7,820 research outputs found
Renormalization group and triviality in noncompact lattice QED with light fermions
In the framework of noncompact lattice QED with light fermions, we derive the
functional dependence of the average energy per plaquette on the bare
parameters using block-spin Renormalization Group arguments and assuming that
the renormalized coupling vanishes. Our numerical results for this quantity in
and lattices show evidence for triviality in the weak coupling
phase and point to a non vanishing value for the renormalized coupling constant
in the strong coupling phase.Comment: 9 page
Propagation of UHECRs in cosmological backgrounds: some results from SimProp
Ultra-High-Energy Cosmic Ray (UHECR) nuclei propagating in cosmological
radiation backgrounds produce secondary particles detectable at Earth. SimProp
is a one dimensional code for extragalactic propagation of UHECR nuclei,
inspired by the kinetic approach of Aloisio et al. As in this approach, only a
subset of nuclei and nuclear channels are used as representative. We discuss
the validation of the code and present applications to UHECR experimental
results. In particular we present the expected fluxes of neutrinos produced in
some astrophysical scenario.Comment: Poster presented by A. Di Matteo at the 33rd International Cosmic Ray
Conference, Rio De Janeiro (Brasil) July 2-9 201
Cosmogenic neutrinos and ultra-high energy cosmic ray models
We use an updated version of {\it SimProp}, a Monte Carlo simulation scheme
for the propagation of ultra-high energy cosmic rays, to compute cosmogenic
neutrino fluxes expected on Earth in various scenarios. These fluxes are
compared with the newly detected IceCube events at PeV energies and with recent
experimental limits at EeV energies of the Pierre Auger Observatory. This
comparison allows us to draw some interesting conclusions about the source
models for ultra-high energy cosmic rays. We will show how the available
experimental observations are almost at the level of constraining such models,
mainly in terms of the injected chemical composition and cosmological evolution
of sources. The results presented here will also be important in the evaluation
of the discovery capabilities of the future planned ultra-high energy cosmic
ray and neutrino observatories.Comment: 15 pages, 8 figures, some reference added, version accepted for
publication in JCA
Diquark condensation in two colour QCD
Unquenched lattice SU(2) is studied at nonzero chemical potential in the
strong coupling limit. The topic of diquark condensation is addressed analyzing
the probability distribution function of the diquark condensate. We present
results at zero external source without using any potentially dangerous
extrapolation procedure. We find strong evidences for a (high density) second
order phase transition where a diquark condensate appears, and show
quantitative agreement of lattice calculations with low-energy effective
Lagrangian calculations.Comment: 9 pages, 6 figures, to be published in the proceedings of the
``International Workshop on Non-Perturbative Methods and Lattice QCD'',
Guangzhou, China, 15-21 May 200
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