The n MSM

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

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

3. Neutrino oscillations • The MSM contradicts with n oscillation experiments!! • Solar, atmospheric, reactor and accelerator experiments • Neutrino mass scales: • A simplest extension including neutrino masses is The nMSM

4. What is the nMSM? • 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. Seesaw mechanism • If Dirac masses << Majorana masses, • The mixing in the charged current • Active neutrinos • Sterile neutrinos

6. Scale of the nMSM • What are the scales of Majorana masses??

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

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

11. Dark matter in the nMSM • 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 • Hot dark matter of active massive neutrinos is excluded • by the LSS and CMBR Sterile neutrinos as “warm dark matter”

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. 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 ! Dolgov, Hansen ’00, Abazajian, Fuller, Patel ‘01 TA, Blanchet, Shaposhnikov ‘05

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-a forest • Only a small window is left Abazajian, Fuller, Tucker ‘01 Viel, Lesgourgues, Haehnelt, Matarrese, Riotto ‘05

15. Implications of DM sterile neutrinos • Dark matter constraints: • Consistency with n 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 m1<O(10-5)eV TA, Blanchet, Shaposhnikov ‘05

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. The nMSM with two sterile neutrinos • Active n masses: • When both sterile neutrinos are DM, … Contradiction !!

18. The nMSM with two sterile neutrinos • Active n masses: • When one sterile neutrino is DM, … Contradiction !!

19. The nMSM 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. Masses of active neutrinos • We can determine the absolute values of active n masses

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. CMBR+Ly-a X-ray Abazajian, Fuller, Tucker ‘01

22. Summary • We discussed the extension of the MSM • by adding several right-handed neutrinos -The nMSM- • 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 n masses are determined • The DM sterile neutrinos may be tested in the future X-ray observations

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

24. Conclusions n MSM