22,407 research outputs found
Phase transitions in Ising model on a Euclidean network
A one dimensional network on which there are long range bonds at lattice
distances with the probability has been taken
under consideration. We investigate the critical behavior of the Ising model on
such a network where spins interact with these extra neighbours apart from
their nearest neighbours for . It is observed that there is
a finite temperature phase transition in the entire range. For , finite size scaling behaviour of various quantities are consistent with
mean field exponents while for , the exponents depend on
. The results are discussed in the context of earlier observations on
the topology of the underlying network.Comment: 7 pages, revtex4, 7 figures; to appear in Physical Review E, minor
changes mad
Inverse cascades in turbulence and the case of rotating flows
We first summarize briefly several properties concerning the dynamics of
two-dimensional (2D) turbulence, with an emphasis on the inverse cascade of
energy to the largest accessible scale of the system. In order to study a
similar phenomenon in three-dimensional (3D) turbulence undergoing strong
solid-body rotation, we test a previously developed Large Eddy Simulation (LES)
model against a high-resolution direct numerical simulation of rotating
turbulence on a grid of points. We then describe new numerical results
on the inverse energy cascade in rotating flows using this LES model and
contrast the case of 2D versus 3D forcing, as well as non-helical forcing
(i.e., with weak overall alignment between velocity and vorticity) versus the
fully helical Beltrami case, both for deterministic and random forcing. The
different scaling of the inverse energy cascade can be attributed to the
dimensionality of the forcing, with, in general, either a or a
energy spectrum of slow modes at large scales, perpendicular
referring to the direction of rotation. We finally invoke the role of shear in
the case of a strongly anisotropic deterministic forcing, using the so-called
ABC flow.Comment: 10 pages, 3 figure
Cosmology in scalar tensor theory and asymptotically de-Sitter Universe
We have investigated the cosmological scenarios with a four dimensional
effective action which is connected with multidimensional, supergravity and
string theories. The solution for the scale factor is such that initially
universe undergoes a decelerated expansion but in late times it enters into the
accelerated expansion phase. Infact, it asymptotically becomes a de-Sitter
universe. The dilaton field in our model is a decreasing function of time and
it becomes a constant in late time resulting the exit from the scalar tensor
theory to the standard Einstein's gravity. Also the dilaton field results the
existence of a positive cosmological constant in late times.Comment: 7 pages, Revtex Style, 6 Postscript figure
Dyon Spectrum in CHL Models
We propose a formula for the degeneracy of quarter BPS dyons in a class of
CHL models. The formula uses a modular form of a subgroup of the genus two
modular group Sp(2,Z). Our proposal is S-duality invariant and reproduces
correctly the entropy of a dyonic black hole to first non-leading order for
large values of the charges.Comment: LaTeX file, 38 pages, minor changes in section 3.3(v2), minor changes
in introduction, appendix A and C(v3
On the universality of distribution of ranked cluster masses at critical percolation
The distribution of masses of clusters smaller than the infinite cluster is
evaluated at the percolation threshold. The clusters are ranked according to
their masses and the distribution of the scaled masses M for any
rank r shows a universal behaviour for different lattice sizes L (D is the
fractal dimension). For different ranks however, there is a universal
distribution function only in the large rank limit, i.e., (y and are defined in the text), where the
universal scaling function g is found to be Gaussian in nature.Comment: 4 pages, to appear in J. Phys.
Dyon Spectrum in N=4 Supersymmetric Type II String Theories
We compute the spectrum of quarter BPS dyons in freely acting Z_2 and Z_3
orbifolds of type II string theory compactified on a six dimensional torus. For
large charges the result for statistical entropy computed from the degeneracy
formula agrees with the corresponding black hole entropy to first non-leading
order after taking into account corrections due to the curvature squared terms
in the effective action. The result is significant since in these theories the
entropy of a small black hole, computed using the curvature squared corrections
to the effective action, fails to reproduce the statistical entropy associated
with elementary string states.Comment: LaTeX file, 32 pages; v2:minor change
Dyon Spectrum in Generic N=4 Supersymmetric Z_N Orbifolds
We find the exact spectrum of a class of quarter BPS dyons in a generic N=4
supersymmetric Z_N orbifold of type IIA string theory on K3\times T^2 or T^6.
We also find the asymptotic expansion of the statistical entropy to first
non-leading order in inverse power of charges and show that it agrees with the
entropy of a black hole carrying same set of charges after taking into account
the effect of the four derivative Gauss-Bonnet term in the effective action of
the theory.Comment: LaTeX file, 39 pages; minor change
Channel Capacities versus Entanglement Measures in Multiparty Quantum States
For quantum states of two subsystems, entanglement measures are related to
capacities of communication tasks -- highly entangled states give higher
capacity of transmitting classical as well as quantum information. However, we
show that this is no more the case in general: quantum capacities of
multi-access channels, motivated by communication in quantum networks, do not
have any relation with genuine multiparty entanglement measures. Along with
revealing the structural richness of multi-access channel capacities, this
gives us a tool to classify multiparty quantum states from the perspective of
its usefulness in quantum networks, which cannot be visualized by known
multiparty entanglement measures.Comment: 6 pages, 2 figures, RevTeX4; v2: minor changes, some implications
strengthene
Black Hole Microstates and Attractor Without Supersymmetry
Due to the attractor mechanism, the entropy of an extremal black hole does
not vary continuously as we vary the asymptotic values of various moduli
fields. Using this fact we argue that the entropy of an extremal black hole in
string theory, calculated for a range of values of the asymptotic moduli for
which the microscopic theory is strongly coupled, should match the statistical
entropy of the same system calculated for a range of values of the asymptotic
moduli for which the microscopic theory is weakly coupled. This argument does
not rely on supersymmetry and applies equally well to nonsupersymmetric
extremal black holes. We discuss several examples which support this argument
and also several caveats which could invalidate this argument.Comment: 50 pages; references adde
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