8,140 research outputs found
Domain walls and chaos in the disordered SOS model
Domain walls, optimal droplets and disorder chaos at zero temperature are
studied numerically for the solid-on-solid model on a random substrate. It is
shown that the ensemble of random curves represented by the domain walls obeys
Schramm's left passage formula with kappa=4 whereas their fractal dimension is
d_s=1.25, and therefore is NOT described by "Stochastic-Loewner-Evolution"
(SLE). Optimal droplets with a lateral size between L and 2L have the same
fractal dimension as domain walls but an energy that saturates at a value of
order O(1) for L->infinity such that arbitrarily large excitations exist which
cost only a small amount of energy. Finally it is demonstrated that the
sensitivity of the ground state to small changes of order delta in the disorder
is subtle: beyond a cross-over length scale L_delta ~ 1/delta the correlations
of the perturbed ground state with the unperturbed ground state, rescaled by
the roughness, are suppressed and approach zero logarithmically.Comment: 23 pages, 11 figure
Observation of Galactic Gamma-ray Sources with VERITAS
We report on VERITAS observations at energies above 200 GeV of known or
potential galactic gamma-ray sources. The observed objects comprise pulsars,
pulsar wind nebulae, high-mass X-ray binaries and gamma-ray sources with
unknown counterparts in other wavelengths. Among the highlights are the
observation of variable gamma-ray emission from the X-ray binary LS I +61 303
and the detection of MGRO J1906+06/HESS J1906+063, an extended gamma-ray source
which could not be associated with any obvious counterpart at lower energies.Comment: Fixed typos in source name
Finite temperature behavior of strongly disordered quantum magnets coupled to a dissipative bath
We study the effect of dissipation on the infinite randomness fixed point and
the Griffiths-McCoy singularities of random transverse Ising systems in chains,
ladders and in two-dimensions. A strong disorder renormalization group scheme
is presented that allows the computation of the finite temperature behavior of
the magnetic susceptibility and the spin specific heat. In the case of Ohmic
dissipation the susceptibility displays a crossover from Griffiths-McCoy
behavior (with a continuously varying dynamical exponent) to classical Curie
behavior at some temperature . The specific heat displays Griffiths-McCoy
singularities over the whole temperature range. For super-Ohmic dissipation we
find an infinite randomness fixed point within the same universality class as
the transverse Ising system without dissipation. In this case the phase diagram
and the parameter dependence of the dynamical exponent in the Griffiths-McCoy
phase can be determined analytically.Comment: 23 pages, 12 figure
Continuous loading of an electrostatic trap for polar molecules
A continuously operated electrostatic trap for polar molecules is
demonstrated. The trap has a volume of ~0.6 cm^3 and holds molecules with a
positive Stark shift. With deuterated ammonia from a quadrupole velocity
filter, a trap density of ~10^8/cm^3 is achieved with an average lifetime of
130 ms and a motional temperature of ~300 mK. The trap offers good starting
conditions for high-precision measurements, and can be used as a first stage in
cooling schemes for molecules and as a "reaction vessel" in cold chemistry.Comment: 4 pages, 3 figures v2: several small improvements, new intr
Ground state properties of fluxlines in a disordered environment
A new numerical method to calculate exact ground states of multi-fluxline
systems with quenched disorder is presented, which is based on the minimum cost
flow algorithm from combinatorial optimization. We discuss several models that
can be studied with this method including their specific implementations,
physically relevant observables and results: 1) the N-line model with N
fluxlines (or directed polymers) in a d-dimensional environment with point
and/or columnar disorder and hard or soft core repulsion; 2) the vortex glass
model for a disordered superconductor in the strong screening limit and 3) the
Sine-Gordon model with random pase shifts in the strong coupling limit.Comment: 4 pages RevTeX, 3 eps-figures include
Off-Equilibrium Dynamics of a 4D Spin Glass with Asymmetric Couplings
We study the off-equilibrium dynamics of the Edwards-Anderson spin glass in
four dimensions under the influence of a non-hamiltonian perturbation. We find
that for small asymmetry the model behaves as the hamiltonian one, while for
large asymmetry the behaviour of the model can be well described by an
interrupted aging scenario. The autocorrelation function C(t_w+\tau,t_w) scales
as \tau/t_w^\beta, with \beta a function of the asymmetry. For very long
waiting times the previous regime crosses over to a time translational
invariant regime (TTI) with stretched exponential relaxation. The model does
not show signs of reaching a TTI regime for weak asymmetry, but in the aging
regime the exponent \beta is always different from one, showing a non trivial
aging scenario.Comment: Latex, 12 pages, 9 figure
On the Stability of the Mean-Field Glass Broken Phase under Non-Hamiltonian Perturbations
We study the dynamics of the SK model modified by a small non-hamiltonian
perturbation. We study aging, and we find that on the time scales investigated
by our numerical simulations it survives a small perturbation (and is destroyed
by a large one). If we assume we are observing a transient behavior the scaling
of correlation times versus the asymmetry strength is not compatible with the
one expected for the spherical model. We discuss the slow power law decay of
observable quantities to equilibrium, and we show that for small perturbations
power like decay is preserved. We also discuss the asymptotically large time
region on small lattices.Comment: 34 page
Gamma ray emission and stochastic particle acceleration in galaxy clusters
FERMI (formely GLAST) will shortly provide crucial information on
relativistic particles in galaxy clusters. We discuss non-thermal emission in
the context of general calculations in which relativistic particles (protons
and secondary electrons due to proton-proton collisions) interact with MHD
turbulence generated in the cluster volume during cluster mergers. Diffuse
cluster-scale radio emission (Radio Halos) and hard X-rays are produced during
massive mergers while gamma ray emission, at some level, is expected to be
common in galaxy clusters.Comment: 4 pages, 2 Figure, proc. of the 4th Heidelberg International
Symposium on High Energy Gamma-ray Astronom
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