17,802 research outputs found
String Effects on Fermi--Dirac Correlation Measurements
We investigate some recent measurements of Fermi--Dirac correlations by the
LEP collaborations indicating surprisingly small source radii for the
production of baryons in -annihilation at the peak. In the
hadronization models there are besides the Fermi--Dirac correlation effect also
a strong dynamical (anti-)correlation. We demonstrate that the extraction of
the pure FD effect is highly dependent on a realistic Monte Carlo event
generator, both for separation of those dynamical correlations which are not
related to Fermi--Dirac statistics, and for corrections of the data and
background subtractions. Although the model can be tuned to well reproduce
single particle distributions, there are large model-uncertainties when it
comes to correlations between identical baryons. We therefore, unfortunately,
have to conclude that it is at present not possible to make any firm conclusion
about the source radii relevant for baryon production at LEP
Tidal stripping as a mechanism for placing globular clusters on wide orbits: the case of MGC1 in M31
The globular clusters of large spiral galaxies can be divided into two
populations: one which formed in-situ and one which comprises clusters tidally
stripped away from other galaxies. In this paper we investigate the
contribution to the outer globular cluster population in the M31 galaxy through
donation of clusters from dwarf galaxies. We test this numerically by comparing
the contribution of globular clusters from simulated encounters to the observed
M31 globular cluster population. To constrain our simulations, we specifically
investigate the outermost globular cluster in the M31 system, MGC1. The remote
location of MGC1 favours the idea of it being captured, however, the cluster is
devoid of features associated with tidal interactions. Hence we separate
simulations where tidal features are present and where they are hidden. We find
that our simulated encounters can place clusters on MGC1-like orbits. In
addition, we find that tidal stripping of clusters from dwarf galaxies leaves
them on orbits having a range of separations, broadly matching those observed
in M31. We find that the specific energies of globular clusters captured by M31
closely matches those of the incoming host dwarf galaxies. Furthermore, in our
simulations we find an equal number of accreted clusters on co-rotating and
counter-rotating orbits within M31 and use this to infer the fraction of
clusters that has been accreted. We find that even close in roughly 50% of the
clusters are accreted, whilst this figure increases to over 80% further out.Comment: 17 pages, 12 figures. Accepted for publication in MNRA
The Feynman-Wilson gas and the Lund model
We derive a partition function for the Lund fragmentation model and compare
it with that of a classical gas. For a fixed rapidity ``volume'' this partition
function corresponds to a multiplicity distribution which is very close to a
binomial distribution. We compare our results with the multiplicity
distributions obtained from the JETSET Monte Carlo for several scenarios.
Firstly, for the fragmentation vertices of the Lund string. Secondly, for the
final state particles both with and without decays.Comment: Latex, 21+1 pages, 11 figure
The Merger of Small and Large Black Holes
We present simulations of binary black holes mergers in which, after the
common outer horizon has formed, the marginally outer trapped surfaces (MOTSs)
corresponding to the individual black holes continue to approach and eventually
penetrate each other. This has very interesting consequences according to
recent results in the theory of MOTSs. Uniqueness and stability theorems imply
that two MOTSs which touch with a common outer normal must be identical. This
suggests a possible dramatic consequence of the collision between a small and
large black hole. If the penetration were to continue to completion then the
two MOTSs would have to coalesce, by some combination of the small one growing
and the big one shrinking. Here we explore the relationship between theory and
numerical simulations, in which a small black hole has halfway penetrated a
large one.Comment: 17 pages, 11 figure
Shock propagation and stability in causal dissipative hydrodynamics
We studied the shock propagation and its stability with the causal
dissipative hydrodynamics in 1+1 dimensional systems. We show that the presence
of the usual viscosity is not enough to stabilize the solution. This problem is
solved by introducing an additional viscosity which is related to the
coarse-graining scale of the theory.Comment: 14 pages, 16 figure
A microfluidic device for the study of the orientational dynamics of microrods
We describe a microfluidic device for studying the orientational dynamics of
microrods. The device enables us to experimentally investigate the tumbling of
microrods immersed in the shear flow in a microfluidic channel with a depth of
400 mu and a width of 2.5 mm. The orientational dynamics was recorded using a
20 X microscopic objective and a CCD camera. The microrods were produced by
shearing microdroplets of photocurable epoxy resin. We show different examples
of empirically observed tumbling. On the one hand we find that short stretches
of the experimentally determined time series are well described by fits to
solutions of Jeffery's approximate equation of motion [Jeffery, Proc. R. Soc.
London. 102 (1922), 161-179]. On the other hand we find that the empirically
observed trajectories drift between different solutions of Jeffery's equation.
We discuss possible causes of this orbit drift.Comment: 11 pages, 8 figure
Time-resolved extinction rates of stochastic populations
Extinction of a long-lived isolated stochastic population can be described as
an exponentially slow decay of quasi-stationary probability distribution of the
population size. We address extinction of a population in a two-population
system in the case when the population turnover -- renewal and removal -- is
much slower than all other processes. In this case there is a time scale
separation in the system which enables one to introduce a short-time
quasi-stationary extinction rate W_1 and a long-time quasi-stationary
extinction rate W_2, and develop a time-dependent theory of the transition
between the two rates. It is shown that W_1 and W_2 coincide with the
extinction rates when the population turnover is absent, and present but very
slow, respectively. The exponentially large disparity between the two rates
reflects fragility of the extinction rate in the population dynamics without
turnover.Comment: 8 pages, 4 figure
Multiplicity dependence of correlation functions in \bar{p}p reactions at sqrt(s) = 630 GeV
Discussions about Bose-Einstein correlations between decay products of
coproduced W-bosons again raise the question about the behaviour of
correlations if several strings are produced. This is studied by the
multiplicity dependence of correlation functions of particle pairs with
like-sign and opposite-sign charge in \bar{p}p reactions at sqrt{s} = 630 GeV.Comment: 11 pages latex, 4 figs, includes elsart.cls, submitted to Phys Lett
Enhancement of singly and multiply strangeness in p-Pb and Pb-Pb collisions at 158A GeV/c
The idea that the reduction of the strange quark suppression in string
fragmentation leads to the enhancement of strange particle yield in
nucleus-nucleus collisions is applied to study the singly and multiply strange
particle production in p-Pb and Pb-Pb collisions at 158A GeV/c. In this
mechanism the strange quark suppression factor is related to the effective
string tension, which increases in turn with the increase of the energy, of the
centrality and of the mass of colliding system. The WA97 observation that the
strange particle enhancement increases with the increasing of centrality and of
strange quark content in multiply strange particles in Pb-Pb collisions with
respect to p-Pb collisions was accounted reasonably.Comment: 8 pages, 3 PostScript figures, in Latex form. submitted to PR
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