Texture-induced microwave background anisotropies

Abstract

We use numerical simulations to calculate the cosmic microwave background anisotropy induced by the evolution of a global texture field, with special emphasis on individual textures. Both spherically symmetric and general configurations are analyzed, and in the latter case we consider field configurations which exhibit unwinding events and also ones which do not. We compare the results given by evolving the field numerically under both the expanded core (XCORE) and nonlinear u model (NLSM) approximations with the analytic predictions of the NLSM exact solution for a spherically symmetric self-similar (SSSS) unwinding. We find that the random unwinding configuration spots' typical peak height is 60-75 % and angular size typically only 10% of those of the SSSS unwinding, and that random configurations without an unwinding event nonetheless may generate indistinguishable hot and cold spots. A brief comparison is made with other work. PACS number(s): 98.80. Cq, 11.27.+d, 98.70.V~

Analytical modeling of large-angle CMBR anisotropies from textures

“…The Gaussian profile is particularly amenable to analytical work, thus providing a good check on the numerics. Furthermore it is probably a good approximation to the peaks found in [8]. Finally, there is no harm in considering the SSSS profile, for it might have something to do with reality after all.…”

“…Simulations [2,8] suggest that the well known SSSS profile may be oversimplified. We find that the exact profile form has little impact on the C1 spectra.…”

“…Such simulations are considerably easier to perform. A prototype of this type of study is [8]. In the case of textures, the shortcut which we have described has been adopted by [9] where a "scaling-spot-throwing" process was implemented on a computer.…”

Cosmology from Topological Defects

“…The main problem today is that current realistic models of cosmic strings fall out of the parameter range that is needed to fit the observations. At the moment, only the (non-minimal) models with either a varying speed of light or hybrid contribution of strings+inflation are the only ones involving topological defects that to some extent can match the observations 16 . One possible way to distinguish their predictions from those of inflationary models would be by computing key non-Gaussian statistical quantities, such as the CMB bispectrum.…”

“…This is the scaling regime for textures, and when it holds simulations show that one should expect to find of order 0.04 unwinding collapses per horizon volume per Hubble time [Turok, 1989]. However, unwinding events are not the most frequent feature [Borrill et al, 1994], and when one considers random field configurations without an unwinding event the number raises to about 1 collapse per horizon volume per Hubble time.…”