Research Outputs

Permanent URI for this communityhttps://hdl.handle.net/20.500.14288/2

Browse

Filters

2020 - 20224

Advanced Search

Filter by

Settings

Subject: search.filters.subject.Gravitation

Search Results

Now showing 1 - 4 of 4
  • Placeholder
    PublicationMetadata only
    Echoes from the event horizon of a superfluid vortex
    (IOP Publishing Ltd, 2022) Demirkaya B.; Department of Physics; Güven, Kaan; Faculty Member; Department of Physics; College of Sciences; 52290
    A vortex formed in the superfluid state of a Bose-Einstein condensate may exhibit superradiance a la blackhole for radially propagating acoustic fluctuations. The analogy is usually based on the so-called draining bathtub model of the vortex, in which an event horizon and ergosphere emerges when the radial velocity of the superfluid exceeds the propagation speed of sound in the condensate. The acoustic fluctuations mimic a massless scalar field in the curved Lorentzian space-time of the vortex and are governed by the Klein-Gordon wave equation. One common main approximation is the constant background density of the superfluid even in the presence of the vortex. This sets a constant relativistic sound speed. However, the vortex state solution of the Gross-Pitaevskii equation clearly shows that both the density and the speed of sound vary radially near the vortex core, where the event horizon and thus the superradiance will take place. What changes would this complex interdependence bring to the formulation and to the outcomes of the superradiance based on constant density approximation? Here, we recount this question posed under the guidance of Prof. Tekin Dereli and present recent results. We show that the self-consistent density modifies the amplification dynamics near the event horizon significantly, thereby altering the temporal and spectral fingerprint of the superradiance of the vortex. © 2021 Published under licence by IOP Publishing Ltd.
  • Thumbnail Image
    PublicationRestricted
    Generalized theories of gravity and supergravity in three dimensions
    (Koç University, 2022) Yetişmişoğlu, Cem; Dereli, Tekin; 0000-0002-6244-6054; Koç University Graduate School of Sciences and Engineering; Physics; 201358
  • Thumbnail Image
    PublicationOpen Access
    Gravitational Higgs mechanism and resulting observational effects
    (American Physical Society (APS), 2020) Krall, Verena; Kokkotas, Kostas D.; Department of Physics; Coates, Andrew; Researcher; Department of Physics; College of Sciences
    Recently, a toy model was introduced to demonstrate that screening mechanisms in alternative theories of gravitation can hide additional effects. In this model a scalar field is charged under a U(1) symmetry. In sufficiently compact objects the scalar field spontaneously grows, i.e., the object scalarizes, spontaneously breaking the U(1) symmetry. Exactly as in the U(1) Higgs mechanism this leads to the emergence of a mass for the gauge field. The aim of this paper is to provide an example of the physical consequences if we consider this toy model as a prototype of Weak Equivalence Principle (WEP) violations. We model neutron stars with a dipolar magnetic field to compare the magnetic field behavior of stars in Einstein-Maxwell theory on the one hand and in scalar-tensor theory with the, so-called, gravitational Higgs mechanism on the other hand.
  • Thumbnail Image
    PublicationRestricted
    Theory and observation of spontaneous scalarization
    (Koç University, 2022) Akram, Fathima Afra Mohamed; Ramazanoğlu, Fethi Mübin; 0000-0003-3075-1457; Koç University Graduate School of Sciences and Engineering; Physics; 254225