Abstract
Abstract
The thermal plasma filling the early universe generated a stochastic
gravitational wave background that peaks in the microwave frequency
range today. If the graviton production rate is expressed as a series in a
fine-structure constant, α, and the temperature over the Planck mass,
T
2/m
pl
2, then the lowest-order contributions come from single
(∼αT
2/m
pl
2) and double (∼T
4/m
pl
4)
graviton production via 2 → 2 scatterings.
We show that in the Standard Model,
single-graviton production dominates if the maximal
temperature is smaller than
4 × 1018 GeV. This justifies previous calculations
which relied solely on single-graviton production.
We mention Beyond the Standard Model scenarios in which the single and
double-graviton contributions could be of comparable magnitudes.
Finally, we elaborate on what these results imply for the range of
applicability of General Relativity as an effective theory.