Two-time autocorrelation function in phase-ordering kinetics from local scale-invariance

The time-dependent scaling of the two-time autocorrelation function of spin systems without disorder undergoing phase-ordering kinetics is considered. Its form is shown to be determined by an extension of dynamical scaling to a local scale-invariance which turns out to be a new version of conformal invariance. The predicted autocorrelator is in agreement with Monte-Carlo data on the autocorrelation function of the 2D kinetic Ising model with Glauber dynamics quenched to a temperature below criticality.Comment: Latex2e, 7 pages with 2 figures, with epl macro, final from, to appear in EP

Arp 220 - IC 4553/4: understanding the system and diagnosing the ISM

Arp220 is a nearby system in final stages of galaxy merger with powerful ongoing star-formation at and surrounding the two nuclei. Arp 220 was detected in HI absorption and OH Megamaser emission and later recognized as the nearest ultra-luminous infrared galaxy also showing powerful molecular and X-ray emissions. In this paper we review the available radio and mm-wave observational data of Arp 220 in order to obtain an integrated picture of the dense interstellar medium that forms the location of the powerful star-formation at the two nuclei.Comment: 9 pages, 4 figures, to appear in: IAU Symposium 242 Astrophysical Masers and their Environment

Equal-time correlation function for directed percolation

We suggest an equal-time n-point correlation function for systems in the directed percolation universality class which is well defined in all phases and independent of initial conditions. It is defined as the probability that all points are connected with a common ancestor in the past by directed paths.Comment: LaTeX, 12 pages, 8 eps figure

Opportunities for maser studies with the Square Kilometre Array

The Square Kilometre Array (SKA) is the radio telescope of the next generation, providing an increase in sensitivity and angular resolution of two orders of magnitude over existing telescopes. Currently, the SKA is expected to span the frequency range 0.1-25 GHz with capabilities including a wide field-of-view and measurement of polarised emission. Such a telescope has enormous potential for testing fundamental physical laws and producing transformational discoveries. Important science goals include using H2O megamasers to make precise estimates of H0, which will anchor the extragalactic distance scale, and to probe the central structures of accretion disks around supermassive black holes in AGNs, to study OH megamasers associated with extreme starburst activity in distant galaxies and to study with unprecedented precision molecular gas and star formation in our Galaxy.Comment: 5 pages, to appear in: IAU Symposium 242 Astrophysical Masers and their Environment

Local scale invariance as dynamical space-time symmetry in phase-ordering kinetics

The scaling of the spatio-temporal response of coarsening systems is studied through simulations of the 2D and 3D Ising model with Glauber dynamics. The scaling functions agree with the prediction of local scale invariance, extending dynamical scaling to a space-time dynamical symmetry.Comment: Latex, 4 pages, 4 figure

On the feasibility of studying vortex noise in 2D superconductors with cold atoms

We investigate the feasibility of using ultracold neutral atoms trapped near a thin superconductor to study vortex noise close to the Kosterlitz-Thouless-Berezinskii transition temperature. Alkali atoms such as rubidium probe the magnetic field produced by the vortices. We show that the relaxation time $T_1$ of the Zeeman sublevel populations can be conveniently adjusted to provide long observation times. We also show that the transverse relaxation times $T_2$ for Zeeman coherences are ideal for studying the vortex noise. We briefly consider the motion of atom clouds held close to the surface as a method for monitoring the vortex motion.Comment: 4 pages, 1 figur

Kinetics of the long-range spherical model

The kinetic spherical model with long-range interactions is studied after a quench to $T < T_c$ or to $T = T_c$. For the two-time response and correlation functions of the order-parameter as well as for composite fields such as the energy density, the ageing exponents and the corresponding scaling functions are derived. The results are compared to the predictions which follow from local scale-invariance.Comment: added "fluctuation-dissipation ratios"; fixed typo

The association between water kilomasers and compact radio sources in the starburst galaxy NGC2146

We report the detection of 22 GHz water vapor emission toward the starburst galaxy NGC2146, made using the Effelsberg 100-m telescope. Interferometric observations with the Very Large Array (VLA) show that a part of the emission originates from two prominent sites of star formation that are associated with compact radio continuum sources, likely ultra-compact HII regions. It is concluded that the emission arises from the most luminous and distant water `kilomasers' detected so far. Our data increase the number of water maser detections in northern galaxies (Dec > -30 deg) with 100 micron IRAS point source fluxes > 50 Jy to 18%.Comment: 4 pages including 3 figures, accepted for publication in A&A Lette

DOMAIN WALLS IN THE QUANTUM TRANSVERSE ISING MODEL

We discuss several problems concerning domain walls in the spin $S$ Ising model at zero temperature in a magnetic field, $H/(2S)$, applied in the $x$ direction. Some results are also given for the planar ($y$-$z$) model in a transverse field. We treat the quantum problem in one dimension by perturbation theory at small $H$ and numerically over a large range of $H$. We obtain the spin density profile by fixing the spins at opposite ends of the chain to have opposite signs of $S_z$. One dimension is special in that there the quantum width of the wall is proportional to the size $L$ of the system. We also study the quantitative features of the `particle' band which extends up to energies of order $H$ above the ground state. Except for the planar limit, this particle band is well separated from excitations having energy $J/S$ involving creation of more walls. At large $S$ this particle band develops energy gaps and the lowest sub-band has tunnel splittings of order $H2^{1-2S}$. This scale of energy gives rise to anomalous scaling with respect to a) finite size, b) temperature, or c) random potentials. The intrinsic width of the domain wall and the pinning energy are also defined and calculated in certain limiting cases. The general conclusion is that quantum effects prevent the wall from being sharp and in higher dimension would prevent sudden excursions in the configuration of the wall.Comment: 40 pages and 13 figures, Phys. Rev. B, to be publishe