Abstract
Supersymmetric extensions of the standard model contain additional heavy neutral Higgs bosons that are coupled to heavy scalar top quarks (stops). This system exhibits interesting field theoretic phenomena when the Higgs mass is close to the stop-antistop production threshold. Existing work in the literature has examined the digluon-to-diphoton cross section near threshold and has focused on enhancements in the cross section that might arise either from the perturbative contributions to the Higgs-to-digluon and Higgs-to-diphoton form factors or from mixing of the Higgs boson with stoponium states. Near threshold, enhancements in the relevant amplitudes that go as inverse powers of the stop-antistop relative velocity require resummations of perturbation theory and/or nonperturbative treatments. We present a complete formulation of threshold effects at leading order in the stop-antistop relative velocity in terms of nonrelativistic effective field theory. We give detailed numerical calculations for the case in which the stop-antistop Green's function is modeled with a Coulomb-Schr\"odinger Green's function. We find several general effects that do not appear in a purely perturbative treatment. Higgs-stop-antistop mixing effects displace physical masses from the threshold region, thereby rendering the perturbative threshold enhancements inoperative. In the case of large Higgs-stop-antistop couplings, the displacement of a physical state above threshold substantially increases its width, owing to its decay width to a stop-antistop pair, and greatly reduces its contribution to the cross section.
Highlights
In extensions of the standard model (SM), new heavy particles typically appear
We provide a detailed analysis of the interplay between a heavy Higgs boson and a heavy stopantistop pair for Higgs masses that are close to the stopantistop production threshold
For Higgs masses near threshold, we find that several mechanisms that arise from Higgs-stopantistop mixing suppress the diphoton rate relative to the rates that are obtained in perturbative calculations: (1) for small stop widths, mixing significantly increases the width of the narrowest physical state relative to the width of the unmixed stoponium state; (2) mixing shifts masses of physical states away from the region in which form-factor enhancements occur; (3) mixing shifts some physical-state masses above threshold, where, in the case of strong Higgsstop-antistop couplings, the states develop large decay widths into stop-antistop pairs; (4) for strong Higgs-stopantistop couplings, the mixing changes the heights and widths of the physical resonances that lie below threshold
Summary
In extensions of the standard model (SM), new heavy particles typically appear. For example, supersymmetric extensions of the SM include heavy stop quarks (stops), which are the supersymmetric partners of a top quark [1,2,3,4,5]. The presence of new Higgs doublets is motivated by weak-scale extensions of the SM that aim to address the disparity between the electroweak and Planck scales and to provide explanations of the origins of flavor and of the matter-antimatter asymmetry In these theories, the SM description is recovered in the so-called decoupling regime, in which the masses of the heavy Higgs bosons become large. We find that effects of Higgs-stop-antistop mixing go beyond the modification of the Hgg and Hγγ form factors and significantly change the diphoton production rate near the stop-antistop threshold with respect to the rate that would be obtained from the simple addition of the Higgs and stoponium contributions.
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