Thermalization of the Primordial Stochastic Gravitational-Wave Background

It is conventionally believed that the Stochastic Gravitational-Wave Background from inflation provides information about the earliest universe. However, in this Letter, we present a different picture.

It is conventionally believed that the Stochastic Gravitational-Wave Background (SGWB) from inflation provides information about the earliest universe. Both individuals and organizations that work with arXivLabs have embraced and accepted our values of openness, community, excellence, and user data privacy.

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Abstract: It is conventionally believed that the Stochastic Gravitational-Wave Background (SGWB) from inflation provides information about the earliest universe. Our analysis starts from the observation that the inflation-predicted spectrum implies gravitons reside in high-occupation states, which significantly enhances their self-interactions and triggers rapid thermalization.

We show that approximately $80\%$ of the primordial gravitons participate in this thermalization, forming a Bose--Einstein distribution and thereby erasing the primordial information. Due to the sharp drop-off away from the peak, the resulting spectrum lies beyond the reach of low-frequency observatories like PTAs, LISA, and LIGO, but remains uniquely accessible to high-frequency detectors such as microwave cavity resonators and dielectric haloscopes.

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