Cosmic-String–Seeded Structure Formation

Abstract

We describe the results of high-resolution numerical simulations of string-induced structure formation in open universes and those with a nonzero cosmological constant. For models with G Vh 0.1 0.2 and a cold dark matter background, we show that the linear density fluctuation power spectrum has both an amplitude at 8h 21 Mpc, s 8 , and an overall shape which are consistent within uncertainties with those currently inferred from galaxy surveys. The cosmic string scenario with hot dark matter requires a strongly scale-dependent bias in order to agree with observations. [S0031-9007(98)07015-X] PACS numbers: 98.80. Cq, 98.62.Ai, 98.65.Dx In this Letter we describe new results from an investigation of cosmic string-seeded structure formation in hot and cold dark matter models. The cosmic string scenario [1] predated inflation as a realistic structure formation model, but it proved computationally much more challenging to make robust predictions with which to confront observation. The present paper relies on high-resolution numerical simulations of a cosmic string network [2] with a dynamic range extending from before the matter-radiation transition through to deep in the matter era (developing on previous work [3]). We calculate the linear power spectrum of density perturbations P ͑k͒ induced by the strings in flat models with and without a cosmological constant, and we then extrapolate to open cosmologies. This work represents a considerable quantitative advance by incorporating important aspects of the relevant physics not included in previous treatments.In the first instance, we consider density perturbations about a flat Friedmann-Robertson-Walker (FRW) model with a cosmological constant L and which are causally sourced by an evolving string network with energymomentum tensor Q ab ͑x, h͒. In the synchronous gauge, the linear evolution equations of the radiation and cold dark matter (CDM) perturbations, d r and d c respectively, are given by (modified from [4])where Q 1 Q 00 1 Q ii , a is the scale factor, the subscript "eq" denotes the epoch of radiation-matter density equality, "0" denotes the epoch today, a dot represents a derivative with respect to conformal time h, V c 8pGr c0 ͞3H 2 0 and V L L͞3H 2 0 . It proves useful to split these linear perturbations into initial ͑I͒ and sub-

Topological defects: A problem for cyclic universes?

“…Both the analytic [11,12,13,39,40,41,42,43] and the numerical [15,16,17] tools which we shall use rely on previous work by some of the present authors. In what follows we will limit ourselves to describing the features that are directly relevant for our analysis.…”

“…We have assumed the usual ansatz for the momentum parameter k(v)-see Eqn. (17) and [13]-while for the loop chopping efficiency we have assumed a constant valuec = 0.23 which was obtained in previous studies of high resolution simulations in expanding universes [13,16].…”

“…Up to now * Electronic address: ppavelin@fc.up.pt † Electronic address: C.J.A.P.Martins@damtp.cam.ac.uk ‡ Electronic address: cssilva@fc.up.pt § Electronic address: E.P.S.Shellard@damtp.cam.ac.uk all these studies, be they analytic [9,10,11,12,13] or numerical [14,15,16], have only been undertaken for the expanding case, and it is clear that while some results may be expected to carry over to the contracting phase, some others clearly won't. This will have consequences not only for the standard string seeded (or hybrid) structure formation scenario [17], but also for other 'non-standard' scenarios involving defects, such as the production of adiabatic and nearly Gaussian density fluctuations [18,19], or those involving anisotropic or inhomogeneous universes [20,21].…”

Dynamics and properties of chiral cosmic strings in Minkowski space

“…In the last few years many high accuracy calculations have been made of cosmological consequences of Nambu-Goto (NG) cosmic strings [1,2,3,4]. Indeed, such predictions were recently compared to the Boomerang data [5,6,7].…”

The cluster abundance in cosmic string models for structure formation

“…[7,8]). The present work relies on high resolution numerical simulations of cosmic string seeded structure formation [9][10][11][12], which are first used to estimate the power spectrum and one point probability distribution functions (PDF) of the induced density perturbations (see also [13][14][15][16] for different approaches). We then employ a simple generalization of the Press-Schechter formalism [17], which is suitable for non-Gaussian perturbations with a general one point PDF [18], in order to obtain the expected number density of collapsed objects with a mass greater that a given threshold.…”