T-duality of α′-correction to DBI action at all orders of gauge field

By explicit calculations of four-field couplings, we observe that the higher derivative corrections to the DBI action in flat space–time, can be either in a covariant form or in a T-duality invariant form. The two forms are related by a non-covariant field redefinition. Using this observation, we then propose a non-covariant but T-duality invariant action which includes all orders of massless fields and has two extra derivatives with respect to the DBI action.