134 research outputs found
Medium Effects in DIS from Polarized Nuclear Targets
The behavior of the nucleon structure functions in lepton nuclei deep
inelastic scattering, both polarized and unpolarized, due to nuclear structure
effects is reanalyzed. The study is performed in two schemes: an x-rescaling
approach, and one in which there is an increase of sea quark components in the
in medium nucleon, related to the low energy N-N interaction. In view of a
recent interesting experimental proposal to study the behavior of the proton
spin structure functions in nuclei we proceed to compare these approaches in an
effort to enlighten the possible phenomenological interest of such difficult
experiment.Comment: 11 pages and 5 figure
Quark masses without Yukawa hierarchies
A model based on the local gauge group SU(3)_c x SU(3)_L x U(1)_X without
particles with exotic electric charges is shown to be able to provide the quark
mass spectrum and their mixing, by means of universal see-saw mechanisms,
avoiding a hierarchy in the Yukawa coupling constants.Comment: 7 pages, 1 eps figure. Published in Europhysics Letter
Approximate solutions for the single soliton in a Skyrmion-type model with a dilaton scalar field
We consider the analytical properties of the single-soliton solution in a
Skyrmion-type Lagrangian that incorporates the scaling properties of quantum
chromodynamics (QCD) through the coupling of the chiral field to a scalar field
interpreted as a bound state of gluons. The model was proposed in previous
works to describe the Goldstone pions in a dense medium, being also useful for
studying the properties of nuclear matter and the in-medium properties of
mesons and nucleons. Guided by an asymptotic analysis of the Euler-Lagrange
equations, we propose approximate analytical representations for the single
soliton solution in terms of rational approximants exponentially localized.
Following the Pad\'e method, we construct a sequence of approximants from the
exact power series solutions near the origin. We find that the convergence of
the approximate representations to the numerical solutions is considerably
improved by taking the expansion coefficients as free parameters and then
minimizing the mass of the Skyrmion using our ans\"atze for the fields. We also
perform an analysis of convergence by computation of physical quantities
showing that the proposed analytical representations are very useful useful for
phenomenological calculations.Comment: 13 pages, 3 eps figures, version to be published in Phys.Rev.
Generalized Borel Transform Technique in Quantum Mechanics
We present the Generalized Borel Transform (GBT). This new approach allows
one to obtain approximate solutions of Laplace/Mellin transform valid in both,
perturbative and non perturbative regimes. We compare the results provided by
the GBT for a solvable model of quantum mechanics with those provided by
standard techniques, as the conventional Borel sum, or its modified versions.
We found that our approach is very efficient for obtaining both the low and the
high energy behavior of the model.Comment: 13 pages, 2 figure
Influence of diffractive interactions on cosmic ray air showers
A comparative study of commonly used hadronic collision simulation packages
is presented. The characteristics of the products of hadron-nucleus collisions
are analyzed from a general perspective, but focusing on their correlation with
diffractive processes. One of the purposes of our work is to give quantitative
estimations of the impact that different characteristics of the hadronic models
have on air shower observables. Several sets of shower simulations using
different settings for the parameters controlling the diffractive processes are
used to analyze the correlations between diffractivity and shower observables.
We find that the relative probability of diffractive processes during the
shower development have a non negligible influence over the longitudinal
profile as well as the distribution of muons at ground level. The implications
on experimental data analysis are discussed
Effective Field Theory Program for Conformal Quantum Anomalies
The emergence of conformal states is established for any problem involving a
domain of scales where the long-range, SO(2,1) conformally invariant
interaction is applicable. Whenever a clear-cut separation of ultraviolet and
infrared cutoffs is in place, this renormalization mechanism produces binding
in the strong-coupling regime. A realization of this phenomenon, in the form of
dipole-bound anions, is discussed.Comment: 15 pages. Expanded, with additional calculational details. To be
published in Phys. Rev.
Hunting long-lived gluinos at the Pierre Auger Observatory
Eventual signals of split sypersymmetry in cosmic ray physics are analyzed in
detail. The study focusses particularly on quasi-stable colorless R-hadrons
originating through confinement of long-lived gluinos (with quarks,
anti-quarks, and gluons) produced in pp collisions at astrophysical sources.
Because of parton density requirements, the gluino has a momentum which is
considerable smaller than the energy of the primary proton, and so production
of heavy (mass ~ 500 GeV) R-hadrons requires powerful cosmic ray engines able
to accelerate particles up to extreme energies, somewhat above 10^{13.6} GeV.
Using a realistic Monte Carlo simulation with the AIRES engine, we study the
main characteristics of the air showers triggered when one of these exotic
hadrons impinges on a stationary nucleon of the Earth atmosphere. We show that
R-hadron air showers present clear differences with respect to those initiated
by standard particles. We use this shower characteristics to construct
observables which may be used to distinguish long-lived gluinos at the Pierre
Auger Observatory.Comment: 13 pages revtex, 9 eps figures. A ps version with high resolution
figures is available at
http://www.hep.physics.neu.edu/staff/doqui/rhadron_highres.p
- …