498 research outputs found
A hybrid-chiral soliton model with broken scale invariance for nuclear matter
We present a model for describing nuclear matter at finite density based on
quarks interacting with chiral fields, sigma and pion. The chiral Lagrangian
also includes a logarithmic potential, associated with the breaking of scale
invariance. We provide results for the soliton in vacuum and at finite density,
using the Wigner-Seitz approximation. We show that the model can reach higher
densities respect to the Linear-sigma model, up to approximately 3 rho_0 for
m_sigma=1200 MeV.Comment: 7 pages, 3 figures, Proceedings of Cortona 2011 XIII Convegno su
Problemi di Fisica Nucleare Teoric
The half-skyrmion phase in a chiral-quark model
The Chiral Dilaton Model, where baryons arise as non-topological solitons
built from the interaction of quarks and chiral mesons, shows in the high
density low temperature regime a two phase scenario in the nuclear matter phase
diagram. Dense soliton matter described by the Wigner-Seitz approximation
generates a periodic potential in terms of the sigma and pion fields that leads
to the formation of a band structure. The analysis up to three times nuclear
matter density shows that soliton matter undergoes two separate phase
transitions: a delocalization of the baryon number density leading to
structures, as in skyrmion matter, at moderate densities, and quark
deconfinement at larger densities. This description fits well into the
so-called quarkyonic phase where, before deconfinement, nuclear matter should
undergo structural changes involving the restoration of fundamental symmetries
of QCD.Comment: 6 pages 4 figure
A chiral quark-soliton model with broken scale invariance for nuclear matter
We present a model for describing nuclear matter at finite density based on
quarks interacting with chiral fields, \sigma and \pi and with vector mesons
introduced as massive gauge fields. The chiral Lagrangian includes a
logarithmic potential, associated with the breaking of scale invariance. We
provide results for the soliton in vacuum and at finite density, using the
Wigner-Seitz approximation. We show that the model can reach higher densities
respect to the linear-\sigma model and that the introduction of vector mesons
allows to obtain saturation. This result was never obtained before in similar
approaches.Comment: 14 pages, 15 figures, 7 tables. Enlarged version including vector
meson
Scaled chiral quark-solitons for nuclear matter
One of the most challenging problems in hadronic and nuclear physics is to study
nuclear matter at finite density by using a scheme which includes one of the
fundamental properties of QCD, namely chiral symmetry.
The problem of studying nuclear matter with chiral Lagrangians is not trivial;
for instance models based on the linear σ-model fail to describe nuclear matter
already at ρ ∼ ρ0 because the normal solution in which chiral symmetry is broken
becomes unstable respect to the Lee-Wick phase. The main problems in these
models are due to the constraints on the scalar field dynamics imposed by the
Mexican hat potential [1]. The interaction terms of σ and π fields in the linear
realization of chiral symmetry allows the chiral fields to move away from the
chiral circle as the density raises and to reach, already at ρ0, the local maximum
where σv = 0 and chiral symmetry is restored.
The difficulty of a too early restoration of chiral symmetry at finite density
can be overcame in two different ways. One could implement chiral symmetry
into the Lagrangian through a non-linear realization [2] where the scalar fields are
forced to stay on the chiral circle. The other approach is still based on a linear
realization of chiral symmetry but with a new potential, which includes terms
not present in the Mexican hat potential. A possible guideline in building such a
potential is scale invariance, which is spontaneously broken in QCD due to the
presence of the parameter ΛQCD coming from the renormalization process and
it is strictly connected to a non vanishing gluon condensate. This fundamental
symmetry of QCD can be implemented in the Lagrangian at mean-field level,
following the approaches in [3, 4], through the introduction of a new scalar field,
the dilaton field, whose dynamics is regulated by a potential chosen in order to
reproduce the scale divergence of QCD.
In this work we will adopt a Chiral Dilaton Model (CDM) which also includes scale invariance introduced by the nuclear physics group of the University of
Minnesota [5–8]. It has already been shown that an hadronic model based on
this dynamics provides a good description of nuclear physics at densities about ρ0
and it describes the gradual restoration of chiral symmetry at higher densities [9].
In the same work the authors have shown a phase diagram, where the interplay
between chiral and scale invariance restoration lead to a scenario similar to that
proposed by McLerran and Pisarski in [10]. It is therefore tempting to explore
the scenario presented in [9] at a more microscopic level.
The new idea we develop in this work is to interpret the fermions as quarks,
to build the hadrons as solitonic solutions of the fields equations as in [11] and,
finally, to explore the properties of the soliton at finite density using the Wigner-
Seitz approximation.
Similar approaches to a finite density system have been investigated in the
past [12–17]. A problem of those works is that the solitonic solutions are unstable
and disappear already at moderate densities when e.g. the linear σ-model is
adopted [16]. We are therefore facing an instability similar to the one discussed
and solved when studying nuclear matter with hadronic chiral Lagrangians. The
first aim of this thesis is to check whether, just by modifying the mesons interaction
with the inclusion of scale invariance, the new logarithmic potential allows the
soliton crystal to reach higher densities. Next, since the CDM also takes into
account the presence of vector mesons, the second and more important aim is
to check whether the inclusion of vector mesons in the dynamics of the quarks
can provide saturation for chiral matter. We should remark that no calculation,
neither in vacuum nor at finite density, exists at the moment for the CDM with
quarks and vector mesons
The baryon number two system in the Chiral Soliton Model
We study the interaction between two B = 1 states in a Chiral Soliton Model
where baryons are described as non-topological solitons. By using the hedgehog
solution for the B = 1 states we construct three possible B = 2 configurations
to analyze the role of the relative orientation of the hedgehog quills in the
dynamics. The strong dependence of the intersoliton interaction on these
relative orientations reveals that studies of dense hadronic matter using this
model should take into account their implications.Comment: 4 pages, 2 figures, Proceedings for the Conference Few-Body Systems
(APFB2011
Freeze-out conditions from net-proton and net-charge fluctuations at RHIC
We calculate ratios of higher-order susceptibilities quantifying fluctuations
in the number of net protons and in the net-electric charge using the Hadron
Resonance Gas (HRG) model. We take into account the effect of resonance decays,
the kinematic acceptance cuts in rapidity, pseudo-rapidity and transverse
momentum used in the experimental analysis, as well as a randomization of the
isospin of nucleons in the hadronic phase. By comparing these results to the
latest experimental data from the STAR collaboration, we determine the
freeze-out conditions from net-electric charge and net-proton distributions and
discuss their consistency.Comment: 7 pages, 6 figures, particle ratio figure adde
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