K-theory and phase transitions at high energies
  The duality between $E_8\times E_8$ heteritic string on manifold $K3\times T^2$ and Type IIA string compactified on a Calabi-Yau manifold induces a correspondence between vector bundles on $K3\times T^2$ and Calabi-Yau manifolds. Vector bundles over compact base space $K3\times T^2$ form the set of isomorphism classes, which is a semi-ring under the operation of Whitney sum and tensor product. The construction of semi-ring $Vect\ X$ of isomorphism classes of complex vector bundles over X leads to the ring $KX=K(Vect\ X)$, called Grothendieck group. As K3 has no isometries and no non-trivial one-cycles, so vector bundle winding modes arise from the $T^2$ compactification. Since we have focused on supergravity in d=11, there exist solutions in d=10 for which space-time is Minkowski space and extra dimensions are $K3\times T^2$. The complete set of soliton solutions of supergravity theory is characterized by RR charges, identified by K-theory. Toric presentation of Calabi-Yau through Batyrev's toric approximation enables us to connect transitions between Calabi-Yau manifolds, classified by enhanced symmetry group, with K-theory classification. 
T.V. Obikhod
hep-th