68 research outputs found
N=2 Liouville Theory with Boundary
We study N=2 Liouville theory with arbitrary central charge in the presence
of boundaries. After reviewing the theory on the sphere and deriving some
important structure constants, we investigate the boundary states of the theory
from two approaches, one using the modular transformation property of annulus
amplitudes and the other using the bootstrap of disc two-point functions
containing degenerate bulk operators. The boundary interactions describing the
boundary states are also proposed, based on which the precise correspondence
between boundary states and boundary interactions is obtained. The open string
spectrum between D-branes is studied from the modular bootstrap approach and
also from the reflection relation of boundary operators, providing a
consistency check for the proposal.Comment: 1+48 pages, no figure. typos corrected and references added. the
version to appear in JHE
Cosmological particle production, causal thermodynamics, and inflationary expansion
Combining the equivalence between cosmological particle creation and an
effective viscous fluid pressure with the fact that the latter represents a
dynamical degree of freedom within the second-order Israel-Stewart theory for
imperfect fluids, we reconsider the possibility of accelerated expansion in
fluid cosmology. We find an inherent self-limitation for the magnitude of an
effective bulk pressure which is due to adiabatic (isentropic) particle
production. For a production rate which depends quadratically on the Hubble
rate we confirm the existence of solutions which describe a smooth transition
from inflationary to noninflationary behavior and discuss their interpretation
within the model of a decaying vacuum energy density. An alternative
formulation of the effective imperfect fluid dynamics in terms of a minimally
coupled scalar field is given. The corresponding potential is discussed and an
entropy equivalent for the scalar field is found.Comment: 16 pages, revtex file, submitted to Phys. Rev.
On Minimal N=4 Topological Strings And The (1,k) Minimal Bosonic String
In this paper we consider tree-level scattering in the minimal N=4
topological string and show that a large class of N-point functions can be
recast in terms of corresponding amplitudes in the (1,k) minimal bosonic
string. This suggests a non-trivial relation between the minimal N=4
topological strings, the (1,k) minimal bosonic strings and their corresponding
ADE matrix models. This relation has interesting and far-reaching implications
for the topological sector of six-dimensional Little String Theories.Comment: lanlmac, 30 pages; v3 minor revisions, version published in JHE
On the absence of ferromagnetism in typical 2D ferromagnets
We consider the Ising systems in dimensions with nearest-neighbor
ferromagnetic interactions and long-range repulsive (antiferromagnetic)
interactions which decay with a power, , of the distance. The physical
context of such models is discussed; primarily this is and where,
at long distances, genuine magnetic interactions between genuine magnetic
dipoles are of this form. We prove that when the power of decay lies above
and does not exceed , then for all temperatures, the spontaneous
magnetization is zero. In contrast, we also show that for powers exceeding
(with ) magnetic order can occur.Comment: 15 pages, CMP style fil
Spectral Flow in AdS(3)/CFT(2)
We study the spectral flowed sectors of the H3 WZW model in the context of
the holographic duality between type IIB string theory in AdS(3)x S^3 x T^4
with NSNS flux and the symmetric product orbifold of T^4. We construct
explicitly the physical vertex operators in the flowed sectors that belong to
short representations of the superalgebra, thus completing the bulk-to-boundary
dictionary for 1/2 BPS states. We perform a partial calculation of the string
three-point functions of these operators. A complete calculation would require
the three-point couplings of non-extremal flowed operators in the H3 WZW model,
which are at present unavailable. In the unflowed sector, perfect agreement has
recently been found between the bulk and boundary three-point functions of 1/2
BPS operators. Assuming that this agreement persists in the flowed sectors, we
determine certain unknown three-point couplings in the H3 WZW model in terms of
three-point couplings of affine descendants in the SU(2) WZW model.Comment: 50 pages, 2 figure
D-branes and SQCD in Non-Critical Superstring Theory
Using exact boundary conformal field theory methods we analyze the D-brane
physics of a specific four-dimensional non-critical superstring theory which
involves the N=2 SL(2)/U(1) Kazama-Suzuki model at level 1. Via the holographic
duality of hep-th/9907178 our results are relevant for D-brane dynamics in the
background of NS5-branes and D-brane dynamics near a conifold singularity. We
pay special attention to a configuration of D3- and D5-branes that realizes N=1
supersymmetric QCD and discuss the massless spectrum and classical moduli of
this setup in detail. We also comment briefly on the implications of this
construction for the recently proposed generalization of the AdS/CFT
correspondence by Klebanov and Maldacena within the setting of non-critical
superstrings.Comment: harvmac, 47 pages, 6 figures; v4 same as v3 due to submission erro
A model of the Universe including Dark Energy accounted for by both a Quintessence Field and a (negative) Cosmological Constant
In this work we present a model of the universe in which dark energy is
modelled explicitely with both a dynamical quintessence field and a
cosmological constant. Our results confirm the possibility of a future
collapsing universe (for a given region of the parameter space), which is
necessary for a consistent formulation of string theory and quantum field
theory. We have also reproduced the measurements of modulus distance from
supernovae with good accuracy.Comment: 11 pages, 4 figures, only the results for the single exponential
potential are preserved. One author added. Some changes in the reference
section. Submitted to Physical Review
SL(2,R)/U(1) Supercoset and Elliptic Genera of Non-compact Calabi-Yau Manifolds
We first discuss the relationship between the SL(2;R)/U(1) supercoset and N=2
Liouville theory and make a precise correspondence between their
representations. We shall show that the discrete unitary representations of
SL(2;R)/U(1) theory correspond exactly to those massless representations of N=2
Liouville theory which are closed under modular transformations and studied in
our previous work hep-th/0311141.
It is known that toroidal partition functions of SL(2;R)/U(1) theory (2D
Black Hole) contain two parts, continuous and discrete representations. The
contribution of continuous representations is proportional to the space-time
volume and is divergent in the infinite-volume limit while the part of discrete
representations is volume-independent.
In order to see clearly the contribution of discrete representations we
consider elliptic genus which projects out the contributions of continuous
representations: making use of the SL(2;R)/U(1), we compute elliptic genera for
various non-compact space-times such as the conifold, ALE spaces, Calabi-Yau
3-folds with A_n singularities etc. We find that these elliptic genera in
general have a complex modular property and are not Jacobi forms as opposed to
the cases of compact Calabi-Yau manifolds.Comment: 39 pages, no figure; v2 references added, minor corrections; v3 typos
corrected, to appear in JHEP; v4 typos corrected in eqs. (3.22) and (3.44
Vanishing of cosmological constant and fully localized gravity in a Brane World with extra time(s)
We construct an intersecting brane configuration in six-dimensional space
with one extra space-like and one extra time-like dimensions. With a certain
additional symmetry imposed on the extra space-time we have found that
effective four-dimensional cosmological constant vanishes automatically,
providing the static solution with gravity fully localized at the intersection
region as there are no propagating massive modes of graviton. In this way, the
same symmetry allows us to eliminate tachyonic states of graviton from the
spectrum of the effective four-dimensional theory, thus avoiding
phenomenological difficulties comming from the matter instability usually
induced in theories with extra time-like dimensions.Comment: 15 pages, comments and references added, version accepted in Phys.
Lett.
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