57 research outputs found
Anomalous dimensions of potential top-partners
We discuss anomalous dimensions of top-partner candidates in theories of
Partial Compositeness. First, we revisit, confirm and extend the computation by
DeGrand and Shamir of anomalous dimensions of fermionic trilinears. We present
general results applicable to all matter representations and to composite
operators of any allowed spin. We then ask the question of whether it is
reasonable to expect some models to have composite operators of sufficiently
large anomalous dimension to serve as top-partners. While this question can be
answered conclusively only by lattice gauge theory, within perturbation theory
we find that such values could well occur for some specific models. In the
Appendix we collect a number of practical group theory results for fourth-order
invariants of general interest in gauge theories with many irreducible
representations of fermions.Comment: 21 pages, 4 figures, 6 tables V2: Added Table 3,4,5, equation (9) and
various comments in reply to questions and suggestions raised by the two
Referees of SciPost. Two references also added. V3: Typo in footnote 6
corrected. Final version in SciPos
Probing Near-Conformal Technicolor through Weak Boson Scattering
The recently observed boson at 125 GeV could be a light composite scalar from
near-conformal technicolor dynamics: a technicolor Higgs. If this is the case,
unitarization of longitudinal weak boson scattering amplitudes, which is due to
exchanges of the Higgs and spin-one vector technimesons, is expected to occur
in a strong regime, with saturation of the unitarity bounds. This implies that
processes, where is either a or a boson, are
enhanced, relative to the standard model. We show that this allows probing
near-conformal technicolor for couplings and masses of the spin-one resonances
which are not directly accessible for direct Drell-Yan production.Comment: 19 pages, 4 figure
Constraining scalar resonances with top-quark pair production at the LHC
Constraints on models which predict resonant top-quark pair production at the
LHC are provided via a reinterpretation of the Standard Model (SM) particle
level measurement of the top-anti-top invariant mass distribution,
. We make use of state-of-the-art Monte Carlo event simulation to
perform a direct comparison with measurements of in the
semi-leptonic channels, considering both the boosted and the resolved regime of
the hadronic top decays. A simplified model to describe various scalar
resonances decaying into top-quarks is considered, including CP-even and
CP-odd, color-singlet and color-octet states, and the excluded regions in the
respective parameter spaces are provided.Comment: 34 pages, 17 figure
Scalar production and decay to top quarks including interference effects at NLO in QCD in an EFT approach
Scalar and pseudo-scalar resonances decaying to top quarks are common
predictions in several scenarios beyond the standard model (SM) and are
extensively searched for by LHC experiments. Challenges on the experimental
side require optimising the strategy based on accurate predictions. Firstly,
QCD corrections are known to be large both for the SM QCD background and for
the pure signal scalar production. Secondly, leading order and approximate
next-to-leading order (NLO) calculations indicate that the interference between
signal and background is large and drastically changes the lineshape of the
signal, from a simple peak to a peak-dip structure. Therefore, a robust
prediction of this interference at NLO accuracy in QCD is necessary to ensure
that higher-order corrections do not alter the lineshapes. We compute the exact
NLO corrections, assuming a point-like coupling between the scalar and the
gluons and consistently embedding the calculation in an effective field theory
within an automated framework, and present results for a representative set of
beyond the SM benchmarks. The results can be further matched to parton shower
simulation, providing more realistic predictions. We find that NLO corrections
are important and lead to a significant reduction of the uncertainties. We also
discuss how our computation can be used to improve the predictions for physics
scenarios where the gluon-scalar loop is resolved and the effective approach is
less applicable.Comment: 32 pages, 17 figures; accepted versio
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