A Cosmological Lithium Solution from Discrete Gauged Baryon Minus Lepton
  Number
  We propose the infrared gauge symmetry of our sector includes an unbroken
discrete gauged subgroup of baryon minus lepton number of order $2 \times 3
\text{ colors} \times 3 \text{ generations}$, the inclusion of which does not
modify local physics. We UV complete this at a scale $\Lambda$ as the familiar
$U(1)_{B-N_cL}$ Abelian Higgs theory, and the early universe phase transition
forms cosmic strings which are charged under an emergent higher-form gauge
symmetry. These topological defects catalyze interactions which turn $3$
baryons into $3$ leptons at strong scale rates in an analogue of the
Callan-Rubakov effect.
  The cosmological lithium problem -- that the observed primordial abundance is
lower than theoretical expectations by a factor of a few -- is perhaps the most
statistically significant anomaly of $\text{SM}+\Lambda\text{CDM}$, and has
resisted decades of attempts by cosmologists, nuclear physicists, and
astronomers alike to root out systematics. We write down a model in which
$B-N_cL$ strings superconduct bosonic global baryon plus lepton number currents
and catalyze solely $3p^+ \rightarrow 3e^+$. We suggest that such cosmic
strings have disintegrated $\mathcal{O}(1)$ of the lithium nuclei formed during
Big Bang Nucleosynthesis and estimate the rate, with our benchmark model
finding $\Lambda \sim 10^8 \text{ GeV}$ gives the right number density of
strings.
