Higher Semiadditivity in Transchromatic Homotopy Theory

Abstract: We study the compatibility of higher semiadditivity across different chromatic heights. We prove that the categorified transchromatic character map assembles into a parameterized semiadditive functor, showing that it is higher semiadditive up to a free loop shift. By decategorification, this implies that the transchromatic character map is compatible with integration maps, generalizing the well-known formula for the character of an induced representation. Through a further decategorification process, we compute the higher semiadditive cardinalities of $\pi$-finite spaces at Lubin-Tate spectra.