Cosmological Hysteresis and the Cyclic Universe

TL;DR

This paper explores how cosmological hysteresis, caused by asymmetries in the equation of state during universe expansion and contraction, can lead to cyclic universe models with increasing or quasi-periodic cycles, independent of specific models.

Contribution

It introduces the concept of cosmological hysteresis in scalar field-driven universes and demonstrates its implications for cyclic cosmology, including anisotropic models and quantum effects.

Findings

Hysteresis loops can be positive or negative, affecting cycle amplitudes.

Negative hysteresis leads to larger, older successive cycles.

The hysteresis effect is model-independent and applicable to various potentials.

Abstract

A Universe filled with a homogeneous scalar field exhibits `Cosmological hysteresis'. Cosmological hysteresis is caused by the asymmetry in the equation of state during expansion and contraction. This asymmetry results in the formation of a hysteresis loop: $\oint pdV$, whose value can be non-vanishing during each oscillatory cycle. For flat potentials, a negative value of the hysteresis loop leads to the increase in amplitude of consecutive cycles and to a universe with older and larger successive cycles. Such a universe appears to possess an arrow of time even though entropy production is absent and all of the equations respect time-reversal symmetry ! Cosmological hysteresis appears to be widespread and exists for a large class of scalar field potentials and mechanisms for making the universe bounce. For steep potentials, the value of the hysteresis loop can be positive as well as negative. The expansion factor in this case displays quasi-periodic behaviour in which successive cycles can be both larger as well as smaller than previous ones. This quasi-regular pattern resembles the phenomenon of BEATS displayed by acoustic systems. Remarkably, the expression relating the increase/decrease in oscillatory cycles to the quantum of hysteresis appears to be model independent. The cyclic scenario is extended to spatially anisotropic models and it is shown that the anisotropy density decreases during successive cycles if the hysteresis loop is negative.