cp violation in the neutrino sector
DESCRIPTION
CP violation in the neutrino sector. Lecture 4: New sources of CP violation?. Walter Winter Nikhef, Amsterdam, 06.03.2014. Contents (overall). Lecture 1: Introduction to neutrino physics, sources of CP violation Lecture 2: Neutrino oscillations in vacuum, measurement of d CP - PowerPoint PPT PresentationTRANSCRIPT
CP violation in the neutrino sectorLecture 4: New sources of CP violation?
Walter Winter
Nikhef, Amsterdam, 06.03.2014
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 2
Contents (overall)
> Lecture 1:Introduction to neutrino physics, sources of CP violation
> Lecture 2:Neutrino oscillations in vacuum, measurement of dCP
> Lecture 3:Matter effects in neutrino oscillations: “extrinsic CP violation”
> Lecture 4:New sources of CP violation?
References:
> WW: “Lectures on neutrino phenomenology“, Nucl. Phys. Proc. Suppl. 203-204 (2010) 45-81
> Giunti, Kim: “Fundamentals of neutrino physics and astrophysics“, Oxford, 2007
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 3
Contents (lecture 4)
> Sterile neutrinos
>Non-standard interactions+ Is it plausible that new physics shows up in neutrino sector only
>Non-unitarity
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 4
Sterile neutrinos
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 5
Evidence for light sterile neutrinos?(addl. generations, not weakly interacting)
> LSND/MiniBooNE
>Reactor+gallium anomalies
Global fits
(Min
iBoo
NE
@ N
eutr
ino
2012
)
(B. F
lemin
g, TA
UP
2011)
(Kopp, Maltoni, Schwetz, 1103.4570)
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 6
Neutrino oscillations in vacuum
>Master formula:
“mass squared difference“ F(L,E)=L/E “spectral dependence“
> For antineutrinos: U U*
>Works for sterile neutrinos as well!
> At short distances: Only large mass squared terms non-vanishing
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 7
Example: 3+1 framework, parameterization-independent
Well known tension between appearance and disapp. data (appearance disappearance in both channels)
Need one or more new experiments which can test ne disappearance (Gallium, reactor anomalies) nm disappearance (overconstrains 3+N frameworks) ne-nm oscillations (LSND, MiniBooNE) Neutrinos and antineutrinos separately (CP violation? Gallium vs reactor?)
Example: nuSTORM - Neutrinos from STORed Muons (LOI: arXiv:1206.0294) Summary of options: Appendix of white paper arXiv:1204.5379
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 8
Again: Necessary conditions for the observation of CPV
> Since
need spectral info!
> Since for a=b
need to observe flavor transitions
>Need (at least) three flavors(actually conclusion in quark sector by Kobayashi, Maskawa, Nobel Prize 2008) No CP violation in two flavor subspaces! Need to be sensitive to (at least) two mass squared splittings at the same time!
>Require at least two (light) sterile neutrinos; then new sources of CPV (but: do not really release tension in data …)
~ Jarlskog invariant
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 9
Non-standard interactions
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 10
Non-standard interactions
> Typically described by effective four fermion interactions (here with leptons)
>May lead to effects in oscillations (for g=d=e)
>May also lead to source/detector effects
How plausible is a modelleading to such NSI(and showing up in
neutrino sector only)?
acc: SM matter effect (later)
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 11
Lepton flavor violation (d=6)
>Charged leptonflavor violation
> Strongbounds
e e
ne nm
NSI
e e
e mCLFV
ne nm
4n-NSIEx.:
ne ne
>Non-standard neutrino interact.
> Effects in neutrino oscillations in matter
>Non-standard int. with 4n
> Effects in environments with high neutrino densities (supernovae)
BUT: These phenomena are not independent (SU(2) gauge invariance!)Is it possible that new physics is present in the neutrino sector only?
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 12
Gauge-inv. d=8 operator?
>Decouple CLFV and NSI by SU(2) symmetry breaking with operator
>Works at effective operator level, but are there theories allowing that? [at tree level]
Davidson, Pena-Garay, Rius, Santamaria, 2003
Project outneutrino field
Project outneutrino field
H, L: SU(2) doublets
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 13
Systematic analysis for d=8
>Decompose all d=8 leptonic operators systematically
The bounds on individual operators from non-unitarity, EWPT, … are very strong! (Antusch, Baumann, Fernandez-Martinez, arXiv:0807.1003)
>Need at least two mediator fields plus a number of cancellation conditions(Gavela, Hernandez, Ota, Winter, Phys. Rev. D79 (2009) 013007)
Basis (Berezhiani, Rossi, 2001)
Combinedifferent
basis elements
C1LEH, C3
LEH
Canceld=8
CLFV
But these mediators cause d=6 effects Additional cancellation condition
(Buchmüller/Wyler – basis)
Avoid CLFVat d=8:
C1LEH=C3
LEH
Feynman diagrams
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 14
On current NSI bounds
> The bounds for the d=6 (e.g.scalar-mediated) operators are strong (CLFV, Lept. univ., etc.)(Antusch, Baumann, Fernandez-Martinez, arXiv:0807.1003)
> The model-independent bounds are much weaker(Biggio, Blennow, Fernandez-Martinez, arXiv:0907.0097)
>However: note that here the NSI have to come from d=8 (or loop d=6?) operators e ~ (v/L)4 ~ 10-4 natural?
> “NSI hierarchy problem“?
t sector least constrained
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 15
Source NSI with nt at a NuFact
> Probably most interesting for near detectors: eets, emt
s (no intrinsic beam BG)
>Near detectors measure zero-distance effect ~ |es|2
> Improving current bounds requires substantial equipment
(Tang, Winter, arXiv:0903.3039)
ND5: OPERA-like ND at d=1 km, 90% CL
This correlation is always present if:- NSI from d=6 operators- No CLFV (Gavela et al,arXiv:0809.3451;see also Schwetz, Ohlsson, Zhang, arXiv:0909.0455 for a particular model)
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 16
Other types of source NSI
> In particular models, also other source NSI (without nt detection) are interesting
> Example: (incoh.)eem
s from addl.Higgs triplet asseesaw (II) mediator
1 kt, 90% CL, perfect CID
(Malinsky, Ohlsson, Zhang, arXiv:0811.3346)
Requires CID!
Geometric effects? Effects of std.
oscillations
Systematics(CID) limitation?CID important!
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 17
CP violation in non-standard interactions
>Discovery potential for new CP violation
(WW, Phys.Lett. B671 (2009) 77)
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 18
For what fraction of the phases can CPV be discovered?
> If additional phases are present, the chances to discover CPV are good!
(WW, Phys.Lett. B671 (2009) 77)
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 19
Non-unitarity
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 20
Non-unitarity of mixing matrix
> Integrating out heavy fermion fields, one obtains neutrino mass and the d=6 operator (here: fermion singlets)
>Re-diagonalizing and re-normalizing the kinetic terms of the neutrinos, one has
> This can be described by an effective (non-unitary) mixing matrix e with N=(1+e) U
> Similar effect to NSI, but source, detector, and matter NSI are correlated in a particular, fundamental way (i.e., process-independent)
also: „MUV“
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 21
Impact of near detector
> Example: (Antusch, Blennow, Fernandez-Martinez, Lopez-Pavon, arXiv:0903.3986)
> nt near detector important to detect zero-distance effect
>Magnetization not mandatory, size matters
Curves: 10kt, 1 kt, 100 t, no ND
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 22
NSI versus NU
> For a neutrino factory, leptonic NSI and NU may have very similar correlations between source and matter effects, e.g.
NU (generic, any exp.)NSI (d=6, no CLFV, NF)
>Difficult to disentangle with NuFact alone SB?
(Meloni, Ohlsson, Winter, Zhang, JHEP 1004 (2010) 041)
NU NSI
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 23
Is it possible/plausible that “new physics” shows up in the neutrino sector only?
>Possible? Yes, but at least non-standard four-fermion interactions require quite some
fine-tuning
It is difficult to find models which would not produce effects elsewhere (LHC, EWPT, …)
>Plausible?
Additional sterile generations are perhaps the most plausible new physics effect:
Short-baseline anomalies (eV steriles)Caveat: would show up in cosmology … (problem or feature?)
Warm dark matter (keV steriles)
Non-unitarity (>> GeV steriles)
Leptogenesis (GUT-scale steriles)
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 24
Summary
> If no new physics will be found at the LHC, the lepton sector may still provide enough CP violation for successful leptogenesis
>Most plausible candidates: see-saw mechanisms in different versions; no necessary implications at the TeV scale; basically “neutrino Standard Model(s)“
> Physics beyond the neutrino Standard Model may also provide new sources of CP violation; however: this kind of physics may have implications elsewhere
>Most interesting candidate, perhaps: sterile neutrinos
Walter Winter | CPV Amsterdam | 06.02.2014 | Page 25
Discussion topics
>Do neutrinos really oscillate? After all, the mass eigenstates travel with different velocities …
>What happens over extremely long distances? Can one measure CP violation then?
>Why are neutrino masses “physics beyond the Standard Model“? Are they? Really?
>Why is there only one CP phase in the lepton mixing matrix, and three if neutrinos are Majorana particles? [after all, a general unitary matrix is parameterized including six phases]
>What do we actually learn from neutrinoless double beta decay?