479 research outputs found
N=4 Supersymmetry and the BPST Instanton
In this paper we construct the Lagrangian and Hamiltonian formulations of N=4
supersymmetric systems describing the motion of an isospin particle on a
conformally flat four-manifold with SO(4) isometry carrying the non-Abelian
field of a BPST instanton. The conformal factor can be specified to yield
various particular systems, such as superconformally invariant mechanics as
well as a particle on the four-sphere, the pseudosphere or on R x S^3. The
isospin degrees of freedom arise as bosonic components of an additional
fermionic N=4 supermultiplet, whose other components are rendered auxiliary by
a nonlocal redefinition. Our on-shell component action coincides with the one
recently proposed in arXiv:0912.3289.Comment: 1+8 pages; v2: two references added, published versio
On a Matrix Model of Level Structure
We generalize the dimensionally reduced Yang-Mills matrix model by adding d=1
Chern-Simons term and terms for a bosonic vector. The coefficient, \kappa of
the Chern-Simons term must be integer, and hence the level structure. We show
at the bottom of the Yang-Mills potential, the low energy limit, only the
linear motion is allowed for D0 particles. Namely all the particles align
themselves on a single straight line subject to \kappa^2/r^2 repulsive
potential from each other. We argue the relevant brane configuration to be
D0-branes in a D4 after \kappa of D8's pass the system.Comment: 1+6 pages, No figure, LaTeX; Minor changes; To appear in Class.
Quant. Gra
Dynamical Cobordisms in General Relativity and String Theory
We describe a class of time-dependent solutions in string- or M-theory that
are exact with respect to alpha-prime and curvature corrections and interpolate
in physical space between regions in which the low energy physics is
well-approximated by different string theories and string compactifications.
The regions are connected by expanding "domain walls" but are not separated by
causal horizons, and physical excitations can propagate between them. As
specific examples we construct solutions that interpolate between oriented and
unoriented string theories, and also between type II and heterotic theories.
Our solutions can be weakly curved and under perturbative control everywhere
and can asymptote to supersymmetric at late times.Comment: 35 pages, 5 figures, LaTeX v2: reference adde
Transient Accelerated Expansion and Double Quintessence
We consider Double Quintessence models for which the Dark Energy sector
consists of two coupled scalar fields. We study in particular the possibility
to have a transient acceleration in these models. In both Double Quintessence
models studied here, it is shown that if acceleration occurs, it is necessarily
transient. We consider also the possibility to have transient acceleration in
two one-field models, the Albrecht-Skordis model and the pure exponential.
Using separate conservative constraints (marginalizing over the other
parameters) on the effective equation of state , the relative density
of the Dark Energy and the present age of the universe, we
construct scenarios with a transient acceleration that has already ended at the
present time, and even with no acceleration at all, but a less conservative
analysis using the CMB data rules out the last possibility. The scenario with a
transient acceleration ended by today, can be implemented for the range of
cosmological parameters and .Comment: Version accepted in Phys. Rev. D, 22 pages, 10 figures, 4 table
A Quantum Hall Fluid of Vortices
In this note we demonstrate that vortices in a non-relativistic Chern-Simons
theory form a quantum Hall fluid. We show that the vortex dynamics is
controlled by the matrix mechanics previously proposed by Polychronakos as a
description of the quantum Hall droplet. As the number of vortices becomes
large, they fill the plane and a hydrodynamic treatment becomes possible,
resulting in the non-commutative theory of Susskind. Key to the story is the
recent D-brane realisation of vortices and their moduli spaces.Comment: 10 pages. v2(3): (More) References adde
D-branes in T-fold conformal field theory
We investigate boundary dynamics of orbifold conformal field theory involving
T-duality twists. Such models typically appear in contexts of non-geometric
string compactifications that are called monodrofolds or T-folds in recent
literature. We use the framework of boundary conformal field theory to analyse
the models from a microscopic world-sheet perspective. In these backgrounds
there are two kinds of D-branes that are analogous to bulk and fractional
branes in standard orbifold models. The bulk D-branes in T-folds allow
intuitive geometrical interpretations and are consistent with the classical
analysis based on the doubled torus formalism. The fractional branes, on the
other hand, are `non-geometric' at any point in the moduli space and their
geometric counterparts seem to be missing in the doubled torus analysis. We
compute cylinder amplitudes between the bulk and fractional branes, and find
that the lightest modes of the open string spectra show intriguing non-linear
dependence on the moduli (location of the brane or value of the Wilson line),
suggesting that the physics of T-folds, when D-branes are involved, could
deviate from geometric backgrounds even at low energies. We also extend our
analysis to the models with SU(2) WZW fibre at arbitrary levels.Comment: 38 pages, no figure, ams packages. Essentially the published versio
Solitons in finite droplets of noncommutative Maxwell-Chern-Simons theory
We find soliton solutions of the noncommutative Maxwell-Chern-Simons theory
confined to a finite quantum Hall droplet. The solitons are exactly as
hypothesized in \cite{Manu}. We also find new variations on these solitons. We
compute their flux and their energies. The model we consider is directly
related to the model proposed by Polychronakos\cite{Poly} and studied by
Hellerman and Van Raamsdonk\cite{HvR} where it was shown that it is equivalent
to the quantum Hall effect.Comment: 18 pages, 7 figures, minor corrections, version accepted for
publication, this time really
The Trouble with de Sitter Space
In this paper we assume the de Sitter Space version of Black Hole
Complementarity which states that a single causal patch of de Sitter space is
described as an isolated finite temperature cavity bounded by a horizon which
allows no loss of information. We discuss the how the symmetries of de Sitter
space should be implemented. Then we prove a no go theorem for implementing the
symmetries if the entropy is finite. Thus we must either give up the finiteness
of the de Sitter entropy or the exact symmetry of the classical space. Each has
interesting implications for the very long time behavior. We argue that the
lifetime of a de Sitter phase can not exceed the Poincare recurrence time. This
is supported by recent results of Kachru, Kallosh, Linde and Trivedi.Comment: 15 pages, 1 figure. v2: added fifth section with comments on long
time stability of de Sitter space, in which we argue that the lifetime can
not exceed the Poincare recurrence time. v3: corrected a minor error in the
appendi
Inflation and Holography in String Theory
The encoding of an inflating patch of space-time in terms of a dual theory is
discussed. Following Bousso's interpretation of the holographic principle, we
find that those are generically described not by states in the dual theory but
by density matrices. We try to implement this idea on simple deformations of
the AdS/CFT examples, and an argument is given as to why inflation is so
elusive to string theory.Comment: 15 pages, LaTeX, 2 figures. Uses psbox.te
Finite Chern-Simons matrix model - algebraic approach
We analyze the algebra of observables and the physical Fock space of the
finite Chern-Simons matrix model. We observe that the minimal algebra of
observables acting on that Fock space is identical to that of the Calogero
model. Our main result is the identification of the states in the l-th tower of
the Chern-Simons matrix model Fock space and the states of the Calogero model
with the interaction parameter nu=l+1. We describe quasiparticle and quasihole
states in the both models in terms of Schur functions, and discuss some
nontrivial consequences of our algebraic approach.Comment: 12pages, jhep cls, minor correction
- …