Modified Gravity and Dark Energy models Beyond $w(z)$CDM Testable by LSST

TL;DR

This paper discusses modified gravity and dark energy models beyond the standard $w(z)$CDM framework, emphasizing their testability with LSST data and prioritizing models based on observational and theoretical considerations.

Contribution

It identifies and prioritizes a subset of alternative models to $ ext{w}(z)$CDM for LSST analysis, providing theoretical details and integration guidance.

Findings

Prioritized models based on observational viability and theoretical plausibility.

Guidelines for integrating models into LSST DESC pipelines.

Justifications for excluding certain models.

Abstract

One of the main science goals of the Large Synoptic Survey Telescope (LSST) is to uncover the nature of cosmic acceleration. In the base analysis, possible deviations from the Lambda-Cold-Dark-Matter ($\Lambda$CDM) background evolution will be probed by fitting a $w(z)$CDM model, which allows for a redshift-dependent dark energy equation of state with $w(z)$, within general relativity (GR). A rich array of other phenomena can arise due to deviations from the standard $\Lambda$CDM+GR model though, including modifications to the growth rate of structure and lensing, and novel screening effects on non-linear scales. Concrete physical models are needed to provide consistent predictions for these (potentially small) effects, to give us the best chance of detecting them and separating them from astrophysical systematics. A complex plethora of possible models has been constructed over the past few decades, with none emerging as a particular favorite. This document prioritizes a subset of these models along with rationales for further study and inclusion into the LSST Dark Energy Science Collaboration (DESC) data analysis pipelines, based on their observational viability, theoretical plausibility, and level of theoretical development. We provide references and theoretical expressions to aid the integration of these models into DESC software and simulations, and give justifications for why other models were not prioritized. While DESC efforts are free to pursue other models, we provide here guidelines on which theories appear to have higher priority for collaboration efforts due to their perceived promise and greater instructional value.