Probing the origins of neutrino masses and baryon asymmetry of the universe

1. Probing the origins of neutrino masses and baryon asymmetry of the universe Takehiko Asaka (Niigata Univ.) @MaskawaInstitute for Science and Culture (2014/01/27)

2. Contents Overview –nMSM – RH neutrinos and Dark Matter RH neutrinos and Baryon Asymmetry Search for RH neutrinos Summary TA, Blanchet, Shaposhnikov ’05 TA, Shaposhnikov ‘05 TA, Ishida ‘10 TA, Eijima, Ishida ‘11, ‘12 TA, Eijima, Watanabe ‘13 TA, Eijima ‘13 Takehiko Asaka (Niigata Univ.)

3. Introduction Higgs had been discovered !! All elementary particles in the Standard Model had been confirmed by experiments !! 2012/07/04 Takehiko Asaka (Niigata Univ.)

4. What’s next after Higgs discovery? Takehiko Asaka (Niigata Univ.)

5. Prologue: Physics beyond the SM • About 20 years ago …, • There was no “convincing” evidence for physics beyond the standard model (SM) • People looked for physics beyond the SM “mainly” based on theoretical argumentsand curiosities: • Hierarchy problem • Naturalness problem • Gravity, String, … • Strong CP problem • Why 3 generations? • Why anomalies cancel? • … Takehiko Asaka (Niigata Univ.)

6. News from the sky Neutrino Oscillations Cosmic Microwave Background (CMB) [SuperK] [WMAP] Takehiko Asaka (Niigata Univ.)

7. Physics beyond the SM • In the last decade(s), we have collected quite “convincing” evidences for physics beyond the SM • Neutrino oscillations • Baryon asymmetry • Dark matter • Dark energy • Primordial density perturbations Takehiko Asaka (Niigata Univ.)

8. Physics beyond the SM • In the last decade(s), we have collected quite “convincing” evidences for physics beyond the SM • Neutrino oscillations • Baryon asymmetry • Dark matter • Dark energy • Primordial density perturbations • Today, I would like to explain nMSM, which can solve first three problems! ?? ?? Takehiko Asaka (Niigata Univ.)

9. Origin of neutrino masses • Neutrino mass scales • Atmospheric: • Solar： ⇒ Need for physics beyond the SM ! • Important questions: • “What is the origin of neutrino masses?” • “How do we test it experimentally?” Takehiko Asaka (Niigata Univ.)

10. Standard Model Higgs Bosons Gauge Bosons Quarks and Leptons (left-handed) (right-handed) Takehiko Asaka (Niigata Univ.)

11. Standard Model Higgs Bosons Gauge Bosons Quarks and Leptons (left-handed) (right-handed) Takehiko Asaka (Niigata Univ.)

12. Neutrino Minimal SM (nMSM) TA, Blanchet, Shappshnikov (‘05), TA, Shaposhnikov (‘05) Higgs Bosons Gauge Bosons Quarks and Leptons (left-handed) (right-handed) Takehiko Asaka (Niigata Univ.)

13. Extension by RH neutrinos • Seesaw mechanism () • Light active neutrinos → explain neutrino oscillations • Heavy neutral leptons • Mass • Mixing Minkowski ’77 Yanagida ’79Gell-Mann, Ramond, Slansky ‘79 Glashow ‘79 Where is the scale of mass? mixing in CC current Takehiko Asaka (Niigata Univ.)

14. Scale of Majorana mass The simplest case: one pair of and Neutrino Yukawa Coupling Majorana Mass Takehiko Asaka (Niigata Univ.)

15. Convenstional seesaw scenario: • Neutrino Yukawa couplings are comparable to those of quarks and charged leptons • Explain smallness of neutrino masses via seesaw • Decays of RH neutrino(s) can account for baryon asymmetry through leptogenesis • Physics of RH neutrino cannot be tested directly by experiments [Yanagida; Gell-Mann, Ramond, Slansky] [Fukugita, Yanagida] Takehiko Asaka (Niigata Univ.)

16. Scale of Majorana mass The simplest case: one pair of and Baryogenesis via leptogenesis Fukugita, Yanagida ‘86 Neutrino Yukawa Coupling Majorana Mass Takehiko Asaka (Niigata Univ.)

17. [TA, Blanchet, Shaposhnikov; TA, Shposhnikov] The nMSM: • No new mass scale is introduced • Oscillation of RH neutrinos can account for baryon asymmetry of the universe • Lightest RH neutrino (~keV) can be DM • Physics of RH neutrinos can be tested directly by experiments [Akhmedov, Rubakov, Smirnov/ TA, Shaposhnikov] [Dodelson, Widrow,…] Takehiko Asaka (Niigata Univ.)

18. Scale of Majorana mass The simplest case: one pair of and Baryogenesis via leptogenesis Fukugita, Yanagida ‘86 Neutrino Yukawa Coupling Baryogenesis via neutrino osc. Akhmedov, Rubakov, Smirnov ‘98 TA, Shaposhnikov ‘05 Majorana Mass Takehiko Asaka (Niigata Univ.)

19. Roles of three HNL • Dark Matter Candidate • Neutrino Oscillation data • Masses and mixings • Baryon Asymmetry of the Universe (BAU) • Mechanism via neutrino oscillation LINK Takehiko Asaka (Niigata Univ.)

20. §2 Dark matter in the nMSM Unique Candidate: lightest heavy neutral lepton N1 with keV mass Dodelson, Widrow / Shi, Fuller / Dolgov, Hansen / Abazajian, Fuller, Patel /… (Incomplete list) Takehiko Asaka (Niigata Univ.)

21. Decays of DM • N1 is not completely stable particle ! • Dominant decay: for keV • Lifetime can be very long • N1 is not completely dark ! • Subdominant decay: • Branching ratio is small • But, severely restricted from X-ray observations + … + … TakehikoAsaka (Niigata Univ.)

22. Production of DM • Due to smallness of Yukawa couplings,N1 is not thermalized in the early universe • Production scenarios: • Dodelson-Widrowscenario • Production via active-sterile neutrino mixing • Dominant production at • Shi-Fuller scenario • Production is boosted in the presence of lepton asymmetry due to the MSW effect na W,Z N1 Takehiko Asaka (Niigata Univ.)

23. Cosmological Constraints • Radiative decays of DM • No signal  Upper bound on mixing angle ! • Light heavy neutral lepton = WDM • Lower bound on mass (Ly-aforest observations) • (DW scenario) • Phase-space analysis (Tremaine-Gunn bound) • Erase structures on smaller scales! Boyarsky, Lesgourgues, Ruchayskiy, Viel ’09,….. Tremaine, Gunn ‘79 Boyarsky, Ruchayskiy, Iakubovskyi ‘08 Gorbunov, Khmelnitsky, Ruvakov‘08 Takehiko Asaka (Niigata Univ.)

24. Dark Matter Laine, Shaposhnikov ‘08 Takehiko Asaka (Niigata Univ.)

25. Dark Matter • Dodelson-Widrow mechanism does not work due to stringent constraints from X-ray and Ly-a • Shi-Fuller mechanism ?? • Entropy production ?? • U(1)_B-L extension ?? (see Ishida, Jeong, Takahashi ‘13) • … • Yukawa couplings of N1 are very suppressed • N1 decouples from the seesaw mechanism -> Lightest active neutrino • N1 contribution is negligible for baryogenesis N2 and N3 are responsible for • Seesaw mass matrix for neutrino masses • Baryon asymmetry of the universe Takehiko Asaka (Niigata Univ.)

26. Entropy Production in the nuMSM TA, Takeda ‘14 Entropy production by heavier neutral lepton N2 and N3 can cool down DM’s velocity dispersion ! Takehiko Asaka (Niigata Univ.)

27. Active neutrino masses exclude the degeneratemasses of active neutrinos Takehiko Asaka (Niigata Univ.)

28. §2 BAU in the nMSM Baryogenesis via neutrino oscillation Akhmedov, Rubakov, Smirnov (’98) TA, Shaposhnikov (‘05) Takehiko Asaka (Niigata Univ.)

29. Baryon v.s. antibaryon • We find baryons mostly, not antibaryons ! • Existence of antiproton In cosmic rays, At TEVATRON, X • Asymmetry between baryons and antibaryons Baryon proton （) neutron （) Antibaryon antiproton （) antineutron （) How large ??? Takehiko Asaka (Niigata Univ.)

30. Baryon asymmetry of the universe (BAU) Baryon Number = (# of baryons) (# of antibaryons) Planck 2013 results arXiv:1303.5076 Baryon number density Entropy density [Strumia 06] Takehiko Asaka (Niigata Univ.)

31. BAU from BBN Primordial abundances of 4He, D, 3He, Li [Strumia 06] [PDG] Takehiko Asaka (Niigata Univ.)

32. Brief history of the universe Inflation generate BAU ! Baryogenesis BBN Recombination Today CMB 4He, D,… Takehiko Asaka (Niigata Univ.)

33. Conditions for baryogenesis Sakharov (1967) “According to our hypothesis, the occurrence of C asymmetry is the consequence of violation of CP invariance in the nonstationary expansion of the hot Universe during the superdense stage, as manifest in the difference between the partial probabilities of the charge-conjugate reactions.” Takehiko Asaka (Niigata Univ.)

34. Conditions for baryogenesis • Sakharov (1967) (1) Baryon number B is violated (2) C and CP symmetries are violated (3) Out of thermal equilibrium Let us see whether the SM satisfies these conditions Takehiko Asaka (Niigata Univ.)

35. B violation in the SM At classical level, B and L are conserved At quantum level, B and L are violated by non-perturbativeanomaly effect BL is conserved, but B+L is violated ! Takehiko Asaka (Niigata Univ.)

36. Energy DB and DL • Chern-Simons number (integer) Takehiko Asaka (Niigata Univ.)

37. Energy DB and DL • At T = 0 Instanton [‘t Hooft ’76] B+L breaking effect is negligible Takehiko Asaka (Niigata Univ.)

38. Energy DB and DL • For high temperatures [Kuzumin, Rubakov, Shaposhnikov ’85] Sphaleron [Moore ‘00] Sphaleron process is in equilibrium [Buchmuller] Takehiko Asaka (Niigata Univ.)

39. Sphaleron conversion Initial (B-L) asymmetry is converted into B [Khlebnikov, Shaposhnikov ‘88, Harvey, Turner ‘90] • (B-L)=0 initially leads to B=0 universe  asymmetries are wahshedout! We have to generate(B-L)>0 initially to explain B>0 universe ! Takehiko Asaka (Niigata Univ.)

40. Baryogenesisconditions in the SM • B+L violations • Sphaleron for T>100GeV • CP violation • 1 CP phase in the quark-mixing (CKM) matrix  too small • Out of equilibrium • Strong 1st order phase transition if but  not satisfied [Kajantie, Laine, Rummukainen, Shaposhnikov] We have to go beyond the SM !! Takehiko Asaka (Niigata Univ.)

41. Overview Neutrino Masses Seesaw Seesaw RH neutrinos Baryogenesis via neutrino osc. Leptogenesis Baryon Asymmetry of the Universe Takehiko Asaka (Niigata Univ.)

42. Leptogenesis [Fukugita, Yanagida’86] • Majorana masses break • RH neutrino decay can produce • Produced L is partially converted into B by sphaleron lepton number Takehiko Asaka (Niigata Univ.)

43. CP violation CP violation in neutrino Yukawa couplings Takehiko Asaka (Niigata Univ.)

44. Out of equilibrium decay For , is in thermal equilibrium For EQ  Out of equilibrium decay of Takehiko Asaka (Niigata Univ.)

45. BAU via Leptogenesis Efficiency factor Number of CP asymmetry Sphaleron conv. [Giudice et al 03] Takehiko Asaka (Niigata Univ.)

46. Lower bound on mass M1 [Giudice et al ‘03] Lower bound on mass Takehiko Asaka (Niigata Univ.)

47. Conventional seesaw scenario Neutrino masses • Smallness of mn &BAU • SUSY GUT • Gauge coupling unification • Naturalness problem • LSP dark matter • REWSB Seesaw RH neutrinos Leptogenesis BAU Exp. test of RH is impossible! Takehiko Asaka (Niigata Univ.)

48. Question Can we have a realistic scenario of baryogenesis, even if RH neutrinos have Majorana masses smaller than ～100GeV ? Answer: Yes! Takehiko Asaka (Niigata Univ.)

49. Baryogenesisvia neutrino oscillation [Akhmedov, Rubakov, Smirnov ‘98] [TA, Shaposhnikov ’05] Takehiko Asaka (Niigata Univ.)

50. Scale of Majorana mass The simplest case: one pair of and Baryogenesis via leptogenesis Fukugita, Yanagida ‘86 Neutrino Yukawa Coupling Baryogenesis via neutrino osc. Akhmedov, Rubakov, Smirnov ‘98 TA, Shaposhnikov ‘05 Majorana Mass Takehiko Asaka (Niigata Univ.)