Published on August 28, 2007
Slide1: Neutrinos, flavour and the origin of the Universe Slide2: Standard Model of particle physics has many remaining puzzles, in particular: 1. The origin of mass: the origin of the weak scale, its stability under radiative corrections, and the solution to the hierarchy problem. 2. The problem of flavour: the problem of the undetermined fermion masses and mixing angles (including neutrino masses and mixing angles) together with the CP violating phases, in conjunction with the observed smallness of flavour changing neutral currents and very small strong CP violation. 3. The question of unification: the question of whether the three known forces of the standard model may be related into a grand unified theory, and whether such a theory could also include a unification with gravity. Slide3: The Standard Model of Cosmology also has its own remaining puzzles, in particular: The origin of dark matter and dark energy: the embarrassing fact that 96% of the mass-energy of the Universe is in a form that is presently unknown, including 23% dark matter and 73% dark energy. 2. The problem of matter-antimatter asymmetry: the problem of why there is a tiny excess of matter over antimatter in the Universe, at a level of one part in a billion, without which there would be no stars, planets or life. 3. The question of the size, age, flatness and smoothness of the Universe: the question of why the Universe is much larger and older than the Planck size and time, and why it has a globally flat geometry with a very smooth cosmic microwave background radiation containing just enough fluctuations to seed the observed galaxy structures. Slide4: t b c s u d e The Flavour Problem Charge +2/3 quarks Charge –1/3 quarks Charged leptons A neutrino hierarchy Why are neutrino masses so small and mixings so large? What is the origin of quark and lepton masses/mixings? Do GUT/Family symmetries play a role? GUTs: GUTs Family Symmetry: Family Symmetry Nothing Slide7: Why are neutrinos so light? Light neutrinos Heavy particles A natural mechanism: Slide8: Type I see-saw mechanism Type II see-saw mechanism (SUSY) The see-saw mechanism Type II Type I P. Minkowski (1977), Gell-Mann, Glashow, Mohapatra, Ramond, Senjanovic, Slanski, Yanagida (1979/1980),Valle… Lazarides, Magg, Mohapatra, Senjanovic, Shafi, Wetterich (1981) Slide9: Type I see-saw for hierarchical neutrinos Technically need a small 23 sub-determinant: Why is the sub-determinant small? Why is the solar angle large? Need to understand: Right-handed neutrino dominance Single Right-Handed Neutrino Dominance : Single Right-Handed Neutrino Dominance If one right-handed neutrino of mass Y dominates then sub-determinant is naturally small Natural explanation of and large atmospheric angle if e~f Sequential dominance : Sequential dominance Same features as SRHND plus natural explanation of large solar angle if a~b-c Slide12: Constrained sequential dominance (plus previous) conditions Tri-bimaximal neutrino mixing Tri-bimaximal mixing from Constrained Sequential dominance …but what about charged lepton contributions to mixing? Harrison, Perkins and Scott – Paul’s talk Effect of small charged lepton mixing angles Antusch, SFK ’05: Effect of small charged lepton mixing angles Antusch, SFK ’05 If 13 angles are small have sum rule: q12+q13cos(d -p)¼ qn12 Typically 35.26± or 45± q13 and d then come from the charged lepton sector This means that d is irrelevant for leptogenesis (the bad news) Slide14: gives prediction for q12 as function of d Current 3s experimental range Tri-bimaximal value predicts maximal CP violation! (NOT zero CP violation!) e.g. tri-bimaximal neutrino mixing plus quark-lepton unification leads to …but d is predicted (the good news) Muon Flavour Violation : Muon Flavour Violation If SUSY is present then neutrino masses inevitably lead to lepton flavour violation due to radiatively generated off-diagonal slepton masses Borzumati, Masiero; Hisano, Moroi, Tobe, Yamaguchi; SFK, Oliveira; Casas, Ibarra; Lavignac, Masina, Savoy; … Unanswered cosmological questions: Unanswered cosmological questions Are neutrinos (partly) responsible for dark matter? Are right-handed neutrinos responsible for leptogenesis? (Silvia Pascoli) Are right-handed sneutrinos responsible for cosmological inflation? Are right-handed neutrinos responsible for dark energy? Slide17: WMAP Slide18: CMB power spectrum Galaxy power spectrum Tegmark (opposite), Wang, Zaldarriaga Galaxy structure limits neutrino mass 2dF Galaxy Redshift survey astro-ph/0204152 Slide19: Member of Physics WG Slide20: Kinney astro-ph/0406670 ? Slide21: Motivation for Inflation Horizon problem Flatness problem Relic removal Structure formation Present universe is inflating Slide22: slow roll of right-handed sneutrino in a false vacuum generates accelerated expansion in the very early universe Sneutrino inflation Slow roll parameters Right-handed sneutrino Slide23: astro-ph/0407372 Allowed regions of and Sneutrino chaotic (Antusch et al 04) (Yanagida et al 93) Slide24: Dark Energy and Right-handed neutrinos Barbieri, Hall, Oliver,Strumia hep-ph/0505124 Antusch, Eyton-Williams, SFK (in progress) The accelerated expansion of the Universe could be due to a tiny but non-zero dark energy of order the neutrino mass scale : A possible microscopic origin of dark energy is a quintessence field associated with a pseudo-Goldstone boson arising from the mass generating mechanism of right-handed neutrinos The model predicts Dirac neutrinos plus extra light 'sterile' neutrinos with interesting phenomenological and cosmological consequences (MiniBoone, BBN,…) Slide25: TOE (M-theory) GUT+Flavour theory See-saw model Muon flavour violation Leptogenesis Neutrino masses and mixings No direct link (need to go via see-saw model) RGE Summary Slide26: 1. The origin of flavour and the quest for unification: In terms of the unanswered questions of the Standard Model, whereas the LHC teaches us about mainly about the origin of mass, the Neutrino Factory will teach us about the problem of flavour and the question of unification. Neutrino masses are very small, and this probably means new physics beyond the Standard Model – the alternative is to have extremely small unexplained Yukawa couplings. The smallness of neutrino masses is commonly explained by the see-saw mechanism, which implies heavy right-handed neutrino Majorana masses. The explanation of the large lepton mixing angles can be readily accounted for in the see-saw mechanism, by the sequential dominance of right-handed neutrinos for example, leading to relations between elements of the neutrino Yukawa matrices. This adds information about the neutrino Yukawa matrices to the information already known in the quark and charged lepton sectors. When this information is taken all together it becomes possible to consider the problem of flavour in the framework of the question of unification. Theories of unification relate quarks to leptons, and motivate the measurement of lepton mixing angles to the same precision as the quark mixing angles. (Antusch, Pascoli, SFK) Discussion… Slide27: 2. The origin of matter in the Universe: In terms of the unanswered questions of Cosmology, whereas the LHC may teach us about the origin of dark matter, a Neutrino Factory may help to provide the solution to the problem of matter-antimatter asymmetry. The basic scenario assumes the see-saw mechanism and heavy right-handed Majorana neutrinos, which are produced in the early Universe and subsequently decay resulting in lepton-antilepton asymmetry in the early Universe, which subsequently becomes converted into baryon-antibaryon asymmetry. The asymmetry requires CP violating phases in the couplings of right-handed neutrinos. The relation between these phases and the oscillation phase is model-dependent. In a particular (GUT ) theory of flavour there may or may not be a relation (if q13 is small there is no relation) (Pascoli, Antusch) 3. The origin of the Universe: The question of the size, age, flatness and smoothness of the Universe is commonly answered by Inflation. The relation of Inflation to neutrino physics (if any) is unclear, but it has been suggested that the right-handed sneutrino (the superpartner to the right-handed neutrino) could be a suitable candidate for the inflaton field. (Antusch, SFK) 4. The origin of dark matter in the Universe: There are strong cosmological limits on the neutrino mass scale from galaxy structure formation – ways out? (Hannestad) 5. The origin of dark energy in the Universe: There may even be a connection between neutrinos and dark energy. The motivation is that the energy scale of dark energy is about , which is similar to the possible mass of some neutrino state e.g. the solar neutrino mass in hierarchical models. Models have been constructed which have experimental implications.(Antusch, SFK) Slide28: These are not disconnected subjects – the plan is to write a coherent document which makes a strong theory case for a neutrino factory The case must be both scientifically sound, and be appealing to a wide readership The main goal main is not to write refereed scientific papers, but this possibility should not be excluded if interesting new results emerge, especially if this benefits the non-tenured authors – in any case such studies frequently stimulate new research Interactions between members of a particular subgroup, and between different sub-groups is essential since the science is interconnected.