1 The Last Chance for Leptogenesis: Electroweak Baryogenesis Hitoshi Murayama What’s ? 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 WMAP Big-Bang Nucleosynthesis Cosmic Microwave Background (Thuan, Izatov) (Burles, Nollett, Turner)

6 Baryon Asymmetry Early Universe They basically have all annihilated away except a tiny difference between them 10,000,000,00110,000,000,000

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

8 Sakharov’s Conditions for Baryogenesis Necessary requirements for baryogenesis: –Baryon number violation –CP violation –Non-equilibrium  (  B>0) >  (  B<0) Possible new consequences in –Proton decay? –CP violation?

9 Baryon Number Violation in 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

10 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 m H <60GeV –CP violation too small because J  det[Y u † Y u, Y d †Y d ] ~ 10 –20 << 10 –10

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) Thermal leptogenesis Buchmüller, Plümacher

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 (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

16 Grand Unification electromagnetic, weak, and strong forces have very different strengths But their strengths become the same at GeV if supersymmetry A natural candidate energy scale  ~ GeV  m ~0.001eV m ~(  m 2 atm ) 1/2 ~0.05eV m ~(  m 2 LMA ) 1/2 ~0.009eV Neutrino mass may be probing unification: Einstein’s dream 

17 The Orthodoxy SUSY-GUT with seesaw Below M GUT : MSSM + N Above M GUT : GUT + possible flavor physics Leptogenesis from N 1 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 doesn’t predict  ~M GUT U(1) B-L breaking can be >>M GUT or <<M GUT w/o spoiling GUT It is only a religion right now 

19 Can we test seesaw? No 1TeV LC ~ 100 MW GeV LC ~ MW cf. world power ~ 10 7 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 M GUT 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  M h 2 =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)

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 y 3 ~1 above M 3 =y 3 2 v 2 /m 3  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 don’t believe mSUGRA) B d  K S shows deviation from the SM consistent with large b R -s R mixing above M GUT Isocurvature fluctuation seen suggestive of N 1 coherent oscillation, avoiding the gravitino problem

27 Large  23 and quarks Large mixing between  and  Make it SU(5) GUT Then a large mixing between s R and b R 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 B s mixing (B s  J/   ) Addt’l CP violation in penguin b  s (B d  K s ) Indirect evidence for lepton-quark unification

29 If all of the above happens I’ll probably believe it. It’s 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 =v 2 /  <<v because v <<  Another way to get small mass with O(1) coupling: m =v( /  n (Dirac) m =v 2 ( 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

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 Z 3 subgroup

34 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)

35 Electroweak Baryogenesis Even with two generations, CP is violated J=Im Tr(YY † M N * Y * Y T M N M N * M N ) Reflection asymmetry ~ J/M N 4 =Im Tr(YY † M N * Y * Y T M N M N * M N )/M N 4 ~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  W 5 ~ 10 -7

37 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 _

38 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.

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