Constraints on cosmic strings due to black holes formed from collapsed cosmic string loops

Abstract

The cosmological features of primordial black holes formed from collapsed cosmic string loops are studied. Observational restrictions on a population of primordial black holes are used to restrict f , the fraction of cosmic string loops which collapse to form black holes, and µ, the cosmic string mass-per-unit-length. Using a realistic model of cosmic strings, we find the strongest restriction on the parameters f and µ is due to the energy density in 100M eV photons radiated by the black holes. We also find that inert black hole remnants cannot serve as the dark matter. If earlier, crude estimates of f are reliable, our results severely restrict µ, and therefore limit the viability of the cosmic string large-scale structure scenario. 0 I. IntroductionThe cosmic string scenario for the formation of large scale structure has many observable features. Primarily, cosmic strings may serve to produce perturbations to the cosmological fluid of the necessary magnitude and distribution to seed the formation of galaxies and clusters, as observed today. Cosmic strings leave an observational signature through these perturbations, as well as through the emission of gravitational radiation. Broadly, then, there are two areas of cosmic string research. These are studies of the large-scale structure produced by cosmic strings, and tests of the compatibility of cosmic strings with cosmological observations. Such tests focus, for example, on the anisotropies produced by cosmic strings in the microwave background and the noise in pulsar timing due to the cosmic string stochastic gravitational wave background. Ultimately, the test of compatibility results in a restriction on µ, the mass-per-unit-length and sole free parameter in the cosmic string model. In this report, we will examine the restrictions on black holes formed from collapsed cosmic string loops.It is well known that a sufficiently smooth, circular cosmic string loop may collapse to form a black hole [1,2,3,4,5]. During the evolution of a network of cosmic strings, some cosmic string loops may collapse to form black holes. In this case, the observational restrictions on a population of primordial black holes may be used to restrict such a cosmic string scenario.The study of primordial black holes has been vigorously carried out in, for example, [6,7,8,9,10,11,12]. We will take advantage of this work in applying constraints to a population of black holes formed from collapsed cosmic string loops. In turn, we will place restrictions on the cosmic string network. In this paper, we will find observational restrictions on the cosmic string scenario from cosmic string loops which collapse to form black holes.The organization of this paper is as follows. In section II we will summarize previous efforts to estimate the fraction f of cosmic string loops which collapse to form black holes. In section III we will present the models of cosmic strings and black hole evaporation used to calculate the energy density in black holes and black hole radiation. In section IV we wil...

Limits on black hole formation from cosmic string loops

“…(Note that this limit was incorrectly interpreted in Eq. (4.1) of [25].) The newly published 30M eV − 120GeV extragalactic γ-ray background measured [26] by the EGRET experiment implies an updated limit on the present black hole density of [32]…”

“…The main reason for the difference is that in Ref. [25] the limit of Ref. [33] was applied incorrectly.…”

“…The constraints on black hole formation from cosmic strings set by the observed γ-ray background at 100M eV have been reanalyzed most recently by Caldwell and Gates [25] and by Caldwell and Casper [24] . In this Letter, we review and correct the analytic arguments in Ref.…”

Constraints on the cosmic string loop collapse fraction from primordial black holes

“…There are tight observational constraints on the abundance of Primordial Black Holes (PBHs), in particular from the products of their evaporation [9]. These constraints can be translated into limits on the cosmic string loop collapse fraction [10,11].…”

Cosmic String Loops Collapsing to Black Holes

“…Interestingly enough, only in one of the pioneering papers on the subject, the one by Polnarev and Zembowicz [2], is the derivation of f based on exact analytical expressions for the cosmic strings involved in the process. In all other discussions the derivation of f is based on linearized expressions for the string configurations (for instance [3,4]), rather general arguments and estimates (for instance [5,6]), observational data concerning high energy cosmic rays (for instance [7]- [9]) or the derivation is purely numerical (for instance [10,11]). And even in Ref.…”