New Physics Searches in Rocks and Stars

Abstract

This thesis explores the use of stellar interiors and ancient minerals as probes of physics beyond the Standard Model. In the first part, we investigate the potential of paleodetection, which utilises ancient minerals as particle detectors over geological timescales. Using TRIM simulations, we refine the modelling of track distributions and find that earlier studies have overestimated the sensitivity of paleodetection. We identify three key results: (a) the recoil energy–track length relation is not one-to-one; (b) at low recoil energies, a substantial fraction of recoils do not yield any tracks; and (c) at high energies, electronic stopping becomes dominant, resulting in a track length barrier at ~200nm. In addition to WIMPs, we also modelled tracks from generalised coherent elastic neutrino–nucleus scattering (CEνNS) via new light mediators and estimated the projected sensitivity for these interactions. In the second part, we turn to stellar systems. Stellar energy loss is a sensitive probe of light, weakly coupled dark sectors, including those containing millicharged particles (MCPs). The emission of MCPs can affect stellar evolution and therefore alter the observed properties of stellar populations. We improve upon the accuracy of existing stellar limits on MCPs by self-consistently modelling (1) the MCP emission rate, accounting for all relevant in-medium effects and production channels; and (2) the evolution of stellar interiors (including backreactions from MCP emission) using the MESA stellar evolution code. We find that MCP emission leads to significant brightening of the tip of the red giant branch. Based on photometric observations of 15 globular clusters, whose bolometric magnitudes are inferred using parallaxes from Gaia astrometry, we obtain robust bounds on the existence of MCPs with masses below 100 keV. We extend this analysis in ongoing work to explore the effects of MCP emission on the evolution of horizontal branch and asymptotic giant branch stars. These phases provide complementary sensitivity due to their different core conditions and energy transport mechanisms. This continued study aims to refine the mapping between energy loss and stellar observables, namely R- and R2-parameters, with the goal of identifying new regions of parameter space that MCPs may leave detectable imprints.