7,066 research outputs found
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
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
Relativity in space-times with short-distance structure governed by an observer-independent (Planckian) length scale
I show that it is possible to formulate the Relativity postulates in a way
that does not lead to inconsistencies in the case of space-times whose
short-distance structure is governed by an observer-independent length scale.
The consistency of these postulates proves incorrect the expectation that
modifications of the rules of kinematics involving the Planck length would
necessarily require the introduction of a preferred class of inertial
observers. In particular, it is possible for every inertial observer to agree
on physical laws supporting deformed dispersion relations of the type , at least for certain types of .Comment: Same formulas and results as in 1st version, but a change of notation
is introduced in order to clarify that the studied illustrative example is
consistent with the R.P. for both choices of the overall sign. 1 ref added
and 2 refs upgraded. Some rewording of the text in Sec5, and addition of an
analogy with background fields in ordinary electromagnetism which I use to
illustrate difference between space-times with an observer-independent Lp,
and space-times in which Lp is introduced without modifications of Special
Relativit
Particle and Antiparticle sectors in DSR1 and kappa-Minkowski space-time
In this paper we explore the problem of antiparticles in DSR1 and
-Minkowski space-time following three different approaches inspired by
the Lorentz invariant case: a) the dispersion relation, b) the Dirac equation
in space-time and c) the Dirac equation in momentum space. We find that it is
possible to define a map which gives the antiparticle sector from the
negative frequency solutions of the wave equation. In -Poincar\'e, the
corresponding map is the antipodal mapping, which is different from
. The difference is related to the composition law, which is crucial
to define the multiparticle sector of the theory. This discussion permits to
show that the energy of the antiparticle in DSR is the positive root of the
dispersion relation, which is consistent with phenomenological approaches.Comment: 15 pages, no figures, some references added, typos correcte
Finite Density Fat QCD
Lattice formulation of Finite Baryon Density QCD is problematic from computer
simulation point of view; it is well known that for light quark masses the
reconstructed partition function fails to be positive in a wide region of
parameter space. For large bare quark masses, instead, it is possible to obtain
more sensible results; problems are still present but restricted to a small
region. We present evidence for a saturation transition independent from the
gauge coupling and for a transition line that, starting from the
temperature critical point at , moves towards smaller with
increasing as expected from simplified phenomenological arguments.Comment: 14 pages, 10 figure
Transition from Galactic to Extra-Galactic Cosmic Rays
In this paper we review the main features of the observed Cosmic Rays
spectrum in the energy range . We
present a theoretical model that explains the main observed features of the
spectrum, namely the second Knee and Dip, and implies a transition from
Galactic to Extra-Galactic cosmic rays at energy eV, with a
proton dominated Extra-Galactic spectrum.Comment: 3 pages, 2 eps figures, talk given at TAUP 2005, Zaragoza (Spain),
10-14 September 200
Diquark and Pion Condensation in Random Matrix Models for two-color QCD
We introduce a random matrix model with the symmetries of QCD with two colors
at nonzero isospin and baryon chemical potentials and temperature. We analyze
its phase diagram and find phases with condensation of pion and diquark states
in addition to the phases with spontaneously broken chiral symmetries. In the
limit of small chemical potentials and quark masses, we reproduce the mean
field results obtained from chiral Lagrangians. As in the case of QCD with
three colors, the presence of two chemical potentials breaks the flavor
symmetry and leads to phases that are characterized by different behaviors of
the chiral condensates for each flavor. In particular, the phase diagram we
obtain is similar to QCD with three colors and three flavors of quarks of equal
masses at zero baryon chemical potential and nonzero isospin and strange
chemical potentials. A tricritical point of the superfluid transitions found in
lattice calculations and from an analysis in terms of chiral Lagrangians does
not appear in the random matrix model. Remarkably, at fixed isospin chemical
potential, for the regions outside of the superfluid phases, the phase diagram
in the temperature - baryon chemical potential plane for two colors and three
colors are qualitatively the same.Comment: 19 pages, 7 figures, RevTeX
Diffusive propagation of UHECR and the propagation theorem
We present a detailed analytical study of the propagation of ultra high
energy (UHE) particles in extragalactic magnetic fields. The crucial parameter
which affects the diffuse spectrum is the separation between sources. In the
case of a uniform distribution of sources with a separation between them much
smaller than all characteristic propagation lengths, the diffuse spectrum of
UHE particles has a {\em universal} form, independent of the mode of
propagation. This statement has a status of theorem. The proof is obtained
using the particle number conservation during propagation, and also using the
kinetic equation for the propagation of UHE particles. This theorem can be also
proved with the help of the diffusion equation. In particular, it is shown
numerically, how the diffuse fluxes converge to this universal spectrum, when
the separation between sources diminishes. We study also the analytic solution
of the diffusion equation in weak and strong magnetic fields with energy losses
taken into account. In the case of strong magnetic fields and for a separation
between sources large enough, the GZK cutoff can practically disappear, as it
has been found early in numerical simulations. In practice, however, the source
luminosities required are too large for this possibility.Comment: 16 pages, 13 eps figures, discussion of the absence of the GZK
cut-off in strong magnetic field added, a misprint in figure 6 corrected,
version accepted for publication in Ap
Finding the sigma pole by analytic extrapolation of scattering data
We investigate the determination of the pole from
scattering data below the threshold, including the new precise
results obtained from decay by NA48/2 Collaboration. We discuss also
the experimental status of the threshold parameters and and the
phase shift . In order to reduce the theoretical bias, we use a
large class of analytic parametrizations of the isoscalar -wave, based on
expansions in powers of conformal variables. The pole obtained with
this method is consistent with the prediction based on ChPT and Roy equations.
However, the theoretical uncertainties are now larger, reflecting the
sensitivity of the pole position to the specific parametrizations valid in the
physical region. We conclude that Roy equations offer the most precise method
for the determination of the pole from elastic scattering
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