112 research outputs found
Large entropy production inside black holes: a simple model
Particles dropped into a rotating black hole can collide near the inner
horizon with enormous energies. The entropy produced by these collisions can be
several times larger than the increase in the horizon entropy due to the
addition of the particles. In this paper entropy is produced by releasing large
numbers of neutrons near the outer horizon of a rotating black hole such that
they collide near the inner horizon at energies similar to those achieved at
the Relativistic Heavy Ion Collider. The increase in horizon entropy is
approximately 80 per dropped neutron pair, while the entropy produced in the
collisions is 160 per neutron pair. The collision entropy is produced inside
the horizon, so this excess entropy production does not violate Bousso's bound
limiting the entropy that can go through the black hole's horizon. The
generalized laws of black hole thermodynamics are obeyed. No individual
observer inside the black hole sees a violation of the second law of
thermodynamicsComment: 10 page
Initial-State Interactions in the Unpolarized Drell-Yan Process
We show that initial-state interactions contribute to the
distribution in unpolarized Drell-Yan lepton pair production and , without suppression. The asymmetry is expressed as a
product of chiral-odd distributions , where the quark-transversity function
is the transverse momentum dependent, light-cone
momentum distribution of transversely polarized quarks in an {\it unpolarized}
proton. We compute this (naive) -odd and chiral-odd distribution function
and the resulting asymmetry explicitly in a quark-scalar diquark
model for the proton with initial-state gluon interaction. In this model the
function equals the -odd (chiral-even) Sivers
effect function . This suggests that the
single-spin asymmetries in the SIDIS and the Drell-Yan process are closely
related to the asymmetry of the unpolarized Drell-Yan process,
since all can arise from the same underlying mechanism. This provides new
insight regarding the role of quark and gluon orbital angular momentum as well
as that of initial- and final-state gluon exchange interactions in hard QCD
processes.Comment: 22 pages, 6 figure
Formation of dense partonic matter in relativistic nucleus-nucleus collisions at RHIC: Experimental evaluation by the PHENIX collaboration
Extensive experimental data from high-energy nucleus-nucleus collisions were
recorded using the PHENIX detector at the Relativistic Heavy Ion Collider
(RHIC). The comprehensive set of measurements from the first three years of
RHIC operation includes charged particle multiplicities, transverse energy,
yield ratios and spectra of identified hadrons in a wide range of transverse
momenta (p_T), elliptic flow, two-particle correlations, non-statistical
fluctuations, and suppression of particle production at high p_T. The results
are examined with an emphasis on implications for the formation of a new state
of dense matter. We find that the state of matter created at RHIC cannot be
described in terms of ordinary color neutral hadrons.Comment: 510 authors, 127 pages text, 56 figures, 1 tables, LaTeX. Submitted
to Nuclear Physics A as a regular article; v3 has minor changes in response
to referee comments. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
Energy and system size dependence of \phi meson production in Cu+Cu and Au+Au collisions
We study the beam-energy and system-size dependence of \phi meson production
(using the hadronic decay mode \phi -- K+K-) by comparing the new results from
Cu+Cu collisions and previously reported Au+Au collisions at \sqrt{s_NN} = 62.4
and 200 GeV measured in the STAR experiment at RHIC. Data presented are from
mid-rapidity (|y|<0.5) for 0.4 < pT < 5 GeV/c. At a given beam energy, the
transverse momentum distributions for \phi mesons are observed to be similar in
yield and shape for Cu+Cu and Au+Au colliding systems with similar average
numbers of participating nucleons. The \phi meson yields in nucleus-nucleus
collisions, normalised by the average number of participating nucleons, are
found to be enhanced relative to those from p+p collisions with a different
trend compared to strange baryons. The enhancement for \phi mesons is observed
to be higher at \sqrt{s_NN} = 200 GeV compared to 62.4 GeV. These observations
for the produced \phi(s\bar{s}) mesons clearly suggest that, at these collision
energies, the source of enhancement of strange hadrons is related to the
formation of a dense partonic medium in high energy nucleus-nucleus collisions
and cannot be alone due to canonical suppression of their production in smaller
systems.Comment: 20 pages and 5 figure
Relating the microscopic rules in coalescence-fragmentation models to the macroscopic cluster size distributions which emerge
Coalescence-fragmentation problems are of great interest across the physical,
biological, and recently social sciences. They are typically studied from the
perspective of the rate equations, at the heart of such models are the rules
used for coalescence and fragmentation. Here we discuss how changes in these
microscopic rules affect the macroscopic cluster-size distribution which
emerges from the solution to the rate equation. More generally, our work
elucidates the crucial role that the fragmentation rule can play in such
dynamical grouping models. We focus on two well-known models whose
fragmentation rules lie at opposite extremes setting the models within the
broader context of binary coalescence-fragmentation models. Further, we provide
a range of generalizations and new analytic results for a well-known model of
social group formation [V. M. Eguiluz and M. G. Zimmermann, Phys. Rev. Lett.
85, 5659 (2000)]. We develop analytic perturbation treatment of the original
model, and extend the mathematical to the treatment of growing and declining
populations
Effects of sleep deprivation on neural functioning: an integrative review
Sleep deprivation has a broad variety of effects on human performance and neural functioning that manifest themselves at different levels of description. On a macroscopic level, sleep deprivation mainly affects executive functions, especially in novel tasks. Macroscopic and mesoscopic effects of sleep deprivation on brain activity include reduced cortical responsiveness to incoming stimuli, reflecting reduced attention. On a microscopic level, sleep deprivation is associated with increased levels of adenosine, a neuromodulator that has a general inhibitory effect on neural activity. The inhibition of cholinergic nuclei appears particularly relevant, as the associated decrease in cortical acetylcholine seems to cause effects of sleep deprivation on macroscopic brain activity. In general, however, the relationships between the neural effects of sleep deprivation across observation scales are poorly understood and uncovering these relationships should be a primary target in future research
Correlated Production of p and p^bar in Au+Au Collisions at sqrt(s_NN) = 200 GeV
Correlations between p and pbar's at transverse momenta typical of enhanced
baryon production in Au+Au collisions are reported. The PHENIX experiment
measures same and opposite sign baryon pairs in Au+Au collisions at sqrt(s_NN)
= 200 GeV. Correlated production of p and p^bar with the trigger particle from
the range 2.5 < p_T < 4.0 GeV/c and the associated particle with 1.8 < p_T <
2.5 GeV/c is observed to be nearly independent of the centrality of the
collisions. Same sign pairs show no correlation at any centrality. The
conditional yield of mesons triggered by baryons (and anti-baryons) and mesons
in the same pT range rises with increasing centrality, except for the most
central collisions, where baryons show a significantly smaller number of
associated mesons. These data are consistent with a picture in which hard
scattered partons produce correlated p and p^bar in the p_T region of the
baryon excess.Comment: 420 authors from 58 institutions, 21 pages,5 figures. Submitted to
Physics Letters B. Plain text data tables for the points plotted in figures
for this and previous PHENIX publications are (or will be) publicly available
at http://www.phenix.bnl.gov/papers.htm
Energy dependence of charged pion, proton and anti-proton transverse momentum spectra for Au+Au collisions at \sqrt{s_NN} = 62.4 and 200 GeV
We study the energy dependence of the transverse momentum (pT) spectra for
charged pions, protons and anti-protons for Au+Au collisions at \sqrt{s_NN} =
62.4 and 200 GeV. Data are presented at mid-rapidity (|y| < 0.5) for 0.2 < pT <
12 GeV/c. In the intermediate pT region (2 < pT < 6 GeV/c), the nuclear
modification factor is higher at 62.4 GeV than at 200 GeV, while at higher pT
(pT >7 GeV/c) the modification is similar for both energies. The p/pi+ and
pbar/pi- ratios for central collisions at \sqrt{s_NN} = 62.4 GeV peak at pT ~ 2
GeV/c. In the pT range where recombination is expected to dominate, the p/pi+
ratios at 62.4 GeV are larger than at 200 GeV, while the pbar/pi- ratios are
smaller. For pT > 2 GeV/c, the pbar/pi- ratios at the two beam energies are
independent of pT and centrality indicating that the dependence of the pbar/pi-
ratio on pT does not change between 62.4 and 200 GeV. These findings challenge
various models incorporating jet quenching and/or constituent quark
coalescence.Comment: 19 pages and 6 figure
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