394 research outputs found
A large- PNJL model with explicit Z symmetry
A PNJL model is built, in which the Polyakov-loop potential is explicitly
Z-symmetric in order to mimic a Yang-Mills theory with gauge group
SU(). The physically expected large- and large- behaviours of the
thermodynamic observables computed from the Polyakov-loop potential are used to
constrain its free parameters. The effective potential is eventually
U(1)-symmetric when is infinite. Light quark flavours are added by using
a Nambu-Jona-Lasinio (NJL) model coupled to the Polyakov loop (the PNJL model),
and the different phases of the resulting PNJL model are discussed in 't
Hooft's large- limit. Three phases are found, in agreement with previous
large- studies. When the temperature is larger than some deconfinement
temperature , the system is in a deconfined, chirally symmetric, phase for
any quark chemical potential . When however, the system is in a
confined phase in which chiral symmetry is either broken or not. The critical
line , signalling the restoration of chiral symmetry, has the same
qualitative features than what can be obtained within a standard PNJL
model.Comment: To appear in Phys Rev
QCD effective action with a most general homogeneous field background
We consider one-loop effective action of SU(3) QCD with a most general
constant chromomagnetic (chromoelectric) background which has two independent
Abelian field components. The effective potential with a pure magnetic
background has a local minimum only when two Abelian components H_{\mu\nu}^3
and H_{\mu\nu}^8 of color magnetic field are orthogonal to each other. The
non-trivial structure of the effective action has important implication in
estimating quark-gluon production rate and p_T-distribution in quark-gluon
plasma. In general the production rate depends on three independent Casimir
invariants, in particular, it depends on the relative orientation between
chromoelectric fields.Comment: 6 pages, 3 figures (9 pages in published version
CP violation in the two-Higgs-doublet model: an example
In a general two-scalar-doublet model without fermions, there is a unique
source of CP violation, , in the gauge interactions of the scalars. It
arises in the mixing of the three neutral physical scalars , and
. CP violation may be observed via different decay rates for and (or, alternatively, for and --- depending on
which decays are kinematically allowed). I compute the part of those
CP-violating decay-rate differences which is proportional to . The
CP-invariant final-state-interaction phase is provided by the absorptive parts
of the one-loop diagrams. I check the gauge invariance of the whole
calculation.Comment: 13 pages LATEX, a bunch of figures that I can mail to you if you ask
me as soon as you finish reading this (because afterwards I'll be in
vacation
Small-Recoil Approximation
In this review we discuss a technique to compute and to sum a class of
Feynman diagrams, and some of its applications. These are diagrams containing
one or more energetic particles that suffer very little recoil in their
interactions. When recoil is completely neglected, a decomposition formula can
be proven. This formula is a generalization of the well-known eikonal formula,
to non-abelian interactions. It expresses the amplitude as a sum of products of
irreducible amplitudes, with each irreducible amplitude being the amplitude to
emit one, or several mutually interacting, quasi-particles. For abelian
interaction a quasi-particle is nothing but the original boson, so this
decomposition formula reduces to the eikonal formula. In non-abelian situations
each quasi-particle can be made up of many bosons, though always with a total
quantum number identical to that of a single boson. This decomposition enables
certain amplitudes of all orders to be summed up into an exponential form, and
it allows subleading contributions of a certain kind, which is difficult to
reach in the usual way, to be computed. For bosonic emissions from a heavy
source with many constituents, a quasi-particle amplitude turns out to be an
amplitude in which all bosons are emitted from the same constituent. For
high-energy parton-parton scattering in the near-forward direction, the
quasi-particle turns out to be the Reggeon, and this formalism shows clearly
why gluons reggeize but photons do not. The ablility to compute subleading
terms in this formalism allows the BFKL-Pomeron amplitude to be extrapolated to
asymptotic energies, in a unitary way preserving the Froissart bound. We also
consider recoil corrections for abelian interactions in order to accommodate
the Landau-Pomeranchuk-Migdal effect.Comment: 21 pages with 4 figure
Heavy flavour production in DGLAP improved saturation model
The charm and beauty quark production in deep inelastic scattering at low
values of the Bjorken variable x is considered in the DGLAP improved saturation
model. After fitting parameters of the model to the structure function F_2, the
heavy quark contributions Fc_2 and Fb_2 are predicted. A good description of
the data is found. Predictions for the longitudinal structure function F_L and
the diffractive structure function FD_2 are also presented.Comment: 16 pages, 7 figures; typos corrected, references added, final
Phys.Rev. D versio
The model of particle production by strong external sources
Using some knowledge of multiplicity disributions for high energy reactions,
it is possible to propose a simple analytical model of particle production by
strong external sources. The model describes qualitatively most peculiar
properties of the distributions. The generating function of the distribution
varies so drastically as it can happen at phase transitions.Comment: 7 pages, no Figures, LATEX; Eq. (10) corrected, Eqs (25), (26) added,
ref [20] corrected; Pisma v Zhetf 84, n5 (2006
Prompt Quark Production by exploding Sphalerons
Following recent works on production and subsequent explosive decay of QCD
sphaleron-like clusters, we discuss the mechanism of quark pair production in
this process. We first show how the gauge field explosive solution of Luscher
and Schechter can be achieved by non-central conformal mapping from the
O(4)-symmetric solution. Our main result is a new solution to the Dirac
equation in real time in this configuration, obtained by the same inversion of
the fermion O(4) zero mode. It explicitly shows how the quark acceleration
occurs, starting from the spherically O(3) symmetric zero energy chiral quark
state to the final spectrum of non-zero energies.
The sphaleron-like clusters with any Chern-Simons number always produce quarks, and the antisphaleron-like clusters the
chirality opposite.
The result are relevant for hadron-hadron and nucleus-nucleus collisions at
large , wherein such clusters can be produced
Interplay between soft and hard hadronic components for identified hadrons in relativistic heavy ion collisions
We investigate the transverse dynamics in Au+Au collisions at \sqrt{s_NN}=200
GeV by emphasis upon the interplay between soft and hard components through p_T
dependences of particle spectra, ratios of yields, suppression factors, and
elliptic flow for identified hadrons. From hydrodynamics combined with
traversing minijets which go through jet quenching in the hot medium, we
calculate interactions of hard jets with the soft hydrodynamic components. It
is shown by the explicit dynamical calculations that the hydrodynamic radial
flow and the jet quenching of hard jets are the keys to understand the
differences among the hadron spectra for pions, kaons, and protons. This leads
to the natural interpretation for N_p/N_\pi ~ 1, R_{AA} >~ 1 for protons, and
v_2^p > v_2^\pi recently observed in the intermediate transverse momentum
region at Relativistic Heavy Ion Collider (RHIC).Comment: 11 pages, 9 figures; some references added; title changed, some data
points included in figure
Coherent gluon production in very high energy heavy ion collisions
The early stages of a relativistic heavy-ion collision are examined in the
framework of an effective classical SU(3) Yang-Mills theory in the transverse
plane. We compute the initial energy and number distributions, per unit
rapidity, at mid-rapidity, of gluons produced in high energy heavy ion
collisions. We discuss the phenomenological implications of our results in
light of the recent RHIC data.Comment: 4 pages, 2 figure
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