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CP violation has been measured in the hadronic sector (K-mesons, B-mesons) and these baryons can decay into leptons, so why is it so important to measure direct CP violation into the lepton sector? I could naively think that we have e.g. too many protons in the universe due to CP violation and then there are too many $K^-$ that decay into electrons (and antineutrinos, what is the ratio between antineutrinos and neutrinos in the universe?) and there you have our universe. I know there has to be a "quantitative" reason to make the search for CP violation in the lepton sector so significant, but I just cannot find it.

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CP violation in the hadronic sector is not enough to explain the observed baryon asymmetry in our universe, and it is one of the main problems in cosmological models.Any proposal that introduces naturally a baryon asymmetry is therefore very interesting.

If CP violation is measured in the lepton sector, there are theories which explain the baryon asymmetry observed in the present universe as mathematically connected with generation of the lepton asymmetry, and these models would become mainstream:

The Standard Model is extended by adding right-handed neutrinos, permitting implementation of the see-saw mechanism and providing the neutrinos with mass. At the same time, the extended model is able to spontaneously generate leptons from the decays of right-handed neutrinos. Finally, the sphalerons are able to convert the spontaneously generated lepton asymmetry into the observed baryonic asymmetry. Due to its popularity, this entire process is sometimes referred to simply as leptogenesis.

This paper describes a similar path.

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