arXiv subjects

Justine Tarrant

Publications and source records attributed to Justine Tarrant.

8 recordsLinked to original sources

arXiv2023

Primordial black holes and the Sunyaev-Zel'dovich effect

Primordial black holes are a popular candidate for dark matter. In the mass regime where their conjectured Hawking evaporation is significant, they have been subject to many constraints via X-rays, gamma-rays, and even radio emission. Previously the Sunyaev-Zel'dovich effect has been considered to place further limits on the M > 10M? primordial black hole abundance via the effects of their accretion of ambient gas. In this work, we will present a novel and robust means of placing abundance limits on low-mass black holes, using the Sunyaev-Zel'dovich effect induced by electrons produced via their Hawking radiation within galaxy clusters.

gr-qc↗

arXiv2022

Studying patched spacetimes for binary black holes

Circumbinary accretion disks have been examined, theoretically, for supermassive and intermediate mass black holes, however, disks for black hole masses in the LIGO regime are poorly understood. Assuming these binaries possess such a disk initially, the question we want to answer is: are they dissipated by outflows or accretion prior to inspiral? To study this problem we propose a novel approach, whereby we consider an approximate, analytic spacetime and solve the geodesic equation for particles in this spacetime so that we can determine the likely fate of particles coming from the accretion disk. Preliminary indications suggest a likelihood of accretion prior to inspiral.

gr-qc↗

arXiv2021

Making light of gravitational-waves

Mixing between photons and low-mass bosons is well considered in the literature. The particular case of interest here is with hypothetical gravitons, as we are concerned with the direct conversion of gravitons into photons in the presence of an external magnetic field. We examine whether such a process could produce direct low-frequency radio counterparts to gravitational-wave events. Our work differs from previous work in the literature in that we use the results of numerical simulations to demonstrate that, although a single such event may be undetectable without at least 100000 dipoles, an unresolved gravitational wave background from neutron star mergers could be potentially detectable with a lunar telescope composed of 1000 elements. This is provided the gravitational wave spectrum only experiences exponential damping above 80 kHz, a full order of magnitude above the limit achieved by present simulation results. In addition, the extrapolation cannot have a power-law slope < -2 (for 100 hours of observation time) and background and foregrounds must be effectively subtracted to obtain the signal. This does not make detection impossible, but suggests it may be unlikely. Furthermore, assuming a potentially detectable spectral scenario we show that, for the case when no detection is made by a lunar array, a lower bound, competitive with those from Lorentz-invariance violation, may be placed on the energy-scale of quantum gravitational effects. The SKA is shown to have very limited prospects for the detection of either a single merger or a background.

astro-ph.HE↗

arXiv2019

Probing quantum gravity using high-energy astrophysics

The events observed by LIGO indicate the existence of a large population of intermediate mass black holes. This unexpected result lead to a resurgence in the interest in theories of the formation of primordial black holes with several studies showing that broad mass distributions can evade or satisfy the stringent constraints on monochromatic populations. If such large populations exist they provide the perfect test-bed for theories beyond the standard model of physics that modify black hole evolution. The case we studied is that of "Planck stars", a hypothetical modification of the black hole evolution where it explodes via quantum loop gravity motivated tunnelling. We determine what the high-frequency background signal of such objects exploding over the whole of cosmic history would look like for various black hole populations to place actual empirical constraints on quantum loop gravity via comparison to observed isotropic background signals at the same frequencies. We find that stringent constraints heavily restrict the amount of energy released via the high-energy channel, thereby casting doubt on whether or not the high-energy signal could result in gamma-ray bursts as speculated in the literature.

astro-ph.CO↗

arXiv2019

Probing quantum gravity at low energies

Planck stars form when a collapsing shell of matter within a black hole reaches the Planck density, roughly equivalent to the mass being compressed into a volumetric size near that of the proton, and rebounds outwards. These planck stars have been considered as accounting for both fast radio bursts and short gamma ray bursts, whilst offering a comparatively low energy perspective onto quantum gravity. The observation of such an event would require black hole masses much smaller than a solar mass, which could be provided by primordial black hole dark matter models. We discuss the low energy isotropic background emissions produced by decaying primordial black holes at all epochs and derive constraints from the spectrum of the extragalactic background light. We find that, in order to avoid exceeding known extragalactic background light emissions, we must restrict the total energy emitted at low frequencies by a planck star exploding in the present epoch to be less than $10^{13}$ erg or restrict the primordial black hole population far below any existing limits. This casts doubt on whether exploding planck stars could actually account for fast radio bursts, as they are speculated to in the literature.

astro-ph.CO↗

arXiv2018

Using Gravitational Wave Observations to Probe Quantum Gravity

Electromagnetic radiation is known to be associated with certain gravitational waves events, i.e. the collision of binary neutron stars. Establishing this connection is non-trivial. However, if electromagnetic counterparts could be produced by directly converting gravitons into photons, then a simple smoking gun test exists linking the two events. This model uses the general and conversion mechanism discussed by Raffelt and Stodolsky. Furthermore, because this mechanism is generic to the symmetries of general relativity and the standard model and because it assumes a quantised gravitational field, we may probe both the existence of the graviton and the scale at which quantum gravity effects (and thus very high-energy phenomena) become relevant using simple low-energy experiments.

astro-ph.HE↗

arXiv2016

Fermionic T-Duality of $AdS_n \times S^n (\times S^n) \times T^m$ using IIA Supergravity

We show that the string backgrounds AdS2 x S2 x T6 and AdSd x Sd x Sd x T{10 - 3d} (d = 2, 3) are self-dual under a series of bosonic and fermionic T-dualities. We do this using the fermionic Buscher rules derived by Berkovits and Maldacena, thus working at the level of the supergravity fields. This allows us to explicitly track the behaviour of the RR fields, from which we see that we need T-duality along some torus directions. For the AdS x S x S cases, which contain cosets of D(2,1;alpha), it is necessary to perform bosonic T-duality along some complexified Killing spinors in one of the spheres.

hep-th↗

arXiv2015

T-Duality of Green-Schwarz Superstrings on AdS(d) x S(d) x M(10-2d)

We verify the self-duality of Green-Schwarz supercoset sigma models on AdS$_d \times S^d $ backgrounds (d=2,3,5) under combined bosonic and fermionic T-dualities without gauge fixing kappa symmetry. We also prove this property for superstrings on AdS$_d \times S^d \times S^d$ (d=2,3) described by supercoset sigma models with the isometries governed by the exceptional Lie supergroups $D(2,1;α)$ (d=2) and $D(2,1;α)\times D(2,1;α)$ (d=3), which requires an additional T-dualisation along one of the spheres. Then, by taking into account the contribution of non-supercoset fermionic modes (up to the second order), we provide evidence for the T-self-duality of the complete type IIA and IIB Green-Schwarz superstring theory on AdS$_d\times S^d \times T^{10-2d}$ (d=2,3) backgrounds with Ramond-Ramond fluxes. Finally, applying the Buscher-like rules to T-dualising supergravity fields, we prove the T-self-duality of the whole class of the AdS$_d\times S^d \times M^{10-2d}$ superbackgrounds with Ramond-Ramond fluxes in the context of supergravity.

hep-th↗