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

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S. Blanchet, NOW 2006, 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

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S. Blanchet, NOW 2006, 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 ``decay parameter´´ CP asymmetry parameter

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S. Blanchet, NOW 2006, Unflavored thermal leptogenesis Notice how it is summed over the flavors The fundamental Boltzmann equations are Strong wash-out when Weak wash-out when CP violationOut-of-equilibrium condition Sphalerons conserve B-L !

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S. Blanchet, NOW 2006, 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 N 1 - dominated scenario.

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S. Blanchet, NOW 2006, WEAK WASH-OUTSTRONG WASH-OUT

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S. Blanchet, NOW 2006, From the upper bound on the CP asymmetry [Asaka et al., 01; Davidson, Ibarra, 02] one obtains a lower bound on M 1 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] : Implications of unflavored leptogenesis

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S. Blanchet, NOW 2006, How does flavor enter leptogenesis? Below some temperature ~ 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]

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S. Blanchet, NOW 2006, Second type of effect: additional contribution to the individual CP asymmetries: First type of effect: the rates of decay and inverse decay in each flavor are suppressed by the projectors How does flavor enter leptogenesis? The fundamental Boltzmann equations become Same as before! [Nardi et al., 06]

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S. Blanchet, NOW 2006, NiNi L NO FLAVOR NjNj Φ Φ LeLe LμLμ LτLτ

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S. Blanchet, NOW 2006, NiNi WITH FLAVOR (all projectors equal) NjNj Φ Φ LτLτ LeLe LμLμ

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S. Blanchet, NOW 2006, Possible scenarios: Alignment case [Nardi et al., 05] Democratic (semi-democratic) case One-flavor dominance General implications of flavor There exists an upper bound on the individual CP asymmetries [Abada, et al., 06] : and It does not decrease when the active neutrino mass scale increases! potentially big effect! like unflavored case factor 2-3 effect

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S. Blanchet, NOW 2006, General implications of flavor Lower bounds 3x10 9 alignment democratic semi- democratic The lowest bounds independent of the initial conditions (K * ) do not change!

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S. Blanchet, NOW 2006, General implications of flavor At fixed K 1, 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)

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S. Blanchet, NOW 2006, 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 U PMNS and purely imaginary Semi-democratic

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S. Blanchet, NOW 2006, Specific example: Majorana phase effects With ~ Semi-democratic One-flavor dominance With

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S. Blanchet, NOW 2006, Summary of with purely imaginary Specific example: Majorana phase effects Case of real cf. talk by Petcov this morning

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S. Blanchet, NOW 2006, 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 M 1 and T reh in the strong wash-out are not relaxed, but the bounds at fixed K are. The upper limit on m 1 seems to disappear when M 1 <10 12 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.

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