Abstract
We investigate the gravitational production of a scalar field χ with a mass exceeding the Hubble scale during inflation mχ ≳ HI, employing both analytical and numerical approaches. We demonstrate that the steepest descent method effectively captures the epochs and yields of gravitational production in a compact and simple analytical framework. These analytical results align with the numerical solutions of the field equation. Our study covers three spacetime backgrounds: de Sitter, power-law inflation, and the Starobinsky inflation model. Within these models, we identify two distinct phases of particle production: during and after inflation. During inflation, we derive an accurate analytic expression for the particle production rate, accounting for a varying Hubble rate. After inflation, the additional burst of particle production depends on the inflaton mass around its minimum. When this mass is smaller than the Hubble scale during inflation, HI, there is no significant extra production. However, if the inflaton mass is larger, post-inflation production becomes the dominant contribution. Furthermore, we explore the implications of gravitationally produced heavy fields for dark matter abundance, assuming their cosmological stability.
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Acknowledgments
We thank Valerie Domcke, Marcos A. G. García, Yohei Ema, Rocky Kolb, Marco Peloso, Riccardo Penco, Mathias Pierre, Michele Redi, Antonio Riotto, Leonardo Senatore and Richard Woodard for useful discussions and comments. D.R. is supported in part by NSF Grant PHY-2014215, DOE HEP QuantISED award #100495, and the Gordon and Betty Moore Foundation Grant GBMF7946. D.R. acknowledges hospitality from the Perimeter Institute for Theoretical Physics during the preparation of this paper. Research at Perimeter Institute is supported in part by the Government of Canada through the Department of Innovation, Science and Economic Development Canada and by the Province of Ontario through the Ministry of Colleges and Universities. S.V. and W.X. are supported in part by the U.S. Department of Energy under grant DE-SC0022148 at the University of Florida.
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Racco, D., Verner, S. & Xue, W. Gravitational production of heavy particles during and after inflation. J. High Energ. Phys. 2024, 129 (2024). https://doi.org/10.1007/JHEP09(2024)129
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DOI: https://doi.org/10.1007/JHEP09(2024)129