Cosmological Radion Problem in Models with Extra Dimensions

Moduli problem is a known common feature of models that involve extra compact dimensions, as the Kaluza‐Klein theories, the String theory, and the large extra dimension models. Moduli are scalar fields that emerge when the configuration of the compact space is perturbed. Usually, these fields feel no potential and represent run away modes which makes it difficult to stabilize the shape of the compact manifold. The radion is a particular example of this type of fields, which is associated to the variations of the total volume of the compact space. Radions usually couple to all other fields, affecting the definition of coupling constants and gravity strength. Thus, they are a potential threat for cosmology of the early Universe. Here we discuss some aspects of radion dynamics during inflation, and show that a heavy radion (m ≫ H) seems to be required for a successful baryogenesis.