Drafts by Theodoros PAPANIKOLAOU
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Papers by Theodoros PAPANIKOLAOU
arXiv (Cornell University), Jun 8, 2023
Bookmarks Related papers MentionsView impact
Physical Review D
Bookmarks Related papers MentionsView impact
Classical and Quantum Gravity
Primordial black holes form in the early Universe and constitute one of the most viable candidate... more Primordial black holes form in the early Universe and constitute one of the most viable candidates for dark matter. The study of their formation process requires the determination of a critical energy density perturbation threshold δ c , which in general depends on the underlying gravity theory. Up to now, the majority of analytic and numerical techniques calculate δ c within the framework of general relativity. In this work, using simple physical arguments we estimate semi-analytically the PBH formation threshold within the framework of quantum gravity, working for concreteness within loop quantum cosmology (LQC). In particular, for low mass PBHs formed close to the quantum bounce, we find a reduction in the value of δ c up to 50 % compared to the general relativistic regime quantifying for the first time to the best of our knowledge how quantum effects can influence PBH formation within a quantum gravity framework. Finally, by varying the Barbero–Immirzi parameter γ of loop quantu...
Bookmarks Related papers MentionsView impact
Physical Review D
Bookmarks Related papers MentionsView impact
arXiv (Cornell University), Mar 29, 2023
Bookmarks Related papers MentionsView impact
arXiv (Cornell University), Mar 1, 2023
Bookmarks Related papers MentionsView impact
arXiv (Cornell University), Jan 24, 2023
Large scale primordial magnetic fields (PMFs) threading the intergalactic medium are observed ubi... more Large scale primordial magnetic fields (PMFs) threading the intergalactic medium are observed ubiquitously in the Universe playing a key role in the cosmic evolution. Their origin is still debated constituting a very active field of research. In the present article, we propose a novel natural ab initio mechanism for the origin of such PMFs through the portal of supermassive primordial black holes (PBHs) forming between the Big Bang Nucleosynthesis and the recombination era. In particular, by considering PBHs furnished with a locally isothermal disk we study the generation of a Biermann battery induced seed magnetic field (MF) due to the vortexlike motion of the primordial plasma around the black hole. Finally, by considering monochromatic PBH mass distributions and deriving the relevant MF power spectrum we make a conservative estimate for the seed PMF in intergalactic scales and at redshift $z=30$, when typical galaxies are considered to form, which reads as $B\simeq 10^{-30}\mathrm{G}\left(\frac{\ell_\mathrm{R}}{10^6}\right)^2\left(\frac{M_\mathrm{PBH}}{10^{14}M_\odot}\right)^{5/2}$, where $M_\mathrm{PBH}$ is the PBH mass and $\ell_\mathrm{R}\equiv R_\mathrm{d}/R_\mathrm{ISCO}$, is the ratio of the radius of the disk, $R_\mathrm{d}$ over the radius of the innermost stable circular orbit, $R_\mathrm{ISCO}$. Interestingly enough, by requiring to seed a PMF of the order of $10^{-30}\mathrm{G}$ necessary to give rise to a present day $10^{-18}\mathrm{G}$ in intergalactic scales, we find a lower bound on the PBH mass within the range $[10^{10}- 10^{16}]M_\odot$ depending on the radius of the PBH disk.
Bookmarks Related papers MentionsView impact
The European Physical Journal C
Primordial black hole (PBH) fluctuations can induce a stochastic gravitational wave background at... more Primordial black hole (PBH) fluctuations can induce a stochastic gravitational wave background at second order, and since this procedure is sensitive to the underlying gravitational theory it can be used as a novel tool to test general relativity and extract constraints on possible modified gravity deviations. We apply this formalism in the framework of f(T) gravity, considering three viable mono-parametric models. In particular, we investigate the induced modifications at the level of the gravitational-wave source, which is encoded in terms of the power spectrum of the PBH gravitational potential, as well as at the level of their propagation, described in terms of the Green function which quantifies the propagator of the tensor perturbations. We find that, within the observationally allowed range of the f(T) model-parameters, the obtained deviations from general relativity, both at the levels of source and propagation, are practically negligible. Hence, we conclude that realistic a...
Bookmarks Related papers MentionsView impact
Physical Review D
Bookmarks Related papers MentionsView impact
arXiv (Cornell University), Sep 9, 2022
Bookmarks Related papers MentionsView impact
arXiv (Cornell University), May 12, 2022
Bookmarks Related papers MentionsView impact
arXiv (Cornell University), Jan 26, 2023
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Bookmarks Related papers MentionsView impact
Uploads
Drafts by Theodoros PAPANIKOLAOU
Papers by Theodoros PAPANIKOLAOU