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arXiv · 1502.01250

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

Vivian Poulin·Pasquale D. Serpico
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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.

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Vivian Poulin, Pasquale D. Serpico. 2015-03-04. A loophole to the universal photon spectrum in electromagnetic cascades: application to the "cosmological lithium problem". https://doi.org/10.1103/physrevlett.114.091101

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