50 research outputs found
Reentrant Behavior of the Spinodal Curve in a Nonequilibrium Ferromagnet
The metastable behavior of a kinetic Ising--like ferromagnetic model system
in which a generic type of microscopic disorder induces nonequilibrium steady
states is studied by computer simulation and a mean--field approach. We pay
attention, in particular, to the spinodal curve or intrinsic coercive field
that separates the metastable region from the unstable one. We find that, under
strong nonequilibrium conditions, this exhibits reentrant behavior as a
function of temperature. That is, metastability does not happen in this regime
for both low and high temperatures, but instead emerges for intermediate
temperature, as a consequence of the non-linear interplay between thermal and
nonequilibrium fluctuations. We argue that this behavior, which is in contrast
with equilibrium phenomenology and could occur in actual impure specimens,
might be related to the presence of an effective multiplicative noise in the
system.Comment: 7 pages, 4 figures; Final version to appear in Phys. Rev. E; Section
V has been revise
Radiative Damping and Functional Differential Equations
We propose a general technique to solve the classical many-body problem with
radiative damping. We modify the short-distance structure of Maxwell
electrodynamics. This allows us to avoid runaway solutions as if we had a
covariant model of extended particles. The resulting equations of motion are
functional differential equations (FDEs) rather than ordinary differential
equations. Using recently developed numerical techniques for stiff FDEs, we
solve these equations for the one-body central force problem with radiative
damping with a view to benchmark our new approach. Our results indicate that
locally the magnitude of radiation damping may be well approximated by the
standard third-order expression but the global properties of our solutions are
dramatically different. We comment on the two body problem and applications to
quantum field theory and quantum mechanics.Comment: (v1) 6 pages, version of Nov 22, 2007 (v2) 24 pages double-spaced.
calculations and results unchanged, explanations elaborate
Manifestly local theory of vacuum energy sequestering
We present a manifestly local, diffeomorphism invariant, and locally Poincaré invariant formulation of vacuum energy sequestering. In this theory, quantum vacuum energy generated by matter loops is canceled by auxiliary fields. The auxiliary fields decouple from gravity almost completely. Their only residual effect is an a priori arbitrary, finite contribution to the curvature of the background geometry, which is radiatively stable. Its value is to be determined by a measurement, like the finite part of any radiatively stable UV-sensitive quantity in quantum field theory