Sakurai Dissertation Award: A Cosmological Lithium Solution*

The cosmological lithium problem---that the observed primordial abundance is lower than theoretical expectations by a factor of a few---is the most statistically significant anomaly of SMΛCDMm_ν, and has resisted decades of attempts by cosmologists, nuclear physicists, and astronomers alike to root out systematics. Beginning with the conspiratorial observation that the atomic number of lithium matches the number of particle generations N_g, we uncover a surprisingly close link to fundamental physics. 

If baryon minus lepton number is gauged and spontaneously broken in the early universe to a discrete subgroup, cosmic strings are formed. As a result of the SM anomaly-free discrete Z_Ng subgroup of lepton number, such topological defects catalyze interactions which turn N_g protons into N_g positrons at strong scale rates in an analogue of the Callan-Rubakov effect. We argue toward a description of this effect in an infrared topological quantum field theory, and estimate the rates possible to demonstrate its cosmic relevance.