7,368 research outputs found

### 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.

### 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

### 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
$\mu$. 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

### 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

### 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

### Ultra High Energy Cosmic Rays: The disappointing model

We develop a model for explaining the data of Pierre Auger Observatory
(Auger) for Ultra High Energy Cosmic Rays (UHECR), in particular, the mass
composition being steadily heavier with increasing energy from 3 EeV to 35 EeV.
The model is based on the proton-dominated composition in the energy range (1 -
3) EeV observed in both Auger and HiRes experiments. Assuming extragalactic
origin of this component, we argue that it must disappear at higher energies
due to a low maximum energy of acceleration, E_p^{\max} \sim (4 - 10) EeV.
Under an assumption of rigidity acceleration mechanism, the maximum
acceleration energy for a nucleus with the charge number Z is ZE_p^{\max}, and
the highest energy in the spectrum, reached by Iron, does not exceed (100 -
200) EeV. The growth of atomic weight with energy, observed in Auger, is
provided by the rigidity mechanism of acceleration, since at each energy
E=ZE_p^{\max} the contribution of nuclei with Z' < Z vanishes. The described
model has disappointing consequences for future observations in UHECR: Since
average energies per nucleon for all nuclei are less than (2 - 4) EeV, (i) pion
photo-production on CMB photons in extragalactic space is absent; (ii) GZK
cutoff in the spectrum does not exist; (iii) cosmogenic neutrinos produced on
CMBR are absent; (iv) fluxes of cosmogenic neutrinos produced on infrared -
optical background radiation are too low for registration by existing detectors
and projects. Due to nuclei deflection in galactic magnetic fields, the
correlation with nearby sources is absent even at highest energies.Comment: Essentially revised version as published in Astropart. Physics 10
pages, 6 figure

### Strongly Coupled QCD at Finite Baryon Density

The analytical results obtained in the infinite mass and strong coupling
limits of QCD are difficult to reconcile with the predictions of the Monomer
Dimer Polymer algorithm. We have reconsidered in detail the results obtained
with this simulation scheme and evidences of severe convergence problems are
presented for the SU(3) and SU(2) gauge group.Comment: LATTICE99(Finite Temperature and Density), 3 pages, 3 postscript
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