1,136 research outputs found
A Note on Noncommutative String theory and its low energy limit
The noncommutative string theory is described by embedding open string theory
in a constant second rank antisymmetric field and the
noncommutative gauge theory is defined by a deformed product. As a
check, study of various scattering amplitudes in both noncommutative string and
noncommutative gauge theory confirm that in the limit, the
noncommutative string theoretic amplitude goes over to the noncommutative gauge
theoretic amplitude, and the couplings are related as
. Furthermore we show that in this
limit there will not be any correction to the gauge theoretic action because of
absence of massive modes. We get sin/cos factors in the scattering amplitudes
depending on the odd/even number of external photons.Comment: 14 pages including 2 figure
More Comments on String Theory on AdS_3
We clarify a number of issues regarding the worldsheet and spacetime
descriptions of string propagation on AdS_3. We construct the vertex operators
of spacetime current algebra and spacetime (super) Virasoro generators in the
full interacting SL(2) WZW theory and study their Ward identities. We also
explain the relation between the analysis in this note and some recent work on
this subject.Comment: 42 pages, harvmac; references adde
What do Topologists want from Seiberg--Witten theory? (A review of four-dimensional topology for physicists)
In 1983, Donaldson shocked the topology world by using instantons from
physics to prove new theorems about four-dimensional manifolds, and he
developed new topological invariants. In 1988, Witten showed how these
invariants could be obtained by correlation functions for a twisted N=2 SUSY
gauge theory. In 1994, Seiberg and Witten discovered dualities for such
theories, and in particular, developed a new way of looking at four-dimensional
manifolds that turns out to be easier, and is conjectured to be equivalent to,
Donaldson theory.
This review describes the development of this mathematical subject, and shows
how the physics played a pivotal role in the current understanding of this area
of topology.Comment: 51 pages, 10 figures, 8 postscript files. Submitted to International
Journal of Modern Physics A, July 2002 Uses Latex 2e with class file
ws-ijmpa.cls (included in tar file
Noncommutativity of the Moving D2-brane Worldvolume
In this paper we study the noncommutativity of a moving membrane with
background fields. The open string variables are analyzed. Some scaling limits
are studied. The equivalence of the magnetic and electric noncommutativities is
investigated. The conditions for equivalence of noncommutativity of the T-dual
theory in the rest frame and noncommutativity of the original theory in the
moving frame are obtained.Comment: 12 pages, Latex, no figure. The equivalence of noncommutativities and
also some scaling limits are adde
Noncommutative Quantum Hall Effect and Aharonov-Bohm Effect
We study a system of electrons moving on a noncommutative plane in the
presence of an external magnetic field which is perpendicular to this plane.
For generality we assume that the coordinates and the momenta are both
noncommutative. We make a transformation from the noncommutative coordinates to
a set of commuting coordinates and then we write the Hamiltonian for this
system. The energy spectrum and the expectation value of the current can then
be calculated and the Hall conductivity can be extracted. We use the same
method to calculate the phase shift for the Aharonov-Bohm effect. Precession
measurements could allow strong upper limits to be imposed on the
noncommutativity coordinate and momentum parameters and .Comment: 9 pages, RevTeX4, references added, small changes in the tex
Space/Time Non-Commutativity and Causality
Field theories based on non-commutative spacetimes exhibit very distinctive
nonlocal effects which mix the ultraviolet with the infrared in bizarre ways.
In particular if the time coordinate is involved in the non-commutativity the
theory seems to be seriously acausal and inconsistent with conventional
Hamiltonian evolution. To illustrate these effects we study the scattering of
wave packets in a field theory with space/time non-commutativity. In this
theory we find effects which seem to precede their causes and rigid rods which
grow instead of Lorentz contract as they are boosted. These field theories are
evidently inconsistent and violate causality and unitarity. On the other hand
open string theory in a background electric field is expected to exhibit
space/time non-commutativity. This raises the question of whether they also
lead to acausal behavior. We show that this is not the case. Stringy effects
conspire to cancel the acausal effects that are present for the non-commutative
field theory.Comment: New version replacing previous incorrect versio
Strings in Background Electric Field, Space/Time Noncommutativity and A New Noncritical String Theory
Searching for space/time noncommutativity we reconsider open strings in a
constant background electric field. The main difference between this situation
and its magnetic counterpart is that here there is a critical electric field
beyond which the theory does not make sense. We show that this critical field
prevents us from finding a limit in which the theory becomes a field theory on
a noncommutative spacetime. However, an appropriate limit toward the critical
field leads to a novel noncritical string theory on a noncommutative spacetime.Comment: 14 page
Ground Rings and Their Modules in 2D Gravity with Matter
All solvable two-dimensional quantum gravity models have non-trivial BRST
cohomology with vanishing ghost number. These states form a ring and all the
other states in the theory fall into modules of this ring. The relations in the
ring and in the modules have a physical interpretation. The existence of these
rings and modules leads to nontrivial constraints on the correlation functions
and goes a long way toward solving these theories in the continuum approach.Comment: 13 page
- …