Stochastic scalar-tensor inflation and beyond
Abstract
During cosmological inflation, inhomogeneities arising from quantum vacuum fluctuations are stretched to become super-Hubble and effectively classical. As many scenarios of the origin involve nonlinearities or a breakdown of perturbativity in the infrared, the limitations of quantum field theory can be addressed using a stochastic description of the dynamics, the so-called stochastic inflation paradigm. However, the stochastic formalism was only recently formulated consistently within full General Relativity and has not yet been extended to more general theories of the early universe, which is the subject of this work. In order to find the stochastic sources for a wide class of fully nonlinear scalar-tensor theories, we apply our gauge-agnostic coarse-graining procedure to the linear equations of the associated effective field theory. Each theory can then be mapped to its own set of stochastic equations of motion by identifying the corresponding coefficients in the former. We illustrate this with a few concrete and, in most cases, unprecedented examples, including Gauss-Bonnet, generalized Brans-Dicke, Horndeski, and braiding theories. Finally, we discuss other natural extensions to provide a phenomenologically complete stochastic framework. For example, we showcase the coarse-graining of multifield inflation in full General Relativity and argue for the generality of our procedure and thus its potential applications beyond the realm of inflation.
Versions
Related
- The alternative scalar field dark sector of the Universe: Cosmological inflation, quintessence and ekpyrotic model in the framework of scalar-tensor cosmology
- Scalar perturbations in two-scalar-field warm inflation
- PrimordialPy: A Python library for single-field inflation, primordial black holes, and scalar-induced gravitational waves
- Scalar-tensor theories at different scales: averaging the scalar sector
- Primordial Tensor Signatures and Gravitational Wave Constraints in Lorentz Violating Inflation with Non-Canonical Kinetics
BibTeX
@misc{launay2026stochastic,
title = {{Stochastic scalar-tensor inflation and beyond}},
author = {Yoann Launay},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2606.07467},
eprint = {2606.07467},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2606.07467},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Stochastic scalar-tensor inflation and beyond
AU - Yoann Launay
PY - 2026
DA - 2026/10/19
PB - arXiv
DO - 10.48550/arxiv.2606.07467
UR - https://arxiv.org/abs/2606.07467
AB - During cosmological inflation, inhomogeneities arising from quantum vacuum fluctuations are stretched to become super-Hubble and effectively classical. As many scenarios of the origin involve nonlinearities or a breakdown of perturbativity in the infrared, the limitations of quantum field theory can be addressed using a stochastic description of the dynamics, the so-called stochastic inflation paradigm. However, the stochastic formalism was only recently formulated consistently within full General Relativity and has not yet been extended to more general theories of the early universe, which is the subject of this work. In order to find the stochastic sources for a wide class of fully nonlinear scalar-tensor theories, we apply our gauge-agnostic coarse-graining procedure to the linear equations of the associated effective field theory. Each theory can then be mapped to its own set of stochastic equations of motion by identifying the corresponding coefficients in the former. We illustrate this with a few concrete and, in most cases, unprecedented examples, including Gauss-Bonnet, generalized Brans-Dicke, Horndeski, and braiding theories. Finally, we discuss other natural extensions to provide a phenomenologically complete stochastic framework. For example, we showcase the coarse-graining of multifield inflation in full General Relativity and argue for the generality of our procedure and thus its potential applications beyond the realm of inflation.
ER -