S. Sciuto

CLASSICAL p-BRANES FROM BOUNDARY STATE ∗

We show that the boundary state description of a Dp-brane is strictly related to the corresponding classical solution of the low-energy string effective action. By projecting the boundary state on the massless states of the closed string we obtain the tension, the R-R charge and the large-distance behavior of the classical solution. We discuss both the case of a single D-brane and that of bound states of two D-branes. We also show that in the R-R sector the boundary state, written in a picture which treats asymmetrically the left and right components, directly yields the R-R gauge potentials.

MICROSCOPIC STRING ANALYSIS OF THE D0-D8 BRANE SYSTEM AND DUAL R-R STATES

Abstract Using the boundary state formalism, we perform a microscopic string analysis of the interaction between two D-branes and provide a local interpretation for the R-R force in the D0–D8 brane system. To do so, we construct BRST invariant vertex operators for the massless R-R states in the asymmetric picture that are proportional to potentials rather than field strengths. The Hilbert space of such R-R states contains combinations of two vectors that decouple from all physical amplitudes, even in the presence of boundaries. Identifying these vectors, we remove the null states and recover duality relations among R-R potentials. If we specify to the D0–D8 brane system, this mechanism implies that the R-R 1-form state has a non-zero overlap with both the D0-brane and the D8-brane, thus explaining from a local point of view the non-vanishing R-R contribution in the interaction for the D0–D8 brane system and those related to it by duality.

N-point g-loop vertex for a free bosonic theory with vacuum charge Q

Starting fron the N-point vertex on the sphere and using the sewing procedure we construct the N-point g-loop vertex for a free bosonic theory with vacuum charge Q. We then show that, when this vertex is saturated with N highest weight states, it gives their correlation function on an arbitrary Riemann surface of genus g. We also extend our formalism to the case of a free scalar field compactified on a circle, which is related to the Coulomb gas description of minimal models.

A simple expression for the multiloop amplitude in the bosonic string

Abstract Using the previously constructed new N-string vertex and BRST invariant twisted propagator we obtain a simple and explicit expression for the multiloop partition function of the bosonic string. We construct also the two-loop amplitude with N external tachyons and give the recipe for writing the amplitude at any perturbative order.

Scattering of Closed Strings from Many D-branes

We develop an operator formalism to compute scattering amplitudes of arbitrary bosonic string states in the background of many D-branes. Specifically, we construct a suitable boundary state which we use to saturate the multi-Reggeon vertex in order to obtain the generator of multi-membrane scattering amplitudes. We explicitly show that the amplitudes with h parallel D-branes are similar to amplitudes with h − 1 open string loops.

N-string, g-loop vertex for the fermionic string

Abstract We construct an N -string, g -loop vertex for the fermionic string, that is the supersymmetric extension of the analogous bosonic vertex. As a byproduct we obtain also the g -vacuum for the fermionic string.

Anyons and quantum groups

Abstract Anyonic oscillators with fractional statistics are built on a two-dimensional square lattice by means of a generalized Jordan-Wigner construction, and their deformed commutation relations are thoroughly discussed. Such anyonic oscillators, which are non-local objects that must not be confused with q-oscillators, are then combined a la Schwinger to construct the generators of the quantum group SU(2)q with q = exp(iπν), where ν is the anyonic statistical parameter.

COVARIANT N STRING AMPLITUDE

The BRST-invariant N-reggeon vertex (for the bosonic string) previously given by us in the operator formulation is considered in more detail. In particular we present a direct derivation from the string path integral. Several crucial symmetry properties found a posteriori before, become a priori clearer in this formulation. A number of delicate points related to zero modes, cut off procedures and normal ordering prescriptions are treated in some detail. The old technique of letting the string field acquire a small dimension 12e → 0+ is found especially elegant.

BRST INVARIANT N REGGEON VERTEX

Abstract An N -reggeon vertex is constructed with the inclusion of the contribution of the ghost coordinates. It is shown that it is projective and BRST invariant.

N-string vertex and loop calculation in the bosonic string

Abstract We construct a BRST invariant twisted propagator and discuss different forms of the N -string vertex. We then use them for constructing loop diagrams in the bosonic string.