Generalized geometry, calibrations and supersymmetry in diverse dimensions
We consider type II backgrounds of the form $$ {\mathbb{R}^{1,d - 1}} \times {\mathcal{M}_{10 - d}} $$ for even d, preserving 2
d/2 real supercharges; for d = 4, 6, 8 this is minimal supersymmetry in d dimensions, while for d = 2 it is $$ \mathcal{N} = \left( {2,0} \right) $$ supersymmetry in two dimensions. For d = 6 we prove, by explicitly solving the Killing-spinor equations, that there is a one-to-one correspondence between background
supersymmetry equations in pure-spinor form and D-brane generalized calibrations; this correspondence had been known to hold
in the d = 4 case. Assuming the correspondence to hold for all d, we list the calibration forms for all admissible D-branes, as well as the background supersymmetry equations in pure-spinor
form. We find a number of general features, including the following: The pattern of codimensions at which each calibration
form appears exhibits a (mod 4) periodicity. In all cases one of the pure-spinor equations implies that the internal manifold
is generalized Calabi-Yau. Our results are manifestly invariant under generalized mirror symmetry.