154 research outputs found
Describing Sr2RuO4 superconductivity in a generalized Ginzburg--Landau theory
We propose a simple explanation of unconventional thermodynamical and
magnetic properties observed for Sr2RuO4. Actually, our two-phase model of
superconductivity, based on a straight generalization of the Ginzburg-Landau
theory, does predict two jumps in the heat capacity as well as a double curve
for the dependence of the critical temperature on an external magnetic field.
Such theoretical previsions well agree with the currently available
experimental data for Sr2RuO4Comment: revtex, 9 pages, 1 eps figur
Baryon asymmetry in the Universe resulting from Lorentz violation
We analyze the phenomenological consequences of a Lorentz violating
energy-momentum dispersion relation in order to give a simple explanation for
the baryon asymmetry in the Universe. By assuming very few hypotheses, we
propose a straightforward mechanism for generating the observed
matter-antimatter asymmetry which entails a Lorentz-breakdown energy scale of
the order of the Greisen-Zatsepin-Kuzmin cut-off.Comment: 7 page
Space-time symmetry restoration in cosmological models with Kalb--Ramond and scalar fields
We study symmetry of space-time in presence of a minimally coupled scalar
field interacting with a Kalb--Ramond tensor fields in a homogeneous but
initially anisotropic universe. The analysis is performed for the two relevant
cases of a pure cosmological constant and a minimal quadratic, renormalizable,
interaction term. In both cases, due to expansion, a complete spatial symmetry
restoration is dynamically obtained.Comment: Latex, 7 pages, 3 eps figure
Magnetic properties of two-phase superconductors
We have recently proposed a theoretical model for superconductors endowed
with two distinct superconducting phases, described by two scalar order
parameters which condensate at different critical temperatures. On analyzing
the magnetic behavior of such systems, we have found some observable
differences with respect to the case of ordinary Ginzburg-Landau
superconductors. In particular, at low temperature the London penetration
length is strongly reduced and the Ginzburg-Landau parameter k becomes a
function of temperature. By contrast, in the temperature region between the two
phase transitions k is constant and the system is a type-I or a type-II
superconductor depending on the ratio between the critical temperatures.Comment: revtex, 5 pages, 1 eps figur
Nonlocal field theory driven by a deformed product: Generalization of Kalb-Ramond duality
A modification of the standard product used in local field theory by means of an associative
deformed product is proposed. We present a class of deformed products, one for
every spin S = 0, 1/2, 1, that induces a nonlocal theory, displaying different form for
different fields. This type of deformed product is naturally supersymmetric and it has
an intriguing duality
The Scalar wave equation in a non-commutative spherically symmetric space-time
Recent work in the literature has studied a version of non-commutative Schwarzschild
black holes where the effects of non-commutativity are described by a mass function
depending on both the radial variable r and a non-commutativity parameter θ. The
present paper studies the asymptotic behavior of solutions of the zero-rest-mass scalar
wave equation in such a modified Schwarzschild space-time in a neighborhood of spatial
infinity. The analysis is eventually reduced to finding solutions of an inhomogeneous
Euler–Poisson–Darboux equation, where the parameter θ affects explicitly the functional
form of the source term. Interestingly, for finite values of θ, there is full qualitative
agreement with general relativity: the conformal singularity at spacelike infinity reduces
in a considerable way the differentiability class of scalar fields at future null infinity.
In the physical space-time, this means that the scalar field has an asymptotic behavior
with a fall-off going on rather more slowly than in flat space-time
Superconductors with two critical temperatures
We propose a simple model for superconductors endowed with two critical
temperatures, corresponding to two second-order phase transitions, in the
framework of the Ginzburg-Landau mean-field theory. For very large Cooper pair
self-interaction, in addition to the standard condensation occurring in the
Ginzburg-Landau theory, we find another phase transition at a lower temperature
with a maximum difference of 15% between the two critical temperatures.Comment: revtex, 3 pages, one eps figur
Second discontinuity in the specific heat of two-phase superconductors
The recently proposed theoretical model of superconductors endowed with two
distinct superconducting phases and critical temperatures is further analyzed
by introducing two distinct order parameters, described by two scalar fields
which condensate at different temperatures. We find some deviations in basic
thermodynamical quantities with respect to the Ginzburg-Landau one-phase
superconductors. In particular, by contrast to the usual case where only one
jump in specific heat takes place at the normal-superconductor transition
temperature, we actually predict an additional discontinuity for C_V when
passing from a superconducting phase to the other one.Comment: revtex, 4 pages, 1 figur
A generalization of the Ginzburg-Landau theory to p-wave superconductors
We succeed to build up a straightforward theoretical model for spin-triplet
p-wave superconductors by introducing in Ginzburg-Landau theory a second order
parameter and a suitable interaction between the two mean fields.Comment: RevTeX, 4 pages, no figure
Black hole evaporation in a spherically symmetric non-commutative space-time
Recent work in the literature has studied the quantum-mechanical decay of a
Schwarzschild-like black hole, formed by gravitational collapse, into
almost-flat space-time and weak radiation at a very late time. The relevant
quantum amplitudes have been evaluated for bosonic and fermionic fields,
showing that no information is lost in collapse to a black hole. On the other
hand, recent developments in noncommutative geometry have shown that, in
general relativity, the effects of non-commutativity can be taken into account
by keeping the standard form of the Einstein tensor on the left-hand side of
the field equations and introducing a modified energy-momentum tensor as a
source on the right-hand side. Relying on the recently obtained
non-commutativity effect on a static, spherically symmetric metric, we have
considered from a new perspective the quantum amplitudes in black hole
evaporation. The general relativity analysis of spin-2 amplitudes has been
shown to be modified by a multiplicative factor F depending on a constant
non-commutativity parameter and on the upper limit R of the radial coordinate.
Limiting forms of F have been derived which are compatible with the adiabatic
approximation.Comment: 8 pages, Latex file with IOP macros, prepared for the QFEXT07
Conference, Leipzig, September 200
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