Multi-Probe Cosmological Constraints on Clustering DBI Dark Energy Scenario

Abstract

We present a multi-probe observational analysis of a clustering tachyonic Dirac-Born-Infeld~(DBI) dark energy model. Its noncanonical kinetic term gives a subluminal sound speed, so dark energy perturbations can grow on subhorizon scales. Working in a multifluid framework that tracks both the background expansion and linear perturbations, we constrain the model with nested sampling, using Planck 2018 compressed CMB distance priors, DESI DR2 BAO, cosmic chronometers, $fσ_8$ growth data, and three Type Ia supernova compilations: Pantheon$+$, DES-SN5YR, and Union3. The standard cosmological parameters agree with $Λ$CDM within $2σ$, with DBI preferring a slightly lower $H_0$ and higher $Ω_{m0}$, with the largest shift being $\simeq1.8σ$ in $H_0$ for Pantheon$+$. The Bayesian evidence favours DBI in every compilation, moderately for Pantheon$+$ ($Δ\ln\mathcal{Z}\simeq3.4$) and inconclusively for DES-SN5YR and Union3 ($Δ\ln\mathcal{Z}\simeq0.6$-$0.7$). The field thaws naturally. Dark energy perturbations stay several orders of magnitude below matter perturbations, yet the noncanonical sound speed still alters the Hubble friction term, raising $S_8$ by only $\approx0.5σ$ relative to $Λ$CDM. Four independent diagnostics, namely the CPL parametrization, $Om(z)$, the statefinder hierarchy, and the growth index, all point to genuinely evolving dark energy rather than a cosmological constant. The thermal history is left intact, with negligible early dark energy. However, one limitation remains. Because $w_ϕ=\dotϕ^2-1\geq-1$, the phantom regime is out of reach, which is in line with the no-go theorem for a single minimally coupled scalar field, so the model cannot follow the DESI DR2 preference for an effective equation of state crossing $w=-1$.