Perspectives from Neutrinos Hitoshi Murayama (UC Berkeley) TAU2002 Santa Cruz, September 12, 2002

Window to beyond the Standard Model! The Question So much activity on neutrino oscillation. Why are we doing this? Window to beyond the Standard Model! Hitoshi Murayama TAU2002

Why Beyond the Standard Model Standard Model is sooooo successful. But none of us are satisfied with the SM. Why? Because it leaves so many great questions unanswered  Drive to go beyond the Standard Model Two ways: Go to high energies Study rare, tiny effects  Hitoshi Murayama TAU2002

Big Questions Charge quantization, anomaly cancellation, bizarre hypercharge assignments in the Standard Model Why are there three seemingly unrelated forces yet all gauge forces? Is there a unified description of all forces as Einstein dreamed about? Why is mW<<MPl? (Hierarchy Problem) Why are there three generations? Why physics determines the pattern of masses and mixings? What is the origin of CP violation? What is the origin of matter anti-matter asymmetry in Universe? Hitoshi Murayama TAU2002

Rare Effects from High-Energies Effects of physics beyond the SM as effective operators Can be classified systematically (Weinberg) Hitoshi Murayama TAU2002

Unique Role of Neutrino Mass Lowest order effect of physics at short distances Tiny effect (mn/En)2~(eV/GeV)2=10–18! Inteferometry (i.e., Michaelson-Morley)! Need coherent source Need interference (i.e., large mixing angles) Need long baseline Nature was kind to provide all of them! “neutrino interferometry” (a.k.a. neutrino oscillation) a unique tool to study physics at very high scales Hitoshi Murayama TAU2002

March 2002 April 2002 with SNO Hitoshi Murayama TAU2002

Historic Era in Neutrino Physics Atmospheric nm is lost (>10s), converted mostly likely to nt (>99%CL) (SK, MACRO) Solar ne is converted to either nm or nt (>5.3s) (SNO) No dark side in solar neutrinos ;-( Explanation is probably neutrino oscillation Other possibilities: Neutrino decay, Violation of equivalence principle, spin resonant rotation, FCNC Possible, but models tend to be ugly Tiny neutrino mass: the first evidence for incompleteness of Minimal Standard Model Hitoshi Murayama TAU2002

Now what? We are pretty much convinced that neutrinos have mass. Now what? What did we learn? What do we want to know more? Why are still working on neutrinos? Any connection to quark sector? Any connection to cosmology? Hitoshi Murayama TAU2002

Outline Introduction Implications of Neutrino Mass Baryon Asymmetry Neutrino and B connection Conclusions Hitoshi Murayama TAU2002

Implications of Neutrino Mass

Neutrinos are Left-handed Hitoshi Murayama TAU2002

Neutrinos must be Massless All neutrinos left-handed  massless If they have mass, can’t go at speed of light. Now neutrino right-handed??  contradiction  can’t be massive Hitoshi Murayama TAU2002

Standard Model We have seen only left-handed neutrinos and right-handed anti-neutrinos (CPT) Neutrinos are strictly massless in the Standard Model Finite mass of neutrinos implies that the Standard Model is incomplete! Not just incomplete but probably a lot more profound Hitoshi Murayama TAU2002

Mass Spectrum What do we do now? Hitoshi Murayama TAU2002

Two ways to go (1) Dirac Neutrinos: There are new particles, right-handed neutrinos, after all Why haven’t we seen them? Right-handed neutrino must be very very weakly coupled Why? Hitoshi Murayama TAU2002

Extra Dimensions All charged particles are on a 3-brane Right-handed neutrinos SM gauge singlet  Can propagate in the “bulk” Makes neutrino mass small (Arkani-Hamed, Dimopoulos, Dvali, March-Russell; Dienes, Dudas, Gherghetta; Grossman, Neubert) mn ~ 1/R if one extra dim  R~10mm An infinite tower of sterile neutrinos Or SUSY breaking (Arkani-Hamed, Hall, HM, Smith, Weiner) Hitoshi Murayama TAU2002

Two ways to go (2) Majorana Neutrinos: There are no new light particles Why if I pass a neutrino and look back? Must be right-handed anti-neutrinos No fundamental distinction between neutrinos and anti-neutrinos!  0nbb Hitoshi Murayama TAU2002

Seesaw Mechanism Why is neutrino mass so small? Need right-handed neutrinos to generate neutrino mass , but nR SM neutral To obtain m3~(Dm2atm)1/2, mD~mt, M3~1015GeV (GUT!) Hitoshi Murayama TAU2002

Neutrino mass may be probing unification: Grand Unification M3 electromagnetic, weak, and strong forces have very different strengths But their strengths become the same at 1016 GeV if supersymmetry To obtain m3~(Dm2atm)1/2, mD~mt  M3~1015GeV! Neutrino mass may be probing unification: Einstein’s dream Hitoshi Murayama TAU2002

Rest In Peace Minimal SUSY SU(5) GUT RGE analysis SuperK limit MHc>7.6 1016 GeV Even if 1st, 2nd generation scalars “decoupled”, 3rd generation contribution (Goto, Nihei) MHc>5.7 1016 GeV (HM, Pierce) Hitoshi Murayama TAU2002

Avoiding Proton Decay Unfortunately, proton decay rate/mode is highly model-dependent more threshold corrections (HM, Pierce) Some fine-tuning (Babu, Barr) GUT breaking by orbifolds (Kawamura; Hall, Nomura) Depends on the triplet-doublet splitting mechanism, Yukawa (non-)unification Many modified models predict decay rate within 10–100 beyond limit Don’t give up! Hitoshi Murayama TAU2002

Superpartners as probe Of course, we need to see SUSY directly Once found, their masses tell us if unification is true (LHC and LC combined) Hitoshi Murayama TAU2002

Baryon Asymmetry

Big-Bang Nucleosynthesis “Crisis” the past few years Thuan-Izotov reevaluation of 4He abundance Sangalia D abundance probably false Now concordance (Thuan, Izatov), (Burles, Nollett, Turner) Hitoshi Murayama TAU2002

Cosmic Microwave Background Hitoshi Murayama TAU2002

Baryon Asymmetry Early Universe 10,000,000,001 10,000,000,000 They basically have all annihilated away except a tiny difference between them Hitoshi Murayama TAU2002

Baryon Asymmetry Current Universe us 1 They basically have all annihilated away except a tiny difference between them Hitoshi Murayama TAU2002

Sakharov’s Conditions for Baryogenesis Necessary requirements for baryogenesis: Baryon number violation CP violation Non-equilibrium  G(DB>0) > G(DB<0) Possible new consequences in Proton decay Hitoshi Murayama TAU2002

Anomaly washout Actually, SM violates B (but not B–L). In Early Universe (T > 200GeV), W/Z are massless and fluctuate in W/Z plasma Energy levels for left-handed quarks/leptons fluctuate correspon-dingly DL=DQ=DQ=DQ=DB=1  D(B–L)=0 Hitoshi Murayama TAU2002

Two Main Directions BL0 gets washed out at T>TEW~174GeV Electroweak Baryogenesis (Kuzmin, Rubakov, Shaposhnikov) Start with B=L=0 First-order phase transition  non-equilibrium Try to create BL0 Leptogenesis (Fukugita, Yanagida) Create L0 somehow from L-violation Anomaly partially converts L to B Hitoshi Murayama TAU2002

Leptogenesis You generate Lepton Asymmetry first. L gets converted to B via EW anomaly Fukugita-Yanagida: generate L from the direct CP violation in right-handed neutrino decay Hitoshi Murayama TAU2002

Leptogenesis Two generations enough for CP violation because of Majorana nature (choose 1 & 3) Right-handed neutrinos decay out-of-equilibrium Much more details worked out in light of oscillation data (Buchmüller, Plümacher; Pilaftsis) M1~1010 GeV OK  want supersymmetry Hitoshi Murayama TAU2002

Does Leptogenesis Work? Some tension with supersymmetry: unwanted gravitino overproduction Thermal production (TRH<109 GeV) Non-thermal production from preheating (TRH<105 GeV?) (Giudice, Riotto, Tkachev) (Kawasaki, Kohri, Moroi) Hitoshi Murayama TAU2002

Leptogenesis Works! Coherent oscillation of right-handed sneutrino (Bose-Einstein condensate) (HM, Yanagida+Hamaguchi) Inflation ends with a large sneutrino amplitude Starts oscillation dominates the Universe Its decay produces asymmetry Consistent with observed oscillation pattern Possible imprint on CMBR (Moroi) Hitoshi Murayama TAU2002

Preheating Oscillating inflaton f (mass ~1013GeV) The coupling to right-handed neutrino (M+gf)NN Mass vanishes at f=M/g  non-adiabatic  explosive production up to 1017GeV (Giudice, Riotto, Tkachev) The case of SUSY more subtle because f complex (Chacko, HM, Perelstein) Nonetheless can produce N up to 1015GeV Hitoshi Murayama TAU2002

CP Violation Possible only if: Can we see CP violation? Dm122, s12 large enough (LMA) q13 large enough Can we see CP violation?  KamLAND  JHF, OANuMI?  ? May need better parameter determination using solar pp neutrinos Hitoshi Murayama TAU2002

Can we prove it experimentally? We studied this question at Snowmass2001 (Ellis, Gavela, Kayser, HM, Chang) Unfortunately, no: it is difficult to reconstruct relevant CP-violating phases from neutrino data alone But: we will probably believe it if 0nbb found CP violation found in neutrino oscillation EW baryogenesis ruled out Archeological evidences Hitoshi Murayama TAU2002

Do we need seesaw? Natural explanation for small neutrino mass Seesaw: mn~<H>2/M What about hn~mSUSY/M? (Arkani-Hamed, Hall, HM, Smith, Weiner) (Borzumati, Nomura) Suppresses neutrino Yukawa coupling Naturally light Dirac neutrinos Light right-handed neutrinos Hitoshi Murayama TAU2002

Small Neutrino Mass From SUSY Breaking <c>~mSUSY+q2 mSUSY MPl breaks SUSY and U(1)N, preserves U(1)L+N Heavy vector-like lepton doublets F, F* Coupling: MFF*+ cLF*+FNHu (HM, Pierce) Most general couplings allowed by lepton number and U(1)N number Exchange of F generates <c>LNHu/M Small Yukawa <c>/M Large and mixing (interesting for LHC/LC) Hitoshi Murayama TAU2002

Dirac Leptogenesis Heavy doublets decay to FcL or NHu Decay produces asymmetry (≥2 gener.) Ln+LN=0, but Ln =–LN0 LN0 protected because of small Yukawa Ln partially converted to B Practially only now (T ~ mn ~ 103 K), Ln & LN equilibriate, but do not cancel any more (Dick, Lindner, Ratz, Wright) The explanation for small neutrino mass provides the origin of baryon asymmetry! (HM, Pierce) Hitoshi Murayama TAU2002

Neutrino and B connection

Large q23 and quarks Large mixing between nt and nm Make it SU(5) Then a large mixing between sR and bR Mixing among right-handed fields drop out from CKM matrix But mixing among superpartners physical Interesting effects in bs transition? Constraints from meg etc prevent effects >10% if nR all degenerate Goto, Okada, Shimizu, Shindou, Tanaka; Moroi In naïve SO(10), O(1) effects on bs transition possible Chang, Masiero, HM Hitoshi Murayama TAU2002

Consequences in B physics CP violation in Bs mixing (BsJ/y f) (Chang, Masiero, HM) Addt’l CP violation in penguin bs (Bdf Ks) (Chang, Masiero, HM) Hitoshi Murayama TAU2002

Bdf Ks ICHEP 2002 @ Amsterdam Compared to W. A. from J/y Ks “sin2f1”=–0.73±0.64±0.18 (Belle) “sin2b”=–0.19±0.51±0.09 (BABAR) Compared to W. A. from J/y Ks +0.731±0.055 Maybe a hint (~2.7s) of SUSY flavor physics? But BdhKs, K+K–Ks? Even if the current “discrepancy” disappears, it remains true that this is a very reasonable place for new physics to show up. Hitoshi Murayama TAU2002

Conclusions Neutrino physics going through a revolution Naturally small neutrino mass requires major plumbing in the theory GUT/seesawMajorana neutrino Extra D/SUSY breakingDirac neutrino Leptogenesis gaining momentum Many viable models (coherent oscillation, preheating) Majorana neutrino not mandatory Interesting possible consequences of neutrino mixing in bs through GUT, models of flavor Need truly multi-prong approach Energy frontier, flavor experiment, non-accelerator experiments

Signals of Electroweak Baryogenesis ~20% enhancements to Dmd, Dms with the same phase as in the SM (HM, Pierce) Find Higgs, stop, charginos (Tevatron?) Eventually need to measure the phase in the chargino sector at LC to establish it Hitoshi Murayama TAU2002

(HM, Pierce) Hitoshi Murayama TAU2002

B-physics Challenges Lattice QCD: need B parameters at 5%  then Bs mixing in business Vtd has been determined from B mixing Not legitimate in presence of SUSY loop Need to determine Vtd from other sides, angles Vub (from q2 distribution?) f1 (from BJ/Ks) possible help from f2 (from Bpp with isospin analysis) Hitoshi Murayama TAU2002