We study the orbifold singularities X=\mathbb{C}^3/\GammaX=ℂ3/Γ
where \GammaΓ
is a finite subgroup of SU(3)SU(3).
M-theory on this orbifold singularity gives rise to a 5d SCFT, which is
investigated with two methods. The first approach is via 3d McKay
correspondence which relates the group theoretic data of
\GammaΓ
to the physical properties of the 5d SCFT. In particular, the 1-form
symmetry of the 5d SCFT is read off from the McKay quiver of
\GammaΓ
in an elegant way. The second method is to explicitly resolve the
singularity XX
and study the Coulomb branch information of the 5d SCFT, which is
applied to toric, non-toric hypersurface and complete intersection
cases. Many new theories are constructed, either with or without an IR
quiver gauge theory description. We find that many resolved Calabi-Yau
threefolds, \widetilde{X}X̃,
contain compact exceptional divisors that are singular by themselves.
Moreover, for certain cases of \GammaΓ,
the orbifold singularity \mathbb{C}^3/\Gammaℂ3/Γ
can be embedded in an elliptic model and gives rise to a 6d (1,0) SCFT
in the F-theory construction. Such 6d theory is naturally related to the
5d SCFT defined on the same singularity. We find examples of rank-1 6d
SCFTs without a gauge group, which are potentially different from the
rank-1 E-string theory.