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

KLT relations on image 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 image. Though the relations on image and KLT factorization relations hold on worldsheets with different topologies, we find the field theory limits of image relations also hold in minimal coupling theory of gauge field and gravity. We use the image relations to give three- and four-point tree amplitudes where gluons are minimally coupled to gravitons. We also give a further discussion on general tree amplitudes in minimal coupling theory of gauge field and gravity. In general, any tree amplitude with M gravitons in addition to N gluons can be given by pure-gluon tree amplitudes with image legs.