Showing papers on "Explicit symmetry breaking published in 2014"
TL;DR: In this article, a consistent theory for a self-interacting vector field, breaking an Abelian symmetry in such a way to obtain an interesting behavior for its longitudinal polarization, was discussed.
Abstract: We discuss a consistent theory for a self-interacting vector field, breaking an Abelian symmetry in such a way to obtain an interesting behavior for its longitudinal polarization. In an appropriate decoupling limit, the dynamics of the longitudinal mode is controlled by Galileon interactions. The full theory away from the decoupling limit does not propagate ghost modes, and can be investigated in regimes where non-linearities become important. When coupled to gravity, this theory provides a candidate for dark energy, since it admits de Sitter cosmological solutions characterized by a technically natural value for the Hubble parameter. We also consider the homogeneous evolution when, besides the vector, additional matter in the form of perfect fluids is included. We find that the vector can have an important role in characterizing the universe expansion.
163 citations
TL;DR: In this article, a general analysis of models with an axion and further axion-like particles (ALPs) with decay constants in the intermediate scale range, between 109 GeV and 1013 GeV, is presented.
Abstract: The recent detection of the cosmic microwave background polarimeter experiment BICEP2 of tensor fluctuations in the B-mode power spectrum basically excludes all plausible axion models where its decay constant is above 1013 GeV. Moreover, there are strong theoretical, astrophysical, and cosmological motivations for models involving, in addition to the axion, also axion-like particles (ALPs), with decay constants in the intermediate scale range, between 109 GeV and 1013 GeV. Here, we present a general analysis of models with an axion and further ALPs and derive bounds on the relative size of the axion and ALP photon (and electron) coupling. We discuss what we can learn from measurements of the axion and ALP photon couplings about the fundamental parameters of the underlying ultraviolet completion of the theory. For the latter we consider extensions of the Standard Model in which the axion and the ALP(s) appear as pseudo Nambu-Goldstone bosons from the breaking of global chiral U(1) (Peccei-Quinn (PQ)) symmetries, occurring accidentally as low energy remnants from exact discrete symmetries. In such models, the axion and the further ALP are protected from disastrous explicit symmetry breaking effects due to Planck-scale suppressed operators. The scenarios considered exploit heavy right handed neutrinos getting their mass via PQ symmetry breaking and thus explain the small mass of the active neutrinos via a seesaw relation between the electroweak and an intermediate PQ symmetry breaking scale. For a number of explicit models, we determine the parameters of the low-energy effective field theory describing the axion, the ALPs, and their interactions with photons and electrons, in terms of the input parameters, in particular the PQ symmetry breaking scales. We show that these models can accommodate simultaneously an axion dark matter candidate, an ALP explaining the anomalous transparency of the universe for γ-rays, and an ALP explaining the recently reported 3.55 keV gamma line from galaxies and clusters of galaxies, if the respective decay constants are of intermediate scale. Moreover, they do not suffer severely from the domain wall problem.
153 citations
TL;DR: It is shown that when PT-symmetric quantum theory has a local PT symmetry acting on composite systems, it violates the nonsignaling principle of relativity.
Abstract: Bender et al. [Phys. Rev. Lett. 80, 5243 (1998)] have developed PT-symmetric quantum theory as an extension of quantum theory to non-Hermitian Hamiltonians. We show that when this model has a local PT symmetry acting on composite systems, it violates the nonsignaling principle of relativity. Since the case of global PT symmetry is known to reduce to standard quantum mechanics A. Mostafazadeh [J. Math. Phys. 43, 205 (2001)], this shows that the PT-symmetric theory is either a trivial extension or likely false as a fundamental theory.
147 citations
TL;DR: It is shown that the selection rule can be imposed by the rotational symmetry of metacrystals embedded into an isotropic organic nonlinear thin film, which may open new avenues for designing symmetry-dependent nonlinear optical responses with tailored plasmonic nanostructures.
Abstract: Nonlinear processes are often governed by selection rules imposed by the symmetries of the molecular configurations. The most well-known examples include the role of centrosymmetry breaking for the generation of even harmonics, and the selection rule related to the rotational symmetry in harmonic generation for fundamental beams with circular polarizations. While the role of centrosymmetry breaking in second harmonic generation has been extensively studied in plasmonic systems, the investigation of selection rules pertaining to circular polarization states of harmonic generation is limited to crystals, i.e., symmetries at the atomic level. In this Letter we demonstrate the rotational symmetry dependent third harmonic generation from nonlinear plasmonic metacrystals. We show that the selection rule can be imposed by the rotational symmetry of metacrystals embedded into an isotropic organic nonlinear thin film. The results presented here may open new avenues for designing symmetry-dependent nonlinear optical responses with tailored plasmonic nanostructures.
121 citations
TL;DR: In this paper, a general analysis of models with an axion and further axion-like particles (ALPs) with decay constants in the intermediate scale range, between $10^9$ GeV and $10^{13}$GeV, is presented.
Abstract: The recent detection of the cosmic microwave background polarimeter experiment BICEP2 of tensor fluctuations in the B-mode power spectrum basically excludes all plausible axion models where its decay constant is above $10^{13}$ GeV. Moreover, there are strong theoretical, astrophysical, and cosmological motivations for models involving, in addition to the axion, also axion-like particles (ALPs), with decay constants in the intermediate scale range, between $10^9$ GeV and $10^{13}$ GeV. Here, we present a general analysis of models with an axion and further ALPs and derive bounds on the relative size of the axion and ALP photon (and electron) coupling. We discuss what we can learn from measurements of the axion and ALP photon couplings about the fundamental parameters of the underlying ultraviolet completion of the theory. For the latter we consider extensions of the Standard Model in which the axion and the ALP(s) appear as pseudo Nambu-Goldstone bosons from the breaking of global chiral $U(1)$ (Peccei-Quinn (PQ)) symmetries, occuring accidentally as low energy remnants from exact discrete symmetries. In such models, the axion and the further ALP are protected from disastrous explicit symmetry breaking effects due to Planck-scale suppressed operators. The scenarios considered exploit heavy right handed neutrinos getting their mass via PQ symmetry breaking and thus explain the small mass of the active neutrinos via a seesaw relation between the electroweak and an intermediate PQ symmetry breaking scale. We show some models that can accommodate simultaneously an axion dark matter candidate, an ALP explaining the anomalous transparency of the universe for $\gamma$-rays, and an ALP explaining the recently reported 3.55 keV gamma line from galaxies and clusters of galaxies, if the respective decay constants are of intermediate scale.
95 citations
TL;DR: In this paper, the authors explore chiral symmetry breaking in a magnetic field within a Nambu-Jona-Lasinio model of interacting massless quarks including tensor channels.
Abstract: We explore chiral symmetry breaking in a magnetic field within a Nambu-Jona-Lasinio model of interacting massless quarks including tensor channels. We show that the new interaction channels open up via Fierz identities due to the explicit breaking of the rotational symmetry by the magnetic field. We demonstrate that the magnetic catalysis of chiral symmetry breaking leads to the generation of two independent condensates, the conventional chiral condensate and a spin-one condensate. While the chiral condensate generates a dynamical fermion mass, the new condensate gives rise to a dynamical anomalous magnetic moment for the fermions. As a consequence, the spectrum of the excitations in all Landau levels, except the lowest one, exhibits Zeeman splitting. Since the pair, formed by a quark and an antiquark with opposite spins, possesses a resultant magnetic moment, an external magnetic field can align it giving rise to a net magnetic moment for the ground state. This is the physical interpretation of the spin-one condensate. Our results show that the magnetically catalyzed ground state in QCD is actually richer than previously thought. The two condensates contribute to the effective mass of the LLL quasiparticles in such a way that the critical temperature for chiral symmetry restoration becomes enhanced.
84 citations
TL;DR: In this article, the authors investigate the simplest models where baryon and lepton numbers are defined as local symmetries spontaneously broken at the low scale and discuss the implications for cosmology.
81 citations
TL;DR: In this paper, the symmetry transformation properties of field degrees of freedom have been investigated and the inverse Higgs constraints are interpreted as giving a field parametrization that makes these transformation properties manifest.
Abstract: It has long been known that when spacetime symmetry is spontaneously broken, some of the broken generators may not give rise to independent gapless Nambu-Goldstone excitations. We provide two complementary viewpoints of this phenomenon. On the one hand, we show that the corresponding field degrees of freedom have the same symmetry transformation properties as massive matter fields. The ``inverse Higgs constraints,'' sometimes employed to eliminate these modes from the theory, are reinterpreted as giving a field parametrization that makes these transformation properties manifest. On the other hand, relations among classical symmetry transformations generally lead to identities for the associated Noether currents that allow saturation of the Ward-Takahashi identities for all the broken symmetries with fewer gapless excitations than suggested by the mere counting of broken generators.
72 citations
TL;DR: In this paper, the authors harness symmetry to control transport and statistics in open quantum systems, enabled by a first-order-type dynamic phase transition in current statistics and the associated coexistence of different transport channels classified by symmetry.
Abstract: Symmetry is a powerful concept in physics, and its recent application to understand nonequilibrium behavior is providing deep insights and groundbreaking exact results. Here we show how to harness symmetry to control transport and statistics in open quantum systems. Such control is enabled by a first-order-type dynamic phase transition in current statistics and the associated coexistence of different transport channels (or nonequilibrium steady states) classified by symmetry. Microreversibility then ensues, via the Gallavotti-Cohen fluctuation theorem, a twin dynamic phase transition for rare current fluctuations. Interestingly, the symmetry present in the initial state is spontaneously broken at the fluctuating level, where the quantum system selects the symmetry sector that maximally facilitates a given fluctuation. We illustrate these results in a qubit network model motivated by the problem of coherent energy harvesting in photosynthetic complexes, and introduce the concept of a symmetry-controlled quantum thermal switch, suggesting symmetry-based design strategies for quantum devices with controllable transport properties.
66 citations
TL;DR: In this paper, the authors argue that the natural interpretation of the stabilizer, from the viewpoint of the shift symmetry, is a three-form multiplet, which has a natural string theory interpretation.
Abstract: Most successful models of inflation in supergravity have a shift symmetry for the inflaton and contain a stabilizer field coupled to the inflaton in a particular way. We argue that the natural interpretation of the stabilizer, from the viewpoint of the shift symmetry, is a three-form multiplet. Its coupling to the inflaton is uniquely determined by the shift symmetry and the invariance under three-form gauge transformations and has a natural string theory interpretation.
64 citations
TL;DR: In this article, a supersymmetric model based on Delta(48) family symmetry and generalised CP symmetry is constructed, and this new mixing pattern is exactly reproduced, and a new interesting mixing pattern in which both lepton mixing angles and CP phases are nontrivial functions of a single parameter theta.
Abstract: We provide a systematic and thorough exploration of the A(48) family symmetry and the consistent generalised CP symmetry. A model-independent analysis of the achievable lepton flavor mixing is performed by considering all the possible remnant symmetries in the neutrino and the charged lepton sectors. We find a new interesting mixing pattern in which both lepton mixing angles and CP phases are nontrivial functions of a single parameter theta. The value of theta can be fixed by the measured reactor mixing angle theta(13), and the excellent agreement with the present data can be achieved. A supersymmetric model based on Delta(48) family symmetry and generalised CP symmetry is constructed, and this new mixing pattern is exactly reproduced.
TL;DR: In this article, the authors lay out the detailed formalism for detecting broken symmetry states in correlated electron systems, and present a theoretical framework for the detection of these states in a correlated electron system.
Abstract: In this theoretical paper, but written primarily for experimentalists, the author lays out the detailed formalism for detecting broken symmetry states in correlated electron systems.
TL;DR: In this paper, the authors study the phase diagram of a holographic model realizing a U ( 2 ) global symmetry on the boundary and show that at low temperature a phase with both scalar s and vector p condensates exists.
Abstract: We study the phase diagram of a holographic model realizing a U ( 2 ) global symmetry on the boundary and show that at low temperature a phase with both scalar s and vector p condensates exists. This is the s + p -wave phase where the global U ( 2 ) symmetry and also the spatial rotational symmetry are spontaneously broken. By studying the free energy we show that this phase is preferred when it exists. We also consider unbalanced configurations where a second chemical potential is turned on. They present a rich phase diagram characterized by the competition and coexistence of the s and p order parameters.
TL;DR: In this article, the authors present general arguments to show that topologically stable zero energy modes can be protected by the coexistence of both chiral symmetry and spatial symmetry, and show that these properties can be achieved by both spatial and chiral symmetries.
Abstract: In this clear and thorough contribution, the authors present general arguments to show that topologically stable zero energy modes can be protected by the coexistence of both chiral symmetry and spatial symmetry.
TL;DR: In this paper, the stability/instability criteria for nonchiral conformal field theories with parity symmetry were developed for topological phases protected by parity symmetry or parity symmetry combined with an on-site unitary symmetry.
Abstract: We generalize Laughlin's flux insertion argument, originally discussed in the context of the quantum Hall effect, to topological phases protected by non-on-site unitary symmetries, in particular by parity symmetry or parity symmetry combined with an on-site unitary symmetry. As a model, we discuss fermionic or bosonic systems in two spatial dimensions with CP symmetry, which are, by the CPT theorem, related to time-reversal symmetric topological insulators (e.g., the quantum spin Hall effect). In particular, we develop the stability/instability (or ``gappability''/``ingappablity'') criteria for nonchiral conformal field theories with parity symmetry that may emerge as an edge state of a symmetry-protected topological phase. A necessary ingredient, as it turns out, is to consider the edge conformal field theories on unoriented surfaces, such as the Klein bottle, which arises naturally from enforcing parity symmetry by a projection operation.
TL;DR: In this paper, a reduction of symmetry from C6v to C3v leads to the opening of a band gap in the otherwise gapless semiconductor graphene, which can be discussed in terms of tight-binding approximation, accurately resolving the wave vector space to a very high accuracy.
Abstract: A reduction of symmetry from C6v to C3v leads to the opening of a band gap in the otherwise gapless semiconductor graphene Simple models provide a fairly complete picture of this mechanism for opening a band gap and in fact can be discussed in terms of the tight-binding approximation, accurately resolving the wave-vector space to a very high accuracy This picture is consistent with experiments that yield a band gap due to A and B graphene-site symmetry breaking due to substrate interactions
TL;DR: In this article, the scale symmetry was broken by Yang-Mills instantons, which lead to a very small vacuum energy for our Universe, and a new mechanism for breaking scale symmetry in 4D theories of gravity plus matter fields.
TL;DR: In this article, the existence of geometric quantum phases in the relativistic and non-relativistic quantum dynamics of a Dirac neutral particle from the effects of the violation of the Lorentz symmetry in the cosmic string spacetime is investigated.
Abstract: By starting from the modified Maxwell theory coupled to gravity, the arising of geometric quantum phases in the relativistic and nonrelativistic quantum dynamics of a Dirac neutral particle from the effects of the violation of the Lorentz symmetry in the cosmic string spacetime is investigated. It is shown that the Dirac equation can be written in terms of an effective metric and a relativistic geometric phase stems from the topology of the cosmic string spacetime and the Lorentz symmetry breaking effects. Further, the nonrelativistic limit of the Dirac equation is discussed, and it is shown that both Lorentz symmetry breaking effects and the topology of the defect yields a phase shift in the wave function of the nonrelativistic spin-$1/2$ particle.
TL;DR: In this article, symmetry breaking of solitons in a class of one-dimensional parity-time (PT) symmetric complex potentials with cubic nonlinearity is reported, where the base branch changes stability, and the bifurcated branch can be stable.
Abstract: Symmetry breaking of solitons in a class of one-dimensional parity-time (PT) symmetric complex potentials with cubic nonlinearity is reported. In generic PT-symmetric potentials, such symmetry breaking is forbidden. However, in a special class of PT-symmetric potentials $V(x)=g^2(x)+\alpha g(x)+ i g'(x)$, where $g(x)$ is a real and even function and $\alpha$ a real constant, symmetry breaking of solitons can occur. That is, a branch of non-PT-symmetric solitons can bifurcate out from the base branch of PT-symmetric solitons when the base branch's power reaches a certain threshold. At the bifurcation point, the base branch changes stability, and the bifurcated branch can be stable.
TL;DR: Tan et al. as mentioned in this paper studied the effects of the Lorentz symmetry violation in the nonrelativistic quantum dynamics of a spin-1/2 neutral particle interacting with external fields confined to a two-dimensional quantum ring.
Abstract: We study the effects of the Lorentz symmetry violation in the nonrelativistic quantum dynamics of a spin-1/2 neutral particle interacting with external fields confined to a two-dimensional quantum ring (W.-C. Tan, J.C. Inkson, Semicond. Sci. Technol. 11, 1635 (1996)). We show a possible scenario for the Lorentz symmetry breaking that permits us to make an analogy with the Landau-Aharonov-Casher system (M. Ericsson, E. Sjoqvist, Phys. Rev. A 65, 013607 (2001)), where a change in the angular frequency characteristic of the confinement of a quantum particle to a two-dimensional ring is obtained. Then, we show that an upper bound for the Lorentz symmetry breaking parameters may be set up. Besides, we analyse another possible scenario of the Lorentz symmetry violation by showing the presence of an analogue of the Coulomb potential. We obtain the bound states solutions to the Schrodinger-Pauli equation and discuss a quantum effect characterized by the dependence of the angular frequency on the quantum numbers of the system.
TL;DR: An extension of effective field theories for finite systems with emergent symmetry breaking was proposed in this paper, which showed how symmetry arguments aloneyield the universal features of the low-lying excitations.
Abstract: An extension of effective field theories for finite systems with``emergent symmetry breaking'' shows how symmetry arguments aloneyield the universal features of the low-lying excitations. Applied tothe structure of nonspherical atomic nuclei, some well-known resultsemerge from a new perspective, such as the nuclear vibrations that arethe heads of rotational bands.
TL;DR: In this article, the authors investigated the possibility of extending the "partially massless" symmetry of a spin-2 field in de Sitter to nonlinear order, and they showed that no consistent Lagrangian that contains at most two derivatives of the fields can realize this symmetry.
Abstract: We investigate the possibility of extending the "partially massless" symmetry of a spin-2 field in de Sitter to nonlinear order. To do so, we impose a closure condition on the symmetry transformations. This requirement imposes strong constraints on the form of the nonlinear symmetry while making only minimal assumptions about the form of the nonlinear partially massless action. We find a unique nonlinear extension of the free partially massless symmetry. However, we show that no consistent Lagrangian that contains at most two derivatives of the fields can realize this symmetry.
TL;DR: In this paper, the authors extend coupled-cluster theory performed on top of a Slater determinant breaking rotational symmetry to allow for the exact restoration of the angular momentum at any truncation order.
Abstract: We extend coupled-cluster theory performed on top of a Slater determinant breaking rotational symmetry to allow for the exact restoration of the angular momentum at any truncation order. The main objective relates to the description of near-degenerate finite quantum systems with an open-shell character. As such, the newly developed many-body formalism offers a wealth of potential applications and further extensions dedicated to the ab initio description of, e.g., doubly open-shell atomic nuclei and molecule dissociation. The formalism, which encompasses both single-reference coupled cluster theory and projected Hartree-Fock theory as particular cases, permits the computation of usual sets of connected diagrams while consistently incorporating static correlations through the highly non-perturbative restoration of rotational symmetry. Interestingly, the yrast spectroscopy of the system, i.e. the lowest energy associated with each angular momentum, is accessed within a single calculation. A key difficulty presently overcome relates to the necessity to handle generalized energy {\it and} norm kernels for which naturally terminating coupled-cluster expansions could be eventually obtained. The present work focuses on $SU(2)$ but can be extended to any (locally) compact Lie group and to discrete groups, such as most point groups. In particular, the formalism will be soon generalized to $U(1)$ symmetry associated with particle number conservation. This is relevant to Bogoliubov coupled cluster theory that was recently formulated and applied to singly open-shell nuclei.
TL;DR: The nuclear symmetry energy represents a response to the neutron-proton asymmetry as discussed by the authors, and the symmetry energy is defined in terms of symmetry energy in the framework of nuclear density functional theory.
Abstract: The nuclear symmetry energy represents a response to the neutron-proton asymmetry. In this paper we discuss various aspects of symmetry energy in the framework of nuclear density functional theory, considering both non-relativistic and relativistic self-consistent mean-field realizations side by side. Key observables pertaining to bulk nucleonic matter and finite nuclei are reviewed. Constraints on the symmetry energy and correlations between observables and symmetry energy parameters, using statistical covariance analysis, are investigated. Perspectives for future work are outlined in the context of ongoing experimental efforts.
TL;DR: In this paper, the Stueckelberg trick of introducing an auxiliary field along with a local symmetry in the initial Lagrangian is used to convert the second-class constraints present in the original Lagrangians to first-class ones.
Abstract: The quantization of a vector model presenting spontaneous breaking of Lorentz symmetry in flat Minkowski spacetime is discussed. The Stueckelberg trick of introducing an auxiliary field along with a local symmetry in the initial Lagrangian is used to convert the second-class constraints present in the initial Lagrangian to first-class ones. An additional deformation is employed in the resulting Lagrangian to handle properly the first-class constraints, and the equivalence with the initial model is demonstrated using the BRST invariance of the deformed Lagrangian. The framework for performing perturbation theory is constructed and the structure of the Fock space is discussed. Despite the presence of ghost and tachyon modes in the spectrum of the theory, it is shown that one can implement consistent conditions to define a unitary and stable reduced Fock space. Within the restricted Fock space, the free model turns out to be equivalent to the Maxwell electrodynamics in the temporal gauge.
TL;DR: In this article, it was shown that the anti-D3 brane charge at the tip of the conifold is always positive in the phase with unbroken chiral symmetry.
TL;DR: Tan et al. as discussed by the authors studied the influence of a Rashba-like coupling induced by a Lorentz symmetry violation background on the Tan-Inkson potential, and showed that the effect of such a coupling on the potential of a spin-1/2 neutral particle interacting with external fields is independent of the quantum dynamics.
Abstract: The arising of a Rashba-like coupling, a Zeeman-like term and a Darwin-like term induced by Lorentz symmetry breaking effects in the non-relativistic quantum dynamics of a spin-1/2 neutral particle interacting with external fields is studied. Moreover, the influence of a Rashba-like coupling induced by a Lorentz symmetry violation background on the Tan–Inkson potential [W.-C. Tan and J. C. Inkson, Semicond. Sci. Technol. 11, 1635 (1996)] is discussed.
TL;DR: A good number of theoretical results on symmetries of polynomial curves, algorithms for detecting rotation and mirror symmetry, and closed formulas to determine the symmetry center and the symmetry axis, when they exist are provided.
TL;DR: In this article, the authors proposed a formula for the spin-Chern charge as a derivative of the Chern number in terms of the Green function in such a way that it is valid and related to the associated Hall current even when the symmetry is broken.
TL;DR: In this article, a possible scenario of the Lorentz symmetry violation background that allows us to build an analogue of the Landau system for a nonrelativistic Dirac neutral particle interacting with a field configuration of crossed electric and magnetic fields is studied.
Abstract: We study a possible scenario of the Lorentz symmetry violation background that allows us to build an analogue of the Landau system for a nonrelativistic Dirac neutral particle interacting with a field configuration of crossed electric and magnetic fields. We also discuss the arising of analogues of the Rashba coupling, the Zeeman term and the Darwin term from the Lorentz symmetry breaking effects, and the influence of these terms on the analogue of the Landau system confined to a two-dimensional quantum ring. Finally, we show that this analogy with the Landau system confined to a two-dimensional quantum ring allows us to establish an upper bound for the Lorentz symmetry breaking parameters.