148 research outputs found
Gluinos on the lattice: quenched calculations
As a preparation for the numerical study of the SU(2) gauge theory with
gluinos, the spectral properties of the fermion matrix and the masses of
pseudoscalar and scalar states are investigated in the quenched approximation.
The behaviour of the disconnected fermion diagrams on small lattices is also
studied.Comment: latex2e, 12 pages, 5 figures with epsfi
Three-dimensional gonihedric spin system
We perform Monte Carlo simulations of a three-dimensional spin system with a
Hamiltonian which contains only four-spin interaction term. This system
describes random surfaces with extrinsic curvature - gonihedric action. We
study the anisotropic model when the coupling constants for the
space-like plaquettes and for the transverse-like plaquettes are
different. In the two limits and the system has been
solved exactly and the main interest is to see what happens when we move away
from these points towards the isotropic point, where we recover the original
model. We find that the phase transition is of first order for while away from this point it becomes weaker and
eventually turns to a crossover. The conclusion which can be drown from this
result is that the exact solution at the point in terms of
2d-Ising model should be considered as a good zero order approximation in the
description of the system also at the isotropic point and
clearly confirms the earlier findings that at the isotropic point the original
model shows a first order phase transition.Comment: 11 pages, 10 figures, shortened versio
Phase structure of four-dimensional gonihedric spin system
We perform Monte Carlo simulations of a gauge invariant spin system which
describes random surfaces with gonihedric action in four dimensions. The
Hamiltonian is a mixture of one-plaquette and additional two- and
three-plaquette interaction terms with specially adjusted coupling constants.
For the system with the large self-intersection coupling constant we
observe the second-order phase transition at temperature . The string tension is generated by quantum fluctuations as it was
expected theoretically. This result suggests the existence of a noncritical
string in four dimensions. For smaller values of the system undergoes the
first order phase transition and for close to zero exhibits a smooth
crossover.Comment: 14 pages, Latex, 10 figure
Four-dimensional gonihedric gauge spin system
We perform Monte Carlo simulations of a four-dimensional gauge invariant spin
system which describes random surfaces with gonihedric action. We develop the
analogy between the flat-crumpled phase transition of the lattice surface model
and the liquid-gas phase transition of non-ideal gases, and identify the
self-intersection coupling constant of the surface model with the pressure
. As increases the system moves to a critical point in complete analogy
with the situation for non-ideal gases, where the liquid and the gas phases
approach each other with increasing . We measure vacuum expectation values
of various operators and the corresponding critical indices.Comment: 12 pages, Late
Three-dimensional lattice U(1) gauge-Higgs model at low
We study the non-compact version of the U(1) gauge-Higgs model in three
dimensions for We found that, using this formulation, rather
modest lattices approach quite well the infinite volume behaviour.The phase
transition is first order, as expected for this Higgs mass. The latent heat (in
units of ) is compatible with the predictions of the two-loop
effective potential; it is an order of magnitude less than the corresponding
SU(2) value. The transition temperature and in units of
the critical temperature are also compatible with the perturbative results.Comment: 15 pages, latex, 9 figures, changes in the comparison with
perturbation theor
The Abelian Higgs Model in Three Dimensions with Improved Action
We study the Abelian Higgs Model using an improved form of the action in the
scalar sector. The subleading corrections are carefully analysed and the
connection between lattice and continuous parameters is worked out. The
simulation shows a remarkable improvement of the numerical performance.Comment: Minor correction to one-loop relations;reference adde
Catalysis of chiral symmetry breaking by external magnetic fields in three-dimensional lattice QED
The enhancement of the fermionic condensate due to the presence of both
homogeneous and non-homogeneous external magnetic fields is studied for
three-dimensional QED.Comment: 5 pages, contribution to "Strong and electroweak matter 98",
Copenhagen, December 199
Exact Gravity Dual of a Gapless Superconductor
A model of an exact gravity dual of a gapless superconductor is presented in
which the condensate is provided by a charged scalar field coupled to a bulk
black hole of hyperbolic horizon in asymptotically AdS spacetime. Below a
critical temperature, the black hole acquires its hair through a phase
transition while an electromagnetic perturbation of the background Maxwell
field determines the conductivity of the boundary theory.Comment: 21 pages, 8 figures, a section on the stability of the MTZ black hole
is added, references are added, version to be published in JHE
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