1. Neutrino mass and DM direct detection Daijiro Suematsu (Kanazawa Univ.) Erice2013 21 Sept., 2013 Based on the collaboration with S.Kashiwase PRD86 (2012) 053001, EPJC73 (2013) 2484 1

2. Outline Motivation and ｂ asic idea Model and its features Neutrino mass and mixing Dark matter Leptogenesis Dark matter direct search Summary 2

3. Motivation  The SM is a successful model to explain various experimental results. However, several recent experimental results require to extend the SM. existence of neutrino masses existence of dark matter baryon number asymmetry in the Universe  We consider the extension of the SM on the basis of these experimental results. 3

4. Basic idea Dirac mass terms exist at tree level ⇒ right-handed neutrinos should be heavy enough. ordinary seesaw mechanism Dirac mass terms are forbidden at tree level by some symmetry ⇒ small neutrino masses may be induced radiatively even for rather light right-handed neutrinos. radiative seesaw mechanism origin of neutrino mass origin of dark matter Neutrino oscillation data suggest neutrino masses are very small : ( @Planck) The same symmetry may guarantee the stability of some neutral particle (a dark matter candidate). 4

5. A radiative neutrino mass model  Field contents Lightest one with odd parity is stable ⇒ DM No Dirac mass term  Z ２ invariant interaction and potential Ma is imposed to forbid Dirac neutrino masses at tree level. 5

6. Neutrino mass New physics is expected in lepton sector at TeV regions. Correction to the ordinary Seesaw formula small neutrino masses are realized even if masses of are 6

7. Dark matter Two dark matter candidates : Neutrino mass Dark matter abundance Lepton flavor violating processes Neutrino Yukawa couplings New particle masses constraint 7 (real part of neutral components)

8. ⇒ LFV constraint might be easily evaded. Two scenarios for dark matter If is DM, the neutrino Yukawa coupling should be to explain its relic abundance. If is DM, the neutrino Yukawa coupling could be irrelevant to the relic abundance of DM. Ma, Kubo, D.S. D.S., Toma, Yoshida ⇒ LFV imposes severe constraints. Barbieri, et al. Hambye, et al. ……. the neutrino Yukawa couplings could be small consistently with DM relic abundance. 8

9. Dark matter abundance Freeze-out DM abundance follows the usual thermal relic scenario. It is determined by the number density at the freeze-out temperature TF. In the DM scenario, there is Dominant parts of annihilation cross section could be determined by the scalar quartic couplings. Hambye, et al., Longitudinal components of gauge bosons give large contribution. coannihilation among 9

10. Relic abundance of  or required relic abundance is realized  Neutrino Yukawa couplings are irrelevant to the relic abundance. ⇒ Neutrino Yukawa couplings could be small. LFV constraints are easily satisfied. 10 Relic abundance

11. Constraints on DM direct search gives such a constraint. Inelastic scattering can contribute to the direct search experiments. Since the direct search finds no confirmed evidence, the mass difference should be δ ＞ 150 keV. Cui, et al. Arina, et al. Neutrino mass satisfies Neutrino mass has to be considered under this constraints. 11 Constraint on is crucial.

12. Determination of model parameters can be diagonalized by tri-bimaximal mixing matrix To explain the neutrino oscillation data, we just assume flavor structure of the neutrino Yukawa couplings : 12

13. Normal hierarchy One mass eigenvalue is extremely small 13 For out-of equilibrium decay of in leptogenesis solutions

14. An example of favored parameters Region consistent with all neutrino oscillation data 14 q2q2 q3q3 Contours of neutrino oscillation parameters in (q 2,q 3 ) plane Fixed parameters Diagonalization of

15. Inverted hierarchy One mass eigenvalue is extremely small 15 For out-of equilibrium decay of solutions

16. An example of favored parameters Region consistent with all neutrino oscillation data 16 Contours of neutrino oscillation parameters in (q 1,q 2 ) plane q1q1 q2q2 Fixed parameters

17. Leptogenesis Lepton number asymmetry is expected to be generated through the out-of equilibrium decay of at TeV-scale. Generated lepton asymmetry ⇒ smaller than the required value Washout effects are large 17 Lepton asymmetry CP asymmetry

18. Resonant leptogenesis To suppress the washout effects, we can make neutrino Yukawa couplings smaller. neutrino masses become smaller. CP asymmetry becomes smaller. This can be recovered by taking a larger This can be recovered by assuming the nearly degenerate 18 However, there appear other effects. ⇒ TeV scale resonant leptogenesis

19. The required baryon asymmetry can be generated for This degeneracy is rather mild compared with the ordinary case Normal hierarchyInverted hierarchy Required degeneracy 19 Baryon number asymmetry Generated Baryon number asymmetry

20. Dark matter direct search  Inelastic scattering Inelastic scattering occurs only if the DM velocity satisfies It might be difficult to detect this DM through this process by Xenon1T. required for the present Xenon100 bound has already exceeded 20 Two possible scattering processes Escape velocity from our galaxy

21.  Elastic scattering due to Higgs exchange DM-nucleon scattering cross section Excluded by Xenon100 Xenon1T cannot reach Xenon1T could find this DM for the parameters which are consistent with other phenomenological constraints. Xenon1T cannot reach Xenon1T cannot reach 21 Promising parameter region in for Xenon1T

22. Summary Neutrino masses and dark matter could be closely related each other. The radiative neutrino mass model by Ma gives a simple example for such an idea. There are noticeable phenomenological features.  The model could explain neutrino oscillation data, dark matter abundance, baryon number asymmetry, simultaneously.  The observed baryon asymmetry can be explained through resonant leptogenesis. However, the required mass degeneracy can be rather mild compared with the ordinary TeV scale resonant leptogenesis.  Inert doublet DM could be found through the direct search experiment at Xenon1T for the parameters which could explain other experimental results consistently. 22