Constraints on scalar–tensor theory of gravity by the recent observational results on gravitational waves

The speed of gravitational waves provides us a new tool to test alternative theories of gravity. The constraint on the speed of gravitational waves from GW170817 and GRB170817A is used to test some classes of Horndeski theory. In particular, we consider the coupling of a scalar field to Einstein tensor and the coupling of the Gauss–Bonnet term to a scalar field. The coupling strength of the Gauss–Bonnet coupling is constrained to be in the order of 10-15\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$10^{-15}$$\end{document}. In the Horndeski theory we show that in order for this theory to satisfy the stringent constraint on the speed of GWs the mass scale M introduced in the non-minimally derivative coupling is constrained to be in the range 1015GeV≫M≳2×10-35\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$10^{15} \,\,\text {GeV}\gg M \gtrsim 2\times 10^{-35}$$\end{document} GeV taking also under consideration the early times upper bound for the mass scale M. The large mass ranges require no fine-tuning because the effect of non-minimally derivative coupling is negligible at late times.