The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform

Tod M Wright - One of the best experts on this subject based on the ideXlab platform.

  • many body physics in the Classical Field description of a degenerate bose gas
    Physical Review A, 2011
    Co-Authors: Tod M Wright, N P Proukakis, Matthew J Davis
    Abstract:

    The Classical-Field formalism has been widely applied in the calculation of normal correlation functions, and the characterization of condensation, in finite-temperature Bose gases. Here we discuss the extension of this method to the calculation of more general correlations, including the so-called anomalous correlations of the Field, without recourse to symmetry-breaking assumptions. Our method is based on the introduction of U(1)-symmetric Classical-Field variables analogous to the modified quantum ladder operators of number-conserving approaches to the degenerate Bose gas, and allows us to rigorously quantify the anomalous and non-Gaussian character of the Field fluctuations. We compare our results for anomalous correlation functions with the predictions of mean-Field theories, and demonstrate that the nonlinear Classical-Field dynamics incorporate a full description of many-body processes which modify the effective mean-Field potentials experienced by condensate and noncondensate atoms. We discuss the role of these processes in shaping the condensate mode, and thereby demonstrate the consistency of the Penrose-Onsager definition of the condensate orbital in the Classical-Field equilibrium. We consider the contribution of various noncondensate-Field correlations to the overall suppression of density fluctuations and interactions in the Field, and demonstrate the distinct roles of phase and density fluctuations in the transition of the Field to the normal phase.

  • temporal coherence anomalous moments and pairing correlations in the Classical Field description of a degenerate bose gas
    Physical Review A, 2010
    Co-Authors: Tod M Wright, P B Blakie, R J Ballagh
    Abstract:

    The coherence properties of degenerate Bose gases have usually been expressed in terms of spatial correlation functions, neglecting the rich information encoded in their temporal behavior. In this article we show, using a Hamiltonian Classical-Field formalism, that temporal correlations can be used to characterize familiar properties of a finite-temperature degenerate Bose gas. The temporal coherence of a Bose-Einstein condensate is limited only by the slow diffusion of its phase, and thus the presence of a condensate is indicated by a sharp feature in the temporal power spectrum of the Field. We show that the condensate mode can be obtained by averaging the Field for a short time in an appropriate phase-rotating frame, and that for a wide range of temperatures, the condensate obtained in this approach agrees well with that defined by the Penrose-Onsager criterion based on one-body (spatial) correlations. For time periods long compared to the phase diffusion time, the Field will average to zero, as we would expect from the overall U(1) symmetry of the Hamiltonian. We identify the emergence of the first moment on short time scales with the concept of U(1) symmetry breaking that is central to traditional mean-Field theories of Bose condensation. We demonstrate thatmore » the short-time averaging procedure constitutes a general analog of the ''anomalous'' averaging operation of symmetry-broken theories by calculating the anomalous thermal density of the Field, which we find to have form and temperature dependence consistent with the results of mean-Field theories.« less

Sacha Davidson - One of the best experts on this subject based on the ideXlab platform.

  • axions bose einstein condensate or Classical Field
    Astroparticle Physics, 2015
    Co-Authors: Sacha Davidson
    Abstract:

    Abstract The axion is a motivated dark matter candidate, so it would be interesting to find features in Large Scale Structures specific to axion dark matter. Such features were proposed for a Bose Einstein condensate of axions, leading to confusion in the literature (to which I contributed) about whether axions condense due to their gravitational interactions. This note argues that the Bose Einstein condensation of axions is a red herring: the axion dark matter produced by the misalignment mechanism is already a Classical Field, which has the distinctive features attributed to the axion condensate (BE condensates are described as Classical Fields). This note also estimates that the rate at which axion particles condense to the Field, or the Field evaporates to particles, is negligible.

Katarzyna Rejzner - One of the best experts on this subject based on the ideXlab platform.

Klaus Fredenhagen - One of the best experts on this subject based on the ideXlab platform.

  • Algebraic Structure of Classical Field Theory: Kinematics and Linearized Dynamics for Real Scalar Fields
    Communications in Mathematical Physics, 2019
    Co-Authors: Romeo Brunetti, Klaus Fredenhagen, Pedro Lauridsen Ribeiro
    Abstract:

    We describe the elements of a novel structural approach to Classical Field theory, inspired by recent developments in perturbative algebraic quantum Field theory. This approach is local and focuses mainly on the observables over Field configurations, given by certain spaces of functionals which are studied here in depth. The analysis of such functionals is characterized by a combination of geometric, analytic and algebraic elements which (1) make our approach closer to quantum Field theory, (2) allow for a rigorous analytic refinement of many computational formulae from the functional formulation of Classical Field theory and (3) provide a new pathway towards understanding dynamics. Particular attention will be paid to aspects related to nonlinear hyperbolic partial differential equations and their linearizations.

  • batalin vilkovisky formalism in the functional approach to Classical Field theory
    Communications in Mathematical Physics, 2012
    Co-Authors: Klaus Fredenhagen, Katarzyna Rejzner
    Abstract:

    We develop the Batalin-Vilkovisky formalism for Classical Field theory on generic globally hyperbolic spacetimes. A crucial aspect of our treatment is the incorporation of the principle of local covariance which amounts to formulate the theory without reference to a distinguished spacetime. In particular, this allows a homological construction of the Poisson algebra of observables in Classical gravity. Our methods heavily rely on the differential geometry of configuration spaces of Classical Fields.

Kazimierz Rzazewski - One of the best experts on this subject based on the ideXlab platform.

  • Classical Fields approximation for bosons at nonzero temperatures
    Journal of Physics B, 2007
    Co-Authors: Mirosław Brewczyk, Mariusz Gajda, Kazimierz Rzazewski
    Abstract:

    Experiments with Bose–Einstein condensates of dilute atomic gases require temperatures as low as hundreds of nanokelvins but obviously cannot be performed at zero absolute temperature. So the approximate theory of such a gas at nonzero temperatures is needed. In this topical review we describe a Classical Field approximation which satisfies this need. As modes of light, also modes of atomic Field may be treated as Classical waves, provided they contain sufficiently many quanta. We present a detailed description of the Classical Field approximation stressing the significant role of the observation process as the necessary interface between our calculations and measurements. We also discuss in detail the determination of temperature in our approach and stress its limitations. We also review several applications of the Classical Field approximation to dynamical processes involving atomic condensates.

  • thermodynamics of an interacting trapped bose einstein gas in the Classical Field approximation
    Physical Review A, 2002
    Co-Authors: Krzysztof Goral, Mariusz Gajda, Kazimierz Rzazewski
    Abstract:

    We present a convenient technique describing the condensate in dynamical equilibrium with the thermal cloud, at temperatures close to the critical one. We show that the whole isolated system may be viewed as a single Classical Field undergoing nonlinear dynamics leading to a steady state. In our procedure it is the observation process and the finite detection time that allow for splitting the system into the condensate and the thermal cloud.