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

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.)

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 ? Nuclear Reactions responsible: Things would have been different if there was anti-matter…

Matter Amount Detailed analysis

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

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).

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: )

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 M R =0, (too small) whereas even with TeV M R, (more reasonable) Minkowski; Gell-Mann, Ramond Slansky,Yanagida, R.N.M.,Senjanovic,Glashow B-L breaking crucial to seesaw:

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.

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

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,

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: degenerate N’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)

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 T R >10^9 GeV. If unstable, Once produced they live too long -affect BBN.. (Kohri et al.) Possible tension between LFV and leptogen.

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

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 !

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-

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.

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-

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.

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

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 )

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

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

Questions: Is the lower limit in the LHC accessible range ? Yes; M Z’ > 2.5 TeV for M Z’ > 2M N Can LHC directly probe the primordial lepton asymmetry ?

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: ) Basic idea: At LHC, PP  Z’+X 12.5% of time NN  l Xl X Look for a CP violating observable !

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 M Z’ >2.5 TeV.

Numbers 300 fb^-1, expect 255 dilepton events (85% det eff.) 90% of events with jets or one missing E. With no CP violation: 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 !

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.

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.

Left-right embedding Left-right Model: Solves SUSY and Strong CP in addition to automatic RP Unless M W R > 18 TeV, L-violating scatterings e.g. will erase lepton asymmetry. (Frere, Hambye and Vertongen) - Sym br. to U(1) I3R xU(1) B-L  SM at TeV- to do resonant leptogenesis.

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.

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 !!

A specific LR model: LR+extra symmetries: xU(1) x xU(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.

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.

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);

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.

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 3. Explains Origin of matter 4.Z’ and like sign dileptons at LHC 5. DM gravitino/Neutralino

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.

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

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.

Q-L unify TeV seesaw SU(2) L xU(1) R xU(1) B-L SU(2) L xU(1) R xSU(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 to U(1) B-L above 100 TeV

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)

Origin of matter (Babu, Nasri, RNM, 2006) Call Re = S r ; 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.

Upper limits on S r and color sextet masses: Two key constraints:  M S < GeV to get right amount of baryons. Decay before QCD phase transition temp: Implies M S < M X < 2 M S.

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.

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

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

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.

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

Details of FCNC constraints: Hadronic:

Examples of color sextet couplings that work. Down sector: Fits neutrino mass via type I seesaw.

Collider signal with WR Depends on mass of WR; for WR in the few TeV range, N-decay profile changes: No WR case: With WR (TeV) No missing E in second case; Trilepton signal very sub-dominant.