Boundary States for Supertubes in Flat Spacetime and Godel Universe

TL;DR

This paper constructs boundary states for supertubes in flat spacetime and Godel universe, analyzing their open string spectra, vacuum amplitudes, and stability, revealing critical energies and the disappearance of tachyonic instabilities due to stringy effects.

Contribution

It introduces a covariant formalism for boundary states of supertubes and their T-duals, and explores their properties in Godel universe, including stability and spectrum analysis.

Findings

Critical energy values for on-shell open strings on supertubes.

Stringy corrections eliminate tachyonic instabilities related to closed timelike curves.

Boundary states enable calculation of vacuum amplitudes and spectra in complex backgrounds.

Abstract

We construct boundary states for supertubes in the flat spacetime. The T-dual objects of supertubes are moving spiral D1-branes (D-helices). Since we can obtain these D-helices from the usual D1-branes via null deformation, we can construct the boundary states for these moving D-helices in the covariant formalism. Using these boundary states, we calculate the vacuum amplitude between two supertubes in the closed string channel and read the open string spectrum via the open closed duality. We find there are critical values of the energy for on-shell open strings on the supertubes due to the non-trivial stringy correction. We also consider supertubes in the type IIA Godel universe in order to use them as probes of closed timelike curves. This universe is the T-dual of the maximally supersymmetric type IIB PP-wave background. Since the null deformations of D-branes are also allowed in this PP-wave, we can construct the boundary states for supertubes in the type IIA Godel universe in the same way. We obtain the open string spectrum on the supertube from the vacuum amplitude between supertubes. As a consequence, we find that the tachyonic instability of open strings on the supertube, which is the signal of closed time like curves, disappears due to the stringy correction.