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Title: Probing New physics with high-redshift quasars: axions and non-standard cosmology
Abstract The Hubble diagram of quasars, as candidates to “standardizable” candles, has been used to measure the expansion history of the Universe at late times, up to very high redshifts (z∼ 7). It has been shown that this history, as inferred from the quasar dataset, deviates at ≳ 3σlevel from the concordance (ΛCDM) cosmology model preferred by the cosmic microwave background (CMB) and other datasets. In this article, we investigate whether new physics beyond ΛCDM (BΛCDM) or beyond the Standard Model (BSM) could make the quasar data consistent with the concordance model. We first show that an effective redshift-dependent relation between the quasar UV and X-ray luminosities, complementing previous phenomenological work in the literature, can potentially remedy the discrepancy. Such a redshift dependence can be realized in a BSM model with axion-photon conversion in the intergalactic medium (IGM), although the preferred parameter space is in tension with various other astrophysical constraints on axions, at a level depending on the specific assumptions made regarding the IGM magnetic field. We briefly discuss a variation of the axion model that could evade these astrophysical constraints. On the other hand, we show that models beyond ΛCDM such as one with a varying dark energy equation of state (wCDM) or the phenomenological cosmographic model with a polynomial expansion of the luminosity distance, cannot alleviate the tension. The code for our analysis, based onemcee[1] andcorner.py[2], is publicly available atgithub.com/ChenSun-Phys/high_z_candles.  more » « less
Award ID(s):
2210361
PAR ID:
10598489
Author(s) / Creator(s):
; ;
Publisher / Repository:
IOP Science
Date Published:
Journal Name:
Journal of Cosmology and Astroparticle Physics
Volume:
2024
Issue:
06
ISSN:
1475-7516
Page Range / eLocation ID:
037
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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