Spontaneous symmetry breaking in an electromagnetic field-insulator system

Conditions for spontaneous symmetry breaking and generation of quasi-particles in an insulator through which an electromagnetic field propagates are considered. The order parameter of the system is determined. The mass spectrum of the quasi-particles is found in the cases of linear and nonlinear propagation through the medium with and without interfaces.     

Spontaneous symmetry breaking in a time-dependent space-time

Spontaneous symmetry breaking of a ⁴ quantum of field theory in a time-dependent space-time, de Sitter space, is discussed in the Schrödinger picture. Instead of the usual cutoff method we use an-regularization procedure to deal with the divergent integrals.     

Spontaneous symmetry breaking in QCD

We study dynamical chiral symmetry breaking in massless QCD by the use of the generalized Hartree-Fock method. As the order parameter of chiral symmetry we choose the dynamical quark mass in the zero momentum limit which we call low energy quark mass. We calculate the low energy mass to the second order of diagrammatic expansion around shifted perturbative vacuum. We then show that the mass is finite and renormalization group invariant. After the improvement of the result by the method of effective charges we estimate the mass in the true vacuum under the gap and stationarity conditions and demonstrate that both of them produce non-zero mass proportional to a conventional scale, which breaks down the chiral symmetry.     

Dissipation-induced symmetry breaking in a driven optical lattice

We analyze the atomic dynamics in an ac driven periodic optical potential which is symmetric in both time and space. We experimentally demonstrate that in the presence of dissipation the symmetry is broken, and a current of atoms through the optical lattice is generated as a result.     

Spontaneous symmetry breaking of arbitrage

We introduce the concept of spontaneous symmetry breaking to arbitrage modeling. In the model, the arbitrage strategy is considered as being in the symmetry breaking phase and the phase transition between arbitrage mode and no-arbitrage mode is triggered by a control parameter. We estimate the control parameter for a momentum strategy with real historical data. The momentum strategy aided by symmetry breaking shows stronger performance and has a better risk measure than the naive momentum strategy in U.S. and South Korean markets.     

Spontaneous symmetry breaking of population in a nonadiabatically driven atomic trap: an Ising-class phase transition

We have observed spontaneous symmetry breaking of the population of Brownian particles between two moving potentials in the spatiotemporally symmetric system. Cold atoms preferentially occupy one of the dynamic double-well potentials, produced in the parametrically driven dissipative magneto-optical trap far from equilibrium, above a critical number of atoms. We find that the population asymmetry, which may be interpreted as the biased Brownian motion, can be qualitatively described by the mean-field Ising-class phase transition. This in situ study may be useful for investigation of dynamic phase transition or temporal behavior of critical phenomena.     

Spontaneous symmetry breaking on a mutiple-channel hollow cylinder

This Letter investigates coupled asymmetric exclusion processes with two types of particles on multiple parallel channels of a hollow cylinder. The model is inspired by the structure of microtubules, along which motor proteins such as kinesins and dyneins move in opposite directions. Interactions between two-species particles are assumed to take place only on the left and right boundaries where a rule of narrow entrances is applied. Narrow entrances mean that a particle cannot enter the system if either of two nearest-neighbor sites on the neighboring channels is occupied by a particle of the other species. This rule is similar to, but different from, that in [E. Pronina, A.B. Kolomeisky, J. Phys. A 40 (2007) 2275] since the narrow entrance rule in our model involves two neighbors. The phase diagram of our model is studied theoretically and via Monte Carlo simulations. The spontaneous symmetry breaking (SSB) is observed in the system. There are four possible phases in the system and with SSB occurring in two of them: high/low density and asymmetric low/low density. Bulk density and particle currents are also computed. Theoretical calculations deviate from Monte Carlo simulation results due to the neglecting of correlations in particles dynamics in mean-field analysis.     

Spontaneous symmetry breaking in Reggeon field theory

We consider a Reggeon field theory when the bare or input Regge intercept α_O is greater than one. This corresponds to a negative mass squared term in conventional field theory and allows for a spontaneous symmetry break-down. A theory with Regge intercept at one emerges, restoring the Froissart bound by t-channel considerations alone. In our elementary example the resulting bare trajectory is nearly of the square root variety familiar from s-channel eikonalization of models which violate the Froissart bound.     

Spontaneous symmetry breaking for zero mass

We investigate spontaneous symmetry breaking of a zero mass free Lagrangian within a functional formalism. We find that the boundary conditions of field solutions are responsible for the spontaneous symmetry breaking and this can be incorporated naturally in a functional method.     

Spontaneous symmetry breaking and response functions

We study the quantum phase transition occurring in an infinite homogeneous system of spin 1/2 fermions in a non-relativistic context. As an example we consider neutrons interacting through a simple spin-spin Heisenberg force. The two critical values of the coupling strength—signaling the onset into the system of a finite magnetization and of the total magnetization, respectively—are found and their dependence upon the range of the interaction is explored. The spin response function of the system in the region where the spin-rotational symmetry is spontaneously broken is also studied. For a ferromagnetic interaction the spin response along the direction of the spontaneous magnetization occurs in the particle-hole continuum and displays, for not too large momentum transfers, two distinct peaks. The response along the direction orthogonal to the spontaneous magnetization displays instead, beyond a softened and depleted particle-hole continuum, a collective mode to be identified with a Goldstone boson of type II. Notably, the random phase approximation on a Hartree-Fock basis accounts for it, in particular for its quadratic—close to the origin—dispersion relation. It is shown that the Goldstone boson contributes to the saturation of the energy-weighted sum rule for ≈25% when the system becomes fully magnetized (that is in correspondence of the upper critical value of the interaction strength) and continues to grow as the interaction strength increases.     

Spontaneous breaking of chiral symmetry in QCD

The consistency of iso-spin (SU(3)) symmetry of the vacuum with the spontaneous breakdown of chiral symmetry without the appearance of a U(1) Goldstone boson, is investigated.     

Spontaneous symmetry breaking vacuum energy in cosmology

The gravitational effect of spontaneous symmetry breaking vacuum energy density is investigated by subtracting the flat space-time contribution from the energy in the curved space-time. We find that the remaining effective energy-momentum tensor is too small to cause the acceleration of the universe, although it satisfies the characteristics of dark energy. However, it could provide a promising explanation to the puzzle of why the gravitational effect produced by the huge symmetry breaking vacuum energy in the electroweak theory has not been observed, as it has a sufficiently small value (smaller than the observed cosmic energy density by a factor of 1032).     

Spontaneous phase symmetry breaking in a four-frequency ring gas laser

Lasing regimes of a single-mode four-frequency class-A ring gas laser with elliptical polarization of the emitted waves are studied numerically. Stationary regimes typical of both standing-and traveling-wave lasing are discovered. Self-oscillations exhibiting the properties of asymmetric and symmetric limit cycles are also found. It is shown that transition between cycles with different symmetry may result in the spontaneous phase symmetry breaking and the appearance of chaos arising due to the period doubling bifurcation cascade of the asymmetric limit cycle.     

Spontaneous symmetry breaking of optimum fluctuations in semiconductors

The optimum fluctuation method (OFM) has been applied to the tails of the density of states, arising near the edges of the spherically symmetric degenerate bands. In this case the optimum fluctuations (OF) have been shown to undergo a qualitative change, as compared to the case of nondegenerate bands, they lose the spherical symmetry and become elongated or flattened. This means that spontaneous breaking of symmetry takes place. In addition to the usual mechanism of tailing due to the potential of impurities, another mechanism connected with the field of random deformations, arising due to difference in the size of the guest and host atoms, has been also considered. The method used for treating this problem is intimately related to the techniques of the theory of self-trapping. The density of states in the tails, and in some cases the shape of OFs, have been found for all the cases under consideration.