5,070 research outputs found
Baryonic Strangeness and Related Susceptibilities in QCD
The ratios of off-diagonal to diagonal conserved charge susceptibilities
e.g., chi_{BS}/chi_{S}, chi_{QS}/chi_{S}, related to the quark flavor
susceptibilities, have proven to be discerning probes of the flavor carrying
degrees of freedom in hot strongly interacting matter. Various constraining
relations between the different susceptibilities are derived based on the
Gell-Mann-Nishijima formula and the assumption of isospin symmetry. Using
generic models of deconfined matter and results form lattice QCD, it is
demonstrated that the flavor carrying degrees of freedom at a temperature above
1.5T_c are quark-like quasiparticles. A new observable related by isospin
symmetry to C_{BS} = -3chi_{BS}/chi_{S} and equal to it in the baryon free
regime is identified. This new observable, which is blind to neutral and
non-strange particles, carries the potential of being measured in relativistic
heavy-ion collisions.Comment: 12 pages, 5 figures, RevTex
3+1D hydrodynamic simulation of relativistic heavy-ion collisions
We present MUSIC, an implementation of the Kurganov-Tadmor algorithm for
relativistic 3+1 dimensional fluid dynamics in heavy-ion collision scenarios.
This Riemann-solver-free, second-order, high-resolution scheme is characterized
by a very small numerical viscosity and its ability to treat shocks and
discontinuities very well. We also incorporate a sophisticated algorithm for
the determination of the freeze-out surface using a three dimensional
triangulation of the hyper-surface. Implementing a recent lattice based
equation of state, we compute p_T-spectra and pseudorapidity distributions for
Au+Au collisions at root s = 200 GeV and present results for the anisotropic
flow coefficients v_2 and v_4 as a function of both p_T and pseudorapidity. We
were able to determine v_4 with high numerical precision, finding that it does
not strongly depend on the choice of initial condition or equation of state.Comment: 16 pages, 11 figures, version accepted for publication in PRC,
references added, minor typos corrected, more detailed discussion of
freeze-out routine adde
Viscous photons in relativistic heavy ion collisions
Theoretical studies of the production of real thermal photons in relativistic
heavy ion collisions at the Relativistic Heavy Ion Collider (RHIC) are
performed. The space-time evolution of the colliding system is modelled using
MUSIC, a 3+1D relativistic hydrodynamic simulation, using both its ideal and
viscous versions. The inclusive spectrum and its azimuthal angular anisotropy
are studied separately, and the relative contributions of the different photon
sources are highlighted. It is shown that the photon v2 coefficient is
especially sensitive to the details of the microscopic dynamics like the
equation of state, the ratio of shear viscosity over entropy density, eta/s,
and to the morphology of the initial state.Comment: 15 pages, 12 figures. References updated and discussion adde
Higher excitations of and in dilepton spectra
We consider lepton pair production via two-hadron annihilation through
various isoscalar vector mesons within hot, baryon-free matter. This is
tantamount to constructing effective form factors which we model using a
vector-meson-dominance approach and compare with experiment. In particular, we
consider the reactions and + c.c. . We find that and are visible in the mass
spectrum for the thermal production rate above the
tail and even above the results---both of which were
considered important in their respective mass regions.Comment: RevTeX, 9 pages, 6 (uuencoded) figures; to appear in Phys. Rev
Stable Noncrossing Matchings
Given a set of men represented by points lying on a line, and
women represented by points lying on another parallel line, with each
person having a list that ranks some people of opposite gender as his/her
acceptable partners in strict order of preference. In this problem, we want to
match people of opposite genders to satisfy people's preferences as well as
making the edges not crossing one another geometrically. A noncrossing blocking
pair w.r.t. a matching is a pair of a man and a woman such that
they are not matched with each other but prefer each other to their own
partners in , and the segment does not cross any edge in . A
weakly stable noncrossing matching (WSNM) is a noncrossing matching that does
not admit any noncrossing blocking pair. In this paper, we prove the existence
of a WSNM in any instance by developing an algorithm to find one in a
given instance.Comment: This paper has appeared at IWOCA 201
Strong Color Field Baryonic Remnants in Nucleus-Nucleus Collisions at 200A GeV
The effects of strong color electric fields (SCF) on the baryon production at
RHIC are studied in the framework of HIJING/B\=B (v2.0) model. The particle
species dependence of nuclear modification factors (NMF) are analyzed for Au+Au
collisions at 200A GeV. A doubling of the string tension leading to a
modification of the strangeness suppression according to Schwinger mechanism is
shown to provide an alternate explanation to coalescence models for the
interpretation of the observed baryon and meson production at moderate
and results in a predicted enhancement in the (multi)strange (anti)hyperon
production.Comment: 6 pages, Latex(Revtex), 4 figures;Added new references, one figure,
text slightly modified. final version accepted for publication in Pnys. Rev.
C (october,05
Energy Loss of Leading Hadrons and Direct Photon production in Evolving Quark-Gluon Plasma
We calculate the nuclear modification factor of neutral pions and the photon
yield at high p_T in central Au-Au collisions at RHIC (\sqrt{s}=200 GeV) and
Pb-Pb collisions at the LHC (\sqrt{s}=5500 GeV). A leading-order accurate
treatment of jet energy loss in the medium has been convolved with a physical
description of the initial spatial distribution of jets and a (1+1) dimensional
expansion. We reproduce the nuclear modification factor of pion R_{AA} at RHIC,
assuming an initial temperature T_i=370 MeV and a formation time \tau_i=0.26
fm/c, corresponding to dN/dy=1260. The resulting suppression depends on the
particle rapidity density dN/dy but weakly on the initial temperature. The jet
energy loss treatment is also included in the calculation of high p_T photons.
Photons coming from primordial hard N-N scattering are the dominant
contribution at RHIC for p_T > 5 GeV, while at the LHC, the range 8<p_T<14 GeV
is dominated by jet-photon conversion in the plasma.Comment: 21 pages, 16 figures. Discussions and references added. New figure
includind photon dat
High-threshold mechanosensitive ion channels blocked by a novel conopeptide mediate pressure-evoked pain
Little is known about the molecular basis of somatosensory mechanotransduction in mammals. We screened a library of peptide toxins for effects on mechanically activated currents in cultured dorsal root ganglion neurons. One conopeptide analogue, termed NMB-1 for noxious mechanosensation blocker 1, selectively inhibits (IC50 1 µM) sustained mechanically activated currents in a subset of sensory neurons. Biotinylated NMB-1 retains activity and binds selectively to peripherin-positive nociceptive sensory neurons. The selectivity of NMB-1 was confirmed by the fact that it has no inhibitory effects on voltage-gated sodium and calcium channels, or ligand-gated channels such as acid-sensing ion channels or TRPA1 channels. Conversely, the tarantula toxin, GsMTx-4, which inhibits stretch-activated ion channels, had no effects on mechanically activated currents in sensory neurons. In behavioral assays, NMB-1 inhibits responses only to high intensity, painful mechanical stimulation and has no effects on low intensity mechanical stimulation or thermosensation. Unexpectedly, NMB-1 was found to also be an inhibitor of rapid FM1-43 loading (a measure of mechanotransduction) in cochlear hair cells. These data demonstrate that pharmacologically distinct channels respond to distinct types of mechanical stimuli and suggest that mechanically activated sustained currents underlie noxious mechanosensation. NMB-1 thus provides a novel diagnostic tool for the molecular definition of channels involved in hearing and pressure-evoked pain
The effects of meson mixing on dilepton spectra
The effect of scalar and vector meson mixing on the dilepton radiation from
hot and dense hadronic matter is estimated in different isospin channels. In
particular, we study the effect of - and mixing and
calculate the corresponding rates. Effects are found to be significant compared
to standard - and - annihilations. While the mixing in
the isoscalar channel mostly gives a contribution in the invariant mass range
between the two-pion threshold and the peak, the isovector channel
mixing induces an additional peak just below that of the .
Experimentally, the dilepton signals from - mixing seem to be more
tractable than those from - mixing.Comment: 10 pages, 9 figure
Aspects of meson properties in dense nuclear matter
We investigate the modification of meson spectral densities in dense nuclear
matter at zero temperature. These effects are studied in a fully relativistic
mean field model which goes beyond the linear density approximation and also
includes baryon resonances. In particular, the role of N*(1520) and N*(1720) on
the rho meson spectral density is highlighted. Even though the nucleon-nucleon
loop and the nucleon-resonance loop contribute with the opposite sign, an
overall reduction of rho meson mass is still observed at high density.
Importantly, it is shown that the resonances cause substantial broadening of
the rho meson spectral density in matter and also induces non-trivial momentum
dependence. The spectral density of the a0 meson is also shown. We study the
dispersion relations and collective oscillations induced by the rho meson
propagation in nuclear matter together with the influence of the mixing of rho
with the a0 meson. The relevant expression for the plasma frequency is also
recovered analytically in the appropriate limit.Comment: 19 pages, 17 figure
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