Disk relations for tree amplitudes in minimal coupling theory of gauge field and gravity

Understand

KLT relations on $S_2$ factorize closed string amplitudes into product of open string tree amplitudes.

• The field theory limits of KLT factorization relations hold in minimal coupling theory of gauge field and gravity.
• In this paper, we consider the field theory limits of relations on $D_2$.
• Though the relations on $D_2$ and KLT factorization relations hold on worldsheets with different topologies, we find the field theory limits of $D_2$ relations also hold in minimal coupling theory of gauge field and gravity.