6,852 research outputs found
Volkov solution for two laser beams and ITER
We find the solution of the Dirac equation for two plane waves (laser beams)
and we determine the modified Compton formula for the scattering of two photons
on an alectron. The practical meaning of the two laser beams is, that two laser
beams impinging on a targed which is constituted from material in the form of a
foam, can replace 100-200 laser beams impinging on a normal targed. It means
that the nuclear fusion with two laser beams is realistic in combination with
the nuclear reactor such as ITER.Comment: 13 page
Phase Mixing of Nonlinear Plasma Oscillations in an Arbitrary Mass Ratio Cold Plasma
Nonlinear plasma oscillations in an arbitrary mass ratio cold plasma have
been studied using 1-D particle-in-cell simulation. In contrast to earlier work
for infinitely massive ion plasmas it has been found that the oscillations
phase mix away at any amplitude and that the rate at which phase mixing occurs,
depends on the mass ratio () and the amplitude. A
perturbation theoretic calculation carried upto third order predicts that the
normalized phase mixing time depends on the amplitude
and the mass ratio as . We have confirmed this scaling in our simulations and
conclude that stable non-linear oscillations which never phase mix, exist only
for the ideal case with and . These cold plasma results
may have direct relevance to recent experiments on superintense laser beam
plasma interactions with applications to particle acceleration, fast ignitor
concept etc.Comment: pp 10 and two figures in PS forma
Effect of topological defects and Coulomb charge on the low energy quantum dynamics of gapped graphene
We study the combined effect of a conical topological defect and a Coulomb
charge impurity on the dynamics of Dirac fermions in gapped graphene. Beyond a
certain strength of the Coulomb charge, quantum instability sets in, which
demarcates the boundary between sub and supercritical values of the charge. In
the subcritical regime, for certain values of the system parameters, the
allowed boundary conditions in gapped graphene cone can be classified in terms
of a single real parameter. We show that the observables such as local density
of states, scattering phase shifts and the bound state spectra are sensitive to
the value of this real parameter, which is interesting from an empirical point
of view. For a supercritical Coulomb charge, we analyze the system with a
regularized potential as well as with a zigzag boundary condition and find the
effect of the sample topology on the observable features of the system.Comment: 22 pages, 23 figure
Reflection coefficient and localization length of waves in one-dimensional random media
We develop a novel and powerful method of exactly calculating various
transport characteristics of waves in one-dimensional random media with (or
without) coherent absorption or amplification. Using the method, we compute the
probability densities of the reflectance and of the phase of the reflection
coefficient, together with the localization length, of electromagnetic waves in
sufficiently long random dielectric media. We find substantial differences
between our exact results and the previous results obtained using the random
phase approximation (RPA). The probabilty density of the phase of the
reflection coefficient is highly nonuniform when either disorder or absorption
(or amplification) is strong. The probability density of the reflectance when
the absorption or amplification parameter is large is also quite different from
the RPA result. We prove that the probability densities in the amplifying case
are related to those in the absorbing case with the same magnitude of the
imaginary part of the dielectric permeability by exact dual relationships. From
the analysis of the average reflectance that shows a nonmonotonic dependence on
the absorption or amplification parameter, we obtain a useful criterion for the
applicability of the RPA. In the parameter regime where the RPA is invalid, we
find the exact localization length is substantially larger than the RPA
localization length.Comment: 16 pages, 9 figure
Time-Dependent Multi-Centre Solutions from New Metrics with Holonomy Sim(n-2)
The classifications of holonomy groups in Lorentzian and in Euclidean
signature are quite different. A group of interest in Lorentzian signature in n
dimensions is the maximal proper subgroup of the Lorentz group, SIM(n-2).
Ricci-flat metrics with SIM(2) holonomy were constructed by Kerr and Goldberg,
and a single four-dimensional example with a non-zero cosmological constant was
exhibited by Ghanam and Thompson. Here we reduce the problem of finding the
general -dimensional Einstein metric of SIM(n-2) holonomy, with and without
a cosmological constant, to solving a set linear generalised Laplace and
Poisson equations on an (n-2)-dimensional Einstein base manifold. Explicit
examples may be constructed in terms of generalised harmonic functions. A
dimensional reduction of these multi-centre solutions gives new time-dependent
Kaluza-Klein black holes and monopoles, including time-dependent black holes in
a cosmological background whose spatial sections have non-vanishing curvature.Comment: Typos corrected; 29 page
Multifractal Behaviour of n-Simplex Lattice
We study the asymptotic behaviour of resistance scaling and fluctuation of
resistance that give rise to flicker noise in an {\em n}-simplex lattice. We
propose a simple method to calculate the resistance scaling and give a
closed-form formula to calculate the exponent, , associated with
resistance scaling, for any n. Using current cumulant method we calculate the
exact noise exponent for n-simplex lattices.Comment: Latex, 9 pages including one figur
Logarithmic Corrections to N=2 Black Hole Entropy: An Infrared Window into the Microstates
Logarithmic corrections to the extremal black hole entropy can be computed
purely in terms of the low energy data -- the spectrum of massless fields and
their interaction. The demand of reproducing these corrections provides a
strong constraint on any microscopic theory of quantum gravity that attempts to
explain the black hole entropy. Using quantum entropy function formalism we
compute logarithmic corrections to the entropy of half BPS black holes in N=2
supersymmetric string theories. Our results allow us to test various proposals
for the measure in the OSV formula, and we find agreement with the measure
proposed by Denef and Moore if we assume their result to be valid at weak
topological string coupling. Our analysis also gives the logarithmic
corrections to the entropy of extremal Reissner-Nordstrom black holes in
ordinary Einstein-Maxwell theory.Comment: LaTeX file, 66 page
Logarithmic Corrections to Extremal Black Hole Entropy from Quantum Entropy Function
We evaluate the one loop determinant of matter multiplet fields of N=4
supergravity in the near horizon geometry of quarter BPS black holes, and use
it to calculate logarithmic corrections to the entropy of these black holes
using the quantum entropy function formalism. We show that even though
individual fields give non-vanishing logarithmic contribution to the entropy,
the net contribution from all the fields in the matter multiplet vanishes. Thus
logarithmic corrections to the entropy of quarter BPS black holes, if present,
must be independent of the number of matter multiplet fields in the theory.
This is consistent with the microscopic results. During our analysis we also
determine the complete spectrum of small fluctuations of matter multiplet
fields in the near horizon geometry.Comment: LaTeX file, 52 pages; v2: minor corrections, references adde
Supersymmetry, Localization and Quantum Entropy Function
AdS_2/CFT_1 correspondence leads to a prescription for computing the
degeneracy of black hole states in terms of path integral over string fields
living on the near horizon geometry of the black hole. In this paper we make
use of the enhanced supersymmetries of the near horizon geometry and
localization techniques to argue that the path integral receives contribution
only from a special class of string field configurations which are invariant
under a subgroup of the supersymmetry transformations. We identify saddle
points which are invariant under this subgroup. We also use our analysis to
show that the integration over infinite number of zero modes generated by the
asymptotic symmetries of AdS_2 generate a finite contribution to the path
integral.Comment: LaTeX file, 31 pages; v2: minor correction; v3: typos correcte
Cardy and Kerr
The Kerr/CFT correspondence employs the Cardy formula to compute the entropy
of the left moving CFT states. This computation, which correctly reproduces the
Bekenstein--Hawking entropy of the four-dimensional extremal Kerr black hole,
is performed in a regime where the temperature is of order unity rather than in
a high-temperature regime. We show that the comparison of the entropy of the
extreme Kerr black hole and the entropy in the CFT can be understood within the
Cardy regime by considering a D0-D6 system with the same entropic properties.Comment: 20 pages; LaTeX; JHEP format; v.2 references added, v.3 Section 4
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