39,881 research outputs found

    Fields in nonaffine bundles. III. Effective symmetries and conserved currents in strings and higher branes

    Full text link
    The principles of a previously developed formalism for the covariant treatment of multi-scalar fields for which (as in a nonlinear sigma model) the relevant target space is not of affine type -- but curved -- are recapitulated. Their application is extended from ordinary harmonic models to a more general category of "harmonious" field models, with emphasis on cases in which the field is confined to a string or higher brane worldsheet, and for which the relevant internal symmetry group is non Abelian, so that the conditions for conservation of the corresponding charge currents become rather delicate, particularly when the symmetry is gauged. Attention is also given to the conditions for conservation of currents of a different kind -- representing surface fluxes of generalised momentum or energy -- associated with symmetries not of the internal target space but of the underlying spacetime background structure, including the metric and any relevant gauge field. For the corresponding current to be conserved the latter need not be manifestly invariant: preservation modulo a gauge adjustment will suffice. The simplest case is that of "strong" symmetry, meaning invariance under the action of an effective Lie derivative (an appropriately gauge adjusted modification of an ordinary Lie derivative). When the effective symmetry is of the more general "weak" kind, the kinetic part of the current is not conserved by itself but only after being supplemented by a suitable contribution from the background.Comment: 27 pages Latex (color

    The Equation of State for Cool Relativistic Two-Constituent Superfluid Dynamics

    Get PDF
    The natural relativistic generalisation of Landau's two constituent superfluid theory can be formulated in terms of a Lagrangian LL that is given as a function of the entropy current 4-vector sρs^\rho and the gradient ∇φ\nabla\varphi of the superfluid phase scalar. It is shown that in the ``cool" regime, for which the entropy is attributable just to phonons (not rotons), the Lagrangian function L(s⃗,∇φ)L(\vec s, \nabla\varphi) is given by an expression of the form L=P−3ψL=P-3\psi where PP represents the pressure as a function just of ∇φ\nabla\varphi in the (isotropic) cold limit. The entropy current dependent contribution ψ\psi represents the generalised pressure of the (non-isotropic) phonon gas, which is obtained as the negative of the corresponding grand potential energy per unit volume, whose explicit form has a simple algebraic dependence on the sound or ``phonon" speed cPc_P that is determined by the cold pressure function PP.Comment: 26 pages, RevTeX, no figures, published in Phys. Rev. D. 15 May 199

    Recent developments in Vorton Theory

    Get PDF
    This article provides a concise overview of recent theoretical results concerning the theory of vortons, which are defined to be (centrifugally supported) equilibrium configurations of (current carrying) cosmic string loops. Following a presentation of the results of work on the dynamical evolution of small circular string loops, whose minimum energy states are the simplest examples of vortons, recent order of magnitude estimates of the cosmological density of vortons produced in various kinds of theoretical scenario are briefly summarised.Comment: 6 pages Latex. Contribution to 1996 Cosmology Meeting, Peyresq, Franc

    Renormalisation of gravitational self interaction for wiggly strings

    Get PDF
    It is shown that for any elastic string model with energy density UU and tension TT, the divergent contribution from gravitational self interaction can be allowed for by an action renormalisation proportional to (U−T)2(U-T)^2. This formula is applied to the important special case of a bare model of the transonic type (characterised by a constant value of the product UTUT) that represents the macroscopically averaged effect of shortwavelength wiggles on an underlying microscopic model of the Nambu-Goto type (characterised by U=TU=T).Comment: 11 pages, Latex; original 8 page version extended to include estimates of relevant orders of magnitude. To be published in Physical Review,

    The Secular Bar-Mode Instability in Rapidly Rotating Stars Revisited

    Full text link
    Uniformly rotating, homogeneous, incompressible Maclaurin spheroids that spin sufficiently rapidly are secularly unstable to nonaxisymmetric, bar-mode perturbations when viscosity is present. The intuitive explanation is that energy dissipation by viscosity can drive an unstable spheroid to a stable, triaxial configuration of lower energy - a Jacobi ellipsoid. But what about rapidly rotating compressible stars? Unlike incompressible stars, which contain no internal energy and therefore immediately liberate all the energy dissipated by viscosity, compressible stars have internal energy and can retain the dissipated energy as internal heat. Now compressible stars that rotate sufficiently rapidly and also manage to liberate this dissipated energy very quickly are known to be unstable to bar-mode perturbations, like their incompressible counterparts. But what is the situation for rapidly rotating compressible stars that have very long cooling timescales, so that all the energy dissipated by viscosity is retained as heat, whereby the total energy of the star remains constant on a secular (viscous) evolution timescale? Are such stars also unstable to the nonlinear growth of bar modes, or is the viscous heating sufficient to cause them to expand, drive down the ratio of rotational kinetic to gravitational potential energy T/|W| ~ 1/R, where R is the equatorial radius, and turn off the instability before it gets underway? If the instability still arises in such stars, at what rotation rate do they become unstable, and to what final state do they evolve? We provide answers to these questions in the context of the compressible ellipsoid model for rotating stars. The results should serve as useful guides for numerical simulations in 3+1 dimensions for rotating stars containing viscosity.Comment: Accepted for publication in ApJ 613, 1213-1220, 200

    Poly-essential and general Hyperelastic World (brane) models

    Get PDF
    This article provides a unified treatment of an extensive category of non-linear classical field models whereby the universe is represented (perhaps as a brane in a higher dimensional background) in terms of a structure of a mathematically convenient type describable as hyperelastic, for which a complete set of equations of motion is provided just by the energy-momentum conservation law. Particular cases include those of a perfect fluid in quintessential backgrounds of various kinds, as well as models of the elastic solid kind that has been proposed to account for cosmic acceleration. It is shown how an appropriately generalised Hadamard operator can be used to construct a symplectic structure that controles the evolution of small perturbations, and that provides a characteristic equation governing the propagation of weak discontinuities of diverse (extrinsic and extrinsic) kinds. The special case of a poly-essential model - the k-essential analogue of an ordinary polytropic fluid - is examined and shown to be well behaved (like the fluid) only if the pressure to density ratio ww is positive.Comment: 16 pages Latex, Contrib. to 10th Peyresq Pysics Meeting, June 2005: Micro and Macro Structures of Spacetim

    Interaction of gravitational waves with an elastic solid medium

    Get PDF
    Contents. 1. Introduction. 2. Kinematics of a Material Medium: Material Representation. 3. Kinematics of a Material Medium: Convected Differentials. 4. Kinematics of a Perfect Elastic Medium. 5. Small Gravitational Perturbations of an Elastic Medium.Comment: 14 pages TeX file of contrib. to proc. Gravitational Radiation, Les Houches 1982, ed N. Deruelle, T. Piran, 455-464 (North Holland, Amsterdam, 1983

    Transonic Elastic Model for Wiggly Goto-Nambu String

    Full text link
    The hitherto controversial proposition that a ``wiggly" Goto-Nambu cosmic string can be effectively represented by an elastic string model of exactly transonic type (with energy density UU inversely proportional to its tension TT) is shown to have a firm mathematical basis.Comment: 8 pages, plain TeX, no figure

    Chaotic string-capture by black hole

    Full text link
    We consider a macroscopic charge-current carrying (cosmic) string in the background of a Schwarzschild black hole. The string is taken to be circular and is allowed to oscillate and to propagate in the direction perpendicular to its plane (that is parallel to the equatorial plane of the black hole). Nurmerical investigations indicate that the system is non-integrable, but the interaction with the gravitational field of the black hole anyway gives rise to various qualitatively simple processes like "adiabatic capture" and "string transmutation".Comment: 13 pages Latex + 3 figures (not included), Nordita 93/55

    Cosmic Vortons and Particle Physics Constraints

    Get PDF
    We investigate the cosmological consequences of particle physics theories that admit stable loops of superconducting cosmic string - {\it vortons}. General symmetry breaking schemes are considered, in which strings are formed at one energy scale and subsequently become superconducting in a secondary phase transition at what may be a considerably lower energy scale. We estimate the abundances of the ensuing vortons, and thereby derive constraints on the relevant particle physics models from cosmological observations. These constraints significantly restrict the category of admissible Grand Unified theories, but are quite compatible with recently proposed effects whereby superconducting strings may have been formed close to the electroweak phase transition.Comment: 33 pages, 2 figures, RevTe
    • 

    corecore