Sterile Neutrinos

1. PASCOS 2004 Sterile Neutrinos Probing with cosmology, astrophysics,  experiments… Marco Cirelli (Yale) with G.Marandella, A.Strumia, F.Vissani hep-ph/0403158 (--> NPB) and with Yi-Zen Chu (in preparation)

2. (SNO) no, e, e s ? solar: atmo:  s? no,   (SK, Macro) Introduction and Purpose We want to studySterile Neutrinos i.e. - (light) spin 1/2 fermions, - neutral under all SM forces, - have a mixing with active . Oscillations into s are now excluded as the dominant solution in solar and atmospheric neutrinos: (details…) (details…)

3. Perform a complete analysis: (1) for any possible e,,- s mixing pattern (2) including the established e-, and - mixing (= in a full 4 mixing formalism) (3) study all neutrino sources ( experiments, astrophysics, cosmology) • set present bounds • look for sterile evidence in present data. None. • identify future signals Now the relevant issues become: - which subdominant role is still possible for s? - where can we detect the s? - how can we detect the s?

4. Are sterile neutrinosstill interesting at all? • Yes, sterile neutrinos invoked for so many • “puzzles” … ( ?) right-handed neutrino axino goldstino majorino • Yes, “new light neutral fermions” in so many • Beyond the SM constructions… branino dilatino radino modulino familino -behave effectively as s -parameterize with s , ms2 mirror fermions … pulsar kicks r-process nucleosynthesis Dark Matter galactic ionization … • …LSND

5. Present bounds are computed in a limited 2 formalism: l cossl’+sin s s . We want instead a full 4 formalism. A simple parametrization: define a complex unit 3-vectorn n identifies the combination of active  : which mixes with s with a single angle 4 mixing formalism more details

6. ( l ·n =  ) ( i ·n = 2 ) In the following: s has arbitrary mass m4 and it mixes with angle s with eOROR OR 1OR 2OR 3 Also: take best-fit values for sun and atm , choose 13 = 0, Normal Hierarchy.

7. CMB Sun BBN SN Early Universe LSS Astrophysics Atmo & Experiments s AGN Atmosphere SBL Combined Results reactors accelerators

8. Sterile effects in the Early Universe Neutrinos in the Early Universe are: (1) a lot (as abundant as photons) (2) the main component of the (relativistic) energy density that sets the expansion rate (3) trapped in the dense early plasma non trivial matter effects (4) important for the outcoming chemical composition An extra scan make a big difference.

9. BigBang Nucleosynthesis ms2 , s es es N (T ~ 1 MeV) BBN 4He D 3Li 3He … n/p b (nuclear rates, n mean life, weak cross sections…) CMB (WMAP)

10. kinetic equ.s for neutrino densitiese(T),  (T),  (T), s (T) equation for n/p equations of light nuclei (4He , D) production 4 (4He , D) observations (B) mixing e -s depletion of e effect on n p reactions For every choice of ms2 , s , for T >> MeV 0.07 MeV follow: Roadmap ( = What we do) (BBN ends, les jeux sont fait) • Assumptions: • no large lepton asymmetries • neglect spectral distortions Where does a s enter the BBN game? (A)s production  larger total energy density  faster expansion

11. Bounds in the parameter space 4He=25.8% N = 3.8 4He=25.0% N = 3.2

12. Upper bound on: 1,2,3 ands 2dF+WMAP : scontribute to   bound onms i.e. m2s. but: if s do not fully thermalize  s << 1  weaker bound Large Scale Structure The primordial free streaming of massive neutrinos affects the LSS power spectrum observed today. M.Tegmark webpage

13. Bounds in the parameter space h2= 10 -2 h2= 10 -3

14. Cosmic Microwave Background The primordial neutrino energy densities affect the acoustic peaks of CMB power spectrum. Barger et al., PLB566, 2003 Bound on the effective NCMB  e ,  ,  , s . N = 1, 2.75, 5, 7 At present: NCMB= 32 Bound on the ms2,s (that determine the s).

15. All bounds from cosmology 4He=25.8% N = 3.8 4He=25.0% N = 3.2 h2= 10 -2 h2= 10 -3

16. LSND claims evidence for e with m2  m2sun, atm(if oscillations) se LSND: in or out? Requires a new (= sterile) neutrino: How does the LSND s fit in cosmology? LSND ~ es s

17. CMB Sun BBN SN Early Universe LSS Astrophysics Atmo & Experiments s AGN Atmosphere SBL Combined Results reactors accelerators

18. Set present bounds Overall picture confirmed by SN1987a Thousands of events from future SN Propose future probes Sterile effects in SN Neutrinos from SN: (1) are a lot (99% of emitted energy) (2) undergo “extreme” matter effects (3) come from very far away (~10 kpc) (4) have the right energy (~10 MeV) for present detectors An extra scan make a big difference.

19. s core mantle Matter oscillations in the star mantle: A.Burrows et al., 2001, 2002, 2003 SK  SNO  e -sphere

20. At each crossing there is a crossing probability “lost” Matter eigenstates in the mantle: Output: final fluxes of e, and  on Earth .

21. Excluded by SN1987a Results: percentual reduction of e events (in a large Cerenkov detector) (ep  ne+) Beware of theoretical uncertainties…

22. The energy dependance of matter/vacuum conversions causes spectral distortions: Possible very clear feature!

23. CMB Sun BBN SN Early Universe LSS Astrophysics Atmo & Experiments s AGN Atmosphere SBL Combined Results reactors accelerators

24. Neutrinos from ‘extragalactic’ sources • produced in high-energy astrophysical processes • expected flavor ratios e :  : = 1 : 2 : 0 at production • 1 : 1 : 1 after (active) oscillations • if a s is introduced, a selective depletion can occur . But: • initial fluxes totally unknown • we tag  and  which nevertheless equiparate (atmo oscillations)… Not a very interesting probe.

25. CMB Sun BBN SN Early Universe LSS Astrophysics Atmo & Experiments s AGN Atmosphere SBL Combined Results reactors accelerators

26. Set present bounds Look for evidence of s effectsaround the LMA solution. None Identify future probes Sterile effects in solar neutrinos Neutrinos from the sun: (1) are a lot, and very well studied (2) undergo matter effects in the sun and in the Earth (3) come from far away (~150 Mkm) An extra scan make a difference. more details

27. Solar e spectrum: LMA e-, resonance -input e flux -crossings in sun matter Active-sterile resonance -output fluxes “lost” (production regions) Gonzalez-Garcia, Nir, review 2002 Bahcall, Pinsonneault 2001 Evolution: -vacuum oscillations -(matter oscillations in Earth)

28. Neutrino density matrix formalism: 4x4 density matrix at production (e in the sun) is mixing matrices in matter (Vm) are computed diagonalizing the matter Hamiltonian evolve with evolution matrix at eachijmatter level crossing rotates of with ( m effective mixing angle in matter) at detection (back to flavor basis) E.g. P(ee)corresponds to ee…

29. Results (with KamLAND): excluded effect in a low energy exper. (sub-MeV)

30. Spectral distortions: - the energy dependance in the (matter and vacuum) oscillations distorts the original (well known) solar e spectrum - a very distinctive feature! - mainly at low energies Pe  Pe e Pe s

31. The “still allowed component” of s in solar neutrinos: means the naïve limit e coss,+sin s s . In our framework: sin2s < 0.2

32. CMB Sun BBN SN Early Universe LSS Astrophysics Atmo & Experiments s AGN Atmosphere SBL Combined Results reactors accelerators

33. Sterile effects in atmospheric neutrinos Evidence for oscillations is disappearance of  “from below”. Basics: SK coll. Where do they go?  ,  s or a combination? 3 sensitive probes to discriminate and put bounds:

34. If s : larger flux of thru-muons (1b) larger number of PC events fewer NC-enriched events (3) tau appearance… We perform a global 2 analysis of SK + Macro + K2K data. “No improvements” w.r.t. pure   found:  no evidence for sterile neutrinos  excluded regions .

35. Results: excluded 5%,1% effect on NC at MINOS

36. means the naïve limit  coss+sin s s . In our framework: sin2s <0.16 The “still allowed component” of s in atmospheric neutrinos:

37. CMB Sun BBN SN Early Universe LSS Astrophysics Atmo & Experiments s AGN Atmosphere SBL Combined Results reactors accelerators

38. Sterile effects in SBL neutrinos Chooz + Bugey + CDHS + CCFR + Karmen + Nomad + Chorus Main constraint comes from “no-disappearance”. excluded future SBL at reactor?

39. CMB Sun BBN SN Early Universe LSS Astrophysics Atmo & Experiments s AGN Atmosphere SBL Combined Results reactors accelerators

40. Combined Results

41. ConclusionsandExecutive Summary • the “direct/easy way” for sterile neutrinos to enter our world • (solar anomaly, atmospheric anomaly) is now ruled out • performing a general analysis, we looked • at more subtle and more interesting manifestations • we find no evidence for sterile neutrinos so far • we set the present bounds(in particular: LSND excluded by Standard Cosmology) • cosmology, astro-ph and  experiments probe • different and complementary patterns: • measure better 4HeandD(different physics, different systematics) • (+CMB and LSS) • detect thenext SN- improve standard theory models • - look for non-standard  fluxes and spectra • measure better low energy solar neutrinos • … combinedata from different fields