Silke Weinfurtner

Publications (35)29.48 Total impact

• Source

  Available from: Matt Visser

  Article: Solution generating theorems for the TOV equation

  Petarpa Boonserm, Matt Visser, Silke Weinfurtner
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  ABSTRACT: The Tolman-Oppenheimer-Volkov [TOV] equation constrains the internal structure of general relativistic static perfect fluid spheres. We develop several "solution generating" theorems for the TOV, whereby any given solution can be "deformed" to a new solution. Because the theorems we develop work directly in terms of the physical observables -- pressure profile and density profile -- it is relatively easy to check the density and pressure profiles for physical reasonableness. This work complements our previous article [Phys. Rev. D71 (2005) 124307; gr-qc/0503007] wherein a similar "algorithmic" analysis of the general relativistic static perfect fluid sphere was presented in terms of the spacetime geometry -- in the present analysis the pressure and density are primary and the spacetime geometry is secondary. In particular, our "deformed" solutions to the TOV equation are conveniently parameterized in terms of delta rho_c and delta p_c, the finite shift in the central density and central pressure. We conclude by presenting a new physical and mathematical interpretation of the TOV equation -- as an integrability condition on the density and pressure profiles.
  08/2006;
• Source

  Available from: Matt Visser

  Article: Analogue spacetime based on 2-component Bose-Einstein condensates

  Silke Weinfurtner, Stefano Liberati, Matt Visser
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  ABSTRACT: Analogue spacetimes are powerful models for probing the fundamental physical aspects of geometry - while one is most typically interested in ultimately reproducing the pseudo-Riemannian geometries of interest in general relativity and cosmology, analogue models can also provide useful physical probes of more general geometries such as pseudo-Finsler spacetimes. In this chapter we shall see how a 2-component Bose-Einstein condensate can be used to model a specific class of pseudo-Finsler geometries, and after suitable tuning of parameters, both bi-metric pseudo-Riemannian geometries and standard single metric pseudo-Riemannian geometries, while independently allowing the quasi-particle excitations to exhibit a "mass". Furthermore, when extrapolated to extremely high energy the quasi-particles eventually leave the phononic regime and begin to act like free bosons. Thus this analogue spacetime exhibits an analogue of the "Lorentz violation" that is now commonly believed to occur at or near the Planck scale defined by the interplay between quantum physics and gravitational physics. In the 2-component Bose-Einstein analogue spacetime we will show that the mass generating mechanism for the quasi-particles is related to the size of the Lorentz violations. This relates the "mass hierarchy" to the so-called "naturalness problem". In short the analogue spacetime based on 2-component Bose-Einstein condensates exhibits a very rich mathematical and physical structure that can be used to investigate many issues of interest to the high-energy physics, cosmology, and general relativity communities.
  06/2006;
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  Available from: Matt Visser

  Article: Naturalness in an emergent analogue spacetime.

  Stefano Liberati, Matt Visser, Silke Weinfurtner
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  ABSTRACT: Effective field theories (EFTs) have been widely used as a framework in order to place constraints on the Planck suppressed Lorentz violations predicted by various models of quantum gravity. There are, however, technical problems in the EFT framework when it comes to ensuring that small Lorentz violations remain small--this is the essence of the "naturalness" problem. Herein we present an "emergent" spacetime model, based on the "analogue gravity" program, by investigating a specific condensed-matter system. Specifically, we consider the class of two-component BECs subject to laser-induced transitions between the components, and we show that this model is an example for Lorentz invariance violation due to ultraviolet physics. Furthermore, our model explicitly avoids the naturalness problem, and makes specific suggestions regarding how to construct a physically reasonable quantum gravity phenomenology.
  Physical Review Letters 05/2006; 96(15):151301. · 7.37 Impact Factor
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  Available from: Matt Visser

  Article: Modelling Planck-scale Lorentz violation via analogue models

  Silke Weinfurtner, Stefano Liberati, Matt Visser
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  ABSTRACT: Astrophysical tests of Planck-suppressed Lorentz violations had been extensively studied in recent years and very stringent constraints have been obtained within the framework of effective field theory. There are however still some unresolved theoretical issues, in particular regarding the so called "naturalness problem" - which arises when postulating that Planck-suppressed Lorentz violations arise only from operators with mass dimension greater than four in the Lagrangian. In the work presented here we shall try to address this problem by looking at a condensed-matter analogue of the Lorentz violations considered in quantum gravity phenomenology. Specifically, we investigate the class of two-component BECs subject to laser-induced transitions between the two components, and we show that this model is an example for Lorentz invariance violation due to ultraviolet physics. We shall show that such a model can be considered to be an explicit example high-energy Lorentz violations where the ``naturalness problem'' does not arise.
  01/2006;
• Source

  Available from: Matt Visser

  Article: Naturalness in emergent spacetime

  Stefano Liberati, Matt Visser, Silke Weinfurtner
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  ABSTRACT: Effective field theories (EFTs) have been widely used as a framework in order to place constraints on the Planck suppressed Lorentz violations predicted by various models of quantum gravity. There are however technical problems in the EFT framework when it comes to ensuring that small Lorentz violations remain small -- this is the essence of the "naturalness" problem. Herein we present an "emergent" space-time model, based on the "analogue gravity'' programme, by investigating a specific condensed-matter system that is in principle capable of simulating the salient features of an EFT framework with Lorentz violations. Specifically, we consider the class of two-component BECs subject to laser-induced transitions between the components, and we show that this model is an example for Lorentz invariance violation due to ultraviolet physics. Furthermore our model explicitly avoids the "naturalness problem", and makes specific suggestions regarding how to construct a physically reasonable quantum gravity phenomenology. Comment: V1:4 pages, revtex4; V2: slight changes in title, presentation, and conclusions. This version to appear in Physical Review Letters
  12/2005;
• Source

  Available from: Matt Visser

  Article: Analogue model for quantum gravity phenomenology

  Silke Weinfurtner, Stefano Liberati, Matt Visser
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  ABSTRACT: So called "analogue models" use condensed matter systems (typically hydrodynamic) to set up an "effective metric" and to model curved-space quantum field theory in a physical system where all the microscopic degrees of freedom are well understood. Known analogue models typically lead to massless minimally coupled scalar fields. We present an extended "analogue space-time" programme by investigating a condensed-matter system - in and beyond the hydrodynamic limit - that is in principle capable of simulating the massive Klein-Gordon equation in curved spacetime. Since many elementary particles have mass, this is an essential step in building realistic analogue models, and an essential first step towards simulating quantum gravity phenomenology. Specifically, we consider the class of two-component BECs subject to laser-induced transitions between the components, and we show that this model is an example for Lorentz invariance violation due to ultraviolet physics. Furthermore our model suggests constraints on quantum gravity phenomenology in terms of the "naturalness problem" and "universality issue". Comment: Talk given at 7th Workshop on Quantum Field Theory Under the Influence of External Conditions (QFEXT 05), Barcelona, Catalonia, Spain, 5-9 Sep 2005
  11/2005;
• Source

  Available from: Matt Visser

  Article: Analogue quantum gravity phenomenology from a two-component Bose-Einstein condensate

  Stefano Liberati, Matt Visser, Silke Weinfurtner
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  ABSTRACT: We present an analogue spacetime model that reproduces the salient features of the most common ansatz for quantum gravity phenomenology. We do this by investigating a system of two coupled Bose-Einstein condensates. This system can be tuned to have two "phonon" modes (one massive, one massless) which share the same limiting speed in the hydrodynamic approximation [Phys. Rev. D72 (2005) 044020, gr-qc/0506029; cond-mat/0409639]. The system nevertheless possesses (possibly non-universal) Lorentz violating terms at very high energies where "quantum pressure" becomes important. We investigate the physical interpretation of the relevant fine-tuning conditions, and discuss the possible lessons and hints that this analogue spacetime could provide for the phenomenology of real physical quantum gravity. In particular we show that the effective field theory of quasi-particles in such an emergent spacetime does not exhibit the so called "naturalness problem". Comment: V1: 36 pages, uses iopart.sty; V2: 31 pages, presentation simplified, conclusions clarified, discussion of some side issues eliminated, several references added, this version to appear in Classical and Quantum Gravity
  10/2005;
• Article: Massive Klein-Gordon equation from a Bose-Einstein-condensation-based analogue spacetime

  Matt Visser, Silke Weinfurtner
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  ABSTRACT: We extend the “analogue spacetime” program by investigating a condensed-matter system that is in principle capable of simulating the massive Klein-Gordon equation in curved spacetime. Since many elementary particles have mass, this is an essential step in building realistic analogue models, and a first step towards simulating quantum gravity phenomenology. Specifically, we consider the class of two-component BECs subject to laser-induced transitions between the components. This system exhibits a complicated spectrum of normal mode excitations, which can be viewed as two interacting phonon modes that exhibit the phenomenon of refringence. We study the conditions required to make these two phonon modes decouple. Once decoupled, the two distinct phonons generically couple to distinct effective spacetimes, representing a bi-metric model, with one of the modes acquiring a mass. In the eikonal limit the massive mode exhibits the dispersion relation of a massive relativistic particle ω=√ω02+c2k2, plus curved-space modifications. Furthermore, it is possible to tune the system so that both modes can be arranged to travel at the same speed, in which case the two phonon excitations couple to the same effective metric. From the analogue spacetime perspective this situation corresponds to the Einstein equivalence principle being satisfied.
  Phys. Rev. D. 08/2005; 72(4).
• Source

  Available from: Matt Visser

  Article: Massive Klein--Gordon equation from a BEC-based analogue spacetime

  Matt Visser, Silke Weinfurtner
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  ABSTRACT: We extend the "analogue spacetime" programme by investigating a condensed-matter system that is in principle capable of simulating the massive Klein--Gordon equation in curved spacetime. Since many elementary particles have mass, this is an essential step in building realistic analogue models, and a first step towards simulating quantum gravity phenomenology. Specifically, we consider the class of two-component BECs subject to laser-induced transitions between the components. This system exhibits a complicated spectrum of normal mode excitations, which can be viewed as two interacting phonon modes that exhibit the phenomenon of "refringence". We study the conditions required to make these two phonon modes decouple. Once decoupled, the two distinct phonons generically couple to distinct effective spacetimes, representing a bi-metric model, with one of the modes acquiring a mass. In the eikonal limit the massive mode exhibits the dispersion relation of a massive relativistic particle: omega = sqrt[omega_0^2 + c^2 k^2], plus curved-space modifications. Furthermore, it is possible to tune the system so that both modes can be arranged to travel at the same speed, in which case the two phonon excitations couple to the same effective metric. From the analogue spacetime perspective this situation corresponds to the Einstein equivalence principle being satisfied. Comment: V1: 10 pages; uses revtex4; V2: two references and brief comments added
  06/2005;
• Source

  Available from: Matt Visser

  Article: Generating perfect fluid spheres in general relativity

  Petarpa Boonserm, Matt Visser, Silke Weinfurtner
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  ABSTRACT: Ever since Karl Schwarzschild's 1916 discovery of the spacetime geometry describing the interior of a particular idealized general relativistic star -- a static spherically symmetric blob of fluid with position-independent density -- the general relativity community has continued to devote considerable time and energy to understanding the general-relativistic static perfect fluid sphere. Over the last 90 years a tangle of specific perfect fluid spheres has been discovered, with most of these specific examples seemingly independent from each other. To bring some order to this collection, in this article we develop several new transformation theorems that map perfect fluid spheres into perfect fluid spheres. These transformation theorems sometimes lead to unexpected connections between previously known perfect fluid spheres, sometimes lead to new previously unknown perfect fluid spheres, and in general can be used to develop a systematic way of classifying the set of all perfect fluid spheres. Comment: 18 pages, 4 tables, 4 figures
  03/2005;
• Source

  Available from: Matt Visser

  Article: Effective refractive index tensor for weak field gravity

  Petarpa Boonserm, Celine Cattoen, Tristan Faber, Matt Visser, Silke Weinfurtner
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  ABSTRACT: Gravitational lensing in a weak but otherwise arbitrary gravitational field can be described in terms of a 3 x 3 tensor, the "effective refractive index". If the sources generating the gravitational field all have small internal fluxes, stresses, and pressures, then this tensor is automatically isotropic and the "effective refractive index" is simply a scalar that can be determined in terms of a classic result involving the Newtonian gravitational potential. In contrast if anisotropic stresses are ever important then the gravitational field acts similarly to an anisotropic crystal. We derive simple formulae for the refractive index tensor, and indicate some situations in which this will be important.
  12/2004;
• Source

  Available from: Matt Visser

  Article: Massive phonon modes from a BEC-based analog model

  Matt Visser, Silke Weinfurtner
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  ABSTRACT: Two-component BECs subject to laser-induced coupling exhibit a complicated spectrum of excitations, which can be viewed as two interacting phonon modes. We study the conditions required to make these two phonon modes decouple. Once decoupled, the phonons not only can be arranged travel at different speeds, but one of the modes can be given a mass -- it exhibits the dispersion relation of a massive relativistic particle: omega = sqrt{omega_0^2 + c^2 k^2}. This is a new and unexpected excitation mode for the coupled BEC system. Apart from its intrinsic interest to the BEC community, this observation is also of interest for the ``analogue gravity'' programme, as it opens the possibility for using BECs to simulate massive relativistic particles in an effective ``acoustic geometry''.
  10/2004;
• Source

  Available from: Matt Visser

  Article: Vortex geometry for the equatorial slice of the Kerr black hole

  Matt Visser, Silke Weinfurtner
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  ABSTRACT: The spacetime geometry on the equatorial slice through a Kerr black hole is formally equivalent to the geometry felt by phonons entrained in a rotating fluid vortex. We analyse this situation in some detail: First, we find the most general ``acoustic geometry'' compatible with the fluid dynamic equations in a collapsing/expanding perfect-fluid line vortex. Second, we demonstrate that there is a suitable choice of coordinates on the equatorial slice through a Kerr black hole that puts it into this vortex form; though it is not possible to put the entire Kerr spacetime into perfect-fluid ``acoustic'' form. Finally, we briefly discuss the implications of this formal equivalence; both with respect to gaining insight into the Kerr spacetime and with respect to possible vortex-inspired experiments. Comment: V1: 24 pages, 5 figures (some use of colour); V2: 21 pages, 5 figures, uses iopart.cls Changes of style and emphasis, no major changes in physics conclusions. This version accepted for publication in Classical and Quantum Gravity
  09/2004;
• Article: Emergent spacetimes

  Silke Weinfurtner, Matt Visser
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  ABSTRACT: We discuss the possibility that spacetime geometry may be an emergent phenomenon. This idea has been motivated by the Analogue Gravity programme. These are systems where the kinematics of small perturbations are dominated by an effective gravitational field. In these models there is no obvious connection between the "gravitational" field tensor and the Einstein equations, as the emergent spacetime geometry arises as a consequence of linearising around some classical field. After a brief introduction on this topic, we present our recent contributions to the field.
• Article: Solution generating theorems for the Tolman-Oppenheimer-Volkov equation

  Petarpa Boonserm, Matt Visser, Silke Weinfurtner
  [show abstract] [hide abstract]
  ABSTRACT: The Tolman-Oppenheimer-Volkov (TOV) equation constrains the internal structure of general relativistic static perfect fluid spheres. We develop several “solution generating” theorems for the TOV equation, whereby any given solution can be deformed into a new solution. Because the theorems we develop work directly in terms of the physical observables—pressure profile and density profile—it is relatively easy to check the density and pressure profiles for physical reasonableness. This work complements our previous article [ Phys. Rev. D 71 124037 (2005)] wherein a similar algorithmic analysis of the general relativistic static perfect fluid sphere was presented in terms of the spacetime geometry—in the present analysis the pressure and density are primary and the spacetime geometry is secondary. In particular, our deformed solutions to the TOV equation are conveniently parametrized in terms of δρc and δpc, the finite shift in the central density and central pressure. We conclude by presenting a new physical and mathematical interpretation for the TOV equation—as an integrability condition on the density and pressure profiles.
  Phys. Rev. D. 76(4).