167 research outputs found
Double Field Theory, T-Duality, and Courant Brackets
These lecture notes are based on three lectures, each ninety minutes long,
given by the author at the "International School on Strings and Fundamental
Physics" which took place in Garching/Munich from July 25 to August 6, 2010.
These lectures, aimed at graduate students, require only a basic knowledge of
string theory and give a simple introduction to double field theory. These
notes were prepared by Marco Baumgartl and Nicolas Moeller.Comment: 25 page
Interpolating String Field Theories
A minimal area problem imposing different length conditions on open and
closed curves is shown to define a one parameter family of covariant
open-closed quantum string field theories. These interpolate from a recently
proposed factorizable open-closed theory up to an extended version of Witten's
open string field theory capable of incorporating on shell closed strings. The
string diagrams of the latter define a new decomposition of the moduli spaces
of Riemann surfaces with punctures and boundaries based on quadratic
differentials with both first order and second order poles.Comment: 12 pages, 7 figures (not included
A Solvable Toy Model for Tachyon Condensation in String Field Theory
The lump solution of \phi^3 field theory provides a toy model for unstable
D-branes of bosonic string theory. The field theory living on this lump is
itself a cubic field theory involving a tachyon, two additional scalar fields,
and a scalar field continuum. Its action can be written explicitly because the
fluctuation spectrum of the lump turns out to be governed by a solvable
Schroedinger equation; the \ell=3 case of a series of reflectionless
potentials. We study the multiscalar tachyon potential both exactly and in the
level expansion, obtaining insight into issues of convergence, branches of the
solution space, and the mechanism for removal of states after condensation. In
particular we find an interpretation for the puzzling finite domain of
definition of string field marginal parameters.Comment: 27 pages, 6 figures, LaTeX. Added references to reflectionless
potentials, minor typos correcte
Building string field theory around non-conformal backgrounds
The main limitations of string field theory arise because its present
formulation requires a background representing a classical solution, a
background defined by a strictly conformally invariant theory. Here we sketch a
construction for a gauge-invariant string field action around non-conformal
backgrounds. The construction makes no reference to any conformal theory. Its
two-dimensional field-theoretic aspect is based on a generalized BRST operator
satisfying a set of Weyl descent equations. Its geometric aspect uses a complex
of moduli spaces of two-dimensional Riemannian manifolds having ordinary
punctures, and organized by the number of special punctures which goes from
zero to infinity. In this complex there is a Batalin-Vilkovisky algebra that
includes naturally the operator which adds one special puncture. We obtain a
classical field equation that appears to relax the condition of conformal
invariance usually taken to define classical string backgrounds.Comment: 38 pages, 4 figures, phyzzx and BoxedEPS include
Non-perturbative de Sitter vacua via corrections
The higher-derivative corrections consistent with duality
invariance can be completely classified for cosmological, purely time-dependent
backgrounds. This result is used to show that there are duality invariant
theories featuring string-frame de Sitter vacua as solutions that are
non-perturbative in , thus suggesting that classical string theory may
realize de Sitter solutions in an unexpected fashion.Comment: 7 pages, Second Prize Essay for the Gravity Research Foundation 2019
Awards for Essays on Gravitatio
Double Metric, Generalized Metric and -Geometry
We relate the unconstrained `double metric' of the `-geometry'
formulation of double field theory to the constrained generalized metric
encoding the spacetime metric and b-field. This is achieved by integrating out
auxiliary field components of the double metric in an iterative procedure that
induces an infinite number of higher-derivative corrections. As an application
we prove that, to first order in and to all orders in fields, the
deformed gauge transformations are Green-Schwarz-deformed diffeomorphisms. We
also prove that to first order in the spacetime action encodes
precisely the Green-Schwarz deformation with Chern-Simons forms based on the
torsionless gravitational connection. This seems to be in tension with
suggestions in the literature that T-duality requires a torsionful connection,
but we explain that these assertions are ambiguous since actions that use
different connections are related by field redefinitions.Comment: 20 page
Tachyon condensation in string field theory
It has been conjectured that at a stationary point of the tachyon potential
for the D-brane of bosonic string theory, the negative energy density exactly
cancels the D-brane tension. We evaluate this tachyon potential by off-shell
calculations in open string field theory. Surprisingly, the condensation of the
tachyon mode alone into the stationary point of its cubic potential is found to
cancel about 70% of the D-brane tension. Keeping relevant scalars up to four
mass levels above the tachyon, the energy density at the shifted stationary
point cancels 99% of the D-brane tension.Comment: 13 pages, LaTe
D-Branes, Tachyons, and String Field Theory
In these notes we provide a pedagogical introduction to the subject of
tachyon condensation in Witten's cubic bosonic open string field theory. We use
both the low-energy Yang-Mills description and the language of string field
theory to explain the problem of tachyon condensation on unstable D-branes. We
give a self-contained introduction to open string field theory using both
conformal field theory and overlap integrals. Our main subjects are the Sen
conjectures on tachyon condensation in open string field theory and the
evidence that supports these conjectures. We conclude with a discussion of
vacuum string field theory and projectors of the star-algebra of open string
fields. We comment on the possible role of string field theory in the
construction of a nonperturbative formulation of string theory that captures
all possible string backgrounds.Comment: 103 pages, 11 figures. Lectures presented at TASI 2001. v2:
references added. v3: minor errors corrected; reference, discussion added
regarding other results on open string spectrum in stable vacuu
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