Constraining String Gauge Field By Galaxy Rotation Curve And Planet Perihelion Precession

We discuss a cosmological model in which the string gauge field couples to matter and leads to an extra force which would have various effect on cosmological observations. We first introduce the model from considerations in string theory. Several tests on the model are then performed using astronomical observations including galaxy rotation curves and perihelion precession in the solar system.For a set of 22 galaxies, we fitted their rotation curves with both the string model and a particular dark matter model. The two models showed similar fitting power for this set of curves. The string field strengths in these galaxies, which is a parameter adjusted to fit these curves, are found to lie in a range spanning about 2 orders of magnitude. By dimensional analysis, we derived from the string model a relation between field strength, galaxy size and luminosity which is then verified with data of the 22 galaxies.The model is also used to explain anomalous perihelion precession of planets in the solar system. We solved precession motions for perturbations of 1) a magnetic-like force and 2) a general power law central force. For the latter case, a simple rule judging pro- or retrograde precession is derived. We then attributed the anomalous precession to the magnetic-like force due to string field and calculated field strengths in various locations in the solar system. The field distribution looks like a dipole field centered at the Sun. This feature is further explored using a field profile consisting of one part generated by the Sun and another background due to other matter in the Milky Way. As a compare with the result from precession, we also estimated the field strength in the Milky way by rotation curve, which turns out to be on a similar order of magnitude.