3,113 research outputs found
Closed String Tachyon Condensation: An Overview
These notes are an expanded version of a review lecture on closed string
tachyon condensation at the RTN workshop in Copenhagen in September 2003. We
begin with a lightning review of open string tachyon condensation, and then
proceed to review recent results on localized closed string tachyon
condensation, focusing on two simple systems, C/Z_n orbifolds and twisted
circle compactifications.Comment: harvmac, 59 pages; references adde
Tachyon condensation and Boundary States in Bosonic String
We discuss tachyon configuration for the unoriented bosonic string theory
which produces a bosonic string theory with SO(32) gauge symmetry in ten
dimensions. It is closely related to the tachyon condensation scenario proposed
by A. Sen. We also give the boundary state description of the tachyon
condensation process, with some emphasis on the r\^ole of orbifold conformal
field theory.Comment: Proceeding of the talk given at YITP workshop ``Tachyon condensation
and boundary state''(October 27-29, 1999), latex fil
Remarks on Black Hole Instabilities and Closed String Tachyons
Physical arguments stemming from the theory of black-hole thermodynamics are
used to put constraints on the dynamics of closed-string tachyon condensation
in Scherk--Schwarz compactifications. A geometrical interpretation of the
tachyon condensation involves an effective capping of a noncontractible cycle,
thus removing the very topology that supports the tachyons. A semiclassical
regime is identified in which the matching between the tachyon condensation and
the black-hole instability flow is possible. We formulate a generalized
correspondence principle and illustrate it in several different circumstances:
an Euclidean interpretation of the transition from strings to black holes
across the Hagedorn temperature and instabilities in the brane-antibrane
system.Comment: harvmac, 20 pp, 4 eps figures. Contribution to Jacob Bekenstein's
Festschrif
Inhomogeneous tachyon condensation
We investigate the spacetime-dependent condensation of the tachyon in
effective field theories. Previous work identified singularities in the field
which appear in finite time: infinite gradients at the kinks, and (in the
eikonal approximation) caustics near local minima. By performing a perturbation
analysis, and with numerical simulations, we demonstrate and explain key
features of the condensation process: perturbations generically freeze, and
minima develop singular second derivatives in finite time (caustics). This last
has previously been understood in terms of the eikonal approximation to the
dynamics. We show explicitly from the field equations how this approximation
emerges, and how the caustics develop, both in the DBI and BSFT effective
actions. We also investigate the equation of state parameter of tachyon matter
showing that it is small, but generically non-zero. The energy density tends to
infinity near field minima with a charateristic profile. A proposal to regulate
infinities by modifying the effective action is also studied. We find that
although the infinities at the kinks are successfully regularised in the
time-dependent case, caustics still present.Comment: 4 figures,19p
Cosmological tachyon condensation
We consider the prospects for dark matter/energy unification in k-essence
type theories. General mappings are established between the k-essence scalar
field, the hydrodynamic and braneworld descriptions. We develop an extension of
the general relativistic dust model that incorporates the effects of both
pressure and the associated acoustic horizon. Applying this to a tachyon model,
we show that this inhomogeneous "variable Chaplygin gas" does evolve into a
mixed system containing cold dark matter like gravitational condensate in
significant quantities. Our methods can be applied to any dark energy model as
well as to mixtures of dark energy and traditional dark matter.Comment: 22 pages, 3 figures, title changed, typos corrected, accepted in
Phys. Rev.
AdS Bubbles, Entropy and Closed String Tachyons
We study the conjectured connection between AdS bubbles (AdS solitons) and
closed string tachyon condensations. We confirm that the entanglement entropy,
which measures the degree of freedom, decreases under the tachyon condensation.
The entropies in supergravity and free Yang-Mills agree with each other
remarkably. Next we consider the tachyon condensation on the AdS twisted circle
and argue that its endpoint is given by the twisted AdS bubble, defined by the
double Wick rotation of rotating black 3-brane solutions. We calculated the
Casimir energy and entropy and checked the agreements between the gauge and
gravity results. Finally we show an infinite boost of a null linear dilaton
theory with a tachyon wall (or bubble), leads to a solvable time-dependent
background with a bulk tachyon condensation. This is the simplest example of
spacetimes with null boundaries in string theory.Comment: 45 pages, 6 figures, harvmac, eq.(2.16) corrected, references adde
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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