arXiv subjects

Jian-Qi Liu

Publications and source records attributed to Jian-Qi Liu.

4 recordsLinked to original sources

arXiv2025

Observational constraints on phenomenological emergent dark energy and barotropic dark matter characterized by a constant equation of state parameter

While cold dark matter is widely supported by a range of cosmological observations, it encounters several difficulties at smaller scales. These issues have prompted the investigation of various alternative dark matter candidates, leaving the question "What is dark matter?" still open. In this work, we propose a new cosmological model that considers dark matter as a barotropic fluid with a constant equation of state parameter and interprets dark energy as the phenomenological emergent dark energy rather than a cosmological constant. We then place constraints on our new model using the Planck 2018 Cosmic Microwave Background (CMB) anisotropy measurements, Baryon Acoustic Oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument (DESI), the Pantheon Plus (PP) compilation of Type Ia supernovae (Ia SNe), and the Redshift Space Distortions (RSD) data from Gold2018. The results show statistically significant signal for positive dark matter equation of state and square of sound speed $w_{\rm dm}=c_{\rm s,dm}^2$ ($10^{7}w_{\rm dm}$ = $4.0^{+2.5}_{-2.3}$ at the 95\% confidence level) for the data combination CMB+DESI+PP+RSD. However, Bayesian evidence indicates that this data combination favors the $Λ$CDM model with very strong evidence.

astro-ph.CO↗

arXiv2025

Hints of noncold dark matter? Observational constraints on barotropic dark matter with a constant equation of state parameter

This study investigates the potential of a cosmological model termed $Λw$DM, in which a cosmological constant play the role of dark energy and dark matter is barotropic and has a constant equation of state parameter ($w_{\rm dm}$), to address the $S_8$ tension between early- and late- universe observations. By incorporating the latest cosmological datasets -- including Planck Cosmic Microwave Background (CMB), Baryon Acoustic Oscillation (BAO), Ia supernovae (SNe Ia), Redshift Space Distortions (RSD), and weak lensing (WL) -- we constrain the $Λw$DM compared to $Λ$CDM. Our analysis reveals a marginal preference for a non-zero $w_{\rm dm}=2.7^{+2.0}_{-1.9}\times10^{-7}$( at 95\% confidence level) when combining CMB, SDSS BAO, SNe Ia, RSD, and WL data, and a marginal preference for a non-zero $w_{\rm dm} = 2.29^{+1.9}_{-2.0} \times 10^{-7}$( at 95\% confidence level) when combining CMB, DESI Y1 BAO, SNe Ia, RSD, and WL data. In addition, we find that, compared to $Λ$CDM, $Λw$DM can alleviate the $S_8$ tension from $>3σ$ to $<1σ$. Furthermore, we find that, for CMB+SDSS+PP+RSD+WL datasets, the $Λw$DM model is close to being positively preferred over the $Λ$CDM model.

astro-ph.CO↗

arXiv2025

Narrowing down the Hubble tension to the first two rungs of distance ladders

The decade-persistent Hubble tension has become a $5σ$ crisis of modern cosmology between the early-Universe extrapolation from globally fitting the standard $Λ$CDM to Planck-CMB measurements and the late-Universe measurement from the three-rung distance ladder with SH0ES calibration. Regarding the current dilemma of theoretical resolutions, recent focus has shifted to systematics inspection. Here we find an associated $5σ$ tension in the intercept of the supernova magnitude-redshift relation between the second-rung and third-rung supernovae from the PantheonPlus compilation independent of calibrations in use. As required by the consistency of the distance-ladder method, we propose a method to eliminate the intercept tension, directly constraining $H_0=73.4\pm1.0\;\mathrm{km/s/Mpc}$ from the first two-rung distance ladder alone without referring to the third-rung supernovae but still consistent with both SH0ES typical three-rung and first two-rung constraints, which not only supports our method to rebuild the intercept consistency but also rules out third-rung supernova systematics including the late-time transition in supernova absolute magnitude. Further crosschecking with the Carnegie Supernova Project revealed that different calibrators alone still consistently prefer our results. Therefore, the original Hubble tension between the Planck-CMB measurements and SH0ES three-rung distance ladder can be narrowed down to a tension between the Planck-CMB and the first two-rung measurements.

astro-ph.CO↗

arXiv2024

A new unified dark sector model and its implications on the $σ_8$ and $S_8$ tensions

In this paper, we introduced the Unified Three-Form Dark Sector (UTFDS) model, a unified dark sector model that combines dark energy and dark matter through a three-form field. In this framework, the potential of the three-form field acts as dark matter, while the kinetic term represents dark energy. The interaction between dark matter and dark energy is driven by the energy exchange between these two terms. Given the dynamical equations of UTFDS, we provide an autonomous system of evolution equations for UTFDS and perform a stability analysis of its fixed points. The result aligns with our expectations for a unified dark sector. Furthermore, we discover that the dual Lagrangian of the UTFDS Lagrangian is equivalent to a Dirac-Born-Infeld (DBI) Lagrangian. By fixing the parameter $κX_0$ to 250, 500, 750, we refer to the resulting models as the $\overline{\rm UTFDS}$ model with $κX_0$=250, 500, 750, respectively. We then place constraints on these three $\overline{\rm UTFDS}$ models and the $Λ$CDM model in light of the Planck 2018 Cosmic Microwave Background (CMB) anisotropies, Redshift Space Distortions (RSD) observations, Baryon Acoustic Oscillation (BAO) measurements, and the $S_8$ prior chosen according to the KiDS1000 Weak gravitational Lensing (WL) measuement. We find that the $\overline{\rm UTFDS}$ model with $κX_0$=500 is the only one among the four models where both $σ_8$ and $S_8$ tensions, between CMB and RSD+BAO+WL datasets, are below 2.0$σ$. Furthermore, the tensions are relieved without exacerbating the $H_0$ tension. Although both the CMB and RSD+BAO+WL datasets provide definite/positive evidence favoring $Λ$CDM over the $\overline{\rm UTFDS}$ model with $κX_0$=500, the evidence is not strong enough to rule out further study of this model.

astro-ph.CO↗