STERILE NEUTRINOS and WARM DARK MATTER
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Transcript of STERILE NEUTRINOS and WARM DARK MATTER
STERILE NEUTRINOSand
WARM DARK MATTER
The 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=-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, N, N
A simple calculationIn the Universe at large:
Dark matter 25%Ordinary matter(nucleons) 5%Nucleon/photon = 6 10-10
400 /cm3, 100 e/ cm3
Putting all the numbers togetherIn the Universe at largeN/ = 3.6 10-6/m
(m in MeV)
Thus : N/e = 1.2 10-5/m
UNe2 > 1.2 10-5/m
Testing the anomalies
Reactor and rad source anomaly 1.2 10-5/m = 7%
m = 180 eV !!
LSND anomaly 1.2 10-5/m = 1%
m = 1.2 keV
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/sYearly modulation
In December 5,1 109/m /cm2/sIn June 6,9 109/m /cm2/s
Possible experiments?
Decay of sterile neutrinos If mass < 1 MeV
If mass > 1 MeVPurely weak decay: Lifetime for e+e-
2.8 104 (1/m(MeV)5)(1/U2)(s)
+ phase-space
W
e
Radiative decay: GIM suppressed = 7 1013 (1/m(MeV)5)(1/U2)(s)
Weak/radiative ~ 1010
Heavy neutrinos at accelerators
• Mixed with active neutrinos
• In all weak processes they appear at the level U2Nl
Their mass is limited by kinematics
e N m(N) < 130 MeV
N m(N) < 20 MeV
K e N m(N) < 450 MeV
K N m(N) < 350 MeV
… W e N m(N) < 80 GeV
PRESENT LIMITS
Consistancy problemUNe
2 > 1.2 10-5/m ??
Livetime must be greater than the age of the Universe
For N → e+ e-
2.8 104 (1/m(MeV)5)(1/U2)→ m<10keV !
For N → = 7 1013 (1/m(MeV)5)(1/U2)
→m<1.5 MeV
Astrophysics searches
A.Boyarsky, D.Malyshev, A.Neronov, O.Ruchaysky arXiv:0710.4922H.J.de Vega, N.G.Sanchez Mon.Not.R.Astron.Soc.(2010)
From SPI (Integral) and XMM-Newton
Laboratory search?Flux 61012/m(keV) /cm2/s
Radiative decay = 7 1028 (1/m(keV)5)(1/U2)(s)
But matter enhancement
e
W
e
0/m ~ 3 1012 (Ne/1024)2 (m/E) (keV/m)4
m ~ 2 1016 (keV/m)(1/U2)
Probability of decay is l/(c) = 0,7 10-3, = 1
In 1 m3 detector N = 1.3 U2 events/day
Interactions of keV sterile neutrinos: S.Ando, A.Kusenko arXiv:1001.5273
Conclusion
• Heavy neutrinos probably exist• Potentially predicting Warm Dark Matter
(… but problematic consistancy)
• Experimentally extremelly challenging