2,703 research outputs found
Energy-Momentum Complex in M\o ller's Tetrad Theory of Gravitation
M\o ller's Tetrad Theory of Gravitation is examined with regard to the
energy-momentum complex. The energy-momentum complex as well as the
superpotential associated with M\o ller's theory are derived. M\o ller's field
equations are solved in the case of spherical symmetry. Two different
solutions, giving rise to the same metric, are obtained. The energy associated
with one solution is found to be twice the energy associated with the other.
Some suggestions to get out of this inconsistency are discussed at the end of
the paper.Comment: LaTeX2e with AMS-LaTeX 1.2, 13 page
Mean field theory and Monte Carlo simulation of Phase transitions and Magnetic Properties of a tridimensional Fe7S8 Compound
The structural, electronic and magnetic properties of Fe7S8 material have
been studied within the framework of the ab-initio calculations, the mean field
approximation (MFA) and Monte Carlo simulation (MCS). Our study shows that two
forms of the iron atoms, Fe2+ with spin S=2, and Fe3+ with spin {\sigma}=5/2
are the most probable configurations. A mixed Ising model with ferromagnetic
spin coupling between Fe2+ and Fe3+ ions and between Fe3+ and Fe3+ ions, and
with antiferromagnetic spin coupling between Fe2+ ions of adjacent layers has
been used to study the magnetic properties of this compound. We demonstrated
that the magnetic phase transition can be either of the first or of the second
order, depending on the value of the exchange interaction and crystal field.
The presence of vacancies in every second iron layer leads to incomplete
cancellation of magnetic moments, hence to the emergence of the ferrimagnetism.
Anomalies in the magnetization behavior have been found and compared with the
experimental results.Comment: 18 pages, 14 Figures, 4 Table
Inspiratory muscle warm-up does not improve cycling time-trial performance
Purpose: This study examined the effects of an active cycling warm-up, with and without the addition of an inspiratory muscle warm-up (IMW), on 10-km cycling time-trial performance
Effective theories of scattering with an attractive inverse-square potential and the three-body problem
A distorted-wave version of the renormalisation group is applied to
scattering by an inverse-square potential and to three-body systems. In
attractive three-body systems, the short-distance wave function satisfies a
Schroedinger equation with an attractive inverse-square potential, as shown by
Efimov. The resulting oscillatory behaviour controls the renormalisation of the
three-body interactions, with the renormalisation-group flow tending to a limit
cycle as the cut-off is lowered. The approach used here leads to single-valued
potentials with discontinuities as the bound states are cut off. The
perturbations around the cycle start with a marginal term whose effect is
simply to change the phase of the short-distance oscillations, or the
self-adjoint extension of the singular Hamiltonian. The full power counting in
terms of the energy and two-body scattering length is constructed for
short-range three-body forces.Comment: 19 pages (RevTeX), 2 figure
Free field realization of superstring theory on AdS3
The Coulomb gas representation of expectation values in SU(2) conformal field
theory developed by Dotsenko is extended to the SL(2,R) WZW model and applied
to bosonic string theory on AdS3 and to Type II superstrings on AdS3 x N. The
spectral flow symmetry is included in the free field realization of vertex
operators creating superstring states of both Ramond and Neveu-Schwarz sectors.
Conjugate representations for these operators are constructed and a background
charge prescription is designed to compute correlation functions. Two and three
point functions of bosonic and fermionic string states in arbitrary winding
sectors are calculated. Scattering amplitudes that violate winding number
conservation are also discussed.Comment: 40 pages, typos corrected, references added, minor changes in
presentation and details completed in the calculation of the R sector 2-point
function. Version to appear in JHE
Hydrodynamics of galactic dark matter
We consider simple hydrodynamical models of galactic dark matter in which the
galactic halo is a self-gravitating and self-interacting gas that dominates the
dynamics of the galaxy. Modeling this halo as a sphericaly symmetric and static
perfect fluid satisfying the field equations of General Relativity, visible
barionic matter can be treated as ``test particles'' in the geometry of this
field. We show that the assumption of an empirical ``universal rotation curve''
that fits a wide variety of galaxies is compatible, under suitable
approximations, with state variables characteristic of a non-relativistic
Maxwell-Boltzmann gas that becomes an isothermal sphere in the Newtonian limit.
Consistency criteria lead to a minimal bound for particle masses in the range
and to a constraint between the central
temperature and the particles mass. The allowed mass range includes popular
supersymmetric particle candidates, such as the neutralino, axino and
gravitino, as well as lighter particles ( keV) proposed by numerical
N-body simulations associated with self-interactive CDM and WDM structure
formation theories.Comment: LaTeX article style, 16 pages including three figures. Final version
to appear in Classical and Quantum Gravit
False Vacuum Inflation with Einstein Gravity
We investigate chaotic inflation models with two scalar fields, such that one
field (the inflaton) rolls while the other is trapped in a false vacuum state.
The false vacuum becomes unstable when the inflaton field falls below some
critical value, and a first or second order transition to the true vacuum
ensues. Particular attention is paid to Linde's second-order `Hybrid
Inflation'; with the false vacuum dominating, inflation differs from the usual
true vacuum case both in its cosmology and in its relation to particle physics.
The spectral index of the adiabatic density perturbation can be very close to
1, or it can be around ten percent higher. The energy scale at the end of
inflation can be anywhere between \,GeV and \,GeV, though
reheating is prompt so the reheat temperature can't be far below
GeV. Topological defects are almost inevitably produced at the end
of inflation, and if the inflationary energy scale is near its upper limit they
can have significant effects.
Because false vacuum inflation occurs with the inflaton field far below the
Planck scale, it is easier to implement in the context of supergravity than
standard chaotic inflation. That the inflaton mass is small compared with the
inflationary Hubble parameter is still a problem for generic supergravity
theories, but remarkably this can be avoided in a natural way for a class of
supergravity models which follow from orbifold compactification of
superstrings. This opens up the prospect of a truly realistic, superstringComment: 37 pages, LaTeX (3 figures available as hard copies only), SUSSEX-AST
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