Modeling parity-violating spectra in Galactic dust polarization with filaments and its applications to cosmic birefringence searches

We extend the dust-filament-based model presented in Hervías-Caimapo and Huffenberger [Astrophys. J. 928, 65 (2022)] to produce parity-violating foreground spectra by manipulating the filament orientations relative to the magnetic field. We calibrate our model to observations of the misalignment angle using cross-correlations of Planck and HI 21-cm line data, producing a fiducial model that predicts a 𝒟𝐸⁢𝐵ℓ∼few  μ⁢K² dust signal at 353 GHz and where  ∼56% of filaments have a positive misalignment angle. The main purpose of this model is to be used as dust with nonzero parity-violating emission in forecasting a measurement of cosmic birefringence by upcoming experiments. Here, we also use our fiducial model to assess the impact of dust in measurements of the isotropic cosmic birefringence angle 𝛽 with Planck data by measuring the misalignment angle as a function of scale, as well as directly using our model’s 𝒟𝐸⁢𝐵ℓ prediction as a template. In both cases, we measure 𝛽 to be consistent within 0.83⁢𝜎 of the analyses that use the 353 GHz channel of Planck to constrain the filamentary misalignment or that use the commander sky model as a template for the dust 𝒟𝐸⁢𝐵ℓ spectrum. We attribute this consistency to the extra degrees of freedom introduced by the ad hoc amplitude parameters for the dust parity-violating spectrum, which are capable of absorbing most of the differences between the model and data as long as a reasonable dust model is provided.