# Ab initio calculation of the neutron-proton mass difference

- Institution: CERN
- Department: TH Theoretical Seminar
- Speaker: Laurent Lellouch
- Year: 2015
- Language: English
- Source: [CERN](https://videos.cern.ch/record/3016631)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Teens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

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 and has significant astrophysical and cosmological implications. A slightly smaller or larger value would have led to a dramatically different universe. After an introduction to the problem and to lattice quantum chromodynamics (QCD), I will show how this difference can be computed precisely by carefully accounting for electromagnetic and mass isospin breaking effects in lattice computations. I will also report on results for splittings in the \Sigma, \Xi, D and \Xi_{cc} isospin multiplets, some of which are predictions. The computations are performed in lattice QCD plus QED with four, non-degenerate quark flavors..

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## Lectures

1. [Ab initio calculation of the neutron-proton mass difference](https://invisiblenetwork.ai/learn/cern/3016631/40f81f1e11e0), 1 h 9 min (CERN's player)