Cosmic String Spacetime in Dilaton Gravity and Flat Rotation Curves.pdf

arXiv:gr-qc/0412125v1 29 Dec 2004 COSMIC STRING SPACETIME IN DILATON GRAVITY AND FLAT ROTATION CURVES Tae Hoon Lee ? Department of Physics, Soongsil University, Seoul 156-743Korea (Dated: February 7, 2008) In dilaton gravity theories, we consider a string-like topological defect formed duringU(1) gauge symmetry-breaking phase transition in the early Universe,and far from the cosmic string we have vacuum solutions of the generalized Einstein equation. We discuss how they can be related to the ?atness of galactic rotation curves. PACS numbers: .+h, .+d, .+d I. INTRODUCTION Topological defects of various kinds could be generated when symmetry-breaking phase transitions took place in the early Universe. Defects such as global monopoles or cosmic strings were thought of as the seeds for galaxy and large-scale structure formation,[1] and their remnants might remain as galactic dark matter. The observed ?atness[2] of spiral galaxy rotation curves suggests the existence of dark matter whose energy density goes like 1/r 2. Since the global monopole which was found by Barriola and Vilenkin[3] as a solution of Einstein’s equations has energy density proportional to 1/r 2, it was suggested by Nucamendi and others[4] that the global monopole could account for some fraction of the galactic dark matter. Even though Harari and Loust′o[5] noticed that the monopole core mass