CERN Lattice Coffee

Ab initio calculation of the neutron-proton mass difference

by Antonin Portelli (Southampton University)

Europe/Zurich
4/2-011 - TH common room (CERN)

4/2-011 - TH common room

CERN

15
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Description
(based on arXiv:1406.4088) The existence and stability of atoms relies on the fact that neutrons are more massive than protons. The mass difference is only 0.14% of the average. This tiny mass splitting has significant astrophysical and cosmological implications. A slightly smaller or larger value would have led to a dramatically different universe. Here we show, how this difference results from the competition between electromagnetic and mass isospin breaking effects. We compute the neutron-proton mass splitting and show that it is greater than zero by five standard deviations. Furthermore, splittings in the \Sigma, \Xi, D and \Xi_{cc} isospin multiplets are determined providing also predictions. We perform lattice Quantum-Chromodynamics plus Quantum-Electrodynamics computations with four, non-degenerate Wilson fermion flavours. Four lattice spacings and pion masses down to 195 MeV are used.