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Unraveling Neutrino Masses and Leptogenesis: Recent Insights from CMB and Baryogenesis Models

Explore the latest developments in neutrino mass research and leptogenesis as presented by Pasquale Di Bari at the 2007 Aarhus conference. This summary delves into the implications of the cosmic microwave background, matter-antimatter asymmetry, and various baryogenesis models. Key topics include the see-saw mechanism, lepton asymmetries, CP violation, and the interplay between neutrino mass bounds and cosmological observations. The findings emphasize the need for new physics to address unresolved questions and challenge existing models of inflation and baryogenesis.

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Unraveling Neutrino Masses and Leptogenesis: Recent Insights from CMB and Baryogenesis Models

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  1. Pasquale Di Bari (Max Planck, Munich) ‘The path to neutrino mass’ , Aarhus, 3-6 September, 2007 Recent developments in Leptogenesis

  2. CMB CMB SM Matter-antimatter asymmetry • Symmetric Universe with matter- anti matter domains ?Excluded by CMB + cosmic rays )B = (6.1± 0.2) x 10-10>>B (WMAP 2006) • Pre-existing ? It conflicts with inflation ! (Dolgov ‘97) ) dynamical generation (baryogenesis) • A Standard Model Solution ?B ¿ B : too low ! (Sakharov ’67) New Physics is needed!

  3. From phase transitions: -Electroweak Baryogenesis: * in the SM * in the MSSM * ……………. Affleck-Dine: - at preheating - Q-balls - ………. From Black Hole evaporation Spontaneous Baryogenesis ………………………………… From heavy particle decays: - GUT Baryogenesis - LEPTOGENESIS Models of Baryogenesis

  4. Neutrino masses: m1 < m2 < m3 Tritium  decay : me < 2.3 eV (Mainz 95% CL) 0 : m < 0.3 – 1.0 eV (Heidelberg-Moscow 90% CL, similar result by CUORICINO ) using the flat prior (0=1): CMB+LSS :  mi < 0.94 eV (WMAP+SDSS) CMB+LSS + Ly :  mi < 0.17 eV (Seljak et al.)

  5. Minimal RH neutrino implementation • 3 limiting cases : • pure Dirac: MR= 0 • pseudo-Dirac : MR << mD • see-saw limit: MR >> mD

  6. See-saw mechanism 3 light LH neutrinos: N2 heavy RH neutrinos: N1, N2 , … SEE-SAW m n  M • the `see-saw’ pivot scale  is then an important quantity to understand the role of RH neutrinos in cosmology

  7. * ~ 1 GeV • > *  high pivot see-saw scale `heavy’ RH neutrinos • < *  low pivot see-saw scale  `light’RH neutrinos

  8. The see-saw orthogonal matrix

  9. Basics of leptogenesis (Fukugita,Yanagida ’86) M, mD, mare complex matrices  natural source of CP violation CP asymmetry If i≠ 0 alepton asymmetryis generated from Ni decays and partly converted into a baryon asymmetry by sphaleron processes if Treh 100 GeV ! (Kuzmin,Rubakov,Shaposhnikov, ’85) efficiency factors# of Ni decaying out-of-equilibrium

  10. ‘Vanilla’ leptogenesis • Unflavoured regime • Semi-hierarchical heavy neutrino spectrum :

  11. Total CP asymmetry (Flanz,Paschos,Sarkar’95; Covi,Roulet,Vissani’96; Buchm¨uller,Pl ¨umacher’98) (Davidson, Ibarra ’02; Buchmüller,PDB,Plümacher’03;PDB’05 ) It does not depend on U !

  12. Efficiency factor (Buchm¨uller,PDB, Pl ¨umacher ‘04)

  13. z´ M1/ T K1´ tU(T=M1)/1 (Blanchet, PDB ‘06) WEAK WASH-OUT STRONG WASH-OUT zd

  14. Dependence on the initial conditions m1 msol M11014 GeV Neutrino mixing data favor the strong wash-out regime !

  15. Neutrino mass bounds ~ 10-6 ( M1 / 1010 GeV) Upper bound on the absolute neutrino mass scale (Buchmüller, PDB, Plümacher ‘02) 0.12 eV Lower bound on M1 (Davidson, Ibarra ’02; Buchmüller, PDB, Plümacher ‘02) 3x109 GeV Lower bound on Treh: Treh 1.5 x 109 GeV (Buchmüller, PDB, Plümacher ‘04)

  16. Need of a very hot Universe for Leptogenesis

  17. Beyond the minimal picture • M2 M3 • N2-dominated scenario • beyond the hierarchical limit • flavor effects

  18. A poorly known detail If M3  M2 : (Hambye,Notari,Papucci,Strumia ’03; PDB’05; Blanchet, PDB ‘06 )

  19. N2-dominated scenario (PDB’05) Four things happen simultaneously: For a special choice of the see-saw orthogonal matrix:  The lower bound on M1 disappears and is replaced by a lower bound on M2 …that however stillimplies a lower bound on Treh !

  20. Beyond the hierarchical limit (Pilaftsis ’97, Hambye et al ’03, Blanchet,PDB ‘06) Different possibilities, for example: • partial hierarchy: M3 >> M2 , M1 • heavy N3: M3 >> 1014 GeV 3 Effects play simultaneously a role for 2  1 :

  21. Flavor effects (Nardi,Roulet’06;Abada et al.’06;Blanchet,PDB’06) Flavour composition: Does it play any role ? but for lower values of M1 the-Yukawa interactions, are fast enough to break the coherent evolution of the and quantum states and project them on the flavour basis within the horizon  potentially a fully flavored regime holds!

  22. Fully flavoured regime Let us introduce theprojectors (Barbieri,Creminelli,Strumia,Tetradis’01) : These 2 terms correspond to 2 different flavour effects : • In each inverse decay the Higgs interacts now with • incoherent flavour eigenstates !  the wash-out is reduced and • 2. In general and this produces an additional CP violating contribution to the flavoured CP asymmetries: Interestingly one has that this additional contribution depends on U!

  23. In pictures: 1) N1 2)   N1  

  24. Classic Kinetic Equations in the fully flavored regime The asymmetries have to be tracked separately in each flavour: conserved in sphaleron transitions !

  25. General scenarios (K1 >> 1) • Alignment case • Democratic (semi-democratic) case • One-flavor dominance and and Remember that: big effect!  the one-flavor dominance scenario can be realized if the P1 term dominates !

  26. Lower bound on M1 semi-democratic (Blanchet,PDB’06) alignment The lowest bounds independent of the initial conditions (at K1=K*) don’t change!(Blanchet, PDB ‘06) democratic 3x109 But for a fixed K1, there is a relaxation of the lower boundsof a factor 2 (semi-democratic) or 3 (democratic) that can become much larger in the case of one flavor dominance.

  27. A relevant specific case • Let us consider: • Since the projectors and flavored asymmetries depend on U • one has to plug the information from neutrino mixing experiments • For m1=0(fully hierarchical light neutrinos) •   Semi-democratic case Flavor effects represent just a correction in this case !

  28. The role of Majorana phases • However allowing for a non-vanishing m1 the effects become much • larger especially when Majorana phases are turned on ! 1= 0 1= -  M1min (GeV) m1=matm 0.05 eV K1

  29. Is the upper bound on neutrino masses removed by flavour effects ? (Blanchet, PDB ’06) 0.12 eV EXCLUDED (Abada, Davidson, Losada, Riotto’06) M1 (GeV) FULLY FLAVORED REGIME EXCLUDED EXCLUDED m1(eV) Is the fully flavoured regime suitable to answer the question ?

  30. (Blanchet, PDB ’06) NO FLAVOR N1 N1 Φ l1 Φ

  31. (Blanchet, PDB ’06) R WITH FLAVOR Lτ N1 Φ Lµ l1 N1 Φ

  32. When the fully flavored regime applies ? (Blanchet,PDB,Raffelt ‘06) • Consider the rate  of processes like • The condition  > H (Nardi et al. ’06; Abada et al. ‘06) • (equivalent to T  M1 1012GeV) is sufficient for the validity of the fully flavored regime and of the classic Boltzmann equations only in the weak wash-out regime where H > ID , however all interesting flavour effects occur in the strong wash-out regime !! • In the strong wash-out regime the condition  > ID is stronger than •  > H and is equivalent to: • If K1K1 WID  1M1  1012 GeV • but if K1<< K1 WID >> 1much more restrictive ! • This applies in particular to the one-flavor dominated scenario through which the upper bound on neutrino masses would be removed in a classic description.

  33. Is the upper bound on neutrino masses killed by flavor effects ? ? 0.12 eV M1 (GeV) Condition of validity of a classic description in the fully flavored regime m1(eV) A definitive answer requires a genuine quantum kinetic calculation for a correct description of the `intermediate regime’ !

  34. Leptogenesis from low energy phases ? (Blanchet, PDB ’06) Let us now further impose  real setting Im(13)=0 M1min traditional unflavored case Majorana phases 1= - /2 2= 0  = 0 Dirac phase • The lower bound gets more stringent but still successful leptogenesis is possible just with CP violation from ‘low energy’ phases that can be • tested in 0 decay (Majorana phases) (very difficult) and more realistically in neutrino mixing (Dirac phase)

  35. -Leptogenesis (Anisimov, Blanchet, PDB, in preparation ) In the hierarchical limit (M3>> M2 >> M1 ): In this region the results from the full flavored regime are expected to undergo severe corrections that tend to reduce the allowed region M1 (GeV) 1= 0 2= 0  = -/2 sin13=0.20 Here some minor corrections are also expected • -leptogenesis represents another important motivation for a full Quantum Kinetic description • Going beyond the hierarchical limit these lower bounds can be relaxed :

  36. Unflavored versus flavored leptogenesis

  37. A wish-list for see-saw and leptogenesis • Treh  100 GeV (improved CMB data ? Discovery of GW background ?) • Electroweak Baryogenesis non viable • normal hierarchical neutrinos • discovery of CP violation in neutrino mixing • discovery of 0 • SUSY discovery with the right features: • - Electro-weak Baryogenesis non viable (this should be clear) • - discovery of LFV processes, discovery of EDM’s • discovery of heavy RH neutrinos: • - dream: directly at LHC or ILC • - more realistically: some indirect effect (EW precision measurements?, • some new cosmological effect, [e.g. RH neutrinos as DM] ? …… )

  38. Summary • Cosmological observations CDM model in conflict with the SM: • 4 puzzles aiming at new physics • Leptogenesisprovides a strong motivation fro heavy RH neutrinos and flavor effects open new prospects to test it in 0 decay experiments (Majorana phases)and (more realistically) in neutrino mixing experiments (Dirac phase) • Discovery of neutrino masses strongly motivates to search for solutions in terms of neutrino physics; adding RH neutrinos and taking the see-saw limit seems the simplest way to explain neutrino masses and to addressin an attractive way some of the puzzles; • Between lightand heavy RH neutrinos the second option appears currently • more robustly motivated (things could change for example if a N  0 is • discovered); • A unified picture of leptogenesis and dark matter is challenging but maybe • not impossible ! However a simultaneous solution of all puzzles seems to • require a deeper SM extension like (at least) GUT’s

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