Bulk viscous cosmology in curvature-matter coupled f(R,Lm) gravity

We study late-time cosmic acceleration in curvature-matter coupled gravity described by an arbitrary function [Formula: see text]. We investigate a spatially flat FLRW Universe filled with a bulk viscous cosmic fluid, the only dissipative contribution compatible with homogeneity and isotropy. By assuming a dust-like background and adopting the phenomenological ansatz [Formula: see text], we focus on the model [Formula: see text]. For [Formula: see text], the cosmological equations admit an analytic solution for the Hubble parameter [Formula: see text] (for [Formula: see text]), allowing the reconstruction of key cosmological observables. The free parameters [Formula: see text] are constrained using independent [Formula: see text], Pantheon+SH0ES and DESI data. We find that [Formula: see text] is tightly constrained around [Formula: see text] and satisfies [Formula: see text], ensuring positivity of the energy density, while the viscosity coefficient is consistently positive, indicating physically viable entropy production. The model predicts a transition from decelerated to accelerated expansion, with present-day [Formula: see text], a quintessence-like effective equation of state [Formula: see text], late-time violation of the strong energy condition and a negative slope of the [Formula: see text] diagnostic. These results show that bulk viscous [Formula: see text] gravity presents a viable phenomenological description at the background level, although current BAO data favor [Formula: see text]CDM.

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