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

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

Photoproduction of η\eta 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 $\eta$ and $\pi^0$ mesons. Different interpretations of a dip-bump structure of the $\eta$ photoproduction cross section in the 1670 MeV region are presented and discussed. Helicity amplitudes for two low-mass $S_{11}$ states are determined.Comment: 11 pages, 13 figure

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 Δ(2200)7/2−\Delta(2200)7/2^- 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 $E$ for the reactions $\gamma p\to \pi^+ n$ and $\gamma p\to \pi^0 p$ 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 $\Delta(2200)7/2^-$. This is the lowest-mass $\Delta^*$ resonance with spin-parity $J^P=7/2^-$. Its mass is significantly higher than the mass of its parity partner $\Delta(1950)7/2^+$ which is the lowest-mass $\Delta^*$ resonance with spin-parity $J^P=7/2^+$. 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

N∗N^{\bf *} decays to NωN\omega from new data on γp→ωp\gamma p\to \omega p

Data on the reaction $\gamma p\to \omega p$ with $\omega\to\pi^0\gamma$, taken with unpolarized or polarized beams in combination with an unpolarized or polarized proton-target, were analyzed within the Bonn-Gatchina (BnGa) partial wave analysis. Differential cross sections, several spin density matrix elements, the beam asymmetry $\Sigma$, the normalized helicity difference $E$, and the correlation $G$ between linear photon and longitudinal target polarization were included in a large data base on pion and photo-induced reactions. The data on $\omega$ photoproduction are used to determine twelve $N^*\to N\omega$ branching ratios; most of these are determined for the first time.Comment: 6 pages, 4 figures, 2 table