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Sterile neutrinos:. searches & implications. A. Yu. Smirnov. International Centre for Theoretical Physics, Trieste, Italy. Planck 2011, May29, Lisbon. Sterile neutrino. n s. Light. No weak interactions: - singlets of the SM symmetry group. RH - components of neutrinos.

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A yu smirnov

Sterile neutrinos:

searches & implications

A. Yu. Smirnov

International Centre for Theoretical Physics, Trieste, Italy

Planck 2011, May29, Lisbon


A yu smirnov

Sterile neutrino

ns

Light

No weak interactions:

- singlets of the SM

symmetry group

RH - components

of neutrinos

Couple with usual neutrinos

via (Dirak) mass terms

Mix with active neutrinos

may have Majorana

mass terms

maximal mixing?

Sov. Phys. JETP 26 984 (1968)

in the context of idea of

neutrino–antineutrino oscillations


A yu smirnov

LSND is back?

Large Scintillator

Neutrino Detector

p ->

p+ -> m+ + nm

-> e+ + ne + nm

Los Alamos Meson Physics Facility

ne + p  e+ + n

decay at rest

nm

nm ->ne

ne

L = 30 m

P = (2.64 +/- 0.67 +/- 0.45) 10-3

Oscillations?

n

Dm2 > 0.2 eV2

e+

3.8s excess

t

200 t mineral

oil scintillator

Cherenkov cone + scintillations


A yu smirnov

Sterile neutrinos as

solution of all the problems

Plan:

1. New evidences?

2. The Sun: sterile shining

3. Searching for sterile in ice


A yu smirnov

New evidences?


A yu smirnov

MiniBooNE: anti-nu

L = 541 m, <En> ~ 800 MeV

12 m diameter tank

450 t (mineral oil) 1280 PMT


A yu smirnov

Reactor neutrino anomaly

Revised value of

cross-section

G.Mention et al,

arXiv: 1101.2755

Increase of the

Mean flux by 3%

Rreact = 0.937 +/- 0.027

2.14 s

Dm2 > 1.5 eV2

sin2 2q = 0.17 +/- 0.1


A yu smirnov

Gallium anomaly

Calibration

Source + reactor

Gallex/GNO 51Cr

SAGE 51 Cr, 37Ar

RGa = 0.87 +/- 0.05

G.Mention et al,

arXiv: 1101.2755

sin22q = 0.24

C Giunti, M. Laveder

Dm2 = 2.15 eV2


A yu smirnov

Controversial and

not convincing

Consistency

With reactor anomaly global fit of data in terms of nu-sterile becomes better

Limit on Ue4 becomes weaker

|Ue4|2 : 0.02  0.04

Smaller values of Um4 are allowed to explain LSND/MiniBooNE –

less tension with SBL experiment bounds

|Um4|2 : 0.04  0.02

3 + 2

scheme

Global fit

n5

n4

Dm512 = 0.87 eV2

Dm412 = 0.47 eV2

Ue4 = 0.128

Ue5 = 0.138

J Kopp, M. Maltoni,T.Schwetz

1103.4570 [hep-ph]

Um5 = 0.148

Um4 = 0.165


A yu smirnov

Extra radiation in the Universe

Effective number of neutrino species

- WMAP-7

- Barion Acoustic Oscillations

- Hubble constant

E. Komatsu et al

arXiv: 1001.4538

[astro-ph.CO]

+ 0.86

- 0.88

Neff = 4.34 (68 % CL)

- WMAP–7

- Atacama Cosmology Telescope

Neff = 5.3 +/- 1.3 (68% CL)

J. Dunkley et al

arXiv:1009.0866

[astro-ph.CO]

D Neff = (0.02 – 2.2) (68% CL)

J. Hamann et al

PRL 105 (2010)181301

BBN

Y. I. Izotov and T X Thuan

Astrophys J 710 (2010) L67

+ 0.80

- 0.70

Neff = 3.68 (68 % CL)


A yu smirnov

Cosmological bounds

E Giusarma et al 1102.4774 [astro-ph]

J R Kristiansen, O Elgaroy

1104.0704 [astro-ph]

LCDM

Inverse approach:

Dm2 < 0.25 eV2

wCDM + 2nS

1). w < -1

ruling out L

2). Age of the Universe

12.58 +/- 0.26 Gyr

68 %

95%

too young?

  • WMAP

  • SDSS (red galaxy clustering)

  • Hubble (prior on H0 )

The oldest globular clusters

13.4 +/- 0.8 +/- 0.6 Gyr

run 1 (blue)

+ BBN

  • Supernova Ia Union

  • Compilation 2 (in add)

run 2 (red)


A yu smirnov

Mass scales

- LSND, MiniBooNE

40 - 70 MeV

1 MeV

ns

  • Warm Dark matter

  • Pulsar kick

~ 10 keV

1 keV

  • - LSND, MiniBooNE

  • Reactor anomaly

  • Calibration experiments

  • - Extra radiation

0.5 - 2 eV

1 eV

(2 – 4) 10-3 eV

- Solar neutrinos

- Extra radiation

in the Universe

10-3 eV


A yu smirnov

Mixing

ne

nm

nt

mee mem met

… mmm mmt

… … mtt

meS

mmS

mtS

Mass

matrix

nS

… … …

mSS

For mSS ~ 1 eV

tanqjS = mjS/mSS

~ 0.2 - is not small

produces large corrections to the active neutrino mass matrix

dmij ~ - tanqiStanqjS mSS ~ 0.04 mSS

mSS >> mab , maS

In general can not be considered as small perturbation!

Effect can be small if

J. Barry,

W. Rodejohann,

He Zhang

arXiv: 1105.3911

Active neutrino spectrum

is quasi degenerate

meS mmS mtS have

certain symmetry

mSS ~ mab


A yu smirnov

Applications

mn = ma + dm

Original active mass

matrix e.g. from see-saw

Induced mass matrix

due to mixing with nu sterile

dm can change structure (symmetries) of the original

mass matrix completely (not a perturbation)

produce dominant mt - block

with small determinant

Enhance lepton mixing

Be origin of difference of

Generate TBM mixing

UPMNS

and

VCKM


A yu smirnov

The Sun:

shining in sterile

P. C. de Holanda, A. Yu. S. 1012.5627 [hep-ph]


A yu smirnov

Homestake

BOREXINO

SNO

SuperKamiokande


A yu smirnov

Problem?

QArexp <

QArLMA

2.55 +/- 0.25 SNU

> 3.1 SNU

No turn up of the spectrum in SK

P. de Holanda, A.S.

Phys. Rev. D69 (2004)

113002 hep-ph 0307266

Light sterile neutrino

RD = Dm012 /Dm212 << 1

  • << 1 - mixing angle of sterile- active neutrinos

 dip in survival probability

Motivation for the low energy solar neutrino

experiments BOREXINO, KamLAND …


A yu smirnov

Up-turn?

pp 7Be CNO 8B

SNO: LETA

gap

BOREXINO

ne- survival probability from solar

neutrino data vs LMA-MSW solution


A yu smirnov

(3 + 1) scheme

ne

ns

nt

nm

n3

Dm2atm

mass

n2

Dm2sun

n0

Dm2dip

n1


A yu smirnov

Level crossing

H

D m012 > (0.2 - 2) 10-5 eV2

ne

n2m

sin2 2a= 10-4 - 10-3

ns

non-adiabatic

level crossing

nm/t

n0m

sterile resonances

n1m

density


A yu smirnov

Mixing scheme and transitions

ns

ne

na

n0

n1

n2

U = Uq Ua

Uq - rotation in 12-plane on q12

ns mixes inn0and n1

Ua - rotation in 01- plane on a

Scheme of transitions

n2

n2m

ne

n1m

ne

n1

interference

 wiggles

n0m

n0

ns

P(nene) ~ |Ue1mA11 + Ue0mA01|2 |Ue1 |2 + |Ue2 m|2|Ue2|2


A yu smirnov

Survival probability

- dip

- wiggles


A yu smirnov

Spectra

sin22a = 10-3 (red), 5 10-3 (blue)

SK-I

SNO-LETA

P. De Holanda, A.S.

SK-III

Borexino

SNO-LETA

RD = 0.2

Dm2 = 1.5 10-5 eV2


A yu smirnov

BOREXINO: Be line

data

excluded

excluded

RD = 0.007 - 0.07

Be

Dm012 > 0.5 10-5 eV2

pep

Predictions for pep-neutrinos

RD = 0.07 - 0.115

P(pep) = 0.2 – 0.3

P(Be) = 0.55

pep-suppressed

RD > 0.12

P(pep) = 0.53


A yu smirnov

Fit of spectra

c2 fit of spectra with sterile neutrino dip:

SK-I, SK-III, SNO-LETA, SNO-NC, Borexino

Best fit values:

Dc2 = 7.5

sin2 2a ~ 10-3

Dm012 ~ 1.5 10-5 eV2

Interval with

sin22a ~ (0.5 – 1) 10-3

D m012 = (1 – 2) 10-5 eV2

Dc2 > 6

m0 > 0.003 eV

Alternative: mixing with level n2m

sin22a ~ (0.5 – 1) 10-3

RD = Dm012 /Dm212 = 1.1


A yu smirnov

Implications

m0 ~ 0.003 eV

M2

MPlanck

m0 =

M ~ 2 - 3 TeV

mixing

h vEW

M

sin2 2a ~ 10-3

h = 0.1

a ~

vEW

M

sin2 2b ~ 10-1

b ~


A yu smirnov

Level crossing scheme

P. De Holanda, A.S.

Mixing with the third active state

ns


A yu smirnov

Extra radiation in the Universe

Production of sterile in the Early universe

Mixing of ns in n3

M Cirelli G Marandella A Strumia F Vissani

n3 = cosb nt’ + sinb ns

nt’ = cosq23 nt + sinq23 nm

where

Dm302 ~ 2.5 10-3 eV2

Atmospheric neutrinos:

sin2b < 0.2 – 0.3 (90%)

MINOS:

sin2b < 0.23 (90%)

tan2b


A yu smirnov

Other consequences

Atmospheric neutrinos

ER ~ 12 GeV

nt’ – ns resonance

nmns resonance peak 10 – 15 GeV

IceCube Deep Core

Supernova neutrinos

Additional suppression of ne flux


A yu smirnov

Searching for sterile

in Ice

S Razzaque and A. S.

arXiv:1104.1390 [hep-ph]


A yu smirnov

Test

H Nunokawa O L G Peres

R Zukanovich-Funchal

Phys. Lett B562 (2003) 279

nm - ns oscillations with Dm2 ~ 1 eV2 are enhanced

in matter of the Earth in energy range 0.5 – few TeV

This distorts the energy spectrum and zenith angle distribution

of the atmospheric muon neutrinos, also modifies m/e ratio

S Choubey JHEP 0712 (2007) 014

Can be tested by IceCube

First data from IceCube

  • Check theoretical considerations,

  • generalize …

  • - perform analysis of the data


A yu smirnov

IceCube


A yu smirnov

IceCube results

R. Abbasi et al, arXiv:1010.3980

[astro-ph.CO]

Zenith angle distribution

Unfolded neutrino spectrum

April 2008 – May 2009

40 strings

100 GeV – 400 TeV

18 000 up-going muons


A yu smirnov

(3 + 1) scheme

ne

ns

nt

nm

LSND/MiniBooNE: vacuum

oscillations

n4

P ~ 4|Ue4 |2|Um4 |2

Dm2LSND

mass

Restricted by short baseline

experiments CHOOZ, CDHS,

NOMAD

n3

Dm2atm

n2

Dm2sun

n1

With new reactor data:

Dm412 = 1.78 eV2

Ue4 = 0.15

Um4 = 0.23


A yu smirnov

Level crossing scheme

Normal mass hierarchy in

the flavor block; m0 ~ 1 eV

Three new level crossings

|Ue4 |2 |Um4 |2

are large enough, so that

evel crossings are adiabatic

Ve - Vs = 2 GF (ne – nn /2)


A yu smirnov

nS

- mass mixing scheme

ns

nt

nm

n0

n3

n2

Uf = U23 Ua

ns mixes in the mass states n3andn0

~

n0 = - sina n3 + cosa ns

where

~

~

n3 = cosa n3+ sina ns

n3 = cosq23 nt + sinq23 nm

~

~

n2 = cosq23 nm - sinq23 nt

n2 = n2

~

ns mixes with n3

~

~

ns, n3, n2

Propagation basis:

Evolution is reduced to 2n-problem exactly


A yu smirnov

Evolution

Propagation basis

~

nf = U23 n

ns

ns

ns

ns

~

~

nt

nt

n3

n3

A33

~

~

nm

nm

n2

n2

A22

decouples

propagation

projection

projection

S

P(nmnm) = |cos2q23A22 + sin2q23A33 |2


A yu smirnov

Survival probability

Effect of phase shift

for the nm - ntoscillations

due to matter effects

neutrinos

antineutrinos

MSW resonance dip


A yu smirnov

Energy spectra


A yu smirnov

Suppression

factor

S = N(osc.)/N(no osc.)

Eth = 0.1 TeV


A yu smirnov

Zenith

angle

distribution

nS - mass mixing case

Free normalization

and tilt factor


A yu smirnov

Bounds on mixing

Illustrative fit

in the simplest

mixing scheme

+ 5% uncorrelated

systematic errors

LSND:

sin2a > 0.04

Statistical errors +

free normalization + tilt


A yu smirnov

ns-nm

- mixing

ns

nt

nm

n0

n3

n2

Uf = Ub U23

ns mixes with nm

n0 = - sinb nm + cosb ns

n3 = - cosb sinq23 nm + cos q23nt - sinb sinq23 ns

n2 = - sinb cosq23 nm + sin q23nt - cosb cosq23 ns

Propagation basis = flavor basis

Evolution is not reduced to the 2n - evolution exactly


A yu smirnov

Probabilities

antineutrinos

neutrinos


A yu smirnov

Zenith

angle

distribution

nS - nm mixing

Free normalization

and tilt factor

Fit with sterile is even better

Eth = 0.1 TeV


A yu smirnov

Suppression factors

Eth = 1 TeV

Eth = 0.1 TeV


A yu smirnov

Summary

New evidences/hints of existence of sterile: MiniBooNE, reactors,

Gallium calibration, solar, additional radiation in the Universe

Convincing? Consistent? Controversial?

Light sterile neutrino mixed

in n1 or/and n2 with

D m012 ~ 1.5 10-5 eV2

sin2 2a ~ 10-3

leads to the dip in the spectrum which explains

an absence of the up turn of the spectrum,

reduces prediction for the Ar production rate

Being mixed in n3 with sin2b ~ 0.2 sterile can be generated

in the Early Universe DNeff ~ 1, thus explaining additional radiation


A yu smirnov

IceCube has high sensitivity

to sterile mixing with

D m012 ~ 1 eV2

sin2a > 0.01

Depending on values of parameters, Um4, Ut4 , Dm422

large variety of zenith angle distribution can be obtained.

With present data only part of the parameter space

relevant for LSND/MiniBooNE can be excluded and

in some ranges the fit can be even improved.

Future high statistics studies of the zenith angle distributions

in different energy regions (with different energy thresholds)

can provide sensitive search of sterile in whole parameter space

and discriminate different mixing scenarios.


A yu smirnov

MINOS bound

E = 475 MeV

E = 200 MeV


A yu smirnov

Dependence on mixing scheme

In general,

the Hamiltonian

H = D0 V0 x V0T + D2 V2 x V2T

(i = 0, 2)

ViT = ( USi , Ut i , Um i ),

Di = Dmi32 / 2E

In the lowest

order at high

energies

H ~ D0 V0 x V0T

V0T = ( US0 , Ut 0 , Um 0 )

P(nmnm) ~ | sin2q’A33(a) + cos2q’|2

tanq ’ = - Um 0 / Ut 0

sin2a = |Um 0|2 + | Ut 0|2

Dm032 = 1 eV2

|Um 0|2 ~ 0.02 – 0.04

LSND/MiniBooNE

|Ut 0|2 < 0.5

MINOS, Atmospheric neutrinos


A yu smirnov

Fluxes


A yu smirnov

Gallium anomaly

Reactor, miniboone

Gallium calibration

Gallex/GNO 51Cr

SAGE 51 Cr, 37Ar

G.Mention et al,

arXiv: 1101.2755

Calibration

C Giunti, M. Laveder

RGa = 0.87 +/- 0.05


A yu smirnov

Wiggles

Evolution between two sterile resonances

Interference of two amplitudes

of transition

projection

transitions

adiabatic

n1m

Ue1m

n1

ne

n0m

non-adiabatic

Ueom


A yu smirnov

Suppression

factor

Eth = 1 TeV


A yu smirnov

Energy spectra

Narrowing the zenith angle

interval – enhances

Effect 40 %


A yu smirnov

Number of events

E Fm Aeff

Flux of muon neutrinos:

Fm = Fm0 Pmm + Fe0 Pem +

+ Fm0 Pmt(kE) Bm

~ Fm0 Pmm


A yu smirnov

Production of sterile in the

Early universe

D Neff = 0.8 - 1

can be generated

A D Dolgov, F L Villante

log( Dm2 /eV2 )

sin2 2b

sin2 2b


A yu smirnov

Probabilities

for different

mixing schemes

sin2b = 1

0.5 nS - mass mixing

sin2b =

1.0 nS -nm-mixing

sin2b

no strong suppression in vertical bin

With increase of |Ut 0|2

sin2b decreases

sin2b

sin2a increases,

resonance disappears

distortion of the E and qZ

distributions becomes weaker


A yu smirnov

Survival probability


A yu smirnov

Zenith angle distributions

For different

mixing schemes

Varying |Ut0|2

s242

s242 + s342

sin2b =


A yu smirnov

Probabilities


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