AST 324: HOMEWORK 3
Based on the laws of conserved quantities, decide whether the
following reactions can occur. You can assume that sufficient energy is
always available, so you only have to consider charge, lepton number, and
baryon number. Explain your answers.
What happens when the temperature of the Universe drops below 6 x 109
K, the threshold temperature for pair production of electrons and
positrons? What is the wavelength of the photons that are capable of this
Given that muons ((mu)- or (mu)+) have masses which are
about 200 times
that of the electron, what temperature would be needed for pair production
of muons? How old was the Universe when the temperature was this high?
Explain why the fraction of baryons in the form of neutrons shrinks
from roughly 50% to about 13% during the first 3 to 4 minutes of the
Universe's history. Explain why the fraction is not even smaller by the
time 3 to 4 minutes has elapsed.
Evans's 324 |