Showing papers on "Explicit symmetry breaking published in 2006"
TL;DR: In this article, a simple class of models with meta-stable dynamical supersymmetry breaking was presented, where the free-magnetic dual of the supersymmetric QCD is used.
Abstract: Dynamical supersymmetry breaking in a long-lived meta-stable vacuum is a phenomenologically viable possibility. This relatively unexplored avenue leads to many new models of dynamical supersymmetry breaking. Here, we present a surprisingly simple class of models with meta-stable dynamical supersymmetry breaking: = 1 supersymmetric QCD, with massive flavors. Though these theories are strongly coupled, we definitively demonstrate the existence of meta-stable vacua by using the free-magnetic dual. Model building challenges, such as large flavor symmetries and the absence of an R-symmetry, are easily accommodated in these theories. Their simplicity also suggests that broken supersymmetry is generic in supersymmetric field theory and in the landscape of string vacua.
757 citations
TL;DR: Spontaneous symmetry breaking is explored in 87Rb spinor condensates, rapidly quenched across a quantum phase transition to a ferromagnetic state, and phase-sensitive in situ detection of spin vortices is demonstrated.
Abstract: A central goal in condensed matter and modern atomic physics is the exploration of quantum phases of matter--in particular, how the universal characteristics of zero-temperature quantum phase transitions differ from those established for thermal phase transitions at non-zero temperature. Compared to conventional condensed matter systems, atomic gases provide a unique opportunity to explore quantum dynamics far from equilibrium. For example, gaseous spinor Bose-Einstein condensates (whose atoms have non-zero internal angular momentum) are quantum fluids that simultaneously realize superfluidity and magnetism, both of which are associated with symmetry breaking. Here we explore spontaneous symmetry breaking in 87Rb spinor condensates, rapidly quenched across a quantum phase transition to a ferromagnetic state. We observe the formation of spin textures, ferromagnetic domains and domain walls, and demonstrate phase-sensitive in situ detection of spin vortices. The latter are topological defects resulting from the symmetry breaking, containing non-zero spin current but no net mass current.
746 citations
TL;DR: A model based on a few-state description of the charge-transfer processes characterizing the low-energy physics of multipolar molecular systems is developed, offering important clues to understand basic properties of materials of interest for NLO and energy-harvesting applications.
Abstract: We present a joint theoretical and experimental work aimed to understand the spectroscopic behavior of multipolar dyes of interest for nonlinear optics (NLO) applications. In particular, we focus on the occurrence of broken-symmetry states in quadrupolar organic dyes and their spectroscopic consequences. To gain a unified description, we have developed a model based on a few-state description of the charge-transfer processes characterizing the low-energy physics of these systems. The model takes into account the coupling between electrons and slow degrees of freedom, namely, molecular vibrations and polar solvation coordinates. We predict the occurrence of symmetry breaking in either the ground or first excited state. In this respect, quadrupolar chromophores are classified in three different classes, with distinctively different spectroscopic behavior. Cases of true and false symmetry breaking are discriminated and discussed by making resort to nonadiabatic calculations. The theoretical model is applied to three representative quadrupolar chromophores: their qualitatively different solvatochromic properties are connected to the presence or absence of broken-symmetry states and related to two-photon absorption (TPA) cross-sections. The proposed approach provides useful guidelines for the synthesis of dyes for TPA application and represents a general and unifying reference frame to understand energy-transfer processes in multipolar molecular systems, offering important clues to understand basic properties of materials of interest for NLO and energy-harvesting applications.
365 citations
TL;DR: In this paper, the see-saw mechanism was used to generate a fermion mass structure consistent with all quark and lepton masses and mixing angles in a model with an SU ( 3 ) f family symmetry.
218 citations
TL;DR: In this article, the authors present twin Higgs models based on the extension of the Standard Model to left-right symmetry that protect the weak scale against radiative corrections up to scales of order 5 TeV.
Abstract: We present twin Higgs models based on the extension of the Standard Model to left-right symmetry that protect the weak scale against radiative corrections up to scales of order 5 TeV. In the ultraviolet the Higgs sector of these theories respects an approximate global symmetry, in addition to the discrete parity symmetry characteristic of left-right symmetric models. The Standard Model Higgs field emerges as the pseudo-Goldstone boson associated with the breaking of the global symmetry. The parity symmetry tightly constrains the form of radiative corrections to the Higgs potential, allowing natural electroweak breaking. The minimal model predicts a rich spectrum of exotic particles that will be accessible to upcoming experiments, and which are necessary for the cancellation of one-loop quadratic divergences. These include right-handed gauge bosons with masses not to exceed a few TeV and a pair of vector-like quarks with masses of order several hundred GeV.
185 citations
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TL;DR: The general properties of non-linear systems are reviewed and the basic techniques, used universally, to study the symmetry breaking and bifurcation properties are shown.
Abstract: We review the general properties of non-linear systems and show the basic techniques, used universally, to study the symmetry breaking and bifurcation properties. We exemplify these characteristics by using a Turing system that is general enough as to present many of the universal features of non-linear systems. We then show some interesting applications to various problems that we have treated in the past.
176 citations
TL;DR: In this paper, a simple model of supersymmetry breaking with all small mass scales generated dynamically is proposed. But the model is not suitable for general supersymmetric Yang-Mills models.
Abstract: We provide a method for obtaining simple models of supersymmetry breaking, with all small mass scales generated dynamically, and illustrate it with explicit examples. We start from models of perturbative supersymmetry breaking, such as O'Raifeartaigh and Fayet models, that would respect an R symmetry if their small input parameters transformed as the superpotential does. By coupling the system to a pure supersymmetric Yang-Mills theory (or a more general supersymmetric gauge theory with dynamically small vacuum expectation values), these parameters are replaced by powers of its dynamical scale in a way that is naturally enforced by the symmetry. We show that supersymmetry breaking in these models may be straightforwardly mediated to the supersymmetric Standard Model, obtain complete models of direct gauge mediation, and comment on related model building strategies that arise in this simple framework.
173 citations
TL;DR: The non-Abelian discrete symmetry A_4 appears unsuitable as a family symmetry in grand unification as mentioned in this paper, since it does not transform in the same way as A_5.
Abstract: In the recent successful applications of the non-Abelian discrete symmetry A_4 to the tribimaximal mixing of neutrinos, lepton doublets and singlets do not transform in the same way. It appears thus to be unsuitable as a family symmetry in grand unification. A simple resolution of this dilemma is proposed.
126 citations
TL;DR: In this paper, an angle-resolved phase-sensitive technique was proposed to accurately determine the in-plane pairing symmetry, and demonstrated this technique in optimally doped YBa2Cu3O7-.
Abstract: Understanding the nature of the ground state and its low-lying excitations in the copper oxide superconductors is a prerequisite for determining the origin of high-temperature superconductivity. A superconducting order parameter (that is, the energy gap) with a predominantly dx2-y2 symmetry is well-established. However, various deviations from a pure d-wave pair state, such as the possibility of Cooper pairing with broken time-reversal symmetry or an admixed dx2-y2+s pair state, have been theoretically predicted and actively sought in numerous experimental studies. Here, we present an angle-resolved phase-sensitive technique for accurately determining the in-plane pairing symmetry, and demonstrate this technique in optimally doped YBa2Cu3O7-. We find that the gap along the b-axis (Cu–O chain) direction is at least 20% larger than that along the a-axis direction, and that any imaginary idxy, is or ip component must be smaller than a few per cent of the dx2-y2 component of the gap.
117 citations
TL;DR: The results of the Doppler-shift attenuation method lifetime measurements in partner bands of 128Cs and 132La show that 128Cs is the best known example revealing the chiral symmetry breaking phenomenon.
Abstract: The results of the Doppler-shift attenuation method lifetime measurements in partner bands of 128 Cs and 132 La are presented. Experimental reduced transition probabilities in 128 Cs are compared with theoretical calculations done in the frame of the core-quasiparticle coupling model. The electromagnetic properties, energy and spin of levels belonging to the partner bands show that 128 Cs is the best known example revealing the chiral symmetry breaking phenomenon.
109 citations
TL;DR: In this article, the Higgs field is identified as the internal component of a gauge field in the flat space R 4 × S 1 / Z 2, by relaxing the constraint of having unbroken SO ( 4, 1 ) Lorentz symmetry in the bulk.
TL;DR: In this paper, the authors discuss methods of data analysis which can be useful for making such inferences, and apply them to the problem of determining whether the preferred order in the cuprates is "stripes" or "checkerboards".
Abstract: In two dimensions, quenched disorder always rounds transitions involving the breaking of spatial symmetries so, in practice, it can often be difficult to infer what form the symmetry breaking would take in the 'ideal,' zero disorder limit We discuss methods of data analysis which can be useful for making such inferences, and apply them to the problem of determining whether the preferred order in the cuprates is 'stripes' or 'checkerboards' In many cases we show that the experiments clearly indicate stripe order, while in others (where the observed correlation length is short), the answer is presently uncertain
TL;DR: In this article, it was shown that the depth of the potential at a stationary point that breaks CB or CP, relative to the U ( 1 ) em preserving minimum, is proportional to the squared mass of the charged or pseudoscalar Higgs, respectively.
TL;DR: In this article, the authors analyzed the symmetries and the self-consistent perturbative approaches of dynamical field theories for glass-forming liquids and obtained symmetry-preserving mode-coupling equations and discussed their advantages and drawbacks.
Abstract: We analyse the symmetries and the self-consistent perturbative approaches of dynamical field theories for glass-forming liquids. In particular, we focus on the time-reversal symmetry, which is crucial to obtain fluctuation–dissipation relations (FDRs). Previous field theoretical treatment violated this symmetry, whereas others pointed out that constructing symmetry-preserving perturbation theories is a crucial and open issue. In this work we solve this problem and then apply our results to the mode-coupling theory of the glass transition (MCT). We show that in the context of dynamical field theories for glass-forming liquids time-reversal symmetry is expressed as a nonlinear field transformation that leaves the action invariant. Because of this nonlinearity, standard perturbation theories generically do not preserve time-reversal symmetry and in particular fluctuation–dissipation relations. We show how one can cure this problem and set up symmetry preserving perturbation theories by introducing some auxiliary fields. As an outcome we obtain Schwinger–Dyson dynamical equations that automatically preserve FDR and that serve as a basis for carrying out symmetry-preserving approximations. We apply our results to the mode-coupling theory of the glass transition, revisiting previous field theory derivations of MCT equations and showing that they generically violate FDR. We obtain symmetry-preserving mode-coupling equations and discuss their advantages and drawbacks. Furthermore, we show, contrary to previous works, that the structure of the dynamic equations is such that the ideal glass transition is not cut off at any finite order of perturbation theory, even in the presence of coupling between current and density. The opposite results found in previous field theoretical works, such as the ones based on nonlinear fluctuating hydrodynamics, were only due to an incorrect treatment of time-reversal symmetry.
TL;DR: A mass-independent texture is a set of linear relations of fermion mass-matrix elements which imposes no constraint on the fermionic masses nor the Majorana phases as mentioned in this paper.
Abstract: A mass-independent texture is a set of linear relations of the fermion mass-matrix elements which imposes no constraint on the fermionic masses nor the Majorana phases. Magic and 2\char21{}3 symmetries are examples. We discuss the general construction and the properties of these textures, as well as their relation to the quark and neutrino mixing matrices. Such a texture may be regarded as a symmetry, whose unitary generators of the symmetry group can be explicitly constructed. In particular, the symmetries connected with the tribimaximal neutrino mixing matrix are discussed, together with the physical consequence of breaking one symmetry but preserving another.
TL;DR: In this article, the authors investigated the S 3 permutation symmetry and derived the general forms of mass matrices in various types of S 3 theories, and showed typical examples of charge assignments which not only produce hierarchical orders of mass eigenvalues but also prohibit non-renormalizable operators which disturb the hierarchies in first-order estimation.
TL;DR: In this article, the effect of spin-orbit coupling and tunnel barrier strength on zero-conductance resonances appearing in a one-dimensional conducting Aharonov-Bohm ring symmetrically coupled to two leads was investigated.
Abstract: We investigate the effect of Rashba spin-orbit coupling and of a tunnel barrier on the zero-conductance resonances appearing in a one-dimensional conducting Aharonov-Bohm (AB) ring symmetrically coupled to two leads. The transmission function of the corresponding one-electron problem is derived within the scattering matrix approach and analyzed in the complex energy plane with focus on the role of the tunnel barrier strength on the zero-pole structure characteristic of transmission (anti)resonances. The lifting of the real conductance zeros is related to the breaking of the spin-reversal symmetry and time-reversal symmetry of Aharonov-Casher and AB rings, as well as to rotational symmetry breaking in the presence of a tunnel barrier. We show that the polarization direction of transmitted electrons can be controlled via the tunnel barrier strength and discuss a possible spin-filtering design in one-dimensional rings with tunable spin-orbit interaction.
25 Sep 2006
TL;DR: In this paper, some new propagators for breaking symmetries in constraint satisfaction problems are described, and symmetry breaking constraints are introduced to deal with symmeter acts acting simultaneously on variables and values, conditional symmeter acting on set and other types of variables.
Abstract: We describe some new propagators for breaking symmetries in constraint satisfaction problems. We also introduce symmetry breaking constraints to deal with symmetries acting simultaneously on variables and values, conditional symmetries, as well as symmeties acting on set and other types of variables.
TL;DR: In this paper, the authors introduce the method of diagonalizing or block-diagonalizing continuously a Hamiltonian and explain how this procedure can be used to analyse the two-dimensional Hubbard model.
Abstract: First we give an introduction to the method of diagonalizing or block-diagonalizing continuously a Hamiltonian and explain how this procedure can be used to analyse the two-dimensional Hubbard model. Then we give a short survey on applications of this flow equation on other models. Finally we outline, how symmetry breaking can be introduced by means of a symmetry breaking of the normal ordering, not of the Hamiltonian.
TL;DR: In this paper, a flat axially symmetric Finslerian space of events, which is the generalization of Minkowski space, is given to a spontaneous breaking of initial gauge symmetry and the formation of anisotropic fermion-antifermion condensate.
TL;DR: In this paper, the pseudospin symmetry and spin symmetry in the relativistic Woods-Saxon are investigated systematically by solving the Dirac equation with scalar and vector potentials.
TL;DR: In this article, the confinement of static charges from spontaneous symmetry breaking of scale invariance in a gauge theory was shown to be possible. But it was only at the quantum level, using a path-dependent variables formalism, that the Cornell confining potential was obtained.
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TL;DR: In this paper, the authors compare the tree level estimate of the electro-weak precision parameters in two (exactly solvable) toy models of dynamical symmetry breaking in which the strong dynamics is assumed to be described by a five-dimensional (weakly coupled) gravity dual.
Abstract: I compare the tree level estimate of the electro-weak precision parameters in two (exactly solvable) toy models of dynamical symmetry breaking in which the strong dynamics is assumed to be described by a five-dimensional (weakly coupled) gravity dual. I discuss the effect of brane-localized kinetic terms, their use as regulators for the couplings of otherwise non-normalizable modes, and the impact of a large deviation from its natural value for the scaling dimension of the background field responsible for spontaneous symmetry breaking. The latter is assumed to model the effects of walking dynamics, i.e. of a large anomalous dimension of the chiral condensate, it has a strong impact of the spectrum of spin-1 fields and, as a consequence, on the electro-weak precision parameters. The main conclusion is that models of dynamical symmetry breaking based on a large-Nc strongly interacting SU(Nc) gauge theory are compatible with precision electro-weak constraints, and produce a very distinctive signature testable at the LHC. Some of the considerations discussed are directly relevant for analogous models in the context of AdS-QCD.
TL;DR: In this article, the relation between symmetry reduction before and after quantization of a field theory is discussed using a toy model: the axisymmetric Klein-Gordon field, and three possible notions of symmetry at the quantum level: invariance under the group action, and two notions derived from imposing symmetry as a system of constraints in the manner of Dirac, reformulated as a first class system.
Abstract: The relation between symmetry reduction before and after quantization of a field theory is discussed using a toy model: the axisymmetric Klein–Gordon field. We consider three possible notions of symmetry at the quantum level: invariance under the group action, and two notions derived from imposing symmetry as a system of constraints in the manner of Dirac, reformulated as a first class system. One of the latter two turns out to be the most appropriate notion of symmetry in the sense that it satisfies a number of physical criteria, including the commutativity of quantization and symmetry reduction. Somewhat surprisingly, the requirement of invariance under the symmetry group action is not appropriate for this purpose. A generalization of the physically selected notion of symmetry to loop quantum gravity is presented and briefly discussed.
TL;DR: It is shown that the combined effect of a thermal environment and coupling to leads, involving tunneling events charging and discharging the molecule, leads to a dynamical symmetry breaking where quasidegenerate eigenstates acquire different occupations.
Abstract: We analyze the interplay between vibrational and electronic degrees of freedom in charge transport across a molecular single-electron transistor. We focus on the wide class of molecules which possess quasidegenerate vibrational eigenstates, while no degeneracy occurs for their anionic configuration. We show that the combined effect of a thermal environment and coupling to leads, involving tunneling events charging and discharging the molecule, leads to a dynamical symmetry breaking where quasidegenerate eigenstates acquire different occupations. This imbalance gives rise to a characteristic asymmetry of the current versus an applied gate voltage.
TL;DR: In this paper, it was shown that chiral symmetry breaking can be directly traced from QCD sum rules for two point functions assuming, in the large number of colors limit, exact duality between the operator product expansion and the spectrum described by linearly (or nearly linear) rising Regge trajectories as predicted by string theory.
Abstract: We show how such important features of QCD as chiral symmetry breaking or the formation of a mass-gap can be directly traced from QCD sum rules for two point functions assuming, in the large number of colors limit, exact duality between the operator product expansion and the spectrum described by linearly (or nearly linear) rising Regge trajectories as predicted by string theory. We see how the presence of chiral symmetry breaking is intimately related to confinement in this scenario, as expected from general arguments, and how Regge trajectories change when chiral symmetry is broken. As a result the whole meson mass spectrum can be parametrized with a good accuracy by the constant fπ only, thus realizing the program proposed by Migdal some time ago.
TL;DR: It turns out that all mean-field solvable models do meet this requirement, whereas the presence of strong correlations leads to a violation of this condition, which results in an order-induced enhancement of entanglement.
Abstract: We study the effect of symmetry breaking in a quantum phase transition on pairwise entanglement in spin-$1/2$ models. We give a set of conditions on correlation functions a model has to meet in order to keep the pairwise entanglement unchanged by a parity symmetry breaking. It turns out that all mean-field solvable models do meet this requirement, whereas the presence of strong correlations leads to a violation of this condition. This results in an order-induced enhancement of entanglement, and we report on two examples where this takes place.
TL;DR: In this paper, the authors examined the bifurcation behavior of a planar pendulum subjected to high-frequency parametric excitation along a tilted angle and found that small deviations from either a perfectly vertical or horizontal excitation will result in symmetry breaking bifurocations as opposed to pitchfork bifurbation.
Abstract: This paper examines the bifurcation behavior of a planar pendulum subjected to high-frequency parametric excitation along a tilted angle. Parametric nonlinear identification is performed on the experimental system via an optimization approach that utilizes a developed approximate analytical solution. Experimental and theoretical efforts then consider the influence of a subtle tilt angle in the applied parametric excitation by contrasting the predicted and observed mean angle bifurcations with the bifurcations due to excitation applied in either the vertical or horizontal direction. Results show that small deviations from either a perfectly vertical or horizontal excitation will result in symmetry breaking bifurcations as opposed to pitchfork bifurcations.
TL;DR: In this article, a variational Monte Carlo (VMC) study of spontaneous Fermi surface symmetry breaking in the t-J model is presented, and it is shown that the variational energy of a Gutzwiller projected fermi sea is lowered by allowing for a finite asymmetry between the x-and the y-directions.
Abstract: We present a variational Monte Carlo (VMC) study of spontaneous Fermi surface symmetry breaking in the t-J model. We find that the variational energy of a Gutzwiller projected Fermi sea is lowered by allowing for a finite asymmetry between the x- and the y-directions. However, the best variational state remains a pure superconducting state with d-wave symmetry, as long as the underlying lattice is isotropic. Our VMC results are in good overall agreement with slave boson mean field theory (SBMFT) and renormalized mean field theory (RMFT), although apparent discrepancies do show up in the half-filled limit, revealing some limitations of mean field theories. VMC and complementary RMFT calculations also confirm the SBMFT predictions that many-body interactions can enhance any anisotropy in the underlying crystal lattice. Thus, our results may be of consequence for the description of strongly correlated superconductors with an anisotropic lattice structure.