33,555 research outputs found

### Time and Tachyon

Recent analysis suggests that the classical dynamics of a tachyon on an
unstable D-brane is described by a scalar Born-Infeld type action with a
runaway potential. The classical configurations in this theory at late time are
in one to one correspondence with the configuration of a system of
non-interacting (incoherent), non-rotating dust. We discuss some aspects of
canonical quantization of this field theory coupled to gravity, and explore,
following earlier work on this subject, the possibility of using the scalar
field (tachyon) as the definition of time in quantum cosmology. At late `time'
we can identify a subsector in which the scalar field decouples from gravity
and we recover the usual Wheeler - de Witt equation of quantum gravity.Comment: LaTeX file, 24 page

### D-Brane Probe and Closed String Tachyons

We consider a D-brane probe in unstable string background associated with
flux branes. The twist in spacetime metric reponsible for the supersymmetry
breaking is shown to manifest itself in mixing of open Wilson lines with the
phases of some adjoint matter fields, resulting in a nonlocal and
nonsupersymmetric form of Yang-Mills theory as the probe dynamics. This
provides a setup where one can study fate of a large class of unstable closed
string theories that include as a limit type 0 theories and various orbifolds
of type II and type 0 theories. We discuss the limit of ${\bf C}/Z_n$ orbifold
in some detail and speculate on couplings with closed string tachyons.Comment: LaTeX, 17 pages, typos fixed, references update

### Energy Momentum Tensor and Marginal Deformations in Open String Field Theory

Marginal boundary deformations in a two dimensional conformal field theory
correspond to a family of classical solutions of the equations of motion of
open string field theory. In this paper we develop a systematic method for
relating the parameter labelling the marginal boundary deformation in the
conformal field theory to the parameter labelling the classical solution in
open string field theory. This is done by first constructing the
energy-momentum tensor associated with the classical solution in open string
field theory using Noether method, and then comparing this to the answer
obtained in the conformal field theory by analysing the boundary state. We also
use this method to demonstrate that in open string field theory the tachyon
lump solution on a circle of radius larger than one has vanishing pressure
along the circle direction, as is expected for a codimension one D-brane.Comment: LaTeX file, 25 pages; v2: minor addition

### D0-brane tension in string field theory

We compute the D0-brane tension in string field theory by representing it as
a tachyon lump of the D1-brane compactified on a circle of radius $R$. To this
aim, we calculate the lump solution in level truncation up to level L=8. The
normalized D0-brane tension is independent on $R$. The compactification radius
is therefore chosen in order to cancel the subleading correction $1/L^2$. We
show that an optimal radius $R^*$ indeed exists and that at $R^*$ the
theoretical prediction for the tension is reproduced at the level of $10^{-5}$.
As a byproduct of our calculation we also discuss the determination of the
marginal tachyon field at $R\to 1$.Comment: 13 pages, 3 Eps figure

### Black Hole Entropy Function and the Attractor Mechanism in Higher Derivative Gravity

We study extremal black hole solutions in D dimensions with near horizon
geometry AdS_2\times S^{D-2} in higher derivative gravity coupled to other
scalar, vector and anti-symmetric tensor fields. We define an entropy function
by integrating the Lagrangian density over S^{D-2} for a general AdS_2\times
S^{D-2} background, taking the Legendre transform of the resulting function
with respect to the parameters labelling the electric fields, and multiplying
the result by a factor of 2\pi. We show that the values of the scalar fields at
the horizon as well as the sizes of AdS_2 and S^{D-2} are determined by
extremizing this entropy function with respect to the corresponding parameters,
and the entropy of the black hole is given by the value of the entropy function
at this extremum. Our analysis relies on the analysis of the equations of
motion and does not directly make use of supersymmetry or specific structure of
the higher derivative terms.Comment: LaTeX file, 12page

### Delocalized, non-SUSY $p$-branes, tachyon condensation and tachyon matter

We construct non-supersymmetric $p$-brane solutions of type II supergravities
in arbitrary dimensions ($d$) delocalized in one of the spatial transverse
directions. By a Wick rotation we convert these solutions into Euclidean
$p$-branes delocalized in the transverse time-like direction. The former
solutions in $d=10$ nicely interpolate between the $(p+1)$-dimensional non-BPS
D-branes and the $p$-dimensional BPS D-branes very similar to the picture of
tachyon condensation for the tachyonic kink solution on the non-BPS D-branes.
On the other hand the latter solutions interpolate between the
$(p+1)$-dimensional non-BPS D-branes and the tachyon matter supergravity
configuration very similar to the picture of rolling tachyon on the non-BPS
D-branes.Comment: 15 pages, typos correcte

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