3,783 research outputs found

    Condensate density and superfluid mass density of a dilute Bose gas near the condensation transition

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    We derive, through analysis of the structure of diagrammatic perturbation theory, the scaling behavior of the condensate and superfluid mass density of a dilute Bose gas just below the condensation transition. Sufficiently below the critical temperature, TcT_c, the system is governed by the mean field (Bogoliubov) description of the particle excitations. Close to TcT_c, however, mean field breaks down and the system undergoes a second order phase transition, rather than the first order transition predicted in Bogoliubov theory. Both condensation and superfluidity occur at the same critical temperature, TcT_c and have similar scaling functions below TcT_c, but different finite size scaling at TcT_c to leading order in the system size. Through a simple self-consistent two loop calculation we derive the critical exponent for the condensate fraction, 2β0.662\beta\simeq 0.66.Comment: 4 page

    Event-by-Event Fluctuations in Ultrarelativistic Heavy-Ion Collisions

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    Motivated by forthcoming experiments at RHIC and LHC, we study event-by-event fluctuations in ultrarelativistic heavy-ion collisions in participant nucleon as well as thermal models. The calculated physical observables, including multiplicity, kaon to pion ratios, and transverse momenta agree well with recent NA49 data at the SPS, and indicate that such studies do not yet reveal the presence of new physics. Finally, we present a simple model of how a first order phase transition can be signaled by very large fluctuations.Comment: final version, 4 pages, to appear in Phys. Lett.

    RHIC: From dreams to beams in two decades

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    This talk traces the history of RHIC over the last two decades, reviewing the scientific motivations underlying its design, and the challenges and opportunities the machine presents.Comment: To be published in Proceedings of Quark Matter '01. 10 pages, 1 figur

    Neutron stars and quark matter

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    Recent observations of neutron star masses close to the maximum predicted by nucleonic equations of state begin to challenge our understanding of dense matter in neutron stars, and constrain the possible presence of quark matter in their deep interiors.Comment: To be published in the proceedings of Quark Confinement and the Hadron Spectrum VII, Sept. 2006, Ponta Delgada, Azores. 7 pages, 3 figures, aipro

    Vortex lattices in rapidly rotating Bose-Einstein condensates: modes and correlation functions

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    After delineating the physical regimes which vortex lattices encounter in rotating Bose-Einstein condensates as the rotation rate, Ω\Omega, increases, we derive the normal modes of the vortex lattice in two dimensions at zero temperature. Taking into account effects of the finite compressibility, we find an inertial mode of frequency 2Ω\ge 2\Omega, and a primarily transverse Tkachenko mode, whose frequency goes from being linear in the wave vector in the slowly rotating regime, where Ω\Omega is small compared with the lowest compressional mode frequency, to quadratic in the wave vector in the opposite limit. We calculate the correlation functions of vortex displacements and phase, density and superfluid velocities, and find that the zero-point excitations of the soft quadratic Tkachenko modes lead in a large system to a loss of long range phase correlations, growing logarithmically with distance, and hence lead to a fragmented state at zero temperature. The vortex positional ordering is preserved at zero temperature, but the thermally excited Tkachenko modes cause the relative positional fluctuations to grow logarithmically with separation at finite temperature. The superfluid density, defined in terms of the transverse velocity autocorrelation function, vanishes at all temperatures. Finally we construct the long wavelength single particle Green's function in the rotating system and calculate the condensate depletion as a function of temperature.Comment: 11 pages Latex, no figure

    Renormalization of interactions of ultracold atoms in simulated Rashba gauge fields

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    Interactions of ultracold atoms with Rashba spin-orbit coupling, currently being studied with simulated (artificial) gauge fields, have nontrivial ultraviolet and infrared behavior. Examining the ultraviolet structure of the Bethe-Salpeter equation, we show that the linear ultraviolet divergence in the bare interaction can be renormalized as usual in terms of low-energy scattering lengths, and that for both bosons and fermions ultraviolet logarithmic divergences are absent. Calculating the leading order effective interaction with full dependence on the spin-orbit coupling strength and the center-of-mass momentum of the colliding pair, we elucidate the relation between mean-field interactions and physical three-dimensional scattering lengths. As a consequence of infrared logarithmic divergences in the two-particle propagator, the effective interaction vanishes as the center-of-mass momentum approaches zero.Comment: 4 pages, 2 figures, published versio