Arshad Momen

Edge states in gravity and black hole physics

Abstract We show in the context of canonical gravity that the removal of a spatial region leads to the appearance of an infinite set of observables and their associated edge states localized at its boundary. Such a boundary occurs in certain approaches to the physics of black holes like the one based on the membrane paradigm. The edge states can contribute to the black hole entropy in these models. A “complementary principle” is also shwon to emerge whereby certain “edge” observables are accessible only to certain observers. The physical significance of edge observables and their states are discussed using their similarities to the corresponding quantities in the quantum Hall effect. The coupling of the edge to the bulk states of the gravitational field is demonstrated in the context of (2+1)-dimensional gravity.

Edge dynamics for BF theories and gravity

Abstract We discuss BF theories defined on manifolds with spatial boundaries. Variational arguments show that one needs to augment the usual action with a boundary term for specific types of boundary conditions. We also show how to use this procedure to find the boundary actions for theories of gravity with first order formulations. Possible connection with the membrane approach is also pointed out.

Induced dilaton in topologically massive quantum field theory

We consider the conformally-invariant coupling of topologically massive gravity to a dynamical massless scalar field theory on a three-manifold with boundary. We show that, in the phase of spontaneously broken Lorentz and Weyl symmetries, this theory induces the target space zero mode of the vertex operator for the string dilaton field on the boundary of the three-dimensional manifold. By a further coupling to topologically massive gauge fields in the bulk, we demonstrate directly from the three-dimensional theory that this dilaton field transforms in the expected way under duality transformations so as to preserve the mass gaps in the spectra of the gauge and gravitational sectors of the quantum field theory. We show that this implies an intimate dynamical relationship between T-duality and S-duality transformations of the quantum string theory. The dilaton in this model couples bulk and worldsheet degrees of freedom to each other and generates a dynamical string coupling.

Domain formation in finite-time quenches

We study the formation of domains in a continuous phase transition with a finite-temperature quench. The model treated is the {Phi}{sup 4} theory in two spatial dimensions with global O(2) symmetry. We investigate this using real-time thermal field theory, following Boyanovsky and collaborators, and find that domain sizes appear to be smaller than those produced in an instantaneous quench in the tree-level approximation. We also propose that a more physical picture emerges by examining the two-point functions which do not involve any cutoff on the short wavelength Goldstone modes. {copyright} {ital 1998} {ital The American Physical Society}

Induced magnetic moments in three-dimensional gauge theories with external magnetic fields

We study the appearance of induced parity-violating magnetic moment, in the presence of external magnetic fields, for even-number of fermion species coupled to dynamical fields in three dimensions. Specifically, we use an SU(2)×U(1) gauge model for dynamical gauge symmetry breaking, which has also been proposed recently as a field theoretical model for high-Tc superconductors. By decomposing the fermionic degrees of freedom in terms of Landau levels, we show that, in the effective theory with the lowest Landau levels, a parity-violating magnetic moment interaction is induced by the higher Landau levels when the fermions are massive. The possible relevance of this result for a recently observed phenomenon in high-Tc superconductors is also discussed.

Magnetic catalysis in even-flavor three-dimensional QED

In this paper, we discuss the role of an external magnetic field on the dynamically generated fermion mass in even-flavor QED in three space-time dimensions. Based on some reasonable approximations, we present analytic arguments on the fact that, for weak fields, the magnetically-induced mass increases quadratically with increasing field, while at strong fields one crosses over to a mass scaling logarithmically with the external field. We also confirm this type of scaling behavior through quenched lattice calculations using the non-compact version for the gauge field. Both the zero and finite temperature cases are examined. A preliminary study of the fermion condensate in the presence of magnetic flux tubes on the lattice is also included.

A comment on curvature effects in CFTs and the Cardy–Verlinde formula

Abstract We examine the Cardy–Verlinde formula for finite temperature N=4 super-Yang–Mills theory on R×S3, and its AdS dual. We find that curvature effects introduce non-trivial corrections to thermodynamic quantities computed on both sides. We find a modified version of the Cardy–Verlinde formula for the SYM theory, incorporating these. On the gravity side, these corrections imply that the Cardy–Verlinde formula is exact.

Even flavor QED3 in an external magnetic field

The magnetically induced fermionic condensate is studied at zero and finite temperatures. The effects of a non-homogeneous external magnetic fields is briefly considered.The magnetically induced fermionic condensate is studied at zero and finite temperatures. The effects of a non-homogeneous external magnetic fields is briefly considered.

Deconfinement transition and flux-string models

Flux-string models can be used to study the deconfining phase transition. In this paper, we study the models proposed by Patel. We also study the large N{sub c} limits of Patel{close_quote}s model. To discuss the validity of the mean field theory results, the one-loop Coleman-Weinberg effective potential is calculated for N{sub c}=3. We argue that the quantum corrections vanish at large N{sub c} when the energy of the so-called baryonic vertices scale with N{sub c}. {copyright} {ital 1997} {ital The American Physical Society}