title: Ab initio calculation of the neutron-proton mass difference.
abstract: The existence and stability of atoms rely on the fact that neutrons are more massive than protons. The measured mass difference is only 0.14% of the average of the two masses. A slightly smaller or larger value would have led to a dramatically different universe. Here, we show that this difference results from the competition between electromagnetic and mass isospin breaking effects. We performed lattice quantum-chromodynamics and quantum-electrodynamics computations with four nondegenerate Wilson fermion flavors and computed the neutron-proton mass-splitting with an accuracy of 300 kilo-electron volts, which is greater than 0 by 5 standard deviations. We also determine the splittings in the Σ, Ξ, D, and Ξcc isospin multiplets, exceeding in some cases the precision of experimental measurements.
authors: Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany.
authors: Sz
authors: S
authors: Borsanyi
authors: Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany. Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52428 Jülich, Germany.
authors: S
authors: S
authors: Durr
authors: Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany. Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52428 Jülich, Germany. Institute for Theoretical Physics, Eötvös University, H-1117 Budapest, Hungary. fodor@bodri.elte.hu.
authors: Z
authors: Z
authors: Fodor
authors: Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany.
authors: C
authors: C
authors: Hoelbling
authors: Institute for Theoretical Physics, Eötvös University, H-1117 Budapest, Hungary. Lendület Lattice Gauge Theory Research Group, Magyar Tudományos Akadémia-Eötvös Loránd University, H-1117 Budapest, Hungary.
authors: S D
authors: SD
authors: Katz
authors: Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany. Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52428 Jülich, Germany.
authors: S
authors: S
authors: Krieg
authors: CNRS, Aix-Marseille Université, Université de Toulon, CPT UMR 7332, F-13288, Marseille, France.
authors: L
authors: L
authors: Lellouch
authors: Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany. Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52428 Jülich, Germany.
authors: T
authors: T
authors: Lippert
authors: CNRS, Aix-Marseille Université, Université de Toulon, CPT UMR 7332, F-13288, Marseille, France. School of Physics and Astronomy, University of Southampton, Southampton SO17 1BJ, UK.
authors: A
authors: A
authors: Portelli
authors: Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany. Jülich Supercomputing Centre, Forschungszentrum Jülich, D-52428 Jülich, Germany.
authors: K K
authors: KK
authors: Szabo
authors: Department of Physics, University of Wuppertal, D-42119 Wuppertal, Germany.
authors: B C
authors: BC
authors: Toth