Showing papers on "Symmetry (physics) published in 2009"
TL;DR: DAMMIF, an enhanced and significantly faster implementation of the ab-initio shape-determination program DAMMIN for small-angle scattering data, is presented.
Abstract: DAMMIF, a revised implementation of the ab-initio shape-determination program DAMMIN for small-angle scattering data, is presented. The program was fully rewritten, and its algorithm was optimized for speed of execution and modified to avoid limitations due to the finite search volume. Symmetry and anisometry constraints can be imposed on the particle shape, similar to DAMMIN. In equivalent conditions, DAMMIF is 25–40 times faster than DAMMIN on a single CPU. The possibility to utilize multiple CPUs is added to DAMMIF. The application is available in binary form for major platforms.
1,482 citations
TL;DR: In this paper, the density dependence of the symmetry energy at subnormal density was analyzed and the results from the present work were compared to constraints put forward in other recent analyses, where the results of the calculations reproduce isospin diffusion data from two different observables and the ratios of neutron and proton spectra.
Abstract: Collisions involving $^{112}\mathrm{Sn}$ and $^{124}\mathrm{Sn}$ nuclei have been simulated with the improved quantum molecular dynamics transport model. The results of the calculations reproduce isospin diffusion data from two different observables and the ratios of neutron and proton spectra. By comparing these data to calculations performed over a range of symmetry energies at saturation density and different representations of the density dependence of the symmetry energy, constraints on the density dependence of the symmetry energy at subnormal density are obtained. The results from the present work are compared to constraints put forward in other recent analyses.
483 citations
TL;DR: In this paper, the authors consider holographic superconductors whose bulk description consists of gravity minimally coupled to a Maxwell field and a charged scalar field with general potential, and they give an analytic argument that there is no ''hard gap'': the real part of the conductivity at low frequency remains nonzero (although typically exponentially small).
Abstract: We consider holographic superconductors whose bulk description consists of gravity minimally coupled to a Maxwell field and charged scalar field with general potential. We give an analytic argument that there is no ``hard gap'': the real part of the conductivity at low frequency remains nonzero (although typically exponentially small) even at zero temperature. We also numerically construct the gravitational dual of the ground state of some holographic superconductors. Depending on the charge and dimension of the condensate, the infrared theory can have emergent conformal or just Poincare symmetry. In all cases studied, the area of the horizon of the dual black hole goes to zero in the extremal limit, consistent with a nondegenerate ground state.
420 citations
TL;DR: Gapped phases of noninteracting fermions, with and without charge conservation and time-reversal symmetry, are classified using Bott periodicity as mentioned in this paper, which is robust with respect to disorder, provided electron states near the Fermi energy are absent or localized.
Abstract: Gapped phases of noninteracting fermions, with and without charge conservation and time-reversal symmetry, are classified using Bott periodicity. The symmetry and spatial dimension determines a general universality class, which corresponds to one of the 2 types of complex and 8 types of real Clifford algebras. The phases within a given class are further characterized by a topological invariant, an element of some Abelian group that can be 0, Z, or Z_2. The interface between two infinite phases with different topological numbers must carry some gapless mode. Topological properties of finite systems are described in terms of K-homology. This classification is robust with respect to disorder, provided electron states near the Fermi energy are absent or localized. In some cases (e.g., integer quantum Hall systems) the K-theoretic classification is stable to interactions, but a counterexample is also given.
398 citations
TL;DR: In this article, the authors consider holographic superconductors whose bulk description consists of gravity minimally coupled to a Maxwell field and a charged scalar field with general potential, and they give an analytic argument that there is no "hard gap": the real part of the conductivity at low frequency remains nonzero (although typically exponentially small).
Abstract: We consider holographic superconductors whose bulk description consists of gravity minimally coupled to a Maxwell field and charged scalar field with general potential. We give an analytic argument that there is no "hard gap": the real part of the conductivity at low frequency remains nonzero (although typically exponentially small) even at zero temperature. We also numerically construct the gravitational dual of the ground state of some holographic superconductors. Depending on the charge and dimension of the condensate, the infrared theory can have emergent conformal or just Poincare symmetry. In all cases studied, the area of the horizon of the dual black hole goes to zero in the extremal limit, consistent with a nondegenerate ground state.
318 citations
TL;DR: In this paper, nonlinear anomalous diffusion equations with time fractional derivatives (Riemann-Liouville and Caputo) of the order of 0-2 are considered.
Abstract: In this paper, nonlinear anomalous diffusion equations with time fractional derivatives (Riemann–Liouville and Caputo) of the order of 0–2 are considered. Lie point symmetries of these equations are investigated and compared. Examples of using the obtained symmetries for constructing exact solutions of the equations under consideration are presented.
250 citations
TL;DR: A new full-scale, three-dimensional quantitative model has been developed for crossed-beam energy transfer, allowing calculations of the propagation and coupling of multiple laser beams and their associated plasma waves in ignition hohlraums.
Abstract: Radiative hydrodynamics simulations of ignition experiments show that energy transfer between crossing laser beams allows tuning of the implosion symmetry. A new full-scale, three-dimensional quantitative model has been developed for crossed-beam energy transfer, allowing calculations of the propagation and coupling of multiple laser beams and their associated plasma waves in ignition hohlraums. This model has been implemented in a radiative-hydrodynamics code, demonstrating control of the implosion symmetry by a wavelength separation between cones of laser beams.
237 citations
TL;DR: In this paper, the expectation values of supersymmetric Wilson loops in Chern-Simons theories with matter were computed using localization techniques, and the pathintegral reduces to a non-Gaussian matrix model.
Abstract: We use localization techniques to compute the expectation values of supersymmetric Wilson loops in Chern-Simons theories with matter. We find the path-integral reduces to a non-Gaussian matrix model. The Wilson loops we consider preserve a single complex supersymmetry, and exist in any N=2 theory, though the localization requires superconformal symmetry. We present explicit results for the cases of pure Chern-Simons theory with gauge group U(N), showing agreement with the known results, and ABJM, showing agreement with perturbative calculations. Our method applies to other theories, such as Gaiotto-Witten theories, BLG, and their variants.
206 citations
TL;DR: In this article, the authors investigate the possibility of using icosahedral symmetry as a family symmetry group in the lepton sector, and present a basic toolbox for model building using ICs, including representation matrices and tensor product rules.
Abstract: We investigate the possibility of using icosahedral symmetry as a family symmetry group in the lepton sector. The rotational icosahedral group, which is isomorphic to A{sub 5}, the alternating group of five elements, provides a natural context in which to explore (among other possibilities) the intriguing hypothesis that the solar neutrino mixing angle is governed by the golden ratio, {phi}=(1+{radical}(5))/2. We present a basic toolbox for model building using icosahedral symmetry, including explicit representation matrices and tensor product rules. As a simple application, we construct a minimal model at tree level in which the solar angle is related to the golden ratio, the atmospheric angle is maximal, and the reactor angle vanishes to leading order. The approach provides a rich setting in which to investigate the flavor puzzle of the standard model.
201 citations
TL;DR: In this paper, the Hohenberg-Kohn energy functional was used to construct isoscalar and isovector densities for a half-infinite particle-stable nuclear-matter.
189 citations
Journal Article•
TL;DR: In this article, the pairing symmetry of a two-orbital J1-J2 model for FeAs layers in oxypnictides was studied, and it was shown that the mixture of an intraorbital unconventional s-x;{2}y,{2}} approximately cos(k_{x})cos(k-y}) pairing symmetry was favored for J2>J1.
Abstract: We study the pairing symmetry of a two-orbital J1-J2 model for FeAs layers in oxypnictides. We show that the mixture of an intraorbital unconventional s_{x;{2}y;{2}} approximately cos(k_{x})cos(k_{y}) pairing symmetry, which changes sign between the electron and hole Fermi surfaces, and a very small d_{x;{2}-y;{2}} approximately cos(k_{x})-cos(k_{y}) component is favored in a large part of the J1-J2 phase diagram. A pure s_{x;{2}y;{2}} pairing state is favored for J2>J1. The signs of the d_{x;{2}-y;{2}} order parameters in the two different orbitals are opposite. While a small d_{xy} approximately sin(k_{x})sin(k_{y}) interorbital pairing coexists in the above phases, the intraorbital d_{xy} pairing is not favored even for large J2.
TL;DR: An automated procedure for calculating second-order elastic constants for crystalline systems of any symmetry using the CRYSTAL program is described and a set of test cases covering many of the crystal classes is used to document the numerical accuracy of the scheme.
CERN1
TL;DR: In this article, a see-saw A4 model for tri-bimaximal mixing is presented, which is based on a very economical flavour symmetry and field content and still possesses all the good features of A4 models, in particular the charged lepton mass hierarchies are determined by the A4 × Z4 flavour symmetry itself without invoking a Froggatt-Nielsen U(1) symmetry.
Abstract: We present a see-saw A4 model for Tri-Bimaximal mixing which is based on a very economical flavour symmetry and field content and still possesses all the good features of A4 models. In particular the charged lepton mass hierarchies are determined by the A4 × Z4 flavour symmetry itself without invoking a Froggatt–Nielsen U(1) symmetry. Tri-Bimaximal mixing is exact in leading order while all the mixing angles receive corrections of the same order in next-to-leading approximation. As a consequence the predicted value of θ13 is within the sensitivity of the experiments which will take data in the near future. The light neutrino spectrum, typical of A4 see-saw models, with its phenomenological implications, also including leptoproduction, is studied in detail.
TL;DR: In this article, it was shown that lepton lepton tribimaximal mixing can be realized in different ways and for each one the superpotential that leads to the correct breaking of the flavor symmetry was discussed.
Abstract: Group theoretical arguments seem to indicate the discrete symmetry ${S}_{4}$ as the minimal flavor symmetry compatible with tribimaximal neutrino mixing. We prove in a model-independent way that indeed ${S}_{4}$ can realize exact tribimaximal mixing through different symmetry breaking patterns. We present two models in which lepton tribimaximal mixing is realized in different ways and for each one we discuss the superpotential that leads to the correct breaking of the flavor symmetry.
TL;DR: In this article, the electroweak and flavour structure of a model with a warped extra dimension and the bulk gauge group SU(3)c × SU(2)L × SU (2)R × PLR × U(1)X were presented.
Abstract: We present the electroweak and flavour structure of a model with a warped extra dimension and the bulk gauge group SU(3)c × SU(2)L × SU(2)R × PLR × U(1)X. The presence of SU(2)R implies an unbroken custodial symmetry in the Higgs system allowing to eliminate large contributions to the T parameter, whereas the PLR symmetry and the enlarged fermion representations provide a custodial symmetry for flavour diagonal and flavour changing couplings of the SM Z boson to left-handed down-type quarks. We diagonalise analytically the mass matrices of charged and neutral gauge bosons including the first KK modes. We present the mass matrices for quarks including heavy KK modes and discuss the neutral and charged currents involving light and heavy fields. We give the corresponding complete set of Feynman rules in the unitary gauge.
TL;DR: In this article, a correlation between the density derivative of the nuclear symmetry energy at saturation and the ratio of the bulk symmetry energy $J$ to the so-called surface stiffness coefficient $Q$ has in the droplet model a prominent role in driving the size of neutron skins.
Abstract: We analyze the neutron skin thickness in finite nuclei with the droplet model and effective nuclear interactions. The ratio of the bulk symmetry energy $J$ to the so-called surface stiffness coefficient $Q$ has in the droplet model a prominent role in driving the size of neutron skins. We present a correlation between the density derivative of the nuclear symmetry energy at saturation and the $J/Q$ ratio. We emphasize the role of the surface widths of the neutron and proton density profiles in the calculation of the neutron skin thickness when one uses realistic mean-field effective interactions. Next, taking as experimental baseline the neutron skin sizes measured in 26 antiprotonic atoms along the mass table, we explore constraints arising from neutron skins on the value of the $J/Q$ ratio. The results favor a relatively soft symmetry energy at subsaturation densities. Our predictions are compared with the recent constraints derived from other experimental observables. Though the various extractions predict different ranges of values, one finds a narrow window $L~45\text{\ensuremath{-}}75$ MeV for the coefficient $L$ that characterizes the density derivative of the symmetry energy that is compatible with all the different empirical indications.
TL;DR: In toroidal plasmas, the symmetry along a magnetic field line usually constrains the radial flux of parallel momentum to zero in the absence of background flows but by breaking the up-down symmetry of the toroidal currents this constraint can be relaxed.
Abstract: The symmetry of a physical system strongly impacts on its properties. In toroidal plasmas, the symmetry along a magnetic field line usually constrains the radial flux of parallel momentum to zero in the absence of background flows. By breaking the up-down symmetry of the toroidal currents, this constraint can be relaxed. The parallel asymmetry in the magnetic configuration then leads to an incomplete cancellation of the turbulent momentum flux across a flux surface. The magnitude of the subsequent toroidal rotation increases with the up-down asymmetry and its sign depends on the direction of the toroidal magnetic field and plasma current. Such a mechanism offers new insights in the interpretation and control of the intrinsic toroidal rotation in present day experiments.
TL;DR: In this article, the authors study viscous hydrodynamics of hot conformal field theory plasma with multiple/non-Abelian symmetries in the framework of AdS/CFT correspondence, using a recently proposed method of directly solving bulk gravity in derivative expansion of local plasma parameters.
Abstract: We study viscous hydrodynamics of hot conformal field theory plasma with multiple/non-Abelian symmetries in the framework of AdS/CFT correspondence, using a recently proposed method of directly solving bulk gravity in derivative expansion of local plasma parameters. Our motivation is to better describe the real QCD plasma produced at RHIC, incorporating its U(1)Nf flavor symmetry as well as SU(2)I non-Abelian iso-spin symmetry. As concrete examples, we choose to study the STU model for multiple U(1)3 symmetries, which is a sub-sector of 5D N=4 gauged SUGRA dual to N=4 Super Yang-Mills theory, capturing Cartan U(1)3 dynamics inside the full R-symmetry. For SU(2), we analyze the minimal 4D N=3 gauged SUGRA whose bosonic action is simply an Einstein-Yang-Mills system, which corresponds to SU(2) R-symmetry dynamics on M2-branes at a Hyper-Kahler cone. By generalizing the bosonic action to arbitrary dimensions and Lie groups, we present our analysis and results for any non-Abelian plasma in arbitrary dimensions.
TL;DR: In this paper, the Bianchi identities of the Lagrangians were used to recover the local metric-like unconstrained Lagrangian and field equations for higher spin gauge fields of mixed symmetry in flat space.
TL;DR: In this article, a scalar field with a Liouville potential coupled to a Maxwell field is analyzed in arbitrary dimensions and in the presence of a scalars field with LiouVILLE potential coupled with a constant curvature.
Abstract: We find and analyze solutions of Einstein's equations in arbitrary dimensions and in the presence of a scalar field with a Liouville potential coupled to a Maxwell field. We consider spacetimes of cylindrical symmetry or again subspaces of dimension $d\ensuremath{-}2$ with constant curvature and analyze in detail the field equations and manifest their symmetries. The field equations of the full system are shown to reduce to a single or couple of ordinary differential equations, which can be used to solve analytically or numerically the theory for the symmetry at hand. Further solutions can also be generated by a solution-generating technique akin to the electromagnetic duality in the absence of a cosmological constant. We then find and analyze explicit solutions including black holes and gravitating solitons for the case of four-dimensional relativity and the higher-dimensional oxidized five-dimensional spacetime. The general solution is obtained for a certain relation between couplings in the case of cylindrical symmetry.
TL;DR: In this article, four-dimensional N = 2 superconformal quiver gauge theories with alternating SO and USp gauge groups were constructed as compactifications of the six-dimensional D_N theory with defects, which can be used to analyze infinitely strongly coupled limits and S-dualities of such theories.
Abstract: We realize four-dimensional N=2 superconformal quiver gauge theories with alternating SO and USp gauge groups as compactifications of the six-dimensional D_N theory with defects. The construction can be used to analyze infinitely strongly-coupled limits and S-dualities of such gauge theories, resulting in a new class of isolated four-dimensional N=2 superconformal field theories with SO(2N)^3 flavor symmetry.
TL;DR: In this article, the stability of the axisymmetric steady wake in the framework of the global stability theory is investigated and both the direct and adjoint eigenvalue problems are solved.
Abstract: Direct numerical simulations (DNS) of the wake of a circular disk placed normal to a uniform flow show that, as the Reynolds number is increased, the flow undergoes a sequence of successive bifurcations, each state being characterized by specific time and space symmetry breaking or recovering (Fabre, Auguste & Magnaudet, Phys. Fluids, vol. 20 (5), 2008, p. 1). To explain this bifurcation scenario, we investigate the stability of the axisymmetric steady wake in the framework of the global stability theory. Both the direct and adjoint eigenvalue problems are solved. The threshold Reynolds numbers Re and characteristics of the destabilizing modes agree with the study of Natarajan & Acrivos (J. Fluid Mech., vol. 254, 1993, p. 323): the first destabilization occurs for a stationary mode of azimuthal wavenumber m = 1 at RecA = 116.9, and the second destabilization of the axisymmetric flow occurs for two oscillating modes of azimuthal wavenumbers m ± 1 at RecB = 125.3. Since these critical Reynolds numbers are close to one another, we use a multiple time scale expansion to compute analytically the leading-order equations that describe the nonlinear interaction of these three leading eigenmodes. This set of equations is given by imposing, at third order in the expansion, a Fredholm alternative to avoid any secular term. It turns out to be identical to the normal form predicted by symmetry arguments. Though, all coefficients of the normal form are here analytically computed as the scalar product of an adjoint global mode with a resonant third-order forcing term, arising from the second-order base flow modification and harmonics generation. We show that all nonlinear interactions between modes take place in the recirculation bubble, as the contribution to the scalar product of regions located outside the recirculation bubble is zero. The normal form accurately predicts the sequence of bifurcations, the associated thresholds and symmetry properties observed in the DNS calculations.
TL;DR: In this article, the Lagrange-d'Alembert principle is used to derive non-holonomic systems with symmetry, and the relationship between asymptotic dynamics and discrete symmetries of the system is also elucidated.
Abstract: This article is concerned with the theory of quasivelocities for non-holonomic systems. The equations of non-holonomic mechanics are derived using the Lagrange-d'Alembert principle written in an arbitrary configuration-dependent frame. The article also shows how quasivelocities may be used in the formulation of non-holonomic systems with symmetry. In particular, the use of quasivelocities in the analysis of symmetry that leads to unusual momentum conservation laws is investigated, as is the applications of these conservation laws and discrete symmetries to the qualitative analysis of non-holonomic dynamics. The relationship between asymptotic dynamics and discrete symmetries of the system is also elucidated.
TL;DR: In this article, the modified Newtonian dynamics (MOND) limit is shown to follow from a requirement of spacetime scale invariance of the equations of motion for nonrelativistic, purely gravitational systems.
Abstract: The modified Newtonian dynamics (MOND) limit is shown to follow from a requirement of spacetime scale invariance of the equations of motion for nonrelativistic, purely gravitational systems, i.e., invariance of the equations of motion under (t, r) → (λt, λr) in the limit a 0 → ∞. It is suggested that this should replace the definition of the MOND limit based on the low-acceleration behavior of a Newtonian-MOND interpolating function. In this way, the salient, deep-MOND results—asymptotically flat rotation curves, the mass-rotational-speed relation (baryonic Tully-Fisher relation), the Faber-Jackson relation, etc.,—follow from a symmetry principle. For example, asymptotic flatness of rotation curves reflects the fact that radii change under scaling, while velocities do not. I then comment on the interpretation of the deep-MOND limit as one of "zero mass": rest masses, whose presence obstructs scaling symmetry, become negligible compared to the "phantom," dynamical masses—those that some would attribute to dark matter. Unlike the former masses, the latter transform in a way that is consistent with the symmetry. Finally, I discuss the putative MOND-cosmology connection in light of another, previously known symmetry of the deep-MOND limit. In particular, it is suggested that MOND is related to the asymptotic de Sitter geometry of our universe. It is conjectured, for example that in an exact de Sitter cosmos, deep-MOND physics would exactly apply to local systems. I also point out, in this connection, the possible relevance of a de Sitter-conformal-field-theory (dS/CFT) duality.
TL;DR: In this article, the Noether Symmetry Approach is used to obtain general exact solutions for the cosmological equations. This result is achieved by the quintessential (phantom) potential determined by the existence of the symmetry itself.
Abstract: In the framework of phantom quintessence cosmology, we use the Noether Symmetry Approach to obtain general exact solutions for the cosmological equations. This result is achieved by the quintessential (phantom) potential determined by the existence of the symmetry itself. A comparison between the theoretical model and observations is worked out. In particular, we use type Ia supernovae and large-scale structure parameters determined from the 2-degree Field Galaxy Redshift Survey and from the Wide part of the VIMOS-VLT Deep Survey ). It turns out that the model is compatible with the presently available observational data. Moreover we extend the approach to include radiation. We show that it is compatible with data derived from recombination and it seems that quintessence do not affect nucleosynthesis results.
TL;DR: It is found that the peculiar Rashba effect is simply understood by the two-dimensional symmetry of the surface, and that this effect leads to an unconventional nonvortical Rashba spin structure at a point with time-reversal invariance.
Abstract: A peculiar Rashba effect is found at a point in the Brillouin zone, where the time-reversal symmetry is broken, though this symmetry was believed to be a necessary condition for Rashba splitting. This finding obtained experimentally by photoemission measurements on a Bi/Si(111)-(sqrt(3) x sqrt(3)) surface is fully confirmed by a first-principles theoretical calculation. We found that the peculiar Rashba effect is simply understood by the two-dimensional symmetry of the surface, and that this effect leads to an unconventional nonvortical Rashba spin structure at a point with time-reversal invariance.
TL;DR: In this article, the authors study three-dimensional systems where strong repulsion leads to an insulating state via spontaneously generated spin-orbit interactions and discuss a microscopic model where the resulting state is topological.
Abstract: We study three-dimensional systems where strong repulsion leads to an insulating state via spontaneously generated spin-orbit interactions. We discuss a microscopic model where the resulting state is topological. Such topological ``Mott'' insulators differ from their band-insulator counterparts in that they possess an additional order parameter, a rotation matrix, which describes the spontaneous breaking of spin-rotation symmetry. We show that line defects of this order are associated with protected one-dimensional modes in the strong topological Mott insulator that provides a bulk characterization of this phase. Possible physical realizations in cold-atom systems are discussed.
TL;DR: In this paper, a systematic account of supergravity theories in which the global scaling symmetry is gauged is presented, and the algebraic framework for the maximal theories in various dimensions is developed, related to "pure-spinor-like" structures for the exceptional groups.
TL;DR: In this article, a unitary meson-baryon coupled-channel model that treats the heavy pseudoscalar and vector mesons on equal footing as required by heavy-quark symmetry is proposed.
Abstract: We study charmed baryon resonances that are generated dynamically within a unitary meson-baryon coupled-channel model that treats the heavy pseudoscalar and vector mesons on equal footing as required by heavy-quark symmetry. It is an extension of recent SU(4) models with t-channel vector-meson exchanges to an SU(8) spin-flavor scheme, but differs considerably from the SU(4) approach in how the strong breaking of the flavor symmetry is implemented. Some of our dynamically generated states can be readily assigned to recently observed baryon resonances, while others do not have a straightforward identification and require the compilation of more data as well as an extension of the model to d-wave meson-baryon interactions and p-wave coupling in the neglected s- and u-channel diagrams. Of several
TL;DR: In this paper, the complex group theoretical Clebsch-Gordon coefficients were proposed as a novel origin of CP violation, which is manifest in a model based on SU ( 5 ) combined with the T ′ group as the family symmetry.