56,588 research outputs found
Yang-Lee Theory for a Nonequilibrium Phase Transition
To analyze phase transitions in a nonequilibrium system we study its grand
canonical partition function as a function of complex fugacity. Real and
positive roots of the partition function mark phase transitions. This behavior,
first found by Yang and Lee under general conditions for equilibrium systems,
can also be applied to nonequilibrium phase transitions. We consider a
one-dimensional diffusion model with periodic boundary conditions. Depending on
the diffusion rates, we find real and positive roots and can distinguish two
regions of analyticity, which can identified with two different phases. In a
region of the parameter space both of these phases coexist. The condensation
point can be computed with high accuracy.Comment: 4 pages, accepted for publication in Phys.Rev.Let
Exact Solution for the Time Evolution of Network Rewiring Models
We consider the rewiring of a bipartite graph using a mixture of random and
preferential attachment. The full mean field equations for the degree
distribution and its generating function are given. The exact solution of these
equations for all finite parameter values at any time is found in terms of
standard functions. It is demonstrated that these solutions are an excellent
fit to numerical simulations of the model. We discuss the relationship between
our model and several others in the literature including examples of Urn,
Backgammon, and Balls-in-Boxes models, the Watts and Strogatz rewiring problem
and some models of zero range processes. Our model is also equivalent to those
used in various applications including cultural transmission, family name and
gene frequencies, glasses, and wealth distributions. Finally some Voter models
and an example of a Minority game also show features described by our model.Comment: This version contains a few footnotes not in published Phys.Rev.E
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Criterion for phase separation in one-dimensional driven systems
A general criterion for the existence of phase separation in driven
one-dimensional systems is proposed. It is suggested that phase separation is
related to the size dependence of the steady-state currents of domains in the
system. A quantitative criterion for the existence of phase separation is
conjectured using a correspondence made between driven diffusive models and
zero-range processes. Several driven diffusive models are discussed in light of
the conjecture
The Effect of Weak Interactions on the Ultra-Relativistic Bose-Einstein Condensation Temperature
We calculate the ultra-relativistic Bose-Einstein condensation temperature of
a complex scalar field with weak lambda Phi^4 interaction. We show that at high
temperature and finite density we can use dimensional reduction to produce an
effective three-dimensional theory which then requires non-perturbative
analysis. For simplicity and ease of implementation we illustrate this process
with the linear delta expansion.Comment: Latex2e, 12 pages, three eps figures, replacement with additional
discussion and extra figur
Phase Transition in Two Species Zero-Range Process
We study a zero-range process with two species of interacting particles. We
show that the steady state assumes a simple factorised form, provided the
dynamics satisfy certain conditions, which we derive. The steady state exhibits
a new mechanism of condensation transition wherein one species induces the
condensation of the other. We study this mechanism for a specific choice of
dynamics.Comment: 8 pages, 3 figure
A Gaussian process framework for modelling instrumental systematics: application to transmission spectroscopy
Transmission spectroscopy, which consists of measuring the
wavelength-dependent absorption of starlight by a planet's atmosphere during a
transit, is a powerful probe of atmospheric composition. However, the expected
signal is typically orders of magnitude smaller than instrumental systematics,
and the results are crucially dependent on the treatment of the latter. In this
paper, we propose a new method to infer transit parameters in the presence of
systematic noise using Gaussian processes, a technique widely used in the
machine learning community for Bayesian regression and classification problems.
Our method makes use of auxiliary information about the state of the
instrument, but does so in a non-parametric manner, without imposing a specific
dependence of the systematics on the instrumental parameters, and naturally
allows for the correlated nature of the noise. We give an example application
of the method to archival NICMOS transmission spectroscopy of the hot Jupiter
HD 189733, which goes some way towards reconciling the controversy surrounding
this dataset in the literature. Finally, we provide an appendix giving a
general introduction to Gaussian processes for regression, in order to
encourage their application to a wider range of problems.Comment: 6 figures, 1 table, accepted for publication in MNRA
A 125GeV Higgs Boson and Muon g-2 in More Generic Gauge Mediation
Recently, the ATLAS and CMS collaborations reported exciting hints of a
Standard Model-like Higgs boson with a mass around 125GeV. A Higgs boson this
heavy is difficult to realize in conventional models of gauge mediation. Here
we revisit the lightest Higgs boson mass in "more generic gauge mediation,"
where the Higgs doublets mix with the messenger doublets. We show that a Higgs
boson mass around 125GeV can be realized in more generic gauge mediation
models, even for a relatively light gluino mass ~1TeV. We also show that the
muon anomalous magnetic moment can be within 1sigma of the experimental value
for these models, even when the Higgs boson is relatively heavy. We also
discuss the LHC constraints and the prospects of discovery.Comment: 28 pages, 7 figures. Corrections and references are adde
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