Lumps and P-branes in Open String Field Theory

We describe numerical methods for constructing lump solutions in open string field theory. According to Sen, these lumps represent lower dimensional Dp-Branes and numerical evaluation of their energy can be compared with the expected value for the tension. We take particular care of all higher derivative terms inherent in Witten's version of open string field theory. The importance of these terms for off shell phenomena is argued in the text. Detailed numerical calculations done for the case of general $p$ brane show very good agreement with Sen's conjectured value. This gives credence to the conjecture itself and establishes further the usefulness of Witten's version of SFT .