“…The Casimir effect in rectangular boxes has been a topic for several decades (see book 19 and references therein and also Refs. 36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65). While focusing on the sign changing depending on the geometry of the configuration and the type of boundary conditions, it is also a typical example to compare the two regularization methods and give the interpretation of the divergent terms in vacuum energy.…”