We discuss the phenomena of symmetry nonrestoration and inverse symmetry breaking in the context of multi-scalar field theories at finite temperatures and present its consequences for the relativistic HiggsKibble multi-field sector as well as for a nonrelativistic model of hard core spheres. For relativistic scalar field models, it has been shown previously that temperature effects on the couplings do not alter, qualitatively, the phase transition pattern. Here, we show that for the nonrelativistic analogue of these models inverse symmetry breaking, as well as symmetry nonrestoration, cannot take place, at high temperatures, when the temperature dependence of the two-body couplings is considered. However, the temperature behavior in the nonrelativistic models allows for the appearance of reentrant phases.

Abstract. We study and compare the information loss of a large class of Gaussian bipartite systems. It includes the usual Caldeira-Leggett type model as well as Anosov models (parametric oscillators, the inverted oscillator environment, etc), which exhibit instability, one of the most important characteristics of chaotic systems. We establish a rigorous connection between the quantum Lyapunov exponents and coherence loss and show that in the case of unstable environments, coherence loss is completely determined by the upper quantum Lyapunov exponent, a behavior which is more universal than that of the Caldeira-Leggett type model.

We show that it is possible to quantify the information content of a nonautonomous free field state in curved space-time. A covariance matrix is defined and it is shown that, for symmetric Gaussian field states, the matrix is connected to the entropy of the state. This connection is maintained throughout a quadratic nonautonomous (including possible phase transitions) evolution. Although particle-antiparticle correlations are dynamically generated, the evolution is isoentropic. If the current standard cosmological model for the inflationary period is correct, in absence of decoherence such correlations will be preserved, and could potentially lead to observable effects, allowing for a test of the model.

We show that multi-loop hysteresis, recently observed by Cotta and Matinaga in semiconductor optical cavities in the strong coupling regime [Phys. Rev. B. 76, 073308 (2007)], can be explained as a competition between the externally controlled pumping intensity and the delayed response of the well in delivering heat to the bottom of the base. As the external pump intensity grows, the material heats proportionally. However, when the pump intensity decreases, the system cannot deliver heat to the cooled base at the same rate, and the temperature decreases with a delay in relation to the pump intensity. This time mismatch is responsible for the hysteresis and the crossing of the curves. We also show how this type of experiment can be used to clarify the complicated process of thermal dynamics in semiconductors.