{AE}ther compactification and the eta problem in inflationary models

A Lorentz violating vector "{\ae}ther" field in five dimensional spacetime can give rise to an inflation model in which the eta problem can be avoided. By identifying the inflaton field with the moduli field describing the radius of the extra dimension, we demonstrate that non-vanishing vacuum expectation value of the {\ae}ther field can suppress contributions from operators that usually destroy the flatness of the inflaton potential. We also show that the latest observational data can put the lower bound on the vacuum expectation value of the {\ae}ther field.