Showing papers on "Explicit symmetry breaking published in 2011"
TL;DR: The process of symmetry breaking in the presence of a small symmetry-breaking field is explored and its dependence on the rate at which the critical point is crossed is studied.
Abstract: We study symmetry breaking at the Dicke quantum phase transition by coupling a motional degree of freedom of a Bose-Einstein condensate to the field of an optical cavity. Using an optical heterodyne detection scheme, we observe symmetry breaking in real time and distinguish the two superradiant phases. We explore the process of symmetry breaking in the presence of a small symmetry-breaking field and study its dependence on the rate at which the critical point is crossed. Coherent switching between the two ordered phases is demonstrated.
359 citations
TL;DR: Chen et al. as discussed by the authors extended the classification of 1D gapped phases by considering SPT phases with combined time reversal, parity, and/or on-site unitary symmetries and also the possibility of symmetry breaking.
Abstract: Quantum phases with different orders exist with or without breaking the symmetry of the system. Recently, a classification of gapped quantum phases which do not break time reversal, parity, or on-site unitary symmetry has been given for 1D spin systems by X. Chen, Z.-C. Gu, and X.-G. Wen [Phys. Rev. B 83, 035107 (2011)]. It was found that such symmetry-protected topological (SPT) phases are labeled by the projective representations of the symmetry group which can be viewed as a symmetry fractionalization. In this paper, we extend the classification of 1D gapped phases by considering SPT phases with combined time reversal, parity, and/or on-site unitary symmetries and also the possibility of symmetry breaking. We clarify how symmetry fractionalizes with combined symmetries and also how symmetry fractionalization coexists with symmetry breaking. In this way, we obtain a complete classification of gapped quantum phases in 1D spin systems. We find that in general, symmetry fractionalization, symmetry breaking, and long-range entanglement (present in 2 or higher dimensions) represent three main mechanisms to generate a very rich set of gapped quantum phases. As an application of our classification, we study the possible SPT phases in 1D fermionic systems, which can be mapped to spin systems by Jordan-Wigner transformation.
284 citations
TL;DR: In this article, the authors discuss the physics of ABS from the viewpoint of the odd-frequency pairing, the topological bulk-edge correspondence, and the interplay of these two issues, and describe how the symmetry of the pairing and topological indices determine the absence/presence of the ZEABS, its energy dispersion, and properties as the Majorana fermions.
Abstract: Superconductivity is a phenomenon where the macroscopic quantum coherence appears due to the pairing of electrons. This offers a fascinating arena to study the physics of broken gauge symmetry. However, the important symmetries in superconductors are not only the gauge invariance. Especially, the symmetry properties of the pairing, i.e., the parity and spin-singlet/spin-triplet, determine the physical properties of the superconducting state. Recently it has been recognized that there is the important third symmetry of the pair amplitude, i.e., even or odd parity with respect to the frequency. The conventional uniform superconducting states correspond to the even-frequency pairing, but the recent finding is that the odd-frequency pair amplitude arises in the spatially non-uniform situation quite ubiquitously. Especially, this is the case in the Andreev bound state (ABS) appearing at the surface/interface of the sample. The other important recent development is on the nontrivial topological aspects of superconductors. As the band insulators are classified by topological indices into (i) conventional insulator, (ii) quantum Hall insulator, and (iii) topological insulator, also are the gapped superconductors. The influence of the nontrivial topology of the bulk states appears as the edge or surface of the sample. In the superconductors, this leads to the formation of zero energy ABS (ZEABS). Therefore, the ABSs of the superconductors are the place where the symmetry and topology meet each other which offer the stage of rich physics. In this review, we discuss the physics of ABS from the viewpoint of the odd-frequency pairing, the topological bulk-edge correspondence, and the interplay of these two issues. It is described how the symmetry of the pairing and topological indices determines the absence/presence of the ZEABS, its energy dispersion, and properties as the Majorana fermions.
230 citations
01 Jan 2011
TL;DR: It is demonstrated the presence of parity-time (PT) symmetry for the non-Hermitian two-state Hamiltonian of a dissipative microwave billiard in the vicinity of an exceptional point (EP).
Abstract: (Dated: July 22, 2011)We demonstrate the presence of parity-time (PT ) symmetry for the non-Hermitian two-stateHamiltonian of a dissipative microwave billiard in the vicinity of an exceptional point (EP). Theshape of the billiard depends on two parameters. The Hamiltonian is determined from the measuredresonance spectrum on a fine grid in the parameter plane. On a curve, which passes through theEP, the Hamiltonian has either real or complex conjugate eigenvalues. An appropriate basis choicereveals its PT symmetry. Spontaneous symmetry breaking occurs at the EP.
176 citations
TL;DR: This Letter considers a chiral situation beginning with only a left global scaling symmetry and does not assume Lorentz invariance, and finds that a left conformal symmetry is still implied, while right translations are enhanced either to a right conformAL symmetry or a left U(1) Kac-Moody symmetry.
Abstract: It is well known that a local, unitary Poincare-invariant 2D quantum field theory with a global scaling symmetry and a discrete non-negative spectrum of scaling dimensions necessarily has both a left and a right local conformal symmetry. In this Letter, we consider a chiral situation beginning with only a left global scaling symmetry and do not assume Lorentz invariance. We find that a left conformal symmetry is still implied, while right translations are enhanced either to a right conformal symmetry or a left U(1) Kac-Moody symmetry.
153 citations
TL;DR: These observations, which agree with predictions derived from hydrodynamic fluctuation theory, strongly suggest that rare events are generically associated with coherent, self-organized patterns which enhance their probability.
Abstract: Phase transitions not allowed in equilibrium steady states may happen, however, at the fluctuating level. We observe for the first time this striking and general phenomenon measuring current fluctuations in an isolated diffusive system. While small fluctuations result from the sum of weakly correlated local events, for currents above a critical threshold the system self-organizes into a coherent traveling wave which facilitates the current deviation by gathering energy in a localized packet, thus breaking translation invariance. This results in Gaussian statistics for small fluctuations but non-Gaussian tails above the critical current. Our observations, which agree with predictions derived from hydrodynamic fluctuation theory, strongly suggest that rare events are generically associated with coherent, self-organized patterns which enhance their probability.
114 citations
TL;DR: A correlation functional that is termed exact-exchange random phase approximation (EXX-RPA) functional and is obtained with the exact frequency-dependent exchange kernel via the fluctuation-dissipation theorem is shown to correctly describe electron pair bonds in the dissociation limit without the need to resort to symmetry breaking in spin space.
Abstract: A correlation functional that is termed exact-exchange random phase approximation (EXX-RPA) functional and is obtained with the exact frequency-dependent exchange kernel via the fluctuation-dissipation theorem is shown to correctly describe electron pair bonds in the dissociation limit without the need to resort to symmetry breaking in spin space. Because the functional also yields more accurate electronic energies for molecules in their equilibrium geometry than standard correlation functionals, it combines accuracy at equilibrium bond distances and in dissociation processes with a correct description of spin, something all commonly employed correlation functionals fail to do. The reason why the EXX-RPA correlation functional yields distinctively and qualitatively better results than RPA approaches based on Hartree-Fock and time-dependent Hartree-Fock is explained.
107 citations
TL;DR: Using infinite projected entangled-pair states, exact diagonalization, and flavor-wave theory, it is shown that the SU(4) Heisenberg model undergoes a spontaneous dimerization on the square lattice, in contrast with its SU(2) and SU(3) counterparts, which develop Néel and three-sublattice stripelike long-range order.
Abstract: Using infinite projected entangled-pair states, exact diagonalization, and flavor-wave theory, we show that the SU(4) Heisenberg model undergoes a spontaneous dimerization on the square lattice, in contrast with its SU(2) and SU(3) counterparts, which develop Neel and three-sublattice stripelike long-range order. Since the ground state of a dimer is not a singlet for SU(4) but a 6-dimensional irreducible representation, this leaves the door open for further symmetry breaking. We provide evidence that, unlike in SU(4) ladders, where dimers pair up to form singlet plaquettes, here the SU(4) symmetry is additionally broken, leading to a gapless spectrum in spite of the broken translational symmetry.
80 citations
TL;DR: In this paper, the Hilbert basis method for determining all D-flat configurations and efficient algorithms for identifying field configurations with a desired residual symmetry were presented. But these algorithms were used in an explicit example, in which a supersymmetric Minkowski vacuum configuration with the phenomenologically attractive Z 4 R symmetry was constructed.
79 citations
TL;DR: In this article, it was shown that non-Bernal rotations preserve the graphene symmetry with only a small perturbation due to weak effective interlayer coupling, and they detect neither a Van Hove singularity nor any significant change in the Fermi velocity.
Abstract: Graphene stacked in a Bernal configuration (${60}^{\ifmmode^\circ\else\textdegree\fi{}}$ relative rotations between sheets) differs electronically from isolated graphene due to the broken symmetry introduced by interlayer bonds forming between only one of the two graphene unit cell atoms. A variety of experiments have shown that non-Bernal rotations restore this broken symmetry; consequently, these stacking varieties have been the subject of intensive theoretical interest. Most theories predict substantial changes in the band structure ranging from the development of a Van Hove singularity and an angle-dependent electron localization that causes the Fermi velocity to go to zero as the relative rotation angle between sheets goes to zero. In this work we show by direct measurement that non-Bernal rotations preserve the graphene symmetry with only a small perturbation due to weak effective interlayer coupling. We detect neither a Van Hove singularity nor any significant change in the Fermi velocity. These results suggest significant problems in our current theoretical understanding of the origins of the band structure of this material.
15 Sep 2011
TL;DR: In this article, the authors introduce the seven fundamental symmetries of physics in relation to the group of the molecular Hamiltonian and the current standard model of particle physics (SMPP).
Abstract: After an introductory survey, we introduce the seven fundamental symmetries of physics in relation to the group of the molecular Hamiltonian and the current standard model of particle physics (SMPP). We discuss the relation of these symmetries to conservation laws and fundamentally nonobservable properties of nature with the example of parity violation. The particular importance of experiments on detecting symmetry breakings is outlined and the three distinct, basic concepts of symmetry breaking (spontaneous, de facto, de lege) are illustrated with the example of space inversion symmetry breaking and parity violation in chiral molecules. Similar conceptual situations are found for our understanding of the underlying physics of molecular chirality by various types of symmetry breakings, of the evolution of biomolecular homochirality and of irreversibility as breaking of time reversal symmetry. The current status of the quantitative theory of molecular parity violation in the framework of electroweak quantum chemistry is reviewed, including the change of order of magnitude, which was found in recent years and has since been confirmed repeatedly.
The concepts of high-resolution spectroscopic experiments on parity violation in chiral molecules are discussed and the status of current attempts toward detecting molecular parity violation is summarized with particular emphasis on the possibilities of measuring time-dependent parity violation in the exceptional (still hypothetical) unstable parity isomers of chiral molecules. The concept of successive symmetry breakings in the quantum dynamics of molecules is illustrated with the wide range of time-scales for symmetry-breaking processes ranging from femtoseconds in experiments on very fast intramolecular vibrational redistribution (IVR) to the theoretical times of seconds for molecular parity violation.
The role of approximate symmetries and conservation laws for our understanding of selection rules in spectroscopy and in chemical reaction dynamics is analyzed in some detail with the example of approximate parity and nuclear spin symmetry conservation in radiative and reactive molecular processes. This includes the use of permutation-inversion symmetry groups in applications to spectroscopy and state-selected chemical reactions. Statistical concepts for the description of molecular energy levels are presented for use in high-resolution spectroscopy and chemical reactions in relation to symmetry properties.
We conclude with a summary of the current status of the following symmetries and their violations in spectroscopy and molecular dynamics: nuclear spin symmetry in chemical processes, space inversion symmetry and parity violation in chiral molecules, time reversal symmetry in intramolecular processes, and combined charge conjugation, parity, and time reversal (CPT) symmetry in relation to more fundamental aspects of time reversal and speculations on mass differences in chiral molecules and chiral neutrinos and their antimatter counterparts.
Keywords:
fundamental symmetries;
symmetry violations;
chirality;
molecular parity violation;
nuclear spin symmetry;
densities of states;
CPT symmetry;
symmetry selection rules;
statistical theory of spectra;
kinetics;
molecular primary processes;
intramolecular vibrational redistribution (IVR);
chemical reaction dynamics, permutation symmetry;
parity and inversion symmetry;
time reversal symmetry
TL;DR: In this article, a definition of soft breaking of BRST symmetry in the field-antifield formalism is proposed, valid for general gauge theories and arbitrary gauge fixing The Ward identities for the generating functionals of Green's functions are derived, and their gauge dependence is investigated.
Abstract: A definition of soft breaking of BRST symmetry in the field-antifield formalism is proposed, valid for general gauge theories and arbitrary gauge fixing The Ward identities for the generating functionals of Green’s functions are derived, and their gauge dependence is investigated We discuss the Gribov-Zwanziger action to the one-parameter family of R
ξ gauges It is argued that gauge theories with a soft breaking of BRST symmetry are inconsistent
TL;DR: In this article, the scaling behavior of the two-flavor chiral phase transition using an effective quark-meson model was investigated, and the transition between infinite-volume and finite-volume scaling behavior when the system is placed in a finite box.
Abstract: We study the scaling behavior of the two-flavor chiral phase transition using an effective quark–meson model. We investigate the transition between infinite-volume and finite-volume scaling behavior when the system is placed in a finite box. We can estimate effects that the finite volume and the explicit symmetry breaking by the current quark masses have on the scaling behavior which is observed in full QCD lattice simulations. The model allows us to explore large quark masses as well as the chiral limit in a wide range of volumes, and extract information about the scaling regimes. In particular, we find large scaling deviations for physical pion masses and significant finite-volume effects for pion masses that are used in current lattice simulations.
TL;DR: In this article, a method for systematically finding ground states of spinor Bose-Einstein condensates by utilizing the symmetry properties of the system was proposed, which can find not only an inert state, whose symmetry is maximal in the manifold under consideration, but also a noninert state, which has lower symmetry and depends on the parameters in the Hamiltonian.
Abstract: We propose a method for systematically finding ground states of spinor Bose-Einstein condensates by utilizing the symmetry properties of the system. By this method, we can find not only an inert state, whose symmetry is maximal in the manifold under consideration, but also a noninert state, which has lower symmetry and depends on the parameters in the Hamiltonian. We establish the symmetry-classification method for the spin-1, 2, and 3 cases at zero magnetic field, and find an additional phase in the last case. The properties of the vortices in the spin-3 system are also discussed.
TL;DR: The unique sensitivity of optical response to different types of symmetry breaking can be used to detect and identify spontaneously ordered many-body states in bilayer graphene, characterized by spontaneously broken time-reversal symmetry and lattice rotation symmetry.
Abstract: The unique sensitivity of optical response to different types of symmetry breaking can be used to detect and identify spontaneously ordered many-body states in bilayer graphene. We predict a strong response at optical frequencies, sensitive to electronic phenomena at low energies, which arises because of nonzero interband matrix elements of the electric current operator. In particular, the polar Kerr rotation and reflection anisotropy provide fingerprints of the quantum anomalous Hall state and the nematic state, characterized by spontaneously broken time-reversal symmetry and lattice rotation symmetry, respectively. These optical signatures, which undergo a resonant enhancement in the near-infrared regime, lie well within reach of existing experimental techniques.
TL;DR: In this paper, the behavior of meson propagators when removing increasingly more of those modes in the valence sector was studied, thus partially removing effects of chiral symmetry breaking.
Abstract: In quantum chromodynamics (QCD) the eigenmodes of the Dirac operator with small absolute eigenvalues have a close relationship to the dynamical breaking of the chiral symmetry. In a simulation with two dynamical quarks, we study the behavior of meson propagators when removing increasingly more of those modes in the valence sector, thus partially removing effects of chiral symmetry breaking. We find that some of the symmetry aspects are restored (e.g., the masses of $\ensuremath{\rho}$ and ${a}_{1}$ approach each other) while confining properties persist.
TL;DR: In this article, the symmetry breaking potentials of non-Abelian discrete family symmetries with tri-bimaximal lepton mixing were discussed. But the symmetry-breaking potentials were not discussed in detail.
Abstract: Non-Abelian discrete family symmetries play a pivotal role in the formulation of models with tri-bimaximal lepton mixing. We discuss how to obtain symmetries such as $ {\mathcal{A}_4} $
, $ {\mathcal{Z}_7} $
⋊ $ {\mathcal{Z}_3} $
and Δ(27) from an underlying SU(3) gauge symmetry. Higher irreducible representations are required to achieve the spontaneous breaking of the continuous group. We present methods of identifying the required vacuum alignments and discuss in detail the symmetry breaking potentials.
TL;DR: In this article, the authors give an up-to-date account of dual conformal symmetry, focussing on its status at loop level, and make the symmetry exact, despite the infrared divergences.
Abstract: Dual conformal symmetry has had a huge impact on our understanding of planar scattering amplitudes in N=4 super Yang-Mills. At tree level, it combines with the original conformal symmetry generators to a Yangian algebra, a hallmark of integrability, and helps in determining the tree-level amplitudes. The latter are now known in closed form. At loop level, it determines the functional form of the four- and five-point scattering amplitudes to all orders in the coupling constant, and gives restrictions at six points and beyond. The symmetry is best understood at loop level in terms of a novel AdS-inspired infrared regularization which makes the symmetry exact, despite the infrared divergences. This has important consequences for the basis of loop integrals in this theory. Recently, a number of selective reviews have appeared which discuss dual conformal symmetry, mostly at tree level. Here, we give an up-to-date account of dual conformal symmetry, focussing on its status at loop level.
28 Dec 2011
TL;DR: In this paper, the program of symmetry building in consistent gauge models is described and the key issues include the flavor symmetry breaking, connection of mixing and masses, ad hoc prescription of flavor charges, missing representations, existence of new particles, possible accidental character of the TBM mixing.
Abstract: Evidences of a discrete symmetry behind the pattern of lepton mixing are analyzed. The program of symmetry building is outlined. Generic features and problems of realization of this program in consistent gauge models are formulated. The key issues include the flavor symmetry breaking, connection of mixing and masses, ad hoc prescription of flavor charges, missing representations, existence of new particles, possible accidental character of the TBM mixing. Various ways are considered to extend the leptonic symmetries to the quark sector and to reconcile them with Grand Unification. In this connection the quark-lepton complementarity could be a viable alternative to TBM. Observational consequences of the symmetries and future experimental tests of their existence are discussed.
TL;DR: In this article, a symmetry breaking parameter associated with the violation of null translation invariance in the direction opposite to the laser beam is proposed to quantify the radiation reaction in terms of a symmetry-breaking parameter.
Abstract: We discuss radiation reaction effects on charges propagating in ultraintense laser fields. Our analysis is based on an analytic solution of the Landau-Lifshitz equation. We suggest quantifying radiation reaction in terms of a symmetry breaking parameter associated with the violation of null translation invariance in the direction opposite to the laser beam. As the Landau-Lifshitz equation is nonlinear, the energy transfer within the pulse is rather sensitive to initial conditions. This is elucidated by comparing colliding and fixed target modes in electron laser collisions.
TL;DR: In this article, the authors investigated chiral symmetry breaking in strong magnetic fields at finite temperature and densities in a 3 flavor Nambu Jona Lasinio model including the Kobayashi Maskawa 't Hooft determinant term, using an explicit structure for the ground state in terms of quarkantiquark condensates.
Abstract: We investigate chiral symmetry breaking in strong magnetic fields at finite temperature and densities in a 3 flavor Nambu Jona Lasinio model including the Kobayashi Maskawa 't Hooft determinant term, using an explicit structure for the ground state in terms of quark-antiquark condensates. The mass gap equations are solved self consistently and are used to compute the thermodynamic potential. We also derive the equation of state for strange quark matter in the presence of strong magnetic fields which could be relevant for proto-neutron stars.
TL;DR: In this article, spontaneous symmetry probing (SSP) was introduced for relativistic quantum field theories, i.e., states that evolve in time along a symmetry direction and have a Lagrangian that is explicitly time independent.
Abstract: For relativistic quantum field theories, we consider Lorentz breaking, spatially homogeneous field configurations or states that evolve in time along a symmetry direction. We dub this situation "spontaneous symmetry probing" (SSP). We mainly focus on internal symmetries, i.e. on symmetries that commute with the Poincare group. We prove that the fluctuations around SSP states have a Lagrangian that is explicitly time independent, and we provide the field space parameterization that makes this manifest. We show that there is always a gapless Goldstone excitation that perturbs the system in the direction of motion in field space. Perhaps more interestingly, we show that if such a direction is part of a non-Abelian group of symmetries, the Goldstone bosons associated with spontaneously broken generators that do not commute with the SSP one acquire a gap, proportional to the SSP state's "speed". We outline possible applications of this formalism to inflationary cosmology.
TL;DR: This work uses the cubic-quintic Swift-Hohenberg equation with an additional quadratic term to determine the qualitative effects of breaking the midplane reflection symmetry on the properties of spatially localized structures in convective systems, including binary fluid convection.
Abstract: The cubic-quintic Swift-Hohenberg equation (SH35) provides a convenient order parameter description of several convective systems with reflection symmetry in the layer midplane, including binary fluid convection. We use SH35 with an additional quadratic term to determine the qualitative effects of breaking the midplane reflection symmetry on the properties of spatially localized structures in these systems. Our results describe how the snakes-and-ladders organization of localized structures in SH35 deforms with increasing symmetry breaking and show that the deformation ultimately generates the snakes-and-ladders structure familiar from the quadratic-cubic Swift-Hohenberg equation. Moreover, in nonvariational systems, such as convection, odd-parity convectons necessarily drift when the reflection symmetry is broken, permitting collisions among moving localized structures. Collisions between both identical and nonidentical traveling states are described.
01 Mar 2011
TL;DR: In this article, the physics of a warped extra dimension and the AdS/CFT correspondence are introduced and a dictionary is given which leads to a 4D holographic view of the 5th dimension.
Abstract: We provide an introduction to the physics of a warped extra dimension and the AdS/CFT correspondence. An AdS/CFT dictionary is given which leads to a 4D holographic view of the 5th dimension. With a particular emphasis on beyond the standard model physics, this provides a window into the strong dynamics associated with either electroweak symmetry breaking or supersymmetry breaking. In this way hierarchies associated with either the electroweak or supersymmetry breaking scale, together with the fermion mass spectrum, can be addressed in a consistent framework.
TL;DR: In this paper, the authors presented the symmetry realization of the phenomenologically viable Frampton-Glashow-Marfatia (FGM) two zero texture neutrino mass matrices in the flavor basis.
TL;DR: In this article, the radial symmetry of extremals was analyzed for a class of interpolation inequalities known as Caffarelli-Kohn-Nirenberg inequalities, and for a weighted logarithmic Hardy inequalities which appear as limiting cases of the first ones.
Abstract: We analyze the radial symmetry of extremals for a class of interpolation inequalities known as Caffarelli–Kohn–Nirenberg inequalities, and for a class of weighted logarithmic Hardy inequalities which appear as limiting cases of the first ones. In both classes we show that there exists a continuous surface that splits the set of admissible parameters into a region where extremals are symmetric and a region where symmetry breaking occurs. In previous results, the symmetry breaking region was identified by showing the linear instability of the radial extremals. Here we prove that symmetry can be broken even within the set of parameters where radial extremals correspond to local minima for the variational problem associated with the inequality. For interpolation inequalities, such a symmetry breaking phenomenon is entirely new.
TL;DR: In this paper, it was shown that no MSSM model with either ZM⩾3R or U(1)R symmetry can be completed by a four-dimensional GUT in the ultraviolet.
TL;DR: In this paper, the authors exploit spatial symmetry in calculations of ground state energy and analytic first derivatives of closed-shell molecules based on their previously developed coupled-cluster (CC) approach with spin-orbit coupling.
Abstract: In the present work, we report exploitation of spatial symmetry in calculations of ground state energy and analytic first derivatives of closed-shell molecules based on our previously developed coupled-cluster (CC) approach with spin-orbit coupling. Both time-reversal symmetry and spatial symmetry for D(2h) and its subgroups are exploited in the implementation. The symmetry of a certain spin case for the amplitude, intermediate, or density matrix is determined by the symmetry of the corresponding spin functions and the direct product decomposition method is employed in computations involving these quantities. The reduction in computational effort achieved through the use of spatial symmetry is larger than the order of the molecular single point group. Symmetry exploitation renders application of the CC approaches with spin-orbit coupling to larger closed-shell molecules containing heavy elements with high accuracy.
TL;DR: In this paper, it is conjectured that flavor mixing furnishes a universal mechanism for the spontaneous breaking of supersymmetry, which is proved explicitly for the mixing of two chiral N = 1 supermultiplets and arguments for its general validity are given.