Pair Production By Primordial Black Hole Evaporation

Author

Shaun Hampton, Clemson UniversityFollow

Date of Award

5-2013

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Physics

Committee Chair/Advisor

Hartmann, Dieter

Committee Member

Marinescu , Catalina

Committee Member

Leising , Mark

Abstract

Here we investigate the evaporation of a 8.2 _ 1010 kg primordial black hole. This mass is shown to
satifisfy the compactness parameter constraint L/R ≥ 1031 ergscm−1s−1. We assume only photon-photon
production according to a Planck distribution. We calculate the distance from the black hole at which the
optical depth due to photon-photon collisions to produce positron/electron pairs becomes unity in which a
pair plasma is produced within a volume of inner radius of 90RS and outer radius 123000R_S respectively.
We then calculate corresponding positron/electron production rates, production rate densities, and optical
depth rates due to subsequent Compton scattering by photons. We quantitatively investigate annihilation
rate densities and number of annihilations for number densities generated by an initially static fireball that
after a time △t_L = 5 _ 10−20s is allowed to propagate radially at the speed of light. We show that the
annihilation rate per particle is given by < σv >= 1.2_10−39m3s−1 where we approximate cos θ ≈ 1 between
positron and electron collisions and derive a probability distribution function by Monte Carlo methods for
positron and electron velocities sourced by field and target photons emitted by the black hole given by the
approximation γ ₊= γ₋ ≈ (E+ε)/(2m_ec2) whose corresponding velocities are directed radially. We show that no
annihilations occur within the expanding fireball and that electrons and positrons freely stream from the proximity of the BH. We investigate the spectra produced by different mass (thermal energy) BH's that are currently evaporating. We analyze their limiting behavior and compare with blackbody emission from stars. We then discuss detection methods and limitations from possible gamma ray and positron sources including the 511 keV line emission from the galactic center, high energy cosmic ray positron production, and direct gamma ray burst events.

Recommended Citation

Hampton, Shaun, "Pair Production By Primordial Black Hole Evaporation" (2013). All Theses. 1600.
https://open.clemson.edu/all_theses/1600