High Energy Physics has established that all known natural phenomena can be described by a Beyond the Standard Model local quantum field theory which is invariant under: 3+1 dimensional Lorentz transformations SO(3, 1) and translations • Bogdan Dobrescu (Fermilab) SU(3) SU(2) U(1) gauge transformations • C × W × Y = all elementary particles belong to certain Outline: ⇒ representations of the Lorentz and gauge groups: Electroweak symmetry breaking (Lecture 1) • Spin-1 bosons Spin-1/2 fermions Quark and lepton masses; vectorlike quarks (Lecture 2) • New gauge bosons (Lecture 3) qL :(3, 2, +1/6) • Gµ :(8, 1, 0) u :(3, 1, +2/3) R WIMPs and cascade decays (Lecture 4) W µ :(1, 3, 0) 3 d :(3, 1, 1/3) • × R − Bµ :(1, 1, 0) l :(1, 2, 1/2) How to search for new phenomena (Lecture 5) L − • eR :(1, 1, 1) − September 2011 - European School of HEP Spin-2: graviton Dark matter particle (spin =?) . 1.1 . Electroweak symmetry breaking High Energy Physics has established that all known natural phenomena can be described by a We know that SU(2) U(1) U(1) local quantum field theory which is invariant under: W × Y → Q 3+1 dimensional Lorentz transformations SO(3, 1) and translations W and Z have not only transverse polarizations, • ⇒ ± SU(3) SU(2) U(1) gauge transformations • C × W × Y but also longitudinal ones: three spin-0 states have = all elementary particles belong to certain been eaten. ⇒ representations of the Lorentz and gauge groups: What is the origin of EWSB? Spin-1 bosons Spin-1/2 fermions We don’t know: qL :(3, 2, +1/6) µ + G :(8, 1, 0) uR :(3, 1, +2/3) what unitarizes W W scattering? µ L L− W :(1, 3, 0) 3 dR :(3, 1, 1/3) • µ × − B :(1, 1, 0) lL :(1, 2, 1/2) e :(1, 1, −1) why is there a VEV that breaks SU(2) U(1) ? R − • × what has a VEV that breaks SU(2) U(1) ? Spin-2: graviton Dark matter particle (spin =?) • × . 1.4 Electroweak symmetry breaking + WL WL− scattering: We know that SU(2) U(1) U(1) W × Y → Q W and Z have not only transverse polarizations, ⇒ ± 2 but also longitudinal ones: three spin-0 states have Perturbatively: + + GF s σ W W − W W − L L → L L ≈ 16π been eaten. % & This makes sense only up to √s 1 TeV (see Lecture 5 of E. Dudas). ∼ What is the origin of EWSB? At higher energy scales: We don’t know: # A new particle: Higgs boson + what unitarizes W W − scattering? • L L OR # New strong interactions (perturbative expansion breaks down) why is there a VEV that breaks SU(2) U(1) ? • × OR what has a VEV that breaks SU(2) U(1) ? • × # Quantum field theory description breaks down . 1.5 . 1.6 Alternative to Higgs boson: spin-1 particles (ρT ) coupled to WW. Homework 1.1 Unitarity in WW scattering may be restored by ρT exchange. Draw the Feynman diagrams for WW WW and WZ WZ in → → However, ρT ρT and ρT W scattering are then non-unitary, unless the standard model which are relevant in the M M limit. h ( W some other particles exist. Devise experimental searches for the Higgs boson using thesepro- cesses. a whole tower of heavy particles is needed .... it sounds like → QCD, but at a scale 103 higher! Hint: the LHC is not only a gg or gq or qq collider, but also a WW and a WZ collider! “Technicolor”: a new gauge interaction which becomes strong at the TeV scale. Techni-fermion condensate breaks electroweak symmetry (same . 1.7 as chiral symmetry breaking in QCD). ρT is the techni-rho. 1.8 Searches for the standard-model Higgs boson: Technicolor has problems with the fits to the electroweak ob- SM ATLAS Preliminary CLs Limits ! / servables. However, strongly coupled field theories are poorly ! Observed Expected understood, so it is hard to make precise predictions. Ldt = 1.0-2.3 fb-1 10 ± 1 ! " ± 2 ! s = 7 TeV 95% CL Limit on on Limit CL 95% Another example of spin-1 particles that unitarize WW scatter- 1 ing: Kaluza-Klein modes in a model with one extra dimension where the electroweak symmetry is broken by boundary condi- -1 10 200 300 400 500 600 tions: mH [GeV] ”Higgsless models” Csaki, Grojean, Pilo, Terning: hep-ph/0308038 Tevatron Run II Preliminary, L # 8.6 fb-1 LEP Exclusion Tevatron lightest spin-1 resonances around 1.2 TeV 10 Exclusion Expected → Observed ±1! Expected ±2! Expected Room for SM Higgs boson has shrank dramatically this 1.9 95% CL Limit/SM . 1 summer! SM=1 1.10 . Tevatron Exclusion July 17, 2011 100 110 120 130 140 150 160 170 180 190 200 2 mH(GeV/c ) Hidding the Higgs boson Hidding the Higgs boson SM gluon fusion SM gluon fusion non-standard production ± g . ? h0 ? g g t t g ? h0 h0 t t g ? t t g g h0 g ? The cross section for gluon fusion may be reduced, but only if there are new colored particles at the electroweak scale. 1.12 SM Exp. Obs. Exp. Obs. Nonstandard Higgs decays: a case study ! -1 -1 -1 -1 / H% $$ H (1.08% $$ (1.08 fb ) fb ) H% ZZH% ZZ llll% (1.96-2.28llll (1.96-2.28 fb fb) ) -1 -1 -1 -1 ! H% WWH%% WW l&%l& l & (1.70l& (1.70 fb fb) ) H% ZZH% ZZ llqq% llqq (1.04 (1.04 fb fb) ) -1 -1 W/Z H,W/Z H %H, Hbb % bb(1.04 (1.04 fb -1fb) ) H% ZZH% ZZ ll&%& ll (1.04&& (1.04 fb-1 fb) ) -1 -1 H% '' H %(1.06'' (1.06 fb )fb ) Standard model + a scalar singlet S: cH†HS†S 1 iA0/ S 0 10 S = (ϕS + S ) e ) * , A is a CP-odd spin-0 particle (axion) √2 ) * 1/2 cv c2 v2 M 2 95% CL limit on h0A0A0 coupling Γ(h0 A0A0)= 1 4 A ⇒ → − 2 2 32πMh ' Mh ( 1 -1 ATLAS Preliminary " L dt ~ 1.0-2.3 fb , s=7 TeV CLs limits 100 200 300 400 500 600 Dobrescu, Landsberg, Matchev, hep-ph/0005308 mH [GeV] Homework 1.2: What other channels can be used? . 1.14 . 1.13 0 B(A γγ) 3 If χ is both colored and electrically charged: → 10− . The subsequent decays of A0 are model dependent. B(A0 gg) ≈ → h A0A0 (γγ)(jj) may be the most interesting decay, with → → Example: = ξSχLχR +h.c. V (H, S) , χ is a new fermion the diphoton and dijet peaks having same mass. (Chang, Fox, Weiner, L − hep-ph/0608310, ... ) γ γ (g) χ g y 0 A0 A χ h0 γ χ y γ (g) g A0 g y g Effective coupling of the axion to pairs of gluons and photons: √ 2 0 µνρσ 2 − A ) T2(χ)αs GµνGρσ + Nce α FµνFρσ Homework 1.3: 16π S χ ) * ) * Draw the Feynman diagrams for pp Wh W γγjj. → → Roughly estimate the LHC cross section for this signal and identify the . 1.15 main backgrounds. (Hint: see A. Martin, hep-ph/0703247) . 1.16 Hierarchy problem For a light A0, this may appear in the detector as h A0A0 (γγ)j or h A0A0 “γ” j. → → → → Quantum fluctuations tend to increase the γ g 0 h0 0 A A vacuum expectation value of the Higgs field. γ g h, W Homework 1.4: t '$ h '$ h hh Estimate MA such that: a) the jets overlap; b) the photons overlap. &% &% (assume Mh =120GeV) Stability of the electroweak scale requires a modifica- If χ is electrically-neutral but carries color B(A0 jj) 100% ⇒ → ≈ h A0A0 4j is the main decay mode for M < 2M tion of the standard model at scales above 1 TeV. → → h W ∼ huge background at the LHC, ⇒ Higgs boson will be hard to discover ... (use jet substructure?) . 1.18 . 1.17 Energy Solution #1: Supersymmetric Standard Model TT 16 No quadratic divergences because loops with superpartners par- 10 TeV quantum gravity tially cancel the SM loops h, W Dynamical susy t '$ 8 h '$ h hh 10 10 TeV breaking sector &% ∼ − &% t˜ H,˜ W˜ c '$ 7 Messenger sector hhh '$ h 10 10 TeV ? − &% &% c Additional structures required to explain why H M ,µ. ) *∼ SUSY 1 TeV MSSM ∼ . 1.19 . 1.20 Solution #2: Technicolor Solution #3: A warped extra dimension Energy TT L. Randall, R. Sundrum, hep-ph/9905221 1016 TeV quantum gravity Technicolor gauge coupling: gTC O(1) ∼ wave function of © graviton 0-mode Planck logarithmic running of gTC “brane” Standard Model % (increases at lower scales, “brane” just as in QCD) E 0y πyrc z Interaction of the graviton 0-mode (the massless 4D spin-2 field) c with Standard Model particles is suppressed by its exponentially gTC O(4π) Technifermions condense small wave function at the SM brane. 1 TeV ∼ ⇒ ∼ electroweak symmetry is broken ⇒ Hierarchy between the Planck and electroweak scales is explained! . 1.21 . 1.22 Solution #4: Composite Higgs models Higgs boson is a bound state of top quark with a new quark χ. “Top seesaw model” (Chivukula et al, hep-ph/9809470) Scales of RS1 model (measured on the SM brane): Binding may be due to some strongly-interacting heavy gauge bosons TT Energy χ t Graviton KK modes are strongly coupled 1 TeV Scale of Higgs compositeness may be as low as a few TeV. ∼ Standard Model Homework 1.5: What are quantum numbers of χ?Howwouldyou search for this hypothetical particle? .