The s-wave SU(5) monopole-fermion system reduces to a coupled set of exactly solvable QFTs
NASA Astrophysics Data System (ADS)
Craigie, N. S.; Nahm, W.
1984-11-01
By establishing that the SU(2) colour sector of fermions in the SU(5) 't Hooft-Polyakov monopole system has an underlying SU(2) Kac-Moody algebra with central charge unity, we show for massless fermions that the whole system can be reduced to a coupled set of exactly integrable two-dimensional QFT's in radial space. Consequently all the non-perturbative effects in the Green functions governing baryon number non-conservation can be explicitly computed up to the effect of the ordinary QCD confining vacuum, which is relevant only at long distances from the monopole's core.
Miller, M C; Reus, J F; Matzke, R P; Arrighi, W J; Schoof, L A; Hitt, R T; Espen, P K; Butler, D M
2001-02-07
This paper describes the Sets and Fields (SAF) scientific data modeling system. It is a revolutionary approach to interoperation of high performance, scientific computing applications based upon rigorous, math-oriented data modeling principles. Previous technologies have required all applications to use the same data structures and/or meshes to represent scientific data or lead to an ever expanding set of incrementally different data structures and/or meshes. SAF addresses this problem by providing a small set of mathematical building blocks--sets, relations and fields--out of which a wide variety of scientific data can be characterized. Applications literally model their data by assembling these building blocks. A short historical perspective, a conceptual model and an overview of SAF along with preliminary results from its use in a few ASCI codes are discussed.
Entrepreneurial Academics: Developing Scientific Careers in Changing University Settings
ERIC Educational Resources Information Center
Duberley, Joanne; Cohen, Laurie; Leeson, Elspeth
2007-01-01
This paper examines the impact of entrepreneurial initiatives within universities on scientific careers. Based on the career accounts of university-based bioscientists involved in a government-sponsored entrepreneurship training initiative, the paper explores the concept of academic entrepreneurialism. Three groups were identified in the data.…
Entanglement in fermionic systems
Banuls, Mari-Carmen; Cirac, J. Ignacio; Wolf, Michael M.
2007-08-15
The anticommuting properties of fermionic operators, together with the presence of parity conservation, affect the concept of entanglement in a composite fermionic system. Hence different points of view can give rise to different reasonable definitions of separable and entangled states. Here we analyze these possibilities and the relationship between the different classes of separable states. The behavior of the various classes when taking multiple copies of a state is also studied, showing that some of the differences vanish in the asymptotic regime. In particular, in the case of only two fermionic modes all the classes become equivalent in this limit. We illustrate the differences and relations by providing a complete characterization of all the sets defined for systems of two fermionic modes. The results are applied to Gibbs states of infinite chains of fermions whose interaction corresponds to a XY Hamiltonian with transverse magnetic field.
Fermions from classical statistics
Wetterich, C.
2010-12-15
We describe fermions in terms of a classical statistical ensemble. The states {tau} of this ensemble are characterized by a sequence of values one or zero or a corresponding set of two-level observables. Every classical probability distribution can be associated to a quantum state for fermions. If the time evolution of the classical probabilities p{sub {tau}} amounts to a rotation of the wave function q{sub {tau}}(t)={+-}{radical}(p{sub {tau}}(t)), we infer the unitary time evolution of a quantum system of fermions according to a Schroedinger equation. We establish how such classical statistical ensembles can be mapped to Grassmann functional integrals. Quantum field theories for fermions arise for a suitable time evolution of classical probabilities for generalized Ising models.
NASA Technical Reports Server (NTRS)
Strecker, Kevin; Truscott, Andrew; Partridge, Guthrie; Chen, Ying-Cheng
2003-01-01
Dual evaporation gives 50 million fermions at T = 0.1 T(sub F). Demonstrated suppression of interactions by coherent superposition - applicable to atomic clocks. Looking for evidence of Cooper pairing and superfluidity.
SAF - Sets and Fields parallel I/O and scientific data modeling system
Energy Science and Technology Software Center (ESTSC)
2005-07-01
SAF is being developed as part of the Data Models and Formats (DMF) component of the Accelerated Strategic Computing Initiative (ASCI). SAF represents a revolutionary approach to interoperation of high performance, scientific computing applications based upon rigorous, math oriented data modeling principles. Previous technologies have required all applications to use the same data structures and/or mesh objects to represent scientific data or lead to an ever expanding set of incrementally different data structures and/or meshmore » objects. SAF addresses this problem by providing a small set of mathematical building blocks, sets, relations and fields, out of which a wide variety of scientific data can be characterized. Applications literally model their data by assembling these building blocks. Sets and fields building blocks are at once, both primitive and abstract: * They are primitive enough to model a wide variety of scientific data. * They are abstract enough to model the data in terms of what it represents in a mathematical or physical sense independent of how it is represented in an implementation sense. For example, while there are many ways to represent the airflow over the wing of a supersonic aircraft in a computer program, there is only one mathematical/physical interpretation: a field of 3D velocity vectors over a 2D surface. This latter description is immutable. It is independent of any particular representation or implementation choices. Understanding this what versus how relationship, that is what is represented versus how it is represented, is key to developing a solution for large scale integration of scientific software.« less
SAF - Sets and Fields parallel I/O and scientific data modeling system
Matzke, Robb; Illescas, Eric; Espen, Peter; Jones, Jake S.; Sjaardema, Gregory; Miller, Mark C.; Schoof, Larry A.; Reus, James F.; Arrighi, William; Hitt, Ray T.; O'Brien, Matthew J.
2005-07-01
SAF is being developed as part of the Data Models and Formats (DMF) component of the Accelerated Strategic Computing Initiative (ASCI). SAF represents a revolutionary approach to interoperation of high performance, scientific computing applications based upon rigorous, math oriented data modeling principles. Previous technologies have required all applications to use the same data structures and/or mesh objects to represent scientific data or lead to an ever expanding set of incrementally different data structures and/or mesh objects. SAF addresses this problem by providing a small set of mathematical building blocks, sets, relations and fields, out of which a wide variety of scientific data can be characterized. Applications literally model their data by assembling these building blocks. Sets and fields building blocks are at once, both primitive and abstract: * They are primitive enough to model a wide variety of scientific data. * They are abstract enough to model the data in terms of what it represents in a mathematical or physical sense independent of how it is represented in an implementation sense. For example, while there are many ways to represent the airflow over the wing of a supersonic aircraft in a computer program, there is only one mathematical/physical interpretation: a field of 3D velocity vectors over a 2D surface. This latter description is immutable. It is independent of any particular representation or implementation choices. Understanding this what versus how relationship, that is what is represented versus how it is represented, is key to developing a solution for large scale integration of scientific software.
NASA Astrophysics Data System (ADS)
Javarone, Marco Alberto
2016-08-01
We study the structure of fermionic networks, i.e. a model of networks based on the behavior of fermionic gases, and we analyze dynamical processes over them. In this model, particle dynamics have been mapped to the domain of networks, hence a parameter representing the temperature controls the evolution of the system. In doing so, it is possible to generate adaptive networks, i.e. networks whose structure varies over time. As shown in previous works, networks generated by quantum statistics can undergo critical phenomena as phase transitions and, moreover, they can be considered as thermodynamic systems. In this study, we analyze fermionic networks and opinion dynamics processes over them, framing this network model as a computational model useful to represent complex and adaptive systems. Results highlight that a strong relation holds between the gas temperature and the structure of the achieved networks. Notably, both the degree distribution and the assortativity vary as the temperature varies, hence we can state that fermionic networks behave as adaptive networks. On the other hand, it is worth to highlight that we did not finding relation between outcomes of opinion dynamics processes and the gas temperature. Therefore, although the latter plays a fundamental role in gas dynamics, on the network domain, its importance is related only to structural properties of fermionic networks.
NASA Astrophysics Data System (ADS)
Stokes, George Gabriel; Larmor, Joseph
2010-06-01
Volume 1: Preface; Part I. Personal and Biographical; Part II. General Scientific Career; Part IIIa. Special Scientific Correspondence; Appendix; Index. Volume 2: Part. III. Special Scientific Correspondence; Index.
Wang, Zhijun; Alexandradinata, A; Cava, R J; Bernevig, B Andrei
2016-04-14
Spatial symmetries in crystals may be distinguished by whether they preserve the spatial origin. Here we study spatial symmetries that translate the origin by a fraction of the lattice period, and find that these non-symmorphic symmetries protect an exotic surface fermion whose dispersion relation is shaped like an hourglass; surface bands connect one hourglass to the next in an unbreakable zigzag pattern. These 'hourglass' fermions are formed in the large-gap insulators, KHgX (X = As, Sb, Bi), which we propose as the first material class whose band topology relies on non-symmorphic symmetries. Besides the hourglass fermion, another surface of KHgX manifests a three-dimensional generalization of the quantum spin Hall effect, which has previously been observed only in two-dimensional crystals. To describe the bulk topology of non-symmorphic crystals, we propose a non-Abelian generalization of the geometric theory of polarization. Our non-trivial topology originates from an inversion of the rotational quantum numbers, which we propose as a criterion in the search for topological materials. PMID:27075096
NASA Astrophysics Data System (ADS)
Wang, Zhijun; Alexandradinata, A.; Cava, Robert J.; Bernevig, B. Andrei
Spatial symmetries in crystals are distinguished by whether they preserve the spatial origin. We show how this basic geometric property gives rise to a new topology in band insulators. We study spatial symmetries that translate the origin by a fraction of the lattice period, and find that these nonsymmorphic symmetries protect a novel surface fermion whose dispersion is shaped like an hourglass; surface bands connect one hourglass to the next in an unbreakable zigzag pattern. These exotic fermions are materialized in the large-gap insulators: KHg X (X = As,Sb,Bi), which we propose as the first material class whose topology relies on nonsymmorphic symmetries. Beside the hourglass fermion, a different surface of KHg X manifests a 3D generalization of the quantum spin Hall effect. To describe the bulk topology of nonsymmorphic crystals, we propose a non-Abelian generalization of the geometric theory of polarization. Our nontrivial topology originates not from an inversion of the parity quantum numbers, but rather of the rotational quantum numbers, which we propose as a fruitful in the search for topological materials. Finally, KHg X uniquely exemplifies a cohomological insulator, a concept that we will introduce in a companion work.
Mead, Geoffrey; Lammerding, Anna M; Cox, Nelson; Doyle, Michael P; Humbert, Florence; Kulikovskiy, Alexander; Panin, Alexander; do Nascimento, Vladimir Pinheiro; Wierup, Martin
2010-08-01
Concerns about foodborne salmonellosis have led many countries to introduce microbiological criteria for certain food products. If such criteria are not well-grounded in science, they could be an unjustified obstacle to trade. Raw poultry products are an important part of the global food market. Import and export ambiguities and regulatory confusion resulting from different Salmonella requirements were the impetus for convening an international group of scientific experts from 16 countries to discuss the scientific and technical issues that affect the setting of a microbiological criterion for Salmonella contamination of raw chicken. A particular concern for the group was the use of criteria implying a zero tolerance for Salmonella and suggesting complete absence of the pathogen. The notion can be interpreted differently by various stakeholders and was considered inappropriate because there is neither an effective means of eliminating Salmonella from raw poultry nor any practical method for verifying its absence. Therefore, it may be more useful at present to set food safety metrics that involve reductions in hazard levels. Such terms as "zero tolerance" or "absence of a microbe" in relation to raw poultry should be avoided unless defined and explained by international agreement. Risk assessment provides a more meaningful approach than a zero tolerance philosophy, and new metrics, such as performance objectives that are linked to human health outcomes, should be utilized throughout the food chain to help define risk and identify ways to reduce adverse effects on public health. PMID:20819373
The Gaussian entropy of fermionic systems
Prokopec, Tomislav; Schmidt, Michael G.; Weenink, Jan
2012-12-15
We consider the entropy and decoherence in fermionic quantum systems. By making a Gaussian Ansatz for the density operator of a collection of fermions we study statistical 2-point correlators and express the entropy of a system fermion in terms of these correlators. In a simple case when a set of N thermalised environmental fermionic oscillators interacts bi-linearly with the system fermion we can study its time dependent entropy, which also represents a quantitative measure for decoherence and classicalization. We then consider a relativistic fermionic quantum field theory and take a mass mixing term as a simple model for the Yukawa interaction. It turns out that even in this Gaussian approximation, the fermionic system decoheres quite effectively, such that in a large coupling and high temperature regime the system field approaches the temperature of the environmental fields. - Highlights: Black-Right-Pointing-Pointer We construct the Gaussian density operator for relativistic fermionic systems. Black-Right-Pointing-Pointer The Gaussian entropy of relativistic fermionic systems is described in terms of 2-point correlators. Black-Right-Pointing-Pointer We explicitly show the growth of entropy for fermionic fields mixing with a thermal fermionic environment.
EUDAT and EPOS moving towards the efficient management of scientific data sets
NASA Astrophysics Data System (ADS)
Fiameni, Giuseppe; Bailo, Daniele; Cacciari, Claudio
2016-04-01
This abstract presents the collaboration between the European Collaborative Data Infrastructure (EUDAT) and the pan-European infrastructure for solid Earth science (EPOS) which draws on the management of scientific data sets through a reciprocal support agreement. EUDAT is a Consortium of European Data Centers and Scientific Communities whose focus is the development and realisation of the Collaborative Data Infrastructure (CDI), a common model for managing data spanning all European research data centres and data repositories and providing an interoperable layer of common data services. The EUDAT Service Suite is a set of a) implementations of the CDI model and b) standards, developed and offered by members of the EUDAT Consortium. These EUDAT Services include a baseline of CDI-compliant interface and API services - a "CDI Gateway" - plus a number of web-based GUIs and command-line client tools. On the other hand,the EPOS initiative aims at creating a pan-European infrastructure for the solid Earth science to support a safe and sustainable society. In accordance with this scientific vision, the mission of EPOS is to integrate the diverse and advanced European Research Infrastructures for solid Earth Science relying on new e-science opportunities to monitor and unravel the dynamic and complex Earth System. EPOS will enable innovative multidisciplinary research for a better understanding of the Earth's physical and chemical processes that control earthquakes, volcanic eruptions, ground instability and tsunami as well as the processes driving tectonics and Earth's surface dynamics. Through the integration of data, models and facilities EPOS will allow the Earth Science community to make a step change in developing new concepts and tools for key answers to scientific and socio-economic questions concerning geo-hazards and geo-resources as well as Earth sciences applications to the environment and to human welfare. To achieve this integration challenge and the
Cooling an acute muscle injury: can basic scientific theory translate into the clinical setting?
Bleakley, C M; Glasgow, P; Webb, M J
2012-03-01
Ice is commonly used after acute muscle strains but there are no clinical studies of its effectiveness. By comparison, there are a number of basic scientific studies on animals which show that applying ice after muscle injury has a consistent effect on a number of important cellular and physiological events relating to recovery. Some of these effects may be temperature dependant; most animal studies induce significant reductions in muscle temperature at the injury site. The aim of this short report was to consider the cooling magnitudes likely in human models of muscle injury and to discuss its relevance to the clinical setting. Current best evidence shows that muscle temperature reductions in humans are moderate in comparison to most animal models, limiting direct translation to the clinical setting. Further important clinical questions arise when we consider the heterogenous nature of muscle injury in terms of injury type, depth and insulating adipose thickness. Contrary to current practice, it is unlikely that a 'panacea' cooling dose or duration exists in the clinical setting. Clinicians should consider that in extreme circumstances of muscle strain (eg, deep injury with high levels of adipose thickness around the injury site), the clinical effectiveness of cooling may be significantly reduced. PMID:21677317
The Scientific Basis of Uncertainty Factors Used in Setting Occupational Exposure Limits
Dankovic, D. A.; Naumann, B. D.; Maier, A.; Dourson, M. L.; Levy, L. S.
2015-01-01
The uncertainty factor concept is integrated into health risk assessments for all aspects of public health practice, including by most organizations that derive occupational exposure limits. The use of uncertainty factors is predicated on the assumption that a sufficient reduction in exposure from those at the boundary for the onset of adverse effects will yield a safe exposure level for at least the great majority of the exposed population, including vulnerable subgroups. There are differences in the application of the uncertainty factor approach among groups that conduct occupational assessments; however, there are common areas of uncertainty which are considered by all or nearly all occupational exposure limit-setting organizations. Five key uncertainties that are often examined include interspecies variability in response when extrapolating from animal studies to humans, response variability in humans, uncertainty in estimating a no-effect level from a dose where effects were observed, extrapolation from shorter duration studies to a full life-time exposure, and other insufficiencies in the overall health effects database indicating that the most sensitive adverse effect may not have been evaluated. In addition, a modifying factor is used by some organizations to account for other remaining uncertainties—typically related to exposure scenarios or accounting for the interplay among the five areas noted above. Consideration of uncertainties in occupational exposure limit derivation is a systematic process whereby the factors applied are not arbitrary, although they are mathematically imprecise. As the scientific basis for uncertainty factor application has improved, default uncertainty factors are now used only in the absence of chemical-specific data, and the trend is to replace them with chemical-specific adjustment factors whenever possible. The increased application of scientific data in the development of uncertainty factors for individual chemicals also
The Scientific Basis of Uncertainty Factors Used in Setting Occupational Exposure Limits.
Dankovic, D A; Naumann, B D; Maier, A; Dourson, M L; Levy, L S
2015-01-01
The uncertainty factor concept is integrated into health risk assessments for all aspects of public health practice, including by most organizations that derive occupational exposure limits. The use of uncertainty factors is predicated on the assumption that a sufficient reduction in exposure from those at the boundary for the onset of adverse effects will yield a safe exposure level for at least the great majority of the exposed population, including vulnerable subgroups. There are differences in the application of the uncertainty factor approach among groups that conduct occupational assessments; however, there are common areas of uncertainty which are considered by all or nearly all occupational exposure limit-setting organizations. Five key uncertainties that are often examined include interspecies variability in response when extrapolating from animal studies to humans, response variability in humans, uncertainty in estimating a no-effect level from a dose where effects were observed, extrapolation from shorter duration studies to a full life-time exposure, and other insufficiencies in the overall health effects database indicating that the most sensitive adverse effect may not have been evaluated. In addition, a modifying factor is used by some organizations to account for other remaining uncertainties-typically related to exposure scenarios or accounting for the interplay among the five areas noted above. Consideration of uncertainties in occupational exposure limit derivation is a systematic process whereby the factors applied are not arbitrary, although they are mathematically imprecise. As the scientific basis for uncertainty factor application has improved, default uncertainty factors are now used only in the absence of chemical-specific data, and the trend is to replace them with chemical-specific adjustment factors whenever possible. The increased application of scientific data in the development of uncertainty factors for individual chemicals also has
Stereoscopy in Static Scientific Imagery in an Informal Education Setting: Does It Matter?
NASA Astrophysics Data System (ADS)
Price, C. Aaron; Lee, H.-S.; Malatesta, K.
2014-12-01
Stereoscopic technology (3D) is rapidly becoming ubiquitous across research, entertainment and informal educational settings. Children of today may grow up never knowing a time when movies, television and video games were not available stereoscopically. Despite this rapid expansion, the field's understanding of the impact of stereoscopic visualizations on learning is rather limited. Much of the excitement of stereoscopic technology could be due to a novelty effect, which will wear off over time. This study controlled for the novelty factor using a variety of techniques. On the floor of an urban science center, 261 children were shown 12 photographs and visualizations of highly spatial scientific objects and scenes. The images were randomly shown in either traditional (2D) format or in stereoscopic format. The children were asked two questions of each image—one about a spatial property of the image and one about a real-world application of that property. At the end of the test, the child was asked to draw from memory the last image they saw. Results showed no overall significant difference in response to the questions associated with 2D or 3D images. However, children who saw the final slide only in 3D drew more complex representations of the slide than those who did not. Results are discussed through the lenses of cognitive load theory and the effect of novelty on engagement.
NASA Astrophysics Data System (ADS)
Cook, H. M.; Cook, G. W.
2015-12-01
The mystery box is a well-known and well-loved teaching tool designed to encourage students to engage in making observations in order to draw conclusions. We have adapted this exercise, normally used in laboratory settings, for use in a lecture setting in introductory earth science classes. We have tied it to the scientific method such that students are engaging in mystery-box- based inquiry while exploring the steps of the scientific method. It is used in conjunction with a PowerPoint presentation that illustrates and discusses the steps and process integral to the scientific method, which is fundamental to science. Students are encouraged to explore the formal and informal use of the scientific method throughout their educational careers and in their daily lives. Furthermore, students are challenged to analyze the necessity of the scientific method as means for conducting scientific inquiry and exploring the results of such inquiry. A follow-up assignment to the activity asks students to evaluate the efficacy of the activity and associated PowerPoint and discussion. Students consistently report having enjoyed and learned from the process.
ERIC Educational Resources Information Center
Furberg, Anniken; Ludvigsen, Sten
2008-01-01
This article reports on a study concerning secondary school students' meaning-making of socio-scientific issues in Information and Communication Technology-mediated settings. Our theoretical argument has as its point of departure the analytical distinction between "doing science" and "doing school," as two different forms of classroom activity. In…
ERIC Educational Resources Information Center
Fives, Allyn; Russell, Daniel W.; Canavan, John; Lyons, Rena; Eaton, Patricia; Devaney, Carmel; Kearns, Norean; O'Brien, Aoife
2015-01-01
In a randomized controlled trial (RCT), treatments are assigned randomly and treatments are withheld from participants. Is it ethically permissible to conduct an RCT in a social setting? This paper addresses two conditions for justifying RCTs: that there should be a state of equipoise and that the trial should be scientifically promising.…
Fermionization and Hubbard models
NASA Astrophysics Data System (ADS)
Dargis, P.; Maassarani, Z.
1998-12-01
We introduce a transformation which allows the fermionization of operators of any one-dimensional spin-chain. This fermionization procedure is independent of any eventual integrable structure and is compatible with it. We illustrate this method on various integrable and non-integrable chains, and deduce some general results. In particular, we fermionize XXC spin-chains and study their symmetries. Fermionic realizations of certain Lie algebras and superalgebras appear naturally as symmetries of some models. We also fermionize recently obtained Hubbard models, and obtain for the first time multispecies analogues of the Hubbard model, in their fermionic form. We comment on the conflict between symmetry enhancement and integrability of these models. Finally, the fermionic versions of the non-integrable spin-1 and spin- {3}/{2} Heisenberg chains are obtained.
Open fermionic quantum systems
Artacho, E.; Falicov, L.M. Materials Sciences Division, Lawrence Berkeley Laboratory, Berkeley, California 94720 )
1993-01-15
A method to treat a quantum system in interaction with a fermionic reservoir is presented. Its most important feature is that the dynamics of the exchange of particles between the system and the reservoir is explicitly included via an effective interaction term in the Hamiltonian. This feature gives rise to fluctuations in the total number of particles in the system. The system is to be considered in its full structure, whereas the reservoir is described only in an effective way, as a source of particles characterized by a small set of parameters. Possible applications include surfaces, molecular clusters, and defects in solids, in particular in highly correlated electronic materials. Four examples are presented: a tight-binding model for an adsorbate on the surface of a one-dimensional lattice, the Anderson model of a magnetic impurity in a metal, a two-orbital impurity with interorbital hybridization (intermediate-valence center), and a two-orbital impurity with interorbital repulsive interactions.
Visualization and Evolution of the Scientific Structure of Fuzzy Sets Research in Spain
ERIC Educational Resources Information Center
Lopez-Herrera, A. G.; Cobo, M. J.; Herrera-Viedma, E.; Herrera, F.; Bailon-Moreno, R.; Jimenez-Contreras, E.
2009-01-01
Introduction: Presents the first bibliometric study on the evolution of the fuzzy sets theory field. It is specially focused on the research carried out by the Spanish community. Method. The CoPalRed software, for network analysis, and the co-word analysis technique are used. Analysis: Bibliometric maps showing the main associations among the…
Stereoscopy in Static Scientific Imagery in an Informal Education Setting: Does It Matter?
ERIC Educational Resources Information Center
Price, C. Aaron; Lee, H.-S.; Malatesta, K.
2014-01-01
Stereoscopic technology (3D) is rapidly becoming ubiquitous across research, entertainment and informal educational settings. Children of today may grow up never knowing a time when movies, television and video games were not available stereoscopically. Despite this rapid expansion, the field's understanding of the impact of stereoscopic…
An Analysis Framework Addressing the Scale and Legibility of Large Scientific Data Sets
Childs, H R
2006-11-20
Much of the previous work in the large data visualization area has solely focused on handling the scale of the data. This task is clearly a great challenge and necessary, but it is not sufficient. Applying standard visualization techniques to large scale data sets often creates complicated pictures where meaningful trends are lost. A second challenge, then, is to also provide algorithms that simplify what an analyst must understand, using either visual or quantitative means. This challenge can be summarized as improving the legibility or reducing the complexity of massive data sets. Fully meeting both of these challenges is the work of many, many PhD dissertations. In this dissertation, we describe some new techniques to address both the scale and legibility challenges, in hope of contributing to the larger solution. In addition to our assumption of simultaneously addressing both scale and legibility, we add an additional requirement that the solutions considered fit well within an interoperable framework for diverse algorithms, because a large suite of algorithms is often necessary to fully understand complex data sets. For scale, we present a general architecture for handling large data, as well as details of a contract-based system for integrating advanced optimizations into a data flow network design. We also describe techniques for volume rendering and performing comparisons at the extreme scale. For legibility, we present several techniques. Most noteworthy are equivalence class functions, a technique to drive visualizations using statistical methods, and line-scan based techniques for characterizing shape.
NASA Astrophysics Data System (ADS)
Raker, Jeffrey R.
Reform efforts in science education have called for instructional methods and resources that mirror the practice of science. Little research and design methods have been documented in the literature for designing such materials. The purpose of this study was to develop problems sets for sophomore-level organic chemistry instruction. This research adapted an instructional design methodology from the science education literature for the creation of new curricular problem sets. The first phase of this study was to establish an understanding of current curricular problems in sophomore-level organic chemistry instruction. A sample of 792 problems was collected from four organic chemistry courses. These problems were assessed using three literature reported problem typologies. Two of these problem typologies have previously been used to understand general chemistry problems; comparisons between general and organic chemistry problems were thus made. Data from this phase was used to develop a set of five problems for practicing organic chemists. The second phase of this study was to explore practicing organic chemists' experiences solving problems in the context of organic synthesis research. Eight practicing organic chemists were interviewed and asked to solve two to three of the problems developed in phase one of this research. These participants spoke of three problem types: project level, synthetic planning, and day-to-day. Three knowledge types (internal knowledge, knowledgeable others, and literature) were used in solving these problems in research practice and in the developed problems. A set of guiding factors and implications were derived from this data and the chemistry education literature for the conversion of the problems for practicing chemists to problems for undergraduate students. A subsequent conversion process for the five problems occurred. The third, and last phase, of this study was to explore undergraduate students' experiences solving problems in
NASA Astrophysics Data System (ADS)
Zeman, Antonín; Šmíd, Michal; Havelcová, Martina; Coufalová, Lucie; Kučková, Štěpánka; Velčovská, Martina; Hynek, Radovan
2013-11-01
Degenerative aortic stenosis has become a common and dangerous disease in recent decades. This disease leads to the mineralization of aortic valves, their gradual thickening and loss of functionality. We studied the detailed assessment of the proportion and composition of inorganic and organic components in the ossified aortic valve, using a set of analytical methods applied in science: polarized light microscopy, scanning electron microscopy, X-ray fluorescence, X-ray diffraction, gas chromatography/mass spectrometry and liquid chromatography-tandem mass spectrometry. The sample valves showed the occurrence of phosphorus and calcium in the form of phosphate and calcium carbonate, hydroxyapatite, fluorapatite and hydroxy-fluorapatite, with varying content of inorganic components from 65 to 90 wt%, and with phased development of degenerative disability. The outer layers of the plaque contained an organic component with peptide bonds, fatty acids, proteins and cholesterol. The results show a correlation between the formation of fluorapatite in aortic valves and in other parts of the human bodies, associated with the formation of bones.
Bold Diagrammatic Monte Carlo for Fermionic and Fermionized Systems
NASA Astrophysics Data System (ADS)
Svistunov, Boris
2013-03-01
In three different fermionic cases--repulsive Hubbard model, resonant fermions, and fermionized spins-1/2 (on triangular lattice)--we observe the phenomenon of sign blessing: Feynman diagrammatic series features finite convergence radius despite factorial growth of the number of diagrams with diagram order. Bold diagrammatic Monte Carlo technique allows us to sample millions of skeleton Feynman diagrams. With the universal fermionization trick we can fermionize essentially any (bosonic, spin, mixed, etc.) lattice system. The combination of fermionization and Bold diagrammatic Monte Carlo yields a universal first-principle approach to strongly correlated lattice systems, provided the sign blessing is a generic fermionic phenomenon. Supported by NSF and DARPA
NASA Astrophysics Data System (ADS)
Iliesiu, Luca; Kos, Filip; Poland, David; Pufu, Silviu S.; Simmons-Duffin, David; Yacoby, Ran
2016-03-01
We study the conformal bootstrap for a 4-point function of fermions < ψψψψ> in 3D. We first introduce an embedding formalism for 3D spinors and compute the conformal blocks appearing in fermion 4-point functions. Using these results, we find general bounds on the dimensions of operators appearing in the ψ × ψ OPE, and also on the central charge C T . We observe features in our bounds that coincide with scaling dimensions in the GrossNeveu models at large N . We also speculate that other features could coincide with a fermionic CFT containing no relevant scalar operators.
NASA Astrophysics Data System (ADS)
Weiner, Richard M.
2010-05-01
It is conjectured that all known fermions are topological solitons. This could explain the non-observation of bosonic leptons and baryons and provide a physical mechanism for the Pauli exclusion principle.
Canonical gravity with fermions
Bojowald, Martin; Das, Rupam
2008-09-15
Canonical gravity in real Ashtekar-Barbero variables is generalized to allow for fermionic matter. The resulting torsion changes several expressions in Holst's original vacuum analysis, which are summarized here. This in turn requires adaptations to the known loop quantization of gravity coupled to fermions, which is discussed on the basis of the classical analysis. As a result, parity invariance is not manifestly realized in loop quantum gravity.
A geometrical formulation of fermionic integrable systems
Das, A.; Huang, W.; Roy, S. )
1991-10-01
A fermionic Hamiltonian system is formulated on a supermanifold. It is shown that if the system possesses a bi-Hamiltonian structure, one can naturally define a Lax equation associated with a (1,1) tensor on this supermanifold and this allows one to construct a set of conserved quantities. Furthermore, if the corresponding Nijenhuis tensor vanishes, it is shown that all these conserved quantities would be in involution which is a sufficient condition for integrability of the system. The fermionic extension of the KdV equation with a bi-Hamiltonian structure within this geometrical approach is studied.
NASA Astrophysics Data System (ADS)
Marino, Eduardo
The electron, discovered by Thomson by the end of the nineteenth century, was the first experimentally observed particle. The Weyl fermion, though theoretically predicted since a long time, was observed in a condensed matter environment in an experiment reported only a few weeks ago. Is there any linking thread connecting the first and the last observed fermion (quasi)particles? The answer is positive. By generalizing the method known as bosonization, the first time in its full complete form, for a spacetime with 3+1 dimensions, we are able to show that both electrons and Weyl fermions can be expressed in terms of the same boson field, namely the Kalb-Ramond anti-symmetric tensor gauge field. The bosonized form of the Weyl chiral currents lead to the angle-dependent magneto-conductance behavior observed in these systems.
Grossman, Yuval; Harnik, Roni; Perez, Gilad; Schwartz, MatthewD.; Surujon, Ze'ev
2004-07-30
The observed flavor structure of the standard model arises naturally in ''split fermion'' models which localize fermions at different places in an extra dimension. It has, until now, been assumed that the bulk masses for such fermions can be chosen to be flavor diagonal simultaneously at every point in the extra dimension, with all the flavor violation coming from the Yukawa couplings to the Higgs. We consider the more natural possibility in which the bulk masses cannot be simultaneously diagonalized, that is, that they are twisted in flavor space. We show that, in general, this does not disturb the natural generation of hierarchies in the flavor parameters. Moreover, it is conceivable that all the flavor mixing and CP-violation in the standard model may come only from twisting, with the five-dimensional Yukawa couplings taken to be universal.
Grossman, Y
2004-07-24
The observed flavor structure of the standard model arises naturally in ''split fermion'' models which localize fermions at different places in an extra dimension. It has, until now, been assumed that the bulk masses for such fermions can be chosen to be flavor diagonal simultaneously at every point in the extra dimension, with all the flavor violation coming from the Yukawa couplings to the Higgs. We consider the more natural possibility in which the bulk masses cannot be simultaneously diagonalized, that is, that they are twisted in flavor space. We show that, in general, this does not disturb the natural generation of hierarchies in the flavor parameters. Moreover, it is conceivable that all the flavor mixing and CP-violation in the standard model may come only from twisting, with the five-dimensional Yukawa couplings taken to be universal.
Technology Transfer Automated Retrieval System (TEKTRAN)
On September 11-14, 2012, the US Environmental Protection Agency convened a public meeting of the FIFRA Scientific Advisory Panel (SAP) to address scientific issues associated with the Office of Pesticides Program’s (OPP) proposed “Pollinator Risk Assessment Framework”. Several sources have reporte...
s-Wave collisional frequency shift of a fermion clock.
Hazlett, Eric L; Zhang, Yi; Stites, Ronald W; Gibble, Kurt; O'Hara, Kenneth M
2013-04-19
We report an s-wave collisional frequency shift of an atomic clock based on fermions. In contrast to bosons, the fermion clock shift is insensitive to the population difference of the clock states, set by the first pulse area in Ramsey spectroscopy, θ(1). The fermion shift instead depends strongly on the second pulse area θ(2). It allows the shift to be canceled, nominally at θ(2)=π/2, but correlations perturb the null to slightly larger θ(2). The frequency shift is relevant for optical lattice clocks and increases with the spatial inhomogeneity of the clock excitation field, naturally larger at optical frequencies. PMID:23679589
NASA Technical Reports Server (NTRS)
Schofield, Norman J. (Editor); Parthasarathy, R. (Editor); Hills, H. Kent (Editor)
1988-01-01
The main purpose of the data catalog series is to provide descriptive references to data generated by space science flight missions. The data sets described include all of the actual holdings of the Space Science Data Center (NSSDC), all data sets for which direct contact information is available, and some data collections held and serviced by foreign investigators, NASA and other U.S. government agencies. This volume contains narrative descriptions of data sets from geostationary and high altitude scientific spacecraft and investigations. The following spacecraft series are included: Mariner, Pioneer, Pioneer Venus, Venera, Viking, Voyager, and Helios. Separate indexes to the planetary and interplanetary missions are also provided.
NASA Technical Reports Server (NTRS)
Jackson, John E. (Editor); Horowitz, Richard (Editor)
1986-01-01
The main purpose of the data catalog series is to provide descriptive references to data generated by space science flight missions. The data sets described include all of the actual holdings of the Space Science Data Center (NSSDC), all data sets for which direct contact information is available, and some data collections held and serviced by foreign investigators, NASA and other U.S. government agencies. This volume contains narrative descriptions of data sets from low and medium altitude scientific spacecraft and investigations. The following spacecraft series are included: Mariner, Pioneer, Pioneer Venus, Venera, Viking, Voyager, and Helios. Separate indexes to the planetary and interplanetary missions are also provided.
Hadron Properties with FLIC Fermions
James Zanotti; Wolodymyr Melnitchouk; Anthony Williams; J Zhang
2003-07-01
The Fat-Link Irrelevant Clover (FLIC) fermion action provides a new form of nonperturbative O(a)-improvement in lattice fermion actions offering near continuum results at finite lattice spacing. It provides computationally inexpensive access to the light quark mass regime of QCD where chiral nonanalytic behavior associated with Goldstone bosons is revealed. The motivation and formulation of FLIC fermions, its excellent scaling properties and its low-lying hadron mass phenomenology are presented.
The Set Point Theory of Well-Being Has Serious Flaws: On the Eve of a Scientific Revolution?
ERIC Educational Resources Information Center
Headey, Bruce
2010-01-01
Set-point theory is the main research paradigm in the field of subjective well-being (SWB). It has been extended and refined for 30 years to take in new results. The central plank of the theory is that adult set-points do not change, except temporarily in the face of major life events. There was always some "discordant data," including evidence…
Nucleon Resonances from FLIC Fermions
Derek Leinweber; J. Hedditch; Wally Melnitchouk; Anthony Williams
2003-01-01
The Fat Link Irrelevant Glover (FL1C) fermion action and its associated phenomenology is described. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative O(a) improvement where near-continuum results are obtained at finite lattice spacing spin-1/2 and spin-3/2 , even and odd parity nucleon resonances are investigated.
Unconventional superconductivity in heavy-fermion compounds
White, B. D.; Thompson, J. D.; Maple, M. B.
2015-02-27
Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion com- pounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates andmore » iron-based superconductors. Lastly, we conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.« less
Unconventional superconductivity in heavy-fermion compounds
White, B. D.; Thompson, J. D.; Maple, M. B.
2015-02-27
Over the past 35 years, research on unconventional superconductivity in heavy-fermion systems has evolved from the surprising observations of unprecedented superconducting properties in compounds that convention dictated should not superconduct at all to performing explorations of rich phase spaces in which the delicate interplay between competing ground states appears to support emergent superconducting states. In this article, we review the current understanding of superconductivity in heavy-fermion com- pounds and identify a set of characteristics that is common to their unconventional superconducting states. These core properties are compared with those of other classes of unconventional superconductors such as the cuprates and iron-based superconductors. Lastly, we conclude by speculating on the prospects for future research in this field and how new advances might contribute towards resolving the long-standing mystery of how unconventional superconductivity works.
Mather, M. E.; Parrish, D.L.; Dettmers, J.M.
2008-01-01
In the last 25 years, the number and scope of fish-related journals have changed. New and existing journals are increasingly specialized. Journals that are read and cited are changing because of differential accessibility via electronic databases. In this review, we examine shifts in numbers and foci of existing fish-related journals. We ask how these fish-related metrics differ across type of application, ecological system, taxa, and discipline. Although many journals overlap to some extent in content, there are distinct groups of journals for authors to consider. By systematically reviewing the focus of an individual manuscript, comparing it to the suite of journals available and examining the audience for the manuscript, we believe that authors can make informed decisions about which journals are most suitable for their work. Our goal here is to help authors find relevant journals and deliver scientific publications to the appropriate readership.
Technology Transfer Automated Retrieval System (TEKTRAN)
The purpose of this statement is to provide an overview of new and emerging tools and strategies for discussing weight and assisting overweight and obese patients. Only tools and strategies that can be used practically in busy ambulatory settings are included. The goal is to provide clinicians with ...
ERIC Educational Resources Information Center
Graves, Chiron; Rutherford, Sandra
2012-01-01
Educational research focused on questioning techniques used in classroom settings is quite extensive. However, research regarding a teacher's ability to generate research questions is virtually nonexistent. Posing research or "testable" questions is a key component of inquiry-based instruction, and teachers must be able to both generate these…
EDITORIAL: International Conference on Finite Fermionic Systems: Nilsson Model 50 Years
NASA Astrophysics Data System (ADS)
2006-06-01
In 1955 Sven Gösta Nilsson published the paper `Binding States of Individual Nucleons in Strongly Deformed Nuclei'. This eminent work has been crucial for the understanding of the structure of deformed atomic nuclei. Moreover, the so-called Nilsson model has been widely used for the description of other types of finite systems of fermions such as quantum dots and cold fermionic atoms. During one week in June 2005 we celebrated in Lund the 50th anniversary of the Nilsson model with the International Conference on Finite Fermionic Systems - Nilsson Model 50 Years. With the historical view in mind, the conference focused on present and future problems in nuclear structure physics as well as on the physics of other types of finite Fermi systems. As a background to the recent developments Nobel Laureate Ben Mottelson presented a recollection of early applications and achievements of the Nilsson model in the first talk of the conference, including a personal view of Sven Gösta Nilsson. We are particularly pleased that this contribution could be included in these proceedings. The scientific programme was structured according to the following subjects: Shell structure and deformations The heaviest elements and beyond Nuclei far from stability Pairing correlations Nuclear spectroscopy: large deformations Nuclear spectroscopy: rotational states Order and chaos Cold fermionic atoms Quantum dots Many new and interesting results were presented in the 15 invited talks, 30 oral contributions, and in the 33 papers of the poster sessions. The present volume of Physica Scripta contains most of the talks, as well as the short contributions of the posters. We thank the speakers and all participants who actively contributed to give this memorable conference a very high scientific level in the presented contributions, as well as in numerous discussions inside and outside the sessions. We also thank the international advisory committee for their invaluable work in helping us setting up
Dynamical symmetries for fermions
Guidry, M.
1989-01-01
An introduction is given to the Fermion Dynamical Symmetry Model (FDSM). The analytical symmetry limits of the model are then applied to the calculation of physical quantities such as ground-state masses and B(E{sub 2}) values in heavy nuclei. These comparisons with data provide strong support for a new principle of collective motion, the Dynamical Pauli Effect, and suggest that dynamical symmetries which properly account for the pauli principle are much more persistent in nuclear structure than the corresponding boson symmetries. Finally, we present an assessment of criticisms which have been voiced concerning the FDSM, and a discussion of new phenomena and exotic spectroscopy'' which may be suggested by the model. 14 refs., 8 figs., 4 tabs.
Unlocking fermionic mode entanglement
NASA Astrophysics Data System (ADS)
Friis, Nicolai
2016-06-01
Aside from other puzzling features of entanglement, it has been debated whether a physically meaningful notion of entanglement requires two (or more) particles as carriers of the correlated degrees-of-freedom, or if a single particle could be considered to be entangled as well. While the usefulness of single-boson entanglement has been demonstrated some time ago, the restrictions of superselection rules have previously thwarted attempts at similar arguments for single fermions. In Dasenbrook et al (2016 New J. Phys. 18 043036) this obstacle is overcome. The authors propose a scheme for a Bell test on two copies of single-electron states whose entanglement is individually not accessible. The discussed scheme, which makes use of recent progress in electronic quantum optics, provides an experimentally viable and theoretically unambiguous way to assert that certain single-electron states can be considered to be entangled.
FLIC Fermions and Hadron Phenomenology
D. Leinweber; J.N. Hedditch; W. Melnitchouk; A.W. Thomas; A.G. Williams; R.D. Young; J.M. Zanotti; J.B. Zhang
2002-06-01
A pedagogical overview of the formulation of the Fat Link Irrelevant Clover (FLIC) fermion action and its associated phenomenology is described. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative order (a) improvement where near-continuum results are obtained at finite lattice spacing. Spin-1/2 and spin-3/2, even and odd parity baryon resonances are investigated in quenched QCD, where the nature of the Roper resonance and Lambda (1405) are of particular interest. FLIC fermions allow efficient access to the light quark-mass regime, where evidence of chiral nonanalytic behavior in the Delta mass is observed.
NASA Astrophysics Data System (ADS)
Hofmeister, Richard; Lemmen, Carsten; Nasermoaddeli, Hassan; Klingbeil, Knut; Wirtz, Kai
2015-04-01
Data and models for describing coastal systems span a diversity of disciplines, communities, ecosystems, regions and techniques. Previous attempts of unifying data exchange, coupling interfaces, or metadata information have not been successful. We introduce the new Modular System for Shelves and Coasts (MOSSCO, http://www.mossco.de), a novel coupling framework that enables the integration of a diverse array of models and data from different disciplines relating to coastal research. In the MOSSCO concept, the integrating framework imposes very few restrictions on contributed data or models; in fact, there is no distinction made between data and models. The few requirements are: (1) principle coupleability, i.e. access to I/O and timing information in submodels, which has recently been referred to as the Basic Model Interface (BMI) (2) open source/open data access and licencing and (3) communication of metadata, such as spatiotemporal information, naming conventions, and physical units. These requirements suffice to integrate different models and data sets into the MOSSCO infrastructure and subsequently built a modular integrated modeling tool that can span a diversity of processes and domains. We demonstrate how diverse coastal system constituents were integrated into this modular framework and how we deal with the diverging development of constituent data sets and models at external institutions. Finally, we show results from simulations with the fully coupled system using OGC WebServices in the WiMo geoportal (http://kofserver3.hzg.de/wimo), from where stakeholders can view the simulation results for further dissemination.
AdS{sub 5} black holes with fermionic hair
Burrington, Benjamin A.; Liu, James T.; Sabra, W. A.
2005-05-15
The study of new Bogomol'nyi-Prasad-Sommerfield (BPS) objects in AdS{sub 5} has led to a deeper understanding of AdS/CFT. To help complete this picture, and to fully explore the consequences of the supersymmetry algebra, it is also important to obtain new solutions with bulk fermions turned on. In this paper we construct superpartners of the 1/2 BPS black hole in AdS{sub 5} using a natural set of fermion zero modes. We demonstrate that these superpartners, carrying fermionic hair, have conserved charges differing from the original bosonic counterpart. To do so, we find the R-charge and dipole moment of the new system, as well as the mass and angular momentum, defined through the boundary stress tensor. The complete set of superpartners fits nicely into a chiral representation of AdS{sub 5} supersymmetry, and the spinning solutions have the expected gyromagnetic ratio, g=1.
Observing remnants by fermions' tunneling
Chen, D.Y.; Wu, H.W.; Yang, H. E-mail: iverwu@uestc.edu.cn
2014-03-01
The standard Hawking formula predicts the complete evaporation of black holes. In this paper, we introduce effects of quantum gravity into fermions' tunneling from Reissner-Nordstrom and Kerr black holes. The quantum gravity effects slow down the increase of Hawking temperatures. This property naturally leads to a residue mass in black hole evaporation. The corrected temperatures are affected by the quantum numbers of emitted fermions. Meanwhile, the temperature of the Kerr black hole is a function of θ due to the rotation.
Standard electromagnetically driven cosmology coupled with fermionic source
Mello, M. M. C.; Klippert, R.
2015-03-10
Dirac fermions and electromagnetic fields are considered as the source of gravitation in the framework of standard Friedmann-Lemaître-Robertson-Walker (FLRW) cosmology. It is shown that all solutions for the scale-factor a(t) are non-singular, provided the cosmological constant Λ is set to be less than the positive inverse of a quantum scale.
Staggered fermions, zero modes, and flavor-singlet mesons
Donald, Gordon C; Davies, Christine T.H.; Follana, Eduardo; Kronfeld, Andreas S.
2011-09-12
We examine the taste structure of eigenvectors of the staggered-fermion Dirac operator. We derive a set of conditions on the eigenvectors of modes with small eigenvalues (near-zero modes), such that staggered fermions reproduce the 't Hooft vertex in the continuum limit. We also show that, assuming these conditions, the correlators of flavor-singlet mesons are free of contributions singular in 1/m, where m is the quark mass. This conclusion holds also when a single flavor of sea quark is represented by the fourth root of the staggered-fermion determinant. We then test numerically, using the HISQ action, whether these conditions hold onmore » realistic lattice gauge fields. We find that the needed structure does indeed emerge.« less
Staggered fermions, zero modes, and flavor-singlet mesons
Donald, Gordon C; Davies, Christine T.H.; Follana, Eduardo; Kronfeld, Andreas S.
2011-09-12
We examine the taste structure of eigenvectors of the staggered-fermion Dirac operator. We derive a set of conditions on the eigenvectors of modes with small eigenvalues (near-zero modes), such that staggered fermions reproduce the 't Hooft vertex in the continuum limit. We also show that, assuming these conditions, the correlators of flavor-singlet mesons are free of contributions singular in 1/m, where m is the quark mass. This conclusion holds also when a single flavor of sea quark is represented by the fourth root of the staggered-fermion determinant. We then test numerically, using the HISQ action, whether these conditions hold on realistic lattice gauge fields. We find that the needed structure does indeed emerge.
Fermionic corrections to fluid dynamics from BTZ black hole
NASA Astrophysics Data System (ADS)
Gentile, L. G. C.; Grassi, P. A.; Mezzalira, A.
2015-11-01
We reconstruct the complete fermionic orbit of the non-extremal BTZ black hole by acting with finite supersymmetry transformations. The solution satisfies the exact supergravity equations of motion to all orders in the fermonic expansion and the final result is given in terms of fermionic bilinears. By fluid/gravity correspondence, we derive linearized Navier-Stokes equations and a set of new differential equations from Rarita-Schwinger equation. We compute the boundary energy-momentum tensor and we interpret the result as a perfect fluid with a modified definition of fluid velocity. Finally, we derive the modified expression for the entropy of the black hole in terms of the fermionic bilinears.
Fermion localization on thick branes
Melfo, Alejandra; Pantoja, Nelson; Tempo, Jose David
2006-02-15
We consider chiral fermion confinement in scalar thick branes, which are known to localize gravity, coupled through a Yukawa term. The conditions for the confinement and their behavior in the thin-wall limit are found for various different BPS branes, including double walls and branes interpolating between different AdS{sub 5} spacetimes. We show that only one massless chiral mode is localized in all these walls, whenever the wall thickness is keep finite. We also show that, independently of wall's thickness, chiral fermionic modes cannot be localized in dS{sub 4} walls embedded in a M{sub 5} spacetime. Finally, massive fermions in double wall spacetimes are also investigated. We find that, besides the massless chiral mode localization, these double walls support quasilocalized massive modes of both chiralities.
Fermion production during and after axion inflation
Adshead, Peter; Sfakianakis, Evangelos I.
2015-11-11
We study derivatively coupled fermions in axion-driven inflation, specifically m{sub ϕ}{sup 2}ϕ{sup 2} and monodromy inflation, and calculate particle production during the inflationary epoch and the post-inflationary axion oscillations. During inflation, the rolling axion acts as an effective chemical potential for helicity which biases the gravitational production of one fermion helicity over the other. This mechanism allows for efficient gravitational production of heavy fermion states that would otherwise be highly suppressed. Following inflation, the axion oscillates and fermions with both helicities are produced as the effective frequency of the fermion field changes non-adiabatically. For certain values of the fermion mass and axion-fermion coupling strength, the two helicity states are produced asymmetrically, resulting in unequal number-densities of left- and right-helicity fermions.
Fermionic influence on inflationary fluctuations
NASA Astrophysics Data System (ADS)
Boyanovsky, Daniel
2016-04-01
Motivated by apparent persistent large scale anomalies in the cosmic microwave background we study the influence of fermionic degrees of freedom on the dynamics of inflaton fluctuations as a possible source of violations of (nearly) scale invariance on cosmological scales. We obtain the nonequilibrium effective action of an inflaton-like scalar field with Yukawa interactions (YD ,M) to light fermionic degrees of freedom both for Dirac and Majorana fields in de Sitter space-time. The effective action leads to Langevin equations of motion for the fluctuations of the inflaton-like field, with self-energy corrections and a stochastic Gaussian noise. We solve the Langevin equation in the super-Hubble limit implementing a dynamical renormalization group resummation. For a nearly massless inflaton its power spectrum of super-Hubble fluctuations is enhanced, P (k ;η )=(H/2 π )2eγt[-k η ] with γt[-k η ]=1/6 π2 [∑i =1 NDYi,D 2+2 ∑j =1 NMYj,M 2]{ln2[-k η ]-2 ln [-k η ]ln [-k η0]} for ND Dirac and NM Majorana fermions, and η0 is the renormalization scale at which the inflaton mass vanishes. The full power spectrum is shown to be renormalization group invariant. These corrections to the super-Hubble power spectrum entail a violation of scale invariance as a consequence of the coupling to the fermionic fields. The effective action is argued to be exact in the limit of a large number of fermionic fields. A cancellation between the enhancement from fermionic degrees of freedom and suppression from light scalar degrees of freedom conformally coupled to gravity suggests the possibility of a finely tuned supersymmetry among these fields.
Fermionic composite models from complementarity
NASA Astrophysics Data System (ADS)
Bordi, F.; Casalbuoni, R.; Dominici, D.; Gatto, R.
1982-08-01
Composite models for (in principle massless) quarks and leptons without fundamental scalars are constructed with the aim of providing for fermionic realizations of models which include elementary bosons (by Abbott and Farhi, Casalbuoni and Gatto and Barbieri, Mohapatra and Masiero). The models use one confining unitary (subcolor) group (with left-handed fermions in the fundamental, in its conjugate, and either in the adjoint, or in the symmetric, or in the antisymmetric representation of subcolor) or two confining groups. Families may arise from discrete symmetries.
NASA Astrophysics Data System (ADS)
Colangeli, Matteo; Pezzotti, Federica; Pulvirenti, Mario
2015-05-01
We introduce a stochastic N-particle system and show that, as N → ∞, an effective description ruled by the homogeneous fermionic Uehling-Uhlenbeck equation is recovered. The particle model we consider is the same as the Kac model for the homogeneous Boltzmann equation with an additional exclusion constraint taking into account the Pauli Exclusion Principle.
Technology Transfer Automated Retrieval System (TEKTRAN)
On December 2-4, 2014, the US Environmental Protection Agency convened a public meeting of the FIFRA Scientific Advisory Panel (SAP) to address scientific issues associated with the agency’s “Integrated Endocrine Bioactivity and Exposure-Based Prioritization and Screening” methods. EPA is proposing ...
Searches for Fourth Generation Fermions
Ivanov, A.; /Fermilab
2011-09-01
We present the results from searches for fourth generation fermions performed using data samples collected by the CDF II and D0 Detectors at the Fermilab Tevatron p{bar p} collider. Many of these results represent the most stringent 95% C. L. limits on masses of new fermions to-date. A fourth chiral generation of massive fermions with the same quantum numbers as the known fermions is one of the simplest extensions of the SM with three generations. The fourth generation is predicted in a number of theories, and although historically have been considered disfavored, stands in agreement with electroweak precision data. To avoid Z {yields} {nu}{bar {nu}} constraint from LEP I a fourth generation neutrino {nu}{sub 4} must be heavy: m({nu}{sub 4}) > m{sub Z}/2, where m{sub Z} is the mass of Z boson, and to avoid LEP II bounds a fourth generation charged lepton {ell}{sub 4} must have m({ell}{sub 4}) > 101 GeV/c{sup 2}. At the same time due to sizeable radiative corrections masses of fourth generation fermions cannot be much higher the current lower bounds and masses of new heavy quarks t' and b' should be in the range of a few hundred GeV/c{sup 2}. In the four-generation model the present bounds on the Higgs are relaxed: the Higgs mass could be as large as 1 TeV/c{sup 2}. Furthermore, the CP violation is significantly enhanced to the magnitude that might account for the baryon asymmetry in the Universe. Additional chiral fermion families can also be accommodated in supersymmetric two-Higgs-doublet extensions of the SM with equivalent effect on the precision fit to the Higgs mass. Another possibility is heavy exotic quarks with vector couplings to the W boson Contributions to radiative corrections from such quarks with mass M decouple as 1/M{sup 2} and easily evade all experimental constraints. At the Tevatron p{bar p} collider 4-th generation chiral or vector-like quarks can be either produced strongly in pairs or singly via electroweak production, where the latter can be
Radiative fermion masses in local D-brane models
NASA Astrophysics Data System (ADS)
Burgess, C. P.; Krippendorf, Sven; Maharana, Anshuman; Quevedo, Fernando
2011-05-01
In the context of D-brane model building, we present a realistic framework for generating fermion masses that are forbidden by global symmetries. We show that the string theoretical Large volume scenario circumvents the standard lore that fermion masses generated by loop effects are too small in generic gravity mediated scenarios. We argue that the fact that in toric singularity models, the up quark masses have always a zero eigenvalue, corresponding to the lightest generation, is due to the presence of approximate global symmetries that we explicitly identify in del Pezzo singularities. These symmetries are broken by global effects and therefore proportional to inverse powers of the volume. We estimate the generic size of radiative corrections to fermion masses in different phenomenological manifestations of the Large volume scenario. Concrete realizations in terms of flavor violating soft-terms are estimated and contrasted with current bounds on flavour changing neutral currents. Contributions from generic extra Higgs-like fields set bounds on their masses close to the GUT scale to produce realistic fermion masses.
Domain wall fermion quenched spectroscopy
NASA Astrophysics Data System (ADS)
Malureanu, Catalin Ionut
We measure y and the hadron spectrum on quenched ensembles using the domain wall fermion formulation. For the first time a 1/mf behavior of y for small valence masses has been observed. Our measurements of y on two different volumes of 83 x 32 and 163 x 32 at β = 5.85 suggest the behavior goes away on large enough volumes. Extensive spectrum calculations were done on 8 3 x 32 lattices at β = 5.7 and 5.85 corresponding roughly to a box size of 1.6 fm and 1.0 fm respectively. We have investigated five values of the extent of the fifth dimension Ls = 10, 16, 24, 32 and 48 with valence masses in the range 0.02 to 0.2 for the β = 5.7 ensemble and two values of Ls = 10 and 16 with valence masses in the range 0.02 to 0.08 for the β = 5.85 ensemble. Our pion remains massive in the infinite Ls extrapolation. This may be a finite volume effect. The nucleon to rho mass ratio stays constant at 1.4(1). Scaling violations for domain wall fermions are smaller roughly by a factor of four compared to the scaling violations in similar calculations done with staggered fermions.
Superdeformations and fermion dynamical symmetries
Wu, Cheng-Li . Dept. of Physics and Atmospheric Science Tennessee Univ., Knoxville, TN . Dept. of Physics and Astronomy Joint Inst. for Heavy Ion Research, Oak Ridge, TN )
1990-01-01
In this talk, I will present a link between nuclear collective motions and their underlying fermion dynamical symmetries. In particular, I will focus on the microscopic understanding of deformations. It is shown that the SU{sub 3} of the one major shell fermion dynamical symmetry model (FDSM) is responsible for the physics of low and high spins in normal deformation. For the recently observed phenomena of superdeformation, the physics of the problem dictates a generalization to a supershell structure (SFDSM), which also has an SU{sub 3} fermion dynamical symmetry. Many recently discovered feature of superdeformation are found to be inherent in such an SU{sub 3} symmetry. In both cases the dynamical Pauli effect plays a vital role. A particularly noteworthy discovery from this model is that the superdeformed ground band is not the usual unaligned band but the D-pair aligned (DPA) band, which sharply crosses the excited bands. The existence of such DPA band is a key point to understand many properties of superdeformation. Our studies also poses new experimental challenge. This is particularly interesting since there are now plans to build new and exciting {gamma}-ray detecting systems, like the GAMMASPHERE, which could provide answers to some of these challenges. 34 refs., 11 figs., 5 tabs.
Dephasing time of composite fermions
Lee, P.A.; Mucciolo, E.R.
1996-09-01
We study the dephasing of fermions interacting with a fluctuating transverse-gauge field. The divergence of the imaginary part of the fermion self-energy at finite temperatures is shown to result from a breakdown of Fermi{close_quote}s golden rule due to a faster than exponential decay in time. The strong dephasing affects experiments where phase coherence is probed. This result is used to describe the suppression of Shubnikov{endash}de Haas (SdH) oscillations of composite fermions (oscillations in the conductivity near the half-filled Landau level). We find that it is important to take into account both the effect of dephasing and the mass renormalization. We conclude that while it is possible to use the conventional theory to extract an effective mass from the temperature dependence of the SdH oscillations, the resulting effective mass differs from the {ital m}{sup {asterisk}} of the quasiparticle in Fermi-liquid theory. {copyright} {ital 1996 The American Physical Society.}
Light scattering of degenerate fermions
NASA Astrophysics Data System (ADS)
Aubin, S.; Leblanc, L. J.; Myrskog, S.; Extavour, M. H. T.; McKay, D.; Stummer, A.; Thywissen, J. H.
2006-05-01
We report on progress in measuring the suppression of resonant light scattering in a gas of degenerate fermions. A gas of trapped degenerate fermions is expected to exhibit narrower optical linewidths and longer excited state lifetimes than single atoms when the Fermi energy is larger than the photon recoil energy [1-3]. In this case, the number of available states into which a scattered atom can recoil is significantly reduced due to the filling of the Fermi sea. We produce a degenerate gas of 4x10^4 ultra-cold fermionic ^40K atoms by sympathetic cooling with bosonic ^87Rb in a micro-magnetic chip trap. The atoms can then be loaded into a tight dipole trap just above the surface of the chip and probed with a near resonance laser pulse. [1] Th. Busch, J. R. Anglin, J. I. Cirac, and P. Zoller, Europhys. Lett. 44, 1 (1998). [2] B. DeMarco and D. S. Jin, Phys. Rev. A 58, R4267 (1998). [3] J. Javanainen and J. Ruostekosky, Phys. Rev. A 52, 3033 (1995). Work supported by NSERC, CFI, OIT, Research Corporation, and PRO.
Issues in heavy fermions and in high-T c superconductive materials raised at this conference
NASA Astrophysics Data System (ADS)
Varma, C. M.
1991-05-01
In this closing session at the conference I would like, in the light of the presentations at this conference to briefly summarize the remarkable progress achieved in the heavy-fermion and heavy-fermion superconductivity problems, and point to what seem to me the principal problems remaining. The situation in the theory of high- Tc materials, on the face of it, appears much less bright. Unlike the heavy fermions, there is no agreement on what model represents the essentials of the problem. I believe, the difficulty in achieving a consensus here is only partly scientific. It is also sociological. I will paint a rather sanguine picture of the scientific developments there as well.
NASA Astrophysics Data System (ADS)
Baisden, T. W.
2013-12-01
Setting limits on pollution is an inherently political process negotiated between stakeholders within society. Science has a critical, but not dominant role in setting environmental limits. Over the past 20 years, nations have had the opportunity to build on a period of major international successes, limiting ozone-depleting chemicals and sulphur emissions causing acid rain. The science and politics of solutions attempted during this time has become vastly more complicated, and the outcome has been disappointing: global greenhouse gas emissions remain at business-as-usual trajectories. It seems logical and timely to examine the landscape before forging onward. In a brief review of lessons learned from the perspective of earth-system science within New Zealand, I highlight key examples and opportunities for creating more promising way forward. Among the lessons are that small-scale limit setting can host important innovation, while collapses can occur when systems that are too-big-to-fail but lack critical pre-requisites. In this sense, implementation of cap-and-trade for water quality may represent the former, while the collapse of C prices highlight the latter. Of critical importance is the simple observation that perceived uncertainties must be brought within bounds that make decisions possible. The way in which system are framed scientifically can be of overarching significance. Cap and trade for nutrients in New Zealand catchments has enabled small-scale illustrations of how the system frame can be vital in successful policy. For example, the N budget of Lake Taupo is simplified by focusing on inputs to the land, while 100-year forcing equivalence still raises questions about managing climate change. Relationships between emissions and activity must be distilled based on sound science, in a manner simple and certain enough for people and businesses to meaningfully consider in decisions that are made every day. With trust becoming a major limiting factor in the
Fermionic thermocoherent state: Efficiency of electron transport
NASA Astrophysics Data System (ADS)
Karmakar, Anirban; Gangopadhyay, Gautam
2016-02-01
On the basis of the fermionic coherent state of Cahill and Glauber [Phys. Rev. A 59, 1538 (1999)], 10.1103/PhysRevA.59.1538, we have introduced here the fermionic thermocoherent state in terms of the quasiprobability distribution which shows the appropriate thermal and coherent limits as in the bosonic case or the Glauber-Lachs state. It is shown that the fermionic thermocoherent state can be realized as a displaced thermal state of fermions. Its relation with the fermionic displaced number state and the fermion-added coherent state are explored in the spirit of the bosonic case. We have investigated the nature of the average current and the suppression of noise due to the thermocoherent character of the source. The theory is applied to the problem of electronic conduction. A modification of the Landauer conductance formula is suggested which reflects the role of nonzero coherence of the source in electron transport.
Cold collisions between boson or fermion molecules
Kajita, Masatoshi
2004-01-01
We theoretically investigate collisions between electrostatically trapped cold polar molecules and compare boson and fermion isotopes. Evaporative cooling seems possible for fermion molecules as the ratio of the collision loss cross section to the elastic collision cross section (R) gets smaller as the molecular temperature T lowers. With boson molecules, R gets larger as T lowers, which makes evaporative cooling difficult. The elastic collision cross section between fermion molecules can be larger than that for boson molecules with certain conditions.
Fermion back reaction and the sphaleron
Roberge, A. )
1994-02-15
Using a simple model, a new sphaleron solution which incorporates finite fermionic density effects is obtained. The main result is that the height of the potential barrier (sphaleron energy) decreases as the fermion density increases. This suggests that the rate of sphaleron-induced transitions increases when the fermionic density increases. However the rate increase is not expected to change significantly the predictions from the standard sphaleron-induced baryogenesis scenarios.
Myers, Teresa A; Maibach, Edward; Peters, Ellen; Leiserowitz, Anthony
2015-01-01
Human-caused climate change is happening; nearly all climate scientists are convinced of this basic fact according to surveys of experts and reviews of the peer-reviewed literature. Yet, among the American public, there is widespread misunderstanding of this scientific consensus. In this paper, we report results from two experiments, conducted with national samples of American adults, that tested messages designed to convey the high level of agreement in the climate science community about human-caused climate change. The first experiment tested hypotheses about providing numeric versus non-numeric assertions concerning the level of scientific agreement. We found that numeric statements resulted in higher estimates of the scientific agreement. The second experiment tested the effect of eliciting respondents' estimates of scientific agreement prior to presenting them with a statement about the level of scientific agreement. Participants who estimated the level of agreement prior to being shown the corrective statement gave higher estimates of the scientific consensus than respondents who were not asked to estimate in advance, indicating that incorporating an "estimation and reveal" technique into public communication about scientific consensus may be effective. The interaction of messages with political ideology was also tested, and demonstrated that messages were approximately equally effective among liberals and conservatives. Implications for theory and practice are discussed. PMID:25812121
Myers, Teresa A.; Maibach, Edward; Peters, Ellen; Leiserowitz, Anthony
2015-01-01
Human-caused climate change is happening; nearly all climate scientists are convinced of this basic fact according to surveys of experts and reviews of the peer-reviewed literature. Yet, among the American public, there is widespread misunderstanding of this scientific consensus. In this paper, we report results from two experiments, conducted with national samples of American adults, that tested messages designed to convey the high level of agreement in the climate science community about human-caused climate change. The first experiment tested hypotheses about providing numeric versus non-numeric assertions concerning the level of scientific agreement. We found that numeric statements resulted in higher estimates of the scientific agreement. The second experiment tested the effect of eliciting respondents’ estimates of scientific agreement prior to presenting them with a statement about the level of scientific agreement. Participants who estimated the level of agreement prior to being shown the corrective statement gave higher estimates of the scientific consensus than respondents who were not asked to estimate in advance, indicating that incorporating an “estimation and reveal” technique into public communication about scientific consensus may be effective. The interaction of messages with political ideology was also tested, and demonstrated that messages were approximately equally effective among liberals and conservatives. Implications for theory and practice are discussed. PMID:25812121
Light quark simulations with FLIC fermions
J.M. Zanotti; D.B. Leinweber; W. Melnitchouk; A.G. Williams; J.B. Zhang
2002-06-01
Hadron masses are calculated in quenched lattice QCD in order to probe the scaling behavior of a novel fat-link clover fermion action in which only the irrelevant operators of the fermion action are constructed using APE-smeared links. Light quark masses corresponding to an m{sub pi}/m{sub p} ratio of 0.35 are considered to assess the exceptional configuration problem of clover-fermion actions. This Fat-Link Irrelevant Clover (FLIC) fermion action provides scaling which is superior to mean-field improvement and offers advantages over nonperturbative improvement, including reduced exceptional configurations.
Aharonov-Bohm radiation of fermions
Chu Yizen; Mathur, Harsh; Vachaspati, Tanmay
2010-09-15
We analyze Aharonov-Bohm radiation of charged fermions from oscillating solenoids and cosmic strings. We find that the angular pattern of the radiation has features that differ significantly from that for bosons. For example, fermionic radiation in the lowest harmonic is approximately isotropically distributed around an oscillating solenoid, whereas for bosons the radiation is dipolar. We also investigate the spin polarization of the emitted fermion-antifermion pair. Fermionic radiation from kinks and cusps on cosmic strings is shown to depend linearly on the ultraviolet cutoff, suggesting strong emission at an energy scale comparable to the string energy scale.
ERIC Educational Resources Information Center
Shapero, Albert
This is a second report of a study of the use of scientific and technical information in industrial and nonprofit settings. It focuses on mapping the information-communication behavior of the engineering division of the Southwest Research Institute. Data include questionnaires, library records, travel records, telephone records, and contractual…
STOUT SMEARING FOR TWISTED FERMIONS.
SCHOLZ,W.; JANSEN, K.; McNEILE, C.; MONTVAY, I.; RICHARDS, C.; URBACH, C.; WENGER, U.
2007-07-30
The effect of Stout smearing is investigated in numerical simulations with twisted mass Wilson quarks. The phase transition near zero quark mass is studied on 12{sup 3} x 24, 16{sup 3} x 32 and 24{sup 3} x 48 lattices at lattice spacings a {approx_equal} 0.1-0.125 fm. The phase structure of Wilson fermions with twisted mass ({mu}) has been investigated in [1,2]. As it is explained there, the observed first order phase transition limits the minimal pion mass which can be reached in simulations at a given lattice spacing: m{sub k}{sup min} {approx_equal} {theta}(a). The phase structure is schematically depicted in the left panel of Fig. I . The phase transition can be observed in simulations with twisted mass fermions, for instance, as a ''jump'' or even metastabilities in the average plaquette value as a function of the hopping parameter ({kappa}). One possibility to weaken the phase transition and therefore allow for lighter pion masses at a given lattice spacing is to use an improved gauge action like the DBW2, Iwasaki, or tree-level Symanzik (tlSym) improved gauge action instead of the simple Wilson gauge action. This has been successfully demonstrated in [3,4,5]. Here we report on our attempts to use a smeared gauge field in the fermion lattice Dirac operator to further reduce the strength of the phase transition. This is relevant in simulations with N{sub f} = 2 + 1 + 1 (u,d,s,c) quark flavors [6] where the first order phase transition becomes stronger compared to N{sub f} = 2 simulations. The main impact of the above mentioned improved gauge actions on the gauge fields occurring in simulations is to suppress short range fluctuations (''dislocations'') and the associated ''exceptionally small'' eigenvalues of the fermion matrix. The same effect is expected from smearing the gauge field links in the fermion action. The cumulated effect of the improved gauge action and smeared links should allow for a smaller pion mass at a given lattice spacing and volume. Our
Paired States of Composite Fermions
NASA Astrophysics Data System (ADS)
Bonesteel, N. E.
2002-03-01
There is compelling theoretical evidence(R. Morf, Phys. Rev. Lett. 80), 1505 (1998). that the ν=5/2 fractional quantum Hall state is a Moore-Read state(G. Moore and N. Read, Nucl. Phys. B 360), 362 (1991). -- a state which can be viewed as a spin-polarized p-wave `superconductor' of composite fermions. The question remains, how can one test this hypothesis experimentally? To address this we have developed a semi-phenomenological description of this state in which the Halperin-Lee-Read(B.I. Halperin, P.A. Lee, and N. Read, Phys. Rev. B 47), 7312 (1993). theory of the half-filled Landau level is modified by adding a p-wave pairing interaction between composite fermions by hand. The electromagnetic response functions for the resulting mean-field superconducting state are then calculated and used in an RPA calculation of the physical electronic response. For a clean enough sample, and for q << k_f, the transverse electromagnetic response function for composite fermions is governed by type-II coherence factors and shows a `Hebel-Slichter'-like peak as a function of temperature for low enough frequency. The possibility (and potential difficulties) of observing this peak indirectly in surface-acoustic-wave propagation experiments will be discussed. The observation of such a coherence peak would provide strong evidence of BCS pairing in the 5/2 state. Work supported by US DOE Grant No. DE-FG02-97ER45639. Work done in collaboration with K.C. Foster (FSU) and S.H. Simon (Lucent). note
Fermion dipole moment and holography
NASA Astrophysics Data System (ADS)
Kulaxizi, Manuela; Rahman, Rakibur
2015-12-01
In the background of a charged AdS black hole, we consider a Dirac particle endowed with an arbitrary magnetic dipole moment. For non-zero charge and dipole coupling of the bulk fermion, we find that the dual boundary theory can be plagued with superluminal modes. Requiring consistency of the dual CFT amounts to constraining the strength of the dipole coupling by an upper bound. We briefly discuss the implications of our results for the physics of holographic non-Fermi liquids.
Fermionic Quantization of Hopf Solitons
NASA Astrophysics Data System (ADS)
Krusch, S.; Speight, J. M.
2006-06-01
In this paper we show how to quantize Hopf solitons using the Finkelstein-Rubinstein approach. Hopf solitons can be quantized as fermions if their Hopf charge is odd. Symmetries of classical minimal energy configurations induce loops in configuration space which give rise to constraints on the wave function. These constraints depend on whether the given loop is contractible. Our method is to exploit the relationship between the configuration spaces of the Faddeev-Hopf and Skyrme models provided by the Hopf fibration. We then use recent results in the Skyrme model to determine whether loops are contractible. We discuss possible quantum ground states up to Hopf charge Q=7.
Coulomb interactions and fermion condensation
Capstick, S.; Cutkosky, R.E.; Joensen, M.A. ); Wang, K.C. )
1990-08-15
The influence of the Coulomb interaction in states containing massless and flavorless fermion-antifermion pairs is studied, using a continuum formulation within the finite volume {ital S}{sup 3}. Several different forms for the Coulomb interaction are examined, including confining potentials as well as nonconfining potentials. The calculations show that if the interaction is strong enough, the Coulomb interaction leads to condensation of pairs, and that this condensation has a chiral character. The condensation does not depend on whether the interaction is confining. It is found that simplified variational approximations are not accurate enough for an adequate description of the states.
Scientific Literacy: Whose Responsibility?
ERIC Educational Resources Information Center
Evans, Thomas P.
1970-01-01
Identifies various components of scientific literacy and characteristics of scientifically literate people. Discusses factors inhibiting scientific literacy. Suggested remedies: federal support for special programs, redesign of teacher education programs and science content courses at all levels, and setting up means of interpreting science to the…
Quantum electrodynamics with complex fermion mass
McKellar, B.J.H. . School of Physics); Wu, D.D. . School of Physics Academia Sinica, Beijing, BJ . Inst. of High Energy Physics Superconducting Super Collider Lab., Dallas, TX )
1991-08-01
The quantum electrodynamics (QED) with a complex fermion mass -- that is, a fermion mass with a chiral phase -- is restudied, together with its chirally rotated version. We show how fake electric dipole moment can be obtained and how to avoid it. 10 refs.
Superalgebra and fermion-boson symmetry
Miyazawa, Hironari
2010-01-01
Fermions and bosons are quite different kinds of particles, but it is possible to unify them in a supermultiplet, by introducing a new mathematical scheme called superalgebra. In this article we discuss the development of the concept of symmetry, starting from the rotational symmetry and finally arriving at this fermion-boson (FB) symmetry. PMID:20228617
Mass-induced transition in fermion number
Aragao de Carvalho, C.; Pureza, J. M.
1989-05-15
We show that if we increase the mass of fermions in interaction with a topological (kink) scalar background in 1+1 dimensions, the fractional fermion number of the system will eventually vanish. The transition is sharp and corresponds to the disappearance of localized states from the spectrum of a Dirac operator which is exactly solvable. Possible applications to different physical systems are discussed.
Fermionic T-Duality a Snapshot Review
NASA Astrophysics Data System (ADS)
Ó Colgáin, Eoin
2012-11-01
Through a self-dual mapping of the geometry AdS5 ×S5, fermionic T-duality provides a beautiful geometric interpretation of hidden symmetries for scattering amplitudes in N = 4 super-Yang-Mills. Starting with Green-Schwarz sigma-models, we consolidate developments in this area into this small review. In particular, we discuss the translation of fermionic T-duality into the supergravity fields via pure spinor formalism and show that a general class of fermionic transformations can be identified directly in the supergravity. In addition to discussing fermionic T-duality for the geometry AdS4 × ℂP3, dual to N = 6 ABJM theory, we review work on other self-dual geometries. Finally, we present a short round-up of studies with a formal interest in fermionic T-duality.
Tunable Dirac Fermion Dynamics in Topological Insulators
NASA Astrophysics Data System (ADS)
Chen, Chaoyu; Xie, Zhuojin; Feng, Ya; Yi, Hemian; Liang, Aiji; He, Shaolong; Mou, Daixiang; He, Junfeng; Peng, Yingying; Liu, Xu; Liu, Yan; Zhao, Lin; Liu, Guodong; Dong, Xiaoli; Zhang, Jun; Yu, Li; Wang, Xiaoyang; Peng, Qinjun; Wang, Zhimin; Zhang, Shenjin; Yang, Feng; Chen, Chuangtian; Xu, Zuyan; Zhou, X. J.
2013-08-01
Three-dimensional topological insulators are characterized by insulating bulk state and metallic surface state involving relativistic Dirac fermions which are responsible for exotic quantum phenomena and potential applications in spintronics and quantum computations. It is essential to understand how the Dirac fermions interact with other electrons, phonons and disorders. Here we report super-high resolution angle-resolved photoemission studies on the Dirac fermion dynamics in the prototypical Bi2(Te,Se)3 topological insulators. We have directly revealed signatures of the electron-phonon coupling and found that the electron-disorder interaction dominates the scattering process. The Dirac fermion dynamics in Bi2(Te3-xSex) topological insulators can be tuned by varying the composition, x, or by controlling the charge carriers. Our findings provide crucial information in understanding and engineering the electron dynamics of the Dirac fermions for fundamental studies and potential applications.
Fermion hierarchy from sfermion anarchy
NASA Astrophysics Data System (ADS)
Altmannshofer, Wolfgang; Frugiuele, Claudia; Harnik, Roni
2014-12-01
We present a framework to generate the hierarchical flavor structure of Standard Model quarks and leptons from loops of superpartners. The simplest model consists of the minimal supersymmetric standard model with tree level Yukawa couplings for the third generation only and anarchic squark and slepton mass matrices. Agreement with constraints from low energy flavor observables, in particular Kaon mixing, is obtained for supersymmetric particles with masses at the PeV scale or above. In our framework both the second and the first generation fermion masses are generated at 1-loop. Despite this, a novel mechanism generates a hierarchy among the first and second generations without imposing a symmetry or small parameters. A second-to-first generation mass ratio of order 100 is typical. The minimal supersymmetric standard model thus includes all the necessary ingredients to realize a fermion spectrum that is qualitatively similar to observation, with hierarchical masses and mixing. The minimal framework produces only a few quantitative discrepancies with observation, most notably the muon mass is too low. We discuss simple modifications which resolve this and also investigate the compatibility of our model with gauge and Yukawa coupling Unification.
Fermion hierarchy from sfermion anarchy
Altmannshofer, Wolfgang; Frugiuele, Claudia; Harnik, Roni
2014-12-31
We present a framework to generate the hierarchical flavor structure of Standard Model quarks and leptons from loops of superpartners. The simplest model consists of the minimal supersymmetric standard model with tree level Yukawa couplings for the third generation only and anarchic squark and slepton mass matrices. Agreement with constraints from low energy flavor observables, in particular Kaon mixing, is obtained for supersymmetric particles with masses at the PeV scale or above. In our framework both the second and the first generation fermion masses are generated at 1-loop. Despite this, a novel mechanism generates a hierarchy among the first andmore » second generations without imposing a symmetry or small parameters. A second-to-first generation mass ratio of order 100 is typical. The minimal supersymmetric standard model thus includes all the necessary ingredients to realize a fermion spectrum that is qualitatively similar to observation, with hierarchical masses and mixing. The minimal framework produces only a few quantitative discrepancies with observation, most notably the muon mass is too low. Furthermore, we discuss simple modifications which resolve this and also investigate the compatibility of our model with gauge and Yukawa coupling Unification.« less
Fermion hierarchy from sfermion anarchy
Altmannshofer, Wolfgang; Frugiuele, Claudia; Harnik, Roni
2014-12-31
We present a framework to generate the hierarchical flavor structure of Standard Model quarks and leptons from loops of superpartners. The simplest model consists of the minimal supersymmetric standard model with tree level Yukawa couplings for the third generation only and anarchic squark and slepton mass matrices. Agreement with constraints from low energy flavor observables, in particular Kaon mixing, is obtained for supersymmetric particles with masses at the PeV scale or above. In our framework both the second and the first generation fermion masses are generated at 1-loop. Despite this, a novel mechanism generates a hierarchy among the first and second generations without imposing a symmetry or small parameters. A second-to-first generation mass ratio of order 100 is typical. The minimal supersymmetric standard model thus includes all the necessary ingredients to realize a fermion spectrum that is qualitatively similar to observation, with hierarchical masses and mixing. The minimal framework produces only a few quantitative discrepancies with observation, most notably the muon mass is too low. Furthermore, we discuss simple modifications which resolve this and also investigate the compatibility of our model with gauge and Yukawa coupling Unification.
A new phase from compression of carbon nanotubes with anisotropic Dirac fermions
Dong, Xiao; Hu, Meng; He, Julong; Tian, Yongjun; Wang, Hui-Tian
2015-01-01
Searching for novel functional carbon materials is an enduring topic of scientific investigations, due to its diversity of bonds, including sp-, sp2-, and sp3-hybridized bonds. Here we predict a new carbon allotrope, bct-C12 with the body-centered tetragonal I4/mcm symmetry, from the compression of carbon nanotubes. In particular, this structure behaviors as the Dirac fermions in the kz direction and the classic fermions in the kx and ky directions. This anisotropy originates from the interaction among zigzag chains, which is inherited from (n, n)-naotubes. PMID:26030232
A new phase from compression of carbon nanotubes with anisotropic Dirac fermions.
Dong, Xiao; Hu, Meng; He, Julong; Tian, Yongjun; Wang, Hui-Tian
2015-01-01
Searching for novel functional carbon materials is an enduring topic of scientific investigations, due to its diversity of bonds, including sp-, sp(2)-, and sp(3)-hybridized bonds. Here we predict a new carbon allotrope, bct-C12 with the body-centered tetragonal I4/mcm symmetry, from the compression of carbon nanotubes. In particular, this structure behaviors as the Dirac fermions in the kz direction and the classic fermions in the kx and ky directions. This anisotropy originates from the interaction among zigzag chains, which is inherited from (n, n)-naotubes. PMID:26030232
Resonances of Spin-1/2 Fermions in Eddington-Inspired Born-Infeld Gravity
NASA Astrophysics Data System (ADS)
Fu, Qi-Ming; Zhao, Li; Du, Yun-Zhi; Gu, Bao-Min
2016-03-01
We investigate the fermionic resonances for both chiralities in five-dimensional Eddington-inspired Born-Infeld (EiBI) theory. In order to localize fermion on the brane, it needs to be considered the Yukawa coupling between the fermion and the background scalar field. In our models, since the background scalar field has kink, double kink, or anti-kink solution, the system has rich resonant Kaluza–Klein (KK) modes structure. The massive KK fermionic modes feel a volcano potential, which result in a fermionic zero mode and a set of continuous massive KK modes. The inner structure of the branes and a free parameter in background scalar field influence the resonant behaviors of the massive KK fermions. Supported in part by the National Natural Science Foundation of China under Grant No. 11075065, the Huo Ying-Dong Education Foundation of Chinese Ministry of Education under Grant No. 121106 and the Fundamental Research Funds for the Central Universities under Grant No. lzujbky-2014-31
Cooling a Band Insulator with a Metal: Fermionic Superfluid in a Dimerized Holographic Lattice
NASA Astrophysics Data System (ADS)
Haldar, Arijit; Shenoy, Vijay B.
A cold atomic realization of a quantum correlated state of many fermions on a lattice, eg. superfluid, has eluded experimental realization due to the entropy problem. Here we propose a route to realize such a state using holographic lattice and confining potentials. The potentials are designed to produces a band insulating state (low heat capacity) at the trap center, and a metallic state (high heat capacity) at the periphery. The metal ``cools'' the central band insulator by extracting out the excess entropy. The central band insulator can be turned into a superfluid by tuning an attractive interaction between the fermions. Crucially, the holographic lattice allows the emergent superfluid to have a high transition temperature - even twice that of the effective trap temperature. The scheme provides a promising route to a laboratory realization of a fermionic lattice superfluid, even while being adaptable to simulate other many body states. Reference: Scientific Reports 4, 6665 (2014). Work supported by CSIR, DST and DAE.
Fermion tunneling from dynamical horizons
NASA Astrophysics Data System (ADS)
Di Criscienzo, R.; Vanzo, L.
2008-06-01
The instability against emission of fermionic particles by the trapping horizon of an evolving black hole is analyzed and confirmed using the Hamilton-Jacobi tunneling method. This method automatically selects one special expression for the surface gravity of a changing horizon. The results also apply to point masses embedded in an expanding universe. As a bonus of the tunneling method, we gain the insight that the surface gravity still defines a temperature parameter as long as the evolution is sufficiently slow that the black-hole pass through a sequence of quasi-equilibrium states, and that black holes should be semi-classically unstable even in a hypothetical world without bosonic fields.
Zimbardi, Kirsten; Bugarcic, Andrea; Colthorpe, Kay; Good, Jonathan P; Lluka, Lesley J
2013-12-01
Science graduates require critical thinking skills to deal with the complex problems they will face in their 21st century workplaces. Inquiry-based curricula can provide students with the opportunities to develop such critical thinking skills; however, evidence suggests that an inappropriate level of autonomy provided to underprepared students may not only be daunting to students but also detrimental to their learning. After a major review of the Bachelor of Science, we developed, implemented, and evaluated a series of three vertically integrated courses with inquiry-style laboratory practicals for early-stage undergraduate students in biomedical science. These practical curricula were designed so that students would work with increasing autonomy and ownership of their research projects to develop increasingly advanced scientific thinking and communication skills. Students undertaking the first iteration of these three vertically integrated courses reported learning gains in course content as well as skills in scientific writing, hypothesis construction, experimental design, data analysis, and interpreting results. Students also demonstrated increasing skills in both hypothesis formulation and communication of findings as a result of participating in the inquiry-based curricula and completing the associated practical assessment tasks. Here, we report the specific aspects of the curricula that students reported as having the greatest impact on their learning and the particular elements of hypothesis formulation and communication of findings that were more challenging for students to master. These findings provide important implications for science educators concerned with designing curricula to promote scientific thinking and communication skills alongside content acquisition. PMID:24292906
Green's functions for a CPn - 1 model with massless fermions
NASA Astrophysics Data System (ADS)
Schaposnik, F. A.
1983-07-01
We study the CPn - 1 model with massless fermions making a chiral change in the fermionic variables. We construct the generating functional and discuss relevant features of the theory. The factorization of a pure fermionic part shows a power law correction to the free fermion Green's function. The dynamical gauge field becomes massive and a screening phenomenon occurs. Member of CIC, Buenos Aires, Argentina
Flavor symmetries and fermion masses
Rasin, A.
1994-04-01
We introduce several ways in which approximate flavor symmetries act on fermions and which are consistent with observed fermion masses and mixings. Flavor changing interactions mediated by new scalars appear as a consequence of approximate flavor symmetries. We discuss the experimental limits on masses of the new scalars, and show that the masses can easily be of the order of weak scale. Some implications for neutrino physics are also discussed. Such flavor changing interactions would easily erase any primordial baryon asymmetry. We show that this situation can be saved by simply adding a new charged particle with its own asymmetry. The neutrality of the Universe, together with sphaleron processes, then ensures a survival of baryon asymmetry. Several topics on flavor structure of the supersymmetric grand unified theories are discussed. First, we show that the successful predictions for the Kobayashi-Maskawa mixing matrix elements, V{sub ub}/V{sub cb} = {radical}m{sub u}/m{sub c} and V{sub td}/V{sub ts} = {radical}m{sub d}/m{sub s}, are a consequence of a large class of models, rather than specific properties of a few models. Second, we discuss how the recent observation of the decay {beta} {yields} s{gamma} constrains the parameter space when the ratio of the vacuum expectation values of the two Higgs doublets, tan{Beta}, is large. Finally, we discuss the flavor structure of proton decay. We observe a surprising enhancement of the branching ratio for the muon mode in SO(10) models compared to the same mode in the SU(5) model.
Fitting fermion masses and mixings in F-theory GUTs
NASA Astrophysics Data System (ADS)
Carta, Federico; Marchesano, Fernando; Zoccarato, Gianluca
2016-03-01
We analyse the structure of Yukawa couplings in local SU(5) F-theory models with E 7 enhancement. These models are the minimal setting in which the whole flavour structure for the MSSM charged fermions is encoded in a small region of the entire compactification space. In this setup the E 7 symmetry is broken down to SU(5) by means of a 7-brane T-brane background, and further to the MSSM gauge group by means of a hypercharge flux that also implements doublet-triplet splitting. At tree-level only one family of quarks and charged leptons is massive, while the other two obtain hierarchically smaller masses when stringy non-perturbative effects are taken into account. We find that there is a unique E 7 model with such hierarchical flavour structure. The relative simplicity of the model allows to perform the computation of Yukawa couplings for a region of its parameter space wider than previous attempts, obtaining realistic fermion masses and mixings for large parameter regions. Our results are also valid for local models with E 8 enhancement, pointing towards a universal structure to describe realistic fermion masses within this framework.
Instantons and Massless Fermions in Two Dimensions
DOE R&D Accomplishments Database
Callan, C. G. Jr.; Dashen, R.; Gross, D. J.
1977-05-01
The role of instantons in the breakdown of chiral U(N) symmetry is studied in a two dimensional model. Chiral U(1) is always destroyed by the axial vector anomaly. For N = 2 chiral SU(N) is also spontaneously broken yielding massive fermions and three (decoupled) Goldstone bosons. For N greater than or equal to 3 the fermions remain massless. Realistic four dimensional theories are believed to behave in a similar way but the critical N above which the fermions cease to be massive is not known in four dimensions.
Fermion localization on a split brane
Chumbes, A. E. R.; Vasquez, A. E. O.; Hott, M. B.
2011-05-15
In this work we analyze the localization of fermions on a brane embedded in five-dimensional, warped and nonwarped, space-time. In both cases we use the same nonlinear theoretical model with a nonpolynomial potential featuring a self-interacting scalar field whose minimum energy solution is a soliton (a kink) which can be continuously deformed into a two-kink. Thus a single brane splits into two branes. The behavior of spin 1/2 fermions wave functions on the split brane depends on the coupling of fermions to the scalar field and on the geometry of the space-time.
Fermionic quantum critical point of spinless fermions on a honeycomb lattice
NASA Astrophysics Data System (ADS)
Wang, Lei; Corboz, Philippe; Troyer, Matthias
2014-10-01
Spinless fermions on a honeycomb lattice provide a minimal realization of lattice Dirac fermions. Repulsive interactions between nearest neighbors drive a quantum phase transition from a Dirac semimetal to a charge-density-wave state through a fermionic quantum critical point, where the coupling of the Ising order parameter to the Dirac fermions at low energy drastically affects the quantum critical behavior. Encouraged by a recent discovery (Huffman and Chandrasekharan 2014 Phys. Rev. B 89 111101) of the absence of the fermion sign problem in this model, we study the fermionic quantum critical point using the continuous-time quantum Monte Carlo method with a worm-sampling technique. We estimate the transition point V/t=1.356(1) with the critical exponents ν =0.80(3) and η =0.302(7). Compatible results for the transition point are also obtained with infinite projected entangled-pair states.
Pfaffian wave functions and topology of fermion nodes
NASA Astrophysics Data System (ADS)
Mitas, Lubos
2007-03-01
Pfaffian is defined as a signed sum of all pair partitions of even number of elements and it can be viewed as a nontrivial generalization of determinant. Pfaffian enables to define the simplest possible antisymmetric wave function based on pair spinorbital(s) and therefore represents a pairing generalization of the Slater determinant of one-particle orbitals. Pfaffians actually accomodate several types of pairing wave functions, for example, one special case is the Bardeen-Cooper- Schrieffer wave function. Using this platform we propose pfaffian wave functions with simultaneous pairings both in singlet and triplet channels and we benchmark their performance in fixed-node quantum Monte Carlo. We implement Gaussian elimination-like algorithm which enables to calculate pfaffians with efficiency similar to calculation of determinants. For a testing set of first row atoms and molecules we show that single pfaffians provide correlation energies systematically at the level of about 95%. Linear combinations of small number of pfaffians recover another fraction of the missing correlation energy comparable to significantly larger determinantal expansions. In addition, we show that pfaffians possess an important property of fermionic wave functions, namely, the minimal number of two nodal domains defined by fermion nodes. This is related to the proof that under rather general conditions closed-shell ground state wave functions of fermionic systems in d>1 have two nodal domains for arbitrary system size. The explicit proofs cover a number of paradigmatic models such as fermions on a sphere surface, in a periodic box, atomic states, etc, and we discuss the implications of this on efficient construction of wave functions and on several types of many-body effects. Supported by NSF and done in collaboration with M. Bajdich, L.K. Wagner, G. Drobny, and K.E Schmidt.Refs: L. Mitas, PRL 96, 240402 (2006); L. Mitas, cond-mat/0605550; M. Bajdich et al, PRL 96, 130201 (2006); cond
Kizilersue, Ayse; Pennington, Michael R.
2009-06-15
In principle, calculation of a full Green's function in any field theory requires knowledge of the infinite set of multipoint Green's functions, unless one can find some way of truncating the corresponding Schwinger-Dyson equations. For the fermion and boson propagators in QED this requires an ansatz for the full 3-point vertex. Here we illustrate how the properties of gauge invariance, gauge covariance and multiplicative renormalizability impose severe constraints on this fermion-boson interaction, allowing a consistent truncation of the propagator equations. We demonstrate how these conditions imply that the 3-point vertex in the propagator equations is largely determined by the behavior of the fermion propagator itself and not by knowledge of the many higher-point functions. We give an explicit form for the fermion-photon vertex, which in the fermion and photon propagator fulfills these constraints to all orders in leading logarithms for massless QED, and accords with the weak coupling limit in perturbation theory at O({alpha}). This provides the first attempt to deduce nonperturbative Feynman rules for strong physics calculations of propagators in massless QED that ensure a more consistent truncation of the 2-point Schwinger-Dyson equations. The generalization to next-to-leading order and masses will be described in a longer publication.
Lifetime of a one-dimensional fermion
NASA Astrophysics Data System (ADS)
Khodas, Maxim; Ussishkin, Iddo; Pustilnik, Michael; Kamenev, Alex; Glazman, Leonid
2007-03-01
Interaction between fermions in one dimension is usually accounted for within the exactly solvable Tomonaga-Luttinger model. The crucial simplification made in this model is the linearization of the fermionic spectrum. That simplification leads to an infinite lifetime of a fermion at the mass shell, i.e., the corresponding Green function G(,k) diverges at ɛ=ξk. We find that inclusion of the curvature of electron spectrum, ξk=vFk+k^2/2m, yields a finite decay rate of a fermion, 1/τ(ξk)θ(k)k^8/m^3; here for definiteness we consider right-moving particles, and k is measured from the Fermi wave vector. The found finite lifetime allows one to assess the limitations of the Luttinger liquid paradigm.
Quantum Materials: Weyl fermions go into orbit
NASA Astrophysics Data System (ADS)
Dai, Xi
2016-08-01
Due to their chirality, the massless fermions inside Weyl semimetals can take unusual paths that are governed by chiral dynamics, potentially providing a direct method to explore their topological nature.
Majorana Fermions and Topology in Superconductors
NASA Astrophysics Data System (ADS)
Sato, Masatoshi; Fujimoto, Satoshi
2016-07-01
Topological superconductors are novel classes of quantum condensed phases, characterized by topologically nontrivial structures of Cooper pairing states. On the surfaces of samples and in vortex cores of topological superconductors, Majorana fermions, which are particles identified with their own anti-particles, appear as Bogoliubov quasiparticles. The existence and stability of Majorana fermions are ensured by bulk topological invariants constrained by the symmetries of the systems. Majorana fermions in topological superconductors obey a new type of quantum statistics referred to as non-Abelian statistics, which is distinct from bose and fermi statistics, and can be utilized for application to topological quantum computation. Also, Majorana fermions give rise to various exotic phenomena such as "fractionalization", non-local correlation, and "teleportation". A pedagogical review of these subjects is presented. We also discuss interaction effects on topological classification of superconductors, and the basic properties of Weyl superconductors.
Quantum-gas microscope for fermionic atoms.
Cheuk, Lawrence W; Nichols, Matthew A; Okan, Melih; Gersdorf, Thomas; Ramasesh, Vinay V; Bakr, Waseem S; Lompe, Thomas; Zwierlein, Martin W
2015-05-15
We realize a quantum-gas microscope for fermionic ^{40}K atoms trapped in an optical lattice, which allows one to probe strongly correlated fermions at the single-atom level. We combine 3D Raman sideband cooling with high-resolution optics to simultaneously cool and image individual atoms with single-lattice-site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site-resolved imaging of fermions enables the direct observation of magnetic order, time-resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement. PMID:26024169
Chiral fermions in asymptotically safe quantum gravity
NASA Astrophysics Data System (ADS)
Meibohm, J.; Pawlowski, J. M.
2016-05-01
We study the consistency of dynamical fermionic matter with the asymptotic safety scenario of quantum gravity using the functional renormalisation group. Since this scenario suggests strongly coupled quantum gravity in the UV, one expects gravity-induced fermion self-interactions at energies of the Planck scale. These could lead to chiral symmetry breaking at very high energies and thus to large fermion masses in the IR. The present analysis which is based on the previous works (Christiansen et al., Phys Rev D 92:121501, 2015; Meibohm et al., Phys Rev D 93:084035, 2016), concludes that gravity-induced chiral symmetry breaking at the Planck scale is avoided for a general class of NJL-type models. We find strong evidence that this feature is independent of the number of fermion fields. This finding suggests that the phase diagram for these models is topologically stable under the influence of gravitational interactions.
Quantum-Gas Microscope for Fermionic Atoms
NASA Astrophysics Data System (ADS)
Cheuk, Lawrence W.; Nichols, Matthew A.; Okan, Melih; Gersdorf, Thomas; Ramasesh, Vinay V.; Bakr, Waseem S.; Lompe, Thomas; Zwierlein, Martin W.
2015-05-01
We realize a quantum-gas microscope for fermionic 40K atoms trapped in an optical lattice, which allows one to probe strongly correlated fermions at the single-atom level. We combine 3D Raman sideband cooling with high-resolution optics to simultaneously cool and image individual atoms with single-lattice-site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site-resolved imaging of fermions enables the direct observation of magnetic order, time-resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement.
Creutz fermions on an orthogonal lattice
Borici, Artan
2008-10-01
In a recent paper, Creutz has given a new action describing two species of Dirac fermions with exact chiral symmetry on the lattice. This action depends on parameters which may be fixed at certain values in order to get the right continuum limit. In this letter, we elaborate more on this idea and present an action which is free of any other parameter except the fermion mass.
Fermionic Subspaces of the Bosonic String
NASA Astrophysics Data System (ADS)
Chattaraputi, A.; Englert, F.; Houart, L.; Taormina, A.
A universal symmetric truncation of the bosonic string Hilbert space yields all known closed fermionic string theories in ten dimensions, their D-branes and their open descendants. We highlight the crucial role played by group theory and two-dimensional conformal field theory in the construction and emphasize the predictive power of the truncation. Such circumstantial evidence points towards the existence of a mechanism which generates space-time fermions out of bosons dynamically within the framework of bosonic string theory.
Fermionic subspaces of the bosonic string
NASA Astrophysics Data System (ADS)
Chattaraputi, Auttakit; Englert, François; Houart, Laurent; Taormina, Anne
2003-06-01
A universal symmetric truncation of the bosonic string Hilbert space yields all known closed fermionic string theories in ten dimensions, their D-branes and their open descendants. We highlight the crucial role played by group theory and two-dimensional conformal field theory in the construction and emphasize the predictive power of the truncation. Such circumstantial evidence points towards the existence of a mechanism which generates spacetime fermions out of bosons dynamically within the framework of bosonic string theory.
The physics and chemistry of heavy fermions.
Fisk, Z; Sarrao, J L; Smith, J L; Thompson, J D
1995-01-01
The heavy fermions are a subset of the f-electron intermetallic compounds straddling the magnetic/nonmagnetic boundary. Their low-temperature properties are characterized by an electronic energy scale of order 1-10 K. Among the low-temperature ground states observed in heavy fermion compounds are exotic superconductors and magnets, as well as unusual semiconductors. We review here the current experimental and theoretical understanding of these systems. PMID:11607558
Ground state degeneracy of interacting spinless fermions
NASA Astrophysics Data System (ADS)
Wei, Zhong-Chao; Han, Xing-Jie; Xie, Zhi-Yuan; Xiang, Tao
2015-10-01
We propose an eigenoperator scheme to study the lattice model of interacting spinless fermions at half filling and show that this model possesses a hidden form of reflection positivity in its Majorana fermion representation. Based on this observation, we prove rigourously that the ground state of this model is either unique or doubly degenerate if the lattice size N is even, and is always doubly degenerate if N is odd. This proof holds in all dimensions with arbitrary lattice structures.
Dual of QCD with one adjoint fermion
Mojaza, Matin; Nardecchia, Marco; Pica, Claudio; Sannino, Francesco
2011-03-15
We construct the magnetic dual of QCD with one adjoint Weyl fermion. The dual is a consistent solution of the 't Hooft anomaly matching conditions, allows for flavor decoupling, and remarkably constitutes the first nonsupersymmetric dual valid for any number of colors. The dual allows to bound the anomalous dimension of the Dirac fermion mass operator to be less than one in the conformal window.
Quantum Gas Microscope for Fermionic Atoms
NASA Astrophysics Data System (ADS)
Okan, Melih; Cheuk, Lawrence; Nichols, Matthew; Lawrence, Katherine; Zhang, Hao; Zwierlein, Martin
2016-05-01
Strongly interacting fermions define the properties of complex matter throughout nature, from atomic nuclei and modern solid state materials to neutron stars. Ultracold atomic Fermi gases have emerged as a pristine platform for the study of many-fermion systems. In this poster we demonstrate the realization of a quantum gas microscope for fermionic 40 K atoms trapped in an optical lattice and the recent experiments which allows one to probe strongly correlated fermions at the single atom level. We combine 3D Raman sideband cooling with high- resolution optics to simultaneously cool and image individual atoms with single lattice site resolution at a detection fidelity above 95%. The imaging process leaves the atoms predominantly in the 3D motional ground state of their respective lattice sites, inviting the implementation of a Maxwell's demon to assemble low-entropy many-body states. Single-site resolved imaging of fermions enables the direct observation of magnetic order, time resolved measurements of the spread of particle correlations, and the detection of many-fermion entanglement. NSF, AFOSR-PECASE, AFOSR-MURI on Exotic Phases of Matter, ARO-MURI on Atomtronics, ONR, a Grant from the Army Research Office with funding from the DARPA OLE program, and the David and Lucile Packard Foundation.
Iterants, Fermions and Majorana Operators
NASA Astrophysics Data System (ADS)
Kauffman, Louis H.
Beginning with an elementary, oscillatory discrete dynamical system associated with the square root of minus one, we study both the foundations of mathematics and physics. Position and momentum do not commute in our discrete physics. Their commutator is related to the diffusion constant for a Brownian process and to the Heisenberg commutator in quantum mechanics. We take John Wheeler's idea of It from Bit as an essential clue and we rework the structure of that bit to a logical particle that is its own anti-particle, a logical Marjorana particle. This is our key example of the amphibian nature of mathematics and the external world. We show how the dynamical system for the square root of minus one is essentially the dynamics of a distinction whose self-reference leads to both the fusion algebra and the operator algebra for the Majorana Fermion. In the course of this, we develop an iterant algebra that supports all of matrix algebra and we end the essay with a discussion of the Dirac equation based on these principles.
Fermionic pentagons and NMHV hexagon
NASA Astrophysics Data System (ADS)
Belitsky, A. V.
2015-05-01
We analyze the near-collinear limit of the null polygonal hexagon super Wilson loop in the planar N = 4 super-Yang-Mills theory. We focus on its Grassmann components which are dual to next-to-maximal helicity-violating (NMHV) scattering amplitudes. The kinematics in question is studied within a framework of the operator product expansion that encodes propagation of excitations on the background of the color flux tube stretched between the sides of Wilson loop contour. While their dispersion relation is known to all orders in 't Hooft coupling from previous studies, we find their form factor couplings to the Wilson loop. This is done making use of a particular tessellation of the loop where pentagon transitions play a fundamental role. Being interested in NMHV amplitudes, the corresponding building blocks carry a nontrivial charge under the SU(4) R-symmetry group. Restricting the current consideration to twist-two accuracy, we analyze two-particle contributions with a fermion as one of the constituents in the pair. We demonstrate that these nonsinglet pentagons obey bootstrap equations that possess consistent solutions for any value of the coupling constant. To confirm the correctness of these predictions, we calculate their contribution to the super Wilson loop demonstrating agreement with recent results to four-loop order in 't Hooft coupling.
Heavy fermion behavior explained by bosons
NASA Technical Reports Server (NTRS)
Kallio, A.; Poykko, S.; Apaja, V.
1995-01-01
Conventional heavy fermion (HF) theories require existence of massive fermions. We show that heavy fermion phenomena can also be simply explained by existence of bosons with moderate mass but temperature dependent concentration below the formation temperature T(sub B), which in turn is close to room temperature. The bosons B(++) are proposed to be in chemical equilibrium with a system of holes h(+): B(++) = h(+) + h(+). This equilibrium is governed by a boson breaking function f(T), which determines the decreasing boson density and the increasing fermion density with increasing temperature. Since HF-compounds are hybridized from minimum two elements, we assume in addition existence of another fermion component h(sub s)(+) with temperature independent density. This spectator component is thought to be the main agent in binding the bosons in analogy with electronic or muonic molecules. Using a linear boson breaking function we can explain temperature dependence of the giant linear specific heat coefficient gamma(T) coming essentially from bosons. The maxima in resistivity, Hall coefficient, and susceptibility are explained by boson localization effects due to the Wigner crystallization. The antiferromagnetic transitions in turn are explained by similar localization of the pairing fermion system when their density n(sub h)(T(sub FL)) becomes lower than n(sub WC), the critical density of Wigner crystallization. The model applies irrespective whether a compound is superconducting or not. The same model explains the occurrence of low temperature antiferromagnetism also in high-T(sub c) superconductors. The double transition in UPt3 is proposed to be due to the transition of the pairing fermion liquid from spin polarized to unpolarized state.
Fermionic entanglement that survives a black hole
Martin-Martinez, Eduardo; Leon, Juan
2009-10-15
We introduce an arbitrary number of accessible modes when analyzing bipartite entanglement degradation due to Unruh effect between two partners Alice and Rob. Under the single mode approximation (SMA) a fermion field only had a few accessible levels due to Pauli exclusion principle conversely to bosonic fields which had an infinite number of excitable levels. This was argued to justify entanglement survival in the fermionic case in the SMA infinite acceleration limit. Here we relax SMA. Hence, an infinite number of modes are excited as the observer Rob accelerates, even for a fermion field. We will prove that, despite this analogy with the bosonic case, entanglement loss is limited. We will show that this comes from fermionic statistics through the characteristic structure it imposes on the infinite dimensional density matrix for Rob. Surprisingly, the surviving entanglement is independent of the specific maximally entangled state chosen, the kind of fermionic field analyzed, and the number of accessible modes considered. We shall discuss whether this surviving entanglement goes beyond the purely statistical correlations, giving insight concerning the black hole information paradox.
Instabilities in fermions and BEC mixtures
NASA Astrophysics Data System (ADS)
Tsai, Shan-Wen; Kalas, Ryan M.; Timmermans, Eddy
2010-03-01
We study instabilities in a mixture of interacting fermionic and bosonic ultra-cold atoms. We focus on BCS transitions of the fermions that can be generated from attractive interactions mediated by bosons that are in a BEC phase. We study the p-wave instability [1] for indistinguishable (single spin) fermions in detail, taking into account the dynamical part of the mediated interaction. We employ a functional renormalization-group approach that takes retardation effects into account [2], calculate the renormalized interaction vertices and self-energies for this system, and obtain the phase diagram, sub-dominant instabilities, and transition temperatures, giving estimates for realistic parameters. We also investigate what happens in this system close to the phase-separation transition [3], and explore other possible fermionic phases, including fermion BCS pairings with other pairing symmetries. [4pt] [1] D. V. Efremov and L. Viverit, Phys. Rev. B 65, 134519 (2002)[0pt] [2] S.-W. Tsai et al., Phys. Rev. B 72, 054531 (2005)[0pt] [3] D. H. Santamore and E. Timmermans, Phys. Rev. A 78, 013619 (2008)
Fermionic entanglement that survives a black hole
NASA Astrophysics Data System (ADS)
Martín-Martínez, Eduardo; León, Juan
2009-10-01
We introduce an arbitrary number of accessible modes when analyzing bipartite entanglement degradation due to Unruh effect between two partners Alice and Rob. Under the single mode approximation (SMA) a fermion field only had a few accessible levels due to Pauli exclusion principle conversely to bosonic fields which had an infinite number of excitable levels. This was argued to justify entanglement survival in the fermionic case in the SMA infinite acceleration limit. Here we relax SMA. Hence, an infinite number of modes are excited as the observer Rob accelerates, even for a fermion field. We will prove that, despite this analogy with the bosonic case, entanglement loss is limited. We will show that this comes from fermionic statistics through the characteristic structure it imposes on the infinite dimensional density matrix for Rob. Surprisingly, the surviving entanglement is independent of the specific maximally entangled state chosen, the kind of fermionic field analyzed, and the number of accessible modes considered. We shall discuss whether this surviving entanglement goes beyond the purely statistical correlations, giving insight concerning the black hole information paradox.
Contraction of fermionic operator circuits and the simulation of strongly correlated fermions
NASA Astrophysics Data System (ADS)
Barthel, Thomas; Pineda, Carlos; Eisert, Jens
2009-10-01
A fermionic operator circuit is a product of fermionic operators of usually different and partially overlapping support. Further elements of fermionic operator circuits (FOCs) are partial traces and partial projections. The presented framework allows for the introduction of fermionic versions of known qudit operator circuits (QUOC), important for the simulation of strongly correlated d -dimensional systems: the multiscale entanglement renormalization ansätze (MERA), tree tensor networks (TTN), projected entangled pair states (PEPS), or their infinite-size versions (iPEPS etc.). After the definition of a FOC, we present a method to contract it with the same computation and memory requirements as a corresponding QUOC, for which all fermionic operators are replaced by qudit operators of identical dimension. A given scheme for contracting the QUOC relates to an analogous scheme for the corresponding fermionic circuit, where additional marginal computational costs arise only from reordering of modes for operators occurring in intermediate stages of the contraction. Our result hence generalizes efficient schemes for the simulation of d -dimensional spin systems, as MERA, TTN, or PEPS to the fermionic case.
Plutonium-Based Heavy-Fermion Systems
NASA Astrophysics Data System (ADS)
Bauer, E. D.; Thompson, J. D.
2015-03-01
An effective mass of charge carriers that is significantly larger than the mass of a free electron develops at low temperatures in certain lanthanide- and actinide-based metals, including those formed with plutonium, owing to strong electron-electron interactions. This heavy-fermion mass is reflected in a substantially enhanced electronic coefficient of specific heat Î³, which for elemental Pu is much larger than that of normal metals. By our definition, there are twelve Pu-based heavy-fermion compounds, most discovered recently, whose basic properties are known and discussed. Relative to other examples, these Pu-based heavy-fermion systems are particularly complex owing in part to the possible simultaneous presence of multiple, nearly degenerate 5fn configurations. This complexity poses significant opportunities as well as challenges, including understanding the origin of unconventional superconductivity in some of these materials.
Apparatus for Ultra-Cold Fermion Interferometry
NASA Astrophysics Data System (ADS)
Aubin, Seth; Garcia, Aiyana; Desalvo, Brian
2008-05-01
We present progress on the construction of an apparatus for ultra-cold fermion interferometry experiments. The apparatus consists of two connected glass vacuum cells: Fermionic potassium (^40K) and bosonic rubidium (^87Rb) atoms are cooled and collected in a dual-species magneto-optical trap (MOT) in the first cell and are then transported magnetically to the second cell, where they are loaded into a micro-magnetic chip trap. We use radio-frequency (RF) evaporation to cool the rubidium atoms, which in turn sympathetically cool the potassium atoms. The apparatus takes advantage of the rapid cooling inherent to micro-magnetic traps, while also benefiting from the ultra high vacuum achievable with a two chamber vacuum system. In describing our experimental approach, we address the experimental challenges and possible force-sensing applications of fermion interferometers on chips.
QCD with many fermions and QCD topology
NASA Astrophysics Data System (ADS)
Shuryak, Edward
2013-04-01
Major nonperturbative phenomena in QCD - confinement and chiral symmetry breaking - are known to be related with certain topological objects. Recent lattice advances into the domain of many Nf = O(10) fermion flavors have shown that both phase transitions had shifted in this case to much stronger coupling. We discuss confinement in terms of monopole Bose condensation, and discuss how it is affected by fermions "riding" on the monopoles, ending with the Nf dependence of the critical line. Chiral symmetry breaking is discussed in terms of the (anti)selfdual dyons, the instanton constituents. The fermionic zero modes of those have a different meaning and lead to strong interaction between dyons and antidyons. We report some qualitative consequences of this theory and also some information about our first direct numerical study of the dyonic ensemble, in respect to both chiral symmetry breaking and confinement (via back reaction to the holonomy potential).
Fermionic semi-annihilating dark matter
NASA Astrophysics Data System (ADS)
Cai, Yi; Spray, Andrew
2016-01-01
Semi-annihilation is a generic feature of dark matter theories with symmetries larger than Z_2 . We investigate two examples with multi-component dark sectors comprised of an SU(2) L singlet or triplet fermion besides a scalar singlet. These are respectively the minimal fermionic semi-annihilating model, and the minimal case for a gauge-charged fermion. We study the relevant dark matter phenomenology, including the interplay of semi-annihilation and the Sommerfeld effect. We demonstrate that semi-annihilation in the singlet model can explain the gamma ray excess from the galactic center. For the triplet model we scan the parameter space, and explore how signals and constraints are modified by semi-annihilation. We find that the entire region where the model comprises all the observed dark matter is accessible to current and planned direct and indirect searches.
Fermions on one or fewer kinks
Chu Yizen; Vachaspati, Tanmay
2008-01-15
We find the full spectrum of fermion bound states on a Z{sub 2} kink. In addition to the zero mode, there are int[2m{sub f}/m{sub s}] bound states, where m{sub f} is the fermion and m{sub s} the scalar mass. We also study fermion modes on the background of a well-separated kink-antikink pair. Using a variational argument, we prove that there is at least one bound state in this background, and that the energy of this bound state goes to zero with increasing kink-antikink separation, 2L, and faster than e{sup -a2L} where a=min(m{sub s},2m{sub f}). By numerical evaluation, we find some of the low lying bound states explicitly.
Search for Majorana Fermions in Superconductors
NASA Astrophysics Data System (ADS)
Beenakker, C. W. J.
2013-04-01
Majorana fermions (particles that are their own antiparticle) may or may not exist in nature as elementary building blocks, but in condensed matter they can be constructed out of electron and hole excitations. What is needed is a superconductor to hide the charge difference and a topological (Berry) phase to eliminate the energy difference from zero-point motion. A pair of widely separated Majorana fermions, bound to magnetic or electrostatic defects, has non-Abelian exchange statistics. A qubit encoded in this Majorana pair is expected to have an unusually long coherence time. I discuss strategies to detect Majorana fermions in a topological superconductor, as well as possible applications in a quantum computer. The status of the experimental search is reviewed.
Dark Energy from Interacting Dark Fermions
NASA Astrophysics Data System (ADS)
Goldman, Terrence; McKellar, Bruce; Alsing, Paul; Stephenson, Gerard
2010-11-01
Physics is rife with interacting systems that exhibit negative pressure: atomic nuclei are very well known examples. We examine the range of parameters, for neutral fermions interacting only by exchange of an extraordinarily light scalar particle, that produce a negative pressure on the scale of the Universe over time periods where Dark Energy is or may be relevant. Of known or expected neutral Majorana fermions, active neutrinos can be ruled out but sterile neutrinos would work, as well as the LSP, to describe the recent observations of Dark Energy effects. After a phase change required by the instability responsible for the negative pressure, the resulting clouds of neutral fermions will contribute to Dark Matter. Nothing requires that this can only happen once.
Coffman-Kundu-Wootters inequality for fermions
NASA Astrophysics Data System (ADS)
Sárosi, Gábor; Lévay, Péter
2014-11-01
We derive an inequality for three fermions with six single-particle states which reduces to the sum of the famous Coffman-Kundu-Wootters inequalities when an embedded three-qubit system is considered. We identify the quantities which are playing the role of the concurrence, the three-tangle and the invariant detρA+detρB+detρC for this tripartite system. We show that this latter one is almost interchangeable with the von Neumann entropy and conjecture that it measures the entanglement of one fermion with the rest of the system. We prove that the vanishing of the fermionic "concurrence" implies that the two-particle reduced-density matrix is a mixture of separable states. Also, the vanishing of this quantity is only possible in the Greenberger-Horne-Zeilinger class, where some genuine tripartite entanglement is present and in the separable class. Based on this, we conjecture that this "concurrence" measures the amount of entanglement between pairs of fermions. We identify the well-known "spin-flipped" density matrix in the fermionic context as the reduced-density matrix of a special particle-hole dual state. We show that, in general, this dual state is always canonically defined by the Hermitian inner product of the fermionic Fock space and that it can be used to calculate covariants under stochastic local operations and classical communication (SLOCC). We show that Fierz identities known from the theory of spinors relate SLOCC covariants with reduced-density-matrix elements of the state and its spin-flipped dual.
Fermion boson metamorphosis in field theory
Ha, Y.K.
1982-01-01
In two-dimensional field theories many features are especially transparent if the Fermi fields are represented by non-local expressions of the Bose fields. Such a procedure is known as boson representation. Bilinear quantities appear in the Lagrangian of a fermion theory transform, however, as simple local expressions of the bosons so that the resulting theory may be written as a theory of bosons. Conversely, a theory of bosons may be transformed into an equivalent theory of fermions. Together they provide a basis for generating many interesting equivalences between theories of different types. In the present work a consistent scheme for constructing a canonical Fermi field in terms of a real scalar field is developed and such a procedure is valid and consistent with the tenets of quantum field theory is verified. A boson formulation offers a unifying theme in understanding the structure of many theories. This is illustrated by the boson formulation of a multifermion theory with chiral and internal symmetries. The nature of dynamical generation of mass when the theory undergoes boson transmutation and the preservation of continuous chiral symmetry in the massive case are examined. The dynamics of the system depends to a great extent on the specific number of fermions and different models of the same system can have very different properties. Many unusual symmetries of the fermion theory, such as hidden symmetry, duality and triality symmetries, are only manifest in the boson formulation. The underlying connections between some models with U(N) internal symmetry and another class of fermion models built with Majorana fermions which have O(2N) internal symmetry are uncovered.
Fermion-fermion scattering in quantum field theory with superconducting circuits.
García-Álvarez, L; Casanova, J; Mezzacapo, A; Egusquiza, I L; Lamata, L; Romero, G; Solano, E
2015-02-20
We propose an analog-digital quantum simulation of fermion-fermion scattering mediated by a continuum of bosonic modes within a circuit quantum electrodynamics scenario. This quantum technology naturally provides strong coupling of superconducting qubits with a continuum of electromagnetic modes in an open transmission line. In this way, we propose qubits to efficiently simulate fermionic modes via digital techniques, while we consider the continuum complexity of an open transmission line to simulate the continuum complexity of bosonic modes in quantum field theories. Therefore, we believe that the complexity-simulating-complexity concept should become a leading paradigm in any effort towards scalable quantum simulations. PMID:25763944
Condensation of gauge interacting massless fermions
Siringo, Fabio
2004-09-15
A single massless fermionic field with an Abelian U(1) gauge interaction (electrodynamics of a massless Dirac fermion) is studied by a variational method. Even without the insertion of any extra interaction the vacuum is shown to be unstable towards a particle-antiparticle condensate. The single particle excitations do acquire a mass and behave as massive Fermi particles. An explicit low-energy gap equation has been derived and numerically solved. Some consequences of condensation and mass generation are discussed in the framework of the standard model.
Massless rotating fermions inside a cylinder
Ambruş, Victor E.; Winstanley, Elizabeth
2015-12-07
We study rotating thermal states of a massless quantum fermion field inside a cylinder in Minkowski space-time. Two possible boundary conditions for the fermion field on the cylinder are considered: the spectral and MIT bag boundary conditions. If the radius of the cylinder is sufficiently small, rotating thermal expectation values are finite everywhere inside the cylinder. We also study the Casimir divergences on the boundary. The rotating thermal expectation values and the Casimir divergences have different properties depending on the boundary conditions applied at the cylinder. This is due to the local nature of the MIT bag boundary condition, while the spectral boundary condition is nonlocal.
Novel Fat-Link Fermion Actions
J. M. Zanotti; S. Bilson-Thompson; F. D. R. Bonnet; P. D. Coddington; D. B. Leinweber; A. G. Williams; J. B. Zhang; W. Melnitchouk; F. X. Lee
2001-07-01
The hadron mass spectrum is calculated in lattice QCD using a novel fat-link clover fermion action in which only the irrelevant operators in the fermion action are constructed using smeared links. The simulations are performed on a 16{sup 3} x 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat-Link Irrelevant Clover (FLIC) action provides scaling which is superior to mean-field improvement, and offers advantages over nonperturbative 0(a) improvement.
Global analysis of fermion mixing with exotics
NASA Technical Reports Server (NTRS)
Nardi, Enrico; Roulet, Esteban; Tommasini, Daniele
1991-01-01
The limits are analyzed on deviation of the lepton and quark weak-couplings from their standard model values in a general class of models where the known fermions are allowed to mix with new heavy particles with exotic SU(2) x U(1) quantum number assignments (left-handed singlets or right-handed doublets). These mixings appear in many extensions of the electroweak theory such as models with mirror fermions, E(sub 6) models, etc. The results update previous analyses and improve considerably the existing bounds.
Fermion path integrals and topological phases
NASA Astrophysics Data System (ADS)
Witten, Edward
2016-07-01
Symmetry-protected topological (SPT) phases of matter have been interpreted in terms of anomalies, and it has been expected that a similar picture should hold for SPT phases with fermions. Here a description is given in detail of what this picture means for phases of quantum matter that can be understood via band theory and free fermions. The main examples considered are time-reversal invariant topological insulators and superconductors in two or three space dimensions. Along the way, the precise meaning of the statement that in the bulk of a 3D topological insulator, the electromagnetic θ angle is equal to π , is clarified.
Quark seesaw, vectorlike fermions and diphoton excess
NASA Astrophysics Data System (ADS)
Dev, P. S. Bhupal; Mohapatra, Rabindra N.; Zhang, Yongchao
2016-02-01
We present a possible interpretation of the recent diphoton excess reported by the early √{s}=13 TeV LHC data in quark seesaw left-right models with vectorlike fermions proposed to solve the strong CP problem without the axion. The gauge singlet real scalar field responsible for the mass of the vectorlike fermions has the right production cross section and diphoton branching ratio to be identifiable with the reported excess at around 750 GeV diphoton invariant mass. Various ways to test this hypothesis as more data accumulates at the LHC are proposed.
Non-Markovian dynamics with fermions
NASA Astrophysics Data System (ADS)
Sargsyan, V. V.; Adamian, G. G.; Antonenko, N. V.; Lacroix, D.
2014-08-01
Employing the quadratic fermionic Hamiltonians for the collective and internal subsystems with a linear coupling, we studied the role of fermionic statistics on the dynamics of the collective motion. The transport coefficients are discussed as well as the associated fluctuation-dissipation relation. Due to different nature of the particles, the path to equilibrium is slightly affected. However, in the weak-coupling regime, the time scale for approaching equilibrium is found to be globally unchanged. The Pauli-blocking effect can modify the usual picture in open quantum system. In some limits, contrary to boson, this effect can strongly hinder the influence of the bath by blocking the interacting channels.
Resonant pairing between fermions with unequal masses
Wu, Shin-Tza; Pao, C.-H.; Yip, S.-K.
2006-12-01
We study via mean-field theory the pairing between fermions of different masses, especially at the unitary limit. At equal populations, the thermodynamic properties are identical with the equal mass case provided an appropriate rescaling is made. At unequal populations, for sufficiently light majority species, the system does not phase separate. For sufficiently heavy majority species, the phase separated normal phase have a density larger than that of the superfluid. For atoms in harmonic traps, the density profiles for unequal mass fermions can be drastically different from their equal-mass counterparts.
Scaling of fat-link irrelevant-clover fermions
Zanotti, J.M.; Lasscock, B.; Leinweber, D.B.; Williams, A.G.
2005-02-01
Hadron masses are calculated in quenched lattice QCD on a variety of lattices in order to probe the scaling behavior of the Fat-Link Irrelevant Clover (FLIC) fermion action, a fat-link clover fermion action in which the purely irrelevant operators of the fermion action are constructed using APE-smeared links. The scaling analysis indicates FLIC fermions provide a new form of nonperturbative O(a) improvement where near-continuum results are obtained at finite lattice spacing.
Origin of fermion masses without spontaneous symmetry breaking
NASA Astrophysics Data System (ADS)
Ayyar, Venkitesh; Chandrasekharan, Shailesh
2016-04-01
Using large scale Monte Carlo calculations in a simple three dimensional lattice fermion model, we establish the existence of a second order quantum phase transition between a massless fermion phase and a massive one, both of which have the same symmetries. This shows that fermion masses can arise due to dynamics without the need for spontaneous symmetry breaking. Universality suggests that this alternate origin of the fermion mass should be of fundamental interest.
The bosonic mother of fermionic D-branes
NASA Astrophysics Data System (ADS)
Chattaraputi, Auttakit; Englert, François; Houart, Laurent; Taormina, Anne
2002-09-01
We extend the search for fermionic subspaces of the bosonic string compactified on E8 × SO(16) lattices to include all fermionic D-branes. This extension constraints the truncation procedure previously proposed and relates the fermionic strings, supersymmetric or not, to the global structure of the SO(16) group. The specific properties of all the fermionic D-branes are found to be encoded in its universal covering, whose maximal toroid defines the configuration space torus of their mother bosonic theory.
Spontaneous polarization of composite fermions in the n = 1 Landau level of graphene
NASA Astrophysics Data System (ADS)
Coimbatore Balram, Ajit; Tőke, Csaba; Wójs, Arkadiusz; Jain, Jainendra
Motivated by experiments that reveal expansive fractional quantum Hall states in the n = 1 graphene Landau level and suggest a nontrivial role of the spin degree of freedom [Amet et al., Nat. Commun. 6, 5838 (2014)], we perform accurate quantitative study of the the competition between fractional quantum Hall states with different spin polarizations in the n = 1 graphene Landau level. We find that the fractional quantum Hall effect is well described in terms of composite fermions, but the spin physics is qualitatively different from that in the n = 0 Landau level. In particular, for the states at filling factors ν = s / (2 s +/- 1) , s integer, a combination of exact diagonalization and the composite fermion theory shows that the ground state is fully spin polarized and supports a robust spin wave mode even in the limit of vanishing Zeeman coupling. Thus, even though composite fermions are formed, a mean field description that treats them as weakly interacting particles breaks down, and the exchange interaction between them is strong enough to cause a qualitative change in the behavior by inducing full spin polarization. We also find that the fully spin polarized composite fermion Fermi sea has lower energy than the paired Pfaffian state at the relevant half fillings. Award No. DE-SC0005042 (ACB, JKJ), Hungarian Scientific Research Funds No. K105149 (CT), the Polish NCN Grant 2014/14/A/ST3/00654 and the EU Marie Curie Grant PCIG09-GA-2011-294186 (AW).
Zero-energy modes, charge conjugation, and fermion number
Sudarshan, E.C.G.; Yajnik, U.A.
1986-03-15
States with a half-integer fermion number occur when a fermionic field coupled to a soliton possesses a zero mode. This paper spells out the circumstances under which one can retain an integer fermion number as also a charge-conjugation-invariant ground state. It is necessary to make the representation reducible but it is kept irreducible by introducing an additional operator.
Fermionic computation is non-local tomographic and violates monogamy of entanglement
NASA Astrophysics Data System (ADS)
D'Ariano, G. M.; Manessi, F.; Perinotti, P.; Tosini, A.
2014-07-01
We show that the computational model based on local fermionic modes in place of qubits does not satisfy local tomography and monogamy of entanglement, and has mixed states with maximal entanglement of formation. These features directly follow from the parity superselection rule. We generalize quantum superselection rules to general probabilistic theories as sets of linear constraints on the convex set of states. We then provide a link between the cardinality of the superselection rule and the degree of holism of the resulting theory.
Fermion-fermion interaction in a dilute gas-mixture Bose condensate
Mogilyuk, T. I.
2011-11-15
A mixture of a one-component Bose gas and two-component Fermi gas is considered at temperatures at which the Bose gas is completely condensed. Two fermions in such a mixture can interact with each other exchanging bosons from the condensate or supercondensate. The interaction potential, a change in the effective mass, the decay, and fermion spectrum are calculated in this quantum Fermi-Bose mixture.
Finite volume renormalization scheme for fermionic operators
Monahan, Christopher; Orginos, Kostas
2013-11-01
We propose a new finite volume renormalization scheme. Our scheme is based on the Gradient Flow applied to both fermion and gauge fields and, much like the Schr\\"odinger functional method, allows for a nonperturbative determination of the scale dependence of operators using a step-scaling approach. We give some preliminary results for the pseudo-scalar density in the quenched approximation.
Ideal fermion delocalization in Higgsless models
Chivukula, R. Sekhar; Simmons, Elizabeth H.; He, Hong-Jian; Kurachi, Masafumi; Tanabashi, Masaharu
2005-07-01
In this note we examine the properties of deconstructed Higgsless models for the case of a fermion whose SU(2) properties arise from delocalization over many sites of the deconstructed lattice. We derive expressions for the correlation functions and use these to establish a generalized consistency relation among correlation functions. We discuss the form of the W boson wavefunction and show that if the probability distribution of the delocalized fermions is appropriately related to the W wavefunction, then deviations in precision electroweak parameters are minimized. In particular, we show that this ''ideal fermion delocalization'' results in the vanishing of three of the four leading zero-momentum electroweak parameters defined by Barbieri et al. We then discuss ideal fermion delocalization in the context of two continuum Higgsless models, one in Anti-deSitter space and one in flat space. Our results may be applied to any Higgsless linear moose model with multiple SU(2) groups, including those with only a few extra vector bosons.
Unpaired Floquet Majorana fermions without magnetic fields
NASA Astrophysics Data System (ADS)
Reynoso, Andres A.; Frustaglia, Diego
2013-03-01
Quantum wires subject to the combined action of spin-orbit and Zeeman coupling in the presence of s-wave pairing potentials (superconducting proximity effect in semiconductors or superfluidity in cold atoms) are one of the most promising systems for the developing of topological phases hosting Majorana fermions. The breaking of time-reversal symmetry is essential for the appearance of unpaired Majorana fermions. By implementing a time-dependent spin rotation, we show that the standard magnetostatic model maps into a nonmagnetic one where the breaking of time-reversal symmetry is guaranteed by a periodical change of the spin-orbit coupling axis as a function of time. This suggests the possibility of developing the topological superconducting state of matter driven by external forces in the absence of magnetic fields and magnetic elements. From a practical viewpoint, the scheme avoids the disadvantages of conjugating magnetism and superconductivity, even though the need of a high-frequency driving of spin-orbit coupling may represent a technological challenge. We describe the basic properties of this Floquet system by showing that finite samples host unpaired Majorana fermions at their edges despite the fact that the bulk Floquet quasienergies are gapless and that the Hamiltonian at each instant of time preserves time-reversal symmetry. Remarkably, we identify the mean energy of the Floquet states as a topological indicator. We additionally show that the localized Floquet Majorana fermions are robust under local perturbations. Our results are supported by complementary numerical Floquet simulations.
Odd frequency pairing of interacting Majorana fermions
NASA Astrophysics Data System (ADS)
Huang, Zhoushen; Woelfle, Peter; Balatsky, Alexandar
Majorana fermions are rising as a promising key component in quantum computation. While the prevalent approach is to use a quadratic (i.e. non-interacting) Majorana Hamiltonian, when expressed in terms of Dirac fermions, generically the Hamiltonian involves interaction terms. Here we focus on the possible pair correlations in a simple model system. We study a model of Majorana fermions coupled to a boson mode and show that the anomalous correlator between different Majorana fermions, located at opposite ends of a topological wire, exhibits odd frequency behavior. It is stabilized when the coupling strength g is above a critical value gc. We use both, conventional diagrammatic theory and a functional integral approach, to derive the gap equation, the critical temperature, the gap function, the critical coupling, and a Ginzburg-Landau theory allowing to discuss a possible subleading admixture of even-frequency pairing. Work supported by USDOE DE-AC52-06NA25396 E304, Knut and Alice Wallenberg Foundation, and ERC DM-321031.
Fermions Living in a Flat World
Jesus Anguiano-Galicia, Ma. de; Bashir, A.
2006-09-25
In a plane, parity transformation, which changes the sign of only one spatial coordinate, swaps the fermion fields living in two inequivalent representations. A parity invariant Lagrangian thus contains fields corresponding to both the representations. For such a Lagrangian, we show that we can also define a chiral symmetry.
Estimation for entanglement negativity of free fermions
NASA Astrophysics Data System (ADS)
Herzog, Christopher P.; Wang, Yihong
2016-07-01
In this letter we study the negativity of one dimensional free fermions. We derive the general form of the {{{Z}}N} symmetric term in moments of the partial transposed (reduced) density matrix, which is an algebraic function of the end points of the system. Such a path integral turns out to be a convenient tool for making estimations for the negativity.
Observation of Weyl fermions in condensed matter
NASA Astrophysics Data System (ADS)
Ding, Hong
In 1929, a German mathematician and physicist Hermann Weyl proposed that a massless solution of the Dirac equation represents a pair of new type of particles, the so-called Weyl fermions. However, their existence in particle physics remains elusive after more than eight decades, e.g., neutrino has been regarded as a Weyl fermion in the Standard Model until it was found to have mass. Recently, significant advances in topological materials have provided an alternative way to realize Weyl fermions in condensed matter as an emergent phenomenon. Weyl semimetals are predicted as a class of topological materials that can be regarded as three-dimensional analogs of graphene breaking time reversal or inversion symmetry. Electrons in a Weyl semimetal behave exactly as Weyl fermions, which have many exotic properties, such as chiral anomaly, magnetic monopoles in the crystal momentum space, and open Fermi arcs on the surface. In this talk I will report our experimental discovery of a Weyl semimetal in TaAs by observing Fermi arcs with a characteristic spin texture in the surface states and Weyl nodes in the bulk states using angle-resolved photoemission spectroscopy.
Ideal fermion delocalization in Higgsless models
NASA Astrophysics Data System (ADS)
Chivukula, R. Sekhar; Simmons, Elizabeth H.; He, Hong-Jian; Kurachi, Masafumi; Tanabashi, Masaharu
2005-07-01
In this note we examine the properties of deconstructed Higgsless models for the case of a fermion whose SU(2) properties arise from delocalization over many sites of the deconstructed lattice. We derive expressions for the correlation functions and use these to establish a generalized consistency relation among correlation functions. We discuss the form of the W boson wavefunction and show that if the probability distribution of the delocalized fermions is appropriately related to the W wavefunction, then deviations in precision electroweak parameters are minimized. In particular, we show that this “ideal fermion delocalization” results in the vanishing of three of the four leading zero-momentum electroweak parameters defined by Barbieri et al. We then discuss ideal fermion delocalization in the context of two continuum Higgsless models, one in Anti-deSitter space and one in flat space. Our results may be applied to any Higgsless linear moose model with multiple SU(2) groups, including those with only a few extra vector bosons.
Flavor Constraints on Split Fermion Models
Lillie, Ben
2003-06-26
We examine the contributions to rare processes that arise in models where the Standard Model fermions are localized at distinct points in compact extra dimensions. Tree-level flavor changing neutral current interactions for the Kaluza-Klein (KK) gauge field excitations are induced in such models, and hence strong constraints are thought to exist on the size of the additional dimensions. We find a general parameterization of the model which does not depend on any specific fermion geography and show that typical values of the parameters can reproduce the fermion hierarchy pattern. Using this parameterization, we reexamine the contributions to neutral meson mixing, rare meson decays, and single top-quark production in e{sup +}e{sup -} collisions. We find that is it possible to evade the stringent bounds for natural regions of the parameters, while retaining finite separations between the fermion fields and without introducing a new hierarchy. The resulting limits on the size of the compact dimension can be as low as TeV{sup -1}.
Gross, Charles
2016-01-01
Scientific misconduct has been defined as fabrication, falsification, and plagiarism. Scientific misconduct has occurred throughout the history of science. The US government began to take systematic interest in such misconduct in the 1980s. Since then, a number of studies have examined how frequently individual scientists have observed scientific misconduct or were involved in it. Although the studies vary considerably in their methodology and in the nature and size of their samples, in most studies at least 10% of the scientists sampled reported having observed scientific misconduct. In addition to studies of the incidence of scientific misconduct, this review considers the recent increase in paper retractions, the role of social media in scientific ethics, several instructional examples of egregious scientific misconduct, and potential methods to reduce research misconduct. PMID:26273897
Fermionic-mode entanglement in non-Markovian environment
Cheng, Jiong; Han, Yan; An, Qing-zhi; Zhou, Ling
2015-03-15
We evaluate the non-Markovian effects on the entanglement dynamics of a fermionic system interacting with two dissipative vacuum reservoirs. The exact solution of density matrix is derived by utilizing the Feynman–Vernon influence functional theory in the fermionic coherent state representation and the Grassmann calculus, which are valid for both the fermionic and bosonic baths, and their difference lies in the dependence of the parity of the initial states. The fermionic entanglement dynamics is presented by adding an additional restriction to the density matrix known as the superselection rules. Our analysis shows that the usual decoherence suppression schemes implemented in qubits systems can also be achieved for systems of identical fermions, and the initial state proves its importance in the evolution of fermionic entanglement. Our results provide a potential way to decoherence controlling of identical fermions.
Utilizing Traditional Knowledge in a Scientific Setting.
ERIC Educational Resources Information Center
Boyne, Grace M.
2003-01-01
A nuclear physicist feels that his Navajo upbringing, with its emphasis on the structure of nature and abstract reasoning, prepared him well for the world of physics. Traditional Navajo sandpaintings helped him understand physics concepts. Native American students show strengths in learning visual, perceptual, or spatial information, and they…
NASA Astrophysics Data System (ADS)
Xiang-Guo, Meng; Ji-Suo, Wang; Hong-Yi, Fan; Cheng-Wei, Xia
2016-04-01
We solve the fermionic master equation for a thermal bath to obtain its explicit Kraus operator solutions via the fermionic state approach. The normalization condition of the Kraus operators is proved. The matrix representation for these solutions is obtained, which is incongruous with the result in the book completed by Nielsen and Chuang [Quantum Computation and Quantum Information, Cambridge University Press, 2000]. As especial cases, we also present the Kraus operator solutions to master equations for describing the amplitude-decay model and the diffusion process at finite temperature. Project supported by the National Natural Science Foundation of China (Grant No. 11347026), the Natural Science Foundation of Shandong Province, China (Grant Nos. ZR2013AM012 and ZR2012AM004), and the Research Fund for the Doctoral Program and Scientific Research Project of Liaocheng University, Shandong Province, China.
Superfluid state of repulsively interacting three-component fermionic atoms in optical lattices
NASA Astrophysics Data System (ADS)
Suga, Sei-Ichiro; Inaba, Kensuke
2013-03-01
We investigate the superfluid state of repulsively interacting three-component (color) fermionic atoms in optical lattices using Feynman diagrammatic approaches and the dynamical mean field theory. When the anisotropy of the three repulsive interactions is strong, atoms of two of the three colors form Cooper pairs and atoms of the third color remain a Fermi liquid. This superfluid emerges close to half filling at which the Mott insulating state characteristic of the three-component repulsive fermions appears. An effective attractive interaction is induced by density fluctuations of the third-color atoms. The superfluid state is stable against the phase separation that occurs in the strongly repulsive region. We determine the phase diagrams in terms of temperature, filling, and the anisotropy of the repulsive interactions. This work was supported by Grant-in-Aid for Scientific Research (C) (No. 23540467) from the Japan Society for the Promotion of Science.
ERIC Educational Resources Information Center
Goodstein, David
1991-01-01
A discussion of fraud in the presentation of results of scientific research cites cases looks at variations in the degree of misrepresentation, kinds and intents of fraud, attention given by public agencies (National Institutes of Health, National Science Foundation, Public Health Service), and differences between scientific and civil fraud. (MSE)
Functional representation for fermionic quantum fields
NASA Astrophysics Data System (ADS)
Floreanini, R.; Jackiw, R.
1988-04-01
A functional representation for fermionic quantum fields is developed in analogy to familiar results for bosonic fields. The infinite Clifford algebra of the field anticommutator is realized reducibly on a Grassmann functional space. On this space, transformation groups may be represented without normal ordering with respect to a Fock vacuum, and a projective representation for the two-dimensional conformal group is found, which is compared to the corresponding representation in terms of bosonic fields. When a quadratic Hamiltonian for the Fermi fields is posited, a Fock space can be constructed after a prescription for filling the Dirac sea is selected. Different filling prescriptions lead to inequivalent Fock spaces within the functional space. Explicit eigenfunctionals exhibit the peculiarities of fermionic field theory, such as fractional charge, Berry's phase, and anomalies.
Peltier cooling of fermionic quantum gases.
Grenier, Ch; Georges, A; Kollath, C
2014-11-14
We propose a cooling scheme for fermionic quantum gases, based on the principles of the Peltier thermoelectric effect and energy filtering. The system to be cooled is connected to another harmonically trapped gas acting as a reservoir. The cooling is achieved by two simultaneous processes: (i) the system is evaporatively cooled, and (ii) cold fermions from deep below the Fermi surface of the reservoir are injected below the Fermi level of the system, in order to fill the "holes" in the energy distribution. This is achieved by a suitable energy dependence of the transmission coefficient connecting the system to the reservoir. The two processes can be viewed as simultaneous evaporative cooling of particles and holes. We show that both a significantly lower entropy per particle and faster cooling rate can be achieved in this way than by using only evaporative cooling. PMID:25432033
Ultrasoft fermionic excitation at finite chemical potential
NASA Astrophysics Data System (ADS)
Blaizot, Jean-Paul; Satow, Daisuke
2014-05-01
It has been suggested previously that an ultrasoft fermionic excitation develops, albeit with a small spectral weight, in a system of massless fermions and scalar bosons with Yukawa interaction at high temperature T. In this paper we study how this excitation is modified at finite chemical potential μ. We relate the existence of the ultrasoft mode to symmetries, in particular charge conjugation, and a supersymmetry of the free system which is spontaneously broken by finite temperature and finite density effects, as argued earlier by Lebedev and Smilga. A nonvanishing chemical potential breaks both symmetries explicitly and maximally at zero temperature where the mode ceases to exist. A detailed calculation indicates that the ultrasoft excitation persists as long as T≥0.71μ.
Playing with fermion couplings in Higgsless models
Casalbuoni, R.; De Curtis, S.; Dolce, D.; Dominici, D.
2005-04-01
We discuss the fermion couplings in a four dimensional SU(2) linear moose model by allowing for direct couplings between the left-handed fermions on the boundary and the gauge fields in the internal sites. This is realized by means of a product of nonlinear {sigma}-model scalar fields which, in the continuum limit, is equivalent to a Wilson line. The effect of these new nonlocal couplings is a contribution to the {epsilon}{sub 3} parameter which can be of opposite sign with respect to the one coming from the gauge fields along the string. Therefore, with some fine-tuning, it is possible to satisfy the constraints from the electroweak data.
Fermionic field theory for trees and forests.
Caracciolo, Sergio; Jacobsen, Jesper Lykke; Saleur, Hubert; Sokal, Alan D; Sportiello, Andrea
2004-08-20
We prove a generalization of Kirchhoff's matrix-tree theorem in which a large class of combinatorial objects are represented by non-Gaussian Grassmann integrals. As a special case, we show that unrooted spanning forests, which arise as a q-->0 limit of the Potts model, can be represented by a Grassmann theory involving a Gaussian term and a particular bilocal four-fermion term. We show that this latter model can be mapped, to all orders in perturbation theory, onto the N-vector model at N=-1 or, equivalently, onto the sigma model taking values in the unit supersphere in R(1|2). It follows that, in two dimensions, this fermionic model is perturbatively asymptotically free. PMID:15447166
Exact holographic mapping in free fermion systems
NASA Astrophysics Data System (ADS)
Lee, Ching Hua; Qi, Xiao-Liang
2016-01-01
In this paper, we perform a detailed analysis of the exact holographic mapping first introduced in arXiv:1309.6282, which was proposed as an explicit example of holographic duality between quantum many-body systems and gravitational theories. We obtain analytic results for free fermion systems that not only confirm previous numerical results, but also elucidate the exact relationships between the various physical properties of the bulk and boundary systems. These analytic results allow us to study the asymptotic properties that are difficult to probe numerically, such as the near-horizon regime of the black-hole geometry. We shall also explore a few interesting but hitherto unexplored bulk geometries, such as that corresponding to a boundary critical fermion with a nontrivial dynamical critical exponent. Our analytic framework also allows us to study the holographic mapping of some of these boundary theories in dimensions 2+1 or higher.
A closer look at the elementary fermions
Goldhaber, Maurice
2002-01-01
Although there have been many experimental and theoretical efforts to measure and interpret small deviations from the standard model of particle physics, the gap that the model leaves in understanding why there are only three generations of the elementary fermions, with hierarchical masses, has not received the attention it deserves. I present here an attempt to fill this gap. Although our findings are mostly only qualitative, they nevertheless may be of heuristic value. Rules concerning the elementary fermions, some previously known and some new, lead to a number of conclusions and questions that seem worth pursuing. Some clarify the standard model, and others suggest possible modifications, the implications of which are discussed. PMID:11773637
A Quantum Gas Microscope for Fermionic Potassium
NASA Astrophysics Data System (ADS)
Cheuk, Lawrence; Nichols, Matthew; Okan, Melih; Lawrence, Katherine; Zhang, Hao; Zwierlein, Martin
2016-05-01
Ultracold atoms in optical lattices have enabled experimental studies of quantum many-body physics in Hubbard-type lattice systems in a clean and well-controlled environment. In particular, the advent of quantum gas microscopes has made available new experimental probes ideally suited for observing magnetic order and spatial correlations. In the past year, several groups, including ours, first realized quantum gas microscopes for fermionic atoms. In this talk, we describe our experimental setup, which combines high-resolution imaging with Raman sideband cooling to achieve single-site-resolved fluorescent imaging of fermionic 40 K atoms. We also report on recent progress towards observing quantum phases of the Fermi-Hubbard model with single-site resolution.
Unextendible product basis for fermionic systems
NASA Astrophysics Data System (ADS)
Chen, Jianxin; Chen, Lin; Zeng, Bei
2014-08-01
We discuss the concept of unextendible product basis (UPB) and generalized UPB for fermionic systems, using Slater determinants as an analogue of product states, in the anti-symmetric subspace wedge ^ N {{C}}^M. We construct an explicit example of generalized fermionic unextendible product basis (FUPB) with minimum cardinality N(M - N) + 1 for any N ⩾ 2, M ⩾ 4. We also show that any bipartite anti-symmetric space wedge ^ 2 {{C}}^M of codimension two is spanned by Slater determinants, and the spaces of higher codimension may not be spanned by Slater determinants. Furthermore, we construct an example of complex FUPB of N = 2, M = 4 with minimum cardinality 5. In contrast, we show that a real FUPB does not exist for N = 2, M = 4. Finally, we provide a systematic construction for FUPBs of higher dimensions by using FUPBs and UPBs of lower dimensions.
Explicit Hamiltonians inducing volume law for entanglement entropy in fermionic lattices
NASA Astrophysics Data System (ADS)
Gori, Giacomo; Paganelli, Simone; Sharma, Auditya; Sodano, Pasquale; Trombettoni, Andrea
2015-06-01
We show how the area law for entanglement entropy may be violated by free fermions on a lattice, and we look for conditions leading to the emergence of a volume law. We give an explicit construction of the states with maximal entanglement entropy based on the fact that, once a bipartition of the lattice in two complementary sets A and A ¯ is given, the states with maximal entanglement entropy (volume law) may be factored into Bell pairs (BPs) formed by two states with support on A and A ¯. We then exhibit, for translational invariant fermionic systems on a lattice, a Hamiltonian whose ground state is such that it yields an exact volume law. As expected, the corresponding Fermi surface has a fractal topology. We also provide some examples of fermionic models for which the ground state may have an entanglement entropy SA between the area and the volume law, building an explicit example of a one-dimensional free fermion model where SA(L ) ∝Lβ , with β being intermediate between β =0 (area law) and β =1 (BP state inducing volume law). For this model, the dispersion relation has a "zigzag" structure leading to a fractal Fermi surface whose counting box dimension equals, for large lattices, β . Our analysis clearly relates the violation of the area law for the entanglement entropy of the ground state to the emergence of a nontrivial topology of the Fermi surface.
Sen, Aditi; Sen, Ujjwal; Gromek, Bartosz; Lewenstein, Maciej
2007-02-15
We consider information transmission through a noiseless quantum channel, where the information is encoded into massive indistinguishable particles: bosons or fermions. We study the situation in which the particles are noninteracting. The encoding input states obey a set of physically motivated constraints on the mean values of the energy and particle number. In such a case, the determination of both classical and quantum capacity reduces to a constrained maximization of entropy. In the case of noninteracting bosons, signatures of Bose-Einstein condensation can be observed in the behavior of the capacity. A major motivation for these considerations is to compare the information-carrying capacities of channels that carry bosons with those that carry fermions. We show analytically that fermions generally provide higher channel capacity, i.e., they are better suited for transferring bits as well as qubits, in comparison to bosons. This holds for a large range of power-law potentials, and for moderate to high temperatures. Numerical simulations seem to indicate that the result holds for all temperatures. Also, we consider the low-temperature behavior for the three-dimensional box and harmonic trap, and again we show that the fermionic capacity is higher than the bosonic one for sufficiently low temperatures.
Point contact spectroscopy of heavy fermions
NASA Astrophysics Data System (ADS)
Moser, M.; Wachter, P.; Franse, J. J. M.; Meisner, G. P.; Walker, E.
Point contact spectroscopy (PCS) has been performed on the heavy fermion systems CeAl3, CeCu6, UPt3, U6Co and U2PtC2. The dynamical resistance dU/dI is a function of the electronic density of states (EDS) at E/sub F/. The width of the EDS inferred from the PC measurements can be compared with the (GAMMA)-value of the specific heat.
Fermion masses from SO(10) Hermitian matrices
Moorhouse, R. G.
2008-03-01
Masses of fermions in the SO(10) 16-plet are constructed using only the 10, 120, and 126 scalar multiplets. The mass matrices are restricted to be Hermitian and the theory is constructed to have certain assumed quark masses, charged lepton masses, and Cabibbo-Kobayashi-Maskawa (CKM) matrix in accord with data. The remaining free parameters are found by fitting to light neutrino masses and Maki-Nakagawa-Sakata (MNS) matrices result as predictions.
Fermion masses from SO(10) Hermitian matrices
NASA Astrophysics Data System (ADS)
Moorhouse, R. G.
2008-03-01
Masses of fermions in the SO(10) 16-plet are constructed using only the 10, 120, and 126¯ scalar multiplets. The mass matrices are restricted to be Hermitian and the theory is constructed to have certain assumed quark masses, charged lepton masses, and Cabibbo-Kobayashi-Maskawa (CKM) matrix in accord with data. The remaining free parameters are found by fitting to light neutrino masses and Maki-Nakagawa-Sakata (MNS) matrices result as predictions.
Magnetization of planar four-fermion systems
Caldas, Heron; Ramos, Rudnei O.
2009-09-15
We consider a planar system of fermions, at finite temperature and density under a static magnetic field parallel to the two-dimensional plane. This magnetic field generates a Zeeman effect and then a spin polarization of the system. The critical properties are studied from the Landau's free energy. The possible observable consequences of the magnetization of planar systems such as polymer films and graphene are discussed.
Strong coupling QED with two fermionic flavors
Wang, K.C.
1990-11-01
We report the recent results of our simulation of strong coupling QED, with non-compact action, on lattices 10{sup 4} and 16{sup 4}. Since we are dealing with two staggered fermionic flavors, we use hybrid algorithm to do the simulation. In addition to the measurement of the chiral order parameter {l angle}{bar {psi}}{psi}{r angle}, we also measure magnetic monopole susceptibility, {chi}, throughout the region of chiral transition. 6 refs., 6 figs.
Renormalization group for non-relativistic fermions.
Shankar, R
2011-07-13
A brief introduction is given to the renormalization group for non-relativistic fermions at finite density. It is shown that Landau's theory of the Fermi liquid arises as a fixed point (with the Landau parameters as marginal couplings) and its instabilities as relevant perturbations. Applications to related areas, nuclear matter, quark matter and quantum dots, are briefly discussed. The focus will be on explaining the main ideas to people in related fields, rather than addressing the experts. PMID:21646269
Rotating fermions inside a cylindrical boundary
NASA Astrophysics Data System (ADS)
Ambruş, Victor E.; Winstanley, Elizabeth
2016-05-01
We study a quantum fermion field inside a cylinder in Minkowski space-time. On the surface of the cylinder, the fermion field satisfies either spectral or MIT bag boundary conditions. We define rigidly-rotating quantum states in both cases, assuming that the radius of the cylinder is sufficiently small that the speed-of-light surface is excluded from the space-time. With this assumption, we calculate rigidly-rotating thermal expectation values of the fermion condensate, neutrino charge current and stress-energy tensor relative to the bounded vacuum state. These rigidly-rotating thermal expectation values are finite everywhere inside and on the surface of the cylinder, and their detailed properties depend on the choice of boundary conditions. We also compute the Casimir divergence of the expectation values of these quantities in the bounded vacuum state relative to the unbounded Minkowski vacuum. We find that the rate of divergence of the Casimir expectation values depends on the conditions imposed on the boundary.
Composite gauge-bosons made of fermions
NASA Astrophysics Data System (ADS)
Suzuki, Mahiko
2016-07-01
We construct a class of Abelian and non-Abelian local gauge theories that consist only of matter fields of fermions. The Lagrangian is local and does not contain an auxiliary vector field nor a subsidiary condition on the matter fields. It does not involve an extra dimension nor supersymmetry. This Lagrangian can be extended to non-Abelian gauge symmetry only in the case of SU(2) doublet matter fields. We carry out an explicit diagrammatic computation in the leading 1 /N order to show that massless spin-one bound states appear with the correct gauge coupling. Our diagram calculation exposes the dynamical features that cannot be seen in the formal auxiliary vector-field method. For instance, it shows that the s -wave fermion-antifermion interaction in the 3S1 channel (ψ ¯ γμψ ) alone cannot form the bound gauge bosons; the fermion-antifermion pairs must couple to the d -wave state too. One feature common to our class of Lagrangian is that the Noether current does not exist. Therefore it evades possible conflict with the no-go theorem of Weinberg and Witten on the formation of the non-Abelian gauge bosons.
Strong CP, Flavor, and Twisted Split Fermions
Harnik, Roni; Perez, Gilad; Schwartz, Matthew D.; Shirman, Yuri
2004-11-10
We present a natural solution to the strong CP problem in the context of split fermions. By assuming CP is spontaneously broken in the bulk, a weak CKM phase is created in the standard model due to a twisting in flavor space of the bulk fermion wavefunctions. But the strong CP phase remains zero, being essentially protected by parity in the bulk and CP on the branes. As always in models of spontaneous CP breaking, radiative corrections to theta bar from the standard model are tiny, but even higher dimension operators are not that dangerous. The twisting phenomenon was recently shown to be generic, and not to interfere with the way that split fermions naturally weaves small numbers into the standard model. It follows that out approach to strong CP is compatible with flavor, and we sketch a comprehensive model. We also look at deconstructed version of this setup which provides a viable 4D model of spontaneous CP breaking which is not in the Nelson-Barr class.
Scalar meson spectroscopy with lattice staggered fermions
Bernard, Claude; DeTar, Carleton; Fu Ziwen; Prelovsek, Sasa
2007-11-01
With sufficiently light up and down quarks the isovector (a{sub 0}) and isosinglet (f{sub 0}) scalar meson propagators are dominated at large distance by two-meson states. In the staggered-fermion formulation of lattice quantum chromodynamics, taste-symmetry breaking causes a proliferation of two-meson states that further complicates the analysis of these channels. Many of them are unphysical artifacts of the lattice approximation. They are expected to disappear in the continuum limit. The staggered-fermion fourth-root procedure has its purported counterpart in rooted staggered chiral perturbation theory (rS{chi}PT). Fortunately, the rooted theory provides a strict framework that permits the analysis of scalar meson correlators in terms of only a small number of low-energy couplings. Thus the analysis of the point-to-point scalar meson correlators in this context gives a useful consistency check of the fourth-root procedure and its proposed chiral realization. Through numerical simulation we have measured correlators for both the a{sub 0} and f{sub 0} channels in the 'Asqtad' improved staggered-fermion formulation in a lattice ensemble with lattice spacing a=0.12 fm. We analyze those correlators in the context of rS{chi}PT and obtain values of the low-energy chiral couplings that are reasonably consistent with previous determinations.
The Feynman problem and fermionic entanglement: Fermionic theory versus qubit theory
NASA Astrophysics Data System (ADS)
D'Ariano, Giacomo Mauro; Manessi, Franco; Perinotti, Paolo; Tosini, Alessandro
2014-06-01
The present paper is both a review on the Feynman problem, and an original research presentation on the relations between Fermionic theories and qubits theories, both regarded in the novel framework of operational probabilistic theories. The most relevant results about the Feynman problem of simulating Fermions with qubits are reviewed, and in the light of the new original results, the problem is solved. The answer is twofold. On the computational side, the two theories are equivalent, as shown by Bravyi and Kitaev [S. B. Bravyi and A. Y. Kitaev, Ann. Phys. 298, 210 (2002)]. On the operational side, the quantum theory of qubits and the quantum theory of Fermions are different, mostly in the notion of locality, with striking consequences on entanglement. Thus the emulation does not respect locality, as it was suspected by Feynman [R. Feynman, Int. J. Theor. Phys. 21, 467 (1982)].
Scientific Globish versus scientific English.
Tychinin, Dmitry N; Kamnev, Alexander A
2013-10-01
The proposed adoption of 'scientific Globish' as a simplified language standard for scholarly communication may appeal to authors who have difficulty with English proficiency. However, Globish might not justify the hopes being pinned on it and might open the door to further deterioration of the quality of English-language scientific writing. PMID:23928006
Mixtures of Bosonic and Fermionic atoms
NASA Astrophysics Data System (ADS)
Albus, Alexander
2003-12-01
The theory of atomic Boson-Fermion mixtures in the dilute limit beyond mean-field is considered in this thesis. Extending the formalism of quantum field theory we derived expressions for the quasi-particle excitation spectra, the ground state energy, and related quantities for a homogenous system to first order in the dilute gas parameter. In the framework of density functional theory we could carry over the previous results to inhomogeneous systems. We then determined to density distributions for various parameter values and identified three different phase regions: (i) a stable mixed regime, (ii) a phase separated regime, and (iii) a collapsed regime. We found a significant contribution of exchange-correlation effects in the latter case. Next, we determined the shift of the Bose-Einstein condensation temperature caused by Boson-Fermion interactions in a harmonic trap due to redistribution of the density profiles. We then considered Boson-Fermion mixtures in optical lattices. We calculated the criterion for stability against phase separation, identified the Mott-insulating and superfluid regimes both, analytically within a mean-field calculation, and numerically by virtue of a Gutzwiller Ansatz. We also found new frustrated ground states in the limit of very strong lattices. ----Anmerkung: Der Autor ist Träger des durch die Physikalische Gesellschaft zu Berlin vergebenen Carl-Ramsauer-Preises 2004 für die jeweils beste Dissertation der vier Universitäten Freie Universität Berlin, Humboldt-Universität zu Berlin, Technische Universität Berlin und Universität Potsdam. Ziel der Arbeit war die systematische theoretische Behandlung von Gemischen aus bosonischen und fermionischen Atomen in einem Parameterbereich, der sich zur Beschreibung von aktuellen Experimenten mit ultra-kalten atomaren Gasen eignet. Zuerst wurde der Formalismus der Quantenfeldtheorie auf homogene, atomare Boson-Fermion Gemische erweitert, um grundlegende Größen wie Quasiteilchenspektren
Semiclassical fermion pair creation in de Sitter spacetime
Stahl, Clément Eckhard, Strobel
2015-12-17
We present a method to semiclassically compute the pair creation rate of bosons and fermions in de Sitter spacetime. The results in the bosonic case agree with the ones in the literature. We find that for the constant electric field the fermionic and bosonic pair creation rate are the same. This analogy of bosons and fermions in the semiclassical limit is known from several flat spacetime examples.
Trapped resonant fermions above the superfluid transition temperature
Cheng, C.-H.; Yip, S.-K.
2007-01-01
We investigate trapped resonant fermions with unequal populations within the local density approximation above the superfluid transition temperature. By tuning the attractive interaction between fermions via Feshbach resonance, the system evolves from weakly interacting fermi gas to strongly interacting fermi gas, and finally becomes a Bose-Fermi mixture. The density profiles of fermions are examined and compared with experiments. We also point out the simple relationships between the local density, the axial density, and the gas pressure within the local density approximation.
Drone-fermions in the two-dimensional antiferromagnet
NASA Astrophysics Data System (ADS)
Krivenko, S.; Khaliullin, G.
1995-02-01
Two different representations of spins - via the conventional fermions, or via the Mattis drone-fermions - are compared considering the planar antiferromagnetic Heisenberg model as an example. Mean-field spin correlation functions calculated for the uniform and flux RVB states show that the drone-fermion approach has an advantage in giving the lower energy and the enhanced AF correlations, because of the absence of unphysical spinless states in this representation.
Quantum Hall Effect of Massless Dirac Fermions and Free Fermions in Hofstadter's Butterfly
NASA Astrophysics Data System (ADS)
Yoshioka, Nobuyuki; Matsuura, Hiroyasu; Ogata, Masao
2016-06-01
We propose a new physical interpretation of the Diophantine equation of σxy for the Hofstadter problem. First, we divide the energy spectrum, or Hofstadter's butterfly, into smaller self-similar areas called "subcells", which were first introduced by Hofstadter to describe the recursive structure. We find that in the energy gaps between subcells, there are two ways to account for the quantization rule of σxy, that are consistent with the Diophantine equation: Landau quantization of (i) massless Dirac fermions or (ii) free fermions in Hofstadter's butterfly.
NASA Astrophysics Data System (ADS)
de Vega, H. J.; Medrano, M. Ramon; Sanchez, N.
1992-07-01
We investigate the physical implications and particle content of superstring scattering in the supergravity shock-wave background recently found by us. The amplitudes for the different particle transmutation processes taking place in this geometry are explicitly computed for Gree-Schwarz superstring, including the new phenomena of fermion to boson and boson to fermion transmutations. Transition amplitudes among the ground states, first and second excited states are obtained. Particularly interesting are the amplitudes within the massless particle sector, which lead to physical massive particles upon supersymmetry breaking at low energies.
ERIC Educational Resources Information Center
Goodstein, David
2002-01-01
Explores scientific fraud, asserting that while few scientists actually falsify results, the field has become so competitive that many are misbehaving in other ways; an example would be unreasonable criticism by anonymous peer reviewers. (EV)
Fermion frontiers in vector lattice gauge theories: Proceedings. Volume 8
1998-11-01
The inclusion of fermions into simulations of lattice gauge theories is very difficult both theoretically and numerically. With the presence of Teraflops-scale computers for lattice gauge theory, the authors wanted a forum to discuss new approaches to lattice fermions. The workshop concentrated on approaches which are ripe for study on such large machines. Although lattice chiral fermions are vitally important to understand, there is not technique at hand which is viable on these Teraflops-scale machines for real-world problems. The discussion was therefore focused on recent developments and future prospects for QCD-like theories. For the well-known fermion formulations, the Aoki phase in Wilson fermions, novelties of U{sub A}(1) symmetry and the {eta}{prime} for staggered fermions and new approaches for simulating the determinant for Wilson fermions were discussed. The newer domain-wall fermion formulation was reviewed, with numerical results given by many speakers. The fermion proposal of Friedberg, Lee and Pang was introduced. They also were able to compare and contrast the dependence of QCD and QCD-like SUSY theories on the number of quark flavors. These proceedings consist of several transparencies and a summary page from each speaker. This should serve to outline the major points made in each talk.
Four-fermion interaction from torsion as dark energy
NASA Astrophysics Data System (ADS)
Popławski, Nikodem J.
2012-02-01
The observed small, positive cosmological constant may originate from a four-fermion interaction generated by the spin-torsion coupling in the Einstein-Cartan-Sciama-Kibble gravity if the fermions are condensing. In particular, such a condensation occurs for quark fields during the quark-gluon/hadron phase transition in the early Universe. We study how the torsion-induced four-fermion interaction is affected by adding two terms to the Dirac Lagrangian density: the parity-violating pseudoscalar density dual to the curvature tensor and a spinor-bilinear scalar density which measures the nonminimal coupling of fermions to torsion.
Wilson Fermions and Axion Electrodynamics in Optical Lattices
Bermudez, A.; Martin-Delgado, M. A.; Mazza, L.; Rizzi, M.; Goldman, N.; Lewenstein, M.
2010-11-05
We show that ultracold Fermi gases in optical superlattices can be used as quantum simulators of relativistic lattice fermions in 3+1 dimensions. By exploiting laser-assisted tunneling, we find an analogue of the so-called naive Dirac fermions, and thus provide a realization of the fermion doubling problem. Moreover, we show how to implement Wilson fermions, and discuss how their mass can be inverted by tuning the laser intensities. In this regime, our atomic gas corresponds to a phase of matter where Maxwell electrodynamics is replaced by axion electrodynamics: a 3D topological insulator.
Chiral lattice fermions with correct vacuum polarization and chiral anomaly
Pryor, C. )
1991-04-15
An action for chiral lattice fermions is proposed, which avoids the Nielsen-Ninomiya theorem by virtue of its nonlocality and nonbilinearity. The action is constructed by eliminating the extra fermion modes with a gauge-violating Majorana-type Wilson mass, which is then rendered invariant by an integration over gauge transformations. The free propagator is calculated, and the one-loop vacuum polarization is shown to be identical to that for Wilson fermions, even at nonzero lattice spacing. Also the chiral anomaly is shown to be the same as for Wilson fermions in the continuum limit.
Discovering correlated fermions using quantum Monte Carlo.
Wagner, Lucas K; Ceperley, David M
2016-09-01
It has become increasingly feasible to use quantum Monte Carlo (QMC) methods to study correlated fermion systems for realistic Hamiltonians. We give a summary of these techniques targeted at researchers in the field of correlated electrons, focusing on the fundamentals, capabilities, and current status of this technique. The QMC methods often offer the highest accuracy solutions available for systems in the continuum, and, since they address the many-body problem directly, the simulations can be analyzed to obtain insight into the nature of correlated quantum behavior. PMID:27518859
8B structure in Fermionic Molecular Dynamics
NASA Astrophysics Data System (ADS)
Henninger, K. R.; Neff, T.; Feldmeier, H.
2015-04-01
The structure of the light exotic nucleus 8B is investigated in the Fermionic Molecular Dynamics (FMD) model. The decay of 8B is responsible for almost the entire high- energy solar-neutrino flux, making structure calculations of 8B important for determining the solar core temperature. 8B is a proton halo candidate thought to exhibit clustering. FMD uses a wave-packet basis and is well-suited for modelling clustering and halos. For a multiconfiguration treatment we construct the many-body Hilbert space from antisymmetrised angular-momentum projected 8-particle states. First results show formation of a proton halo.
Generating functions for canonical systems of fermions.
Pain, Jean-Christophe; Gilleron, Franck; Porcherot, Quentin
2011-06-01
The method proposed by Pratt to derive recursion relations for systems of degenerate fermions [S. Pratt, Phys. Rev. Lett. 84, 4255 (2000)] relies on diagrammatic techniques. This efficient formalism assumes no explicit two-body interactions, makes possible the inclusion of conservation laws, and requires low computational time. In this Brief Report, we show that such recursion relations can be obtained from generating functions, without any restriction in relation to the number of conservation laws (e.g., total energy or angular momentum). PMID:21797523
Discovering correlated fermions using quantum Monte Carlo
NASA Astrophysics Data System (ADS)
Wagner, Lucas K.; Ceperley, David M.
2016-09-01
It has become increasingly feasible to use quantum Monte Carlo (QMC) methods to study correlated fermion systems for realistic Hamiltonians. We give a summary of these techniques targeted at researchers in the field of correlated electrons, focusing on the fundamentals, capabilities, and current status of this technique. The QMC methods often offer the highest accuracy solutions available for systems in the continuum, and, since they address the many-body problem directly, the simulations can be analyzed to obtain insight into the nature of correlated quantum behavior.
Continuum regularization of gauge theory with fermions
Chan, H.S.
1987-03-01
The continuum regularization program is discussed in the case of d-dimensional gauge theory coupled to fermions in an arbitrary representation. Two physically equivalent formulations are given. First, a Grassmann formulation is presented, which is based on the two-noise Langevin equations of Sakita, Ishikawa and Alfaro and Gavela. Second, a non-Grassmann formulation is obtained by regularized integration of the matter fields within the regularized Grassmann system. Explicit perturbation expansions are studied in both formulations, and considerable simplification is found in the integrated non-Grassmann formalism.
Some Improved Nonperturbative Bounds for Fermionic Expansions
NASA Astrophysics Data System (ADS)
Lohmann, Martin
2016-06-01
We reconsider the Gram-Hadamard bound as it is used in constructive quantum field theory and many body physics to prove convergence of Fermionic perturbative expansions. Our approach uses a recursion for the amplitudes of the expansion, discovered in a model problem by Djokic (2013). It explains the standard way to bound the expansion from a new point of view, and for some of the amplitudes provides new bounds, which avoid the use of Fourier transform, and are therefore superior to the standard bounds for models like the cold interacting Fermi gas.
Zero-point energy of confined fermions
Milton, K.A.
1980-01-01
A closed form for the reduced Green's function of massless fermions in the interior of a spherical bag is obtained. In terms of this Green's function, the corresponding zero-point or Casimir energy is computed. It is proposed that a resulting quadratic divergence can be absorbed by renormalizing a suitable parameter in the bag model (that is, absorbed by a contact term). The residual Casimir stress is attractive, but smaller than the repulsive Casimir stress of gluons in the model. The result for the total zero-point energy is in substantial disagreement with bag model phenomenological values.
Boson formulation of fermion field theories
Ha, Y.K.
1984-04-15
The nonperturbative connection between a canonical Fermi field and a canonical Bose field in two dimensions is developed and its validity verified according to the tenets of quantum field theory. We advocate the point of view that a boson formulation offers a unifying theme in understanding the structure of many theories. This is illustrated by the boson formulation of a multifermion theory with chiral and internal symmetries. Many features of the massless theory, such as dynamical mass generation with asymptotic-freedom behavior, hidden chiral symmetry, and connections with models of apparently different internal symmetries, are readily transparent through such fermion-boson metamorphosis.
Complete Boson-Fermion Model of Superconductivity
NASA Astrophysics Data System (ADS)
de Llano, Manuel
2003-03-01
The unification of the 1957 BCS theory with that of Bose-Einstein condensation (BEC) that gives roughly good first-principles transition temperature Tc predictions in either 2D or 3D for all of the ``Uemura plot'' ``exotic'' or conventional superconductors without abandoning the much-maligned phonon interaction mechanism has recently been achieved [1]-[3]. The same dynamical mechanism also allows for room-temperature superconductivity. The only condition is that one depart moderately from the perfect electron (e)-/hole (h)-Cooper-pair (CP) symmetry to which BCS (and indeed also the somewhat more general BCS-Bose crossover) theory are restricted by construction. It now becomes feasible to explain, among other things, why largely all superconductors empirically have substantially higher T_c's if their normal-state charge carriers are holes rather than electrons. A complete (in the sense that 2h-CPs are not ignored) boson-fermion model (CBFM) has been developed that reduces in the appropriate special cases to: a) ordinary BCS theory for weak boson-fermion coupling; b) the BCS-Bose ``crossover'' theory dating back to 1967; and, for no 2h-CPs to: c) the 1989 boson-fermion (BF) BEC model by T.D. Lee et al. of superconductors which without 2h-CPs is unrelated to BCS theory; d) an ideal BF binary-gas model [4] predicting nonzero BEC T_c's even in 2D; and finally to e) ordinary BEC (1925). The CBFM is a BF statistical model similar to those developed in the mid-50's by Schafroth, Blatt & Butler but which now includes 2h-CPs on an equal footing with 2e-CPs, and which unlike these models also contains the empirically well-established fermionic energy gap. [1] V.V. Tolmachev, Phys. Lett. A 266, 400 (2000). [2] M. Fortes, M.A. Solis, M. de Llano & V.V. Tolmachev, Physica C 364, 95 (2001). [3] M. de Llano & V.V. Tolmachev, Physica A 317, 546 (2003). [4] M. Casas, N.J. Davidson, M. de Llano, T.A. Mamedov, A. Puente, R.M. Quick, A. Rigo & M.A. Solis, Physica A 295, 146 (2001
Weinberg, A.M.
1997-12-01
Today, for the first time, scientific concerns are seriously being addressed that span future times--hundreds, even thousands, or more years in the future. One is witnessing what the author calls scientific millenarianism. Are such concerns for the distant future exercises in futility, or are they real issues that, to the everlasting gratitude of future generations, this generation has identified, warned about and even suggested how to cope with in the distant future? Can the four potential catastrophes--bolide impact, CO{sub 2} warming, radioactive wastes and thermonuclear war--be avoided by technical fixes, institutional responses, religion, or by doing nothing? These are the questions addressed in this paper.
Reducing finite lattice spacing errors for staggered fermions
NASA Astrophysics Data System (ADS)
Luo, Yubing
1998-12-01
In this thesis we study on-shell-improved lattice QCD with staggered fermions using Symanzik's improvement program. We present a complete and detailed discussion of the finite lattice spacing corrections to staggered fermion matrix elements. Expanding upon arguments of Sharpe, we explicitly implement the Symanzik improvement program demonstrating the absence of order a terms in the on-shell-improved action. We propose a general program to improve fermion operators to remove all O(a) corrections from their matrix elements, and demonstrate this program for the examples of matrix elements of fermion bilinears and BK. We find the former does have O(a) corrections while the latter does not. Also, we give an explicit form of lattice currents which are accurate to order a2 at the tree-level. Furthermore, we find that there are as many as 15 independent lattice operators of dimension-6 (including both gauge and fermion operators) which must be added to the unimproved action to form an O(a2)-improved action. Among them, the total number of dimension-6 gauge operators and fermion bilinears is 5. The other ten terms are four- fermion operators. At the tree level and tadpole-improved tree level, all ten four-fermion operators are absent.
Elementary formula for entanglement entropies of fermionic systems
Levay, Peter; Nagy, Szilvia; Pipek, Janos
2005-08-15
An elementary formula for the von Neumann and Renyi entropies describing quantum correlations in two-fermionic systems having four single-particle states is presented. An interesting geometric structure of fermionic entanglement is revealed. A connection with the generalized Pauli principle is established.
Charged fermions tunneling from accelerating and rotating black holes
Rehman, Mudassar; Saifullah, K. E-mail: saifullah@qau.edu.pk
2011-03-01
We study Hawking radiation of charged fermions from accelerating and rotating black holes with electric and magnetic charges. We calculate the tunneling probabilities of incoming and outgoing fermionic particles and find the Hawking temperature of these black holes. We also provide an explicit expression of the classical action for the massive and massless particles in the background of these black holes.
A streamlined method for chiral fermions on the lattice
Bodwin, G.T. . High Energy Physics Div.); Kovacs, E.V. )
1992-11-10
We discussed the use of renormalization counterterms to restore the chiral gauge symmetry in a lattice theory of Wilson fermions. We show that a large class of counterterms can be implemented automatically by making a simple modification to the fermion determinant.
Kink modes and effective four dimensional fermion and Higgs brane models
George, Damien P.; Volkas, Raymond R.
2007-05-15
In the construction of a classical smoothed out brane world model in five dimensions, one uses a dynamically generated domain wall (a kink) to localize an effective four dimensional theory. At the level of the Euler-Lagrange equations the kink sets up a potential well, a mechanism which has been employed extensively to obtain localized, four dimensional, massless chiral fermions. We present the generalization of this kink trapping mechanism for both scalar and fermionic fields, and retain all degrees of freedom that were present in the higher dimensional theory. We show that a kink background induces a symmetric modified Poeschl-Teller potential well, and give explicit analytic forms for all the bound modes and a restricted set of the continuum modes. We demonstrate that it is possible to confine an effective four dimensional scalar field with a quartic potential of arbitrary shape. This can be used to place the standard model electroweak Higgs field on the brane, and also generate nested kink solutions. We also consider the limits of the parameters in the theory which give thin kinks and localized and delocalized scalar and fermionic fields.
NASA Astrophysics Data System (ADS)
Hoelbling, Christian; Zielinski, Christian
2016-07-01
We follow up on a suggestion by Adams and construct explicit domain wall fermion operators with staggered kernels. We compare different domain wall formulations, namely the standard construction as well as Boriçi's modified and Chiu's optimal construction, utilizing both Wilson and staggered kernels. In the process, we generalize the staggered kernels to arbitrary even dimensions and introduce both truncated and optimal staggered domain wall fermions. Some numerical investigations are carried out in the (1 +1 )-dimensional setting of the Schwinger model, where we explore spectral properties of the bulk, effective and overlap Dirac operators in the free-field case, on quenched thermalized gauge configurations and on smooth topological configurations. We compare different formulations using the effective mass, deviations from normality and violations of the Ginsparg-Wilson relation as measures of chirality.
Real-time evolution of strongly coupled fermions driven by dissipation
NASA Astrophysics Data System (ADS)
Huffman, E.; Banerjee, D.; Chandrasekharan, S.; Wiese, U.-J.
2016-09-01
We consider the real-time evolution of a strongly coupled system of lattice fermions whose dynamics is driven entirely by dissipative Lindblad processes, with linear or quadratic quantum jump operators. The fermion 2-point functions obey a closed set of differential equations, which can be solved with linear algebra methods. The staggered occupation order parameter of the t- V model decreases exponentially during the dissipative time evolution. The structure factor associated with the various Fourier modes shows the slowing down of low-momentum modes, which is due to particle number conservation. The processes with nearest-neighbor-dependent Lindblad operators have a decay rate that is proportional to the coordination number of the spatial lattice.
Many-body formalism for fermions: Enforcing the Pauli principle on paper
NASA Astrophysics Data System (ADS)
Watson, D. K.
2015-07-01
Confined quantum systems involving N identical interacting fermions are found in many areas of physics, including condensed matter, atomic, nuclear, and chemical physics. In a previous series of papers, a many-body perturbation method that is applicable to both weakly and strongly interacting systems of bosons has been set forth by the author and coworkers. A symmetry-invariant perturbation theory was developed that uses group theory coupled with the dimension of space as the perturbation parameter to obtain an analytic correlated wave function through first order for a system under spherical confinement with a general two-body interaction. In the present paper, we extend this formalism to large systems of fermions, circumventing the numerical demands of applying the Pauli principle by enforcing the Pauli principle on paper. The method does not scale in complexity with N and has minimal numerical cost. We apply the method to a unitary Fermi gas and compare to recent Monte Carlo values.
Observing fermionic statistics with photons in arbitrary processes
Matthews, Jonathan C. F.; Poulios, Konstantinos; Meinecke, Jasmin D. A.; Politi, Alberto; Peruzzo, Alberto; Ismail, Nur; Wörhoff, Kerstin; Thompson, Mark G.; O'Brien, Jeremy L.
2013-01-01
Quantum mechanics defines two classes of particles-bosons and fermions-whose exchange statistics fundamentally dictate quantum dynamics. Here we develop a scheme that uses entanglement to directly observe the correlated detection statistics of any number of fermions in any physical process. This approach relies on sending each of the entangled particles through identical copies of the process and by controlling a single phase parameter in the entangled state, the correlated detection statistics can be continuously tuned between bosonic and fermionic statistics. We implement this scheme via two entangled photons shared across the polarisation modes of a single photonic chip to directly mimic the fermion, boson and intermediate behaviour of two-particles undergoing a continuous time quantum walk. The ability to simulate fermions with photons is likely to have applications for verifying boson scattering and for observing particle correlations in analogue simulation using any physical platform that can prepare the entangled state prescribed here. PMID:23531788
Beyond Dirac and Weyl fermions: Unconventional quasiparticles in conventional crystals.
Bradlyn, Barry; Cano, Jennifer; Wang, Zhijun; Vergniory, M G; Felser, C; Cava, R J; Bernevig, B Andrei
2016-08-01
In quantum field theory, we learn that fermions come in three varieties: Majorana, Weyl, and Dirac. Here, we show that in solid-state systems this classification is incomplete, and we find several additional types of crystal symmetry-protected free fermionic excitations. We exhaustively classify linear and quadratic three-, six-, and eight-band crossings stabilized by space group symmetries in solid-state systems with spin-orbit coupling and time-reversal symmetry. Several distinct types of fermions arise, differentiated by their degeneracies at and along high-symmetry points, lines, and surfaces. Some notable consequences of these fermions are the presence of Fermi arcs in non-Weyl systems and the existence of Dirac lines. Ab initio calculations identify a number of materials that realize these exotic fermions close to the Fermi level. PMID:27445310
Fermion tunneling from higher-dimensional black holes
NASA Astrophysics Data System (ADS)
Lin, Kai; Yang, Shu-Zheng
2009-03-01
Via the semiclassical approximation method, we study the 1/2-spin fermion tunneling from a higher-dimensional black hole. In our work, the Dirac equations are transformed into a simple form, and then we simplify the fermion tunneling research to the study of the Hamilton-Jacobi equation in curved space-time. Finally, we get the fermion tunneling rates and the Hawking temperatures at the event horizon of higher-dimensional black holes. We study fermion tunneling of a higher-dimensional Schwarzschild black hole and a higher-dimensional spherically symmetric quintessence black hole. In fact, this method is also applicable to the study of fermion tunneling from four-dimensional or lower-dimensional black holes, and we will take the rainbow-Finsler black hole as an example in order to make the fact explicit.
Fermion tunneling from higher-dimensional black holes
Lin Kai; Yang Shuzheng
2009-03-15
Via the semiclassical approximation method, we study the 1/2-spin fermion tunneling from a higher-dimensional black hole. In our work, the Dirac equations are transformed into a simple form, and then we simplify the fermion tunneling research to the study of the Hamilton-Jacobi equation in curved space-time. Finally, we get the fermion tunneling rates and the Hawking temperatures at the event horizon of higher-dimensional black holes. We study fermion tunneling of a higher-dimensional Schwarzschild black hole and a higher-dimensional spherically symmetric quintessence black hole. In fact, this method is also applicable to the study of fermion tunneling from four-dimensional or lower-dimensional black holes, and we will take the rainbow-Finsler black hole as an example in order to make the fact explicit.
Quantum phases of AB 2 fermionic chains
NASA Astrophysics Data System (ADS)
Murcia-Correa, L. S.; Franco, R.; Silva-Valencia, J.
2016-02-01
A fermionic chain is a one-dimensional system with fermions that interact locally and can jump between sites in the lattice, in particular an AB n chain type, where A and B are sites that exhibit a difference in energy level of Δ and site B is repeated n-times, such that the unit cell has n +1 sites. A limit case of this model, called the ionic Hubbard model (n = 1), has been widely studied due to its interesting physics and applications. In this paper, we study the ground state of an AB 2 chain, which describes the material R 4[Pt 2(P 2O5H2)4X] · nH 2 O. Specifically, we consider a filling with two electrons per unit cell, and using the density matrix renormalization group method we found that the system exhibits the band insulator and Mott correlated insulator phases, as well as an intermediate phase between them. For couplings of Δ = 2,10 and 20, we estimate the critical points that separate these phases through the structure factor and the energy gap in the sector of charge and spin, finding that the position of the critical point rises as a function of Δ.
Perturbative Corrections for Staggered Fermion Bilinears
Patel, Apoorva; Sharpe, Stephen
1992-01-01
We calculate the perturbative corrections to fermion bilinears that are used in numerical simulations when extracting weak matric elements using staggered fermions.This extends previous calculations of Golterman and Smit, and Daniel and Sheard.In particular, we calculate the corrections for non-local bilinears defined in Landau gauge with gauge links excluded.We do this for the simplest operators, i.e. those defined on a 2^4 hypercube, and for tree level improved operators which live on 4^4 hypercubes.We also consider gauge invariant operators in which the "tadpole" contributions are suppressed by projecting the sums of products of gauge links back in to the gauge group.In all cases, we find that the variation in the size of the perturbative corrections is smaller than those with the gauge invariant unimproved operators.This is most strikingly true for the smeared operators.We investigate the efficacy of the mean-field method of Lepage and Mackenzie at summing up tadpole
New Fermionic Soft Theorems for Supergravity Amplitudes.
Chen, Wei-Ming; Huang, Yu-Tin; Wen, Congkao
2015-07-10
Soft limits of a massless S matrix are known to reflect the symmetries of the theory. In particular, for theories with Goldstone bosons, the double-soft limit of scalars reveals the coset structure of the vacuum manifold. In this Letter, we propose that such universal double-soft behavior is not only true for scalars, but also for spin-1/2 particles in four dimensions and fermions in three dimensions. We first consider the Akulov-Volkov theory and demonstrate that the double-soft limit of Goldstinos yields the supersymmetry algebra. More surprisingly, we also find that amplitudes in 4≤N≤8 supergravity theories in four dimensions as well as N=16 supergravity in three dimensions behave universally in the double-soft-fermion limit, analogous to the scalar ones. The validity of the new soft theorems at loop level is also studied. The results for supergravity are beyond what is implied by supersymmetry Ward identities and may impose nontrivial constraints on the possible counterterms for supergravity theories. PMID:26207460
Search for Majorana fermions in topological superconductors.
Pan, Wei; Shi, Xiaoyan; Hawkins, Samuel D.; Klem, John Frederick
2014-10-01
The goal of this project is to search for Majorana fermions (a new quantum particle) in a topological superconductor (a new quantum matter achieved in a topological insulator proximitized by an s-wave superconductor). Majorana fermions (MFs) are electron-like particles that are their own anti-particles. MFs are shown to obey non-Abelian statistics and, thus, can be harnessed to make a fault-resistant topological quantum computer. With the arrival of topological insulators, novel schemes to create MFs have been proposed in hybrid systems by combining a topological insulator with a conventional superconductor. In this LDRD project, we will follow the theoretical proposals to search for MFs in one-dimensional (1D) topological superconductors. 1D topological superconductor will be created inside of a quantum point contact (with the metal pinch-off gates made of conventional s-wave superconductors such as niobium) in a two-dimensional topological insulator (such as inverted type-II InAs/GaSb heterostructure).
ERIC Educational Resources Information Center
Pieper, Gail W.
1980-01-01
Describes how scientific documentation is taught in three 50-minute sessions in a technical writing course. Tells how session one distinguishes between in-text notes, footnotes, and reference entries; session two discusses the author-year system of citing references; and session three is concerned with the author-number system of reference…
ERIC Educational Resources Information Center
National Science Teachers Association (NJ1), 2004
2004-01-01
Scientific inquiry reflects how scientists come to understand the natural world, and it is at the heart of how students learn. From a very early age, children interact with their environment, ask questions, and seek ways to answer those questions. Understanding science content is significantly enhanced when ideas are anchored to inquiry…
Kraft, Giuliano
2002-01-01
To give a correct and effective scientific presentation, is an arduous task that asks for close examination of basic techniques of communication. This article proposes indications and suggestions to help public speakers to be communicators, to use visual aids and it explains how to capture the audience attention. PMID:12599721
Technology Transfer Automated Retrieval System (TEKTRAN)
On September 15-17th, 2014, the US Environmental Protection Agency convened a public meeting of the FIFRA Scientific Advisory Panel (SAP) to address scientific issues associated with the agency’s “Development of a Spatial Aquatic Model (SAM) for Pesticide Risk Assessment”. The goal of SAM is to impr...
Technology Transfer Automated Retrieval System (TEKTRAN)
On July 29-31, 2014, the US Environmental Protection Agency convened a public meeting of the FIFRA Scientific Advisory Panel (SAP) to address scientific issues associated with the agency’s “new High Throughput Methods to Estimate Chemical Exposure”. EPA is proposing to use these methods to identify...
Scientific and Technical Document Database
National Institute of Standards and Technology Data Gateway
NIST Scientific and Technical Document Database (PC database for purchase) The images in NIST Special Database 20 contain a very rich set of graphic elements from scientific and technical documents, such as graphs, tables, equations, two column text, maps, pictures, footnotes, annotations, and arrays of such elements.
Nonequilibrium steady states of ideal bosonic and fermionic quantum gases
NASA Astrophysics Data System (ADS)
Vorberg, Daniel; Wustmann, Waltraut; Schomerus, Henning; Ketzmerick, Roland; Eckardt, André
2015-12-01
We investigate nonequilibrium steady states of driven-dissipative ideal quantum gases of both bosons and fermions. We focus on systems of sharp particle number that are driven out of equilibrium either by the coupling to several heat baths of different temperature or by time-periodic driving in combination with the coupling to a heat bath. Within the framework of (Floquet-)Born-Markov theory, several analytical and numerical methods are described in detail. This includes a mean-field theory in terms of occupation numbers, an augmented mean-field theory taking into account also nontrivial two-particle correlations, and quantum-jump-type Monte Carlo simulations. For the case of the ideal Fermi gas, these methods are applied to simple lattice models and the possibility of achieving exotic states via bath engineering is pointed out. The largest part of this work is devoted to bosonic quantum gases and the phenomenon of Bose selection, a nonequilibrium generalization of Bose condensation, where multiple single-particle states are selected to acquire a large occupation [Phys. Rev. Lett. 111, 240405 (2013), 10.1103/PhysRevLett.111.240405]. In this context, among others, we provide a theory for transitions where the set of selected states changes, describe an efficient algorithm for finding the set of selected states, investigate beyond-mean-field effects, and identify the dominant mechanisms for heat transport in the Bose-selected state.
Nonequilibrium steady states of ideal bosonic and fermionic quantum gases.
Vorberg, Daniel; Wustmann, Waltraut; Schomerus, Henning; Ketzmerick, Roland; Eckardt, André
2015-12-01
We investigate nonequilibrium steady states of driven-dissipative ideal quantum gases of both bosons and fermions. We focus on systems of sharp particle number that are driven out of equilibrium either by the coupling to several heat baths of different temperature or by time-periodic driving in combination with the coupling to a heat bath. Within the framework of (Floquet-)Born-Markov theory, several analytical and numerical methods are described in detail. This includes a mean-field theory in terms of occupation numbers, an augmented mean-field theory taking into account also nontrivial two-particle correlations, and quantum-jump-type Monte Carlo simulations. For the case of the ideal Fermi gas, these methods are applied to simple lattice models and the possibility of achieving exotic states via bath engineering is pointed out. The largest part of this work is devoted to bosonic quantum gases and the phenomenon of Bose selection, a nonequilibrium generalization of Bose condensation, where multiple single-particle states are selected to acquire a large occupation [Phys. Rev. Lett. 111, 240405 (2013)]. In this context, among others, we provide a theory for transitions where the set of selected states changes, describe an efficient algorithm for finding the set of selected states, investigate beyond-mean-field effects, and identify the dominant mechanisms for heat transport in the Bose-selected state. PMID:26764644
Fermion masses in the economical 3-3-1 model
Dong, P. V.; Huong, Tr. T.; Huong, D. T.; Long, H. N.
2006-09-01
We show that, in frameworks of the economical 3-3-1 model, all fermions get masses. At the tree level, one up-quark and two down-quarks are massless, but the one-loop corrections give all quarks the consistent masses. This conclusion is in contradiction to the previous analysis in which the third scalar triplet has been introduced. This result is based on the key properties of the model: First, there are three quite different scales of vacuum expectation values: {omega}{approx}O(1) TeV, v{approx_equal}246 GeV, and u{approx}O(1) GeV. Second, there exist two types of Yukawa couplings with different strengths: the lepton-number conserving couplings h's and the lepton-number violating ones s's satisfying the condition in which the second are much smaller than the first ones: s<
Scientific Claims versus Scientific Knowledge.
ERIC Educational Resources Information Center
Ramsey, John
1991-01-01
Provides activities that help students to understand the importance of the scientific method. The activities include the science of fusion and cold fusion; a group activity that analyzes and interprets the events surrounding cold fusion; and an application research project concerning a current science issue. (ZWH)
NASA Astrophysics Data System (ADS)
Gu, Zheng-Cheng; Wen, Xiao-Gang
2014-09-01
Symmetry-protected topological (SPT) phases are gapped short-range-entangled quantum phases with a symmetry G, which can all be smoothly connected to the trivial product states if we break the symmetry. It has been shown that a large class of interacting bosonic SPT phases can be systematically described by group cohomology theory. In this paper, we introduce a (special) group supercohomology theory which is a generalization of the standard group cohomology theory. We show that a large class of short-range interacting fermionic SPT phases can be described by the group supercohomology theory. Using the data of supercocycles, we can obtain the ideal ground state wave function for the corresponding fermionic SPT phase. We can also obtain the bulk Hamiltonian that realizes the SPT phase, as well as the anomalous (i.e., non-onsite) symmetry for the boundary effective Hamiltonian. The anomalous symmetry on the boundary implies that the symmetric boundary must be gapless for (1+1)-dimensional [(1+1)D] boundary, and must be gapless or topologically ordered beyond (1+1)D. As an application of this general result, we construct a new SPT phase in three dimensions, for interacting fermionic superconductors with coplanar spin order (which have T2=1 time-reversal Z2T and fermion-number-parity Z2f symmetries described by a full symmetry group Z2T×Z2f). Such a fermionic SPT state can neither be realized by free fermions nor by interacting bosons (formed by fermion pairs), and thus are not included in the K-theory classification for free fermions or group cohomology description for interacting bosons. We also construct three interacting fermionic SPT phases in two dimensions (2D) with a full symmetry group Z2×Z2f. Those 2D fermionic SPT phases all have central-charge c =1 gapless edge excitations, if the symmetry is not broken.
NASA Astrophysics Data System (ADS)
Moore, John W.
2002-12-01
These cases provide a good basis for discussions of scientific ethics, particularly with respect to the responsibilities of colleagues in collaborative projects. With increasing numbers of students working in cooperative or collaborative groups, there may be opportunities for more than just discussion—similar issues of responsibility apply to the members of such groups. Further, this is an area where, “no clear, widely accepted standards of behavior exist” (1). Thus there is an opportunity to point out to students that scientific ethics, like science itself, is incomplete and needs constant attention to issues that result from new paradigms such as collaborative research. Finally, each of us can resolve to pay more attention to the contributions we and our colleagues make to collaborative projects, applying to our own work no less critical an eye than we would cast on the work of those we don’t know at all.
(Strongly interacting fermion systems: Emphasis on heavy fermions: Annual performance report)
Not Available
1987-01-01
The research has been concentrated into two areas: heavy fermions and development of new methods for electronic properties (henceforth referred to as the ''electronic structure program''). This first area is going into deep hibernation due to the new interest in the high-T/sub c/ materials; notwithstanding this development, there has been significant progress. On the other hand, in the electronic structure program there has been a period of intense development which is just starting to yield results.
SU(8) Family Unification with Boson Fermion Balance
NASA Astrophysics Data System (ADS)
Adler, Stephen L.
2015-03-01
We formulate an SU(8) family unification model motivated by requiring that the theory should incorporate the graviton, gravitinos, and the fermions and gauge fields of the standard model, with boson.fermion balance. Gauge field SU(8) anomalies cancel between the gravitinos and spin 1/2 fermions. The 56 of scalars breaks SU(8) to SU(3)family×SU(5)×U(1)/Z5, with the fermion representation content needed for "flipped" SU(5) with three families, and with residual scalars in the 10 and overline {10} representations that break flipped SU(5) to the standard model. Dynamical symmetry breaking can account for the generation of 5 representation scalars needed to break the electroweak group. Yukawa couplings of the 56 scalars to the fermions are forbidden by chiral and gauge symmetries, so in the first stage of SU(8) breaking fermions remain massless. In the limit of vanishing gauge coupling, there are N = 1 and N = 8 supersymmetries relating the scalars to the fermions, which restrict the form of scalar self-couplings and should improve the convergence of perturbation theory, if not making the theory finite and "calculable." In an Appendix we give an analysis of symmetry breaking by a Higgs component, such as the (1, 1)(-15) of the SU(8) 56 under SU(8) ⊃ SU(3) × SU(5) × U(1), which has nonzero U(1) generator.
Polarization of massive fermions in a vortical fluid
NASA Astrophysics Data System (ADS)
Fang, Ren-hong; Pang, Long-gang; Wang, Qun; Wang, Xin-nian
2016-08-01
Fermions become polarized in a vortical fluid due to spin-vorticity coupling. Such a polarization can be calculated from the Wigner function in a quantum kinetic approach. By extending previous results for chiral fermions, we derive the Wigner function for massive fermions up to next-to-leading order in spatial gradient expansion. The polarization density of fermions can be calculated from the axial vector component of the Wigner function and is found to be proportional to the local vorticity ω . The polarizations per particle for fermions and antifermions decrease with the chemical potential and increase with energy (mass). Both quantities approach the asymptotic value ℏ ω /4 in the large energy (mass) limit. The polarization per particle for fermions is always smaller than that for antifermions, whose ratio of fermions to antifermions also decreases with the chemical potential. The polarization per particle on the Cooper-Frye freeze-out hypersurface can also be formulated and is consistent with the previous result of Becattini et al.
Dynamical fermion mass generation and exciton spectra in graphene
Zhang Chunxu; Liu Guozhu; Huang Mingqiu
2011-03-15
The Coulomb interaction between massless Dirac fermions may induce dynamical chiral symmetry breaking by forming excitonic pairs in clean graphene, leading to semimetal-insulator transition. If the Dirac fermions have zero bare mass, an exact continuous chiral symmetry is dynamically broken and thus there are massless Goldstone excitons. If the Dirac fermions have a small bare mass, an approximate continuous chiral symmetry is dynamically broken and the resultant Goldstone-type excitons become massive, which is analogous to what happens in QCD. In this paper, after solving the Dyson-Schwinger gap equation in the presence of a small bare fermion mass, we found a remarkable reduction of the critical Coulomb interaction strength for excitonic pair formation and a strong enhancement of dynamical fermion mass. We then calculate the masses of Goldstone-type excitons using the Shifman-Vainshtein-Zakharov sum-rule method and operator product expansion technique developed in QCD and find that the exciton masses are much larger than bare fermion mass but smaller than the width of dynamical fermion mass gap. We also study the spin susceptibilities and estimate the masses of non-Goldstone-type excitons using the same tools.
Excited Baryons from the FLIC Fermion Action
Melnitchouk, Wally; Hedditch, J N; Leinweber, D B; Williams, A G; Zanoti, J; Zhang, J B
2002-06-01
Masses of positive and negative parity excited nucleons and hyperons are calculated in quenched lattice QCD using an order (a{sup 2}) improved gluon action and a fat-link clover fermion action in which only the irrelevant operators are constructed with fat links. The results are in agreement with earlier N* simulations with improved actions, and exhibit a clear mass splitting between the nucleon and its parity partner, as well as a small mass splitting between the low-lying J{sup P}=1/2{sup -}N* states. Study of different Lambda interpolating fields suggests a similar splitting between the lowest two 1/2{sup -}Lambda* states, although the empirical mass suppression of the Lambda*(1405) is not seen.
Penguin diagrams for improved staggered fermions
Lee, Weonjong
2005-01-01
We calculate, at the one-loop level, penguin diagrams for improved staggered fermion operators constructed using various fat links. The main result is that diagonal mixing coefficients with penguin operators are identical between the unimproved operators and the improved operators using such fat links as Fat7, Fat7+Lepage, Fat7, HYP (I) and HYP (II). In addition, it turns out that the off-diagonal mixing vanishes for those constructed using fat links of Fat7, Fat7 and HYP (II). This is a consequence of the fact that the improvement by various fat links changes only the mixing with higher dimension operators and off-diagonal operators. The results of this paper, combined with those for current-current diagrams, provide complete matching at the one-loop level with all corrections of O(g{sup 2}) included.
Standard model fermions and K (E10)
NASA Astrophysics Data System (ADS)
Kleinschmidt, Axel; Nicolai, Hermann
2015-07-01
In recent work [1] it was shown how to rectify Gell-Mann's proposal for identifying the 48 quarks and leptons of the Standard Model with the 48 spin-1/2 fermions of maximal SO(8) gauged supergravity remaining after the removal of eight Goldstinos, by deforming the residual U(1) symmetry at the SU(3) × U(1) stationary point of N = 8 supergravity, so as to also achieve agreement of the electric charge assignments. In this Letter we show that the required deformation, while not in SU(8), does belong to K (E10), the 'maximal compact' subgroup of E10 which is a possible candidate symmetry underlying M theory. The incorporation of infinite-dimensional Kac-Moody symmetries of hyperbolic type, apparently unavoidable for the present scheme to work, opens up completely new perspectives on embedding Standard Model physics into a Planck scale theory of quantum gravity.
Majorana fermions in nanowires without gating superconductors
NASA Astrophysics Data System (ADS)
Lin, Chien-Hung; Hui, Hoi Yin; Sau, Jay; Das Sarma, Sankar
2011-03-01
Majorana fermions have been proposed to be realizable at the end of the semiconductor nanowire on top of an s-wave superconductor [1,2]. These proposals require gating the nanowire directly in contact with a superconductor which may be difficult in experiments. We analyze [1,2] in configurations where the wire is only gated away from the superconductor. We show that some signatures of the Majorana mode remain but the Majorana mode is not localized and hence not suitable for quantum computation. Therefore we propose an 1D periodic heterostructure which can support localized Majorana modes at the end of the wire without gating on the superconductor. This work is supported by DARPA-QuEST, JQI-NSF-PFC, and LPS-NSA.
Diagrammatic Monte Carlo for dual fermions
NASA Astrophysics Data System (ADS)
Iskakov, Sergei; Antipov, Andrey E.; Gull, Emanuel
2016-07-01
We introduce a numerical algorithm to stochastically sample the dual fermion perturbation series around the dynamical mean field theory, generating all topologies of two-particle interaction vertices. We show results in the weak and strong coupling regime of the half-filled Hubbard model in two dimensions, illustrating that the method converges quickly where dynamical mean field theory is a good approximation, and show that corrections are large in the strong correlation regime at intermediate interaction. The fast convergence of dual corrections to dynamical mean field results illustrates the power of the approach and opens a practical avenue towards the systematic inclusion of nonlocal correlations in correlated materials simulations. An analysis of the frequency scale shows that only low-frequency propagators contribute substantially to the diagrams, putting the inclusion of higher order vertices within reach.
Controlling interactions in ultracold fermionic ytterbium-173
NASA Astrophysics Data System (ADS)
Höfer, Moritz; Riegger, Luis; Hofrichter, Chrisitian; Rio Fernandes, Diogo; Bloch, Immanuel; Fölling, Simon
2016-05-01
The possibility to tune the interactions of ultracold atomic gases with an external magnetic field has become a vital tool for many quantum gas experiments. For fermionic ytterbium-173 both the 1 S0 ground state and 3 P0 metastable state have vanishing angular momentum J = 0 and therefore no magnetic Feshbach resonances are expected. Here we report on the discovery of a novel type of Feshbach resonance, which was predicted to exist due to orbital-mixing interactions. It occurs universally for all hyperfine-state combinations of ytterbium-173 and is located at experimentally accessible magnetic fields. The scattering properties are characterized by inter-orbital cross-thermalization measurements in the bulk as well as high resolution clock-line spectroscopy in a three-dimensional lattice. Furthermore, we study the dynamics of a strongly interacting two-orbital quantum gas in two dimensions.
Topological Thouless pumping of ultracold fermions
NASA Astrophysics Data System (ADS)
Nakajima, Shuta; Tomita, Takafumi; Taie, Shintaro; Ichinose, Tomohiro; Ozawa, Hideki; Wang, Lei; Troyer, Matthias; Takahashi, Yoshiro
2016-04-01
An electron gas in a one-dimensional periodic potential can be transported even in the absence of a voltage bias if the potential is slowly and periodically modulated in time. Remarkably, the transferred charge per cycle is sensitive only to the topology of the path in parameter space. Although this so-called Thouless charge pump was first proposed more than thirty years ago, it has not yet been realized. Here we report the demonstration of topological Thouless pumping using ultracold fermionic atoms in a dynamically controlled optical superlattice. We observe a shift of the atomic cloud as a result of pumping, and extract the topological invariance of the pumping process from this shift. We demonstrate the topological nature of the Thouless pump by varying the topology of the pumping path and verify that the topological pump indeed works in the quantum regime by varying the speed and temperature.
Fermionic path integrals and local anomalies
NASA Astrophysics Data System (ADS)
Roepstorff, G.
2003-05-01
No doubt, the subject of path integrals proved to be an immensely fruitful human, i.e. Feynman's idea. No wonder it is more timely than ever. Some even claim that it is the most daring, innovative and revolutionary idea since the days of Heisenberg and Bohr. It is thus likely to generate enthusiasm, if not addiction among physicists who seek simplicity together with perfection. Professor Devreese's long-lasting interest in, if not passion on the subject stems from his firm conviction that, beyond being the tool of choice, path integration provides the key to all quantum phenomena, be it in solid state, atomic, molecular or particle physics as evidenced by the impressive list of publications at the address http://lib.ua.ac.be/AB/a867.html. In this note, I review a pitfall of fermionic path integrals and a way to get around it in situations relevant to the Standard Model of particle physics.
Fermionic density functional at a Feshbach resonance
Seidl, Michael; Bhaduri, Rajat K.
2007-05-15
We consider a dilute gas of neutral unpolarized fermionic atoms at zero temperature. The atoms interact via a short-range (tunable) attractive interaction. We demonstrate analytically a curious property of the gas at unitarity. Namely, the correlation energy of the gas, evaluated by second-order perturbation theory, has the same density dependence as the first-order exchange energy, and the two almost exactly cancel each other at a Feshbach resonance irrespective of the shape of the potential, provided ({mu}r{sub s})>>1. Here ({mu}){sup -1} is the range of the two-body potential, and r{sub s} is defined through the number density, n=3/(4{pi}r{sub s}{sup 3}). The implications of this result for universality are discussed.
Phenomenology with Wilson fermions using smeared sources
Patel, Apoorva; Daniel, D.; Kilcup, Gregory; Gupta, Rajan; Sharpe, Stephen
1992-01-01
We investigate the use of two types of non-local ("smeared") sources for quark propagators in quenched lattice QCD at beta=6.0 using Wilson fermions at k=0.154 and 0.155. We present results for the hadron mass spectrum, meson decay constants, quark masses, the chiral condensate and the quark distribution amplitude of the pion. The use of smeared sources leads to a considerable improvement over previous results. We find a disturbing discrepancy between the baryon spectra obtained using Wuppertal and wall sources. We find good signals in the ratio of correlators used to calculate the quark mass and the chiral condensate and show that the extrapolation to the chiral limit is smooth.
Tomography of Majorana fermions with STM tips
NASA Astrophysics Data System (ADS)
Chevallier, Denis; Klinovaja, Jelena
2016-07-01
We investigate numerically the possibility to detect the spatial profile of Majorana fermions (MFs) by using STM tips that are made of either normal or superconducting material. In both cases, we are able to resolve the localization length and the oscillation period of the MF wave function. We show that the tunneling between the substrate and the tip, necessary to get the information on the wave-function oscillations, has to be weaker in the case of a superconducting probe. In the strong tunneling regime, the differential conductance saturates making it more difficult to observe the exponential decay of MFs. The temperature broadening of the profile is strongly suppressed in the case of the superconducting tip resulting, generally, in better resolution.
Neutron scattering studies of heavy Fermions
NASA Astrophysics Data System (ADS)
Shapiro, S. M.
1985-08-01
Heavy Fermions are f electron materials characterized by a large linear term in the low temperature specific heat and a large magnetic susceptibility at low temperatures. This implies that there is a narrow peak in the f electron density of states at the Fermi energy. Typical examples are CeAl3, UBe13, CeCu2Si2, CeCu6, U2Zn17 and UPt3. Neutron scattering measurements can play an important role in understanding the magnetic interactions in these systems. Measurements of the form reveal details about the nature of the wave functions. Inelastic scattering studies gives information about the energy scale of the spin fluctuations and the narrow f-resonance. Such measurements on the above systems are reviewed with the goal of establishing systematics between the information obtained in neutron studies and that from bulk measurements.
Charged fermions tunneling from regular black holes
Sharif, M. Javed, W.
2012-11-15
We study Hawking radiation of charged fermions as a tunneling process from charged regular black holes, i.e., the Bardeen and ABGB black holes. For this purpose, we apply the semiclassical WKB approximation to the general covariant Dirac equation for charged particles and evaluate the tunneling probabilities. We recover the Hawking temperature corresponding to these charged regular black holes. Further, we consider the back-reaction effects of the emitted spin particles from black holes and calculate their corresponding quantum corrections to the radiation spectrum. We find that this radiation spectrum is not purely thermal due to the energy and charge conservation but has some corrections. In the absence of charge, e = 0, our results are consistent with those already present in the literature.
Composite fermions and broken symmetries in graphene.
Amet, F; Bestwick, A J; Williams, J R; Balicas, L; Watanabe, K; Taniguchi, T; Goldhaber-Gordon, D
2015-01-01
The electronic properties of graphene are described by a Dirac Hamiltonian with a four-fold symmetry of spin and valley. This symmetry may yield novel fractional quantum Hall (FQH) states at high magnetic field depending on the relative strength of symmetry-breaking interactions. However, observing such states in transport remains challenging in graphene, as they are easily destroyed by disorder. In this work, we observe in the first two Landau levels the two-flux composite-fermion sequences of FQH states between each integer filling factor. In particular, the odd-numerator fractions appear between filling factors 1 and 2, suggesting a broken-valley symmetry, consistent with our observation of a gap at charge neutrality and zero field. Contrary to our expectations, the evolution of gaps in a parallel magnetic field suggests that states in the first Landau level are not spin-polarized even up to very large out-of-plane fields. PMID:25562690
Composite fermions and broken symmetries in graphene
NASA Astrophysics Data System (ADS)
Amet, F.; Bestwick, A. J.; Williams, J. R.; Balicas, L.; Watanabe, K.; Taniguchi, T.; Goldhaber-Gordon, D.
2015-01-01
The electronic properties of graphene are described by a Dirac Hamiltonian with a four-fold symmetry of spin and valley. This symmetry may yield novel fractional quantum Hall (FQH) states at high magnetic field depending on the relative strength of symmetry-breaking interactions. However, observing such states in transport remains challenging in graphene, as they are easily destroyed by disorder. In this work, we observe in the first two Landau levels the two-flux composite-fermion sequences of FQH states between each integer filling factor. In particular, the odd-numerator fractions appear between filling factors 1 and 2, suggesting a broken-valley symmetry, consistent with our observation of a gap at charge neutrality and zero field. Contrary to our expectations, the evolution of gaps in a parallel magnetic field suggests that states in the first Landau level are not spin-polarized even up to very large out-of-plane fields.
Reasonable fermionic quantum information theories require relativity
NASA Astrophysics Data System (ADS)
Friis, Nicolai
2016-03-01
We show that any quantum information theory based on anticommuting operators must be supplemented by a superselection rule deeply rooted in relativity to establish a reasonable notion of entanglement. While quantum information may be encoded in the fermionic Fock space, the unrestricted theory has a peculiar feature: the marginals of bipartite pure states need not have identical entropies, which leads to an ambiguous definition of entanglement. We solve this problem, by proving that it is removed by relativity, i.e., by the parity superselection rule that arises from Lorentz invariance via the spin-statistics connection. Our results hence unveil a fundamental conceptual inseparability of quantum information and the causal structure of relativistic field theory.
Mean-Field Evolution of Fermionic Systems
NASA Astrophysics Data System (ADS)
Benedikter, Niels; Porta, Marcello; Schlein, Benjamin
2014-11-01
The mean field limit for systems of many fermions is naturally coupled with a semiclassical limit. This makes the analysis of the mean field regime much more involved, compared with bosonic systems. In this paper, we study the dynamics of initial data close to a Slater determinant, whose reduced one-particle density is an orthogonal projection ω N with the appropriate semiclassical structure. Assuming some regularity of the interaction potential, we show that the evolution of such an initial data remains close to a Slater determinant, with reduced one-particle density given by the solution of the Hartree-Fock equation with initial data ω N . Our result holds for all (semiclassical) times, and gives effective bounds on the rate of the convergence towards the Hartree-Fock dynamics.
Cosmological baryon and lepton number in the presence of electroweak fermion-number violation
NASA Technical Reports Server (NTRS)
Harvey, Jeffrey A.; Turner, Michael S.
1990-01-01
In the presence of rapid fermion-number violation due to nonperturbative electroweak effects certain relations between the baryon number of the Universe and the lepton numbers of the Universe are predicted. In some cases the electron-neutrino asymmetry is exactly specified in terms of the baryon asymmetry. Without introducing new particles, beyond the usual quarks and leptons, it is necessary that the Universe possess a nonzero value of B - L prior to the epoch of fermion-number violation if baryon and lepton asymmetries are to survive. Contrary to intuition, even though electroweak processes violate B + L, a nonzero value of B + L persists after the epoch of rapid fermion-number violation. If the standard model is extended to include lepton-number violation, for example through Majorana neutrino masses, then electroweak processes will reduce the baryon number to zero even in the presence of an initial B - L unless 20 M(sub L) approximately greater than the square root of (T(sub B - L) m(sub P1)) where M(sub L) sets the scale of lepton number violation and T(sub B - L) is the temperature at which a B - L asymmetry is produced. In many models this implies that neutrinos must be so light that they cannot contribute appreciably to the mass density of the Universe.
Fermionic extensions of the Standard Model in light of the Higgs couplings
NASA Astrophysics Data System (ADS)
Bizot, Nicolas; Frigerio, Michele
2016-01-01
As the Higgs boson properties settle, the constraints on the Standard Model extensions tighten. We consider all possible new fermions that can couple to the Higgs, inspecting sets of up to four chiral multiplets. We confront them with direct collider searches, electroweak precision tests, and current knowledge of the Higgs couplings. The focus is on scenarios that may depart from the decoupling limit of very large masses and vanishing mixing, as they offer the best prospects for detection. We identify exotic chiral families that may receive a mass from the Higgs only, still in agreement with the hγγ signal strength. A mixing θ between the Standard Model and non-chiral fermions induces order θ 2 deviations in the Higgs couplings. The mixing can be as large as θ ˜ 0 .5 in case of custodial protection of the Z couplings or accidental cancellation in the oblique parameters. We also notice some intriguing effects for much smaller values of θ, especially in the lepton sector. Our survey includes a number of unconventional pairs of vector-like and Majorana fermions coupled through the Higgs, that may induce order one corrections to the Higgs radiative couplings. We single out the regions of parameters where hγγ and hgg are unaffected, while the hγZ signal strength is significantly modified, turning a few times larger than in the Standard Model in two cases. The second run of the LHC will effectively test most of these scenarios.
Induced fermionic current by a magnetic tube in the cosmic string spacetime
NASA Astrophysics Data System (ADS)
Maior de Sousa, M. S.; Ribeiro, R. F.; Bezerra de Mello, E. R.
2016-02-01
In this paper, we consider a charged massive fermionic quantum field in the spacetime of an idealized cosmic string, in the presence of a magnetic field confined in a cylindrical tube of finite radius. Three distinct configurations for the magnetic field are taken into account: (i) a cylindrical shell of radius a , (ii) a magnetic field proportional to 1 /r , and (iii) a constant magnetic field. In these three cases, the axis of the infinitely long tube of radius a coincides with the cosmic string. Our main objective is to analyze the induced vacuum fermionic current densities outside the tube. In order to do that, we explicitly construct the wave functions inside and outside the tube for each case. Having the complete set of normalized wave functions, we use the summation method to develop our analysis. We show that, in the region outside the tube, the induced currents are decomposed into parts corresponding to a zero-thickness magnetic flux in addition to core-induced contributions. The latter presents a specific form depending on the magnetic field configuration considered. We also see that the only nonvanishing component of fermionic current corresponds to the azimuthal one. The zero-thickness contribution depends only on the fractional part of the ration of the magnetic flux inside the tube by the quantum one. As to the core-induced contribution, it depends on the total magnetic flux inside the tube and, consequently, it is not, in general, a periodic function of the flux.
Fermions in a mixed vector-scalar double-step potential via continuous chiral transformation
NASA Astrophysics Data System (ADS)
Castilho, W. M.; de Castro, A. S.
2016-04-01
The behaviour of fermions in the background of a double-step potential is analyzed with a general mixing of scalar and vector couplings via continuous chiral-conjugation transformation. Provided the vector coupling does not exceed the scalar coupling, a Sturm-Liouville approach for the double-step potential shows that the transmission coefficient exhibits oscillations and that a finite set of intrinsically relativistic bound-state solutions might appear as poles of the transmission amplitude in a strong coupling regime. An isolated bound-state solution resulting from coupled first-order equations might also come into sight. It is also shown that all those possible bound solutions disappear asymptotically as one approaches the conditions for the realization of the so-called spin and pseudospin symmetries in a four-dimensional space-time. Furthermore, we show that due to the additional mass acquired by the fermion from the scalar background the high localization of the fermion in an extreme relativistic regime does not violate the Heisenberg uncertainty principle.
Neutrino masses via the Zee mechanism in the 5D split fermion model
Chang, We-Fu; Chen, I-Ting; Liou, Siao-Cing
2011-01-15
We study the original version of the Zee model, where both of the SU(2){sub L} Higgs doublets are allowed to couple to the leptons, in the framework of the split fermion model in M{sub 4}xS{sub 1}/Z{sub 2} space-time. The neutrino masses are generated through 1-loop diagrams without introducing the right-handed neutrinos. By assuming an order one anarchical complex 5D Yukawa couplings, all the effective 4D Yukawa couplings are determined by the wave function overlap between the split fermions and the bulk scalars in the fifth dimension. The predictability of the Yukawa couplings is in sharp contrast to the original Zee model in 4D where the Yukawa couplings are unknown free parameters. This setup exhibits a geometrical alternative to the lepton flavor symmetry. By giving four explicit sets of the split fermion locations, we demonstrate that it is possible to simultaneously fit the lepton masses and neutrino oscillation data by just a handful free parameters without much fine tuning. Moreover, we are able to make definite predictions for the mixing angle {theta}{sub 13}, the absolute neutrino masses, and the lepton flavor violation processes for each configuration.
Higher representations on the lattice: Numerical simulations, SU(2) with adjoint fermions
Del Debbio, Luigi; Patella, Agostino; Pica, Claudio
2010-05-01
We discuss the lattice formulation of gauge theories with fermions in arbitrary representations of the color group and present in detail the implementation of the hybrid Monte Carlo (HMC)/rational HMC algorithm for simulating dynamical fermions. We discuss the validation of the implementation through an extensive set of tests and the stability of simulations by monitoring the distribution of the lowest eigenvalue of the Wilson-Dirac operator. Working with two flavors of Wilson fermions in the adjoint representation, benchmark results for realistic lattice simulations are presented. Runs are performed on different lattice sizes ranging from 4{sup 3}x8 to 24{sup 3}x64 sites. For the two smallest lattices we also report the measured values of benchmark mesonic observables. These results can be used as a baseline for rapid cross-checks of simulations in higher representations. The results presented here are the first steps toward more extensive investigations with controlled systematic errors, aiming at a detailed understanding of the phase structure of these theories, and of their viability as candidates for strong dynamics beyond the standard model.
Feshbach resonance described by boson-fermion coupling
Domanski, T.
2003-07-01
We consider a possibility to describe the Feshbach resonance in terms of the boson-fermion (BF) model. Using such a model, we show that after a gradual disentangling of the boson from fermion subsystem, the resonant-type scattering between fermions is indeed generated. We decouple the subsystems via (a) the single step and (b) the continuous canonical transformation. With the second one, we investigate the feedback effects effectively leading to the finite amplitude of the scattering strength. We study them in detail in the normal T>T{sub c} and superconducting T{<=}T{sub c} states.
On the Modified Palatini Action Coupled to Fermionic Matter
Lagraa, Meriem Hadjer
2010-10-31
From the generalized Palatini's action proposed recently in [1], we show that we can obtain the standard effective action of the theory of Einstein-Cartan coupled to the fermionic matter without the usual current-current interaction. Therefore, an effective action which is free from the Barbero-Immirzi parameter [2] and the non-vanishing torsion resulting from the presence of the minimal coupling of fermionic matter. This establishes the equivalence between the theories of general relativity and Einstein-Cartan minimally coupled to fermions [3].
Two-dimensional thermofield bosonization II: Massive fermions
Amaral, R.L.P.G.
2008-11-15
We consider the perturbative computation of the N-point function of chiral densities of massive free fermions at finite temperature within the thermofield dynamics approach. The infinite series in the mass parameter for the N-point functions are computed in the fermionic formulation and compared with the corresponding perturbative series in the interaction parameter in the bosonized thermofield formulation. Thereby we establish in thermofield dynamics the formal equivalence of the massive free fermion theory with the sine-Gordon thermofield model for a particular value of the sine-Gordon parameter. We extend the thermofield bosonization to include the massive Thirring model.
Hidden Fermionic Excitation Boosting High-Temperature Superconductivity in Cuprates.
Sakai, Shiro; Civelli, Marcello; Imada, Masatoshi
2016-02-01
The dynamics of a microscopic cuprate model, namely, the two-dimensional Hubbard model, is studied with a cluster extension of the dynamical mean-field theory. We find a nontrivial structure of the frequency-dependent self-energies, which describes an unprecedented interplay between the pseudogap and superconductivity. We show that these properties are well described by quasiparticles hybridizing with (hidden) fermionic excitations, emergent from the strong electronic correlations. The hidden fermion enhances superconductivity via a mechanism distinct from a conventional boson-mediated pairing, and originates the normal-state pseudogap. Though the hidden fermion is elusive in experiments, it can solve many experimental puzzles. PMID:26894730
A possible connection between massive fermions and dark energy
Goldman, Terrance; Stephenson, G J; Alsing, P M; Mckellar, B H J
2009-01-01
In a dense cloud of massive fermions interacting by exchange of a light scalar field, the effective mass of the fermion can become negligibly small. As the cloud expands, the effective mass and the total energy density eventually increase with decreasing density. In this regime, the pressure-density relation can approximate that required for dark energy. They apply this phenomenon to the expansion of the Universe with a very light scalar field and infer relations between the parameters available and cosmological observations. Majorana neutrinos at a mass that may have been recently determined, and fermions such as the Lightest Supersymmetric Particle (LSP) may both be consistent with current observations of dark energy.
Collective Interference of Composite Two-Fermion Bosons
NASA Astrophysics Data System (ADS)
Tichy, Malte C.; Bouvrie, Peter Alexander; Mølmer, Klaus
2012-12-01
The composite character of two-fermion bosons manifests itself in the interference of many composites as a deviation from the ideal bosonic behavior. A state of many composite bosons can be represented as a superposition of different numbers of perfect bosons and fermions, which allows us to provide the full Hong-Ou-Mandel-like counting statistics of interfering composites. Our theory quantitatively relates the deviation from the ideal bosonic interference pattern to the entanglement of the fermions within a single composite boson.
Hidden Fermionic Excitation Boosting High-Temperature Superconductivity in Cuprates
NASA Astrophysics Data System (ADS)
Sakai, Shiro; Civelli, Marcello; Imada, Masatoshi
2016-02-01
The dynamics of a microscopic cuprate model, namely, the two-dimensional Hubbard model, is studied with a cluster extension of the dynamical mean-field theory. We find a nontrivial structure of the frequency-dependent self-energies, which describes an unprecedented interplay between the pseudogap and superconductivity. We show that these properties are well described by quasiparticles hybridizing with (hidden) fermionic excitations, emergent from the strong electronic correlations. The hidden fermion enhances superconductivity via a mechanism distinct from a conventional boson-mediated pairing, and originates the normal-state pseudogap. Though the hidden fermion is elusive in experiments, it can solve many experimental puzzles.
NASA Astrophysics Data System (ADS)
Brandt, Benedikt B.; Yannouleas, Consatntine; Landman, Uzi
We report on exact benchmark configuration-interaction computational solutions of the many-body Hamiltonian, uncovering the spectral evolution, wave function anatomy, and entanglement properties of a few interacting ultracold fermions in the entire parameter range, including crossover from an single-well to a double-well confinement and a controllable energy imbalance between the wells. According to recent experiments, the two wells are taken as quasi-one-dimensional and both the linear and parrallel configurations of them are considered. We demonstrate attractive pairing and formation of repulsive, highly correlated, ultracold Wigner molecules, associated with the emergence of Heisenberg spin chains. For two fermions, the entanglement measure of the von-Neumann entropy is used as a diagnostic tool for identifying maximally entangled two-qubit Bell states. Supported by the Air Force Office of Scientific Research.
Kawarabayashi, Tohru; Honda, Takahiro; Aoki, Hideo; Hatsugai, Yasuhiro
2013-12-04
The effect of disorder on the Landau levels of massless Dirac fermions is examined for the cases with and without the fermion doubling. To tune the doubling a tight-binding model having a complex transfer integral is adopted to shift the energies of two Dirac cones, which is theoretically proposed earlier and realizable in cold atoms in an optical lattice. In the absence of the fermion doubling, the n = 0 Landau level is shown to exhibit an anomalous sharpness even if the disorder is uncorrelated in space (i.e., large K-K' scattering). This anomaly occurs when the disorder respects the chiral symmetry of the Dirac cone.
Universal Subspaces for Local Unitary Groups of Fermionic Systems
NASA Astrophysics Data System (ADS)
Chen, Lin; Chen, Jianxin; Đoković, Dragomir Ž.; Zeng, Bei
2015-01-01
Let be the N-fermion Hilbert space with M-dimensional single particle space V and 2 N ≤ M. We refer to the unitary group G of V as the local unitary (LU) group. We fix an orthonormal (o.n.) basis | v 1⟩,...,| v M > of V. Then the Slater determinants with i 1 < ... < i N form an o.n. basis of . Let be the subspace spanned by all such that the set { i 1,..., i N } contains no pair {2 k-1,2 k}, k an integer. We say that the are single occupancy states (with respect to the basis | v 1⟩,...,| v M ⟩). We prove that for N = 3 the subspace is universal, i.e., each G-orbit in meets , and that this is false for N > 3. If M is even, the well known BCS states are not LU-equivalent to any single occupancy state. Our main result is that for N = 3 and M even there is a universal subspace spanned by M( M-1)( M-5)/6 states . Moreover, the number M( M-1)( M-5)/6 is minimal.
Skyrmion Superfluidity in Two-Dimensional Interacting Fermionic Systems
Palumbo, Giandomenico; Cirio, Mauro
2015-01-01
In this article we describe a multi-layered honeycomb lattice model of interacting fermions which supports a new kind of parity-preserving skyrmion superfluidity. We derive the low-energy field theory describing a non-BCS fermionic superfluid phase by means of functional fermionization. Such effective theory is a new kind of non-linear sigma model, which we call double skyrmion model. In the bi-layer case, the quasiparticles of the system (skyrmions) have bosonic statistics and replace the Cooper-pairs role. Moreover, we show that the model is also equivalent to a Maxwell-BF theory, which naturally establishes an effective Meissner effect without requiring a breaking of the gauge symmetry. Finally, we map effective superfluidity effects to identities among fermionic observables for the lattice model. This provides a signature of our theoretical skyrmion superfluidy that can be detected in a possible implementation of the lattice model in a real quantum system. PMID:26083978
Classical simulation of noninteracting-fermion quantum circuits
NASA Astrophysics Data System (ADS)
Terhal, Barbara M.; Divincenzo, David P.
2002-03-01
We show that a class of quantum computations that was recently shown to be efficiently simulatable on a classical computer by Valiant [in Proceedings of the 33rd ACM Symposium on the Theory of Computing (2001), p. 114] corresponds to a physical model of noninteracting fermions in one dimension. We give an alternative proof of his result using the language of fermions and extend the result to noninteracting fermions with arbitrary pairwise interactions, where gates can be conditioned on outcomes of complete von Neumann measurements in the computational basis on other fermionic modes in the circuit. This last result is in remarkable contrast with the case of noninteracting bosons where universal quantum computation can be achieved by allowing gates to be conditioned on classical bits [E. Knill, R. Laflamme, and G. Milburn, Nature (London) 409, 46 (2001)].
Non-relativistic metrics from back-reacting fermions
NASA Astrophysics Data System (ADS)
Hung, Ling-Yan; Jatkar, Dileep P.; Sinha, Aninda
2011-01-01
It has recently been pointed out that under certain circumstances the back-reaction of charged, massive Dirac fermions causes important modifications to AdS2 spacetimes arising as the near-horizon geometry of extremal black holes. In a WKB approximation, the modified geometry becomes a non-relativistic Lifshitz spacetime. In three dimensions, it is known that integrating out charged, massive fermions gives rise to gravitational and Maxwell Chern-Simons terms. We show that Schrödinger (warped AdS3) spacetimes exist as solutions to a gravitational and Maxwell Chern-Simons theory with a cosmological constant. Motivated by this, we look for warped AdS3 or Schrödinger metrics as exact solutions to a fully back-reacted theory containing Dirac fermions in three and four dimensions. We work out the dynamical exponent in terms of the fermion mass and generalize this result to arbitrary dimensions.
Fermionic Molecular Dynamics for Nuclear Dynamics and Thermodynamics
NASA Astrophysics Data System (ADS)
Hasnaoui, K. H. O.; Chomaz, Ph; Gulminelli, F.
A new Fermionic Molecular Dynamics (FMD) model based on a Skyrme functional is proposed in this paper. After introducing the basic formalism, some first applications to nuclear structure and nuclear thermodynamics are presented.
Theory of Green functions of free Dirac fermions in graphene
NASA Astrophysics Data System (ADS)
Hieu Nguyen, Van; Nguyen, Bich Ha; Dung Dinh, Ngoc
2016-03-01
This work is the beginning of our research on graphene quantum electrodynamics (GQED), based on the application of the methods of traditional quantum field theory to the study of the interacting system of quantized electromagnetic field and Dirac fermions in single-layer graphene. After a brief review of the known results concerning the lattice and electronic structures of single-layer graphene we perform the construction of the quantum fields of free Dirac fermions and the establishment of the corresponding Heisenberg quantum equations of these fields. We then elaborate the theory of Green functions of Dirac fermions in a free Dirac fermion gas at vanishing absolute temperature T = 0, the theory of Matsubara temperature Green functions and the Keldysh theory of non-equilibrium Green functions.
A note on the loop formula for the fermionic determinant
NASA Astrophysics Data System (ADS)
Seiler, Erhard; Stamatescu, Ion-Olimpiu
2016-08-01
A formula expressing the fermionic determinant as an infinite product of smaller determinants is derived and discussed. These smaller determinants are of a fixed size, independent of the size of the lattice and are indexed by loops of increasing length.
Asymptotic Safety of the CARTAN Induced Four-Fermion Interaction?
NASA Astrophysics Data System (ADS)
Mielke, Eckehard W.
2015-01-01
The difference between Einstein's general relativity and its Cartan extension is analyzed within the scenario of asymptotic safety. In particular, the four-fermion interaction is studied which distinguishes the Einstein-Cartan theory from its Riemannian limit.
High-order correlation of chaotic bosons and fermions
NASA Astrophysics Data System (ADS)
Liu, Hong-Chao
2016-08-01
We theoretically study the high-order correlation functions of chaotic bosons and fermions. Based on the different parity of the Stirling number, the products of the first-order correlation functions are well classified and employed to represent the high-order correlation function. The correlation of bosons conduces a bunching effect, which will be enhanced as order N increases. Different from bosons, the anticommutation relation of fermions leads to the parity of the Stirling number, which thereby results in a mixture of bunching and antibunching behaviors in high-order correlation. By further investigating third-order ghost diffraction and ghost imaging, the differences between the high-order correlations of bosons and fermions are discussed in detail. A larger N will dramatically improve the ghost image quality for bosons, but a good strategy should be carefully chosen for the fermionic ghost imaging process due to its complex correlation components.
Gravitational four-fermion interaction in the early Universe
NASA Astrophysics Data System (ADS)
Rudenko, A. S.; Khriplovich, I. B.
2014-02-01
If torsion exists, it generates gravitational four-fermion interaction (GFFI), essential on the Planck scale. We analyze the influence of this interaction on the Friedmann-Lemaitre-Robertson-Walker cosmology. An explicit analytic solution is derived for the problem where both the energy-momentum tensor generated by GFFI and the common ultrarelativistic energy-momentum tensor are included. We demonstrate that gravitational four-fermion interaction does not result in a Big Bounce.
Gravitational Four-Fermion Interaction in the Early Universe
NASA Astrophysics Data System (ADS)
Khriplovich, I.; Rudenko, A.
If torsion exists, it generates gravitational four-fermion interaction (GFFI), essential on the Planck scale. We analyze the influence of this interaction on the Friedmann-Lemaitre-Robertson-Walker cosmology. Explicit analytical solution is derived for the problem where both the energy-momentum tensor generated by GFFI and the common ultrarelativistic energy-momentum tensor are included. We demonstrate that gravitational four-fermion interaction does not result in Big Bounce.
Gravitational four-fermion interaction in the early Universe
NASA Astrophysics Data System (ADS)
Khriplovich, I. B.; Rudenko, A. S.
2014-07-01
If torsion exists, it generates gravitational four-fermion interaction (GFFI), essential on the Planck scale. We analyze the influence of this interaction on the Friedmann-Lemaitre-Robertson-Walker cosmology. Explicit analytical solution is derived for the problem where both the energy-momentum tensor generated by GFFI and the common ultrarelativistic energy-momentum tensor are included. We demonstrate that gravitational four-fermion interaction does not result in Big Bounce.
A gauge field theory of fermionic continuous-spin particles
NASA Astrophysics Data System (ADS)
Bekaert, X.; Najafizadeh, M.; Setare, M. R.
2016-09-01
In this letter, we suggest a local covariant action for a gauge field theory of fermionic Continuous-Spin Particles (CSPs). The action is invariant under gauge transformations without any constraint on both the gauge field and the gauge transformation parameter. The Fang-Fronsdal equations for a tower of massless fields with all half-integer spins arise as a particular limit of the equation of motion of fermionic CSPs.
Quantum Pumping with Ultracold Atoms on Microchips: Fermions versus Bosons
Das, Kunal K.; Aubin, Seth
2009-09-18
We present a design for simulating quantum pumping of electrons in a mesoscopic circuit with ultracold atoms in a micromagnetic chip trap. We calculate theoretical results for quantum pumping of both bosons and fermions, identifying differences and common features, including geometric behavior and resonance transmission. We analyze the feasibility of experiments with bosonic {sup 87}Rb and fermionic {sup 40}K atoms with an emphasis on reliable atomic current measurements.
Neutron scattering studies of the heavy Fermion superconductors
NASA Astrophysics Data System (ADS)
Goldman, A. I.
Recent neutron scattering measurements of the heavy Fermion superconductors are described. Those materials offer an exciting opportunity for neutron scattering since the f-electrons, which couple directly to magnetic scattering measurements, seem to be the same electrons which form the superconducting state below T sub c. In addition, studies of the magnetic fluctuations in these, and other heavy Fermion systems, by inelastic magnetic neutron scattering can provide information about the nature of the low temperature Fermi liquid character of these novel compounds.
Disorder operators in Chern-Simons-fermion theories
NASA Astrophysics Data System (ADS)
Rađičević, Ðorde
2016-03-01
Building on the recent progress in solving Chern-Simons-matter theories in the planar limit, we compute the scaling dimensions of a large class of disorder ("monopole") operators in U(N ) k Chern-Simons-fermion theories at all 't Hooft couplings. We find that the lowest-dimension operator of this sort has dimension 2/3{k}^{3/2} . We comment on the implications of these results to analyzing maps of fermionic disorder operators under 3D bosonization.
Reprint of : Floquet Majorana fermions in superconducting quantum dots
NASA Astrophysics Data System (ADS)
Benito, Mónica; Platero, Gloria
2016-08-01
We consider different configurations of ac driven quantum dots coupled to superconductor leads where Majorana fermions can exist as collective quasiparticles. The main goal is to tune the existence, localization and properties of these zero energy quasiparticles by means of periodically driven external gates. In particular, we analyze the relevance of the system and driving symmetry. We predict the existence of different sweet spots with Floquet Majorana fermions in configurations where they are not present in the undriven system.
Chiral fermions in noncommutative electrodynamics: Renormalizability and dispersion
Buric, Maja; Latas, Dusko; Radovanovic, Voja; Trampetic, Josip
2011-02-15
We analyze quantization of noncommutative chiral electrodynamics in the enveloping algebra formalism in linear order in noncommutativity parameter {theta}. Calculations show that divergences exist and cannot be removed by ordinary renormalization; however, they can be removed by the Seiberg-Witten redefinition of fields. Performing redefinitions explicitly, we obtain renormalizable Lagrangian and discuss the influence of noncommutativity on field propagation. Noncommutativity affects the propagation of chiral fermions only: half of the fermionic modes become massive and birefringent.
A note on the path integral representation for Majorana fermions
NASA Astrophysics Data System (ADS)
Greco, Andrés
2016-04-01
Majorana fermions are currently of huge interest in the context of nanoscience and condensed matter physics. Different to usual fermions, Majorana fermions have the property that the particle is its own anti-particle thus, they must be described by real fields. Mathematically, this property makes nontrivial the quantization of the problem due, for instance, to the absence of a Wick-like theorem. In view of the present interest on the subject, it is important to develop different theoretical approaches in order to study problems where Majorana fermions are involved. In this note we show that Majorana fermions can be studied in the context of field theories for constrained systems. Using the Faddeev-Jackiw formalism for quantum field theories with constraints, we derived the path integral representation for Majorana fermions. In order to show the validity of the path integral we apply it to an exactly solvable problem. This application also shows that it is rather simple to perform systematic calculations on the basis of the present framework.
Symmetry-protected topological phases in noninteracting fermion systems
NASA Astrophysics Data System (ADS)
Wen, Xiao-Gang
2012-02-01
Symmetry-protected topological (SPT) phases are gapped quantum phases with a certain symmetry, which can all be smoothly connected to the same trivial product state if we break the symmetry. For noninteracting fermion systems with time reversal (T̂), charge conjugation (Ĉ), and/or U(1) (N̂) symmetries, the total symmetry group can depend on the relations between those symmetry operations, such as T̂N̂T̂-1=N̂ or T̂N̂T̂-1=-N̂. As a result, the SPT phases of those fermion systems with different symmetry groups have different classifications. In this paper, we use Kitaev's K-theory approach to classify the gapped free-fermion phases for those possible symmetry groups. In particular, we can view the U(1) as a spin rotation. We find that superconductors with the Sz spin-rotation symmetry are classified by Z in even dimensions, while superconductors with the time reversal plus the Sz spin-rotation symmetries are classified by Z in odd dimensions. We show that all 10 classes of gapped free-fermion phases can be realized by electron systems with certain symmetries. We also point out that, to properly describe the symmetry of a fermionic system, we need to specify its full symmetry group that includes the fermion number parity transformation (-)N̂. The full symmetry group is actually a projective symmetry group.
Gauge covariant fermion propagator in quenched, chirally symmetric quantum electrodynamics
Roberts, C.D.; Dong, Z.; Munczek, H.J.
1995-08-01
The chirally symmetric solution of the massless, quenched, Dyson-Schwinger equation (DSE) for the fermion propagator in three- and four-dimensional quantum electrodynamics was obtained. The DSEs are a valuable nonperturbative tool for studying field theories. In recent years a good deal of progress was made in addressing the limitations of the DSE approach in the study of Abelian gauge theories. Key to this progress is an understanding of the role of the dressed fermion/gauge-boson vertex in ensuring gauge covariance and multiplicative renormalizability of the solution of the fermion DSE. The solutions we obtain are manifestly gauge covariant and a general gauge covariance constraint on the fermion/gauge-boson vertex is presented, which motivates a vertex Ansatz that, for the first time, both satisfies the Ward identity when the fermion self-mass is zero and ensures gauge covariance of the fermion propagator. This research facilitates gauge-invariant, nonperturbative studies of continuum quantum electrodynamics and has already been used by others in studies of the chiral phase transition.
ERIC Educational Resources Information Center
Eraut, Michael; And Others
A research project evaluated the contribution of biological, behavioral, and social sciences to nursing and midwifery education programs in Britain. The study of scientific knowledge relevant to recently qualified nurses and midwives was confined to six topics: fluids, electrolytes, and renal systems; nutrition; acute pain; shock; stress; and…
Hansson, Sven Ove; Aven, Terje
2014-07-01
This article discusses to what extent risk analysis is scientific in view of a set of commonly used definitions and criteria. We consider scientific knowledge to be characterized by its subject matter, its success in developing the best available knowledge in its fields of study, and the epistemic norms and values that guide scientific investigations. We proceed to assess the field of risk analysis according to these criteria. For this purpose, we use a model for risk analysis in which science is used as a base for decision making on risks, which covers the five elements evidence, knowledge base, broad risk evaluation, managerial review and judgment, and the decision; and that relates these elements to the domains experts and decisionmakers, and to the domains fact-based or value-based. We conclude that risk analysis is a scientific field of study, when understood as consisting primarily of (i) knowledge about risk-related phenomena, processes, events, etc., and (ii) concepts, theories, frameworks, approaches, principles, methods and models to understand, assess, characterize, communicate, and manage risk, in general and for specific applications (the instrumental part). PMID:24919396
A Phenomenological Theory of Metamagnetism in Ce-Based Heavy Fermion Compounds
NASA Astrophysics Data System (ADS)
Matsumoto, K.; Kosaka, S.; Murayama, S.
2016-04-01
A phenomenological theory is developed for the metamagnetism observed in heavy Fermion compounds by extension of the Landau theory for phase transitions. From simple analysis, the crossover behavior in high magnetic fields is indicated for the extended Landau-type free energy density. According to the finite temperature behavior of the extended Landau free energy density, theoretical magnetic phase diagrams that resemble those observed in CeRu2Si2 and Ce(Ru_{0.92}Rh_{0.08})2Si2 are obtained by using two sets of parameters, respectively.
Thermal leptogenesis in a 5D split fermion scenario with bulk neutrinos
NASA Astrophysics Data System (ADS)
Maalampi, Jukka; Vilja, Iiro; Virtanen, Heidi
2010-07-01
We study the thermal leptogenesis in a hybrid model, which combines the so-called split fermion model and the bulk neutrino model defined in five-dimensional spacetime. This model predicts the existence of a heavy neutrino pair nearly degenerate in mass, whose decays might generate a CP violation large enough for creating the baryon asymmetry of the Universe through leptogenesis. We investigate numerically the constraints this sets on the parameters of the model such as the size of the compactified fifth dimension.
Highly anisotropic Dirac fermions in square graphynes
NASA Astrophysics Data System (ADS)
Zhang, Lizhi; Wang, Zhengfei; Rao, Jiansheng; Li, Ziheng; Huang, Wulin; Wang, Zhiming; Du, Shixuan; Gao, Hongjun; Liu, Feng
Recently, there have been intense search of new 2D materials, and one especially appealing class of 2D materials is the all-carbon allotropes of Dirac materials. Here, we predict a new family of 2D carbon allotropes, square graphynes (S-graphynes) that exhibit highly anisotropic Dirac Fermions, using first-principle calculations within density functional theory. The equal-energy contour of their 3D band structure shows a crescent shape, and the Dirac crescent has varying Fermi velocities from 0.6 x 105 to 7.2 x 105 m/s along different k directions. Near the Fermi level, the Dirac crescent can be nicely expressed by an extended 2D Dirac model Hamiltonian. Furthermore, tight-binding band fitting reveals that the Dirac crescent originates from the next-nearest-neighbor interactions between C atoms. Our findings enrich the Dirac physics founded in other 2D Dirac systems, and offer a new design mechanism for creating Dirac band by tuning the interaction range. We envision that the highly anisotropic Dirac crescent may be exploited in all-carbon-based electronic devices for manipulating anisotropic electron propagation.
Highly anisotropic Dirac fermions in square graphynes
NASA Astrophysics Data System (ADS)
Zhang, Lizhi; Wang, Zhengfei; Rao, Jiansheng; Li, Ziheng; Huang, Wulin; Wang, Zhiming; Du, Shixuan; Gao, Hongjun; Liu, Feng
Recently, there have been intense search of new 2D materials, and one especially appealing class of 2D materials is the all-carbon allotropes of Dirac materials. Here, we predict a new family of 2D carbon allotropes, square graphynes (S-graphynes) that exhibit highly anisotropic Dirac Fermions, using first-principle calculations within density functional theory. The equal-energy contour of their 3D band structure shows a crescent shape, and the Dirac crescent has varying Fermi velocities from 0.6 ×105 to 7.2 ×105 m/s along different k directions. Near the Fermi level, the Dirac crescent can be nicely expressed by an extended 2D Dirac model Hamiltonian. Furthermore, tight-binding band fitting reveals that the Dirac crescent originates from the next-nearest-neighbor interactions between C atoms. Our findings enrich the Dirac physics founded in other 2D Dirac systems, and offer a new design mechanism for creating Dirac band by tuning the interaction range. We envision that the highly anisotropic Dirac crescent may be exploited in all-carbon-based electronic devices for manipulating anisotropic electron propagation.
Topological aspects of fermions on hyperdiamond
Saidi, E. H.; Fassi-Fehri, O.; Bousmina, M.
2012-07-15
Motivated by recent results on the index of the Dirac operator D={gamma}{sup {mu}}D{sub {mu}} of QCD on lattice and also by results on topological features of electrons and holes of two-dimensional graphene, we compute in this paper the index of D for fermions living on a family of even-dimensional lattices denoted as L{sub 2N} and describing the 2N-dimensional generalization of the graphene honeycomb. The calculation of this topological index is done by using the direct method based on solving explicitly the gauged Dirac equation and also by using specific properties of the lattices L{sub 2N}, which are shown to be intimately linked with the weight lattices of SU(2N+ 1). The index associated with the two leading N= 1 and N= 2 elements of this family describe precisely the chiral anomalies of graphene and QCD{sub 4}. Comments on the method using the spectral flow approach as well as the computation of the topological charges on 2-cycles of 2N-dimensional compact supercell in L{sub 2N} and applications to QCD{sub 4} are also given.
Composite fermions for fractionally filled Chern bands
NASA Astrophysics Data System (ADS)
Shankar, R.
2012-02-01
We consider fractionally filled bands with a non-zero Chern index that exhibit the Fractional Quantum Hall Effect in zero external fieldootnotetextR. Roy and S. Sondhi, Physics 4, 46 (2011) and papers reviewed therein. a possibility supported by numerical work.ootnotetextIbid. Analytic treatments are complicated by a non-constant Berry flux and the absence of Composite Fermions (CF), which would not only single out preferred fractions, but also allow us compute numerous response functions at nonzero frequencies, wavelengths and temperature using either Chern-Simons field theory or our Hamiltonian formalism.ootnotetextG. Murthy and R. Shankar, Rev. Mod. Phys., 75, 1101, (2003) We describe a way to introduce CF's by embedding the Chern band in an auxiliary problem involving Landau levels. The embedded band can be designed to approximate a prescribed Chern density in k space which determines the commutation relations of the charge densities and hence preserve all dynamical and algebraic aspects of the original problem. We find some states for which the filling fraction and dimensionless Hall conductance are not equal. The approach extends to two-dimensional time-reversal invariant topological insulators and to composite bosons.
Goldstone bosons and fermions in QCD
Zwanziger, Daniel
2010-06-15
We consider the version of QCD in Euclidean Landau gauge in which the restriction to the Gribov region is implemented by a local, renormalizable action. This action depends on the Gribov parameter {gamma}, with dimensions of (mass){sup 4}, whose value is fixed in terms of {Lambda}{sub QCD}, by the gap equation, known as the horizon condition, ({partial_derivative}{Gamma}/{partial_derivative}{gamma})=0, where {Gamma} is the quantum effective action. The restriction to the Gribov region suppresses gluons in the infrared, which nicely explains why gluons are not in the physical spectrum, but this only makes more mysterious the origin of the long-range force between quarks. In the present article we exhibit the symmetries of {Gamma}, and show that the solution to the gap equation, which defines the classical vacuum, spontaneously breaks some of the symmetries of {Gamma}. This implies the existence of massless Goldstone bosons and fermions that do not appear in the physical spectrum. Some of the Goldstone bosons may be exchanged between quarks, and are candidates for a long-range confining force. As an exact result we also find that in the infrared limit the gluon propagator vanishes like k{sup 2}.
Majorana fermions in condensed-matter physics
NASA Astrophysics Data System (ADS)
Leggett, A. J.
2016-06-01
It is an honor and a pleasure to have been invited to give a talk in this conference celebrating the memory of the late Professor Abdus Salam. To my regret, I did not know Professor Salam personally, but I am very aware of his work and of his impact on my area of specialization, condensed matter physics, both intellectually through his ideas on spontaneously broken symmetry and more practically through his foundation of the ICTP. Since I assume that most of this audience are not specialized in condensed-matter physics, I thought I would talk about one topic which to some extent bridges this field and the particle-physics interests of Salam, namely Majorana fermions (M.F.s). However, as we shall see, the parallels which are often drawn in the current literature may be a bit too simplistic. I will devote most of this talk to a stripped-down exposition of the current orthodoxy concerning M.F.s. in condensed-matter physics and their possible applications to topological quantum computing (TQC), and then at the end briefly indicate why I believe this orthodoxy may be seriously misleading.
Dirac Fermions in Nanoassembled Artificial Graphene
NASA Astrophysics Data System (ADS)
Gomes, Kenjiro K.; Ko, Wonhee; Mar, Warren; Manoharan, Hari C.
2011-03-01
In condensed matter, electronic properties derive from the energy band structure created by a periodic potential formed by the atoms that constitute a particular material. The power to design unique electronic states is ultimately tied to the power to design the atomic lattice. Utilizing the technique of atomic manipulation with a scanning tunneling microscope, we create an artificial lattice potential that reshapes the band structure of a normal 2D electron gas---found in the surface states of a normal metal---into a unique and distinct 2D gas of massless Dirac fermions. We present scanning tunneling spectroscopic measurements of nanoassembled honeycomb electron lattices, and we characterize their band structure through Fourier transform analysis of impurity scattering maps. The control of every atomic position in the lattice provides unprecedented control over physical parameters elusive in natural graphene systems. These abilities include atomically sharp doping configurations and the power to embed topological singularities, resulting in unique electronic states rarely encountered in natural systems. Supported by the DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under contract DE-AC02-76SF00515.
Topological aspects of fermions on hyperdiamond
NASA Astrophysics Data System (ADS)
Saidi, E. H.; Fassi-Fehri, O.; Bousmina, M.
2012-07-01
Motivated by recent results on the index of the Dirac operator D = γμDμ of QCD on lattice and also by results on topological features of electrons and holes of two-dimensional graphene, we compute in this paper the index of D for fermions living on a family of even-dimensional lattices denoted as {L}_{2N} and describing the 2N-dimensional generalization of the graphene honeycomb. The calculation of this topological index is done by using the direct method based on solving explicitly the gauged Dirac equation and also by using specific properties of the lattices {L} _{2N}, which are shown to be intimately linked with the weight lattices of SU(2N + 1). The index associated with the two leading N = 1 and N = 2 elements of this family describe precisely the chiral anomalies of graphene and QCD4. Comments on the method using the spectral flow approach as well as the computation of the topological charges on 2-cycles of 2N-dimensional compact supercell in {L}_{2N} and applications to QCD4 are also given.
Path Integral Monte Carlo Methods for Fermions
NASA Astrophysics Data System (ADS)
Ethan, Ethan; Dubois, Jonathan; Ceperley, David
2014-03-01
In general, Quantum Monte Carlo methods suffer from a sign problem when simulating fermionic systems. This causes the efficiency of a simulation to decrease exponentially with the number of particles and inverse temperature. To circumvent this issue, a nodal constraint is often implemented, restricting the Monte Carlo procedure from sampling paths that cause the many-body density matrix to change sign. Unfortunately, this high-dimensional nodal surface is not a priori known unless the system is exactly solvable, resulting in uncontrolled errors. We will discuss two possible routes to extend the applicability of finite-temperatue path integral Monte Carlo. First we extend the regime where signful simulations are possible through a novel permutation sampling scheme. Afterwards, we discuss a method to variationally improve the nodal surface by minimizing a free energy during simulation. Applications of these methods will include both free and interacting electron gases, concluding with discussion concerning extension to inhomogeneous systems. Support from DOE DE-FG52-09NA29456, DE-AC52-07NA27344, LLNL LDRD 10- ERD-058, and the Lawrence Scholar program.
NASA Technical Reports Server (NTRS)
1989-01-01
Tensegritoy, inspired by the tensegrity concepts of R. Buckminster Fuller, is an erector set like toy designed to give students an understanding of structural stability. It is used by children, architects, engineers, and teachers. The manufacturer, Tensegrity Systems Corporation, also offers a collapsible point of purchase display which incorporates technology developed for space station trusses described in "NASA Tech Briefs." The tech brief described deployable trusses that can be collapsed into small packages for space shuttle transport, then unfolded in space. As a result, the display occupies a minimum amount of floor space, freight cost savings are substantial and assembly can be completed quickly.
Transport properties of Dirac fermions in two dimensions
NASA Astrophysics Data System (ADS)
DaSilva, Ashley M.
The Dirac equation in particle physics is used to describe spin 1/2 fermions (such as electrons) moving at relativistic speeds. In condensed matter physics, this is usually not relevant, since particles in matter move slowly compared to the speed of light. However, recent progress has revealed two-dimensional realizations of Dirac fermions in condensed matter systems with zero mass and a redefined "speed of light." One of these systems, graphene, has been studied theoretically for decades as a building block of graphite. The other, the topological insulator, is quite new; this state of matter was predicted less than 10 years ago. Graphene was first isolated in 2004, and since then there has been an explosion of graphene research in the physics community. Much of the recent excitement has to do with the potential applications of graphene in devices. In this dissertation, I will discuss two problems related to graphene devices, and in particular how to use the strong interaction of graphene with its surroundings as an asset. I will show that a Boltzmann transport theory with all scattering mechanisms describes the current vs voltage of a graphene sheet extremely well using no adjustable parameters. One crucial element of this model is the transfer of energy from electrons directly to the substrate via scattering with optical phonons at the interface. The interaction is due to an electric field that is set up by these optical phonons, which is so strongly interacting in part due to the two dimensionality of the graphene. I will also discuss the adsorption of He atoms on a graphene sheet. This causes a change in the graphene conductivity which is large enough to be measurable. Work in this direction could provide a route to graphene sensors. The topological insulator is a recently predicted state of matter which is nominally an insulator but has metallic surface states which are topologically protected. This topological protection arises from the symmetry of the system
Study of Majorana fermionic dark matter
NASA Astrophysics Data System (ADS)
Chua, Chun-Khiang; Wong, Gwo-Guang
2016-08-01
We construct a generic model of Majorana fermionic dark matter (DM). Starting with two Weyl spinor multiplets η1 ,2˜(I ,∓Y ) coupled to the Standard Model Higgs, six additional Weyl spinor multiplets with (I ±1 /2 ,±(Y ±1 /2 )) are needed in general. It has 13 parameters in total, five mass parameters and eight Yukawa couplings. The DM sector of the minimal supersymmetric Standard Model is a special case of the model with (I ,Y )=(1 /2 ,1 /2 ). Therefore, this model can be viewed as an extension of the neutralino DM sector. We consider three typical cases: the neutralinolike, the reduced, and the extended cases. For each case, we survey the DM mass mχ in the range of (1,2500) GeV by random sampling from the model parameter space and study the constraints from the observed DM relic density; the direct search of LUX, XENON100, and PICO experiments; and the indirect search of Fermi-LAT data. We investigate the interplay of these constraints and the differences among these cases. It is found that the direct detection of spin-independent DM scattering off nuclei and the indirect detection of DM annihilation to the W+W- channel will be more sensitive to the DM searches in the near future. The allowed mass for finding H ˜-, B ˜-, W ˜-, and non-neutralino-like DM particles and the predictions on ⟨σ (χ χ →Z Z ,Z H ,t t ¯)v ⟩ in the indirect search are given.
NASA Astrophysics Data System (ADS)
Nori, Franco
2014-03-01
We study a heterostructure which consists of a topological insulator and a superconductor with a hole. This system supports a robust Majorana fermion state bound to the vortex core. We study the possibility of using scanning tunneling spectroscopy (i) to detect the Majorana fermion in this setup and (ii) to study excited states bound to the vortex core. The Majorana fermion manifests itself as an H-dependent zero-bias anomaly of the tunneling conductance. The excited states spectrum differs from the spectrum of a typical Abrikosov vortex, providing additional indirect confirmation of the Majorana state observation. We also study how to manipulate and probe Majorana fermions using super-conducting circuits. In we consider a semiconductor nanowire quantum dot with strong spin-orbit coupling (SOC), which can be used to achieve a spin-orbit qubit. In contrast to a spin qubit, the spin-orbit qubit can respond to an external ac electric field, i.e., electric-dipole spin resonance. We develop a theory that can apply in the strong SOC regime. We find that there is an optimal SOC strength ηopt = √ 2/2, where the Rabi frequency induced by the ac electric field becomes maximal. Also, we show that both the level spacing and the Rabi frequency of the spin-orbit qubit have periodic responses to the direction of the external static magnetic field. These responses can be used to determine the SOC in the nanowire. FN is partly supported by the RIKEN CEMS, iTHES Project, MURI Center for Dynamic Magneto-Optics, JSPS-RFBR Contract No. 12-02-92100, Grant-in-Aid for Scientific Research (S), MEXT Kakenhi on Quantum Cybernetics, and the JSPS via its FIRST program.
Holographic fermions in asymptotically scaling geometries with hyperscaling violation
NASA Astrophysics Data System (ADS)
Fan, ZhongYing
2013-07-01
We investigate holographic fermions in general asymptotically scaling geometries with hyperscaling violation exponent θ, which is a natural generalization of fermions in Lifshitz space-time. We prove that the retarded Green functions in this background satisfy the angle-resolved photoemission spectroscopy sum rules by introducing a dynamical source on a UV brane for zero density fermionic systems. The big difference from the Lifshitz case is that the mass of probe fermions decoupled from the UV theory and thus has no longer been restricted by the unitarity bound. We also study finite density fermions at finite temperature, with dynamical exponent z=2. We find that the dispersion relation is linear, but the logarithm of the spectral function is not linearly related to the logarithm of k⊥=k-kF, independent of charge q and θ. Furthermore, we show that, with the increasing of charge, new branches of Fermi surfaces emerge and tend to gather together to form a shell-like structure when the charge reaches some critical value beyond which a wide band pattern appears in the momentum-charge plane. However, all sharp peaks will be smoothed out when θ increases, no matter how much large the charge is.
Signatures of Majorana fermions in an elliptical quantum ring
NASA Astrophysics Data System (ADS)
Ghazaryan, Areg; Manaselyan, Aram; Chakraborty, Tapash
2016-06-01
We have investigated the signatures of zero-energy Majorana fermions in an anisotropic semiconductor quantum ring that contains a few electrons, has a strong spin-orbit interaction, and proximity coupled to an s -wave superconductor. We have found that for rings with sizes of few hundred angstroms and for certain range of values of the chemical potential and an applied magnetic field, the system is very likely in a topological phase with possible indications of the presence of Majorana fermions. In particular, the ground-state energies and the average electron numbers for the states with even and odd electron numbers are almost identical. We have analyzed the wave functions of Majorana fermions in the ring and have shown that Majorana fermions are well separated from each other in the angular coordinates. We have also determined the charge-density jumps due to the presence of the Majoranas, that are found to be uniformly distributed along the ring and can perhaps be detected by scanning charge measurements. While a definitive proof of the existence of these exotic particles in a ring has not been provided here, our study indicates the likelihood of the presence of these objects in our chosen system. As the semiconductor quantum rings with a few interacting electrons are available in the laboratories, we believe that the long sought-after Majorana fermions could perhaps be observed in such a system.
Fermion actions extracted from lattice super Yang-Mills theories
NASA Astrophysics Data System (ADS)
Misumi, Tatsuhiro
2013-12-01
We revisit 2D = (2, 2) super Yang-Mills lattice formulation (Sugino model) to investigate its fermion action with two (Majorana) fermion flavors and exact chiral-U(1) R symmetry. We show that the reconcilement of chiral symmetry and absence of further species-doubling originates in the 4D clifford algebra structure of the action, where 2D two flavors are spuriously treated as a single 4D four-spinor with four 4D gamma matrices introduced into kinetic and Wilson terms. This fermion construction based on the higher-dimensional clifford algebra is extended to four dimensions in two manners: (1) pseudo-8D sixteen-spinor treatment of 4D four flavors with eight 8D gamma matrices, (2) pseudo-6D eight-spinor treatment of 4D two flavors with five out of six 6D gamma matrices. We obtain 4D four-species and two-species lattice fermions with unbroken subgroup of chiral symmetry and other essential properties. We discuss their relations to staggered and Wilson twisted-mass fermions. We also discuss their potential feedback to 4D super Yang-Mills lattice formulations.
Effective fermion couplings in warped 5D Higgsless theories
NASA Astrophysics Data System (ADS)
Bechi, J.; Casalbuoni, R.; de Curtis, S.; Dominici, D.
2006-11-01
We consider a 5-dimensional SU(2) gauge theory with fermions in the bulk and with additional SU(2) and U(1) kinetic terms on the branes. The electroweak breaking is obtained by boundary conditions. After deconstruction, fermions in the bulk are eliminated by using their equations of motion. In this way, standard model fermion mass terms and direct couplings to the internal gauge bosons of the moose are generated. The presence of these new couplings gives a new contribution to the γ3 parameter in addition to the gauge boson term. This allows the possibility of a cancellation between the two contributions, which can be local (site by site) or global. Going back to the continuum, we show that the implementation of local cancellation in any generic warped metric leaves massless fermions. This is due to the presence of one horizon on the infrared brane. However, we can require a global cancellation of the new physics contributions to the γ3 parameter. This fixes relations among the warp factor and the parameters of the fermion and gauge sectors. It turns out that the warping of the metric does not substantially modify the results obtained in the flat case.
Effective fermion couplings in warped 5D Higgsless theories
Bechi, J.; Casalbuoni, R.; De Curtis, S.; Dominici, D.
2006-11-01
We consider a 5-dimensional SU(2) gauge theory with fermions in the bulk and with additional SU(2) and U(1) kinetic terms on the branes. The electroweak breaking is obtained by boundary conditions. After deconstruction, fermions in the bulk are eliminated by using their equations of motion. In this way, standard model fermion mass terms and direct couplings to the internal gauge bosons of the moose are generated. The presence of these new couplings gives a new contribution to the {epsilon}{sub 3} parameter in addition to the gauge boson term. This allows the possibility of a cancellation between the two contributions, which can be local (site by site) or global. Going back to the continuum, we show that the implementation of local cancellation in any generic warped metric leaves massless fermions. This is due to the presence of one horizon on the infrared brane. However, we can require a global cancellation of the new physics contributions to the {epsilon}{sub 3} parameter. This fixes relations among the warp factor and the parameters of the fermion and gauge sectors. It turns out that the warping of the metric does not substantially modify the results obtained in the flat case.
Consistent interactions for high-spin fermion fields
NASA Astrophysics Data System (ADS)
Vrancx, Tom; de Cruz, Lesley; Ryckebusch, Jan; Vancraeyveld, Pieter
2011-10-01
We address the issue of consistent interactions for off-shell fermion fields of arbitrary spin. These interactions play a crucial role in the quantum hadrodynamical description of high-spin baryon resonances in hadronic processes. The Rarita-Schwinger (R-S) description of high-spin fermion fields involves unphysical degrees of freedom associated with their lower-spin content. These enter the interaction if not eliminated outright. The invariance condition of the interaction under the unconstrained R-S gauge removes the lower-spin content of the fermion propagator and leads to a consistent description of the interaction. We develop the most general consistent interaction structure for high-spin fermions. We find that the power of the momentum dependence of a consistent interaction rises with the spin of the fermion field. This leads to unphysical structures in the energy dependence of the computed tree-level cross sections when the short-distance physics is cut off with standard hadronic form factors. A spin-dependent hadronic form factor is proposed that suppresses the unphysical artifacts.
Extra neutral scalars with vectorlike fermions at the LHC
NASA Astrophysics Data System (ADS)
Gopalakrishna, Shrihari; Mukherjee, Tuhin Subhra; Sadhukhan, Soumya
2016-03-01
Many theories beyond the standard model (BSM) contain new C P -odd and C P -even neutral scalars ϕ ={A ,H } , and new vectorlike fermions (ψV L). The couplings of the C P -odd scalar A to two standard model (SM) gauge bosons cannot occur from renormalizable operators in a C P -conserving sector, but can be induced at the quantum loop level. We compute these effective couplings at the 1-loop level induced by the SM fermions and vectorlike fermions, present analytical expressions for them, and plot them numerically. Using the 8 TeV Large Hadron Collider (LHC) γ γ , τ+τ- and t t ¯ channel data, we derive constraints on the effective couplings of the ϕ to standard model gauge bosons and fermions. We present the gluon-fusion channel cross sections of the ϕ at the 8 and 14 TeV LHC, and its branching ratios into SM fermion and gauge-boson pairs. We first present our results in a model independent manner, and then we provide results for some simple models containing ϕ and ψV L in the singlet and doublet representations of S U (2 ). In the doublet case, we focus on the two-Higgs-doublet (2HDM) Type-II and Type-X models in the alignment limit.
Heavy fermion nondecoupling effects in triple gauge boson vertices
NASA Astrophysics Data System (ADS)
Dedes, Athanasios; Suxho, Kristaq
2012-05-01
Within a spontaneously broken gauge group we carefully analyze and calculate triple gauge boson vertices dominated by triangle one-loop Feynman diagrams involving heavy fermions compared to external momenta and gauge boson masses. We perform our calculation strictly in four dimensions and derive a general formula for the off-shell, one-particle irreducible (1PI) effective vertex which satisfies the relevant Ward Identities and the Goldstone boson equivalence theorem. Our goal is to search for nondecoupling heavy fermion effects highlighting their synergy with gauge chiral anomalies. Particularly in the standard model, we find that when the arbitrary anomaly parameters are fixed by gauge invariance and/or Bose symmetry, the heavy fermion contribution cancels its anomaly contribution leaving behind anomaly and mass independent contributions from the light fermions. We apply these results in calculating the corresponding CP-invariant one-loop induced corrections to triple gauge boson vertices in the SM, minimal Z' models as well as their extensions with a fourth fermion generation, and compare with experimental data.
Study of neutral-current four-fermion and ZZ production in e+e- collisions at sqrt(s)= 183 GeV
NASA Astrophysics Data System (ADS)
L3 Collaboration; Acciarri, M.; Achard, P.; Adriani, O.; Aguilar-Benitez, M.; Alcaraz, J.; Alemanni, G.; Allaby, J.; Aloisio, A.; Alviggi, M. G.; Ambrosi, G.; Anderhub, H.; Andreev, V. P.; Angelescu, T.; Anselmo, F.; Arefiev, A.; Azemoon, T.; Aziz, T.; Bagnaia, P.; Baksay, L.; Balandras, A.; Ball, R. C.; Banerjee, S.; Banerjee, Sw.; Banicz, K.; Barczyk, A.; Barillère, R.; Barone, L.; Bartalini, P.; Basile, M.; Battiston, R.; Bay, A.; Becattini, F.; Becker, U.; Behner, F.; Berdugo, J.; Berges, P.; Bertucci, B.; Betev, B. L.; Bhattacharya, S.; Biasini, M.; Biland, A.; Blaising, J. J.; Blyth, S. C.; Bobbink, G. J.; Böhm, A.; Boldizsar, L.; Borgia, B.; Bourilkov, D.; Bourquin, M.; Braccini, S.; Branson, J. G.; Brigljevic, V.; Brochu, F.; Buffini, A.; Buijs, A.; Burger, J. D.; Burger, W. J.; Busenitz, J.; Button, A.; Cai, X. D.; Campanelli, M.; Capell, M.; Cara Romeo, G.; Carlino, G.; Cartacci, A. M.; Casaus, J.; Castellini, G.; Cavallari, F.; Cavallo, N.; Cecchi, C.; Cerrada, M.; Cesaroni, F.; Chamizo, M.; Chang, Y. H.; Chaturvedi, U. K.; Chemarin, M.; Chen, A.; Chen, G.; Chen, G. M.; Chen, H. F.; Chen, H. S.; Chereau, X.; Chiefari, G.; Cifarelli, L.; Cindolo, F.; Civinini, C.; Clare, I.; Clare, R.; Coignet, G.; Colijn, A. P.; Colino, N.; Conventi, F.; Costantini, S.; Cotorobai, F.; de La Cruz, B.; Csilling, A.; Dai, T. S.; van Dalen, J. A.; D'Alessandro, R.; de Asmundis, R.; Deglon, P.; Degré, A.; Deiters, K.; della Pietra, M.; della Volpe, D.; Denes, P.; Denotaristefani, F.; de Salvo, A.; Diemoz, M.; van Dierendonck, D.; di Lodovico, F.; Dionisi, C.; Dittmar, M.; Dominguez, A.; Doria, A.; Dova, M. T.; Duchesneau, D.; Dufournand, D.; Duinker, P.; Duran, I.; El Mamouni, H.; Engler, A.; Eppling, F. J.; Erné, F. C.; Extermann, P.; Fabre, M.; Faccini, R.; Falagan, M. A.; Falciano, S.; Favara, A.; Fay, J.; Fedin, O.; Felcini, M.; Ferguson, T.; Ferroni, F.; Fesefeldt, H.; Fiandrini, E.; Field, J. H.; Filthaut, F.; Fisher, P. H.; Fisk, I.; Forconi, G.; Fredj, L.; Freudenreich, K.; Furetta, C.; Galaktionov, Yu.; Ganguli, S. N.; Garcia-Abia, P.; Gataullin, M.; Gau, S. S.; Gentile, S.; Gheordanescu, N.; Giagu, S.; Goldfarb, S.; Gong, Z. F.; Gruenewald, M. W.; van Gulik, R.; Gupta, V. K.; Gurtu, A.; Gutay, L. J.; Haas, D.; Hasan, A.; Hatzifotiadou, D.; Hebbeker, T.; Hervé, A.; Hidas, P.; Hirschfelder, J.; Hofer, H.; Holzner, G.; Hoorani, H.; Hou, S. R.; Iashvili, I.; Jin, B. N.; Jones, L. W.; de Jong, P.; Josa-Mutuberría, I.; Khan, R. A.; Kamrad, D.; Kapustinsky, J. S.; Kaur, M.; Kienzle-Focacci, M. N.; Kim, D.; Kim, D. H.; Kim, J. K.; Kim, S. C.; Kinnison, W. W.; Kirkby, J.; Kiss, D.; Kittel, W.; Klimentov, A.; König, A. C.; Kopp, A.; Korolko, I.; Koutsenko, V.; Kraemer, R. W.; Krenz, W.; Kunin, A.; Lacentre, P.; Ladron de Guevara, P.; Laktineh, I.; Landi, G.; Lapoint, C.; Lassila-Perini, K.; Laurikainen, P.; Lavorato, A.; Lebeau, M.; Lebedev, A.; Lebrun, P.; Lecomte, P.; Lecoq, P.; Le Coultre, P.; Lee, H. J.; Le Goff, J. M.; Leiste, R.; Leonardi, E.; Levtchenko, P.; Li, C.; Lin, C. H.; Lin, W. T.; Linde, F. L.; Lista, L.; Liu, Z. A.; Lohmann, W.; Longo, E.; Lu, Y. S.; Lübelsmeyer, K.; Luci, C.; Luckey, D.; Luminari, L.; Lustermann, W.; Ma, W. G.; Maity, M.; Majumder, G.; Malgeri, L.; Malinin, A.; Maña, C.; Mangeol, D.; Marchesini, P.; Marian, G.; Martin, J. P.; Marzano, F.; Massaro, G. G. G.; Mazumdar, K.; McNeil, R. R.; Mele, S.; Merola, L.; Meschini, M.; Metzger, W. J.; von der Mey, M.; Migani, D.; Mihul, A.; Milcent, H.; Mirabelli, G.; Mnich, J.; Molnar, P.; Monteleoni, B.; Moulik, T.; Muanza, G. S.; Muheim, F.; Muijs, A. J. M.; Nahn, S.; Napolitano, M.; Nessi-Tedaldi, F.; Newman, H.; Niessen, T.; Nippe, A.; Nisati, A.; Nowak, H.; Oh, Y. D.; Organtini, G.; Ostonen, R.; Palomares, C.; Pandoulas, D.; Paoletti, S.; Paolucci, P.; Park, H. K.; Park, I. H.; Pascale, G.; Passaleva, G.; Patricelli, S.; Paul, T.; Pauluzzi, M.; Paus, C.; Pauss, F.; Peach, D.; Pedace, M.; Pei, Y. J.; Pensotti, S.; Perret-Gallix, D.; Petersen, B.; Petrak, S.; Piccolo, D.; Pieri, M.; Piroué, P. A.; Pistolesi, E.; Plyaskin, V.; Pohl, M.; Pojidaev, V.; Postema, H.; Pothier, J.; Produit, N.; Prokofiev, D.; Quartieri, J.; Rahal-Callot, G.; Raja, N.; Rancoita, P. G.; Raven, G.; Razis, P.; Ren, D.; Rescigno, M.; Reucroft, S.; van Rhee, T.; Riemann, S.; Riles, K.; Robohm, A.; Rodin, J.; Roe, B. P.; Romero, L.; Rosier-Lees, S.; Rubio, J. A.; Ruschmeier, D.; Rykaczewski, H.; Sakar, S.; Salicio, J.; Sanchez, E.; Sanders, M. P.; Sarakinos, M. E.; Schäfer, C.; Schegelsky, V.; Schmidt-Kaerst, S.; Schmitz, D.; Scholz, N.; Schopper, H.; Schotanus, D. J.; Schwenke, J.; Schwering, G.; Sciacca, C.; Sciarrino, D.; Servoli, L.; Shevchenko, S.; Shivarov, N.; Shoutko, V.; Shukla, J.; Shumilov, E.; Shvorob, A.; Siedenburg, T.; Son, D.; Smith, B.
1999-03-01
A study of neutral-current four-fermion processes is performed using a data sample corresponding to 55.3 pb-1 of integrated luminosity collected by the L3 detector at LEP at an average centre-of-mass energy of 183 GeV. The neutral-current four-fermion cross sections for final states with a pair of charged leptons plus jets and with four charged leptons are measured to be consistent with the Standard Model predictions. Events with fermion pair masses close to the Z boson mass are selected in all observable final states and the ZZ production cross section is measured to be σZZ=0.30+0.22 +0.07-0.16 -0.03 pb, in agreement with the Standard Model expectation. No evidence for the existence of anomalous triple gauge boson ZZZ and ZZγ couplings is found and limits on these couplings are set.
Fermion-induced quantum critical points: beyond Landau criterion
NASA Astrophysics Data System (ADS)
Yao, Hong; Li, Zi-Xiang; Jiang, Yi-Fan; Jian, Shao-Kai
According to Landau criterion, phase transitions must be first-order when cubic terms of order parameters in the Landau-Ginzburg free energy are allowed by symmetry. Here, from both renormalization group analysis and sign-problem-free quantum Monte Carlo simulations, we show that second-order quantum phase transitions can occur at such putatively-first-order quantum phase transitions in strongly-interacting Dirac semimetals in two spatial dimensions. Such type of Landau-criterion-violating quantum critical points are induced by massless fermionic modes at the quantum phase transitions. We call them ``fermion-induced quantum critical points''. From Majorana-quantum-Monte-Carlo simulations and renormalization analysis, we find that the critical exponentials at the kekule valence-bond-solid transition of the Dirac fermions on the honeycomb lattice are highly-nonclassical. We also discuss experimental signatures of the kekule quantum critical point which may be realized in graphene-like systems.
Quenched dynamics of superconducting Dirac fermions on honeycomb lattice
NASA Astrophysics Data System (ADS)
Lu, Ming; Xie, X. C.; X. C. Xie's group Team
We study the BCS paring dynamics for the superconducting Dirac fermions on honeycomb lattice after a sudden quench of pairing strength. We observe two distinct phases, one is the synchronized phase with undamped oscillations of paring amplitude; the other phase has the paring amplitude oscillates from positive to negative. The exact phase transition point is given by investigating the integrability of the system. Different from the previous work on normal superconducting fermions, which has three distinct phases, our results shows the absence of the Landau damped phase and over damped phase. Moreover, we present a linear analysis in the weakly quenched regime, showing that in a rather long time scale, the dynamics can be approximated as the periodic oscillation with 2Δ∞ angular frequency along with the logarithmic decay of the pairing amplitude, in contrast of the t - 1 / 2 decay for the normal fermions, namely the Landau damped phase. The presenter's advisor.
Millikelvin cooling by heavy-fermion-based tunnel junctions
NASA Astrophysics Data System (ADS)
Prest, Martin; Min, Gao; Whall, Terry
2015-12-01
This paper addresses a high-performance electron-tunneling cooler based on a novel heavy-fermion/insulator/superconductor junction for millikelvin cooling applications. We show that the cooling performance of an electronic tunneling refrigerator could be significantly improved using a heavy-fermion metal to replace the normal metal in a conventional normal metal/insulator/superconductor junction. The calculation, based on typical parameters, indicates that, for a bath temperature of 300 mK, the minimum cooling temperature of an electron tunneling refrigerator is reduced from around 170 mK to below 50 mK if a heavy-fermion metal is employed in place of the normal metal. The improved cooling is attributed to an enhancement in electron tunneling due to the existence of a resonant density of states at the Fermi level.
Experiments with Ultracold Quantum-degenerate Fermionic Lithium Atoms
NASA Technical Reports Server (NTRS)
Ketterle, Wolfgang
2003-01-01
Experimental methods of laser and evaporative cooling, used in the production of atomic Bose-Einstein condensates have recently been extended to realize quantum degeneracy in trapped Fermi gases. Fermi gases are a new rich system to explore the implications of Pauli exclusion on scattering properties of the system, and ultimately fermionic superfluidity. We have produced a new macroscopic quantum system, in which a degenerate Li-6 Fermi gas coexists with a large and stable Na-23 BEC. This was accomplished using inter-species sympathetic cooling of fermionic 6Li in a thermal bath of bosonic Na-23. We have achieved high numbers of both fermions (less than 10(exp 5) and bosons (less than 10(exp 6), and Li-6 quantum degeneracy corresponding to one half of the Fermi temperature. This is the first time that a Fermi sea was produced with a condensate as a "refrigerator".
Heterotic free fermionic and symmetric toroidal orbifold models
NASA Astrophysics Data System (ADS)
Athanasopoulos, P.; Faraggi, A. E.; Nibbelink, S. Groot; Mehta, V. M.
2016-04-01
Free fermionic models and symmetric heterotic toroidal orbifolds both constitute exact backgrounds that can be used effectively for phenomenological explorations within string theory. Even though it is widely believed that for Z_2× Z_2 orbifolds the two descriptions should be equivalent, a detailed dictionary between both formulations is still lacking. This paper aims to fill this gap: we give a detailed account of how the input data of both descriptions can be related to each other. In particular, we show that the generalized GSO phases of the free fermionic model correspond to generalized torsion phases used in orbifold model building. We illustrate our translation methods by providing free fermionic realizations for all Z_2× Z_2 orbifold geometries in six dimensions.
Birefringent breakup of Dirac fermions on a square optical lattice
Kennett, Malcolm P.; Komeilizadeh, Nazanin; Kaveh, Kamran; Smith, Peter M.
2011-05-15
We introduce a lattice model for fermions in a spatially periodic magnetic field that also has spatially periodic hopping amplitudes. We discuss how this model might be realized with cold atoms in an artificial magnetic field on a square optical lattice. When there is an average flux of half a flux quantum per plaquette, the spectrum of low-energy excitations can be described by massless Dirac fermions in which the usually doubly degenerate Dirac cones split into cones with different ''speeds of light.'' These gapless birefringent Dirac fermions arise because of broken chiral symmetry in the kinetic energy term of the effective low-energy Hamiltonian. We characterize the effects of various perturbations to the low-energy spectrum, including staggered potentials, interactions, and domain-wall topological defects.
Gauge invariance and anomalous theories at finite fermionic density
Roberge, A. )
1990-04-15
We investigate the issue of stability of anomalous matter at finite fermionic density using a two-dimensional toy model. In particular, we pay careful attention to the issue of gauge invariance. We find that, contrary to some recent claims, the effective free energy (obtained by integrating out the fermions) cannot be obtained by the simple inclusion of a Chern-Simons term multiplying the fermionic chemical potential. We obtain some conditions for stability of anomalous charges when some finite density of conserved charge is present as well as for the neutral case. We also show that, under reasonable conditions, no sphaleron-type solution can exist in the toy model unless the anomalous charge density vanishes. We argue that this could be the case for more realistic models as well.
Landau Levels of Majorana Fermions in a Spin Liquid.
Rachel, Stephan; Fritz, Lars; Vojta, Matthias
2016-04-22
Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels-highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles-for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudomagnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation. PMID:27152821
Millikelvin cooling by heavy-fermion-based tunnel junctions
Prest, Martin; Min, Gao; Whall, Terry
2015-12-28
This paper addresses a high-performance electron-tunneling cooler based on a novel heavy-fermion/insulator/superconductor junction for millikelvin cooling applications. We show that the cooling performance of an electronic tunneling refrigerator could be significantly improved using a heavy-fermion metal to replace the normal metal in a conventional normal metal/insulator/superconductor junction. The calculation, based on typical parameters, indicates that, for a bath temperature of 300 mK, the minimum cooling temperature of an electron tunneling refrigerator is reduced from around 170 mK to below 50 mK if a heavy-fermion metal is employed in place of the normal metal. The improved cooling is attributed to an enhancement in electron tunneling due to the existence of a resonant density of states at the Fermi level.
Yang-Mills Theory and Fermionic Path Integrals
NASA Astrophysics Data System (ADS)
Fujikawa, Kazuo
The Yang-Mills gauge field theory, which was proposed 60 years ago, is extremely successful in describing the basic interactions of fundamental particles. The Yang-Mills theory in the course of its developments also stimulated many important field theoretical machinery. In my talk I discuss the path integral techniques, in particular, the fermionic path integrals which were developed together with the successful applications of quantized Yang-Mills field theory. I start with the Faddeev-Popov path integral formula with emphasis on the treatment of fermionic ghosts as an application of Grassmann numbers. I then discuss the ordinary fermionic path integrals and the general treatment of quantum anomalies. The contents of this talk are mostly pedagogical except for a recent analysis of path integral bosonization.
Yang-Mills theory and fermionic path integrals
NASA Astrophysics Data System (ADS)
Fujikawa, Kazuo
2016-01-01
The Yang-Mills gauge field theory, which was proposed 60 years ago, is extremely successful in describing the basic interactions of fundamental particles. The Yang-Mills theory in the course of its developments also stimulated many important field theoretical machinery. In this brief review I discuss the path integral techniques, in particular, the fermionic path integrals which were developed together with the successful applications of quantized Yang-Mills field theory. I start with the Faddeev-Popov path integral formula with emphasis on the treatment of fermionic ghosts as an application of Grassmann numbers. I then discuss the ordinary fermionic path integrals and the general treatment of quantum anomalies. The contents of this review are mostly pedagogical except for a recent analysis of path integral bosonization.
Probing the fermionic Higgs portal at lepton colliders
NASA Astrophysics Data System (ADS)
Fedderke, Michael A.; Lin, Tongyan; Wang, Lian-Tao
2016-04-01
We study the sensitivity of future electron-positron colliders to UV completions of the fermionic Higgs portal operator {H}^{dagger }{H}_{overline{χ}χ } . Measurements of precision electroweak S and T parameters and the e + e - → Zh cross-section at the CEPC, FCC-ee, and ILC are considered. The scalar completion of the fermionic Higgs portal is closely related to the scalar Higgs portal, and we summarize existing results. We devote the bulk of our analysis to a singlet-doublet fermion completion. Assuming the doublet is sufficiently heavy, we construct the effective field theory (EFT) at dimension-6 in order to compute contributions to the observables. We also provide full one-loop results for S and T in the general mass parameter space. In both completions, future precision measurements can probe the new states at the (multi-)TeV scale, beyond the direct reach of the LHC.
Ferromagnetism and Borromean binding in three-fermion clusters.
Kornilovitch, Pavel
2014-02-21
A three-particle spin-12 fermion problem with on-site repulsion and nearest-neighbor attraction is solved on the two-dimensional square lattice by discretizing a Schrödinger equation in momentum space. Energies of bound complexes (trions) and their binding conditions are obtained. For total spin S=1/2, a wide region of trion instability toward decaying into a stable singlet pair plus a free fermion is identified. The instability is attributed to the formation of a wave function node upon addition of the third fermion. In the S=3/2 sector, trions are found to form in the absence of bound pairs indicating Borromean binding. In the strong coupling limit the system transitions from an S=1/2 ground state to a ferromagnetic S=3/2 ground state in agreement with the Nagaoka theorem for a four-site plaquette. PMID:24579630
Majorana Fermion Surface Code for Universal Quantum Computation
NASA Astrophysics Data System (ADS)
Vijay, Sagar; Hsieh, Tim; Fu, Liang
We introduce an exactly solvable model of interacting Majorana fermions realizing Z2 topological order with a Z2 fermion parity grading and lattice symmetries permuting the three fundamental anyon types. We propose a concrete physical realization by utilizing quantum phase slips in an array of Josephson-coupled mesoscopic topological superconductors, which can be implemented in a wide range of solid state systems, including topological insulators, nanowires or two-dimensional electron gases, proximitized by s-wave superconductors. Our model finds a natural application as a Majorana fermion surface code for universal quantum computation, with a single-step stabilizer measurement requiring no physical ancilla qubits, increased error tolerance, and simpler logical gates than a surface code with bosonic physical qubits. We thoroughly discuss protocols for stabilizer measurements, encoding and manipulating logical qubits, and gate implementations.
Majorana Fermion Surface Code for Universal Quantum Computation
NASA Astrophysics Data System (ADS)
Vijay, Sagar; Hsieh, Timothy H.; Fu, Liang
2015-10-01
We introduce an exactly solvable model of interacting Majorana fermions realizing Z2 topological order with a Z2 fermion parity grading and lattice symmetries permuting the three fundamental anyon types. We propose a concrete physical realization by utilizing quantum phase slips in an array of Josephson-coupled mesoscopic topological superconductors, which can be implemented in a wide range of solid-state systems, including topological insulators, nanowires, or two-dimensional electron gases, proximitized by s -wave superconductors. Our model finds a natural application as a Majorana fermion surface code for universal quantum computation, with a single-step stabilizer measurement requiring no physical ancilla qubits, increased error tolerance, and simpler logical gates than a surface code with bosonic physical qubits. We thoroughly discuss protocols for stabilizer measurements, encoding and manipulating logical qubits, and gate implementations.
Magnetoelectric effects in heavy-fermion superconductors without inversion symmetry
NASA Astrophysics Data System (ADS)
Fujimoto, Satoshi
2005-07-01
We investigate the effects of strong electron correlation on magnetoelectric transport phenomena in noncentrosymmetric superconductors with particular emphasis on its application to the recently discovered heavy-fermion superconductor CePt3Si . Taking into account electron correlation effects in a formally exact way, we obtain the expression of the magnetoelectric coefficient for the Zeeman-field-induced paramagnetic supercurrent, the existence of which was predicted more than a decade ago. It is found that in contrast to the usual Meissner current, which is much reduced by the mass renormalization factor in the heavy-fermion state, the paramagnetic supercurrent is not affected by the Fermi liquid effect. This result implies that the experimental observation of the magnetoelectric effect is more feasible in heavy-fermion systems than that in conventional metals with moderate effective mass.
Fermion Mass Renormalization Using Time-dependent Relativistic Quantum Mechanics
NASA Astrophysics Data System (ADS)
Kutnink, Timothy; Santrach, Amelia; Hocket, Sarah; Barcus, Scott; Petridis, Athanasios
2015-10-01
The time-dependent electromagnetically self-coupled Dirac equation is solved numerically by means of the staggered-leap-frog algorithm with refcecting boundary conditions. The stability region of the method versus the interaction strength and the spatial-grid size over time-step ratio is established. The expectation values of several dynamic operators are then evaluated as functions of time. These include the fermion and electromagnetic energies and the fermion dynamic mass, as the self-interacting spinors are no longer mass-eigenfunctions. There is a characteristic, non-exponential, oscillatory dependence leading to asymptotic constants of these expectation values. In the case of the fermion mass this amounts to renormalization. The dependence of the expectation values on the spatial-grid size is evaluated in detail. Statistical regularization is proposed to remove the grid-size dependence.
Mixing of fermions and spectral representation of propagator
NASA Astrophysics Data System (ADS)
Kaloshin, A. E.; Lomov, V. P.
2016-03-01
We develop the spectral representation of propagator for n mixing fermion fields in the case of P-parity violation. The approach based on the eigenvalue problem for inverse matrix propagator makes possible to build the system of orthogonal projectors and to represent the matrix propagator as a sum of poles with positive and negative energies. The procedure of multiplicative renormalization in terms of spectral representation is investigated and the renormalization matrices are obtained in a closed form without the use of perturbation theory. Since in theory with P-parity violation the standard spin projectors do not commute with the dressed propagator, they should be modified. The developed approach allows us to build the modified (dressed) spin projectors for a single fermion and for a system of fermions.
Gap solitons in superfluid boson-fermion mixtures
Adhikari, Sadhan K.; Malomed, Boris A.
2007-10-15
Using coupled equations for the bosonic and fermionic order parameters, we construct families of gap solitons (GSs) in a nearly one-dimensional Bose-Fermi mixture trapped in a periodic optical-lattice (OL) potential, the boson and fermion components being in the states of the Bose-Einstein condensation and Bardeen-Cooper-Schrieffer superfluid, respectively. Fundamental GSs are compact states trapped, essentially, in a single cell of the lattice. Full families of such solutions are constructed in the first two band gaps of the OL-induced spectrum, by means of variational and numerical methods, which are found to be in good agreement. The families include both intragap and intergap solitons, with the chemical potentials of the boson and fermion components falling in the same or different band gaps, respectively. Nonfundamental states, extended over several lattice cells, are constructed too. The GSs are stable against strong perturbations.
Boson representations of fermion systems: Proton-neutron systems
NASA Astrophysics Data System (ADS)
Sambataro, M.
1988-05-01
Applications of a procedure recently proposed to construct boson images of fermion Hamiltonians are shown for proton-neutron systems. First the mapping from SD fermion onto sd boson spaces is discussed and a Qπ.Qν interaction investigated. A Hermitian one-body Q boson operator is derived and analytical expressions for its coefficients are obtained. A (Qπ+Qν).(Qπ+Qν) interaction is, then, studied for particle-hole systems and the connections with the SU*(3) dynamical symmetry of the neutron-proton interacting boson model are discussed. Finally, an example of mapping from SDG onto sdg spaces is analyzed. Fermion spectra and E2 matrix elements are well reproduced in the boson spaces.
Anisotropic composite fermions and fractional quantum Hall effect
NASA Astrophysics Data System (ADS)
Mueed, M. A.; Kamburov, D.; Hasdemir, S.; Pfeiffer, L. N.; West, K. W.; Baldwin, K. W.; Shayegan, M.
2016-05-01
We study the role of anisotropy on the transport properties of composite fermions near Landau level filling factor ν =1 /2 in two-dimensional holes confined to a GaAs quantum well. By applying a parallel magnetic field, we tune the composite fermion Fermi sea anisotropy and monitor the relative change of the transport scattering time at ν =1 /2 along the principal directions. Interpreted in a simple Drude model, our results suggest that the scattering time is longer along the longitudinal direction of the composite fermion Fermi sea. Furthermore, the measured energy gap for the fractional quantum Hall state at ν =2 /3 decreases when anisotropy becomes significant. The decrease, however, might partly stem from the charge distribution becoming bilayerlike at very large parallel magnetic fields.
Landau levels of Majorana fermions in a spin liquid
NASA Astrophysics Data System (ADS)
Rachel, Stephan; Fritz, Lars; Vojta, Matthias
Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels - highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles - for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudo-magnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation.
Landau Levels of Majorana Fermions in a Spin Liquid
NASA Astrophysics Data System (ADS)
Rachel, Stephan; Fritz, Lars; Vojta, Matthias
2016-04-01
Majorana fermions, originally proposed as elementary particles acting as their own antiparticles, can be realized in condensed-matter systems as emergent quasiparticles, a situation often accompanied by topological order. Here we propose a physical system which realizes Landau levels—highly degenerate single-particle states usually resulting from an orbital magnetic field acting on charged particles—for Majorana fermions. This is achieved in a variant of a quantum spin system due to Kitaev which is distorted by triaxial strain. This strained Kitaev model displays a spin-liquid phase with charge-neutral Majorana-fermion excitations whose spectrum corresponds to that of Landau levels, here arising from a tailored pseudomagnetic field. We show that measuring the dynamic spin susceptibility reveals the Landau-level structure by a remarkable mechanism of probe-induced bound-state formation.
Detection of Majorana fermions by Fano resonance in hybrid nanostructures
NASA Astrophysics Data System (ADS)
Xia, Jun-Jie; Duan, Su-Qing; Zhang, Wei
2015-05-01
The realization and detection of Majorana fermions in condensed matter systems are of considerable importance and interest. We propose a scheme to detect the Majorana fermions by Fano resonance in hybrid nanostructures made of semiconductor quantum dots and quantum wire in proximity to superconductor. Through detailed theoretical studies of the transport properties of our hybrid nanostructures based on the non-equilibrium Green's function technique and the equation of motion approach, it is found that the Fano resonance in the current response due to the interference among different transmission paths may give clear signature of the existence of Majorana modes. Moreover, we have found a peculiar relationship between the Fano factor q and the Majorana bound state coupling strength/the length of nanowire, which can be used for a design of an electronic nanoruler. Our method of detection of Majorana fermions based on Fano resonance is related to the global conductance profile, thus is robust to perturbations.
Detection of Majorana fermions by Fano resonance in hybrid nanostructures.
Xia, Jun-Jie; Duan, Su-Qing; Zhang, Wei
2015-01-01
The realization and detection of Majorana fermions in condensed matter systems are of considerable importance and interest. We propose a scheme to detect the Majorana fermions by Fano resonance in hybrid nanostructures made of semiconductor quantum dots and quantum wire in proximity to superconductor. Through detailed theoretical studies of the transport properties of our hybrid nanostructures based on the non-equilibrium Green's function technique and the equation of motion approach, it is found that the Fano resonance in the current response due to the interference among different transmission paths may give clear signature of the existence of Majorana modes. Moreover, we have found a peculiar relationship between the Fano factor q and the Majorana bound state coupling strength/the length of nanowire, which can be used for a design of an electronic nanoruler. Our method of detection of Majorana fermions based on Fano resonance is related to the global conductance profile, thus is robust to perturbations. PMID:26034416
Two-Species Fermion Mixtures with Population Imbalance
Iskin, M.; Sa de Melo, C. A. R.
2006-09-08
We analyze the phase diagram of uniform superfluidity for two-species fermion mixtures from the Bardeen-Cooper-Schrieffer to Bose-Einstein condensation (BEC) limit as a function of the scattering parameter and population imbalance. We find at zero temperature that the phase diagram of population imbalance versus scattering parameter is asymmetric for unequal masses, having a larger stability region for uniform superfluidity when the lighter fermions are in excess. In addition, we find topological quantum phase transitions associated with the disappearance or appearance of momentum space regions of zero quasiparticle energies. Lastly, near the critical temperature, we derive the Ginzburg-Landau equation and show that it describes a dilute mixture of composite bosons and unpaired fermions in the BEC limit.
Phase Manipulation of Fermionic Cold Atoms in Mixed Dimensions
NASA Astrophysics Data System (ADS)
Irwin, Kyle Airell
Ultra-cold fermionic atoms trapped in optical lattices may be a candidate for the discovery of new novel phenomena in condensed matter systems. Experiments afford the creation of virtually any lattice geometry, and physical parameters of tight binding type lattice models can be accurately and easily tuned. Although some theoretical work has been conducted, few have used the power of the functional renormalization group method to unearth rigorous methods for determining collective many-body phases in this regime. Motivated by recent theoretical achievements, we investigate novel condensed matter systems involving interacting fermions which are engineered to be confined in different dimensions. In this sense, we seek low energy effective theories for low-dimensional fermionic lattice systems embedded into higher dimensional lattice systems, and show how tuning physical quantities, such as the filling or density, can have dramatic effects on the behavior of the lower dimensional system.
Strongly-correlated fermionic matter in the dilute limit
Mihaila, Bogdan; Cardenas, Andres L
2008-01-01
We study 'the ground-state properties of the many-body system composed of spin-l/2 fermions interacting via a zero-range, infinite scattering length contact interaction.' Sometimes referred to as the George Bertsch problem, it is of particular interest in astrophysics in connection with the equation of state for neutron matter and has been revisited recently with the advent of experimental studies of the BCS to BEC crossover in ultracold fermionic atom gases. We will show that new insights into the solution to this problem are obtained in the context of a coupled-cluster (exp S) expansion approach to calculating the equation of state for dilute fermionic systems and that present state-of-the-art Monte Carlo calculations have not yet provided the definitive answer.
Fermions and bosons on an atom chip
NASA Astrophysics Data System (ADS)
Extravour, Marcius H. T.
Ultra-cold dilute gases of neutral atoms are attractive candidates for creating controlled mesoscopic quantum systems. In particular, quantum degenerate gases of bosonic and fermionic atoms can be used to model the correlated many-body behaviour of Bose and Fermi condensed matter systems, and to study matter wave interference and coherence. This thesis describes the experimental realization and manipulation of Bose-Einstein condensates (BECs) of 87Rb and degenerate Fermi gases (DFGs) of 40K using static and dynamic magnetic atom chip traps. Atom chips are versatile modern tools used to manipulate atomic gases. The chips consist of micrometre-scale conductors supported by a planar insulating substrate, and can be used to create confining potentials for neutral atoms tens or hundreds of micrometres from the chip surface. We demonstrate for the first time that a DFG can be produced via sympathetic cooling with a BEC using a simple single-vacuum-chamber apparatus. The large 40 K-87Rb collision rate afforded by the strongly confining atom chip potential permits rapid cooling of 40K to quantum degeneracy via sympathetic cooling with 87Rb. By studying 40K-87Rb cross-thermalization as a function of temperature, we observe the Ramsauer-Townsend reduction in the 40K-87Rb elastic scattering cross-section. We achieve DFG temperatures as low as T ≈ 0:1TF, and observe Fermi pressure in the time-of-flight expansion of the gas. This thesis also describes the radio-frequency (RF) manipulation of trapped atoms to create dressed state double-well potentials for BEC and DFG. We demonstrate for the first time that RF-dressed potentials are species-selective, permitting the formation of simultaneous 87Rb double-well and 40K single-well potentials using a 40K-87Rb mixture. We also develop tools to measure fluctuations of the relative atom number and relative phase of a dynamically split 87Rb BEC. In particular, we observe atom number fluctuations at the shot-noise level using time
Charmonium Spectrum from Quenched QCD with Overlap Fermions
S. Tamhankar; A. Alexandru; Y. Chen; S.J. Dong; T. Draper; I. Horvath; F.X. Lee; K.F. Liu; N. Mathur; J.B. Zhang
2005-07-20
We present the first study of the charmonium spectrum using overlap fermions, on quenched configurations. Simulations are performed on 16{sup 3} x 72 lattices, with Wilson gauge action at {beta} = 6.3345. We demonstrate that we have discretization errors under control at about 5%. We obtain 88(4) MeV for hyperfine splitting using the {sub 0} scale, and 121(6) MeV using the (1{bar P}-1{bar S}) scale. This paper raises the possibility that the discrepancy between the lattice results and the experimental value for charmonium hyperfine splitting can be resolved using overlap fermions to simulate the charm quark on lattice.
Phase conjugation of a quantum-degenerate atomic fermion beam.
Search, Chris P; Meystre, Pierre
2003-09-01
We discuss the possibility of phase conjugation of an atomic Fermi field via nonlinear wave mixing in an ultracold gas. It is shown that for a beam of fermions incident on an atomic phase-conjugate mirror, a time-reversed backward propagating fermionic beam is generated similar to the case in nonlinear optics. By adopting an operational definition of the phase, we show that it is possible to infer the presence of the phase-conjugate field by the loss of the interference pattern in an atomic interferometer. PMID:14525466
Baryon Resonances from a Novel Fat-Link Fermion Action
W. Melnitchouk; S. Bilson-Thompson; F. D. R. Bonnet; P. D. Coddington; F. X. Lee; D. B. Leinweber; A. G. Williams; J. M. Zanotti; J. B. Zhang
2001-07-01
We present first results for masses of positive and negative parity excited baryons in lattice QCD using an O(a{sup 2}) improved gluon action and a Fat Link Irrelevant Clover (FLIC) fermion action in which only the irrelevant operators are constructed with fat links. The results are in agreement with earlier calculations of N* resonances using improved actions and exhibit a clear mass splitting between the nucleon and its chiral partner, even for the Wilson fermion action. The results also indicate a splitting between the lowest J{sup P}=1/2{sup -} states for the standard nucleon interpolating fields.
Scaling analysis of fat-link irrelevant clover fermion actions
Kamleh, Waseem; Lasscock, Ben; Leinweber, Derek B.; Williams, Anthony G.
2008-01-01
The fat-link irrelevant clover fermion action is a variant of the O(a)-improved Wilson action where the irrelevant operators are constructed using smeared links. While the use of such smearing allows for the use of highly improved definitions of the field strength tensor F{sub {mu}}{sub {nu}}, we show that the standard 1-loop clover term with a mean field improved coefficient c{sub sw} is sufficient to remove the O(a) errors, avoiding the need for nonperturbative tuning. This result enables efficient dynamical simulations in QCD with the fat-link irrelevant clover fermion action.
Microscopic Observation of Pauli Blocking in Degenerate Fermionic Lattice Gases.
Omran, Ahmed; Boll, Martin; Hilker, Timon A; Kleinlein, Katharina; Salomon, Guillaume; Bloch, Immanuel; Gross, Christian
2015-12-31
The Pauli exclusion principle is one of the most fundamental manifestations of quantum statistics. Here, we report on its local observation in a spin-polarized degenerate gas of fermions in an optical lattice. We probe the gas with single-site resolution using a new generation quantum gas microscope avoiding the common problem of light induced losses. In the band insulating regime, we measure a strong local suppression of particle number fluctuations and a low local entropy per atom. Our work opens a new avenue for studying quantum correlations in fermionic quantum matter both in and out of equilibrium. PMID:26764988
Decay of fermionic quasiparticles in one-dimensional quantum liquids.
Matveev, K A; Furusaki, A
2013-12-20
The low-energy properties of one-dimensional quantum liquids are commonly described in terms of the Tomonaga-Luttinger liquid theory, in which the elementary excitations are free bosons. To this approximation, the theory can be alternatively recast in terms of free fermions. In both approaches, small perturbations give rise to finite lifetimes of excitations. We evaluate the decay rate of fermionic excitations and show that it scales as the eighth power of energy, in contrast to the much faster decay of bosonic excitations. Our results can be tested experimentally by measuring the broadening of power-law features in the density structure factor or spectral functions. PMID:24483750
Magnetic domain walls of relic fermions as Dark Energy
Yajnik, Urjit A.
2005-12-02
We show that relic fermions of the Big Bang can enter a ferromagnetic state if they possess a magnetic moment and satisfy the requirements of Stoner theory of itinerant ferromagnetism. The domain walls of this ferromagnetism can successfully simulate Dark Energy over the observable epoch spanning {approx} 10 billion years. We obtain conditions on the anomalous magnetic moment of such fermions and their masses. Known neutrinos fail to satisfy the requirements thus pointing to the possibility of a new ultralight sector in Particle Physics.
Hadron Masses From Novel Fat-Link Fermion Actions
J. M. Zanotti; S. Bilson-Thompson; F. D. R. Bonnet; P. D. Coddington; D. B. Leinweber; A. G. Williams; J. B. Zhang; W. Melnitchouk; F. X. Lee
2001-11-01
The hadron mass spectrum is calculated in lattice QCD using a novel fat-link clover fermion action in which only the irrelevant operators in the fermion action are constructed using smeared links. The simulations are performed on a 16{sup 3} x 32 lattice with a lattice spacing of a=0.125 fm. We compare actions with n=4 and 12 smearing sweeps with a smearing fraction of 0.7. The n=4 Fat-Link Irrelevant Clover (FLIC) action provides scaling which is superior to mean-field improvement, and offers advantages over nonperturbative 0(a) improvement, including a reduced exceptional configuration problem.
Scattering of universal fermionic clusters in the resonating group method
NASA Astrophysics Data System (ADS)
Naidon, Pascal; Endo, Shimpei; García-García, Antonio M.
2016-02-01
Mixtures of polarized fermions of two different masses can form weakly bound clusters, such as dimers and trimers, that are universally described by the scattering length between the heavy and light fermions. We use the resonating group method to investigate the low-energy scattering processes involving dimers or trimers. The method reproduces approximately the known particle–dimer and dimer–dimer scattering lengths. We use it to estimate the trimer–trimer scattering length, which is presently unknown, and find it to be positive.
Microscopic Observation of Pauli Blocking in Degenerate Fermionic Lattice Gases
NASA Astrophysics Data System (ADS)
Omran, Ahmed; Boll, Martin; Hilker, Timon A.; Kleinlein, Katharina; Salomon, Guillaume; Bloch, Immanuel; Gross, Christian
2015-12-01
The Pauli exclusion principle is one of the most fundamental manifestations of quantum statistics. Here, we report on its local observation in a spin-polarized degenerate gas of fermions in an optical lattice. We probe the gas with single-site resolution using a new generation quantum gas microscope avoiding the common problem of light induced losses. In the band insulating regime, we measure a strong local suppression of particle number fluctuations and a low local entropy per atom. Our work opens a new avenue for studying quantum correlations in fermionic quantum matter both in and out of equilibrium.
Ultracold Fermions in a Cavity-Induced Artificial Magnetic Field.
Kollath, Corinna; Sheikhan, Ameneh; Wolff, Stefan; Brennecke, Ferdinand
2016-02-12
We propose how a fermionic quantum gas confined to an optical lattice and coupled to an optical cavity can self-organize into a state where the spontaneously emerging cavity field amplitude induces an artificial magnetic field. The fermions form either a chiral insulator or a chiral liquid carrying chiral currents. The feedback mechanism via the dynamical cavity field enables robust and fast switching in time of the chiral phases, and the cavity output can be employed for a direct nondestructive measurement of the chiral current. PMID:26918972
Digital quantum simulation of fermionic models with a superconducting circuit
NASA Astrophysics Data System (ADS)
Barends, R.; Lamata, L.; Kelly, J.; García-Álvarez, L.; Fowler, A. G.; Megrant, A.; Jeffrey, E.; White, T. C.; Sank, D.; Mutus, J. Y.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Hoi, I.-C.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Roushan, P.; Vainsencher, A.; Wenner, J.; Solano, E.; Martinis, John M.
2015-07-01
One of the key applications of quantum information is simulating nature. Fermions are ubiquitous in nature, appearing in condensed matter systems, chemistry and high energy physics. However, universally simulating their interactions is arguably one of the largest challenges, because of the difficulties arising from anticommutativity. Here we use digital methods to construct the required arbitrary interactions, and perform quantum simulation of up to four fermionic modes with a superconducting quantum circuit. We employ in excess of 300 quantum logic gates, and reach fidelities that are consistent with a simple model of uncorrelated errors. The presented approach is in principle scalable to a larger number of modes, and arbitrary spatial dimensions.
GUP Corrected Fermion Tunnelling from 2 + 1 Dimensional Black String
NASA Astrophysics Data System (ADS)
Tang, Jian; Feng, Zhongwen; Ren, Wei; Chen, Bingbing
2016-01-01
In this paper, using the generalized Dirac equation which is modified by GUP, we study the fermion tunneling from 2 + 1 dimensional black string. Our results show that the Hawking temperature is not only depended on the event horizon of black string but also related to the quantum number of emitted fermion (energy and mass). Meanwhile, we find the GUP can slow down the Hawking temperature increase and lead to the remnants. It implies that the GUP can avoid the evaporation of black holes.
Condensation of fermion zero modes in the vortex
NASA Astrophysics Data System (ADS)
Volovik, G. E.
2016-08-01
The energy levels of the fermions bound to the vortex are considered for vortices in the superfluid/superconducting systems which contain the symmetry protected plane of zeroes in the gap function in bulk. The Caroli-de Gennes-Matricon branches with different n approach zero energy level at p z → 0. The density of states of the bound fermions diverges at zero energy giving rise to the √ Ω dependence of DoS in the polar phase of superfluid 3He rotating with the angular velocity Ω and to the √ B dependence of DoS for superconductors in the (d xz + id yz )-wave pairing state.
Digital quantum simulation of fermionic models with a superconducting circuit.
Barends, R; Lamata, L; Kelly, J; García-Álvarez, L; Fowler, A G; Megrant, A; Jeffrey, E; White, T C; Sank, D; Mutus, J Y; Campbell, B; Chen, Yu; Chen, Z; Chiaro, B; Dunsworth, A; Hoi, I-C; Neill, C; O'Malley, P J J; Quintana, C; Roushan, P; Vainsencher, A; Wenner, J; Solano, E; Martinis, John M
2015-01-01
One of the key applications of quantum information is simulating nature. Fermions are ubiquitous in nature, appearing in condensed matter systems, chemistry and high energy physics. However, universally simulating their interactions is arguably one of the largest challenges, because of the difficulties arising from anticommutativity. Here we use digital methods to construct the required arbitrary interactions, and perform quantum simulation of up to four fermionic modes with a superconducting quantum circuit. We employ in excess of 300 quantum logic gates, and reach fidelities that are consistent with a simple model of uncorrelated errors. The presented approach is in principle scalable to a larger number of modes, and arbitrary spatial dimensions. PMID:26153660
Fermion Monte Carlo Calculations on Liquid-3He
Kalos, M H; Colletti, L; Pederiva, F
2004-03-16
Methods and results for calculations of the ground state energy of the bulk system of {sup 3}He atoms are discussed. Results are encouraging: they believe that they demonstrate that their methods offer a solution of the ''fermion sign problem'' and the possibility of direct computation of many-fermion systems with no uncontrolled approximations. Nevertheless, the method is still rather inefficient compared with variational or fixed-node approximate methods. There appears to be a significant populations size effect. The situation is improved by the inclusion of ''Second Stage Importance Sampling'' and of ''Acceptance/Rejection'' adapted to their needs.
Ward identities and chiral anomalies for coupled fermionic chains
NASA Astrophysics Data System (ADS)
Costa, L. C.; Ferraz, A.; Mastropietro, Vieri
2013-12-01
Coupled fermionic chains are usually described by an effective model written in terms of bonding and anti-bonding fermionic fields with linear dispersion in the vicinities of the respective Fermi points. We derive for the first time exact Ward Identities (WI) for this model, proving the existence of chiral anomalies which verify the Adler-Bardeen non-renormalization property. Such WI are expected to play a crucial role in the understanding of the thermodynamic properties of the system. Our results are non-perturbative and are obtained analyzing Grassmann functional integrals by means of constructive quantum field theory methods.
[ital I]=2 pion scattering amplitude with Wilson fermions
Gupta, R. ); Patel, A. ); Sharpe, S.R. )
1993-07-01
We present an exploratory calculation of the [ital I]=2 [pi][pi] scattering amplitude at threshold using Wilson fermions in the quenched approximation, including all the required contractions. We find good agreement with the predictions of chiral perturbation theory even for pions of mass 560--700 MeV. Within 10% error, we do not see the onset of the bad chiral behavior expected for Wilson fermions. We also derive rigorous inequalities that apply to two-particle correlators and as a consequence show that the interaction in the antisymmetric state of two pions has to be attractive.
Entanglement in algebraic quantum mechanics: Majorana fermion systems
NASA Astrophysics Data System (ADS)
Benatti, F.; Floreanini, R.
2016-07-01
Many-body entanglement is studied within the algebraic approach to quantum physics in systems made of Majorana fermions. In this framework, the notion of separability stems from partitions of the algebra of observables and properties of the associated correlation functions, rather than on particle tensor products. This allows a complete characterization of non-separable Majorana fermion states to be obtained. These results may have direct application in quantum metrology: using Majorana systems, sub-shot-noise accuracy in parameter estimations can be achieved without preliminary resource-consuming, state entanglement operations.
Residual entanglement of accelerated fermions is not nonlocal
Friis, Nicolai; Koehler, Philipp; Bertlmann, Reinhold A.; Martin-Martinez, Eduardo
2011-12-15
We analyze the operational meaning of the residual entanglement in noninertial fermionic systems in terms of the achievable violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality. We demonstrate that the quantum correlations of fermions, which were previously found to survive in the infinite acceleration limit, cannot be considered to be nonlocal. The entanglement shared by an inertial and an accelerated observer cannot be utilized for the violation of the CHSH inequality in case of high accelerations. Our results are shown to extend beyond the single-mode approximation commonly used in the literature.
2. QUANTUM HALL EFFECT: Magnetooptics of composite fermions
NASA Astrophysics Data System (ADS)
Kukushkin, I. V.; Smet, J. H.; von Klitzing, K.; Eberl, K.
2001-10-01
The Fermi energy and the Zeeman splitting of composite fermions are measured from the temperature dependence of the electron spin polarization at v = 1/2. We demonstrate that the Zeeman splitting of composite fermions is enhanced by a factor of 2.5 due to the interaction between CFs. The latter is very sensitive on the finite width of the 2D channel. The spin polarization at v = 1/3 and v = 2/3 displays an activated behavior and the derived spin-wave gaps are compared with simultaneously measured transport values.
Ultracold Fermions in a Cavity-Induced Artificial Magnetic Field
NASA Astrophysics Data System (ADS)
Kollath, Corinna; Sheikhan, Ameneh; Wolff, Stefan; Brennecke, Ferdinand
2016-02-01
We propose how a fermionic quantum gas confined to an optical lattice and coupled to an optical cavity can self-organize into a state where the spontaneously emerging cavity field amplitude induces an artificial magnetic field. The fermions form either a chiral insulator or a chiral liquid carrying chiral currents. The feedback mechanism via the dynamical cavity field enables robust and fast switching in time of the chiral phases, and the cavity output can be employed for a direct nondestructive measurement of the chiral current.
Dark matter massive fermions and Einasto profiles in galactic haloes
NASA Astrophysics Data System (ADS)
Siutsou, I.; Argüelles, C. R.; Ruffini, R.
2015-07-01
On the basis of a fermionic dark matter model we fit rotation curves of The HI Nearby Galaxy Survey (THINGS) sample and compare our 3-parametric model to other models widely used in the literature: 2-parametric Navarro-Frenk-White, pseudoisothermal sphere, Burkhert models, and 3-parametric Einasto model, suggested as the new "standard dark matter profile" model in the paper by Chemin et al., Astron. J. 142 (2011) 109. The results from the fitting procedure provides evidence for an underlying fermionic nature of the dark matter candidate, with rest mass above the keV regime.
Strongly-correlated fermionic matter in the dilute limit
Mihaila, Bogdan; Cardenas, Andres L
2008-01-01
We study the solution of the following problem: What are the ground-state properties of the many-body system composed of spin-l/2 fermions interacting via a zerorange, infinite scattering length contact interaction? Sometimes referred to as the 'George Bertsch problem', it is of particular interest in astrophysics in connection with the equation of state for neutron matter and has been revisited recently with the advent of experimental studies in ultracold fermionic atom gases of the crossover from the regime of Bardeen-Schriffer-Cooper (BCS) weakly-bound Cooper pairs to the regime of Bose-Einstein condensation (BEC) of diatomic molecules.
The Emergence of Fermions and the E11 Content
NASA Astrophysics Data System (ADS)
Englert, François; Houart, Laurent
Claudio's warm and endearing personality adds to our admiration for his achievements in physics a sense of friendliness. His constant interest in fundamental questions motivated the following presentation of our attempt to understand the nature of fermions. This problem is an essential element of the quantum world and might be related to the quest for quantum gravity. We shall review how space-time fermions can emerge out of bosons in string theory and how this fact affects the extended Kac-Moody approach to the M-theory project.
Fermion excitations of a tense brane black hole
Cho, H. T.; Cornell, A. S.; Doukas, Jason; Naylor, Wade
2008-02-15
By finding the spinor eigenvalues for a single deficit angle (d-2)-sphere, we derive the radial potential for fermions on a d-dimensional black hole background that is embedded on a codimension-two brane with conical singularity, where the deficit angle is related to the brane tension. From this we obtain the quasinormal mode spectrum for bulk fermions on such a background. As a by-product of our method, this also gives a rigorous proof for integer spin fields on the deficit 2-sphere.
QCD at nonzero density and canonical partition functions with Wilson fermions
Alexandru, Andrei; Wenger, Urs
2011-02-01
We present a reduction method for Wilson-Dirac fermions with nonzero chemical potential which generates a dimensionally reduced fermion matrix. The size of the reduced fermion matrix is independent of the temporal lattice extent and the dependence on the chemical potential is factored out. As a consequence the reduced matrix allows a simple evaluation of the Wilson fermion determinant for any value of the chemical potential and hence the exact projection to the canonical partition functions.
Guan, X. W.; Lee, J.-Y.; Batchelor, M. T.; Yin, X.-G.; Chen Shu
2010-08-15
A simple set of algebraic equations is derived for the exact low-temperature thermodynamics of one-dimensional multicomponent strongly attractive fermionic atoms with enlarged SU(N) spin symmetry and Zeeman splitting. Universal multicomponent Tomonaga-Luttinger liquid (TLL) phases are thus determined. For linear Zeeman splitting, the physics of the gapless phase at low temperatures belongs to the universality class of a two-component asymmetric TLL corresponding to spin-neutral N-atom composites and spin-(N-1)/2 single atoms. The equation of state which we obtained provides a precise description of multicomponent composite fermions and opens up the study of quantum criticality in one-dimensional systems of N-component Fermi gases with population imbalance.
NASA Astrophysics Data System (ADS)
Val'kov, V. V.; Val'kova, T. A.; Mitskan, V. A.
2015-09-01
In the framework of the t- J 1- J 2- V model, the integral equation determining the order parameter Δ( p) of the superconducting phase is derived for an ensemble of strongly correlated fermions on a triangular lattice using the diagram technique for the Hubbard operators. Taking into account the interaction between the Hubbard fermions within two coordination spheres, we demonstrate that the exact analytical solution Δ2( p) of this equation for the superconducting phase with the (( {{d_{{x^2} - {y^2}}} + i{d_{xy}}} )) symmetry can be expressed as a superposition of two chiral basis functions. This gives rise to a new set of nodal points for the complex parameter Δ2( p). Moreover, at some critical value x c of the charge carrier density, we obtain a gapless phase with six Dirac points. The passing of x through x = x c is accompanied by the topological quantum transition corresponding to the change in the topological parameter Q.
Composite fermions and the first-Landau-level fine structure of the fractional quantum Hall effect
NASA Astrophysics Data System (ADS)
Haxton, W. C.; Haxton, Daniel J.
2016-04-01
A set of scalar operators, originally introduced in connection with an analytic first-Landau-level (FLL) construction of fractional quantum Hall (FQHE) wave functions for the sphere, are employed in a somewhat different way to generate explicit representations of both hierarchy states (e.g., the series of fillings ν =1 /3 , 2/5, 3/7,⋯) and their conjugates (ν =1 , 2/3, 3/5,⋯) as noninteracting quasielectrons filling fine-structure subshells within the FLL. This yields, for planar and spherical geometries, a quasielectron representation of the incompressible FLL state of filling p /(2 p +1 ) in a magnetic field of strength B that is algebraically identical to the IQHE state of filling ν =p in a magnetic field of strength B /(2 p +1 ) . The construction provides a precise definition of the quasielectron/composite fermion that differs in some respects from common descriptions: they are eigenstates of L ,Lz ; they and the FLL subshells they occupy carry a third index I that is associated with breaking of scalar pairs; they absorb in their internal wave functions one, not two, units of magnetic flux; and they share a common, simple structure as vector products of a spinor creating an electron and one creating magnetic flux. We argue that these properties are a consequence of the breaking of the degeneracy of noninteracting electrons within the FLL by the scale-invariant Coulomb potential. We discuss the sense in which the wave function construction supports basic ideas of both composite fermion and hierarchical descriptions of the FQHE. We describe symmetries of the quasielectrons in the ν =1 /2 limit, where a deep Fermi sea of quasielectrons forms, and the quasielectrons take on Majorana and pseudo-Dirac characters. Finally, we show that the wave functions can be viewed as fermionic excitations of the bosonic half-filled shell, producing at ν =1 /2 an operator that differs from but plays the same role as the Pfaffian.
Study of {beta}-Decay in the Proton-Neutron Interacting Boson-Fermion Model
Zuffi, L.; Brant, S.; Yoshida, N.
2006-04-26
We study {beta}-decay in odd-A nuclei together with the energy levels and other properties in the proton-neutron interacting-boson-fermion model. We also report on the preliminary results in the odd-odd nuclei in the proton-neutron interacting boson-fermion-fermion model.
Perturbative quantum field theory in the framework of the fermionic projector
Finster, Felix
2014-04-15
We give a microscopic derivation of perturbative quantum field theory, taking causal fermion systems and the framework of the fermionic projector as the starting point. The resulting quantum field theory agrees with standard quantum field theory on the tree level and reproduces all bosonic loop diagrams. The fermion loops are described in a different formalism in which no ultraviolet divergences occur.
NASA Astrophysics Data System (ADS)
Fasshauer, Elke; Lode, Axel U. J.
2016-03-01
We report on an implementation of the multiconfigurational time-dependent Hartree method (MCTDH) for spin-polarized fermions (MCTDHF). Our approach is based on a mapping for operators in Fock space that allows a compact and efficient application of the Hamiltonian and solution of the MCTDHF equations of motion. Our implementation extends, builds on, and exploits the recursive implementation of MCTDH for bosons (r-mctdhb) package. Together with r-mctdhb, the present implementation of MCTDHF forms the mctdh-x package. We benchmark the accuracy of the algorithm with the harmonic interaction model and a time-dependent generalization thereof. These models consider parabolically trapped particles that interact through a harmonic interaction potential. We demonstrate that MCTDHF is capable of solving the time-dependent many-fermion Schrödinger equation to an arbitrary degree of precision and can hence yield numerically exact results even in the case of Hamiltonians with time-dependent one-body and two-body potentials. We study the problem of two initially parabolically confined and charged fermions tunneling through a barrier to open space. We demonstrate the validity of a model proposed previously for the many-body tunneling to open space of bosonic particles with contact interactions [Proc. Natl. Acad. Sci. USA 109, 13521 (2012), 10.1073/pnas.1201345109]. The many-fermion tunneling can be built up from sequentially happening single-fermion tunneling processes. The characteristic momenta of these processes are determined by the chemical potentials of trapped subsystems of smaller particle numbers: The escaped fermions convert the different chemical potentials into kinetic energy. Using the two-body correlation function, we present a detailed picture of the sequentiality of the process and are able to tell tunneling from over-the-barrier escape.
LANGUAGE TEACHING, A SCIENTIFIC APPROACH.
ERIC Educational Resources Information Center
LADO, ROBERT
DESIGNED TO UPDATE THE CONTEMPORARY LANGUAGE TEACHER'S KNOWLEDGE OF THE INNOVATIONS IN HIS FIELD, THIS BOOK INTRODUCES SOME OF THE ESSENTIAL MAJOR AREAS OF WHICH HE SHOULD HAVE AN UNDERSTANDING TO APPROACH HIS WORK SCIENTIFICALLY. PART ONE, DEALING IN GENERAL TERMS WITH LANGUAGE AND LANGUAGE LEARNING, SETS THE TONE OF THE BOOK WITH DISCUSSIONS OF…
Scientific Reasoning: No Child's Play
ERIC Educational Resources Information Center
Cavanagh, Sean
2009-01-01
The students, from the Academy of the Americas, a public school a few miles from downtown, are being asked to do the painstaking work of science, in an unlikely setting. It's part of a curriculum and professional-development program called BioKIDS, which seeks to build students' skill in complex scientific reasoning. The approach goes well beyond…
The Meaning of Scientific Literacy
ERIC Educational Resources Information Center
Holbrook, Jack; Rannikmae, Miia
2009-01-01
This paper sets out to provide an overview of scientific literacy specifically related to whether emphasis is placed on the "science" or the "literacy" aspect, accepting that literacy, wherever used, is wider than simply reading and writing. It does this from a general rather than a country perspective. The emphasis in giving meaning to scientific…
Scientific Word Processors Proliferate.
ERIC Educational Resources Information Center
Analytical Chemistry, 1985
1985-01-01
Briefly describes most of the currently available scientific word processing software packages. Unless noted, these products (including Molecular Presentation Graphics, ProofWriter, Spellbinder Scientific, Volkswriter Scientific, and WordMARC) run on the IBM PC family of microcomputers. (JN)
Anomalous effects in lattice QCD with staggered fermions
NASA Astrophysics Data System (ADS)
Kaehler, Adrian Leslie
1999-12-01
In this thesis we investigate the role of the anomaly in lattice QCD, paying particular attention to the role of topology, and the effects of suppressing the fermion determinant in numerical simulations. QCD with staggered fermions is studied just above the deconfining phase transition, where anomalous effects are expected to contribute a residual breaking of chiral symmetry, and where that residual breaking is expected to manifest itself as a source of unphysical divergences in the quenched approximation. These divergences are expected to arise from exact zero eigenvalues in the spectrum of the Dirac operator, which would be suppressed by the fermion determinant in an un-quenched simulation. The signal for this anomalous divergence is investigated first in a semi-classical environment in which smooth backgrounds allow us to better understand the manner in which these effects appear in the staggered fermion formulation. An older study on a 163 x 4 lattice is revisited and a new study is conducted on a 323 x 8 lattice. No signal is found in either study. An exploratory study on a 323 x 12 lattice is presented. In this case however, the spatial volume is insufficient to avoid tunneling into the confined phase, and other Z 3 phases in which there are known to be small eigenvalues resulting from chiral symmetry breaking, unrelated to the anomaly.
Phase transitions in fermionic systems with many-body interaction
NASA Technical Reports Server (NTRS)
Bozzolo, G.; Plastino, A.; Ferrante, J.
1989-01-01
A linearized version of the Hartree-Fock method is used as a probe to investigate phase transitions in fermionic systems with many-body interactions. An application to a new exactly solvable model which includes two- and three-body forces is shown.
Big Bounce and Inflation from Gravitational Four-Fermion Interaction
NASA Astrophysics Data System (ADS)
Khriplovich, I. B.
2013-11-01
The four-fermion gravitational interaction is induced by torsion. It gets dominating below the Planck scale. The regular, axial-axial part of this interaction by itself does not stop the gravitational compression. However, the anomalous, vector-vector interaction results in a natural way both in big bounce and in inflation.
Photoelectron spectroscopy in heavy fermions: Inconsistencies with the Kondo model
Arko, A.J.; Joyce, J.J.; Blyth, R.R.; Canfield, P.C.; Thompson, J.D.; Bartlett, R.J.; Fisk, Z.; Lawrence, J.; Tang, J.; Riseborough, P.
1992-09-01
We have investigated a number of Ce and Yb heavy fermion compounds via photoelectron spectroscopy and compared the results to the predictions of the Imurity Anderson Hamiltonian within the Gunnarson-Schonhammer approach. For the low T{sub K} materials investigated we find little or no correlation with T{sub K}, the only parameter that can be determined independent of photoemission.
Fermion mutilation on a body-centered tesseract
Celmaster, W.; Krausz, F.
1983-09-15
We construct a chiral Lagrangian on a body-centered four-dimensional hypercubic lattice. A form of fermion doubling is observed in the continuum limit. However, because some of the spurious excitations do not propagate as particles, the resulting continuum field theory is not Lorentz invariant.
Fermion mutilation on a body-centered tesseract
NASA Astrophysics Data System (ADS)
Celmaster, William; Krausz, Frank
1983-09-01
We construct a chiral Lagrangian on a body-centered four-dimensional hypercubic lattice. A form of fermion doubling is observed in the continuum limit. However, because some of the spurious excitations do not propagate as particles, the resulting continuum field theory is not Lorentz invariant.
The electronic structure of heavy fermions: Narrow temperature independent bands
Arko, A.J.; Joyce, J.J.; Smith, J.L.; Andrews, A.B.
1996-08-01
The electronic structure of both Ce and U heavy fermions appears to consist of extremely narrow temperature independent bands. There is no evidence from photoemission for a collective phenomenon normally referred to as the Kondo resonance. In uranium compounds a small dispersion of the bands is easily measurable.
Fermion Masses from Six Dimensions and Implications for Majorana Neutrinos
NASA Astrophysics Data System (ADS)
Frère, J.-M.; Libanov, M.; Mollet, S.; Troitsky, S.
2015-06-01
In these notes, we review the main results of our approach to fermion masses. The marge mass ratios between fermions, confronted with a unique breaking mechanism leading to vector bosons masses, led us to consider the possibility that they result from the overlap of fermion wave functions. Such overlaps vary indeed very strongly if the observed fermion families in 4 dimensions originate in a single family in 6 dimensions, through localized wave functions. This framework leads in a natural way to large mass ratios and small mixing angles between quarks. What came as a surprise is that if we impose that neutrinos behave as 2- component (“Majorana”) particles in 4D, a completely different situation is obtained for them. Instead of diagonal mass matrices, anti-diagonal ones emerge and lead to a generic prediction of combined inverted hierarchy, large mixing angles in the leptonicsector, and a suppression of neutrinoless-double beta decay placing it at the lower limit of the inverted hierarchy branch, a challenging situation for on-going and planned experiments. Our approach predicted the size of the θ13 mixing angle before its actual measurement. Possible signals at colliders are only briefly evoked.
Effective field theories for QCD with rooted staggered fermions
Bernard, Claude; Golterman, Maarten; Shamir, Yigal
2008-04-01
Even highly improved variants of lattice QCD with staggered fermions show significant violations of taste symmetry at currently accessible lattice spacings. In addition, the 'rooting trick' is used in order to simulate with the correct number of light sea quarks, and this makes the lattice theory nonlocal, even though there is good reason to believe that the continuum limit is in the correct universality class. In order to understand scaling violations, it is thus necessary to extend the construction of the Symanzik effective theory to include rooted staggered fermions. We show how this can be done, starting from a generalization of the renormalization-group approach to rooted staggered fermions recently developed by one of us. We then explain how the chiral effective theory follows from the Symanzik action, and show that it leads to 'rooted' staggered chiral perturbation theory as the correct chiral theory for QCD with rooted staggered fermions. We thus establish a direct link between the renormalization-group based arguments for the correctness of the continuum limit and the success of rooted staggered chiral perturbation theory in fitting numerical results obtained with the rooting trick. In order to develop our argument, we need to assume the existence of a standard partially-quenched chiral effective theory for any local partially-quenched theory. Other technical, but standard, assumptions are also required.
Heavy-fermion quantum criticality and destruction of the Kondo effect in a nickel oxypnictide
NASA Astrophysics Data System (ADS)
Luo, Yongkang; Pourovskii, Leonid; Rowley, S. E.; Li, Yuke; Feng, Chunmu; Georges, Antoine; Dai, Jianhui; Cao, Guanghan; Xu, Zhu'An; Si, Qimiao; Ong, N. P.
2014-08-01
A quantum critical point arises at a continuous transformation between distinct phases of matter at zero temperature. Studies in antiferromagnetic heavy-fermion materials have revealed that quantum criticality has several classes, with an unconventional type that involves a critical destruction of the Kondo entanglement. To understand such varieties, it is important to extend the materials basis beyond the usual setting of intermetallic compounds. Here we show that a nickel oxypnictide, CeNiAsO, exhibits a heavy-fermion antiferromagnetic quantum critical point as a function of either pressure or P/As substitution. At the quantum critical point, non-Fermi-liquid behaviour appears, which is accompanied by a divergent effective carrier mass. Across the quantum critical point, the low-temperature Hall coefficient undergoes a rapid sign change, suggesting a sudden jump of the Fermi surface and a destruction of the Kondo effect. Our results imply that the enormous materials basis for the oxypnictides, which has been so crucial in the search for high-temperature superconductivity, will also play a vital role in the effort to establish the universality classes of quantum criticality in strongly correlated electron systems.
Driven-dissipative many-body pairing states for cold fermionic atoms in an optical lattice
NASA Astrophysics Data System (ADS)
Yi, W.; Diehl, S.; Daley, A. J.; Zoller, P.
2012-05-01
We discuss the preparation of many-body states of cold fermionic atoms in an optical lattice via controlled dissipative processes induced by coupling the system to a reservoir. Based on a mechanism combining Pauli blocking and phase locking between adjacent sites, we construct complete sets of jump operators describing coupling to a reservoir that leads to dissipative preparation of pairing states for fermions with various symmetries in the absence of direct inter-particle interactions. We discuss the uniqueness of these states, and demonstrate it with small-scale numerical simulations. In the late-time dissipative dynamics, we identify a ‘dissipative gap’ that persists in the thermodynamic limit. This gap implies exponential convergence of all many-body observables to their steady-state values. We then investigate how these pairing states can be used as a starting point for the preparation of the ground state of the Fermi-Hubbard Hamiltonian via an adiabatic state preparation process also involving the parent Hamiltonian of the pairing state. We also provide a proof-of-principle example for implementing these dissipative processes and the parent Hamiltonians of the pairing states, based on 171Yb atoms in optical lattice potentials.
Review of the fermionic dark matter model applied to galactic structures
Krut, A.; Argüelles, C. R.; Rueda, J.; Ruffini, R.
2015-12-17
Baryonic components (e.g. bulge and disk) of galactic structures are assumed to be embedded in an isothermal dark matter halo of fermionic nature. Besides the Pauli principle only gravitational interaction is considered. Using the underlying Fermi-Dirac phase space distribution, typical of collisionless relaxation processes, it yields an one-parameter family of scaled solutions which reproduces the observed flat rotation curves in galaxies, and additionally predicts a degenerate core through their centers. In order to provide the right DM halo properties of galaxies a set of four parameters (particle mass, degeneracy parameter at the galactic center, central density and the velocity dispersion) is necessary. The more general density profile shows three regimes depending on radius: an almost uniform very dense quantum core followed by a steep fall, a plateau in the diluted regime and a Boltzmannian tail representing the halo. In contrast to purely Boltzmannian configurations the fermionic DM model containing a quantum core allows to determine the particle mass. We show that the quantum core can be well approximated by a polytrope of index n = 3/2, while the halo can be perfectly described by an isothermal sphere with a halo scale length radius equal to approximately 3/4 of the King-radius.
Embedding qubits into fermionic Fock space: Peculiarities of the four-qubit case
NASA Astrophysics Data System (ADS)
Lévay, Péter; Holweck, Frédéric
2015-06-01
We give a fermionic Fock space description of embedded entangled qubits. Within this framework the problem of classification of pure state entanglement boils down to the problem of classifying spinors. The usual notion of separable states turns out to be just a special case of the one of pure spinors. By using the notion of single, double and mixed occupancy representation with intertwiners relating them a natural physical interpretation of embedded qubits is found. As an application of these ideas one can make a physical sound meaning of some of the direct sum structures showing up in the context of the so-called black-hole/qubit correspondence. We discuss how the usual invariants for qubits serving as measures of entanglement can be obtained from invariants for spinors in an elegant manner. In particular a detailed case study for recovering the invariants for four-qubits within a spinorial framework is presented. We also observe that reality conditions on complex spinors defining Majorana spinors for embedded qubits boil down to self-conjugate states under the Wootters spin flip operation. Finally we conduct a study on the explicit structure of Spin(16 ,C ) invariant polynomials related to the structure of possible measures of entanglement for fermionic systems with eight modes. Here we find an algebraically independent generating set of the generalized stochastic local operations and classical communication invariants and calculate their restriction to the dense orbit. We point out the special role the largest exceptional group E8 is playing in these considerations.
Review of the fermionic dark matter model applied to galactic structures
NASA Astrophysics Data System (ADS)
Krut, A.; Argüelles, C. R.; Rueda, J.; Ruffini, R.
2015-12-01
Baryonic components (e.g. bulge and disk) of galactic structures are assumed to be embedded in an isothermal dark matter halo of fermionic nature. Besides the Pauli principle only gravitational interaction is considered. Using the underlying Fermi-Dirac phase space distribution, typical of collisionless relaxation processes, it yields an one-parameter family of scaled solutions which reproduces the observed flat rotation curves in galaxies, and additionally predicts a degenerate core through their centers. In order to provide the right DM halo properties of galaxies a set of four parameters (particle mass, degeneracy parameter at the galactic center, central density and the velocity dispersion) is necessary. The more general density profile shows three regimes depending on radius: an almost uniform very dense quantum core followed by a steep fall, a plateau in the diluted regime and a Boltzmannian tail representing the halo. In contrast to purely Boltzmannian configurations the fermionic DM model containing a quantum core allows to determine the particle mass. We show that the quantum core can be well approximated by a polytrope of index n = 3/2, while the halo can be perfectly described by an isothermal sphere with a halo scale length radius equal to approximately 3/4 of the King-radius.
Canonical form of three-fermion pure-states with six single particle states
Chen, Lin; Ž Ðoković, Dragomir; Grassl, Markus; Zeng, Bei
2014-08-01
We construct a canonical form for pure states in Λ³(C⁶), the three-fermion system with six single particle states, under local unitary (LU) transformations, i.e., the unitary group U(6). We also construct a minimal set of generators of the algebra of polynomial U(6)-invariants on Λ³(C⁶). It turns out that this algebra is isomorphic to the algebra of polynomial LU-invariants of three-qubits which are additionally invariant under qubit permutations. As a consequence of this surprising fact, we deduce that there is a one-to-one correspondence between the U(6)-orbits of pure three-fermion states in Λ³(C⁶) and the LU orbits of pure three-qubit states when qubit permutations are allowed. As an important byproduct, we obtain a new canonical form for pure three-qubit states under LU transformations U(2) × U(2) × U(2) (no qubit permutations allowed)
ERIC Educational Resources Information Center
Giorgis, Cyndi; Johnson, Nancy J.
2002-01-01
Presents annotations of approximately 30 titles grouped in text sets. Defines a text set as five to ten books on a particular topic or theme. Discusses books on the following topics: living creatures; pirates; physical appearance; natural disasters; and the Irish potato famine. (SG)
Spin-foam fermions: PCT symmetry, Dirac determinant and correlation functions
NASA Astrophysics Data System (ADS)
Han, Muxin; Rovelli, Carlo
2013-04-01
We discuss fermion coupling in the framework of spin-foam quantum gravity. We analyze the gravity-fermion spin-foam model and its fermion correlation functions. We show that there is a spin-foam analogue of PCT symmetry for the fermion fields on a spin-foam model, which is proved for spin-foam fermion correlation functions. We compute the determinant of the Dirac operator for the fermions, where two presentations of the Dirac determinant are given in terms of diagram expansions. We compute the fermion correlation functions and show that they can be given by Feynman diagrams on the spin-foams, where the Feynman propagators can be represented by a discretized path integral of a world-line action along the edges of the underlying 2-complex.
Influence of the quantum interference on the bosonic and fermionic ion-ion collisions
NASA Astrophysics Data System (ADS)
Hong, Woo-Pyo; Jung, Young-Dae
2014-03-01
The quantum interference effects on the bosonic-bosonic (He-4)-(He-4), fermionic-fermionic (He-3)-(He-3), and bosonic-fermionic (He-4)-(He-3) ion-ion collisions are investigated by using the isotope of the He nucleus in dense semiclassical Coulomb systems with the Faxen-Holtzmark method. It is found that the scattering cross section for the fermionic-fermionic ion-ion collision is greater than the bosonic-bosonic and bosonic-fermionic ion collision cross sections. It is also found that the collisional induced quantum interference effect enhances the ion-ion collision cross section in semiclassical Coulomb systems. The variation of the quantum-mechanical effect on the bosonic and fermionic ion-ion collisions is also discussed. This paper is dedicated to the late Prof. P. K. Shukla in memory of exciting and stimulating collaborations on physical processes in semiclassical Coulomb systems.
Plate tectonics: Scientific revolution or scientific program?
NASA Astrophysics Data System (ADS)
Mareschal, Jean-Claude
In The Structure of Scientific Revolutions, Thomas S. Kuhn suggested that science progresses discontinuously: As a scientific theory becomes obsolete, a period of crisis results, at the end of which the old theory is overthrown and replaced by a new, sounder, more complete theory [Kuhn, 1962]. After the scientific community has accepted the new [paradigm,] it undertakes only routine research until a new crisis occurs, usually as a result of an anomalous experiment that accidentally happens to be critical.
Scientific Writing: A Blended Instructional Model
ERIC Educational Resources Information Center
Clark, MaryAnn; Olson, Valerie
2010-01-01
Scientific writing is composed of a unique skill set and corresponding instructional strategies are critical to foster learning. In an age of technology, the blended instructional model provides the instrumental format for student mastery of the scientific writing competencies. In addition, the course management program affords opportunities for…
Ground-state energetics of helium and deuterium fermion fluids
NASA Astrophysics Data System (ADS)
Krotscheck, E.; Smith, R. A.; Clark, J. W.; Panoff, R. M.
1981-12-01
The method of correlated basis functions (CBF) is applied to the evaluation of the ground-state energy of atomic fermion fluids as a function of density. As a first step, liquid 3He in both unpolarized and fully polarized spin configurations is considered variationally, using Slater-Jastrow trial wave functions. Results are reported for a conventional analytic choice of the state-independent two-body correlation function f(r) and for the optimal f(r) determined by the solution of a suitable Euler equation. The Jastrow treatment is found to be inadequate in that (i) the energy expectation value lies above the experimental equilibrium energy by some 1.5 K, and (ii) the polarized phase is predicted to be more stable than the unpolarized one. For a given polarization, a correlated basis is formed by application of the assumed Jastrow correlation factor to the elements of a complete set of noninteracting-Fermi-gas Slater determinants. The exact ground-state energy may be developed in a perturbation expansion in the correlated basis, the leading term being the Jastrow energy expectation value. Considerable improvement on the Jastrow description of the unpolarized phase is achieved upon inclusion of the correlated two-particle-two-hole component of the second-order CBF perturbation correction. At the experimental equilibrium density, this contribution, which incorporates important momentum- and spin-dependent correlations, can amount to some 0.6-1.1 K [depending on the choice of f(r)]. The required correlated-basis matrix elements are calculated by Fermi hypernetted-chain (FHNC) techniques, crucial Pauli effects of the elementary diagrams being introduced through the FHNC/C algorithm. The Euler equation is approximated within the same framework. The momentum-space integrations in the second-order perturbation correction are evaluated by a Monte Carlo procedure. One may reasonably expect that further refinements of the CBF method will lead to an accurate microscopic
The eigSUMR inverter for overlap fermions
NASA Astrophysics Data System (ADS)
Cundy, Nigel; Lee, Weonjong
2016-06-01
We discuss the usage and applicability of deflation methods for the overlap lattice Dirac operator, focusing on calculating the eigenvalues using a method similar to the eigCG algorithm used for other Dirac operators. The overlap operator, which contains several theoretical advantages over other formulations of lattice Quantum Chromodynamics, is more computationally expensive because it requires the computation of the matrix sign function. The principal change made compared to deflation methods for other formulations of lattice QCD is that it is necessary for best performance to tune the accuracy of the matrix sign function as the computation proceeds. We present two possible relaxation strategies, one which provides a rigorous bound for the eigenvalues but seems to be too conservative in practice, and a second which is less conservative but, while its stability is not guaranteed, seems to work well in practice. We adapt the original eigCG algorithm for two of the preferred inversion algorithms for overlap fermions, GMRESR(relCG) and GMRESR(relSUMR). Before deflation, the rate of convergence of these routines in terms of iterations is similar, but, since the Shifted Unitary Minimal Residual (SUMR) algorithm only requires one call to the matrix sign function compared to the two calls required for Conjugate Gradient (CG), SUMR is usually preferred for single inversions of the Dirac operator. We construct bounds for the required accuracy of the matrix sign function during the eigenvalue calculation. For the SUMR algorithm, we use a variant of the Galerkin projection to perform the deflation; while for the CG algorithm, we are able to use a considerably superior spectral pre-conditioner. The superior performance of the spectral pre-conditioner, and its need for less accurate eigenvalues, almost erodes SUMR's advantage over CG as an inversion algorithm. We see factor of three gains for the inversion algorithm from the deflation on our small test lattices; we expect
Inhomogeneous disorder Dirac Fermions: from heavy fermion superconductors to graphene. Final report
Vekhter, Ilya
2013-08-11
This is the final report on the award designed to foster a partnership between Louisiana State University and Los Alamos National Laboratory (LANL) in conducting fundamental research in support of energy needs. The general focus of the research effort was on developing a better understanding of materials with new functionalities. We investigated two distinct and very promising classes of new materials, which serve as a testing ground for many of the novel phenomena in condensed matter physics: the heavy fermion 115 series, where the interplay of strong interactions between the electrons leads to a rich variety of competing phases and anomalous properties, and newly discovered pnictide superconductors. The former focus was planned; the latter emerged during the collaborative effort with LANL. Our objective was to determine the origin, and to establish a functional effective theory description of the phases in these systems, and transitions between them. We report on the main accomplishments under the award that serves to clarify the nature of superconductivity in both families of materials. In particular, we collaborated with experimentalists to predict and analyze the magnetic field and temperature dependence of the bulk thermodynamic and transport properties and to determine the gap shape in CeCoIn₅ and in Ba(Fe_{1-x}Co_{x})₂As₂, investigated the Kondo temperature in the presence of spin-orbit coupling in the conduction band, and provided theoretical guidance for local probes such as scanning tunneling spectroscopy of vortex cores and impurity resonances, and magnetic force microscopy of the superconducting states.
Pressure and field tuning in the heavy fermion ferromagnet CeAgSb2
NASA Astrophysics Data System (ADS)
Logg, Peter; Feng, Zhuo; Ebihara, Takao; Goh, Swee K.; Alireza, Patricia; Grosche, F. Malte
2012-12-01
The intermetallic compound CeAgSb2 is an unusual example of a ferromagnetically ordered heavy fermion system. Ferromagnetism sets in below the Curie temperature Tc=9.6 K at ambient pressure. We have investigated the magnetisation of CeAgSb2 under applied hydrostatic pressure of up to 45 kbar. Tc is suppressed rapidly, and at pressures > 35 kbar it is replaced by an unidentified ordered phase, possibly antiferromagnetism. The ordered magnetic moment in CeAgSb2 is aligned along the c-axis. We investigate the effect of transverse field tuning on Tc, and show that magnetic order at low temperature is suppressed by in-plane fields exceeding about 3 T.
Coherent Dynamics of Open Quantum System in the Presence of Majorana Fermions
NASA Astrophysics Data System (ADS)
Assuncao, Maryzaura O.; Diniz, Ginetom S.; Vernek, Edson; Souza, Fabricio M.
In recent years the research on quantum coherent dynamics of open systems has attracted great attention due to its relevance for future implementation of quantum computers. In the present study we apply the Kadanoff-Baym formalism to simulate the population dynamics of a double-dot molecular system attached to both a superconductor and fermionic reservoirs. We solve both analytically and numerically a set of coupled differential equations that account for crossed Andreev reflection (CAR), intramolecular hopping and tunneling. We pay particular attention on how Majorana bound states can affect the population dynamics of the molecule. We investigate on how initial state configuration affects the dynamics. For instance, if one dot is occupied and the other one is empty, the dynamics is dictated by the inter dot tunneling. On the other hand, for initially empty dots, the CAR dominates. We also investigate how the source and drain currents evolve in time. This work was supporte by FAPEMIG, CNPq and CAPES.
Fermion creation in 5D space-time with a warped extra dimension
NASA Astrophysics Data System (ADS)
Chekireb, R.; Haouat, S.
2015-05-01
The phenomenon of fermion production in a 5D FRW space-time with a warped extra dimension is studied by considering the canonical method based on Bogoliubov transformation connecting the "in" with the "out" states. For an exactly solvable model, two sets of exact solution are expressed in terms of Bessel functions. Studying the semiclassical Hamilton-Jacobi equation, the "in" and "out" states are identified. The pair creation probability and the mean number of created particles are calculated from the Bogoliubov coefficients. It is shown that the particle creation probability and the number density of created particles depend on the ratio of the scale factors associated with the ordinary space {x} and the extra dimension. It is also shown that the contraction of the extra dimension induces particle creation like the ordinary space expansion.
Spinor path integral Quantum Monte Carlo for fermions
NASA Astrophysics Data System (ADS)
Shin, Daejin; Yousif, Hosam; Shumway, John
2007-03-01
We have developed a continuous-space path integral method for spin 1/2 fermions with fixed-phase approximation. The internal spin degrees of freedom of each particle is represented by four extra dimensions. This effectively maps each spinor onto two of the excited states of a four dimensional harmonic oscillator. The phases that appear in the problem can be treated within the fixed-phase approximation. This mapping preserves rotational invariance and allows us to treat spin interactions and fermionic exchange on equal footing, which may lead to new theoretical insights. The technique is illustrated for a few simple models, including a spin in a magnetic field and interacting electrons in a quantum dot in a magnetic field at finite temperature. We will discuss possible extensions of the method to molecules and solids using variational and diffusion Quantum Monte Carlo.
Singlet fermion dark matter within left-right model
NASA Astrophysics Data System (ADS)
Patra, Sudhanwa; Rao, Soumya
2016-08-01
We discuss singlet fermion dark matter within a left-right symmetric model promoting baryon and lepton numbers as separate gauge symmetries. We add a simple Dirac fermionic dark matter singlet under SU(2) L , R with nonzero and equal baryon and lepton number which ensures electric charge neutrality. Such a dark matter candidate interacts with SM particles through the extra ZB,ℓ gauge bosons. This can give rise to a dark matter particle of a few hundred GeV that couples to ∼TeV scale gauge bosons to give the correct relic density. This model thus accommodates TeV scale ZB,ℓ gauge bosons and other low scale BSM particles, which can be easily probed at LHC.
Dipolar Fermions in Quasi-Two-Dimensional Square Lattice
NASA Astrophysics Data System (ADS)
Lai, Chen-Yen; Tsai, Shan-Wen
2013-03-01
Motivated by recent experimental realization of quantum degenerate dipolar Fermi gas, we study a system of ultralcold single- and two-species polar fermions in a double layer two-dimensional square lattice. The long-range anisotropic nature of dipole-dipole interaction has shown a rich phase diagram on a two dimensional square lattice*. We investigate how the interlayer coupling affects the monolayer system. Our study focuses on the regime where the fermions are closed to half-filling, which is when lattice effects play an important role. We find several correlated phases by using a functional renormalization group technique, which also provides estimates for the critical temperature of each phase. [*] S. G. Bhongale et. al. arXiv:1209.2671 and Phys. Rev. Lett. 108 145301 (2012).
Topological phases of fermionic ladders with periodic magnetic fields
NASA Astrophysics Data System (ADS)
Sun, Gaoyong
2016-02-01
In recent experiments bosonic [Atala et al., Nat. Phys. 10, 588 (2014), 10.1038/nphys2998; Stuhl et al., Science 349, 1514 (2015), 10.1126/science.aaa8515] as well as fermionic ladders [Mancini et al. Science 349, 1510 (2015), 10.1126/science.aaa8736] with a uniform flux were studied and different interesting many-body states were observed. Motivated by these experiments, we extend the uniform synthetic magnetic field to a periodic case and show that a commensurate synthetic magnetic field offers an alternative scheme to realize topological phases in many-body systems of ultracold Fermi gases in ladderlike optical lattices. Using the exact diagonalization, we numerically determine the topological band structure, edge states, nonzero Chern numbers, Hofstadter-butterfly-like spectrum, and a complete phase diagram of noninteracting fermionic ladders.
High-pressure studies on heavy fermion systems
NASA Astrophysics Data System (ADS)
Ye, Chen; Zongfa, Weng; Smidman, Michael; Xin, Lu; Huiqiu, Yuan
2016-07-01
In this review article, we give a brief overview of heavy fermions, which are prototype examples of strongly correlated electron systems. We introduce the application of physical pressure in heavy fermion systems to construct their pressure phase diagrams and to study the close relationship between superconductivity (SC) and other electronic instabilities, such as antiferromagnetism (AFM), ferromagnetism (FM), and valence transitions. Field-angle dependent heat capacity and point-contact spectroscopic measurements under pressure are taken as examples to illustrate their ability to investigate novel physical properties of the emergent electronic states. Project supported by the National Basic Research Program of China (Grant No. 2011CBA00103), the National Natural Science Foundation of China (Grant Nos. 11174245 and 11374257), the Science Challenge Program of China, and the Fundamental Research Funds for the Central Universities of China.
Bold Diagrammatic Monte Carlo Method Applied to Fermionized Frustrated Spins
NASA Astrophysics Data System (ADS)
Kulagin, S. A.; Prokof'ev, N.; Starykh, O. A.; Svistunov, B.; Varney, C. N.
2013-02-01
We demonstrate, by considering the triangular lattice spin-1/2 Heisenberg model, that Monte Carlo sampling of skeleton Feynman diagrams within the fermionization framework offers a universal first-principles tool for strongly correlated lattice quantum systems. We observe the fermionic sign blessing—cancellation of higher order diagrams leading to a finite convergence radius of the series. We calculate the magnetic susceptibility of the triangular-lattice quantum antiferromagnet in the correlated paramagnet regime and reveal a surprisingly accurate microscopic correspondence with its classical counterpart at all accessible temperatures. The extrapolation of the observed relation to zero temperature suggests the absence of the magnetic order in the ground state. We critically examine the implications of this unusual scenario.
Cavity-induced chiral states of fermionic quantum gases
NASA Astrophysics Data System (ADS)
Sheikhan, Ameneh; Brennecke, Ferdinand; Kollath, Corinna
2016-04-01
We investigate ultracold fermions placed into an optical cavity and subjected to optical lattices which confine the atoms to ladder structures. A transverse running-wave laser beam induces together with the dynamical cavity field a two-photon Raman-assisted tunneling process with spatially dependent phase imprint along the rungs of the ladders. We identify the steady states which can occur by the feedback mechanism between the cavity field and the atoms. We find the spontaneous emergence of a finite cavity field amplitude which leads to an artificial magnetic field felt by the fermionic atoms. These form a chiral insulating or chiral liquid state carrying a chiral current. We explore the rich state diagram as a function of the power of the transverse laser beam, the atomic filling, and the phase imprint during the cavity-induced tunneling. Both a sudden onset or a slow exponential activation with the transverse laser power of the self-organized chiral states can occur.
Site-resolved imaging of a fermionic Mott insulator.
Greif, Daniel; Parsons, Maxwell F; Mazurenko, Anton; Chiu, Christie S; Blatt, Sebastian; Huber, Florian; Ji, Geoffrey; Greiner, Markus
2016-02-26
The complexity of quantum many-body systems originates from the interplay of strong interactions, quantum statistics, and the large number of quantum-mechanical degrees of freedom. Probing these systems on a microscopic level with single-site resolution offers important insights. Here we report site-resolved imaging of two-component fermionic Mott insulators, metals, and band insulators, using ultracold atoms in a square lattice. For strong repulsive interactions, we observed two-dimensional Mott insulators containing over 400 atoms. For intermediate interactions, we observed a coexistence of phases. From comparison to theory, we find trap-averaged entropies per particle of 1.0 times the Boltzmann constant (k(B)). In the band insulator, we find local entropies as low as 0.5 k(B). Access to local observables will aid the understanding of fermionic many-body systems in regimes inaccessible by modern theoretical methods. PMID:26917766
Topologically induced fermion parity flips in superconductor vortices
NASA Astrophysics Data System (ADS)
Teo, Jeffrey C. Y.; Khan, Mayukh Nilay; Vishveshwara, Smitha
2016-06-01
A highlighting feature of Majorana bound states in two-dimensional topological superconductors is that they gain a phase factor of π upon being orbited by a vortex. This work focuses on the vortex degree of freedom itself and demonstrates that the change in the Majorana state is accompanied by a fermion parity change within the vortex. Such a parity flip is interpreted as a higher dimensional analog of the fermion parity pump mechanism in superconducting wires as well as through general topological arguments. It is demonstrated in terms of level crossings in three different situations: in (i) spin-triplet paired superconductors and in proximity-induced superconducting systems involving (ii) quantum spin Hall-ferromagnet hybrids and (iii) Chern insulators.
Steady States in Fermionic Interacting Dissipative Floquet Systems
NASA Astrophysics Data System (ADS)
Seetharam, Karthik; Bardyn, Charles; Lindner, Netanel; Rudner, Mark; Refael, Gil
The possibility to drive quantum systems periodically in time offers unique ways to deeply modify their fundamental properties, as exemplified by Floquet topological insulators. It also opens the door to a variety of non-equilibrium effects. Resonant driving fields, in particular, lead to excitations which can expose the system to heating. We previously demonstrated that the analog of thermal states can be achieved and controlled in a fermionic Floquet system in the presence of phonon scattering, spontaneous emission, and an energy filtered fermionic bath. However, interactions play an important role in thermalization and present additional sources of heating. We analyze the effects of weak interactions in the presence of dissipation and the role of coherences in determining the steady state of the driven system. Interactions generically create additional excitations and, in contrast to phonons, may sustain inter-Floquet-band coherences at steady state.
Mixtures of bosonic and fermionic atoms in optical lattices
Albus, Alexander; Illuminati, Fabrizio; Eisert, Jens
2003-08-01
We discuss the theory of mixtures of bosonic and fermionic atoms in periodic potentials at zero temperature. We derive a general Bose-Fermi Hubbard Hamiltonian in a one-dimensional optical lattice with a superimposed harmonic trapping potential. We study the conditions for linear stability of the mixture and derive a mean-field criterion for the onset of a bosonic superfluid transition. We investigate the ground-state properties of the mixture in the Gutzwiller formulation of mean-field theory, and present numerical studies of finite systems. The bosonic and fermionic density distributions and the onset of quantum phase transitions to demixing and to a bosonic Mott-insulator are studied as a function of the lattice potential strength. The existence is predicted of a disordered phase for mixtures loaded in very deep lattices. Such a disordered phase possessing many degenerate or quasidegenerate ground states is related to a breaking of the mirror symmetry in the lattice.
Quadratic Forms for the Fermionic Unitary Gas Model
NASA Astrophysics Data System (ADS)
Finco, Domenico; Teta, Alessandro
2012-04-01
We consider a quantum system in dimension three composed by a group of N identical fermions, with mass 1/2, interacting via zero-range interaction with a group of M identical fermions of a different type, with mass m/2. Exploiting a renormalization procedure, we construct the corresponding quadratic form and define the so-called Skornyakov-Ter-Martirosyan extension Hα, which is the natural candidate as a possible Hamiltonian of the system. It is shown that if the form is unbounded from below then Hα is not a self-adjoint and bounded from below operator, and this in particular suggests that the so-called Thomas effect could occur. In the special case N = 2, M = 1 we prove that this is in fact the case when a suitable condition on the parameter m is satisfied.
Fermion gases in magnetic fields: a semiclassical treatment
NASA Astrophysics Data System (ADS)
Molinari, V. G.; Sumini, M.; Rocchi, F.
The study of quantum degenerate gases has received much interest in these last years essentially thanks to the extremely important experimental results of the achievement of Bose-Einstein condensation of atoms and, very recently, of almost complete degeneracy of atomic fermion gases. Here we want to present the results of a semi-analytical method for the study of an interacting degenerate fermion gas based on semiclassical kinetic theory; special care has been devoted to the study of a rotating electron gas, in a cylindrically symmetrical configuration, radially confined by a uniform magnetic field. The model will lead to a particular Thomas-Fermi equation which is generalized to take into account finite temperature and average velocity of the gas, and which is further developed to consider the effects of external fields.
A Closer Look at Fermions in Optical Lattices
NASA Astrophysics Data System (ADS)
Pertot, Daniel; Miller, Luke; Cocchi, Eugenio; Bohn, Johanna; Drewes, Jan; Brennecke, Ferdinand; Koschorreck, Marco; Köhl, Michael
2014-05-01
Quantum gases of interacting fermionic atoms in optical lattices promise to shed new light on the low-temperature phases of Hubbard-type models, such as spin-ordered phases or, in particular, on possible d-wave superconductivity. However, reaching the very low temperatures required necessitates the implementation of novel cooling schemes. As a first step towards this goal, we employ high-resolution imaging together with radio-frequency spectroscopy in order to spatially resolve the in-trap distributions of singly and doubly-occupied lattice sites after having loaded a quantum degenerate two-component Fermi gas of 40K atoms into a three-dimensional optical lattice geometry. Here, I will report on our recent progress towards the observation and characterization of a fermionic Mott insulator, together with an outlook on future steps towards lowering the temperature in the lattice.
Pinning of fermionic occupation numbers: Higher spatial dimensions and spin
NASA Astrophysics Data System (ADS)
Tennie, Felix; Vedral, Vlatko; Schilling, Christian
2016-07-01
The role of the generalized Pauli constraints (GPCs) in higher spatial dimensions and by incorporating spin degrees of freedom is systematically explored for a system of interacting fermions confined by a harmonic trap. Physical relevance of the GPCs is confirmed by analytical means for the ground state in the regime of weak couplings by finding its vector of natural occupation numbers close to the boundary of the allowed region. Such quasipinning is found to become weaker in the intermediate- and strong-coupling regime. The study of crossovers between different spatial dimensions by detuning the harmonic trap frequencies suggests that quasipinning is essentially an effect for systems with reduced spatial dimensionality. In addition, we find that quasipinning becomes stronger by increasing the degree of spin polarization. Consequently, the number of states available around the Fermi level plays a key role for the occurrence of quasipinning. This suggests that quasipinning emerges from the conflict between energy minimization and fermionic exchange symmetry.
Cumulant t-expansion for strongly correlated fermions
NASA Astrophysics Data System (ADS)
Zhuravlev, A. K.
2016-05-01
A systematic nonperturbative scheme is implemented to calculate the ground state energy for a wide class of strongly correlated fermion models. The scheme includes: (a) a method of automatic calculations of the cumulants of the model Hamiltonian, (b) a method of the ground state energy calculation from these cumulants using the t-expansion proposed by Horn and Weinstein (1984) [9] with new procedure of its extrapolation to t → ∞. As an example of application of the scheme all cumulants up to the 8-th order for spinless fermion model are calculated exactly, and converging sequences of approximations to the ground state energy are obtained for one-, two- and three-dimensional versions of the model.
Lorentz symmetric quantum field theory for symplectic fermions
Robinson, Dean J.; Kapit, Eliot; LeClair, Andre
2009-11-15
A free quantum field theory with Lorentz symmetry is derived for spin-half symplectic fermions in 2+1 dimensions. In particular, we show that fermionic spin-half fields may be canonically quantized in a free theory with a Klein-Gordon Lagrangian. This theory is shown to have all the required properties of a consistent free quantum field theory, namely, causality, unitarity, adherence to the spin-statistics theorem, CPT symmetry, and the Hermiticity and positive definiteness of the Hamiltonian. The global symmetry of the free theory is Sp(4){approx_equal}SO(5). Possible interacting theories of both the pseudo-Hermitian and Hermitian variety are then examined briefly.
Dark matter and localised fermions from spherical orbifolds?
NASA Astrophysics Data System (ADS)
Cacciapaglia, Giacomo; Deandrea, Aldo; Deutschmann, Nicolas
2016-04-01
We study a class of six-dimensional models based on positive curvature surfaces (spherical 2-orbifolds) as extra-spaces. Using the Newman-Penrose formalism, we discuss the particle spectrum in this class of models. The fermion spectrum problem, which has been addressed with flux compactifications in the past, can be avoided using localised fermions. In this framework, we find that there are four types of geometry compatible with the existence of a stable dark matter candidate and we study the simplest case in detail. Using the complementarity between collider resonance searches and relic density constraints, we show that this class of models is under tension, unless the model lies in a funnel region characterised by a resonant Higgs s-channel in the dark matter annihilation.
Left-right symmetric model with SU(2)-triplet fermions
Gu Peihong
2011-11-01
We consider an SU(3){sub c} x SU(2){sub L} x SU(2){sub R} x U(1){sub B-L} left-right symmetric model with three Higgs scalars including an SU(2){sub L} doublet, an SU(2){sub R} doublet and an SU(2){sub L} x SU(2){sub R} bidoublet. In addition to usual SU(2)-doublet fermions, our model contains SU(2)-triplet fermions with Majorana masses. The neutral components of the left-handed triplets can contribute a canonical seesaw while the neutral components of the right-handed triplets associated with the right-handed neutrinos can contribute a double/inverse-type seesaw. Our model can be embedded into an SO(10) grand unification theory where the triplets belong to the 45=(1,3,1,0)+(1,1,3,0)+... representations.
Stability of composite fermion states in Chern insulators
NASA Astrophysics Data System (ADS)
Potasz, Pawel; Jaworowski, Blazej
We analyze an existence of composite fermion (CF) states in fractional Chern insulators (FCI) using exact diagonalization. The consider Chern insulator models for spinless fermions exhibit a signature of CF states at 2/5 and 3/7 filling factors. Evidences of fractional quantum Hall type phases for a region in a parameter space with larger energy gap are shown by looking at momenta of the n-fold degenerate ground state, spectral flow, quasihole excitation spectrum, and entanglement spectra. We analyze stability of phases as a function of model parameters showing strong correlation with flatness of Berry curvature. The authors acknowledges partial financial support from the sources Granted for science development in the years 2013-2016, Grant No. IP2012 007372.
Searches for excited fermions in /ep collisions at HERA
NASA Astrophysics Data System (ADS)
ZEUS Collaboration; Chekanov, S.; Derrick, M.; Krakauer, D.; Magill, S.; Musgrave, B.; Pellegrino, A.; Repond, J.; Yoshida, R.; Mattingly, M. C. K.; Antonioli, P.; Bari, G.; Basile, M.; Bellagamba, L.; Boscherini, D.; Bruni, A.; Bruni, G.; Cara Romeo, G.; Cifarelli, L.; Cindolo, F.; Contin, A.; Corradi, M.; de Pasquale, S.; Giusti, P.; Iacobucci, G.; Levi, G.; Margotti, A.; Massam, T.; Nania, R.; Palmonari, F.; Pesci, A.; Sartorelli, G.; Zichichi, A.; Aghuzumtsyan, G.; Brock, I.; Goers, S.; Hartmann, H.; Hilger, E.; Irrgang, P.; Jakob, H.-P.; Kappes, A.; Katz, U. F.; Kerger, R.; Kind, O.; Paul, E.; Rautenberg, J.; Schnurbusch, H.; Stifutkin, A.; Tandler, J.; Voss, K. C.; Weber, A.; Wieber, H.; Bailey, D. S.; Brook, N. H.; Cole, J. E.; Foster, B.; Heath, G. P.; Heath, H. F.; Robins, S.; Rodrigues, E.; Scott, J.; Tapper, R. J.; Wing, M.; Capua, M.; Mastroberardino, A.; Schioppa, M.; Susinno, G.; Jeoung, H. Y.; Kim, J. Y.; Lee, J. H.; Lim, I. T.; Ma, K. J.; Pac, M. Y.; Caldwell, A.; Helbich, M.; Liu, X.; Mellado, B.; Paganis, S.; Schmidke, W. B.; Sciulli, F.; Chwastowski, J.; Eskreys, A.; Figiel, J.; Klimek, K.; Olkiewicz, K.; Przybycień, M. B.; Stopa, P.; Zawiejski, L.; Bednarek, B.; Grabowska-Bold, I.; Jeleń, K.; Kisielewska, D.; Kowal, A. M.; Kowal, M.; Kowalski, T.; Mindur, B.; Przybycień, M.; Rulikowska-Zarȩbska, E.; Suszycki, L.; Szuba, D.; Szuba, J.; Kotański, A.; Bauerdick, L. A. T.; Behrens, U.; Borras, K.; Chiochia, V.; Crittenden, J.; Dannheim, D.; Desler, K.; Drews, G.; Fox-Murphy, A.; Fricke, U.; Geiser, A.; Goebel, F.; Göttlicher, P.; Graciani, R.; Haas, T.; Hain, W.; Hartner, G. F.; Hebbel, K.; Hillert, S.; Kötz, U.; Kowalski, H.; Labes, H.; Löhr, B.; Mankel, R.; Martens, J.; Martínez, M.; Milite, M.; Moritz, M.; Notz, D.; Petrucci, M. C.; Polini, A.; Schneekloth, U.; Selonke, F.; Stonjek, S.; Surrow, B.; Whitmore, J. J.; Wichmann, R.; Wolf, G.; Youngman, C.; Zeuner, W.; Coldewey, C.; Lopez-Duran Viani, A.; Meyer, A.; Schlenstedt, S.; Barbagli, G.; Gallo, E.; Pelfer, P. G.; Bamberger, A.; Benen, A.; Coppola, N.; Markun, P.; Raach, H.; Wölfle, S.; Bell, M.; Bussey, P. J.; Doyle, A. T.; Glasman, C.; Lee, S. W.; Lupi, A.; McCance, G. J.; Saxon, D. H.; Skillicorn, I. O.; Bodmann, B.; Gendner, N.; Holm, U.; Salehi, H.; Wick, K.; Yildirim, A.; Ziegler, A.; Carli, T.; Garfagnini, A.; Gialas, I.; Lohrmann, E.; Foudas, C.; Gonçalo, R.; Long, K. R.; Metlica, F.; Miller, D. B.; Tapper, A. D.; Walker, R.; Cloth, P.; Filges, D.; Kuze, M.; Nagano, K.; Tokushuku, K.; Yamada, S.; Yamazaki, Y.; Barakbaev, A. N.; Boos, E. G.; Pokrovskiy, N. S.; Zhautykov, B. O.; Ahn, S. H.; Lee, S. B.; Park, S. K.; Lim, H.; Son, D.; Barreiro, F.; García, G.; González, O.; Labarga, L.; del Peso, J.; Redondo, I.; Terrón, J.; Vázquez, M.; Barbi, M.; Bertolin, A.; Corriveau, F.; Ochs, A.; Padhi, S.; Stairs, D. G.; St-Laurent, M.; Tsurugai, T.; Antonov, A.; Bashkirov, V.; Danilov, P.; Dolgoshein, B. A.; Gladkov, D.; Sosnovtsev, V.; Suchkov, S.; Dementiev, R. K.; Ermolov, P. F.; Golubkov, Yu. A.; Katkov, I. I.; Khein, L. A.; Korotkova, N. A.; Korzhavina, I. A.; Kuzmin, V. A.; Levchenko, B. B.; Lukina, O. Yu.; Proskuryakov, A. S.; Shcheglova, L. M.; Solomin, A. N.; Vlasov, N. N.; Zotkin, S. A.; Bokel, C.; Engelen, J.; Grijpink, S.; Koffeman, E.; Kooijman, P.; Maddox, E.; Schagen, S.; Tassi, E.; Tiecke, H.; Tuning, N.; Velthuis, J. J.; Wiggers, L.; de Wolf, E.; Brümmer, N.; Bylsma, B.; Durkin, L. S.; Gilmore, J.; Ginsburg, C. M.; Kim, C. L.; Ling, T. Y.; Boogert, S.; Cooper-Sarkar, A. M.; Devenish, R. C. E.; Ferrando, J.; Große-Knetter, J.; Matsushita, T.; Rigby, M.; Ruske, O.; Sutton, M. R.; Walczak, R.; Brugnera, R.; Carlin, R.; dal Corso, F.; Dusini, S.; Limentani, S.; Longhin, A.; Parenti, A.; Posocco, M.; Stanco, L.; Turcato, M.; Adamczyk, L.; Iannotti, L.; Oh, B. Y.; Saull, P. R. B.; Toothacker, W. S.; Iga, Y.; D'Agostini, G.; Marini, G.; Nigro, A.; Cormack, C.; Hart, J. C.; McCubbin, N. A.; Heusch, C.; Park, I. H.; Pavel, N.; Abramowicz, H.; Dagan, S.; Gabareen, A.; Kananov, S.; Kreisel, A.; Levy, A.; Abe, T.; Fusayasu, T.; Kohno, T.; Umemori, K.; Yamashita, T.; Hamatsu, R.; Hirose, T.; Inuzuka, M.; Kitamura, S.; Matsuzawa, K.; Nishimura, T.; Arneodo, M.; Cartiglia, N.; Cirio, R.; Costa, M.; Ferrero, M. I.; Maselli, S.; Monaco, V.; Peroni, C.; Ruspa, M.; Sacchi, R.; Solano, A.; Staiano, A.; Bailey, D. C.; Fagerstroem, C.-P.; Galea, R.; Koop, T.; Levman, G. M.; Martin, J. F.; Mirea, A.; Sabetfakhri, A.; Butterworth, J. M.; Gwenlan, C.; Hall-Wilton, R.; Hayes, M. E.; Heaphy, E. A.; Jones, T. W.; Lane, J. B.; Lightwood, M. S.; West, B. J.; Ciborowski, J.; Ciesielski, R.; Grzelak, G.; Nowak, R. J.; Pawlak, J. M.; Smalska, B.; Tymieniecka, T.; Ukleja, A.; Ukleja, J.; Zakrzewski, J. A.; Żarnecki, A. F.; Adamus, M.; Plucinski, P.; Sztuk, J.; Eisenberg, Y.; Gladilin, L. K.; Hochman, D.; Karshon, U.; Breitweg, J.; Chapin, D.; Cross, R.; Kçira, D.; Lammers, S.; Reeder, D. D.; Savin, A. A.; Smith, W. H.; Deshpande, A.; Dhawan, S.; Hughes, V. W.; Straub, P. B.; Bhadra, S.; Catterall, C. D.; Frisken, W. R.; Khakzad, M.; Menary, S.
2002-11-01
Searches in /ep collisions for heavy excited fermions have been performed with the ZEUS detector at HERA. Excited states of electrons and quarks have been searched for in e+p collisions at a centre-of-mass energy of 300 GeV using an integrated luminosity of 47.7 pb-1. Excited electrons have been sought via the decays e*-->eγ, e*-->eZ and e*-->νW. Excited quarks have been sought via the decays q*-->qγ and q*-->qW. A search for excited neutrinos decaying via ν*-->νγ, ν*-->νZ and ν*-->eW is presented using e-p collisions at 318 GeV centre-of-mass energy, corresponding to an integrated luminosity of 16.7 pb-1. No evidence for any excited fermion is found, and limits on the characteristic couplings are derived for masses /<~250 GeV.
Quark matter and fermionic dark matter compact stars
NASA Astrophysics Data System (ADS)
Samanta, Chhanda; Mukhopadhyay, Somenath; Basu, Devasish Narayan
2016-03-01
Compact stars, made of quark matter and fermionic dark matter with arbitrary masses and interaction strengths, are studied by solving the Tolman-Oppenheimer-Volkoff equation of general relativity. The mass-radius relation for quark matter compact stars is obtained from the MIT bag model equation of state (EoS) with thin crust for different bag constants. The EoS of non-self-annihilating dark matter for an interacting Fermi gas with dark matter particle of 1-100 GeV mass is studied. For sufficiently strong interactions, the maximum stable mass of compact stars and its radius are controlled by the parameter of the interaction, both increasing linearly with the interaction strength. The mass-radius relation for compact stars made of strongly interacting fermions shows that the radius remains approximately constant for a wide range of compact stars.
Boundary conditions for star matter and other periodic fermionic systems
NASA Astrophysics Data System (ADS)
Gulminelli, F.; Furuta, T.; Juillet, O.; Leclercq, C.
2011-12-01
Bulk fermionic matter, as can be notably found in supernova matter and neutrons stars, is subject to correlations of infinite range due to the antisymmetrization of the N-body wave function, which cannot be explicitly accounted for in a practical simulation. This problem is usually addressed in condensed matter physics by means of the so-called twist averaged boundary condition method. A different ansatz based on the localized Wannier representation has been proposed in the context of antisymmetrized molecular dynamics. In this paper we work out the formal relation between the two approaches. We show that, while the two coincide when working with exact eigenstates of the N-body Hamiltonian, differences appear in the case of variational approaches, which are currently used for the description of stellar matter. Some model applications with fermionic molecular dynamics are shown.
Coulomb interaction effect in tilted Weyl fermion in two dimensions
NASA Astrophysics Data System (ADS)
Isobe, Hiroki; Nagaosa, Naoto
Weyl fermions with tilted linear dispersions characterized by several different velocities appear in some systems including the quasi-two-dimensional organic semiconductor α-(BEDT-TTF)2I3 and three-dimensional WTe2. The Coulomb interaction between electrons modifies the velocities in an essential way in the low energy limit, where the logarithmic corrections dominate. Taking into account the coupling to both the transverse and longitudinal electromagnetic fields, we derive the renormalization group equations for the velocities of the tilted Weyl fermions in two dimensions, and found that they increase as the energy decreases and eventually hit the velocity of light c to result in the Cherenkov radiation. Especially, the system restores the isotropic Weyl cone even when the bare Weyl cone is strongly tilted and the velocity of electrons becomes negative in certain directions.
Finite-lattice form factors in free-fermion models
NASA Astrophysics Data System (ADS)
Iorgov, N.; Lisovyy, O.
2011-04-01
We consider the general {Z}_2 -symmetric free-fermion model on the finite periodic lattice, which includes as special cases the Ising model on the square and triangular lattices and the {Z}_n -symmetric BBS τ(2)-model with n = 2. Translating Kaufman's fermionic approach to diagonalization of Ising-like transfer matrices into the language of Grassmann integrals, we determine the transfer matrix eigenvectors and observe that they coincide with the eigenvectors of a square lattice Ising transfer matrix. This allows us to find exact finite-lattice form factors of spin operators for the statistical model and the associated finite-length quantum chains, of which the most general is equivalent to the XY chain in a transverse field.
Naturalness and ultraviolet structure of gauge theories with massive fermions
NASA Astrophysics Data System (ADS)
Gellas, G. C.; Karanikas, A. I.; Ktorides, C. N.
1997-04-01
According to the principle of naturalness a small, with respect to the cutoff, mass parameter entering a quantum field system is natural only when it is compatible with some symmetry in the limit where it vanishes. In this paper, advantage is taken of the liberty afforded by the renormalization procedure in order to harmonize the cutoff with the physical mass in a non-Abelian gauge field theory with spin-1/2 matter fields. The ultraviolet structure of the theory, from such a vantage point, is explored at the level of the full fermionic propagator, as well as the vertex function, using the world line approach. An interplay between this ultraviolet structure and the infrared behavior of the same system, but from the customary viewpoint ``cutoff much greater than mass,'' is pointed out. Direct implications for open fermionic lines in the world line path integral casting of field theories are also made.
Site-resolved imaging of a fermionic Mott insulator
NASA Astrophysics Data System (ADS)
Chiu, Christie; Greif, Daniel; Parsons, Maxwell F.; Mazurenko, Anton; Blatt, Sebastian; Huber, Florian; Ji, Geoffrey; Greiner, Markus
2016-05-01
Quantum gas microscopy of ultracold fermionic atoms in an optical lattice opens new perspectives for addressing long-standing open questions on strongly correlated low-temperature phases in the Hubbard model. Here we report on site-resolved imaging of two-component fermionic Mott insulators, metals, and band insulators with Lithium-6. For strong repulsive interactions we observe Mott insulators with more than 400 atoms and for intermediate interactions we observe a coexistence of phases. From comparison to theory, we find trap-averaged entropies per particle of 1 . 0kB in the Mott insulator and local entropies in the band insulator as low as 0 . 5kB . Our measurements serve as a benchmark for the performance of our experiment and are a starting point for accessing the low-temperature regime of magnetic ordering. Current address: Max-Planck-Institut für Quantenoptik, 85748 Garching, Germany.
Microscopic Observation of Pauli Blocking in Degenerate Fermionic Lattice Gases
NASA Astrophysics Data System (ADS)
Hilker, Timon; Omran, Ahmed; Boll, Martin; Salomon, Guillaume; Bloch, Immanuel; Gross, Christian
2016-05-01
Ultracold atoms in optical lattices provide a powerful platform for the controlled study of quantum many-body physics. We present here the first studies with a new generation quantum gas microscope, which allows to observe the full atom number statistics on every site. The common problem of light induced losses during imaging is avoided by an additional small scale ``pinning lattice'' used for Raman sideband cooling in the imaging process. We report the local observation of the Pauli exclusion principle in a spin-polarized degenerate gas of 6 Li fermions in an optical lattice. In the band insulating regime, we measure a tenfold suppression of particle number fluctuations per site compared to classical particles. From the remaining fluctuations we extract a local entropy as low as 0.3 kB per atom. Our work opens an exciting avenue for studying local density and even magnetic correlations in fermionic quantum matter both in and out of equilibrium.
Stability of renormalization group trajectories and the fermion flavor problem
NASA Astrophysics Data System (ADS)
Goldfain, Ervin
2007-04-01
An outstanding puzzle of the current standard model for particle physics (SM) is that both leptons and quarks arise in replicated patterns. Our work suggests that the number of fermion flavors occurring in the SM may be directly derived from the dynamics of renormalization group equations. The starting point is the system describing the coupling flow in the gauge sector [ dgidt.= βi(gi)=bi(N,nf)gi^3 +O(gi^5 ) ] where i=(1,2,3) labels the gauge group of dimension N, nf is the number of fermion flavors and t the sliding scale. With the help of the Routh-Hurwitz criterion, we find that the SM solution nf=6 follows from demanding stability of the linearized flow about its fixed points.
Thermal corrections to Rényi entropies for free fermions
NASA Astrophysics Data System (ADS)
Herzog, Christopher P.; Spillane, Michael
2016-04-01
We calculate thermal corrections to Rényi entropies for free massless fermions on a sphere. More specifically, we take a free fermion on {R}× {{S}}^{{{}^d}^{-1}} and calculate the leading thermal correction to the Rényi entropies for a cap like region with opening angle 2 θ. By expanding the density matrix in a Boltzmann sum, the problem of finding the Rényi entropies can be mapped to the problem of calculating a two point function on an n sheeted cover of the sphere. We follow previous work for conformal field theories to map the problem on the sphere to a conical region in Euclidean space. By using the method of images, we calculate the two point function and recover the Rényi entropies.
Fermionic quantum gases with tunable interactions in optical lattices
NASA Astrophysics Data System (ADS)
Schneider, Ulrich; Hackermüller, Lucia; Best, Thorsten; Will, Sebastian; Braun, Simon; Moreno Cardoner, Maria; Paredes, Belen; Bloch, Immanuel
2009-03-01
Fermionic atoms in optical lattices can serve as a model system for condensed matter physics, as they present an implementation of the Hubbard hamiltonian with high experimental control of the relevant parameters. In our system we sympathetically cool ^87Rb and ^40K in an optically plugged quadrupole trap and an optical dipole trap. After evaporation, a balanced spin mixture of 40K atoms is loaded into a blue detuned optical lattice where the interactions can be changed via a Feshbach resonance. We present experimental and theoretical studies of the behaviour of fermionic atoms for both attractive and repulsive interactions. For repulsive interactions we show a transition from compressible, metallic states to Mott-insulating and finally band insulating states. On the attractive side we investigate an anomalous expansion when the interaction is strongly attractive and study the dynamics of atoms and repulsively and attractively bound pairs.
On Some Troubles with the Metaphysics of Fermionic Compositions
NASA Astrophysics Data System (ADS)
Bigaj, Tomasz
2016-05-01
In this paper I discuss some metaphysical consequences of an unorthodox approach to the problem of the identity and individuality of "indistinguishable" quantum particles. This approach is based on the assumption that the only admissible way of individuating separate components of a given system is with the help of the permutation-invariant qualitative properties of the total system. Such a method of individuation, when applied to fermionic compositions occupying so-called GMW-nonentangled states, yields highly implausible consequences regarding the number of distinct components of a given composite system. I specify the problem (which I call the problem of fermionic inflation) in detail, and I consider several strategies of solving it. The preferred solution of the problem is based on the premise that spatial location should play a privileged role in identifying and making reference to quantum-mechanical systems.
Grassmann phase space methods for fermions. I. Mode theory
NASA Astrophysics Data System (ADS)
Dalton, B. J.; Jeffers, J.; Barnett, S. M.
2016-07-01
In both quantum optics and cold atom physics, the behaviour of bosonic photons and atoms is often treated using phase space methods, where mode annihilation and creation operators are represented by c-number phase space variables, with the density operator equivalent to a distribution function of these variables. The anti-commutation rules for fermion annihilation, creation operators suggest the possibility of using anti-commuting Grassmann variables to represent these operators. However, in spite of the seminal work by Cahill and Glauber and a few applications, the use of Grassmann phase space methods in quantum-atom optics to treat fermionic systems is rather rare, though fermion coherent states using Grassmann variables are widely used in particle physics. The theory of Grassmann phase space methods for fermions based on separate modes is developed, showing how the distribution function is defined and used to determine quantum correlation functions, Fock state populations and coherences via Grassmann phase space integrals, how the Fokker-Planck equations are obtained and then converted into equivalent Ito equations for stochastic Grassmann variables. The fermion distribution function is an even Grassmann function, and is unique. The number of c-number Wiener increments involved is 2n2, if there are n modes. The situation is somewhat different to the bosonic c-number case where only 2 n Wiener increments are involved, the sign of the drift term in the Ito equation is reversed and the diffusion matrix in the Fokker-Planck equation is anti-symmetric rather than symmetric. The un-normalised B distribution is of particular importance for determining Fock state populations and coherences, and as pointed out by Plimak, Collett and Olsen, the drift vector in its Fokker-Planck equation only depends linearly on the Grassmann variables. Using this key feature we show how the Ito stochastic equations can be solved numerically for finite times in terms of c-number stochastic
Twisted vertex algebras, bicharacter construction and boson-fermion correspondences
Anguelova, Iana I.
2013-12-15
The boson-fermion correspondences are an important phenomena on the intersection of several areas in mathematical physics: representation theory, vertex algebras and conformal field theory, integrable systems, number theory, cohomology. Two such correspondences are well known: the types A and B (and their super extensions). As a main result of this paper we present a new boson-fermion correspondence of type D-A. Further, we define a new concept of twisted vertex algebra of order N, which generalizes super vertex algebra. We develop the bicharacter construction which we use for constructing classes of examples of twisted vertex algebras, as well as for deriving formulas for the operator product expansions, analytic continuations, and normal ordered products. By using the underlying Hopf algebra structure we prove general bicharacter formulas for the vacuum expectation values for two important groups of examples. We show that the correspondences of types B, C, and D-A are isomorphisms of twisted vertex algebras.
Convergent perturbation theory for lattice models with fermions
NASA Astrophysics Data System (ADS)
Sazonov, V. K.
2016-05-01
The standard perturbation theory in QFT and lattice models leads to the asymptotic expansions. However, an appropriate regularization of the path or lattice integrals allows one to construct convergent series with an infinite radius of the convergence. In the earlier studies, this approach was applied to the purely bosonic systems. Here, using bosonization, we develop the convergent perturbation theory for a toy lattice model with interacting fermionic and bosonic fields.
One-loop chiral perturbation theory with two fermion representations
NASA Astrophysics Data System (ADS)
DeGrand, Thomas; Golterman, Maarten; Neil, Ethan T.; Shamir, Yigal
2016-07-01
We develop chiral perturbation theory for chirally broken theories with fermions in two different representations of the gauge group. Any such theory has a nonanomalous singlet U (1 )A symmetry, yielding an additional Nambu-Goldstone boson when spontaneously broken. We calculate the next-to-leading order corrections for the pseudoscalar masses and decay constants, which include the singlet Nambu-Goldstone boson, as well as for the two condensates. The results can be generalized to more than two representations.
Chaotic spin precession in anisotropic universes and fermionic dark matter
NASA Astrophysics Data System (ADS)
Kamenshchik, A. Yu.; Teryaev, O. V.
2016-05-01
We consider the precession of a Dirac particle spin in some anisotropic Bianchi universes. This effect is present already in the Bianchi-I universe. In the Bianchi-IX universe it acquires the chaotic character due to the stochasticity of the oscillatory approach to the cosmological singularity. The related helicity flip of fermions in the veryearly Universe may produce the sterile particles contributing to dark matter.
Novel p-wave superfluids of fermionic polar molecules
NASA Astrophysics Data System (ADS)
Fedorov, A. K.; Matveenko, S. I.; Yudson, V. I.; Shlyapnikov, G. V.
2016-06-01
Recently suggested subwavelength lattices offer remarkable prospects for the observation of novel superfluids of fermionic polar molecules. It becomes realistic to obtain a topological p-wave superfluid of microwave-dressed polar molecules in 2D lattices at temperatures of the order of tens of nanokelvins, which is promising for topologically protected quantum information processing. Another foreseen novel phase is an interlayer p-wave superfluid of polar molecules in a bilayer geometry.
Dynamical overlap fermions in the epsilon-regime
NASA Astrophysics Data System (ADS)
Fukaya, Hidenori
2006-12-01
We report on the two-flavor QCD simulation in the ɛ-regime using the overlap fermion formu- lation. Sea quark mass is reduced to ˜ 2 MeV on a 163 × 32 lattice with the lattice spacing a 0.11 fm. Topological charge is fixed at Q = 0. We compare the eigenvalue distribution of the overlap-Dirac operator with the prediction of the chiral random matrix theory. Preliminary results on meson correlators are also reported.
A Lagrangian for mass dimension one fermionic dark matter
NASA Astrophysics Data System (ADS)
Lee, Cheng-Yang
2016-09-01
The mass dimension one fermionic field associated with Elko satisfies the Klein-Gordon but not the Dirac equation. However, its propagator is not a Green's function of the Klein-Gordon operator. We propose an infinitesimal deformation to the propagator such that it admits an operator in which the deformed propagator is a Green's function. The field is still of mass dimension one, but the resulting Lagrangian is modified in accordance with the operator.
Fermion masses and mixings from heterotic orbifold models
Park, Jae-hyeon
2005-12-02
We search for a possibility of getting realistic fermion mass ratios and mixing angles from renormalizable couplings on the Z6-I heterotic orbifold with one pair of Higgs doublets. In the quark sector, we find cases with reasonable results if we ignore the first family. In the lepton sector, we can fit the charged lepton mass ratios, the neutrino mass squared difference ratio, and the lepton mixing angles, considering all three families00.
Novel p-wave superfluids of fermionic polar molecules
Fedorov, A. K.; Matveenko, S. I.; Yudson, V. I.; Shlyapnikov, G. V.
2016-01-01
Recently suggested subwavelength lattices offer remarkable prospects for the observation of novel superfluids of fermionic polar molecules. It becomes realistic to obtain a topological p-wave superfluid of microwave-dressed polar molecules in 2D lattices at temperatures of the order of tens of nanokelvins, which is promising for topologically protected quantum information processing. Another foreseen novel phase is an interlayer p-wave superfluid of polar molecules in a bilayer geometry. PMID:27278711
Qualitative analysis of trapped Dirac fermions in graphene
Jakubský, Vít Krejčiřík, David
2014-10-15
We study the confinement of Dirac fermions in graphene and in carbon nanotubes by an external magnetic field, mechanical deformations or inhomogeneities in the substrate. By applying variational principles to the square of the Dirac operator, we obtain sufficient and necessary conditions for confinement of the quasi-particles. The rigorous theoretical results are illustrated on the realistic examples of the three classes of traps.
Criteria for two distinguishable fermions to form a boson
Ramanathan, Ravishankar; Chuan, Tan Kok; Kurzynski, Pawel; Santos, Marcelo F.; Kaszlikowski, Dagomir
2011-09-15
We study the necessary conditions for systems composed of two distinguishable fermions to exhibit bosonic behavior. We base our analysis on tools of quantum information theory such as entanglement, local operations and classical communication and the majorization criterion for probability distributions. Introduction of these tools yields new insights into the old and important problem of identifying the conditions for existence of composite bosons. We precisely identify the role entanglement plays in the formation and behavior of such composite particles.
Dirac fermions on an anti-de Sitter background
Ambruş, Victor E. Winstanley, Elizabeth
2014-11-24
Using an exact expression for the bi-spinor of parallel transport, we construct the Feynman propagator for Dirac fermions in the vacuum state on anti-de Sitter space-time. We compute the vacuum expectation value of the stress-energy tensor by removing coincidence-limit divergences using the Hadamard method. We then use the vacuum Feynman propagator to compute thermal expectation values at finite temperature. We end with a discussion of rigidly rotating thermal states.
Novel p-wave superfluids of fermionic polar molecules.
Fedorov, A K; Matveenko, S I; Yudson, V I; Shlyapnikov, G V
2016-01-01
Recently suggested subwavelength lattices offer remarkable prospects for the observation of novel superfluids of fermionic polar molecules. It becomes realistic to obtain a topological p-wave superfluid of microwave-dressed polar molecules in 2D lattices at temperatures of the order of tens of nanokelvins, which is promising for topologically protected quantum information processing. Another foreseen novel phase is an interlayer p-wave superfluid of polar molecules in a bilayer geometry. PMID:27278711
Parallel processing for scientific computations
NASA Technical Reports Server (NTRS)
Alkhatib, Hasan S.
1995-01-01
The scope of this project dealt with the investigation of the requirements to support distributed computing of scientific computations over a cluster of cooperative workstations. Various experiments on computations for the solution of simultaneous linear equations were performed in the early phase of the project to gain experience in the general nature and requirements of scientific applications. A specification of a distributed integrated computing environment, DICE, based on a distributed shared memory communication paradigm has been developed and evaluated. The distributed shared memory model facilitates porting existing parallel algorithms that have been designed for shared memory multiprocessor systems to the new environment. The potential of this new environment is to provide supercomputing capability through the utilization of the aggregate power of workstations cooperating in a cluster interconnected via a local area network. Workstations, generally, do not have the computing power to tackle complex scientific applications, making them primarily useful for visualization, data reduction, and filtering as far as complex scientific applications are concerned. There is a tremendous amount of computing power that is left unused in a network of workstations. Very often a workstation is simply sitting idle on a desk. A set of tools can be developed to take advantage of this potential computing power to create a platform suitable for large scientific computations. The integration of several workstations into a logical cluster of distributed, cooperative, computing stations presents an alternative to shared memory multiprocessor systems. In this project we designed and evaluated such a system.
Solvable Models with Massless Light-Front Fermions
NASA Astrophysics Data System (ADS)
Martinovic̆, L'ubomír; Grangé, Pierre
2015-09-01
Two-dimensional models with massless fermions (Thirring model, Thirring-Wess and Schwinger model, among others) have been solved exactly a long time ago in the conventional (space-like) form of field theory and in some cases also in the conformal field theoretical approach. However, solutions in the light-front form of the theory have not been obtained so far. The primary obstacle is the apparent difficulty with light-front quantization of free massless fermions, where one half of the fermionic degrees of freedom seems to "disappear" due to the structure of a non-dynamical constraint equation. We shall show a simple way how the missing degree of freedom can be recovered as the massless limit of the massive solution of the constraint. This opens the door to the genuine light front solution of the above models since their solvability is related to free Heisenberg fields, which are the true dynamical variables in these models. In the present contribution, we give an operator solution of the light front Thirring model, including the correct form of the interacting quantum currents and of the Hamiltonian. A few remarks on the light-front Thirring-Wess models are also added. Simplifications and clarity of the light-front formalism turn out to be quite remarkable.
Probabilistic Q-function distributions in fermionic phase-space
NASA Astrophysics Data System (ADS)
Rosales-Zárate, Laura E. C.; Drummond, P. D.
2015-03-01
We obtain a positive probability distribution or Q-function for an arbitrary fermionic many-body system. This is different to previous Q-function proposals, which were either restricted to a subspace of the overall Hilbert space, or used Grassmann methods that do not give probabilities. The fermionic Q-function obtained here is constructed using normally ordered Gaussian operators, which include both non-interacting thermal density matrices and BCS states. We prove that the Q-function exists for any density matrix, is real and positive, and has moments that correspond to Fermi operator moments. It is defined on a finite symmetric phase-space equivalent to the space of real, antisymmetric matrices. This has the natural SO(2M) symmetry expected for Majorana fermion operators. We show that there is a physical interpretation of the Q-function: it is the relative probability for observing a given Gaussian density matrix. The distribution has a uniform probability across the space at infinite temperature, while for pure states it has a maximum value on the phase-space boundary. The advantage of probabilistic representations is that they can be used for computational sampling without a sign problem.
Fermions on the worldsheet of effective strings via coset construction
NASA Astrophysics Data System (ADS)
Mohsen, Ali
2016-05-01
In this paper the detailed Coleman-Callan-Wess-Zumino procedure for introducing fermions on the world sheet of a string propagating in flat space-time is presented. The theory of nonlinear realizations is used to derive the transformation as well as the interactions of fermionic matter fields under arbitrary spinorial representations of the unbroken subgroup. This demonstrates that even for nonsupersymmetric spinors, the interactions are still severely restricted by the nonlinearly realized symmetry. We also explain how supersymmetric models provide an example for this construction with Goldstinos as matter fields, and how one can use the κ -symmetry of the Green Schwarz action in particular, to verify this nonlinear transformation for a specific matter field representation. We finally restrict the target space dimension without reference to supersymmetry, but rather by imposing one-loop integrability on a fermionic string that nonlinearly realizes Poincare symmetry. This singles out the critical dimension D =10 for heterotic, Green-Schwarz and Ramond-Neveu-Schwarz supersymmetric strings.
Free Expansion of ultracold fermions in an optical lattice
NASA Astrophysics Data System (ADS)
Schneider, Ulrich; Hackermueller, Lucia; Ronzheimer, Jens Philipp; Will, Sebastian; Braun, Simon; Best, Thorsten; Schreiber, Michael; Chung Fong, Kin; Bloch, Immanuel
2010-03-01
Recent experiments with ultracold fermions in optical lattices face two main challenges in the quest of realizing complex strongly-correlated states: While the need to realize low entropy samples resulted in several recent proposals of advanced cooling schemes there remains the problem of the unknown adiabaticity timescales in these inhomogeneous systems. In order to measure the characteristic timescales of density redistribution, we experimentally investigate the free expansion of fermionic ^40K atoms in an homogeneous optical lattice. In an initially non-interacting band-insulater, created in the combination of a blue-detuned optical lattice and a red-detuned optical dipole trap, interactions are introduced by use of a Feshbach resonance. Subsequently the expansion is initiated by quickly ramping down the dipole trap while retaining the optical lattice. In the case of negligible interactions, the atoms expand ballistically performing a continuous quantum walk. For interacting fermions, the expansion becomes diffusive with a density dependent diffusion constant that is independent of the sign of interactions. These measurements demonstrate previously unobserved transport dynamics and give insight into the characteristic timescales of density redistribution.
A quantum-gas microscope for fermionic 40-potassium
NASA Astrophysics Data System (ADS)
Kuhr, Stefan
2016-05-01
Single-atom-resolved detection in optical lattices using quantum-gas microscopes has enabled a new generation of experiments in the field of quantum simulation. Here we demonstrate single-site- and single-atom-resolved florescence imaging of fermionic potassium-40 atoms in a quantum-gas microscope setup using electromagnetically-induced-transparency cooling. We detected on average 1000 fluorescence photons from a single atom within 1.5 s, while keeping it close to the vibrational ground state of the optical lattice. Our fermionic quantum-gas microscope will provide the possibility to probe quantities that are difficult to access in bulk systems, such as spin-spin-correlation functions or string-order. It would allow the study of, e.g. the Fermi-Hubbard Model and allow for the direct observation of band insulators, metallic phases and Mott insulators at the single-atom level. Future studies could include out-of-equilibrium dynamics, and the direct observation of entanglement build-up of in many-particle fermionic quantum systems.
Electric dipole moments of charged leptons with sterile fermions
NASA Astrophysics Data System (ADS)
Abada, Asmaa; Toma, Takashi
2016-02-01
We address the impact of sterile fermions on charged lepton electric dipole moments. Any experimental signal of these observables calls for scenarios of physics beyond the Standard Model providing new sources of CP violation. In this work, we consider a minimal extension of the Standard Model via the addition of sterile fermions which mix with active neutrinos and we derive the corresponding analytical expressions for the electric dipole moments of charged leptons at two-loop order. Our study reveals that, in order to have a non-vanishing contribution in this framework, the minimal extension necessitates the addition of at least 2 sterile fermion states to the Standard Model field content. Our conclusion is that sterile neutrinos can give significant contributions to the charged lepton electric dipole moments, some of them lying within present and future experimental sensitivity if the masses of the non-degenerate sterile states are both above the electroweak scale. The Majorana nature of neutrinos is also important in order to allow for significative contributions to the charged lepton electric dipole moments. In our analysis we impose all available experimental and observational constraints on sterile neutrinos and we further discuss the prospect of probing this scenario at low and high energy experiments.
Fermion masses and mixing in general warped extra dimensional models
NASA Astrophysics Data System (ADS)
Frank, Mariana; Hamzaoui, Cherif; Pourtolami, Nima; Toharia, Manuel
2015-06-01
We analyze fermion masses and mixing in a general warped extra dimensional model, where all the Standard Model (SM) fields, including the Higgs, are allowed to propagate in the bulk. In this context, a slightly broken flavor symmetry imposed universally on all fermion fields, without distinction, can generate the full flavor structure of the SM, including quarks, charged leptons and neutrinos. For quarks and charged leptons, the exponential sensitivity of their wave functions to small flavor breaking effects yield hierarchical masses and mixing as it is usual in warped models with fermions in the bulk. In the neutrino sector, the exponential wave-function factors can be flavor blind and thus insensitive to the small flavor symmetry breaking effects, directly linking their masses and mixing angles to the flavor symmetric structure of the five-dimensional neutrino Yukawa couplings. The Higgs must be localized in the bulk and the model is more successful in generalized warped scenarios where the metric background solution is different than five-dimensional anti-de Sitter (AdS5 ). We study these features in two simple frameworks, flavor complimentarity and flavor democracy, which provide specific predictions and correlations between quarks and leptons, testable as more precise data in the neutrino sector becomes available.
Mutual information area laws for thermal free fermions
NASA Astrophysics Data System (ADS)
Bernigau, H.; Kastoryano, M. J.; Eisert, J.
2015-02-01
We provide a rigorous and asymptotically exact expression of the mutual information of translationally invariant free fermionic lattice systems in a Gibbs state. In order to arrive at this result, we introduce a novel framework for computing determinants of Töplitz operators with smooth symbols, and for treating Töplitz matrices with system size dependent entries. The asymptotically exact mutual information for a partition of the 1D lattice satisfies an area law, with a prefactor which we compute explicitly. As examples, we discuss the fermionic XX model in one dimension and free fermionic models on the torus in higher dimensions in detail. Special emphasis is put on the discussion of the temperature dependence of the mutual information, scaling like the logarithm of the inverse temperature, hence confirming an expression suggested by conformal field theory. We also comment on the applicability of the formalism to treat open systems driven by quantum noise. In the appendix, we derive useful bounds to the mutual information in terms of purities. Finally, we provide a detailed error analysis for finite system sizes. This analysis is valuable in its own right for the abstract theory of Töplitz determinants.
Fermion flavor mixing in models with dynamical mass generation
Benes, Petr
2010-03-15
We present a model-independent method of dealing with fermion flavor mixing in the case when instead of constant, momentum-independent mass matrices one has rather momentum-dependent self-energies. This situation is typical for strongly coupled models of dynamical fermion mass generation. We demonstrate our approach on the example of quark mixing. We show that quark self-energies with a generic momentum dependence lead to an effective Cabibbo-Kobayashi-Maskawa matrix, which turns out to be in general nonunitary, in accordance with previous claims of other authors, and to nontrivial flavor changing electromagnetic and neutral currents. We also discuss some conceptual consequences of the momentum-dependent self-energies and show that in such a case the interaction basis and the mass basis are not related by a unitary transformation. In fact, we argue that the latter is merely an effective concept, in a specified sense. While focusing mainly on the fermionic self-energies, we also study the effects of momentum-dependent radiative corrections to the gauge bosons and to the proper vertices. Our approach is based on an application of the Lehmann-Symanzik-Zimmermann reduction formula and for the special case of constant self-energies it gives the same results as the standard approach based on the diagonalization of mass matrices.
Fermions in five-dimensional brane world models
NASA Astrophysics Data System (ADS)
Smolyakov, Mikhail N.
2016-06-01
In the present paper the fermion fields, living in the background of five-dimensional warped brane world models with compact extra dimension, are thoroughly examined. The Kaluza-Klein decomposition and isolation of the physical degrees of freedom is performed for those five-dimensional fermion field Lagrangians, which admit such a decomposition to be performed in a mathematically consistent way and provide a physically reasonable four-dimensional effective theory. It is also shown that for the majority of five-dimensional fermion field Lagrangians there are no (at least rather obvious) ways to perform the Kaluza-Klein decomposition consistently. Moreover, in these cases one may expect the appearance of various pathologies in the four-dimensional effective theory. Among the cases, for which the Kaluza-Klein decomposition can be performed in a mathematically consistent way, the case, which reproduces the Standard Model by the zero Kaluza-Klein modes most closely regardless of the size of the extra dimension, is examined in detail in the background of the Randall-Sundrum model.
Exponentially more precise quantum simulation of fermions in second quantization
NASA Astrophysics Data System (ADS)
Babbush, Ryan; Berry, Dominic W.; Kivlichan, Ian D.; Wei, Annie Y.; Love, Peter J.; Aspuru-Guzik, Alán
2016-03-01
We introduce novel algorithms for the quantum simulation of fermionic systems which are dramatically more efficient than those based on the Lie-Trotter-Suzuki decomposition. We present the first application of a general technique for simulating Hamiltonian evolution using a truncated Taylor series to obtain logarithmic scaling with the inverse of the desired precision. The key difficulty in applying algorithms for general sparse Hamiltonian simulation to fermionic simulation is that a query, corresponding to computation of an entry of the Hamiltonian, is costly to compute. This means that the gate complexity would be much higher than quantified by the query complexity. We solve this problem with a novel quantum algorithm for on-the-fly computation of integrals that is exponentially faster than classical sampling. While the approaches presented here are readily applicable to a wide class of fermionic models, we focus on quantum chemistry simulation in second quantization, perhaps the most studied application of Hamiltonian simulation. Our central result is an algorithm for simulating an N spin-orbital system that requires \\tilde{{ O }}({N}5t) gates. This approach is exponentially faster in the inverse precision and at least cubically faster in N than all previous approaches to chemistry simulation in the literature.
Heavy-fermion systems studied by {mu}SR technique
Amato, A.
1997-10-01
The author attempts to give a comprehensive discussion of studies performed with the positive-muon spin rotation and relaxation technique (also known as the {mu}SR technique) on heavy-fermion compounds. The subtle competition between the demagnetizing Kondo interaction and the intersite Ruderman-Kittel-Kasuya-Yosida exchange interaction is believed to be the primary ingredient for the wealth of different ground states observed for this class of rare-earth{endash} and actinide-containing intermetallic compounds. Due to its microscopic character, its sensitivity to extremely small internal fields, and its capacity to detect spatially inhomogeneous magnetic features, the {mu}SR technique has been extensively utilized to investigate the peculiar magnetic properties of these ground states and improve our knowledge of heavy-fermion phenomena. In addition to providing a short introduction to {mu}SR, where the intrinsic difficulties of the method are clearly stated, this article reviews the main results obtained by this technique on the best-known heavy-fermion compounds (superconductors, band magnets, local-moment magnets, non-Fermi-liquid systems, and Kondo insulators). Special emphasis is placed on the particular information obtainable by monitoring the implanted muon. {copyright} {ital 1997} {ital The American Physical Society}
Topological Effective Field Theories for Dirac Fermions from Index Theorem
NASA Astrophysics Data System (ADS)
Palumbo, Giandomenico; Catenacci, Roberto; Marzuoli, Annalisa
2014-01-01
Dirac fermions have a central role in high energy physics but it is well-known that they emerge also as quasiparticles in several condensed matter systems supporting topological order. We present a general method for deriving the topological effective actions of (3+1)-massless Dirac fermions living on general backgrounds and coupled with vector and axial-vector gauge fields. The first step of our strategy is standard (in the Hermitian case) and consists in connecting the determinants of Dirac operators with the corresponding analytical indices through the zeta-function regularization. Then, we introduce a suitable splitting of the heat kernel that naturally selects the purely topological part of the determinant (i.e., the topological effective action). This topological effective action is expressed in terms of gauge fields using the Atiyah-Singer index theorem which computes the analytical index in topological terms. The main new result of this paper is to provide a consistent extension of this method to the non-Hermitian case, where a well-defined determinant does not exist. Quantum systems supporting relativistic fermions can thus be topologically classified on the basis of their response to the presence of (external or emergent) gauge fields through the corresponding topological effective field theories (TEFTs).
Conformal versus confining scenario in SU(2) with adjoint fermions
Del Debbio, L.; Pica, C.; Lucini, B.; Patella, A.; Rago, A.
2009-10-01
The masses of the lowest-lying states in the meson and in the gluonic sector of an SU(2) gauge theory with two Dirac flavors in the adjoint representation are measured on the lattice at a fixed value of the lattice coupling {beta}=4/g{sub 0}{sup 2}=2.25 for values of the bare fermion mass m{sub 0} that span a range between the quenched regime and the massless limit, and for various lattice volumes. Even for light constituent fermions the lightest glueballs are found to be lighter than the lightest mesons. Moreover, the string tension between two static fundamental sources strongly depends on the mass of the dynamical fermions and becomes of the order of the inverse squared lattice linear size before the chiral limit is reached. The implications of these findings for the phase of the theory in the massless limit are discussed and a strategy for discriminating between the (near-)conformal and the confining scenario is outlined.
ERIC Educational Resources Information Center
Elkins, Aaron J.
1977-01-01
The author questions the extent to which educators have relied on "relevance" and learner participation in objective-setting in the past decade. He describes a useful approach to learner-oriented evaluation in which content relevance was not judged by participants until after they had been exposed to it. (MF)
Two-dimensional Confinement of Heavy Fermions in Artificial Superlattices
NASA Astrophysics Data System (ADS)
Shishido, Hiroaki
2011-03-01
Low dimensionality and strong electron-electron Coulomb interactions are both key parameters for novel quantum states of condensed matter. A metallic system with the strongest electron correlations is reported in rare-earth and actinide compounds with f electrons, known as heavy-fermion compounds, where the effective mass of the conduction electrons are strikingly enhanced by the electron correlations up to some hundreds times the free electron mass. To date the electronic structure of all heavy-fermion compounds is essentially three-dimensional. We realized experimentally a two-dimensional heavy fermion system, adjusting the dimensionality in a controllable fashion. We grew artificial superlattices of CeIn 3 (m)/ LaIn 3 (n), in which m -layers of heavy-fermion antiferromagnet CeIn 3 and n -layers of a non-magnetic isostructual compound LaIn 3 are stacked alternately, by a molecular beam epitaxy. By reducing the thickness of the CeIn 3 layers, the magnetic order was suppressed and the effective electron mass was further enhanced. The Néel temperature becomes zero at around m = 2 , concomitant with striking deviations from the standard Fermi liquid low-temperature electronic properties. Standard Fermi liquid behaviors are, however, recovered under high magnetic field. These behaviors imply new ``dimensional tuning'' towards a quantum critical point. We also succeeded to fabricate artificial superlattices of a heavy fermion superconductor CeCoIn 5 and non-magnetic divalent Yb-compound YbCoIn 5 . Superconductivity survives even in CeCoIn 5 (3)/ YbCoIn 5 (5) films, while the thickness of CeCoIn 5 layer, 2.3 nm, is comparable to the c -axis coherence length ξc ~ 2 nm. This work has been done in collaboration with Y. Mizukami, S. Yasumoto, M. Shimozawa, H. Kontani, T. Shibauchi, T. Terashima and Y. Matsuda.superconductivity is realized in the artificial superlattices. This work has been done in collaboration with Y. Mizukami, S. Yasumoto, M. Shimozawa, H. Kontani, T
Heavy fermions: From nodal metals to super-spins
NASA Astrophysics Data System (ADS)
Ramires Neves de Oliveira, Aline
Condensed matter physics is an area of research which lies at a sweet spot between two complementary perspectives: the atomistic point of view which takes into account all the details of the system of interest; and the framework of universality and emergent phenomena, which allows us to make drastic simplifications to the microscopic description of materials while still being able to explain much of the experimentally observed phenomena. This thesis addresses problems from both perspectives, focusing on heavy fermion systems. Heavy fermion systems are prototype materials for the study of strongly correlations and quantum criticality. Theoretical understanding of these systems is important for the design of new materials and for the fundamental understanding of quantum critical phenomena. This thesis is strongly motivated by recent experiments in an intrinsically quantum critical material, beta-YbAlB 4. This system shows anomalous critical exponents in transport and thermodynamics. In Chapter 2 we construct a phenomenological theory for the heavy fermion metal beta-YbAlB4 based on the Anderson model, taking into account the peculiarities of this specific material. We analyze the consequences of a non-trivial, momentum-dependent, hybridization matrix between f-electrons and conduction electrons, which gives rise to a nodal metal with unusual dispersion and singular thermodynamic properties, in accordance with experiments. In Chapter 3 we analyze the Electron Spin Resonance experiments in this same material and propose a theory including spin-orbit coupling, crystal electric fields and hyperfine coupling which can account for many of the features of the experimentally observed signal. Within a broader perspective on heavy fermion systems, the absence of a single unified theoretical description which can account for the plethora of phenomena observed in this class of materials also motivates us to consider new theoretical approaches. In Chapter 4 we generalize the
SETS. Set Equation Transformation System
Worrel, R.B.
1992-01-13
SETS is used for symbolic manipulation of Boolean equations, particularly the reduction of equations by the application of Boolean identities. It is a flexible and efficient tool for performing probabilistic risk analysis (PRA), vital area analysis, and common cause analysis. The equation manipulation capabilities of SETS can also be used to analyze noncoherent fault trees and determine prime implicants of Boolean functions, to verify circuit design implementation, to determine minimum cost fire protection requirements for nuclear reactor plants, to obtain solutions to combinatorial optimization problems with Boolean constraints, and to determine the susceptibility of a facility to unauthorized access through nullification of sensors in its protection system.
ERIC Educational Resources Information Center
Blystone, Robert V.; Blodgett, Kevin
2006-01-01
The scientific method is the principal methodology by which biological knowledge is gained and disseminated. As fundamental as the scientific method may be, its historical development is poorly understood, its definition is variable, and its deployment is uneven. Scientific progress may occur without the strictures imposed by the formal…
Code of Federal Regulations, 2010 CFR
2010-01-01
... 3 The President 1 2010-01-01 2010-01-01 false Scientific Integrity Presidential Documents Other Presidential Documents Memorandum of March 9, 2009 Scientific Integrity Memorandum for the Heads of Executive Departments and Agencies Science and the scientific process must inform and guide decisions of my Administration on a wide range of...
Redefining the "Scientific Method".
ERIC Educational Resources Information Center
Spiece, Kelly R.; Colosi, Joseph
2000-01-01
Surveys 15 introductory biology textbooks for their presentation of the scientific method. Teaching the scientific method involves more than simplified steps and subjectivity--human politics, cultural influences, and chance are all a part of science. Presents an activity for students to experience the scientific method. (Contains 34 references.)…
NASA Astrophysics Data System (ADS)
Kaczorowski, D.; Pikul, A. P.; Gnida, D.; Tran, V. H.
2009-07-01
Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The compound was found to be a heavy fermion clean-limit superconductor with Tc=0.68K. Most remarkably, the superconductivity in this system emerges out of the antiferromagnetic state that sets in at TN=10K, and both cooperative phenomena coexist in a bulk at ambient pressure conditions.
Kaczorowski, D; Pikul, A P; Gnida, D; Tran, V H
2009-07-10
Single crystals of Ce2PdIn8 were studied by means of magnetic susceptibility, electrical resistivity, and specific heat measurements. The compound was found to be a heavy fermion clean-limit superconductor with Tc=0.68 K. Most remarkably, the superconductivity in this system emerges out of the antiferromagnetic state that sets in at TN=10 K, and both cooperative phenomena coexist in a bulk at ambient pressure conditions. PMID:19659236
Chain of Majorana states from superconducting Dirac fermions at a magnetic domain wall.
Neupert, Titus; Onoda, Shigeki; Furusaki, Akira
2010-11-12
We study theoretically a strongly type-II s-wave superconducting state of two-dimensional Dirac fermions in proximity to a ferromagnet having in-plane magnetization. It is shown that a magnetic domain wall can host a chain of equally spaced vortices in the superconducting order parameter, each of which binds a Majorana-fermion state. The overlap integral of neighboring Majorana states is sensitive to the position of the chemical potential of the Dirac fermions. Thermal transport and scanning tunneling microscopy experiments to probe the Majorana fermions are discussed. PMID:21231252
Vantournhout, Klaas; Jachowicz, Natalie; Ryckebusch, Jan
2011-09-15
We present a method that offers perspectives to perform fully antisymmetrized simulations for inhomogeneous bulk fermion matter. The technique bears resemblance to classical periodic boundary conditions, using localized single-particle states. Such localized states are an ideal tool to discuss phenomena where spatial localization plays an important role. The antisymmetrization is obtained introducing a doubly periodic structure in the many-body fermion wave functions. This results in circulant matrices for the evaluation of expectation values, leading to a computationally tractable formalism to study fully antisymmetrized bulk fermion matter. We show that the proposed technique is able to reproduce essential fermion features in an elegant and computationally advantageous manner.
A four-dimensional model with the fermionic determinant exactly evaluated
NASA Astrophysics Data System (ADS)
Mignaco, J. A.; Rego Monteiro, M. A.
1986-07-01
A method is presented to compute the fermion determinant of some class of field theories. By this method the following results of the fermion determinant in two dimensions are easily recovered: (i) Schwinger model without reference to a particular gauge. (ii) QCD in the light-cone gauge. (iii) Gauge invariant result of QCD. The method is finally applied to give an analytical solution of the fermion determinant of a four-dimensional, non-abelian, Dirac-like theory with massless fermions interacting with an external vector field through a pseudo-vectorial coupling. Fellow of the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq), Brazil.
NASA Astrophysics Data System (ADS)
Van Horne, Katie
This dissertation investigates the implementation issues and the educational opportunities associated with "taking the practice turn" in science education. This pedagogical shift focuses instructional experiences on engaging students in the epistemic practices of science both to learn the core ideas of the disciplines, as well as to gain an understanding of and personal connection to the scientific enterprise. In Chapter 2, I examine the teacher-researcher co-design collaboration that supported the classroom implementation of a year-long, project-based biology curriculum that was under development. This study explores the dilemmas that arose when teachers implemented a new intervention and how the dilemmas arose and were managed throughout the collaboration of researchers and teachers and between the teachers. In the design-based research of Chapter 3, I demonstrate how students' engagement in epistemic practices in contemporary science investigations supported their conceptual development about genetics. The analysis shows how this involved a complex interaction between the scientific, school and community practices in students' lives and how through varied participation in the practices students come to write about and recognize how contemporary investigations can give them leverage for science-based action outside of the school setting. Finally, Chapter 4 explores the characteristics of learning environments for supporting the development of scientific practice-linked identities. Specific features of the learning environment---access to the intellectual work of the domain, authentic roles and accountability, space to make meaningful contributions in relation to personal interests, and practice-linked identity resources that arose from interactions in the learning setting---supported learners in stabilizing practice-linked science identities through their engagement in contemporary scientific practices. This set of studies shows that providing students with the
Pati, Jogesh C.
2002-05-10
It is noted that one is now in possession of a set of facts, which may be viewed as the matching pieces of a puzzle; in that all of them can be resolved by just one idea--that is grand unification. These include (i) the observed family-structure, (ii) quantization of electric charge, (iii) the meeting of the three gauge couplings, (iv) neutrino oscillations [in particular the value {Delta}m{sup 2}({nu}{sub {mu}}-{nu}{sub {tau}}), suggested by SuperK], (v) the intricate pattern of the masses and mixings of the fermions, including the smallness of V{sub cb} and the largeness of {theta}{sub {nu}{sub {mu}}{nu}{sub {tau}}}{sup osc}, and (vi) the need for B-L as a generator to implement baryogenesis (via leptogenesis). All these pieces fit beautifully together within a single puzzle board framed by supersymmetric unification, based on either SO(10) or a string-unified G(224)-symmetry. The two notable pieces of the puzzle still missing, however, are proton decay and supersymmetry. A concrete proposal is presented within a predictive SO(10)/G(224)-framework that successfully describes the masses and mixings of all fermions, including the neutrinos--with eight predictions, all in agreement with observation. Within this framework, a systematic study of proton decay is carried out, which (a) pays special attention to its dependence on the fermion masses, and (b) limits the threshold corrections so as to preserve natural coupling unification. The study updates prior work by Babu, Pati and Wilczek, in the context of both MSSM and its (interesting) variant, the so-called ESSM, by allowing for improved values of the matrix elements and of the short- and long-distance renormalization effects. It shows that a conservative upper limit on the proton lifetime is about (1/3-2) x 10{sup 34} years, with {bar {nu}}K{sup +} being the dominant decay mode, and quite possibly {mu}{sup +}K{sup 0} and e{sup +}{pi}{sup 0} being prominent. This in turn strongly suggests that an improvement in the
The Scientific Papers of James Prescott Joule 2 Volume Set
NASA Astrophysics Data System (ADS)
Prescott Joule, James
2011-03-01
Volume 1: Description of an electro-magnetic engine; Description of an electro-magnetic engine, with experiments; On the use of electro-magnets made of iron wire for the electro-magnetic engine; Investigations in magnetism and electro-magnetism; Investigations in magnetism and electro-magnetism; Description of an electro-magnetic engine; On electro-magnetic forces; On electro-magnetic forces; On electro-magnetic forces; Description of a new electro-magnet; On a new class of magnetic forces; On voltaic apparatus; On the production of heat by voltaic electricity; On the heat evolved by metallic conductors of electricity, and in the cells of a battery during electrolysis; On the electric origin of the heat of combustion; On the electrical origin of chemical heat; On Sir G. C. Haughton's experiments; On the heat evolved during the electrolysis of water; On the calorific effects of magneto-electricity, and on the mechanical value of heat; On the intermittent character of the voltaic current in certain cases of electrolysis; and on the intensities of various voltaic arrangements; On the changes of temperature produced by the rarefaction and condensation of air; On specific heat; On a new method for ascertaining the specific heat of bodies; Note on the employment of electrical currents for ascertaining the specific heat of bodies; On the mechanical equivalent of heat; On the existence of an equivalent relation between heat and the ordinary forms of mechanical power; On the heat disengaged in chemical combinations; On the effects of magnetism upon the dimensions of iron and steel bars; On matter, living force, and heat; On the mechanical equivalent of heat, as determined from the heat evolved by the function of fluids; On the theoretical velocity of sound; Expériences sur l'identité entre le calorique et la force méchanique. Détermination de l'équivalent par la chaleur dégagée pendant la friction du mercure; On shooting-stars; On the mechanical equivalent of heat, and on the constitution of elastic fluids; Some remarks on heat and the constitution of elastic fluids; On the mechanical equivalent of heat; On a remarkable appearance of lightning; On some amalgams; On the air-engine; Account of experiments with a powerful electro-magnet; On the economical production of mechanical effect from chemical forces; An account of some experiments with a large electro-magnet; Introductory research on the induction of magnetism by electric currents; On the fusion of metals by voltaic electricity; Note on Dalton's determination of the expansion of air by heat; On the utilization of the sewage of London and other large towns; Notice of experiments on the heat developed by friction in air; On the intensity of light during the recent solar eclipse; On an improved galvanometer; On the thermo-electricity of ferruginous metals, and on the thermal effects of stretching solid bodies; On the thermal effects of longitudinal compression of solids, with an investigation on the alterations of temperature accompanying changes of pressure in fluids; On some thermo-dynamic properties of solids; On the thermal effects of compressing fluids; On a method of testing the strength of steam-boilers; Experiments on the total heat of steam; Experiments on the passage of air through pipes and apertures in thin plates; On some amalgams; On the probable cause of electric storms; On the surface-condensation of steam; Notice of a compressing air-pump; Note on a mirage at Douglas; On a sensitive barometer; On a sensitive thermometer; Note on the meteor of February 6th, 1818; On a method of hardening steel wires for magnetic needles; On an instrument for showing rapid changes in magnetic declination; Determination of the dynamical equivalent of heat from the thermal effects of electric currents; Observations on the alteration of the freezing-point in thermometers; On a new
Scientific dishonesty and good scientific practice.
Andersen, D; Axelsen, N H; Riis, P
1993-04-01
Scientific dishonesty has been the subject of much public interest in recent years. Although the problem has had a low profile in Denmark, there is no reason to believe that it is non-existent. Several preconditions known to be important prevail here as well as in other countries, such as pressure to publish and severe competition for research grants and senior academic positions. The Danish Medical Research Council (DMRC) decided to respond to this problem by preparing a report on scientific dishonesty with suggestions to the research institutions on rules for good scientific practice and procedures for investigation of suspected dishonesty. To this end, an investigatory system was suggested. The system should consist of two regional committees and one national committee. They should be headed by high court judges and experienced health sciences researchers as members. The committees will investigate cases reported to them and conclude on whether dishonesty has been established and on whether the scientific work should be retracted. Sanctions shall remain the task of the institutions. Preventive measures comprise open access to and a long storage period for scientific data. PMID:8495601
Fermion pseudogap from fluctuations of an order parameter
NASA Astrophysics Data System (ADS)
Tchernyshyov, Oleg Vladimirovich
Pseudogap behavior, observed in cuprate superconductors and Peierls chains, is studied using various phenomenological approaches. (1) A work of M. V. Sadovskii on Peierls chains with Gaussian fluctuations of the order parameter is revisited. A more transparent diagrammatic method is given and a serious error is pointed out. The method is applied to a recent work of J. Schmalian, B. Stojkovic and D. Pines on "hot spots". It is shown that, while their model is not affected by Sadovskii's mistake, it predicts no pseudogap in the local density of states. (2) A simple analytical treatment based on the self-consistent t-matrix approach is suggested to describe Cooper pair fluctuations deeply in the pseudogap regime. It is argued that a pronounced depletion of the fermion density of states by the pseudogap suppresses the decay of pairing fluctuations, giving them a propagating, rather than diffusing, nature. In view of an approximate particle-hole symmetry at the Fermi surface, both electron pairs and hole pairs should exist in the pseudogap regime, in addition to gapped fermions. Near 2 dimensions, the condensation temperature of these pairs is linearly proportional to the fermion density (the Uemura scaling). (3) A work of J. R. Schrieffer and A. R. Kampf on the crossover between an antiferromagnetic (AFM) insulator and a Fermi liquid is complemented by an exactly solvable toy model with all essential features intact. Based on that solution, the three bands of Schrieffer and Kampf are reinterpreted as just two AFM bands with a gap slowly varying in time or across the sample.
Majorana fermions in semiconductor nanowires: fundamentals, modeling, and experiment.
Stanescu, T D; Tewari, S
2013-06-12
After a recent series of rapid and exciting developments, the long search for the Majorana fermion-the elusive quantum entity at the border between particles and antiparticles-has produced the first positive experimental results, but is not over yet. Originally proposed by E Majorana in the context of particle physics, Majorana fermions have a condensed matter analogue in the zero-energy bound states emerging in topological superconductors. A promising route to engineering topological superconductors capable of hosting Majorana zero modes consists of proximity coupling semiconductor thin films or nanowires with strong spin-orbit interaction to conventional s-wave superconductors in the presence of an external Zeeman field. The Majorana zero mode is predicted to emerge above a certain critical Zeeman field as a zero-energy state localized near the order parameter defects, namely, vortices for thin films and wire ends for the nanowire. These Majorana bound states are expected to manifest non-Abelian quantum statistics, which makes them ideal building blocks for fault-tolerant topological quantum computation. This review provides an update on the current status of the search for Majorana fermions in semiconductor nanowires by focusing on the recent developments, in particular the period following the first reports of experimental signatures consistent with the realization of Majorana bound states in semiconductor nanowire-superconductor hybrid structures. We start with a discussion of the fundamental aspects of the subject, followed by considerations on the realistic modeling, which is a critical bridge between theoretical predictions based on idealized conditions and the real world, as probed experimentally. The last part is dedicated to a few intriguing issues that were brought to the fore by the recent encouraging experimental advances. PMID:23665894
Fermion particle production in semiclassical Boltzmann-Vlasov transport theory
Dawson, John F.; Mihaila, Bogdan; Cooper, Fred
2009-07-01
We present numerical solutions of the semiclassical Boltzmann-Vlasov equation for fermion particle-antiparticle production by strong electric fields in boost-invariant coordinates in (1+1) and (3+1) dimensional QED. We compare the Boltzmann-Vlasov results with those of recent quantum field theory calculations and find good agreement. We conclude that extending the Boltzmann-Vlasov approach to the case of QCD should allow us to do a thorough investigation of how backreaction affects recent results on the dependence of the transverse momentum distribution of quarks and antiquarks on a second Casimir invariant of color SU(3)
Advances on tensor network theory: symmetries, fermions, entanglement, and holography
NASA Astrophysics Data System (ADS)
Orús, Román
2014-11-01
This is a short review on selected theory developments on tensor network (TN) states for strongly correlated systems. Specifically, we briefly review the effect of symmetries in TN states, fermionic TNs, the calculation of entanglement Hamiltonians from projected entangled pair states (PEPS), and the relation between the multi-scale entanglement renormalization ansatz (MERA) and the AdS/CFT or gauge/gravity duality. We stress the role played by entanglement in the emergence of several physical properties and objects through the TN language. Some recent results along these lines are also discussed.
Compact Multigluonic Scattering Amplitudes with Heavy Scalars and Fermions
Ferrario, Paola; Rodrigo, German; Talavera, Pere
2006-05-12
Combining the Berends-Giele and on-shell recursion relations we obtain an extremely compact expression for the scattering amplitude of a complex massive scalar-antiscalar pair and an arbitrary number of positive helicity gluons. This is one of the basic building blocks for constructing other helicity configurations from recursion relations. We also show explicitly that the scattering amplitude of massive fermions to gluons, all with positive helicity, is proportional to the scalar one, confirming in this way the recently advocated SUSY-like Ward identities relating both amplitudes.
Global surpluses of spin-base invariant fermions
NASA Astrophysics Data System (ADS)
Gies, Holger; Lippoldt, Stefan
2015-04-01
The spin-base invariant formalism of Dirac fermions in curved space maintains the essential symmetries of general covariance as well as similarity transformations of the Clifford algebra. We emphasize the advantages of the spin-base invariant formalism both from a conceptual as well as from a practical viewpoint. This suggests that local spin-base invariance should be added to the list of (effective) properties of (quantum) gravity theories. We find support for this viewpoint by the explicit construction of a global realization of the Clifford algebra on a 2-sphere which is impossible in the spin-base non-invariant vielbein formalism.