Modeling the Beam of Gravitational Radiation from a Cosmic String Loop

Abstract

We investigate exact and approximate techniques to calculate the emission of gravitational radiation from cosmic string loops in order to generate beam models covering the entire celestial sphere for a wide range of modes $m$. One approach entails summing over contributions of stationary and nearly-stationary points of individual, factorized, left- and right-moving modes. This "multipoint method" generalizes traditional methods that rely on expansions around exact stationary points of mode products. A second complementary approach extends the method of steepest descent to generate an asymptotic description of the beam as $m \to \infty$. We present example calculations of the emission of power from cusp-containing loops and compare the results with those obtained by numerically exact techniques as well as by previous approaches. The multipoint method achieves its best results at an intermediate range of modes, improving over previous methods in terms of accuracy. It handles the emission from all regions of the loop not just those near cusps. We demonstrate this capability by making a detailed study of the "pseudocusp" phenomenon.