Testing CIBER cosmic infrared background measurements and axionlike particles with observations of TeV blazars

TL;DR

This study tests whether the excess near-infrared background light measured by CIBER can be explained by axion-like particles affecting gamma-ray transparency, comparing models with and without ALP effects against observations of TeV blazars.

Contribution

It provides a comprehensive analysis of EBL models with and without ALP effects, showing that recent EBL models can explain gamma-ray observations without needing ALPs.

Findings

ALP-photon coupling improves fit significance by 7.6σ for CIBER excess model.

Gilmore's EBL model aligns better with observed spectra overall.

Some individual blazars favor ALP-including models.

Abstract

The first measurements from the CIBER experiment of extragalactic background light (EBL) in near-infrared (NIR) band exhibit a higher intensity than those inferred through $\gamma$-ray observations. Recent theoretical-EBL intensities are typically consistent with the very high energy (VHE) $\gamma$-ray observations. Yet, it is possible that the excess NIR radiation is a new component of EBL and not in tension with the TeV spectra of distant blazars, since the hypothetical axion-like particle (ALP) may lead to a reduced opacity of the Universe for VHE $\gamma$-rays. In order to probe whether the excess component arises mainly from EBL, thirteen observed spectra in high energy and VHE ranges from ten distant TeV BL Lac objects are fitted by four theoretical spectra which involve theoretical EBL (Gilmore ), Gilmore's EBL model including photon/ALP coupling, Gilmore's EBL with CIBER excess and the latter including photon/ALP coupling respectively. We find the goodness of fit for the model with CIBER excess can be improved with a significance of $7.6~\sigma$ after including the photon/ALP coupling; Thus, the ALP/photon mixing mechanism can effectively alleviate the tension; However, the Gilmore EBL model, on the whole, is more compatible with the observed spectra compared to those with ALP, although individual blazars such as PKS 1424+240 and 1ES 1101-232 prefer the ALP-model. Our results suggest that the recent EBL models can solely explain the VHE $\gamma$-ray observations, and assuming the existence of the ALP to alleviate the tension is not required in a statistical sense, thus the excess over the EBL models is less likely to be a new EBL component.