Misinterpreting modified gravity as dark energy: a quantitative study

Abstract

Standard cosmological data analyses typically constrain simple phenomenological dark-energy parameters, for example the present-day value of the equation of state parameter, w 0, and its variation with scale factor, w a. However, results from such an analysis cannot easily indicate the presence of modified gravity. Even if general relativity does not hold, experimental data could still be fit sufficiently well by a phenomenological w 0 w aCDM, unmodified-gravity model. Hence, it would be very useful to know if there are generic signatures of modified gravity in standard analyses. Here we present, for the first time to our knowledge, a quantitative mapping showing how modified gravity models look when (mis)interpreted within the standard unmodified-gravity analysis. Scanning through a broad space of modified-gravity (Horndeski) models, and assuming a near-future survey consisting of CMB, BAO, and SNIa observations, we report values of the best-fit set of cosmological parameters including (w 0, w a) that would be inferred if modified gravity were at work. We find that modified gravity models that can masquerade as standard gravity lead to very specific biases in standard-parameter spaces. We also comment on implications for measurements of the amplitude of mass fluctuations described by the parameter S 8.

Parametric and nonparametric methods hint dark energy evolution

“…It should be emphasized as well that dynamical DE does not necessarily imply modified gravity as alluded in Ref. [33]. Particularly, it may just so happen that a better fit can be obtained with data even if the underlying physical model is standard cosmology, or unmodified gravity.…”

“…Theory-agnostic frameworks, on the other hand, offer a refreshing take to studying DE phenomenology [28][29][30][31][32], and is the direction to be considered in this work. Adding new substance to this approach, it was recently shown how modified gravity can lead to preferred directions in the parameter space when viewed as dynamical DE [33].…”

Confronting quantum-corrected teleparallel cosmology with observations

“…It should be emphasized as well that a better fit to the background observation does not necessarily imply modified gravity [59]. A better fit with data may just so happen to occur even if the underlying physics is governed by standard cosmology, in other words, unmodified gravity.…”

Confronting quantum-corrected teleparallel cosmology with observations

“…It should be emphasized as well that a better fit to the background observation does not necessarily imply modified gravity [54]. A better fit with data may just so happen to occur even if the underlying physics is governed by standard cosmology, in other words, unmodified gravity.…”