Small time asymptotics of spectral heat contents for subordinate killed Brownian motions related to isotropic {α}-stable processes

In this paper we study the small time asymptotic behavior of the spectral heat content $\widetilde{Q}_D^{(\alpha)}(t)$ of an arbitrary bounded $C^{1,1}$ domain $D$ with respect to the \textit{subordinate killed Brownian motion} in $D$ via an $(\alpha/2)$-stable subordinator. For all $\alpha\in (0,2)$, we establish a two-term small time expansion for $\widetilde{Q}_D^{(\alpha)}(t)$ in all dimensions. When $\alpha\in (1,2)$ and $d\geq 2$, we establish a three-term small time expansion for $\widetilde{Q}_D^{(\alpha)}(t)$.