Sultana--Dyer Black Hole Spacetime and $h$-Almost Yamabe Solitons

Abstract

This paper investigates Yamabe-type soliton structures on the Sultana-Dyer (SD) black-hole spacetime. By employing the explicit metric and curvature quantities associated with the SD spacetime, we demonstrate that the non-Killing vector field $\partial_t$ induces an $h$-almost Yamabe soliton for explicitly determined functions $h$ and $λ$. We also establish the condition under which this structure reduces to an almost Yamabe soliton and examine why the coordinate vector fields $\partial_r$ and $\partial_θ$ do not satisfy the corresponding Yamabe flow conditions. Furthermore, we show that the energy-momentum tensor, consisting of a timelike dust component and a null radiation fluid, is compatible with the Riemann, conformal (Weyl), concircular, conharmonic, and projective curvature structures. This compatibility reveals a strong geometric correspondence between the matter distribution and the causal structure of the spacetime. However, when the time-dependent scalar-curvature profile is subject to the constraints associated with late-stage cosmic expansion, the null, weak, and dominant energy conditions are violated. These findings provide a geometric characterization of the time-dependent Sultana-Dyer spacetime within the framework of generalized Yamabe solitons.