Dynamic Structure Factor of Normal Fermi Gas from Collisionless to Hydrodynamic Regime

The dynamic structure factor of a normal Fermi gas is investigated by using the moment method for the Boltzmann equation. We determine the spectral function at finite temperatures over the full range of crossover from the collisionless regime to the hydrodynamic regime. We find that the Brillouin peak in the dynamic structure factor exhibits a smooth crossover from zero to first sound as functions of temperature and interaction strength. The dynamic structure factor obtained using the moment method also exhibits a definite Rayleigh peak ($/omega /sim 0$), which is a characteristic of the hydrodynamic regime. We compare the dynamic structure factor obtained by the moment method with that obtained from the hydrodynamic equations.Comment: 19 pages, 9 figure

Relaxation Mechanism for Ordered Magnetic Materials

We have formulated a relaxation mechanism for ferrites and ferromagnetic metals whereby the coupling between the magnetic motion and lattice is based purely on continuum arguments concerning magnetostriction. This theoretical approach contrasts with previous mechanisms based on microscopic formulations of spin-phonon interactions employing a discrete lattice. Our model explains for the first time the scaling of the intrinsic FMR linewidth with frequency, and 1/M temperature dependence and the anisotropic nature of magnetic relaxation in ordered magnetic materials, where M is the magnetization. Without introducing adjustable parameters our model is in reasonable quantitative agreement with experimental measurements of the intrinsic magnetic resonance linewidths of important class of ordered magnetic materials, insulator or metals

Vector order parameter in general relativity. Covariant equations

Phase transitions with spontaneous symmetry breaking and vector order parameter are considered in multidimensional theory of general relativity. Covariant equations, describing the gravitational properties of topological defects, are derived. The topological defects are classified in accordance with the symmetry of the covariant derivative of the vector order parameter. The abilities of the derived equations are demonstrated in application to the brane world concept. New solutions of the Einstein equations with a transverse vector order parameter are presented. In the vicinity of phase transition the solutions are found analytically

Tunable pinning of a superconducting vortex a by a magnetic vortex

The interaction between a straight vortex line in a superconducting film and a soft magnetic nanodisk in the magnetic vortex state in the presence of a magnetic field applied parallel to the film surfaces is studied theoretically. The superconductor is described by London theory and the nanodisk by the Landau-Lifshitz continuum theory of magnetism, using the approximation known as the rigid vortex model. Pinning of the vortex line by the nanodisk is found to result, predominantly, from the interaction between the vortex line and the changes in the nanodisk magnetization induced by the magnetic field of the vortex line and applied field. In the context of the rigid vortex model, these changes result from the displacement of the magnetic vortex. This displacement is calculated analytically by minimizing the energy, and the pinning potential is obtained. The applied field can tune the pinning potential by controlling the displacement of the magnetic vortex. The nanodisk magnetization curve is predicted to change in the presence of the vortex lineComment: 9 pages, 8 figures. Submitted to Phys. Rev.

Surprises in nonperturbative dynamics in sigma-model at finite density

The linear $SU(2)_L \times SU(2)_R$ sigma-model occupies a unique place in elementary particle physics and quantum field theory. It has been recently realized that when a chemical potential for hypercharge is added, it becomes a toy model for the description of the dynamics of the kaon condensate in high density QCD. We review recent results in nonperturbative dynamics obtained in the ungauged and gauged versions of this model.Comment: Brief review. 16 pages, 5 figure

Unified approach to structure factors and neutrino processes in nucleon matter

We present a unified approach to neutrino processes in nucleon matter based on Landau's theory of Fermi liquids that includes one- and two-quasiparticle-quasihole pair states as well as mean-field effects. We show how rates of neutrino processes involving two nucleons may be calculated in terms of the collision integral in the Landau transport equation for quasiparticles. Using a relaxation time approximation, we solve the transport equation for density and spin-density fluctuations and derive a general form for the response functions. We apply our approach to neutral-current processes in neutron matter, where the spin response function is crucial for calculations of neutrino elastic and inelastic scattering, neutrino-pair bremsstrahlung and absorption from strongly-interacting nucleons. We calculate the relaxation rates using modern nuclear interactions and including many-body contributions, and find that rates of neutrino processes are reduced compared with estimates based on the one-pion exchange interaction, which is used in current simulations of core-collapse supernovae.Comment: 16 pages, 4 figures; NORDITA-2008-30; published versio

Microwave Response and Spin Waves in Superconducting Ferromagnets

Excitation of spin waves is considered in a superconducting ferromagnetic slab with the equilibrium magnetization both perpendicular and parallel to the surface. The surface impedance is calculated and its behavior near propagation thresholds is analyzed. Influence of non-zero magnetic induction at the surface is considered in various cases. The results provide a basis for investigation of materials with coexisting superconductivity and magnetism by microwave response measurements.Comment: 10 pages, 7 figure

Temperature-dependent resistivity of suspended graphene

In this paper we investigate the electron-phonon contribution to the resistivity of suspended single layer graphene. In-plane as well as flexural phonons are addressed in different temperature regimes. We focus on the intrinsic electron-phonon coupling due to the interaction of electrons with elastic deformations in the graphene membrane. The competition between screened deformation potential vs fictitious gauge field coupling is discussed, together with the role of tension in the suspended flake. In the absence of tension, flexural phonons dominate the phonon contribution to the resistivity at any temperature $T$ with a $T^{5/2}_{}$ and $T^{2}_{}$ dependence at low and high temperatures, respectively. Sample-specific tension suppresses the contribution due to flexural phonons, yielding a linear temperature dependence due to in-plane modes. We compare our results with recent experiments.Comment: 11 pages, 3 figure

Temperature dependence of the spin susceptibility of a clean Fermi gas with repulsion

Spin susceptibility of a clean Fermi gas with repulsion in any dimension is considered using a supersymmetric low energy theory of interacting spin excitations and renormalization scheme recently proposed by Aleiner and Efetov [cond-mat/0602309]. We generalize this method to include the coupling to the magnetic field. As a result, we obtain for the correction $\delta \chi$ to the Pauli susceptibility a non-analytic temperature dependence of the form $T^{d-1}\gamma_{b}^{2}(T)$ in dimensions $d=2,3,$ where $\gamma_{b}(T)$ is an effective $d$-dependent logarithmically renormalized backscattering amplitude. In one dimension, $\delta \chi$ is proportional to $\gamma_{b}(T)$, and we reproduce a well known result obtained long ago by a direct calculation.Comment: 25 pages, 10 figure

Quarkonia and Quark Drip Lines in Quark-Gluon Plasma

We extract the $Q$-$\bar Q$ potential by using the thermodynamic quantities obtained in lattice gauge calculations. The potential is tested and found to give dissociation temperatures that agree well with those from lattice gauge spectral function analysis. Using such a $Q$-$\bar Q$ potential, we examine the quarkonium states in a quark-gluon plasma and determine the `quark drip lines' which separate the region of bound color-singlet $Q\bar Q$ states from the unbound region. The characteristics of the quark drip lines severely limit the region of possible bound $Q\bar Q$ states with light quarks to temperatures close to the phase transition temperature. Bound quarkonia with light quarks may exist very near the phase transition temperature if their effective quark mass is of the order of 300-400 MeV and higher.Comment: 24 pages, 13 figures, in LaTe