Can an editor review manuscript without sending to reviewers? I submitted my manuscript to a journal one month ago and the status is "with editor" up to now. As the editor of my paper is one of the leading scientists in the field of my research paper (mathematics), I would like to know that can an editor do the review of paper by him/herself without sending to other reviewers?
Yes, an editor can review a manuscript themselves, but you cannot infer an editor is reviewing themselves when a manuscript has been with "a journal [for] one  month...and the status is 'with editor' up to now."