Neutrinoless Double Beta Decay in the Standard Model
The study explores key points, extensions, and implications of the Standard Model in relation to neutrino masses, baryon asymmetry, dark matter, and baryogenesis. Collaboration and findings from recent conferences are highlighted.
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On neutrinoless double beta decay in the MSM Hiroyuki Ishida (NCTS) 1 @Nufact2016, Quy Nhon, Vietnam 2016/08/25 Collaborators : T. Asaka (Niigata), S. Eijima (EPFL) Ref : arXiv:1606.06686
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 2
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 MSM 3
The MSM [Asaka, Blanchet, and Shaposhnikov (2005)] The most economical extension of the SM : SM + 3RH s Key assumption Dirac masses ; Majorana masses ; *Neutrino mass matrix *Seesaw mechanism Tiny neutrino masses can explain by the seesaw mechanism 4
The MSM [Asaka, Blanchet, and Shaposhnikov (2005)] Generic form of Yukawa coupling When 2RH explain the tiny masses by seesaw mechanism [Casas, Ibarra(2001)] * * * for N.H. for I.H. * is arbitrary complex, Hereafter, 5
The MSM Dark matter in the MSM [Asaka, Blanchet, and Shaposhnikov (2005)] The lightest right-handed neutrino in keV scale Highly constrained from X-ray observations and structure formation Phase space density X-ray observations Upper bounds on mixing angle between ordinary neutrinos DM production [Dodelson and Widrow (1993)] [Laine and Shaposhnikov (2008)] To avoid over abundant DM by DW mechanism 6
The MSM [Asaka, Blanchet, and Shaposhnikov (2005)] Baryogenesis in the MSM [Akhemedov, Rubakov, and Smirnov ( 98)] [Asaka and Shaposhnikov (2005)] Baryogenesis via neutrino oscillation Initial condition : No RH Produced by scattering processes Depart from thermal equilibrium RH s start to oscillate at TL Typical temperature to oscillate 7
The MSM [Asaka, Blanchet, and Shaposhnikov (2005)] Baryogenesis in the MSM [Akhemedov, Rubakov, and Smirnov ( 98)] [Asaka and Shaposhnikov (2005)] Baryogenesis via neutrino oscillation Through RH s oscillation, CPV occurs via Yukawa couplings however, No asymmetry in the end @F4order Asymmetry is produced @F6order effects 8
The MSM [Asaka, Blanchet, and Shaposhnikov (2005)] Baryogenesis in the MSM [Akhemedov, Rubakov, and Smirnov ( 98)] [Asaka and Shaposhnikov (2005)] Baryogenesis via neutrino oscillation Important thing : total lepton number is conserved Lepton number separation Baryon number is produced through sphaleron [Khlebnikov; Shaposhnikov(1988)] [Harvey; Turner(1990)] 9
The MSM [Asaka, Blanchet, and Shaposhnikov (2005)] Baryogenesis in the MSM [Akhemedov, Rubakov, and Smirnov ( 98)] [Asaka and Shaposhnikov (2005)] Baryogenesis via neutrino oscillation Evolution of asymmetries(Each flavor) Evolution of asymmetries(Total) 10
The MSM [Asaka, Blanchet, and Shaposhnikov (2005)] Baryogenesis in the MSM [Akhemedov, Rubakov, and Smirnov ( 98)] [Asaka and Shaposhnikov (2005)] Baryogenesis via neutrino oscillation 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 RH s is enhanced 11
Neutrinoless double beta decay Evidence of Majorana particles Diagram Maximal value of SM prediction (2 massive active neutrinos) : NH : IH 12
Neutrinoless double beta decay in the MSM Diagram where <p2> : nucleon Fermi momentum in the nucleus [Faessler, Gonzalez, Kovalenko, and Simkovic (2014)] If all of Rh s are enough lighter than , However, such RH s cannot have enough short lifetime In this analysis, we consider 13
Neutrinoless double beta decay in the MSM In the MSM, only DM is enough light DM contribution Heavy 2RH s contributions SM part 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 , , and Re are just free parameters 14
Neutrinoless double beta decay in the MSM Contribution from DM Phase space density Contribution from DM is negligibly small [Asaka, Eijima, and H.I. JHEP 1104 (2011)] Two of 3RH s contribute to the effective mass of neutrinoless double beta decay in this model 15
Neutrinoless double beta decay in the MSM Contribution from rest 2RH s In our previous result, [Asaka, Eijima, and H.I. (2011)] was negligibly small, since Only destructive contribution from RH s 16
Neutrinoless double beta decay in the MSM 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!! 17
Neutrinoless double beta decay in the MSM 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 18
Neutrinoless double beta decay in the MSM Results of IH NH BAU BAU In almost of all region, the effective mass is as large as the SM prediction at most 19
Neutrinoless double beta decay in the MSM Results of IH NH BAU BAU In the IH case, the effective mass becomes close to be twice (Magenta) as much as the SM 20
Neutrinoless double beta decay in the MSM Results of IH NH BAU BAU In the IH case, the effective mass becomes three times larger (Blue) as the SM prediction 21
Conclusions The MSM The most economical extension of the SM masses, BAU, and DM can be explained at the same time Neutrinoless double beta decay in the MSM 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! 22
