CP violation

The discrete symmetries known as Charge conjugation (C) and parity (P) plays a very important role in Particle physics. C interchanges a particle with its antiparticle whereas P changes the handedness by reversing the space-coordinates x --> -x. The Standard model of particle physics which describes the observed fundamental particles and their interactions very successfully, violates both of these two discrete symmetries maximally. It violates C in the sense that the particle spectra has left handed neutrino but not the left handed anti-neutrino. P is violated in the sense that only left handed fermions have charged weak interactions and not the right handed ones. The combined operation of these two discrete symmetries CP is also violated in the Standard Model due to the presence of a CP violating phase in the quark mixing matrix (CKM matrix). C and CP violations are two of the four necessary criteria (Shakarov's conditions) required to produce the matter-antimatter asymmetry in the Universe. But the amount of CP violation in the quark sector of the Standard Model is too tiny to produce the large matter-antimatter asymmetry. This is one of the motivations to go beyond the Standard Model. This motivation got multiplied many times recently by the observed CP violation in Tevatron, Fermilab. One of it's detectors called DO has claimed to observe like-sign dimuon asymmetry in B meson decay which is 3.2 sigma away from the Standard Model predictions. Although this claim is yet to be confirmed, it has been taken very seriously across the world. I have already seen around ten papers which has explained this asymmetry by incorporating various new physics beyond the standard model. I am not sure whether this amount of CP violation (if confirmed to be correct) will be enough to produce the matter-antimatter asymmetry. If this suffices, then it will basically imply matter-antimatter asymmetry is generated at the TeV scale only. Since Tevatron is supposed to run till 2014 according to a recent proposal, we still have hope that it will verify this claim with much larger precision.

CP violations in Standard Model

In my previous post I wrote about my confusions regarding the contribution of CP violations present in the standard model to leptogenesis/baryogenesis. I have now got it cleared now. Basically the Shakarov's conditions talk about the violation of total baryon number, not generation wise violation which is intrinsic in the standard model also because of CP violation. Before electroweak symmetry breaking there was no CP violations in the Standard Model since the mass eigenstates and the flavour eigenstates were identical. But for Baryogenesis to occur we must have total baryon number violating processes at high energies which are of course suppressed at low energies.

CP violation

While reading some stuffs related to neutrino oscillations, I realized that neutrino oscillations can happen only after Electroweak Symmetry Breaking (EWSB). Since before EWSB happens, neutrinos( in fact all leptons and quarks) are massless and hence there is no oscillation and thus there is no CP violations. I started wondering about the cosmological significance of the CP violation in the leptonic sector. According to Shakarov's criteria CP violation is a must for leptogenesis to start. Now if the CP violation we see in the leptonic sector has something to contribute to leptogenesis then EWSB must happen before leptogenesis started. But according to current understanding of the thermal history of the Universe the matter-antimatter asymmetry started long before the Gev scale (EWSB). Thus whatever CP violation is there in the leptonic sector has no contribution to the leptogenesis. Although I have very little knowledge in leptogenesis, I found this point interesting. I asked my supervisor regarding other sources of CP violations which can contribute to leptogenesis. Then he said right handed heavy neutrinos is one such source. I have seen many models with B-L extended gauge symmetries which can accomodate right handed neutrinos. Now there are certain things which are not clear to me:
1. Why right handed neutrinos should preferentially decay to leptons rather than anti-leptons. I want to know how the CP violations take place in this case. Its definitely not like the oscillation of leptons which gives rise to CP violation in the usual leptonic sector.
2. Is it true that total lepton number is violated in such decay of right handed neutrinos? If yes then how can we incorporate these lepton number violating interactions in B-L extended gauge models where B-L breaking scale is not as high as the scale of leptogenesis.
I think I need to do some more careful studies rather than blindly coming into any conclusions. If anyone can help me with some references or comments that will be highly applauded.