From Mysterious Exotic Particles to Axion Stars: Insights from Effective Field Theory

by Dr Abhishek Mohapatra ((Technical University of Munich)

Thursday 26 Feb 2026, 14:30 → 15:30 Asia/Kolkata

AG66

Nonrelativistic bound states lie at the heart of quantum physics, from particle and nuclear physics to atomic and condensed-matter systems. In this colloquium, I will discuss two striking examples: the XYZ exotic hadrons in QCD and axion stars, gravitationally bound states of nonrelativistic axions. A unifying theme will be how nonrelativistic effective field theories (EFTs) provide systematic and predictive insight into their structure and dynamics.

The discovery of more than fifty XYZ states—especially those containing two heavy quarks—poses a major challenge to our understanding of QCD. I will present a QCD-derived Born–Oppenheimer effective field theory (BOEFT) framework that offers a unified description of exotic hadrons of arbitrary composition. In this picture, hidden-heavy exotics arise naturally as bound states or resonances in potentials that are repulsive at short distances, intersect heavy-hadron thresholds, and approach them from below, explaining their near-threshold nature without predicting an unphysical excess of states. I will then turn to another arena where nonrelativistic EFT has played a central role: axion stars, gravitationally bound states of nonrelativistic axions, which are well-motivated dark-matter candidates. I will describe how an axion nonrelativistic EFT (axion EFT) can be constructed and used to analyze the axion stars as well as the prospects for their detection.