A loophole to the universal photon spectrum in electromagnetic cascades: application to the "cosmological lithium problem"

Abstract

The standard theory of electromagnetic cascades onto a photon background predicts a quasi-universal shape for the resulting non-thermal photon spectrum. This has been applied to very disparate fields, including non-thermal big bang nucleosynthesis (BBN). However, once the energy of the injected photons falls below the pair-production threshold the spectral shape is very different, a fact that has been overlooked in past literature. This loophole may have important phenomenological consequences, since it generically alters the BBN bounds on non-thermal relics: for instance it allows to re-open the possibility of purely electromagnetic solutions to the so-called "cosmological lithium problem", which were thought to be excluded by other cosmological constraints. We show this with a proof-of-principle example and a simple particle physics model, compared with previous literature.

5 pages, 2 figures, typos corrected; matches version published in PRL. (Version 1 of this article was submitted to arxiv on Jan. 8th, kept on hold by arxiv moderators due to unspecified classification doubts for almost one month.)

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Cited by in corpus (14)

• Challenges for $\Lambda$CDM: An update
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• The 7Be(n,alpha)4He reaction and the Cosmological Lithium Problem: measurement of the cross section in a wide energy range at n_TOF (CERN)
• BBN constraints on the annihilation of MeV-scale dark matter
• Non-universal BBN bounds on electromagnetically decaying particles
• Machine learning constraints on deviations from general relativity from the large scale structure of the Universe
• Cosmology Intertwined: A Review of the Particle Physics, Astrophysics, and Cosmology Associated with the Cosmological Tensions and Anomalies
• Production of heavy sterile neutrinos from vector boson decay at electroweak temperatures
• Cosmological Bounds on sub-GeV Dark Vector Bosons from Electromagnetic Energy Injection
• Manifesting hidden dynamics of a sub-component dark matter
• Light Dark Matter: A Common Solution to the Lithium and $H_0$ Problems
• BBN Photodisintegration Constraints on Gravitationally Produced Vector Bosons
• Updated cosmological constraints on Macroscopic Dark Matter
• Cosmological constraints on the decay of heavy relics into neutrinos