CMB anisotropies from acausal scaling seeds

TL;DR

This paper explores models where superluminal expanding shells act as seeds for cosmic structure formation, offering an alternative to inflation that can fit current CMB and large-scale structure data.

Contribution

It introduces acausally expanding shells as a novel mechanism for structure formation, demonstrating their viability compared to traditional inflationary models.

Findings

Superluminal shells can fit CMB and large-scale structure data.

Causally expanding shells alone cannot fit the data.

Hybrid models with causal shells and inflation also fit well.

Abstract

We investigate models where structure formation is initiated by scaling seeds: We consider rapidly expanding relativistic shells of energy and show that they can fit current CMB and large scale structure data if they expand with super-luminal velocities. These acausally expanding shells provide a viable alternative to inflation for cosmological structure formation with the same minimal number of parameters to characterize the initial fluctuations. Causally expanding shells alone cannot fit present data. Hybrid models where causal shells and inflation are mixed also provide good fits.