Flavor effects on leptogenesis

1. Neutrino Oscillation Workshop Conca Specchiulla, Otranto, Italy, Sep. 9-16 2006 Flavor effects on leptogenesis Steve Blanchet Max-Planck-Institut für Physik, Munich Based on: SB, P. Di Bari, hep-ph/0607330 September 15, 2006

2. Outline • Review of unflavored leptogenesis and its implications • Idea of how flavor enters leptogenesis • General implications of flavor • Specific example • Non-zero Majorana phases can lead to large effects • Summary and conclusions

3. Unflavored thermal leptogenesis • Minimal extension of the SM • The BAU can be generated because [Fukugita, Yanagida, 86] : • CP is violated in the decay of heavy neutrinos • Baryon number is violated in sphaleron processes • Decays are out of equilibrium at some point, parametrized by CP asymmetry parameter ``decay parameter´´

4. Unflavored thermal leptogenesis • Notice how it is summed over the flavors • The fundamental Boltzmann equations are • Strong wash-out when • Weak wash-out when Sphalerons conserve B-L ! CP violation Out-of-equilibrium condition

5. Unflavored thermal leptogenesis • It is convenient to write the solution in the form where are the final efficiency factors. • The final baryon asymmetry is given by and should be compared to the measured value [WMAP,06] • Assuming one typically has a N1-dominated scenario.

6. WEAK WASH-OUT STRONG WASH-OUT

7. Implications of unflavored leptogenesis • From the upper bound on the CP asymmetry[Asaka et al., 01; Davidson, Ibarra, 02] one obtains a lower bound on M1 and on the reheating temperature independent of the initial conditions[Davidson, Ibarra, 02; Buchmüller, Di Bari, Plümacher, 02] : • The suppression of the CP asymmetry for growing absolute neutrino mass scale leads to a stringent upper bound[Buchmüller, Di Bari, Plümacher, 02] :

8. How does flavor enter leptogenesis? • Below some temperature ~109-11 GeV, the muon and tauon charged lepton interactions are in equilibrium. • These interactions are then fast enough to ‘measure’ the flavor of the state produced in the decay of the heavy neutrino; a 3-flavor basis is defined. [Barbieri, Creminelli, Strumia, Tetradis, 99 ; Endoh, Morozumi, Xiong, 03; Abada, Davidson, Josse-Michaux, Losada, Riotto, 06 ; Nardi, Nir, Racker, Roulet, 06]

9. How does flavor enter leptogenesis? • The fundamental Boltzmann equations become Same as before! • First type of effect: the rates of decay and inverse decay in each flavor are suppressed by the projectors [Nardi et al., 06] • Second type of effect: additional contribution to the individual CP asymmetries: [Nardi et al., 06]

10. NO FLAVOR Nj Φ L Le Lμ Ni Lτ Φ

11. WITH FLAVOR (all projectors equal) Nj Φ Le Lμ Lτ Ni Φ

12. General implications of flavor • There exists an upper bound on the individual CP asymmetries [Abada, et al., 06]: It does not decrease when the active neutrino mass scale increases! • Possible scenarios: • Alignment case [Nardi et al., 05] • Democratic (semi-democratic) case • One-flavor dominance and like unflavored case factor 2-3 effect and potentially big effect!

13. General implications of flavor semi-democratic alignment • Lower bounds democratic 3x109 The lowest bounds independent of the initial conditions (K*) do not change!

14. General implications of flavor • At fixed K1, there is a relaxation of the lower bounds [Abada et al., 06] . How much? Factor 2-3 typically, but it depends on the projectors (could be much more!). • However, the region of independence of initial conditions shrinks when the flavor effects increase (small projector, i.e. one-flavor dominance)

15. Specific example • Let us now study a specific case, , using the known information about the PMNS mixing matrix. • For a fully hierarchical light neutrino spectrum one obtains a semi-democratic situation where • For a real UPMNS and purely imaginary Semi-democratic

16. Specific example: Majorana phase effects • With ~ Semi-democratic • With One-flavor dominance

17. Specific example: Majorana phase effects • Summary of with purely imaginary • Case of real cf. talk by Petcov this morning

18. Summary and conclusions • Flavor effects can be important, but when they are, the region of the parameter space where leptogenesis does not depend on the initial conditions shrinks. • The lower bounds on M1 and Treh in the strong wash-out are not relaxed, but the bounds at fixed K are. The upper limit on m1 seems to disappear when M1<1012 GeV. • Quantitatively, flavor effects yield O(1) modification of the usual results, except either when there is one-flavor dominance or when the total CP asymmetry vanishes. In both cases, Majorana phases play an important role. • The one-flavor dominance seems to occur mainly when light neutrinos are quasi-degenerate. • In conclusion, leptogenesis provides another phenomenology where Majorana phases matter.