12,676 research outputs found
Effect of realistic interatomic interactions and two-body correlation on the heat capacity of a trapped BEC
An approximate many-body theory has been used to calculate the heat capacity
and the condensate fraction of a BEC with effective repulsive interaction. The
effect of interactions has been analyzed and compared with the non-interacting
case. It has been found that the repulsive interaction lowers the critical
temperature from the value found in the non-interacting case. The difference
between the critical temperatures increases with the increase in the total
number of atoms in the trap.Comment: 15 pages, 5 figure
Quantum Gravity Equation In Schroedinger Form In Minisuperspace Description
We start from classical Hamiltonian constraint of general relativity to
obtain the Einstein-Hamiltonian-Jacobi equation. We obtain a time parameter
prescription demanding that geometry itself determines the time, not the matter
field, such that the time so defined being equivalent to the time that enters
into the Schroedinger equation. Without any reference to the Wheeler-DeWitt
equation and without invoking the expansion of exponent in WKB wavefunction in
powers of Planck mass, we obtain an equation for quantum gravity in
Schroedinger form containing time. We restrict ourselves to a minisuperspace
description. Unlike matter field equation our equation is equivalent to the
Wheeler-DeWitt equation in the sense that our solutions reproduce also the
wavefunction of the Wheeler-DeWitt equation provided one evaluates the
normalization constant according to the wormhole dominance proposal recently
proposed by us.Comment: 11 Pages, ReVTeX, no figur
Self-Gravitational Corrections to the Cardy-Verlinde Formula and the FRW Brane Cosmology in SdS_5 Bulk
The semiclassical corrections to the Cardy-Verlinde entropy of a
five-dimensional Schwarzschild de-Sitter black hole (SdS_5) are explicitly
evaluated. These corrections are considered within the context of KKW analysis
and arise as a result of the self-gravitation effect. In addition, a
four-dimensional spacelike brane is considered as the boundary of the SdS_5
bulk background. It is already known that the induced geometry of the brane is
exactly given by that of a radiation-dominated FRW universe. By exploiting the
CFT/FRW-cosmology relation, we derive the self-gravitational corrections to the
first Friedmann-like equation which is the equation of the brane motion. The
additional term that arises due to the semiclassical analysis can be viewed as
stiff matter where the self-gravitational corrections act as the source for it.
This result is contrary to standard analysis that regards the charge of SdS_5
bulk black hole as the source for stiff matter. Furthermore, we rewrite the
Friedmann-like equation in a such way that it represents the conservation
equation of energy of a point particle moving in a one-dimensional effective
potential. The self-gravitational corrections to the effective potential and,
consequently, to the point particle's motion are obtained. A short analysis on
the asymptotic behavior of the 4-dimensional brane is presented.Comment: 16 pages, LaTeX; (v2) references added and correcte
Time in Quantum Gravity
The Wheeler-DeWitt equation in quantum gravity is timeless in character. In
order to discuss quantum to classical transition of the universe, one uses a
time prescription in quantum gravity to obtain a time contained description
starting from Wheeler-DeWitt equation and WKB ansatz for the WD wavefunction.
The approach has some drawbacks. In this work, we obtain the time-contained
Schroedinger-Wheeler-DeWitt equation without using the WD equation and the WKB
ansatz for the wavefunction. We further show that a Gaussian ansatz for SWD
wavefunction is consistent with the Hartle-Hawking or wormhole dominance
proposal boundary condition. We thus find an answer to the small scale boundary
conditions.Comment: 12 Pages, LaTeX, no figur
Collapse of the charge ordering gap of Nd_{0.5}Sr_{0.5}MnO_{3} in an applied magnetic field
We report results of tunneling studies on the charge ordering compound
Nd_{0.5}Sr_{0.5}MnO_{3} in a magnetic field up to 6T and for temperature down
to 25K.We show that a gap (2\Delta_{CO} \approx 0.5eV opens up in the density
of state (DOS) at the Fermilevel (E_F) on charge ordering (T_{CO}=150K) which
collapses in an applied magnetic field when the charge ordered state melts.
There is a clear correspondence between the behavior of the resistivity and the
gap formation and its collapse in an applied magnetic field. We conclude that a
gap in the DOS at E_F is necessary for the stability of the charge ordered
state.Comment: 4 pages REVTeX, 5 postscript figures included, submitted to Phys.
Rev. Let
The Topology of Parabolic Character Varieties of Free Groups
Let G be a complex affine algebraic reductive group, and let K be a maximal
compact subgroup of G. Fix elements h_1,...,h_m in K. For n greater than or
equal to 0, let X (respectively, Y) be the space of equivalence classes of
representations of the free group of m+n generators in G (respectively, K) such
that for each i between 1 and m, the image of the i-th free generator is
conjugate to h_i. These spaces are parabolic analogues of character varieties
of free groups. We prove that Y is a strong deformation retraction of X. In
particular, X and Y are homotopy equivalent. We also describe explicit examples
relating X to relative character varieties.Comment: 16 pages, version 2 includes minor revisions and some modified
proofs, accepted for publication in Geometriae Dedicat
Periodic Orbits in Polygonal Billiards
We review some properties of periodic orbit families in polygonal billiards
and discuss in particular a sum rule that they obey. In addition, we provide
algorithms to determine periodic orbit families and present numerical results
that shed new light on the proliferation law and its variation with the genus
of the invariant surface. Finally, we deal with correlations in the length
spectrum and find that long orbits display Poisson fluctuations.Comment: 30 pages (Latex) including 11 figure
Coupled Inflation and Brane Gases
We study an effective four-dimensional theory with an action with two scalar
fields minimally coupled to gravity, and with a matter action which couples to
the two scalar fields via an overall field-dependent coefficient in the action.
Such a theory could arise from a dimensional reduction of supergravity coupled
to a gas of branes winding the compactified dimensions. We show the existence
of solutions corresponding to power-law inflation. The graceful exit from
inflation can be obtained by postulating the decay of the branes, as would
occur if the branes are unstable in the vacuum and stabilized at high densities
by plasma effects. This construction provides an avenue for connecting string
gas cosmology and the late-time universe.Comment: 11 page
Kinetic exchange opinion model: solution in the single parameter map limit
We study a recently proposed kinetic exchange opinion model (Lallouache et.
al., Phys. Rev E 82:056112, 2010) in the limit of a single parameter map.
Although it does not include the essentially complex behavior of the multiagent
version, it provides us with the insight regarding the choice of order
parameter for the system as well as some of its other dynamical properties. We
also study the generalized two- parameter version of the model, and provide the
exact phase diagram. The universal behavior along this phase boundary in terms
of the suitably defined order parameter is seen.Comment: 14 pages, 9 figure
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