The decay h → γγ in the Standard-Model Effective Field Theory

A. Dedes, M. Paraskevas, J. Rosiek, K. Suxho, L. Trifyllis
2018 Journal of High Energy Physics  
Assuming that new physics effects are parametrized by the Standard-Model Effective Field Theory (SMEFT) written in a complete basis of up to dimension-6 operators, we calculate the CP-conserving one-loop amplitude for the decay h→γγ in general R_ξ-gauges. We employ a simple renormalisation scheme that is hybrid between on-shell SM-like renormalised parameters and running MS Wilson coefficients. The resulting amplitude is then finite, renormalisation scale invariant, independent of the gauge
more » ... nt of the gauge choice (ξ) and respects SM Ward identities. Remarkably, the S-matrix amplitude calculation resembles very closely the one usually known from renormalisable theories and can be automatised to a high degree. We use this gauge invariant amplitude and recent LHC data to check upon sensitivity to various Wilson coefficients entering from a more complete theory at the matching energy scale. We present a closed expression for the ratio R_h→γγ, of the Beyond the SM versus the SM contributions as appeared in LHC h→γγ searches. The most important contributions arise at tree level from the operators Q_φ B, Q_φ W, Q_φ WB, and at one-loop level from the dipole operators Q_uB,Q_uW. Our calculation shows also that, for operators that appear at tree level in SMEFT, one-loop corrections can modify their contributions by less than 10 bounded from current LHC h→γγ data -- in some cases an order of magnitude stronger than from other searches. Finally, we correct results that appeared previously in the literature.
doi:10.1007/jhep08(2018)103 fatcat:7rugyqp3ybgcrgbezi6eogdh54