Thursday, May 5 2022, 3:55pm Zoom Meeting Departmental Colloquium J. Christopher Howk Department of Physics University of Notre Dame The predictions of light element abundances in standard Big Bang Nucleosynthesis agree very well with astrophysical probes of primordial material, with the exception of lithium. Most of the observational constraints we have on the primordial abundance and cosmic evolution of Li comes by way of the Li abundance in stellar atmospheres, which are four times lower than BBN predictions in the Planck era. A broad range of potential solutions to this "lithium problem" have been suggested, from stellar astrophysics solutions (depletion of the surface Li abundances in stars) to physics beyond the Standard Model (annihilating or decaying dark matter in the epoch of BBN). We have adopted a new approach to this problem, using observations of Li in interstellar gas of low-metallicity galaxies to probe the cosmic evolution of Li. I will summarize our results using this approach, including new estimates of the 7Li/6Li ratio that show no evidence for non-standard model approaches.
