Density matrix renormalization group study of optical conductivity in the one-dimensional Mott insulator Sr_2CuO_3

Applying newly developed dynamical density matrix renormalization group techniques at zero and finite temperatures to a Hubbard-Holstein model at half-filling, we examine the optical conductivity of a typical one-dimensional Mott insulator Sr_2CuO_3. We find a set of parameters in the Hubbard-Holstein model, which can describe optical conductivity for both Mott-gap excitation in the high-energy region and phonon-assisted spin excitation in the low-energy region. We also find that electron-phonon interaction gives additional broadening in the temperature dependence of the Mott-gap excitation.Comment: 5 pages, 3figure

Non-axial Octupole Deformations of N=Z Nuclei in A∼60−80A \sim 60-80 Mass Region

By performing a fully three dimensional Hartree-Fock calculation with use of the Skyrm forces, we demonstrate possibility of exotic deformations violating both the reflection and the axial symmetries of N=Z nuclei in $A \sim 60-80$ mass region. The \Ytwo tetrahedral shape predicted in excited \Zr arises from a shell gap at $N,Z = 40$ which is enhanced for the tetrahedron deformation. Softness toward the \Ythree triangular deformation of the oblate state in \Se is also predicted.Comment: 10 page

Interaction and Localization of One-electron Orbitals in an Organic Molecule: Fictitious Parameter Analysis for Multi-physics Simulations

We present a new methodology to analyze complicated multi-physics simulations by introducing a fictitious parameter. Using the method, we study quantum mechanical aspects of an organic molecule in water. The simulation is variationally constructed from the ab initio molecular orbital method and the classical statistical mechanics with the fictitious parameter representing the coupling strength between solute and solvent. We obtain a number of one-electron orbital energies of the solute molecule derived from the Hartree-Fock approximation, and eigenvalue-statistical analysis developed in the study of nonintegrable systems is applied to them. Based on the results, we analyze localization properties of the electronic wavefunctions under the influence of the solvent.Comment: 4 pages, 5 figures, the revised version will appear in J. Phys. Soc. Jpn. Vol.76 (No.1

Origin of spatial variation of pairing gap in Bi-based high-Tc cuprates

Recently, scanning tunneling microscopy on Bi-2212 cuprate superconductor has revealed a spatial variation of the energy gap that is directly correlated with a modulation of the apical oxygen position. We identify two mechanisms by which out-of-plane oxygens can modulate the pairing interaction within the CuO_2 layer: a covalency between the x^2-y^2 band and apical p-orbital, and a screening of correlation U by apical oxygen polarization. Both effects strongly depend on the apical oxygen position and their cooperative action explains the experiment.Comment: 4 pages, 3 figures, revised version to appear in PR

Enhanced Pairing Correlations near Oxygen Dopants in Cuprate Superconductors

Recent experiments on Bi-based cuprate superconductors have revealed an unexpected enhancement of the pairing correlations near the interstitial oxygen dopant ions. Here we propose a possible mechanism -- based on local screening effects -- by which the oxygen dopants do modify the electronic parameters within the CuO_2 planes and strongly increase the superexchange coupling J. This enhances the spin pairing effects locally and may explain the observed spatial variations of the density of states and the pairing gap.Comment: 4 pages, 4 figures, minor revisions, to appear in PR

Neutron-star Radius from a Population of Binary Neutron Star Mergers

We show how gravitational-wave observations with advanced detectors of tens to several tens of neutron-star binaries can measure the neutron-star radius with an accuracy of several to a few percent, for mass and spatial distributions that are realistic, and with none of the sources located within 100 Mpc. We achieve such an accuracy by combining measurements of the total mass from the inspiral phase with those of the compactness from the postmerger oscillation frequencies. For estimating the measurement errors of these frequencies we utilize analytical fits to postmerger numerical-relativity waveforms in the time domain, obtained here for the first time, for four nuclear-physics equations of state and a couple of values for the mass. We further exploit quasi-universal relations to derive errors in compactness from those frequencies. Measuring the average radius to well within 10% is possible for a sample of 100 binaries distributed uniformly in volume between 100 and 300 Mpc, so long as the equation of state is not too soft or the binaries are not too heavy.Comment: 9 pages and 7 figure

Host redshifts from gravitational-wave observations of binary neutron star mergers

Inspiralling compact binaries as standard sirens will soon become an invaluable tool for cosmology when advanced interferometric gravitational-wave detectors begin their observations in the coming years. However, a degeneracy in the information carried by gravitational waves between the total rest-frame mass $M$ and the redshift $z$ of the source implies that neither can be directly extracted from the signal, but only the combination $M(1+z)$, the redshifted mass. Recent work has shown that for binary neutron star systems, a tidal correction to the gravitational-wave phase in the late-inspiral signal that depends on the rest-frame source mass could be used to break the mass-redshift degeneracy. We propose here to use the signature encoded in the post-merger signal to deduce the redshift to the source. This will allow an accurate extraction of the intrinsic rest-frame mass of the source, in turn permitting the determination of source redshift and luminosity distance solely from gravitational-wave observations. This will herald a new era in precision cosmography and astrophysics. Using numerical simulations of binary neutron star mergers of very slightly different mass, we model gravitational-wave signals at different redshifts and use Bayesian parameter estimation to determine the accuracy with which the redshift can be extracted for a source of known mass. We find that the Einstein Telescope can determine the source redshift to $sim 10$--$20$ at redshifts of $z<0.04$.Comment: 10 pages, 4 figures; same as the version before except for acknowledgment

Radiative impact of mixing state of black carbon aerosol in Asian outflow

The radiative impact of the mixing state of black carbon (BC) aerosol is investigated in Asian outflow. The mixing state and size distribution of BC aerosol were measured with a ground-based single-particle soot photometer at a remote island (Fukue) in Japan in spring 2007. The mass concentration of BC in Asian continental air masses reached 0.5 μg m-3, with a mass median diameter of 200-220 nm. The median value of the shell/core diameter ratio increased to ∼1.6 in Asian continental and maritime air masses with a core diameter of 200 mn, while in free tropospheric and Japanese air masses it was 1.3-1.4. On the basis of theoretical calculations using the size distribution and mixing state of BC aerosol, scattering and absorption properties of PM1 aerosols were calculated under both dry and ambient conditions, considering the hygroscopic growth of aerosols. It was estimated that internal mixing enhanced the BC absorption by a factor of 1.5-1.6 compared to external mixing. The calculated absorption coefficient was 2-3 times higher in Asian continental air masses than in clean air. Coatings reduced the single-scattering albedo (SSA) of PM1 aerosol by 0.01 -0.02, which indicates the importance of the mixing state of BC aerosol in evaluating its radiative influence. The SSA was sensitive to changes in air mass type, with a value of ∼0.98 in Asian continental air masses and ∼0.95 in Japanese and free tropospheric air masses under ambient conditions. Copyright 2008 by the American Geophysical Union

A quasi-radial stability criterion for rotating relativistic stars

The stability properties of relativistic stars against gravitational collapse to black hole is a classical problem in general relativity. A sufficient criterion for secular instability was established by Friedman, Ipser and Sorkin (1988), who proved that a sequence of uniformly rotating barotropic stars is secularly unstable on one side of a turning point and then argued that a stronger result should hold: that the sequence should be stable on the opposite side, with the turning point marking the onset of secular instability. We show here that this expectation is not met. By computing in full general relativity the $F$-mode frequency for a large number of rotating stars, we show that the neutral-stability point, i.e., where the frequency becomes zero, differs from the turning point for rotating stars. Using numerical simulations we validate that the new criterion can be used to assess the dynamical stability of relativistic rotating stars