# Lepto-genesis and electroweak theory

Is there any term in standard electroweak theory that breaks CP-symmetry and thus explains lepto-genesis?

In the Standard Model, the lepton sector does not have CP violating couplings (at tree level). The quark sector however has CP-violating couplings (through the CKM matrix).

The PMNS matrix (describing neutrino mixing), may have a complex phase (implying CP violation). Whether it has a nonzero phase or not remains to be tested experimentally. This is however strictly speaking not part of the Standard Model.

I don't know however whether these effects can be large enough to explain the lepton/anti-lepton asymmetry in today's universe.

CP-violation in standard model is due to CKM complex phase of the quarks sector. You can see the parametrization of CKM matrix, like Wolfenstein parametrization, and see that there is only a phase in CKM matrix, the work of Kobayashi-Maskawa is about to understand that you need three generation of quarks to have CP-violation.

Now you can have a similar matrix for leptons sector Pontecorvo–Maki–Nakagawa–Sakata matrix, the fact is that we don't know this matrix like the CKM, for the simple fact that neutrinos have a little cross section so experiments with them are difficult. In the modern electroweak theory we have only "left" neutrino, and standard model seem to conserve leptonic flavour, but neutrinos oscillations give evidences against that, so you have to include "right" neutrinos or to think about neutrino like Majorana particle, but you are beyond standard model. From what I know you need one of these hypothesis to explain lepto-genesis, or something new beyond standard model.

You can try to explain it with baryo-genesis, but CP-violation in standard model is too low to explain our universe, to LHCb they are trying to find new physics effect in CP-violation in bottom-decay, because at some energy this need to exist.

An answer that I feel to give you is that leptonic sector in standard model is not so much clear now, neutrinos are now a big question mark, you can see for example neutrinoless double beta decay, a big puzzle for modern physics.