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## Neutrino Mass Physics at LHC

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**Neutrino Mass Physics at LHC**R. N. Mohapatra University of Maryland NO-VE, 2008, Venice**Neutrino mass Physics**• Neutrino masses and mixings are now facts: we are entering the era of Precision Neutrino Mass Science (PNMS era) • There is surely a great deal of physics beyond the standard model associated with this. • How can LHC help us to unravel this physics ?**Two broad new kinds of physics for neutrino mass:**• (i) Why ? (new scale, new particles, ..) • (ii) Why two mixing angles are so large ? (new flavor symmetries or GUTs ?)**Small neutrino mass and Seesaw mechanism**• Why ? • Seesaw solution: Add right handed neutrinos to SM with Majorana mass: new • Breaks B-L : New scale, new symmetry and new physics beyond SM. After electroweak symmetry breaking leads to seesaw formula:**Seesaw Mechanism**• After Electroweak Sym Breaking mass matrix is given by • which gives (type I seesaw) • Minkowski,Gell-Mann, Ramond, Slansky,Yanagida,R.N.M.,Senjanovic,Glashow**Seesaw and B-L symmetry**• SM Higgs boson represents physics of the electroweak symmetry breaking and its discovery will complete understanding of SM symmetry. • Seesaw mechanism tells us that there is a new symmetry breaking scale associated with RH neutrino mass:B-L symmetry . This talk discusses how to search for the Higgs fields associated with this symmetry and improve our understanding of B-L symmetry.**Testing the seesaw idea and B-L symmetry.**• Important for testing seesaw are two considerations: (i) How big is the seesaw or B-L scale ? (ii) What is the new physics associated with this new scale ? –are there new forces, new Higgs fields, etc ?**Seesaw with no new forces at LHC**• If there is no new interaction: Only way to test seesaw is to produce N; This can happen only through mixing if is in sub-TeV range and further only if mixing is > (del Aguila,Aguilar-Savedra, Pittau; Han, Zhang…) – However • Tiny and 100 GeV implies and ; can only be large under highly contrived cases:(Kersten, Smirnov) ; Unlikely to test seesaw this way!**Situation changes drastically with new interactions:**• With new gauge forces coupled to RH neutrinos, seesaw can be tested despite tiny ; • A simple possibility is where there is a B-L gauge force coupling to matter as part of an gauge symmetry. RH neutrino mass in this case is associated with the breaking of this new symmetry . • This provides new signals for seesaw at LHC.**Two well motivated scenarios:**• (i) Large • Grand unification is an independently well motivated hypothesis which suggests for Yukawa coupings: implying GeV • Gauge coupling unification scale • High scale seesaw goes well with GUT s; e.g. SO(10). • However in this case, few signals of seesaw: • One direct test is search for assuming susy ! • GUTs have problems too: doublet triplet splitting; vs**Lower scale non-GUT type seesaw: Subject of this talk:**• (ii) Small Yukawas: • Note the dependence of in the seesaw formula compared to linear on for ; so not too small Yukawas can lead to e.g. Implies seesaw or B-L physics scale in few TeV range. • In general scale far below GUT scale- • Simple example is - low scale left-right model.**SUSY LR attractive for other reasons:**• Supersymmetric left-right model: • (i) Expialns the origin of parity violation: • (ii) Solves gauge hierarchy problem (as in MSSM); • (iii) Gives automatic R-parity (unlike MSSM) and hence natural neutralino dark matter and naturally stable proton. • (iv) Solves susy CP and strong CP problem (unlike MSSM). • (v) Helps in understanding a supersymmetry breaking mechanism (unlike MSSM).**SUSYLR DETAILS:**• Gauge group: • Fermion assignment • Higgs fields (R.N.M., Senjanovic, 79)**Detailed Higgs content and Sym Breaking**Break symmetry and give fermion masses**SUSY essential for lower scale left-right seesaw**Without SUSY neutrino mass too large since v_L~GeV. (type I+II seesaw) , SUSY implies ; (pure type I seesaw) nu-mass in the eV range even for TeV seesaw.**SUSY breaking constraints and sub-TeV - Higgs**• An important question in supersymmetry is: how is supersymmetry broken ? • Scenarios: (i) Minimal Supergravity: FCNC problem (ii) Gauge mediation (needs many particles, does not have cold dark matter etc.) (iii) Anomaly mediation: (potential to solve both these problems.)(Randall, Sundrum; Giudice, Luty, Murayama, Rattazzi) • Consistency of case iii with electric charge conservation requires sub-TeV - Higgs**Two cases with LHC signal**• (i) Multi-TeV scale WR: In this case, Sub-TeV to TeV scale WR, Z’, which can be searched for in colliders: • (ii) Higher scale B-L (or WR): New result: If , one will have in the sub-TeV range and observable. • Searching for Higgses can probe B-L scale upto .**TeV mass WR case:(A): Direct production at LHC**• Looking for TeV scaleat LHC : Signal: Very little background; already used in D0, CDF ; Present limits: 780 GeV (Keung, Senjanovic, 83) (Does not depend on ) LHC reach 4 TeV (Azuelos et al)**(B):Neutrinoless double beta decay**• TeV scale WR contributes to nu-less double decay regardless of how small nu- Majorana mass mass is . • (P. Vogel’s talk) • Dependence on WR mass is M^-5 – Present bound is ~1 TeV can go up to2 TeV.**(C): New Relaxed Upper bound on light Higgs mass**• MSSM: Light Higgs mass: GeV • For Low scale WR, new contribution from D-term+ 1-loop • Zhang,RNM,Ji,An arXiv:0804.0268**TeV and Higher scale Seesaw and Higgs**• A generic prediction of all these models: doubly charged Higgs and Higgsinos, triplet Higgses ( , )in the TeV range – without fine tuning. • Different from triplet Higgs of type II seesaw models discussed inPerez,Han, Huang, Wang,Li, Si, Akeroyd,Aoki, Sugiyama; …… • Different from usual SUSY modelswhich only have neutral and singly charged Higgs**Doubly charged Higgs:**• Very different from known Higgs in that it couples only to leptons and not to quarks: Coupling not small. • One coupling to left and another to the right sector: • Both decay to lepton pairs (from coupling) • For left Delta,**Difference from type II models**• In type II models, it is only the triplet that is present; its coupling f to leptons depends on the < >=v since • So only for eV vev for f is measurable; • Pro: it tracks neutrino mass matrices; Measuring different branching ratios gives neutrino mass matrix • Con: such small vevs come out naturally only if triplets are superheavy and beyond the reach of LHC. One needs to do a severe fine tuning (~ ) • The models I discuss are not fine tuned:**Difference of type II models from type I:**• Type II: decays: • Whereas for type I models we discuss:**Present lower bounds on doubly charged Higgs mass:**• Drell-Yan pair production main mechanism at hadron colliders: Signal: pp --> or all muon • Collider:CDF, D0: GeV • HERA > 141 GeV • Low energy: Muonium-anti-muonium osc. (PSI) • For , M++ >250 GeV. • g-2 of muon: 100 GeV order.**Production process:**• Drell-Yan via exchange; • Signal: peak in like sign lepton invariant mass plot for double charged case; • trilepton + missing E in case.**LHC prospects:**• Gunion, Loomis and Petit; Akyroid, Aoki; Azuelos et al., Mukhopadhyaya,Han,Wang,Si; Huitu,Malaampi,Raidal; Dutta.. Main BgZZ production: LHC Mass Reach ~TeV with 300 fb^-1.**Doubly charged Higgs and muonium-antimuonium Osc.:**• Muonium-anti-muonium can provide better probe for some models: • If SUSY is broken by anomalies: • and also M < 10 TeV. • Lower limit on • PRISM expt. Reach:**Doubly charged Higgs atCollider**• collider at 1 TeV cm E can probedoubly charged Higgs upto 900 GeV mass. (Mukhopadhyay, S. Rai) • The relevant processes:**Singly charged signal**• Properties of singly chargeddifferent from MSSM singly charged • couples only to leptons- has L=2 • Present bound on mass comes from wrong kind of muon decay: • and nuTeV expt looking for**Bounds on**• NuTeV bound(Formaggio et al, 2001) • Mass bound in 100 GeV range for reasonable values of f-couplings. • New proposal NUSONG expt (Conrad et al. 2007) will improve this limit by a factor of 4 .**AT LHC**• LHC signal: • pp + missing E • K. Wang et al.**Why are naturally light even for high scale seesaw ?**• (i) If LR scale is less than few TeV , clearly these Higgs can have in the sub-TeV mass. • (ii) For higher scale seesaw accidental global symmetry leads to sub-TeV as long as or less. (iii) If SUSY is broken by anomaly mediation, these fields with sub-TeV to TeV masses become essential to avoid electric charge non-conservation. Strongest case for light .**Basic point is the constraint of supersymmetry:**• SM • Minimum corresponds to: • Conserves electric charge. Higgs mass prop to and hence Higgs mass arbitrary. • Bring in Supersymmetry: and hence an upper limit on Higgs mass <130 GeV. • For SUSYLR seesaw models, SUSY constrains the Higgs potential so much that • Necessary consequence is light below 10 TeV . Otherwise, electric charge broken by vacuum.**Light Higgs for High seesaw scale**• Naïve logic: Higgs mass is of the order of symmetry breaking scale; breaks down when there are accidental symmetries. • SUSYLR superpotential: • Has U(6,c) global symmetry which breaks down to U(5,c) (in the absence of higher dim term.) • eleven massless complex Higgs bosons: 3 absorbed in gauge sym. breaking from SU(2)xU(1) to U(1). Eight left are two doubly charged Higgs bosons and two SM triplets;**How do get masses ?**• The nonrenormalizable term • Where could be the new physics scale above WR scale or Planck scale. • Breaks this enhanced global symmetry and give mass to fields. • Mass is of order: ; • implying for Delta mass sub-TeV.(Aulakh, Melfo, Senjanovic; Chacko, RNM, 97) • Observation of probes seesaw scale far below GUT scale.**Anomaly mediation and light**Squark and slepton masses in AMSB: • So for the case of MSSM+AMSB, slepton mass squares negative-vacuum breaks electric charge:**Slepton masses in SUSYLR +AMSB**Where f is the Yukawa coupling and g is the generic gauge coupling: slepton masses become positive if SUSYLR cures the tachyonic slepton problem of AMSB without fine tuning assumptions: (Setzer, Spinner, RNM, Phys. Rev. D and arXiv:0802.1208- JHEP )**Limit on Higgs mass, couplings from detailed study:**• For AMSB cure to work, we must have • (i) • (ii) ;also triplets. • This implies • Prism proposal:**Summary and Conclusion:**• Minimal SUSY seesaw in conjunction with a way to understand SUSY breaking (AMSB) predicts the existence of sub-TeV • They can be observable in LHC as well as in muonium-anti-muonium oscillation experiments. In particular it predicts: • Search for Delta Higgses can probe seesaw below**Summary and Conclusion:**• (i) < few TeVs or • (ii) >GeV ; • (iii) If SUSY is broken by anomaly mediation, then • GeV • (iii) In these models, there are 100 GeV to TeV scale SU(2)-triplet and doubly charged Higgs fields. • (iv) Case (i)- Upward shift of light Higgs mass**Range of Double charged Higgs masses**• Upper limit for AMSB to work: • Lower limit on muonium-anti-muonium oscillation amplitude for this model (PSI) • Higher precision search for important. • TeV scale WR models have many collider tests: e.g. Higher Higgs mass, like sign dilepton events and of course sub-TeV scale doubly charged Higgs**Dark matter issue:**• Neutralino unstable ! • Butgravitino though unstable due to R-P breaking but still quite long lived to be dark matter: • Decay diagram: • Longer than the age of the universe ! (Ibarra, etal)**Displaced vertices:**• Neutralino decays but with a nano to pico sec. lifetime; hence leads to displaced vertices: • (Zhang, Nussinov, et al. to appear)**Constraints on WR in SUSYLR : Theory details**• Higgs superfields break SU(2)_R • V=V_F+V_D+V_S (V_F,V_D >0) • Look for minimum of the potential**What is the smallest value of the D-term ?**• When is =0 • Since in general • If RP conserved i.e. • V is minimum when V_D vanishes and that occurs when: • since • But this breaks electric charge !**Charge conservation-> RP violation**So only choice left to get a charge conserving minimum is when • It breaks R-parity and Lepton number but not Baryon number. So proton stability is guaranteed. • Corollary: Seesaw scale has an upper limit of a few TeV. • (Kuchimanchi, RNM, 95)**Why GeV ?**• As the seesaw scale increases, higher dim terms in superpotential become important : restore R-parity and give a stable charge conserving vacuum: • Typically, they are (if no new physics till Planck-otherwise replace by new Phys scale) • + • Lower limit on WR when above terms are of order weak scale i.e. >**How do they get masses ?**• The second nonrenormalizable term breaks this enhanced global symmetry and give mass tofields. • Mass is of order: ; LEP bound then implies • GeV implying v_R • (Aulakh, Melfo, Senjanovic; Chacko, RNM, 97)