Existence and Convergence of Least-Energy Solutions Involving the Logarithmic Schrödinger Operator

In this paper, we study critical semilinear nonlocal elliptic equations involving the logarithmic Schrödinger operator and its fractional pseudo-relativistic counterpart, both arising in quantum models with nonlocal and relativistic effects. We first establish the existence, uniqueness, and regularity of weak solutions to equations involving the logarithmic operator $(I-\mathrm{\Delta }{)}^{\ln }$ with subcritical logarithmic nonlinearities. We then investigate a Brezis–Nirenberg-type problem involving the fractional pseudo-relativistic Schrödinger operator $(I-\mathrm{\Delta }{)}^s$, and prove the existence of least-energy solutions under both subcritical and critical nonlinearities. In particular, we show that these least-energy solutions converge, up to a subsequence, to a nontrivial least-energy solution of the limiting problem as $s\to 0^{+}$. Our approach relies on variational methods, including the geometry of the Nehari manifold, uniform positive lower bounds, mountain-pass structure, the Palais–Smale condition, and delicate asymptotic analysis.