14,715 research outputs found
Ferromagnetism of Weakly-Interacting Electrons in Disordered Systems
It was realized two decades ago that the two-dimensional diffusive Fermi
liquid phase is unstable against arbitrarily weak electron-electron
interactions. Recently, using the nonlinear sigma model developed by
Finkelstein, several authors have shown that the instability leads to a
ferromagnetic state. In this paper, we consider diffusing electrons interacting
through a ferromagnetic exchange interaction. Using the Hartree-Fock
approximation to directly calculate the electron self energy, we find that the
total energy is minimized by a finite ferromagnetic moment for arbitrarily weak
interactions in two dimensions and for interaction strengths exceeding a
critical proportional to the conductivity in three dimensions. We discuss the
relation between our results and previous ones
Evolution of Primordial Black Holes in Loop Quantum Gravity
In this work, we study the evolution of Primordial Black Holes within the
context of Loop Quantum Gravity. First we calculate the scale factor and energy
density of the universe for different cosmic era and then taking these as
inputs we study evolution of primordial black holes. From our estimation it is
found that accretion of radiation does not affect evolution of primordial black
holes in loop quantum gravity even though a larger number of primordial black
holes may form in early universe in comparison with Einstein's or scalar-tensor
theories.Comment: 8 pages, 1 figur
Overtones of Isoscalar Giant Resonances in medium-heavy and heavy nuclei
A semi-microscopic approach based on both the
continum-random-phase-approximation (CRPA) method and a phenomenological
treatment of the spreading effect is extended and applied to describe the main
properties (particle-hole strength distribution, energy-dependent transition
density, partial direct-nucleon-decay branching ratios) of the isoscalar giant
dipole, second monopole, and second quadrupole resonances. Abilities of the
approach are checked by description of gross properties of the main-tone
resonances. Calculation results obtained for the resonances in a few singly-
and doubly-closed-shell nuclei are compared with available experimental data.Comment: 12 pages, 14 figures, submitted to Phys. Rev.
Present Acceleration of Universe, Holographic Dark Energy and Brans-Dicke Theory
The present day accelerated expansion of the universe is naturally addressed
within the Brans-Dicke theory just by using holographic dark energy model with
inverse of Hubble scale as IR cutoff. It is also concluded that if the universe
continues to expand, then one day it might be completely filled with dark
energy.Comment: 10 page
Titanate-Zircon-Apatite Bearing Diorite-Monzodiorites and their Resource Potentiality
Placer beach sand deposits are considered as the reserve for ilmenite, rutile, zircon, monazite, xenotime. The global reserve for titanium, zirconium and rare earth metals is accounted from the distribution of these miner-als in the beach sand. It is proposed to look into Archean diorites and monzodiorites as the potential resource for these minerals. These rocks contain sphene, ilmenite, zircon and apatite in trace amount but account for about
3 wt% of TiO,, 700 ppm of Zr, and about 500-800 ppm of rare earth in bulk. The mineralogical and geochemical
characteristic of such rocks is discussed. The potentia-lity of sphene as a resource for titanium is highlighte
Gyroscopic Precession and Inertial Forces in Axially Symmetric Stationary Spacetimes
We study the phenomenon of gyroscopic precession and the analogues of
inertial forces within the framework of general relativity. Covariant
connections between the two are established for circular orbits in stationary
spacetimes with axial symmetry. Specializing to static spacetimes, we prove
that gyroscopic precession and centrifugal force both reverse at the photon
orbits. Simultaneous non-reversal of these in the case of stationary spacetimes
is discussed. Further insight is gained in the case of static spacetime by
considering the phenomena in a spacetime conformal to the original one.
Gravi-electric and gravi-magnetic fields are studied and their relation to
inertial forces is established.Comment: 21 pages, latex, no figures, http://202.41.67.76/~nayak/gpifass.te
Environment assisted entanglement enhancement
We consider dissipative atom-cavity systems and show that their collective
dynamics leads to the maximization of entanglement for intermediate values of
the cavity leakage parameter . We discuss possible ways the reservoir
influences entanglement. We first consider the entanglement of a single
two-level atom with a microwave cavity that is coupled to another cavity. We
show that the atom-cavity entanglement can be made to increase with cavity
leakage. We next show that the entanglement between two atoms passing
successively through a cavity can be maximised for intermediate values of
. We finally consider the micromaser where the increase of two-atom
entanglement for stronger cavity-environment coupling is demonstrated for
experimentally attainable values of the micromaser parameters.Comment: 4 pages, Revtex, 1 eps figure; minor changes to match with published
versio
Fractional Exclusion Statistics for the Multicomponent Sutherland Model
We show by microscopic calculation that thermodynamics of the multicomponent
Sutherland model is equivalent to that of a free particle system with
fractional exclusion statistics at all temperatures. The parameters for
exclusion statistics are given by the strength of the repulsive interaction,
and have both intra- and inter-species components. We also show that low
temperature properties of the system are described in terms of free fractional
particles without the statistical parameters for different species. The
effective exclusion statistics for intra-species at low temperatures depend on
polarization of the system.Comment: 13 pages, using RevTex, 5 figures on reques
Brans-Dicke Theory and primordial black holes in Early Matter-Dominated Era
We show that primordial black holes can be formed in the matter-dominated era
with gravity described by the Brans-Dicke theory. Considering an early
matter-dominated era between inflation and reheating, we found that the
primordial black holes formed during that era evaporate at a quicker than those
of early radiation-dominated era. Thus, in comparison with latter case, less
number of primordial black holes could exist today. Again the constraints on
primordial black hole formation tend towards the larger value than their
radiation-dominated era counterparts indicating a significant enhancement in
the formation of primordial black holes during the matter-dominaed era.Comment: 9 page
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