539 research outputs found
Phase transition and thermodynamics of a hot and dense system in a scaled NJL model
The chiral phase transition of a hot and dense system of quarks is studied
within a modified SU(3) NJL lagrangian that implements the QCD scale anomaly.
The u- and s-quark condensates can feel or not the same chiral restoration
depending on the considered region of the 3-dimension space T_c(\mu_uc,\mu_sc).
The temperature behaviour of the pressure and of the energy and entropy
densities of the u- and s-quark system is investigated. At high temperature,
the non-vanishing bare s-quark mass only modifies slightly the usual behaviour
associated with an ideal quark gas.Comment: 23 pages, LaTeX, uses elsart.sty. This version of the paper includes
the figures (ps
Probing the density dependence of the symmetry potential with peripheral heavy-ion collisions
The peripheral heavy-ion collisions of at are studied by means of the Improved Quantum Molecular Dynamics
Model(ImQMD). It is shown that the slope of the average N/Z ratio of emitted
nucleons vs impact parameters for these reactions is very sensitive to the
density dependence of the symmetry energy. Our study also shows that the yields
of and decrease with impact parameters and slope of the yield
of vs impact parameters as well as the ratio of Y()/Y()
depend on the symmetry potential strongly for peripheral heavy-ion collisions.Comment: 10 pages,6 figures, accepted by Phys.Rev.
Unified description of fission in fusion and spallation reactions
We present a statistical-model description of fission, in the framework of
compound-nucleus decay, which is found to simultaneously reproduce data from
both heavy-ion-induced fusion reactions and proton-induced spallation reactions
at around 1 GeV. For the spallation reactions, the initial compound-nucleus
population is predicted by the Li\`{e}ge Intranuclear Cascade Model. We are
able to reproduce experimental fission probabilities and fission-fragment mass
distributions in both reactions types with the same parameter sets. However, no
unique parameter set was obtained for the fission probability. The introduction
of fission transients can be offset by an increase of the ratio of
level-density parameters for the saddle-point and ground-state configurations.
Changes to the finite-range fission barriers could be offset by a scaling of
the Bohr-Wheeler decay width as predicted by Kramers. The parameter sets
presented allow accurate prediction of fission probabilities for excitation
energies up to 300 MeV and spins up to 60 \hbar.Comment: 16 pages, 20 figures. Submitted to Phys. Rev.
A Model for the Off-forward Structure Functions of the Pion
We extend our model for the pion, which we used previously to calculate its
diagonal structure function, to the off-forward case. The imaginary part of the
off-forward gamma* pi -> gamma* pi scattering amplitude is evaluated in the
chiral limit (m_pi=0) and related to the twist-two and twist-three generalised
parton distributions, H, H3, H3tilde. Non-perturbative effects, linked to the
size of the pion and still preserving gauge invariance, are included.
Remarkable new relations between H, H3 and H3tilde are obtained and discussed.Comment: 9 pages, 20 figures, LaTeX, uses ulg_ptf.cls (included); v2: Form
factors dropped in favour of GPD's, comparison between Wandzura-Wilczek
approximation and our relations adde
A Model for the Generalized Parton Distribution of the Pion
We calculate the off-forward structure function of the pion within a simple
model where the size of the pion is accounted for using a momentum cut-off.
Twist-two and twist-three generalized parton distributions are extracted.
Relations between twist-three and twist-two contributions are obtained, the
origin of which is not kinematical as they differ from those arising from the
Wandzura-Wilczek approximation.Comment: Presented at 6th Conference on Quark Confinement and the Hadron
Spectrum, Villasimius, Sardinia, Italy, 21-25 Sep 2004, 3 pages, 4 figures,
LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty (included
A toy model for generalised parton distributions
We give the results of a simple model for the diagonal and off-diagonal
valence quark distributions of a pion. We show that structure can be
implemented in a gauge-invariant manner. This explicit model questions the
validityof the momentum sum rule, and gives an explicit counter-example to the
Wandzura-Wilczek ansatz for twist-3 GPD's.Comment: 11 pages, presented at HADRONIC PHYSICS (HLPR 2004): Joint
Meeting-Heidelberg-Liege-Paris-Rostock, Spa, Belgium, 16-18 December 2004, 11
pages, 11 figures, LaTe
Core-collapse supernova neutrinos and neutrino properties
Core-collapse supernovae are powerful neutrino sources. The observation of a
future (extra-)galactic supernova explosion or of the relic supernova neutrinos
might provide important information on the supernova dynamics, on the supernova
formation rate and on neutrino properties. One might learn more about unknown
neutrino properties either from indirect effects in the supernova (e.g. on the
explosion or on in the r-process) or from modifications of the neutrino time or
energy distributions in a detector on Earth. Here we will discuss in particular
possible effects of CP violation in the lepton sector. We will also mention the
interest of future neutrino-nucleus interaction measurements for the precise
knowledge of supernova neutrino detector response to electron neutrinos.Comment: 9 pages, 5 figures, Proceedings to "Three days of Strong Interactions
& Astrophysics HLPW08", 6-8 March 2008, SP
The Valence Quark Distribution of the Pion
The pion structure function is investigated in a simple model, where the pion
and its constituent quark fields are coupled through the simplest pseudoscalar
coupling. The imaginary part of the forward gamma* pi -> gamma* pi scattering
amplitude is evaluated and related to the structure functions. It is shown that
the introduction of non-perturbative effects, linked to the size of the pion,
allows a connection with the quark distribution. It is predicted that
higher-twist terms become negligible for Q^2 larger than ~2 GeV^2, that quarks
in the pion have a momentum fraction smaller than in the proton case, and that
the momentum sum rule is violated for the pion.Comment: Presented by J. P. Lansberg at the XXII Physics in Collision
Conference (PIC02), Stanford, California, June 20-22, 2002, 3 pages, 4
figures, LaTeX, uses pic02.sty (included
Pion Structure Function and Violation of the Momentum Sum Rule
We present a method to evaluate the pion structure functions from a box
diagram calculation. Pion and constituent quark fields are coupled through the
simplest pseudoscalar coupling. The gamma^* pi -> q \bar q cross-section is
evaluated and related to the structure functions. We then show that the
introduction of non-perturbative effects, related to the pion size and
preserving gauge invariance, provides us with a straighforward relation with
the quark distribution. It is predicted that higher-twist terms become
negligible for Q^2 larger than about 2 GeV^2 and that quarks in the pion have a
momentum fraction smaller than in the proton. We enlarge the discussion
concerning this violation of the momentum sum rule, emphasizing that the sum
rule is recovered in the chiral limit and also when the finite size condition
is not imposed.Comment: Presented by J.P. Lansberg at the II International Workshop on Hadron
Physics, 25-29 September, 2002, Coimbra, Portugal, 14 pages, 9 figures,
LaTeX, uses aip-6s.clo, aipproc.cls and aipxfm.sty (included
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