Sensitivity of rotational transitions in CH and CD to a possible variation of fundamental constants

TL;DR

This study investigates how rotational transitions in CH and CD molecules are sensitive to potential variations in fundamental constants, identifying specific transitions with enhanced sensitivity but weak transition strengths, and proposing a radioastronomy test for cosmological observations.

Contribution

It reveals enhanced sensitivity coefficients in certain CH and CD transitions due to accidental degeneracies and proposes a robust radioastronomy test to detect fundamental constant variations.

Findings

Enhanced sensitivity coefficients found for specific transitions due to degeneracies.

Transition strengths are suppressed despite high sensitivity, limiting observational relevance.

A proposed radioastronomy test for high-redshift objects to detect variations.

Abstract

The sensitivity of rotational transitions in CH and CD to a possible variation of fundamental constants has been investigated. Largely enhanced sensitivity coefficients are found for specific transitions which are due to accidental degeneracies between the different fine-structure manifolds. These degeneracies occur when the spin-orbit coupling constant is close to four times the rotational constant. CH and particularly CD match this condition closely. Unfortunately, an analysis of the transition strengths shows that the same condition that leads to an enhanced sensitivity suppresses the transition strength, making these transitions too weak to be of relevance for testing the variation of fundamental constants over cosmological time scales. We propose a test in CH based on the comparison between the rotational transitions between the e and f components of the Omega'=1/2,J=1/2 and Omega'=3/2,J=3/2 levels at 532 and 536 GHz and other rotational or Lambda-doublet transitions in CH involving the same absorbing ground levels. Such a test, to be performed by radioastronomy of highly redshifted objects, is robust against systematic effects.