Neutrino mass and DM direct detection

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

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

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.

4. Basic idea Neutrino oscillation data suggest neutrino masses are very small : ( @Planck) • 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 The same symmetry may guarantee the stability of some neutral particle (a dark matter candidate). origin of neutrino mass origin of dark matter

5. A radiative neutrino mass model Ma is imposed to forbid Dirac neutrino masses at tree level. • Field contents • Lightest one with odd parity is stable ⇒ DM • No Dirac mass term • Z２invariant interaction and potential

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

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

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

9. Dark matter abundance 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 Freeze-out coannihilation among 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.

10. Relic abundance of Relic abundance Relic abundance • 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.

11. Constraints on Neutrino mass satisfies Constraint on is crucial. 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 has to be considered under this constraints.

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

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

14. An example of favored parameters Diagonalization of Fixed parameters Contours of neutrino oscillation parameters in (q2,q3) plane q3 Region consistent with all neutrino oscillation data q2

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

16. An example of favored parameters Contours of neutrino oscillation parameters in (q1,q2) plane Fixed parameters q2 Region consistent with all neutrino oscillation data q1

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

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

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

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

21. Elastic scattering due to Higgs exchange DM-nucleon scattering cross section Promising parameter region in forXenon1T Xenon1T cannot reach Xenon1T cannot reach Xenon1T cannot reach Excluded by Xenon100 Xenon1T could find this DM for the parameters which are consistent with other phenomenological constraints.

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.