2,978 research outputs found
Quantum Statistics and Parton Distributions
A novel approach to parton distributions parameterization in terms of quantum
statistical functions is here outlined. The description, already proposed in
previous publications, is here improved by adding to the statistical
distributions an unpolarized {\it liquid} component. This new contribution to
fermion partons is able to reproduce the expected low behaviour of
structure functions. The analysis provides a satisfactory description of
polarized and unpolarized deep inelastic data and shows a possible connection
between the Gottfried and Bjorken sum rules.Comment: 20 pages, LaTeX, 8 epsfigures as uuencoded file. Contributed paper to
LP9
Inflationary Cosmology from Noncommutative Geometry
In the framework of the Connes-Lott model based on noncommutative geometry,
the basic features of a gauge theory in the presence of gravity are reviewed,
in order to show the possible physical relevance of this scheme for
inflationary cosmology. These models naturally contain at least two scalar
fields, interacting with each other whenever more than one fermion generation
is assumed. In this paper we propose to investigate the behaviour of these two
fields (one of which represents the distance between the copies of a
two-sheeted space-time) in the early stages of the universe evolution. In
particular the simplest abelian model, which preserves the main characteristics
of more complicate gauge theories, is considered and the corresponding
inflationary dynamics is studied. We find that a chaotic inflation is naturally
favoured, leading to a field configuration in which no symmetry breaking occurs
and the final distance between the two sheets of space-time is smaller the
greater the number of -fold in each sheet.Comment: 29 pages, plain Latex, + 2 figures as uuencoded postscript files,
substantially revised version to appear in the Int. Jour. Mod. Phys.
Constraints on Unified Gauge Theories from Noncommutative Geometry
The Connes and Lott reformulation of the strong and electroweak model
represents a promising application of noncommutative geometry. In this scheme
the Higgs field naturally appears in the theory as a particular `gauge boson',
connected to the discrete internal space, and its quartic potential, fixed by
the model, is not vanishing only when more than one fermion generation is
present. Moreover, the exact hypercharge assignments and relations among the
masses of particles have been obtained. This paper analyzes the possibility of
extensions of this model to larger unified gauge groups. Noncommutative
geometry imposes very stringent constraints on the possible theories, and
remarkably, the analysis seems to suggest that no larger gauge groups are
compatible with the noncommutative structure, unless one enlarges the fermionic
degrees of freedom, namely the number of particles.Comment: 18 pages, Plain LaTeX, no figure
Secondary radiation from the Pamela/ATIC excess and relevance for Fermi
The excess of electrons/positrons observed by the Pamela and ATIC experiments
gives rise to a noticeable amount of synchrotron and Inverse Compton Scattering
(ICS) radiation when the e^+e^- interact with the Galactic Magnetic Field, and
the InterStellar Radiation Field (ISRF). In particular, the ICS signal produced
within the WIMP annihilation interpretation of the Pamela/ATIC excess shows
already some tension with the EGRET data. On the other hand, 1 yr of Fermi data
taking will be enough to rule out or confirm this scenario with a high
confidence level. The ICS radiation produces a peculiar and clean "ICS Haze"
feature, as well, which can be used to discriminate between the astrophysical
and Dark Matter scenarios. This ICS signature is very prominent even several
degrees away from the galactic center, and it is thus a very robust prediction
with respect to the choice of the DM profile and the uncertainties in the ISRF.Comment: 5 pages, 3 figures; v2: improved figures, enlarged discussion on the
gamma signal and data; to appear in ApJ
Ultrahigh energy neutrinos with a mediterranean neutrino telescope
A study of the ultra high energy neutrino detection performances of a km^3
Neutrino Telescope sitting at the three proposed sites for "ANTARES", "NEMO"
and "NESTOR" in the Mediterranean sea is here performed. The detected charged
leptons energy spectra, entangled with their arrival directions, provide an
unique tool to both determine the neutrino flux and the neutrino-nucleon cross
section.Comment: 10 pages, 10 figures, Proceedings of XII International Workshop on
Neutrino Telescopes, Venezia 200
Three Flavour Majorana Neutrinos with Magnetic Moments in a Supernova
The resonant transition effects MSW and NSFP for three flavour Majorana
neutrinos in a supernova are considered, where the transition magnetic moments
are likely to play a relevant role in neutrino physics. In this scenario, the
deformed thermal neutrino distributions are obtained for different choices of
the electron-tau mixing angle. Detailed predictions for the future large
neutrino detectors are also given in terms of the ratio between the spectra of
recoil electrons for deformed and undeformed spectra.Comment: 20 pages, LaTeX, 5 figures.p
The standard and degenerate primordial nucleosynthesis versus recent experimental data
We report the results on Big Bang Nucleosynthesis (BBN) based on an updated
code, with accuracy of the order of 0.1% on He4 abundance, compared with the
predictions of other recent similar analysis. We discuss the compatibility of
the theoretical results, for vanishing neutrino chemical potentials, with the
observational data. Bounds on the number of relativistic neutrinos and baryon
abundance are obtained by a likelihood analysis. We also analyze the effect of
large neutrino chemical potentials on primordial nucleosynthesis, motivated by
the recent results on the Cosmic Microwave Background Radiation spectrum. The
BBN exclusion plots for electron neutrino chemical potential and the effective
number of relativistic neutrinos are reported. We find that the standard BBN
seems to be only marginally in agreement with the recent BOOMERANG and MAXIMA-1
results, while the agreement is much better for degenerate BBN scenarios for
large effective number of neutrinos, N_\nu \sim 10.Comment: LaTeX2e, 41 pages, 20 figures. Minor changes and 4 figures slightly
modifie
Three-dimensional Wings of Maximum Lift-to- Drag Ratio in Hypersonic Flow
Optimizing lift-to-drag ratio of slender, flat-top wing of given planform in hypersonic flow by using variational calculus method
Three-dimensional, lifting wings of minimum drag in hypersonic flow
Three-dimensional lifting wings of minimum drag in hypersonic flo
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