Scaling property and peculiar velocity of global monopoles

We investigate the scaling property of global monopoles in the expanding universe. By directly solving the equations of motion for scalar fields, we follow the time development of the number density of global monopoles in the radiation dominated (RD) universe and the matter dominated (MD) universe. It is confirmed that the global monopole network relaxes into the scaling regime and the number per hubble volume is a constant irrespective of the cosmic time. The number density $n(t)$ of global monopoles is given by $n(t) \simeq (0.43\pm0.07) / t^{3}$ during the RD era and $n(t) \simeq (0.25\pm0.05) / t^{3}$ during the MD era. We also examine the peculiar velocity $v$ of global monopoles. For this purpose, we establish a method to measure the peculiar velocity by use of only the local quantities of the scalar fields. It is found that $v \sim (1.0 \pm 0.3)$ during the RD era and $v \sim (0.8 \pm 0.3)$ during the MD era. By use of it, a more accurate analytic estimate for the number density of global monopoles is obtained.Comment: 17 pages, 8 figures, to appear in Phys. Rev.

Anomalous Dimensions from a Spinning D5-Brane

We consider the anomalous dimension of a certain twist two operator in N=4 super Yang-Mills theory. At strong coupling and large-N it is captured by the classical dynamics of a spinning D5-brane. The present calculation generalizes the result of Gubser, Klebanov and Polyakov (hep-th/0204051): in order to calculate the anomalous dimension of a bound state of k coincident strings, the spinning closed string is replaced by a spinning D5 brane that wraps an S4 inside the S5 part of the AdS5 times S5 metric.Comment: 8 pages, LaTex. v2: figure added. minor changes. To appear in JHE

Exotic mesons with double charm and bottom flavor

We study exotic mesons with double charm and bottom flavor, whose quark configuration is \bar{Q}\bar{Q}qq. This quark configuration has no annihilation process of quark and antiquark, and hence is a genuinely exotic states. We take a hadronic picture by considering the molecular states composed of a pair of heavy mesons, such as DD, DD* and D*D* for charm flavor, and BB, BB* and B*B* for bottom flavor. The interactions between heavy mesons are derived from the heavy quark effective theory. All molecular states are classified by I(J^P) quantum numbers, and are systematically studied up to the total angular momentum J \leq 2. By solving the coupled channel Schrodinger equations, due to the strong tensor force of one pion exchanging, we find bound and/or resonant states of various quantum numbers.Comment: 24 pages, 3 figure

Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: acetonitrile in water, methanol in water, and methanol in acetonitrile

We present results of theoretical study and numerical calculation of the dynamics of molecular liquids based on combination of the memory equation formalism and the reference interaction site model - RISM. Memory equations for the site-site intermediate scattering functions are studied in the mode-coupling approximation for the first order memory kernels, while equilibrium properties such as site-site static structure factors are deduced from RISM. The results include the temperature-density(pressure) dependence of translational diffusion coefficients D and orientational relaxation times t for acetonitrile in water, methanol in water and methanol in acetonitrile, all in the limit of infinite dilution. Calculations are performed over the range of temperatures and densities employing the SPC/E model for water and optimized site-site potentials for acetonitrile and methanol. The theory is able to reproduce qualitatively all main features of temperature and density dependences of D and t observed in real and computer experiments. In particular, anomalous behavior, i.e. the increase in mobility with density, is observed for D and t of methanol in water, while acetonitrile in water and methanol in acetonitrile do not show deviations from the ordinary behavior. The variety exhibited by the different solute-solvent systems in the density dependence of the mobility is interpreted in terms of the two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions which, respectively, increase and decrease with increasing density.Comment: 13 pages, 8 eps-figures, 3 tables, RevTeX4-forma

Evolution of superconductivity by oxygen annealing in FeTe0.8S0.2

Oxygen annealing dramatically improved the superconducting properties of solid-state-reacted FeTe0.8S0.2, which showed only a broad onset of superconducting transition just after the synthesis. The zero resistivity appeared and reached 8.5 K by the oxygen annealing at 200\degree C. The superconducting volume fraction was also enhanced from 0 to almost 100%. The lattice constants were compressed by the oxygen annealing, indicating that the evolution of bulk superconductivity in FeTe0.8S0.2 was correlated to the shrinkage of lattice.Comment: 13 pages, 6 figure

Competition between ferromagnetism and spin glass: the key for large magnetoresistance in oxygen deficient perovskites SrCo1-xMxO3-d (M = Nb, Ru)

The magnetic and magnetotransport properties of the oxygen deficient perovskites, SrCo1-xMxO3-d with M = Nb and Ru, were investigated. Both Nb- and Ru-substituted cobaltites are weak ferromagnets, with transition temperatures Tm of 130-150 K and 130-180 K, respectively, and both exhibit a spin glass behavior at temperatures below Tf = 80-90 K. It is demonstrated that there exists a strong competition between ferromagnetism and spin glass state, where Co4+ induces ferromagnetism, whereas Nb or Ru substitution at the cobalt sites induces magnetic disorder, and this particular magnetic behavior is the origin of large negative magnetoresistance of these oxides, reaching up to 30% at 5 K in 7 T. The differences between Nb- and Ru-substituted cobaltites are discussed on the basis of the different electronic configuration of niobium and ruthenium cations.Comment: 32 pages, 9 figures, to appear in Phys. Rev.

Evolution of a global string network in a matter dominated universe

We evolve the network of global strings in the matter-dominated universe by means of numerical simulations. The existence of the scaling solution is confirmed as in the radiation-dominated universe but the scaling parameter $\xi$ takes a slightly smaller value, $\xi \simeq 0.6 \pm 0.1$, which is defined as $\xi = \rho_{s} t^{2} / \mu$ with $\rho_{s}$ the energy density of global strings and $\mu$ the string tension per unit length. The change of $\xi$ from the radiation to the matter-dominated universe is consistent with that obtained by Albrecht and Turok by use of the one-scale model. We also study the loop distribution function and find that it can be well fitted with that predicted by the one-scale model, where the number density $n_{l}(t)$ of the loop with the length $l$ is given by $n_{l}(t) = \nu/[t^2 (l + \kappa t)^2]$ with $\nu \sim 0.040$ and $\kappa \sim 0.48$. Thus, the evolution of the global string network in the matter-dominated universe can be well described by the one-scale model as in the radiation-dominated universe.Comment: 10 pages, 5 figure

Symmetry of high-piezoelectric Pb-based complex perovskites at the morphotropic phase boundary II. Theoretical treatment

The structural characteristics of the perovskite- based ferroelectric Pb(Zn1/3Nb2/3)O3-9%PbTiO3 at the morphotropic phase boundary (MPB) region (x≃0.09) have been analyzed. The analysis is based on the symmetry adapted free energy functions under the assumption that the total polarization and the unit cell volume are conserved during the transformations between various morphotropic phases. Overall features of the relationships between the observed lattice constants at various conditions have been consistently explained. The origin of the anomalous physical properties at MPB is discussed