18,094 research outputs found
Inverse Symmetry Breaking in Multi-Scalar Field Theories
We review how the phenomena of inverse symmetry breaking (and symmetry
nonrestoration) may arise in the context of relativistic as well as
nonrelativistic multi-scalar field theories. We discuss how the consideration
of thermal effects on the couplings produce different transition patterns for
both theories. For the relativistic case, these effects allow the appearance of
inverse symmetry breaking (and symmetry nonrestoration) at arbitrarily large
temperatures. On the other hand, the same phenomena are suppressed in the
nonrelativistic case, which is relevant for condensed matter physics. In this
case, symmetry nonrestoration does not happen while inverse symmetry is allowed
only to be followed by symmetry restoration characterizing a reentrant phase.
The aim of this paper is to give more insight concerning the, qualitatively
correct, results obtained by using one loop perturbation theory in the
evaluation of thermal masses and couplings.Comment: 7 pages, 3 figures, talk given at the workshop on Quantum Fields
Under the Influence of External Conditions, QFEXT05, Barcelona, sep-200
Symmetry Aspects in Nonrelativistic Multi-Scalar Field Models and Application to a Coupled Two-Species Dilute Bose Gas
We discuss unusual aspects of symmetry that can happen due to entropic
effects in the context of multi-scalar field theories at finite temperature. We
present their consequences, in special, for the case of nonrelativistic models
of hard core spheres. We show that for nonrelativistic models phenomena like
inverse symmetry breaking and symmetry non-restoration cannot take place, but a
reentrant phase at high temperatures is shown to be possible for some region of
parameters. We then develop a model of interest in studies of Bose-Einstein
condensation in dilute atomic gases and discuss about its phase transition
patterns. In this application to a Bose-Einstein condensation model, however,
no reentrant phases are found.Comment: 8 pages, 1 eps figure, IOP style. Based on a talk given by R. O.
Ramos at the QFEXT05 workshop, Barcelona, Spain, September 5-9, 2005. One
reference was update
Shaping the Laser Control Landscape of a Hydrogen Transfer Reaction by Vibrational Strong Coupling. A Direct Optimal Control Approach
Controlling molecular reactivity by shaped laser pulses is a long-standing
goal in chemistry. Here we suggest a direct optimal control approach which
combines external pulse optimization with other control parameters arising in
the upcoming field of vibro-polaritonic chemistry, for enhanced controllability
The direct optimal control approach is characterized by a simultaneous
simulation and optimization paradigm, meaning that the equations of motion are
discretized and converted into a set of holonomic constraints for a nonlinear
optimization problem given by the control functional. Compared with indirect
optimal control this procedure offers great flexibility such as final time or
Hamiltonian parameter optimization. Simultaneous direct optimal control
(SimDOC) theory will be applied to a model system describing H-atom transfer in
a lossy Fabry-P\'erot cavity under vibrational strong coupling conditions.
Specifically, optimization of the cavity coupling strength and thus of the
control landscape will be demonstrated
- …