Pasquale Di Bari (Max Planck, Munich)

1. Pasquale Di Bari (Max Planck, Munich) Università di Milano, February 8, 2007 Can neutrinos help to solve the puzzles of modern cosmology ?

2. Outline • A cosmological Standard Model ? • Puzzles of Modern Cosmology • Right-handed neutrinos in cosmology: light vs. heavy • Leptogenesis

3. A cosmological Standard Model ?

4. WMAP

5. Large Scale Structure The Universe observed: Sloan Digital Sky Survey The Universe simulated : • Open problems: • cusps (too much Dark Matter in halo centers ?) • Halo substructure issues (too many satellite galaxies ?) • Halo and galaxy merging (too much galaxy merging ?)

6. Toward a Cosmological SM ?

7. The Mass-Energy budget today

8. The Universe is accelerating ! ( , M) = (0.7 , 0.3) q = 0 ( , M) = (0, 0.3) ( , M) = (0,1) Hubble diagram: High-redshift type Ia supernovae probe the expansion history and reveal accelerated expansion

9. Cosmological Concordance Clusters of galaxies are a laboratory for studying and measuring Dark Matter in a variety of ways: gravitational lensing effects, x-ray, radio, optical ….

10. Thermal history of the Universe

11. Matter - antimatter asymmetry Dark matter Accelerating Universe Inflation Puzzles of Modern Cosmology

12. Matter-antimatter asymmetry • Symmetric Universe with matter- anti matter domains ?Excluded by CMB + cosmic rays )B = (6.3± 0.3) x 10-10>>B • Pre-existing ? It conflicts with inflation ! (Dolgov ‘97) ) dynamical generation (baryogenesis) • A Standard Model Solution ?B ¿ B : too low ! CMB (Sakharov ’67) CMB SM New Physics is needed!

13. Dark Matter • What do we need today to explain Dark Matter : a new particle … … or a new description of gravity ? Modification of Newtonian Dynamics (MOND) • For accelerations a < a0' 10-8 cm s-2 usual Newton law is modified (Milgrom ’83) • Relativistic tensor-vector-scalar field theory for MOND (Bekenstein ’04) • However different observations (gravitational lensing, CMB, baryon acoustic oscillation peak, ‘bullet’ cluster, …) tend to exclude it and we will not consider it ! Particle Dark Matter It is the most conservative option with many theoretical motivations: SUSY DM (neutralinos,gravitinos,…),extra DIM’s, Wimpzilla’s, sterile neutrinos, .. Today we know that the new particles have to be slowly moving at the matter-radiation equivalence (T ~ 3 eV )Cold Dark Matter (M10KeV) Neutrinos behave as HOT Dark Matter

14. C.C.  ? Why small ? SUSY breaking - Anthropic principle(Weinberg ’87) - only the fluctuations of the vacuum energy contribute to  and not its absolute value (Zel’dovich 67) Quintessence ? A light scalar field still rolling down: w  -1 in general Without Dark Energy modifying gravity At large distances, motivated in brane world scenarios (Dvali,Gabadadze,Porrati `00) without modifying gravity attempt to explain acceleration without new physics: acceleration would arise frominhomogeneities inside the horizon it would solve the coincidence problem but……..unfortunately it is unlikely to work ! Accelerating Universe With Dark Energy

15. Inflation • It solves the well known problems of ‘old’ cosmology (horizon problem, flatness problem, initial conditions, spectrum of primordial perturbations…) • supported by CMB data • On the other hand it leads to serious problems that require to go beyond the SM: - where inflation comes from ? what is the inflaton ? - flatness of the potential - trans-Planckian scales inside the horizon - does not solve the problem of singularity (it is only shifted at earlier times) - cosmological constant problem (the large quantum vacuum energy of field theories does not gravitate today and thus we do not want it….but it is necessary for inflation !)

16. Some considerations Experimental long-standing issues have been solved and the puzzles of modern cosmology are nicely expressed in a particle physics `language’ but they cannot be explained within the SM ! In other words: cosmologists have cleaned their room but they swept away all the dust in the particle physicists lounge ! Which model beyond the Standard Model of Particle Physics can solve the cosmological puzzles ?

17. Neutrino masses: m1< m2 < m3

18. RH neutrinos in cosmology: light vs. heavy

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

20. 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

21. * ~ 1 GeV • > *  high pivot see-saw scale `heavy’ RH neutrinos • < *  low pivot see-saw scale  `light’RH neutrinos

22. Light RH neutrinos and…. • …..LSND A see-saw mechanism with ~0.1eV can accommodate LSND with a ‘3+2’ data fit (De Gouvea’05) but potential problems with BBN and CMB ~0.1eV • …..CMB • -0.3< N < 1.6 (95% CL) (no Ly) • (Hannestad,Raffelt) • 0.6< N < 4.4 (95% CL) (with Ly) • (Seljak,Slosar,McDonald) A future 5 th cosmological puzzle ? It would be very interesting especially for neutrinos

23. …Dark Matter • active-RH neutrino mixing: N ~ mD/M << 1 , the RH neutrino production is enhanced by matter effects and (Dodelson,Widrow’94;Dolgov,Hansen’01; Abazajian,Fuller,Patel’01) • For `see-saw ‘ RH neutrinos the condition can be fullfilled if m1<10-5 eV and the Dark Matter RH neutrino is the lightest one with M1 ~ O(KeV) (Asaka,Blanchet,Shaposhnikov’05) • Bad news: the same flavor-mixing mechanism describing the production, also lead to radiative decay: N1   +  •  >> t0 M1  10 KeV - SDSS Ly: M1 > (10-14) KeV (Seljak et al. ’06;Lesgourgues et al)

24. Heavy RH neutrinos 2 solid motivations: • See-saw original philosophy is not spoiled:  ~ Mew , MR~MGUT there is no need to introduce new fundamental scales to explain neutrino masses; • Leptogenesis from heavy RH neutrino decays: it is simple and it works easily without requiring a particular tuning of parameters Objections: • How to prove it ? • Can one explain Dark Matter ?

25. 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

26. Kinetic Equations CP violation in decays Wash-out term from inverse decays ``decay parameters´´ • Strong wash-out when Ki  3 • Weak wash-out when Ki 3

27. The traditional picture • flavor composition of leptons is neglected • hierarchical heavy neutrino spectrum • asymmetry generated from the lightest RH • neutrino decays (N1-dominated scenario) It does not depend on low energy phases !

30. Neutrino mass bounds ~ 10-6 ( M1 / 1010 GeV) m1=0 M1 (GeV)

32. Beyond the traditional picture • N2-dominated scenario • beyond the hierarchical limit • flavor effects

33. N2-dominated scenario Beyond the hierarchical limit (PDB’05) The lower bound on M1 disappears and is replaced by a lower bound on M2. The lower bound on Treh remains (Pilaftsis ’97, Hambye et al ’03, Blanchet,PDB ‘06) 3 Effects play simultaneously a role for 2  1 :

34. Flavor effects (Barbieri et a l. ’01; Endo et al. ’04; Pilaftsis,Underwood ’05; Nardi,Roulet’06;Abada et al.’06;Blanchet,PDB’06) Flavor composition: Does it play any role ? However for lower temperatures the charged lepton Yukawa couplings, are strong enough to break the coherent evolution of the and of the , that are then projected on a flavor basis: ‘flavor’ is measured and comes into play ! It is then necessary to track the asymmetries separately in each flavor:

35. How flavor effects modify leptogenesis? (Nardi et al., 06) • The kinetic equations become : • First effect: wash-out is suppressed by the projectors: • Second effect: additional contribution to the ‘flavored’ CP asymmetries: Same as before! The additional contribution depends on the low energy phases !

36. NO FLAVOR Nj Φ L Le Lµ Ni Lτ Φ

37. WITH FLAVOR Nj Φ Le Lµ Lτ Ni Φ

38. General scenarios (K1 >> 1) and • Alignment case • Democratic (semi-democratic) case • One-flavor dominance big effect! and

39. 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 1= 0 The lowest bound does not change! (Blanchet, PDB ‘06) 1= -  m1=matm 0.05 eV Majorana phases play a role !!

40. Leptogenesis testable at low energies ? Let us now further impose 1= 0 setting Im(13)=0 M1min traditional unflavored case • More stringent lower bound but still successful leptogenesis is possible with CP violation stemming just from ‘low energy’ phases testable in: • 0 decay (Majorana phases) and neutrino mixing (Dirac phase) • Considering the degenerate limit these lower bounds can be relaxed ! (Blanchet,PDB 06)

41. When flavor effects are important ? (Blanchet,PDB,Raffelt ‘06) • Consider the rate  of processes like • It was believed that the condition  > H is sufficient ! • This is equivalent to T  M1 1012GeV • In the weak wash-out regime this is true since H > ID • However, in the strong wash-out regime the condition  > ID is stronger than  > H and is equivalent to • If zfl  zB WID1M1  1012 GeV • but if zfl<< zB WID >> 1much more restrictive ! • This applies to the one-flavor dominated scenario through which the upper bound on neutrino masses could be circumvented .

42. Is the upper bound on neutrino masses be circumvented when flavor effects are accounted for ? (Blanchet,PDB,Raffelt ‘06) 0.12 eV A definitive answer requires a genuine quantum kinetic calculation !

43. Conclusions • The cosmological observations of the last ten years have pointed to a robust phenomenological model: (the CDM model) a cosmological SM ? • 4 puzzles that can be solved only with ‘new physics’ • Discovery of neutrino masses strongly motivate solutions of the cosmological puzzles in terms of neutrino physics and RH neutrinos in the see-saw limit are the simplest way to explain neutrino masses; • Between light and heavy RH neutrinos the second option appears more robustly motivated; • Leptogenesisis one motivation and flavor effects open new prospects to test it in 0 decay experiments (Majorana phases) and neutrino mixing experiments (Dirac phase)