… the effective field theory of dark energy. Considering as case study Horndeski theories with
the speed of gravitational waves equal to that of light, we show how constraints on the free …

… The second line is clearly not, which makes the constraint second class, and, from its … This
ensures that the theory is healthy and does not propagate Ostrogradski ghosts. Notice that the …

… , I examine the various existing constraints on gravity with large-… Before we delve into what
it means to modify gravity, let us … In practice this involves making the Planck mass (or Newton's …

… The first class of modified gravity theories we want to cover is … of theories goes by the name
Tensor-(Vector)-Scalar theories or … constraints that are imposed on each gravity theory. The …

… the physical basis functions of Planck mass evolution, sound … our new basis, we show that
there are no general limitations … Before engaging in the construction of a theoretically healthy …

… Constrained gravity approaches exploit minimal departures … We note that one can have
healthy theories with higher-than-… For clarity, we denote the Planck mass by κ in this and the …

… to models of gravity and how they are constrained through … Using the HL as a paradigm of
modified gravity, we focus on its … are theories without a mass scale in addition to the Planck …

… Interestingly, the GR limit of these modified gravity … introduction to nonmetricity theories of
modified gravity. In this very … By contrast, a healthy behavior enabling the normalization in the …

… Planck mass. In the quasi-static limit, it turns out that for the effective Newton’s constant for the
… of GWs placed surprisingly stringent constraints on the theory space of gravity models, and …

… ∂tN − NiDiN, and explore a larger class of healthy scalar-tensor theories with three dof [25]. …
-wavelength limits. In both limits, we will see that the effect of modification of gravity comes …