Sensitivity of the H3O+ inversion-rotational spectrum to changes in m_e/m_p

TL;DR

This paper investigates how the inversion-rotational spectrum of H3O+ is highly sensitive to variations in the electron-to-proton mass ratio, offering a new method to test fundamental physics in different cosmic environments.

Contribution

It demonstrates the potential of H3O+ spectral lines as probes for variations in mu, expanding the tools available for testing fundamental constants in space.

Findings

H3O+ inversion-rotational transitions are highly sensitive to mu variations.

Different transitions have opposite sensitivity signs, enabling differential measurements.

H3O+ can serve as an independent probe for environmental dependence of fundamental constants.

Abstract

Quantum mechanical tunneling inversion transition in ammonia NH3 is actively used as a sensitive tool to study possible variations of the electron-to-proton mass ratio, mu = m_e/m_p. The molecule H3O+ has the inversion barrier significantly lower than that of NH3. Consequently, its tunneling transition occurs in the far-infrared (FIR) region and mixes with rotational transitions. Several such FIR and submillimiter transitions are observed from the interstellar medium in the Milky Way and in nearby galaxies. We show that the rest-frame frequencies of these transitions are very sensitive to the variation of mu, and that their sensitivity coefficients have different signs. Thus, H3O+ can be used as an independent target to test hypothetical changes in mu measured at different ambient conditions of high (terrestrial) and low (interstellar medium) matter densities. The environmental dependence of mu and coupling constants is suggested in a class of chameleon-type scalar field models - candidates to dark energy carrier.