Neutrino mass and 　　　　　 DM direct detection

Daijiro Suematsu (Kanazawa Univ.)

Erice201321 Sept., 2013

Based on the collaboration with S.Kashiwase PRD86 (2012) 053001, EPJC73 (2013) 2484

1

Outline

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

2

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

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 arevery small : ( @Planck)

The same symmetry may guarantee the stability of some neutral particle (a dark matter candidate).

4

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

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

Dark matterTwo dark matter candidates :

Neutrino mass

Dark matter abundance

Lepton flavor violating processes

Neutrino Yukawa couplingsNew particle massesconstraint

7

(real part of neutral components)

⇒ 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 consistentlywith DM relic abundance.

8

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

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

Re

lic

abu

nd

ance

Re

lic

abu

nd

ance

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.

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

Normal hierarchy

One mass eigenvalue is extremely small

13

For out-of equilibrium decay of in leptogenesis

solutions

An example of favored parameters

Region consistent withall neutrino oscillation data

14

q2

q3Contours of neutrino oscillationparameters in (q2,q3) plane

Fixed parametersDiagonalization of

Inverted hierarchy

One mass eigenvalue is extremely small

15

For out-of equilibrium decay of

solutions

An example of favored parameters

Region consistent withall neutrino oscillation data

16

Contours of neutrino oscillationparameters in (q1,q2) plane

q1

q2Fixed parameters

LeptogenesisLepton 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

Resonant leptogenesisTo suppress the washout effects, we can make neutrinoYukawa 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

The required baryon asymmetry can be generated for

This degeneracy is rather mild compared with the ordinary case

Normal hierarchy Inverted hierarchy

Required degeneracy

19

Bar

yon

num

ber

asym

met

ry

Generated Baryon number asymmetry

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

Elastic scattering due to Higgs exchangeDM-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

SummaryNeutrino 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