5,693 research outputs found
RANDOM MATRIX THEORY APPROACH TO THE INTENSITY DISTRIBUTIONS OF WAVES PROPAGATING IN A RANDOM MEDIUM
Statistical properties of coherent radiation propagating in a quasi - 1D
random media is studied in the framework of random matrix theory. Distribution
functions for the total transmission coefficient and the angular transmission
coefficient are obtained.Comment: 8 pages, latex, no figures. Submitted to Phys.Rev.
A note on the improvement ambiguity of the stress tensor and the critical limits of correlation functions
I study various properties of the critical limits of correlators containing
insertions of conserved and anomalous currents. In particular, I show that the
improvement term of the stress tensor can be fixed unambiguously, studying the
RG interpolation between the UV and IR limits. The removal of the improvement
ambiguity is encoded in a variational principle, which makes use of sum rules
for the trace anomalies a and a'. Compatible results follow from the analysis
of the RG equations. I perform a number of self-consistency checks and discuss
the issues in a large set of theories.Comment: 15 page
World Sheet Logarithmic CFT in AdS Strings, Ghost-Matter Mixing and M-theory
We discuss several closely related concepts in the NSR formulation of
superstring theory. We demonstrated that recently proposed NSR model for
superstrings on is described by the world-sheet logarithmic
conformal field theory (LCFT). The origin of LCFT on a world-sheet is closely
connected to the matter-ghost mixing in the structure of a brane-like vortex
operators. We suggest a dynamical origin of M theory as a string theory with an
extra dimension given by bosonised superconformal ghosts.Comment: 20 pages, no figures, harvmac, corrected some typo
Stars creating a gravitational repulsion
In the framework of the Theory of General Relativity, models of stars with an
unusual equation of state where is the mass density
and is the pressure, are constructed. These objects create outside
themselves the forces of gravitational repulsion. The equilibrium of such stars
is ensured by a non-standard balance of forces. Negative mass density, acting
gravitationally on itself, creates an acceleration of the negative mass,
directed from the center. Therefore in the absence of pressure such an object
tends to expand. At the same time, the positive pressure, which falls just like
in ordinary stars from the center to the surface, creates a force directed from
the center. This force acts on the negative mass density, which causes
acceleration directed the opposite of the acting force, that is to the center
of the star. This acceleration balances the gravitational repulsion produced by
the negative mass. Thus, in our models gravity and pressure change roles: the
negative mass tends to create a gravitational repulsion, while the gradient of
the pressure acting on the negative mass tends to compress the star. In this
paper, we construct several models of such a star with various equations of
state.Comment: 6 pages, 4 figure
Electron-Acoustic Phonon Energy Loss Rate in Multi-Component Electron Systems with Symmetric and Asymmetric Coupling Constants
We consider electron-phonon (\textit{e-ph}) energy loss rate in 3D and 2D
multi-component electron systems in semiconductors. We allow general asymmetry
in the \textit{e-ph} coupling constants (matrix elements), i.e., we allow that
the coupling depends on the electron sub-system index. We derive a
multi-component \textit{e-ph}power loss formula, which takes into account the
asymmetric coupling and links the total \textit{e-ph} energy loss rate to the
density response matrix of the total electron system. We write the density
response matrix within mean field approximation, which leads to coexistence of\
symmetric energy loss rate and asymmetric energy loss rate
with total energy loss rate at temperature
. The symmetric component F_{S}(T) F_{S}(T)\propto T^{n_{S}}n_{S}F_{A}(T). Screening strongly
reduces the symmetric coupling, but the asymmetric coupling is unscreened,
provided that the inter-sub-system Coulomb interactions are strong. The lack of
screening enhances and the total energy loss rate .
Especially, in the strong screening limit we find . A
canonical example of strongly asymmetric \textit{e-ph} matrix elements is the
deformation potential coupling in many-valley semiconductors.Comment: v2: Typos corrected. Some notations changed. Section III.C is
embedded in Section III.B. Paper accepted to PR
Spectroscopy of the quantum black hole
We develop the idea that, in quantum gravity where the horizon fluctuates, a
black hole should have a discrete mass spectrum with concomitant line emission.
Simple arguments fix the spacing of the lines, which should be broad but
unblended. Assuming uniformity of the matrix elements for quantum transitions
between near levels, we work out the probabilities for the emission of a
specified series of quanta and the intensities of the spectral lines. The
thermal character of the radiation is entirely due to the degeneracy of the
levels, the same degeneracy that becomes manifest as black hole entropy. One
prediction is that there should be no lines with wavelength of order the black
hole size or larger. This makes it possible to test quantum gravity with black
holes well above Planck scale.Comment: RevTeX, 9 page
Renormalization of Schr\"odinger Equation and Wave Functional for Rapidly Oscillating Fields in QCD
Background field method is used to perform renormalization group
transformations for Schr\"odinger equation in QCD. The dependence of the ground
state wave functional on rapidly oscillating fields is found.Comment: 8pp., Late
Local conductivity and the role of vacancies around twin walls of (001)-BiFeO3 thin films
BiFeO3 thin films epitaxially grown on SrRuO3-buffered (001)-oriented SrTiO3
substrates show orthogonal bundles of twin domains, each of which contains
parallel and periodic 71o domain walls. A smaller amount of 109o domain walls
are also present at the boundaries between two adjacent bundles. All as-grown
twin walls display enhanced conductivity with respect to the domains during
local probe measurements, due to the selective lowering of the Schottky barrier
between the film and the AFM tip (see S. Farokhipoor and B. Noheda, Phys. Rev.
Lett. 107, 127601 (2011)). In this paper we further discuss these results and
show why other conduction mechanisms are discarded. In addition we show the
crucial role that oxygen vacancies play in determining the amount of conduction
at the walls. This prompts us to propose that the oxygen vacancies migrating to
the walls locally lower the Schottky barrier. This mechanism would then be less
efficient in non-ferroelastic domain walls where one expects no strain
gradients around the walls and thus (assuming that walls are not charged) no
driving force for accumulation of defects
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