📝 SummarXiv

Abstract

We present a model-independent null test of the late-time cosmological response to a reduced sound horizon, as typically required by early-universe solutions to the Hubble tension. In this approach, we phenomenologically impose a shorter sound horizon without modeling early-universe physics to isolate its impact on late-time dark energy inference. Using baryon acoustic oscillations (BAO), supernovae (SN), big bang nucleosynthesis (BBN), and local $H_0$ data, while explicitly avoiding CMB anisotropies, we examine how this calibration shift propagates into constraints on the dark energy equation of state. We find that lowering $r_d$ systematically drives the $w_0$-$w_a$ posterior toward less dynamical, quintessence-like behavior, bringing it closer to $\Lambda$CDM. This result underscores that some of the apparent evidence for evolving or phantom-like dark energy may reflect early-universe assumptions rather than genuine late-time dynamics. More broadly, our analysis highlights the importance of carefully disentangling calibration effects from physical evolution in interpreting forthcoming results from DESI and future surveys.