118,445 research outputs found
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
STRING STRING DUALITY CONJECTURE IN SIX DIMENSIONS AND CHARGED SOLITONIC STRINGS
It has recently been conjectured that the type IIA string theory compactified
on K3 and the heterotic string theory compactified on a four dimensional torus
describe identical string theories. The fundamental heterotic string can be
regarded as a non-singular soliton solution of the type IIA string theory with
a semi-infinite throat. We show that this solution admits 24 parameter
non-singular deformation describing a fundamental heterotic string carrying
electric charge and current. The charge is generated due to the coupling of the
gauge fields to the anti-symmetric tensor field, and not to an explicit source
term. This clarifies how soliton solutions carrying charge under the
Ramond-Ramond fields can be constructed in the type IIA theory, and provides
further support to the string string duality conjecture. Similarly, the
fundamental type IIA string can be regarded as a non-singular solution of the
heterotic string theory with a semi-infinite throat, but this solution does not
admit any deformation representing charged string. This is also consistent with
the expectation that a fundamental type IIA string does not carry any charge
that couples to the fields originating in the Ramond-Ramond sector.Comment: 17 pages, LaTeX fil
Open/Closed Duality, Unstable D-Branes, and Coarse-Grained Closed Strings
At the final stage of unstable D-brane decay in the effective field theory
approach, all energy and momentum of the initial state are taken up by two
types of fluids, known as string fluid and tachyon matter. In this note, we
compare motion of this fluid system to that of macroscopic collection of
stretched closed strings and find a precise match at classical level. The
string fluid reflects low frequency undulation of the stretched strings while
the tachyon matter encodes the average effect of high frequency oscillations
turned on those strings. In particular, the combined fluid system has been
known to have a reduced speed of light, depending on the composition, and we
show that this property is exactly reproduced in classical motion on the closed
string side. Finally we illustrate how the tachyon matter may be viewed as an
effective degrees of freedom carrying high frequency energy-momentum of
Nambu-Goto strings by coarse-graining the dynamics of the latter.Comment: LaTeX, 29 pages, 4 figure file
Benford's Law Detects Quantum Phase Transitions similarly as Earthquakes
A century ago, it was predicted that the first significant digit appearing in
a data would be nonuniformly distributed, with the number one appearing with
the highest frequency. This law goes by the name of Benford's law. It holds for
data ranging from infectious disease cases to national greenhouse gas
emissions. Quantum phase transitions are cooperative phenomena where
qualitative changes occur in many-body systems at zero temperature. We show
that the century-old Benford's law can detect quantum phase transitions, much
like it detects earthquakes. Therefore, being certainly of very different
physical origins, seismic activity and quantum cooperative phenomena may be
detected by similar methods. The result has immediate implications in precise
measurements in experiments in general, and for realizable quantum computers in
particular. It shows that estimation of the first significant digit of measured
physical observables is enough to detect the presence of quantum phase
transitions in macroscopic systems.Comment: v1: 3 pages, 2 figures; v2: 6 (+epsilon) epl pages, 5 figures,
significant additions, previous results unchange
Symmetries of Four-dimensional String Effective Action with Cosmological Constant
Classical solutions for a four-dimensional Minkowskian string effective
action and an Euclidean one with cosmological constant term are derived. The
former corresponds to electrovac solutions whereas the later solutions are
identified as gravitational instanton solutions for Fubini-Study metric. The
symmetries of the effective actions are identified and new classical solutions
are generated by implementing appropriate noncompact transformations. The
S-duality transformations on the equations of motion are discussed and it is
found that they are S-duality noninvariant due to the presence of cosmological
constant term.Comment: 13 pages, RevTex file, text is improved, no changes in the final
results, also some references are added. (version to appear in Phys. Lett. B
Electric Tachyon Inflation
We propose that under certain conditions the universal open string tachyon
can drive topological inflation in moduli stabilised frameworks. Namely, the
presence of electric field in the world volume of the D-brane can slow down its
decay leading to a phenomenological model of inflation. The conditions for
inflation to take place are difficult to satisfy in the standard warped
deformed conifold but easier to realise in other geometries.Comment: 8 pages; Contribution to the proceedings of the RTN workshop
"Constituents, Fundamental Forces and Symmetries of the Universe", Corfu,
Greece, 20-26 September 2005. v2: Typos corrected, reference adde
D-Brane Dynamics in Dp-Brane Background
By using Dirac-Born-Infeld action we study the real time dynamics of D-branes
in the vicinity of a stack of Dp-branes where the role of the tachyon of the
open string models is played by the radial mode on the D-branes. We examine the
behaviour of the tachyon potential and study the hamiltonian formulation and
classical solutions of such systems. We also study the homogeneous solutions of
the classical equations of motion in these cases.Comment: 14 pages, minor modifications, to appear in Phys. Lett.
Ultrasonic Blind Stick for Completely Blind People to Avoid any Kind of Obstacles
The ability to live without being controlled by any action, judgment and any
outside factors including any opinions and regulations is defined by the term
Independent. But in reality physical movement for travelling or simply walking
through a crowded street pose great challenge for a visually impaired person.
Also they must learn every detail about the home environment such as placement
of tables; chairs etc. to prevent injury. Because of this disability they have
to sacrifice their independence in daily living by depending on the sighted
people in every busy place like bus, footpaths, railway stations etc. This
paper aims to design an artificial navigating system with adjustable
sensitivity with the help of ultrasonic proximity sensor to assist these blind
persons to walk fearlessly and independently in both indoor and outdoor
environment. This system can detect any type of upcoming obstacles and potholes
using the reflection properties of ultrasound. Attachment of the system to
different body areas makes its utilization more versatile and reliable
Disorder-induced Effects in Noisy Dynamics of Bose-Hubbard and Fermi-Hubbard Quantum Glasses
We address the effects of quenched disorder averaging in the time-evolution
of systems of ultracold atoms in optical lattices in the presence of noise,
imposed by of an environment. For bosonic systems governed by the Bose-Hubbard
Hamiltonian, we quantify the response of disorder in Hamiltonian parameters in
terms of physical observables, including bipartite entanglement in the ground
state and report the existence of disorder-induced enhancement in weakly
interacting cases. For systems of two-species fermions described by the
Fermi-Hubbard Hamiltonian, we find similar results. In both cases, our
dynamical calculations show no appreciable change in the effects of disorder
from that of the initial state of the evolution. We explain our findings in
terms the statistics of the disorder in the parameters and the behaviour of the
observables with the parameters
- âŠ