297 research outputs found
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
New Examples of Flux Vacua
Type IIB toroidal orientifolds are among the earliest examples of flux vacua.
By applying T-duality, we construct the first examples of massive IIA flux
vacua with Minkowski space-times, along with new examples of type IIA flux
vacua. The backgrounds are surprisingly simple with no four-form flux at all.
They serve as illustrations of the ingredients needed to build type IIA and
massive IIA solutions with scale separation. To check that these backgrounds
are actually solutions, we formulate the complete set of type II supergravity
equations of motion in a very useful form that treats the R-R fields
democratically.Comment: 38 pages, LaTeX; references updated; additional minor comments added;
published versio
Nonabelian D-branes and Noncommutative Geometry
We discuss the nonabelian world-volume action which governs the dynamics of N
coincident Dp-branes. In this theory, the branes' transverse displacements are
described by matrix-valued scalar fields, and so this is a natural physical
framework for the appearance of noncommutative geometry. One example is the
dielectric effect by which Dp-branes may be polarized into a noncommutative
geometry by external fields. Another example is the appearance of
noncommutative geometries in the description of intersecting D-branes of
differing dimensions, such as D-strings ending on a D3- or D5-brane. We also
describe the related physics of giant gravitons.Comment: 21 pages, Latex, ref. adde
Note About Unstable M3-brane Action
We construct an action for unstable M3-brane in M-theory. We argue that in
order to find M3-brane action that upon direct dimensional reduction leads to
non-BPS D3-brane action in type IIA theory we have to presume that the
background possesses Killing isometry and that this isometry has to be gauged
on the world-volume of M3-brane. Then we construct singular tachyon kink on
world-volume of M3-brane and we show that the dynamics of resulting topological
defect is governed by an action that upon direct dimensional reduction leads to
D2-brane in type IIA theory and that is equivalent to standard M2-brane action
in flat background.Comment: 20 pages, references adde
More on WZ action of non-BPS branes
We calculate the disk level S-matrix element of one Ramond-Ramond, two gauge
fields and one tachyon vertex operators in the world volume of non-BPS branes.
We then find the momentum expansion of this amplitude and show that the
infinite tachyon/massless poles and the contact terms of this amplitude can be
reproduced by the tachyon DBI and the WZ actions, and by their higher
derivative corrections.Comment: 17 pages, no figure
Singular tachyon kinks from regular profiles
We demonstrate how Sen's singular kink solution of the Born-Infeld tachyon
action can be constructed by taking the appropriate limit of initially regular
profiles. It is shown that the order in which different limits are taken plays
an important role in determining whether or not such a solution is obtained for
a wide class of potentials. Indeed, by introducing a small parameter into the
action, we are able circumvent the results of a recent paper which derived two
conditions on the asymptotic tachyon potential such that the singular kink
could be recovered in the large amplitude limit of periodic solutions. We show
that this is explained by the non-commuting nature of two limits, and that
Sen's solution is recovered if the order of the limits is chosen appropriately.Comment: 7 pages, 3 figures. References adde
Tachyon kinks on non BPS D-branes
We consider solitonic solutions of the DBI tachyon effective action for a
non-BPS brane. When wrapped on a circle, these solutions are regular and have a
finite energy. We show that in the decompactified limit, these solitons give
Sen's infinitely thin finite energy kink -- interpreted as a BPS brane --
provided that some conditions on the potential hold. In particular, if for
large the potential is exponential, , then Sen's solution is
only found for . For power-law potentials , one must have
. If these conditions are not satisfied, we show that the lowest energy
configuration is the unstable tachyon vacuum with no kinks. We examine the
stability of the solitons and the spectrum of small perturbations.Comment: 16 pages, 2 figure
Regular and Periodic Tachyon Kinks
We search for regular tachyon kinks in an extended model, which includes the
tachyon action recently proposed to describe the tachyon field. The extended
model that we propose adds a new contribution to the tachyon action, and seems
to enrich the present scenario for the tachyon field. We have found stable
tachyon kinks of regular profile, which may appropriately lead to the singular
kink found by Sen sometime ago. Also, under specific conditions we may find
periodic array of kink-antikink configurations.Comment: 10 pages, 1 figure. Version to be published in Mod. Phys. Lett.
On RR couplings on D-branes at order
Recently, it has been found that there are couplings of the RR field strength
and the B-field strength on the world volume of D-branes at
order . These couplings which have both world-volume and
transverse indices, are invariant under the linear T-duality transformations.
Consistency with the nonlinear T-duality indicates that the RR field strength
in these couplings should be replaced by where . This replacement, however, reproduces some
non-gauge invariant terms. On the other hand, the nonlinear terms are invariant
under the linear T-duality transformations at the level of two B-fields. This
allows one to remove some of the nonlinear terms in . We fix
this by comparing the nonlinear couplings with the S-matrix element of one RR
and two NSNS vertex operators. Our results indicate that in the expansion of
one should keep only the B-field gauge invariant terms, e.g.
where both indices of B-field lie along the brane.
Moreover, in this case one should replace with to have the
-field gauge invariance.Comment: 23 pages, Latex file, 1 figure; v2:typos corrected, to appear in JHE
On effective actions of BPS branes and their higher derivative corrections
We calculate in detail the disk level S-matrix element of one Ramond-Ramond
field and three gauge field vertex operators in the world volume of BPS branes,
to find four gauge field couplings to all orders of up to on-shell
ambiguity. Then using these infinite couplings we find that the massless pole
of the field theory amplitude is exactly equal to the massless pole S-matrix
element of this amplitude for the case to all orders of .
Finally we show that the infinite massless poles and the contact terms of this
amplitude for the case can be reproduced by the Born-Infeld action and
the Wess-Zumino actions and by their higher derivative corrections.Comment: 26 pages, 2 figures, minor corrections,references added and version
published in JHE
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