Question

2. The present-day acceleration of the Universe could also be due to the existence of a false vacuum which will eventually decay. Assume that the energy of the false vacuum is εΛ 0.73 ε00, the energy of m atter is e,n,0 0.27 Eco, the Universe is flat, and e,0 5200 MeV m-3 a) What is the value of the Hubble parameter once completely dominates the expan- sion? Express it in units of km s-1 Mpc-1 and in units of to (where to = 13.75 Gyr is the present age of Universe). [10 pts b) Suppose that the false vacuun decays spontaneously at a time tf = 30to and all the energy is converted into radiation with a blackbody spectrum. To what temperature will the Universe be reheated? [10 pts c) What will the energy density of matter be when t-tf. [Hint, assume we are already -dominated at t to.] [10 pts] d) After the decay the Universe is dominated by radiation. At what time will the Universe again be dominated by matter? [10 pts

Answer 1

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2. H hubble dnta Ca STTG 3

Ro ㄥ at t=t (e 142 Jci