The Hart-Shelah example, in stronger logics

Abstract

We generalize the Hart-Shelah example \cite{HaSh:323} to higher infinitary logics. We build, for each natural number $k\geq 2$ and for each infinite cardinal $\lambda$, a sentence $\psi_k^\lambda$ of the logic $L_{(2^\lambda)^+,\omega}$ that (modulo mild set theoretical hypotheses around $\lambda$ and assuming $2^\lambda < \lambda^{+m}$) is categorical in $\lambda^+,\dots,\lambda^{+k-1}$ but not in $\beth_{k+1}(\lambda)^+$ (or beyond); we study the dimensional encoding of combinatorics involved in the construction of this sentence and study various model-theoretic properties of the resulting abstract elementary class ${\mathcal K}^*(\lambda,k)=(Mod(\psi_k^\lambda),\prec_{(2^\lambda)^+,\omega})$ in the finite interval of cardinals $\lambda,\lambda^+,\dots,\lambda^{+k}$.