6,818 research outputs found
New Ideas in Finite Density QCD
We introduce a new approach to analyze the phase diagram of QCD at finite
chemical potential and temperature, based on the definition of a generalized
QCD action. Several details of the method will be discussed, with particular
emphasis on the advantages respect to the imaginary chemical potential
approach.Comment: Talk presented at Lattice2004 (non-zero), Fermilab, June 21-26, 2004;
3 pages, 2 figure
Three and Two Colours Finite Density QCD at Strong Coupling: A New Look
Simulations in finite density, beta=0 lattice QCD by means of the
Monomer-Dimer-Polymer algorithm show a signal of first order transition at
finite temporal size. This behaviour agrees with predictions of the mean field
approximation, but is difficult to reconcile with infinite mass analytical
solution. The MDP simulations are considered in detail and severe convergence
problems are found for the SU(3) gauge group, in a wide region of chemical
potential. Simulations of SU(2) model show discrepancies with MDP results as
well.Comment: 18 pages, 9 figures, to appear in Nucl. Phys.
Disappointing model for ultrahigh-energy cosmic rays
Data of Pierre Auger Observatory show a proton-dominated chemical composition
of ultrahigh-energy cosmic rays spectrum at (1 - 3) EeV and a steadily heavier
composition with energy increasing. In order to explain this feature we assume
that (1 - 3) EeV protons are extragalactic and derive their maximum
acceleration energy, E_p^{max} \simeq 4 EeV, compatible with both the spectrum
and the composition. We also assume the rigidity-dependent acceleration
mechanism of heavier nuclei, E_A^{max} = Z x E_p^{max}. The proposed model has
rather disappointing consequences: i) no pion photo-production on CMB photons
in extragalactic space and hence ii) no high-energy cosmogenic neutrino fluxes;
iii) no GZK-cutoff in the spectrum; iv) no correlation with nearby sources due
to nuclei deflection in the galactic magnetic fields up to highest energies.Comment: 4 pages, 7 figures, the talk presented by A. Gazizov at NPA5
Conference, April 3-8, 2011, Eilat, Israe
Rigorous arguments against current wisdoms in finite density QCD
QCD at finite chemical potential is analytically investigated in the region
of large bare fermion masses. We show that, contrary to the general wisdom, the
phase of the fermion determinant is irrelevant at zero temperature. However if
the system is put at finite temperature, the contribution of the phase is
finite. We also discuss on the quenched approximation and suggest that the
origin of the failure of this approximation in finite density QCD could relay
on the fundamental role that Pauli exclusion principle plays in this case.Comment: 16 pages, 5 figure
Anti-GZK effect in UHECR spectrum
In this paper we discuss the anti-GZK effect that arises in the framework of
the diffusive propagation of Ultra High Energy (UHE) protons. This effect
consists in a jump-like increase of the maximum distance from which UHE protons
can reach the observer. The position of the jump is independent of the
Intergalactic Magnetic Field (IMF) strength and depends only on the energy
losses of protons, namely on the transition energy from adiabatic and
pair-production energy losses. The Ultra High Energy Cosmic Rays (UHECR)
spectrum presents a low-energy steepening approximately at this energy, which
is very close to the position of the observed second knee. The dip, seen in the
universal spectrum as a signature of the proton interaction with the Cosmic
Microwave Background (CMB) radiation, is also present in the case of diffusive
propagation in magnetic fields.Comment: 4 pages, 4 eps figures, talk given at IFAE 2005: Incotri Fisica Alte
Energie, Catania, Italy, 30 March - 2 April 200
Phase transition(s) in finite density QCD
The Grand Canonical formalism is generally used in numerical simulations of
finite density QCD since it allows free mobility in the chemical potential
. We show that special care has to be used in extracting numerical results
to avoid dramatic rounding effects and spurious transition signals. If we
analyze data correctly, with reasonable statistics, no signal of first order
phase transition is present and results using the Glasgow prescription are
practically coincident with the ones obtained using the modulus of the
fermionic determinant.Comment: 6 pages, 5 ps figs. To appear in Proceedings of "QCD at Finite Baryon
Density" workshop, Bielefeld, 27-30 April 199
Finite density QCD with heavy quarks
In the large fermion mass limit of QCD at finite density the structure of the
partition function greatly simplifies and can be studied analytically. We show
that, contrary to general wisdom, the phase of the Dirac determinant is
relevant only at finite temperature and can be neglected for zero temperature
fields.Comment: LATTICE98(hightemp), 3 pages, 3 figure
- …