Effects of Variable Newton Constant During Inflation

TL;DR

This paper investigates how a time-varying Newton constant G during inflation affects curvature perturbations, revealing potential signatures like sinusoidal modulations in the power spectrum that could explain CMB anomalies.

Contribution

It introduces a formalism for curvature perturbations with a variable G and analyzes the impact of sudden G changes on the inflationary power spectrum.

Findings

G increases decrease curvature perturbation amplitude

Sinusoidal modulations are induced in the power spectrum

Constraints on ΔG during inflation are comparable to current universal bounds

Abstract

In this paper the effects of time-dependent Newton constant G during inflation are studied. We present the formalism of curvature perturbations in an inflationary system with a time-dependent Newton constant. As an example we consider a toy model in which G undergoes a sudden change during inflation. By imposing the appropriate matching conditions the imprints of this sharp change in G on curvature perturbation power spectrum are studied. We show that if G increases (decreases) during the transition the amplitude of curvature perturbations on large scales decreases (increases). In our model with a sudden change in G a continuous sinusoidal modulations on curvature power spectrum is induced. However, in a realistic scenario in which the change in G has some finite time scale we expect these sinusoidal modulations to be damped on short scales. The generated features may be used to explain the observed glitches on CMB power spectrum. This puts a bound on $\Delta G$ during inflation of roughly the same order as current bounds on $\Delta G$ during the entire observed age of the universe.