Abstract
We compute the leading corrections to the differential cross section for top-pair production via gluon fusion due to dimension-six operators at leading order in QCD. The Standard Model fields are assumed to couple only weakly to the hypothetical new sector. A systematic approach then suggests treating single insertions of the operator class containing gluon field strength tensors on the same footing as expli\-citly loop suppressed contributions from four-fermion operators. This is in particular the case for the chromomagnetic operator $Q_{(uG)}$ and the purely bosonic operators $Q_{(G)}$ and $Q_{(\varphi G)}$. All leading order dimension-six contributions are consequently suppressed with a loop factor $1/16\pi^2$.
Highlights
After the discovery of the Higgs-boson in 2012, a lot of attention has been paid to the unknown physics beyond the Standard Model (SM)
A model independent approach with as few assumptions about the new physics sector as possible is provided by the Standard Model effective field theory (SMEFT), which essentially enlarges the at most fourdimensional operators of the SM with nonrenormalizable higher dimensional ones
Before we dive into the actual calculation, we review some aspects of power counting in SMEFT
Summary
After the discovery of the Higgs-boson in 2012, a lot of attention has been paid to the unknown physics beyond the Standard Model (SM). While at proton colliders like the Large Hadron Collider (LHC) focus has mostly been put on the direct detection of new resonances by virtue of high center-of-mass energies, searching for indirect evidence of new particles through their virtual effects on the interactions between SM particles might represent a fruitful alternative. In this context several questions should be addressed, in particular the question whether higher loop orders have to be included for a given fixed canonical order calculation. This crucially depends on the coupling strengths of the SM fields to the new sector. All our analytical results for the cross sections are listed in an Appendix
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