Logo
ScienceStack
Table of Contents
Fetching ...
Sign In

Cosmology in a String-Dominated Universe

David Spergel, Ue-Li Pen

TL;DR

The paper explores a string-dominated cosmology in which a network of light, non-Abelian strings contributes an $a^{-2}$ energy-density term to the Friedmann equation, allowing a flat geometry to mimic an open universe while remaining observationally viable. It develops and analyzes non-Abelian string networks using a PST-based nonlinear sigma model, illustrating the rich interactions, junctions, and entanglement that arise in biaxial nematic–like systems. The model can accommodate $"Omega_0\sim0.4$–$0.6$ and $H_0\sim60$–$70$ km s$^{-1}$ Mpc$^{-1}$, consistent with CMB, large-scale structure, cluster abundances, and ages, and remains compatible with high-redshift supernovae and lensing statistics. Distinguishing tests include CMB Doppler peak positions and detailed distance-redshift relations to separate flat string-dominated cosmologies from open universes and from vacuum-energy models; the approach also motivates new physics at the TeV scale. Overall, the work offers a viable, testable alternative to cosmological constant cosmologies, linking non-Abelian string dynamics to observable cosmic expansion.

Abstract

The string-dominated universe locally resembles an open universe, and fits dynamical measures of power spectra, cluster abundances, redshift distortions, lensing constraints, luminosity and angular diameter distance relations and microwave background observations. We show examples of networks which might give rise to recent string-domination without requiring any fine-tuned parameters. We discuss how future observations can distinguish this model from other cosmologies.

Cosmology in a String-Dominated Universe

TL;DR

The paper explores a string-dominated cosmology in which a network of light, non-Abelian strings contributes an energy-density term to the Friedmann equation, allowing a flat geometry to mimic an open universe while remaining observationally viable. It develops and analyzes non-Abelian string networks using a PST-based nonlinear sigma model, illustrating the rich interactions, junctions, and entanglement that arise in biaxial nematic–like systems. The model can accommodate – and – km s Mpc, consistent with CMB, large-scale structure, cluster abundances, and ages, and remains compatible with high-redshift supernovae and lensing statistics. Distinguishing tests include CMB Doppler peak positions and detailed distance-redshift relations to separate flat string-dominated cosmologies from open universes and from vacuum-energy models; the approach also motivates new physics at the TeV scale. Overall, the work offers a viable, testable alternative to cosmological constant cosmologies, linking non-Abelian string dynamics to observable cosmic expansion.

Abstract

The string-dominated universe locally resembles an open universe, and fits dynamical measures of power spectra, cluster abundances, redshift distortions, lensing constraints, luminosity and angular diameter distance relations and microwave background observations. We show examples of networks which might give rise to recent string-domination without requiring any fine-tuned parameters. We discuss how future observations can distinguish this model from other cosmologies.

Paper Structure

This paper contains 9 sections, 9 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Physics of Non-Abelian Strings
  3. What are Non-Abelian Strings?
  4. Dynamics of a Biaxial Nematic Crystal
  5. Dynamics of More Complex String Networks
  6. Astrophysics of String Dominated Universe
  7. Expansion of the universe: $H_0,q_0,\Omega _0$ and $t_0$
  8. Microwave Background Fluctuations
  9. Conclusions

Figures (4)

  • Figure 1: The network of a $N=3$ string system, which exhibits dynamics very similar to biaxial nematic liquid crystals. The strings are color coded according to the generator they belong to.
  • Figure 2: This figure shows the evolution of the string density (normalised to the scaling density) as a function of time in different models. In scaling solutions, the string density should asymptote to a constant value in this plot. Note that the large $N$ models do not scale and become tangled.
  • Figure 3: This figure compares the predicted multipole spectrum for three different models: a flat standard CDM model with $\Omega_0=1.0$ and $H_0 = 50$ km/s/Mpc (solid line); a string-dominated flat cosmology with $\Omega_0 = 0.4$ and $\Omega_0 = 0.6$. Because COBE did not detect a large quadrupole, the relative likelihood of the $\Omega_0 = 0.4$ to the $\Omega_0 = 1.0$ model is 0.05.
  • Figure 4: This figure combines constraints from various astrophysical measurements. The vertically shaded region lie outside the best determinations of the Hubble Constant: $H_0 = 73 \pm 6 \pm 8$ km/s/Mpc (Freedman, Madore & Kennicutt 1997); the horizontally shaded regions do not agree with measurements of the shape of the galaxy power spectrum, $\Gamma = 0.25\pm 0.05$ (Peacock & Dodds 1994), and with measurements of the fluctuation amplitude from clusters, $\sigma _8\Omega _0^{0.6} =0.6 \pm 0.1$ (Eke et al. 1996; Viana and Liddle 1996; Pen 1996a); and the region shaded with lines at 45$^o$ angle corresponds to cosmic ages less than 11 Gyr.