4,184 research outputs found
Chiral transition in a magnetic field and at finite baryon density
We consider the quark-meson model with two quark flavors in a constant
external magnetic field at finite temperature and finite baryon
chemical potential . We calculate the full renormalized effective
potential to one-loop order in perturbation theory. We study the system in the
large- limit, where we treat the bosonic modes at tree level. It is shown
that the system exhibits dynamical chiral symmetry breaking, i. e. that an
arbitrarily weak magnetic field breaks chiral symmetry dynamically, in
agreement with earlier calculations using the NJL model. We study the influence
on the phase transition of the fermionic vacuum fluctuations. For strong
magnetic fields, and in the chiral limit, the transition
is first order in the entire plane if vacuum fluctuations are not
included and second order if they are included. At the physical point, the
transition is a crossover for with and without vacuum fluctuations.Comment: 11 pages. 5figs. V2: fixed a few typos and added refs. Submitted to
PRD. V3: Added refs and substantial revision of tex
Sonoluminescence as Quantum Vaccum Radiation
We argue that the available experimental data is not compatible with models
of sonoluminescence which invoke dynamical properties of the interface without
regard to the compositional properties of the trapped gas inside the bubble.Comment: 2 pages,Revtex,No figures,Submitted to PRL(comments
Mesons and tachyons with confinement and chiral restoration, and NA60
In this paper the spectrum of quark-antiquark systems, including light mesons
and tachyons, is studied in the true vacuum and in the chiral invariant vacuum.
The mass gap equation for the vacua and the Salpeter-RPA equation for the
mesons are solved for a simple chiral invariant and confining quark model. At
T=0 and in the true vacuum, the scalar and pseudoscalar, or the vector and
axial vector are not degenerate, and in the chiral limit, the pseudoscalar
groundstates are Goldstone bosons. At T=0 the chiral invariant vacuum is an
unstable vacuum, decaying through an infinite number of scalar and pseudoscalar
tachyons. Nevertheless the axialvector and vector remain mesons, with real
masses. To illustrate the chiral restoration, an arbitrary path between the two
vacua is also studied. Different families of light-light and heavy-light
mesons, sensitive to chiral restoration, are also studied. At higher
temperatures the potential must be suppressed, and the chiral symmetry can be
restored without tachyons, but then all mesons have small real masses.
Implications for heavy-ion collisions, in particular for the recent vector
meson spectra measured by the NA60 collaboration, are discussed.Comment: 9 pages, 5 figures, 3 table
Symmetries and Ambiguities in the linear sigma model with light quarks
We investigate the role of undetermined finite contributions generated by
radiative corrections in a linear sigma model with quarks.
Although some of such terms can be absorbed in the renormalization procedure,
one such contribution is left in the expression for the pion decay constant.
This arbitrariness is eliminated by chiral symmetry.Comment: 9 pages. Added references through the text; an author was added due
to an important contribution; corrected typos; the title also was changed.
Submitted to Modern Physics Letter
Thermodynamic potential with correct asymptotics for PNJL model
An attempt is made to resolve certain incongruities within the Nambu -
Jona-Lasinio (NJL) and Polyakov loop extended NJL models (PNJL) which currently
are used to extract the thermodynamic characteristics of the quark-gluon
system. It is argued that the most attractive resolution of these incongruities
is the possibility to obtain the thermodynamic potential directly from the
corresponding extremum conditions (gap equations) by integrating them, an
integration constant being fixed in accordance with the Stefan-Boltzmann law.
The advantage of the approach is that the regulator is kept finite both in
divergent and finite valued integrals at finite temperature and chemical
potential. The Pauli-Villars regularization is used, although a standard 3D
sharp cutoff can be applied as well.Comment: 16 pages, 5 figures, extended version, title change
Mechanisms for Stable Sonoluminescence
A gas bubble trapped in water by an oscillating acoustic field is expected to
either shrink or grow on a diffusive timescale, depending on the forcing
strength and the bubble size. At high ambient gas concentration this has long
been observed in experiments. However, recent sonoluminescence experiments show
that in certain circumstances when the ambient gas concentration is low the
bubble can be stable for days. This paper presents mechanisms leading to
stability which predict parameter dependences in agreement with the
sonoluminescence experiments.Comment: 4 pages, 3 figures on request (2 as .ps files
Strong and Radiative Meson Decays in a Generalized Nambu--Jona-Lasinio Model
We investigate strong and radiative meson decays in a generalized
Nambu--Jona-Lasinio model. The one loop order calculation provides a
satisfactory agreement with the data for the mesonic spectrum and for radiative
decays. Higher order effects for strong decays of and are
estimated to be large. We also discuss the role of the flavour mixing
determinantal interaction.Comment: 7 pages, LaTeX, 2 figs available upon request, CRN 92-4
Momentum Dependent Vertices , and : The NJL Scalar Hidden by Chiral Symmetry
We calculate the momentum dependence of three particle vertices , and in the context of a
Nambu Jona Lasinio type model. We show how they influence the processes , and and how chiral symmetry
shadows the presence of the .Comment: 9 pages (latex), 5 figures available from the authors, preprint
Coimbra 940506, IJS-TP-94/10, accepted for publication in Zeit. f. Physik
Pion Observables in the Extended NJL Model with Vector and Axial-Vector Mesons
The momentum-space bosonization method of a Nambu and Jona-Lasinio type model
with vector and axial-vector mesons is applied to scattering. Unlike
the case in earlier published papers, we obtain the scattering
amplitude using the linear and nonlinear realizations of chiral symmetry and
fully taking into account the momentum dependence of meson vertices. We show
the full physical equivalence between these two approaches. The chiral
expansion procedure in this model is discussed in detail. Chiral expansions of
the quark mass, pion mass and constant are obtained. The low-energy
phase shifts are compared to the available data. We also study the
scalar form factor of the pion.Comment: 39 pp, LaTeX file, uses epsf, 7 figures (appended as compressed tar
files in pion.uu
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