7,404 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
. 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
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
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
Approaching Space Time Through Velocity in Doubly Special Relativity
We discuss the definition of velocity as dE/dp, where E,p are the energy and
momentum of a particle, in Doubly Special Relativity (DSR). If this definition
matches dx/dt appropriate for the space-time sector, then space-time can in
principle be built consistently with the existence of an invariant length
scale. We show that, within different possible velocity definitions, a
space-time compatible with momentum-space DSR principles can not be derived.Comment: 11 pages, no figures, minor changes, references added, final version
to appear in PR
Probability Distribution Function of the Diquark Condensate in Two Colours QCD
We consider diquark condensation in finite density lattice SU(2). We first
present an extension of Vafa-Witten result, on spontaneous breaking of
vector-like global symmetries, that allows us to formulate a no-go theorem for
diquark condensation in a region of the chemical potential-mass parameter
space. We then describe a new technique to calculate diquark condensation at
any number of flavours directly at zero external source without using any
potentially dangerous extrapolation procedure. We apply it to the strong
coupling limit and find compelling evidences for a second order phase
transition, where a diquark condensate appears, as well as quantitative
agreement between lattice results and low-energy effective Lagrangian
calculations.Comment: 21 pages, 7 figure
Report on the EU-US Workshop on Large Scientific Databases
This joint workshop was set up under the auspices of the Joint European Commission/National Science Foundation Strategy Group that met in Budapest in September 1998. The meeting derived from a joint collaboration agreement between the EC and NSF, signed by Dr. George Metakides (Director of Information Technologies for the EC) and Prof. Juris Hartmanis (Director of Computer and Information Science and Engineering at the NSF). Some themes that were identified include:
digital libraries
human-centered computing and virtual environments
large scientific databases, and
intelligent implants
This report expresses the conclusions and recommendations of the Workshop on Large Scientific Databases, held in Annapolis, Maryland, USA in September 1999. The purpose of the workshop was to develop a report to the funding agencies outlining a possible solicitation to the research community, with emphasis on joint European-US work on Large Scientific Databases. Before the workshop, each participant submitted a position paper (these are available at the web site http://www.cacr.caltech.edu/euus). The results of the position papers, presentations, and group discussion are summarized in this report. There were 12 participants from Europe and 12 from the United States, and they are listed at the end of this report. The last section of this report describes possible funding mechanisms
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