6,106 research outputs found
Free energies of static three quark systems
We study the behaviour of free energies of baryonic systems composed of three
heavy quarks on the lattice in SU(3) pure gauge theory at finite temperature.
For all temperatures above we find that the connected part of the singlet
(decuplet) free energy of the three quark system is given by the sum of the
connected parts of the free energies of -triplets (-sextets). Using
renormalized free energies we can compare free energies in different colour
channels as well as those of - and -systems on an unique energy scale.Comment: 5 pages, 6 figures, Contribution to Strong and Electroweak Matter
2004 (SEWM04), Helsinki, Finland 16-19 June 200
Open and Hidden Charm Production in d Collisions at RHIC and LHC
We discuss aspects of open and hidden charm production in deuterium-nucleus
collisions at RHIC and LHC energies. We describe calculations of the total cross section and the charm quark transverse momentum distributions. We
next explain how shadowing and moderate nuclear absorption can explain the
PHENIX dAu/ ratios and predict the combined effect of shadowing
and absorption in 6.2 TeV d+Pb collisions.Comment: 6 pages, 4 figures, European Physics Journal conference proceedings
style files included, in proceedings of Hard Probes, 2004 Ericeira, Portuga
Heavy quark free energies for three quark systems at finite temperature
We study the free energy of static three quark systems in singlet, octet,
decuplet and average color channels in the quenched approximation and in
2-flavor QCD at finite temperature. We show that in the high temperature phase
singlet and decuplet free energies of three quark systems are well described by
the sum of the free energies of three diquark systems plus self energy
contributions of the three quarks. In the confining low temperature phase we
find evidence for a Y-shaped flux tube in SU(3) pure gauge theory, which is
less evident in 2-flavor QCD due to the onset of string breaking. We also
compare the short distance behavior of octet and decuplet free energies to the
free energies of single static quarks in the corresponding color
representations.Comment: 11 pages, 17 figure
The last orbit of binary black holes
We have used our new technique for fully numerical evolutions of orbiting
black-hole binaries without excision to model the last orbit and merger of an
equal-mass black-hole system. We track the trajectories of the individual
apparent horizons and find that the binary completed approximately one and a
third orbits before forming a common horizon. Upon calculating the complete
gravitational radiation waveform, horizon mass, and spin, we find that the
binary radiated 3.2% of its mass and 24% of its angular momentum. The early
part of the waveform, after a relatively short initial burst of spurious
radiation, is oscillatory with increasing amplitude and frequency, as expected
from orbital motion. The waveform then transitions to a typical `plunge'
waveform; i.e. a rapid rise in amplitude followed by quasinormal ringing. The
plunge part of the waveform is remarkably similar to the waveform from the
previously studied `ISCO' configuration. We anticipate that the plunge
waveform, when starting from quasicircular orbits, has a generic shape that is
essentially independent of the initial separation of the binary.Comment: 5 pages, 5 figures, revtex
Classification of non-parametric regression functions in longitudinal data models
We investigate a longitudinal data model with non-parametric regression functions that may vary across the observed individuals. In a variety of applications, it is natural to impose a group structure on the regression curves. Specifically, we may suppose that the observed individuals can be grouped into a number of classes whose members all share the same regression function. We develop a statistical procedure to estimate the unknown group structure from the data. Moreover, we derive the asymptotic properties of the procedure and investigate its finite sample performance by means of a simulation study and a real data example
Accurate Evolutions of Orbiting Black-Hole Binaries Without Excision
We present a new algorithm for evolving orbiting black-hole binaries that
does not require excision or a corotating shift. Our algorithm is based on a
novel technique to handle the singular puncture conformal factor. This system,
based on the BSSN formulation of Einstein's equations, when used with a
`pre-collapsed' initial lapse, is non-singular at the start of the evolution,
and remains non-singular and stable provided that a good choice is made for the
gauge. As a test case, we use this technique to fully evolve orbiting
black-hole binaries from near the Innermost Stable Circular Orbit (ISCO)
regime. We show fourth order convergence of waveforms and compute the radiated
gravitational energy and angular momentum from the plunge. These results are in
good agreement with those predicted by the Lazarus approach.Comment: 4 pages, revtex4, 3 figs, references added, typos fixe
Accurate black hole evolutions by fourth-order numerical relativity
We present techniques for successfully performing numerical relativity
simulations of binary black holes with fourth-order accuracy. Our simulations
are based on a new coding framework which currently supports higher order
finite differencing for the BSSN formulation of Einstein's equations, but which
is designed to be readily applicable to a broad class of formulations. We apply
our techniques to a standard set of numerical relativity test problems,
demonstrating the fourth-order accuracy of the solutions. Finally we apply our
approach to binary black hole head-on collisions, calculating the waveforms of
gravitational radiation generated and demonstrating significant improvements in
waveform accuracy over second-order methods with typically achievable numerical
resolution.Comment: 17 pages, 25 figure
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The Effect of Fragmentation in Trading on Market Quality in the UK Equity Market
We investigate the effects of fragmentation in equity markets on the quality of trading outcomes in a panel of FTSE stocks over the period 2008-2011. This period coincided with a great deal of turbulence in the UK equity markets which had multiple causes that need to be controlled for. To achieve this, we use the common correlated effects estimator for large heterogeneous panels. We extend this estimator to quantile regression to analyze the whole conditional distribution of market quality. We find that both fragmentation in visible order books and dark trading that is offered outside the visible order book lower volatility. But dark trading increases the variability of volatility, while visible fragmentation has the opposite effect in particular at the upper quantiles of the conditional distribution. The transition from a monopolistic to a fragmented market is non-monotone
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