Home > Research > Publications & Outputs > Itô, Stratonovich, and zoom-in schemes in stoch...

Associated organisational unit

Links

Text available via DOI:

View graph of relations

Itô, Stratonovich, and zoom-in schemes in stochastic inflation

Research output: Contribution to Journal/MagazineJournal articlepeer-review

Published
<mark>Journal publication date</mark>30/04/2025
<mark>Journal</mark>Journal of Cosmology and Astroparticle Physics
Issue number04
Volume2025
Publication StatusPublished
<mark>Original language</mark>English

Abstract

The Itô and Stratonovich approaches are two ways to integrate stochastic differential equations. Detailed knowledge of the origin of the stochastic noise is needed to determine which approach suits a particular problem. I discuss this topic pedagogically in stochastic inflation, where the noise arises from a changing comoving coarse-graining scale or, equivalently, from `zooming in' into inflating space. I introduce a zoom-in scheme where deterministic evolution alternates with instantaneous zoom-in steps. I show that this alternating zoom-in scheme is equivalent to the Itô approach in the Markovian limit, while the Stratonovich approach doesn't have a similar interpretation. In the full non-Markovian setup, the difference vanishes. The framework of zoom-in schemes clarifies the relationship between computations in stochastic inflation, linear perturbation theory, and the classical ΔN formalism. It informs the numerical implementation of stochastic inflation and is a building block for a first-principles derivation of the stochastic equations.