MILLIMETER AND RADIOASTRONOMICAL CONSTRAINTS ON THE COSMOLOGICAL EVOLUTION OF STRINGS

Abstract

We study and place constraints on cosmic strings and on their cosmological evolution with emphasis on the results of five measurements: (i) millisecond pulsar timings, (ii) binary pulsar timings, (iii) spatial fluctuations in the intensity of the cosmic microwave background radiation (MBR). For superconducting strings (hereafter SCS), we add two other results: the spectrum of the MBR in (iv) the Rayleigh-Jean side and in (v) the Wien side. We find compatibility conditions between these five results which constrain the string evolution parameters independently of any numerical simulation result. We compare and comment about the gravitational decay rate of fundamental quantum strings in D=4, which appears closely related to that of classical cosmic strings. The absence of distortion recently reported by COBE’s FIRAS experiment leads to the following upper limits on: (a) the comptonization parameter, y≤10−3; (b) the chemical potential due to SCS, μoscs≤0.5 10−3; (c) the electromagnetic radiation to gravitational radiation ratio, f≤2.3 10−2; (d) the string parameter: Gμ<10−6 for generic values of string evolution parameters, Gμ<10−7 for values derived from numerical simulations. The small value of f shows that the decay of SCS must be governed by gravitation. The latest PSR 1937+21 timing measurements and the preliminary COBE data converge to the same upper limits on Gμ. These limits continue to descend but the breaking point is not yet reached.