arXiv subjects

Chaoqian Ai

Publications and source records attributed to Chaoqian Ai.

3 recordsLinked to original sources

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↗