Diversity of universes created by pure gravity

TL;DR

This paper explores how multidimensional gravity with high-order curvature invariants can address key cosmological problems, such as universe acceleration, black hole formation, and extra dimensions, without additional fields.

Contribution

It introduces a general method using slow-change approximation for multidimensional gravity, revealing diverse effective theories based on extra space configurations, and applies it to several cosmological issues.

Findings

Potential explanation for universe's accelerated expansion with small cosmological constant

Mechanism for primordial black hole formation via closed wall production

Universe may contain large spatial domains with extra dimensions

Abstract

We show that a number of problems of modern cosmology may be solved in the framework of multidimensional gravity with high-order curvature invariants, without invoking other fields. We use a method employing a slow-change approximation, able to work with rather a general form of the gravitational action, and consider Kaluza-Klein type space-times with one or several extra factor spaces. A vast choice of effective theories suggested by the present framework may be stressed: even if the initial Lagrangian is entirely fixed, one obtains quite different models for different numbers, dimensions and topologies of the extra factor spaces. As examples of problems addressed we consider (i) explanation of the present accelerated expansion of the Universe, with a reasonably small cosmological constant, and the problem of its fine tuning is considered from a new point of view; (ii) the mechanism of closed wall production in the early Universe; such walls are necessary for massive primordial black hole formation which is an important stage in some scenarios of cosmic structure formation; (iii) sufficient particle production rate at the end of inflation; (iv) it is shown that our Universe may contain spatial domains with a macroscopic size of extra dimensions. We also discuss chaotic attractors appearing at possible nodes of the kinetic term of the effective scalar field Lagrangian.