Constraining cosmic string parameters with curl mode of CMB lensing

TL;DR

This paper uses curl mode measurements of CMB lensing from Planck and ACT data to constrain cosmic string parameters, providing new bounds on string tension and reconnection probability, especially for small P values.

Contribution

It introduces the use of curl mode of CMB lensing to constrain cosmic string parameters, offering tighter bounds for low reconnection probabilities compared to temperature power spectrum methods.

Findings

Upper bound on string tension Gμ = 6.6×10⁻⁵ from Planck curl mode.

Curl mode constraints are tighter than temperature spectrum constraints for P ≲ 10⁻².

Combined constraints on Gμ and P improve bounds on cosmic string properties.

Abstract

We present constraints on a cosmic string network with a measurement of weak gravitational lensing from CMB temperature map. The cosmic string network between observer and last scattering surface of CMB photons generates vector and/or tensor metric perturbations, and the deflection of CMB photons by these gravitational fields has curl mode which is not produced by the scalar metric perturbations. In this paper, we use the power spectrum of curl mode obtained from Planck to constrain the string tension, G\mu, and the reconnection probability, P. In demonstrating the parameter constraints with Planck curl mode, we also measure the lensing power spectrum from the Atacama Cosmology Telescope (ACT) 2008 season data, which have better angular resolution with lower instrumental noise on a much smaller chunk of the sky. Assuming P=1, the upper bound on tension is G\mu = 6.6\times 10^{-5} with 2\sigma (95% C.L.), using curl mode from Planck, which is weaker than that from the small-scale temperature power spectrum. For small values of P, however, the constraint from curl mode becomes tighter compared to that from temperature power spectrum. For P\lsim 10^{-2}, we obtain the constraint on the combination of the string parameters as G\mu P^{-1}\leq 3.4\times 10^{-5} at more than 2\sigma (95% C.L.).