New estimates of the deceleration parameter in weak gravity

TL;DR

This paper investigates weak gravity effects at low accelerations, revealing a transition in galaxy rotation curves linked to cosmological parameters, and proposes using future surveys to distinguish between dark energy models.

Contribution

It introduces a new approach to estimate the deceleration parameter in weak gravity regimes, connecting galaxy dynamics with cosmological background parameters.

Findings

Galaxy rotation curves show sharp transition indicating weak gravity effects.

Correlations between galaxy dynamics and the deceleration parameter are identified.

Future measurements of the deceleration parameter's evolution can test dark energy models.

Abstract

We consider weak gravity at accelerations $\alpha<a_H$ when Rindler and cosmological horizon collude at $R_H=c/H$, where $c$ is the velocity of light and $H$ is the Hubble parameter. This is manifest in reduced inertia $m$, below the value $m_0$ in Newtonian gravity. Striking evidence for a sharp transition to weak gravity is found in galaxy rotation curves. Their sensitivity to the cosmological background is expressed by correlations to the deceleration parameter $q=1-(4\pi a_0/cH)^{2}$ and $q=-1/2 -3 (\Omega_b/\sqrt{2}\sqrt{\pi})^{1/2}$, where $a_0$ is Milgrom's scale in the baryonic Tully-Fisher relation of spiral galaxies and $\Omega_b$ is the baryonic matter density. The Planck value $\Omega_b=0.048$ with $H\simeq 73$ km s$^{-1}$ Mpc$^{-1}$ shows $q\simeq-0.85$. Future surveys may determine $Q_0=\left.dq(z)/dz\right|_{z=0}$ to provide a direct test for dynamical dark energy ($Q_0>2.5$) versus $\Lambda$CDM ($Q_0<1$).