arXiv subjects

Yangjun Shi

Publications and source records attributed to Yangjun Shi.

5 recordsLinked to original sources

arXiv2026

Interacting dark energy constraints from Fermi GRBs and Pantheon+ SNe Ia with full GRB covariance

The standard $\Lambda$CDM model faces long-standing theoretical and observational problems, such as the Hubble tension, which motivate extensions beyond $\Lambda$CDM, including interacting dark energy (IDE). Type Ia supernovae (SNe Ia) are precise probes of the late-time expansion history, while gamma-ray bursts (GRBs) can extend distance measurements to higher redshifts. However, GRB cosmology depends on the calibration of luminosity relations, the covariance treatment, and the intrinsic scatter. In this work, we use 15 years of Fermi/GBM long-GRB observations and Pantheon+ SNe Ia to test whether current distance data provide evidence in favor of IDE models over $\Lambda$CDM. We compare four flat models: $\Lambda$CDM, $w$CDM, IDE-$\rho_{\rm de}$, and IDE-$\rho_{\rm c}$. The GRB covariance is constructed by propagating the Amati-relation calibration covariance, and the GRB intrinsic scatter is sampled as a nuisance parameter. A diagonal GRB covariance is also considered as a robustness test. With the full GRB covariance, both the GOLD and FULL samples give $H_0\simeq 72.8~{\rm km~s^{-1}~Mpc^{-1}}$ in $\Lambda$CDM. The IDE models do not improve the fit enough to compensate for their extra parameters, and the BIC favors the simpler $\Lambda$CDM model. The diagonal-covariance test gives the same model-selection conclusion, although it changes the fitted GRB intrinsic scatter. We conclude that, for the two interaction forms considered here and at the present level of GRB systematics, current GRB and Pantheon+ data do not provide evidence for interacting dark energy. Current GRBs mainly provide a high-redshift extension of the Hubble diagram and test the shape of the expansion history.

astro-ph.CO↗

arXiv2026

Testing the cosmological principle with quasars

The inferred velocity is consistent at the 1.56 {\sigma} level with the value of 370 km/s from a purely kinematic interpretation of the CMB dipole. Based on the motion direction component analysis, we have not found any significant deviation from cosmological principle in current released quasars data. The cosmological principle posits that the universe is homogeneous and isotropic on the large scales. In history, the cosmological principle was confirmed by various cosmological observations from CMB to large scale structure. However, several new challenges to the cosmological principle were reported in recent years, particularly in radio observations from overdispersed radio source counts to quasars. Here, we firstly present studies on the peculiar velocity of large-scale anisotropy by measuring the dipole signal from the DESI DR1 catalogue with a sample of 1,176,570 quasars (0.8 < z < 3.0). Our analysis reveals the peculiar velocity of $|v| = 443.8 \pm 204.1$ km/s towards $(l, b) = (107.4^\circ \pm 86.8^\circ, 28.4^\circ \pm 45.2^\circ)$ in Galactic coordinates.The motion direction deviates from the CMB dipole (264.02$^\circ$, 48.253$^\circ$). The inferred velocity is consistent at the 1.56 $\sigma$ level with the value of 370 km/s from a purely kinematic interpretation of the CMB dipole. Based on the motion direction component analysis, we have not found any significant deviation from cosmological principle in current released quasars data.

astro-ph.CO↗

arXiv2025

Holographic dark energy in a coasting cosmology

Coasting cosmology offers an intriguing and straightforward framework for understanding the universe. In this work, we employ the Trans-Planckian Censorship Criterion (TCC) conjecture to test the viability of the coasting cosmology and propose an entropic dark energy (EDE) model within this framework. By applying the holographic principle to constrain the dark energy density and adopting the Bekenstein entropy and Tsallis entropy as the constraining entropies of the system, we find that, in a holographic coasting cosmological framework where dark energy and dark matter evolve independently, the Tsallis entropy satisfies certain general assumptions better than the Bekenstein entropy. Thus, there may be a fundamental relationship between Tsallis entropy and dark energy. We utilize observational data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Chronometers (CC) to constrain EDE model. The optimal Tsallis parameter obtained aligns well with theoretical expectations. To evaluate the model's fit to the observed data, we calculate the Akaike Information Criterion (AIC), Bayesian Information Criterion (BIC), and Kullback Information Criterion (KIC), and compare these metrics with those derived from $\Lambda$CDM, under which the model shows some improvement. Overall, this model provides a novel and simple on the evolution of the universe.

astro-ph.CO↗

arXiv2025

Reconstructing Barrow Holographic Dark Energy in $f(Q,T)$ Gravity and Cosmic Constraint

In this work, we reconstruct the cosmological evolution of Barrow Holographic Dark Energy (BHDE) within the framework of modified gravity $f(Q,T)$. Working in the coincident gauge, we incorporate the holographic principle into non-metric gravity with non-minimal matter coupling. To address the dynamical complexity, we adopt a reconstruction approach, deriving the matter density evolution from the modified field equations rather than imposing a conserved fluid a priori. We perform parameter estimation using the latest observational data, including Type Ia supernovae, BAO, and direct Hubble parameter measurements. Our results show that the model provides a theoretical framework to describe late-time cosmic evolution and the universe's accelerated expansion. Despite the additional complexity introduced, the model offers an alternative approach for investigating dark energy within modified gravity theories.

astro-ph.CO↗

arXiv2025

Testing Cosmic Distance Duality Relation and Transparency with DESI DR2

The Cosmic Distance Duality Relation (CDDR) is a fundamental principle of standard cosmology, linking luminosity (LD) and angular diameter distances (ADD). This work investigates the validity of the CDDR and cosmic transparency by combining the latest Baryon Acoustic Oscillations (BAO) data from DESI DR2, Type Ia Supernovae from Pantheon+, and cosmic chronometers. To address the redshift mismatch between datasets, two distinct reconstruction techniques are employed: Gaussian Process Regression (GPR) and the Free-Knots Method (FKM). The analysis performs null tests on the CDDR under different cosmological priors, finding that the null hypothesis holds and the CDDR is valid within statistical uncertainties. Although mild deviations are observed from the local distance ladder prior, internal consistency calibration indicates that these discrepancies and the Hubble tension may share a common origin, possibly related to systematic effects or new physics. Using multiple phenomenological parameterizations, the deviation parameter is also found to be statistically consistent with zero (e.g., $\eta_1 = 0.023 \pm 0.027$ for the linear model under Planck priors). Furthermore, the study finds no statistically significant evidence for cosmic opacity. The average of the opacity derivative is compatible with zero ($\langle d\tau/dz \rangle = 0.0409 \pm 0.1024$ for GPR and $0.0730 \pm 0.1607$ for FKM). Based on these null results, stringent constraints are placed on the parameter space of Axion-Like Particles (ALPs) and Mini-Charged Particles (MCPs).

astro-ph.CO↗