Showing papers on "Explicit symmetry breaking published in 2007"
TL;DR: In this article, the rotational symmetry number for different molecular configurations and how to apply them to transition state theory is discussed. But special care is advised in the evaluation of symmetry numbers in the following situations: (i) reaction is symmetric, (ii) if reactants and/or transition states are chiral, (iii) if the reaction has multiple conformers for reactants or transition states and, (iv) if there is an internal rotation of part of the molecular system.
Abstract: This article shows how to evaluate rotational symmetry numbers for different molecular configurations and how to apply them to transition state theory. In general, the symmetry number is given by the ratio of the reactant and transition state rotational symmetry numbers. However, special care is advised in the evaluation of symmetry numbers in the following situations: (i) if the reaction is symmetric, (ii) if reactants and/or transition states are chiral, (iii) if the reaction has multiple conformers for reactants and/or transition states and, (iv) if there is an internal rotation of part of the molecular system. All these four situations are treated systematically and analyzed in detail in the present article. We also include a large number of examples to clarify some complicated situations, and in the last section we discuss an example involving an achiral diasteroisomer.
336 citations
TL;DR: In this paper, the authors argue that metastable supersymmetry breaking is inevitable and also illustrate various general issues regarding spontaneous and explicit R-symmetry breaking, using simple toy models of supersymmetric breaking.
Abstract: Models of spontaneous supersymmetry breaking generically have an R-symmetry, which is problematic for obtaining gaugino masses and avoiding light R-axions. The situation is improved in models of metastable supersymmetry breaking, which generically have only an approximate R-symmetry. Based on this we argue, with mild assumptions, that metastable supersymmetry breaking is inevitable. We also illustrate various general issues regarding spontaneous and explicit R-symmetry breaking, using simple toy models of supersymmetry breaking.
224 citations
TL;DR: In this paper, the authors use the symmetries of monolayer graphene to write a set of constraints that must be satisfied by any electron-phonon interaction Hamiltonian.
Abstract: We use the symmetries of monolayer graphene to write a set of constraints that must be satisfied by any electron-phonon interaction Hamiltonian. The explicit solution as a series expansion in the momenta gives the most general, model-independent couplings between electrons and long-wavelength acoustic and optical phonons. As an application, the possibility of describing elastic strains in terms of effective electromagnetic fields is considered in detail, with an emphasis on group-theory conditions and the role of time-reversal symmetry.
208 citations
TL;DR: In this article, a unified description of strongly correlated phenomena in finite systems of repelling particles (whether fermions or bosons) is presented through the development of a two-step method of symmetry breaking at the unrestricted Hartree-Fock level and of subsequent symmetry restoration via post Hartree Fock projection techniques.
Abstract: Investigations of emergent symmetry breaking phenomena occurring in small finite-size systems are reviewed, with a focus on the strongly correlated regime of electrons in two-dimensional semicoductor quantum dots and trapped ultracold bosonic atoms in harmonic traps. Throughout the review we emphasize universal aspects and similarities of symmetry breaking found in these systems, as well as in more traditional fields like nuclear physics and quantum chemistry, which are characterized by very different interparticle forces. A unified description of strongly correlated phenomena in finite systems of repelling particles (whether fermions or bosons) is presented through the development of a two-step method of symmetry breaking at the unrestricted Hartree-Fock level and of subsequent symmetry restoration via post Hartree-Fock projection techniques. Quantitative and qualitative aspects of the two-step method are treated and validated by exact diagonalization calculations.
Strongly-correlated phenomena emerging from symmetry breaking include: (I) Chemical bonding, dissociation, and entanglement (at zero and finite magnetic fields) in quantum dot molecules and in pinned electron molecular dimers formed within a single anisotropic quantum dot. (II) Electron crystallization, with particle localization on the vertices of concentric polygonal rings, and formation of rotating electron molecules (REMs) in circular quantum dots. (III) At high magnetic fields, the REMs are described by parameter-free analytic wave functions, which are an alternative to the Laughlin and composite-fermion approaches. (IV) Crystalline phases of strongly repelling bosons. In rotating traps and in analogy with the REMs, such repelling bosons form rotating boson molecules (RBMs).
165 citations
TL;DR: Gauge mediation of supersymmetry breaking is simplified using generic superpotentials without $U(1{)}_{R}$ symmetry by allowing metastable vacua as mentioned in this paper. But this approach is not suitable for supersymmetric breaking.
Abstract: Gauge mediation of supersymmetry breaking is drastically simplified using generic superpotentials without $U(1{)}_{R}$ symmetry by allowing metastable vacua.
157 citations
TL;DR: In this article, the D{sub 4} family symmetry was obtained in Z{sub 3}xZ{sub 2} orbifold constructions, which constrains fermion masses, as well as the soft SUSY breaking mass terms.
Abstract: In this paper we show how some flavor symmetries may be derived from the heterotic string, when compactified on a 6D orbifold. In the body of the paper we focus on the D{sub 4} family symmetry, recently obtained in Z{sub 3}xZ{sub 2} orbifold constructions. We show how this flavor symmetry constrains fermion masses, as well as the soft SUSY breaking mass terms. Flavor symmetry breaking can generate the hierarchy of fermion masses and at the same time the flavor symmetry suppresses large flavor changing neutral current processes.
124 citations
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TL;DR: In this paper, the warp-modified moduli space metric is used to analyze supersymmetry breaking by anti-self-dual flux in the deformed conifold.
Abstract: We analyze supersymmetry breaking by anti-self-dual flux in the deformed conifold. This theory has been argued to be a dual realization of susy breaking by antibranes. As such, one might expect it to lead to a hierarchically small breaking scale, but only if the warp factor is taken into account. We verify this by explicitly computing the warp-modified moduli space metric. This leads to a new term, with a power-like divergence at the conifold point, which lowers the breaking scale. We finally point out various puzzles regarding the gauge theory interpretation of these results.
110 citations
TL;DR: In this paper, the relation between Bose-Einstein condensation and spontaneous gauge symmetry breaking is analyzed, and it is shown that spontaneous breaking of gauge symmetry is the necessary and sufficient condition for BEE.
Abstract: The fundamental problem is analyzed, the relation between Bose-Einstein condensation and spontaneous gauge symmetry breaking. This relation is largerly misunderstood in physics community. Numerous articles and books contain the statement that, though gauge symmetry breaking helps for describing Bose-Einstein condensation, but the latter, in principle, does not require any symmetry breaking. This, however, is not correct. The analysis is based on the known mathematical theorems. But in order not to overcomplicate the presentation and to make it accessible to all readers, technical details are often omitted here. The emphasis is made on the following basic general facts: Spontaneous breaking of gauge symmetry is the necessary and sufficient condition for Bose-Einstein condensation. Condensate fluctuations, in thermodynamic limit, are negligible. Their catastrophic behavior can arise only as a result of incorrect calculations, when a Bose-condensed system is described without gauge symmetry breaking. It is crucially important to employ the representative statistical ensembles equipped with all conditions that are necessary for a unique and mathematically correct description of the given statistical system. Only then one is able to develop a self-consistent theory, free of paradoxes.
93 citations
TL;DR: In this paper, it was shown that the phase-structure of the free energy as the temperature drops, is indeed such that there is a second order phase transition in the direction of the non-susy vacuum at a finite time interval.
Abstract: We look at the recently proposed idea that susy breaking can be accomplished in a meta-stable vacuum. In the context of one of the simplest models (the Seiberg-dual of super-QCD), we address the following question: if we look at this theory as it cools from high temperature, is it at all possible that we can end up in a susy-breaking meta-stable vacuum? To get an idea about the answer, we look at the free energy of the system at high temperature. We conclude that the phase-structure of the free-energy as the temperature drops, is indeed such that there is a second order phase transition in the direction of the non-susy vacuum at a finite $T=T_c^Q$. On the other hand, the potential barrier in the direction of the susy vacuum is there all the way till $T \sim 0$.
88 citations
TL;DR: In this article, the authors considered a 2D nonlinear Schrodinger equation with self-focusing nonlinearity and a quasi-1D double-channel potential, i.e., a straightforward 2D extension of the well-known double-well potential.
Abstract: We consider a two-dimensional (2D) nonlinear Schr\"odinger equation with self-focusing nonlinearity and a quasi-1D double-channel potential, i.e., a straightforward 2D extension of the well-known double-well potential. The model may be realized in terms of nonlinear optics and Bose-Einstein condensates. The variational approximation (VA) predicts a bifurcation breaking the symmetry of 2D solitons trapped in the double channel, the bifurcation being of the subcritical type. The predictions of the VA are confirmed by numerical simulations. The work presents an original example of the spontaneous symmetry breaking of 2D solitons in dual-core systems.
74 citations
TL;DR: In this paper, it was shown that some of the quantum Hall states exhibit spontaneous symmetry breaking that is driven by electron-electron interaction and the collective charge and neutral excitations associated with symmetry breaking.
TL;DR: In this article, the authors studied a class of intersecting D-brane models in which fermions localized at different intersections interact via exchange of bulk fields and analyzed the conditions under which this happens as one varies the dimensions of the branes and of the intersections.
TL;DR: In this paper, the authors review the recent development which has led to a better understanding of the nature and definition of non-Abelian monopoles, as well as their role in confinement and dynamical symmetry breaking in strongly interacting theories.
Abstract: Non-Abelian monopoles are present in the fully quantum–mechanical low-energy effective action of many solvable supersymmetric theories. They behave perfectly as point-like particles carrying non-Abelian dual magnetic charges. They play a crucial role in confinement and in dynamical symmetry breaking in these theories. There is a natural identification of these excitations within the semiclassical approach, which involves the flavor symmetry in an essential manner. We review in an introductory fashion the recent development which has led to a better understanding of the nature and definition of non-Abelian monopoles, as well as of their role in confinement and dynamical symmetry breaking in strongly interacting theories.
TL;DR: In this paper, the authors discuss O'Raifeartaigh models with general R-charge assignments, introduced by Shih to break R-symmetry spontaneously, and argue that most of these models have runaway directions related to the R-Symmetry.
Abstract: We discuss O'Raifeartaigh models with general R-charge assignments, introduced by Shih to break R-symmetry spontaneously. We argue that most of these models have runaway directions related to the R-symmetry. In addition, we study the simplest model with a U(N) global symmetry and show that in a range of parameters R-symmetry is spontaneously broken in a metastable vacuum.
TL;DR: In this paper, it was shown that in the deconfined phase the axial symmetry remains unbroken to all orders in 1/Nc, and that the instanton gas approximation is possibly regulated in the IR, which would imply an η' mass-squared of order exp (−Nc).
Abstract: We analyze the resolution of the U(1)A problem in the Sakai-Sugimoto holographic dual of large Nc QCD at finite temperature. It has been shown that in the confining phase the axial symmetry is broken at order 1/Nc, in agreement with the ideas of Witten and Veneziano. We show that in the deconfined phase the axial symmetry remains unbroken to all orders in 1/Nc. In this case the breaking is due to instantons which are described by spacelike D0-branes, in agreement with 't Hooft's resolution. The holographic dual of the symmetry breaking fermion condensate is a state of spacelike strings between the D0-brane and the flavor D8-branes, which result from a spacelike version of the string creation effect. In the intermediate phase of deconfinement with broken chiral symmetry the instanton gas approximation is possibly regulated in the IR, which would imply an η' mass-squared of order exp (−Nc).
TL;DR: In this paper, a generalized reflection symmetry predicts a simple relation between the Dirac and Majorana phases, which can lead to an arbitrary phase that depends on the parameter of the symmetry transformation.
Abstract: Discovery of the CP-violation in the lepton sector is one of the challenges of the particle physics. We search for possible principles, symmetries and phenomenological relations that can lead to particular values of the CP-violating Dirac phase, δ. In this connection we discuss two extreme cases: the zero phase, δ = 0, and the maximal CP-violation, δ = ±π/2, and relate them to the peculiar pattern of the neutrino mixing. The maximal CP-violation can be related to the νμ−ντ reflection symmetry. We study various aspects of this symmetry and introduce a generalized reflection symmetry that can lead to an arbitrary phase that depends on the parameter of the symmetry transformation. The generalized reflection symmetry predicts a simple relation between the Dirac and Majorana phases. We also consider the possibility of certain relations between the CP-violating phases in the quark and lepton sectors.
TL;DR: The results present the first example of spontaneous symmetry breaking in two-dimensional lattice solitons, which has no counterpart in the continuum limit because of the collapse instability in the latter case.
Abstract: We examine one- and two-dimensional models of linearly coupled lattices of the discrete-nonlinear-Schrodinger type. Analyzing ground states of the system with equal powers (norms) in the two components, we find a symmetry-breaking phenomenon beyond a critical value of the total power. Asymmetric states, with unequal powers in their components, emerge through a subcritical pitchfork bifurcation, which, for very weakly coupled lattices, changes into a supercritical one. We identify the stability of various solution branches. Dynamical manifestations of the symmetry breaking are studied by simulating the evolution of the unstable branches. The results present the first example of spontaneous symmetry breaking in two-dimensional lattice solitons. This feature has no counterpart in the continuum limit because of the collapse instability in the latter case.
TL;DR: In this paper, the Higgs mechanism has been used to confers masses on the weak force carriers W± and Z in the standard model of particle physics, and it also opens the door to masses for the quarks and leptons.
Abstract: Electroweak theory joins electromagnetism with the weak force in a single quantum field theory, ascribing the two fundamental interactions—so different in their manifestations—to a common symmetry principle. How the electroweak gauge symmetry is hidden is one of the most urgent and challenging questions facing particle physics. The provisional answer incorporated in the 'standard model' of particle physics was formulated in the 1960s by Higgs, by Brout and Englert and by Guralnik, Hagen, and Kibble: the agent of electroweak symmetry breaking is an elementary scalar field whose self-interactions select a vacuum state in which the full electroweak symmetry is hidden, leaving a residual phase symmetry of electromagnetism. By analogy with the Meissner effect of the superconducting phase transition, the Higgs mechanism, as it is commonly known, confers masses on the weak force carriers W± and Z. It also opens the door to masses for the quarks and leptons, and shapes the world around us. It is a good story—though an incomplete story—and we do not know how much of the story is true. Experiments that explore the Fermi scale (the energy regime around 1 TeV) during the next decade will put the electroweak theory to decisive test, and may uncover new elements needed to construct a more satisfying completion of the electroweak theory. The aim of this article is to set the stage by reporting what we know and what we need to know, and to set some 'big questions' that will guide our explorations.
TL;DR: In this paper, a mean-field model of electrons on a square lattice with two types of interaction, forward scattering favoring a d-wave Pomeranchuk instability and a BCS pairing interaction, is analyzed.
Abstract: We analyze a mean-field model of electrons on a square lattice with two types of interaction: forward scattering favoring a d-wave Pomeranchuk instability and a BCS pairing interaction driving d-wave superconductivity. Tuning the interaction parameters a rich variety of phase diagrams is obtained. If the BCS interaction is not too strong, Fermi surface symmetry breaking is stabilized around van Hove filling, and coexists with superconductivity at low temperatures. For pure forward scattering Fermi surface symmetry breaking occurs typically via a first order transition at low temperatures. The presence of superconductivity reduces the first order character of this transition and, if strong enough, can turn it into a continuous one. This gives rise to a quantum critical point within the superconducting phase. The superconducting gap tends to suppress Fermi surface symmetry breaking. For a relatively strong BCS interaction, Fermi surface symmetry breaking can be limited to intermediate temperatures, or can be suppressed completely by pairing.
TL;DR: In this article, a mathematically simple procedure is presented to explain spontaneous symmetry breaking in quantum systems. But the procedure is applicable to a wide range of models and can be easily used to explain the existence of a symmetry broken state in crystals, antiferromagnets, and even superconductors.
Abstract: We present a mathematically simple procedure to explain spontaneous symmetry breaking in quantum systems. The procedure is applicable to a wide range of models and can be easily used to explain the existence of a symmetry broken state in crystals, antiferromagnets, and even superconductors. It has the advantage that it automatically brings to the fore the main players in spontaneous symmetry breaking: the symmetry-breaking field, the thermodynamic limit, and the global excitations of a “thin” spectrum.
TL;DR: In this paper, the spontaneous breaking of U(1)R symmetry with two gauge singlets with R-charges 1 and 1 was parametrized in the Intriligator-Seiberg-Shih model.
Abstract: In the Intriligator-Seiberg-Shih model, we parametrize spontaneous breaking of U(1)R symmetry with two gauge singlets with R-charges 1 and –1. These singlets can play the role of the messengers. The messenger scale is dynamically generated, and hence there is no hierarchy problem between the supersymmetry breaking scale and the messenger scale. In the gauge mediation scenario, supersymmetry breaking scale turns out to be around (106) GeV.
TL;DR: In this article, the authors used the three flavour Nambu-Jona-Lasinio type model with 't Hooft and eight-quark interaction terms and showed that the local minimum of the effective potential catalyzed by the constant magnetic field is smoothed out with increasing strength of the field at the characteristic scale H ∼ 10 19 G.
TL;DR: The symmetry classification problem for wave equation on sphere is considered in this paper, where symmetry algebra is found and a classification of its subalgebras, up to conjugacy, is obtained.
TL;DR: In this article, the nature of polyamorphism and amorphous-to-amorphous transitions is investigated by means of an exactly solvable model with quenched disorder, the spherical $s+p$ multispin interaction model.
Abstract: The nature of polyamorphism and amorphous-to-amorphous transitions is investigated by means of an exactly solvable model with quenched disorder, the spherical $s+p$ multispin interaction model. The analysis is carried out in the framework of replica symmetry breaking theory and leads to the identification of low-temperature glass phases of different kinds. Besides the usual one-step solution, known to reproduce all basic properties of structural glasses, also a physically consistent two-step solution arises. More complicated phases are found as well, as temperature is further decreased, expressing a complex variety of metastable-state structures for amorphous systems.
TL;DR: In this paper, the static potential of a heavy quark-antiquark pair from spontaneous symmetry breaking of scale invariance in a non-Abelian gauge theory was determined.
30 Jul 2007
TL;DR: In this article, the phase structure of the twisted Eguchi-Kawai model was studied using numerical simulations and it was shown that the symmetry breaking point from the weak coupling side cannot be taken.
Abstract: We study the phase structure of the four-dimensional twisted Eguchi-Kawai model using numerical simulations. This model is an effective tool for studying SU(N) gauge theory in the large-N limit and provides a nonperturbative formulation of the gauge theory on noncommutative spaces. Recently it was found that its Z{sub n}{sup 4} symmetry, which is crucial for the validity of this model, can break spontaneously in the intermediate coupling region. We investigate in detail the symmetry breaking point from the weak coupling side. Our simulation results show that the continuum limit of this model cannot be taken.
TL;DR: In this article, a model of metastable dynamical supersymmetry breaking was proposed, in which all scales are generated dynamically, by renormalizable couplings to an auxiliary supersymmetric QCD sector.
Abstract: We propose a model of metastable dynamical supersymmetry breaking in which all scales are generated dynamically. Our construction is a simple variant of the Intriligator-Seiberg-Shih model, with quark masses induced by renormalizable couplings to an auxiliary supersymmetric QCD sector. Since all scales arise from dimensional transmutation, the model has no fundamental dimensionful parameters. It also does not rely on higher-dimensional operators.
TL;DR: In this paper, the authors show that metastable supersymmetry breaking is generic near certain enhanced symmetry points of gauge theory moduli spaces and that the metastable vacua appear as a result of a balance between non-perturbative and perturbative quantum effects along a pseudo-runaway direction.
Abstract: We show that metastable supersymmetry breaking is generic near certain enhanced symmetry points of gauge theory moduli spaces. Our model consists of two sectors coupled by a singlet and combines dynamical supersymmetry breaking with an O'Raifeartaigh mechanism in terms of confined variables. All relevant mass parameters, including the supersymmetry breaking scale, are generated dynamically. The metastable vacua appear as a result of a balance between non-perturbative and perturbative quantum effects along a pseudo-runaway direction.
TL;DR: In a diffeomorphism invariant theory, symmetry breaking may be used as a mask for coordinate choice as mentioned in this paper, and symmetry breaking can be used for coordinate selection in any dimension.
Abstract: In a diffeomorphism invariant theory, symmetry breaking may be a mask for coordinate choice.
TL;DR: In this paper, a finite-range density and momentum-dependent effective interaction was used to calculate the density and temperature dependence of the symmetry energy coefficient of infinite nuclear matter, which was then used in the local density approximation to evaluate the excitation energy dependence.
Abstract: A finite-range density and momentum-dependent effective interaction is used to calculate the density and temperature dependence of the symmetry energy coefficient ${C}_{\mathrm{sym}}(\ensuremath{\rho},T)$ of infinite nuclear matter. This symmetry energy is then used in the local density approximation to evaluate the excitation energy dependence of the symmetry energy coefficient of finite nuclei in a microcanonical formulation that accounts for thermal and expansion effects. The results are in good harmony with the recently reported experimental data from energetic nucleus-nucleus collisions.