1. 21 Sept. 20051 The MSM -- Neutrino Masses and Dark matter -- Takehiko Asaka (Tohoku University) TA, S.Blanchet, M.Shaposhnikov [hep-ph/0503065] TA, M.Shaposhnikov [hep-ph/0505013]

2. 21 Sept. 2005 2 Neutrino oscillations The MSM contradicts with oscillation experiments!! –Solar, atmospheric, reactor and accelerator experiments –Neutrino mass scales: A simplest extension including neutrino masses is

3. 21 Sept. 2005 3 Neutrino oscillations The MSM contradicts with oscillation experiments!! –Solar, atmospheric, reactor and accelerator experiments –Neutrino mass scales: A simplest extension including neutrino masses is The MSM

4. 21 Sept. 2005 4 What is the MSM? The MSM + Several right-handed neutrinos –Dirac masses and Majorana masses –If Dirac masses << Majorana masses, the seesaw mechanism works Not new!!! Minkowski ’77, Yanagida ’79, Gell-Mann, Ramond, Slansky ’79 Glashow ‘79

5. 21 Sept. 2005 5 Seesaw mechanism If Dirac masses << Majorana masses, The mixing in the charged current Active neutrinos Sterile neutrinos

6. 21 Sept. 2005 6 Scale of the MSM What are the scales of Majorana masses??

7. 21 Sept. 2005 7 Conventional approach F ~ Yukawa couplings in quarks and charged leptons The new energy scale is introduced Can explain neutrino oscillations Can explain baryon asymmetry of the universe via “leptogenesis” Fukugita and Yanagida ‘86

8. 21 Sept. 2005 8 Approach here Majorana masses are weak scale (~100GeV) or below No new energy scale is introduced Can explain neutrino oscillations Can explain baryon asymmetry of the universe via neutrino oscillations Can explain dark matter of the universe Very small neutrino Yukawa couplings

9. 21 Sept. 2005 9 In this talk Q. How many right-handed neutrinos are required? A. Minimal possibility is “three”!! Neutrino Osc. The minimal # is “two” Neutrino Osc. + Baryon Asymmetry “two” Neutrino Osc. + Baryon Asymmetry + Dark Matter “three”

10. 21 Sept. 2005 10 Dark matter in the universe Contents of the universe: The MSM cannot offer a particle physics candidate for dark matter (DM)!! Baryon PDG Dark Energy Dark Matter

11. 21 Sept. 2005 11 Dark matter in the MSM The unique candidate: The allowed mass range is (see later discussion) Long-lived sterile neutrinos Peebles ’82, Olive, Turner ’82 Dodelson, Widrow ’94, Shi, Fuller ’99 Dolgov, Hansen ’00, Abazajian, Fuller, Patel ‘01 Sterile neutrinos as “warm dark matter” Hot dark matter of active massive neutrinos is excluded by the LSS and CMBR

12. 21 Sept. 2005 12 Lifetime of sterile neutrinos When Yukawa couplings are very small, sterile neutrinos can be very long-lived!! Main decay cannel: Lifetime can exceed the age of universe Barger, Phillips, Sarkar ‘95

13. 21 Sept. 2005 13 Production of sterile neutrinos When Yukawa couplings are very small, sterile neutrinos are not thermalized Main production is due to the scatterings at Dirac mass is determined ! TA, Blanchet, Shaposhnikov ‘05 Dolgov, Hansen ’00, Abazajian, Fuller, Patel ‘01

14. 21 Sept. 2005 14 Cosmological constraints Radiative decays of DM sterile neutrinos are limited by X-ray observations Warm dark matter is limited by structure formation –WMAP + Matter power spectrum inferred from Ly-  forest Only a small window is left Abazajian, Fuller, Tucker ‘01 Viel, Lesgourgues, Haehnelt, Matarrese, Riotto ‘05

15. 21 Sept. 2005 15 Implications of DM sterile neutrinos Dark matter constraints: Consistency with oscillation experiments lead to The point is The minimal number of sterile neutrinos is “three” Only ”one” sterile neutrino can be dark matter The lightest active neutrino mass is m 1 <O(10 -5 )eV TA, Blanchet, Shaposhnikov ‘05

16. 21 Sept. 2005 16 Seesaw mass matrix Parameterization The following arguments is based on calculating the trace and determinant of (XX) Independent on the neutrino mixing matrix U!!!

17. 21 Sept. 2005 17 The MSM with two sterile neutrinos Active masses: When both sterile neutrinos are DM, … Contradiction !!

18. 21 Sept. 2005 18 The MSM with two sterile neutrinos Active masses: When one sterile neutrino is DM, … Contradiction !!

19. 21 Sept. 2005 19 The MSM with three sterile neutrinos We can similarly exclude the cases in which two and three sterile neutrinos are dark matter When one sterile neutrino is dark matter,… Upper bound on the lightest active neutrino mass !!

20. 21 Sept. 2005 20 Masses of active neutrinos We can determine the absolute values of active masses

21. 21 Sept. 2005 21 Test for DM sterile neutrino Radiative decays of DM sterile neutrinos may be seen in X-ray observations!! The current status The future experiments will detect or exclude the sterile neutrino dark matter. X-ray CMBR+Ly-  Abazajian, Fuller, Tucker ‘01

22. 21 Sept. 2005 22 Summary We discussed the extension of the MSM by adding several right-handed neutrinos -The MSM- Only particle physics candidate for dark matter is long-lived sterile neutrino –The minimal number of RH neutrinos is three –Only one sterile neutrino can be dark matter –The lightest active neutrino mass The absolute values of active masses are determined The DM sterile neutrinos may be tested in the future X- ray observations

23. 21 Sept. 2005 23 Conclusions We can solve experimental and observational problems -- oscillations, dark matter and baryon asymmetry-- in the MSM

24. 21 Sept. 2005 24 Conclusions MSM