of neutrino mass
Delve into the enigmatic world of neutrino mass, exploring its hidden nature, unique properties, and the challenging riddles it presents to physicists. Dive deep into the realms of particle physics where the smallest of masses hold profound secrets waiting to be unraveled.
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The A. Yu. Smirnov R i d Max-Planck Institute for Nuclear Physics, Heidelberg, Germany NOW 2014 September 8 13, 2014 d l e of neutrino mass
The riddle of neutrino mass: There is something hidden and beyond the standards which strongly suppresses badly confuses and mixes violates the law which is difficult to prove and probably the first and the second are because of the third What is this?
Version adapted to physicist: what is behind of 1. Smallness of neutrino mass in comparison to masses of the charged leptons and quarks 2. Unusual lepton mixing pattern with two large mixing angles (one is close to maximal) and one small which differs from the quark mixing 3. Weaker (or no) mass hierarchy than the hierarchy of charged leptons and quarks In general, what is the type of mass spectrum and mass ordering?
and connected questions: Nature of neutrino mass are they of Dirac or Majorana type? are they hard or soft (medium dependent)? Recall that in oscillation experiments we probe dispersion relations and not masses immediately Effective neutrino masses in oscillation experiments in beta decay in cosmology and bb-decay can be different Does the nature of neutrino mass differ from the nature of the quarks and charged lepton masses? Usual neutrino masses can be strongly suppressed, e.g. by the seesaw, so that unusual contributions dominate Are sterile neutrinos (if exist) relevant for the solution ?
Content: Challenging the riddle . Scales of new physics 3. Mixing and CP violation Steriles the key? . Some guesses
Challenging the riddle are we asking right questions? do we interpret the data correctly?
The riddle and the solution It is not excluded that the correct solution (or the key to the solution) already exists among hundreds of approaches, models, mechanisms, schemes, etc. Still something fundamental can be missed
Smallness of mass? comparing within generation: Special m3 m Similar for other generations if spectrum is hierarchical ~ 3 10-11 Neutrinos: no clear generation structure as well as the correspondence light flavor light mass, especially if the mass hierarchy is inverted or spectrum is quasi-degenerate me mt Normal? m3 me ~ 3 10-6 ~ 3 10-6 ? gap 103 100 1012 106 10-3 109 mass, eV
Leptons & quarks The riddle is formulated as comparison with masses (and mixing) of quarks There is no solution of the riddle of quark masses Can we solve the neutrino mass riddle? Do efforts make sense? Yes, if we still hope (as it was before) that neutrinos will uncover something simple and insightful which will allow to solve the quark mass riddle neutrino mass generation and generation of the charged lepton and quark masses are independent Higgs triplet Radiative mechanisms Seesaw type III, etc. we will try to explain the difference of masses and mixing of neutrinos and quarks, and not masses and mixing completely
Masses and mixing Should mixing be included in the riddle? Quarks Relation between masses and mixing Leptons Maximal mixing - quasi- degenerate mass states ? md ms Tri-Bi-Maximal mixing (TBM) sin C ~ no connection between masses and mixing (at least in the lowest order) In 3 generations: Fritzsch ansatz Realized in the residual symmetry approach Form invariance of the mass matrices
Mixing: quarks and leptons Completely related Largely unrelated Partially related with the only difference that originates from Majorana nature of neutrinos, symmetries Higgs triplet Seesaw type I, Quark-lepton unification Radiative mechanisms GUT, seesaw type II Seesaw type II and III
The riddle and Dark Universe Neutrino mass riddle Dark Matter Riddle Dark radiation Dark Energy Riddle Baryon asymmetry in the Universe Inflation
The riddle and scales of New Physics The riddle of new physics
Two types of new physics Neutrino new physics CKM type additional structures in lepton sector such as the see saw common for quarks and leptons responsible for small quark mixing and hierarchical structure of the Dirac masses responsible for smallness of neutrino mass and large lepton mixing These two types are different but probably should somehow know about each other Counter example, seesaw with degenerate RH neutrinos does not work in this framework
Scales of new physics GUT Planck mass VEW2 m High scale seesaw Quark- lepton symmetry /analogy GUT Low scale seesaw, radiative mechanisms, RPV, high dimensional operators Electroweak LHC Looking under the lamp Scale of neutrino masses themselves Relation to dark energy, MAVAN? eV- m sub-eV Neutrino mass itself is the fundamental scale of new physics Spurious scale?
High scale seesaw, unification 1 MR m = - mDT mD q l similarity: mD ~ mq ~ ml MGUT ~ 1016 GeV for the heaviest in the presence of mixing MGUT2 MPl many heavy singlets (RH neutrinos) string theory MR ~ 108 - 1014 GeV 1016 - 1017 GeV double seesaw N ~ 102 In favor Gauge coupling unification BICEP-II ? Leptogenesis
High scale seesaw, unification Natural, minimalistic, in principles Realizes relations: Partial relation of the quark and neutrino properties T. Higaki et al, arViv:1405.0013 Neutrinoful Universe Seesaw sector is responsible for inflation (scalar which breaks B-L and gives masses of RH neutrinos), dark matter, leptogenesis - Proton decay - Majorana masses Testable?
High scale line: the problem Simplest seesaw implies new physical scale << MPl MR ~ mD2 /m ~ 1014 GeV (Another indication: unification of gauge couplings) F. Vissani hep-phl9709409 R L H H J Elias-Miro et al, 1112.3022 [hep-ph] R y2 mH2 ~ MR2 log (q /MR) (2 )2 MR3 m (2 v)2 M. Fabbrichesi Cancellation? ~ log (q /MR) AYS New physics below Planck scale MR < 107 GeV Small Yukawas, Leptogenesis ? Partial SUSY?
EW LHC scale - No hierarchy problem (even without SUSY) - testable at LHC, new particles at 0.1 few TeV scale - LNV decays Low scale seesawRadiativeSmall VEV Higgs Triplet Two loops Low scale Neutralino as RH neutrino Radiative seesaw Inverse seesaw Connection to Dark Matter
MSM M. Shaposhnikov et al Everything below EW scale small Yukawa couplings L R - generate light mass of neutrinos - generate via oscillations lepton asymmetry in the Universe - can be produced in B-decays (BR ~ 10-10 ) Few 100 MeV GeV split ~ eV very small split BAU very small mixing WDM 3 - 10 kev - warm dark matter - radiative decays 3.5 kev line Normal Mass hierarchy Higgs inflation EW seesaw Nothing new below Planck scale
eV - sub eV scale physics - new scalar bosons, majorons, axions, - new fermions (sterile neutrinos, baryonic nu) , - new gauge bosons (e.g. Dark photons) Very light sector which may include M. Pospelov Maybe related to Dark energy, MAVAN Generate finite neutrino masses, usual Dirac masses can be suppressed by seesaw with MR = MPl or multi singlet mechanism eV scale Seesaw with RH neutrinos for sterile anomalies LSND/ MiniBooNE .... A. De Gouvea 5th force searches experiments Modification of dynamics of neutrino oscillations Checks of standard oscillation formulas, searches for deviations Tests:
Mixing and CP violation
In a spirit two types of new physics and partial relations PMNS & CKM C. Giunti, M. Tanimoto UPMNS = VCKM+ UX H. Minakata, A Y S From charged leptons or Dirac matrices of charged leptons and neutrinos CKM type new physics Related to mechanism of neutrino mass generation New neutrino structure Related to (any) mechanism that explains smallness of neutrino mass In general, has similar hierarchical structure determined (as in Wolfenstein parametrization) by powers of = sin C Should be fixed to reproduce correct Lepton mixing angles UX ~ UTBM VCKM ~ I
Prediction: 13 ~ c Pheno. level C. Giunti, M. Tanimoto H. Minakata, A Y S . can be obtained in the context of UPMNS = VCKM+ UX if UX =U23( /2) U12 Realized in QLC (Quark-Lepton Complementarity) TBM-Cabibbo scheme e.g. UX= UBM, UTBM S. F. King et al U12 ( c) U23( /2) permutation - to reduce the lepton mixing matrix to the standard form leads to 13~ c sin2 13~ sin2 C
The same value with completely different implications 3 mixing implications relation Quark-Lepton Complementarity GUT, family symmetry, ~ sin2 C m212 m322 ``Naturalness , absence of fine tuning of mass matrix O(1) sin2 13 Analogy with quark mixing relation sin2 12sin2 23 ? ~ cos2 2 23 universal symmetry violation 13 = 21/2( - 23) Eby,Frampton, Matsuzaki > 0.025 Mixing anarchy
CP-phase prediction UPMNS ~ VCKM+ UX No CPV If the only source of CP violation B. Dasgupta, A.S. sin 13 sin CP = (-cos 23) sin 13q sin q 3 q = 1.2 +/- 0.08 rad sin CP ~ 3/s13 ~ 2 ~ 0.046 where = (s13q /s13) c23 sin q CP ~ - or + If the phase CP deviates substantially from 0 or , new sources of CPV beyond CKM should exists (e.g. from the RH sector) or another framework New sources may have specific symmetries or structures which lead to particular values of CP e.g. - /2, and q - l unification will give just small corrections
In general neglecting terms of the order ~ 3 sin CP = s13-1 [sin( + X)Vud|Xe3| sin e |Vcd|X 3 ] here , X and e are parameters of the RH neutrinos Some special values of CP can be obtained under certain assumptions ifXe3 = 0 we have sin CP ~ sin e CP ~ 3 /2 if e = /2 One can find structure of the RH sector which lead to these conditions
In the Seesaw type I B Dasgupta A.S mD ~ mDq Ux is the matrix diagonalizes MX = - mDdiagUR+ (MR)-1 UR* mDdiag Here mD = UL(mD diag) UR+ In contrast to quarks for Majorana neutrinos the RH rotation that diagonalizes mD becomes relevant and contributes to PMNS CPV from UR UX = UR US In the LR symmetric basis From seesaw Minimal extension is the L- R symmetry: UR = UL ~ VCKM* and no CPV in MR Seesaw can enhance this small CPV effect so that resulting phase in PMNS is large
Quark lepton universality Vub = Vus Vcb sin 13 ~ sin 12 sin 23 The same relations between coupling strength between generations Similar structure of mass matrices but with different expansion parameter l= 1 - q Realization: Fritzsch Anzatz similar to quark sector, RH neutrinos with equal masses Normal mass hierarhy, relation between masses and mixing Expectations: Flavor alignment in mass matrix
Steriles is the key?
s New neutrino states mixing aS2 m ~ aS2 mS 1 MeV - Warm Dark matter - Pulsar kick (1 2) 10-8 eV 2 10-11 5 - 10 keV 1 keV - LSND, MB - Reactor Ga anomalies - Extra radiation 0.02 eV 1 eV 0.02 0.5 - 2 eV 10-6 eV 10-3 (2 4) 10-3 eV - Solar neutrinos - Extra radiation in the Universe 10-3 eV Compare with large elements of the mass matrix 0.02 eV
Effect of sterile neutrinos m = ma + m Original active mass matrix e.g. from see-saw ma = 0.025 eV Induced mass matrix due to mixing with nu sterile Decouples from generation of the light neutrino masses argument that this is not RH neutrino but has some other origin m << ma For keV Not a small perturbation m ~ ma For eV m can change structure (symmetries) of the original mass matrix completely be origin of difference of and can be be considered as very small perturbation of the 3 system For meV m << ma
New physics: neutrino portal New structure (but physics is the same) 1 n(F)- 3/2 Through this portal neutrino gets mass L H F where F is the fermionic operator R S is the key to the solution of the riddle? R L S H S S Neutrino new physics S Scale symmetries S S
Some guesses
Two different types of new physics are involved in explanation of data: the CKM type common to quarks and leptons and physics responsible for smallness of neutrino mass and large lepton mixing. The latter may have certain symmetries It makes sense to identify the second one which explains the difference between the quarks and leptons Still generation of quark and neutrino masses can be essentially independent High (GUT) scale new physics: still appealing EW scale: see LHC14 results Sub eV eV scale: interesting, worth to explore New neutrino physics may have certain symmetries which leads to specific values of mixing angles and CP phase. Phase from CKM part is strongly suppressed Sterile neutrinos may be the key to solution to a riddle
