Non-BPS Solutions of the Noncommutative CP^1 Model in 2+1 Dimensions

We find non-BPS solutions of the noncommutative CP^1 model in 2+1 dimensions. These solutions correspond to soliton anti-soliton configurations. We show that the one-soliton one-anti-soliton solution is unstable when the distance between the soliton and the anti-soliton is small. We also construct time-dependent solutions and other types of solutions.Comment: 11 pages, minor correction

Plastic Flow in Two-Dimensional Solids

A time-dependent Ginzburg-Landau model of plastic deformation in two-dimensional solids is presented. The fundamental dynamic variables are the displacement field \bi u and the lattice velocity {\bi v}=\p {\bi u}/\p t. Damping is assumed to arise from the shear viscosity in the momentum equation. The elastic energy density is a periodic function of the shear and tetragonal strains, which enables formation of slips at large strains. In this work we neglect defects such as vacancies, interstitials, or grain boundaries. The simplest slip consists of two edge dislocations with opposite Burgers vectors. The formation energy of a slip is minimized if its orientation is parallel or perpendicular to the flow in simple shear deformation and if it makes angles of $\pm \pi/4$ with respect to the stretched direction in uniaxial stretching. High-density dislocations produced in plastic flow do not disappear even if the flow is stopped. Thus large applied strains give rise to metastable, structurally disordered states. We divide the elastic energy into an elastic part due to affine deformation and a defect part. The latter represents degree of disorder and is nearly constant in plastic flow under cyclic straining.Comment: 16pages, Figures can be obtained at http://stat.scphys.kyoto-u.ac.jp/index-e.htm

Non-Gaussianity from Inflation

Correlated adiabatic and isocurvature perturbation modes are produced during inflation through an oscillation mechanism when extra scalar degrees of freedom other than the inflaton field are present. We show that this correlation generically leads to sizeable non-Gaussian features both in the adiabatic and isocurvature perturbations. The non-Gaussianity is first generated by large non-linearities in some scalar sector and then efficiently transferred to the inflaton sector by the oscillation process. We compute the cosmic microwave background angular bispectrum, providing a characteristic feature of such inflationary non-Gaussianity,which might be detected by upcoming satellite experiments.Comment: Revised version accepted for publication in Phys. Rev. D. 19 pages, LaTeX fil

Large Scale Structures in Kinetic Gravity Braiding Model That Can Be Unbraided

We study cosmological consequences of a kinetic gravity braiding model, which is proposed as an alternative to the dark energy model. The kinetic braiding model we study is characterized by a parameter n, which corresponds to the original galileon cosmological model for n=1. We find that the background expansion of the universe of the kinetic braiding model is the same as the Dvali-Turner's model, which reduces to that of the standard cold dark matter model with a cosmological constant (LCDM model) for n equal to infinity. We also find that the evolution of the linear cosmological perturbation in the kinetic braiding model reduces to that of the LCDM model for n=\infty. Then, we focus our study on the growth history of the linear density perturbation as well as the spherical collapse in the nonlinear regime of the density perturbations, which might be important in order to distinguish between the kinetic braiding model and the LCDM model when n is finite. The theoretical prediction for the large scale structure is confronted with the multipole power spectrum of the luminous red galaxy sample of the Sloan Digital Sky survey. We also discuss future prospects of constraining the kinetic braiding model using a future redshift survey like the WFMOS/SuMIRe PFS survey as well as the cluster redshift distribution in the South Pole Telescope survey.Comment: 41 pages, 20 figures; This version was accepted for publication in JCA

Crossover between Equilibrium and Shear-controlled Dynamics in Sheared Liquids

We present a numerical simulation study of a simple monatomic Lennard-Jones liquid under shear flow, as a function of both temperature and shear rate. By investigating different observables we find that i) It exists a line in the (temperature-shear) plane that sharply marks the boarder between an ``equilibrium'' and a ``shear-controlled'' region for both the dynamic and the thermodynamic quantities; and ii) Along this line the structural relaxation time, is proportional to the inverse shear rate, i.e. to the typical time-scale introduced by the shear flow. Above the line the liquid dynamics is unaffected by the shear flow, while below it both temperature and shear rate control the particle motion.Comment: 14 pages, 5 figure

Light Lambda-Lambda Hypernuclei and the Onset of Stability for Lambda-Xi Hypernuclei

New Faddeev-Yakubovsky calculations for light Lambda-Lambda hypernuclei are presented in order to assess the self consistency of the Lambda-Lambda hypernuclear binding-energy world data and the implied strength of the Lambda-Lambda interaction, in the wake of recent experimental reports on Lambda-Lambda-4H and Lambda-Lambda-6He. Using Gaussian soft-core simulations of Nijmegen one-boson-exchange model interactions, the Nijmegen soft-core model NSC97 simulations are found close to reproducing the recently reported binding energy of Lambda-Lambda-6He, but not those of other species. For stranger systems, Faddeev calculations of light Lambda-Xi hypernuclei, using a simulation of the strongly attractive Lambda-Xi interactions due to the same model, suggest that Lambda-Xi-6He marks the onset of nuclear stability for Xi hyperons.Comment: 5 pages, 3 postscript figures; fig.2 replaced, minor changes, accepted as Rapid Communication in PR

Simulating (electro)hydrodynamic effects in colloidal dispersions: smoothed profile method

Previously, we have proposed a direct simulation scheme for colloidal dispersions in a Newtonian solvent [Phys.Rev.E 71,036707 (2005)]. An improved formulation called the ``Smoothed Profile (SP) method'' is presented here in which simultaneous time-marching is used for the host fluid and colloids. The SP method is a direct numerical simulation of particulate flows and provides a coupling scheme between the continuum fluid dynamics and rigid-body dynamics through utilization of a smoothed profile for the colloidal particles. Moreover, the improved formulation includes an extension to incorporate multi-component fluids, allowing systems such as charged colloids in electrolyte solutions to be studied. The dynamics of the colloidal dispersions are solved with the same computational cost as required for solving non-particulate flows. Numerical results which assess the hydrodynamic interactions of colloidal dispersions are presented to validate the SP method. The SP method is not restricted to particular constitutive models of the host fluids and can hence be applied to colloidal dispersions in complex fluids

Brueckner Rearrangement Effects in Λ5^5_\LambdaHe and ΛΛ6^6_{\Lambda\Lambda}He

Rearrangement effects in light hypernuclei are investigated in the framework of the Brueckner theory. We can estimate without detailed numerical calculations that the energy of the $\alpha$-core is reduced by more than 2.5 MeV when the $\Lambda$ adheres to $^4$He to form $^5_\Lambda$He. Similar assessment of rearrangement contributions is essential to deduce the strength of $\Lambda\Lambda$ interaction from experimentally observed $\Delta B_{\Lambda\Lambda}$. The recently observed experimental value of $\sim$ 1 MeV for the $\Delta B_{\Lambda\Lambda}$ of \hll suggests that the matrix element of $$ in \hll is around -2 MeV.Comment: 7 pages, to appear in Phys. Rev.

Boson gas in a periodic array of tubes

We report the thermodynamic properties of an ideal boson gas confined in an infinite periodic array of channels modeled by two, mutually perpendicular, Kronig-Penney delta-potentials. The particle's motion is hindered in the x-y directions, allowing tunneling of particles through the walls, while no confinement along the z direction is considered. It is shown that there exists a finite Bose- Einstein condensation (BEC) critical temperature Tc that decreases monotonically from the 3D ideal boson gas (IBG) value $T_{0}$ as the strength of confinement $P_{0}$ is increased while keeping the channel's cross section, $a_{x}a_{y}$ constant. In contrast, Tc is a non-monotonic function of the cross-section area for fixed $P_{0}$. In addition to the BEC cusp, the specific heat exhibits a set of maxima and minima. The minimum located at the highest temperature is a clear signal of the confinement effect which occurs when the boson wavelength is twice the cross-section side size. This confinement is amplified when the wall strength is increased until a dimensional crossover from 3D to 1D is produced. Some of these features in the specific heat obtained from this simple model can be related, qualitatively, to at least two different experimental situations: $^4$He adsorbed within the interstitial channels of a bundle of carbon nanotubes and superconductor-multistrand-wires Nb$_{3}$Sn.Comment: 9 pages, 10 figures, submitte