We study the off-shell production of the Higgs boson at the LHC to probe Higgs physics at higher energy scales utilizing the process $g g rightarrow h^{*} rightarrow ZZ$. We focus on the energy scale dependence of the off-shell Higgs propagation, and
of the top quark Yukawa coupling, $y_t (Q^2)$. Extending our recent study in arXiv:1710.02149, we first discuss threshold effects in the Higgs propagator due to the existence of new states, such as a gauge singlet scalar portal, and a possible continuum of states in a conformal limit, both of which would be difficult to discover in other traditional searches. We then examine the modification of $y_t (Q^2)$ from its Standard Model (SM) prediction in terms of the renormalization group running of the top Yukawa, which could be significant in the presence of large flat extra-dimensions. Finally, we explore possible strongly coupled new physics in the top-Higgs sector that can lead to the appearance of a non-local $Q^2$-dependent form factor in the effective top-Higgs vertex. We find that considerable deviations compared to the SM prediction in the invariant mass distribution of the $Z$-boson pair can be conceivable, and may be probed at a $2sigma$-level at the high-luminosity 14 TeV HL-LHC for a new physics scale up to $mathcal{O}(1 {~rm TeV})$, and at the upgraded 27 TeV HE-LHC for a scale up to $mathcal{O}(3 {~rm TeV})$. For a few favorable scenarios, $5sigma$-level observation may be possible at the HE-LHC for a scale of about $mathcal{O}(1 {~rm TeV})$.
The measurement of the triple Higgs coupling is a key benchmark for the LHC and future colliders. It directly probes the Higgs potential and its fundamental properties in connection to new physics beyond the Standard Model. There exist two phase spac
e regions with an enhanced sensitivity to the Higgs self-coupling, the Higgs pair production threshold and an intermediate top pair threshold. We show how the invariant mass distribution of the Higgs pair offers a systematic way to extract the Higgs self-coupling, focusing on the leading channel $ppto hh+Xto bbar b gammagamma+X$. We utilize new features of the signal events at higher energies and estimate the potential of a high-energy upgrade of the LHC and a future hadron collider with realistic simulations. We find that the high-energy upgrade of the LHC to 27 TeV would reach a 5$sigma$ observation with an integrated luminosity of 2.5 ab$^{-1}$. It would have the potential to reach 15% (30%) accuracy at the 68% (95%) confidence level to determine the SM Higgs boson self-coupling. A future 100 TeV collider could improve the self-coupling measurement to better than 5% (10%) at the 68% (95%) confidence level.
Examining the Higgs sector at high energy scales through off-shell Higgs production can potentially shed light on the naturalness problem of the Higgs mass. We propose such a study at the LHC by utilizing a representative model with a new scalar fiel
d ($S$) coupled to the Standard Model Higgs doublet ($H$) in a form $ |S|^2 |H|^2$. In the process $p p rightarrow h^* rightarrow ZZ$, the dominant momentum-dependent part of the one-loop scalar singlet corrections, especially above the new threshold at $2m_S$, leads to a measurable deviation in the differential distribution of the $Z$-pair invariant mass, in accordance with the quadratic divergence cancellation to the Higgs mass. We find that it is conceivable to probe such new physics at the $5sigma$ level at the high-luminosity LHC, improving further with the upgraded $27$ TeV LHC, without requiring the precise measurement of the Higgs boson total width. The discovery of such a Higgs portal could also have important implications for thermal dark matter as well as for electroweak baryogenesis.
In the recent paper on The Higgs Legacy of the LHC Run I we interpreted the LHC Higgs results in terms of an effective Lagrangian using the SFitter framework. For the on-shell Higgs analysis of rates and kinematic distributions we relied on a linear
representation based on dimension-6 operators with a simplified fermion sector. In this addendum we describe how the extension of Higgs couplings modifications in a linear dimension-6 Lagrangian can be formally understood in terms of the non-linear effective field theory. It turns out that our previous results can be translated to the non-linear framework through a simple operator rotation.
Based on Run I data we present a comprehensive analysis of Higgs couplings. For the first time this SFitter analysis includes independent tests of the Higgs-gluon and top Yukawa couplings, Higgs decays to invisible particles, and off-shell Higgs meas
urements. The observed Higgs boson is fully consistent with the Standard Model, both in terms of coupling modifications and effective field theory. Based only on Higgs total rates the results using both approaches are essentially equivalent, with the exception of strong correlations in the parameter space induced by effective operators. These correlations can be controlled through additional experimental input, namely kinematic distributions. Including kinematic distributions the typical Run I reach for weakly interacting new physics now reaches 300 to 500 GeV.
We present search results based on next-to-leading order predictions for the pair production of color-adjoint leptons at the LHC. Quantum effects are sizable, dominated by pure QCD corrections, and sensitive to threshold effects. We illustrate the st
abilization of scale dependences and confirm an excellent agreement between fixed-order and multi-jet predictions for representative distributions. Finally, we examine the trademark collider signatures of leptogluon pairs. Based on the CMS leptoquark search we derive a mass bound of 1.2-1.3 TeV for charged leptogluons, significantly improving the constraints available in the literature.
We present completely general next-to-leading order predictions for squark and gluino production at the LHC, based on the fully automated MadGolem tool. Without any assumptions on the mass spectrum we predict production rates and examine the structur
e of the massless and massive quantum corrections. This allows us to quantify theory uncertainties induced by the spectrum assumptions commonly made. Going beyond total rates we compare general fixed-order distributions to resummed predictions from jet merging. As part of this comprehensive study we present the MadGolem treatment of ultraviolet, infrared and on-shell divergences.
