Hi all, A question about the vacuum energy density and spectrum. The only spectrum that is frame invariant involves the cube of the frequency. Is it also possible to have a constant offset term (which would also be frame invariant), to 'adjust' the energy density so it doesn't turn out to be huge? The constant offset would correspond to a harmonic oscillator with frequency zero, which wouldn't make sense. I'm wondering a) if such a term (a constant) has been considered, and b) if there are any hypotheses as to the 'meaning' of the term? (i.e., what would the constant negative offset correspond to physically?) Thanks!