Cladogenesis: Baryon-Dark Matter Coincidence from Branchings in Moduli Decay

TL;DR

The paper proposes that late-time decay of a string-theory modulus can provide a common, non-thermal origin for both the baryon asymmetry and dark matter. By diluting pre-existing relics with a modulus yield $Y_ au$ in the range $10^{-9}-10^{-7}$, and by controlling the branching fractions to a B− and CP‑violating state $N$ and to $R$-parity odd states that ultimately yield dark matter, the observed densities can be naturally reproduced without relying on dark matter annihilation. The framework yields $ _B/s = Y_ au r_N \e$ and $n_ ext{χ}/s = Y_ au r_ ext{χ}$, leading to a baryon–dark matter coincidence for DM mass in $(5-500)$ GeV with ${ m Br}_χ \gtrsim 10^{-3}$; achieving this requires suppressing two-body modulus decays to $R$-parity odd particles, which can arise from the modulus sector's geometry (local vs non-local vs hidden-sector moduli). If realized, this scenario links baryogenesis and dark matter to a single late-time cosmological event and offers a natural explanation for the observed coincidence.

Abstract

We propose late-time moduli decay as the common origin of baryons and dark matter. The baryon asymmetry is produced from the decay of new TeV scale particles, while dark matter is created from the (chain) decay of R-parity odd particles without undergoing any annihilation. The baryon and dark matter abundances are mainly controlled by the dilution factor from moduli decay, which is typically in the range 10^{-9}-10^{-7}. The exact number densities are determined by simple branching fractions from modulus decay, which are expected to be of similar order in the absence of symmetries. This scenario can naturally lead to the observed baryon asymmetry and, for moderate suppression of the two-body decays of the modulus to R-parity odd particles, can also yield the correct dark matter abundance for a dark matter mass in the (5-500) GeV range.