257 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
One-loop analysis with nonlocal boundary conditions
In the eighties, Schroder studied a quantum mechanical model where the
stationary states of Schrodinger's equation obey nonlocal boundary conditions
on a circle in the plane. For such a problem, we perform a detailed one-loop
calculation for three choices of the kernel characterizing the nonlocal
boundary conditions. In such cases, the zeta(0) value is found to coincide with
the one resulting from Robin boundary conditions. The detailed technique here
developed may be useful for studying one-loop properties of quantum field
theory and quantum gravity if nonlocal boundary conditions are imposed.Comment: 17 pages, Revtex4. In the final version, the presentation in section
5 has been improved, and important References have been adde
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
Self-dual road to noncommutative gravity with twist: a new analysis
The field equations of noncommutative gravity can be obtained by replacing
all exterior products by twist-deformed exterior products in the action
functional of general relativity, and are here studied by requiring that the
torsion 2-form should vanish, and that the Lorentz-Lie-algebra- valued part of
the full connection 1-form should be self-dual. Other two conditions,
expressing self-duality of a pair 2-forms occurring in the full curvature
2-form, are also imposed. This leads to a systematic solution strategy, here
displayed for the first time, where all parts of the connection 1-form are
first evaluated, hence the full curvature 2-form, and eventually all parts of
the tetrad 1-form, when expanded on the basis of {\gamma}-matrices. By assuming
asymptotic expansions which hold up to first order in the noncommutativity
matrix in the neighbourhood of the vanishing value for noncommutativity, we
find a family of self-dual solutions of the field equations. This is generated
by solving first a inhomogeneous wave equation on 1-forms in a classical curved
spacetime (which is itself self-dual and solves the vacuum Einstein equations),
subject to the Lorenz gauge condition. In particular, when the classical
undeformed geometry is Kasner spacetime, the above scheme is fully computable
out of solutions of the scalar wave equation in such a Kasner model.Comment: 37 pages, Revtex. Appendix A is a recollection of mathematical tools
used in the paper. In the final version, Appendix C and some valuable
References have been added. arXiv admin note: text overlap with
arXiv:hep-th/0703014 by other authors. Misprints in Eq. (10.23) and (10.25)
have been amended, as well as their propagation in Sec.
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 theta. The present paper studies the asymptotic
behaviour of solutions of the zero-rest-mass scalar wave equation in such a
modified Schwarzschild space-time in a neighbourhood of spatial infinity. The
analysis is eventually reduced to finding solutions of an inhomogeneous
Euler--Poisson--Darboux equation, where the parameter theta affects explicitly
the functional form of the source term. Interestingly, for finite values of
theta, 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
behaviour with a fall-off going on rather more slowly than in flat space-time.Comment: 19 pages, Revtex4, 7 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
Non-commutative Einstein equations and Seiberg-Witten map
The Seiberg--Witten map is a powerful tool in non-commutative field theory,
and it has been recently obtained in the literature for gravity itself, to
first order in non-commutativity. This paper, relying upon the pure-gravity
form of the action functional considered in Ref. 2, studies the expansion to
first order of the non-commutative Einstein equations, and whether the
Seiberg--Witten map can lead to a solution of such equations when the
underlying classical geometry is Schwarzschild.Comment: 6 and 1/2 pages, based on talk prepared for the Friedmann Seminar,
May-June 2011. In the final version, the presentation has been improved,
including a better notatio
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
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