Dynamical centers for the elliptic quantum algebra $B_{q,\lambda }({\widehat{gl}}_2{)}_c$

We identify generating functionals that satisfy dynamical exchange relations with the Lax matrices defining the face-type elliptic quantum algebra $B_{q,\lambda }({\widehat{gl}}_2{)}_c$, when the central charge takes the two possible values $c=\pm 2$. These generating functionals are constructed as quadratic trace-like objects in terms of the Lax matrices. The obtained structures are characterized as 'dynamical centers', i.e. the centrality property is deformed by dynamical shifts. For these values, the functionals define (genuine) abelian subalgebras of $B_{q,\lambda }({\widehat{gl}}_2{)}_c$. (paper)