Gauge Field Strength Tensor from the Overlap Dirac Operator

We derive the classical continuum limit of the operator tr$_s \sigma_{\mu\nu} D^{ov}(x,x)$ with $D^{ov}$ being the overlap Dirac operator and show that it corresponds to the gauge field strength tensor $F_{\mu\nu}(x)$.Comment: 17 page

Shear viscosity over entropy density ratio with extended quasi-particles

We consider an effective field theory description of beyond-quasi-particle excitations aiming to associate the transport properties of the system with the spectral density of states. Tuning various properties of the many-particle correlations, we investigate how the robust microscopic features are translated into the macroscopic observables like shear viscosity and entropy density. The liquid-gas crossover is analysed using several examples. A thermal constraint on the fluidity measure, the ratio of shear viscosity to entropy density, is discussed.Comment: 13 pages, 7 figures, uses revtex4-1; published versio

Search for Gamma-Ray Burst Classes with the RHESSI Satellite

A sample of 427 gamma-ray bursts (GRBs), measured by the RHESSI satellite, is studied statistically with respect to duration and hardness ratio. Standard statistical tests are used, such as $\chi^2$, F-test and the maximum likelihood ratio test, in order to compare the number of GRB groups in the RHESSI database with that of the BATSE database. Previous studies based on the BATSE Catalog claim the existence of an intermediate GRB group, besides the long and short groups. Using only the GRB duration $T_{90}$ as information and $\chi^2$ or F-test, we have not found any statistically significant intermediate group in the RHESSI data. However, maximum likelihood ratio test reveals a significant intermediate group. Also using the 2-dimensional hardness / $T_{90}$ plane, the maximum likelihood analysis reveals a significant intermediate group. Contrary to the BATSE database, the intermediate group in the RHESSI data-set is harder than the long one. The existence of an intermediate group follows not only from the BATSE data-set, but also from the RHESSI one.Comment: Accepted for publication in Astronomy and Astrophysics, 9 pages, 4 figure

Anisotropy of the sky distribution of gamma-ray bursts

The isotropy of gamma-ray bursts collected in current BATSE catalog is studied. It is shown that the quadrupole term being proportional to \sim sin 2b sin l is non-zero with a probability of 99.9%. The occurrence of this anisotropy term is then confirmed by the binomial test even with the probability of 99.97 %. Hence, the sky distribution of all known gamma-ray bursts is anisotropic. It is also argued that this anisotropy cannot be caused exclusively by instrumental effects due to the nonuniform sky exposure of BATSE instrument. Separating the GRBs into short and long subclasses, it is shown that the short ones are distributed anisotropically, but the long ones seem to be distributed still isotropically. The character of anisotropy suggests that the cosmological origin of short GRBs further holds, and there is no evidence for their Galactical origin

The three-dimensional carrier-envelope-phase map of focused few-cycle pulsed Gaussian beams

We derive an analytical expression that describes the complete three-dimensional carrier-envelope phase (CEP) distribution of in the focal volume of ultrashort pulsed Gaussian beams focused by spherical mirrors or lenses. The focal CEP map depends on the so-called factor $g$ specifying the frequency-dependence of the beam width of the source few-cycle pulse, on its chirp and on the small chromatic aberration introduced by a lens without appreciably distorting or broadening the few-cycle pulse. We show how to tailor the CEP map of mirror-focused and lens-focused few-cycle pulses in order to produce negligible transversal and axial CEP variations in specific regions of the focal volume for phase-sensitive interactions of light with matter taking place in a volume or on a surface. We propose a quasi-achromatic doublet lens that can implement in practice these tailored CEP distributions.Comment: 9 pages, 6 figure

Factor analysis of the long gamma-ray bursts

We study statistically 197 long gamma-ray bursts, detected and measured in detail by the BATSE instrument of the Compton Gamma-Ray Observatory. In the sample 10 variables, describing for any burst the time behavior of the spectra and other quantities, are collected. The factor analysis method is used to find the latent random variables describing the temporal and spectral properties of GRBs. The application of this particular method to this sample indicates that five factors and the \REpk spectral variable (the ratio of peak energies in the spectrum) describe the sample satisfactorily. Both the pseudo-redshifts inferred from the variability, and the Amati-relation in its original form, are disfavored.Comment: 5 pages, acceptod to A&

The Nappi-Witten string in the light-cone gauge

Some of the motivations for as well as the main points of the quantization of the Nappi Witten string in the light cone gauge are reviewed.Comment: 21 pages, Plain Tex, to appear in the E.P. Wigner memorial volume of Acta Physica Hungaric