  In this note we describe hadrons: mesons and baryons as strings with electric
charges on their endpoints. We consider here only the neutral system with
opposite charges coupled to an external constant electric and magnetic fields.
We derive certain classical solutions including rotating folded open strings.
We write down the mode expansion and canonically quantize the system. The OPEs
associated with such strings are determined. We re-derive the non-commutativity
of the zero modes and the fact that the charges modify the spacetime metric. We
show that the quantum worldsheet energy momentum tensor on the boundary is
affected by the endpoint charges and differs from the corresponding Noether
current. We determine the generalization of the Veneziano scattering amplitude
for such strings in the critical dimension. Phenomenological implications are
addressed and in particular we show that the external magnetic field can be
tuned so that the amplitude vanishes for particular kinematic setups. We
discuss the generalization of such strings to non-critical four dimensional
spacetime. In particular we renormalize the divergence of the
Polchinski-Strominger effective action associated with the rotating folded
string.
