749 research outputs found

### Space-Time Noncommutativity from Particle Mechanics

We exploit the reparametrization symmetry of a relativistic free particle to
impose a gauge condition which upon quantization implies space-time
noncommutativity. We show that there is an algebraic map from this gauge back
to the standard `commuting' gauge. Therefore the Poisson algebra, and the
resulting quantum theory, are identical in the two gauges. The only difference
is in the interpretation of space-time coordinates. The procedure is repeated
for the case of a coupling with a constant electromagnetic field, where the
reparametrization symmetry is preserved. For more arbitrary interactions, we
show that standard dynamical system can be rendered noncommutative in space and
time by a simple change of variables.Comment: 13 p

### Extended de Sitter Theory of Two Dimensional Gravitational Forces

We present a simple unifying gauge theoretical formulation of gravitational
theories in two dimensional spacetime. This formulation includes the effects of
a novel matter-gravity coupling which leads to an extended de Sitter symmetry
algebra on which the gauge theory is based. Contractions of this theory
encompass previously studied cases.Comment: 19pp, no figs., CTP 2228, UCONN-93-

### String-Inspired Gravity Coupled to Yang-Mills Fields

String-inspired 1+1-dimensional gravity is coupled to Yang-Mills fields in
the Cangemi-Jackiw gauge-theoretical formulation, based on the extended
Poincar\'e group. A family of couplings, which involves metrics obtainable from
the physical metric with a conformal rescaling, is considered, and the
resulting family of models is investigated both at the classical and the
quantum level. In particular, also using a series of Kirillov-Kostant phases,
the wave functionals that solve the constraints are identified.Comment: 15 pages, LaTex

### The Structure of AdS Black Holes and Chern Simons Theory in 2+1 Dimensions

We study anti-de Sitter black holes in 2+1 dimensions in terms of Chern
Simons gauge theory of anti-de Sitter group coupled to a source. Taking the
source to be an anti-de Sitter state specified by its Casimir invariants, we
show how all the relevant features of the black hole are accounted for. The
requirement that the source be a unitary representation leads to a discrete
tower of states which provide a microscopic model for the black hole.Comment: 17 pages, LaTex. The presentation in Section 5 was improved; other
minor improvements. Final form of the manuscrip

### Exact Physical Black Hole States in Generic 2-D Dilaton Gravity

The quantum mechanics of black holes in generic 2-D dilaton gravity is
considered. The Hamiltonian surface terms are derived for boundary conditions
corresponding to an eternal black hole with slices on the interior ending on
the horizon bifurcation point. The quantum Dirac constraints are solved exactly
for these boundary conditions to yield physical eigenstates of the energy
operator. The solutions are obtained in terms of geometrical phase space
variables that were originally used by Cangemi, Jackiw and Zwiebach in the
context of string inspired dilaton gravity. The spectrum is continuous in the
Lorentzian sector, but in the Euclidean sector the thermodynamic entropy must
be $2\pi n/G$ where $n$ is an integer. The general class of models considered
contains as special cases string inspired dilaton gravity, Jackiw-Teitelboim
gravity and spherically symmetry gravity.Comment: 11 pages, Revte

### A WZW model based on a non-semi-simple group

We present a conformal field theory which desribes a homogeneous four
dimensional Lorentz-signature space-time. The model is an ungauged WZW model
based on a central extension of the Poincar\'e algebra. The central charge of
this theory is exactly four, just like four dimensional Minkowski space. The
model can be interpreted as a four dimensional monochromatic plane wave. As
there are three commuting isometries, other interesting geometries are expected
to emerge via $O(3,3)$ duality.Comment: 8 pages, phyzzx, IASSNS-HEP-93/61 Texable versio

### Topological quantum transition driven by charge-phonon coupling in the Haldane Chern insulator

In condensed matter physics many features can be understood in terms of their
topological properties. Here we report evidence of a topological quantum
transition driven by the charge-phonon coupling in the spinless Haldane model
on a honeycomb lattice, a well-known prototypical model of Chern insulator.
Starting from parameters describing the topological phase in the bare Haldane
model, we show that the increasing of the strength of the charge lattice
coupling drives the system towards a trivial insulator. The average number of
fermions in the Dirac point, characterized by the lowest gap, exhibits a finite
discontinuity at the transition point and can be used as direct indicator of
the topological quantum transition. Numerical simulations show, also, that the
renormalized phonon propagator exhibits a two peak structure across the quantum
transition, whereas, in absence of the mass term in the bare Hadane model,
there is indication of a complete softening of the effective vibrational mode
signaling a charge density wave instability.Comment: 5 pages, 4 figure

### Two channel model for optical conductivity of high mobility organic crystals

We show that the temperature dependence of conductivity of high mobility
organic crystals Pentacene and Rubrene can be quantitatively described in the
framework of the model where carriers are scattered by quenched local
impurities and interact with phonons by Su-Schrieffer-Hegger (SSH) coupling.
Within this model, we present approximation free results for mobility and
optical conductivity obtained by world line Monte Carlo, which we generalize to
the case of coupling both to phonons and impurities. We find fingerprints of
carrier dynamics in these compounds which differ from conventional metals and
show that the dynamics of carriers can be described as a superposition of a
Drude term representing diffusive mobile particles and a Lorentz term
associated with dynamics of localized charges.Comment: 6 pages, 5 figure

### Gauge semi-simple extension of the Poincar\'e group

Based on the gauge semi-simple tensor extension of the Poincar\'e group
another alternative approach to the cosmological term problem is proposed.Comment: Latex, 4 pages. Correction of misprint

### Functional Schroedinger and BRST Quantization of (1+1)--Dimensional Gravity

We discuss the quantization of pure string--inspired dilaton--gravity in
$(1+1)$--dimensions, and of the same theory coupled to scalar matter. We
perform the quantization using the functional Schroedinger and BRST formalisms.
We find, both for pure gravity and the matter--coupled theory, that the two
quantization procedures give inequivalent ``physical'' results.Comment: 40 pages, Late

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