arXiv subjects

Zhihuan Zhou

Publications and source records attributed to Zhihuan Zhou.

11 recordsLinked to original sources

arXiv2026

Hierarchical Gaussian-process reconstruction of late-time expansion with DESI BAO and compressed Planck priors

We reconstruct the late-time expansion history with a hierarchical Gaussian process (GP) that co-samples the kernel hyperparameters $(σ_f,l)$ together with $(\Hzero,\Om,\Ok,ω_b h^2)$. The data are 37 cosmic-chronometer $H(z)$ points, DESI DR2 BAO, Planck 2018 compressed distance priors, and Pantheon+ supernovae, coupled by a Monte-Carlo effective likelihood. DESI's headline Chevallier--Polarski--Linder (CPL) preference at $2.8$--$4.2σ$ uses the full Planck likelihood; we do not reproduce or refute that result. On this compressed-CMB pipeline the baseline posterior is $w(z\simeq 0)=-0.80^{+0.26}_{-0.23}$ (68\%~C.L.), less than $1σ$ from $w=-1$, with $l=3.79^{+0.81}_{-1.12}$. A CPL fit on the same data improves nested $\lcdm$ by only $Δχ^2\sim 1$; Akaike's criterion prefers nested $\lcdm$ ($Δ\mathrm{AIC}\simeq 3$), while BIC is quoted only as an indicative check for correlated supernovae. The reconstructed $f_{\rm DE}=1$ lies inside the 68\% band at every grid point with $z\le 1.6$. Ablations that fix $(σ_f,l)$, drop SN or LRG1/2 BAO, replace the radial-basis kernel by a Matérn family, swap the SN catalogue (Union3, DES-Y5, DES-Dovekie), or nest a residual GP around $\lcdm$ leave the median $w(0)$ within $\lesssim 1σ$ of $-1$.

astro-ph.CO↗

arXiv2026

Geometric obstruction to resolving the Hubble tension: orthogonality of scale and shape in distance measurements

We identify a geometric obstruction to resolving the Hubble tension by combining early-time sound-horizon reduction with late-time smooth dark energy. Within $Λ$CDM, the BAO--SN matter-density gap $ΔΩ_m = 0.037$ is exactly invariant under the sound-horizon rescaling $α\equiv r_s^{\rm mod}/r_s^{Λ{\rm CDM}}$, and late-time $w(z)$ deformations cannot eliminate this gap either: reconciling the two datasets requires \emph{opposite} deformations -- phantom ($w < -1$) for BAO, quintessence ($w > -1$) for SN at $z < 0.5$ -- an anti-alignment quantified by $\cosθ= -0.97$ in $w(z)$ space. A full MCMC analysis of DESI DR2 BAO, Planck plik\_lite, and Pantheon+ bears this out: the optimal $α^* = 0.992$ ($0.8\%$ $r_s$ reduction) brings the joint fit to $H_0 = 70.3 \pm 0.3\;\mathrm{km\,s^{-1}\,Mpc^{-1}}$, still $3.2σ$ below SH0ES, with the inter-dataset tension reduced but not removed. The obstruction reflects not a shortage of model freedom but an irreducible disagreement between probes. The deformation space $\{α, β_{\rm damp}, w(z)\}$ already spans $93\%$ of the $Ω_m$ response direction; nonetheless BAO and SN constrain $Ω_m$ through independent channels and disagree, while the residual $H_0$ deficit, anchored by the local distance ladder, resides in the absolute distance scale that $w(z)$ reshapes but cannot rescale.

astro-ph.CO↗

arXiv2025

Redshift-dependent Distance Duality Violation in Resolving Multidimensional Cosmic Tensions

In this work, we investigate whether violations of the distance-duality relation (DDR) can resolve the multidimensional cosmic tensions characterized by the $H_0$ and $S_8$ discrepancies. Using the Fisher-bias formalism, we reconstruct minimal, data-driven $η(z)$ profiles that capture the late-time deviations required to reconcile early- and late-Universe calibrations. While a constant DDR offset preserves the Pantheon-inferred matter density $Ω_m = 0.334 \pm 0.018$--leaving its inconsistency with the Planck best-fit $Λ$CDM model and weak-lensing surveys unresolved--a time-varying DDR substantially reduces cross-dataset inconsistencies and improves the global fit, yielding $Δχ^2 \simeq -10$ relative to $Λ$CDM when the SH0ES prior is excluded. This result suggests that the $Ω_m$ discrepancy may represent indirect evidence for a time-varying DDR. A hybrid scenario combining a time-dependent DDR with a phantom-like dark energy transition achieves the most consistent global reconciliation, reducing the tension with DES-Y3 measurements to below $2σ$. These findings indicate that a mild DDR violation, coupled with evolving dark energy, offers a coherent pathway toward jointly addressing the $H_0$ and $S_8$ tensions.

astro-ph.CO↗

arXiv2025

What Prevents Resolving the Hubble Tension through Late-Time Expansion Modifications?

We demonstrate that Type Ia supernovae (SNe Ia) observations impose the critical constraint for resolving the Hubble tension through late-time expansion modifications. Applying the Fisher-bias optimization framework to cosmic chronometers (CC), baryon acoustic oscillations (BAO) from DESI DR2, Planck CMB, and Pantheon+ data, we find that: (i) deformations in $H(z \lesssim 3)$ (via $w(z)$ reconstruction) can reconcile tensions between CC, Planck, DESI BAO, and SH0ES measurements while maintaining or improving fit quality ($Δχ^2 < 0$ relative to $Λ$CDM); (ii) In the neighborhood of Planck best-fit $Λ$CDM model, no cosmologically viable solutions targeting $H_0 \gtrsim 69$ satisfy SNe Ia constraints. MCMC validation confirms the maximum achievable $H_0 = 69.09\pm0.30$ ($χ^2_{\rm BF} \approx χ^2_{Λ\rm CDM}$) across all data combinations, indicating that the conflict between late-time $w(z)$ modifications and SNe Ia observations prevents complete resolution of the Hubble tension.

astro-ph.CO↗

arXiv2024

Kinetically Coupled Scalar Fields Model and Cosmological Tensions

In this paper, we investigate the kinetically coupled early dark energy (EDE) and scalar field dark matter to address cosmological tensions. The EDE model presents an intriguing theoretical approach to resolving the Hubble tension, but it exacerbates the large-scale structure tension. We consider the interaction between dark matter and EDE, such that the drag of dark energy on dark matter suppresses structure growth, which can alleviate large-scale structure tension. We replace cold dark matter with scalar field dark matter, which has the property of suppressing structure growth on small scales. We employed the Markov Chain Monte Carlo method to constrain the model parameters, our new model reveals a non-zero coupling constant of $0.030 \pm 0.026$ at a 68% confidence level. The coupled model yields the Hubble constant value of $72.38^{+0.71}_{-0.82}$ km/s/Mpc, which resolves the Hubble tension. However, similar to the EDE model, it also obtains a larger $S_8$ value compared to the $Λ$CDM model, further exacerbating the large-scale structure tension. The EDE model and the new model yield the best-fit values of $0.8316$ and $0.8146$ for $S_8$, respectively, indicating that the new model partially alleviates the negative effect of the EDE model. However, this signature disappears when comparing marginalised posterior probabilities, and both models produce similar results. The values obtained from the EDE model and the new model are $0.822^{+0.011}_{-0.0093}$ and $0.819^{+0.013}_{-0.0092}$, respectively, at a 68% confidence level.

astro-ph.CO↗

arXiv2024

Cosmological Constraints on Thermal Friction of Axion Dark Matter

In this paper, we investigate the process in which axion dark matter undergoes thermal friction, resulting in energy injection into dark radiation, with the aim of mitigating the Hubble tension and large-scale structure tension. In the early universe, this scenario led to a rapid increase in the energy density of dark radiation; in the late universe, the evolution of axion dark matter is similar to that of cold dark matter, with this scenario resembling decaying dark matter and serving to ease the large-scale structure tension. We employ cosmological observational data, including cosmic microwave background (CMB), baryon acoustic oscillation (BAO), supernova data (SNIa), $H_0$ measurement from SH0ES, and $S_8$ from the Dark Energy Survey Year-3 (DES), to study and analyze this model. Our results indicate that the thermal friction model offers partial alleviation of the large-scale structure tension, while its contribution on alleviating Hubble tension can be ignored. The new model yields the value of $S_8$ is $0.795\pm 0.011$ at a 68% confidence level, while the $Λ$CDM model yields a result of $0.8023\pm 0.0085$. In addition, the new model exhibits a lower $χ^2_\mathrm{tot}$ value, with a difference of -2.60 compared to the $Λ$CDM model. Additionally, we incorporate Lyman-$α$ data to re-constrain the new model and find a slight improvement in the results, with the values of $H_0$ and $S_8$ being $68.76^{+0.39}_{-0.35}$ km/s/Mpc and $0.791\pm 0.011$ at a 68% confidence level, respectively.

astro-ph.CO↗

arXiv2023

A Measurement of Hubble Constant Using Cosmographic Approach from Fast Radio Bursts and SNe Ia

The Hubble constant ${H}_0$ is a crucial parameter in cosmology. However, different cosmic observations have resulted in varying posterior results for ${H}_0$, leading to what is known as the ${H}_0$ tension. In order to address this issue, it is beneficial to use other dataset to constrain ${H}_0$. In this paper, via the cosmographic approach based on the Friedman-Lemaitre-Robertson-Walker (FLRW) metric to the dispersion measure of the intergalactic medium ${\rm{DM}}_{\rm{IGM}}(z)$ of Fast Radio Bursts (FRBs), we obtain the Taylor expansion of $\langle{\rm{DM}}_{\rm{IGM}}(z)\rangle$ in terms redshift $z$. The result for Hubble constant $H_0=65.5^{+6.4}_{-5.4}$ ${\rm{km~s^{-1}~Mpc^{-1}}}$ $(68$$\%$ ${\rm{C.L.}}) $, cosmological deceleration parameter $q_0=-0.50\pm 0.20 $ and the jerk parameter $j_0=-0.1^{+2.0}_{-2.5}$ using uncalibrated Supernova Ia (SNe Ia) Pantheon dataset combined with 18 localized FRBs are obtained. To demonstrate the impact of parameter degeneracies on our analysis methods, we compare the results using three different forms of $f_{\rm{IGM}}(z)$ and two different prior distributions for $Ω_{\rm{b,0}}$. Then we find that the uncertainty in $H_0$ is not significantly affected by the prior range of $f_{\rm{IGM}}(z)$ and $Ω_{\rm{b,0}}$, but the mean value is influenced by the priors for $f_{\rm{IGM}}(z)$ and $Ω_{\rm{b,0}}$ due to parameter degeneracies with $H_0$. Employing $f_{\rm{IGM}}(z)$ that evolves with redshift, we obtain the constraints for $H_0=69.0^{+6.7}_{-5.7}$ ${\rm{km~s^{-1}~Mpc^{-1}}}$. Furthermore, the mock analyses give a posterior estimation of $H_0$ with an accuracy of 4.6\% and higher precision for $q_0$ and $j_0$ in the near future.

astro-ph.CO↗

arXiv2023

Alleviating Cosmological Tensions with a Coupled Scalar Fields Model

In this paper, we investigate the interaction between early dark energy (EDE) and scalar field dark matter, proposing a coupled scalar fields model to address the Hubble tension and $S_8$ tension. While the EDE model successfully alleviates the Hubble tension, it exacerbates the $S_8$ tension. To mitigate the negative impact of EDE, we introduce the interaction between EDE and dark matter. Specifically, we replace cold dark matter with scalar field dark matter, given its capability to suppress structure growth on small scales. We constrained the new model using cosmological observations including the temperature and polarization anisotropy power spectra data of cosmic microwave background radiation (CMB) from \textit{Planck} 2018 results, baryon acoustic oscillations (BAO) measurements extracted from 6dFGS, SDSS and BOSS, the Pantheon sample of type Ia supernovae (SNIa), the local distance-ladder data (SH0ES), and the Dark Energy Survey Year-3 data. Employing Markov Chain Monte Carlo method, we find that this novel model yields best-fit values of $H_0$ and $S_8$ equal to $71.13$ km/s/Mpc and $0.8256$, respectively. Compared to the $Λ$CDM model, the new model alleviates the Hubble tension but still fails to resolve the $S_8$ tension. However, we obtain a smaller value of $S_8$ compared to the result of $0.8316$ obtained for EDE model, which mitigates to some extent the shortcoming of the EDE model.

astro-ph.CO↗

arXiv2022

Equality scale-based and sound horizon-based analysis of the Hubble tension

The Hubble horizon at matter-radiation equality ($k^{-1}_{\rm{eq}}$) and the sound horizon at the last scattering surface ($r_s(z_*)$) provides interesting consistency check for the $Λ$CDM model and its extensions. It is well known that the reduction of $r_s$ can be compensated by the increase of $H_0$, while the same is true for the standard rulers $k_{\rm{eq}}$. Adding extra radiational component to the early universe can reduce $k_{\rm{eq}}$. The addition of early dark energy (EDE), however, tends to increase $k_{\rm{eq}}$. We perform $k_{\rm{eq}}$- and $r_s$-based analyses in both the EDE model and the Wess-Zumino Dark Radiation (WZDR) model. In the latter case we find $ΔH_0 = 0.4$ between the $r_s$- and $k_{\rm{eq}}$-based datasets, while in the former case we find $ΔH_0 = 1.2$. This result suggests that the dark radiation scenario is more consistent in the fit of the two standard rulers ($k_{\rm{eq}}$ and $r_s$). As a forecast analyses, we fit the two models with a mock $k_{\rm{eq}}$ prior derived from \emph{Planck} best-fit $Λ$CDM model. Compared with the best-fit $H_0$ in baseline $Λ$CDM model, we find $ΔH_0 = 1.1$ for WZDR model and $ΔH_0 = - 2.4$ for EDE model.

astro-ph.CO↗

arXiv2022

Limit on the dark matter mass from its interaction with photons

In this work, we explore the phenomenology of generalized dark matter (GDM) which interacts with photons ($γ$). We assume that DM establishes elastic scattering with $γ$ when it has already become nonrelativistic, otherwise the abundance of DM today is disfavored by current observations. Within this scenario, the equation of state (EoS) of DM is determined by its mass ($m_χ$) and the DM-$γ$ scattering cross-section. The distinctive imprints of a nonzero EoS of DM on CMB angular power spectrum allow us to set a lower limit on $m_χ$ with Planck 2018 data alone, i.e., $m_χ > 8.7$ keV at $95\%$ C.L. In the study of cosmic concordance problems, we find that the GDM scenario preserves the sound horizon ($r_s(z_*)$) predicted in the fiducial $Λ$CDM model, and thus does not solve the $H_0$ tension. When performing the joint analysis of Planck+LSS datasets, the best-fit $S_8= 0.785\pm 0.017$ closely matches the given $S_8$ prior. This suggests that the GDM scenario can be counted as a viable candidate to restore the $S_8$ ($σ_{8}$) tension.

astro-ph.CO↗

arXiv2022

Can phantom transition at $z\sim 1$ restore the Cosmic concordance?

The tension among inferences of Hubble constant ($H_0$) is found in a large array of datasets combinations. Modification to the late expansion history is the most direct solution to this discrepancy. In this work, we examine the viability of restoring the cosmological concordance with a novel version of transitional dark energy (TDE). The main anchors for the cosmic distance scale: cosmic microwave background (CMB) radiation, baryon acoustic oscillation (BAO), and Type Ia supernova (SNe Ia) calibrated by Cepheids form a "impossible trinity", i.e., it's plausible to reconcile with any two of the three but unlikely to accommodate them all. Particularly, the tension between BAO and the calibrated SNe Ia can not be reconciled within the scenarios of late dark energy. Nevertheless, our analysis suggests that the TDE model can reconcile with CMB and SNe Ia calibrated by its absolute magnitude ($M_{\rm{B}}$) when the equation of state (EoS) of DE transits around $z\sim1$. Meanwhile, we see a positive sign that the EoS transits with the inclusion of a local prior on $M_{\rm{B}}$, whereas the opposite is true without the $M_{\rm{B}}$ prior.

astro-ph.CO↗