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Sterile neutrinos at the eV scale?Padova, 11 May 2012
Thomas Schwetz-Mangold
Max-Planck-Institut für KernphysikHeidelberg
T. Schwetz 1
Outline
Introduction
Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data
Active-sterile mixing
Can we explain all the hints together?
More exotic proposals
Cosmology
How to proceed?
Conclusions
T. Schwetz 2
Introduction
Outline
Introduction
Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data
Active-sterile mixing
Can we explain all the hints together?
More exotic proposals
Cosmology
How to proceed?
Conclusions
T. Schwetz 3
Introduction
Global fit within three-flavour framework
Gonzalez-Garcia, Maltoni, Salvado, TS, in prep.
with SBL reactor data:
sin2 θ13 = 0.022+0.0033−0.0030
sin2 2θ13 = 0.086± 0.012
θ13 = (8.5+0.62−0.61)
6.9σ significance
without SBL data using2011 flux prediction:
sin2 θ13 = 0.026+0.0034−0.0032
sin2 2θ13 = 0.101+0.013−0.012
θ13 = (9.3± 0.59)
8.0σ significance
T. Schwetz 4
Introduction
Let us consider the existence of “sterile neutrinos”
“sterile neutrinos”: fermionic gauge singlets or right-handed neutrinos
Yukawa term:LY = −yLLφNR + h.c.
bare Majorana mass term:
12
NTR C−1M∗
RNR + h.c.
we have no (very little) guidance about their mass (y and MR)
T. Schwetz 5
Introduction
Sterile neutrinos at which scale?
I a comon prejustice is that they should be heavy:1015 GeV (GUT-motivation?) → seesaw1010 GeV (Leptogenesis)
I maybe they have mass in the GeV range(Leptogenesis by oscillations) Shaposhnikov et al
I maybe they have mass in the keV range (warm dark matter)
I maybe they have mass in the eV range (SBL neutrino oscillations)
I maybe they have a mass highly degenerate with the active neutrinos(10−5 eV2) → missing upturn of Pee in solar neutrinos deHolanda, Smirnov
T. Schwetz 6
Introduction
Sterile neutrinos at which scale?
I a comon prejustice is that they should be heavy:1015 GeV (GUT-motivation?) → seesaw1010 GeV (Leptogenesis)
I maybe they have mass in the GeV range(Leptogenesis by oscillations) Shaposhnikov et al
I maybe they have mass in the keV range (warm dark matter)
I maybe they have mass in the eV range (SBL neutrino oscillations)
I maybe they have a mass highly degenerate with the active neutrinos(10−5 eV2) → missing upturn of Pee in solar neutrinos deHolanda, Smirnov
T. Schwetz 6
Introduction
Sterile neutrinos at which scale?
I a comon prejustice is that they should be heavy:1015 GeV (GUT-motivation?) → seesaw1010 GeV (Leptogenesis)
I maybe they have mass in the GeV range(Leptogenesis by oscillations) Shaposhnikov et al
I maybe they have mass in the keV range (warm dark matter)
I maybe they have mass in the eV range (SBL neutrino oscillations)
I maybe they have a mass highly degenerate with the active neutrinos(10−5 eV2) → missing upturn of Pee in solar neutrinos deHolanda, Smirnov
T. Schwetz 6
Introduction
Sterile neutrinos at which scale?
I a comon prejustice is that they should be heavy:1015 GeV (GUT-motivation?) → seesaw1010 GeV (Leptogenesis)
I maybe they have mass in the GeV range(Leptogenesis by oscillations) Shaposhnikov et al
I maybe they have mass in the keV range (warm dark matter)
I maybe they have mass in the eV range (SBL neutrino oscillations)
I maybe they have a mass highly degenerate with the active neutrinos(10−5 eV2) → missing upturn of Pee in solar neutrinos deHolanda, Smirnov
T. Schwetz 6
Introduction
Sterile neutrinos at which scale?
I a comon prejustice is that they should be heavy:1015 GeV (GUT-motivation?) → seesaw1010 GeV (Leptogenesis)
I maybe they have mass in the GeV range(Leptogenesis by oscillations) Shaposhnikov et al
I maybe they have mass in the keV range (warm dark matter)
I maybe they have mass in the eV range (SBL neutrino oscillations)
I maybe they have a mass highly degenerate with the active neutrinos(10−5 eV2) → missing upturn of Pee in solar neutrinos deHolanda, Smirnov
T. Schwetz 6
Introduction
Sterile neutrinos at which scale?
I a comon prejustice is that they should be heavy:1015 GeV (GUT-motivation?) → seesaw1010 GeV (Leptogenesis)
I maybe they have mass in the GeV range(Leptogenesis by oscillations) Shaposhnikov et al
I maybe they have mass in the keV range (warm dark matter)
I maybe they have mass in the eV range (SBL neutrino oscillations)
I maybe they have a mass highly degenerate with the active neutrinos(10−5 eV2) → missing upturn of Pee in solar neutrinos deHolanda, Smirnov
T. Schwetz 6
Introduction
Sterile neutrinos at which scale?
I a comon prejustice is that they should be heavy:1015 GeV (GUT-motivation?) → seesaw1010 GeV (Leptogenesis)
I maybe they have mass in the GeV range(Leptogenesis by oscillations) Shaposhnikov et al
I maybe they have mass in the keV range (warm dark matter)
I maybe they have mass in the eV range (SBL neutrino oscillations)
I maybe they have a mass highly degenerate with the active neutrinos(10−5 eV2) → missing upturn of Pee in solar neutrinos deHolanda, Smirnov
T. Schwetz 6
Introduction
4-neutrino schemes
3+1: small perturbation to 3-active case
T. Schwetz 7
Introduction
5-neutrino schemes
(3+2) scheme∆m
2
LSND
∆m2
sol
∆m2
atm
∆m2
LSND
νe
νµ ντ νs
m2
i
Peres, Smirnov, hep-ph/0011054; Sorel, Conrad, Shaevitz, hep-ph/0305255
T. Schwetz 8
Hints for sterile neutrinos
Outline
Introduction
Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data
Active-sterile mixing
Can we explain all the hints together?
More exotic proposals
Cosmology
How to proceed?
Conclusions
T. Schwetz 9
Hints for sterile neutrinos The reactor anomaly
New reactor flux calculationsI to predict the νe flux from nuclear reactors one has to convert the
measured e− spectra from 235U, 239Pu, 241Pu into neutrino spectraSchreckenbach et al., 82, 85, 89
I recent improved calculation Mueller et al., 1101.2663
(ab initio calculations + virtual branches for missing part)∼ 3% higher fluxes
T. Schwetz 10
Hints for sterile neutrinos The reactor anomaly
New reactor flux calculations
I confirmed by independent calculation P. Huber, 1106.0687
(virtual branches)
I increase of predicted number of neutrino-induced events compared toold flux calculations:
235U 239Pu 241Pu 238U3.7% 4.2% 4.7% 9.8%
T. Schwetz 11
Hints for sterile neutrinos The reactor anomaly
New reactor flux calculations
I confirmed by independent calculation P. Huber, 1106.0687
(virtual branches)
I increase of predicted number of neutrino-induced events compared toold flux calculations:
235U 239Pu 241Pu 238U3.7% 4.2% 4.7% 9.8%
T. Schwetz 11
Hints for sterile neutrinos The reactor anomaly
New reactor flux calculations
data from short-baseline reactorexperiments:
µ = 0.927± 0.023
2.9σ away from 1
Mention et al, 1101.2755 (2012 upd)
T. Schwetz 12
Hints for sterile neutrinos The reactor anomaly
New reactor fluxes and reactor dataMention et al., 1101.2755 (2012 upd)
I non-zero θ13 can reduce flux at L & 1 km but not shorter baselinesI sterile neutrino with ∆m2 ∼ 1 eV2 can account for rate reduction at
L & 10− 100 mI all based on ILL electron spectrum measurement
systematic error...?
T. Schwetz 13
Hints for sterile neutrinos The reactor anomaly
Reactor data and sterile neutrinos
3 4 5 6 7 8E
pos [MeV]
0.8
0.9
1
1.1
obse
rved
/ pr
edic
ted
rate
3 4 5 6 7 8E
pos [MeV]
0.9
1
Bugey3 15 m Bugey3 40 m
Bugey4
χ2
no osc = 59.0/69
χ2
3+1 = 50.1/67
χ2
3+2 = 46.5/65
10-2
10-1
100
sin22θ
react
10-1
100
101
∆m2 41
[eV
2 ]
90%, 99% CL (2 dof)
curves: old fluxescolors: new fluxes
sin2 2θreact = 4|U2e4|(1 − |U2
e4|) ≈ 4|U2e4|
∆m241 [eV2] |Ue4| ∆m2
51 [eV2] |Ue5| ∆χ2(no osc)3+1 1.78 0.151 8.5 (98% CL 2 dof)3+2 0.46 0.108 0.89 0.124 12.1 (98% CL 4 dof)
bounds on Ue4,5 become “preferred regions” with new reactor fluxesMention et al., 11; Kopp, Maltoni, TS, 11
T. Schwetz 14
Hints for sterile neutrinos The reactor anomaly
3+1 and 3+2 fit to SBL reactor data
0.1 1 10
∆m2
41 [eV
2]
50
55
60
65
χ2
0.1 1 1050
55
60
65
dashed:old fluxsolid:new fluxSBL reactor data (84 data points)
(3+1)
(3+2)
preference for sterile neutrino oscillations with new fluxes
I ∆χ2(3 + 1/no-osc) = 8.5 → 98.6% CL (2 dof)I ∆χ2(3 + 2/no-osc) = 12.1 → 98.3% CL (4 dof)I old flux: ∆χ2 = 3.6(4.4) for 3+1 (3+2)I further improvement of fit for 3+2 wrt 3+1 with new fluxes
Kopp, Maltoni, TS, 11
T. Schwetz 15
Hints for sterile neutrinos Gallium anomaly
The Gallium anomaly
callibration data in galliumsolar neutrino experimentsνe +71 Ga →71 Ge + e−
ratio of measured topredicted rate:
RBahcall = 0.86± 0.05 (2.8σ)
RHaxton = 0.76± 0.09 (2.7σ)
Acero, Giunti, Laveder, 0711.4222; Giunti, Laveder, 1006.3244
T. Schwetz 16
Hints for sterile neutrinos Gallium anomaly
The Gallium anomaly
comparing Gallium and reactor anomalies:
T. Schwetz 17
Hints for sterile neutrinos Gallium anomaly
Constraint from LSND and KARMENLSND and KARMEN measure the cross section for νe +12 C →12 N + e−
consistent with expectations → limit on νe disappearance
Conrad, Shaevitz, 1106.5552
T. Schwetz 18
Hints for sterile neutrinos Gallium anomaly
Constraint from LSND and KARMEN
T. Schwetz 19
Hints for sterile neutrinos SBL appearance data
νµ → νe data at the E/L ∼ 1 eV2 scale
I LSND νµ → νe , 87.9± 22.4± 6.0 excess eventsP = (0.264± 0.067± 0.045)% ∼ 3.8σ away from zero
I MiniBooNE νµ → νeE > 475: no excess, E < 475: ∼ 3σ excess
I MiniBooNE νµ → νe , inconclusiveconsistent with MBν as well as with LSND in 2ν framework
I KARMEN νµ → νe , tight constraint on LSND region(slightly smaller L/E than LSND)
T. Schwetz 20
Hints for sterile neutrinos SBL appearance data
Latest MiniBooNE results Z. Djurcic @ NuFact11
T. Schwetz 21
Active-sterile mixing
Outline
Introduction
Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data
Active-sterile mixing
Can we explain all the hints together?
More exotic proposals
Cosmology
How to proceed?
Conclusions
T. Schwetz 22
Active-sterile mixing
What do we know about active-sterile mixing?
U =
Ue1 Ue2 Ue3 Ue4Uµ1 Uµ2 Uµ3 Uµ4Uτ1 Uτ2 Uτ3 Uτ4Us1 Us2 Us3 Us4
independent information on Uα4 mainly from disappearance exps
T. Schwetz 23
Active-sterile mixing
Ue4
from reactor and Gallium anomalies: Ue4 ≈ 0.15
T. Schwetz 24
Active-sterile mixing
Uµ4
H
10-3 10-2 10-1
|Uµ4|2
10-2
10-1
100
101
∆m2 41
[eV
2 ]
atmospheric
CDHS
Kopp, Maltoni, TS, in prepMiniBooNE, 1106.5685
sin2 2θ = 4|U2µ4|(1 − |U2
µ4|)
I νµ disappearance CDHS (and also MiniBooNE)I atmospheric neutrinos Bilenky, Giunti, Grimus, TS 99; Maltoni, TS, Valle 01
I MINOS CC/NC data 1001.0336, 1104.3922
I additional constraints from MiniB νµ(νµ) at ∆m2 & 1 eV2
T. Schwetz 25
Active-sterile mixing
Uτ4
|U2µ4| = sin2 θ24 < 0.03 |U2
τ4| = cos2 θ24 sin2 θ34 < 0.16
T. Schwetz 26
Active-sterile mixing
What do we know about active-sterile mixing?
U =
Ue1 Ue2 Ue3 ≈ 0.15Uµ1 Uµ2 Uµ3 < 0.17Uτ1 Uτ2 Uτ3 < 0.4Us1 Us2 Us3 Us4
|U2
e4| ≈ 0.025|U2
µ4| < 0.03|U2
τ4| < 0.16
for 3+n:
limit on |U2α4| → limit on
3+n∑i=4
|U2αi |
T. Schwetz 27
Active-sterile mixing
What do we know about active-sterile mixing?
U =
Ue1 Ue2 Ue3 ≈ 0.15Uµ1 Uµ2 Uµ3 < 0.17Uτ1 Uτ2 Uτ3 < 0.4Us1 Us2 Us3 Us4
|U2
e4| ≈ 0.025|U2
µ4| < 0.03|U2
τ4| < 0.16
for 3+n:
limit on |U2α4| → limit on
3+n∑i=4
|U2αi |
T. Schwetz 27
Can we explain all the hints together?
Outline
Introduction
Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data
Active-sterile mixing
Can we explain all the hints together?
More exotic proposals
Cosmology
How to proceed?
Conclusions
T. Schwetz 28
Can we explain all the hints together?
Short-baseline (SBL) experiments
I νµ → νe , νµ → νe appearance searchesLSND, MiniBooNE, KARMEN, NOMAD
I νe disappearance experiments (reactors)Bugey-3 (15, 40, 95), Bugey-4, Goessgen, Krasnoyarsk, Rovno, ILL,Chooz, Palo Verde
I νµ disappearanceCDHS, MiniBooNE, atmospheric neutrinos, MINOS CC/NC
SBL: E/L ∼ eV2 → set ∆m221 ≈ ∆m2
31 ≈ 0exceptions: Chooz, Palo Verde, atmospheric, MINOS
T. Schwetz 29
Can we explain all the hints together?
3+1 SBL oscillations
appearance
Pµe = sin2 2θapp sin2 ∆m241L
4Esin2 2θapp = 4|Ue4|2|Uµ4|2
disappearance
Pαα = 1− sin2 2θdis sin2 ∆m241L
4Esin2 2θdis = 4|Uα4|2(1− |Uα4|2)
I effective 2-flavour oscillationsI no CP violation → can’t reconcile ν (LSND, MB) and ν (MB) dataI constraints from νe (νµ) disappearance experiments on Ue4 (Uµ4)
appearance mixing angle quadratically suppressed
T. Schwetz 30
Can we explain all the hints together?
3+2 SBL oscillationsappearance:
Pνµ→νe = 4 |Ue4|2|Uµ4|2 sin2 φ41 + 4 |Ue5|2|Uµ5|2 sin2 φ51
+ 8 |Ue4Uµ4Ue5Uµ5| sin φ41 sin φ51 cos(φ54 − δ)
disappearance:
Pνα→να ≈ 1− 4∑i=4,5
|Uαi |2 sin2 φi1 − 4 |Uα4|2|Uα5|2 sin2 φ54
[φij ≡ ∆m2
ijL/4E]
I phase δ ≡ arg(
U∗e4Uµ4Ue5U∗
µ5
)→ CP violation Karagiorgi et al. 06; Maltoni, TS 07
I BUT: constrain |Uei | and |Uµi | (i = 4, 5) from disappearanceto be reconciled with appearance amplitudes |UeiUµi |
T. Schwetz 31
Can we explain all the hints together?
3+1 global fit
10-4
10-3
10-2
10-1
sin22θ
SBL
10-1
100
101
∆m2 41
[eV
2 ]
99% CL (2 dof)
LSND + MBν−
MBνKARMENNOMAD
disappearance90, 99% CL
Kopp, Maltoni, TS, 11
Giunti, Laveder, 1109.4033
I no CP violation → LSND versus MBν
I despite relaxed constraints on Ue4 no improvement of global 3+1 fitI LSND+MBν versus rest → compatibility of less than 10−5
T. Schwetz 32
Can we explain all the hints together?
3+1 global fit
10-4
10-3
10-2
10-1
sin22θ
SBL
10-1
100
101
∆m2 41
[eV
2 ]
99% CL (2 dof)
LSND + MBν−
MBνKARMENNOMAD
disappearance90, 99% CL
Kopp, Maltoni, TS, 11 Giunti, Laveder, 1109.4033
I no CP violation → LSND versus MBν
I despite relaxed constraints on Ue4 no improvement of global 3+1 fitI LSND+MBν versus rest → compatibility of less than 10−5
T. Schwetz 32
Can we explain all the hints together?
3+2 global fit
Kopp, Machado, Maltoni, TS, work in prep. Giunti, Laveder, 1109.4033
T. Schwetz 33
Can we explain all the hints together?
3+2 global fit
3 4 5 6 7 8Epos [MeV]
0.8
0.9
1
1.1
obse
rved
/ pr
edic
ted
rate
3 4 5 6 7 8Epos [MeV]
0.9
1
Bugey3 15 m Bugey3 40 m
Bugey4
3+2 react3+2 global
0.3 0.6 0.9 1.2 1.5 3
EνCCQE [GeV]
0
0.2
0.4
0.6
0.8
1
exce
ss e
vent
s
MiniBooNE(neutrinos)
LSND
0.3 0.6 0.9 1.2 1.5 3
EνCCQE [GeV]
0
0.1
0.2
0.3
MiniBooNE(anti-neutrinos)
0.1
0.2
0.3
0.4
PL
SND
[%
]
I 3+2 fit to appearance data only (LSND, MBν, MBν, KARMEN,NOMAD) allows for explanation of MB low energy excess Maltoni, TS, 07
I BUT: this requires large Ue4, Ue5, Uµ4, Uµ5 in sever disagreement withdisappearance bounds
I MB low-E excess cannot be explained using global data
T. Schwetz 34
Can we explain all the hints together?
Have we already discovered CP violation?
90
100
110
90
100
110
0 0.5 1 1.5 2δ [π]
10
20
30
χ2
0 0.5 1 1.5 2
MB475
MB300
MB300
MB475
global data
appearance data
Maltoni, TS 07 Giunti, Laveder, 1109.4033
T. Schwetz 35
Can we explain all the hints together?
There is severe tension in the 3+2 fit
Giunti, Laveder, 1109.4033
T. Schwetz 36
Can we explain all the hints together?
There is severe tension in the 3+2 fit
LSND+MB(ν) vs rest appearance vs disapp.old new old new
χ2PG/dof 25.1/5 19.9/5 19.9/4 14.7/4PG 10−4 0.13% 5× 10−4 0.53%adding MINOS CC/NC Kopp, Machado, Maltoni, TS, work in prep.
χ2PG/dof 30.0/5 24.8/5 24.7/4 19.5/4PG 10−5 10−4 5× 10−5 6× 10−4
I explanation of appearance signal requires Uei and Uµi (i = 4, 5)I no hint for oscillations seen in νµ disappearance⇒ constraints on Uµi in tension with signals
I MINOS data make compatibility worse by one order of magnitude
T. Schwetz 37
Can we explain all the hints together?
Summary so-far
I If we assume that the 3+n oscillation scenario is correct there issevere tension in the global fit and not all data can be explained.
I If we neglect LSND, the hint for νe disappearance from the reactorand Gallium anomalies remain, not in direct conflict with other data(relies on complicated theoretical calculations, uncertainties difficultto estimate)
I If we stick to LSND, probably we have to discard more than one otherexperiment (several experiments constrain νµ disappearance)
T. Schwetz 38
Can we explain all the hints together?
Summary so-far
I If we assume that the 3+n oscillation scenario is correct there issevere tension in the global fit and not all data can be explained.
I If we neglect LSND, the hint for νe disappearance from the reactorand Gallium anomalies remain, not in direct conflict with other data(relies on complicated theoretical calculations, uncertainties difficultto estimate)
I If we stick to LSND, probably we have to discard more than one otherexperiment (several experiments constrain νµ disappearance)
T. Schwetz 38
Can we explain all the hints together?
Summary so-far
I If we assume that the 3+n oscillation scenario is correct there issevere tension in the global fit and not all data can be explained.
I If we neglect LSND, the hint for νe disappearance from the reactorand Gallium anomalies remain, not in direct conflict with other data(relies on complicated theoretical calculations, uncertainties difficultto estimate)
I If we stick to LSND, probably we have to discard more than one otherexperiment (several experiments constrain νµ disappearance)
T. Schwetz 38
More exotic proposals
Outline
Introduction
Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data
Active-sterile mixing
Can we explain all the hints together?
More exotic proposals
Cosmology
How to proceed?
Conclusions
T. Schwetz 39
More exotic proposals
More exotic proposals
I 3-neutrinos and CPT violation Murayama, Yanagida 01;Barenboim, Borissov, Lykken 02; Gonzalez-Garcia, Maltoni, TS 03
I 4-neutrinos and CPT violation Barger, Marfatia, Whisnant 03
I Exotic muon-decay Babu, Pakvasa 02
I CPT viol. quantum decoherence Barenboim, Mavromatos 04
I Lorentz violation Kostelecky et al., 04, 06; Gouvea, Grossman 06
I mass varying ν Kaplan,Nelson,Weiner 04; Zurek 04; Barger,Marfatia,Whisnant 05
I shortcuts of sterile νs in extra dim Paes, Pakvasa, Weiler 05
I decaying sterile neutrino Palomares-Riuz, Pascoli, TS 05; Gninenko 10
I 2 decaying sterile neutrinos with CPVI energy dependent quantum decoherence Farzan, TS, Smirnov 07
I sterile neutrinos and new gauge boson Nelson, Walsh 07
I sterile ν with energy dep. mass or mixing TS 07
I sterile ν with nonstandard interactions Akhmedov, TS 10
most of these proposals
T. Schwetz 40
More exotic proposals
More exotic proposals
I 3-neutrinos and CPT violation Murayama, Yanagida 01;Barenboim, Borissov, Lykken 02; Gonzalez-Garcia, Maltoni, TS 03
I 4-neutrinos and CPT violation Barger, Marfatia, Whisnant 03
I Exotic muon-decay Babu, Pakvasa 02
I CPT viol. quantum decoherence Barenboim, Mavromatos 04
I Lorentz violation Kostelecky et al., 04, 06; Gouvea, Grossman 06
I mass varying ν Kaplan,Nelson,Weiner 04; Zurek 04; Barger,Marfatia,Whisnant 05
I shortcuts of sterile νs in extra dim Paes, Pakvasa, Weiler 05
I decaying sterile neutrino Palomares-Riuz, Pascoli, TS 05; Gninenko 10
I 2 decaying sterile neutrinos with CPVI energy dependent quantum decoherence Farzan, TS, Smirnov 07
I sterile neutrinos and new gauge boson Nelson, Walsh 07
I sterile ν with energy dep. mass or mixing TS 07
I sterile ν with nonstandard interactions Akhmedov, TS 10
most of these proposals involve sterile neutrinos
T. Schwetz 40
More exotic proposals
More exotic proposals
I 3-neutrinos and CPT violation Murayama, Yanagida 01;Barenboim, Borissov, Lykken 02; Gonzalez-Garcia, Maltoni, TS 03
I 4-neutrinos and CPT violation Barger, Marfatia, Whisnant 03
I Exotic muon-decay Babu, Pakvasa 02
I CPT viol. quantum decoherence Barenboim, Mavromatos 04
I Lorentz violation Kostelecky et al., 04, 06; Gouvea, Grossman 06
I mass varying ν Kaplan,Nelson,Weiner 04; Zurek 04; Barger,Marfatia,Whisnant 05
I shortcuts of sterile νs in extra dim Paes, Pakvasa, Weiler 05
I decaying sterile neutrino Palomares-Riuz, Pascoli, TS 05; Gninenko 10
I 2 decaying sterile neutrinos with CPVI energy dependent quantum decoherence Farzan, TS, Smirnov 07
I sterile neutrinos and new gauge boson Nelson, Walsh 07
I sterile ν with energy dep. mass or mixing TS 07
I sterile ν with nonstandard interactions Akhmedov, TS 10
most of these proposals have problems with some data
T. Schwetz 40
More exotic proposals Sterile neutrino + NSI
3+1 + NSI Akhmedov, TS 10
assume
I a 4th neutrino with ∆m241 ∼ 1 eV2
I a new type of CC-like interaction
LNSI = −2√
2GF∑α,β
εff ′αβ(f PL,Rγµf ′)(lαPLγµνβ) + h.c.
f , f ′ fermions depending on production or detection process
(NC-like NSI will have no relevant effect in short-baseline experimentssince matter effect is very small)
T. Schwetz 41
More exotic proposals Sterile neutrino + NSI
3+1 + NSI
I zero-distance effects and CPV (NSI-oscillation interference)I can decouple LSND/KARMEN from the rest:
source detectionLSND/KARMEN µ decay ν-nucl CC (e)MiniB/NOMAD π decay ν-nucl CC (e)
CDHS (atm) π decay ν-nucl CC (µ)Bugey/Chooz ν-nucl CC (e) ν-nucl CC (e)
|αLKµe |, |βLK
µe |, δLK, αe , αµ, |βµe |, δ, ∆m241
→ 8 parameters (7 for 3+2 osc)
T. Schwetz 42
More exotic proposals Sterile neutrino + NSI
3+1 + NSI
I χ2(3+1)osc − χ2
(3+1)NSI = 18.5(5 dof) → 99.76% CLappearance versus disappearance: PG compatibility of 15%
I |Ue4| ≈ 0.116, |Uµ4| ≈ 0.205 (more freedom from new react flux)|εud
µs | ≈ 0.05, |εudeµ| ≈ 0.011, |εeν
µs | ≈ 0.03, |εeνµe | ≈ 0.01
strength of new interactions at the level of few % compared to GFin agreement with bounds Biggio, Blennow, Fernandez-Martinez, 0907.0097
I if due to dim-6 operator εGF (f f ′)(¯ν) expect a charged mediatorwith mφ ∼ mW /
√ε ∼ TeV → excellent prospect at LHC
I BUT: seems difficult (impossible?) to obtain such operators at dim-6in gauge invariant way → go to dim-8 and involve some fine tuningGavela, Hernandez, Ota, Winter, 0809.3451; Antusch, Baumann, Fernandez, 0807.1003
severe constraints from colliders Davidson, Sanz, 1108.5320
T. Schwetz 43
More exotic proposals Sterile neutrino + NSI
3+1 + NSI
I χ2(3+1)osc − χ2
(3+1)NSI = 18.5(5 dof) → 99.76% CLappearance versus disappearance: PG compatibility of 15%
I |Ue4| ≈ 0.116, |Uµ4| ≈ 0.205 (more freedom from new react flux)|εud
µs | ≈ 0.05, |εudeµ| ≈ 0.011, |εeν
µs | ≈ 0.03, |εeνµe | ≈ 0.01
strength of new interactions at the level of few % compared to GFin agreement with bounds Biggio, Blennow, Fernandez-Martinez, 0907.0097
I if due to dim-6 operator εGF (f f ′)(¯ν) expect a charged mediatorwith mφ ∼ mW /
√ε ∼ TeV → excellent prospect at LHC
I BUT: seems difficult (impossible?) to obtain such operators at dim-6in gauge invariant way → go to dim-8 and involve some fine tuningGavela, Hernandez, Ota, Winter, 0809.3451; Antusch, Baumann, Fernandez, 0807.1003
severe constraints from colliders Davidson, Sanz, 1108.5320
T. Schwetz 43
More exotic proposals Sterile neutrino + NSI
3+1 + NSI
I χ2(3+1)osc − χ2
(3+1)NSI = 18.5(5 dof) → 99.76% CLappearance versus disappearance: PG compatibility of 15%
I |Ue4| ≈ 0.116, |Uµ4| ≈ 0.205 (more freedom from new react flux)|εud
µs | ≈ 0.05, |εudeµ| ≈ 0.011, |εeν
µs | ≈ 0.03, |εeνµe | ≈ 0.01
strength of new interactions at the level of few % compared to GFin agreement with bounds Biggio, Blennow, Fernandez-Martinez, 0907.0097
I if due to dim-6 operator εGF (f f ′)(¯ν) expect a charged mediatorwith mφ ∼ mW /
√ε ∼ TeV → excellent prospect at LHC
I BUT: seems difficult (impossible?) to obtain such operators at dim-6in gauge invariant way → go to dim-8 and involve some fine tuningGavela, Hernandez, Ota, Winter, 0809.3451; Antusch, Baumann, Fernandez, 0807.1003
severe constraints from colliders Davidson, Sanz, 1108.5320
T. Schwetz 43
More exotic proposals Sterile neutrino + NSI
3+1 + NSI
I χ2(3+1)osc − χ2
(3+1)NSI = 18.5(5 dof) → 99.76% CLappearance versus disappearance: PG compatibility of 15%
I |Ue4| ≈ 0.116, |Uµ4| ≈ 0.205 (more freedom from new react flux)|εud
µs | ≈ 0.05, |εudeµ| ≈ 0.011, |εeν
µs | ≈ 0.03, |εeνµe | ≈ 0.01
strength of new interactions at the level of few % compared to GFin agreement with bounds Biggio, Blennow, Fernandez-Martinez, 0907.0097
I if due to dim-6 operator εGF (f f ′)(¯ν) expect a charged mediatorwith mφ ∼ mW /
√ε ∼ TeV → excellent prospect at LHC
I BUT: seems difficult (impossible?) to obtain such operators at dim-6in gauge invariant way → go to dim-8 and involve some fine tuningGavela, Hernandez, Ota, Winter, 0809.3451; Antusch, Baumann, Fernandez, 0807.1003
severe constraints from colliders Davidson, Sanz, 1108.5320
T. Schwetz 43
More exotic proposals Soft decoherence
Energy dependent quantum decoherence Farzan, TS, Smirnov 07
I no sterile neutrino needed
I postulate quantum-decoherence of the mass states ⇒damping of the interference terms in the oscillation probabilities.
I damping affects only oscillations with ∆m231 and rapidly decreases
with the neutrino energy
I reconcile LSND signal with MBν and other null-result exps.
I standard explanations of solar, atmos, KamL, MINOS not affected
I LSND signal controlled by the 1-3 mixing: 0.0014 < sin2 θ13 < 0.034
I consistent with reactor anomaly
I positive signal for θ13 in long-baseline accelerator experimentsBUT: near/far comparisonat reactors: null-result →Excluded by Daya Bay/RENO!
T. Schwetz 44
More exotic proposals Soft decoherence
Energy dependent quantum decoherence Farzan, TS, Smirnov 07
I no sterile neutrino needed
I postulate quantum-decoherence of the mass states ⇒damping of the interference terms in the oscillation probabilities.
I damping affects only oscillations with ∆m231 and rapidly decreases
with the neutrino energy
I reconcile LSND signal with MBν and other null-result exps.
I standard explanations of solar, atmos, KamL, MINOS not affected
I LSND signal controlled by the 1-3 mixing: 0.0014 < sin2 θ13 < 0.034
I consistent with reactor anomaly
I positive signal for θ13 in long-baseline accelerator experimentsBUT: near/far comparisonat reactors: null-result →Excluded by Daya Bay/RENO!
T. Schwetz 44
Cosmology
Outline
Introduction
Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data
Active-sterile mixing
Can we explain all the hints together?
More exotic proposals
Cosmology
How to proceed?
Conclusions
T. Schwetz 45
Cosmology
eV sterile neutrinos and cosmologyHamann et al., 1006.5276
68, 95, 99% CL
I CMB, SDSS, HST: prefer some extra radiation, but limit on HDMexcludes two eV-scale neutrinos
I BBN: Ns < 1.2 (95% CL) Mangano, Serpico, 1103.1261
I PLANCK: obtain δNs ≈ 0.1 very soon
How bad is the fit if eV-scale neutrinos are imposed?
T. Schwetz 46
Cosmology
eV sterile neutrinos and cosmologyHamann et al., 1006.5276
68, 95, 99% CL
I CMB, SDSS, HST: prefer some extra radiation, but limit on HDMexcludes two eV-scale neutrinos
I BBN: Ns < 1.2 (95% CL) Mangano, Serpico, 1103.1261
I PLANCK: obtain δNs ≈ 0.1 very soon
How bad is the fit if eV-scale neutrinos are imposed?T. Schwetz 46
Cosmology
eV sterile neutrinos and cosmology
bounds assume full equilibration of sterile neutrinos
Hannestad, Tamborra, Tram, 1204.5861
... typically fulfilled for LSND-like mass/mixingEnqvist, Kainulainen, Thomson, NPB92; Shi, Schramm, Fields, astro-ph/9307027; Okada, Yasuda, hep-ph/9606411;
Bilenky, Giunti, Grimus, TS, hep-ph/9804421; DiBari, hep-ph/0108182
T. Schwetz 47
Cosmology
How to accommodate eV sterile neutrinos with cosmology?
invent a mechanism to avoid thermalization
I large chemical potential: Lµ = 10−2
Hannestad, Tamborra, Tram, 1204.5861
Foot, Volkas, hep-ph/9508275; Chu, Cirelli, astro-ph/0608206; Smith, Fuller, Kishimoto, Abazajian, astro-ph/0608377
I assume very low re-heating temperature (dangerously close to BBN)Gelmini, Palomares-Ruiz, Pascoli, astro-ph/0403323
T. Schwetz 48
Cosmology
How to accommodate eV sterile neutrinos with cosmology?
invent a mechanism to avoid thermalization
I large chemical potential: Lµ = 10−2
Hannestad, Tamborra, Tram, 1204.5861
Foot, Volkas, hep-ph/9508275; Chu, Cirelli, astro-ph/0608206; Smith, Fuller, Kishimoto, Abazajian, astro-ph/0608377
I assume very low re-heating temperature (dangerously close to BBN)Gelmini, Palomares-Ruiz, Pascoli, astro-ph/0403323
T. Schwetz 48
Cosmology
How to accommodate eV sterile neutrinos with cosmology?
Hamann, Hannestad, Raffelt, Wong, 1108.4136
I limit on neutrino mass (HDM) can be evaded by allowing extraradiation ∆Nml ' 1− 2 and/or DE equation of statew < −1 Elgaroy, Kristiansen, 1104.0704
I BBN constraints on extra radiation can be avoided by introducing achemical potential of νe .
I modifies other cosmological parameters, e.g. ΩCDM (+20%-75%)
⇒ all those options require substantial modification of standard cosmology
T. Schwetz 49
Cosmology
How to accommodate eV sterile neutrinos with cosmology?
Hamann, Hannestad, Raffelt, Wong, 1108.4136
I limit on neutrino mass (HDM) can be evaded by allowing extraradiation ∆Nml ' 1− 2 and/or DE equation of statew < −1 Elgaroy, Kristiansen, 1104.0704
I BBN constraints on extra radiation can be avoided by introducing achemical potential of νe .
I modifies other cosmological parameters, e.g. ΩCDM (+20%-75%)
⇒ all those options require substantial modification of standard cosmology
T. Schwetz 49
How to proceed?
Outline
Introduction
Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data
Active-sterile mixing
Can we explain all the hints together?
More exotic proposals
Cosmology
How to proceed?
Conclusions
T. Schwetz 50
How to proceed?
Many ideas to test eV sterile neutrinos
I radioactive source experiments to test reactor and Gallium anomalies(e.g., in Borexino, SNO+, KamLAND) Cribier et al, 1107.2335; Garvin et al, 1006.2103;
Vergados, Novikov, 1006.3862; Grieb, Link, Raghavan, hep-ph/0611178,...
I several ideas at FNAL (MINOS+, MicroBooNE, MiniBooNEextensions, very-low-E NuFact) B. Louis @ NuFact11
I ICARUS at CERN PS C. Rubbia et al. 0909.0355
I experiments with ∼100 kW proton synchrotronsConrad, Shaevitz 09; Huber, Agarwalla 10; Agarwalla, Conrad, Shaevitz, 11
I signatures in IceCube (Deep Core)Nunokawa, Peres, Zukanovich, hep-ph/0302039; Coubey, 0709.1937; Razzaque, Smirnov, 1104.1390; 1203.5406
T. Schwetz 51
How to proceed?
Many ideas to test eV sterile neutrinos
2011 sterile neutrino workshops:
I LNGS, Italy, May 2011
I FNAL, USA, May 2011
I Virginia Tech, Blacksburg, USA, Sept 2011
White paper on sterile neutrinos published on arxiv: 1204.5379
T. Schwetz 52
Conclusions
Outline
Introduction
Hints for sterile neutrinosThe reactor anomalyGallium anomalySBL appearance data
Active-sterile mixing
Can we explain all the hints together?
More exotic proposals
Cosmology
How to proceed?
Conclusions
T. Schwetz 53
Conclusions
Conclusions
I There are a couple of "hints" for sterile neutrinos at the eV scale
I Unfortunately none of these "hints" is convincing by itself(at the level of ∼ 3σ)
I It is intriguing that they all point to a similar mass rangeBUT, significant tension remains in the global fit(non-observation of νµ disappearance)No consistent picture has emerged so far.
I Are these sterile neutrinos consistent with cosmology?(CMB, LSS, BBN)
I Let’s take the hints serious and try to solve this questionunambigously. Establishing the existence of sterile neutrinos would bea great discovery of physics beyond the SM.
Thank you for your attention!
T. Schwetz 54
Conclusions
Conclusions
I There are a couple of "hints" for sterile neutrinos at the eV scale
I Unfortunately none of these "hints" is convincing by itself(at the level of ∼ 3σ)
I It is intriguing that they all point to a similar mass rangeBUT, significant tension remains in the global fit(non-observation of νµ disappearance)No consistent picture has emerged so far.
I Are these sterile neutrinos consistent with cosmology?(CMB, LSS, BBN)
I Let’s take the hints serious and try to solve this questionunambigously. Establishing the existence of sterile neutrinos would bea great discovery of physics beyond the SM.
Thank you for your attention!
T. Schwetz 54
Conclusions
Conclusions
I There are a couple of "hints" for sterile neutrinos at the eV scale
I Unfortunately none of these "hints" is convincing by itself(at the level of ∼ 3σ)
I It is intriguing that they all point to a similar mass rangeBUT, significant tension remains in the global fit(non-observation of νµ disappearance)No consistent picture has emerged so far.
I Are these sterile neutrinos consistent with cosmology?(CMB, LSS, BBN)
I Let’s take the hints serious and try to solve this questionunambigously. Establishing the existence of sterile neutrinos would bea great discovery of physics beyond the SM.
Thank you for your attention!
T. Schwetz 54
Conclusions
Conclusions
I There are a couple of "hints" for sterile neutrinos at the eV scale
I Unfortunately none of these "hints" is convincing by itself(at the level of ∼ 3σ)
I It is intriguing that they all point to a similar mass rangeBUT, significant tension remains in the global fit(non-observation of νµ disappearance)No consistent picture has emerged so far.
I Are these sterile neutrinos consistent with cosmology?(CMB, LSS, BBN)
I Let’s take the hints serious and try to solve this questionunambigously. Establishing the existence of sterile neutrinos would bea great discovery of physics beyond the SM.
Thank you for your attention!
T. Schwetz 54
Conclusions
Conclusions
I There are a couple of "hints" for sterile neutrinos at the eV scale
I Unfortunately none of these "hints" is convincing by itself(at the level of ∼ 3σ)
I It is intriguing that they all point to a similar mass rangeBUT, significant tension remains in the global fit(non-observation of νµ disappearance)No consistent picture has emerged so far.
I Are these sterile neutrinos consistent with cosmology?(CMB, LSS, BBN)
I Let’s take the hints serious and try to solve this questionunambigously. Establishing the existence of sterile neutrinos would bea great discovery of physics beyond the SM.
Thank you for your attention!T. Schwetz 54