THE DYNAMICS OF OPEN STRINGS IN A BACKGROUND ELECTROMAGNETIC FIELD

Abstract

The classical and quantum dynamics of an open bosonic string propagating in the D-dimensional space-time in the presence of a background electromagnetic field is investigated. An important point in this consideration is the use of the generalized light-like gauge. There are considered the two types of strings: the neutral strings with charges at their ends obeying the condition q1+q2=0 and the charged strings having a net charge q1+q2≠0. The consistency of the theory demands that the background electric field does not exceed its critical value. The distance between the mass levels of the neutral open string decreases (1−e2) times in comparison with the free string where e is the dimensionless strength of the electric field. The magnetic field does not affect this distance. It is shown that at a classical level, the squared mass of the neutral open string has a tachyonic contribution due to the motion of the string as a whole in transverse directions. The tachyonic term disappears if one considers, instead of M2, the string energy in a special reference frame where the projection of the total canonical momentum of the string onto the electric field vanishes. The contributions due to zero point fluctuations to the energy spectrum of the neutral string and to the Virasoro operators in the theory of charged string are found. It is shown that the constraint on the strength of an external electric field is absent when the open bosonic string is placed in an external electromagnetic field of a special configuration. In the case of four-dimensional space-time, it corresponds to the electric and magnetic fields which are equal and perpendicular to each other (isotropic configuration). The external electromagnetic field does not act on the fermionic variables of the spinning string.