A Unitary Fixed Point Away from Threshold: Momentum-Surface EFT for Strong Mixing
Abstract
Radiative capture in a non-relativistic system can become non-perturbative even when the underlying transition interaction is weak. We demonstrate this mechanism in a simple quantum-mechanical two-channel model with a systematic power counting, where strong mixing between scattering and bound states develops in a narrow region around a finite momentum k0, leading to a perturbative violation of unitarity. In this regime, the enhanced contributions factorize, reducing the dynamics to a free scattering state interacting through a strong local coupling. Under RG evolution in the factorization scale, this local interaction approaches a unitary fixed point, analogous to that of systems with an anomalously large scattering length. This motivates an EFT organized around the finite-momentum surface |k|=k0, describing fermions at unitarity with a linear dispersion relation. The resummation resulting from the EFT restores unitarity and provides a systematic expansion for both elastic scattering and radiative capture.
Related
- Low Primordial Helium as a Probe of Non-Unitary Neutrino Mixing
- Parametrization of unitary matrices, parametrizing the symmetric S matrix and the NN S matrix above the inelastic threshold
- Analytical Cosmological Collider at Strong Mixing in Laplace Space
- Unitary fault-tolerant encoding of Pauli states in surface codes
- Cosmological Collider Signals at Strong Mixing
BibTeX
@misc{ros2026unitary,
title = {{A Unitary Fixed Point Away from Threshold: Momentum-Surface EFT for Strong Mixing}},
author = {Lorenzo De Ros and Javier Reig Navarro},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.25219},
eprint = {2609.25219},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.25219},
}
RIS
TY - UNPB
TI - A Unitary Fixed Point Away from Threshold: Momentum-Surface EFT for Strong Mixing
AU - Lorenzo De Ros
AU - Javier Reig Navarro
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2609.25219
UR - https://arxiv.org/abs/2609.25219
AB - Radiative capture in a non-relativistic system can become non-perturbative even when the underlying transition interaction is weak. We demonstrate this mechanism in a simple quantum-mechanical two-channel model with a systematic power counting, where strong mixing between scattering and bound states develops in a narrow region around a finite momentum k_0, leading to a perturbative violation of unitarity. In this regime, the enhanced contributions factorize, reducing the dynamics to a free scattering state interacting through a strong local coupling. Under RG evolution in the factorization scale, this local interaction approaches a unitary fixed point, analogous to that of systems with an anomalously large scattering length. This motivates an EFT organized around the finite-momentum surface |k|=k_0, describing fermions at unitarity with a linear dispersion relation. The resummation resulting from the EFT restores unitarity and provides a systematic expansion for both elastic scattering and radiative capture.
ER -