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The Last Chance for Leptogenesis:Electroweak Baryogenesis

Hitoshi Murayama

What’s ?

Madrid, May 19, 2005

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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?

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Outline

• Baryogenesis

• Looking Up

• Looking Down

• Conclusions

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Baryogenesis

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WMAP

Big-Bang NucleosynthesisCosmic Microwave Background

η=nB

nγ= 4.7−0.8

+1.0( )×10

−10

5.0±0.5( )×10−10

(Thuan, Izatov)

(Burles, Nollett, Turner)

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Baryon AsymmetryEarly Universe

q q

They basically have all annihilated away except a tiny difference between them

10,000,000,001 10,000,000,000

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Baryon AsymmetryCurrent Universe

q q

They basically have all annihilated away except a tiny difference between them

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us

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Sakharov’s Conditionsfor Baryogenesis

• Necessary requirements for baryogenesis:– Baryon number violation– CP violation– Non-equilibrium

(B>0) > (B<0)

• Possible new consequences in– Proton decay?– CP violation?

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Baryon Number Violationin the Standard Model

• Electroweak anomaly 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 correspondingly

L=Q=Q=Q=B=1 B–L)=0

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Baryogenesis in the Standard Model?

• Sakharov’s 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 mH<60GeV– CP violation too small because

J det[Yu†Yu, Yd

†Yd] ~ 10–20 << 10–10

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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)

ε =Γ(N1→ νiH)−Γ(N1→ ν iH)Γ(N1→ νiH)+Γ(N1→ ν iH)

~18π

Im(h13h13h33* h33

* )

h132

M1

M3

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Gravitino Problem

• Gravitinos produced in early universe

• If decays after the BBN, destroys synthesized light elements

• Hadronic decays particularly bad (Kawasaki, Kohri, Moroi)

€

n3/2

s=1.5 ×10−12 TRH

1010 GeV

Thermal leptogenesisBuchmüller, Plümacher

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Looking Up

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Rare Effects from High-Energies

• Effects of physics beyond the SM as effective operators

• Can be classified systematically (Weinberg)

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Unique Role of Neutrino Mass

• Lowest order effect of physics at short distances

• Tiny effect (m/E)2~(eV/GeV)2=10–18!

• 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

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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 ~2 1016GeV

m~0.001eV• m~(m2

atm)1/2~0.05eV• m~(m2

LMA)1/2~0.009eV

Neutrino mass may be probing unification:

Einstein’s dream

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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?

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Do I believe it?

• No.• Gauge coupling

unification is one coincidence

• GUT doesn’t predict ~MGUT

• U(1)B-L breaking can be >>MGUT or <<MGUT w/o spoiling GUT

• It is only a religion right now

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Can we test seesaw?

No

1TeV LC ~ 100 MW

1015GeV LC ~ 1038 MW

cf. world power ~ 107 MW

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Will I believe it?

Possible

It will take a lot but conceivable

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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.

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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)

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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 Mh2=0.14

• 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)

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“Normal” cosmology

ΩM =0.756(n+1)xf

n+1

g1/2σannMPl3

3s08πH0

2 ≈α2 /(TeV)2

σann

Annihilation cross section B-mode fluctuation

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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 y3~1 above M3=y3

2v2/m3

neutrino parameters consistent with leptogenesis

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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 don’t 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

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Large 23 and quarks

• Large mixing between and

• 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 bs transition possible

(Chang, Masiero, HM)

• Expect CP violation in neutrino sector especially if leptogenesis

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Consequences in B physics

• CP violation in Bs mixing (BsJ/ )

• Addt’l CP violation in penguin bs

(Bd Ks)

Indirect evidence for lepton-quark unification

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If all of the above happens

I’ll probably believe it.

It’s conceivable.

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Looking Down

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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

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Late neutrino mass

• Seesaw formula: m=v2/<<v because v << • Another way to get small mass with O(1)

coupling:

m =v(<>/n (Dirac)

m =v2(<>n/n+1 (Majorana) Even if ~TeV, <><<v works.

• “Late” neutrino mass because <><<v implies a late time phase transition

• e.g., n=2, ~TeV <>~MeV

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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

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Viable

• Remarkably, phenomenological constraint weak despite the low scale

• For m>1MeV, 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)

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Electroweak Baryogenesis

• Even with two generations, CP is violated J=Im Tr(YY†MN

*Y*YTMNMN*MN)

• Reflection asymmetry ~ J/MN4

=Im Tr(YY†MN*Y*YTMNMN

*MN)/MN4 ~O(1)

Hall,HM,Perez

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Electroweak Baryogenesis

• L decays quickly as Ll,

• l asymmetry converted to baryon asymmetry by sphaleron with rate ~ 20W

5 ~ 10-7

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Electroweak Baryogenesis

• Last chance for leptogenesis: electroweak scale

• Can generate enough asymmetry thanks to anarchy of neutrinos

• Vector-like L+L 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

_

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Electroweak Baryogenesis

• Need 1st order phase transition

• Low-cutoff theory allows for higher dimension operator such as V~|H|6/2

• Can cause 1st order phase transition without a too-light Higgs (Grojean, Servant, Wells)

• No gravitino problem, needs normal cosmology only below TeV.

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Conclusion

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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