Flavor Violating Axions in the Early Universe

Understand

Flavor violating axion couplings can be in action before recombination, and they can fill the early universe with an additional radiation component.

• Working within a model-independent framework, we consider an effective field theory for the axion field and quantify axion production.
• Current cosmological data exclude already a fraction of the available parameter space, and the bounds will improve significantly with future CMB-S4 surveys.
• Remarkably, we find that future cosmological bounds will be comparable or even stronger than the ones obtained in our terrestrial laboratories.