152 research outputs found
Non-Abelian Duality for Open Strings
We examine non-abelian duality transformations in the open string case. After
gauging the isometries of the target space and developing the general
formalism, we study in details the duals oftarget spaces with SO(N) isometries
which, for the SO(2) case, reduces to the known abelian T-duals. We apply the
formalism to electrically and magnetically charged 4D black hole solutions and,
as in the abelian case, dual coordinates satisfy Dirichlet conditions.Comment: 18 pages, Latex. Some formulas are added. Final version to appear in
Nucl. Phys.
Semiclassical quantization of rotating superstring in AdS_5 x S^5
Motivated by recent proposals in hep-th/0202021 and hep-th/0204051 we develop
semiclassical quantization of superstring in . We start with a
classical solution describing string rotating in and boosted along
large circle of . The energy of the classical solution is a function
of the spin and the momentum (R-charge) which interpolates between the
limiting cases S=0 and J=0 considered previously. We derive the corresponding
quadratic fluctuation action for bosonic and fermionic fields from the GS
string action and compute the string 1-loop (large \lambda= {R^4\over \a'^2})
correction to the classical energy spectrum in the sector. We find that
the 1-loop correction to the ground-state energy does not cancel for non-zero
. For large it scales as , i.e. as the classical term, with no
higher powers of appearing. This supports the conjecture made in
hep-th/0204051 that the classical scaling can be interpolated
to weak coupling to reproduce the corresponding operator anomalous dimension
behaviour in gauge theory.Comment: harvmac, 35p. v2,3: minor corrections; v4: added remarks about
higher-loop corrections in section 4 and an argument suggesting the absence
of higher than log S corrections to the energy to all orders in string
tension in section 6.1; v5: factor 1/2 misprints corrected in eqs. (6.6) and
(6.8) and thus in (6.5) and (6.9
Brane Universes and the Cosmological Constant
The cosmological constant problem and brane universes are reviewed briefly.
We discuss how the cosmological constant problem manifests itself in various
scenarios for brane universes. We review attempts - and their difficulties -
that aim at a solution of the cosmological constant problem.Comment: corrected typos, added references, 13 pages, accepted by MPLA as
brief revie
Dynamical Instability of Self-Tuning Solution with Antisymmetric Tensor Field
We consider the dynamical stability of a static brane model that incorporates
a three-index antisymmetric tensor field and has recently been proposed as a
possible solution to the cosmological constant problem. Ultimately, we are able
to establish the existence of time-dependent, purely gravitational
perturbations. As a consequence, the static solution of interest is
``dangerously'' located at an unstable saddle point. This outcome is suggestive
of a hidden fine tuning in what is an otherwise self-tuning model.Comment: 16 Pages, Latex; Discussion added but conclusions unchange
Model for self-tuning the cosmological constant
The vanishing cosmological constant in the four dimensional space-time is
obtained in a 5D Randall-Sundrum model with a brane (B1) located at . The
matter fields can be located at the brane. For settling any vacuum energy
generated at the brane to zero, we need a three index antisymmetric tensor
field with a specific form for the Lagrangian. For the self-tuning
mechanism, the bulk cosmological constant should be negative.Comment: LaTeX file of 4 pages, to appear in Phys. Rev. Let
AdS2xS2 as an exact heterotic string background
An exact heterotic string theory on an AdS2xS2 background supported by an
electromagnetic flux is found as a marginal deformation of an SL(2,R)xSU(2) WZW
model. Based on a talk given at NATO Advanced Study Institute and EC Summer
School on String Theory: from Gauge Interactions to Cosmology, Cargese,
Corsica, France, 7 Jun - 19 Jun 2004.Comment: 5 page
Brane gravity, massless bulk scalar and self-tuning of the cosmological constant
We show that a self-tuning mechanism of the cosmological constant could work
in 5D non-compact space-time with a symmetry in the presence of a
massless scalar field. The standard model matter fields live only on the 4D
brane. The change of vacuum energy on the brane (brane cosmological constant)
by, for instance, electroweak and QCD phase transitions, just gives rise to
dynamical shifts of the profiles of the background metric and the scalar field
in the extra dimension, keeping 4D space-time flat without any fine-tuning. To
avoid naked singularities in the bulk, the brane cosmological constant should
be negative. We introduce an additional brane-localized 4D Einstein-Hilbert
term so as to provide the observed 4D gravity with the non-compact extra
dimension. With a general form of brane-localized gravity term allowed by the
symmetries, the low energy Einstein gravity is successfully reproduced on the
brane at long distances. We show this phenomenon explicitly for the case of
vanishing bulk cosmological constant.Comment: 1+15 pages, no figure, Version to appear in PR
Wilson loops from supergravity and string theory
We present a theorem that determines the value of the Wilson loop associated
with a Nambu-Goto action which generalizes the action of the
model. In particular we derive sufficient conditions for confining behavior. We
then apply this theorem to various string models. We go beyond the classical
string picture by incorporating quadratic quantum fluctuations. We show that
the bosonic determinant of branes with 16 supersymmetries yields a
Luscher term.
We confirm that the free energy associated with a BPS configuration of a
single quark is free from divergences. We show that unlike for a string in flat
space time in the case of the fermionic determinant does not
cancel the bosonic one. For a setup that corresponds to a confining gauge
theory the correction to the potential is attractive. We determine the form of
the Wilson loop for actions that include non trivial field. The
issue of an exact determination of the value of the stringy Wilson loop is
discussed. Talk presented in string 99 Potsdam.Comment: 12 pages Late
Wave function of the radion in the brane background with a massless scalar field and a self-tuning problem
We consider flat solutions in the brane background with a massless scalar
field appearing in 5D . Since there exist bulk singularities or
arises the divergent 4D Planck mass, we should introduce a compact extra
dimension, the size of which is then fixed by brane tension(s) and a bulk
cosmological constant. Inspecting scalar perturbations around the flat
solutions, we find that the flat solutions are stable vacua from the positive
mass spectrum of radion. We show that the massless radion mode is projected out
by the boundary condition arising in cutting off the extra dimension. Thus, the
fixed extra dimension is not alterable, which is not useful toward a
self-tuning of the cosmological constant.Comment: Latex file of 18 pages including 1 eps figur
- …