Detecting cosmological recombination lines with a non-ideal antenna: A first step to practical realization

Photons emitted during the formation of primordial hydrogen and helium atoms over the Epoch of Recombination are expected to be preserved as additive distortions to the Cosmic Microwave Background (CMB) spectrum. The ‘ripple’ like spectral features from Cosmological Recombination Radiation (CRR) have never been detected, and are expected to be 9 orders of magnitude fainter than the CMB. Array of Precision Spectrometers for the Epoch of Recombination (APSERa) is an upcoming ground-based experiment to detect the CRR signal over 2–6 GHz. While astrophysical foregrounds may be theoretically separated from the CRR signal using their inherently different spectral characteristics, instrument-generated systematics present a practical problem. We present the first-ever study to detect the CRR lines in the presence of a non-ideal antenna, adopting a toy model for antenna beam chromaticity. Using Euclidean distance and Pearson correlation coefficient as metrics to distinguish between CRR signal presence and absence in a simulation pipeline, we demonstrate that it is indeed possible to detect the signal using a chromatic antenna. Furthermore, we show that there are different tolerances to the antenna non-ideality based on the type of chromaticity, observing location, and LST. These can inform antenna and experiment design for a practical detection.