Moving branes in the presence of background tachyon fields

We compute the boundary state associated with a moving Dp-brane in the presence of the open string tachyon field as a background field. The effect of the tachyon condensation on the boundary state is discussed. It leads to a boundary state associated with a lower-dimensional moving D-brane or a stationary instantonic D-brane. The former originates from condensation along the spatial directions and the latter comes from the temporal direction of the D-brane worldvolume. Using the boundary state, we also study the interaction amplitude between two arbitrary Dp ₁- and Dp ₂-branes. The long-range behavior of the amplitude is investigated, demonstrating an obvious deviation from the conventional form, due to the presence of the background tachyon field.