The nMSM

1
The nMSM

• -- Neutrino Masses and Dark matter --

Takehiko Asaka (Tohoku University)
TA, S.Blanchet, M.Shaposhnikov hep-ph/0503065 TA
, M.Shaposhnikov hep-ph/0505013
2
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

3
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
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What is the nMSM?

• The MSM Several right-handed neutrinos
• Dirac masses and Majorana
  masses
• If Dirac masses ltlt Majorana masses,
• the seesaw mechanism works

Not new!!!
Minkowski 77, Yanagida 79, Gell-Mann, Ramond,
Slansky 79 Glashow 79
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Seesaw mechanism

• If Dirac masses ltlt Majorana masses,
• The mixing in the charged current

• Active neutrinos
• Sterile neutrinos

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Scale of the nMSM

• What are the scales of Majorana masses??

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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
8
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

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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

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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
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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
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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
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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
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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
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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 m1ltO(10-5)eV

TA, Blanchet, Shaposhnikov 05
16
Seesaw mass matrix

• Parameterization
• The following arguments is based on calculating
  the trace and determinant of (XX)

Independent on the neutrino mixing matrix U!!!
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The nMSM with two sterile neutrinos

• Active n masses
• When both sterile neutrinos are DM,

Contradiction !!
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The nMSM with two sterile neutrinos

• Active n masses
• When one sterile neutrino is DM,

Contradiction !!
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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
!!
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Masses of active neutrinos

• We can determine the absolute values of active n
  masses

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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.

X-ray
CMBRLy-a
Abazajian, Fuller, Tucker 01
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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

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Conclusions

• We can solve experimental and observational
  problems
• --n oscillations, dark matter and baryon
  asymmetry--
• in the

MSM
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Conclusions
n
MSM