arXiv subjects

Shengqing Gao

Publications and source records attributed to Shengqing Gao.

6 recordsLinked to original sources

arXiv2026

Cosmic acceleration and the Hubble tension from baryon acoustic oscillation data

We investigate the null tests of cosmic accelerated expansion by using the Baryon Acoustic Oscillation (BAO) data measured by the Dark Energy Spectroscopic Instrument (DESI) and reconstruct the dimensionless Hubble parameter $E(z)$ from the DESI BAO Alcock-Paczynski (AP) data using Gaussian process to perform the null test. We find strong evidence of accelerated expansion from the DESI BAO AP data. By reconstructing the deceleration parameter $q(z)$ from the DESI BAO AP data, we find that accelerated expansion persisted until $z \lesssim 0.7$ with a 99.7\% confidence level. Additionally, to provide insights into the Hubble tension problem, we propose combining the reconstructed $E(z)$ with $D_H/r_d$ data to derive the model-independent result $r_d h=99.8\pm 3.1$ Mpc. This result is consistent with measurements from cosmic microwave background (CMB) anisotropies using the $Λ$CDM model. We also propose a model-independent method for reconstructing the comoving angular diameter distance $D_M(z)$ from the distance modulus $μ$ using SNe Ia data and combining this result with DESI BAO data of $D_M/r_d$ to constrain the value of $r_d$. We find that the value of $r_d$ derived from this model-independent method is smaller than that obtained from CMB measurements, with a significant discrepancy of at least 4.17$σ$. All the conclusions drawn in this paper are independent of cosmological models and gravitational theories.

astro-ph.CO↗

arXiv2025

Null tests with Gaussian Process

We investigate the null tests of spatial flatness and the flat $Λ$CDM model using the Baryon Acoustic Oscillation (BAO) data measured by the Dark Energy Spectroscopic Instrument (DESI), the cosmic chronometers (CCH) $H(z)$ data, and the Union3 and Pantheon Plus type Ia supernovae (SNe Ia) datasets. We propose a novel non-parametric reconstruction of $F_{AP}$, $D_M/r_d$ and $D'_M/r_d$ from the DESI BAO data to perform the $Ok$ diagnostic, and we also conduct the $Ok$ diagnostic using the combination of CCH and SNe Ia data. The novel method avoids the issue of the dependence on cosmological parameters such as the value of the Hubble constant. There is no evidence of deviation from the flat $Λ$CDM model, nor is there any indication of dynamical dark energy found in the observational data. Since we employ a non-parametric reconstruction method, all the conclusions drawn in this paper remain robust and agnostic to any cosmological model and gravitational theory.

astro-ph.CO↗

arXiv2024

On the evidence of dynamical dark energy

To elucidate the robustness of the baryon acoustic oscillation (BAO) data measured by the Dark Energy Spectroscopic Instrument (DESI) in capturing the dynamical behavior of dark energy, we assess the model dependence of the evidence for dynamical dark energy inferred from the DESI BAO data. While the DESI BAO data slightly tightens the constraints on model parameters and increases the tension between the Chevallier-Polarski-Linder (CPL) model and the $Λ$CDM model, we find that the influence of DESI BAO data on the constraint of $w_0$ is small in the SSLCPL model. In comparison to the CPL model, the tension with the $Λ$CDM model is reduced for the SSLCPL model, suggesting that the evidence for dynamical dark energy from DESI BAO data is dependent on cosmological models. The inclusion of spatial curvature has little impact on the results in the SSLCPL model.

astro-ph.CO↗

arXiv2024

Primordial black holes and scalar-induced gravitational waves from the polynomial attractor model

Primordial black holes (PBHs) generated in the early Universe are considered as one of the candidates for dark matter. To produce PBHs with sufficient abundance, the primordial scalar power spectrum needs to be enhanced to the order of 0.01. Considering the third-order polynomial potential with polynomial $α$ attractors, we show that PBHs with the mass about $10^{17}$g can be produced while satisfying the constraints from the cosmic microwave background observations at the 2$σ$ confidence level. The mass of PBHs produced in the polynomial $α$ attractors can be much bigger than that in the exponential $α$ attractors. By adding a negative power-law term to the polynomials, abundant PBHs with different masses and the accompanying scalar-induced gravitational waves (SIGWs) with different peak frequency are easily generated. The PBHs with masses around $10^{-15}-10^{-12}$ $M_\odot$ can account for almost all dark matter. The SIGWs generated in the nanohertz band can explain the recent detection of stochastic gravitational-wave background by the pulsar timing array observations. The non-Gaussianity of the primordial curvature perturbations in the squeezed and equilateral limits are calculated numerically. We find that the non-Gaussianity correction greatly enhances the PBH abundance which makes the production of PBHs much easier, but the effect of non-Gaussianity on the generation of SIGWs is negligible.

gr-qc↗

arXiv2024

On the duality in constant-roll inflation

There is a duality in the observables $n_s$, $r$ and the inflaton potential between large and small $η_H$ for the constant-roll inflation if the slow-roll parameter $ε_H$ is negligible. In general, the duality between $η_H$ and $\barη_H$ does not hold for the background evolution of the inflation. For some particular solutions for the constant-roll inflation with $η_H$ being a constant, we find that in the small field approximation, the potential takes the quadratic form and it remains the same when the parameter $η_H$ changes to $\barη_H=3-η_H$. If the scalar field is small and the contribution of $ε_H$ is negligible, we find that there exists the logarithmic duality and the duality between large and small $η_H$ for the primordial curvature perturbation in inflationary models with the quadratic potential.

gr-qc↗

arXiv2023

Primordial black holes and scalar induced gravitational waves from Higgs inflation with non-canonical kinetic term

We resolve the potential-restriction problem in K/G inflation by introducing nonminimal coupling. In this context, Higgs field successfully drives inflation satisfying CMB observations while enhancing curvature perturbations at small scales, which in turn accounts for primordial black holes (PBHs) and scalar induced gravitational waves (SIGWs). We then uncover the effect of the non-canonical kinetic coupling function in more detail and study its the observational constraint. Besides, we also give the gauge invariant expression for the integral kernel of SIGWs, which is related to terms propagating with the speed of light. Finally, the non-Gaussian effect on PBH abundance and SIGWs is studied. We find that non-Gaussianity makes PBHs form more easily, but its effect on the energy density of SIGWs is negligible.

gr-qc↗