Spectral density analysis of time correlation functions in lattice QCD using the maximum entropy method

We study various aspects of extracting spectral information from time correlation functions of lattice QCD by means of Bayesian inference with an entropic prior, the maximum entropy method (MEM). Correlator functions of a heavy-light meson-meson system serve as a repository for lattice data with diverse statistical quality. Attention is given to spectral mass density functions, inferred from the data, and their dependence on the parameters of the MEM. We propose to employ simulated annealing, or cooling, to solve the Bayesian inference problem, and discuss practical issues of the approach.Comment: 11 pages, 30 figure files (eps), some references added and updated, requires REVTeX 4.0 and prerequisites (AMS-LaTeX 2.0, graphicx, dcolumn, bm) see http://publish.aps.org/revtex4

Coupling between magnetic ordering and structural instabilities in perovskite biferroics: A first-principles study

We use first-principles density functional theory-based calculations to investigate structural instabilities in the high symmetry cubic perovskite structure of rare-earth (R $=$ La, Y, Lu) and Bi-based biferroic chromites, focusing on $\Gamma$ and $R$ point phonons of states with para-, ferro-, and antiferromagnetic ordering. We find that (a) the structure with G-type antiferromagnetic ordering is most stable, (b) the most dominant structural instabilities in these oxides are the ones associated with rotations of oxygen octahedra, and (c) structural instabilities involving changes in Cr-O-Cr bond angle depend sensitively on the changes in magnetic ordering. The dependence of structural instabilities on magnetic ordering can be understood in terms of how super-exchange interactions depend on the Cr-O-Cr bond angles and Cr-O bond lengths. We demonstrate how adequate buckling of Cr-O-Cr chains can favour ferromagnetism. Born effective charges (BEC) calculated using the Berry phase expression are found to be anomalously large for the A-cations, indicating their chemical relevance to ferroelectric distortions.Comment: 8 pages, 13 figure

Monopoles, confinement and the photon propagator in QED3_3

We study the lattice gauge boson propagator of 3D compact QED in Landau gauge at zero and non-zero temperature. Non-perturbative effects are reflected by the generation of a mass $m$, by an anomalous dimension $\alpha$ and by the photon wave function renormalisation $Z$. These effects can be attributed to monopoles: they are absent in the propagator of the regular part of the gauge field. The r\^ole of Gribov copies is carefully investigated.Comment: 3 pages, 5 figures, Lattice2002(topology

Incipient ferroelectricity in 2.3% tensile-strained CaMnO3 films

Epitaxial CaMnO3 films grown with 2.3% tensile strain on (001)-oriented LaAlO3 substrates are found to be incipiently ferroelectric below 25 K. Optical second harmonic generation (SHG) was used for the detection of the incipient polarization. The SHG analysis reveals that CaMnO3 crystallites with in-plane orientation of the orthorhombic b axis contribute to an electric polarization oriented along the orthorhombic a (resp.\ c) axis in agreement with the predictions from density functional calculations

OH(1720 MHz) Masers As Signposts of Molecular Shocks

We present observations of molecular gas made with the 15-m James Clark Maxwell Telescope toward the sites of OH(1720 MHz) masers in three supernova remnants: W28, W44 and 3C391. Maps made in the 12CO J=3-2 line reveal that the OH masers are preferentially located along the edges of thin filaments or clumps of molecular gas. There is a strong correlation between the morphology of the molecular gas and the relativistic gas traced by synchrotron emission at centimeter wavelengths. Broad CO line widths (dV=30-50 km/s) are seen along these gaseous ridges, while narrow lines are seen off the ridges. The ratio of H2CO line strengths is used to determine temperatures in the broad-line gas of 80 K, and the 13CO J=3-2 column density suggests densities of 10^4-10^5 cm{-3}. These observations support the hypothesis that the OH(1720 MHz) masers originate in post-shock gas, heated by the passage of a supernova remnant shock through dense molecular gas. From the observational constraints on the density, velocity and magnetic field we examine the physical properties of the shock and discuss the shock-production of OH. These OH(1720 MHz) masers are useful ``signposts'', which point to the most promising locations to study supernova remnant/molecular cloud interactions.Comment: ApJ (in press

Symmetry Considerations for the Detection of Second-Harmonic Generation in Cuprates in the Pseudogap phase

A proposal to test the proposed time-reversal and inversion breaking phase in the Pseudogap region of the Cuprate compounds through the variation of Second-harmonic generation intensity with temperature and polarization and angle of incidence is presented.Comment: 7 pages, 2 figures include

Symmetry Analysis of Second Harmonic Generation at Surfaces of Antiferromagnets

Using group theory we classify the nonlinear magneto-optical response at low-index surfaces of fcc antiferromagnets, such as NiO. Structures consisting of one atomic layer are discussed in detail. We find that optical second harmonic generation is sensitive to surface antiferromagnetism in many cases. We discuss the influence of a second type of magnetic atoms, and also of a possible oxygen sublattice distortion on the output signal. Finally, our symmetry analysis yields the possibility of antiferromagnetic surface domain imaging even in the presence of magnetic unit-cell doubling.Comment: 23 pages, 10 figures incorporated. Accepted to Phys. Rev. B, scheduled for July'9

Polarization of Astronomical Maser Radiation. IV. Circular Polarization Profiles

Profile comparison of the Stokes parameters $V$ and $I$ is a powerful tool for maser data analysis, providing the first direct methods for unambiguous determination of (1) the maser saturation stage, (2) the amplification optical depth and intrinsic Doppler width of unsaturated masers, and (3) the comparative magnitudes of Zeeman splitting and Doppler linewidth. Circular polarization recently detected in OH 1720 MHz emission from the Galactic center appears to provide the first direct evidence for maser saturation.Comment: 14 pages, 1 Postscript figures (included), uses aaspp4.sty. To appear in Astrophysical Journa

Chromosomal Localization of the Carcinoembryonic Antigen Gene Family and Differential Expression in Various Tumors

Carcinoembryonic antigen (CEA) is a glycoprotein which is important as a tumor marker for a number of human cancers. It is a member of a gene family comprising about 10 closely related genes. In order to characterize mUNAs transcribed from individual genes we have identified by DNA and RNA hybridization experiments, gene-specific sequences from the 3 ' noncoding regions of CEA, and of nonspecific cross-reacting antigen (NCA) mRNAs, which have been recently cloned. With these probes, CEA mRNAs with lengths of 3.5 and 3.0 kilobases and an NCA mRNA species of 2.5 kilobases were identified in various human tumors. A 2.2-kilobase mRNA species, however, could only be detected in leu kocytes of patients with chronic myeloid leukemia by hybridization with a probe from the immunoglobulin-like repeat domain of CEA. This region is known to be very similar among the various members of the CEA gene family, and indeed the probe hybridizes with all four mRNA species. In situ hybridization with a cross-hybridizing probe from the NCA gene localized the members of the CEA gene family to the short and to the long arm of chromosome 19. In addition, a CEA cDNA probe was found to hybridize to the long arm of chromosome 19 only