Topology and Axions in QCD

QCD topology holds the key to the understanding of many aspects of strong interactions, and opens a window to dark matter. The same topological fluctuations which account for the mass of the eta’ meson give also  mass  to a yet unobserved, but intensively searched for, new particle, the QCD axion. We present here the current status of topological studies on the lattice, and their implication on axion physics. We outline the specific challenges posed by lattice topology,  the different proposals for handling them, the observable effects of  topology on  the QCD spectrum and  its interrelation with chiral and axial symmetries. We  review the transition to the Quark Gluon Plasma, the open issues, the fate of topology at the transition, and the approach to the high temperature limit. We discuss the extrapolations needed to  reach the regime of cosmological relevance, and the resulting constraints on the QCD axion.


  • Maria Paola Lombardo is a senior INFN researcher. Her research focusses on the physics of strong interactions, in particular the phases and phase transitions in QCD. She mostly uses the lattice approach and numerical simulations, and enjoys contrasting and comparing the lattice results with those of other approaches, as well as exploring applications of lattice studies to nearby fields.


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