30 research outputs found
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
Noncommutative Schwarzschild Black Hole and Area Law
Using a graphical analysis, we show that for the horizon radius , the standard semiclassical Bekenstein-Hawking area law for
noncommutative Schwarzschild black hole exactly holds for all orders of
. We also give the corrections to the area law to get the exact nature
of the Bekenstein-Hawking entropy when till the extremal
point .Comment: 11 pages, 8 figures, refs. added, minor modifications, to appear in
Class. Quant. Gra
Spontaneous breaking of chiral symmetry, and eventually of parity, in a -model with two Mexican hats
A sigma-model with two linked Mexican hats is discussed. This scenario could
be realized in low-energy QCD when the ground state and the first excited
(pseudo)scalar mesons are included, and where not only in the subspace of the
ground states, but also in that of the first excited states, a Mexican hat
potential is present. This possibility can change some basic features of a
low-energy hadronic theory of QCD. It is also shown that spontaneous breaking
of parity can occur in the vacuum for some parameter choice of the model.Comment: 10 pages, 1 figur
Dependence of the critical temperature on the Higgs field reparametrization
We show that, despite of the reparametrization symmetry of the Lagrangian
describing the interaction between a scalar field and gauge vector bosons, the
dynamics of the Higgs mechanism is really affected by the representation gauge
chosen for the Higgs field. Actually, we find that, varying the parametrization
for the two degrees of freedom of the complex scalar field, we obtain different
expressions for the Higgs mass: in its turn this entails different expressions
for the critical temperatures, ranging from zero to a maximum value, as well as
different expressions for other basic thermodynamical quantities.Comment: revtex, 12 pages, 2 eps figure
Laboratory bounds on Lorentz symmetry violation in low energy neutrino physics
Quantitative bounds on Lorentz symmetry violation in the neutrino sector have
been obtained by analyzing existing laboratory data on neutron decay
and pion leptonic decays. In particular some parameters appearing in the
energy-momentum dispersion relations for and have been
constrained in two typical cases arising in many models accounting for Lorentz
violation.Comment: revtex, 8 pages, no figures, references added, typos correcte
Noncommutative Inflation and the CMB Multipoles
The first year results of WMAP tentatively indicate running of the spectral
index as well as a deficit of power in the low multipoles in the CMB spectrum.
The former can be rather easily understood in the noncommutative inflation
model, and the latter, as we shall show in this paper, still appears to be an
anomaly, even though the noncommutative inflation model already suppresses the
low multipoles to a certain degree. By fitting the power spectrum, we determine
the string scale to be cm.Comment: 11 pages, 4 figures, harvmac; v2: references adde
Black hole evaporation within a momentum-dependent metric
We investigate the black hole thermodynamics in a "deformed" relativity
framework where the energy-momentum dispersion law is Lorentz-violating and the
Schwarzchild-like metric is momentum-dependent with a Planckian cut-off. We
obtain net deviations of the basic thermodynamical quantities from the
Hawking-Bekenstein predictions: actually, the black hole evaporation is
expected to quit at a nonzero critical mass value (of the order of the Planck
mass), leaving a zero temperature remnant, and avoiding a spacetime
singularity. Quite surprisingly, the present semiclassical corrections to black
hole temperature, entropy, and heat capacity turn out to be identical to the
ones obtained within some quantum approaches
Linearized stability analysis of gravastars in noncommutative geometry
In this work, we find exact gravastar solutions in the context of
noncommutative geometry, and explore their physical properties and
characteristics. The energy density of these geometries is a smeared and
particle-like gravitational source, where the mass is diffused throughout a
region of linear dimension due to the intrinsic uncertainty
encoded in the coordinate commutator. These solutions are then matched to an
exterior Schwarzschild spacetime. We further explore the dynamical stability of
the transition layer of these gravastars, for the specific case of
, where M is the black hole mass, to linearized
spherically symmetric radial perturbations about static equilibrium solutions.
It is found that large stability regions exist and, in particular, located
sufficiently close to where the event horizon is expected to form.Comment: 6 pages, 3 figure
Microcausality and quantization of the fermionic Myers-Pospelov model
We study the fermionic sector of the Myers and Pospelov theory with a general
background . The spacelike case without temporal component is well defined
and no new ingredients came about, apart from the explicit Lorentz invariance
violation. The lightlike case is ill defined and physically discarded. However,
the other case where a nonvanishing temporal component of the background is
present, the theory is physically consistent. We show that new modes appear as
a consequence of higher time derivatives. We quantize the timelike theory and
calculate the microcausality violation which turns out to occur near the light
cone.Comment: 9 pages and 3 figures, new version accepted in EPJC, Volume 72, Issue
9, includes lee-wick review, microcausalit