To add

- Christoph Weis,
*The Drinfel’d centres of String 2-groups*(arXiv:2202.01271)

added publication data for:

- Andre Henriques,
*Integrating $L_\infty$-algebras*, Compositio Mathematica, Volume 144, Issue 4 July 2008 , pp. 1017-1045 (arXiv:math/0603563, doi:10.1112/S0010437X07003405)

added publication data for:

- Thomas Nikolaus, Christoph Sachse, Christoph Wockel,
*A Smooth Model for the String Group*, International Mathematics Research Notices, Volume: 2013 , Issue: 16 , 2013 (arXiv:1104.4288, doi:10.1093/imrn/rns154)

By the way, I think this perspective that the String 2-group, even in the smooth case, “was defined” to be a 3-connected cover is misled:

By it’s very name, the String 2-group is meant to be that $G$ such that $G$-structure encodes cancellation of the Green-Schwarz anomaly.

That for the global GS anomaly (i.e. disregarding differential structure) this is given by a 3-connected cover of the homotopy type pf $Spin$ is a noteworthy phenomenon, but not the definition.

]]>Ok, so have added

]]>with $A$ not necessarily chosen to be $\mathbf{B}U(1)$ but only of the same homotopy type, …

Yes, on p. 29-30:

]]>[ our definition ] is a generalisation as well as a weakening of the following approach to smooth string group extensions (see, for instance, [FRS16]):

Reading that sounds as though the $A$ of the extension could be anything, but it’s limited to being homotopy equivalent to $B U(1)$, right?

Triple adjunction rather than adjoint quadruple, hmm.

]]>Thanks for the pointer.

It seems to have gone largely unrecognized that the cohesive $\infty$-topos-theoretic discussion of the String 2-group is in section 5.1.4 of dcct (p. 583).

]]>Added a (sketchy) pointer to

- Severin Bunk,
*Principal $\infty$-Bundles and Smooth String Group Models*, arXiv:2008.12263