83 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
Majorana and the investigation of infrared spectra of ammonia
An account is given on the first studies on the physics of ammonia, focusing
on the infrared spectra of that molecule. Relevant contributions from several
authors, in the years until 1932, are pointed out, discussing also an unknown
study by E.Majorana on this topic.Comment: 13 page
Fermi, Majorana and the statistical model of atoms
We give an account of the appearance and first developments of the
statistical model of atoms proposed by Thomas and Fermi, focusing on the main
results achieved by Fermi and his group in Rome. Particular attention is
addressed to the unknown contribution to this subject by Majorana, anticipating
some important results reached later by leading physicists.Comment: Latex, 16 pages, 2 figure
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
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
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