LHC Higgs less Higgs or more Higgs John
- Slides: 39
LHC: Higgs, less Higgs, or more Higgs? John Ellis, King’s College London (& CERN)
Has the Higgs been Excluded? Interesting hints around Mh = 125 Ge. V ? ATLAS excludes < 122. 5, > 129, < 539 Ge. V CMS excludes > 127. 5, < 600 Ge. V
Has the Higgs been Discovered? Interesting hints around Mh = 125 Ge. V ? CMS prefers < 125 Ge. V ATLAS prefers > 125 Ge. V
Unofficial Combination of Higgs Search Data from March 7 th Is this the Higgs Boson? No Higgs here!
The Particle Higgsaw Puzzle Is LHC finding the missing piece? Is it the right shape? Is it the right size?
Do we already know the ‘Higgs’ has Spin Zero ? • Decays into γγ, so cannot have spin 1 • 0 or 2? • If it decays into ττ or b-bar: spin 0 or 1 or orbital angular momentum • Can diagnose spin via – angular distribution of γγ – angular correlations of leptons in WW, ZZ decays • Does selection of WW events mean spin 2?
Does the ‘Higgs’ have Spin Zero ? • Polar angle distribution: • Azimuthal angle X 2 γγ distribution: X 0 WW (flat for X 0) JE, Hwang: ar. Xiv: 1202. 6660 (flat for X 2)
Does the ‘Higgs’ have Spin Zero ? • Polar angle distribution for X 2 W+W • Polar angle distribution for X 0 W+W(for φ = π) JE, Hwang: ar. Xiv: 1202. 6660
Measuring Higgs Couplings @ LHC Current LHC hint @ Mh = 125 Ge. V
Flavour-Changing Couplings? • Upper limits from FCNC, EDMs, … • Quark FCNC bounds exclude observability of quark-flavour-violating h decays • Lepton-flavour-violating h decays could be large: BR(τμ) or BR(τe) could be O(10)% B Blankenburg, JE, Isidori: ar. Xiv: 1202. 5704 BR(μe) must be < 2 ✕ 10 -5
STANDARD MODE John Ellis, King’s College London (& CERN)
There be New Physics vi. Xramust Blogger’s Combination March 7 th Data Model Beyondofthe Standard Higgs potential collapses Higgs coupling less than in Standard Model Precision Electroweak data? ? Higgs coupling blows up!!
Estimates of m. H from different Measurements Spread looks natural: no significant disagreement
Heretical Interpretation of EW Data Do all the data tell the same story? e. g. , AL vs AH Chanowitz What attitude towards LEP, Nu. Te. V? What most of us think
Elementary Higgs or Composite? • Higgs field: <0|H|0> ≠ 0 • Quantum loop problems • Fermion-antifermion condensate • Just like QCD, BCS superconductivity Cutoff Λ = 10 Te. V • Top-antitop condensate? needed mt > 200 Ge. V Cut-off Λ ~ 1 Te. V with Supersymmetry? New technicolour force? - Heavy scalar resonance? - Inconsistent with precision electroweak data?
Interpolating Models • Combination of Higgs boson and vector ρ • Two main parameters: mρ and coupling gρ • Equivalently ratio weak/strong scale: gρ / mρ Grojean, Giudice, Pomarol, Rattazzi
Sum Rule for More or Less Higgs Models • What if Higgs-V-V couplings differ from SM? • Unitarity imposes sum rule on scattering in different isospin channels: • If Higgs coupling > Standard Model (a 2 > 1), must have non-zero scattering with I = 2 Fialkowski, Rychkov, Urban: ar. Xiv: 1202. 1532
Higgs as a Pseudo -Goldstone Boson ‘Little Higgs’ models (breakdown of larger symmetry) Loop cancellation mechanism Little Higgs Supersymmetry
Examples of Higgs as Pseudo-Goldstone Boson • Parameterization of effective Lagrangian: • Examples: • To be measured!
What if the Higgs is not quite a Higgs? • Tree-level Higgs couplings ~ masses – Coefficient ~ 1/v • Couplings ~ dilaton of scale invariance • Broken by Higgs mass term –μ 2, anomalies – Cannot remove μ 2 (Coleman-Weinberg) – Anomalies give couplings to γγ, gg • Generalize to pseudo-dilaton of new (nearly) conformal strongly-interacting sector • Pseudo-Goldstone boson of scale symmetry
Effective Lagrangian Framework • • Standard Model Higgs sector = linear σ model Replace by nonlinear chiral Lagrangian Assume ~ scale (conformal) symmetry Realized via (pseudo-)dilaton field χ JE 1970 • Effective χ potential à la Coleman-Weinberg, with small coefficient B: • Large <0|χ|0> = V >> electroweak scale v
A Phenomenological Profile of a Pseudo-Dilaton • Universal suppression of couplings to Standard Model particles: a = c = v/V • Effective potential: • Self-couplings: Compilation Updated of with constraints Dec. 11 constraints • Γ(gg) may be enhanced • Γ(γγ) may be suppressed Pseudo-baryons as dark matter? Campbell, JE, Olive: ar. Xiv: 1111. 4495
General Analysis of ‘Less Higgs’ Models • Parameterization of effective Lagrangian: • Fits a≠c Azatov, Contino, Galloway: ar. Xiv: 1202. 3415 Espinosa, Grojean, Muhlleitner, Trott: ar. Xiv: 1202. 3697
Analysis of ‘Less Higgs’ Models • Rescale couplings: to bosons by a to fermions by c • Standard Model: a=c=1 JE & Tevong You
Electroweak Pseudo-Baryons • Chiral Lagrangian has soliton solutions whenever higher-order term present (generic): • Have non-zero topological quantum number • B is integer, can be identified with baryon # • Underlying SU(N) gauge theory: bosons (fermions) with I = J = 0 (1/2) if N even (odd) – SO(N) gauge theory: B is Z 2 quantum number – Sp(N) gauge theory: baryons decay to mesons Campbell, JE, Olive: ar. Xiv: 1111. 4495
Behaviour at Finite Temperature • Corrections to nonlinear effective theory: • Correction to effective dilaton potential: • Critical temperature when equal free energies • More degrees of freedom in confined phase: Campbell, JE, Olive: ar. Xiv: 1111. 4495
Cosmological Phase Transition • Critical temperature with <0|χ|0> ~ V: • But supercooling to nucleation temperature: • First-order phase transition • Percolation ~ immediate • Short phase of non-adiabatic expansion Campbell, JE, Olive: ar. Xiv: 1111. 4495
Evolution of the Universe • Universe supercoools • Expansion briefly dominated by field energy • Growth in entropy by factor ~ 7 to 200 • Identify confinement, appearance of electroweak ‘baryons’ with transition to <0|χ|0> ≠ 0 Campbell, JE, Olive: ar. Xiv: 1111. 4495
Baryon-to-Entropy Ratio • ‘Kibble’ estimate would be large • But thermal equilibrium thought to be restored • Expect smaller density: : freeze-out • Density smaller than required for cold dark matter: • Need electroweak ‘pseudo-baryon’ asymmetry Campbell, JE, Olive: ar. Xiv: 1111. 4495
Electroweak baryons ? Can we look for them with the LHC?
Electroweak Baryons as Dark Matter • Fermions with I = J = ½? • Expect mass of charged partner > neutral: • Estimate mass difference ~ Ge. V – β-decay lifetime ~ 10 -11 sec – thermal equilibrium down to T ~ Me. V – Small abundance of charged state • BUT some might be trapped in stable charged ‘pseudo-nuclei’ ✕ experiment Campbell, JE, Olive: ar. Xiv: 1111. 4495
Pseudo-Baryonic Dark Matter? • No problem if I = J = 0 bosons • Estimate scattering cross section: where: with • Within range of future experiments Campbell, JE, Olive: ar. Xiv: 1111. 4495 Dark mattter Scattering rate
Classic Supersymmetric Signature Missing transverse energy carried away by dark matter particles
Limits on Heavy MSSM Higgses
Gluino mass --- pre-Higgs ___ Higgs @ 125 … H@125, no g-2 Buchmueller, JE et al: ar. Xiv: 1112. 3564 Favoured values of gluino mass significantly above pre-LHC, > 2 Te. V
The Stakes in the Higgs Search • How is gauge symmetry broken? • Is there any elementary scalar field? • Would have caused phase transition in the Universe when it was about 10 -12 seconds old • May have generated then the matter in the Universe: electroweak baryogenesis • A related inflaton might have expanded the Universe when it was about 10 -35 seconds old • Contributes to today’s dark energy: 1060 too much!
Conversation with Mrs Thatcher: 1982 What do you do? Think of things for the experiments to look for, and hope they find something different Then we would not learn anything! Wouldn’t it be better if they found what you predicted?
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