Detection of cosmic superstrings by geodesic test particle motion

Abstract

(p,q)-strings are bound states of p F-strings and q D-strings and are predicted to form at the end of brane inflation. As such these cosmic superstrings should be detectable in the universe. In this paper we argue that they can be detected by the way that massive and massless test particles move in the space-time of these cosmic superstrings, in particular we study solutions to the geodesic equation in the space-time of field theoretical (p,q)-strings. The geodesics can be classified according to the test particle's energy, angular momentum and momentum in the direction of the string axis. We discuss how the change of the magnetic fluxes, the ratio between the symmetry breaking scale and the Planck mass, the Higgs to gauge boson mass ratios and the binding between the F-and D-strings, respectively, influence the motion of the test particles. While massless test particles can only move on escape orbits, a new feature as compared to the infinitely thin string limit is the existence of bound orbits for massive test particles. In particular, we observe that -in contrast to the space-time of a single Abelian-Higgs string -bound orbits for massive test particles in (p,q)-string space-times are possible if the Higgs boson mass is larger than the gauge boson mass. We also compute the effect of the binding between the p-and the q-string on observables such as the light deflection and the perihelion shift. While light deflection can also be caused by other matter distributions, the possibility of a negative perihelion shift seems to be a feature of finite width cosmic strings that could lead to the unmistakable identification of such objects. In Melvin space-times, which are asymptotically non-conical, massive test particles have to move on bound orbits, while massless test particles can only escape to infinity if their angular momentum vanishes.

Geodesic motion in the space-time of cosmic strings interacting via magnetic fields

“…That this is possible for finite width cosmic strings was shown in [27,28]. We will demonstrate in the following that this is also possible in our model.…”

“…The perihelion shift and light deflection of massive and massless test particles, respectively, has been studied in the space-time of field theoretical cosmic string solutions previously [27,28]. Since our model is similar, we believe that the qualitative results for these two observables will be comparable.…”

“…In this present paper, the two sectors interact via the magnetic fields of the cosmic strings. In analogy to [28] we are hence first interested to see whether bound orbits exist also when the radii of the flux and scalar cores are equal, i.e. for β 1 = β 2 = 2.…”

“…they get deflected by the string. While the cosmic strings have very small width in comparison to their lengths and one would at first think that only the global deficit angle governs the deflection of light, it was shown already in [27,28] that the microscopical structure of the field configuration has an influence on the observables. It was e.g.…”

“…The test particle motion in different space-times containing cosmic strings has been investigated in [20][21][22][23][24], while the complete set of orbits of test particles in the space-time of a black hole pierced by an infinitely thin cosmic string has been given for a Schwarzschild black hole in [25] and for a Kerr black hole in [26]. Moreover, the geodesic motion of test particles in field theoretical cosmic string space-times has been given for Abelian-Higgs strings in [27] and for cosmic superstrings in [28].…”