1. On neutrinoless double beta decay in the nMSM
Hiroyuki Ishida (NCTS)
@Nufact2016, Quy Nhon, Vietnam 2016/08/25
Collaborators : T. Asaka (Niigata), S. Eijima (EPFL)
Ref : arXiv:

2. The standard model is excellent!
Introduction
・Conclusion of recent ICHEP conference is…
The standard model is excellent!
in spite of
Almost of all suspicious excesses have gone
There is no new significant signal for new physics so far

3. Introduction ・Unsatisfactory points in the SM of particle physics
Neutrino masses
Experimentally confirmed
Baryon asymmetry of the universe
Dark matter candidate
want to explain these phenomena at the same time!
The nMSM

4. The nMSM ・The most economical extension of the SM : SM + 3RHns
[Asaka, Blanchet, and Shaposhnikov (2005)]
・The most economical extension of the SM : SM + 3RHns
Key assumption
Dirac masses ;
Majorana masses ;
*Neutrino mass matrix
*Seesaw mechanism
Tiny neutrino masses can explain by the seesaw mechanism

5. The nMSM ・Generic form of Yukawa coupling
[Asaka, Blanchet, and Shaposhnikov (2005)]
・Generic form of Yukawa coupling
[Casas, Ibarra(2001)]
When 2RHn explain the tiny n masses by seesaw mechanism * * * *
for N.H.
for I.H.
is arbitrary complex,
Hereafter,

6. The nMSM Dark matter in the nMSM
[Asaka, Blanchet, and Shaposhnikov (2005)]
Dark matter in the nMSM
The lightest right-handed neutrino in keV scale
Highly constrained from X-ray observations
and structure formation
[Laine and Shaposhnikov (2008)]
Phase space density
X-ray observations
Upper bounds on mixing angle
between ordinary neutrinos
DM production
[Dodelson and Widrow (1993)]
To avoid over abundant DM by DW mechanism

7. The nMSM Baryogenesis in the nMSM
[Asaka, Blanchet, and Shaposhnikov (2005)]
Baryogenesis in the nMSM
Baryogenesis via neutrino oscillation
[Akhemedov, Rubakov, and Smirnov (‘98)]
[Asaka and Shaposhnikov (2005)]
Initial condition : No RHn
Produced by scattering processes
Depart from thermal equilibrium
RHns start to oscillate at TL
Typical temperature to oscillate

8. The nMSM Baryogenesis in the nMSM
[Asaka, Blanchet, and Shaposhnikov (2005)]
Baryogenesis in the nMSM
Baryogenesis via neutrino oscillation
[Akhemedov, Rubakov, and Smirnov (‘98)]
[Asaka and Shaposhnikov (2005)]
Through RHns oscillation, CPV occurs via Yukawa couplings
however,
No asymmetry in the order
Asymmetry is order effects

9. The nMSM Baryogenesis in the nMSM
[Asaka, Blanchet, and Shaposhnikov (2005)]
Baryogenesis in the nMSM
Baryogenesis via neutrino oscillation
[Akhemedov, Rubakov, and Smirnov (‘98)]
[Asaka and Shaposhnikov (2005)]
Important thing : total lepton number is conserved
Lepton number separation
Baryon number is produced through sphaleron
[Khlebnikov; Shaposhnikov(1988)]
[Harvey; Turner(1990)]

10. The nMSM Baryogenesis in the nMSM
[Asaka, Blanchet, and Shaposhnikov (2005)]
Baryogenesis in the nMSM
Baryogenesis via neutrino oscillation
[Akhemedov, Rubakov, and Smirnov (‘98)]
[Asaka and Shaposhnikov (2005)]
Evolution of asymmetries(Total)
Evolution of asymmetries(Each flavor)

11. The nMSM Baryogenesis in the nMSM
[Asaka, Blanchet, and Shaposhnikov (2005)]
Baryogenesis in the nMSM
Baryogenesis via neutrino oscillation
[Akhemedov, Rubakov, and Smirnov (‘98)]
[Asaka and Shaposhnikov (2005)]
Important parameters
・Mass degeneracy
Asymmetry is enhanced
because oscillation starts faster
[Asaka, Eijima, and H.I in progress]
・Phase in the high sector
Production of RHns is enhanced

12. Neutrinoless double beta decay
Evidence of Majorana particles
Diagram
Maximal value of SM prediction (2 massive active neutrinos)
: NH
: IH

13. Neutrinoless double beta decay in the nMSM
Diagram
where
<p2> : nucleon Fermi momentum in the nucleus
[Faessler, Gonzalez, Kovalenko, and Simkovic (2014)]
If all of Rhns are enough lighter than 　　　,
However, such RHns cannot have enough short lifetime
In this analysis, we consider

14. Neutrinoless double beta decay in the nMSM
In the nMSM, only DM is enough light
SM part
DM contribution
Heavy 2RHns contributions
How large are the extra contributions
in the whole parameter space?
We take
best fit values for neutrino oscillation parameters
[Bergstoerm, Gonzalez-Garcia, Maltoni, and Shiwetz, (2015)]
three phases d, h, and Rew are just free parameters

15. Neutrinoless double beta decay in the nMSM
・Contribution from DM
Phase space density
Contribution from DM
is negligibly small
[Asaka, Eijima, and H.I. JHEP 1104 (2011)]
Two of 3RHns contribute to the effective mass
of neutrinoless double beta decay in this model

16. Neutrinoless double beta decay in the nMSM
・Contribution from rest 2RHns
In our previous result,
[Asaka, Eijima, and H.I. (2011)]
was negligibly small, since
Only destructive contribution from RHns

17. Neutrinoless double beta decay in the nMSM
・Take a look term
where, is expressed by active neutrino parameters
: NH
: IH
・If the combination can be much larger than 1
and
This contribution can be significantly large!!

18. Neutrinoless double beta decay in the nMSM
・Recall the parameter space from BAU
and
can be large
at the same time!
Need to reevaluate the effective mass
We will show the ratio

19. Neutrinoless double beta decay in the nMSM
・Results of NH IH
BAU
BAU
In almost of all region,
the effective mass is as large as the SM prediction at most

20. Neutrinoless double beta decay in the nMSM
・Results of NH IH
BAU
BAU
In the IH case,
the effective mass becomes close to be twice (Magenta)
as much as the SM

21. Neutrinoless double beta decay in the nMSM
・Results of NH IH
BAU
BAU
In the IH case,
the effective mass becomes three times larger (Blue)
as the SM prediction

22. Conclusions ・The nMSM The most economical extension of the SM
n masses, BAU, and DM can be explained at the same time
・Neutrinoless double beta decay in the nMSM
Mild mass degeneracy is available for BAU
Analytical expression of the effective mass in the model
There is no significant enhancement in the NH case
However,
Effective mass can be enhanced in the IH case!
Predicted region in the IH case is going to be constrained!

23. Thank you for your attention