Axion cosmology, lattice QCD and the dilute instanton gas

• DOI: 10.1016/j.physletb.2015.11.020
• Publication Date: 2015-11-12T14:49:19Z
• Authors: Sz. Borsanyi; M. Dierigl; Z. Fodor; S.D. Katz; S.W. Mages; D. Nogradi; J. Redondo; A. Ringwald; K.K. Szabo
• Keywords: Instanton; Lattice (music)

Axions are one of the most attractive dark matter candidates. The evolution their number density in early universe can be determined by calculating topological susceptibility $χ(T)$ QCD as a function temperature. Lattice provides an ab initio technique to carry out such calculation. A full result needs two ingredients: physical quark masses and controlled continuum extrapolation from non-vanishing zero lattice spacings. We determine quenched framework (infinitely large masses) extrapolate its values limit. results compared with prediction dilute instanton gas approximation (DIGA). nice agreement is found for temperature dependence, whereas overall normalization DIGA still differs non-perturbative extrapolated factor order ten. discuss consequences our findings amount axion matter.