21,116 research outputs found
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
Remark about Non-BPS D-Brane in Type IIA Theory
In this paper we would like to show simple mechanisms how from the action for
non-BPS D-brane we can obtain action describing BPS D(p-1)-brane in Type IIA
theory.Comment: 13 pages, completely rewritten pape
Tachyons on Dp-branes from Abelian Higgs sphalerons
We consider the Abelian Higgs model in a (p+2)-dimensional space time with
topology M^{p+1} x S^1 as a field theoretical toy model for tachyon
condensation on Dp-branes. The theory has periodic sphaleron solutions with the
normal mode equations resembling Lame-type equations. These equations are
quasi-exactly solvable (QES) for specific choices of the Higgs- to gauge boson
mass ratio and hence a finite number of algebraic normal modes can be computed
explicitely. We calculate the tachyon potential for two different values of the
Higgs- to gauge boson mass ratio and show that in comparison to previously
studied pure scalar field models an exact cancellation between the negative
energy contribution at the minimum of the tachyon potential and the brane
tension is possible for the simplest truncation in the expansion about the
field around the sphaleron. This gives further evidence for the correctness of
Sen's conjecture.Comment: 14 Latex pages including 3 eps-figure
Tachyon condensation on brane sphalerons
We consider a sphaleron solution in field theory that provides a toy model
for unstable D-branes of string theory. We investigate the tachyon condensation
on a Dp-brane. The localized modes, including a tachyon, arise in the spectrum
of a sphaleron solution of a \phi^4 field theory on M^{p+1}\times S^1. We use
these modes to find a multiscalar tachyon potential living on the sphaleron
world-volume. A complete cancelation between brane tension and the minimum of
the tachyon potential is found as the size of the circle becomes small.Comment: To appear in JHEP, 13 pages, 2 eps figures, minor changes and
references adde
Solitons on compact and noncompact spaces in large noncommutativity
We study solutions at the minima of scalar field potentials for Moyal spaces
and torii in the large non-commutativity and interprete these solitons in terms
of non-BPS D-branes of string theory. We derive a mass spectrum formula linking
different D-branes together on quantum torii and suggest that it describes
general systems of D-brane bound states extending the D2-D0 one. Then we
propose a shape for the effective potential approaching these quasi-stable
bound states. We give the gauge symmetries of these systems of branes and show
that they depend on the quantum torii representations.Comment: 25 pages, Latex, 1 figure (use epsfig.sty), corrected formul
Tachyon condensation in open-closed p-adic string theory
We study a simple model of p-adic closed and open strings. It sheds some
light on the dynamics of tachyon condensation for both types of strings. We
calculate the effect of static and decaying D-brane configurations on the
closed string background. For closed string tachyons we find lumps analogous to
D-branes. By studying their fluctuation spectrum and the D-branes they admit,
we argue that closed string lumps should be interpreted as spacetimes of lower
dimensionality described by some noncritical p-adic string theory.Comment: 21 pages, 3 figures; v2: discussion of the fluctuations of the double
lump substantially improve
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 . To this
aim, we calculate the lump solution in level truncation up to level L=8. The
normalized D0-brane tension is independent on . The compactification radius
is therefore chosen in order to cancel the subleading correction . We
show that an optimal radius indeed exists and that at the
theoretical prediction for the tension is reproduced at the level of .
As a byproduct of our calculation we also discuss the determination of the
marginal tachyon field at .Comment: 13 pages, 3 Eps figure
An Imaging Polarimeter(IMPOL) for multi-wavelength observations
Taking advantage of the advances in array detector technology, an imaging
polarimeter (IMPOL) has been constructed for measuring linear polarization in
the wavelength band from 400-800 nm. It makes use of a Wollaston prism as the
analyser to measure simultaneously the two orthogonal polarization components
that define a Stoke's parameter. An achromatic half-wave plate is used to
rotate the plane of polarization with respect to the axis of the analyser so
that the second Stoke's parameter also can be determined. With a field of view
correponding to about 30x30 sq. mm for a 1.2 m, f/13 telescope, a sensitive,
liquid-nitrogen cooled CCD camera as the detector and a built-in acquisition
and guidance unit, the instrument can be used for studying stellar fields or
extended objects with an angular resolution close to 2 arcsec. The instrumental
polarization is less than 0.05% and the accuracies of measurement are primarily
limited by photon noise for typical observations.Comment: 10 pages including 5 embedded figures; submitted to Astronomy and
Astrophysics Supplement Series; available on request to A. N. Ramaprakash
([email protected] or [email protected]); quote report n
Tachyon cosmology with non-vanishing minimum potential: a unified model
We investigate the tachyon condensation process in the effective theory with
non-vanishing minimum potential and its implications to cosmology. It is shown
that the tachyon condensation on an unstable three-brane described by this
modified tachyon field theory leads to lower-dimensional branes (defects)
forming within a stable three-brane. Thus, in the cosmological background, we
can get well-behaved tachyon matter after tachyon inflation, (partially)
avoiding difficulties encountered in the original tachyon cosmological models.
This feature also implies that the tachyon inflated and reheated universe is
followed by a Chaplygin gas dark matter and dark energy universe. Hence, such
an unstable three-brane behaves quite like our universe, reproducing the key
features of the whole evolutionary history of the universe and providing a
unified description of inflaton, dark matter and dark energy in a very simple
single-scalar field model.Comment: 18 p
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