359 research outputs found
D-brane dynamics near compactified NS5-branes
We examine the dynamics of a -brane in the background of coincident,
parallel 5-branes which have had one of their common transverse directions
compactified. We find that for small energy, bound orbits can exist at
sufficiently large distances where there will be no stringy effects. The orbits
are dependent upon the energy density, angular momentum and electric field. The
analysis breaks down at radial distances comparable with the compactification
radius and we must resort to using a modified form of the harmonic function in
this region.Comment: Latex, 20 pages, 6 figs, references adde
D-brane orbiting NS5-branes
We study real time dynamics of a Dp-brane orbiting a stack of NS5-branes. It
is generally known that a BPS D-brane moving in the vicinity of NS5-branes
becomes unstable due to the presence of tachyonic degree of freedom induced on
the D-brane. Indeed, the D-brane necessarily falls into the fivebranes due to
gravitational attraction and eventually collapses into a pressureless fluid.
Such a decay of the D-brane is known to be closely related to the rolling
tachyon problem. In this paper we show that in special cases the decay of
D-brane caused by gravitational attraction can be avoided. Namely for certain
values of energy and angular momentum the D-brane orbits around the fivebranes,
maintaining certain distance from the fivebranes all the time, and the process
of tachyon condensation is suppressed. We show that the tachyonic degree of
freedom induced on such a D-brane really disappears and the brane returns to a
stable D-brane.Comment: 12 pages, latex, added referenc
On the Universal Tachyon and Geometrical Tachyon
We study properties of non-BPS D(p+1)-brane in the background of k
NS5-branes, with one transverse direction compactified on a circle, from the
point of view of Dirac-Born-Infeld action. We present the analysis of two
different embedding of non-BPS D(p+1)-brane in given background and study the
classical solutions of given world-volume theory. We argue for the
configuration of a non-BPS D(p+1)-brane which allows us to find solutions of
the equations of motion that give unified descriptions of G and U-type branes.Comment: 24 pages, minor change
Non Abelian Geometrical Tachyon
We investigate the dynamics of a pair of coincident D5 branes in the
background of NS5 branes. It has been proposed by Kutasov that the system
with a single probing D-brane moving radially in this background is dual to the
tachyonic DBI action for a non-BPS Dp brane. We extend this proposal to the
non-abelian case and find that the duality still holds provided one promotes
the radial direction to a matrix valued field associated with a non-abelian
geometric tachyon and a particular parametrization for the transverse scalar
fields is chosen. The equations of motion of a pair of coincident D5 branes
moving in the NS5 background are determined. Analytic and numerical solutions
for the pair are found in certain simplified cases in which the U(2) symmetry
is broken to corresponding to a small transverse separation
of the pair. For certain range of parameters these solutions describe periodic
motion of the centre of mass of the pair 'bouncing off' a finite sized throat
whose minimum size is limited by the D5 branes separation.Comment: 18 pages, 2 figures, PdfLatex: references added.accepted for
publication in JHE
Penrose limit and string quantization in AdS_3 \times S^3
We consider corrections to the Penrose limit of AdS_3 \times S^3 with NS-NS
flux which are due to the terms next to leading order in inverse radius
expansion. The worldsheet theory of a lightcone string is interacting due to
the presence of quartic terms in the action. Perturbative corrections to the
spectrum are shown to agree with the results from the exact quantization in
AdS_3 \times S^3.Comment: 18 pages v2: typos fixed, reference added, to appear in JHE
Unitarity Meets Channel-Duality for Rolling / Decaying D-Branes
Investigations for decay of unstable D-brane and rolling of accelerated
D-brane dynamics have revealed that various proposed prescriptions give
different result for spectral amplitudes and observables. Here, we study them
with particular attention to unitarity and open-closed channel duality. From
"ab initio" derivation in the open string channel, both in Euclidean and
Lorentzian worldsheet approaches, we find heretofore overlooked contribution to
the spectral amplitudes and obervables. The contribution is fortuitously absent
for decay of unstable D-brane, but is present for rolling of accelerated
D-brane. We finally show that the contribution is imperative for ensuring
unitarity and optical theorem at each order in string loop expansion.Comment: Latex, 28 pages, 2 figures (colored
Dynamics of D1-brane in I-brane Background
This paper is devoted to the study of the effective field theory description
of the probe D1-brane in the background of the system of two stacks of
fivebranes in type IIB theory that intersect on . We study the
properties of the Dirac-Born-Infeld action for D1-brane moving in this
background. We will argue that this action is invariant under an additional
symmetry in the near horizon limit and that this new symmetry is closely
related to the enhanced symmetry of the I-brane background considered recently
in [hep-th/0508025]. We also solve explicitly the equation of motion of
D1-brane in the near horizon limit.Comment: 21 pages, references adde
Variational ansatz for the nonlinear Landau-Zener problem for cold atom association
We present a rigorous analysis of the Landau-Zener linear-in-time term
crossing problem for quadratic-nonlinear systems relevant to the coherent
association of ultracold atoms in degenerate quantum gases. Our treatment is
based on an exact third-order nonlinear differential equation for the molecular
state probability. Applying a variational two-term ansatz, we construct a
simple approximation that accurately describes the whole-time dynamics of
coupled atom-molecular system for any set of involved parameters. Ensuring an
absolute error less than for the final transition probability, the resultant
solution improves by several orders of magnitude the accuracy of the previous
approximations by A. Ishkhanyan et al. developed separately for the weak
coupling [J. Phys. A 38, 3505 (2005)] and strong interaction [J. Phys. A 39,
14887 (2006)] limits. In addition, the constructed approximation covers the
whole moderate-coupling regime, providing for this intermediate regime the same
accuracy as for the two mentioned limits. The obtained results reveal the
remarkable observation that for the strong-coupling limit the resonance
crossing is mostly governed by the nonlinearity, while the coherent
atom-molecular oscillations arising soon after the resonance has been crossed
are basically of linear nature. This observation is supposed to be of a general
character due to the basic attributes of the resonance crossing processes in
the nonlinear quantum systems of the discussed type of involved quadratic
nonlinearity
Double Scaling Limits and Twisted Non-Critical Superstrings
We consider double-scaling limits of multicut solutions of certain one matrix
models that are related to Calabi-Yau singularities of type A and the
respective topological B model via the Dijkgraaf-Vafa correspondence. These
double-scaling limits naturally lead to a bosonic string with c 1. We
argue that this non-critical string is given by the topologically twisted
non-critical superstring background which provides the dual description of the
double-scaled little string theory at the Calabi-Yau singularity. The
algorithms developed recently to solve a generic multicut matrix model by means
of the loop equations allow to show that the scaling of the higher genus terms
in the matrix model free energy matches the expected behaviour in the
topological B-model. This result applies to a generic matrix model singularity
and the relative double-scaling limit. We use these techniques to explicitly
evaluate the free energy at genus one and genus two.Comment: 32 pages, 3 figure
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