5,510 research outputs found
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
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
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
Gamma-Ray Constraints on Neutralino Dark Matter Clumps in the Galactic Halo
According to high resolution cold dark matter (CDM) simulations, large
virialized halos are formed through the constant merging of smaller halos
formed at earlier times. In particular, the halo of our Galaxy may have
hundreds of dark matter clumps. The annihilation of dark matter particles such
as the neutralino in these clumps generates -ray fluxes that can
potentially be detected by future experiments such as GLAST. We find that,
depending on the parameters of the clump density profile and on the
distribution of clumps in the Galactic halo, the contribution to the diffuse
-ray background from clumps can constrain the properties of neutralinos
such as the mass and annihilation cross section. We model the density profile
of clumps by three representative dark matter profiles: singular isothermal
spheres (SIS), Moore profiles, and Navarro, Frenk and White (NFW) density
profiles and calculate the spectrum and angular distribution in the sky of the
-ray flux due to neutralino annihilation in the clumpy halo of the
Galaxy. The calculations are carried out in the context of two different
scenarios for the distribution of clumps in the Galaxy and their
concentrations, which result in very different conclusions.Comment: 24 pages, 7 ps fig
Super Heavy Dark Matter in light of BICEP2, Planck and Ultra High Energy Cosmic Rays Observations
The announcement by BICEP2 of the detection of B-mode polarization consistent
with primordial gravitational waves with a tensor-to-scalar ratio,
, challenged predictions from most inflationary models
of a lower value for . More recent results by Planck on polarized dust
emission show that the observed tensor modes signal is compatible with pure
foreground emission. A more significant constraint on was then obtained by
a joint analysis of Planck, BICEP2 and Keck Array data showing an upper limit
to the tensor to scalar ratio , excluding the case with low
statistical significance. Forthcoming measurements by BICEP3, the Keck Array,
and other CMB polarization experiments, open the possibility for making the
fundamental measurement of . Here we discuss how sets the scale for
models where the dark matter is created at the inflationary epoch, the
generically called super-heavy dark matter models. We also consider the
constraints on such scenarios given by recent data from ultrahigh energy cosmic
ray observatories which set the limit on super-heavy dark matter particles
lifetime. We discuss how super-heavy dark matter can be discovered by a precise
measurement of combined with future observations of ultra high energy
cosmic rays.Comment: 17 pages, 14 eps figures, 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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