79 research outputs found
Sensitivity of lunar particle-detection experiments
The use of the Moon as a detector volume for ultra-high-energy neutrinos and
cosmic rays, by searching for the Askaryan radio pulse produced when they
interact in the lunar regolith, has been attempted by a range of projects over
the past two decades. In this contribution, I discuss some of the technical
considerations relevant to these experiments, and their consequent sensitivity
to ultra-high-energy particles. I also discuss some possible future
experiments, and highlight their potential.Comment: To be published in the Proceedings of the ARENA2016 conference,
Groningen, The Netherland
Limits on the validity of the thin-layer model of the ionosphere for radio interferometric calibration
For a ground-based radio interferometer observing at low frequencies, the
ionosphere causes propagation delays and refraction of cosmic radio waves which
result in phase errors in the received signal. These phase errors can be
corrected using a calibration method that assumes a two-dimensional phase
screen at a fixed altitude above the surface of the Earth, known as the
thin-layer model. Here we investigate the validity of the thin-layer model and
provide a simple equation with which users can check when this approximation
can be applied to observations for varying time of day, zenith angle,
interferometer latitude, baseline length, ionospheric electron content and
observing frequency.Comment: 8 pages, 10 figures, accepted MNRA
Pattern formation in self-propelled particles with density-dependent motility
We study the behaviour of interacting self-propelled particles, whose
self-propulsion speed decreases with their local density. By combining direct
simulations of the microscopic model with an analysis of the hydrodynamic
equations obtained by explicitly coarse graining the model, we show that
interactions lead generically to the formation of a host of patterns, including
moving clumps, active lanes and asters. This general mechanism could explain
many of the patterns seen in recent experiments and simulations
Quenched complexity of the p-spin spherical spin-glass with external magnetic field
We consider the p-spin spherical spin-glass model in the presence of an
external magnetic field as a general example of a mean-field system where a one
step replica symmetry breaking (1-RSB) occurs. In this context we compute the
complexity of the Thouless-Anderson-Palmer states, performing a quenched
computation. We find what is the general connection between this method and the
standard static 1-RSB one, formulating a clear mapping between the parameters
used in the two different calculations. We also perform a dynamical analysis of
the model, by which we confirm the validity of our results.Comment: RevTeX, 11 pages, including 2 EPS figure
Logarithmic Corrections for Spin Glasses, Percolation and Lee-Yang Singularities in Six Dimensions
We study analytically the logarithmic corrections to the critical exponents
of the critical behavior of correlation length, susceptibility and specific
heat for the temperature and the finite-size scaling behavior, for a generic
theory at its upper critical dimension (six). We have also computed
the leading correction to scaling as a function of the lattice size. We
distinguish the obtained formulas to the following special cases: percolation,
Lee-Yang (LY) singularities and -component spin glasses. We have compared
our results for the Ising spin glass case with numerical simulations finding a
very good agreement. Finally, and using the results obtained for the Lee-Yang
singularities in six dimensions, we have computed the logarithmic corrections
to the singular part of the free energy for lattice animals in eight
dimensions.Comment: 18 pages. We have extended the computation to lattice animals in
eight dimensions. To be published in Journal of Physics
A Phase Glass is a Bose Metal: New Conducting State in 2D
In the quantum rotor model with random exchange interactions having a
non-zero mean, three phases, a 1) phase (Bose) glass, 2) superfluid, and 3)
Mott insulator, meet at a bi-critical point. We demonstrate that proximity to
the bi-critical point and the coupling between the energy landscape and the
dissipative degrees of freedom of the phase glass lead to a metallic state at
T=0. Consequently, the phase glass is unique in that it represents a concrete
example of a metallic state that is mediated by disorder, even in 2D. We
propose that the experimentally observed metallic phase which intervenes
between the insulator and the superconductor in a wide range of thin films is
in actuality a phase glass.Comment: 4 pages, 1 .eps figure, final version to appear in Phys. Rev. Let
Response of non-equilibrium systems at criticality: Ferromagnetic models in dimension two and above
We study the dynamics of ferromagnetic spin systems quenched from infinite
temperature to their critical point. We show that these systems are aging in
the long-time regime, i.e., their two-time autocorrelation and response
functions and associated fluctuation-dissipation ratio are non-trivial scaling
functions of both time variables. This is exemplified by the exact analysis of
the spherical model in any dimension D>2, and by numerical simulations on the
two-dimensional Ising model. We show in particular that, for (waiting
time) (observation time), the fluctuation-dissipation ratio possesses a
non-trivial limit value , which appears as a dimensionless amplitude
ratio, and is therefore a novel universal characteristic of non-equilibrium
critical dynamics. For the spherical model, we obtain for
24 (mean-field regime). For the two-dimensional
Ising model we measure .Comment: 31 pages, 5 figure
Finite Size Scaling and Critical Exponents in Critical Relaxation
We simulate the critical relaxation process of the two-dimensional Ising
model with the initial state both completely disordered or completely ordered.
Results of a new method to measure both the dynamic and static critical
exponents are reported, based on the finite size scaling for the dynamics at
the early time. From the time-dependent Binder cumulant, the dynamical exponent
is extracted independently, while the static exponents and
are obtained from the time evolution of the magnetization and its higher
moments.Comment: 24 pages, LaTeX, 10 figure
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