The Cosmological Heavy Ion Collider: Fast Thermalization after Cosmic Inflation. (arXiv:2001.03633v1 [hep-th])
<a href="http://arxiv.org/find/hep-th/1/au:+McDonough_E/0/1/0/all/0/1">Evan McDonough</a>
Heavy-ion colliders have revealed the process of “fast thermalization”. This
experimental break-through has led to new theoretical tools to study the
thermalization process at both weak and strong coupling. We apply this to the
reheating epoch of inflationary cosmology, and the formation of a cosmological
quark gluon plasma (QGP). We compute the thermalization time of the QGP at
reheating, and find it is determined by the energy scale of inflation and the
shear viscosity to entropy ratio $eta/s$; or equivalently, the
tensor-to-scalar ratio and the strong coupling constant at the epoch of
thermalization. Thermalization is achieved near-instantaneously in low-scale
inflation and in strongly coupled systems, and takes less than an e-fold of
expansion for weakly-coupled systems or after high-scale inflation. We then
consider the potential for observing this process: we demonstrate that the
cosmic microwave background is largely insensitive, and the shift in $n_s$ and
$r$ is well below the sensitivity of CMB S4 and Simons Observatory. We also
find a stochastic background of gravitational waves at frequencies accessible
by interferometers, albeit at a level unobservable by even next generation
experiments.
Heavy-ion colliders have revealed the process of “fast thermalization”. This
experimental break-through has led to new theoretical tools to study the
thermalization process at both weak and strong coupling. We apply this to the
reheating epoch of inflationary cosmology, and the formation of a cosmological
quark gluon plasma (QGP). We compute the thermalization time of the QGP at
reheating, and find it is determined by the energy scale of inflation and the
shear viscosity to entropy ratio $eta/s$; or equivalently, the
tensor-to-scalar ratio and the strong coupling constant at the epoch of
thermalization. Thermalization is achieved near-instantaneously in low-scale
inflation and in strongly coupled systems, and takes less than an e-fold of
expansion for weakly-coupled systems or after high-scale inflation. We then
consider the potential for observing this process: we demonstrate that the
cosmic microwave background is largely insensitive, and the shift in $n_s$ and
$r$ is well below the sensitivity of CMB S4 and Simons Observatory. We also
find a stochastic background of gravitational waves at frequencies accessible
by interferometers, albeit at a level unobservable by even next generation
experiments.
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