Editing Mirror symmetry (string theory) (section)

===Theoretical physics===
In addition to its applications in enumerative geometry, mirror symmetry is a fundamental tool for doing calculations in string theory. In the A-model of topological string theory, physically interesting quantities are expressed in terms of infinitely many numbers called [[Gromov–Witten invariant]]s, which are extremely difficult to compute. In the B-model, the calculations can be reduced to classical [[integral]]s and are much easier.<ref>{{harvnb|Zaslow|2008|pages=533–534}}.</ref> By applying mirror symmetry, theorists can translate difficult calculations in the A-model into equivalent but technically easier calculations in the B-model. These calculations are then used to determine the probabilities of various physical processes in string theory. Mirror symmetry can be combined with other dualities to translate calculations in one theory into equivalent calculations in a different theory. By outsourcing calculations to different theories in this way, theorists can calculate quantities that are impossible to calculate without the use of dualities.<ref>{{harvnb|Zaslow|2008|loc=sec. 10}}.</ref>

Outside of string theory, mirror symmetry is used to understand aspects of [[quantum field theory]], the formalism that physicists use to describe [[elementary particle]]s. For example, [[gauge theory|gauge theories]] are a class of highly symmetric physical theories appearing in the standard model of particle physics and other parts of theoretical physics. Some gauge theories which are not part of the standard model, but which are nevertheless important for theoretical reasons, arise from strings propagating on a nearly singular background. For such theories, mirror symmetry is a useful computational tool.<ref>{{harvnb|Hori et al.|2003|page=677}}.</ref> Indeed, mirror symmetry can be used to perform calculations in an important gauge theory in four spacetime dimensions that was studied by [[Nathan Seiberg]] and Edward Witten and is also familiar in mathematics in the context of [[Donaldson invariant]]s.<ref>{{harvnb|Hori et al.|2003|page=679}}.</ref> There is also a generalization of mirror symmetry called [[3D mirror symmetry]] which relates pairs of quantum field theories in three spacetime dimensions.<ref>{{harvnb|Intriligator|Seiberg|1996}}.</ref>