Abstract
The question whether the Higgs boson is connected to additional $CP$ violation is one of the driving forces behind precision studies at the Large Hadron Collider. In this work, we investigate the $CP$ structure of the top quark Yukawa interaction---one of the most prominent places for searching for New Physics---through Higgs boson loops in top quark pair production. We calculate the electroweak corrections including arbitrary $CP$ mixtures at next-to-leading-order in the Standard Model Effective Field Theory. This approach of probing Higgs boson degrees of freedom relies on the large $t\overline{t}$ cross section and the excellent perturbative control. In addition, we consider all direct probes with on-shell Higgs boson production in association with a single top quark or top quark pair. This allows us to contrast loop sensitivity versus on-shell sensitivity in these fundamentally different process dynamics. We find that loop sensitivity in $t\overline{t}$ production and on-shell sensitivity in $t\overline{t}H$ and $tH$ provide complementary handles over a wide range of parameter space.
Highlights
The discovery of the Higgs boson by the ATLAS and CMS Collaborations [1,2,3] in 2012 has sparked an extensive research effort to precisely measure its properties and origin
We investigate the prospects of constraining the CP structure of the coupling of the Higgs boson to the top quark through electroweak loops in tt production
Our results for the loop sensitivity are contrasted with the ones obtained from direct on-shell probes like Higgs production in association with a single top quark or a top quark pair
Summary
The discovery of the Higgs boson by the ATLAS and CMS Collaborations [1,2,3] in 2012 has sparked an extensive research effort to precisely measure its properties and origin. The LHC will have produced almost 500 million top quarks by 2023, while already today, theoretical predictions reach an accuracy of only a few percent [28,29,30,31,32,33] These prospects are only getting brighter with the high-luminosity runs commencing in 2027 and high ambitions of the theory community towards next-tonext-to-next-to-leading order (N3LO) calculations [34,35,36]. Free from penalties of Higgs boson branching fractions and ambiguities of a complicated final state, which is in contrast to on-shell Higgs production processes such as pp → ttH It is at the same order in the perturbative counting. Low-energy measurements of the electric dipole moment yield complementary constraints on the CP-odd components, which are remarkably strong [63,64,65,66,67] and need to be considered in real data analyses
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