Sterile Neutrinos in Cosmology Mikhail Shaposhnikov NEUTRINO 2008 Neutrino 2008, 30 May 2008 – p. 1
Sterile Neutrinos in Cosmology and how to find them in the Lab Mikhail Shaposhnikov NEUTRINO 2008 Neutrino 2008, 30 May 2008 – p. 1
Aim of the talk: to argue that the existing high intensity protons beams NuMi beam at FNAL, CNGS beam at CERN and future accelerator facilities J-PARC in Japan, Project X at FNAL can be used to search for physics beyond the Standard Model in new dedicated experiments Neutrino 2008, 30 May 2008 – p. 2
Possible outcome of these new experiments Discover new neutrino states – massive neutral leptons Neutrino 2008, 30 May 2008 – p. 3
Possible outcome of these new experiments Discover new neutrino states – massive neutral leptons Uncover the origin of neutrino masses Neutrino 2008, 30 May 2008 – p. 3
Possible outcome of these new experiments Discover new neutrino states – massive neutral leptons Uncover the origin of neutrino masses Fix the pattern of neutrino mass hierarchy Neutrino 2008, 30 May 2008 – p. 3
Possible outcome of these new experiments Discover new neutrino states – massive neutral leptons Uncover the origin of neutrino masses Fix the pattern of neutrino mass hierarchy and eventually Neutrino 2008, 30 May 2008 – p. 3
Possible outcome of these new experiments Discover new neutrino states – massive neutral leptons Uncover the origin of neutrino masses Fix the pattern of neutrino mass hierarchy and eventually Discover CP-violation in neutrino sector Neutrino 2008, 30 May 2008 – p. 3
Possible outcome of these new experiments Discover new neutrino states – massive neutral leptons Uncover the origin of neutrino masses Fix the pattern of neutrino mass hierarchy and eventually Discover CP-violation in neutrino sector Reveal the origin of baryon asymmetry of the universe and fix its sign Neutrino 2008, 30 May 2008 – p. 3
Guaranteed outcome of these new experiments Improving constraints of the couplings of new particles by several orders of magnitude Neutrino 2008, 30 May 2008 – p. 4
Outline Theoretical motivation Neutrino masses Dark matter Baryon asymmetry of the Universe How to search for new leptons What to expect at LHC Conclusions Neutrino 2008, 30 May 2008 – p. 5
Theoretical motivation: neutrino masses Neutrinos have mass. Possible origin of this mass - existence of right-handed neutrinos (singlet fermions, sterile neutrinos...) with mass M N and Yukawa couplings to the SM leptons and the Higgs boson. See-saw formula: 1 [ M D ] T , m ν = − M D M D = F v, v = 174 GeV M N tells nothing about scale of M N ! Neutrino 2008, 30 May 2008 – p. 6
Popular choice: GUT see-saw Assume that Yukawa couplings of N to the Higgs and left-handed lepton doublets is similar to those in quark or charged lepton sector (say, F ∼ 1 , as for the top quark) and find M N from requirement that one gets correct active neutrino masses: M N ≃ F 2 v 2 ≃ 6 × 10 14 GeV m atm m atm ≃ 0 . 05 eV is the atmospheric neutrino mass difference. Neutrino 2008, 30 May 2008 – p. 7
GUT see-saw: problems Hierarchy problem: M N is much larger than EW scale: one has to understand not only why M W ≪ M P l , but also why M W ≪ M N and why M N ≪ M P l . Three fine tunings instead of one. Stabilization of hierarchy - SUSY. SUGRA - gravitino production problem. Reheating temperature must be smaller than ∼ 10 10 GeV. Problem with leptogenesis. Extra scale - extra T reh < (4th) hierarchy problem! Why M N ≪ M GUT ? Unfortunately, no direct experimental verification is foreseen Neutrino 2008, 30 May 2008 – p. 8
Alternative: EW see-saw Assume that the Majorana masses of N are smaller or of the same order as the mass of the Higgs boson and find Yukawa couplings from requirement that one gets correct active neutrino masses: √ m atm M N ∼ (10 − 6 − 10 − 13 ) , F ∼ v Advantages: No new energy scale - no new hierarchy or fine tuning problem in comparison with the Standard Model. Different approach to hierarchy problem Neutrino 2008, 30 May 2008 – p. 9
Highlights An extension of the Standard Model by three singlet fermions (the ν MSM, neutrino minimal SM) allows to address all experimentally confirmed signals in favour of physics beyond the SM: Consistent description of neutrino masses and oscillations Can explain dark matter in the Universe Can explain baryon asymmetry of the Universe Can provide inflation (as well as the Standard Model) Masses of new leptons are small: they can be found experimentally. Neutrino 2008, 30 May 2008 – p. 10
the ν MSM There are 36 quark states: left fermionic doublets: ( u , d ) L , ( c , s ) L , ( t , b ) L and u R , d R , c R , s R , t R , b R ( u , d ) L , ( c , s ) L , ( t , b ) L and u R , d R , c R , s R , t R , b R ( u , d ) L , ( c , s ) L , ( t , b ) L and u R , d R , c R , s R , t R , b R , 9 + 3 leptonic states ( ν e , e ) L , ( ν µ , µ ) L , ( ν τ , τ ) L and N D , e R , N C , µ R , N B , τ R 12 SU (3) × SU (2) × U (1) gauge bosons (8+3+1) and one Higgs doublet, in total (3 × 2 + 3 × 2 + 2 + 1 + 0) × 3 × 2 = 90 fermionic and (8 + 3 + 1) × 2 + 4 = 28 bosonic degrees of freedom Neutrino 2008, 30 May 2008 – p. 11
the ν MSM There are 36 quark states: left fermionic doublets: ( u , d ) L , ( c , s ) L , ( t , b ) L and u R , d R , c R , s R , t R , b R ( u , d ) L , ( c , s ) L , ( t , b ) L and u R , d R , c R , s R , t R , b R ( u , d ) L , ( c , s ) L , ( t , b ) L and u R , d R , c R , s R , t R , b R , 9 + 3 leptonic states ( ν e , e ) L , ( ν µ , µ ) L , ( ν τ , τ ) L and N D , e R , N C , µ R , N B , τ R 12 SU (3) × SU (2) × U (1) gauge bosons (8+3+1) and one Higgs doublet, in total (3 × 2 + 3 × 2 + 2 + 1 + 1) × 3 × 2 = 96 fermionic and (8 + 3 + 1) × 2 + 4 = 28 bosonic degrees of freedom Neutrino 2008, 30 May 2008 – p. 12
Theoretical motivation: dark matter Dodelson, Widrow; Shi, Fuller; Dolgov, Hansen; Abazajian, Fuller, Patel; Asaka, Blanchet, M.S., Laine Yukawa couplings are small → sterile N can be very stable. For one flavour: N ν � 5 � � 10 − 8 � 10 keV τ N 1 = 10 14 years Z θ 2 M N 1 ν ν θ 1 = m D M N Main decay mode: N → 3 ν . Subdominant radiative decay channel: N → νγ . Neutrino 2008, 30 May 2008 – p. 13
Constraints on DM sterile neutrino Production. N 1 are created in the early Universe in reactions l ¯ l → νN 1 , q ¯ q → νN 1 etc. We should get correct DM abundance. X-rays. N 1 decays radiatively, N 1 → γν , producing a narrow line which can be detected. This line has not been seen (yet). Structure formation. If N 1 is too light it may have considerable free streaming length and erase fluctuations on small scales. This can be checked by the study of Lyman- α forest spectra of distant quasars. Neutrino 2008, 30 May 2008 – p. 14
DM: production+ X-ray constraints + Lyman- α bounds 10 -6 10 -8 Ω > Ω DM 10 -10 Sin 2 (2 θ 1 ) 10 -12 10 -14 Ω < Ω DM 10 -16 0.3 1 10 100 M 1 [keV] Neutrino 2008, 30 May 2008 – p. 15
DM: production + X-ray constraints+ Lyman- α bounds 10 -6 10 -8 Ω > Ω DM 10 -10 Sin 2 (2 θ 1 ) N 1 → νγ 10 -12 10 -14 Ω < Ω DM 10 -16 0.3 1 10 100 M 1 [keV] Neutrino 2008, 30 May 2008 – p. 16
DM: production + X-ray constraints + Lyman- α bounds 10 -6 10 -8 Ω > Ω DM 10 -10 Sin 2 (2 θ 1 ) N 1 → νγ 10 -12 Lyman- α 10 -14 Ω < Ω DM 10 -16 0.3 1 10 100 M 1 [keV] Neutrino 2008, 30 May 2008 – p. 17
Theoretical motivation: baryon asymmetry Asaka, M.S; Akhmedov, Rubakov, Smirnov Lepton number violation: N 2 , 3 ↔ ν Baryon number violation: electroweak anomaly, sphalerons CP - violation: Dirac and Majorana phases in N 2 , 3 − ν interactions Arrow of time: N 2 , 3 are out of thermal equilibrium for small Yukawa couplings Neutrino 2008, 30 May 2008 – p. 18
Value of baryon asymmetry � 2 � 5 � 10 − 5 3 � n B M 3 3 ≃ 1 . 7 · 10 − 10 δ CP . ∆ M 2 32 /M 2 s 10GeV 3 � ( c 4 L 23 + s 4 L 23 ) c 2 L 13 − s 2 � � δ CP = 4 s R 23 c R 23 s L 12 s L 13 c L 13 · sin( δ L + α 2 ) L 13 � + c L 12 c 3 L 13 s L 23 c L 23 ( c 2 L 23 − s 2 L 23 ) · sin α 2 . δ CP ∼ 1 may be consistent with observed ν oscillations. Nontrivial requirement: | M 2 − M 3 | ≪ M 2 , 3 , i.e. heavier neutrinos must be degenerate in mass. Works best if M 2 2 − M 2 3 ∼ T 3 W /M 0 ≃ 4 (keV) 2 , | M 2 2 − M 2 3 | ∼ M 2 1 ??? Neutrino 2008, 30 May 2008 – p. 19
Constraints on BAU sterile neutrinos BAU generation requires out of equilibrium: mixing angle of N 2 , 3 to active neutrinos cannot be too large Neutrino masses. Mixing angle of N 2 , 3 to active neutrinos cannot be too small Dark matter and BAU. Concentration of DM sterile neutrinos must be much larger than concentration of baryons BBN. Decays of N 2 , 3 must not spoil Big Bang Nucleosynthesis Experiment. N 2 , 3 have not been seen (yet). Neutrino 2008, 30 May 2008 – p. 20
N 2 , 3 : BAU+ DM + BBN + Experiment 10 -5 10 -6 10 -7 B A U 10 -8 2 θ 2 10 -9 10 -10 S e e 10 -11 - s a w 10 -12 0.1 1 10 M 2 [GeV] Neutrino 2008, 30 May 2008 – p. 21
N 2 , 3 : BAU + DM+ BBN + Experiment 10 -5 10 -6 10 -7 B A U 10 -8 2 θ 2 10 -9 10 -10 DM preferred S e e 10 -11 - s a w 10 -12 0.1 1 10 M 2 [GeV] Neutrino 2008, 30 May 2008 – p. 22
Recommend
More recommend
