Investigating Neutrino Masses and Dark Matter in the nMSM Framework
This paper discusses the minimal Standard Model (MSM) extension, known as the nMSM, which introduces right-handed neutrinos to explain neutrino masses and dark matter. We explore the contradictions between the MSM and neutrino oscillation experiments, including solar and atmospheric data. The nMSM addresses the origins of dark matter, baryon asymmetry, and neutrino mass scales, utilizing the seesaw mechanism. We hypothesize that three sterile neutrinos may represent dark matter candidates, examining their properties, production mechanisms, and implications for cosmological observations, including constraints from X-ray data and structure formation.
Investigating Neutrino Masses and Dark Matter in the nMSM Framework
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Presentation Transcript
The nMSM Takehiko Asaka (Tohoku University) -- Neutrino Masses and Dark matter -- TA, S.Blanchet, M.Shaposhnikov [hep-ph/0503065] TA, M.Shaposhnikov [hep-ph/0505013]
Neutrino oscillations • The MSM contradicts with n oscillation experiments!! • Solar, atmospheric, reactor and accelerator experiments • Neutrino mass scales: • A simplest extension including neutrino masses is
Neutrino oscillations • The MSM contradicts with n oscillation experiments!! • Solar, atmospheric, reactor and accelerator experiments • Neutrino mass scales: • A simplest extension including neutrino masses is The nMSM
What is the nMSM? • The MSM + Several right-handed neutrinos • Dirac masses and Majorana masses • If Dirac masses << Majorana masses, • the seesaw mechanism works Not new!!! Minkowski ’77, Yanagida ’79, Gell-Mann, Ramond, Slansky ’79 Glashow ‘79
Seesaw mechanism • If Dirac masses << Majorana masses, • The mixing in the charged current • Active neutrinos • Sterile neutrinos
Scale of the nMSM • What are the scales of Majorana masses??
Conventional approach • F ~ Yukawa couplings in quarks and charged leptons • The new energy scale is introduced • Can explain neutrino oscillations • Can explain baryon asymmetry of the universe • via “leptogenesis” Fukugita and Yanagida ‘86
Approach here • Majorana masses are weak scale (~100GeV) or below • No new energy scale is introduced Very small neutrino Yukawa couplings • Can explain neutrino oscillations • Can explain baryon asymmetry of the universe • via neutrino oscillations • Can explain dark matter of the universe
In this talk • Q. How many right-handed neutrinos are required? • A. Minimal possibility is “three”!! • Neutrino Osc. • The minimal # is “two” • Neutrino Osc. + Baryon Asymmetry • “two” • Neutrino Osc. + Baryon Asymmetry + Dark Matter • “three”
Dark matter in the universe • Contents of the universe: • The MSM cannot offer a particle physics candidate for dark matter (DM)!! Baryon Dark Matter Dark Energy PDG
Dark matter in the nMSM • The unique candidate: • The allowed mass range is (see later discussion) Long-lived sterile neutrinos Peebles ’82, Olive, Turner ’82 Dodelson, Widrow ’94, Shi, Fuller ’99 Dolgov, Hansen ’00, Abazajian, Fuller, Patel ‘01 • Hot dark matter of active massive neutrinos is excluded • by the LSS and CMBR Sterile neutrinos as “warm dark matter”
Lifetime of sterile neutrinos • When Yukawa couplings are very small, • sterile neutrinos can be very long-lived!! • Main decay cannel: • Lifetime can exceed the age of universe Barger, Phillips, Sarkar ‘95
Production of sterile neutrinos • When Yukawa couplings are very small, • sterile neutrinos are not thermalized • Main production is due to the scatterings • at • Dirac mass is determined ! Dolgov, Hansen ’00, Abazajian, Fuller, Patel ‘01 TA, Blanchet, Shaposhnikov ‘05
Cosmological constraints • Radiative decays of DM sterile neutrinos • are limited by X-ray observations • Warm dark matter is limited by structure formation • WMAP + Matter power spectrum inferred from Ly-a forest • Only a small window is left Abazajian, Fuller, Tucker ‘01 Viel, Lesgourgues, Haehnelt, Matarrese, Riotto ‘05
Implications of DM sterile neutrinos • Dark matter constraints: • Consistency with n oscillation experiments lead to • The point is • The minimal number of sterile neutrinos is “three” • Only ”one” sterile neutrino can be dark matter • The lightest active neutrino mass is m1<O(10-5)eV TA, Blanchet, Shaposhnikov ‘05
Seesaw mass matrix • Parameterization • The following arguments is based on calculating the trace and determinant of (XX) Independent on the neutrino mixing matrix U!!!
The nMSM with two sterile neutrinos • Active n masses: • When both sterile neutrinos are DM, … Contradiction !!
The nMSM with two sterile neutrinos • Active n masses: • When one sterile neutrino is DM, … Contradiction !!
The nMSM with three sterile neutrinos • We can similarly exclude the cases in which • two and three sterile neutrinos are dark matter • When one sterile neutrino is dark matter,… Upper bound on the lightest active neutrino mass !!
Masses of active neutrinos • We can determine the absolute values of active n masses
Test for DM sterile neutrino • Radiative decays of DM sterile neutrinos may be seen in X-ray observations!! • The current status • The future experiments will detect or exclude the sterile neutrino dark matter. CMBR+Ly-a X-ray Abazajian, Fuller, Tucker ‘01
Summary • We discussed the extension of the MSM • by adding several right-handed neutrinos -The nMSM- • Only particle physics candidate for dark matter is • long-lived sterile neutrino • The minimal number of RH neutrinos is three • Only one sterile neutrino can be dark matter • The lightest active neutrino mass • The absolute values of active n masses are determined • The DM sterile neutrinos may be tested in the future X-ray observations
Conclusions • We can solve experimental and observational problems • --n oscillations, dark matter and baryon asymmetry-- • in the MSM
Conclusions n MSM
