E8x

E8x is a notation encountered in several disciplines, where the symbol E8 denotes the exceptional Lie group or the E8 lattice, and the "x" is used as a multiplication or direct-product operator. In mathematics, E8 can refer to the E8 root system and lattice in eight dimensions. When written as E8 × E8, it denotes the direct product of two copies of E8, yielding a sixteen-dimensional structure. This product appears in various constructions, notably in string theory and in lattice theory, and the E8 lattice underpins the E8 × E8 even unimodular lattice used for compactifications.

In theoretical physics, E8 × E8 is best known as the gauge group of the E8 × E8 heterotic string theory, a major framework aiming to unify gravity with gauge interactions. The theory is formulated in ten spacetime dimensions with gauge symmetry E8 × E8, and six extra dimensions are typically compactified to produce four-dimensional physics. The symmetry structure has influenced model-building and the study of anomaly cancellation and dualities.

Outside of these contexts, E8x may appear as shorthand in descriptions or notes for E8-related objects, but without context it is ambiguous. The conventional form is E8 × E8 or E8 lattice, depending on the subject.