D-branes as Tachyon Lumps in String Field Theory

TL;DR

This paper develops a systematic method to analyze tachyonic lump solutions in open bosonic string field theory, confirming they represent lower-dimensional D-branes with accurate mass and size estimates.

Contribution

It introduces a refined level expansion scheme accounting for all higher derivatives, enabling precise calculations of D-brane properties in string field theory.

Findings

Lump masses agree with expected D-brane masses within 1%

Lump size estimated at approximately 9.3 times the square root of alpha prime

The method provides a natural infrared and ultraviolet cutoff for string field theory

Abstract

It has been conjectured that the tachyonic lump solution of the open bosonic string field theory describing a D-brane represents a D-brane of one lower dimension. We place the lump on a circle of finite radius and develop a variant of the level expansion scheme that allows systematic account of all higher derivative terms in the string field theory action, and gives a calculational scheme that can be carried to arbitrary accuracy. Using this approach we obtain lump masses that agree with expected D-brane masses to an accuracy of about 1%. We find convincing evidence that in string field theory the lump representing a D-brane is an extended object with a definite profile. A gaussian fit to the lump gives a 6-sigma size of 9.3 \sqrt{\alpha'}. The level truncation scheme developed here naturally gives rise to an infrared and ultraviolet cut-off, and may be useful in the study of quantum string field theory.