339 research outputs found
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
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
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
How large is "large " for Nuclear matter?
We argue that a so far neglected dimensionless scale, the number of neighbors
in a closely packed system, is relevant for the convergence of the large
expansion at high chemical potential. It is only when the number of colors is
large w.r.t. this new scale (\sim \order{10}) that a convergent large
limit is reached. This provides an explanation as to why the large
expansion, qualitatively successful in in vacuum QCD, fails to describe high
baryo-chemical potential systems, such as nuclear matter. It also means that
phenomenological claims about high density matter based on large
extrapolations should be treated with caution.Comment: Proceedings of CPOD2010 conference, in Dubna. Results based on
Phys.Rev.C82, 055202 (2010), http://arxiv.org/abs/1006.247
Evidence for Hydrodynamic Evolution in Proton-Proton Scattering at LHC Energies
In scattering at LHC energies, large numbers of elementary scatterings
will contribute significantly, and the corresponding high multiplicity events
will be of particular interest. Elementary scatterings are parton ladders,
identified with color flux-tubes. In high multiplicity events, many of these
flux tubes are produced in the same space region, creating high energy
densities. We argue that there are good reasons to employ the successful
procedure used for heavy ion collisions: matter is assumed to thermalizes
quickly, such that the energy from the flux-tubes can be taken as initial
condition for a hydrodynamic expansion. This scenario gets spectacular support
from very recent results on Bose-Einstein correlations in scattering at
900 GeV at LHC.Comment: 11 pages, 20 figure
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