The quasiopen string.

Abstract

The quasiopen string in D dimensions is defined by the Nambu-Goto action and the boundary conditions (x'+x)(σ α ,τ)=V α (x'-x) (σ α ,τ), where σ=σ 1 and σ 2 denote the ends of the string, x'≡∂x/∂σ, and the V α (α=1,2) are real symmetric orthogonal matrices. (The usual open string corresponds to V 1 =V 2 =−1.) We impose Poincare invariance in d dimensions, d α ) jk =−δ jk for j,k ∈ Poincare sector and (V α ) jk =0 if only one of j,k belongs to the Poincare sector. Further quantization gives D=26 and a mass spectrum with a ground-state mass squared M G 2 =−(1−J i ||theta i ||(1-||theTa I ||)/4)/α', where ||theta i ||≤(½), exp(2iπtheta i ) are the eigenvalues of V 2 V 1 , and α' is the slope parameter in the string action. A choice of theta i giving a tachyon-free spectrum is thus possible if d≤10.