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Precise predictions for a light Higgs

Precise predictions for a light Higgs. Giuseppe Degrassi Università di Roma Tre I.N.F.N. Sezione di Roma III. SUSY 2005 The Millennium Window to Particle Physics Durham 18-23 July 2005. Summary. The nineties legacy: a light Higgs.

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Precise predictions for a light Higgs

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  1. Precisepredictionsfor a light Higgs Giuseppe Degrassi Università di Roma Tre I.N.F.N. Sezione di Roma III SUSY 2005 The Millennium Window to Particle Physics Durham 18-23 July 2005

  2. Summary The nineties legacy: a light Higgs. How solid is the evidence for a light Higgs? • Recent SUSY results for a light Higgs on: • Mass determination • Production Conclusions

  3. The LEP legacy SM Higgs: HZZ coupling = gMZ l with l = 1/cw

  4. A strong hint for a light Higgs 60%

  5. Swinging top Tevatron: Run I Run I Run I-II (prel. 99) (fin. 04) (prel. 05) Light Higgs indication reenforced: 95% C.L. 285 210 GeV Old considerations are back SM fit is OK (c2/d.of. =18.6/13) it will improve if hadronic asymmetries are excluded pushed down, (depend on )

  6. ) ( Most sensitive observable , To increase the fitted : (smaller ) Is an heavy Higgs ruled out? NO,but we need new physics of a particular kind that can compensate for the heavy Higgs

  7. SM as an effective theory: linear realization of SU(2)xU(1) Buchmuller, Wyler (86); Hall, Kolda (99); Barbieri, Strumia (99); Han, Skiba (04) dimension 6 that can relax the Higgs bound: The other dimension 6 operators should be suppressed! WHY?

  8. cutoff is (TeV) only if K <0 No Higgs scenario: non linear realization of SU(2)xU(1) Kniehl, Sirlin (99); Bagger, Falk, Swartz (99) Theory is not renormalizable; cutoff It is not easy to find models that give K<0

  9. Mechanism of EWSB with a light Higgs are clearly • favored. • The success of the SM fit places strong constraint • on new physics. • New physics of the decoupling type ( ) avoids • “naturally” ( ) the SM fit constraints (SMFC). • Non decoupling physics can exist, i.e. effects that do • not vanish as . However it needs same • “conspiracy” to pass the SMFC. What we learnt from the nineties

  10. Supersymmetry • Is a NP of the decoupling type. • No problem with the SMFC. • Predicts the quartic Higgs coupling. • A light Higgs must be in the spectrum. • Favors the gauge coupling unification. • Has a dark matter candidate. • It has to be broken. Å

  11. Higgs sector of the MSSM Two SU(2)xU(1) doublets: Higgs potential: responsible for EWSB

  12. Tree-level mass matrix for the CP-even sector: exploiting the minimization condition for can be expressed in terms of Spectrum: five physical states. neutral CP-even neutral CP-odd charged decoupling limit: ;

  13. Radiative corrections to the MSSM Higgs sector ruled out by LEP! Quantum corrections push above . = effective potential approximation = external momentum contributions solutions of

  14. SUSY breaking -> incomplete cancellation between loop of particle and susy partners. Main effect: top and stop loops One-loop corrections to : • scale as ; • depend upon • have a logarithmic sensitivity to the stop masses. Large tan b scenario: Okada, Yamaguchi, Yanagida (91); Ellis, Ridolfi, Zwirner (91); Haber, Hempfling (91); Chankowski et al. (92); Brignole (92)......... completely known

  15. band: 1s error on and . tan b= 50 tan b=1.5 Beyond one-loop: Split SUSY Around TEV spectrum: SM + gauginos + higgsinos. Sfermions are very heavy. Mixing is unimportant No bottom corrections. The logarithmic correction is very large. It has to be resummed via Split-RGE. Gauge effects can be relevant. Barbieri, Frigeni, Caravaglios (91); Okada, Yamaguchi, Yanagida (91); Carena et al. (95-96, SubHPole).... (courtesy of A. Romanino)

  16. same accuracy for the minimization condition Dedes, Slavich (03); Dedes, Slavich, GD (03) Beyond one-loop: MSSM ; Two-loop: mixing can be important. Full calculation is relevant. : dominant contributions known (strong and Yukawa corrections to the one-loop top/bottom term). , , , Heinemeyer, Hollik, Weiglein (98); Espinosa, Zhang (00); Slavich, Zwirner, GD (01) Espinosa, Zhang (00); Brignole, Slavich, Zwirner, GD (02) Dedes, Slavich, GD (03) Brignole, Slavich, Zwirner, GD (02); Heinemeyer, Hollik, Rzehak, Weiglein (05) • Important issues: • scheme-dependence of the input parameters; • , large tan b corrections.

  17. Effect of the two-loop corrections Top Bottom

  18. Bottom corrections should be treated with same care in the OS scheme because of large tan b effects. Same renormalization condition of the top-stop sector gives a counterterm contribution that blows up for large tan b from Heinemeyer, Hollik, Rzehak, Weiglein EPJC 39 (2005) 465

  19. Several public computer codes that include all dominant two-loop corrections. Codes employ input parameters defined in different renormalization scheme (OS, ) • OS • FeynHiggs 2.2 (Heinemeyer, Hollik, Weiglein, Hahn) • DR (possibility of input parameters via RG evolution from a set of • high-energy boundary conditions) • SoftSusy 1.9 (Allanach) • SPheno 2.2 (Porod) • Suspect 2.3 (Djoudi, Kneur, Moultaka) DR Scale and scheme dependence estimate of higher order effects Estimate of higher order corrections

  20. Scale dependence in DR fromAllanach et al. JHEP09 (2004) 044 8-10 GeV 1-3 GeV

  21. Scheme dependence fromAllanach et al. JHEP09 (2004) 044

  22. Towards a complete two-loop calculation • The presently available public codes do not include: • electroweak contributions in • Recent progress:(S.P. Martin (02-05)) • complete two-loop (Landau gauge, DR scheme) • complete two-loop • Strong and Yukawa corrections in

  23. from Martin PRD71 (2005) 016012 from Martin PRD67 (2002) 095012 Momentum dependent effects Two-loop electroweak corrections

  24. two-loop electroweak two-loop momentum-dependent leading three-loop corrections Martin’s results are not implemented in the 4 public computer codes.

  25. Bound on Bound depends on and on the chosen range of the SUSY parameter. Fix • assuming relations among the parameters dictated • by an underline theory of SUSY breaking • (mSUGRA, GMSB, AMSB) • scanning in a • “reasonable” region of • the parameter space fromAllanach et al. JHEP09 (2004) 044

  26. Light Higgs decays Split SUSY: viable MSSM: residual

  27. gg h largest and best known process Light Higgs production SM: QCD at NNLO Djouadi, Graudens, Spiras, Zerwas (91-95); Harlander, Kilgore (01-02); Catani, de Florian, M. Grazzini (01) Anastasiou, Melnikov (02); Ravindran, Smith, van Neerven (03) EW at NLO Aglietti, Bonciani,Vicini, GD (04) Maltoni, GD (04)

  28. MSSM: possible negative interference between top and stops Djouadi (98) SUSY-QCD at NLO from Djouadi hep-ph-0503173 Harlander, Steinhauser (04) from Harlander, Steinhauser JHEP09 (2004) 066

  29. Conclusions • New value of the top mass strengthens the indication • for a light Higgs • (but a heavy Higgs is not ruled out, although it needs • some “conspiracy” to survive) • The determination of the mass of the light neutral • Higgs in the MSSM has become very precise • A Split SUSY Higgs can be detected via • h W W* • The gluon fusion production cross-section is now • available at the NLO in the SUSY contribution.

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