Saturated models
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The automorphism group
In a recent paper Nurkhaidarov and Schmerl 2011 proved the following: Let $\kappa$ be regular, uncounale, and such that $\kappa^{<\kappa}=\kappa$. For each completion $T\supseteq\PA$ let $M^\kappa_T$ be the saturated model of $T$ of cardinality $\kappa$. There is a set $\mathcal T$ of completions of $PA$, such that $|{\mathcal T}|=2^{\aleph_0}$ and for all $T, T'\in {\mathcal T}$, if $T\not=T'$, then $\aut(M^\kappa_T)\not\cong\aut(M^\kappa_{T'})$.
