Constraining variability of coupling constants with bright and extreme quasars

The 'extreme Population A (xA) quasars' approaching, sometimes exceeding the Eddington limit, are a type of quasars that could serve as a standard candle to measure distances too large for supernovae type Ia (SNe Ia) to be observable. For using xA quasars as standard candles, it would be beneficial to know how their luminosities would vary if coupling constants varied over cosmic time. Alternatively, when calibrated using SN Ia standard candle, xA quasar observations could constrain the variation of coupling constants. We show that the Hubble diagram of xA quasars provides the same constraint on the constants' variation as the Hubble diagram of SNe Ia from the Pantheon data. The coupling constants vary concurrently in our model, i.e., the variation of the speed of light $c$, the gravitational constant $G$, the Planck constant $h$, and the Boltzmann constant $k$, are interrelated as $G\thicksim c^{3}\thicksim h^{3}\thicksim k^{3/2}$. The constraint thus determined can be expressed in terms of the Hubble constant $H_{0}$ as $(\dot{G}/G)_{0}=3(\dot{c}/c)_{0}=3(\dot{h}/h)_{0}=1.5 (\dot{k}/k)_{0}=5.4H_{0} =3.90(\pm 0.04)\times 10^{-10} yr^{-1}$, where subscript 0 is for the current time. This conclusion is corroborated with the analysis of data on the quasars with correlated UV and X-ray emissions.