Higher-Order Corrections to BFKL Evolution from $t$-Channel Unitarity

Using reggeon diagrams as a partial implementation of $t$-channel unitarity, $O(g^4)$ corrections to the BFKL evolution equation have been obtained. We describe the spectrum and holomorphic factorization properties of the resulting scale-invariant kernel. For a gauge theory, $t$-channel unitarity can be studied directly in the complex $j$-plane by implementing Ward identity constraints together with the group structure of reggeon interactions. We discuss how both the $O(g^2)$ BFKL kernel and the $O(g^4)$ corrections can then be derived.