Elliptic Flow from a Transversally Thermalized Fireball

The agreement of elliptic flow data at RHIC at central rapidity with the hydrodynamic model has led to the conclusion of very rapid thermalization. This conclusion is based on the intuitive argument that hydrodynamics, which assumes instantaneous local thermalization, produces the largest possible elliptic flow values and that the data seem to saturate this limit. We here investigate the question whether incompletely thermalized viscous systems may actually produce more elliptic flow than ideal hydrodynamics. Motivated by the extremely fast primordial longitudinal expansion of the reaction zone, we investigate a toy model which exhibits thermalization only in the transverse directions but undergoes collisionless free-streaming expansion in the longitudinal direction. For collisions at RHIC energies, elliptic flow results from the model are compared with those from hydrodynamics. With the final particle yield and \kt-distribution fixed, the transversally thermalized model is shown not to be able to produce the measured amount of elliptic flow. This investigation provides further support for very rapid local kinetic equilibration at RHIC. It also yields interesting novel results for the elliptic flow of massless particles such as direct photons.Comment: revtex4, 15 pages + 10 embedded EPS figure

Large amplitude MHD waves upstream of the Jovian bow shock: Reinterpretation

Observations of large amplitude magnetohydrodynamic (MHD) waves upstream of the Jovian bow shock were previously interpreted as arising from a resonant electromagnetic ion beam instability. That interpretation was based on the conclusion that the observed fluctuations were predominantly right elliptically polarized in the solar wind rest frame. Because it was noted that the fluctuations are, in fact, left elliptically polarized, a reanalysis of the observations was necessary. Several mechanisms for producing left hand polarized MHD waves in the observed frequency range were investigated. Instabilities excited by protons appear unlikely to account for the observations. A resonant instability excited by relativistic electrons escaping from the Jovian magnetosphere is a likely source of free energy consistent with the observations. Evidence for the existence of such a population of electrons was found in both the Low Energy Charged Particle experiments and Cosmic Ray experiments on Voyager 2

Non-equilibrium chemistry and dust formation in AGB stars as probed by SiO line emission

We have performed high spatial resolution observations of SiO line emission for a sample of 11 AGB stars using the ATCA, VLA and SMA interferometers. Detailed radiative transfer modelling suggests that there are steep chemical gradients of SiO in their circumstellar envelopes. The emerging picture is one where the radial SiO abundance distribution starts at an initial high abundance, in the case of M-stars consistent with LTE chemistry, that drastically decreases at a radius of ~1E15 cm. This is consistent with a scenario where SiO freezes out onto dust grains. The region of the wind with low abundance is much more extended, typically ~1E16 cm, and limited by photodissociation. The surpisingly high SiO abundances found in carbon stars requires non-equilibrium chemical processes.Comment: 2 pages, 1 figure. To be published in the proceedings of the conference "Why Galaxies Care about AGB Stars", held in Vienna, August 7-11, 2006; F. Kerschbaum, C. Charbonnel, B. Wing eds, ASP Conf.Ser. in pres

The Puzzling Mutual Orbit of the Binary Trojan Asteroid (624) Hektor

Asteroids with satellites are natural laboratories to constrain the formation and evolution of our solar system. The binary Trojan asteroid (624) Hektor is the only known Trojan asteroid to possess a small satellite. Based on W.M. Keck adaptive optics observations, we found a unique and stable orbital solution, which is uncommon in comparison to the orbits of other large multiple asteroid systems studied so far. From lightcurve observations recorded since 1957, we showed that because the large Req=125-km primary may be made of two joint lobes, the moon could be ejecta of the low-velocity encounter, which formed the system. The inferred density of Hektor's system is comparable to the L5 Trojan doublet (617) Patroclus but due to their difference in physical properties and in reflectance spectra, both captured Trojan asteroids could have a different composition and origin.Comment: 13 pages, 3 figures, 2 table

Permutation asymmetry inducing entanglement between degrees of freedom in multiphoton states

We describe and examine entanglement between different degrees of freedom in multiphoton states based on the permutation properties. From the state description, the entanglement comes from the permutation asymmetry. According to the different permutation properties, the multiphoton states can be divided into several parts. It will help to deal with the multiphoton interference, which can be used as the measurement of the entanglement.Comment: Final versio

20 cm VLA Radio-Continuum Study of M31 - Images and Point Source Catalogues

We present a series of new high-sensitivity and high-resolution radio-continuum images of M31 at \lambda=20 cm (\nu=1.4 GHz). These new images were produced by merging archived 20 cm radio-continuum observations from the Very Large Array (VLA) telescope. Images presented here are sensitive to rms=60 \mu Jy and feature high angular resolution (<10"). A complete sample of discrete radio sources have been catalogued and analysed across 17 individual VLA projects. We identified a total of 864 unique discrete radio sources across the field of M31. One of the most prominent regions in M31 is the ring feature for which we estimated total integrated flux of 706 mJy at \lambda=20 cm. We compare here, detected sources to those listed in Gelfand et al. (2004) at \lambda=92 cm and find 118 sources in common to both surveys. The majority (61%) of these sources exhibit a spectral index of \alpha <-0.6 indicating that their emission is predominantly non-thermal in nature. That is more typical for background objects.Comment: 28 pages, 25 figures, accepted for publication in the Serbian Astronomical Journa

Indistinguishability of independent single photons

The indistinguishability of independent single photons is presented by decomposing the single photon pulse into the mixed state of different transform limited pulses. The entanglement between single photons and outer environment or other photons induces the distribution of the center frequencies of those transform limited pulses and makes photons distinguishable. Only the single photons with the same transform limited form are indistinguishable. In details, the indistinguishability of single photons from the solid-state quantum emitter and spontaneous parametric down conversion is examined with two-photon Hong-Ou-Mandel interferometer. Moreover, experimental methods to enhance the indistinguishability are discussed, where the usage of spectral filter is highlighted.Comment: 6 pages, 3 figure

Relativistic Modification of the Gamow Factor

In processes involving Coulomb-type initial- and final-state interactions, the Gamow factor has been traditionally used to take into account these additional interactions. The Gamow factor needs to be modified when the magnitude of the effective coupling constant increases or when the velocity increases. For the production of a pair of particles under their mutual Coulomb-type interaction, we obtain the modification of the Gamow factor in terms of the overlap of the Feynman amplitude with the relativistic wave function of the two particles. As a first example, we study the modification of the Gamow factor for the production of two bosons. The modification is substantial when the coupling constant is large.Comment: 13 pages, in LaTe