184 research outputs found
Resolving the J/\psi RHIC puzzles at LHC
Experiments with gold-gold collisions at RHIC have revealed (i) stronger
suppression of charmonium production at forward rapidity than at midrapidity
and (ii) the similarity between the suppression degrees at RHIC and SPS
energies. To describe these findings we employ the model that includes nuclear
shadowing effects, calculated within the Glauber-Gribov theory,
rapidity-dependent absorptive mechanism, caused by energy-momentum
conservation, and dissociation and recombination of the charmonium due to
interaction with co-moving matter. The free parameters of the model are tuned
and fixed by comparison with experimental data at lower energies. A good
agreement with the RHIC results concerning the rapidity and centrality
distributions is obtained for both heavy Au+Au and light Cu+Cu colliding
system. For pA and A+A collisions at LHC the model predicts stronger
suppression of the charmonium and bottomonium yields in stark contrast to
thermal model predictions.Comment: SQM2008 proceedings, 6 page
Nuclear suppression at RHIC and LHC in Glauber-Gribov approach
The approach to problem of nuclear shadowing based on Gribov Reggeon calculus
is presented. Here the total cross section of interaction is found in a
parameter-free description, employing the new data on the gluon density of the
Pomeron, measured with high precision at HERA, as input. The model is then
applied for calculation of production in collisions at top RHIC
energy. It is shown that the theoretical estimates are in a very good agreement
with the PHENIX data, and further predictions for the suppression in
collisions at coming soon LHC are made.Comment: SQM2007 proceedings, 6 page
Anisotropic flow of charged and identified hadrons in the quark-gluon string model for Au+Au collisions at sqrt(s) = 200 GeV
The pseudorapidity behaviour of the azimuthal anisotropy parameters v_1 and
v_2 of inclusive charged hadrons and their dependence on the centrality has
been studied in Au+Au collisions at full RHIC energy of sqrt(s) = 200 GeV
within the microscopic quark-gluon string model. The QGSM simulation results
for the directed flow v_1 show antiflow alignment within the pseudorapidity
range |eta| < 2 in a fair agreement with the experimental v_1(eta) data, but
cannot reproduce the further development of the antiflow up to |eta| around
3.5. The eta dependence of the elliptic flow v_2 extracted from the simulations
agrees well with the experimental data in the whole pseudorapidity range for
different centrality classes. The centrality dependence of the integrated
elliptic flow of charged hadrons in the QGSM almost coincides with the PHOBOS
experimental distribution. The transverse momentum dependence of the elliptic
flow of identified and inclusive charged hadrons is studied also. The model
reproduces quantitatively the low p_T part of the distributions rather good,
but underestimates the measured elliptic flow for transverse momenta p_T > 1
GeV/c. Qualitatively, however, the model is able to reproduce the saturation of
the v_2(p_T) spectra with rising p_T as well as the crossing of the elliptic
flow for mesons and baryons.Comment: REVTeX, 10 pages, 10 figures, v2: extended discussion of the model
results, accepted for publication in Phys. Rev.
Large deviations of the maximal eigenvalue of random matrices
We present detailed computations of the 'at least finite' terms (three
dominant orders) of the free energy in a one-cut matrix model with a hard edge
a, in beta-ensembles, with any polynomial potential. beta is a positive number,
so not restricted to the standard values beta = 1 (hermitian matrices), beta =
1/2 (symmetric matrices), beta = 2 (quaternionic self-dual matrices). This
model allows to study the statistic of the maximum eigenvalue of random
matrices. We compute the large deviation function to the left of the expected
maximum. We specialize our results to the gaussian beta-ensembles and check
them numerically. Our method is based on general results and procedures already
developed in the literature to solve the Pastur equations (also called "loop
equations"). It allows to compute the left tail of the analog of Tracy-Widom
laws for any beta, including the constant term.Comment: 62 pages, 4 figures, pdflatex ; v2 bibliography corrected ; v3 typos
corrected and preprint added ; v4 few more numbers adde
Finite-dimensional reductions of the discrete Toda chain
The problem of construction of integrable boundary conditions for the
discrete Toda chain is considered. The restricted chains for properly chosen
closure conditions are reduced to the well known discrete Painlev\'e equations
, , . Lax representations for these discrete
Painlev\'e equations are found.Comment: Submitted to Jornal of Physics A: Math. Gen., 14 page
On Darboux Integrable Semi-Discrete Chains
Differential-difference equation
with unknown
depending on continuous and discrete variables and is studied.
We call an equation of such kind Darboux integrable, if there exist two
functions (called integrals) and of a finite number of dynamical
variables such that and , where is the operator of total
differentiation with respect to , and is the shift operator:
. It is proved that the integrals can be brought to some
canonical form. A method of construction of an explicit formula for general
solution to Darboux integrable chains is discussed and for a class of chains
such solutions are found.Comment: 19 page
Thermodynamic limit of random partitions and dispersionless Toda hierarchy
We study the thermodynamic limit of random partition models for the instanton
sum of 4D and 5D supersymmetric U(1) gauge theories deformed by some physical
observables. The physical observables correspond to external potentials in the
statistical model. The partition function is reformulated in terms of the
density function of Maya diagrams. The thermodynamic limit is governed by a
limit shape of Young diagrams associated with dominant terms in the partition
function. The limit shape is characterized by a variational problem, which is
further converted to a scalar-valued Riemann-Hilbert problem. This
Riemann-Hilbert problem is solved with the aid of a complex curve, which may be
thought of as the Seiberg-Witten curve of the deformed U(1) gauge theory. This
solution of the Riemann-Hilbert problem is identified with a special solution
of the dispersionless Toda hierarchy that satisfies a pair of generalized
string equations. The generalized string equations for the 5D gauge theory are
shown to be related to hidden symmetries of the statistical model. The
prepotential and the Seiberg-Witten differential are also considered.Comment: latex2e using amsmath,amssymb,amsthm packages, 55 pages, no figure;
(v2) typos correcte
Operator product expansion of higher rank Wilson loops from D-branes and matrix models
In this paper we study correlation functions of circular Wilson loops in
higher dimensional representations with chiral primary operators of N=4 super
Yang-Mills theory. This is done using the recently established relation between
higher rank Wilson loops in gauge theory and D-branes with electric fluxes in
supergravity. We verify our results with a matrix model computation, finding
perfect agreement in both the symmetric and the antisymmetric case.Comment: 28 pages, latex; v2: minor misprints corrected, references adde
Second virial coefficients of light nuclear clusters and their chemical freeze-out in nuclear collisions
Here we develop a new strategy to analyze the chemical freeze-out of light
(anti)nuclei produced in high energy collisions of heavy atomic nuclei within
an advanced version of the hadron resonance gas model. It is based on two
different, but complementary approaches to model the hard-core repulsion
between the light nuclei and hadrons. The first approach is based on an
approximate treatment of the equivalent hard-core radius of a roomy nuclear
cluster and pions, while the second approach is rigorously derived here using a
self-consistent treatment of classical excluded volumes of light (anti)nuclei
and hadrons. By construction, in a hadronic medium dominated by pions, both
approaches should give the same results. Employing this strategy to the
analysis of hadronic and light (anti)nuclei multiplicities measured by ALICE at
TeV and by STAR at GeV, we got rid
of the existing ambiguity in the description of light (anti)nuclei data and
determined the chemical freeze-out parameters of nuclei with high accuracy and
confidence. At ALICE energy the nuclei are frozen prior to the hadrons at the
temperature MeV, while at STAR energy there is a
single freeze-out of hadrons and nuclei at the temperature
MeV. We argue that the found chemical freeze-out volumes of nuclei can be
considered as the volumes of quark-gluon bags that produce the nuclei at the
moment of hadronization.Comment: 15 pages, 4 figures, 3 table
A survey of Hirota's difference equations
A review of selected topics in Hirota's bilinear difference equation (HBDE)
is given. This famous 3-dimensional difference equation is known to provide a
canonical integrable discretization for most important types of soliton
equations. Similarly to the continuous theory, HBDE is a member of an infinite
hierarchy. The central point of our exposition is a discrete version of the
zero curvature condition explicitly written in the form of discrete
Zakharov-Shabat equations for M-operators realized as difference or
pseudo-difference operators. A unified approach to various types of M-operators
and zero curvature representations is suggested. Different reductions of HBDE
to 2-dimensional equations are considered. Among them discrete counterparts of
the KdV, sine-Gordon, Toda chain, relativistic Toda chain and other typical
examples are discussed in detail.Comment: LaTeX, 43 pages, LaTeX figures (with emlines2.sty
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