Observational effects of a running Planck mass

TL;DR

This paper investigates how a running effective Planck mass influences cosmological observations, potentially easing tensions in Hubble constant measurements and CMB data, with a modest hint of positive running that diminishes when additional data are included.

Contribution

It introduces observational effects of a running Planck mass in scalar-tensor gravity and assesses its impact on cosmological data constraints.

Findings

A running Planck mass can increase H_0, aligning better with local measurements.

It slightly relaxes tensions between Planck CMB data and ΛCDM predictions.

The overall evidence for running diminishes with additional low-redshift data.

Abstract

We consider observational effects of a running effective Planck mass in the scalar-tensor gravity theory. At the background level, an increasing effective Planck mass allows a larger Hubble constant $H_0$, which is more compatible with the local direct measurements. At the perturbative level, for cosmic microwave background (CMB) anisotropies, an increasing effective Planck mass ($i$) suppresses the unlensed CMB power at $\ell \lesssim 30$ via the integrated Sachs-Wolfe effect and ($ii$) enhances CMB lensing power. Both effects slightly relax the tension between the current CMB data from the Planck satellite and the standard $\Lambda$CDM model predictions. However, those impacts on the CMB secondary anisotropies are subdominant, and the overall constraints are driven by the background measurements. Combining CMB data from the Planck satellite and an $H_0$ prior from Riess $et$ $al$, we find a $\sim 2\sigma$ hint of a positive running of effective Planck mass. However, the hint goes away when we add other low-redshift observational data including type Ia supernovae, baryon acoustic oscillations and an Universe age estimation using the oldest stars.