p-Wave Resonant Bose Gas: A Finite-Momentum Spinor Superfluid

We show that a degenerate gas of two-species bosonic atoms interacting through a p-wave Feshbach resonance (as realized in, e.g., a 85Rb-87Rb mixture) exhibits a finite-momentum atomic-molecular superfluid (AMSF), sandwiched by a molecular p-wave (orbital spinor) superfluid and by an s-wave atomic superfluid at large negative and positive detunings, respectively. The magnetic field can be used to tune the modulation wave vector of the AMSF state, as well as to drive quantum phase transitions in this rich system.Comment: updated version published in PRL, with minor typos correcte

Thermodynamics of Finite-Momentum States : From Degenerate Atomic Gases to Helical Magnets

We present a theoretical study of finite momentum states in the context of degenerate gases and iron-based magnet. The unifying theme of these seemingly disparate states of condensed matter is the finite momentum of their respective grounds states and the associated enhanced fluctuations. For the degenerate atomic gases, we study in the first part of the thesis a system of two species of bosonic atoms interacting through a p-wave Feshbach resonance as realized in Rubidium-85/ Rubidium-87 mixture. In mapping out the phase diagram, we show that the system exhibits atomic (ASF), molecular (MSF) and atomic-molecular (AMSF) superfluid phases, where atoms, molecules, and atoms and molecules Bose condense, respectively. The ASF and MSF states are respectively characterized by a nonzero s-wave atomic and p-wave (orbital) spinor molecular condensates. The AMSF is distinguished by the presence of both of these condensates, with the s-wave atomic condensate component necessarily periodically modulated at a wavevector that is tunable with a magnetic field; that is, generically AMSF is a robust supersolid, that simultaneously breaks spatial translational and gauge symmetries. We explore the rich phenomenology of these phases and phase transitions between them, that we find to be strongly influenced by the quantum and thermal fluctuations. In the second part of the thesis, we study magnetism in Fe1+yTe, a parent compound of the iron-based high-temperature superconductors. Motivated by earlier studies that have provided evidences of finite momentum spiral states in these materials, we show that a spin-1 exchange model, supplemented by a single-ion anisotropy accounts well for the experimentally observed mag- netic phase diagram, that prominently exhibits commensurate bi-collinear and incommensurate spin-spiral orders with the associated low-energy spin-wave spectra. We derive the low energy hy- drodynamic models for these magnetic states and use it to describe the magneto-structural and commensurate-incommensurate transitions, and the static and dynamic structure functions across temperature - Fe doping phase diagram

A Second-order bias model for the Logarithmic Halo Mass Density

We present an analytic model for the local bias of dark matter halos in a LCDM universe. The model uses the halo mass density instead of the halo number density and is searched for various halo mass cuts, smoothing lengths, and redshift epoches. We find that, when the logarithmic density is used, the second-order polynomial can fit the numerical relation between the halo mass distribution and the underlying matter distribution extremely well. In this model the logarithm of the dark matter density is expanded in terms of log halo mass density to the second order. The model remains excellent for all halo mass cuts (from M_{cut}=3\times10^{11}$to$3\times10^{12}h^{-1}M_{\odot}$), smoothing scales (from$R=5h^{-1}$Mpc to$50h^{-1}$Mpc), and redshift ranges (from z=0 to 1.0) considered in this study. The stochastic term in the relation is found not entirely random, but a part of the term can be determined by the magnitude of the shear tensor.Comment: 8 pages, 7 figures, accepted for publication on Ap

Topology of Luminous Red Galaxies from the Sloan Digital Sky Survey

We present measurements of the genus topology of luminous red galaxies (LRGs) from the Sloan Digital Sky Survey (SDSS) Data Release 7 catalog, with unprecedented statistical significance. To estimate the uncertainties in the measured genus, we construct 81 mock SDSS LRG surveys along the past light cone from the Horizon Run 3, one of the largest N-body simulations to date that evolved 7210^3 particles in a 10815 Mpc/h size box. After carefully modeling and removing all known systematic effects due to finite pixel size, survey boundary, radial and angular selection functions, shot noise and galaxy biasing, we find the observed genus amplitude to reach 272 at 22 Mpc/h smoothing scale with an uncertainty of 4.2%; the estimated error fully incorporates cosmic variance. This is the most accurate constraint of the genus amplitude to date, which significantly improves on our previous results. In particular, the shape of the genus curve agrees very well with the mean topology of the SDSS LRG mock surveys in the LCDM universe. However, comparison with simulations also shows small deviations of the observed genus curve from the theoretical expectation for Gaussian initial conditions. While these discrepancies are mainly driven by known systematic effects such as those of shot noise and redshift-space distortions, they do contain important cosmological information on the physical effects connected with galaxy formation, gravitational evolution and primordial non-Gaussianity. We address here the key role played by systematics on the genus curve, and show how to accurately correct for their effects to recover the topology of the underlying matter. In a forthcoming paper, we provide an interpretation of those deviations in the context of the local model of non-Gaussianity.Comment: 23 pages, 18 figures. APJ Supplement Series 201

Numerical model of journal bearing lubrication considering a bending stiffness effect

An analysis for operating characteristics of journal bearing lubrication system is performed based on the numerical model. Dynamic bearing lubrication characteristics such as oil film pressure and thickness distribution can be analyzed through a numerical model with an integration of elastohydrodynamics and multi-flexible-body dynamics (MFBD). In particular, the oil film thickness variation by elastic deformation is considered in the elastohydrodynamic analysis by applying the bending stiffness effect of journal. And the oil film thickness variation by the bending stiffness effect is applied to the fluid governing equations to calculate the oil film pressure in the elastohydrodynamic lubrication region. A series of process proposed in this study is available for the analysis of realistic elastohydrodynamic lubrication phenomenon. Also, a numerical example for the journal bearing lubrication system is demonstrated and compared with the experimental results. The numerical results considering the bending stiffness effect show a good agreement with the experimental results