A study of spacetime distortion around a scattered recoiling D-particle and possible astrophysical consequences

Abstract

We study a four-dimensional spacetime induced by the recoil of a D(irichlet)-particle, embeded in it, due to scattering by a moving string. The induced spacetime has curvature only up to a radius that depends on the energy of the incident string. Outside that region (`bubble') the spacetime is matched with the Minkowski spacetime. The interior of the bubble is consistent with the effective field theory obtained from strings, with non-trivial tachyon-like and antisymmetric tensor fields (in four dimensions the latter gives rise to an axion pseudoscalar field). The tachyonic mode, however, does not represent the standard flat-spacetime string tachyon, but merely expresses the instability of the distorted spacetime. Due to the non-trivial matter content of the interior of the bubble, there is entropy production, which expresses the fact that information is carried away by the recoil degrees of freedom. We also demonstrate that a particle can be captured by the bubble, depending on the particle's impact parameter. This will result in information loss for an external asymptotic observer, corresponding to production of entropy propotional to the area of the bubble. For the validity of our approach it is essential that the string length is a few orders of magnitude larger than the Planck length, which is a typical situation encountered in many D-brane-world models. A very interesting feature of our model is the emission of high-energy photons from the unstable bubble, which might be related to the observed apparent ``violations'' of the GZK cutoff.