arXiv subjects

M. Baig

Publications and source records attributed to M. Baig.

33 records · Page 2Linked to original sources

arXiv1998

Finite Size Analysis of the U(1) Phase Transition using the World-sheet Formulation

We present a high statistics analysis of the pure gauge compact U(1) lattice theory using the the world-sheet or Lagrangian loop representation. We have applied a simulation method that deals directly with (gauge invariant) integer variables on plaquettes. As a result we get a significant amelioration of the simulation that allows to work with large lattices avoiding the metaestability problems that appear using the standard Wilson formulation.

hep-lat↗

arXiv1997

Monopole Percolation in the Compact Abelian Higgs Model

We have studied the monopole-percolation phenomenon in the four dimensional Abelian theory that contains compact U(1) gauge fields coupled to unitary norm Higgs fields. We have determined the location of the percolation transition line in the plane $(β_g, β_H)$. This line overlaps the confined-Coulomb and the confined-Higgs phase transition lines, originated by a monopole-condensation mechanism, but continues away from the end-point where this phase transition line stops. In addition, we have determined the critical exponents of the monopole percolation transition away from the phase transition lines. We have performed the finite size scaling in terms of the monopole density instead of the coupling, because the density seems to be the natural parameter when dealing with percolation phenomena.

hep-lat↗

arXiv1997

Monopole percolation in scalar QED

Monopole Percolation was first introduced in the study of the non-compact lattice QED in both, the pure case and coupled to Higgs fields. Monopole percolation has been also observed coupled to the monopole condensation in the study of the pure gauge compact QED. We present here the results coming from the analysis of the role of the monopole percolation in the coupled gauge-higgs compact QED.

hep-lat↗

arXiv1997

String tension in gonihedric 3D Ising models

For the 3D gonihedric Ising models defined by Savvidy and Wegner the bare string tension is zero and the energy of a spin interface depends only on the number of bends and self-intersections, in antithesis to the standard nearest-neighbour 3D Ising action. When the parameter kappa weighting the self-intersections is small the model has a first order transition and when it is larger the transition is continuous. In this paper we investigate the scaling of the renormalized string tension, which is entirely generated by fluctuations, using Monte Carlo simulations This allows us to obtain an estimate for the critical exponents alpha and nu using both finite-size-scaling and data collapse for the scaling function.

hep-lat↗

arXiv1996

Random paths with curvature

We present some results coming from a Monte Carlo simulation of a set of random paths with a curvature dependent action. This model can be considered as a toy model of the theory of random surfaces. The transition from free to rigid random paths has been analyzed and the similitude with the crumpling transition have been pointed out.

hep-lat↗

arXiv1996

Evidence for a first order transition in a plaquette 3d Ising-like action

We investigate a 3d Ising action which corresponds to a a class of models defined by Savvidy and Wegner, originally intended as discrete versions of string theories on cubic lattices. These models have vanishing bare surface tension and the couplings are tuned in such a way that the action depends only on the angles of the discrete surface, i.e. on the way the surface is embedded in ${\bf Z}^3$. Hence the name gonihedric by which they are known. We show that the model displays a rather clear first order phase transition in the limit where self-avoidance is neglected and the action becomes a plaquette one. This transition persists for small values of the self avoidance coupling, but it turns to second order when this latter parameter is further increased. These results exclude the use of this type of action as models of gonihedric random surfaces, at least in the limit where self avoidance is neglected.

hep-lat↗

arXiv1995

Matter Fields in the Lagrangian Loop Representation: Scalar QED

We present the extension of the Lagrangian loop gauge invariant representation in such a way to include matter fields. The partition function of lattice compact U(1)-Higgs model is expressed as a sum over closed as much as open surfaces. We have simulated numerically the loop action equivalent to the Villain form of the action and mapped out the beta-gamma phase diagram of this model.

hep-th↗

arXiv1994

Phase Transitions in lattice QED

The main objective of the work presented here is to understand the appearance of phase transitions in pure gauge and scalar lattice QED. Main results are as follows: Pure gauge compact QED with PBC shows a monopole percolation phenomena coupled to the monopole condensation. Pure gauge compact QED with Fixed Boundary Conditions (spherical topology) shows a behaviour compatible with a second order phase transition The $γ\to\infty$ limit of Non Compact Scalar QED with PBC is related to the Villain form of compact QED and also to the Loop Model for QED, showing a first order phase transition. Numerical a analysis of a third rank abelian Z(2) theory shows an intriguing behaviour over the phase transition that may be originated by point-like topological excitations.

hep-lat↗

arXiv1994

The Lagrangian Loop Representation of Lattice U(1) Gauge Theory

It is showed how the Hamiltonian lattice $loop$ $representation$ can be cast straightforwardly in the Lagrangian formalism. The procedure is general and here we present the simplest case: pure compact QED. This connection has been shaded by the non canonical character of the algebra of the fundamental loop operators. The loops represent tubes of electric flux and can be considered the dual objects to the Nielsen-Olesen strings supported by the Higgs broken phase. The lattice loop classical action corresponding to the Villain form is proportional to the quadratic area of the loop world sheets and thus it is similar to the Nambu string action. This loop action is used in a Monte Carlo simulation and its appealing features are discussed.

hep-th↗

arXiv1994

The Phases and Triviality of Scalar Quantum Electrodynamics

The phase diagram and critical behavior of scalar quantum electrodynamics are investigated using lattice gauge theory techniques. The lattice action fixes the length of the scalar (``Higgs'') field and treats the gauge field as non-compact. The phase diagram is two dimensional. No fine tuning or extrapolations are needed to study the theory's critical behovior. Two lines of second order phase transitions are discovered and the scaling laws for each are studied by finite size scaling methods on lattices ranging from $6^4$ through $24^4$. One line corresponds to monopole percolation and the other to a transition between a ``Higgs'' and a ``Coulomb'' phase, labelled by divergent specific heats. The lines of transitions cross in the interior of the phase diagram and appear to be unrelated. The monopole percolation transition has critical indices which are compatible with ordinary four dimensional percolation uneffected by interactions. Finite size scaling and histogram methods reveal that the specific heats on the ``Higgs-Coulomb'' transition line are well-fit by the hypothesis that scalar quantum electrodynamics is logarithmically trivial. The logarithms are measured in both finite size scaling of the specific heat peaks as a function of volume as well as in the coupling constant dependence of the specific heats measured on fixed but large lattices. The theory is seen to be qualitatively similar to $λϕ^{4}$. The standard CRAY random number generator RANF proved to be inadequate

hep-lat↗

arXiv1994

Fixed boundary conditions and phase transitions in pure gauge compact QED

We have simulated the pure gauge compact QED with fixed boundary conditions, on lattices from $6^4$ to $16^4$. We argue that a lattice with this fixed boundary imposition corresponds actually to a lattice with spherical topology. We have found the presence of a phase transition without any trace of discontinuity. Moreover, the specific heat and the Binder cumulant are qualitatively consistent with a second order phase transition. The implications of this observation on the nature of the compact lattice QED are discussed.

hep-lat↗

arXiv1994

Finite-Size analysis of the 4-d abelian surface gauge model

We present the results of a finite-size analysis of the four dimensional abelian surface gauge model. This model is defined assigning abelian variables to the plaquettes of an hypercubical lattice, and is dual to the four dimensional Ising model. This last model is known to present a second order phase transition with mean field critical exponents. We have performed Monte Carlo simulations on several lattice sizes and high statistics. The analysis of the partition function zeroes and the specific heat scaling behaviour allowed us to estimate the critical coupling $β_c$ as well as the critical exponents $ν$ and $α$. Our results are consistent with the second order critical exponents $ν= 1/2$ and $α= 0$. The $β_c$ value is in perfect agreement with duality predictions from the 4-d Ising model. Nevertheless, the energy histograms show a seemingly non-vanishing double peak structure. The interface tension analysis suggests that this may be a finite size effect.

hep-lat↗

arXiv1994

Recent Results in Scalar QED

In this talk we present some recent and new results on the phase structure and the continuum limit of lattice formulation of pure gauge QED coupled to Higgs fields. We show the presence of second order phase transition lines allowing for a continuum limit. Nevertheless, finite size analysis shows that this theory is logarithmically trivial. The role of magnetic monopoles is also shown.

hep-lat↗

arXiv1993

On the Logarithmic Triviality of Scalar Quantum Electrodynamics

Using finite size scaling and histogram methods we obtain numerical results from lattice simulations indicating the logarithmic triviality of scalar quantum electrodynamics, even when the bare gauge coupling is chosen large. Simulations of the non-compact formulation of the lattice abelian Higgs model with fixed length scalar fields on $L^{4}$ lattices with $L$ ranging from $6$ through $20$ indicate a line of second order critical points. Fluctuation-induced first order transitions are ruled out. Runs of over ten million sweeps for each $L$ produce specific heat peaks which grow logarithmically with $L$ and whose critical couplings shift with $L$ picking out a correlation length exponent of $0.50(5)$ consistent with mean field theory. This behavior is qualitatively similar to that found in pure $λϕ^{4}$.

hep-lat↗

arXiv1992

The Crumpling Transition Revisited

The ``crumpling" transition, between rigid and crumpled surfaces, has been object of much discussion over the past years. The common lore is that such transition should be of second order. However, some lattice versions of the rigidity term on fixed connectivity surfaces seem to suggest that the transition is of higher order instead. While some models exhibit what appear to be lattice artifacts, others are really indistiguishable from models where second order transitions have been reported and yet appear to have third order transitions.

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