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

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 γ-ray observations. Recent theoretical-EBL intensities are typically consistent with the very high energy (VHE) γ-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 γ-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 σ 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 γ-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. * EBL intensities (for reviews see e.g. Refs. [1,16,17]) and test the empirical EBL models, e.g. Refs. [8][9][10][11][12][13], by comparing the difference between the assumed-intrinsic spectra and the observed one. Thanks to the discovery of more and more distant Tev blazars, several groups have detected this imprint, e.g. Refs. [15,18,19], and found the intensities were near the galaxy-count lower limits.The spectra of a few individual blazars such as PKS1424+240 appear to be unexpectedly hard [34]. Furthermore, hints for a reduced gamma-ray opacity in the form of a pair-production anomaly [20] (i.e., VHE γ-ray observations require an EBL level below the lower limits from galaxy counts), or unusual redshift-dependent intrinsic (after correction for EBL absorption) spectral hardening found in large samples, have been claimed by several authors [21][22][23][24]. However, no significant and systematic anomalies on the entire sample were revealed by recent systematic studies of spectra fitted with recent theoretical EBL absorption on large samples of VHE blazars, see e.g., 33,34]. The intensities of these recent EBL models (e.g. Franceschini 2008 [8], Dominguez 2011 [9], Kneiske 2010 [10], Finke 2010 [11], Gilmore 2012 [12], Stecker 2016 [13]) are close to that from the galaxy counts. At present, many EBL measurements inferred by γ-ray observations reveal that its intensities are generally consistent with ...

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