Ultraboosted ZtZt and γt\gamma t production at the HL-LHC and FCC-hh

Searches for anomalous $Zt$ and $\gamma t$ production provide an excellent probe of flavour-changing top interactions when the energies considered are very large. In this note we estimate the sensitivity to these interactions at the high luminosity phase of the LHC and a future 100 TeV $pp$ collider (FCC-hh). For the LHC, the expected limits on $t \to uZ / u\gamma$ branching ratios from $Zt$ and $\gamma t$ production will reach the $10^{-5}$ level, one order of magnitude better than the existing projections for $t \to uZ$ from $t \bar t$ production. For the FCC-hh, the limits on $t \to uZ / u\gamma$ could reach an impressive sensitivity at the $10^{-6}$ level, with limits on $t \to cZ / c\gamma$ at the $10^{-5}$ level.Comment: LaTeX 11 pages. Plots fixed, journal versio

New signals in pair production of heavy Q=2/3 singlets at LHC

New quark singlets T can be produced in pairs at LHC through standard QCD interactions, with a large cross section for masses of several hundreds of GeV. Their charged current decays T Tbar T -> W+ b W- bbar, with semileptonic decay of the W pair, give a final state l nu bb jj$, as in top pair production. The mixed decay modes T Tbar -> W+ b H tbar, H t W- bbar -> W+ b W- bbar H, T Tbar -> W+ b Z tbar, Z t W- bbar -> W+ b W- bbar Z, with H,Z -> jj, yield two more jets, l nu bb jjjj, or the same state in the latter case for Z -> nu nubar. We extend previous work examining in detail the extra H and Z contributions and stressing one of the salient features of the T Tbar -> W+ b W- bbar signal: the presence of a very energetic charged lepton. We finally compare with the discovery potential in l nu bbbb jj final states, with four b tags.Comment: LaTeX, 10 pages, 11 PS figures, uses PoS.cls. Contribution to the International Workshop on Top Quark Physics, January 12-15, 2006, Coimbra, Portugal. To appear in the proceeding

Effective operators in top physics

Top interactions beyond the Standard Model can be conveniently described in the framework of gauge-invariant effective operators. We briefly review the general form of the fermion-fermion-gauge boson and fermion-fermion-Higgs interactions arising from dimension-6 operators, focusing on the top quark. We discuss in detail an expansion in powers of 1/Lambda^2, where Lambda is the new physics scale, to consistently calculate observables in terms of top anomalous couplings.Comment: LaTeX 4 pages, 2 PS figures. Presented at ICHEP 2010, Paris, France, July 22-28, 2010, to appear in the proceeding

Running bumps from stealth bosons

For the "stealth bosons" $S$, light boosted particles with a decay $S \to A A \to q \bar q q \bar q$ into four quarks and reconstructed as a single fat jet, the groomed jet mass has a strong correlation with groomed jet substructure variables. Consequently, the jet mass distribution is strongly affected by the jet substructure selection cuts when applied on the groomed jet. We illustrate this fact by recasting a CMS search for low-mass dijet resonances and show a few representative examples. The mass distributions exhibit narrow and wide bumps at several locations in the 100 - 300 GeV range, between the masses of the daughter particles $A$ and the parent particle $S$, depending on the jet substructure selection. This striking observation introduces several caveats when interpreting and comparing experimental results, for the case of non-standard signatures. The possibility that a single boosted particle decaying hadronically produces multiple bumps, at quite different jet masses, and depending on the event selection, brings the game of anomaly chasing to the next level.Comment: LaTeX 21 pages. Added one appendix and some plots. Journal versio