Alexandrou Constantia, Finkenrath Jacob, Funcke Lena, Jansen Karl, Kostrzewa Bartosz, Pittler Ferenc, Urbach Carsten
Department of Physics, University of Cyprus, P.O. Box 20537, 1678 Nicosia, Cyprus.
Computation-Based Science and Technology Research Center, The Cyprus Institute, 20 Konstantinou Kavafi Street, 2121 Nicosia, Cyprus.
Phys Rev Lett. 2020 Dec 4;125(23):232001. doi: 10.1103/PhysRevLett.125.232001.
The infamous strong CP 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 up-quark mass without reintroducing CP 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 strange-quark mass. We find that the size of the topological mass contribution is inconsistent with the massless up-quark solution to the strong CP problem.
