Conformal Frame dependence on Cosmological Observations in Scalar-Tensor Theories of Gravity

TL;DR

This paper investigates how cosmological observations in scalar-tensor gravity theories depend on the choice of conformal frame, demonstrating that observables are frame-dependent when expressed through redshift, impacting model interpretation.

Contribution

It explicitly shows the frame dependence of cosmological observables in scalar-tensor theories and provides a model-independent analysis for both frames.

Findings

Cosmological observables depend on the conformal frame when described by redshift.

Interpreting observables in one frame requires consistent interpretation in that same frame.

The method offers a frame-independent approach to analyze scalar-tensor gravity models.

Abstract

Cosmological observations provide more accurate values both for background evolution of the Universe and for the structure formation. These values are given by the so-called dark energy equation of state, $\omega$ and the growth index parameter, $\gamma$. From these observed parameters, one can reconstruct the model functions in scalar tensor gravity theories. However, there is a long standing debate about the (in)equality between conformally transformed frames in scalar tensor gravity models. We show that cosmological observables are frame dependent when they are described by frame independent parameter, redshift. Thus, if the cosmological observables are interpreted in one frame, then all of the observables should also be interpreted in that frame. This explicitly shows the conformal inequality of cosmological observables. Also, our method provides the model independent analysis for STG models about various observables in both frames.