Constraining modified theory of gravity with galaxy bispectrum

TL;DR

This paper investigates how the galaxy bispectrum can be used to test scalar-tensor theories of gravity, introducing a new parameter that captures nonlinear growth and forecasts future constraints on cosmological models.

Contribution

It introduces the second-order index as a new parameter to probe nonlinear gravitational evolution in scalar-tensor theories and forecasts its potential to improve constraints on cosmological parameters.

Findings

The second-order index effectively traces higher-order growth history.

Galaxy bispectrum provides significant information about nonlinear structure growth.

Forecasts suggest future surveys can tightly constrain the second-order index.

Abstract

We explore the use of galaxy bispectrum induced by the nonlinear gravitational evolution as a possible probe to test general scalar-tensor theories with second-order equations of motion. We find that time dependence of the leading second-order kernel is approximately characterized by one parameter, the second-order index, which is expected to trace the higher-order growth history of the Universe. We show that our new parameter can significantly carry new information about the non-linear growth of structure. We forecast future constraints on the second-order index as well as the equation-of-state parameter and the growth index.