# Mass spectrum of Type I string theory

The massless fields of the Type I string theory are the described by:

$$\begin{array}{*{20}{c}} {{\rm{Sector}}}&{{\rm{Massless fields}}}\\ {{\rm{R - R}}}&{{C_0}}\\ {{\rm{NS - NS}}}&{{g_{\mu \nu }},\Phi }\\ {{\rm{R - NS}}}&{{\Psi _\mu }}\\ {{\rm{NS - R}}}&{\lambda'}\\ {\rm{R}}&{}\\ {{\rm{NS}}}&{} \end{array}$$

1. Are there any (massless) fields in the R and NS sectors (open strings)?
2. What is the projection of state vectors from the Type IIB string theory to the Type I string theory?
3. What's the significance of the ' in $\lambda'$?
4. What exactly are the spectra of state vectors (in terms of $\mathbf{8}_s$, $\mathbf{8}_v$ etc.) in the Type I string theory?
5. If the Type I string theory is a projection of the Type IIB string theory, where do the open strings come from?
6. What is the mass spectrum of the Type I string theory?
• 1) Yes, the gauginos and gauge bosons, respectively. 2) Orientifold projection, as described in any textbook. 3) It's just a notation, convention. 4) The representations are clear from the indices in the notation and described in any textbook. 5) Open strings aren't considered projections of closed strings here; they're an independent sector. Projected closed strings are unorientable closed string. 6) A Hagedorn tower described in any textbook. – Luboš Motl May 13 '13 at 16:18