Transcript Sterile Neutrinos in all sauces

PASCOS 2004
Probing
Sterile Neutrinos
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)
Introduction and Purpose
We want to study Sterile 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:
solar:
e
s ?
no, e
,
(SNO)
atmo:

 s?
no, 

(SK, Macro)
(details…)
(details…)
2
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 ?
Perform a complete analysis:
(1) for any possible e,, - s mixing pattern
(2) including the established e-, and - mixing
(3) study all neutrino sources
(= in a full 4
mixing formalism)
( experiments, astrophysics, cosmology)
• look for sterile evidence in present data. None.
• set present bounds
• identify future signals
3
Are sterile neutrinos still interesting at all?
• Yes, “new light neutral fermions” in so many
Beyond the SM constructions…
-behave effectively as s
-parameterize with s , ms2
• Yes, sterile neutrinos invoked for so many
“puzzles” … (
?)
right-handed neutrino
axino
goldstino
majorino
branino
dilatino
radino
familino modulino
mirror fermions
…
pulsar kicks
r-process nucleosynthesis
Dark Matter
galactic ionization
…
• …LSND
4
4 mixing formalism
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:
more details
define a complex unit 3-vector n
n identifies the combination of active  :
which mixes with s with a single angle
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In the following:
s has arbitrary mass m4 and it mixes with angle s
with e OR  OR  OR 1 OR 2 OR 3
( l ·n =  )
Also: take best-fit values for sun and atm ,
choose 13 = 0, Normal Hierarchy.
( i ·n = 2 )
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CMB
Sun
BBN
LSS
s
Atmosphere
SN
AGN
SBL
Combined
Results
reactors
accelerators
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 s can make a big difference.
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BigBang Nucleosynthesis
ms2 , s
e  N s
(T ~ 1 MeV)
BBN
QuickTime™ and a
GIF decompressor
are needed to see this picture.
4He
n/p
D
3Li
3He
…
b
(nuclear rates, n mean life,
weak cross sections…)
CMB
(WMAP)
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Roadmap ( = What we do)
For every choice of ms2 , s ,
for T >> MeV
0.07 MeV follow:
(BBN ends, les jeux sont fait)
1
kinetic equ.s for neutrino densities e(T),  (T),  (T), s (T)
2
equation for n/p
3
equations of light nuclei (4He , D) production
4
(4He , D) observations
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
(B) mixing e -s  depletion of e  effect on n p reactions
Bounds in the parameter space
4He=25.0%
N = 3.2
4He=25.8%
N = 3.8
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Large Scale Structure
The primordial free streaming
of massive neutrinos
affects
the LSS power spectrum
observed today.
Upper bound on:
QuickTime™ and a
GIF decompressor
are needed to see this picture.
1,2,3 and s
2dF+WMAP :
s contribute to   bound on ms i.e. m2s .
but: if s do not fully thermalize  s << 1  weaker bound
Bounds in the parameter space
27
Cosmic Microwave Background
Bound on the
effective NCMB 
e ,  ,  , s .
Barger et al., PLB566, 2003
The primordial neutrino
energy densities
affect
the acoustic peaks
of CMB power spectrum.
N = 1, 2.75, 5, 7
At present: NCMB = 32
Bound on the ms2 , s (that determine the s).
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All bounds from cosmology
4He=25.0%
N = 3.2
4He=25.8%
N = 3.8
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LSND: in or out?
LSND claims evidence for  e with m2  m2sun, atm
Requires a new (= sterile) neutrino:
 s
e
(if oscillations)
How does the LSND s fit in cosmology?
LSND ~ es s
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CMB
Sun
BBN
LSS
s
Atmosphere
SN
AGN
SBL
Combined
Results
reactors
accelerators
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 s can make a big difference.
Overall picture confirmed by SN1987a
Thousands of events from future SN
Set present bounds
Propose future probes
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s

core
SK
SNO

mantle
e
Matter oscillations in the star mantle:
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Matter eigenstates
in the mantle:
At each crossing there is a
crossing probability
Output: final fluxes of e,  and  on Earth .
“lost”
34
Results: percentual reduction of e events (in a large Cerenkov detector)
(e p  ne+)
Excluded by
SN1987a
Beware of
theoretical
uncertainties…
35
The energy dependance of matter/vacuum conversions causes
spectral distortions:
Possible very clear feature!
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CMB
Sun
BBN
LSS
s
Atmosphere
SN
AGN
SBL
Combined
Results
reactors
accelerators
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.
38
CMB
Sun
BBN
LSS
s
Atmosphere
SN
AGN
SBL
Combined
Results
reactors
accelerators
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 s can make a difference.
Look for evidence of s effects around the LMA solution. None
more details
Set present bounds
Identify future probes
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Solar e spectrum:
Evolution:
-input e flux
-crossings in sun matter
-output fluxes
-vacuum oscillations
-(matter oscillations
in Earth)
(production regions)
LMA e-, resonance
Active-sterile resonance
“lost”
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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 each ij matter 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…
42
Results (with KamLAND):
excluded
effect in a low
energy exper.
(sub-MeV)
43
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
44
The “still allowed component” of s in solar neutrinos:
means the naïve limit e
In our framework:
coss ,+sin s s .
sin2s < 0.2
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CMB
Sun
BBN
LSS
s
Atmosphere
SN
AGN
SBL
Combined
Results
reactors
accelerators
Sterile effects in atmospheric neutrinos
Basics:
Evidence for oscillations is disappearance
of  “from below”.
Where do they go?   ,  s or a combination?
3 sensitive probes to discriminate and put bounds:
47
If 
s :
(1) larger flux of thru-muons
(1b) larger number of PC events
(2) 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 .
48
Results:
excluded
5%,1% effect on NC at MINOS
49
The “still allowed component” of s in atmospheric neutrinos:
means the naïve limit 
coss +sin s s .
In our framework:
sin2s <0.16
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CMB
Sun
BBN
LSS
s
Atmosphere
SN
AGN
SBL
Combined
Results
reactors
accelerators
Sterile effects in SBL neutrinos
Chooz + Bugey + CDHS + CCFR + Karmen + Nomad + Chorus
Main constraint comes from “no-disappearance”.
excluded
future SBL at reactor?
52
CMB
Sun
BBN
LSS
s
Atmosphere
SN
AGN
SBL
Combined
Results
reactors
accelerators
Combined Results
54
Conclusions
and
Executive 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 4He and D (different physics, different systematics)
(+CMB and LSS)
• detect the next SN - improve standard theory models
- look for non-standard  fluxes and spectra
• measure better low energy solar neutrinos
•…
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combine data from different fields