Abstract
We consider extensions of the Standard Model with a number of additional heavy quarks which couple to the Higgs boson via top-like Yukawa interactions. We construct an effective theory valid for a Higgs boson mass which is lighter than twice the lightest heavy quark mass and compute the corresponding Wilson coefficient through NNLO. We present numerical results for the gluon fusion cross-section at the Tevatron for an extension of the Standard Model with a fourth generation of heavy quarks. The gluon fusion cross-section is enhanced by a factor of roughly 9 with respect to the Standard Model value. Tevatron experimental data can place stringent exclusion limits for the Higgs mass in this model.
Highlights
The effective LagrangianWe consider an arbitrary extension of the SM through new heavy quarks transforming under the fundamental representation of the QCD gauge group SU(3)
We consider extensions of the Standard Model with a number of additional heavy quarks which couple to the Higgs boson via top-like Yukawa interactions
Experience from the Standard Model shows that a precise estimate of the gluon-fusion cross-section and the Higgs decay width to gluons requires calculations through next-tonext-to-leading-order (NNLO) in the strong coupling
Summary
We consider an arbitrary extension of the SM through new heavy quarks transforming under the fundamental representation of the QCD gauge group SU(3). Dμ is the covariant derivative in the fundamental representation and LnQlCD is the QCD Lagrangian with only the nl flavours of light quarks. We take these quarks to be massless. When the quarks that couple to the Higgs boson are heavier than half the Higgs boson mass, we can integrate them out In this limit, we can replace the original Lagrangian (2.1) with an effective Lagrangian. In eq (2.2), LeQfCf,Dnl describes the interactions among light quarks It has the same form as LnQlCD, but with different parameters and field normalizations because of the contributions from heavy quarks loops.
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