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

2. 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

3. 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

4. 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

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

6. 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

7. March 2002
April 2002 with SNO
Hitoshi Murayama TAU2002

8. 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

9. 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

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

11. Implications of Neutrino Mass

12. Neutrinos are Left-handed
Hitoshi Murayama TAU2002

13. 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

14. 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

15. Mass Spectrum
What do we do now?
Hitoshi Murayama TAU2002

16. 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

17. 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

18. 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

19. 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

20. 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

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

22. 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

23. 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

24. Baryon Asymmetry

25. 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

26. Cosmic Microwave Background
Hitoshi Murayama TAU2002

27. 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

28. Baryon Asymmetry Current Universeus 1
They basically have all annihilated away except a tiny difference between them
Hitoshi Murayama TAU2002

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

41. 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

42. Neutrino and B connection

43. 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

44. 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

45. Bdf Ks ICHEP 2002 @ Amsterdam Compared to W. A. from J/y Ks
“sin2f1”=–0.73±0.64± (Belle)
“sin2b”=–0.19±0.51± (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

46. 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

47. 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

48. (HM, Pierce)
Hitoshi Murayama TAU2002

49. 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