1,381 research outputs found
Conquest of the ghost pyramid of the superstring
We give a new Becchi-Rouet-Stora-Tyutin operator for the superstring. It
implies a quadratic gauge-fixed action, and a new gauge-invariant action with
first-class constraints. The infinite pyramid of spinor ghosts appears in a
simple way through ghost gamma matrices.Comment: 30 pages, 1 figure, Late
Ground-State and Domain-Wall Energies in the Spin-Glass Region of the 2D Random-Bond Ising Model
The statistics of the ground-state and domain-wall energies for the
two-dimensional random-bond Ising model on square lattices with independent,
identically distributed bonds of probability of and of
are studied. We are able to consider large samples of up to
spins by using sophisticated matching algorithms. We study
systems, but we also consider samples, for different aspect ratios
. We find that the scaling behavior of the ground-state energy and
its sample-to-sample fluctuations inside the spin-glass region () are characterized by simple scaling functions. In particular, the
fluctuations exhibit a cusp-like singularity at . Inside the spin-glass
region the average domain-wall energy converges to a finite nonzero value as
the sample size becomes infinite, holding fixed. Here, large finite-size
effects are visible, which can be explained for all by a single exponent
, provided higher-order corrections to scaling are included.
Finally, we confirm the validity of aspect-ratio scaling for : the
distribution of the domain-wall energies converges to a Gaussian for ,
although the domain walls of neighboring subsystems of size are
not independent.Comment: 11 pages with 15 figures, extensively revise
Regularisation, the BV method, and the antibracket cohomology
We review the Lagrangian Batalin--Vilkovisky method for gauge theories. This
includes gauge fixing, quantisation and regularisation. We emphasize the role
of cohomology of the antibracket operation. Our main example is gravity,
for which we also discuss the solutions for the cohomology in the space of
local integrals. This leads to the most general form for the action, for
anomalies and for background charges.Comment: 12 pages, LaTeX, Preprint-KUL-TF-94/2
Domain wall entropy of the bimodal two-dimensional Ising spin glass
We report calculations of the domain wall entropy for the bimodal
two-dimensional Ising spin glass in the critical ground state. The L * L system
sizes are large with L up to 256. We find that it is possible to fit the
variance of the domain wall entropy to a power function of L. However, the
quality of the data distributions are unsatisfactory with large L > 96.
Consequently, it is not possible to reliably determine the fractal dimension of
the domain walls.Comment: 4 pages, 2 figures, submitted to PR
Random Field Models for Relaxor Ferroelectric Behavior
Heat bath Monte Carlo simulations have been used to study a four-state clock
model with a type of random field on simple cubic lattices. The model has the
standard nonrandom two-spin exchange term with coupling energy and a random
field which consists of adding an energy to one of the four spin states,
chosen randomly at each site. This Ashkin-Teller-like model does not separate;
the two random-field Ising model components are coupled. When , the
ground states of the model remain fully aligned. When , a
different type of ground state is found, in which the occupation of two of the
four spin states is close to 50%, and the other two are nearly absent. This
means that one of the Ising components is almost completely ordered, while the
other one has only short-range correlations. A large peak in the structure
factor appears at small for temperatures well above the transition
to long-range order, and the appearance of this peak is associated with slow,
"glassy" dynamics. The phase transition into the state where one Ising
component is long-range ordered appears to be first order, but the latent heat
is very small.Comment: 7 pages + 12 eps figures, to appear in Phys Rev
Vlasov equation and collisionless hydrodynamics adapted to curved spacetime
The modification of the Vlasov equation, in its standard form describing a
charged particle distribution in the six-dimensional phase space, is derived
explicitly within a formal Hamiltonian approach for arbitrarily curved
spacetime. The equation accounts simultaneously for the Lorentz force and the
effects of general relativity, with the latter appearing as the gravity force
and an additional force due to the extrinsic curvature of spatial
hypersurfaces. For an arbitrary spatial metric, the equations of collisionless
hydrodynamics are also obtained in the usual three-vector form
Topological Defects in the Random-Field XY Model and the Pinned Vortex Lattice to Vortex Glass Transition in Type-II Superconductors
As a simplified model of randomly pinned vortex lattices or charge-density
waves, we study the random-field XY model on square () and simple cubic
() lattices. We verify in Monte Carlo simulations, that the average
spacing between topological defects (vortices) diverges more strongly than the
Imry-Ma pinning length as the random field strength, , is reduced. We
suggest that for the simulation data are consistent with a topological
phase transition at a nonzero critical field, , to a pinned phase that is
defect-free at large length-scales. We also discuss the connection between the
possible existence of this phase transition in the random-field XY model and
the magnetic field driven transition from pinned vortex lattice to vortex glass
in weakly disordered type-II superconductors.Comment: LATEX file; 5 Postscript figures are available from [email protected]
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