A no-go result for regular GR-connected isotropic Morris–Thorne wormholes in f(R, T) = R + σRT gravity
We study the exact Morris–Thorne (MT) wormhole in the trace-curvature coupled theory f(R, T) = R + σRT, using the consistent variational formulation of relativistic perfect fluids in f(R, T) gravity. We ask whether this fixed geometry can be reconstructed from an isotropic perfect fluid on a branch regularly connected to the general relativistic limit. In Einstein form, the MT geometry requires a conserved effective source with unequal radial and tangential pressures. This already signals a tension with an isotropic physical fluid. We show that the tension becomes a genuine obstruction to tangential consistency. At the general relativistic order, the temporal and radial equations impose one isotropic seed, while the tangential equation imposes an incompatible one. Therefore, no regular GR-connected isotropic perfect-fluid branch can satisfy all component equations for the exact MT geometry. We also analyse the reduced temporal–radial branch as a diagnostic example, showing that the small-coupling expansion should be treated as a formal asymptotic diagnostic, with high-order coefficient diagnostics giving no evidence for a positive radius of convergence, and that the branch explicitly fails the tangential equation. Although the perturbative no-go result alone does not exclude disconnected finite-coupling branches, the radial–tangential consistency condition also rules out smooth, asymptotically decaying finite-coupling isotropic branches for the exact MT geometry. Thus, the regular isotropic inverse reconstruction fails once the full angular component of the field equations is imposed.
