A heuristic approach to the weakly interacting Bose gas

Some thermodynamic properties of weakly interacting Bose systems are derived from dimensional and heuristic arguments and thermodynamic relations, without resorting to statistical mechanics

Generalized Emission Functions for Photon Emission from Quark-Gluon Plasma

The Landau-Pomeranchuk-Migdal effects on photon emission from the quark gluon plasma have been studied as a function of photon mass, at a fixed temperature of the plasma. The integral equations for the transverse vector function (${\bf \tilde{f}(\tilde{p}_\perp)}$) and the longitudinal function ($\tilde{g}({\bf \tilde{p}_\perp})$) consisting of multiple scattering effects are solved by the self consistent iterations method and also by the variational method for the variable set \{$p_0,q_0,Q^2$\}, considering the bremsstrahlung and the $\bf aws$ processes. We define four new dynamical scaling variables, $x^b_T$,$x^a_T$,$x^b_L$,$x^a_L$ for bremsstrahlung and {\bf aws} processes and analyse the transverse and longitudinal components as a function of \{$p_0,q_0,Q^2$\}. We generalize the concept of photon emission function and we define four new emission functions for massive photon emission represented by $g^b_T$, $g^a_T$, $g^b_L$, $g^a_L$. These have been constructed using the exact numerical solutions of the integral equations. These four emission functions have been parameterized by suitable simple empirical fits. In terms of these empirical emission functions, the virtual photon emission from quark gluon plasma reduces to one dimensional integrals that involve folding over the empirical $g^{b,a}_{T,L}$ functions with appropriate quark distribution functions and the kinematic factors. Using this empirical emission functions, we calculated the imaginary part of the photon polarization tensor as a function of photon mass and energy.Comment: In nuclear physics journals and arxiv listings, my name used to appear as S.V.S. Sastry. Hereafter, my name will appear as, S.V. Suryanarayan

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

Phenomenological Analysis of pppp and pˉp\bar{p}p Elastic Scattering Data in the Impact Parameter Space

We use an almost model-independent analytical parameterization for $pp$ and $\bar{p}p$ elastic scattering data to analyze the eikonal, profile, and inelastic overlap functions in the impact parameter space. Error propagation in the fit parameters allows estimations of uncertainty regions, improving the geometrical description of the hadron-hadron interaction. Several predictions are shown and, in particular, the prediction for $pp$ inelastic overlap function at $\sqrt{s}=14$ TeV shows the saturation of the Froissart-Martin bound at LHC energies.Comment: 15 pages, 16 figure

Equilibrium topology of the intermediate state in type-I superconductors of different shapes

High-resolution magneto-optical technique was used to analyze flux patterns in the intermediate state of bulk Pb samples of various shapes - cones, hemispheres and discs. Combined with the measurements of macroscopic magnetization these results allowed studying the effect of bulk pinning and geometric barrier on the equilibrium structure of the intermediate state. Zero-bulk pinning discs and slabs show hysteretic behavior due to geometric barrier that results in a topological hysteresis -- flux tubes on penetration and lamellae on flux exit. (Hemi)spheres and cones do not have geometric barrier and show no hysteresis with flux tubes dominating the intermediate field region. It is concluded that flux tubes represent the equilibrium topology of the intermediate state in reversible samples, whereas laminar structure appears in samples with magnetic hysteresis (either bulk or geometric). Real-time video is available in http://www.cmpgroup.ameslab.gov/supermaglab/video/Pb.html NOTE: the submitted images were severely downsampled due to Arxiv's limitations of 1 Mb total size

Three-dimensional Roton-Excitations and Supersolid formation in Rydberg-excited Bose-Einstein Condensates

We study the behavior of a Bose-Einstein condensate in which atoms are weakly coupled to a highly excited Rydberg state. Since the latter have very strong van der Waals interactions, this coupling induces effective, nonlocal interactions between the dressed ground state atoms, which, opposed to dipolar interactions, are isotropically repulsive. Yet, one finds partial attraction in momentum space, giving rise to a roton-maxon excitation spectrum and a transition to a supersolid state in three-dimensional condensates. A detailed analysis of decoherence and loss mechanisms suggests that these phenomena are observable with current experimental capabilities.Comment: 4 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

Comment on "Off-diagonal Long-range Order in Bose Liquids: Irrotational Flow and Quantization of Circulation"

In the context of an application to superfluidity, it is elaborated how to do quantum mechanics of a system with a rotational velocity. Especially, in both the laboratory frame and the non-inertial co-rotating frame, the canonical momentum, which corresponds to the quantum mechanical momentum operator, contains a part due to the rotational velocity.Comment: 2 page, comment on cond-mat/010435

Scaling of v2v_2 in heavy ion collisions

We interpret the scaling of the corrected elliptic flow parameter w.r.t. the corrected multiplicity, observed to hold in heavy ion collisions for a wide variety of energies and system sizes. We use dimensional analysis and power-counting arguments to place constraints on the changes of initial conditions in systems with different center of mass energy $\sqrt{s}$. Specifically, we show that a large class of changes in the (initial) equation of state, mean free path, and longitudinal geometry over the observed $\sqrt{s}$ are likely to spoil the scaling in $v_2$ observed experimentally. We therefore argue that the system produced at most Super Proton Synchrotron (SPS) and Relativistic Heavy Ion Collider (RHIC) energies is fundamentally the same as far as the soft and approximately thermalized degrees of freedom are considered. The ``sQGP'' (Strongly interacting Quark-Gluon Plasma) phase, if it is there, is therefore not exclusive to RHIC. We suggest, as a goal for further low-energy heavy ion experiments, to search for a ``transition'' $\sqrt{s}$ where the observed scaling breaks.Comment: Accepted for publication by Phys. Rev. C Based on presentation in mini-symposium on QGP collective properties, Frankfurt. Discussion expanded, results adde

High-energy gluon bremsstrahlung in a finite medium: harmonic oscillator versus single scattering approximation

A particle produced in a hard collision can lose energy through bremsstrahlung. It has long been of interest to calculate the effect on bremsstrahlung if the particle is produced inside a finite-size QCD medium such as a quark-gluon plasma. For the case of very high-energy particles traveling through the background of a weakly-coupled quark-gluon plasma, it is known how to reduce this problem to an equivalent problem in non-relativistic two-dimensional quantum mechanics. Analytic solutions, however, have always resorted to further approximations. One is a harmonic oscillator approximation to the corresponding quantum mechanics problem, which is appropriate for sufficiently thick media. Another is to formally treat the particle as having only a single significant scattering from the plasma (known as the N=1 term of the opacity expansion), which is appropriate for sufficiently thin media. In a broad range of intermediate cases, these two very different approximations give surprisingly similar but slightly differing results if one works to leading logarithmic order in the particle energy, and there has been confusion about the range of validity of each approximation. In this paper, I sort out in detail the parametric range of validity of these two approximations at leading logarithmic order. For simplicity, I study the problem for small alpha_s and large logarithms but alpha_s log << 1.Comment: 40 pages, 23 figures [Primary change since v1: addition of new appendix reviewing transverse momentum distribution from multiple scattering