260 research outputs found
Three Dimensional Gross-Neveu Model on Curved Spaces
The large N limit of the 3-d Gross-Neveu model is here studied on manifolds
with positive and negative constant curvature. Using the -function
regularization we analyze the critical properties of this model on the spaces
and . We evaluate the free energy density, the
spontaneous magnetization and the correlation length at the ultraviolet fixed
point. The limit , which is interpreted as the zero temperature
limit, is also studied.Comment: 24 pages, LaTeX, two .eps figure
Interpreting IceCube 6-year HESE data as an evidence for hundred TeV decaying Dark Matter
The assumption of a single astrophysical power-law flux to explain the
IceCube 6-year HESE extraterrestrial events yields a large spectral index that
is in tension with gamma-ray observations and the 6-year up-going muon
neutrinos data. Adopting a spectral index belonging to the range
, which is compatible with the one deduced by the
analysis performed on the 6-year up-going muon neutrinos data and with -
astrophysical sources, the latest IceCube data show an up to
excess in the number of events in the energy range 40--200 TeV. We interpret
such an excess as a decaying Dark Matter signal and we perform a
likelihood-ratio statistical test to compare the two-component scenario with
respect to the single-component one.Comment: 7 pages, 4 figures. v2: version published in PL
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
Chances for SUSY-GUT in the LHC Epoch
The magic couple of SUSY and GUT still appears the most elegant and
predictive physics concept beyond the Standard Model. Since up to now LHC found
no evidence for supersymmetric particles it becomes of particular relevance to
determine an upper bound of the energy scale they have to show up. In
particular, we have analyzed a generic SUSY-GUT model assuming one step
unification like in SU(5), and adopting naturalness principles, we have
obtained general bounds on the mass spectrum of SUSY particles. We claim that
if a SUSY gauge coupling unification takes place, the lightest gluino or
Higgsino cannot have a mass larger than about 20 TeV. Such a limit is of
interest for planning new accelerator machines.Comment: 23 pages, 5 figures. Version published in JHEP, minor corrections
added and images improve
Spin, torsion and violation of null energy condition in traversable wormholes
The static spherically symmetric traversable wormholes are analysed in the
Einstein- Cartan theory of gravitation. In particular, we computed the torsion
tensor for matter fields with different spin S = 0; 1/2; 1; 3/2. Interestingly,
only for certain values of the spin the torsion contribution to Einstein-Cartan
field equation allows one to satisfy both faring-out condition and Null Energy
Condition. In this scenario traversable wormholes can be produced by using
usual (non-exotic) spinning matter.Comment: 13 page
Use of ANTARES and IceCube data to constrain a single power-law neutrino flux
We perform the first statistical combined analysis of the diffuse neutrino
flux observed by ANTARES (nine-year) and IceCube (six-year) by assuming a
single astrophysical power-law flux. The combined analysis reduces by a few
percent the best-fit values for the flux normalization and the spectral index.
Both data samples show an excess in the same energy range (40--200 TeV),
suggesting the presence of a second component. We perform a goodness-of-fit
test to scrutinize the null assumption of a single power-law, scanning
different values for the spectral index. The addition of the ANTARES data
reduces the -value by a factor 23. In particular, a single power-law
component in the neutrino flux with the spectral index deduced by the six-year
up-going muon neutrinos of IceCube is disfavored with a -value smaller than
.Comment: 6 pages, 4 figures. Version published in AP
Cosmogenic neutrino fluxes under the effect of active-sterile secret interactions
Ultra High Energy cosmogenic neutrinos may represent a unique opportunity to
unveil possible new physics interactions once restricted to the neutrino sector
only. In the present paper we study the observable effects of a secret
active-sterile interactions, mediated by a pseudoscalar, on the expected flux
of cosmogenic neutrinos. The results show that for masses of sterile neutrinos
and pseudoscalars of hundreds MeV, necessary to evade cosmological,
astrophysical and elementary particle constraints, the presence of such new
interactions can significantly change the energy spectrum of cosmogenic
neutrinos at Earth in the energy range from PeV to ZeV. Interestingly, the
distortion of the spectrum results to be detectable at GRAND apparatus if the
scalar mediator mass is around 250 MeV and the UHECRs are dominated by the
proton component. Larger mediator masses or a chemical composition of UHECRs
dominated by heavier nuclei would require much larger cosmic rays apparatus
which might be available in future.Comment: 10 pages, 3 figure
Continuous and Discontinuous Phase Transitions in the evolution of a polygenic trait under stabilizing selective pressure
The presence of phenomena analogous to phase transition in Statistical
Mechanics, has been suggested in the evolution of a polygenic trait under
stabilizing selection, mutation and genetic drift.
By using numerical simulations of a model system, we analyze the evolution of
a population of diploid hermaphrodites in random mating regime. The
population evolves under the effect of drift, selective pressure in form of
viability on an additive polygenic trait, and mutation. The analysis allows to
determine a phase diagram in the plane of mutation rate and strength of
selection. The involved pattern of phase transitions is characterized by a line
of critical points for weak selective pressure (smaller than a threshold),
whereas discontinuous phase transitions, characterized by metastable
hysteresis, are observed for strong selective pressure. A finite size scaling
analysis suggests the analogy between our system and the mean field Ising model
for selective pressure approaching the threshold from weaker values. In this
framework, the mutation rate, which allows the system to explore the accessible
microscopic states, is the parameter controlling the transition from large
heterozygosity (disordered phase) to small heterozygosity (ordered one).Comment: 8 pages, 7 figures, 1 tabl
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