Energy-momentum correlations for Abelian Higgs cosmic strings

Abstract

We report on the energy-momentum correlators obtained with recent numerical simulations of the Abelian Higgs model, essential for the computation of cosmic microwave background and matter perturbations of cosmic strings. Due to significant improvements both in raw computing power and in our parallel simulation framework, the dynamical range of the simulations has increased fourfold both in space and time, and for the first time we are able to simulate strings with a constant physical width in both the radiation and matter eras. The new simulations improve the accuracy of the measurements of the correlation functions at the horizon scale and confirm the shape around the peak. The normalization is slightly higher in the high wave-number tails, due to a small increase in the string density. We study, for the first time, the behavior of the correlators across cosmological transitions and discover that the correlation functions evolve adiabatically; i.e., the network adapts quickly to changes in the expansion rate. We propose a new method for constructing source functions for Einstein-Boltzmann integrators, comparing it with two other methods previously used. The new method is more consistent, easier to implement, and significantly more accurate.

Redshift-space distortions from vector perturbations

“…Based on large numerical field-theory simulations of cosmic strings, Ref. [6] derived fitting functions to the various unequal time correlators of the defect energymomentum tensor. As discussed in the erratum of [6], the power spectrum of T 0i of a causal source is generically proportional to k 2 on large scales.…”

“…Other mechanisms such as topological defects [5][6][7], magnetic fields [8], inflation with vector fields [9,10] or vector-field-based models of modified gravity [11][12][13][14] can generate vector perturbations throughout the history of the Universe and on a wide range of scales. If they persist until late times, or are even generated there, the presence of such vector perturbations could 'pollute' the measurement of the scalar degrees of freedom and spoil precision cosmology with future large surveys if they are not properly taken into account.…”

Gravitational interactions of finite thickness global topological defects with black holes

“…The evolution of global defects in non-trivial gravitational backgrounds requires the solution of the full dynamical field equations derived by variation of the scalar field action with the appropriate background metric. Such analyses and numerical simulations have been performed in the context of homogeneous expanding FRW background metrics for global defects [93][94][95][96] and gauged strings [97][98][99][100][101][102][103] but not (to our knowledge) in inhomogeneous, spherically symmetric or axisymmetric black hole metrics.…”

Redshift-space distortions from vector perturbations. II. Anisotropic signal

“…Mechanisms such as topological defects [1][2][3], magnetic fields [4], inflation with vector fields [5,6], or vectorfield-based models of modified gravity [7][8][9][10], but also the shell-crossing present in concordance cosmology, can generate vector perturbations throughout the history of the Universe and on a wide range of scales. It is important to properly characterize the signature of these vector degrees of freedom on the observables of large scale galaxy surveys.…”

“…We have fixed the gauge such that the 0i component of the metric has no scalar contribution and the vector part of the ij component vanishes. We also neglect gravitational waves (tensor perturbations) 2. The difference between aΩ j andΩ j is only relevant on large scales.…”