2,584 research outputs found
Structure Functions and Pair Correlations of the Quark-Gluon Plasma
Recent experiments at RHIC and theoretical considerations indicate that the
quark-gluon plasma, present in the fireball of relativistic heavy-ion
collisions, might be in a liquid phase. The liquid state can be identified by
characteristic correlation and structure functions. Here definitions of the
structure functions and pair correlations of the quark-gluon plasma are
presented as well as perturbative results. These definitions might be useful
for verifying the quark-gluon-plasma liquid in QCD lattice calculations.Comment: 9 pages, 1 figure, revised version (new remark on the coupling
parameter on page 2), to be published in Phys. Rev.
What can we learn from electromagnetic plasmas about the quark-gluon plasma?
Ultra-relativistic electromagnetic plasmas can be used for improving our
understanding of the quark-gluon plasma. In the weakly coupled regime both
plasmas can be described by transport theoretical and quantum field theoretical
methods leading to similar results for the plasma properties (dielectric
tensor, dispersion relations, plasma frequency, Debye screening, transport
coefficients, damping and particle production rates). In particular, future
experiments with ultra-relativistic electron-positron plasmas in ultra-strong
laser fields might open the possibility to test these predictions, e.g. the
existence of a new fermionic plasma wave (plasmino). In the strongly coupled
regime electromagnetic plasmas such as complex plasmas can be used as models or
at least analogies for the quark-gluon plasma possibly produced in relativistic
heavy-ion experiments. For example, pair correlation functions can be used to
investigate the equation of state and cross section enhancement for parton
scattering can be explained.Comment: 8 pages, 7 figures, talk given at the SCCS 2008 International
Conference, 29 July - 2 August 2008, Camerino, Ital
Field Theoretic Description of Ultrarelativistic Electron-Positron Plasmas
Ultrarelativistic electron-positron plasmas can be produced in high-intensity
laser fields and play a role in various astrophysical situations. Their
properties can be calculated using QED at finite temperature. Here we will use
perturbative QED at finite temperature for calculating various important
properties, such as the equation of state, dispersion relations of collective
plasma modes of photons and electrons, Debye screening, damping rates, mean
free paths, collision times, transport coefficients, and particle production
rates, of ultrarelativistic electron-positron plasmas. In particular, we will
focus on electron-positron plasmas produced with ultra-strong lasers.Comment: 13 pages, 7 figures, 1 table, published versio
Study of ambiguities in scattering amplitudes
Amplitudes for the reaction are reconstructed from
data on the differential cross section , the recoil
polarization , and on the spin rotation parameter . At low energies,
no data on exist, resulting in ambiguities. An approximation using
and waves leads only to a fair description of the data on
and ; in this case, there are two sets of amplitudes. Including waves,
the data on and are well reproduced by the fit but now,
there are several distinct solutions which describe the data with identical
precision. In the range where the spin rotation parameter was measured,
a full and unambiguous reconstruction of the partial wave amplitudes is
possible. The energy-independent amplitudes are compared to the energy
dependent amplitudes which resulted from a coupled channel fit (BnGa2011-02) to
a large data set including both pion and photo-induced reactions. Significant
deviations are observed. Consistency between energy dependent and energy
independent solutions by choosing the energy independent solution which is
closest to the energy dependent solution. In a second step, the {\it known}
energy dependent solution for low (or high) partial waves is imposed and only
the high (or low) partial waves are fitted leading to smaller uncertainties
Photoproduction of mesons off neutrons from a deuteron target
A formalism is developed for the partial wave analysis of data on meson
photoproduction off deuterons and applied to photoproduction of and
mesons. Different interpretations of a dip-bump structure of the
photoproduction cross section in the 1670 MeV region are presented and
discussed. Helicity amplitudes for two low-mass states are determined.Comment: 11 pages, 13 figure
Decay of a Yukawa fermion at finite temperature and applications to leptogenesis
We calculate the decay rate of a Yukawa fermion in a thermal bath using
finite temperature cutting rules and effective Green's functions according to
the hard thermal loop resummation technique. We apply this result to the decay
of a heavy Majorana neutrino in leptogenesis. Compared to the usual approach
where thermal masses are inserted into the kinematics of final states, we find
that deviations arise through two different leptonic dispersion relations. The
decay rate differs from the usual approach by more than one order of magnitude
in the temperature range which is interesting for the weak washout regime. We
discuss how to arrive at consistent finite temperature treatments of
leptogenesis.Comment: 16 pages, 5 figure
Interference phenomena in the -wave in photoproduction
The recent precise experimental results for the photoproduction of
-mesons off the neutron measured with the Crystal Ball/TAPS calorimeter
at the MAMI accelerator have been investigated in detail in the framework of
the Bonn-Gatchina coupled channel model. The main result is that the narrow
structure observed in the excitation function of
can be reproduced fully with a particular interference pattern in the
partial wave. Introduction of the narrow resonance with
the properties reported in earlier publications deteriorates the quality of the
fit.Comment: 10 pages, 13 figures, accepted for publication in EPJ
Good thinking or gut feeling? Decision-making style and rationality in traders, bankers and financial non-experts
Research in cognitive psychology and behavioural finance has suggested that human decision-making is subject to the use of ‘heuristics’ – simple decision rules that produce systematic biases away from normative decision outcomes (Kahneman, 2003), and that even financial experts may be susceptible to heuristic thinking (e.g., Taleb, 2004).
The current study investigated differences in decision-making style and the susceptibility to heuristics between financial traders, non-trading bank employees, and people not working in finance. Traders scored significantly higher than participants in the other two groups on the cognitive reflection task (CRT; Frederick, 2005) which measures the tendency to inhibit automatic but frequently false responses in reasoning tasks. Scores for traders were also higher on a self-rated scale for reflective thinking (REI; Pacini & Epstein, 1999) in decision-making. There were no group differences in the propensity for intuitive thinking, although self-rated experientiality (REI-E) correlated with age. These results indicate that traders have a higher self-rated tendency for reflective thinking and a greater propensity to inhibit the use of mental shortcuts (heuristics) when solving problems in judgment and decision making. However, traders in the current study showed no elevated preference to use ‘intuition’ in their decision-making compared to other groups. These group effects cannot be explained by differences in sex, age, or qualification, a conclusion that is supported by Toplak, West, and Stanovich (2011) who previously showed that performance on the CRT predicted heuristic thinking even when measures of cognitive ability and executive functioning were controlled for
Evidence for from photoproduction and consequence for chiral-symmetry restoration at high mass
We report a partial-wave analysis of new data on the double-polarization
variable for the reactions and
and of further data published earlier. The analysis within the Bonn-Gatchina
(BnGa) formalism reveals evidence for a poorly known baryon resonance, the
one-star . This is the lowest-mass resonance with
spin-parity . Its mass is significantly higher than the mass of its
parity partner which is the lowest-mass
resonance with spin-parity . It has been suggested that chiral
symmetry might be restored in the high-mass region of hadron excitations, and
that these two resonances should be degenerate in mass. Our findings are in
conflict with this prediction.Comment: 5 pages, 3 figures; Physics Letters B in pres
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