Impact of uncertainties on the cosmic optical and infrared backgrounds on the propagation of astroparticles

When propagating through the universe, gamma rays at very-high energy (VHE, E > 100 GeV) and ultra-high energy cosmic rays (UHECRs, E > 1 EeV) can interact with the optical, infrared and microwave photon fields that permeate the universe. These interactions result in a characteristic absorption imprint in the spectra of extragalactic gamma-ray sources at VHE, and in a change in the mass-composition of UHECRs. The study of both VHE gamma rays and UHECRs therefore requires precise knowledge of the intensity of the cosmic photon fields. In this work, we explore the impact of the current uncertainties on the optical and infrared photon fields on the propagation of astroparticles. We restrict the range of available models to those best matching the recent measurements, and compare the different reconstructions resulting from these models. We find that the knowledge on the cosmic background light is no longer the dominant source of uncertainties in understanding the phenomenology of astroparticle sources in the low redshift universe (z < 0.1), enabling robust spectral and composition inference with the next generation of both gamma-ray and UHECR measurements.