Weak lensing from self-ordering scalar fields

TL;DR

This paper investigates the weak lensing effects caused by global textures modeled via the non-linear sigma model, analyzing curl and B modes, and discusses their detectability with current and future observations.

Contribution

It provides the first detailed analysis of weak lensing curl and B modes from non-topological textures using the NLSM, including analytic estimations and observational prospects.

Findings

Weak lensing signals depend on the parameter _v and can be constrained by CMB and cosmic shear observations.

CMB lensing can reach _v  2.7 -6, improving current Planck constraints by a factor of 10.

Signal-to-noise ratio in cosmic shear depends on mean redshift and number of galaxies, influencing survey design.

Abstract

Cosmological defects result from cosmological phase transitions in the early Universe and the dynamics reflects their symmetry-breaking mechanisms. These cosmological defects may be probed through weak lensing effects because they interact with ordinary matters only through the gravitational force. In this paper, we investigate global textures by using weak lensing curl and B modes. Non-topological textures are modeled by the non-linear sigma model (NLSM), and induce not only the scalar perturbation but also vector and tensor perturbations in the primordial plasma due to the nonlinearity in the anisotropic stress of scalar fields. We show angular power spectra of curl and B modes from both vector and tensor modes based on the NLSM. Furthermore, we give the analytic estimations for curl and B mode power spectra. The amplitude of weak lensing signals depends on a combined parameter $\epsilon^{2}_{v} = N^{-1}\left( v/m_{\rm pl} \right)^{4}$ where $N$ and $v$ are the number of the scalar fields and the vacuum expectation value, respectively. We discuss the detectability of the curl and B modes with several observation specifications. In the case of the CMB lensing observation without including the instrumental noise, we can reach $\epsilon_{v} \approx 2.7\times 10^{-6}$. This constraint is about 10 times stronger than the current one determined from the Planck. For the cosmic shear observation, we find that the signal-to-noise ratio depends on the mean redshift and the observing number of galaxies as $\propto z^{0.7}_{\rm m}$ and $\propto N^{0.2}_{\rm g}$, respectively. In the study of textures using cosmic shear observations, the mean redshift would be one of the key design parameters.