3,643 research outputs found
Symmetries in Fluctuations Far from Equilibrium
Fluctuations arise universally in Nature as a reflection of the discrete
microscopic world at the macroscopic level. Despite their apparent noisy
origin, fluctuations encode fundamental aspects of the physics of the system at
hand, crucial to understand irreversibility and nonequilibrium behavior. In
order to sustain a given fluctuation, a system traverses a precise optimal path
in phase space. Here we show that by demanding invariance of optimal paths
under symmetry transformations, new and general fluctuation relations valid
arbitrarily far from equilibrium are unveiled. This opens an unexplored route
toward a deeper understanding of nonequilibrium physics by bringing symmetry
principles to the realm of fluctuations. We illustrate this concept studying
symmetries of the current distribution out of equilibrium. In particular we
derive an isometric fluctuation relation which links in a strikingly simple
manner the probabilities of any pair of isometric current fluctuations. This
relation, which results from the time-reversibility of the dynamics, includes
as a particular instance the Gallavotti-Cohen fluctuation theorem in this
context but adds a completely new perspective on the high level of symmetry
imposed by time-reversibility on the statistics of nonequilibrium fluctuations.
The new symmetry implies remarkable hierarchies of equations for the current
cumulants and the nonlinear response coefficients, going far beyond Onsager's
reciprocity relations and Green-Kubo formulae. We confirm the validity of the
new symmetry relation in extensive numerical simulations, and suggest that the
idea of symmetry in fluctuations as invariance of optimal paths has
far-reaching consequences in diverse fields.Comment: 8 pages, 4 figure
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
Spectral signatures of symmetry-breaking dynamical phase transitions
Large deviation theory provides the framework to study the probability of
rare fluctuations of time-averaged observables, opening new avenues of research
in nonequilibrium physics. One of the most appealing results within this
context are dynamical phase transitions (DPTs), which might occur at the level
of trajectories in order to maximize the probability of sustaining a rare
event. While the Macroscopic Fluctuation Theory has underpinned much recent
progress on the understanding of symmetry-breaking DPTs in driven diffusive
systems, their microscopic characterization is still challenging. In this work
we shed light on the general spectral mechanism giving rise to continuous DPTs
not only for driven diffusive systems, but for any jump process in which a
discrete symmetry is broken. By means of a symmetry-aided
spectral analysis of the Doob-transformed dynamics, we provide the conditions
whereby symmetry-breaking DPTs might emerge and how the different dynamical
phases arise from the specific structure of the degenerate eigenvectors. We
show explicitly how all symmetry-breaking features are encoded in the
subleading eigenvectors of the degenerate manifold. Moreover, by partitioning
configuration space into equivalence classes according to a proper order
parameter, we achieve a substantial dimensional reduction which allows for the
quantitative characterization of the spectral fingerprints of DPTs. We
illustrate our predictions in three paradigmatic many-body systems: (i) the 1D
boundary-driven weakly asymmetric exclusion process (WASEP), which exhibits a
particle-hole symmetry-breaking DPT for current fluctuations, (ii) the and
-state Potts model, which displays discrete rotational symmetry-breaking DPT
for energy fluctuations, and (iii) the closed WASEP which presents a continuous
symmetry-breaking DPT to a time-crystal phase characterized by a rotating
condensate
Reply to comment on "Simple one-dimensional model of heat conduction which obeys Fourier's law"
In this reply we answer the comment by A. Dhar (cond-mat/0203077) on our
Letter "Simple one dimensional model of heat conduction which obeys Fourier's
law" (Phys. Rev. Lett. 86, 5486 (2001), cond-mat/0104453)Comment: 1 pag., 1 fi
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