When Dark Matter Could Be Produced? (Cosmology / Thermodynamics / Astronomy)

Mambrini and Olive proposed the production of dark matter through the gravitational scattering of the inflaton. They found that sufficient GeV-ZeV dark matter can be obtained with reasonable values of reheating temperature (TRH) and maximum temperature (Tmax) by pure gravitational production through inflaton scattering. Their study recently published in ArXiv on dated 11 Feb 2021.

Inflation is a period of supercooled expansion, when the temperature drops by a factor of 100,000 or so. This relatively low temperature is maintained during the inflationary phase. When inflation ends, the temperature returns to the pre-inflationary temperature; this is called reheating or thermalization because the large potential energy of the inflaton field decays into particles and fills the Universe with Standard Model particles, including electromagnetic radiation, starting the radiation dominated phase of the Universe.

Illustration of the production of dark matter through the gravitational scattering of the inflaton. © Mambrini and Olive

They showed that the final abundance of dark matter depends not only on the reheating temperature, but also on the maximum temperature attained and hence on the detailed evolution of the reheating process.

We saw that GeV-ZeV dark matter can be obtained with reasonable values of TRH and Tmax by pure gravitational production through inflaton scattering

— said Olive

As per Mambrini and Olive, during reheating, a thermal bath is quickly generated with a maximum temperature Tmax, and the temperature decreases as the inflaton continues to decay until the energy densities of radiation and inflaton oscillations are equal, at TRH. During these oscillations, s-channel gravitational production of dark matter occurs.

During these oscillations, the inflaton density is high and the leading contribution to dark matter production occurs at the start of reheating at Tmax. This represents an absolute minimal amount of dark matter production and it contributes independent of any interactions the dark matter may have with the Standard Model (or another dark sector if present).

— said Mambrini.

Reference: Yann Mambrini, Keith A. Olive, “Gravitational Production of Dark Matter during Reheating”, Astronomical Journal, pp. 1-6, 2021. https://arxiv.org/abs/2102.06214


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