Dynamical Casimir effect in a periodically changing domain: A dynamical systems approach

We study the problem of the behavior of a quantum massless scalar field in the space between two parallel infinite perfectly conducting plates, one of them stationary, the other moving periodically. We reformulate the physical problem into a problem about the asymptotic behavior of the iterates of a map of the circle, and then apply results from theory of dynamical systems to study the properties of the map. Many of the general mathematical properties of maps of the circle translate into properties of the field in the cavity. For example, we give a complete classification of the possible resonances in the system, and show that small enough perturbations do not destroy the resonances. We use some mathematical identities to give transparent physical interpretation of the processes of creation and amplification of the quantum field due to the motion of the boundary and to elucidate the similarities and the differences between the classical and quantum fields in domains with moving boundaries.Comment: 19 pages, 7 figure

Free energy of a static quark anti-quark pair and the renormalized Polyakov loop in three flavor QCD

We study the free energy of a static quark anti-quark pair at finite temperature in three flavor QCD with degenerate quark masses using N_tau=4 and 6 lattices with Asqtad staggered fermion action. The static free energy was calculated for different values of the quark mass and the entropy contribution at large distances has been extracted. We also calculate the renormalized Polyakov loop following the approach by Kaczmarek et al.Comment: RevTeX, 7 pages, 8 figures; Minor corrections, added referenc

Periodic variations in the colours of the classical T Tauri star RW Aur A

The classical T Tauri star RW Aur A is an irregular variable with a large amplitude in all photometric bands. In an extended series of photometric data we found small-amplitude periodic variations in the blue colours of the star, with a period of 2.64 days. The period was relatively stable over several years. The amplitude of the periodic signal is 0.21 mag in U-V, 0.07 mag in B-V, and about 0.02 mag in V-R and V-I. No periodicity was found in the V magnitude. The relevance of this photometric period to the recently discovered periodicity in spectral features of the star is discussed, and the hypothesis of a hot spot is critically considered.Comment: 5 pages, 8 figures, uses new aa.cls, accepted for publication in Astronomy and Astrophysic

Simulation of the Gravitational Collapse and Fragmentation of Rotating Molecular Clouds

In this paper we study the process of the subsequent (runaway) fragmentation of the rotating isothermal Giant Molecular Cloud (GMC) complex. Our own developed Smoothed Particle Hydrodynamics (SPH) gas-dynamical model successfully reproduce the observed Cloud Mass-distribution Function (CMF) in our Galaxy (even the differences between the inner and outer parts of our Galaxy). The steady state CMF is established during the collapse within a free-fall timescale of the GMC. We show that one of the key parameters, which defines the observed slope of the present day CMF, is the initial ratio of the rotational (turbulent) and gravitational energy inside the fragmented GMC.Comment: 8 pages, 9 EPS figures, special forma.cls class file is use

Line Structure in the Spectrum of FU Orionis

New high-resolution spectra of FU Ori, obtained with the HIRES spectrograph at the Keck I telescope in 2003-2006, make it possible to compare the optical line profiles with those predicted by the self-luminous accretion disk model. A dependence of line width on excitation potential and on wavelength, expected for a Keplerian disk, is definitely not present in the optical region, nor is the line duplicity due to velocity splitting. The absorption lines observed in the optical region of FU Ori must originate in or near the central object, and here their profiles are shown to be those expected of a rigidly rotating object. They can be fitted by a rapidly rotating (v sin i = 70 km/s) high-luminosity G-type star having a large dark polar spot, with axis inclined toward the line of sight. Over these years, the radial velocity of FU Ori has remained constant to within +/-0.3 km/s, so there is no indication that the star is a spectroscopic binary. These results apply to the optical region ($\lambda< 8800$ \AA); more distant, cooler regions of the disk contribute in the infrared.Comment: 14 pages, 11 figures, accepted by A