Astrophysical constraints on primordial black holes in Brans-Dicke theory

Abstract

We consider cosmological evolution in Brans-Dicke theory with a population of primordial black holes. Hawking radiation from the primordial black holes impacts various astrophysical processes during the evolution of the Universe. The accretion of radiation by the black holes in the radiation dominated era may be effective in imparting them a longer lifetime. We present a detailed study of how this affects various standard astrophysical constraints coming from the evaporation of primordial black holes. We analyze constraints arising from the present density of the Universe, the present photon spectrum, the distortion of the cosmic microwave background spectrum and also from processes affecting light element abundances after nucleosynthesis. We find that the constraints on the initial primordial black hole mass fractions are tightened with increased accretion efficiency.

Study of terrestrial γ-ray background in presence of variable radioactivity from rain water

“…tial to unambiguously establish the phenomenon before embarking on serious attempts at its explanation. In a recent work based on the measurements made during the total solar eclipse of 1 August 2008 at Novosibirsk, Russia, we had also reported a variation in the flux of soft γ -rays over a wider energy region of 0.1-4.6 MeV [3]. These measurements were made with two large volume sodium iodide crystal detectors that were more than an order of magnitude larger than the ones used in the earlier studies.…”

“…Several experiments such as the underground measurement of the radioactivity [4] for dark matter [5,6], and of course, the variation of the cosmic soft γ -ray flux during the total solar eclipse events [3,7], all require a precise measurement of the TGR background. As explained earlier, the TGR background fluctuates with time due to several contributing factors, chief among them being the radon decay products during the episodes of rain or snowfall.…”

Evolution of Primordial Black Hole Mass Spectrum in Brans–dicke Theory

“…where ρ c is present density of the universe ∼ 1.1 × 10 −29 gm/cm 3 . Again using different values of parameters of equations (53), (54) like n 1 ≈ 0.00007 [40,41], n = 3 and C ≈ O(1), we found for absence of accretion (f = 0)…”

Formation and Clustering of Primordial Black Holes in Brans-Dicke Theory

“…The paper [21] considered the effect of the gravitational constant changes in the Brans-Dicke theory on the number of PBHs formed. The evolution of PBHs population in the Brans-Dicke cosmology was also studied in [22,23]. A PBH is only formed from density perturbation that is greater than the certain threshold value.…”