Ruling Out the Massless UpQuark Solution to the Strong C P Problem by Computing the Topological Mass Contribution with Lattice QCD
Abstract
The infamous strong C P problem in particle physics can in principle be solved by a massless up quark. In particular, it was hypothesized that topological effects could substantially contribute to the observed nonzero upquark mass without reintroducing C P violation. Alternatively to previous work using fits to chiral perturbation theory, in this Letter, we bound the strength of the topological mass contribution with direct lattice QCD simulations, by computing the dependence of the pion mass on the dynamical strangequark mass. We find that the size of the topological mass contribution is inconsistent with the massless upquark solution to the strong C P problem.
 Publication:

Physical Review Letters
 Pub Date:
 December 2020
 DOI:
 10.1103/PhysRevLett.125.232001
 arXiv:
 arXiv:2002.07802
 Bibcode:
 2020PhRvL.125w2001A
 Keywords:

 High Energy Physics  Lattice;
 High Energy Physics  Phenomenology;
 High Energy Physics  Theory
 EPrint:
 10 pages, 3 figures, updated references