The tremendous success of string theory in reproducing/predicting physical quantities in ordinary field theories partially owes to the fact that these nonperturbative effects have counterpart in string theory, as D-branes within D-branes The most well-known example is the instantons in 4 dimensional Yang-Mills theory, which are considered to be equivalent to a bound state of DO-branes and D4-branes. The equivalence, so far, has been supported by various consistency checks such as supersymmetries preserved, charges, masses and so on. Precisely speaking, the instantons are gauge field configurations on the D4-brane world volume theory at low energy. This means that for small size of instantons the instanton configurations would receive stringy a1 corrections. Thus the instanton gauge configuration is trustable only for large size of the instantons. On the other hand, the DO-branes are pointlike, and the DO-brane description, using the low energy effective action, should be valid in completely opposite parameter regions. This kind of problems are generic for arguments based on BPS properties and very difficult to solve Therefore it is very interesting to connect these two descriptions explicitly.
展开▼
