1,125 research outputs found
Numerical experiments with p F- and q D-strings: the formation of (p,q) bound states
We investigate the behaviour of (p,q) string networks, focusing on two
aspects: (1) modelling more realistic (p,q) string networks than the Z_N
networks used so far and (2) investigating the effect of long-range
interactions on the evolution of the network. We model the network with no
long-range interactions using two sets of fields, complex scalars coupled to
gauge fields, with a potential chosen such that the two types of strings will
form bound states. This way we can model junctions of 3 strings with different
tension; in Z_N models used so far in simulations all the strings have
identical tensions. In order to introduce long-range interactions we also study
a network in which one of the scalars forms global strings. We observe that in
the absence of long-range interactions the formation of bound states has a
significant influence on the evolution of the network. When long-range
interactions are turned on the bound states are short-lived and have a minimal
effect on the network evolution.Comment: 17 pages, 8 figures, JCAP styl
Rolling tachyon in anti-de Sitter space-time
We study the decay of the unstable D-particle in three-dimensional anti-de
Sitter space-time using worldsheet boundary conformal field theory methods. We
test the open string completeness conjecture in a background for which the
phase space available is only field-theoretic. This could present a serious
challenge to the claim. We compute the emission of closed strings in the AdS(3)
x S^3 x T^4 background from the knowledge of the exact corresponding boundary
state we construct. We show that the energy stored in the brane is mainly
converted into very excited long strings. The energy stored in short strings
and in open string pair production is much smaller and finite for any value of
the string coupling. We find no "missing energy" problem. We compare our
results to those obtained for a decay in flat space-time and to a background in
the presence of a linear dilaton. Some remarks on holographic aspects of the
problem are made.Comment: JHEP style, 45 pages, one figure; v2: typos corrected, references
added, version to appear in JHE
Notes on Non-Critical Superstrings in Various Dimensions
We study non-critical superstrings propagating in dimensional
Minkowski space or equivalently, superstrings propagating on the
two-dimensional Euclidean black hole tensored with d-dimensional Minkowski
space. We point out a subtlety in the construction of supersymmetric theories
in these backgrounds, and explain how this does not allow a consistent
geometric interpretation in terms of fields propagating on a cigar-like
spacetime. We explain the global symmetries of the various theories by using
their description as the near horizon geometry of wrapped NS5-brane
configurations. In the six-dimensional theory, we present a CFT description of
the four-dimensional moduli space and the global O(3) symmetry. The worldsheet
action invariant under this symmetry contains both the N=2 sine-Liouville
interaction and the cigar metric, thereby providing an example where the two
interactions are naturally present in the same worldsheet lagrangian already at
the non-dynamical level.Comment: 33 pages, harvma
Introduction to branes and M-theory for relativists and cosmologists
We review the recent developments in superstrings. We start with a brief
summary of various consistent superstring theories and discuss T-duality which
necessarily leads to the presence of D-branes. The properties of D-branes are
summarized and we discuss how these suggest the existence of 11-dimensional
quantum theory, M-theory, which is believed to give rise to various
superstrings as perturbative expansions around particular backgrounds in the
theory. We also discuss the interpretation of brane solutions as black holes in
string theories and statistical explanation of Bekenstein-Hawking entropy. The
idea behind this interpretation is that there is a fundamental duality between
closed (gravity) and open (gauge theory) string degrees of freedom, one of
whose manifestation is what is kown as AdS/CFT correspondence. The idea is used
to discuss the greybody factors for BTZ black holes. Finally the entropy of
various balck holes are discussed in connection with Cardy-Verlinde formula.Comment: 28 pages, 7 figures, Latex. Lectures at the international workshop
``Brane world'' at YITP, 15--18 January 2002, to be published in Prog. Theor.
Phys. Suppl. ptp style files included. v2: minor corrections, v3: minor
corrections and refs. added, v4: eq.(7.14) correcte
Dp Branes in PP-wave Background
Dirichlet p-branes in the background of pp waves are constructed using the
massive Green-Schwarz worldsheet action for open strings. These branes are
localized at the origin and only for preserve half the
supersymmetries. The spectrum of the brane theory is analyzed and is found to
be in agreement with the spectrum of the small fluctuations of the world-volume
super Yang-Mills theory in this background. These branes are expected to
correspond to objects that are nonperturbative in in the dual gauge theory.Comment: References added; minor correction
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