Geometrical destabilisation of light fields in String Inflation

<!--HTML-->A typical feature of 4D string models is the presence, at tree-level, of a plethora of massless fields called moduli. Some of them are axion-like fields which become massive only via tiny non-perturbative effects which tend to make them naturally very light. When these fields live on a curved manifold a geometrical destabilisation of the inflationary trajectory can be induced since the growth of the isocurvature perturbations quickly brings the system in the non-perturbative regime.