165,031 research outputs found

### A note on brane/flux annihilation and dS vacua in string theory

We reconsider the dynamics of p anti-D3 branes inside the Klebanov-Strassler
geometry, in which M units of R-R 3-form flux and K units of NS-NS 3-form flux
are presented in deformed conifold. We find that anti-D3 branes blow up into a
spherical D5-brane at weak string coupling via quantum tunnelling. The D5-brane
can be either stable or unstable, depending on number of background flux. The
nucleation rate of D5-brane is suppressed by \exp{-Mp^2}. The classical
mechanically the evolution of unstable D5-brane annihilates one unit of R-R
flux and ends with (K-p) D3-branes. This observation is consistent with one by
Kachru, Pearson and Verlinde, who shew that anti-D3 branes in KS geometry can
blow up into a spherical NS5 brane at strong string coupling, because NS5-brane
is lighter that D5-brane at strong string coupling. We also argue that the
system can end with a meta-stable dS vacuum by fine tuning of number of
background flux.Comment: 14 pages, 3 eps figures, v2: typos modified and references adde

### Strings in Noncommutative Spacetime

Free bosonic strings in noncommutative spacetime are investigated. The string
spectrum is obtained in terms of light-cone quantization. We construct two
different models. In the first model the critical dimension is still required
to be 26 while only extreme high energy spectrum is modified by noncommutative
effect. In the second model, however, the critical dimension is reduced to be
less than 26 while low-energy (massless) spectrum only contains degrees of
freedom of our four dimensional physics.Comment: 9 pages, no figure

### The iterative convolution-thresholding method (ICTM) for image segmentation

In this paper, we propose a novel iterative convolution-thresholding method
(ICTM) that is applicable to a range of variational models for image
segmentation. A variational model usually minimizes an energy functional
consisting of a fidelity term and a regularization term. In the ICTM, the
interface between two different segment domains is implicitly represented by
their characteristic functions. The fidelity term is then usually written as a
linear functional of the characteristic functions and the regularized term is
approximated by a functional of characteristic functions in terms of heat
kernel convolution. This allows us to design an iterative
convolution-thresholding method to minimize the approximate energy. The method
is simple, efficient and enjoys the energy-decaying property. Numerical
experiments show that the method is easy to implement, robust and applicable to
various image segmentation models.Comment: 13 pages, 4 figure

### Derivation of Newton's law of gravitation based on a fluidic continuum model of vacuum and a sink flow model of particles

The main purpose of this paper is to seek a mechanical interpretation of
gravitational phenomena. We suppose that the universe may be filled with a kind
of fluid which may be called the $\Omega (0)$ substratum. Thus, the
inverse-square law of gravitation is derived by methods of hydrodynamics based
on a sink flow model of particles. The first feature of this theory of
gravitation is that the gravitational interactions are transmitted by a kind of
fluidic medium. The second feature is the time dependence of gravitational
constant $G$ and gravitational mass. Newton's law of gravitation is derived if
we introduce an assumption that $G$ and the masses of particles are changing so
slowly that they can be treated as constants.Comment: 8 pages, 0 figures, Revtex

### Nature of Integer Quantum Hall Transitions

The mapping between the metal-insulator transition of the quantum Hall system
and a superfluid-to-insulator transition is revisited based on a disordered
anyon model. The one-parameter scaling of the superfluid-to-insulator
transition is employed for the analysis of the scaling behavior of the integer
quantum Hall transitions. The analysis reveals the direct transition from a
quantum Hall plateau to the insulator in weak disorder limit, and a float-down
transition for strong disorders. In either cases, the transition corresponds to
a non-chirality superfluid-to-insulator transition, with the longitudinal and
transverse quantum Hall conductivities following a semi-circle relation

### Derivation of the Maxwell's Equations Based on a Continuum Mechanical Model of Vacuum and a Singularity Model of Electric Charges

We speculate that the universe may be filled with a visco-elastic continuum
which may be called aether. Thus, the Maxwell's equations in vacuum are derived
by methods of continuum mechanics based on a continuum mechanical model of
vacuum and a singularity model of electric charges.Comment: 9 pages, 0 figures, REVTeX

### Derivation of Coulomb's Law of Forces Between Static Electric Charges Based on Spherical Source and Sink Model of Particles

We speculate that the universe may be filled with a continuum which may be
called aether. Based on a spherical source and sink model of electric charges,
we derive Coulomb's law of interactions between static electric charges in
vacuum by methods of hydrodynamics. A reduced form of the Lorentz's force law
of static electric charges is derived based on a definition of electric field.Comment: 8 pages, 0 figures, Version 4.0 of REVTeX. arXiv admin note: text
overlap with arXiv:physics/050606

### Spinning Strings on Deformed AdS_5 x T^{1,1} with NS B-field

We study classical spinning closed string configuration on logarithmically
deformed AdS_5 x T^{1,1} background with non-trivial Neveu-Schwarz B-field in
which IIB string theory is dual to a non-conformal N=1 SU(N+M) x SU(N) gauge
theory. The integrability on original AdS_5 x T^{1,1} background are
significantly reduced by B-field. We find several spinning string solutions
with two different ansatzs. Solutions for point-like strings and few circular
strings are explicitly obtained. Folded spinning string solutions along radial
direction are shown to be allowed in this background. These solutions exhibit
novel properties and bring some challenges to understand them from dual quantum
field theory.Comment: 26 pages, v.4: The discussions on folded strings was improve

### Cosmological Constant as Vacuum Energy Density of Quantum Field Theories on Noncommutative Spacetime

We propose a new approach to understand hierarchy problem for cosmological
constant in terms of considering noncommutative nature of space-time. We
calculate that vacuum energy density of the noncommutative quantum field
theories in nontrivial background, which admits a smaller cosmological constant
by introducing an higher noncommutative scale $\mu_{NC}\sim M_p$. The result
$\rho_\Lambda\sim 10^{-6}\Lambda_{SUSY}^8M_p^4/\mu_{NC}^8$ yields cosmological
constant at the order of current observed value for supersymmetry breaking
scale at 10TeV. It is the same as Banks' phenomenological formula for
cosmological constant.Comment: 7 pages, no figures, v4, references adde

### Holography and (1+1)-dimension non-relativistic Quantum Mechanics

I generalize classical gravity/quantum gauge theory duality in AdS/CFT
correspondence to (1+1)-dimensional non-relativistic quantum mechanical system.
It is shown that (1+1)-dimensional non-relativistic quantum mechanical system
can be reproduced from holographic projection of (2+1)-dimension classical
gravity at semiclassical limit. In this explanation every quantum path in
2-dimension corresponds to a classical path of 3-dimension gravity under
definite holographic projection. I consider free particle and harmonic
oscillator as two examples and find their dual gravity description.Comment: 4 pages, no fig, use revtex4.cl

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