878 research outputs found
Path Intergals and Perturbative Expansions for Non-Compact Symmetric Spaces
We show how to construct path integrals for quantum mechanical systems where
the space of configurations is a general non-compact symmetric space.
Associated with this path integral is a perturbation theory which respects the
global structure of the system. This perturbation expansion is evaluated for a
simple example and leads to a new exactly soluble model. This work is a step
towards the construction of a strong coupling perturbation theory for quantum
gravity.Comment: 16 page
Real fermionic symmetry in type II supergravity
It is known that the transformations of fermionic T-duality, derived from the
worldsheet theory, generically transform real supergravity backgrounds to
complex supergravity backgrounds. We consider the low-energy target space
theory and show that the type II supergravity equations admit a symmetry that
transforms the Ramond-Ramond fields and the dilaton. The transformations given
by this symmetry involve Killing spinors and include the transformations of
Berkovits and Maldacena. However, we show that they also allow real
transformations.Comment: 30 pages; added comments and references. Corrected typo
Off-shell structure of the string sigma model
The off-shell structure of the string sigma model is investigated. In the
open bosonic string, nonperturbative effects are shown to depend crucially on
the regularization scheme. A scheme retaining the notion of string width
reproduces the structure of Witten's string field theory and the associated
unconventional gauge transformations.Comment: 4 page
String-Dominated Cosmology
If string theory controls physics at the string scale, the dynamics of the
early universe before the GUT era will be governed by the low-energy string
equations of motion. Studying these equations for FRW spacetimes, we find that
depending on the initial conditions when the stringy era starts, and on the
time when it ends, there are a wide variety of qualitatively distinct types of
evolution. We classify these, and present the general solution to the equations
of motion
Localization on the Landscape and Eternal Inflation
We investigate the validity of the assertion that eternal inflation populates
the landscape of string theory. We verify that bubble solutions do not satisfy
the Klein Gordon equation for the landscape potential. Solutions to the
landscape potential within the formalism of quantum cosmology are Anderson
localized wavefunctions. Those are inconsistent with inflating bubble
solutions. The physical reasons behind the failure of a relation between
eternal inflation and the landscape are rooted in quantum phenomena such as
interference between wavefunction concentrated around the various vacua in the
landscape.Comment: 21 page
Landau degeneracy and black hole entropy
We consider the supergravity solution describing a configuration of
intersecting D-4-branes with non-vanishing worldvolume gauge fields. The
entropy of such a black hole is calculated in terms of the D-branes quantised
charges. The non-extreme solution is also considered and the corresponding
thermodynamical quantities are calculated in terms of a D-brane/anti-D-brane
system. To perform the quantum mechanical D-brane analysis we study
open-strings with their ends on branes with a magnetic condensate. Applying the
results to our D-brane system we managed to have a perfect agreement between
the D-brane entropy counting and the corresponding semi-classical result. The
Landau degeneracy of the open string states describing the excitations of the
D-brane system enters in a crucial way. We also derive the near-extreme results
which agree with the semi-classical calculations.Comment: 30 pages, 1 figure, latex. Minor corrections, version to appear in
Nuclear Physics
The Physics of 2-d Stringy Spacetimes
We examine the two-dimensional spacetimes that emerge from string theory. We
find all the solutions with no tachyons, and show that the only non-trivial
solution is the black hole spacetime. We examine the role of duality in this
picture. We then explore the thermodynamics of these solutions which is
complicated by the fact that only in two spacetime dimensions is it impossible
to redefine the dilaton field in terms of a canonical scalar field. Finally, we
extend our analysis to the heterotic string, and briefly comment on exact, as
opposed to perturbative, solutions
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