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High Energy Physics - Theory, hep-th
Abstract:
The K3 sigma model based on the Z_2-orbifold of the D_4-torus theory is
studied. It is shown that it has an equivalent description in terms of twelve
free Majorana fermions, or as a rational conformal field theory based on the
affine algebra su(2)^6. By combining these different viewpoints we show that
the N=(4,4) preserving symmetries of this theory are described by the discrete
symmetry group Z_2^8:M_{20}. This model therefore accounts for one of the
largest maximal symmetry groups of K3 sigma models. The symmetry group involves
also generators that, from the orbifold point of view, map untwisted and
twisted sector states into one another.