Bayesian Constraints on Bosonic Dark Matter in Neutron Stars within a Covariant Density-Functional Equation-of-State Ensemble

We investigate neutron stars admixed with repulsively self-interacting bosonic dark matter using current multi-messenger observations. The new analysis still awaits peer review, but it already lays out the central claim clearly.

That matters because cosmology operates at the edge of what current instruments can measure, where systematic errors and model assumptions are never trivial. Small discrepancies between independent measurements have historically pointed toward missing physics rather than simple calibration errors, and the ongoing tension in the Hubble constant is a live example of how a persistent disagreement between methods can reshape the theoretical landscape. Each new dataset that approaches this territory with independent systematics adds real information to a problem that has resisted easy resolution for more than a decade. We investigate neutron stars admixed with repulsively self-interacting bosonic dark matter (DM) using current multi-messenger observations. The dark component is modeled as a complex scalar field coupled to baryonic matter only through gravity, allowing dark-core and dark-halo configurations.

To quantify baryonic equation-of-state (EOS) uncertainties, we combine a three-dimensional scan over $(m_χ, λ, F_χ)$ with 27 DDME2-based covariant density-functional EOSs spanning. The models are confronted in a Bayesian framework with NICER mass--radius measurements from the Amsterdam and Maryland/Illinois analyses and the GW170817 tidal-deformability.

After Bayesian evidence weighting over the EOS ensemble, the EOS-relevant dark-sector scale $μ_χ\equiv m_χ/λ^{1/4}$ is localized around 250 MeV for both NICER data sets. In the $(m_χ, λ)$ parameterization, the marginalized boson-mass posterior peaks at $m_χ\simeq300$--$330$ MeV, while $λ$ remains broadly distributed.

Since the bosonic EOS depends on $m_χ$ and $λ$ only through $μ_χ$, their separate marginals are conditional on the adopted independent priors. The inferred DM fraction is more data-set dependent, with posterior modes near 4% for Maryland/Illinois and 12% for Amsterdam.

The relevance goes beyond one dataset because even small shifts in measured parameters can matter when the field is testing the limits of the standard cosmological model. The Lambda-CDM framework describes the observable universe with remarkable economy, but its success rests on two components, dark matter and dark energy, whose physical nature remains entirely unknown. Any credible measurement that tightens or loosens the constraints on those components moves the entire theoretical enterprise forward, regardless of whether the immediate result looks dramatic on its own terms.

Bosonic DM also shifts the inferred $Q_{\rm sat}$ from negative toward intermediate and positive values, whereas the response of $L_{\rm sym}$ is weaker. This indicates a model-dependent trade-off between DM-induced compactification and the high-density stiffness of baryonic matter.

Because this is still a preprint, the result should be read with genuine interest and proportionate caution. Peer review is not a guarantee of correctness, but it is a process that forces authors to respond to technical criticism from specialists who have no stake in a particular outcome. Preprints that survive that process, often with substantive revisions, emerge with a stronger evidential base than the version that first appeared. Until that stage is complete, the responsible reading keeps uncertainty explicitly visible rather than treating the claims as established findings.

The next step is to see whether the effect survives when independent surveys, different calibration strategies and tighter control of systematic uncertainties enter the picture. Programmes such as Euclid, DESI and the Rubin Observatory will deliver datasets over the next several years that cover the same parameter space with largely independent methods. If the current signal persists through those tests, its theoretical implications will become impossible to set aside. Until peer review and independent follow-up address those open questions, skepticism is not a failure of appreciation for the work; it is part of how science decides what to keep.

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