Current Issues in Leptogenesis

1. APCTP, Yonsei, Sep. 15, 2007 Current Issues in Leptogenesis Eung Jin Chun Korea Institute of Advanced Study, Seoul Current Issues in Leptogenesis

2. Issues in leptogenesis To summarize (not so) new developments in leptogenesis = my two works done in Ann Arbor. • Quintessence and leptogenesis with S. Scopel, arXiv:0706.2375 • Flavor-symmetry for resonant leptogenesis. with K. Turzynski, hep-ph/0703070 Current Issues in Leptogenesis

3. Introduction • Non-zero neutrino masses and mixing angles provide a convincing evidence of physics beyond the Standard Model. • See-saw mechanism: a paradigm to understand neutrino masses. • The see-saw scenario involves a high-energy scale where lepton number L is not conserved: baryogenesis through leptogenesis. Current Issues in Leptogenesis

4. W= Seesaw Mechanism Dimension-5 effective operator: added in Standard Model 3 singlet heavy fermions N (RHN) Current Issues in Leptogenesis

5. k>1 wash-out regime K=/H(T=M) k<1 out-of-equilibrium decay Leptogenesis Fukugita and Yanagida, PLB174, 45 Seesaw mechanism can meet the Sakharov conditions to generate lepton asymmetry from RHN deacy: • L • C and CP • Out-of-equilibrium decay → neutrino mass op. → phases in Y → Γ/H < 1 Hubble constant decay rate SU(2)L sphaleron interactions convert the lepton asymmetry into a baryon asymmetry Current Issues in Leptogenesis

6. Non-standard cosmology & leptogenesis • Standard scenario: 1) population of RHN due to thermalization -- independent of prehistory. 2) RHN freeze-out during radiation-dominated era. 3) Hierarchical RHN mass. • Non-standard scenario: 1) different origins for populating RHN: non-thermal like from inflaton decay. 2) the Universe before big-bang nucleosynthesis may be dominated by non-radiation energy density. 3) Resonance enhancement of CP/L asymmetry: degenerate RHN mass Current Issues in Leptogenesis

7. Quintessential Kination and Leptogenesis Current Issues in Leptogenesis

8. Dark energy & quintessence • ΩDark Energy ~ 0.7 may indicate the existence of a slowly-rolling scalar field,  : Quintessence Caldwell et al., PRL80,1582 • A possibility:  dominance in an earlier stage. Driven by inflation? Chung et al., arXiv:0704.3285 [hep-ph] • A thermal Cold Dark Matter particle decouples earlier and its relic density can be enhanced. Salati., PLB571,121 Current Issues in Leptogenesis

9. Nb) Dark Energy Kination Cosmological evolution of Quintessence ρα a-3(1+w): equation of state: Current Issues in Leptogenesis

10. Tracking solution explainingm»DE Steinhardt et al., PRD59,123504 Current Issues in Leptogenesis

11. Impact on Dark Matter physics During kination the Universe expands faster than during radiation domination a thermal Cold Dark Matter particle decouples earlier and its relic density can be enhanced Salati, PLB571,121 Chung et.al., arXiv:0706.2357 Current Issues in Leptogenesis

12. Kination Cosmology Define Tr at which Tr is a free parameter with the only bound: Current Issues in Leptogenesis

13. a-6 ln(ρ) a-4 ar ln(a) Kination Cosmology isoentropic expansion (a3 s=constant): Current Issues in Leptogenesis

14. T3 T6 ln(ρ) ln(H) T4 T2 Tr Tr ln(T) ln(T) Kination Cosmology time time Current Issues in Leptogenesis

15. (kination) (radiation) Leptogenesis with Kination A useful parametrization: M≡RHN mass Current Issues in Leptogenesis

16. Leptogenesis with Kination g*r=10.75 g*(T)=228.75 (SUSY) When zr» M/Tr >>1 with Tr»1 MeV: Thermal leptogenesis can occur at low temperature. Require thermalization of SM particles & RHN: Γgauge ~ α2T > H Require sphaleron interactons in thermal equilibrium: Γsphaleron ~ α4T > H Current Issues in Leptogenesis

17. Wash-out parameter in Kination Leptogenesis RHN decay rate Effective neutrino mass Wash-out parameter: wide range of possibilities depending on zr, from strong (KÀ 1) to super-weak (K¿ 1) wash-out at fixed effective neutrino mass Current Issues in Leptogenesis

18. Super-weak wash-out regime When kination dominates, zrÀ 1: 1) Vanishing initial number density of RHN: decay & inverse decay too weak to popularize RHN efficiency of leptogenesis suppressed by 1/K 2) Thermal initial distribution of RHN: maximal efficiency Current Issues in Leptogenesis

19. Boltzmann equations CP asymmetry in decay: Current Issues in Leptogenesis

20. Decay & scattering rates decay t-channel scattering s-channel scattering N.B.) scattering is important at high temperature, z<<1 Current Issues in Leptogenesis

21. Final lepton asymmetry Definition of efficiency: If RHNs thermalize early and decay out-of-equilibrium when they are still relativistic (K<1), we get η=1 With vanishing initial RHN distribution, we get » 1 for K» 1 and ¿ 1 for K¿ 1 or KÀ1. Current Issues in Leptogenesis

22. ^ vanishing initial RHN density (N(0)=0) Super-weak wash-out regime (K¿1) Semi-analitic solution defining: negligible, main contribution from z<<1 (n=1 radiation, n=2 kination) Scattering dominates. Neglecting scattering: η ~ K2 Current Issues in Leptogenesis

23. ^ vanishing initial RHN density (N(0)=0) kination radiation Super-weak wash-out regime (K¿1) freeze-out RHN production RHN decay lepton asymmetry produced early Current Issues in Leptogenesis

24. ^ vanishing initial RHN density (N(0)=0) Strongwash-out regime (KÀ1) Semi-analitic solution Strong inverse-decay ) late decoupling (zfÀ 1) (n=1 radiation, n=2 kination) useful fit: For the decoupling to happen when kination still dominates (zf < zr) Current Issues in Leptogenesis

25. Strongwash-out regime (KÀ1) integrating BEs using saddle-point technique: n=1 radiation, n=2 kination RHNs decouple late, when scatterings are negligible decouple later for kination Current Issues in Leptogenesis

26. Strongwash-out regime (KÀ1) kination radiation RHNs thermalize before zf → thermal equilibrium erases any dependence on initial conditions Current Issues in Leptogenesis

27. Evolution of  for various K Current Issues in Leptogenesis

28. radiation kination ^ ^ N(0)=0 N(0)=1 Efficiency vs. K Current Issues in Leptogenesis

29. radiation kination Tr=1 MeV→zr~108 Efficiency vs. zr • smooth transition • from radiation • dominance (zr<1) • to kination • dominance (zr>1). • strong supression • of the efficiency • if zr>>1 • increased efficiency • for 1<zr<100 • if m>0.01 eV Current Issues in Leptogenesis

30. Quasi-degenerate Neutrinos and Leptogenesis with L – L Current Issues in Leptogenesis

31. Neutrino mass pattern and non-resonant leptogensis • Efficient leptogenesis: • With Quasi-degenerate neutrinos: • Gravitino problem constrains RHN mass: Requires resonant mechanism Current Issues in Leptogenesis

32. L-L flavor symmetry Flavon fields and charge assignment: • correction forbidden by Zn : high resonance Fine-tunning: a2/X=bd/Y for m1=m2,3 Automatic maximal atmospheric mixing Current Issues in Leptogenesis

33. Solar mixing and mass differences Perturbative calculation from corrections with 3,4: correction for 23 for Fine-tunings for smaller solar mass difference: Consistent with large solar mixing Current Issues in Leptogenesis

34. Fit to Neutrino data Success rate AFM: 10-3 HKV: 10-2 Ours: 10-4 Current Issues in Leptogenesis

35. Leptogenesis with L-L Baryon asymmetry with degenerate RHNs: CP asymmetry: Current Issues in Leptogenesis

36. Leptogenesis with L-L Degenerate RHNs ) Radiative generations of N & Re[yyy]23 Current Issues in Leptogenesis

37. Successful Leptogenesis Final expression for CP asymmetry: y2 dependence 2 suppression ) Current Issues in Leptogenesis

38. Fit to Leptogenesis Current Issues in Leptogenesis

39. Life in Ann Arobr Convenient rural life; can be boring Beautiful colors in Autumn Too long winter (6 months…) Fantastic spring/summer Current Issues in Leptogenesis