361,237 research outputs found
Effective temperature and glassy dynamics of active matter
A systematic expansion of the many-body master equation for active matter, in
which motors power configurational changes as in the cytoskeleton, is shown to
yield a description of the steady state and responses in terms of an effective
temperature. The effective temperature depends on the susceptibility of the
motors and a Peclet number which measures their strength relative to thermal
Brownian diffusion. The analytic prediction is shown to agree with previous
numerical simulations and experiments. The mapping also establishes a
description of aging in active matter that is also kinetically jammed.Comment: 2 figure
Power-law out of time order correlation functions in the SYK model
We evaluate the finite temperature partition sum and correlation functions of
the Sachdev-Ye-Kitaev (SYK) model. Starting from a recently proposed mapping of
the SYK model onto Liouville quantum mechanics, we obtain our results by exact
integration over conformal Goldstone modes reparameterizing physical time.
Perhaps, the least expected result of our analysis is that at time scales
proportional to the number of particles the out of time order correlation
function crosses over from a regime of exponential decay to a universal
power-law behavior.Comment: 25 pages, 3 figures, minor changes, version accepted for publicatio
Phase separation on a hyperbolic lattice
We report a preliminary numerical study by kinetic Monte Carlo simulation of
the dynamics of phase separation following a quench from high to low
temperature in a system with a single, conserved, scalar order parameter (a
kinetic Ising ferromagnet) confined to a hyperbolic lattice. The results are
compared with simulations of the same system on two different, Euclidean
lattices, in which cases we observe power-law domain growth with an exponent
near the theoretically known value of 1/3. For the hyperbolic lattice we
observe much slower domain growth, consistent to within our current accuracy
with power-law growth with a much smaller exponent near 0.13. The paper also
includes a brief introduction to non-Euclidean lattices and their mapping to
the Euclidean plane.Comment: Computer Simulation Studies in Condensed Matter Physics 26 (CSP13),
Edited by D.P. Landau, S.P. Lewis, H.-B. Schuttle
Determining the HI content of galaxies via intensity mapping cross-correlations
We propose an innovative method for measuring the neutral hydrogen (HI)
content of an optically-selected spectroscopic sample of galaxies through
cross-correlation with HI intensity mapping measurements. We show that the
HI-galaxy cross-power spectrum contains an additive shot noise term which
scales with the average HI brightness temperature of the optically-selected
galaxies, allowing constraints to be placed on the average HI mass per galaxy.
This approach can estimate the HI content of populations too faint to directly
observe through their 21cm emission over a wide range of redshifts. This
cross-correlation, as a function of optical luminosity or colour, can be used
to derive HI-scaling relations. We demonstrate that this signal will be
detectable by cross-correlating upcoming Australian SKA Pathfinder (ASKAP)
observations with existing optically-selected samples. We also use
semi-analytic simulations to verify that the HI mass can be successfully
recovered by our technique in the range M_HI > 10^8 M_solar, in a manner
independent of the underlying power spectrum shape. We conclude that this
method is a powerful tool to study galaxy evolution, which only requires a
single intensity mapping dataset to infer complementary HI gas information from
existing optical and infra-red observations.Comment: 8 pages, 4 figures, submitted to MNRA
Impurity spin relaxation in S=1/2 XX chains
Dynamic autocorrelations (\alpha=x,z) of an
isolated impurity spin in a S=1/2 XX chain are calculated. The impurity spin,
defined by a local change in the nearest-neighbor coupling, is either in the
bulk or at the boundary of the open-ended chain. The exact numerical
calculation of the correlations employs the Jordan-Wigner mapping from spin
operators to Fermi operators; effects of finite system size can be eliminated.
Two distinct temperature regimes are observed in the long-time asymptotic
behavior. At T=0 only power laws are present. At high T the x correlation
decays exponentially (except at short times) while the z correlation still
shows an asymptotic power law (different from the one at T=0) after an
intermediate exponential phase. The boundary impurity correlations follow power
laws at all T. The power laws for the z correlation and the boundary
correlations can be deduced from the impurity-induced changes in the properties
of the Jordan-Wigner fermion states.Comment: Final version to be published in Phys. Rev. B. Three references
added, extended discussion of relation to previous wor
Nonlinear modulation of the HI power spectrum on ultra-large scales. I
Intensity mapping of the neutral hydrogen brightness temperature promises to provide a three-dimensional view of the universe on very large scales. Nonlinear effects are typically thought to alter only the small-scale power, but we show how they may bias the extraction of cosmological information contained in the power spectrum on ultra-large scales. For linear perturbations to remain valid on large scales, we need to renormalize perturbations at higher order. In the case of intensity mapping, the second-order contribution to clustering from weak lensing dominates the nonlinear contribution at high redshift. Renormalization modifies the mean brightness temperature and therefore the evolution bias. It also introduces a term that mimics white noise. These effects may influence forecasting analysis on ultra-large scales
Exact first-passage exponents of 1D domain growth: relation to a reaction diffusion model
In the zero temperature Glauber dynamics of the ferromagnetic Ising or
-state Potts model, the size of domains is known to grow like .
Recent simulations have shown that the fraction of spins which have
never flipped up to time decays like a power law with a non-trivial dependence of the exponent on
and on space dimension. By mapping the problem on an exactly soluble
one-species coagulation model (), we obtain the exact
expression of in dimension one.Comment: latex,no figure
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