Boundary States for Supertubes in Flat Spacetime and Gödel Universe

We construct boundary states for supertubes in the flat spacetime. Since the T-dual objects of supertubes are moving spiral D1-branes (D-helices), which we can obtain 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 Gödel universe in order to use them as probes of closed timelike curves. We construct the boundary states for supertubes 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. [email protected]