“…M-theory compactifications on seven-manifolds with G 2 holonomy also give rise to large ensembles of 4d N = 1 vacua, where singularities at codimension 4, 6, and 7, encode the structure of gauge groups, non-chiral matter, and chiral matter, respectively; see [250] for an early review. More recently, constructions of so-called twisted connected sums [251] have given rise to millions of G 2 manifolds [252], which have been the subject of numerous physics studies in compact twisted connected sums [135,[253][254][255][256][257][258][259], and related Higgs bundle constructions [260][261][262][263][264]. For some recent progress on singular non-compact G 2 constructions and studies on gauge dynamics there, see [265,266].…”