Poisson Brackets, Strings and Membranes

We construct Poisson brackets at boundaries of open strings and membranes with constant background fields which are compatible with their boundary conditions. The boundary conditions are treated as primary constraints which give infinitely many secondary constraints. We show explicitly that we need only two (the primary one and one of the secondary ones) constraints to determine Poisson brackets of strings. We apply this to membranes by using canonical transformations.Comment: 9 pages, references and a note are added, title and abstract is changed, the section 3 is improved, the version to appear in EPJ