Blowing-up Solutions with Residual Mass in a Slightly Subcritical Dirichlet Problem

In this paper, we study the Dirichlet elliptic problem $(\mathcal{P}_\varepsilon)$: $-\Delta u +V\,u = u^{p-\varepsilon}$, $u>0$ in $\Omega$, $u=0$ on $\partial\Omega$, where $\Omega\subset \R^n$ ( $n\geq 3$) is a bounded domain, $V$ is a smooth positive function on $\overline{\Omega}$, $p+1= 2n/(n-2)$ is the critical Sobolev exponent, and $\varepsilon >0$ is a small parameter. First, we show that, unlike the case of weak convergence to zero, interior bubbling solutions with a nonzero weak limit cannot occur in low dimensions. We then treat the general setting by removing the restriction that blow-up points are confined to the interior. Using delicate asymptotic expansions of the gradient of the associated functional, we prove that in dimensions $n=4$ and $n=5$, single blow-up point cannot coexist with residual mass.\\ We further elucidate the role of the sign of the normal derivative of the potential $V$ on the boundary: if it is positive, any single blow-up solution with residual mass must occur in the interior; if it is negative at some boundary point, boundary blow-up solutions with residual mass can be constructed. Finally, we construct both simple and non-simple interior blow-up solutions exhibiting residual mass, without any assumption on the sign of the normal derivative of $V$. These results provide new insights into the interaction between the potential, the geometry of the domain, and the critical nonlinearity.