Neutrino Mass Origin of Matter: Probing at LHC

1. Neutrino Mass Origin of Matter: Probing at LHC R. N. Mohapatra MPI-Heidelberg Seminar,2009

2. Universe is full of matter and “no” anti-matter • How do we know ? (i) Solar probes have not exploded- (ii) Sun sends us billions of particles and no antiparticles since there are no natural fireworks in the sky- (iii) Anti-matter fraction in cosmic rays: 1 in 10,000 (completely understandable in terms of known particle physics.)

3. Big Bang Nucleosynthesis • In the beginning, when the Universe was only a second old, there were only protons and neutrons- so how did all the elements we are made of formed ?

4. Matter Amount • Detailed analysis

5. Was it put in by hand at the beginning ? Not tenable since inflation empties the universe— • It must be created by microphysics during evolution

6. Baryon asymmetry from Microphysics • Sakharov Proposed 3 conditions for generating baryon asymmetry using microphysics (1967) • Baryon number violation; • CP violation; • Out of Thermal Equilibrium. • Standard model cannot do-although it has both CP and B-violation (too small CPV and not light enough Higgs).

7. Premise of the Talk: • Discovery of neutrino mass requires new physics beyond SM which has provided a promising possibility for explaining the matter-antimatter asym. • Can we test this physics at LHC ? • TeV scale Z’ related to -mass: (Blanchet, Chacko, Granor, RNM: arXiv:0904.2974)

8. Seesaw Paradigm for neutrino mass • Why ? • Add right handed neutrinos to SM with Majorana mass: • Breaks B-L sym. of SM: • After electroweak symmetry breaking • Note: if MR=0, (too small) whereas even with TeV MR, (more reasonable) B-L breaking crucial to seesaw: Minkowski; Gell-Mann, Ramond Slansky,Yanagida, R.N.M.,Senjanovic,Glashow

9. Seesaw and Origin of matter • Proposal:(Fukugita and Yanagida ,1986) • Generates lepton asymmetry: • Gets converted to baryons via sphaleron interactions of SM (‘t Hooft) (Kuzmin,Rubakov,Shaposnikov) • No new interactions needed other than those already used for generating neutrino masses !! • Seesaw provides a common understanding of both neutrino masses and origin of matter in the Universe.

10. Scale • What is the seesaw scale ? • Is scale right for baryogenesis ? • Important because scale determines whether the idea is testable !!

11. Seesaw scale • Neutrino masses do not determine the seesaw scale- we do not know in seesaw formula • Type I seesaw + GUT - GeV- Small neutrino mass could be indication for SUSYGUT; Many interesting SO(10) GUT models. • No collider signals ! Possible tests in nu-osc. • With SUSY, in (dependent on SUSY scale) • Seesaw scale is around TeV (corresponding Yukawa~ ) ; • Natural -protected by chiral sym. • Many collider signals, possibly ,

12. Leptogenesis Scale • Diagrams: • Two classes of models depending on RH mass pattern • High Scale leptogenesis: Expected in GUT theories:Adequate asymmetry for lightest RH (for hierarchical masses)(Buchmuller, Plumacher,di Bari; Davidson, Ibarra) • Resonant leptogenesis: degenerateN’s, self energy diagram dominates:~ ; Resonance when ;works for all B-L scales. (Liu and Segre’94; Covi et al’95 ; Flanz et al.’95 Pilaftsis’97)

13. An Issue with High scale SUSY Leptogenesis • Recall the lower bound on the lightest RH neutrino mass for enough baryons in GUTs • Problem for supersymmetric models: they have gravitinos with TeV mass that are produced during inflation reheat along with all SM particles- • Will overclose the universe if stable for TR>10^9 GeV. • If unstable, Once produced they live too long -affect BBN. . (Kohri et al.) • Possible tension between LFV and leptogen.

14. Tension between gravitino and high scale leptogenesis • Overclosure for stable and BBN constraint for unstable ones: (Kawasaki, Kohri, Moroi,Yatsuyanagi,2008)

15. Leptogenesis and • Both depend on RH neutrino mass hierarchy !! • (Chun,Evans,Morrissey,Wells’08; Petcov,Rodejohann,Shindou,Takanishi’05) No such conflict for TeV scale leptogenesis !! Goes well with collider friendly TeV seesaw !

16. Minimal TeV scale seesaw • No new interactions: N production at LHC can happen only through mixing ; cross section observable only if mixing is > • (del Aguila,Aguilar-Savedra, Pittau) • However observed neutrino masses via seesaw for ~100 GeV implies Not observable at LHC. • Exceptions possible with specific extra global symmetries-

17. TeV Seesaw with B-L forces (Z’) • Seesaw effect observable at LHC even with tiny mixings as in generic neutrino models. • pp Z’+X; Z’NN followed by N-decay; • Like sign dileptons is the tell-tale seesaw signal.

18. How plausible is Local B-L ? • Neutrino masses  seesaw scale much lower than Planck scale New symmetry(B-L). • Is B-L global or local ? • SM  only Tr (B-L)[SU(2)]^2=0 but • But SM +  • B-L is a potential gauge symmetry- • Gauged B-L eliminates R-parity problem of MSSM and ensures proton stability and dark matter: Another advantage of B-L(RNM’86; Martin’92) • Extend SM gauge symmetry to include B-L- many ways-

19. Two Faces of B-L • Separate B-L vs SO(10) inspired B-L: • For low B-L scale(TeV range), need B-L=2 Higgs to break symmetry to implement seesaw, if no new physics upto Planck scale.

20. TeV Z’ cross section at LHC • LHC Z’ reach - 4 TeV • Cross section for ppZ’NN (Z’NN branching ratio ~20%) 2.5 TeV Z’ to 5 TeV

21. Testing seesaw with Z’ decay • PPZ’+X; xsection for a 3 TeV Z’ ~fb • Seesaw signal: N=Majorana • N l W , Wjj , • Di and Multi-lepton events: (X=jjjj) • Important for signal to bg: very high pT leptons coming from N-decay; inv mass reconstruction: (Del Aguila, Aguilar-Saavedra; Aguilar-Saavedra )

22. TeV scale Resonant leptogenesis with Z’ • Conditions: (i)RH neutrinos must be degenerate in mass; since h >10^-5 degeneracy ok anywhere from ;technically natural and enough for baryogenesis! (ii) Since there are fast processes at that temperature, the net lepton asymmetry and primordial lepton asym are related by where <1 (efficiency factor); depends on rates for Z’ med. scatt. ;inverse decay

23. Details • Finding : (Buchmuller,di Bari Plumacher) • Note: very small, when S >> D- i.e. lighter Z’; • As MZ’ increases, S ~ D, gets bigger and there is a large range where adequate leptogen is possible. • Adequate leptogenesis implies a lower limit on MZ’

24. Questions: • Is the lower limit in the LHC accessible range ? Yes; MZ’ > 2.5 TeV for MZ’ > 2MN • Can LHC directly probe the primordial lepton asymmetry ?

25. Can LHC Directly probe the primordial lepton asym. ? • Since , small efficiency means large ; Search for where is tiny so is order 1. • Detectable at LHC by searching for like sign leptons • (Blanchet, Chacko, Granor, RNM: arXiv:0904.2974) • Basic idea: • At LHC, PPZ’+X • 12.5% of time NNl Xl X • Look for a CP violating observable !

26. Direct probe of resonant leptogenesis, contd. • Direct link between primordial lepton asymmetry and CP violating LHC observable: • For a ranges of Z’-N mass, very small so that ~0.1-1; visible at LHC: • Similarly for tri-lepton events. • Lower bound on MZ’ >2.5 TeV.

27. Numbers • 300 fb^-1, expect 255 dilepton events (85% det eff.) • 90% of events with jets or one missing E. • With no CP violation: 16 ++ and - - events; • Should rule out at 2 sigma level. • An observation will directly probe leptogenesis, if RH mass deg. is inferred from inv mass study. • How to tell how many N’s ? • For one N, there are 5 observables, but only two inputs; we have three relations of type: • For 2 N’s, 4 inputs and 5 observables; only one relation. none for three !

28. How natural is degenerate RH spectrum ? • Degenerate RH neutrino specctrum might look odd since quark and charged lepton masses are very hierarchical: • RH vs Q,L masses: (i) RH nu’s are Majorana masses whereas q, l masses are Dirac; (ii) RH masses arise at different scale and from a different mechanism (B-L breaking) as against the Q, L masses which arise from SM symmetry br. (iii) Already large neutrino mixings are an indication that in the seesaw formula RH neutrinos must have some peculiarity.

29. A model • Gauge group xO(3)H with RH nu’s triplet under O(3)H – all other fermion fields singlet. • Higgs: 1,2 + SM like Higgs. • Seesaw arises from following Yukawa Lagrangian: • Choose will give desired parameters. • Since Dirac Yukawas are ~10^-5, RH neutrino mass splitting is radiatively stable.

30. Left-right embedding • Left-right Model: • Solves SUSY and Strong CP in addition to automatic RP • UnlessMWR > 18 TeV, • L-violating scatterings e.g. willerase lepton asymmetry. (Frere, Hambye and Vertongen) - Sym br. to U(1)I3RxU(1)B-L SM at TeV- to do resonant leptogenesis.

31. Avoiding the WR bound: • If there are heavy vector like D-quarks mixing with d in such a way that the doublet coupling to WR becomes: for D-mass in the 10 TeV range, the dominant process does not occur. We need to avoid the WR bound. • WR can be in the LHC range but the decay modes purely leptonic.

32. Resonant leptogenesis in generic LR model • Key question is whether degenerate RH neutrino spectrum is radiatively stable to have leptogeneesis possible generic LR models !! • Yes- since largest rad correction to RH masses is • Whereas CP asymmetry is: • Which gives for h~10^-5.5, • Not visible from Z’ decay but nonetheless a viable low scale model for leptogenesis and dark matter !!

33. A specific LR model: • LR+extra symmetries: xU(1)xxU(1)Z • Leads to RH mass matrix of form: • Leads to two deg RH nu’s; • Dirac mass matrix: • Leads to realistic nu masses and mixings as well as resonant leptogenesis with tiny sym br. Effects.

34. New collider signals for LR case • Even if WR may be out of reach due to baryogenesis constraints, other exotic Higgs bosons in LHC reach • gets embedded into • Predicts doubly charged Higgs bosons in the sub-TeV mass range coupling to like sign dileptons: • Resonant leptogenesis  dominant modes; • No but allowed.

35. Unification Prospects: An SO(10) possibility • Triplets with B-L=2 hard to unify to SUSY SO(10). • Both for TeV Z’ and WR, unification possible with B-L =1 doublets breaking U(1)B-L; (Deshpande, Keith and Rizzo; 93; Malinsky, Romao, Valle’05);

36. Neutrino masses • Requires double seesaw for neutrino masses: Add an extra singlet field S in addition to left and RH neutrinos which are part of {16}; • Double seesaw:N S) • (RNM’86; RNM,Valle’86) • Important: Unlike type I seesaw, Majorana character of RH N depends on how large is. • Suppresses like sign dileptons at LHC unless ~1. Leptogenesis possible but visible only for ~1.

37. Low scale SUSY LR-an Alternative to MSSM • MSSM: SO(10) Unified SUSYLR 1. Rapid p-decay due to RP breaking 2. Neutrino mass not easy 3. EW baryo in a corner of parameter space. 4. Light Higgs and stop 5. DM gravitino/Neutra lino • 1.No dim4 p-decay due to B-L • 2.Double seesaw for nu mass • Explains Origin of matter • Z’ and like sign dileptons • at LHC • 5. DM gravitino/Neutralino

38. Conclusion: • LHC can directly probe the seesaw mechanism for neutrino masses if the seesaw scale is in the TeV range and there is a TeV scale Z’ regardless of neutrino mass pattern. • For certain ranges of the Z’-N mass, LHC can probe resonant leptogenesis mechanism for the origin of matter directly -find Z’-N in the allowed range simultaneously with large like sign dilepton CP asymmetry. • Use of inv mass peak and large PT leptons to reduce background. • There are left-right and SO(10) SUSY GUT models where such scenarios can be embedded, providing theoretical motivation for low scale Z’ as well as TeV scale leptogenesis .

39. Extra slides • Post-sphaleron baryogenesis and color sextet scalars at LHC.

40. What if RH neutrinos are TeV scale but non-degenerate ? • Can one have seesaw scale around a TeV so LHC can see it and still understand the origin of matter related to seesaw physics ? • Yes- baryogenesis can arise from seesaw related physics below 100 GeV (but not from RH N decay) (post-sphaleron baryogenesis) (Babu, RNM, Nasri’06) • Predicts light color sextet Higgs (< TeV) that can be observed at LHC via decay to two tops.

41. Q-L unify TeV seesaw • SU(2)LxU(1)RxU(1)B-L SU(2)LxU(1)RxSU(4)PS. • Recall Origin of RH nu mass for seesaw is from • Q-L unif. implies quark partners for i.e. - color sextet scalars coupling to up quarks ; similar for dd- only right handed quarks couple. Come from (1, 1, 10) • SU(4)PS breaks toU(1)B-L above 100 TeV

42. Baryon violation graph • + + h. c. • B=2 but no B=1; hence proton is stable but neutron can convert to anti-neutron! • N-N-bar diagram • coupling crucial to get baryogenesis (see later)

43. Origin of matter • (Babu, Nasri, RNM, 2006) • Call Re = Sr ; TeV mass : S-vev generates seesaw and leading to B-violating decays • Baryogenesis: Due to high dimension of operator, B-violating process goes out of eq. below 100 GeV.

44. Upper limits on Sr and color sextet masses: • Two key constraints:  MS < 500-700 GeV to get right amount of baryons. • Decay before QCD phase transition temp: • Implies MS< MX < 2 MS.

45. Two experimental implications: • oscillation:successful baryogenesis implies that color sextets are light (< TeV) (Babu, RNM, Nasri,06; Babu, Dev, RNM’08); arises via the diagram: • Present limit: ILL >10^8 sec. similar bounds from Soudan,S-K etc. • 10^11 sec. reachable with available facilities !! • A collaboration for NNbar search with about 40 members exists-Exploration of various reactor sites under way for a second round search.

46. Color sextet scalars at LHC • Low seesaw scale + baryogenesis requires that sextet scalars must be around or below a TeV: • Two production modes at LHC: (I) Single production: xsection calculated in (RNM, Okada, Yu’07;) resonance peaks above SM background- decay to tt or tj depending on RH nu Majorana coupling; directly measures seesaw parameters. (II) Drell-Yan pair production: ( Chen, Klem, Rentala, Wang, 08) • Leads to final states: LHC reach < TeV

47. Single Sextet production at LHC: Diquark has a baryon number & LHC is ``pp’’ machine  Depends on Yukawa coupling

48. Pair Production of Deltas • Due to color sextet nature, Drell-Yan production reasonable- independent of Yukawa coupling • Leads to final states: • Can be probed upto a TeV using like sign dilepton mode.

49. Phenomenological Aspects Constraints by rare processes mixing Similarly B-B-bar etc. Can generate neutrino masses - satisfying FCNC

50. Details of FCNC constraints: • Hadronic: