Constraints on the fundamental string coupling from B-mode experiments

TL;DR

This paper investigates how cosmic superstring networks influence CMB B-mode polarization spectra and demonstrates that upcoming experiments can constrain the fundamental string coupling constant $g_s$ through observable spectral shifts.

Contribution

It introduces a method to constrain the string coupling $g_s$ by analyzing the B-mode spectrum shifts caused by cosmic superstring networks with multiple tensions and Y-junctions.

Findings

Observable shift in B-mode peak position linked to $g_s$ values.

Forecasted bounds on $g_s$ and string tension $$ from future CMB experiments.

Detection of spectral differences between large and small $g_s$ scenarios is feasible.

Abstract

We study signatures of cosmic superstring networks containing strings of multiple tensions and Y-junctions, on the cosmic microwave background (CMB) temperature and polarisation spectra. Focusing on the crucial role of the string coupling constant $g_s$, we show that the number density and energy density of the scaling network are dominated by different types of string in the $g_s \sim 1$ and $g_s \ll 1$ limits. This can lead to an observable shift in the position of the B-mode peak --- a distinct signal leading to a direct constraint on $g_s$. We forecast the joint bounds on $g_s$ and the fundamental string tension $\mu_F$ from upcoming and future CMB polarisation experiments, as well as the signal to noise in detecting the difference between B-mode signals in the limiting cases of large and small $g_s$. We show that such a detectable shift is within reach of planned experiments.