Nahuel Mirón Granese - Impact of self-interacting dark radiation on primordial B-modes

We study the effects of self-interacting dark radiation on the angular power spectrum of primordial B modes in CMB polarization.

We consider a specific self-interacting model associated with a new scalar field featuring a $\lambda\phi^4$ potential. The background and perturbed dynamics of this new species are implemented in the Boltzmann solver CLASS. We compute the B-mode angular power spectra for various parameter sets, finding relative differences of approximately 1–5% between the interacting and non-interacting scenarios.

Using these results, we generate simulated B-mode observational data and analyze the estimation of the tensor-to-scalar ratio $r$ through a standard MCMC procedure, assuming a non-interacting model as the fitting template. Our findings indicate that self-interacting dark radiation can introduce a bias in the estimation of $r$, which may be significant given the sensitivity of upcoming experiments.

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