16,728 research outputs found
Hidden Translation and Translating Coset in Quantum Computing
We give efficient quantum algorithms for the problems of Hidden Translation
and Hidden Subgroup in a large class of non-abelian solvable groups including
solvable groups of constant exponent and of constant length derived series. Our
algorithms are recursive. For the base case, we solve efficiently Hidden
Translation in , whenever is a fixed prime. For the induction
step, we introduce the problem Translating Coset generalizing both Hidden
Translation and Hidden Subgroup, and prove a powerful self-reducibility result:
Translating Coset in a finite solvable group is reducible to instances of
Translating Coset in and , for appropriate normal subgroups of
. Our self-reducibility framework combined with Kuperberg's subexponential
quantum algorithm for solving Hidden Translation in any abelian group, leads to
subexponential quantum algorithms for Hidden Translation and Hidden Subgroup in
any solvable group.Comment: Journal version: change of title and several minor update
Experimental study of nonlinear dust acoustic solitary waves in a dusty plasma
The excitation and propagation of finite amplitude low frequency solitary
waves are investigated in an Argon plasma impregnated with kaolin dust
particles. A nonlinear longitudinal dust acoustic solitary wave is excited by
pulse modulating the discharge voltage with a negative potential. It is found
that the velocity of the solitary wave increases and the width decreases with
the increase of the modulating voltage, but the product of the solitary wave
amplitude and the square of the width remains nearly constant. The experimental
findings are compared with analytic soliton solutions of a model Kortweg-de
Vries equation.Comment: The manuscripts includes six figure
On the evolution of tachyonic perturbations at super-Hubble scales
In the slow-roll inflationary scenario, the amplitude of the curvature
perturbations approaches a constant value soon after the modes leave the Hubble
radius. However, relatively recently, it was shown that the amplitude of the
curvature perturbations induced by the canonical scalar field can grow at
super-Hubble scales if there is either a transition to fast roll inflation or
if inflation is interrupted for some period of time. In this work, we extend
the earlier analysis to the case of a non-canonical scalar field described by
the Dirac-Born-Infeld action. With the help of a specific example, we show that
the amplitude of the tachyonic perturbations can be enhanced or suppressed at
super-Hubble scales if there is a transition from slow roll to fast roll
inflation. We also illustrate as to how the growth of the entropy perturbations
during the fast roll regime proves to be responsible for the change in the
amplitude of the curvature perturbations at super-Hubble scales. Furthermore,
following the earlier analysis for the canonical scalar field, we show that the
power spectrum evaluated in the long wavelength approximation matches the exact
power spectrum obtained numerically very well. Finally, we briefly comment on
an application of this phenomenon.Comment: v1: 15 pages, 4 figures; v2: 16 pages, 5 figures, power spectrum
included, discussion in section 5 enlarged, references added; v3: 17 pages, 5
figures, enhancement AS WELL AS suppression of modes at super-Hubble scales
pointed out, title changed, discussions enlarged, references added, to appear
in JCA
On thin-shell wormholes evolving in flat FRW spacetimes
We analize the stability of a class of thin-shell wormholes with spherical
symmetry evolving in flat FRW spacetimes. The wormholes considered here are
supported at the throat by a perfect fluid with equation of state
and have a physical radius equal to , where is a
time-dependent function describing the dynamics of the throat and is the
background scale factor. The study of wormhole stability is done by means of
the stability analysis of dynamic systems.Comment: 8 pages; to appear in MPL
One-loop Evolution of a Rolling Tachyon
We study the time evolution of the one-loop diagram in Sen's rolling tachyon
background. We find that at least in the long cylinder case they grow rapidly
at late time, due to the exponential growth of the timelike oscillator terms in
the boundary state. This can also be interpreted as the virtual open string
pair creation in the decaying brane. This behavior indicates a breakdown of
this rolling tachyon solution at some point during the evolution. We also
discuss the closed string emission from this one-loop diagram, and the
evolution of a one-loop diagram connecting a decaying brane to a stable brane,
which is responsible for the physical open string creation on the stable brane.Comment: 21 pages, 2 figures; v2: references added, comments revised in
various places; v3: footnotes 7&8 added, revised version to appear in PR
Dynamics with Infinitely Many Time Derivatives and Rolling Tachyons
Both in string field theory and in p-adic string theory the equations of
motion involve infinite number of time derivatives. We argue that the initial
value problem is qualitatively different from that obtained in the limit of
many time derivatives in that the space of initial conditions becomes strongly
constrained. We calculate the energy-momentum tensor and study in detail time
dependent solutions representing tachyons rolling on the p-adic string theory
potentials. For even potentials we find surprising small oscillations at the
tachyon vacuum. These are not conventional physical states but rather
anharmonic oscillations with a nontrivial frequency--amplitude relation. When
the potentials are not even, small oscillatory solutions around the bottom must
grow in amplitude without a bound. Open string field theory resembles this
latter case, the tachyon rolls to the bottom and ever growing oscillations
ensue. We discuss the significance of these results for the issues of emerging
closed strings and tachyon matter.Comment: 46 pages, 14 figures, LaTeX. Replaced version: Minor typos corrected,
some figures edited for clarit
Non-Supersymmetric Attractors in String Theory
We find examples of non-supersymmetric attractors in Type II string theory
compactified on a Calabi Yau three-fold. For a non-supersymmetric attractor the
fixed values to which the moduli are drawn at the horizon must minimise an
effective potential. For Type IIA at large volume, we consider a configuration
carrying D0, D2, D4 and D6 brane charge. When the D6 brane charge is zero, we
find for some range of the other charges, that a non-supersymmetric attractor
solution exists. When the D6 brane charge is non-zero, we find for some range
of charges, a supersymmetry breaking extremum of the effective potential.
Closer examination reveals though that it is not a minimum of the effective
potential and hence the corresponding black hole solution is not an attractor.
Away from large volume, we consider the specific case of the quintic in CP^4.
Working in the mirror IIB description we find non-supersymmetric attractors
near the Gepner point.Comment: Added a few clarification
Stability of thin-shell wormholes with spherical symmetry
In this article, the stability of a general class of spherically symmetric
thin-shell wormholes is studied under perturbations preserving the symmetry.
For this purpose, the equation of state at the throat is linearized around the
static solutions. The formalism presented here is applied to dilaton wormholes
and it is found that there is a smaller range of possible stable configurations
for them than in the case of Reissner-Nordstrom wormholes with the same charge.Comment: 14 pages, 3 figure
Proper acceleration, geometric tachyon and dynamics of a fundamental string near D branes
We present a detailed analysis of our recent observation that the origin of
the geometric tachyon, which arises when a D-brane propagates in the
vicinity of a stack of coincident NS5-branes, is due to the proper acceleration
generated by the background dilaton field. We show that when a fundamental
string (F-string), described by the Nambu-Goto action, is moving in the
background of a stack of coincident D-branes, the geometric tachyon mode can
also appear since the overall conformal mode of the induced metric for the
string can act as a source for proper acceleration. We also studied the
detailed dynamics of the F-string as well as the instability by mapping the
Nambu-Goto action of the F-string to the tachyon effective action of the
non-BPS D-string. We qualitatively argue that the condensation of the geometric
tachyon is responsible for the (F,D) bound state formation.Comment: 26 pages, v2: added references, v3: one ref. updated, to appear in
Class. and Quant. Gravit
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