stars. The results match the expectations for the visible mass only, and no dark matter is detected in the volume under analysis. The current models of dark matter halo are excluded with a significance higher than 5, unless a highly prolate halo is assumed, very atypical in cold dark matter simula- tions. The resulting lack of dark matter at the solar position challenges the current models. FULL TEXT IN SPANISH

  14. Condensate dark matter stars

    SciTech Connect

    Li, X.Y.; Harko, T.; Cheng, K.S. E-mail: harko@hkucc.hku.hk

    2012-06-01

    We investigate the structure and stability properties of compact astrophysical objects that may be formed from the Bose-Einstein condensation of dark matter. Once the critical temperature of a boson gas is less than the critical temperature, a Bose-Einstein Condensation process can always take place during the cosmic history of the universe. Therefore we model the dark matter inside the star as a Bose-Einstein condensate. In the condensate dark matter star model, the dark matter equation of state can be described by a polytropic equation of state, with polytropic index equal to one. We derive the basic general relativistic equations describing the equilibrium structure of the condensate dark matter star with spherically symmetric static geometry. The structure equations of the condensate dark matter stars are studied numerically. The critical mass and radius of the dark matter star are given by M{sub crit} ≈ 2(l{sub a}/1fm){sup 1/2}(m{sub χ}/1 GeV){sup −3/2}M{sub s}un and R{sub crit} ≈ 1.1 × 10{sup 6}(l{sub a}/1 fm){sup 1/2}(m{sub χ}/1 GeV){sup −3/2} cm respectively, where l{sub a} and m{sub χ} are the scattering length and the mass of dark matter particle, respectively.

  15. Working the Dark Edges

    ERIC Educational Resources Information Center

    Weston, Anthony

    2014-01-01

    Environmentalism's wider and wilder possibilities today appear as regions of seeming darkness that bracket or frame acceptable environmental thinking. One of these barely-mentionable darknesses is outer space--the cosmos. Another is the inner and chthonic powers of the land and natural beings generally. This essay aims to bring these two kinds of…

  16. Dark Energy, or Worse

    ScienceCinema

    Professor Sean Carroll

    2016-07-12

    General relativity is inconsistent with cosmological observations unless we invoke components of dark matter and dark energy that dominate the universe. While it seems likely that these exotic substances really do exist, the alternative is worth considering: that Einstein's general relativity breaks down on cosmological scales. I will discuss models of modified gravity, tests in the solar system and elsewhere, and consequences for cosmology.

  17. Dark matter annihilation and decay from non-spherical dark halos in galactic dwarf satellites

    NASA Astrophysics Data System (ADS)

    Hayashi, Kohei; Ichikawa, Koji; Matsumoto, Shigeki; Ibe, Masahiro; Ishigaki, Miho N.; Sugai, Hajime

    2016-09-01

    The dwarf spheroidal galaxies (dSphs) in the Milky Way are the primary targets in the indirect searches for particle dark matter. To set robust constraints on candidate dark matter particles, understanding the dark halo structure of these systems is of substantial importance. In this paper, we first evaluate the astrophysical factors for dark matter annihilation and decay for 24 dSphs, taking into account a non-spherical dark halo, using generalized axisymmetric mass models based on axisymmetric Jeans equations. First, from a fitting analysis of the most recent kinematic data available, our axisymmetric mass models are a much better fit than previous spherical ones, thus, our work should be the most realistic and reliable estimator for astrophysical factors. Secondly, we find that among analysed dSphs, the ultra-faint dwarf galaxies Triangulum II and Ursa Major II are the most promising but large uncertain targets for dark matter annihilation while the classical dSph Draco is the most robust and detectable target for dark matter decay. It is also found that the non-sphericity of luminous and dark components influences the estimate of astrophysical factors, even though these factors largely depend on the sample size, the prior range of parameters and the spatial extent of the dark halo. Moreover, owing to these effects, the constraints on the dark matter annihilation cross-section are more conservative than those of previous spherical works. These results are important for optimizing and designing dark matter searches in current and future multi-messenger observations by space and ground-based telescopes.

  18. Dark matter and dark energy: The critical questions

    SciTech Connect

    Michael S. Turner

    2002-11-19

    Stars account for only about 0.5% of the content of the Universe; the bulk of the Universe is optically dark. The dark side of the Universe is comprised of: at least 0.1% light neutrinos; 3.5% {+-} 1% baryons; 29% {+-} 4% cold dark matter; and 66% {+-} 6% dark energy. Now that we have characterized the dark side of the Universe, the challenge is to understand it. The critical questions are: (1) What form do the dark baryons take? (2) What is (are) the constituent(s) of the cold dark matter? (3) What is the nature of the mysterious dark energy that is causing the Universe to speed up.

  19. Cold dark matter halos

    NASA Astrophysics Data System (ADS)

    Dubinski, John Joseph

    The dark halos arising in the Cold Dark Matter (CDM) cosmology are simulated to investigate the relationship between the structure and kinematics of dark halos and galaxies. Realistic cosmological initial conditions and tidal field boundary conditions are used in N-body simulations of the collapse of density peaks to form dark halos. The core radii of dark halos are no greater than the softening radius, rs = 1.4 kpc. The density profiles can be fit with an analytical Hernquist (1990) profile with an effective power law which varies between -1 in the center to -4 at large radii. The rotation curves of dark halos resemble the flat rotation curves of spiral galaxies in the observed range, 1.5 approximately less than r approximately less than 30 kpc. The halos are strongly triaxial and very flat with (c/a) = 0.50 and (b/a) = 0.71. The distribution of ellipticities for dark halos reaches a maximum at epsilon = 0.5 in contrast to the distribution for elliptical galaxies which peaks at epsilon = 0.2 suggesting that ellipticals are much rounder than dark halos. Dark halos are generally flatter than their progenitor density peaks. The final shape and orientation of a dark halo are largely determined by tidal torquing and are sensitive to changes in the strength and orientation of a tidal field. Dark halos are pressure supported objects with negligible rotational support as indicated by the mean dimensionless spin, lamda = 0.042 +/- 0.024. The angular momentum vector tends to align with the true minor axis of dark halos. Elliptical galaxies have a similar behavior implied by the observation of the tendency for alignment of the rotation vector and the apparent minor axis. The origin of this behavior may be traced to the tendency for tidal torques to misalign with the major axis of a density peak. Tidal torques are found to isotropize the velocity ellipsoids of dark halos at large radii, contrary to the expectation of radially anisotropic velocity ellipsoids in cold collapse

  20. New techniques in dark matter mapping

    NASA Astrophysics Data System (ADS)

    Lorenz, Suzanne

    We have developed a new pipeline for mapping dark matter associated with clusters of galaxies via weak gravitational lensing. This method will be useful both with current datasets and future large optical survey telescopes, such as the Large Synoptic Survey Telescope (LSST). We use a novel source finding technique using a wavelet detection method. We then find known photometric and spectroscopic redshifts associated with our sources and measure the ellipticities of galaxies using a second moment technique. The ellipticity and photometric redshift distribution are then converted to a dark matter map. We have represented the dark matter as smoothed particles to invert the ellipticity map. This had yielded both 2D and 3D dark matter distributions when applied to our Subaru archive image of Abell 2218.

  1. Dark interactions and cosmological fine-tuning

    SciTech Connect

    Quartin, Miguel; Calvao, Mauricio O; Joras, Sergio E; Reis, Ribamar R R; Waga, Ioav E-mail: orca@if.ufrj.br E-mail: ribamar@if.ufrj.br

    2008-05-15

    Cosmological models involving an interaction between dark matter and dark energy have been proposed in order to solve the so-called coincidence problem. Different forms of coupling have been studied, but there have been claims that observational data seem to narrow (some of) them down to something annoyingly close to the {Lambda}CDM (CDM: cold dark matter) model, thus greatly reducing their ability to deal with the problem in the first place. The smallness problem of the initial energy density of dark energy has also been a target of cosmological models in recent years. Making use of a moderately general coupling scheme, this paper aims to unite these different approaches and shed some light on whether this class of models has any true perspective in suppressing the aforementioned issues that plague our current understanding of the universe, in a quantitative and unambiguous way.

  2. Astrophysical Constraints of Dark Matter Properties

    NASA Astrophysics Data System (ADS)

    Moustakas, Leonidas A.; Abel, Tom; Brooks, Alyson; Buckley, Matthew; Bullock, James; Collins, Michelle; Cyr-Racine, Francis-Yan; Dawson, William; Drlica-Wagner, Alex; Gaskins, Jennifer; Kaplinghat, Manoj; Keeton, Charles R.; Kim, Stacy; Peter, Annika; Read, Justin; Simon, Joshua D.; Somerville, Rachel S.; Tollerud, Erik Jon; Treu, Tommaso; Wechsler, Risa H.

    2016-01-01

    The nature of the dark matter that fills the universe remains a profound puzzle in physics and astrophysics. Modern astronomical observations have the potential to produce constraints or measurements on properties of dark matter that may have real power for insights into its particle nature. The key lies with understanding what those constraints may be in a way that is interpretable for both the astronomical and particle physics communities, and establishing a community consensus of how diverse astronomical paths can use a common language. The AAS Special Session on the "Astrophysical constraints of dark matter properties" focuses on framing these questions with concrete proposals for astronomical dark matter metrics and potentially figures of merit, and through a series of presentations that serve as points of departure for discussion, ultimately to reach a community consensus that will be useful for current and future pursuits on this topic.

  3. Resonant SIMP dark matter

    NASA Astrophysics Data System (ADS)

    Choi, Soo-Min; Lee, Hyun Min

    2016-07-01

    We consider a resonant SIMP dark matter in models with two singlet complex scalar fields charged under a local dark U(1)D. After the U(1)D is broken down to a Z5 discrete subgroup, the lighter scalar field becomes a SIMP dark matter which has the enhanced 3 → 2 annihilation cross section near the resonance of the heavier scalar field. Bounds on the SIMP self-scattering cross section and the relic density can be fulfilled at the same time for perturbative couplings of SIMP. A small gauge kinetic mixing between the SM hypercharge and dark gauge bosons can be used to make SIMP dark matter in kinetic equilibrium with the SM during freeze-out.

  4. Fingerprinting dark energy

    SciTech Connect

    Sapone, Domenico; Kunz, Martin

    2009-10-15

    Dark energy perturbations are normally either neglected or else included in a purely numerical way, obscuring their dependence on underlying parameters like the equation of state or the sound speed. However, while many different explanations for the dark energy can have the same equation of state, they usually differ in their perturbations so that these provide a fingerprint for distinguishing between different models with the same equation of state. In this paper we derive simple yet accurate approximations that are able to characterize a specific class of models (encompassing most scalar-field models) which is often generically called 'dark energy'. We then use the approximate solutions to look at the impact of the dark energy perturbations on the dark matter power spectrum and on the integrated Sachs-Wolfe effect in the cosmic microwave background radiation.

  5. Loren Shriver carries Olympic torch

    NASA Technical Reports Server (NTRS)

    1996-01-01

    KSC Shuttle Operations Manager Loren J. Shriver proudly displays the Olympic torch that he carried to the top of Launch Pad 39A as his contribution to the July 7, 1996 KSC Olympic torch relay effort. Nineteen other KSC runners also participated in the relay effort at the Center. The Olympic torch arrived at KSC at 1:40 p.m. and traveled a 20-mile course to the pad and then out to the KSC visitor Center. The Space Shuttle Atlantis is behind Shriver, poised for the STS-79 mission, which will feature the fourth docking of the Shuttle with the Russian Mir space station.

  6. Chilly dark sectors and asymmetric reheating

    NASA Astrophysics Data System (ADS)

    Adshead, Peter; Cui, Yanou; Shelton, Jessie

    2016-06-01

    In a broad class of theories, the relic abundance of dark matter is determined by interactions internal to a thermalized dark sector, with no direct involvement of the Standard Model (SM). We point out that these theories raise an immediate cosmological question: how was the dark sector initially populated in the early universe? Motivated in part by the difficulty of accommodating large amounts of entropy carried in dark radiation with cosmic microwave background measurements of the effective number of relativistic species at recombination, N eff , we aim to establish which admissible cosmological histories can populate a thermal dark sector that never reaches thermal equilibrium with the SM. The minimal cosmological origin for such a dark sector is asymmetric reheating, when the same mechanism that populates the SM in the early universe also populates the dark sector at a lower temperature. Here we demonstrate that the resulting inevitable inflaton-mediated scattering between the dark sector and the SM can wash out a would-be temperature asymmetry, and establish the regions of parameter space where temperature asymmetries can be generated in minimal reheating scenarios. Thus obtaining a temperature asymmetry of a given size either restricts possible inflaton masses and couplings or necessitates a non-minimal cosmology for one or both sectors. As a side benefit, we develop techniques for evaluating collision terms in the relativistic Boltzmann equation when the full dependence on Bose-Einstein or Fermi-Dirac phase space distributions must be retained, and present several new results on relativistic thermal averages in an appendix.

  7. Interstellar Gas and a Dark Disk

    NASA Astrophysics Data System (ADS)

    Kramer, Eric David; Randall, Lisa

    2016-10-01

    We introduce a potentially powerful method for constraining or discovering a thin dark matter disk in the Milky Way. The method relies on the relationship between the midplane densities and scale heights of interstellar gas being determined by the gravitational potential, which is sensitive to the presence of a dark disk. We show how to use the interstellar gas parameters to set a bound on a dark disk and discuss the constraints suggested by the current data. However, current measurements for these parameters are discordant, with the uncertainty in the constraint being dominated by the molecular hydrogen midplane density measurement, as well as by the atomic hydrogen velocity dispersion measurement. Magnetic fields and cosmic ray pressure, which are expected to play a role, are uncertain as well. The current models and data are inadequate to determine the disk's existence, but taken at face value, may favor its existence depending on the gas parameters used.

  8. The Dark Energy Survey: more than dark energy - an overview

    NASA Astrophysics Data System (ADS)

    Dark Energy Survey Collaboration; Abbott, T.; Abdalla, F. B.; Aleksić, J.; Allam, S.; Amara, A.; Bacon, D.; Balbinot, E.; Banerji, M.; Bechtol, K.; Benoit-Lévy, A.; Bernstein, G. M.; Bertin, E.; Blazek, J.; Bonnett, C.; Bridle, S.; Brooks, D.; Brunner, R. J.; Buckley-Geer, E.; Burke, D. L.; Caminha, G. B.; Capozzi, D.; Carlsen, J.; Carnero-Rosell, A.; Carollo, M.; Carrasco-Kind, M.; Carretero, J.; Castander, F. J.; Clerkin, L.; Collett, T.; Conselice, C.; Crocce, M.; Cunha, C. E.; D'Andrea, C. B.; da Costa, L. N.; Davis, T. M.; Desai, S.; Diehl, H. T.; Dietrich, J. P.; Dodelson, S.; Doel, P.; Drlica-Wagner, A.; Estrada, J.; Etherington, J.; Evrard, A. E.; Fabbri, J.; Finley, D. A.; Flaugher, B.; Foley, R. J.; Fosalba, P.; Frieman, J.; García-Bellido, J.; Gaztanaga, E.; Gerdes, D. W.; Giannantonio, T.; Goldstein, D. A.; Gruen, D.; Gruendl, R. A.; Guarnieri, P.; Gutierrez, G.; Hartley, W.; Honscheid, K.; Jain, B.; James, D. J.; Jeltema, T.; Jouvel, S.; Kessler, R.; King, A.; Kirk, D.; Kron, R.; Kuehn, K.; Kuropatkin, N.; Lahav, O.; Li, T. S.; Lima, M.; Lin, H.; Maia, M. A. G.; Makler, M.; Manera, M.; Maraston, C.; Marshall, J. L.; Martini, P.; McMahon, R. G.; Melchior, P.; Merson, A.; Miller, C. J.; Miquel, R.; Mohr, J. J.; Morice-Atkinson, X.; Naidoo, K.; Neilsen, E.; Nichol, R. C.; Nord, B.; Ogando, R.; Ostrovski, F.; Palmese, A.; Papadopoulos, A.; Peiris, H. V.; Peoples, J.; Percival, W. J.; Plazas, A. A.; Reed, S. L.; Refregier, A.; Romer, A. K.; Roodman, A.; Ross, A.; Rozo, E.; Rykoff, E. S.; Sadeh, I.; Sako, M.; Sánchez, C.; Sanchez, E.; Santiago, B.; Scarpine, V.; Schubnell, M.; Sevilla-Noarbe, I.; Sheldon, E.; Smith, M.; Smith, R. C.; Soares-Santos, M.; Sobreira, F.; Soumagnac, M.; Suchyta, E.; Sullivan, M.; Swanson, M.; Tarle, G.; Thaler, J.; Thomas, D.; Thomas, R. C.; Tucker, D.; Vieira, J. D.; Vikram, V.; Walker, A. R.; Wechsler, R. H.; Weller, J.; Wester, W.; Whiteway, L.; Wilcox, H.; Yanny, B.; Zhang, Y.; Zuntz, J.

    2016-08-01

    This overview paper describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4 m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion, the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae and other transients. The main goals of DES are to characterize dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large-scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper, we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the Solar system, the Milky Way, galaxy evolution, quasars and other topics. In addition, we show that if the cosmological model is assumed to be Λ+cold dark matter, then important astrophysics can be deduced from the primary DES probes. Highlights from DES early data include the discovery of 34 trans-Neptunian objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).

  9. The Dark Energy Survey: More than dark energy - An overview

    DOE PAGES

    Abbott, T.

    2016-03-21

    This overview article describes the legacy prospect and discovery potential of the Dark Energy Survey (DES) beyond cosmological studies, illustrating it with examples from the DES early data. DES is using a wide-field camera (DECam) on the 4m Blanco Telescope in Chile to image 5000 sq deg of the sky in five filters (grizY). By its completion the survey is expected to have generated a catalogue of 300 million galaxies with photometric redshifts and 100 million stars. In addition, a time-domain survey search over 27 sq deg is expected to yield a sample of thousands of Type Ia supernovae andmore » other transients. The main goals of DES are to characterise dark energy and dark matter, and to test alternative models of gravity; these goals will be pursued by studying large scale structure, cluster counts, weak gravitational lensing and Type Ia supernovae. However, DES also provides a rich data set which allows us to study many other aspects of astrophysics. In this paper we focus on additional science with DES, emphasizing areas where the survey makes a difference with respect to other current surveys. The paper illustrates, using early data (from `Science Verification', and from the first, second and third seasons of observations), what DES can tell us about the solar system, the Milky Way, galaxy evolution, quasars, and other topics. In addition, we show that if the cosmological model is assumed to be Lambda+ Cold Dark Matter (LCDM) then important astrophysics can be deduced from the primary DES probes. Lastly, highlights from DES early data include the discovery of 34 Trans Neptunian Objects, 17 dwarf satellites of the Milky Way, one published z > 6 quasar (and more confirmed) and two published superluminous supernovae (and more confirmed).« less

  10. Exothermic dark matter

    SciTech Connect

    Graham, Peter W.; Saraswat, Prashant; Harnik, Roni; Rajendran, Surjeet

    2010-09-15

    We propose a novel mechanism for dark matter to explain the observed annual modulation signal at DAMA/LIBRA which avoids existing constraints from every other dark matter direct detection experiment including CRESST, CDMS, and XENON10. The dark matter consists of at least two light states with mass {approx}few GeV and splittings {approx}5 keV. It is natural for the heavier states to be cosmologically long-lived and to make up an O(1) fraction of the dark matter. Direct detection rates are dominated by the exothermic reactions in which an excited dark matter state downscatters off of a nucleus, becoming a lower energy state. In contrast to (endothermic) inelastic dark matter, the most sensitive experiments for exothermic dark matter are those with light nuclei and low threshold energies. Interestingly, this model can also naturally account for the observed low-energy events at CoGeNT. The only significant constraint on the model arises from the DAMA/LIBRA unmodulated spectrum but it can be tested in the near future by a low-threshold analysis of CDMS-Si and possibly other experiments including CRESST, COUPP, and XENON100.

  11. Twin Higgs Asymmetric Dark Matter.

    PubMed

    García García, Isabel; Lasenby, Robert; March-Russell, John

    2015-09-18

    We study asymmetric dark matter (ADM) in the context of the minimal (fraternal) twin Higgs solution to the little hierarchy problem, with a twin sector with gauged SU(3)^{'}×SU(2)^{'}, a twin Higgs doublet, and only third-generation twin fermions. Naturalness requires the QCD^{'} scale Λ_{QCD}^{'}≃0.5-20  GeV, and that t^{'} is heavy. We focus on the light b^{'} quark regime, m_{b^{'}}≲Λ_{QCD}^{'}, where QCD^{'} is characterized by a single scale Λ_{QCD}^{'} with no light pions. A twin baryon number asymmetry leads to a successful dark matter (DM) candidate: the spin-3/2 twin baryon, Δ^{'}∼b^{'}b^{'}b^{'}, with a dynamically determined mass (∼5Λ_{QCD}^{'}) in the preferred range for the DM-to-baryon ratio Ω_{DM}/Ω_{baryon}≃5. Gauging the U(1)^{'} group leads to twin atoms (Δ^{'}-τ^{'}[over ¯] bound states) that are successful ADM candidates in significant regions of parameter space, sometimes with observable changes to DM halo properties. Direct detection signatures satisfy current bounds, at times modified by dark form factors. PMID:26430985

  12. Twin Higgs Asymmetric Dark Matter.

    PubMed

    García García, Isabel; Lasenby, Robert; March-Russell, John

    2015-09-18

    We study asymmetric dark matter (ADM) in the context of the minimal (fraternal) twin Higgs solution to the little hierarchy problem, with a twin sector with gauged SU(3)^{'}×SU(2)^{'}, a twin Higgs doublet, and only third-generation twin fermions. Naturalness requires the QCD^{'} scale Λ_{QCD}^{'}≃0.5-20  GeV, and that t^{'} is heavy. We focus on the light b^{'} quark regime, m_{b^{'}}≲Λ_{QCD}^{'}, where QCD^{'} is characterized by a single scale Λ_{QCD}^{'} with no light pions. A twin baryon number asymmetry leads to a successful dark matter (DM) candidate: the spin-3/2 twin baryon, Δ^{'}∼b^{'}b^{'}b^{'}, with a dynamically determined mass (∼5Λ_{QCD}^{'}) in the preferred range for the DM-to-baryon ratio Ω_{DM}/Ω_{baryon}≃5. Gauging the U(1)^{'} group leads to twin atoms (Δ^{'}-τ^{'}[over ¯] bound states) that are successful ADM candidates in significant regions of parameter space, sometimes with observable changes to DM halo properties. Direct detection signatures satisfy current bounds, at times modified by dark form factors.

  13. Heavy spin-2 Dark Matter

    NASA Astrophysics Data System (ADS)

    Babichev, Eugeny; Marzola, Luca; Raidal, Martti; Schmidt-May, Angnis; Urban, Federico; Veermäe, Hardi; von Strauss, Mikael

    2016-09-01

    We provide further details on a recent proposal addressing the nature of the dark sectors in cosmology and demonstrate that all current observations related to Dark Matter can be explained by the presence of a heavy spin-2 particle. Massive spin-2 fields and their gravitational interactions are uniquely described by ghost-free bimetric theory, which is a minimal and natural extension of General Relativity. In this setup, the largeness of the physical Planck mass is naturally related to extremely weak couplings of the heavy spin-2 field to baryonic matter and therefore explains the absence of signals in experiments dedicated to Dark Matter searches. It also ensures the phenomenological viability of our model as we confirm by comparing it with cosmological and local tests of gravity. At the same time, the spin-2 field possesses standard gravitational interactions and it decays universally into all Standard Model fields but not into massless gravitons. Matching the measured DM abundance together with the requirement of stability constrains the spin-2 mass to be in the 1 to 100 TeV range.

  14. Inflation, dark matter, and dark energy in the string landscape.

    PubMed

    Liddle, Andrew R; Ureña-López, L Arturo

    2006-10-20

    We consider the conditions needed to unify the description of dark matter, dark energy, and inflation in the context of the string landscape. We find that incomplete decay of the inflaton field gives the possibility that a single field is responsible for all three phenomena. By contrast, unifying dark matter and dark energy into a single field, separate from the inflaton, appears rather difficult.

  15. Falsification of dark energy by fluid mechanics

    NASA Astrophysics Data System (ADS)

    Gibson, Carl H.

    2011-11-01

    The 2011 Nobel Prize in Physics has been awarded for the discovery from observations of increased supernovae dimness interpreted as distance, so that the Universe expansion rate has changed from a rate decreasing since the big bang to one that is now increasing, driven by anti-gravity forces of a mysterious dark energy material comprising 70% of the Universe mass-energy. Fluid mechanical considerations falsify both the accelerating expansion and dark energy concepts. Kinematic viscosity is neglected in current stan- dard models of self-gravitational structure formation, which rely on cold dark matter CDM condensations and clusterings that are also falsified by fluid mechanics. Weakly collisional CDM particles do not condense but diffuse away. Photon viscosity predicts su- perclustervoid fragmentation early in the plasma epoch and protogalaxies at the end. At the plasma-gas transition, the plasma fragments into Earth-mass gas planets in trillion planet clumps (proto-globular-star-cluster PGCs). The hydrogen planets freeze to form the dark matter of galaxies and merge to form their stars. Dark energy is a systematic dimming error for Supernovae Ia caused by dark matter planets near hot white dwarf stars at the Chandrasekhar carbon limit. Evaporated planet atmospheres may or may not scatter light from the events depending on the line of sight.

  16. Inflatable Dark Matter.

    PubMed

    Davoudiasl, Hooman; Hooper, Dan; McDermott, Samuel D

    2016-01-22

    We describe a general scenario, dubbed "inflatable dark matter," in which the density of dark matter particles can be reduced through a short period of late-time inflation in the early Universe. The overproduction of dark matter that is predicted within many, otherwise, well-motivated models of new physics can be elegantly remedied within this context. Thermal relics that would, otherwise, be disfavored can easily be accommodated within this class of scenarios, including dark matter candidates that are very heavy or very light. Furthermore, the nonthermal abundance of grand unified theory or Planck scale axions can be brought to acceptable levels without invoking anthropic tuning of initial conditions. A period of late-time inflation could have occurred over a wide range of scales from ∼MeV to the weak scale or above, and could have been triggered by physics within a hidden sector, with small but not necessarily negligible couplings to the standard model.

  17. Ghost dark matter

    SciTech Connect

    Furukawa, Tomonori; Yokoyama, Shuichiro; Ichiki, Kiyotomo; Sugiyama, Naoshi; Mukohyama, Shinji E-mail: shu@a.phys.nagoya-u.ac.jp E-mail: naoshi@a.phys.nagoya-u.ac.jp

    2010-05-01

    We revisit ghost dark matter, the possibility that ghost condensation may serve as an alternative to dark matter. In particular, we investigate the Friedmann-Robertson-Walker (FRW) background evolution and the large-scale structure (LSS) in the ΛGDM universe, i.e. a late-time universe dominated by a cosmological constant and ghost dark matter. The FRW background of the ΛGDM universe is indistinguishable from that of the standard ΛCDM universe if M∼>1eV, where M is the scale of spontaneous Lorentz breaking. From the LSS we find a stronger bound: M∼>10eV. For smaller M, ghost dark matter would have non-negligible sound speed after the matter-radiation equality, and thus the matter power spectrum would significantly differ from observation. These bounds are compatible with the phenomenological upper bound M∼<100GeV known in the literature.

  18. Hidden dark matter sector, dark radiation, and the CMB

    NASA Astrophysics Data System (ADS)

    Chacko, Zackaria; Cui, Yanou; Hong, Sungwoo; Okui, Takemichi

    2015-09-01

    We consider theories where dark matter is composed of a thermal relic of weak scale mass, whose couplings to the standard model (SM) are however too small to give rise to the observed abundance. Instead, the abundance is set by annihilation to light hidden sector states that carry no charges under the SM gauge interactions. In such a scenario the constraints from direct and indirect detection, and from collider searches for dark matter, can easily be satisfied. The masses of such light hidden states can be protected by symmetry if they are Nambu-Goldstone bosons, fermions, or gauge bosons. These states can then contribute to the cosmic energy density as dark radiation, leading to observable signals in the cosmic microwave background (CMB). Furthermore, depending on whether or not the light hidden sector states self-interact, the fraction of the total energy density that free-streams is either decreased or increased, leading to characteristic effects on both the scalar and tensor components of the CMB anisotropy that allows these two cases to be distinguished. The magnitude of these signals depends on the number of light degrees of freedom in the hidden sector, and on the temperature at which it kinetically decouples from the SM. We consider a simple model that realizes this scenario, based on a framework in which the SM and hidden sector are initially in thermal equilibrium through the Higgs portal, and show that the resulting signals are compatible with recent Planck results, while large enough to be detected in upcoming experiments such as CMBPol and CMB Stage-IV. Invisible decays of the Higgs into hidden sector states at colliders can offer a complementary probe of this model.

  19. Space Based Dark Energy Surveys

    NASA Astrophysics Data System (ADS)

    Dore, Olivier

    2016-03-01

    Dark energy, the name given to the cause of the accelerating expansion of the Universe, is one of the most tantalizing mystery in modern physics. Current cosmological models hold that dark energy is currently the dominant component of the Universe, but the exact nature of DE remains poorly understood. There are ambitious ground-based surveys underway that seek to understand DE and NASA is participating in the development of significantly more ambitious space-based surveys planned for the next decade. NASA has provided mission enabling technology to the European Space Agency's (ESA) Euclid mission in exchange for US scientists to participate in the Euclid mission. NASA is also developing the Wide Field Infrared Survey Telescope-Astrophysics Focused Telescope Asset (WFIRST) mission for possible launch in 2024. WFIRST was the highest ranked space mission in the Astro2010 Decadal Survey and the current design uses a 2.4m space telescope to go beyond what was then envisioned. Understanding DE is one of the primary science goals of WFIRST-AFTA. This talk will review the state of DE, the relevant activities of the Cosmic Structure Interest Group (CoSSIG) of the PhyPAG, and detail the status and complementarity between Euclid, WFIRST and ot ambitious ground-based efforts.

  20. Elastically Decoupling Dark Matter.

    PubMed

    Kuflik, Eric; Perelstein, Maxim; Lorier, Nicolas Rey-Le; Tsai, Yu-Dai

    2016-06-01

    We present a novel dark matter candidate, an elastically decoupling relic, which is a cold thermal relic whose present abundance is determined by the cross section of its elastic scattering on standard model particles. The dark matter candidate is predicted to have a mass ranging from a few to a few hundred MeV, and an elastic scattering cross section with electrons, photons and/or neutrinos in the 10^{-3}-1  fb range. PMID:27314712

  1. Elastically Decoupling Dark Matter.

    PubMed

    Kuflik, Eric; Perelstein, Maxim; Lorier, Nicolas Rey-Le; Tsai, Yu-Dai

    2016-06-01

    We present a novel dark matter candidate, an elastically decoupling relic, which is a cold thermal relic whose present abundance is determined by the cross section of its elastic scattering on standard model particles. The dark matter candidate is predicted to have a mass ranging from a few to a few hundred MeV, and an elastic scattering cross section with electrons, photons and/or neutrinos in the 10^{-3}-1  fb range.

  2. Dark Matter Effective Theory

    NASA Astrophysics Data System (ADS)

    Del Nobile, Eugenio; Sannino, Francesco

    2012-05-01

    We organize the effective (self-)interaction terms for complex scalar dark matter candidates which are either an isosinglet, isodoublet or an isotriplet with respect to the weak interactions. The classification has been performed ordering the operators in inverse powers of the dark matter (DM) cutoff scale. We assume Lorentz invariance, color and charge neutrality. We also introduce potentially interesting DM induced flavor-changing operators. Our general framework allows for model independent investigations of DM properties.

  3. DARK FLUID: A UNIFIED FRAMEWORK FOR MODIFIED NEWTONIAN DYNAMICS, DARK MATTER, AND DARK ENERGY

    SciTech Connect

    Zhao Hongsheng; Li Baojiu E-mail: b.li@damtp.cam.ac.u

    2010-03-20

    Empirical theories of dark matter (DM) like modified Newtonian dynamics (MOND) gravity and of dark energy (DE) like f(R) gravity were motivated by astronomical data. But could these theories be branches rooted from a more general and hence generic framework? Here we propose a very generic Lagrangian of such a framework based on simple dimensional analysis and covariant symmetry requirements, and explore various outcomes in a top-down fashion. The desired effects of quintessence plus cold DM particle fields or MOND-like scalar field(s) are shown to be largely achievable by one vector field only. Our framework preserves the covariant formulation of general relativity, but allows the expanding physical metric to be bent by a single new species of dark fluid flowing in spacetime. Its non-uniform stress tensor and current vector are simple functions of a vector field with variable norm, not coupled with the baryonic fluid and the four-vector potential of the photon fluid. The dark fluid framework generically branches into a continuous spectrum of theories with DE and DM effects, including the f(R) gravity, tensor-vector-scalar-like theories, Einstein-Aether, and nuLAMBDA theories as limiting cases. When the vector field degenerates into a pure scalar field, we obtain the physics for quintessence. Choices of parameters can be made to pass Big Bang nucleosynthesis, parameterized post-Newtonian, and causality constraints. In this broad setting we emphasize the non-constant dynamical field behind the cosmological constant effect, and highlight plausible corrections beyond the classical MOND predictions.

  4. Symmetryless dark matter

    NASA Astrophysics Data System (ADS)

    Kajiyama, Yuji; Kannike, Kristjan; Raidal, Martti

    2012-02-01

    It is appealing to stabilize dark matter by the same discrete non-Abelian symmetry that is used to explain the structure of quark and lepton mass matrices. However, to generate exact tribimaximal neutrino mixing at tree level, the non-Abelian flavor symmetry must necessarily be broken by vacuum expectation values of flavon scalars, rendering dark matter unstable. We study singlet, doublet, and triplet SU(2) multiplets of both scalar and fermion dark matter candidates and enumerate the conditions under which no d<6 dark matter decay operators are generated even in the case if the flavor symmetry is broken to nothing. We show that under the assumptions that the flavor group is fully broken and that the dark matter decay operators are suppressed only by a high scale, the vacuum expectation values of flavon scalars transforming as higher multiplets (e.g., triplets) of the flavor group must be at the electroweak scale. The most economical way for that is to use standard model Higgs boson(s) as flavons. Such models can be tested by the LHC experiments. This scenario requires the existence of additional Froggatt-Nielsen scalars that generate hierarchies in Yukawa couplings. We study the conditions under which large and small flavor breaking parameters can coexist without destabilizing the dark matter.

  5. Constraining Dark Matter and Dark Energy Models using Astrophysical Surveys

    NASA Astrophysics Data System (ADS)

    Cieplak, Agnieszka M.

    This thesis addresses astrophysical probes to constrain dark matter (DM) and dark energy models. Primordial black holes (PBHs) remain one of the few DM candidates within the Standard Model of Particle Physics. This thesis presents a new probe of this PBH DM, using the microlensing of the source stars monitored by the already existing Kepler satellite. With its photometric precision and the large projected cross section of the nearby stars, it is found that previous constraints on PBH DM could theoretically be extended by two orders of magnitude. Correcting a well-known microlensing formula, a limb-darkening analysis is included, and a new approximation is calculated for future star selection. A preliminary prediction is calculated for the planned Wide-Field Infrared Survey Telescope. A preliminary study of the first two years of publicly available Kepler data is presented. The investigation yields many new sources of background error not predicted in the theoretical calculations, such as stellar flares and comets in the field of view. Since no PBH candidates are detected, an efficiency of detection is therefore calculated by running a Monte Carlo with fake limb-darkened finite-source microlensing events. It is found that with just the first 8 quarters of data, a full order of magnitude of the PBH mass range can be already constrained. Finally, one of the astrophysical probes of dark energy is also addressed - specifically, the baryon acoustic oscillations (BAO) measurement in the gas distribution, as detected in quasar absorption lines. This unique measurement of dark energy at intermediate redshifts is being measured by current telescope surveys. The last part of this thesis therefore focuses on understanding the systematic effects in such a detection. Since the bias between the underlying dark matter distribution and the measured gas flux distribution is based on gas physics, hydrodynamic simulations are used to understand the evolution of neutral hydrogen over

  6. The traces of anisotropic dark energy in light of Planck

    SciTech Connect

    Cardona, Wilmar; Kunz, Martin; Hollenstein, Lukas E-mail: lukas.hollenstein@zhaw.ch

    2014-07-01

    We study a dark energy model with non-zero anisotropic stress, either linked to the dark energy density or to the dark matter density. We compute approximate solutions that allow to characterise the behaviour of the dark energy model and to assess the stability of the perturbations. We also determine the current limits on such an anisotropic stress from the cosmic microwave background data by the Planck satellite, and derive the corresponding constraints on the modified growth parameters like the growth index, the effective Newton's constant and the gravitational slip.

  7. The Present View of Experimental Dark Matter Particle Properties

    NASA Astrophysics Data System (ADS)

    Buckley, Matthew; Kaplinghat, Manoj; Gaskins, Jennifer; Peter, Annika; Kim, Stacy; Moustakas, Leonidas A.

    2016-01-01

    The potential for success of direct, indirect, and production experimental approaches to detecting and quantifying properties of dark matter depends on the class of particle dark matter may be. We discuss the connections between current experimental approaches and classes of particle models, and draw comparisons to the power of astronomical measurement, including laying out several scenarios of complementarity.

  8. Nonthermal dark matter models and signals

    NASA Astrophysics Data System (ADS)

    Okada, Hiroshi; Orikasa, Yuta; Toma, Takashi

    2016-03-01

    Many experiments exploring weakly interacting massive particles (WIMPs) such as direct, indirect and collider searches have been carried out until now. However, a clear signal of a WIMP has not been found yet and it makes us to suspect that WIMPs are questionable as a dark matter candidate. Taking into account this situation, we propose two models in which dark matter relic density is produced by decay of a metastable particle. In the first model, the metastable particle is a feebly interacting massive particle, which is the so-called FIMP, produced by freeze-in mechanism in the early universe. In the second model, the decaying particle is thermally produced the same as the usual WIMP. However decay of the particle into dark matter is led by a higher dimensional operator. As a phenomenologically interesting feature of nonthermal dark matter discussed in this paper, a strong sharp gamma-ray emission as an indirect detection signal occurs due to internal bremsstrahlung, although some parameter space has already been ruled out by this process. Moreover combining other experimental and theoretical constraints such as dark matter relic density, big bang nucleosynthesis, collider, gamma-rays and perturbativity of couplings, we discuss the two nonthermal DM models.

  9. Asymmetric capture of Dirac dark matter by the Sun

    SciTech Connect

    Blennow, Mattias; Clementz, Stefan

    2015-08-18

    Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles and anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.

  10. Asymmetric capture of Dirac dark matter by the Sun

    SciTech Connect

    Blennow, Mattias; Clementz, Stefan E-mail: scl@kth.se

    2015-08-01

    Current problems with the solar model may be alleviated if a significant amount of dark matter from the galactic halo is captured in the Sun. We discuss the capture process in the case where the dark matter is a Dirac fermion and the background halo consists of equal amounts of dark matter and anti-dark matter. By considering the case where dark matter and anti-dark matter have different cross sections on solar nuclei as well as the case where the capture process is considered to be a Poisson process, we find that a significant asymmetry between the captured dark particles and anti-particles is possible even for an annihilation cross section in the range expected for thermal relic dark matter. Since the captured number of particles are competitive with asymmetric dark matter models in a large range of parameter space, one may expect solar physics to be altered by the capture of Dirac dark matter. It is thus possible that solutions to the solar composition problem may be searched for in these type of models.

  11. Dark-matter QCD-axion searches.

    PubMed

    Rosenberg, Leslie J

    2015-10-01

    In the late 20th century, cosmology became a precision science. Now, at the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There's no known such elementary particle, so the strong presumption is the dark matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10(-(6-3)) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. However, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. This article is a selective overview of the current generation of sensitive axion searches. Not all techniques and experiments

  12. Dark-matter QCD-axion searches.

    PubMed

    Rosenberg, Leslie J

    2015-10-01

    In the late 20th century, cosmology became a precision science. Now, at the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There's no known such elementary particle, so the strong presumption is the dark matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10(-(6-3)) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. However, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. This article is a selective overview of the current generation of sensitive axion searches. Not all techniques and experiments

  13. Dark-matter QCD-axion searches

    PubMed Central

    Rosenberg, Leslie J

    2015-01-01

    In the late 20th century, cosmology became a precision science. Now, at the beginning of the next century, the parameters describing how our universe evolved from the Big Bang are generally known to a few percent. One key parameter is the total mass density of the universe. Normal matter constitutes only a small fraction of the total mass density. Observations suggest this additional mass, the dark matter, is cold (that is, moving nonrelativistically in the early universe) and interacts feebly if at all with normal matter and radiation. There’s no known such elementary particle, so the strong presumption is the dark matter consists of particle relics of a new kind left over from the Big Bang. One of the most important questions in science is the nature of this dark matter. One attractive particle dark-matter candidate is the axion. The axion is a hypothetical elementary particle arising in a simple and elegant extension to the standard model of particle physics that nulls otherwise observable CP-violating effects (where CP is the product of charge reversal C and parity inversion P) in quantum chromo dynamics (QCD). A light axion of mass 10−(6–3) eV (the invisible axion) would couple extraordinarily weakly to normal matter and radiation and would therefore be extremely difficult to detect in the laboratory. However, such an axion is a compelling dark-matter candidate and is therefore a target of a number of searches. Compared with other particle dark-matter candidates, the plausible range of axion dark-matter couplings and masses is narrowly constrained. This focused search range allows for definitive searches, where a nonobservation would seriously impugn the dark-matter QCD-axion hypothesis. Axion searches use a wide range of technologies, and the experiment sensitivities are now reaching likely dark-matter axion couplings and masses. This article is a selective overview of the current generation of sensitive axion searches. Not all techniques and

  14. Dynamics of minimally coupled dark energy in spherical halos of dark matter

    NASA Astrophysics Data System (ADS)

    Novosyadlyj, Bohdan; Tsizh, Maksym; Kulinich, Yurij

    2016-03-01

    We analyse the evolution of scalar field dark energy in the spherical halos of dark matter at the late stages of formation of gravitationally bound systems in the expanding Universe. The dynamics of quintessential dark energy at the center of dark matter halo strongly depends on the value of effective sound speed c_s (in units of speed of light). If c_s˜ 1 (classical scalar field) then the dark energy in the gravitationally bound systems is only slightly perturbed and its density is practically the same as in cosmological background. The dark energy with small value of sound speed (c_s<0.1), on the contrary, is important dynamical component of halo at all stages of their evolution: linear, non-linear, turnaround, collapse, virialization and later up to current epoch. These properties of dark energy can be used for constraining the value of effective sound speed c_s by comparison the theoretical predictions with observational data related to the large scale gravitationally bound systems.

  15. New Efforts to Identify Dark Matter

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-09-01

    among them.In the early universe, small density perturbations on sub-galactic scales produce dwarf galaxies in the lambda-CDM model. But in the warm dark matter model, the longer free streaming length of the dark matter particles smooth out some of those small perturbations. This results in the formation of fewer dwarf galaxies which fits better with our current observations.Limits on Warm Dark MatterSo how can we test this alternative model? The maximum number density of dark-matter halos predicted by the warm dark matter model at a given redshift depends on the mass of the candidate dark matter particle: a larger particle mass means that more halos form. We therefore can set lower limits on the mass of dark matter particles in a two-step process:Calculate the maximum number density of dark matter halos predicted by models, andCompare this to the measured abundance of the faintest galaxies at a given redshift.Another way of looking at it: for different values of the dark matter particle mass mX, this shows the maximum number density of dark matter halos predicted at z = 6. The shaded areas represent the observed number density of faint galaxies at different confidence levels. [Menci et al. 2016]Recently, unprecedented new Hubble observations of ultra-faint, lensed galaxies in the Hubble Frontier Fields at z~6 have allowed for the discovery of more faint galaxies at this redshift than ever before. Now, a team of scientists led by Nicola Menci (INAF Rome) have used these observations to set a new limit on the lowest mass that candidate dark matter particles can have.Menci and collaborators find that these new observations constrain the particle masses to be above 2.9 keV at the 1 confidence level. These constitute the tightest constraints on the mass of candidate warm dark matter particles derived to date, and they even allow us to rule out some production mechanisms for theorized particles.Extending this analysis to other clusters with deep observations will only

  16. New Efforts to Identify Dark Matter

    NASA Astrophysics Data System (ADS)

    Kohler, Susanna

    2016-09-01

    among them.In the early universe, small density perturbations on sub-galactic scales produce dwarf galaxies in the lambda-CDM model. But in the warm dark matter model, the longer free streaming length of the dark matter particles smooth out some of those small perturbations. This results in the formation of fewer dwarf galaxies which fits better with our current observations.Limits on Warm Dark MatterSo how can we test this alternative model? The maximum number density of dark-matter halos predicted by the warm dark matter model at a given redshift depends on the mass of the candidate dark matter particle: a larger particle mass means that more halos form. We therefore can set lower limits on the mass of dark matter particles in a two-step process:Calculate the maximum number density of dark matter halos predicted by models, andCompare this to the measured abundance of the faintest galaxies at a given redshift.Another way of looking at it: for different values of the dark matter particle mass mX, this shows the maximum number density of dark matter halos predicted at z = 6. The shaded areas represent the observed number density of faint galaxies at different confidence levels. [Menci et al. 2016]Recently, unprecedented new Hubble observations of ultra-faint, lensed galaxies in the Hubble Frontier Fields at z~6 have allowed for the discovery of more faint galaxies at this redshift than ever before. Now, a team of scientists led by Nicola Menci (INAF Rome) have used these observations to set a new limit on the lowest mass that candidate dark matter particles can have.Menci and collaborators find that these new observations constrain the particle masses to be above 2.9 keV at the 1 confidence level. These constitute the tightest constraints on the mass of candidate warm dark matter particles derived to date, and they even allow us to rule out some production mechanisms for theorized particles.Extending this analysis to other clusters with deep observations will only

  17. STIS Cycle 17 MAMA Dark Monitor

    NASA Astrophysics Data System (ADS)

    Proffitt, Charles

    2009-07-01

    This proposal monitors the behavior of the dark current in each of the MAMA detectors. The basic monitor takes two 1380s ACCUM darks each week with each detector. However, starting Oct 5, pairs are only included for weeks that the LRP has external MAMA observations planned. The weekly pairs of exposures for each detector are linked so that they are taken at opposite ends of the same SAA free interval. This pairing of exposures will make it easier to separate long and short term temporal variability from temperature dependent changes. For both detectors, additional blocks of exposures are taken once every six months. These are groups of five 1314 s FUV-MAMA TIME-TAG darks or five 3x315 s NUV ACCUM darks distributed over a single SAA free interval. This will give more information on the brightness of the FUV MAMA dark current as a function of the amount of time that the HV has been on, and for the NUV MAMA will give a better measure of the short term temperature dependence.

  18. D-Root: a system for cultivating plants with the roots in darkness or under different light conditions.

    PubMed

    Silva-Navas, Javier; Moreno-Risueno, Miguel A; Manzano, Concepción; Pallero-Baena, Mercedes; Navarro-Neila, Sara; Téllez-Robledo, Bárbara; Garcia-Mina, Jose M; Baigorri, Roberto; Gallego, Francisco Javier; del Pozo, Juan C

    2015-10-01

    In nature roots grow in the dark and away from light (negative phototropism). However, most current research in root biology has been carried out with the root system grown in the presence of light. Here, we have engineered a device, called Dark-Root (D-Root), to grow plants in vitro with the aerial part exposed to the normal light/dark photoperiod while the roots are in the dark or exposed to specific wavelengths or light intensities. D-Root provides an efficient system for cultivating a large number of seedlings and easily characterizing root architecture in the dark. At the morphological level, root illumination shortens root length and promotes early emergence of lateral roots, therefore inducing expansion of the root system. Surprisingly, root illumination also affects shoot development, including flowering time. Our analyses also show that root illumination alters the proper response to hormones or abiotic stress (e.g. salt or osmotic stress) and nutrient starvation, enhancing inhibition of root growth. In conclusion, D-Root provides a growing system closer to the natural one for assaying Arabidopsis plants, and therefore its use will contribute to a better understanding of the mechanisms involved in root development, hormonal signaling and stress responses.

  19. D-Root: a system for cultivating plants with the roots in darkness or under different light conditions.

    PubMed

    Silva-Navas, Javier; Moreno-Risueno, Miguel A; Manzano, Concepción; Pallero-Baena, Mercedes; Navarro-Neila, Sara; Téllez-Robledo, Bárbara; Garcia-Mina, Jose M; Baigorri, Roberto; Gallego, Francisco Javier; del Pozo, Juan C

    2015-10-01

    In nature roots grow in the dark and away from light (negative phototropism). However, most current research in root biology has been carried out with the root system grown in the presence of light. Here, we have engineered a device, called Dark-Root (D-Root), to grow plants in vitro with the aerial part exposed to the normal light/dark photoperiod while the roots are in the dark or exposed to specific wavelengths or light intensities. D-Root provides an efficient system for cultivating a large number of seedlings and easily characterizing root architecture in the dark. At the morphological level, root illumination shortens root length and promotes early emergence of lateral roots, therefore inducing expansion of the root system. Surprisingly, root illumination also affects shoot development, including flowering time. Our analyses also show that root illumination alters the proper response to hormones or abiotic stress (e.g. salt or osmotic stress) and nutrient starvation, enhancing inhibition of root growth. In conclusion, D-Root provides a growing system closer to the natural one for assaying Arabidopsis plants, and therefore its use will contribute to a better understanding of the mechanisms involved in root development, hormonal signaling and stress responses. PMID:26312572

  20. Dark energy and dark matter from hidden symmetry of gravity model with a non-Riemannian volume form

    NASA Astrophysics Data System (ADS)

    Guendelman, Eduardo; Nissimov, Emil; Pacheva, Svetlana

    2015-10-01

    We show that dark energy and dark matter can be described simultaneously by ordinary Einstein gravity interacting with a single scalar field provided the scalar field Lagrangian couples in a symmetric fashion to two different spacetime volume forms (covariant integration measure densities) on the spacetime manifold - one standard Riemannian given by √{-g} (square root of the determinant of the pertinent Riemannian metric) and another non-Riemannian volume form independent of the Riemannian metric, defined in terms of an auxiliary antisymmetric tensor gauge field of maximal rank. Integration of the equations of motion of the latter auxiliary gauge field produce an a priori arbitrary integration constant that plays the role of a dynamically generated cosmological constant or dark energy. Moreover, the above modified scalar field action turns out to possess a hidden Noether symmetry whose associated conserved current describes a pressureless "dust" fluid which we can identify with the dark matter completely decoupled from the dark energy. The form of both the dark energy and dark matter that results from the above class of models is insensitive to the specific form of the scalar field Lagrangian. By adding an appropriate perturbation, which breaks the above hidden symmetry and along with this couples dark matter and dark energy, we also suggest a way to obtain growing dark energy in the present universe's epoch without evolution pathologies.

  1. Warm dark matter effects in a spherical collapse model with shear and angular momentum

    NASA Astrophysics Data System (ADS)

    Marciu, Mihai

    2016-03-01

    This paper investigates the nonlinear structure formation in a spherical top-hat collapse model based on the pseudo-Newtonian approximation. The system is composed of warm dark matter and dark energy and the dynamical properties of the collapsing region are analyzed for various parametrizations of the dark matter equation of state which are in agreement with current observations. Concerning dark energy, observational constraints of the Chevallier-Polarski-Linder model and the Jassal-Bagla-Padmanabhan equation of state have been considered. During the collapse, the positive dark matter pressure leads to an increase of growth for dark matter and dark energy perturbations and an accelerated expansion for the spherical region. Hence, in the warm dark matter hypothesis, the structure formation is accelerated and the inconsistencies of the Λ CDM model at the galactic scales could be solved. The results obtained are applicable only to adiabatic warm dark matter physical models which are compatible with the pseudo-Newtonian approach.

  2. Levitating dark matter

    SciTech Connect

    Kaloper, Nemanja; Padilla, Antonio E-mail: antonio.padilla@nottingham.ac.uk

    2009-10-01

    A sizable fraction of the total energy density of the universe may be in heavy particles with a net dark U(1)' charge comparable to its mass. When the charges have the same sign the cancellation between their gravitational and gauge forces may lead to a mismatch between different measures of masses in the universe. Measuring galactic masses by orbits of normal matter, such as galaxy rotation curves or lensing, will give the total mass, while the flows of dark matter agglomerates may yield smaller values if the gauge repulsion is not accounted for. If distant galaxies which house light beacons like SNe Ia contain such dark particles, the observations of their cosmic recession may mistake the weaker forces for an extra 'antigravity', and infer an effective dark energy equation of state smaller than the real one. In some cases, including that of a cosmological constant, these effects can mimic w < −1. They can also lead to a local variation of galaxy-galaxy forces, yielding a larger 'Hubble Flow' in those regions of space that could be taken for a dynamical dark energy, or superhorizon effects.

  3. Levitating dark matter

    NASA Astrophysics Data System (ADS)

    Kaloper, Nemanja; Padilla, Antonio

    2009-10-01

    A sizable fraction of the total energy density of the universe may be in heavy particles with a net dark U(1)' charge comparable to its mass. When the charges have the same sign the cancellation between their gravitational and gauge forces may lead to a mismatch between different measures of masses in the universe. Measuring galactic masses by orbits of normal matter, such as galaxy rotation curves or lensing, will give the total mass, while the flows of dark matter agglomerates may yield smaller values if the gauge repulsion is not accounted for. If distant galaxies which house light beacons like SNe Ia contain such dark particles, the observations of their cosmic recession may mistake the weaker forces for an extra `antigravity', and infer an effective dark energy equation of state smaller than the real one. In some cases, including that of a cosmological constant, these effects can mimic w < -1. They can also lead to a local variation of galaxy-galaxy forces, yielding a larger `Hubble Flow' in those regions of space that could be taken for a dynamical dark energy, or superhorizon effects.

  4. BLOOD SUBSTITUTES: EVOLUTION FROM NON-CARRYING TO OXYGEN AND GAS CARRYING FLUIDS

    PubMed Central

    Cabrales, Pedro; Intaglietta, Marcos

    2013-01-01

    The development of oxygen (O2) carrying blood substitutes has evolved from the goal of replicating blood O2 transports properties to that of preserving microvascular and organ function, reducing the inherent or potential toxicity of the material used to carry O2, and treating pathologies initiated by anemia and hypoxia. Furthermore, the emphasis has shifted from blood replacement fluid to “O2 therapeutics” that restore tissue oxygenation to specific tissues regions. This review covers the different alternatives, potential and limitations of hemoglobin based O2 carriers (HBOCs) and perfluorocarbon based O2 carriers (PFCOCs), with emphasis on the physiological conditions disturbed in the situation that they will be used. It describes how concepts learned from plasma expanders without O2 carrying capacity can be applied to maintain O2 delivery and summarizes the microvascular responses due to HBOCs and PFCOCs. This review also presents alternative applications of HBOCs and PFCOCs namely: 1) How HBOC O2 affinity can be engineered to target O2 delivery to hypoxic tissues; and 2) How the high gas solubility of PFCOCs provides new opportunities for carrying, dissolving and delivering gases with biological activity. It is concluded that current blood substitutes development has amplified their applications horizon by devising therapeutic functions for oxygen carriers requiring limited O2 delivery capacity restoration. Conversely, full, blood-like O2 carrying capacity re-establishment awaits control of O2 carrier toxicity. PMID:23820271

  5. (In)Direct detection of boosted dark matter

    NASA Astrophysics Data System (ADS)

    Agashe, Kaustubh; Cui, Yanou; Necib, Lina; Thaler, Jesse

    2016-05-01

    We present a new multi-component dark matter model with a novel experimental signature that mimics neutral current interactions at neutrino detectors. In our model, the dark matter is composed of two particles, a heavier dominant component that annihilates to produce a boosted lighter component that we refer to as boosted dark matter. The lighter component is relativistic and scatters off electrons in neutrino experiments to produce Cherenkov light. This model combines the indirect detection of the dominant component with the direct detection of the boosted dark matter. Directionality can be used to distinguish the dark matter signal from the atmospheric neutrino background. We discuss the viable region of parameter space in current and future experiments.

  6. Dark Energy: A Crisis for Fundamental Physics

    SciTech Connect

    Stubbs, Christopher

    2010-04-12

    Astrophysical observations provide robust evidence that our current picture of fundamental physics is incomplete. The discovery in 1998 that the expansion of the Universe is accelerating (apparently due to gravitational repulsion between regions of empty space!) presents us with a profound challenge, at the interface between gravity and quantum mechanics. This "Dark Energy" problem is arguably the most pressing open question in modern fundamental physics. The first talk will describe why the Dark Energy problem constitutes a crisis, with wide-reaching ramifications. One consequence is that we should probe our understanding of gravity at all accessible scales, and the second talk will present experiments and observations that are exploring this issue.

  7. Dark Energy: A Crisis for Fundamental Physics

    ScienceCinema

    Stubbs, Christopher [Harvard University, Cambridge, Massachusetts, USA

    2016-07-12

    Astrophysical observations provide robust evidence that our current picture of fundamental physics is incomplete. The discovery in 1998 that the expansion of the Universe is accelerating (apparently due to gravitational repulsion between regions of empty space!) presents us with a profound challenge, at the interface between gravity and quantum mechanics. This "Dark Energy" problem is arguably the most pressing open question in modern fundamental physics. The first talk will describe why the Dark Energy problem constitutes a crisis, with wide-reaching ramifications. One consequence is that we should probe our understanding of gravity at all accessible scales, and the second talk will present experiments and observations that are exploring this issue.

  8. WISPy cold dark matter

    NASA Astrophysics Data System (ADS)

    Arias, Paola; Cadamuro, Davide; Goodsell, Mark; Jaeckel, Joerg; Redondo, Javier; Ringwald, Andreas

    2012-06-01

    Very weakly interacting slim particles (WISPs), such as axion-like particles (ALPs) or hidden photons (HPs), may be non-thermally produced via the misalignment mechanism in the early universe and survive as a cold dark matter population until today. We find that, both for ALPs and HPs whose dominant interactions with the standard model arise from couplings to photons, a huge region in the parameter spaces spanned by photon coupling and ALP or HP mass can give rise to the observed cold dark matter. Remarkably, a large region of this parameter space coincides with that predicted in well motivated models of fundamental physics. A wide range of experimental searches — exploiting haloscopes (direct dark matter searches exploiting microwave cavities), helioscopes (searches for solar ALPs or HPs), or light-shining-through-a-wall techniques — can probe large parts of this parameter space in the foreseeable future.

  9. Nearly Supersymmetric Dark Atoms

    DOE PAGES

    Behbahani, Siavosh R.; Jankowiak, Martin; Rube, Tomas; Wacker, Jay G.

    2011-01-01

    Theories of dark matter that support bound states are an intriguing possibility for the identity of the missing mass of the Universe. This article proposes a class of models of supersymmetric composite dark matter where the interactions with the Standard Model communicate supersymmetry breaking to the dark sector. In these models, supersymmetry breaking can be treated as a perturbation on the spectrum of bound states. Using a general formalism, the spectrum with leading supersymmetry effects is computed without specifying the details of the binding dynamics. The interactions of the composite states with the Standard Model are computed, and several benchmarkmore » models are described. General features of nonrelativistic supersymmetric bound states are emphasized.« less

  10. Asymmetric twin Dark Matter

    SciTech Connect

    Farina, Marco

    2015-11-09

    We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC.

  11. Big Questions: Dark Matter

    SciTech Connect

    Lincoln, Don

    2013-12-05

    Carl Sagan's oft-quoted statement that there are "billions and billions" of stars in the cosmos gives an idea of just how much "stuff" is in the universe. However scientists now think that in addition to the type of matter with which we are familiar, there is another kind of matter out there. This new kind of matter is called "dark matter" and there seems to be five times as much as ordinary matter. Dark matter interacts only with gravity, thus light simply zips right by it. Scientists are searching through their data, trying to prove that the dark matter idea is real. Fermilab's Dr. Don Lincoln tells us why we think this seemingly-crazy idea might not be so crazy after all.

  12. Big Questions: Dark Matter

    ScienceCinema

    Lincoln, Don

    2016-07-12

    Carl Sagan's oft-quoted statement that there are "billions and billions" of stars in the cosmos gives an idea of just how much "stuff" is in the universe. However scientists now think that in addition to the type of matter with which we are familiar, there is another kind of matter out there. This new kind of matter is called "dark matter" and there seems to be five times as much as ordinary matter. Dark matter interacts only with gravity, thus light simply zips right by it. Scientists are searching through their data, trying to prove that the dark matter idea is real. Fermilab's Dr. Don Lincoln tells us why we think this seemingly-crazy idea might not be so crazy after all.

  13. Asymmetric twin Dark Matter

    SciTech Connect

    Farina, Marco

    2015-11-01

    We study a natural implementation of Asymmetric Dark Matter in Twin Higgs models. The mirroring of the Standard Model strong sector suggests that a twin baryon with mass around 5 GeV is a natural Dark Matter candidate once a twin baryon number asymmetry comparable to the SM asymmetry is generated. We explore twin baryon Dark Matter in two different scenarios, one with minimal content in the twin sector and one with a complete copy of the SM, including a light twin photon. The essential requirements for successful thermal history are presented, and in doing so we address some of the cosmological issues common to many Twin Higgs models. The required interactions we introduce predict signatures at direct detection experiments and at the LHC.

  14. Dark matter possibilities

    NASA Astrophysics Data System (ADS)

    Wagner, Orvin

    2015-04-01

    In my research I observe signals that penetrate dense matter and I hypothesize that they are due to waves in dark matter. Since they readily penetrate thick matter I hypothesize that they are due to small dark matter particles instead of the usual hypothesized Wimps. For example I observed signals that penetrate my local hill at near 77 m/s. In addition the solar cycle appears to be due to to dark matter oscillating in the sun producing standing waves that have to due with planet placement and stability of the solar system. Dozens of experiments, over the past 20 years, confirm the penetrating waves. Examples of the experiments are presented on my website darkmatterwaves.com and US patent number 8,669,917 B1.

  15. Nearly Supersymmetric Dark Atoms

    SciTech Connect

    Behbahani, Siavosh R.; Jankowiak, Martin; Rube, Tomas; Wacker, Jay G.; /SLAC /Stanford U., ITP

    2011-08-12

    Theories of dark matter that support bound states are an intriguing possibility for the identity of the missing mass of the Universe. This article proposes a class of models of supersymmetric composite dark matter where the interactions with the Standard Model communicate supersymmetry breaking to the dark sector. In these models supersymmetry breaking can be treated as a perturbation on the spectrum of bound states. Using a general formalism, the spectrum with leading supersymmetry effects is computed without specifying the details of the binding dynamics. The interactions of the composite states with the Standard Model are computed and several benchmark models are described. General features of non-relativistic supersymmetric bound states are emphasized.

  16. Signatures of dark matter

    NASA Astrophysics Data System (ADS)

    Baltz, Edward Anthony

    It is well known that most of the mass in the universe remains unobserved save for its gravitational effect on luminous matter. The nature of this ``dark matter'' remains a mystery. From measurements of the primordial deuterium abundance, the theory of big bang nucleosynthesis predicts that there are not enough baryons to account for the amount of dark matter observed, thus the missing mass must take an exotic form. Several promising candidates have been proposed. In this work I will describe my research along two main lines of inquiry into the dark matter puzzle. The first possibility is that the dark matter is exotic massive particles, such as those predicted by supersymmetric extensions to the standard model of particle physics. Such particles are generically called WIMPs, for weakly interacting massive particles. Focusing on the so-called neutralino in supersymmetric models, I discuss the possible signatures of such particles, including their direct detection via nuclear recoil experiments and their indirect detection via annihilations in the halos of galaxies, producing high energy antiprotons, positrons and gamma rays. I also discuss signatures of the possible slow decays of such particles. The second possibility is that there is a population of black holes formed in the early universe. Any dark objects in galactic halos, black holes included, are called MACHOs, for massive compact halo objects. Such objects can be detected by their gravitational microlensing effects. Several possibilities for sources of baryonic dark matter are also interesting for gravitational microlensing. These include brown dwarf stars and old, cool white dwarf stars. I discuss the theory of gravitational microlensing, focusing on the technique of pixel microlensing. I make predictions for several planned microlensing experiments with ground based and space based telescopes. Furthermore, I discuss binary lenses in the context of pixel microlensing. Finally, I develop a new technique for

  17. Dark-Skies Awareness

    NASA Astrophysics Data System (ADS)

    Walker, Constance E.

    2009-05-01

    The arc of the Milky Way seen from a truly dark location is part of our planet's natural heritage. More than one fifth of the world population, two thirds of the United States population and one half of the European Union population have already lost naked eye visibility of the Milky Way. This loss, caused by light pollution, is a serious and growing issue that impacts astronomical research, the economy, ecology, energy conservation, human health, public safety and our shared ability to see the night sky. For this reason, "Dark Skies” is a cornerstone project of the International Year of Astronomy. Its goal is to raise public awareness of the impact of artificial lighting on local environments by getting people worldwide involved in a variety of programs that: 1. Teach about dark skies using new technology (e.g., an activity-based planetarium show on DVD, podcasting, social networking on Facebook and MySpace, a Second Life presence) 2. Provide thematic events on light pollution at star parties and observatory open houses (Dark Skies Discovery Sites, Nights in the (National) Parks, Sidewalk Astronomy) 3. Organize events in the arts (e.g., a photography contest) 4. Involve citizen-scientists in naked-eye and digital-meter star hunting programs (e.g., GLOBE at Night, "How Many Stars?", the Great World Wide Star Count and the radio frequency interference equivalent: "Quiet Skies") and 5. Raise awareness about the link between light pollution and public health, economic issues, ecological consequences, energy conservation, safety and security, and astronomy (e.g., The Starlight Initiative, World Night in Defense of Starlight, International Dark Sky Week, International Dark-Sky Communities, Earth Hour, The Great Switch Out, a traveling exhibit, downloadable posters and brochures). The presentation will provide an update, describe how people can become involved and take a look ahead at the program's sustainability. For more information, visit www.darkskiesawareness.org.

  18. Dark Photon Searches at the Mainz Microtron MAMI

    NASA Astrophysics Data System (ADS)

    Denig, Achim

    2015-04-01

    We report on competitive searches for an extra U(1) gauge particle (Dark Photon) carried out at the Mainz Microtron MAMI using the A1 high resolution spectrometer setup. No significant indication for a Dark Photon has been found and stringent exclusion limits have been set. A big part of the parameter range motivated by (g - 2) μ could indeed be excluded by these measurements. This work is supported by DFG through Collaborative Research Center CRC-1044.

  19. Accretion of dark matter by stars.

    PubMed

    Brito, Richard; Cardoso, Vitor; Okawa, Hirotada

    2015-09-11

    Searches for dark matter imprints are one of the most active areas of current research. We focus here on light fields with mass m_{B}, such as axions and axionlike candidates. Using perturbative techniques and full-blown nonlinear numerical relativity methods, we show the following. (i) Dark matter can pile up in the center of stars, leading to configurations and geometries oscillating with a frequency that is a multiple of f=2.5×10^{14}(m_{B}c^{2}/eV)  Hz. These configurations are stable throughout most of the parameter space, and arise out of credible mechanisms for dark-matter capture. Stars with bosonic cores may also develop in other theories with effective mass couplings, such as (massless) scalar-tensor theories. We also show that (ii) collapse of the host star to a black hole is avoided by efficient gravitational cooling mechanisms.

  20. CDMS: The Hunt for Dark Matter

    SciTech Connect

    Professor Bernard Sadoulet

    2006-03-06

    Deciphering the nature of dark matter has great scientific importance. A leading hypothesis is that dark matter is made of Weakly Interactive Massive Particles (WIMPs), which may result from supersymmetry or additional spatial dimensions. The underground search for elastic scattering of WIMPs on suitable targets (the so-called “direct detection”) is currently led by the Cryogenic Dark Matter Search II (CDMS II) experiment. Its sensitivity is ten times better than any other experiment and we hope to obtain another factor ten in the coming two years. After a brief recall of our recent results, I will describe the complementarity between direct detection experiments, the LHC and the ILC and I will outline the role that SLAC could play in this SuperCDMS program.

  1. Accretion of dark matter by stars.

    PubMed

    Brito, Richard; Cardoso, Vitor; Okawa, Hirotada

    2015-09-11

    Searches for dark matter imprints are one of the most active areas of current research. We focus here on light fields with mass m_{B}, such as axions and axionlike candidates. Using perturbative techniques and full-blown nonlinear numerical relativity methods, we show the following. (i) Dark matter can pile up in the center of stars, leading to configurations and geometries oscillating with a frequency that is a multiple of f=2.5×10^{14}(m_{B}c^{2}/eV)  Hz. These configurations are stable throughout most of the parameter space, and arise out of credible mechanisms for dark-matter capture. Stars with bosonic cores may also develop in other theories with effective mass couplings, such as (massless) scalar-tensor theories. We also show that (ii) collapse of the host star to a black hole is avoided by efficient gravitational cooling mechanisms. PMID:26406817

  2. Unified origin for baryonic visible matter and antibaryonic dark matter.

    PubMed

    Davoudiasl, Hooman; Morrissey, David E; Sigurdson, Kris; Tulin, Sean

    2010-11-19

    We present a novel mechanism for generating both the baryon and dark matter densities of the Universe. A new Dirac fermion X carrying a conserved baryon number charge couples to the standard model quarks as well as a GeV-scale hidden sector. CP-violating decays of X, produced nonthermally in low-temperature reheating, sequester antibaryon number in the hidden sector, thereby leaving a baryon excess in the visible sector. The antibaryonic hidden states are stable dark matter. A spectacular signature of this mechanism is the baryon-destroying inelastic scattering of dark matter that can annihilate baryons at appreciable rates relevant for nucleon decay searches.

  3. Stellar kinematics and dark matter in dwarf galaxies

    NASA Astrophysics Data System (ADS)

    Battaglia, Giuseppina

    2016-08-01

    In this review I will discuss the current status on determinations of the dark matter content and distribution in Milky Way dwarf spheroidals, for which the available data-sets allow the application of sophisticated mass modeling techniques.

  4. Voids of dark energy

    SciTech Connect

    Dutta, Sourish; Maor, Irit

    2007-03-15

    We investigate the clustering properties of a dynamical dark energy component. In a cosmic mix of a pressureless fluid and a light scalar field, we follow the linear evolution of spherical matter perturbations. We find that the scalar field tends to form underdensities in response to the gravitationally collapsing matter. We thoroughly investigate these voids for a variety of initial conditions, explain the physics behind their formation, and consider possible observational implications. Detection of dark energy voids will clearly rule out the cosmological constant as the main source of the present acceleration.

  5. Dark Energy and The Dark Matter Relic Abundance

    SciTech Connect

    Rosati, Francesca

    2004-11-17

    Two mechanisms by which the quintessence scalar could enhance the relic abundance of dark matter particles are discussed. These effects can have an impact on supersymmetric candidates for dark matter.

  6. The HAWC Sensitivity to Dark Matter Annihilation and Decay

    NASA Astrophysics Data System (ADS)

    Yapici, Tolga; HAWC Collaboration

    2016-03-01

    The High Altitude Water Cherenkov (HAWC) Observatory is an extensive air shower array in the state of Puebla, Mexico at an altitude of 4100m. The HAWC observatory will perform an indirect search for dark matter via GeV-TeV photons resulting from dark matter annihilation and decay, including annihilation from extended dark matter sources. We consider the HAWC sensitivity to a subset of the sources, including the M31 galaxy, the Virgo cluster, and the Galactic center. We simulate the HAWC response to gamma rays from the sources in well-motivated dark matter annihilation channels. We show the limits HAWC can place on the dark matter cross-section or lifetime from these sources if gamma-ray excess is not observed. In particular, for dark matter annihilating into gauge bosons, HAWC will be able to measure a narrow range of dark matter masses to cross-sections below that expected for a thermal relic. HAWC should also be sensitive to cross-sections higher than thermal for masses up to nearly 1000 TeV. HAWC will be sensitive to decaying dark matter for these masses as well. HAWC can explore higher dark matter masses than are currently constrained.

  7. Polytropic dark matter flows illuminate dark energy and accelerated expansion

    NASA Astrophysics Data System (ADS)

    Kleidis, K.; Spyrou, N. K.

    2015-04-01

    Currently, a large amount of data implies that the matter constituents of the cosmological dark sector might be collisional. An attractive feature of such a possibility is that, it can reconcile dark matter (DM) and dark energy (DE) in terms of a single component, accommodated in the context of a polytropic-DM fluid. In fact, polytropic processes in a DM fluid have been most successfully used in modeling dark galactic haloes, thus significantly improving the velocity dispersion profiles of galaxies. Motivated by such results, we explore the time evolution and the dynamical characteristics of a spatially-flat cosmological model, in which, in principle, there is no DE at all. Instead, in this model, the DM itself possesses some sort of fluidlike properties, i.e., the fundamental units of the Universe matter-energy content are the volume elements of a DM fluid, performing polytropic flows. In this case, together with all the other physical characteristics, we also take the energy of this fluid's internal motions into account as a source of the universal gravitational field. This form of energy can compensate for the extra energy, needed to compromise spatial flatness, namely, to justify that, today, the total energy density parameter is exactly unity. The polytropic cosmological model, depends on only one free parameter, the corresponding (polytropic) exponent, Γ. We find this model particularly interesting, because for Γ ≤ 0.541, without the need for either any exotic DE or the cosmological constant, the conventional pressure becomes negative enough so that the Universe accelerates its expansion at cosmological redshifts below a transition value. In fact, several physical reasons, e.g., the cosmological requirement for cold DM (CDM) and a positive velocity-of-sound square, impose further constraints on the value of Γ, which is eventually settled down to the range -0.089 < Γ ≤ 0. This cosmological model does not suffer either from the age problem or from the

  8. Models for SIMP dark matter and dark photon

    NASA Astrophysics Data System (ADS)

    Lee, Hyun Min; Seo, Min-Seok

    2016-06-01

    We give a review on the SIMP paradigm and discuss a consistent model for SIMP dark mesons in the context of a dark QCD with flavor symmetry. The Z'-portal interaction is introduced being compatible with stable dark mesons and is responsible for making the SIMP dark mesons remain in kinetic equilibrium with the SM during the freeze-out process. The SIMP parameter space of the Z' gauge boson can be probed by future collider and direct detection experiments.

  9. Dark energy and dark matter from primordial QGP

    SciTech Connect

    Vaidya, Vaishali Upadhyaya, G. K.

    2015-07-31

    Coloured relics servived after hadronization might have given birth to dark matter and dark energy. Theoretical ideas to solve mystery of cosmic acceleration, its origin and its status with reference to recent past are of much interest and are being proposed by many workers. In the present paper, we present a critical review of work done to understand the earliest appearance of dark matter and dark energy in the scenario of primordial quark gluon plasma (QGP) phase after Big Bang.

  10. Sensitivity of HAWC to high-mass dark matter annihilations

    NASA Astrophysics Data System (ADS)

    Abeysekara, A. U.; Alfaro, R.; Alvarez, C.; Álvarez, J. D.; Arceo, R.; Arteaga-Velázquez, J. C.; Ayala Solares, H. A.; Barber, A. S.; Baughman, B. M.; Bautista-Elivar, N.; Becerra Gonzalez, J.; Belmont, E.; BenZvi, S. Y.; Berley, D.; Bonilla Rosales, M.; Braun, J.; Caballero-Lopez, R. A.; Caballero-Mora, K. S.; Carramiñana, A.; Castillo, M.; Cotti, U.; Cotzomi, J.; de la Fuente, E.; De León, C.; DeYoung, T.; Diaz Hernandez, R.; Diaz-Cruz, L.; Díaz-Vélez, J. C.; Dingus, B. L.; DuVernois, M. A.; Ellsworth, R. W.; Fiorino, D. W.; Fraija, N.; Galindo, A.; Garfias, F.; González, M. M.; Goodman, J. A.; Grabski, V.; Gussert, M.; Hampel-Arias, Z.; Harding, J. P.; Hui, C. M.; Hüntemeyer, P.; Imran, A.; Iriarte, A.; Karn, P.; Kieda, D.; Kunde, G. J.; Lara, A.; Lauer, R. J.; Lee, W. H.; Lennarz, D.; León Vargas, H.; Linares, E. C.; Linnemann, J. T.; Longo, M.; Luna-Garcia, R.; Marinelli, A.; Martinez, H.; Martinez, O.; Martínez-Castro, J.; Matthews, J. A. J.; McEnery, J.; Mendoza Torres, E.; Miranda-Romagnoli, P.; Moreno, E.; Mostafá, M.; Nellen, L.; Newbold, M.; Noriega-Papaqui, R.; Oceguera-Becerra, T.; Patricelli, B.; Pelayo, R.; Pérez-Pérez, E. G.; Pretz, J.; Rivière, C.; Rosa-González, D.; Ryan, J.; Salazar, H.; Salesa, F.; Sanchez, F. E.; Sandoval, A.; Schneider, M.; Silich, S.; Sinnis, G.; Smith, A. J.; Sparks Woodle, K.; Springer, R. W.; Taboada, I.; Toale, P. A.; Tollefson, K.; Torres, I.; Ukwatta, T. N.; Villaseñor, L.; Weisgarber, T.; Westerhoff, S.; Wisher, I. G.; Wood, J.; Yodh, G. B.; Younk, P. W.; Zaborov, D.; Zepeda, A.; Zhou, H.; Abazajian, K. N.; Milagro Collaboration

    2014-12-01

    The High Altitude Water Cherenkov (HAWC) observatory is a wide field-of-view detector sensitive to gamma rays of 100 GeV to a few hundred TeV. Located in central Mexico at 19° North latitude and 4100 m above sea level, HAWC will observe gamma rays and cosmic rays with an array of water Cherenkov detectors. The full HAWC array is scheduled to be operational in Spring 2015. In this paper, we study the HAWC sensitivity to the gamma-ray signatures of high-mass (multi-TeV) dark matter annihilation. The HAWC observatory will be sensitive to diverse searches for dark matter annihilation, including annihilation from extended dark matter sources, the diffuse gamma-ray emission from dark matter annihilation, and gamma-ray emission from nonluminous dark matter subhalos. Here we consider the HAWC sensitivity to a subset of these sources, including dwarf galaxies, the M31 galaxy, the Virgo cluster, and the Galactic center. We simulate the HAWC response to gamma rays from these sources in several well-motivated dark matter annihilation channels. If no gamma-ray excess is observed, we show the limits HAWC can place on the dark matter cross section from these sources. In particular, in the case of dark matter annihilation into gauge bosons, HAWC will be able to detect a narrow range of dark matter masses to cross sections below thermal. HAWC should also be sensitive to nonthermal cross sections for masses up to nearly 1000 TeV. The constraints placed by HAWC on the dark matter cross section from known sources should be competitive with current limits in the mass range where HAWC has similar sensitivity. HAWC can additionally explore higher dark matter masses than are currently constrained.

  11. Proposal for Axion Dark Matter Detection Using an LC Circuit

    DOE PAGES

    Sikivie, P.; Sullivan, N.; Tanner, D. B.

    2014-03-01

    Here, we show that dark matter axions cause an oscillating electric current to flow along magnetic field lines. The oscillating current induced in a strong magnetic field B→ 0 produces a small magnetic field B→ a. We propose to amplify and detect B→ a using a cooled LC circuit and a very sensitive magnetometer. This appears to be a suitable approach to searching for axion dark matter in the 10–7 to 10–9 eV mass range.

  12. Nonthermal production of dark radiation and dark matter

    NASA Astrophysics Data System (ADS)

    Reece, Matthew; Roxlo, Thomas

    2016-09-01

    Dark matter may be coupled to dark radiation: light degrees of freedom that mediate forces between dark sector particles. Cosmological constraints favor dark radiation that is colder than Standard Model radiation. In models with fixed couplings between dark matter and the Standard Model, these constraints can be difficult to satisfy if thermal equilibrium is assumed in the early universe. We construct a model of asymmetric reheating of the visible and dark sectors from late decays of a long-lived particle (for instance, a modulus). We show, as a proof of principle, that such a model can populate a sufficiently cold dark sector while also generating baryon and dark matter asymmetries through the out-of-equilibrium decay. We frame much of our discussion in terms of the scenario of dissipative dark matter, as in the Double-Disk Dark Matter scenario. However, our results may also be of interest for other scenarios like the Twin Higgs model that are in danger of overproducing dark radiation due to nonnegligible dark-visible couplings.

  13. A Brief Analysis of Sister Carrie's Character

    ERIC Educational Resources Information Center

    Yu, Hanying

    2010-01-01

    Carrie is always dreaming while the rocking chair is rocking again and again, this is the deep impression on us after we read "Sister Carrie" which is the first novel of Theodore Dreiser. In this novel the protagonist Sister Carrie is a controversial person. This paper tries to analyze the character of Sister Carrie in order to find out…

  14. The Search for Dark Matter

    SciTech Connect

    Orrell, John

    2013-11-20

    More than 25 years ago, PNNL scientists began the first underground measurements searching for dark matter using specialized radiation detector technology. Dark matter is yet to be discovered says Physicist John L. Orrell.

  15. The Search for Dark Matter

    ScienceCinema

    Orrell, John

    2016-07-12

    More than 25 years ago, PNNL scientists began the first underground measurements searching for dark matter using specialized radiation detector technology. Dark matter is yet to be discovered says Physicist John L. Orrell.

  16. An ecological approach to problems of Dark Energy, Dark Matter, MOND and Neutrinos

    NASA Astrophysics Data System (ADS)

    Zhao, Hong Sheng

    2008-11-01

    Modern astronomical data on galaxy and cosmological scales have revealed powerfully the existence of certain dark sectors of fundamental physics, i.e., existence of particles and fields outside the standard models and inaccessible by current experiments. Various approaches are taken to modify/extend the standard models. Generic theories introduce multiple de-coupled fields A, B, C, each responsible for the effects of DM (cold supersymmetric particles), DE (Dark Energy) effect, and MG (Modified Gravity) effect respectively. Some theories use adopt vanilla combinations like AB, BC, or CA, and assume A, B, C belong to decoupled sectors of physics. MOND-like MG and Cold DM are often taken as antagnising frameworks, e.g. in the muddled debate around the Bullet Cluster. Here we argue that these ad hoc divisions of sectors miss important clues from the data. The data actually suggest that the physics of all dark sectors is likely linked together by a self-interacting oscillating field, which governs a chameleon-like dark fluid, appearing as DM, DE and MG in different settings. It is timely to consider an interdisciplinary approach across all semantic boundaries of dark sectors, treating the dark stress as one identity, hence accounts for several "coincidences" naturally.

  17. Dark matter on top

    SciTech Connect

    Gómez, M.A.; Jackson, C.B.; Shaughnessy, G. E-mail: chris@uta.edu

    2014-12-01

    We consider a simplified model of fermionic dark matter which couples exclusively to the right-handed top quark via a renormalizable interaction with a color-charged scalar. We first compute the relic abundance of this type of dark matter and investigate constraints placed on the model parameter space by the latest direct detection data. We also perform a detailed analysis for the production of dark matter at the LHC for this model. We find several kinematic variables that allow for a clean signal extraction and we show that the parameter space of this model will be well probed during LHC Run-II. Finally, we investigate the possibility of detecting this type of dark matter via its annihilations into gamma rays. We compute the continuum and the line emission (which includes a possible ''Higgs in Space!'' line) and its possible discovery by future gamma-ray telescopes. We find that the annihilation spectrum has distinctive features which may distinguish it from other models.

  18. Asymmetric condensed dark matter

    NASA Astrophysics Data System (ADS)

    Aguirre, Anthony; Diez-Tejedor, Alberto

    2016-04-01

    We explore the viability of a boson dark matter candidate with an asymmetry between the number densities of particles and antiparticles. A simple thermal field theory analysis confirms that, under certain general conditions, this component would develop a Bose-Einstein condensate in the early universe that, for appropriate model parameters, could survive the ensuing cosmological evolution until now. The condensation of a dark matter component in equilibrium with the thermal plasma is a relativistic process, hence the amount of matter dictated by the charge asymmetry is complemented by a hot relic density frozen out at the time of decoupling. Contrary to the case of ordinary WIMPs, dark matter particles in a condensate must be lighter than a few tens of eV so that the density from thermal relics is not too large. Big-Bang nucleosynthesis constrains the temperature of decoupling to the scale of the QCD phase transition or above. This requires large dark matter-to-photon ratios and very weak interactions with standard model particles.

  19. Dark Sky Scotland

    NASA Astrophysics Data System (ADS)

    Hillier, D.

    2008-06-01

    Dark Sky Scotland (DSS) 2006-2008 is a nationwide programme of public and educational astronomy events. It demonstrates successful national partnerships with non-astronomy organisations and effective ways of delivering events in remote rural communities. DSS is looking for international partners for IYA2009.

  20. Dark matter candidates

    SciTech Connect

    Turner, M.S.

    1989-01-01

    One of the simplest, yet most profound, questions we can ask about the Universe is, how much stuff is in it, and further what is that stuff composed of. Needless to say, the answer to this question has very important implications for the evolution of the Universe, determining both the ultimate fate and the course of structure formation. Remarkably, at this late date in the history of the Universe we still do not have a definitive answer to this simplest of questions---although we have some very intriguing clues. It is known with certainty that most of the material in the Universe is dark, and we have the strong suspicion that the dominant component of material in the Cosmos is not baryons, but rather is exotic relic elementary particles left over from the earliest, very hot epoch of the Universe. If true, the Dark Matter question is a most fundamental one facing both particle physics and cosmology. The leading particle dark matter candidates are: the axion, the neutralino, and a light neutrino species. All three candidates are accessible to experimental tests, and experiments are now in progress. In addition, there are several dark horse, long shot, candidates, including the superheavy magnetic monopole and soliton stars. 13 refs.

  1. Inflatable Dark Matter

    DOE PAGES

    Davoudiasl, Hooman; Hooper, Dan; McDermott, Samuel D.

    2016-01-22

    We describe a general scenario, dubbed “Inflatable Dark Matter”, in which the density of dark matter particles can be reduced through a short period of late-time inflation in the early universe. The overproduction of dark matter that is predicted within many otherwise well-motivated models of new physics can be elegantly remedied within this context, without the need to tune underlying parameters or to appeal to anthropic considerations. Thermal relics that would otherwise be disfavored can easily be accommodated within this class of scenarios, including dark matter candidates that are very heavy or very light. Furthermore, the non-thermal abundance of GUTmore » or Planck scale axions can be brought to acceptable levels, without invoking anthropic tuning of initial conditions. Additionally, a period of late-time inflation could have occurred over a wide range of scales from ~ MeV to the weak scale or above, and could have been triggered by physics within a hidden sector, with small but not necessarily negligible couplings to the Standard Model.« less

  2. FUV MAMA Dark Monitor

    NASA Astrophysics Data System (ADS)

    Cox, Colin

    2012-10-01

    The monitor takes six 1300s TIME-TAG darks every six weeks. The exposures are distributed over about six hours from initial turn-on to characterize the rate increase as a function of turn-on time and temperature. The frequency has been reduced from bi-weekly to once every six weeks to stay within a reasonable orbit count.

  3. NUV MAMA Dark Monitor

    NASA Astrophysics Data System (ADS)

    Cox, Colin

    2013-10-01

    The basic monitor takes two 1300s TIME-TAG darks bi-weekly.. The pairs of exposures are linked so that they are taken about 6 hours apart in the same SAA free interval. This pairing of exposures will make it easier to separate long and short term temporal variability from temperature dependent changes.

  4. FUV MAMA Dark Monitor

    NASA Astrophysics Data System (ADS)

    Cox, Colin

    2013-10-01

    The monitor takes six 1300s TIME-TAG darks every six weeks. The exposures are distributed over about six hours from initial turn-on to characterize the rate increase as a function of turn-on time and temperature.

  5. NUV MAMA Dark Monitor

    NASA Astrophysics Data System (ADS)

    Cox, Colin

    2012-10-01

    The basic monitor takes two 1300s TIME-TAG darks bi-weekly.. The pairs of exposures are linked so that they are taken about 6 hours apart in the same SAA free interval. This pairing of exposures will make it easier to separate long and short term temporal variability from temperature dependent changes.

  6. Dark matter detection

    NASA Astrophysics Data System (ADS)

    Baudis, Laura

    2016-08-01

    More than 80 years after its first postulation in modern form, the existence and distribution of dark matter in our Universe is well established. Dark matter is the gravitational glue that holds together galaxies, galaxy clusters and structures on the largest cosmological scales, and an essential component to explain the observed fluctuations in the cosmic microwave background. Yet its existence is inferred indirectly, through its gravitational influence on luminous matter, and its nature is not known. A viable hypothesis is that dark matter is made of new, elementary particles, with allowed masses and interaction strengths spanning a wide range. Two well-motivated classes of candidates are axions and weakly interacting massive particles (WIMPs), and experimental efforts have now reached sensitivities that allow them to test this hypothesis. Axions, produced non-thermally in the early Universe, can be detected by exploiting their predicted couplings to photons and electrons. WIMPs can be detected directly by looking for their collisions with atomic nuclei ultra-low background detectors, or indirectly, through the observation of their annihilation products such as neutrinos, gamma rays, positrons and antiprotons over the astrophysical background. A complementary method is the production of dark matter particles at colliders such as the Large Hadron Collider, where they could be observed indirectly via missing transverse energy, or via associated particle production. I will review the main experimental efforts to search for dark matter particles, and the existing constraints on the interaction cross sections. I will also discuss future experiments, their complementarity and their ability to measure the properties of these particles.

  7. How dark chocolate is processed

    Technology Transfer Automated Retrieval System (TEKTRAN)

    This month’s column will continue the theme of “How Is It Processed?” The column will focus on dark chocolate. The botanical name for the cacao tree is Theobroma cacao, which literally means “food of the Gods.” Dark chocolate is both delicious and nutritious. Production of dark chocolate will be des...

  8. Quantum Dynamics of Dark and Dark-Bright Solitons beyond the Mean-Field Approximation

    NASA Astrophysics Data System (ADS)

    Krönke, Sven; Schmelcher, Peter

    2014-05-01

    Dark solitons are well-known excitations in one-dimensional repulsively interacting Bose-Einstein condensates, which feature a characteristical phase-jump across a density dip and form stability in the course of their dynamics. While these objects are stable within the celebrated Gross-Pitaevskii mean-field theory, the situation changes dramatically in the full many-body description: The condensate being initially in a dark soliton state dynamically depletes and the density notch fills up with depleted atoms. We analyze this process in detail with a particular focus on two-body correlations and the fate of grey solitons (dark solitons with finite density in the notch) and thereby complement the existing results in the literature. Moreover, we extend these studies to mixtures of two repulsively interacting bosonic species with a dark-bright soliton (dark soliton in one component filled with localized atoms of the other component) as the initial state. All these many-body quantum dynamics simulations are carried out with the recently developed multi-layer multi-configuration time-dependent Hartree method for bosons (ML-MCTDHB).

  9. Dark matter and dark energy: summary and future directions.

    PubMed

    Ellis, John

    2003-11-15

    This paper reviews the progress reported at the Discussion Meeting and advertises some possible future directions in our drive to understand dark matter and dark energy. Additionally, a first attempt is made to place in context the exciting new results from the Wilkinson Microwave Anisotropy Probe satellite, which were published shortly after this meeting. In the first part of this paper, pieces of observational evidence shown here that bear on the amounts of dark matter and dark energy are reviewed. Subsequently, particle candidates for dark matter are mentioned, and detection strategies are discussed. Finally, ideas are presented for calculating the amounts of dark matter and dark energy, and possibly relating them to laboratory data.

  10. Extended gamma-ray emission from Coy Dark Matter

    SciTech Connect

    Boehm, Céline; McCabe, Christopher; Spannowsky, Michael; Wallace, Chris J.; Dolan, Matthew J. E-mail: mdolan@slac.stanford.edu E-mail: michael.spannowsky@durham.ac.uk

    2014-05-01

    We show that it is possible for WIMP dark matter to produce a large signal in indirect dark matter searches without producing signals elsewhere. We illustrate our point by fitting the Fermi-LAT extended galactic gamma-ray excess with a simple model of Dirac dark matter that annihilates primarily into b quarks via a pseudoscalar. Current collider constraints are weak while the 14 TeV LHC run will constrain a limited portion of the parameter space. No signal is expected in additional indirect searches or at future direct detection experiments. Our results emphasise the importance of fully understanding potential indirect signals of dark matter as they may provide the only information about the dark matter particle.

  11. Predictions of hydrodynamic simulations for direct dark matter detection

    NASA Astrophysics Data System (ADS)

    Bozorgnia, Nassim; Calore, Francesca; Schaller, Matthieu; Lovell, Mark; Bertone, Gianfranco; Frenk, Carlos S.; Crain, Robert A.; Navarro, Julio F.; Schaye, Joop; Theuns, Tom

    2016-05-01

    We study the effects of galaxy formation on dark matter direct detection using hydrodynamic simulations obtained from the “Evolution and Assembly of GaLaxies and their Environments” (EAGLE) and APOSTLE projects. We extract the local dark matter density and velocity distribution of the simulated Milky Way analogues, and use them directly to perform an analysis of current direct detection data. The local dark matter density of the Milky Way-like galaxies is 0.41–0.73 GeV/cm3, and a Maxwellian distribution (with best fit peak speed of 223–289 km/s) describes well the local dark matter speed distribution. We find that the consistency between the result of different direct detection experiments cannot be improved by using the dark matter distribution of the simulated haloes.

  12. The Cryogenic Dark Matter Search

    NASA Astrophysics Data System (ADS)

    Sander, Joel

    2004-05-01

    The Cryogenic Dark Matter Search (CDMS) is an experiment to search for Weakly Interacting Massive Particles (WIMPs). The experiment initially was deployed at a shallow underground site, and is currently deployed at a deep underground site at the Soudan Mine in Minnesota. The detectors operate at cryogenic temperature, and are capable of distinguishing nuclear recoils from WIMP interactions from various backgrounds. The detectors are shielded from background by both active and passive elements. We will describe the components of the overall experiment, and focus on the novel data acquisition system that has been develop to control and monitor the experiment via the World Wide Web. Preliminary signals from the operation at Soudan will be discussed.

  13. Dark energy in hybrid inflation

    SciTech Connect

    Gong, Jinn-Ouk; Kim, Seongcheol

    2007-03-15

    The situation that a scalar field provides the source of the accelerated expansion of the Universe while rolling down its potential is common in both the simple models of the primordial inflation and the quintessence-based dark energy models. Motivated by this point, we address the possibility of causing the current acceleration via the primordial inflation using a simple model based on hybrid inflation. We trigger the onset of the motion of the quintessence field via the waterfall field, and find that the fate of the Universe depends on the true vacuum energy determined by choosing the parameters. We also briefly discuss the variation of the equation of state and the possible implementation of our scenario in supersymmetric theories.

  14. Organic Species in Infrared Dark Clouds

    NASA Astrophysics Data System (ADS)

    Vasyunina, T.; Vasyunin, A. I.; Herbst, Eric; Linz, Hendrik; Voronkov, Maxim; Britton, Tui; Zinchenko, Igor; Schuller, Frederic

    2014-01-01

    It is currently assumed that infrared dark clouds (IRDCs) represent the earliest evolutionary stages of high-mass stars (>8 M ⊙). Submillimeter and millimeter-wave studies performed over the past 15 yr show that IRDCs possess a broad variety of properties, and hence a wide range of problems and questions that can be tackled. In this paper, we report an investigation of the molecular composition and chemical processes in two groups of IRDCs. Using the Mopra, APEX, and IRAM radio telescopes over the last four years, we have collected molecular line data for CO, H2CO, HNCO, CH3CCH, CH3OH, CH3CHO, CH3OCHO, and CH3OCH3. For all of these species we estimated molecular abundances. We then undertook chemical modeling studies, concentrating on the source IRDC028.34+0.06, and compared observed and modeled abundances. This comparison showed that to reproduce observed abundances of complex organic molecules, a zero-dimensional gas-grain model with constant physical conditions is not sufficient. We achieved greater success with the use of a warm-up model, in which warm-up from 10 K to 30 K occurs following a cold phase. Based on observations carried out with the IRAM 30 m Telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany) and IGN (Spain). This publication is based on data acquired with the Atacama Pathfinder Experiment (APEX). APEX is a collaboration between the Max-Planck-Institut für Radioastronomie, the European Southern Observatory, and the Onsala Space Observatory. The 22 m Mopra antenna is part of the Australia Telescope, which is funded by the Commonwealth of Australia for operations as a National Facility managed by CSIRO. The University of New South Wales Digital Filter Bank used for the observations with the Mopra Telescope was provided with support from the Australian Research Council.

  15. Taking on Titan: Meet Carrie Anderson

    NASA Video Gallery

    When she was a little girl, Carrie Anderson dreamed of becoming an astronomer. Now, as a space scientist at NASA Goddard Space Flight Center, Carrie studies the atmosphere on Titan: one of Saturn's...

  16. Global carrying capacity: how many people?

    PubMed

    1992-07-01

    During 1980-85 energy consumption in developing countries increased by 22%, of which 50% was used to maintain current levels of use and 50% pertained to real economic growth. Commercial energy consumption during 1970-89 tripled in developing countries. Population growth alone is expected to increase world energy consumption from the current 13.5 terawatts (13.5 trillion watts) to 18 terawatts by 2025 at the same level of use. The increased level of consumption (4.5 terawatts) is the equivalent of total current commercial energy consumption. One terawatt is equal to energy use from 5 billion barrels of oil yearly, 1 billion tons of coal, or 1.6 billion tons of wood. Economic development will require even greater levels of energy use. Since the oil price increases of the 1970s, developed countries increased their energy consumption by about 33%, even while becoming more fuel efficient. During 1990-2025, if developing countries double their per capita energy use and developed countries reduce their use by 50%, world energy consumption will still be almost 21 terawatts. If consumption remains constant at current levels without any population increase, the oil supply will be exhausted in 40 years. Coal consumption will last hundreds of years but air pollution will worsen, and global warming will be accelerated. Developed countries, which are wealthier, are having difficulty switching to non-fossil fuels, and the prospects for developing countries pose even greater challenges. Slowing growth buys time for technological development. World population is expected to reach 8 billion by 2020. Stabilization of growth at 8 billion would occur only if world fertility averages 1.7 children per woman by 2025. One opinion is that the carrying capacity has been reached with the present population of 5.4 billion. Others say that with changes in consumption and technological developments the earth can sustain 8 billion people. The physical limits are 1) the finite capacity of natural

  17. Complex Dark Matter

    ScienceCinema

    Lincoln, Don

    2016-07-12

    After a century of study, scientists have come to the realization that the ordinary matter made of atoms is a minority in the universe. In order to explain observations, it appears that there exists a new and undiscovered kind of matter, called dark matter, that is five times more prevalent than ordinary matter. The evidence for this new matter’s existence is very strong, but scientists know only a little about its nature. In today’s video, Fermilab’s Dr. Don Lincoln talks about an exciting and unconventional idea, specifically that dark matter might have a very complex set of structures and interactions. While this idea is entirely speculative, it is an interesting hypothesis and one that scientists are investigating.

  18. Methanol in dark clouds

    NASA Technical Reports Server (NTRS)

    Friberg, P.; Hjalmarson, A.; Madden, S. C.; Irvine, W. M.

    1988-01-01

    The first observation of methanol in cold dark clouds TMC 1, L 134 N, and B 335 is reported. In all three clouds, the relative abundance of methanol was found to be in the range of 10 to the -9th (i.e., almost an order of magnitude more abundant than acetaldehyde), with no observable variation between the clouds. Methanol emission showed a complex velocity structure; in TMC 1, clear indications of non-LTE were observed. Dimethyl ether was searched for in L 134 N; the upper limit of the column density of dimethyl ether in L 134 N was estimated to be 4 x 10 to the 12th/sq cm, assuming 5 K rotation temperature and LTE. This limit makes the abundance ratio (CH3)2O/CH3OH not higher than 1/5, indicating that dimethyl ether is not overabundant in this dark cloud.

  19. Temporal dark polariton solitons.

    PubMed

    Kartashov, Yaroslav V; Skryabin, Dmitry V

    2016-04-15

    We predict that strong coupling between waveguide photons and excitons of quantum well embedded into waveguide results in the formation of hybrid-dark and antidark light-matter solitons. Such temporal solitons exist due to interplay between repulsive excitonic nonlinearity and giant group-velocity dispersion arising in the vicinity of excitonic resonance. Such fully conservative states do not require external pumping to counteract losses and form continuous families parameterized by the power-dependent phase shift and velocity of their motion. Dark solitons are stable in the considerable part of their existence domain, while antidark solitons are always unstable. Both families exist outside the forbidden frequency gap of the linear system. PMID:27082338

  20. Dark Skies Rangers

    NASA Astrophysics Data System (ADS)

    Doran, Rosa

    2015-08-01

    Creating awareness about the importance of the protection of our dark skies is the main goal of the Dark Skies Rangers project, a joint effort from the NOAO and the Galileo Teacher Training Program. Hundreds of schools and thousands of students have been reached by this program. We will focus in particular on the experience being developed in Portugal where several municipalities have now received street light auditing produced by students with suggestions on how to enhance the energy efficiency of illumination of specific urban areas. In the International Year of Light we are investing our efforts in exporting the successful Portuguese experience to other countries. The recipe is simple: train teachers, engage students, foster the participation of local community and involve local authorities in the process. In this symposium we hope to draft the cookbook for the near future.

  1. Complex Dark Matter

    SciTech Connect

    Lincoln, Don

    2015-04-16

    After a century of study, scientists have come to the realization that the ordinary matter made of atoms is a minority in the universe. In order to explain observations, it appears that there exists a new and undiscovered kind of matter, called dark matter, that is five times more prevalent than ordinary matter. The evidence for this new matter’s existence is very strong, but scientists know only a little about its nature. In today’s video, Fermilab’s Dr. Don Lincoln talks about an exciting and unconventional idea, specifically that dark matter might have a very complex set of structures and interactions. While this idea is entirely speculative, it is an interesting hypothesis and one that scientists are investigating.

  2. Distance to Dark Bodies

    NASA Technical Reports Server (NTRS)

    2007-01-01

    Using the unique orbit of NASA's Spitzer Space Telescope and a depth-perceiving trick called parallax, astronomers have determined the distance to an invisible Milky Way object called OGLE-2005-SMC-001. This artist's concept illustrates how this trick works: different views from both Spitzer and telescopes on Earth are combined to give depth perception.

    Our Milky Way galaxy is heavier than it looks, and scientists use the term 'dark matter' to describe all the 'heavy stuff' in the universe that seems to be present but invisible to our telescopes. While much of this dark matter is likely made up of exotic materials, different from the ordinary particles that make up the world around us, some may consist of dark celestial bodies -- like planets, black holes, or failed stars -- that do not produce light or are too faint to detect from Earth. OGLE-2005-SMC-001 is one of these dark celestial bodies.

    Although astronomers cannot see a dark body, they can sense its presence from the way light acts around it. When a dark body like OGLE-2005-SMC-001 passes in front of a bright star, its gravity causes the background starlight to bend and brighten, a process called gravitational microlensing. When the observing telescope, dark body, and star system are closely aligned, the microlensing event reaches maximum, or peak, brightness.

    A team of astronomers first sensed OGLE-2005-SMC-001's presence when it passed in front of a star in a neighboring satellite galaxy called the Small Magellanic Cloud. In this artist's rendering, the satellite galaxy is depicted as the fuzzy structure sitting to the left of Earth. Once they detected this microlensing event, the scientists used Spitzer and the principle of parallax to figure out its distance. Humans naturally use parallax to determine distance. Each eye sees the distance of an object differently. The brain takes each eye's perspective and instantaneously calculates how far away the object is.

    To determine OGLE

  3. Dark Matter Decays from Nonminimal Coupling to Gravity.

    PubMed

    Catà, Oscar; Ibarra, Alejandro; Ingenhütt, Sebastian

    2016-07-01

    We consider the standard model extended with a dark matter particle in curved spacetime, motivated by the fact that the only current evidence for dark matter is through its gravitational interactions, and we investigate the impact on the dark matter stability of terms in the Lagrangian linear in the dark matter field and proportional to the Ricci scalar. We show that this "gravity portal" induces decay even if the dark matter particle only has gravitational interactions, and that the decay branching ratios into standard model particles only depend on one free parameter: the dark matter mass. We study in detail the case of a singlet scalar as a dark matter candidate, which is assumed to be absolutely stable in flat spacetime due to a discrete Z_{2} symmetry, but which may decay in curved spacetimes due to a Z_{2}-breaking nonminimal coupling to gravity. We calculate the dark matter decay widths and we set conservative limits on the nonminimal coupling parameter from experiments. The limits are very stringent and suggest that there must exist an additional mechanism protecting the singlet scalar from decaying via this gravity portal. PMID:27447497

  4. Dark Matter Decays from Nonminimal Coupling to Gravity.

    PubMed

    Catà, Oscar; Ibarra, Alejandro; Ingenhütt, Sebastian

    2016-07-01

    We consider the standard model extended with a dark matter particle in curved spacetime, motivated by the fact that the only current evidence for dark matter is through its gravitational interactions, and we investigate the impact on the dark matter stability of terms in the Lagrangian linear in the dark matter field and proportional to the Ricci scalar. We show that this "gravity portal" induces decay even if the dark matter particle only has gravitational interactions, and that the decay branching ratios into standard model particles only depend on one free parameter: the dark matter mass. We study in detail the case of a singlet scalar as a dark matter candidate, which is assumed to be absolutely stable in flat spacetime due to a discrete Z_{2} symmetry, but which may decay in curved spacetimes due to a Z_{2}-breaking nonminimal coupling to gravity. We calculate the dark matter decay widths and we set conservative limits on the nonminimal coupling parameter from experiments. The limits are very stringent and suggest that there must exist an additional mechanism protecting the singlet scalar from decaying via this gravity portal.

  5. Searching for light dark matter with the SLAC millicharge experiment.

    PubMed

    Diamond, M; Schuster, P

    2013-11-27

    New sub-GeV gauge forces ("dark photons") that kinetically mix with the photon provide a promising scenario for MeV-GeV dark matter and are the subject of a program of searches at fixed-target and collider facilities around the world. In such models, dark photons produced in collisions may decay invisibly into dark-matter states, thereby evading current searches. We reexamine results of the SLAC mQ electron beam dump experiment designed to search for millicharged particles and find that it was strongly sensitive to any secondary beam of dark matter produced by electron-nucleus collisions in the target. The constraints are competitive for dark photon masses in the ~1-30 MeV range, covering part of the parameter space that can reconcile the apparent (g-2)(μ) anomaly. Simple adjustments to the original SLAC search for millicharges may extend sensitivity to cover a sizable portion of the remaining (g-2)(μ) anomaly-motivated region. The mQ sensitivity is therefore complementary to ongoing searches for visible decays of dark photons. Compared to existing direct-detection searches, mQ sensitivity to electron-dark-matter scattering cross sections is more than an order of magnitude better for a significant range of masses and couplings in simple models.

  6. Natural Neutrino Dark Energy

    SciTech Connect

    Gurwich, Ilya

    2010-06-23

    1 construct a general description for neutrino dark energy models, that do not require exotic particles or strange couplings. With the help of the above, this class of models is reduced to a single function with several constraints. It is shown that these models lead to some concrete predictions that can be verified (or disproved) within the next decade, using results from PLANK, EUCLID and JDEM.

  7. Dark energy from QCD

    SciTech Connect

    Urban, Federico R.; Zhitnitsky, Ariel R.

    2010-08-30

    We review two mechanisms rooted in the infrared sector of QCD which, by exploiting the properties of the QCD ghost, as introduced by Veneziano, provide new insight on the cosmological dark energy problem, first, in the form of a Casimir-like energy from quantising QCD in a box, and second, in the form of additional, time-dependent, vacuum energy density in an expanding universe. Based on [1, 2].

  8. THE DARK MOLECULAR GAS

    SciTech Connect

    Wolfire, Mark G.; Hollenbach, David; McKee, Christopher F. E-mail: dhollenbach@seti.or

    2010-06-20

    The mass of molecular gas in an interstellar cloud is often measured using line emission from low rotational levels of CO, which are sensitive to the CO mass, and then scaling to the assumed molecular hydrogen H{sub 2} mass. However, a significant H{sub 2} mass may lie outside the CO region, in the outer regions of the molecular cloud where the gas-phase carbon resides in C or C{sup +}. Here, H{sub 2} self-shields or is shielded by dust from UV photodissociation, whereas CO is photodissociated. This H{sub 2} gas is 'dark' in molecular transitions because of the absence of CO and other trace molecules, and because H{sub 2} emits so weakly at temperatures 10 K dark mass and find that the fraction of the molecular mass in this dark component is remarkably constant ({approx}0.3 for average visual extinction through the cloud A-bar{sub V{approx_equal}}8) and insensitive to the incident ultraviolet radiation field strength, the internal density distribution, and the mass of the molecular cloud as long as A-bar{sub V}, or equivalently, the product of the average hydrogen nucleus column and the metallicity through the cloud, is constant. We also find that the dark mass fraction increases with decreasing A-bar{sub V}, since relatively more molecular H{sub 2} material lies outside the CO region in this case.

  9. Stealth dark matter: Dark scalar baryons through the Higgs portal

    NASA Astrophysics Data System (ADS)

    Appelquist, T.; Brower, R. C.; Buchoff, M. I.; Fleming, G. T.; Jin, X.-Y.; Kiskis, J.; Kribs, G. D.; Neil, E. T.; Osborn, J. C.; Rebbi, C.; Rinaldi, E.; Schaich, D.; Schroeder, C.; Syritsyn, S.; Vranas, P.; Weinberg, E.; Witzel, O.; Lattice Strong Dynamics LSD Collaboration

    2015-10-01

    We present a new model of stealth dark matter: a composite baryonic scalar of an S U (ND) strongly coupled theory with even ND≥4 . All mass scales are technically natural, and dark matter stability is automatic without imposing an additional discrete or global symmetry. Constituent fermions transform in vectorlike representations of the electroweak group that permit both electroweak-breaking and electroweak-preserving mass terms. This gives a tunable coupling of stealth dark matter to the Higgs boson independent of the dark matter mass itself. We specialize to S U (4 ), and investigate the constraints on the model from dark meson decay, electroweak precision measurements, basic collider limits, and spin-independent direct detection scattering through Higgs exchange. We exploit our earlier lattice simulations that determined the composite spectrum as well as the effective Higgs coupling of stealth dark matter in order to place bounds from direct detection, excluding constituent fermions with dominantly electroweak-breaking masses. A lower bound on the dark baryon mass mB≳300 GeV is obtained from the indirect requirement that the lightest dark meson not be observable at LEP II. We briefly survey some intriguing properties of stealth dark matter that are worthy of future study, including collider studies of dark meson production and decay; indirect detection signals from annihilation; relic abundance estimates for both symmetric and asymmetric mechanisms; and direct detection through electromagnetic polarizability, a detailed study of which will appear in a companion paper.

  10. 7 CFR 1437.402 - Carrying capacity.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 7 Agriculture 10 2010-01-01 2010-01-01 false Carrying capacity. 1437.402 Section 1437.402... have a positive impact on the forage's carrying capacity in the crop year NAP assistance is requested... and such practices can be expected to have a positive impact on the forage's carrying capacity in...

  11. 7 CFR 1437.402 - Carrying capacity.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... 7 Agriculture 10 2014-01-01 2014-01-01 false Carrying capacity. 1437.402 Section 1437.402... Determining Coverage of Forage Intended for Animal Consumption § 1437.402 Carrying capacity. (a) CCC will establish a carrying capacity for all grazed forage present in the county for purposes of administering...

  12. 7 CFR 1437.402 - Carrying capacity.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... 7 Agriculture 10 2013-01-01 2013-01-01 false Carrying capacity. 1437.402 Section 1437.402... Determining Coverage of Forage Intended for Animal Consumption § 1437.402 Carrying capacity. (a) CCC will establish a carrying capacity for all grazed forage present in the county for purposes of administering...

  13. 7 CFR 1437.402 - Carrying capacity.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... 7 Agriculture 10 2012-01-01 2012-01-01 false Carrying capacity. 1437.402 Section 1437.402... Determining Coverage of Forage Intended for Animal Consumption § 1437.402 Carrying capacity. (a) CCC will establish a carrying capacity for all grazed forage present in the county for purposes of administering...

  14. Dark matter axions revisited

    NASA Astrophysics Data System (ADS)

    Visinelli, Luca; Gondolo, Paolo

    2009-08-01

    We study for what specific values of the theoretical parameters the axion can form the totality of cold dark matter. We examine the allowed axion parameter region in the light of recent data collected by the WMAP5 mission plus baryon acoustic oscillations and supernovae, and assume an inflationary scenario and standard cosmology. We also upgrade the treatment of anharmonicities in the axion potential, which we find important in certain cases. If the Peccei-Quinn symmetry is restored after inflation, we recover the usual relation between axion mass and density, so that an axion mass ma=(85±3)μeV makes the axion 100% of the cold dark matter. If the Peccei-Quinn symmetry is broken during inflation, the axion can instead be 100% of the cold dark matter for ma<15meV provided a specific value of the initial misalignment angle θi is chosen in correspondence to a given value of its mass ma. Large values of the Peccei-Quinn symmetry breaking scale correspond to small, perhaps uncomfortably small, values of the initial misalignment angle θi.

  15. Unparticle dark energy

    SciTech Connect

    Dai, D.-C.; Stojkovic, Dejan; Dutta, Sourish

    2009-09-15

    We examine a dark energy model where a scalar unparticle degree of freedom plays the role of quintessence. In particular, we study a model where the unparticle degree of freedom has a standard kinetic term and a simple mass potential, the evolution is slowly rolling and the field value is of the order of the unparticle energy scale ({lambda}{sub u}). We study how the evolution of w depends on the parameters B (a function of unparticle scaling dimension d{sub u}), the initial value of the field {phi}{sub i} (or equivalently, {lambda}{sub u}) and the present matter density {omega}{sub m0}. We use observational data from type Ia supernovae, baryon acoustic oscillations and the cosmic microwave background to constrain the model parameters and find that these models are not ruled out by the observational data. From a theoretical point of view, unparticle dark energy model is very attractive, since unparticles (being bound states of fundamental fermions) are protected from radiative corrections. Further, coupling of unparticles to the standard model fields can be arbitrarily suppressed by raising the fundamental energy scale M{sub F}, making the unparticle dark energy model free of most of the problems that plague conventional scalar field quintessence models.

  16. The First dark microhalos

    SciTech Connect

    Zhao, HongSheng; Taylor, James E.; Silk, Joseph; Hooper, Dan; /Oxford U. /Fermilab

    2005-08-01

    Earth-mass dark matter halos are likely to have been the first bound structures to form in the Universe. Whether such objects have survived to the present day in galaxies depends on, among other factors, the rate of encounters with normal stars. In this letter, we estimate the amount of tidal heating and mass loss in microhalos as a result of stellar encounters. We find that while microhalos are only mildly heated in dwarf galaxies of low stellar density, and they should have been completely destroyed in bulge or M32-like regions of high stellar density. In disk galaxies, such as the Milky Way, the disruption rate depends strongly on the orbital parameters of the microhalo; while stochastic radial orbits in triaxial Galactic potential are destroyed first, systems on non-planar retrograde orbits with large pericenters survive the longest. Since many microhalos lose a significant fraction of their material to unbound tidal streams, the final dark matter distribution in the solar neighborhood is better described as a superposition of microstreams rather than as a set of discrete spherical clumps in an otherwise homogeneous medium. Different morphologies of microhalos have implications for direct and indirect dark matter detection experiments.

  17. Perspectives for Dark Photon physics at MESA

    NASA Astrophysics Data System (ADS)

    Denig, Achim

    2015-04-01

    At the Institute of Nuclear Physics in Mainz the new high-intensity electron accelerator MESA (Mainz Energy-Recovering Superconducting Accelerator) is currently being constructed. We report on opportunities regarding Dark Photon physics at this facility. The intensive MESA beam of 155 MeV and 1 mA of beam current in combination with an internal gas target offers a unique and clean environment for electron scattering experiments. We also report on the status of the MAGIX dual-arm spectrometer setup, which can be used for those measurements. Furthermore, we also comment on opportunities for a beam dump experiment at MESA, which would search for dark matter particles directly. This work is supported by DFG through Collaborative Research Center CRC-1044.

  18. Analyzing the Discovery Potential for Light Dark Matter.

    PubMed

    Izaguirre, Eder; Krnjaic, Gordan; Schuster, Philip; Toro, Natalia

    2015-12-18

    In this Letter, we determine the present status of sub-GeV thermal dark matter annihilating through standard model mixing, with special emphasis on interactions through the vector portal. Within representative simple models, we carry out a complete and precise calculation of the dark matter abundance and of all available constraints. We also introduce a concise framework for comparing different experimental approaches, and use this comparison to identify important ranges of dark matter mass and couplings to better explore in future experiments. The requirement that dark matter be a thermal relic sets a sharp sensitivity target for terrestrial experiments, and so we highlight complementary experimental approaches that can decisively reach this milestone sensitivity over the entire sub-GeV mass range. PMID:26722912

  19. Analyzing the Discovery Potential for Light Dark Matter.

    PubMed

    Izaguirre, Eder; Krnjaic, Gordan; Schuster, Philip; Toro, Natalia

    2015-12-18

    In this Letter, we determine the present status of sub-GeV thermal dark matter annihilating through standard model mixing, with special emphasis on interactions through the vector portal. Within representative simple models, we carry out a complete and precise calculation of the dark matter abundance and of all available constraints. We also introduce a concise framework for comparing different experimental approaches, and use this comparison to identify important ranges of dark matter mass and couplings to better explore in future experiments. The requirement that dark matter be a thermal relic sets a sharp sensitivity target for terrestrial experiments, and so we highlight complementary experimental approaches that can decisively reach this milestone sensitivity over the entire sub-GeV mass range.

  20. Carry it on the bad side!

    PubMed

    Tan, V; Klotz, M J; Greenwald, A S; Steinberg, M E

    1998-10-01

    Patients with diseased hips often must carry objects while walking, yet they are rarely instructed which hand to use because little has been published on the subject. We sought to evaluate the situation mathematically by determining the hip forces that result when a load is carried in the ipsilateral versus the contralateral hand. Using a free-body diagram of single-leg supported stance, we found that when a load was carried in the contralateral hand, the resultant forces on the hip were increased considerably. Conversely, when the weight was carried in the ipsilateral hand, the forces were actually lower than when no weight was carried at all. Thus, carrying a weight on the opposite side resulted in hip forces that were substantially greater than when the weight was carried on the same side. PMID:9796709

  1. Dogs steal in the dark.

    PubMed

    Kaminski, Juliane; Pitsch, Andrea; Tomasello, Michael

    2013-05-01

    All current evidence of visual perspective taking in dogs can possibly be explained by dogs reacting to certain stimuli rather than understanding what others see. In the current study, we set up a situation in which contextual information and social cues are in conflict. A human always forbade the dog from taking a piece of food. The part of the room being illuminated was then varied, for example, either the area where the human was seated or the area where the food was located was lit. Results show that dogs steal significantly more food when it is dark compared to when it is light. While stealing forbidden food the dog's behaviour also depends on the type of illumination in the room. Illumination around the food, but not the human, affected the dogs' behaviour. This indicates that dogs do not take the sight of the human as a signal to avoid the food. It also cannot be explained by a low-level associative rule of avoiding illuminated food which dogs actually approach faster when they are in private. The current finding therefore raises the possibility that dogs take into account the human's visual access to the food while making their decision to steal it.

  2. Planet Nine, dark matter and MOND

    NASA Astrophysics Data System (ADS)

    Sivaram, C.; Kenath, Arun; Kiren, O. V.

    2016-07-01

    Here we propose the possibility that the recently postulated Neptune-sized planet with an orbital period of 15,000 years could be a gravitationally condensed dark matter (DM) object. The observed mass of Planet Nine fits with the theoretical mass predicted for such DM objects formed by 60 GeV DM particles, which is the currently favoured DM particles. This object could also provide us with a testing ground for modification of Newtonian dynamics.

  3. FAST TRACK COMMUNICATION: A dark energy multiverse

    NASA Astrophysics Data System (ADS)

    Robles-Pérez, Salvador; Martín-Moruno, Prado; Rozas-Fernández, Alberto; González-Díaz, Pedro F.

    2007-05-01

    We present cosmic solutions corresponding to universes filled with dark and phantom energy, all having a negative cosmological constant. All such solutions contain infinite singularities, successively and equally distributed along time, which can be either big bang/crunches or big rips singularities. Classically these solutions can be regarded as associated with multiverse scenarios, being those corresponding to phantom energy that may describe the current accelerating universe.

  4. Unified dark energy-dark matter model with inverse quintessence

    SciTech Connect

    Ansoldi, Stefano; Guendelman, Eduardo I. E-mail: guendel@bgu.ac.il

    2013-05-01

    We consider a model where both dark energy and dark matter originate from the coupling of a scalar field with a non-canonical kinetic term to, both, a metric measure and a non-metric measure. An interacting dark energy/dark matter scenario can be obtained by introducing an additional scalar that can produce non constant vacuum energy and associated variations in dark matter. The phenomenology is most interesting when the kinetic term of the additional scalar field is ghost-type, since in this case the dark energy vanishes in the early universe and then grows with time. This constitutes an ''inverse quintessence scenario'', where the universe starts from a zero vacuum energy density state, instead of approaching it in the future.

  5. Significant enhancement of neutralino dark matter annihilation from electroweak bremsstrahlung.

    PubMed

    Bringmann, Torsten; Calore, Francesca

    2014-02-21

    Indirect searches for the cosmological dark matter have become ever more competitive during the past years. Here, we report the first full calculation of leading electroweak corrections to the annihilation rate of supersymmetric neutralino dark matter. We find that these corrections can be huge, partially due to contributions that have been overlooked so far. Our results imply a significantly enhanced discovery potential of this well motivated dark matter candidate with current and upcoming cosmic ray experiments, in particular for gamma rays and models with somewhat small annihilation rates at the tree level.

  6. SUSY dark matter and non-universal gaugino masses

    SciTech Connect

    Birkedal-Hansen, Andreas

    2002-04-15

    In this talk the authors investigate the dark matter prospects for supersymmetric models with non-universal gaugino masses. They motivate the use of non-universal gaugino masses from several directions, including problems, with the current favorite scenario, the cMSSM. They then display new corridors of parameter space that allow an acceptable dark matter relic density once gaugino mass universality is relaxed. They finish with a specific string-derived model that allows this universality relaxation and then use the dark matter constraint to make specific statements about the hidden sector of the model.

  7. Exothermic double-disk dark matter

    SciTech Connect

    McCullough, Matthew; Randall, Lisa E-mail: randall@physics.harvard.edu

    2013-10-01

    If a subdominant component of dark matter (DM) interacts via long-range dark force carriers it may cool and collapse to form complex structures within the Milky Way galaxy, such as a rotating dark disk. This scenario was proposed recently and termed ''Double-Disk Dark Matter'' (DDDM). In this paper we consider the possibility that DDDM remains in a cosmologically long-lived excited state and can scatter exothermically on nuclei (ExoDDDM). We investigate the current status of ExoDDDM direct detection and find that ExoDDDM can readily explain the recently announced ∼ 3σ excess observed at CDMS-Si, with almost all of the 90% best-fit parameter space in complete consistency with limits from other experiments, including XENON10 and XENON100. In the absence of isospin-dependent couplings, this consistency requires light DM with mass typically in the 5-15 GeV range. The hypothesis of ExoDDDM can be tested in direct detection experiments through its peaked recoil spectra, reduced annual modulation amplitude, and, in some cases, its novel time-dependence. We also discuss future direct detection prospects and additional indirect constraints from colliders and solar capture of ExoDDDM. As theoretical proof-of-principle, we combine the features of exothermic DM models and DDDM models to construct a complete model of ExoDDDM, exhibiting all the required properties.

  8. Constraining supersymmetric dark matter with synchrotron measurements

    SciTech Connect

    Hooper, Dan

    2008-06-15

    The annihilations of neutralino dark matter (or other dark matter candidate) generate, among other standard model states, electrons and positrons. These particles emit synchrotron photons as a result of their interaction with the galactic magnetic field. In this paper, we use the measurements of the Wilkinson Microwave Anisotropy Probe satellite to constrain the intensity of this synchrotron emission and, in turn, the annihilation cross section of the lightest neutralino. We find this constraint to be more stringent than that provided by any other current indirect detection channel. In particular, the neutralino annihilation cross section must be less than {approx_equal}3x10{sup -26} cm{sup 3}/s (1x10{sup 25} cm{sup 3}/s) for 100 GeV (500 GeV) neutralinos distributed with a Navarro-Frenk-White halo profile. For the conservative case of an entirely flat dark matter distribution within the inner 8 kiloparsecs of the Milky Way, the constraint is approximately a factor of 30 less stringent. Even in this conservative case, synchrotron measurements strongly constrain, for example, the possibility of wino or Higgsino neutralino dark matter produced nonthermally in the early universe.

  9. The Dark Energy Spectroscopic Instrument (DESI)

    NASA Astrophysics Data System (ADS)

    Flaugher, Brenna; Bebek, Chris

    2014-07-01

    The Dark Energy Spectroscopic Instrument (DESI) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar spectroscopic redshift survey. The DESI instrument consists of a new wide-field (3.2 deg. linear field of view) corrector plus a multi-object spectrometer with up to 5000 robotically positioned optical fibers and will be installed at prime focus on the Mayall 4m telescope at Kitt Peak, Arizona. The fibers feed 10 three-arm spectrographs producing spectra that cover a wavelength range from 360-980 nm and have resolution of 2000-5500 depending on the wavelength. The DESI instrument is designed for a 14,000 sq. deg. multi-year survey of targets that trace the evolution of dark energy out to redshift 3.5 using the redshifts of luminous red galaxies (LRGs), emission line galaxies (ELGs) and quasars. DESI is the successor to the successful Stage-III BOSS spectroscopic redshift survey and complements imaging surveys such as the Stage-III Dark Energy Survey (DES, currently operating) and the Stage-IV Large Synoptic Survey Telescope (LSST, planned start early in the next decade).

  10. Global limits and interference patterns in dark matter direct detection

    SciTech Connect

    Catena, Riccardo; Gondolo, Paolo

    2015-08-13

    We compare the general effective theory of one-body dark matter nucleon interactions to current direct detection experiments in a global multidimensional statistical analysis. We derive exclusion limits on the 28 isoscalar and isovector coupling constants of the theory, and show that current data place interesting constraints on dark matter-nucleon interaction operators usually neglected in this context. We characterize the interference patterns that can arise in dark matter direct detection from pairs of dark matter-nucleon interaction operators, or from isoscalar and isovector components of the same operator. We find that commonly neglected destructive interference effects weaken standard direct detection exclusion limits by up to one order of magnitude in the coupling constants.

  11. Heal the world: Avoiding the cosmic doomsday in the holographic dark energy model

    NASA Astrophysics Data System (ADS)

    Zhang, Xin

    2010-01-01

    The current observational data imply that the universe would end with a cosmic doomsday in the holographic dark energy model. However, unfortunately, the big-rip singularity will ruin the theoretical foundation of the holographic dark energy scenario. To rescue the holographic scenario of dark energy, we employ the braneworld cosmology and incorporate the extra-dimension effects into the holographic theory of dark energy. We find that such a mend could erase the big-rip singularity and leads to a de Sitter finale for the holographic cosmos. Therefore, in the holographic dark energy model, the extra-dimension recipe could heal the world.

  12. Detecting Stealth Dark Matter Directly through Electromagnetic Polarizability

    NASA Astrophysics Data System (ADS)

    Appelquist, T.; Berkowitz, E.; Brower, R. C.; Buchoff, M. I.; Fleming, G. T.; Jin, X.-Y.; Kiskis, J.; Kribs, G. D.; Neil, E. T.; Osborn, J. C.; Rebbi, C.; Rinaldi, E.; Schaich, D.; Schroeder, C.; Syritsyn, S.; Vranas, P.; Weinberg, E.; Witzel, O.; Lattice Strong Dynamics LSD Collaboration

    2015-10-01

    We calculate the spin-independent scattering cross section for direct detection that results from the electromagnetic polarizability of a composite scalar "stealth baryon" dark matter candidate, arising from a dark SU(4) confining gauge theory—"stealth dark matter." In the nonrelativistic limit, electromagnetic polarizability proceeds through a dimension-7 interaction leading to a very small scattering cross section for dark matter with weak-scale masses. This represents a lower bound on the scattering cross section for composite dark matter theories with electromagnetically charged constituents. We carry out lattice calculations of the polarizability for the lightest "baryon" states in SU(3) and SU(4) gauge theories using the background field method on quenched configurations. We find the polarizabilities of SU(3) and SU(4) to be comparable (within about 50%) normalized to the stealth baryon mass, which is suggestive for extensions to larger SU(N ) groups. The resulting scattering cross sections with a xenon target are shown to be potentially detectable in the dark matter mass range of about 200-700 GeV, where the lower bound is from the existing LUX constraint while the upper bound is the coherent neutrino background. Significant uncertainties in the cross section remain due to the more complicated interaction of the polarizablity operator with nuclear structure; however, the steep dependence on the dark matter mass, 1 /mB6 , suggests the observable dark matter mass range is not appreciably modified. We briefly highlight collider searches for the mesons in the theory as well as the indirect astrophysical effects that may also provide excellent probes of stealth dark matter.

  13. Detecting Stealth Dark Matter Directly through Electromagnetic Polarizability

    DOE PAGES

    Appelquist, T.; Berkowitz, E.; Brower, R. C.; Buchoff, M. I.; Fleming, G. T.; Jin, X. Y.; Kiskis, J.; Kribs, G. D.; Neil, E. T.; Osborn, J. C.; et al

    2015-10-23

    We calculate the spin-independent scattering cross section for direct detection that results from the electromagnetic polarizability of a composite scalar “stealth baryon” dark matter candidate, arising from a dark SU(4) confining gauge theory—“stealth dark matter.” In the nonrelativistic limit, electromagnetic polarizability proceeds through a dimension-7 interaction leading to a very small scattering cross section for dark matter with weak-scale masses. This represents a lower bound on the scattering cross section for composite dark matter theories with electromagnetically charged constituents. We carry out lattice calculations of the polarizability for the lightest “baryon” states in SU(3) and SU(4) gauge theories using themore » background field method on quenched configurations. We find the polarizabilities of SU(3) and SU(4) to be comparable (within about 50%) normalized to the stealth baryon mass, which is suggestive for extensions to larger SU(N) groups. The resulting scattering cross sections with a xenon target are shown to be possibly detectable in the dark matter mass range of about 200–700 GeV, where the lower bound is from the existing LUX constraint while the upper bound is the coherent neutrino background. Significant uncertainties in the cross section remain due to the more complicated interaction of the polarizablity operator with nuclear structure; however, the steep dependence on the dark matter mass, 1/m6B, suggests the observable dark matter mass range is not appreciably modified. We highlight collider searches for the mesons in the theory as well as the indirect astrophysical effects that may also provide excellent probes of stealth dark matter.« less

  14. Detecting Stealth Dark Matter Directly through Electromagnetic Polarizability.

    PubMed

    Appelquist, T; Berkowitz, E; Brower, R C; Buchoff, M I; Fleming, G T; Jin, X-Y; Kiskis, J; Kribs, G D; Neil, E T; Osborn, J C; Rebbi, C; Rinaldi, E; Schaich, D; Schroeder, C; Syritsyn, S; Vranas, P; Weinberg, E; Witzel, O

    2015-10-23

    We calculate the spin-independent scattering cross section for direct detection that results from the electromagnetic polarizability of a composite scalar "stealth baryon" dark matter candidate, arising from a dark SU(4) confining gauge theory-"stealth dark matter." In the nonrelativistic limit, electromagnetic polarizability proceeds through a dimension-7 interaction leading to a very small scattering cross section for dark matter with weak-scale masses. This represents a lower bound on the scattering cross section for composite dark matter theories with electromagnetically charged constituents. We carry out lattice calculations of the polarizability for the lightest "baryon" states in SU(3) and SU(4) gauge theories using the background field method on quenched configurations. We find the polarizabilities of SU(3) and SU(4) to be comparable (within about 50%) normalized to the stealth baryon mass, which is suggestive for extensions to larger SU(N) groups. The resulting scattering cross sections with a xenon target are shown to be potentially detectable in the dark matter mass range of about 200-700 GeV, where the lower bound is from the existing LUX constraint while the upper bound is the coherent neutrino background. Significant uncertainties in the cross section remain due to the more complicated interaction of the polarizablity operator with nuclear structure; however, the steep dependence on the dark matter mass, 1/m(B)(6), suggests the observable dark matter mass range is not appreciably modified. We briefly highlight collider searches for the mesons in the theory as well as the indirect astrophysical effects that may also provide excellent probes of stealth dark matter.

  15. Detecting Stealth Dark Matter Directly through Electromagnetic Polarizability.

    PubMed

    Appelquist, T; Berkowitz, E; Brower, R C; Buchoff, M I; Fleming, G T; Jin, X-Y; Kiskis, J; Kribs, G D; Neil, E T; Osborn, J C; Rebbi, C; Rinaldi, E; Schaich, D; Schroeder, C; Syritsyn, S; Vranas, P; Weinberg, E; Witzel, O

    2015-10-23

    We calculate the spin-independent scattering cross section for direct detection that results from the electromagnetic polarizability of a composite scalar "stealth baryon" dark matter candidate, arising from a dark SU(4) confining gauge theory-"stealth dark matter." In the nonrelativistic limit, electromagnetic polarizability proceeds through a dimension-7 interaction leading to a very small scattering cross section for dark matter with weak-scale masses. This represents a lower bound on the scattering cross section for composite dark matter theories with electromagnetically charged constituents. We carry out lattice calculations of the polarizability for the lightest "baryon" states in SU(3) and SU(4) gauge theories using the background field method on quenched configurations. We find the polarizabilities of SU(3) and SU(4) to be comparable (within about 50%) normalized to the stealth baryon mass, which is suggestive for extensions to larger SU(N) groups. The resulting scattering cross sections with a xenon target are shown to be potentially detectable in the dark matter mass range of about 200-700 GeV, where the lower bound is from the existing LUX constraint while the upper bound is the coherent neutrino background. Significant uncertainties in the cross section remain due to the more complicated interaction of the polarizablity operator with nuclear structure; however, the steep dependence on the dark matter mass, 1/m(B)(6), suggests the observable dark matter mass range is not appreciably modified. We briefly highlight collider searches for the mesons in the theory as well as the indirect astrophysical effects that may also provide excellent probes of stealth dark matter. PMID:26551103

  16. Detecting Stealth Dark Matter Directly through Electromagnetic Polarizability

    SciTech Connect

    Appelquist, T.; Berkowitz, E.; Brower, R. C.; Buchoff, M. I.; Fleming, G. T.; Jin, X. Y.; Kiskis, J.; Kribs, G. D.; Neil, E. T.; Osborn, J. C.; Rebbi, C.; Rinaldi, E.; Schaich, D.; Schroeder, C.; Syritsyn, S.; Vranas, P.; Weinberg, E.; Witzel, O.

    2015-10-23

    We calculate the spin-independent scattering cross section for direct detection that results from the electromagnetic polarizability of a composite scalar “stealth baryon” dark matter candidate, arising from a dark SU(4) confining gauge theory—“stealth dark matter.” In the nonrelativistic limit, electromagnetic polarizability proceeds through a dimension-7 interaction leading to a very small scattering cross section for dark matter with weak-scale masses. This represents a lower bound on the scattering cross section for composite dark matter theories with electromagnetically charged constituents. We carry out lattice calculations of the polarizability for the lightest “baryon” states in SU(3) and SU(4) gauge theories using the background field method on quenched configurations. We find the polarizabilities of SU(3) and SU(4) to be comparable (within about 50%) normalized to the stealth baryon mass, which is suggestive for extensions to larger SU(N) groups. The resulting scattering cross sections with a xenon target are shown to be possibly detectable in the dark matter mass range of about 200–700 GeV, where the lower bound is from the existing LUX constraint while the upper bound is the coherent neutrino background. Significant uncertainties in the cross section remain due to the more complicated interaction of the polarizablity operator with nuclear structure; however, the steep dependence on the dark matter mass, 1/m6B, suggests the observable dark matter mass range is not appreciably modified. We highlight collider searches for the mesons in the theory as well as the indirect astrophysical effects that may also provide excellent probes of stealth dark matter.

  17. Aspects of dark matter and Higgs phenomenology

    NASA Astrophysics Data System (ADS)

    Edezhath, Ralph Angelus

    The existence of dark matter and the hierarchy problem motivates the search for new physics. The formulation of new search strategies and models is crucial in the hunt for physics beyond the Standard Model, and in this work we present three studies of new physics relevant for current and upcoming experiments. First, we study models that contain a singlet dark matter particle with cubic renormalizable couplings between standard model particles and 'partner' particles with the same gauge quantum numbers as the standard model quark. The dark matter has spin 0, ½, 12, or 1, and may or may not be its own antiparticle. Each model has 3 parameters: the masses of the dark matter and standard model partners, and the cubic coupling. Requiring the correct relic abundance gives a 2-dimensional parameter space where collider and direct detection constraints can be directly compared. We find that collider and direct detection searches are remarkably complementary for these models. Direct detection limits for the cases where the dark matter is not its own antiparticle require dark matter masses to be in the multi-TeV range, where they are extremely difficult to probe in collider experiments. The models where dark matter is its own antiparticle are strongly constrained by collider searches for monojet and jets + MET signals. These models are constrained by direct detection mainly near the limit where the dark matter and partner masses are nearly degenerate, where collider searches become more difficult. Second, we study the case where the singlet dark matter has trilinear couplings to leptons and a new "lepton partner'' particle. The most sensitive collider probe is the search for leptons + MET, while the most sensitive direct detection channel is scattering from nuclei arising from loop diagrams. Collider and direct detection searches are highly complementary: colliders give the only meaningful constraint when dark matter is its own antiparticle, while direct detection is

  18. MEST-The dark hole, dark comet and dark matter are the space-time center

    NASA Astrophysics Data System (ADS)

    Cao, Dayong

    2012-03-01

    The model of dark matter such as dark hole (black hole), dark comet and dark light have the space-time center. The wave is the space-time. Because the dark matter is space-time center, so it has the ``negative'' mass.(http://meetings.aps.org/link/BAPS.2011.MAR.K1.68) (1) Gm1m2r^2=-Gc^4E1E2r^2. (2) 14πɛ0q1q2r^2=-μ0c^24πq1q2r^2. Among it, m: the mass, r: the displacement, E: the energy, q: the quantity of electricity. Like charges repel each other, unlike charges attract; Like magnetic attract, unlike magnetic repel each other. Unlike mass repel each other, like mass attract; like energy repel each other, unlike energy attract. So the dark matter has a repulsive force to the stellar matter. So it can cause the discrepancy between the rotation curves. The nuclear of atom has antielectron. The proton (energy particle) get its charge; the neutron (mass particle) get its mass. It is a new atomic model. Like isospin repel each other, unlike isospin attract, Like spin attract, unlike spin repel each other. The dark nucleus is made up of the isospin and spin particle-space-time particle such as dark photon and dark neutrino. The space-time center of dark light of dark matter has valence mass-valence neutron and valence energy-valence proton. The dark light can take a reaction with neutrino. So we can use neutrino to find it. (3) D^-n+νe->p+e. (4) D^-p-νe->n-e. Among it, D: the center of dark light, -n: the negative valence neutron, νe: electron neutrino, p: proton, e: electron.

  19. Effective field theory of dark matter: a global analysis

    NASA Astrophysics Data System (ADS)

    Liem, Sebastian; Bertone, Gianfranco; Calore, Francesca; de Austri, Roberto Ruiz; Tait, Tim M. P.; Trotta, Roberto; Weniger, Christoph

    2016-09-01

    We present global fits of an effective field theory description of real, and complex scalar dark matter candidates. We simultaneously take into account all possible dimension 6 operators consisting of dark matter bilinears and gauge invariant combinations of quark and gluon fields. We derive constraints on the free model parameters for both the real (five parameters) and complex (seven) scalar dark matter models obtained by combining Planck data on the cosmic microwave background, direct detection limits from LUX, and indirect detection limits from the Fermi Large Area Telescope. We find that for real scalars indirect dark matter searches disfavour a dark matter particle mass below 100 GeV. For the complex scalar dark matter particle current data have a limited impact due to the presence of operators that lead to p-wave annihilation, and also do not contribute to the spin-independent scattering cross-section. Although current data are not informative enough to strongly constrain the theory parameter space, we demonstrate the power of our formalism to reconstruct the theoretical parameters compatible with an actual dark matter detection, by assuming that the excess of gamma rays observed by the Fermi Large Area Telescope towards the Galactic centre is entirely due to dark matter annihilations. Please note that the excess can very well be due to astrophysical sources such as millisecond pulsars. We find that scalar dark matter interacting via effective field theory operators can in principle explain the Galactic centre excess, but that such interpretation is in strong tension with the non-detection of gamma rays from dwarf galaxies in the real scalar case. In the complex scalar case there is enough freedom to relieve the tension.

  20. 7 CFR 1437.402 - Carrying capacity.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... factors, such as soil type, elevation, and topography, result in a significant difference of carrying... management and maintenance practices are improvements over those practices generally associated with...

  1. Dark Matter Velocity Spectroscopy.

    PubMed

    Speckhard, Eric G; Ng, Kenny C Y; Beacom, John F; Laha, Ranjan

    2016-01-22

    Dark matter decays or annihilations that produce linelike spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming experiments will have the precision needed. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications. PMID:26849582

  2. Dark Matter Velocity Spectroscopy.

    PubMed

    Speckhard, Eric G; Ng, Kenny C Y; Beacom, John F; Laha, Ranjan

    2016-01-22

    Dark matter decays or annihilations that produce linelike spectra may be smoking-gun signals. However, even such distinctive signatures can be mimicked by astrophysical or instrumental causes. We show that velocity spectroscopy-the measurement of energy shifts induced by relative motion of source and observer-can separate these three causes with minimal theoretical uncertainties. The principal obstacle has been energy resolution, but upcoming experiments will have the precision needed. As an example, we show that the imminent Astro-H mission can use Milky Way observations to separate possible causes of the 3.5-keV line. We discuss other applications.

  3. Dark Energy Stars

    SciTech Connect

    Chapline, G

    2005-03-08

    Event horizons and closed time-like curves cannot exist in the real world for the simple reason that they are inconsistent with quantum mechanics. Following ideas originated by Robert Laughlin, Pawel Mazur, Emil Mottola, David Santiago, and the speaker it is now possible to describe in some detail what happens physically when one approaches and crosses a region of space-time where classical general relativity predicts there should be an infinite red shift surface. This quantum critical physics provides a new perspective on a variety of enigmatic astrophysical phenomena including supernovae explosions, gamma ray bursts, positron emission, and dark matter.

  4. Dark matter axions

    SciTech Connect

    Sikivie, P. |

    1992-09-01

    The physics of axions is briefly reviewed theoretically, and various constraints on the axion mass are recounted. Then the two main contributions to the present cosmological axion energy density, that due to the realignment of the vacuum during the QCD phase transition and that from axions radiated by cosmic axion strings, are discussed. Next, two detection schemes for axions that are sensitive to different mass ranges, an electromagnetic cavity permeated by a strong magnetic field and a system of superconducting wires embedded in a material transparent to microwave radiation, are described. Finally, the phase space structure of cold dark matter galactic halos is considered. (RWR)

  5. Dark matter axions

    SciTech Connect

    Sikivie, P. . Inst. for Theoretical Physics Florida Univ., Gainesville, FL . Dept. of Physics)

    1992-01-01

    The physics of axions is briefly reviewed theoretically, and various constraints on the axion mass are recounted. Then the two main contributions to the present cosmological axion energy density, that due to the realignment of the vacuum during the QCD phase transition and that from axions radiated by cosmic axion strings, are discussed. Next, two detection schemes for axions that are sensitive to different mass ranges, an electromagnetic cavity permeated by a strong magnetic field and a system of superconducting wires embedded in a material transparent to microwave radiation, are described. Finally, the phase space structure of cold dark matter galactic halos is considered. (RWR)

  6. Dark Two Higgs Doublet Model

    SciTech Connect

    Lee, Hye Sung; Sher, Marc

    2013-06-01

    We perform a detailed study of a specific Two Higgs Doublet Model (2HDM) with a U(1) gauge symmetry, instead of a typical Z{sub 2} discrete symmetry, containing a very light gauge boson Z' (GeV scale or below). The Standard Model (SM) fermions do not carry U(1) charges, but induced couplings to the Z' (called the dark Z) are generated through mixing with the SM neutral gauge bosons. Such a light Z' could explain some astrophysical anomalies as well as the muon g-2 deviation, and has been the subject of great experimental interest. We consider the scenario in which the 125 GeV SM-like Higgs (H) is the heavier scalar state, and focus on the lighter neutral state (h) as well as charged Higgs. We analyze the constraints on the model from various experiments and predict novel channels to search for these Higgs scalars at the LHC. In particular, experiments looking for lepton-jets are among potentially important searches.

  7. Astrophysical constraints on dark energy

    NASA Astrophysics Data System (ADS)

    Ho, Chiu Man; Hsu, Stephen D. H.

    2016-02-01

    Dark energy (i.e., a cosmological constant) leads, in the Newtonian approximation, to a repulsive force which grows linearly with distance and which can have astrophysical consequences. For example, the dark energy force overcomes the gravitational attraction from an isolated object (e.g., dwarf galaxy) of mass 107M⊙ at a distance of 23 kpc. Observable velocities of bound satellites (rotation curves) could be significantly affected, and therefore used to measure or constrain the dark energy density. Here, isolated means that the gravitational effect of large nearby galaxies (specifically, of their dark matter halos) is negligible; examples of isolated dwarf galaxies include Antlia or DDO 190.

  8. MSSM Inflaton: SUSY Dark Matter and LHC

    SciTech Connect

    Mazumdar, A.

    2009-09-08

    In this talk we will discuss how inflation can be embedded within a minimal extension of the Standard Model where the inflaton carries the Standard Model charges. There is no need of an ad-hoc scalar field to be introduced in order to explain the temperature anisotropy of the cosmic microwave background radiation, all the ingredients are present within a minimal supersymmetric Standard Model. For the first time inflaton properties can be directly linked to the particle phenomenology, dark matter, and the baryons of the Standard Model.

  9. Cold dark matter: Controversies on small scales

    PubMed Central

    Weinberg, David H.; Bullock, James S.; Governato, Fabio; Kuzio de Naray, Rachel; Peter, Annika H. G.

    2015-01-01

    The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way’s dwarf galaxy satellites. We review the current observational and theoretical status of these “small-scale controversies.” Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years. PMID:25646464

  10. Cold dark matter: Controversies on small scales.

    PubMed

    Weinberg, David H; Bullock, James S; Governato, Fabio; Kuzio de Naray, Rachel; Peter, Annika H G

    2015-10-01

    The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. We review the current observational and theoretical status of these "small-scale controversies." Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years.

  11. Cold dark matter: Controversies on small scales

    NASA Astrophysics Data System (ADS)

    Weinberg, David H.; Bullock, James S.; Governato, Fabio; Kuzio de Naray, Rachel; Peter, Annika H. G.

    2015-10-01

    The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. We review the current observational and theoretical status of these "small-scale controversies." Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years.

  12. On physical scales of dark matter halos

    SciTech Connect

    Zemp, Marcel

    2014-09-10

    It is common practice to describe formal size and mass scales of dark matter halos as spherical overdensities with respect to an evolving density threshold. Here, we critically investigate the evolutionary effects of several such commonly used definitions and compare them to the halo evolution within fixed physical scales as well as to the evolution of other intrinsic physical properties of dark matter halos. It is shown that, in general, the traditional way of characterizing sizes and masses of halos dramatically overpredicts the degree of evolution in the last 10 Gyr, especially for low-mass halos. This pseudo-evolution leads to the illusion of growth even though there are no major changes within fixed physical scales. Such formal size definitions also serve as proxies for the virialized region of a halo in the literature. In general, those spherical overdensity scales do not coincide with the virialized region. A physically more precise nomenclature would be to simply characterize them by their very definition instead of calling such formal size and mass definitions 'virial'. In general, we find a discrepancy between the evolution of the underlying physical structure of dark matter halos seen in cosmological structure formation simulations and pseudo-evolving formal virial quantities. We question the importance of the role of formal virial quantities currently ubiquitously used in descriptions, models, and relations that involve properties of dark matter structures. Concepts and relations based on pseudo-evolving formal virial quantities do not properly reflect the actual evolution of dark matter halos and lead to an inaccurate picture of the physical evolution of our universe.

  13. Cold dark matter: Controversies on small scales.

    PubMed

    Weinberg, David H; Bullock, James S; Governato, Fabio; Kuzio de Naray, Rachel; Peter, Annika H G

    2015-10-01

    The cold dark matter (CDM) cosmological model has been remarkably successful in explaining cosmic structure over an enormous span of redshift, but it has faced persistent challenges from observations that probe the innermost regions of dark matter halos and the properties of the Milky Way's dwarf galaxy satellites. We review the current observational and theoretical status of these "small-scale controversies." Cosmological simulations that incorporate only gravity and collisionless CDM predict halos with abundant substructure and central densities that are too high to match constraints from galaxy dynamics. The solution could lie in baryonic physics: Recent numerical simulations and analytical models suggest that gravitational potential fluctuations tied to efficient supernova feedback can flatten the central cusps of halos in massive galaxies, and a combination of feedback and low star formation efficiency could explain why most of the dark matter subhalos orbiting the Milky Way do not host visible galaxies. However, it is not clear that this solution can work in the lowest mass galaxies, where discrepancies are observed. Alternatively, the small-scale conflicts could be evidence of more complex physics in the dark sector itself. For example, elastic scattering from strong dark matter self-interactions can alter predicted halo mass profiles, leading to good agreement with observations across a wide range of galaxy mass. Gravitational lensing and dynamical perturbations of tidal streams in the stellar halo provide evidence for an abundant population of low-mass subhalos in accord with CDM predictions. These observational approaches will get more powerful over the next few years. PMID:25646464

  14. Graphene as transparent and current spreading electrode in silicon solar cell

    SciTech Connect

    Behura, Sanjay K. Nayak, Sasmita; Jani, Omkar; Mahala, Pramila

    2014-11-15

    Fabricated bi-layer graphene (BLG) has been studied as transparent and current spreading electrode (TCSE) for silicon solar cell, using TCAD-Silvaco 2D simulation. We have carried out comparative study using both Ag grids and BLG as current spreading electrode (CSE) and TCSE, respectively. Our study reveals that BLG based solar cell shows better efficiency of 24.85% than Ag-based cell (21.44%), in all of the critical aspects, including generation rate, recombination rate, electric field, potential and quantum efficiency. Further BLG based cell exhibits pronounce rectifying behavior, low saturation current, and good turn-on voltage while studying in dark.

  15. A Merging of Pale and Dark

    NASA Technical Reports Server (NTRS)

    2001-01-01

    Close to the city of Manaus, Brazil the Rio Solimoes and the Rio Negro converge to form the Amazon River. This image from MISR's vertical-viewing (nadir) camera was acquired on July 23, 2000 during Terra orbit 3178. Manaus is the gray patch to the right of image center.

    The pale, murky color of the Rio Solimoes heralds its burden of glacial silt and sand, which results from its origin in the Peruvian Andes mountains. The dark color of the Rio Negro is characteristic of clear waters that originate in areas of basement rock and carry little sediment. East of Manaus the pale and dark waters flow side-by-side as distinct flows before they eventually merge.

    Northwest of Manaus on the Rio Negro is the Anavilhanas Archipelago, the largest group of freshwater islands in the world and a wildlife reserve. At the top of the image, a portion of the dark-colored Uatuma River is visible. In the lower right is the very light-colored Rio Madeira, formed from mountain streams originating near the Brazil-Bolivia border. Madeira is Portuguese for wood, and the river is named for the large amount of driftwood that floats on its waters.

    MISR was built and is managed by NASA's Jet Propulsion Laboratory, Pasadena, CA, for NASA's Office of Earth Science, Washington, DC. The Terra satellite is managed by NASA's Goddard Space Flight Center, Greenbelt, MD. JPL is a division of the California Institute of Technology.

  16. Weapon-Carrying and Youth Violence.

    ERIC Educational Resources Information Center

    Page, Randy M.; Hammermeister, Jon

    1997-01-01

    Reviews the prevalence of weapon-carrying among adolescents, focusing on the reasons why they carry weapons, ways that firearms are obtained, firearms and violence, and the controlling of weapons in schools. Details weapon-security measures and argues for cooperative action among schools, communities, and government. (RJM)

  17. Carrie Chapman Catt and Woman Suffrage.

    ERIC Educational Resources Information Center

    Hardesty, Carolyn, Ed.

    1989-01-01

    Most of the material for this issue of the "Goldfinch," which explores the life of Carrie Chapman Catt, came from the archives of the State Historical Society of Iowa. Carrie Chapman Catt (1859-1947) was an Iowan who advocated woman suffrage and spent 26 years actively working for that cause. The issue contains a biography of Catt, and information…

  18. Optical Dark Rogue Wave.

    PubMed

    Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan

    2016-01-01

    Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system. PMID:26864099

  19. Optical Dark Rogue Wave

    PubMed Central

    Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan

    2016-01-01

    Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system. PMID:26864099

  20. Methanol in dark clouds.

    PubMed

    Friberg, P; Madden, S C; Hjalmarson, A; Irvine, W M

    1988-01-01

    We report observations, for the first time, of the 2(0) - 1(0)A+ and E, 2(-1) - 1(-1) E, and 1(0) - 0(0)A+ lines of methanol (CH3OH) in three dark cold clouds, TMC1, L134N, and B335. The CH3OH emission is extended in these clouds and shows a complex velocity structure. Clear indications of non LTE excitation are observed in TMC 1. Estimated column densities are a few 10(13) cm-2. Although less abundant than formaldehyde (H2CO), methanol is almost an order of magnitude more abundant than acetaldehyde (CH3CHO), in these clouds. Dimethyl ether was searched for in L134N, to an upper limit of 4 10(12) cm-2 (3 sigma). Implications for dark cloud excitation and chemistry are discussed. A new, more accurate, rest frequency 96741.39(0.01) MHz is determined for the 2(0) - 1(0) A+ E line of methanol.

  1. (Mainly) axion dark matter

    NASA Astrophysics Data System (ADS)

    Baer, Howard

    2016-06-01

    The strong CP problem of QCD is at heart a problem of naturalness: why is the FF ˜ term highly suppressed in the QCD Lagrangian when it seems necessary to explain why there are three and not four light pions? The most elegant solution posits a spontaneously broken Peccei-Quinn (PQ) symmetry which requires the existence of the axion field a. The axion field settles to the minimum of its potential thus removing the offensive term but giving rise to the physical axion whose coherent oscillations can make up the cold dark matter. Only now are experiments such as ADMX beginning to explore QCD axion parameter space. Since a bonafide scalar particle- the Higgs boson- has been discovered, one might expect its mass to reside at the axion scale fa ˜ 1011 GeV. The Higgs mass is elegantly stabilized by supersymmetry: in this case the axion is accompanied by its axino and saxion superpartners. Requiring naturalness also in the electroweak sector implies higgsino-like WIMPs so then we expect mixed axion-WIMP dark matter. Ultimately we would expect detection of both an axion and a WIMP while signals for light higgsinos may show up at LHC and must show up at ILC.

  2. Optical Dark Rogue Wave.

    PubMed

    Frisquet, Benoit; Kibler, Bertrand; Morin, Philippe; Baronio, Fabio; Conforti, Matteo; Millot, Guy; Wabnitz, Stefan

    2016-01-01

    Photonics enables to develop simple lab experiments that mimic water rogue wave generation phenomena, as well as relativistic gravitational effects such as event horizons, gravitational lensing and Hawking radiation. The basis for analog gravity experiments is light propagation through an effective moving medium obtained via the nonlinear response of the material. So far, analogue gravity kinematics was reproduced in scalar optical wave propagation test models. Multimode and spatiotemporal nonlinear interactions exhibit a rich spectrum of excitations, which may substantially expand the range of rogue wave phenomena, and lead to novel space-time analogies, for example with multi-particle interactions. By injecting two colliding and modulated pumps with orthogonal states of polarization in a randomly birefringent telecommunication optical fiber, we provide the first experimental demonstration of an optical dark rogue wave. We also introduce the concept of multi-component analog gravity, whereby localized spatiotemporal horizons are associated with the dark rogue wave solution of the two-component nonlinear Schrödinger system.

  3. Correlation between dark matter and dark radiation in string compactifications

    SciTech Connect

    Allahverdi, Rouzbeh; Cicoli, Michele; Dutta, Bhaskar; Sinha, Kuver E-mail: mcicoli@ictp.it E-mail: kusinha@syr.edu

    2014-10-01

    Reheating in string compactifications is generically driven by the decay of the lightest modulus which produces Standard Model particles, dark matter and light hidden sector degrees of freedom that behave as dark radiation. This common origin allows us to find an interesting correlation between dark matter and dark radiation. By combining present upper bounds on the effective number of neutrino species N{sub eff} with lower bounds on the reheating temperature as a function of the dark matter mass m{sub DM} from Fermi data, we obtain strong constraints on the (N{sub eff}, m{sub DM})-plane. Most of the allowed region in this plane corresponds to non-thermal scenarios with Higgsino-like dark matter. Thermal dark matter can be allowed only if N{sub eff} tends to its Standard Model value. We show that the above situation is realised in models with perturbative moduli stabilisation where the production of dark radiation is unavoidable since bulk closed string axions remain light and do not get eaten up by anomalous U(1)s.

  4. The Photosynthetic Dark Reactions Do Not Operate in the Dark.

    ERIC Educational Resources Information Center

    Lonergan, Thomas A.

    2000-01-01

    Discusses the common misconception persistent in high school and college level introductory biology texts that "dark reactions" of the Calvin cycle actually occur in the dark. Explains that they are indirectly dependent on the presence of light for their activity. (ASK)

  5. Chemical abundances in cold, dark interstellar clouds.

    PubMed

    Irvine, W M; Ohishi, M; Kaifu, N

    1991-05-01

    The Sun may well have formed in the type of interstellar cloud currently referred to as a cold, dark cloud. We present current tabulations of the totality of known interstellar molecules and of the subset which have been identified in cold clouds. Molecular abundances are given for two such clouds which show interesting chemical differences in spite of strong physical similarities, Taurus Molecular Cloud 1 (TMC-1) and Lynd's 134N (L134N, also referred to as L183). These regions may be at different evolutionary stages.

  6. Gravitational lenses and dark matter - Observations

    NASA Technical Reports Server (NTRS)

    Turner, Edwin L.

    1987-01-01

    Following a few general comments on gravitational lenses from an observer's perspective, the currently available observations of the six known gravitational lenses are summarized. Attention is called to some regularities and peculiarities of the properties of the known lenses and to how they might be interpreted. The most important conclusions, relevant to the dark matter problem, which can be obtained from current observations are that the distributions of mass and light appear to be quite different in at least some of the lensing objects and that objects with projected mass/brightness values about 10 times larger than those ordinarily associated with galaxies exist and are not too rare.

  7. Simulated Milky Way analogues: implications for dark matter direct searches

    NASA Astrophysics Data System (ADS)

    Bozorgnia, Nassim; Calore, Francesca; Schaller, Matthieu; Lovell, Mark; Bertone, Gianfranco; Frenk, Carlos S.; Crain, Robert A.; Navarro, Julio F.; Schaye, Joop; Theuns, Tom

    2016-05-01

    We study the implications of galaxy formation on dark matter direct detection using high resolution hydrodynamic simulations of Milky Way-like galaxies simulated within the EAGLE and APOSTLE projects. We identify Milky Way analogues that satisfy observational constraints on the Milky Way rotation curve and total stellar mass. We then extract the dark matter density and velocity distribution in the Solar neighbourhood for this set of Milky Way analogues, and use them to analyse the results of current direct detection experiments. For most Milky Way analogues, the event rates in direct detection experiments obtained from the best fit Maxwellian distribution (with peak speed of 223–289 km/s) are similar to those obtained directly from the simulations. As a consequence, the allowed regions and exclusion limits set by direct detection experiments in the dark matter mass and spin-independent cross section plane shift by a few GeV compared to the Standard Halo Model, at low dark matter masses. For each dark matter mass, the halo-to-halo variation of the local dark matter density results in an overall shift of the allowed regions and exclusion limits for the cross section. However, the compatibility of the possible hints for a dark matter signal from DAMA and CDMS-Si and null results from LUX and SuperCDMS is not improved.

  8. Minimal model for dark matter and unification

    SciTech Connect

    Mahbubani, Rakhi; Senatore, Leonardo

    2006-02-15

    Gauge coupling unification and the success of TeV-scale weakly-interacting dark matter are usually taken as evidence of low-energy supersymmetry (SUSY). However, if we assume that the tuning of the Higgs can be explained in some unnatural way, from environmental considerations for example, SUSY is no longer a necessary component of any beyond the standard model theory. In this paper we study the minimal model with a dark matter candidate and gauge coupling unification. This consists of the standard model plus fermions with the quantum numbers of SUSY Higgsinos, and a singlet. It predicts thermal dark matter with a mass that can range from 100 GeV to around 2 TeV and generically gives rise to an electric dipole moment (EDM) that is just beyond current experimental limits, with a large portion of its allowed parameter space accessible to next-generation EDM and direct detection experiments. We study precision unification in this model by embedding it in a 5D orbifold GUT where certain large threshold corrections are calculable, achieving gauge coupling and b-{tau} unification, and predicting a rate of proton decay just beyond current limits.

  9. Dark energy, matter creation and curvature

    NASA Astrophysics Data System (ADS)

    Cárdenas, Víctor H.

    2012-09-01

    The most studied way to explain the current accelerated expansion of the universe is to assume the existence of dark energy; a new component that fills the universe, does not form clumps, currently dominates the evolution, and has a negative pressure. In this work I study an alternative model proposed by Lima et al. (Abramo and Lima in Class. Quantum Gravity 13:2953, 1996; Zimdahl in Phys. Rev. D 53:5483, 1996; Zimdahl and Pavón in Mon. Not. R. Astron. Soc. 266:872, 1994), which does not need an exotic equation of state, but assumes instead the existence of gravitational particle creation. Because this model fits the supernova observations as well as the ΛCDM model, I perform in this work a thorough study of this model, considering an explicit spatial curvature. I found that in this scenario we can alleviate the cosmic coincidence problem, basically showing that these two components, dark matter and dark energy, are of the same nature, but they act at different scales. I also shown the inadequacy of some particle creation models, and I study a previously proposed new model that overcomes these difficulties.

  10. Stealth Dark Matter: Dark scalar baryons through the Higgs portal

    DOE PAGES

    Appelquist, T.; Brower, R. C.; Buchoff, M. I.; Fleming, G. T.; Jin, X. -Y.; Kiskis, J.; Kribs, G. D.; Neil, E. T.; Osborn, J. C.; Rebbi, C.; et al

    2015-10-23

    We present a new model of "Stealth Dark Matter": a composite baryonic scalar of an SU(ND) strongly coupled theory with even ND ≥ 4. All mass scales are technically natural, and dark matter stability is automatic without imposing an additional discrete or global symmetry. Constituent fermions transform in vectorlike representations of the electroweak group that permit both electroweak-breaking and electroweak-preserving mass terms. This gives a tunable coupling of stealth dark matter to the Higgs boson independent of the dark matter mass itself. We specialize to SU(4), and investigate the constraints on the model from dark meson decay, electroweak precision measurements,more » basic collider limits, and spin-independent direct detection scattering through Higgs exchange. We exploit our earlier lattice simulations that determined the composite spectrum as well as the effective Higgs coupling of stealth dark matter in order to place bounds from direct detection, excluding constituent fermions with dominantly electroweak-breaking masses. A lower bound on the dark baryon mass mB ≳ 300 GeV is obtained from the indirect requirement that the lightest dark meson not be observable at LEP II. Furthermore, we briefly survey some intriguing properties of stealth dark matter that are worthy of future study, including collider studies of dark meson production and decay; indirect detection signals from annihilation; relic abundance estimates for both symmetric and asymmetric mechanisms; and direct detection through electromagnetic polarizability, a detailed study of which will appear in a companion paper.« less

  11. Stealth Dark Matter: Dark scalar baryons through the Higgs portal

    SciTech Connect

    Appelquist, T.; Brower, R. C.; Buchoff, M. I.; Fleming, G. T.; Jin, X. -Y.; Kiskis, J.; Kribs, G. D.; Neil, E. T.; Osborn, J. C.; Rebbi, C.; Rinaldi, E.; Schaich, D.; Schroeder, C.; Syritsyn, S.; Vranas, P.; Weinberg, E.; Witzel, O.

    2015-10-23

    We present a new model of "Stealth Dark Matter": a composite baryonic scalar of an SU(ND) strongly coupled theory with even ND ≥ 4. All mass scales are technically natural, and dark matter stability is automatic without imposing an additional discrete or global symmetry. Constituent fermions transform in vectorlike representations of the electroweak group that permit both electroweak-breaking and electroweak-preserving mass terms. This gives a tunable coupling of stealth dark matter to the Higgs boson independent of the dark matter mass itself. We specialize to SU(4), and investigate the constraints on the model from dark meson decay, electroweak precision measurements, basic collider limits, and spin-independent direct detection scattering through Higgs exchange. We exploit our earlier lattice simulations that determined the composite spectrum as well as the effective Higgs coupling of stealth dark matter in order to place bounds from direct detection, excluding constituent fermions with dominantly electroweak-breaking masses. A lower bound on the dark baryon mass mB ≳ 300 GeV is obtained from the indirect requirement that the lightest dark meson not be observable at LEP II. Furthermore, we briefly survey some intriguing properties of stealth dark matter that are worthy of future study, including collider studies of dark meson production and decay; indirect detection signals from annihilation; relic abundance estimates for both symmetric and asymmetric mechanisms; and direct detection through electromagnetic polarizability, a detailed study of which will appear in a companion paper.

  12. Cosmological constraints on coupled dark energy

    NASA Astrophysics Data System (ADS)

    Yang, Weiqiang; Li, Hang; Wu, Yabo; Lu, Jianbo

    2016-10-01

    The coupled dark energy model provides a possible approach to mitigate the coincidence problem of cosmological standard model. Here, the coupling term is assumed as bar Q = 3Hξxbar rhox, which is related to the interaction rate and energy density of dark energy. We derive the background and perturbation evolution equations for several coupled models. Then, we test these models by currently available cosmic observations which include cosmic microwave background radiation from Planck 2015, baryon acoustic oscillation, type Ia supernovae, fσ8(z) data points from redshift-space distortions, and weak gravitational lensing. The constraint results tell us there is no evidence of interaction at 2σ level, it is very hard to distinguish different coupled models from other ones.

  13. Light Dark Matter in the NO$\

    SciTech Connect

    Hatzikoutelis, Athanasios

    2015-01-01

    The neutrino oscillations experiment NOA is the agship of Fermi National Laboratory. The neutrino source NuMI is delivering record numbers of protons-on-target surpassing the most stringent dark matter production upper limits of current models in the under-10 GeV mass range. We take advantage of the sophisticated particle identication algorithms of the experiment to interrogate the data from the 300-ton, o-axis, low-Z, Near Detector of NOvA during the rst physics runs. We search for signatures of sub-GeV or Light Dark Matter (LDM), Axion-like-particles, and Heavy or Sterile Neutrinos that may scatter or decay in the volume of the detector.

  14. Gun Carrying by High School Students in Boston, MA: Does Overestimation of Peer Gun Carrying Matter?

    ERIC Educational Resources Information Center

    Hemenway, David; Vriniotis, Mary; Johnson, Renee M.; Miller, Matthew; Azrael, Deborah

    2011-01-01

    This paper investigates: (1) whether high school students overestimate gun carrying by their peers, and (2) whether those students who overestimate peer gun carrying are more likely to carry firearms. Data come from a randomly sampled survey conducted in 2008 of over 1700 high school students in Boston, MA. Over 5% of students reported carrying a…

  15. Plasma dark matter direct detection

    SciTech Connect

    Clarke, J.D.; Foot, R. E-mail: rfoot@unimelb.edu.au

    2016-01-01

    Dark matter in spiral galaxies like the Milky Way may take the form of a dark plasma. Hidden sector dark matter charged under an unbroken U(1)' gauge interaction provides a simple and well defined particle physics model realising this possibility. The assumed U(1)' neutrality of the Universe then implies (at least) two oppositely charged dark matter components with self-interactions mediated via a massless 'dark photon' (the U(1)' gauge boson). In addition to nuclear recoils such dark matter can give rise to keV electron recoils in direct detection experiments. In this context, the detailed physical properties of the dark matter plasma interacting with the Earth is required. This is a complex system, which is here modelled as a fluid governed by the magnetohydrodynamic equations. These equations are numerically solved for some illustrative examples, and implications for direct detection experiments discussed. In particular, the analysis presented here leaves open the intriguing possibility that the DAMA annual modulation signal is due primarily to electron recoils (or even a combination of electron recoils and nuclear recoils). The importance of diurnal modulation (in addition to annual modulation) as a means of probing this kind of dark matter is also emphasised.

  16. Jet and dark substructure: Rise of the machines

    NASA Astrophysics Data System (ADS)

    Cliche, Mathieu

    We currently live in the golden age of experimental particle physics. The Large Hadron Collider (LHC) finally discovered the Higgs particle and may soon allow us to probe TeVscale new physics. Moreover, dark matter indirect detection experiments may have found annihilation products in our galaxy while the direct detection experiments keep improving their upper bounds on dark matter interactions with ordinary matter. That being said, the current efforts to discover any physics beyond the standard model have failed. We thus need to come up with better models and better tools to probe new physics. This thesis which collects the author's PhD research papers is an effort in this direction. We begin by showing how singular dark matter self-interaction can significantly enhance dark matter annihilation in today's Universe. Then we explore a concrete dark matter model where a particle called the dilaton mediate the interactions between the dark sector and the standard model. Finally we devise a new method to discern heavy boosted particles from QCD jets at the LHC.

  17. Significant gamma lines from inert Higgs dark matter.

    PubMed

    Gustafsson, Michael; Lundström, Erik; Bergström, Lars; Edsjö, Joakim

    2007-07-27

    One way to unambiguously confirm the existence of particle dark matter and determine its mass would be to detect its annihilation into monochromatic gamma-rays in upcoming telescopes. One of the most minimal models for dark matter is the inert doublet model, obtained by adding another Higgs doublet with no direct coupling to fermions. For a mass between 40 and 80 GeV, the lightest of the new inert Higgs particles can give the correct cosmic abundance of cold dark matter in agreement with current observations. We show that for this scalar dark matter candidate, the annihilation signal of monochromatic gammagamma and Zgamma final states would be exceptionally strong. The energy range and rates for these gamma-ray line signals make them ideal to search for with the soon upcoming GLAST satellite.

  18. Well-mixed dark matter and the Higgs

    NASA Astrophysics Data System (ADS)

    Feldman, Daniel; Sandick, Pearl

    2013-07-01

    The breaking of electroweak symmetry through renormalization group flow in models that have MSSM spectra is found to produce "well-mixed" neutralino dark matter with a relic density consistent with the WMAP data and elastic scattering cross section with nuclei consistent with current limits from direct dark matter searches. These models predict a Higgs boson mass in the range (125-126) GeV. Well-mixed neutralino dark matter is predominantly bino-like, but has significant Higgsino and wino content, each with fractions of comparable size. With a ∼ 1 TeV gluino mass and sizable neutralino-nucleon scattering cross sections, natural models will be fully tested by both the LHC and future dark matter direct detection experiments.

  19. Direct Detection of Sub-GeV Dark Matter

    SciTech Connect

    Essig, Rouven; Mardon, Jeremy; Volansky, Tomer

    2012-03-20

    Direct detection strategies are proposed for dark matter particles with MeV to GeV mass. In this largely unexplored mass range, dark matter scattering with electrons can cause single-electron ionization signals, which are detectable with current technology. Ultraviolet photons, individual ions, and heat are interesting alternative signals. Focusing on ionization, we calculate the expected dark matter scattering rates and estimate the sensitivity of possible experiments. Backgrounds that may be relevant are discussed. Theoretically interesting models can be probed with existing technologies, and may even be within reach using ongoing direct detection experiments. Significant improvements in sensitivity should be possible with dedicated experiments, opening up a window to new regions in dark matter parameter space.

  20. The dark side of plasmonics.

    PubMed

    Gómez, D E; Teo, Z Q; Altissimo, M; Davis, T J; Earl, S; Roberts, A

    2013-08-14

    Plasmonic dark modes are pure near-field modes that can arise from the plasmon hybridization in a set of interacting nanoparticles. When compared to bright modes, dark modes have longer lifetimes due to their lack of a net dipole moment, making them attractive for a number of applications. We demonstrate the excitation and optical detection of a collective dark plasmonic mode from individual plasmonic trimers. The trimers consist of triangular arrangements of gold nanorods, and due to this symmetry, the lowest-energy dark plasmonic mode can interact with radially polarized light. The experimental data presented confirm the excitation of this mode, and its assignment is supported with an electrostatic approximation wherein these dark modes are described in terms of plasmon hybridization. The strong confinement of energy in these modes and their associated near fields hold great promise for achieving strong coupling to single photon emitters.

  1. Dark matter and cosmological nucleosynthesis

    NASA Technical Reports Server (NTRS)

    Schramm, D. N.

    1986-01-01

    Existing dark matter problems, i.e., dynamics, galaxy formation and inflation, are considered, along with a model which proposes dark baryons as the bulk of missing matter in a fractal universe. It is shown that no combination of dark, nonbaryonic matter can either provide a cosmological density parameter value near unity or, as in the case of high energy neutrinos, allow formation of condensed matter at epochs when quasars already existed. The possibility that correlations among galactic clusters are scale-free is discussed. Such a distribution of matter would yield a fractal of 1.2, close to a one-dimensional universe. Biasing, cosmic superstrings, and percolated explosions and hot dark matter are theoretical approaches that would satisfy the D = 1.2 fractal model of the large-scale structure of the universe and which would also allow sufficient dark matter in halos to close the universe.

  2. Acausality from a dark sector

    NASA Astrophysics Data System (ADS)

    Carone, Christopher D.

    2014-03-01

    Solutions to the hierarchy problem that require partners for each standard model particle often require that these states live at or above the electroweak scale, to satisfy phenomenological bounds. Partners to possible dark sector particles may be significantly lighter, due to the assumed weakness of the couplings between the dark and visible sectors. Here we consider the possibility that a dark sector might include light Lee-Wick particles. We present the formulation of a theory in which a dark photon and its Lee-Wick partner have kinetic mixing with hypercharge. We point out that the Lee-Wick partner of the dark photon will lead to an apparent violation of causality at small distance scales that might be discerned in low-energy experiments.

  3. Light thoughts on dark energy

    SciTech Connect

    Linder, Eric V.

    2004-04-01

    The physical process leading to the acceleration of the expansion of the universe is unknown. It may involve new high energy physics or extensions to gravitation. Calling this generically dark energy, we examine the consistencies and relations between these two approaches, showing that an effective equation of state function w(z) is broadly useful in describing the properties of the dark energy. A variety of cosmological observations can provide important information on the dynamics of dark energy and the future looks bright for constraining dark energy, though both the measurements and the interpretation will be challenging. We also discuss a more direct relation between the spacetime geometry and acceleration, via ''geometric dark energy'' from the Ricci scalar, and superacceleration or phantom energy where the fate of the universe may be more gentle than the Big Rip.

  4. Familon model of dark matter

    NASA Astrophysics Data System (ADS)

    Burdyuzha, V.; Lalakulich, O.; Ponomarev, Yu.; Vereshkov, G.

    2004-05-01

    If the next fundamental level of matter occurs (preons), then dark matter must consist of familons containing a 'hot' component from massless particles and a 'cold' component from massive particles. During the evolution of the Universe this dark matter occurred up to late-time relativistic phase transitions the temperatures of which were different. Fluctuations created by these phase transitions had a fractal character. As a result the structuration of dark matter (and therefore the baryon subsystem) occurred, and in the Universe some characteristic scales which have caused this phenomenon arise naturally. Familons are collective excitations of non-perturbative preon condensates that could be produced during an earlier relativistic phase transition. For structuration of dark matter (and the baryon component), three generations of particles are necessary. The first generation of particles produced the observed baryon world. The second and third generations produced dark matter from particles that appeared when symmetry between the generations was spontaneously broken.

  5. Properties of galactic dark matter: Constraints from astronomical observations

    SciTech Connect

    Burch, B.; Cowsik, R.

    2013-12-10

    The distributions of normal matter and of dark matter in the Galaxy are coupled to each other as they both move in the common gravitational potential. In order to fully exploit this interplay and to derive the various properties of dark matter relevant to their direct and indirect detection, we have comprehensively reviewed the astronomical observations of the spatial and velocity distributions of the components of normal matter. We then postulate that the phase-space distribution of dark matter follows a lowered-isothermal form and self-consistently solve Poisson's equation to construct several models for the spatial and velocity distributions of dark matter. In this paper, we compute the total gravitational potential of the normal and dark matter components and investigate their consistency with current observations of the rotation curve of the Galaxy and of the spatial and velocity distributions of blue horizontal-branch and blue straggler stars. Even with this demand of consistency, a large number of models with a range of parameters characterizing the dark matter distribution remain. We find that the best choice of parameters, within the range of allowed values for the surface density of the disk 55 M {sub ☉} pc{sup –2}, are the following: the dark matter density at the Galactic center ρ{sub DM,} {sub c} ≈ 100-250 GeV cm{sup –3}, the local dark matter density ρ{sub DM}(R {sub 0}) ≈ 0.56-0.72 GeV cm{sup –3}, and the rms speed of dark matter particles 〈v{sub DM}{sup 2}(R{sub 0})〉{sup 1/2}≈490−−550 km s{sup –1}. We also discuss possible astronomical observations that may further limit the range of the allowed models. The predictions of the allowed models for direct and indirect detection will be discussed separately in a companion paper.

  6. Constraints on particle dark matter from cosmic-ray antiprotons

    SciTech Connect

    Fornengo, N.; Vittino, A.; Maccione, L. E-mail: luca.maccione@lmu.de

    2014-04-01

    Cosmic-ray antiprotons represent an important channel for dark matter indirect-detection studies. Current measurements of the antiproton flux at the top of the atmosphere and theoretical determinations of the secondary antiproton production in the Galaxy are in good agreement, with no manifest deviation which could point to an exotic contribution in this channel. Therefore, antiprotons can be used as a powerful tool for constraining particle dark matter properties. By using the spectrum of PAMELA data from 50 MV to 180 GV in rigidity, we derive bounds on the dark matter annihilation cross section (or decay rate, for decaying dark matter) for the whole spectrum of dark matter annihilation (decay) channels and under different hypotheses of cosmic-rays transport in the Galaxy and in the heliosphere. For typical models of galactic propagation, the constraints are strong, setting a lower bound on the dark matter mass of a ''thermal'' relic at about 40–80 GeV for hadronic annihilation channels. These bounds are enhanced to about 150 GeV on the dark matter mass, when large cosmic-rays confinement volumes in the Galaxy are considered, and are reduced to 3–4 GeV for annihilation to light quarks (no bound for heavy-quark production) when the confinement volume is small. Bounds for dark matter lighter than few tens of GeV are due to the low energy part of the PAMELA spectrum, an energy region where solar modulation is relevant: to this aim, we have implemented a detailed solution of the transport equation in the heliosphere, which allowed us not only to extend bounds to light dark matter, but also to determine the uncertainty on the constraints arising from solar modulation modelling. Finally, we estimate the impact of soon-to-come AMS-02 data on the antiproton constraints.

  7. CCP: Sierra Nevada Captive-Carry Test

    NASA Video Gallery

    Sierra Nevada Corporation (SNC) Space System's Dream Chaser design passed one of its most complex tests to date with a successful captive-carry test conducted near the Rocky Mountain Metropolitan A...

  8. 25 CFR 167.6 - Carrying capacities.

    Code of Federal Regulations, 2012 CFR

    2012-04-01

    ...) Carrying capacities shall be stated in terms of sheep units yearlong, in the ratio of horses, mules, and..., goats, cattle, horses, mules, and burros one year of age or older shall be counted against the...

  9. Infections That Pets Carry (For Parents)

    MedlinePlus

    ... eczema should probably avoid aquariums. continue Dogs and Cats Dogs and cats are popular pets but can carry infections such ... be in the intestinal tract of infected dogs, cats, hamsters, birds, and certain farm animals. A person ...

  10. Jovian Dark Spot

    NASA Technical Reports Server (NTRS)

    1998-01-01

    A recently discovered black spot in Jupiter's clouds is darker than any feature ever before observed on the giant planet. The spot may be the result of a downward spiraling wind that blows away high clouds and reveals deeper, very dark cloud layers. These three panels depict the same area of Jupiter's atmosphere. A map of Jovian temperatures near 250 millibar pressure (top) panel is derived from the photopolarimeter-radiometer instrument on NASA's Galileo Jupiter orbiter. This map is compared with maps derived from images of the same area in visible light (middle panel)and thermal radiation sensitive to cloud-top temperatures (bottom panel).

    The single downward-pointing arrow in the top panel indicates the location of a warm area that corresponds to the position of a so-called 'black spot'(shown in the middle panel), a feature that is about a year old. Features this dark are rare on Jupiter. The bottom panel, sensitive to temperatures at Jupiter's cloud tops, shows this feature as a bright object, meaning that upper-level cold clouds are missing - allowing us to see deeper into Jupiter's warmer interior. The dark visible appearance of the feature than most likely represents the color of very deep clouds. The warm temperatures and cloud-free conditions imply that this feature is a region where dry upper-atmospheric gas is being forced to converge, is warmed up and then forced to descend, clearing out clouds. It is the opposite of wet, upwelling gas in areas such as Jupiter's Great Red Spot or white ovals. On the other hand, it is unlike the dry and relatively cloudless feature into which the Galileo probe descended in 1995, because that region had the same temperatures as its surroundings and did not appear nearly as dark as this new spot.

    The temperatures sampled by the photopolarimeter radiometer are near the top of Jupiter's troposphere, where wind motions control the atmosphere. The top row of arrows shows the location of temperature waves in a warm region

  11. Through a glass, darkly.

    PubMed

    Rittenberry, Ronnie

    2005-10-01

    The technology available in today's auto-darkening welding helmets was the stuff of science fiction to welders 30 years ago. A single lens capable of darkening automatically to a variable, preset shade level the instant an arc is struck would have sounded about as realistic as a "Star Trek"-style "transporter" or a cell phone that can take pictures. "It would have been complete and total science fiction," said Kevin Coughlin, president of Hoodlum Welding Gear, Minneapolis. "The technology really didn't exist, so it would be like me telling you your car will be flying in 20 years--you'd look at me and laugh. Even 25 years ago, if someone had told me [the lens] would go from clear to dark when you spark, I'd have said, 'Yeah, right, sure it does.' "

  12. Indirect Dark Matter Signals

    SciTech Connect

    Boer, Wim de

    2008-11-23

    Dark Matter annihilation (DMA) may yield an excess of gamma rays and antimatter particles, like antiprotons and positrons, above the background from cosmic ray interactions. Several signatures, ranging from the positron excess, as observed by HEAT, AMS-01 and PAMELA, the gamma ray excess, as observed by the EGRET spectrometer, the WMAP-haze, and constraints from antiprotons, as observed by CAPRICE, BESS and PAMELA, have been discussed in the literature. Unfortunately, the different signatures all lead to different WIMP masses, indicating that at least some of these interpretations are likely to be incorrect. Here we review them and discuss their relative merits and uncertainties. New x-ray data from ROSAT suggests non-negligible convection in our Galaxy, which leads to an order of magnitude uncertainty in the yield of charged particles from DMA, since even a rather small convection will let drift the charged particles in the halo to outer space.

  13. Dark Matter Burners

    SciTech Connect

    Moskalenko, Igor V.; Wai, Lawrence L.; /SLAC

    2007-02-28

    We show that a star orbiting close enough to an adiabatically grown supermassive black hole (SMBH) can capture weakly interacting massive particles (WIMPs) at an extremely high rate. The stellar luminosity due to annihilation of captured WIMPs in the stellar core may be comparable to or even exceed the luminosity of the star due to thermonuclear burning. The model thus predicts the existence of unusual stars, essentially WIMP burners, in the vicinity of a SMBH. We find that the most efficient WIMP burners are stars with degenerate electron cores, e.g. white dwarfs (WDs); such WDs may have a very high surface temperature. If found, such stars would provide evidence for the existence of particle dark matter and can possibly be used to establish its density profile. On the other hand, the lack of such unusual stars may provide constraints on the WIMP density near the SMBH, as well as the WIMP-nucleus scattering and pair annihilation cross-sections.

  14. Fractality of light's darkness.

    PubMed

    O'Holleran, Kevin; Dennis, Mark R; Flossmann, Florian; Padgett, Miles J

    2008-02-01

    Natural light fields are threaded by lines of darkness. For monochromatic light, the phenomenon is familiar in laser speckle, i.e., the black points that appear in the scattered light. These black points are optical vortices that extend as lines throughout the volume of the field. We establish by numerical simulations, supported by experiments, that these vortex lines have the fractal properties of a Brownian random walk. Approximately 73% of the lines percolate through the optical beam, the remainder forming closed loops. Our statistical results are similar to those of vortices in random discrete lattice models of cosmic strings, implying that the statistics of singularities in random optical fields exhibit universal behavior. PMID:18352372

  15. Dark light Higgs bosons.

    SciTech Connect

    Draper, P.; Liu, T.; Wagner, C. E. M.; Wang, L.-T.; Zhang, H.

    2011-03-24

    We study a limit of the nearly Peccei-Quinn-symmetric next-to-minimal supersymmetric standard model possessing novel Higgs and dark matter (DM) properties. In this scenario, there naturally coexist three light singletlike particles: a scalar, a pseudoscalar, and a singlinolike DM candidate, all with masses of order 0.1-10 GeV. The decay of a standard model-like Higgs boson to pairs of the light scalars or pseudoscalars is generically suppressed, avoiding constraints from collider searches for these channels. For a certain parameter window annihilation into the light pseudoscalar and exchange of the light scalar with nucleons allow the singlino to achieve the correct relic density and a large direct-detection cross section consistent with the DM direct-detection experiments, CoGeNT and DAMA/LIBRA, preferred region simultaneously. This parameter space is consistent with experimental constraints from LEP, the Tevatron, ?, and flavor physics.

  16. Avian dark cells

    NASA Technical Reports Server (NTRS)

    Hara, J.; Plymale, D. R.; Shepard, D. L.; Hara, H.; Garry, Robert F.; Yoshihara, T.; Zenner, Hans-Peter; Bolton, M.; Kalkeri, R.; Fermin, Cesar D.

    2002-01-01

    Dark cells (DCs) of mammalian and non-mammalian species help to maintain the homeostasis of the inner ear fluids in vivo. Although the avian cochlea is straight and the mammalian cochlea is coiled, no significant difference in the morphology and/or function of mammalian and avian DCs has been reported. The mammalian equivalent of avian DCs are marginal cells and are located in the stria vascularis along a bony sheet. Avian DCs hang free from the tegmentum vasculosum (TV) of the avian lagena between the perilymph and endolymph. Frame averaging was used to image the fluorescence emitted by several fluorochromes applied to freshly isolated dark cells (iDCs) from chickens (Gallus domesticus) inner ears. The viability of iDCs was monitored via trypan blue exclusion at each isolation step. Sodium Green, BCECF-AM, Rhodamine 123 and 9-anthroyl ouabain molecules were used to test iDC function. These fluorochromes label iDCs ionic transmembrane trafficking function, membrane electrogenic potentials and Na+/K+ ATPase pump's activity. Na+/K+ ATPase pump sites, were also evaluated by the p-nitrophenyl phosphatase reaction. These results suggest that iDCs remain viable for several hours after isolation without special culturing requirements and that the number and functional activity of Na+/K+ ATPase pumps in the iDCs were indistinguishable from in vivo DCs. Primary cultures of freshly iDCs were successfully maintained for 28 days in plastic dishes with RPMI 1640 culture medium. The preparation of iDCs overcomes the difficulty of DCs accessability in vivo and the unavoidable contamination that rupturing the inner ear microenvironments induces.

  17. HST/WFC3: Improvements to the UVIS Dark Calibration

    NASA Astrophysics Data System (ADS)

    Bourque, Matthew; Baggett, Sylvia M.; WFC3 Team

    2016-06-01

    The Hubble Space Telescope (HST) Wide Field Camera 3 (WFC3) UVIS detector, comprised of two e2v CCDs, exhibits an inherent dark current (in the absence of any illumination) presently measured at ~7 e-/hr and increasing at ~1 e-/hr/yr. Additionally, detector degradation due to on-orbit radiation damage generates a continuously increasing though small population of hot pixels (dark current exceeding 54 e-/hr, currently ~4% of each chip). We present the results of the WFC3/UVIS dark calibration, which provides calibration files used as a correction for these detector characteristics. We also discuss the impacts that Charge Transfer Efficiency (CTE) losses and detector post-flashing have on the hot pixel population, as well as various improvements to the calibration procedure that were introduced in the CALWF3 v3.3 pipeline.

  18. Broadband and Resonant Approaches to Axion Dark Matter Detection

    NASA Astrophysics Data System (ADS)

    Kahn, Yonatan; Safdi, Benjamin R.; Thaler, Jesse

    2016-09-01

    When ultralight axion dark matter encounters a static magnetic field, it sources an effective electric current that follows the magnetic field lines and oscillates at the axion Compton frequency. We propose a new experiment to detect this axion effective current. In the presence of axion dark matter, a large toroidal magnet will act like an oscillating current ring, whose induced magnetic flux can be measured by an external pickup loop inductively coupled to a SQUID magnetometer. We consider both resonant and broadband readout circuits and show that a broadband approach has advantages at small axion masses. We estimate the reach of this design, taking into account the irreducible sources of noise, and demonstrate potential sensitivity to axionlike dark matter with masses in the range of 10-14-10-6 e V . In particular, both the broadband and resonant strategies can probe the QCD axion with a GUT-scale decay constant.

  19. Mechanical analysis of infant carrying in hominoids

    NASA Astrophysics Data System (ADS)

    Amaral, Lia Q.

    2008-04-01

    In all higher nonhuman primates, species survival depends upon safe carrying of infants clinging to body hair of adults. In this work, measurements of mechanical properties of ape hair (gibbon, orangutan, and gorilla) are presented, focusing on constraints for safe infant carrying. Results of hair tensile properties are shown to be species-dependent. Analysis of the mechanics of the mounting position, typical of heavier infant carrying among African apes, shows that both clinging and friction are necessary to carry heavy infants. As a consequence, a required relationship between infant weight, hair-hair friction coefficient, and body angle exists. The hair-hair friction coefficient is measured using natural ape skin samples, and dependence on load and humidity is analyzed. Numerical evaluation of the equilibrium constraint is in agreement with the knuckle-walking quadruped position of African apes. Bipedality is clearly incompatible with the usual clinging and mounting pattern of infant carrying, requiring a revision of models of hominization in relation to the divergence between apes and hominins. These results suggest that safe carrying of heavy infants justify the emergence of biped form of locomotion. Ways to test this possibility are foreseen here.

  20. Detecting dark matter substructure spectroscopically in strong gravitational lenses

    NASA Astrophysics Data System (ADS)

    Moustakas, Leonidas A.; Metcalf, R. Benton

    2003-03-01

    The cold dark matter (CDM) model for galaxy formation predicts that a significant fraction of mass in the dark matter haloes that surround L~L* galaxies is bound in substructures of mass 104-107 Msolar. The number of observable baryonic substructures (such as dwarf galaxies and globular clusters) falls short of these predictions by at least an order of magnitude. We present a method for searching for substructure in the haloes of gravitational lenses that produce multiple images of quasi-stellar objects (QSOs), such as four-image Einstein Cross lenses. Current methods based on broad-band flux ratios cannot cleanly distinguish between substructure, differential extinction, scattering in the radio by ionized regions in the lens galaxy, microlensing by stars and, most importantly, ambiguities in the host lens model. These difficulties may be overcome by utilizing the prediction that, when substructure is present, the magnification will be a function of source size. QSO broad-line and narrow-line emission regions are ~1 pc and >100 pc in size, respectively. The radio emission region is typically intermediate to these and the continuum emission region is much smaller. When narrow-line region (NLR) features are used as a normalization, the relative intensity and equivalent width of broad-line region (BLR) features will respectively reflect substructure-lensing and microlensing effects. Spectroscopic observations of just a few image pairs would probably be able to extract the desired substructure signature cleanly and distinguish it from microlensing - depending on the actual level of projected mass in substructure. In the rest-optical, the Hβ/[OIII] region is ideal, since the narrow wavelength range also largely eliminates differential reddening problems. In the rest-ultraviolet, the region longward of and including Lyα may also work. Simulations of Q2237+0305 are done as an example, to determine the level of substructure that is detectable in this way. Possible