The Last Chance for Leptogenesis: Electroweak Baryogenesis

1
The Last Chance for LeptogenesisElectroweak
Baryogenesis

• Hitoshi Murayama
• Whats ??
• Madrid, May 19, 2005

2
Two Main Questions

• Is neutrino mass probe to physics at very high
  scales, or very low scales?
• What is the relevance of neutrino mass to the
  baryon asymmetry to the universe?

3
Outline

• Baryogenesis
• Looking Up
• Looking Down
• Conclusions

4
Baryogenesis
5
Big-Bang NucleosynthesisCosmic Microwave
Background
(Thuan, Izatov)
(Burles, Nollett, Turner)
6
Baryon AsymmetryEarly Universe
10,000,000,001
10,000,000,000
They basically have all annihilated away except a
tiny difference between them
7
Baryon AsymmetryCurrent Universe
us
1
They basically have all annihilated away except a
tiny difference between them
8
Sakharovs Conditionsfor Baryogenesis

• Necessary requirements for baryogenesis
• Baryon number violation
• CP violation
• Non-equilibrium
• ? G(DBgt0) gt G(DBlt0)
• Possible new consequences in
• Proton decay?
• CP violation?

9
Baryon Number Violationin the Standard Model

• Electroweak anomaly violates B but not BL
• In Early Universe (T gt 200GeV), W/Z are massless
  and fluctuate in W/Z plasma
• Energy levels for left-handed quarks/leptons
  fluctuate correspondingly

• DLDQDQDQDB1 ? D(BL)0

10
Baryogenesis in the Standard Model?

• Sakharovs conditions
• B violation ? EW anomaly
• CP violation ? KM phase
• Non-equilibrium ? 1st order phase trans.
• Standard Model may satisfy all 3 conditions!
• Electroweak Baryogenesis (Kuzmin, Rubakov,
  Shaposhnikov)
• Two big problems in the Standard Model
• First order phase transition requires mHlt60GeV
• CP violation too small because
• J ? detYuYu, YdYd 1020 ltlt 1010

11
Leptogenesis

• You generate Lepton Asymmetry first.
• L gets converted to B via EW anomaly
• generate L from the direct CP violation in
  right-handed neutrino decay
• Two generations enough for CP violation because
  of Majorana nature (choose 1 3)

12
Gravitino Problem

• Gravitinos produced in early universe
• If decays after the BBN, destroys synthesized
  light elements
• Hadronic decays particularly bad (Kawasaki,
  Kohri, Moroi)

13
Looking Up
14
Rare Effects from High-Energies

• Effects of physics beyond the SM as effective
  operators
• Can be classified systematically (Weinberg)

15
Unique Role of Neutrino Mass

• Lowest order effect of physics at short distances
• Tiny effect (mn/En)2(eV/GeV)21018!
• Interferometry (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

16
Grand Unification

• electromagnetic, weak, and strong forces have
  very different strengths
• But their strengths become the same at 1016 GeV
  if supersymmetry
• A natural candidate energy scale L2 1016GeV
• ? mn0.001eV
• mn(Dm2atm)1/20.05eV
• mn(Dm2LMA)1/20.009eV

Neutrino mass may be probing unification Einstein
s dream
17
The Orthodoxy

• SUSY-GUT with seesaw
• Below MGUT
• MSSM N
• Above MGUT
• GUT possible flavor physics
• Leptogenesis from N1 decay

• Solves the hierarchy problem
• Provides dark matter
• Gravitino problem?
• FCNC? CP?

18
Do I believe it?

• No.
• Gauge coupling unification is one coincidence
• GUT doesnt predict ?MGUT
• U(1)B-L breaking can be gtgtMGUT or ltltMGUT w/o
  spoiling GUT
• It is only a religion right now

19
Can we test seesaw?

• No
• 1TeV LC 100 MW
• 1015GeV LC 1038 MW
• cf. world power 107 MW

20
Will I believe it?

• Possible
• It will take a lot but conceivable

21
To believe seesaw

• LHC finds SUSY, LC establishes SUSY
• no more particles beyond the MSSM at TeV scale
• Gaugino masses unify (two more coincidences)
• Scalar masses unify for 1st, 2nd generations (two
  for 10, one for 5, times two)
• Scalar masses unify for the 3rd generation 10
  (two more coincidences)
• ? strong hint that there are no additional
  particles beyond the MSSM below MGUT except for
  gauge singlets.

22
Gaugino and scalars

• Gaugino masses test unification itself
  independent of intermediate scales and extra
  complete SU(5) multiplets

• Scalar masses test beta functions at all scales,
  depend on the particle content

(Kawamura, HM, Yamaguchi)
23
To believe seesaw (cont.)

• The neutralino mass and its coupling to other
  SUSY particles are measured
• Calculate the neutralino annihilation cross
  section, agrees with the ?Mh20.14
• Calculate the neutralino scattering cross
  section, agrees with the direct detection
• B-mode fluctuation in CMB is detected, with a
  reasonable inflationary scale
• ? strong hint that the cosmology has been
  normal since inflation (no extra D etc)

24
Normal cosmology

• Annihilation cross section

• B-mode fluctuation

25
To believe seesaw (cont.)

• 0??? seen, neutrinos are Majorana
• LBL oscillation finds ?13 soon just below the
  CHOOZ limit
• determines the normal hierarchy and finds CP
  violation
• Scalar masses unify for the 3rd generation 5 up
  to the neutrino Yukawa coupling y31 above
  M3y32v2/m3
• ? neutrino parameters consistent with leptogenesis

26
To believe seesaw (cont.)

• Possible additional evidence, e.g.,
• lepton-flavor violation (??e conversion, ????)
  seen at the reasonable level expected in SUSY
  seesaw (even though I dont believe mSUGRA)
• Bd?? KS shows deviation from the SM consistent
  with large bR-sR mixing above MGUT
• Isocurvature fluctuation seen suggestive of N1
  coherent oscillation, avoiding the gravitino
  problem

27
Large q23 and quarks

• Large mixing between nt and nm
• Make it SU(5) GUT
• Then a large mixing between sR and bR
• Mixing among right-handed fields drop out from
  CKM matrix
• But mixing among superpartners physical

• O(1) effects on b?s transition possible
• (Chang, Masiero, HM)
• Expect CP violation in neutrino sector especially
  if leptogenesis

28
Consequences in B physics

• CP violation in Bs mixing (Bs?J/y f)

• Addtl CP violation in penguin b?s
• (Bd?f Ks)

Indirect evidence for lepton-quark unification
29
If all of the above happens

• Ill probably believe it.
• Its conceivable.

30
Looking Down
31
LHC may find different directions

• Suppose LHC will find TeV-scale extra dimensions,
  Randall-Sundrum, etc
• Cosmology goes haywire above TeV
• Need to look for the origin of small neutrino
  mass, baryon asymmetry at low energies
• Even with SUSY, gravitino problem may force us
  this way

32
Late neutrino mass

• Seesaw formula m?v2/?ltltv because v ltlt ?
• Another way to get small mass with O(1) coupling
  
• m? v(lt?gt/??n (Dirac)
• m? v2(lt?gtn/?n1? (Majorana)
• Even if ? TeV, lt?gtltltv works.
• Late neutrino mass because lt?gtltltv implies a
  late time phase transition
• e.g., n2, ? TeV ? lt?gtMeV

33
Explicit Realization
_

• U(1)l l(1), ?(-1), L(0), L(0), N(0)
• Recall anarchy no hierarchy, large mixing
• All Yukawa couplings here are O(1)

Can be gauged for the non-anomalous Z3 subgroup
34
Viable

• Remarkably, phenomenological constraint weak
  despite the low scale
• For m?gt1MeV, ???? above BBN, OK
• SN1987A limit OK because ? couples with strength
  ?m?
• If gauged, the domain walls are becoming
  important only now, possible imprint on CMB
  anisotropy
• (Checko, Hall, Okui, Oliver)
• (Davoudiasl, Kitano, Kribs, HM)

35
Electroweak Baryogenesis

• Even with two generations, CP is violated JIm
  Tr(YYMNYYTMNMNMN)
• Reflection asymmetry J/MN4 Im
  Tr(YYMNYYTMNMNMN)/MN4 O(1)

Hall, HM, Perez
36
Electroweak Baryogenesis

• L decays quickly as L?l?,
• l asymmetry converted to baryon asymmetry by
  sphaleron with rate 20?W5
  10-7

37
Electroweak Baryogenesis

• Last chance for leptogenesis electroweak scale
• Can generate enough asymmetry thanks to anarchy
  of neutrinos
• Vector-like LL induce LFV, tends to be big!

• In principle, all degrees of freedom can be
  produced at accelerators, possibly CP phase
  measured at ILC fully testable

_
38
Electroweak Baryogenesis

• Need 1st order phase transition
• Low-cutoff theory allows for higher dimension
  operator such as ?VH6/?2
• Can cause 1st order phase transition without a
  too-light Higgs (Grojean, Servant, Wells)
• No gravitino problem, needs normal cosmology only
  below TeV.

39
Conclusion
40
Conclusions

• electroweak baryogenesis not possible in the SM
• leptogenesis works, but gravitino problems
• Neutrino mass may look up
• Seesaw not directly testable, but it is
  conceivable that we get convinced
• Neutrino mass may look down
• Late time neutrino mass fully testable in
  principle, interesting alternative
• Even offers the opportunity for the low-scale
  leptogenesis at electroweak phase transition