Brane fusion in the bosonic string and the emergence of fermionic strings

TL;DR

This paper explores how fermionic string theories emerge from bosonic string theories through a truncation process, revealing a potential bosonic origin of space-time fermions, supersymmetry, and D-branes in quantum gravity.

Contribution

It demonstrates a consistent truncation method from bosonic to fermionic strings, linking fermionic properties to bosonic origins and predicting D-brane tensions.

Findings

Fermionic string theories can be derived from bosonic string theories via truncation.

The truncation determines anomaly-free Chan-Paton groups for Type I and O theories.

Predicted tensions of space-filling D-branes in fermionic theories.

Abstract

We review the emergence of the ten-dimensional fermionic closed string theories from subspaces of the Hilbert space of the 26-dimensional bosonic closed string theory compactified on an $E_8\times SO(16)$ lattice. They arise from a consistent truncation procedure which generates space-time fermions out of bosons. This procedure is extended to open string sectors. We prove that truncation of the unique tadpole-free $SO(2^{13})$ bosonic string theory compactified on the above lattice determines the anomaly free Chan-Paton group of the Type I theory and the consistent Chan-Paton groups of Type O theories. It also predicts the tension of space-filling D-branes in these fermionic theories. The derivation of these fermionic string properties from bosonic considerations alone points towards a dynamical origin of the truncation process. Space-time fermions and supersymmetries would then arise from bosonic degrees of freedom and no fermionic degrees of freedom would be needed in a fundamental theory of quantum gravity.