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MeV NEUTRINOS and WARM DARK MATTER

MeV NEUTRINOS and WARM DARK MATTER. The n MSM model. T. Asaka and M. Shaposhnikov Phys.Lett.B620(2005)17 M.Shaposhnokov Nucl.Phys.B763(2007)49 Minimum extension of the SM to accomodate massive neutrinos See-saw formula for active neutrinos m n =-M D (1/M I )(M D ) T Majorana mass M I

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MeV NEUTRINOS and WARM DARK MATTER

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  1. MeV NEUTRINOSand WARM DARK MATTER

  2. The nMSM model • T. Asaka and M. Shaposhnikov Phys.Lett.B620(2005)17 • M.Shaposhnokov Nucl.Phys.B763(2007)49 • Minimum extension of the SM to accomodate massive neutrinos • See-saw formula for active neutrinos mn=-MD(1/MI)(MD)T • Majorana mass MI • Dirac mass MD=fv v=174 GeV vac exp val of Higgs field • Usual choice: f as in quark sector, M = 1010-1015 GeV • Alternative choice: small f  Ne, Nm, Nt

  3. Heavy neutrinos at accelerators • Mixed with active neutrinos • In all weak decays they appear at the level U2Nl Their mass is limited by kinematics p e N m(N) < 130 MeV pm N m(N) < 20 MeV K  e N m(N) < 450 MeV K m N m(N) < 350 MeV … W  e N m(N) < 80 GeV

  4. Decays of heavy neutrinos Purely weak decays: modes depend on the N mass first channel to open e+e-n, then men, m+m-n, e-p+, m-p+…. Lifetime for e+e-n t = 2.8 104 (1/m(MeV)5)(1/U2) + phase-space

  5. A simple calculation We know that: Dark matter 25% Ordinary matter(nucleons) 4% Nucleon/photon = 6 10-10 400 g/cm3, 100 ne/ cm3 Putting all the numbers together In the Universe at large N/g = 3.6 10-6/m Thus : N/ne = 1.5 10-5/m If N(0) = ne N/N(0) = exp(-T/t)= 1.5 10-5/m  t ~ 3 1016 s

  6. N as Dark Matter Candidate Suppose that DM is made of heavy neutrinos of mass m MeV Density of DM 300 MeV/cm3 Number density of N 300/m /cm3 Relative velocity 200 km/s Flux 6109/m /cm2/s But the earth moves at 30 km/s Yearly modulation In December 5,1 109/m /cm2/s In June 6,9 109/m /cm2/s

  7. Decay search on earth Flux of N 6109/m /cm2/s Lifetime for e+e-n : t = 2.8 104 (1/m(MeV)5)(1/U2) Probability of decay is l/(bgct) b = 0,7 10-3, g = 1 In a LENA (105 m3) type detector: Nevt= 70/day for m= 1 MeV 7/day for m= 10 MeV .7/day for m= 100 MeV Possible local amplification?

  8. Conclusion • Heavy neutrinos should exist • Potentially predicting Warm Dark Matter • The MeV region has been little explored • Experimentally challenging but not impossible

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