Might the radiation era extend back to the Big Bang? On dark matter production and the relic graviton background in quadratic gravity
Abstract
Naive estimates based on Einstein gravity with Lagrangian 1/2Mpl2(R−2Λ) suggest that, if the radiation era extended back to the Big Bang (i.e., as far back as the classical spacetime background makes sense), this would result in an over-production of dark matter and a relic cosmic background of thermal gravitons. Here we revisit these conclusions in quadratic gravity, the minimal renormalizable completion of Einstein gravity, whose Lagrangian also includes the terms 1/6f0−2R2−1/2f2−2C2. Assuming the radiation era does extend back to the bang, we find a novel relation between the coefficient f2 and the dark matter mass mdm, needed to obtain the correct dark matter abundance. This yields a new gravitational production mechanism for dark matter (e.g., stable right-handed neutrinos). Moreover, the presence or absence of the relic graviton background (detectable by forthcoming CMB experiments via its small imprint on Neff) will place new constraints on f0, f2.
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BibTeX
@misc{boyle2026might,
title = {{Might the radiation era extend back to the Big Bang? On dark matter production and the relic graviton background in quadratic gravity}},
author = {Latham Boyle and Neil Turok and Vatsalya Vaibhav},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.11750},
eprint = {2609.11750},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.11750},
}
RIS
TY - UNPB
TI - Might the radiation era extend back to the Big Bang? On dark matter production and the relic graviton background in quadratic gravity
AU - Latham Boyle
AU - Neil Turok
AU - Vatsalya Vaibhav
PY - 2026
DA - 2026/09/10
PB - arXiv
DO - 10.48550/arxiv.2609.11750
UR - https://arxiv.org/abs/2609.11750
AB - Naive estimates based on Einstein gravity with Lagrangian 1/2M_pl^2(R−2Λ) suggest that, if the radiation era extended back to the Big Bang (i.e., as far back as the classical spacetime background makes sense), this would result in an over-production of dark matter and a relic cosmic background of thermal gravitons. Here we revisit these conclusions in quadratic gravity, the minimal renormalizable completion of Einstein gravity, whose Lagrangian also includes the terms 1/6f_0^−2R^2−1/2f_2^−2C^2. Assuming the radiation era does extend back to the bang, we find a novel relation between the coefficient f_2 and the dark matter mass m_dm, needed to obtain the correct dark matter abundance. This yields a new gravitational production mechanism for dark matter (e.g., stable right-handed neutrinos). Moreover, the presence or absence of the relic graviton background (detectable by forthcoming CMB experiments via its small imprint on N_eff) will place new constraints on f_0, f_2.
ER -