11,895 research outputs found
Di-jet hadron pair correlation in a hydrodynamical model with a quenching jet
In jet quenching, a hard QCD parton, before fragmenting into a jet of
hadrons, deposits a fraction of its energy in the medium, leading to suppressed
production of high- hadrons. Assuming that the deposited energy quickly
thermalizes, we simulate the subsequent hydrodynamic evolution of the QGP
fluid. Hydrodynamic evolution and subsequent particle emission depend on the
jet trajectories. Azimuthal distribution of excess due to quenching
jet, averaged over all the trajectories, reasonably well reproduce the
di-hadron correlation as measured by the STAR and PHENIX collaboration in
central and in peripheral Au+Au collisions.Comment: 5 pages, 4 figures. Some minor corrections are made in the revised
manuscrip
keV sterile neutrino dark matter in gauge extensions of the standard model
It is known that a keV scale sterile neutrino is a good warm dark matter
candidate. We study how this possibility could be realized in the context of
gauge extensions of the standard model. The na\"ive expectation leads to large
thermal overproduction of sterile neutrinos in this setup. However, we find
that it is possible to use out-of-equilibrium decay of the other right-handed
neutrinos of the model to dilute the present density of the keV sterile
neutrinos and achieve the observed dark matter density. We present the
universal requirements that should be satisfied by the gauge extensions of the
standard model, containing right-handed neutrinos, to be viable models of warm
dark matter, and provide a simple example in the context of the left-right
symmetric model.Comment: RevTex, 13 pages, 5 figures; journal version (corrected typos
Dangerous Angular KK/Glueball Relics in String Theory Cosmology
The presence of Kaluza-Klein particles in the universe is a potential
manifestation of string theory cosmology. In general, they can be present in
the high temperature bath of the early universe. In particular examples, string
theory inflation often ends with brane-antibrane annihilation followed by the
energy cascading through massive closed string loops to KK modes which then
decay into lighter standard model particles. However, massive KK modes in the
early universe may become dangerous cosmological relics if the inner manifold
contains warped throat(s) with approximate isometries. In the complimentary
picture, in the AdS/CFT dual gauge theory with extra symmetries, massive
glueballs of various spins become the dangerous cosmological relics. The decay
of these angular KK modes/glueballs, located around the tip of the throat, is
caused by isometry breaking which results from gluing the throat to the compact
CY manifold. We address the problem of these angular KK particles/glueballs,
studying their interactions and decay channels, from the theory side, and the
resulting cosmological constraints on the warped compactification parameters,
from the phenomenology side. The abundance and decay time of the long-lived
non-relativistic angular KK modes depend strongly on the parameters of the
warped geometry, so that observational constraints rule out a significant
fraction of the parameter space. In particular, the coupling of the angular KK
particles can be weaker than gravitational.Comment: 58 pages, 11 figures, published versio
Elliptic Flow from a Transversally Thermalized Fireball
The agreement of elliptic flow data at RHIC at central rapidity with the
hydrodynamic model has led to the conclusion of very rapid thermalization. This
conclusion is based on the intuitive argument that hydrodynamics, which assumes
instantaneous local thermalization, produces the largest possible elliptic flow
values and that the data seem to saturate this limit. We here investigate the
question whether incompletely thermalized viscous systems may actually produce
more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast
primordial longitudinal expansion of the reaction zone, we investigate a toy
model which exhibits thermalization only in the transverse directions but
undergoes collisionless free-streaming expansion in the longitudinal direction.
For collisions at RHIC energies, elliptic flow results from the model are
compared with those from hydrodynamics. With the final particle yield and
\kt-distribution fixed, the transversally thermalized model is shown not to
be able to produce the measured amount of elliptic flow. This investigation
provides further support for very rapid local kinetic equilibration at RHIC. It
also yields interesting novel results for the elliptic flow of massless
particles such as direct photons.Comment: revtex4, 15 pages + 10 embedded EPS figure
A fully relativistic lattice Boltzmann algorithm
Starting from the Maxwell-Juettner equilibrium distribution, we develop a
relativistic lattice Boltzmann (LB) algorithm capable of handling
ultrarelativistic systems with flat, but expanding, spacetimes. The algorithm
is validated through simulations of quark-gluon plasma, yielding excellent
agreement with hydrodynamic simulations. The present scheme opens the
possibility of transferring the recognized computational advantages of lattice
kinetic theory to the context of both weakly and ultra-relativistic systems.Comment: 12 pages, 8 figure
Quark Recombination and Heavy Quark Diffusion in Hot Nuclear Matter
We discuss resonance recombination for quarks and show that it is compatible
with quark and hadron distributions in local thermal equilibrium. We then
calculate realistic heavy quark phase space distributions in heavy ion
collisions using Langevin simulations with non-perturbative T-matrix
interactions in hydrodynamic backgrounds. We hadronize the heavy quarks on the
critical hypersurface given by hydrodynamics after constructing a criterion for
the relative recombination and fragmentation contributions. We discuss the
influence of recombination and flow on the resulting heavy meson and single
electron R_AA and elliptic flow. We will also comment on the effect of
diffusion of open heavy flavor mesons in the hadronic phase.Comment: Contribution to Quark Matter 2011, submitted to J.Phys.G; 4 pages, 5
figure
Relationship Between the Azimuthal Dependencies of Nuclear Modification Factor and Ridge Yield
The azimuthal angular dependence of the nuclear modification factor
R_{AA}(p_T, phi,N_{part}) recently obtained by PHENIX is related at low p_T to
the trigger phi dependence of the ridge yield as measured by STAR in a
framework in which the azimuthal anisotropy is driven by semihard scattering
near the surface. Careful consideration of the initial geometry leads to the
determination of a surface segment in which the production of semihard partons
are responsible for the phi dependence of the inclusive distribution on the one
hand, and for the angular correlation in ridge phenomenology on the other. With
v_2 also being well reproduced along with R_{AA} and ridge yield, all relevant
phi dependencies in heavy-ion collisions can now be understood in a unified
description that emphasizes the ridge production whether or not a trigger is
used.Comment: This expanded version has additional discussions that render the
paper more readable without change of substance. It is to be published in
Phys. Rev.
Thermodynamics of (2+1)-flavor QCD: Confronting Models with Lattice Studies
The Polyakov-quark-meson (PQM) model, which combines chiral as well as
deconfinement aspects of strongly interacting matter is introduced for three
light quark flavors. An analysis of the chiral and deconfinement phase
transition of the model and its thermodynamics at finite temperatures is given.
Three different forms of the effective Polyakov loop potential are considered.
The findings of the (2+1)-flavor model investigations are confronted to
corresponding recent QCD lattice simulations of the RBC-Bielefeld, HotQCD and
Wuppertal-Budapest collaborations. The influence of the heavier quark masses,
which are used in the lattice calculations, is taken into account. In the
transition region the bulk thermodynamics of the PQM model agrees well with the
lattice data.Comment: 13 pages, 7 figures, 3 tables; minor changes, final version to appear
in Phys. Rev.
Resolving the plasma profile via differential single inclusive suppression
The ability of experimental signatures to resolve the spatio-temporal profile
of an expanding quark gluon plasma is studied. In particular, the single
inclusive suppression of high momentum hadrons versus the centrality of a
heavy-ion collision and with respect to the reaction plane in non-central
collisions is critically examined. Calculations are performed in the higher
twist formalism for the modification of the fragmentation functions. Radically
different nuclear geometries are used. The influence of different initial gluon
distributions as well as different temporal evolution scenarios on the single
inclusive suppression of high momentum pions are outlined. It is demonstrated
that the modification versus the reaction plane is quite sensitive to the
initial spatial density. Such sensitivity remains even in the presence of a
strong elliptic flow.Comment: 5 pages, 4 figures, RevTex
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