English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present a new model-independent method to determine the spatial curvatureand to mitigate the circularity problem affecting the use of quasars asdistance indicators. The cosmic-chronometer measurements are used to constructthe curvature-dependent luminosity distance $D^{\rm cal}_{L}(\Omega_{K},z)$using a polynomial fit. Based on the reconstructed $D^{\rmcal}_{L}(\Omega_{K},z)$ and the known ultraviolet versus X-ray luminositycorrelation of quasars, we simultaneously place limits on the curvatureparameter $\Omega_{K}$ and the parameters characterizing the luminositycorrelation function. This model-independent analysis suggests that a mildlyclosed Universe ($\Omega_{K}=-0.918\pm0.429$) is preferred at the $2.1\sigma$level. With the calibrated luminosity correlation, we build a new data setconsisting of 1598 quasar distance moduli, and use these calibratedmeasurements to test and compare the standard $\Lambda$CDM model and the$R_{\rm h}=ct$ universe. Both models account for the data very well, though theoptimized flat $\Lambda$CDM model has one more free parameter than $R_{\rmh}=ct$, and is penalized more heavily by the Bayes Information Criterion. Wefind that $R_{\rm h}=ct$ is slightly favoured over $\Lambda$CDM with alikelihood of $\sim57.7\%$ versus 42.3\%.

Model-independent Distance Calibration and Curvature Measurement using Quasars and Cosmic Chronometers