405 research outputs found
Tachyon Tunnelling in D-brane-anti-D-brane
Using the tachyon DBI action proposal for the effective theory of
non-coincident D-brane-anti-D-brane system, we study the decay of this
system in the tachyon channel. We assume that the branes separation is held
fixed, i.e. no throat formation, and then find the bounce solution which
describe the decay of the system from false to the true vacuum of the tachyon
potential. We shall show that due to the non-standard form of the kinetic term
in the effective action, the thin wall approximation for calculating the bubble
nucleation rate gives a result which is independent of the branes separation.
This unusual result might indicate that the true decay of this metastable
system should be via a solution that represents a throat formation as well as
the tachyon tunneling.Comment: 15 pages, 4 figures, Latex file, minor changes, reference adde
D-Brane Effective Actions and Particle Production near the Beginning of the Tachyon Condensation
In this paper we will study the quantum field theory of fluctuation modes
around the classical solution that describes tachyon condensation on unstable
D-brane.We will calculate the number of particle produced near the beginning of
the rolling tachyon process. We will perform this calculation for different
tachyon effective actions and we will find that the rate of the particle
production strongly depends on the form of the effective action used for the
description of the early stage of the tachyon condensation.Comment: 21 page
Tachyon Dynamics and the Effective Action Approximation
Recently effective actions have been extensively used to describe tachyon
condensation in string theory. While the various effective actions which have
appeared in the literature have very similar properties for static
configurations, they differ for time-dependent tachyons. In this paper we
discuss general properties of non-linear effective Lagrangians which are first
order in derivatives. In particular we show that some observed properties, such
as asymptotically vanishing pressure, are rather generic features, although the
quantative features differ. On the other hand we argue that certain features of
marginal tachyon profiles are beyond the reach of any first order Lagrangian
description. We also point out that an effective action, proposed earlier,
captures the dynamics of tachyons well.Comment: References added and confusing reference clarifie
On open superstring partition function in inhomogeneous rolling tachyon background
We consider open superstring partition function Z on the disc in
time-dependent tachyon background T= f(x_i) e^{m x_0} where the profile
function f depends on spatial coordinates. We compute Z to second order in
derivatives of f and compare the result with some previously suggested
effective actions depending only on the first derivatives of the tachyon field.
We also compute the target-space stress-energy tensor in this background and
demonstrate its conservation in the ``on-shell'' case of the linear profile f=
f_0 + q_i x_i corresponding to a marginal perturbation. We comment on the role
of the rolling tachyon with linear spatial profile in the decay of an unstable
D-brane.Comment: 32p, latex, v2: introduction revised to expand and correct comments
on the paper by Kutasov and Niarchos, v3: corrected typos and formulas in
section 4, final version to appear in JHE
Wess-Zumino Term in Tachyon Effective Action
We show that the source of RR field computed from the boundary state
describing the decay of a non-BPS brane is reproduced by a particular form of
the Wess-Zumino term in the tachyon effective action. We also obtain a simple
expression of the S-charge associated with rolling tachyons.Comment: 10 pages, lanlma
Constraining Maximally Supersymmetric Membrane Actions
We study the recent construction of maximally supersymmetric field theory
Lagrangians in three spacetime dimensions that are based on algebras with a
triple product. Assuming that the algebra has a positive definite metric
compatible with the triple product, we prove that the only non-trivial examples
are either the well known case based on a four dimensional algebra or direct
sums thereof.Comment: 11 pages, very minor changes. Reference added. Version to be
published in JHE
Moduli Space of Unstable D-branes on a Circle of Critical Radius
We study the moduli space of the boundary conformal field theories describing
an unstable D-brane of type II string theory compactified on a circle of
critical radius. This moduli space has two branches, -- a three dimensional
branch S^3/Z_2 and a two dimensional branch described by a square torus T^2.
These two branches are joined along a circle. We compare this with the moduli
space of classical solutions of tachyon effective field theory compactified on
a circle of critical radius. This moduli space has a very similar structure to
that of the boundary conformal field theory with the only difference that the
S^3 of the S^3/Z_2 component becomes a deformed S^3. This provides one more
indication that the tachyon effective field theory captures qualitatively the
dynamics of the tachyon on an unstable D-brane.Comment: LaTeX file, 24 pages, 2 figures; v2: reference to earlier work adde
Note on D-Brane Effective Action in the Linear Dilaton Background
In this short note we will study effective action for unstable D-brane in
linear dilaton background. We will solve the equation of motion for large T and
we will calculate the stress energy tensor. Then we compare our results with
the calculations performed using exact conformal field theory description of
the open string worldsheet theory.Comment: 12 page
Tachyon Couplings to Fermion
By fixing the internal CP factor of tachyon and massless Ramond vertex
operators in different pictures, we have shown that the internal CP factor of
the disk level S-matrix elements of two fermions and odd number of tachyon
vertex operators in the world volume of non-BPS D-branes/D-brane-anti-D-brane
is zero. We have calculated the S-matrix element of two fermions and two
tachyons which has non vanishing internal CP factor, and found the momentum
expansion of this amplitude. In the abelian case, we have compared the
two-fermion-two-tachyon coupling at low energy with the corresponding coupling
in the gauge-fixed supersymmetric tachyon DBI action. The couplings in the two
cases are exactly the same.Comment: 16 pages, latex file; V2:a missing term in the modified tachyon DBI
action adde
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