Massive quasi-normal mode
  This paper purposes to study quasi-normal modes due to massive scalar fields. We, in particular, investigate the dependence of QNM frequencies on the field mass. By this research, we find that there are quasi-normal modes with arbitrarily long life when the field mass has special values. It is also found that QNM can disappear when the field mass exceed these values. 
Akira Ohashi and Masa-aki Sakagami