A note on grothendieck's standard conjectures of type c+ and d in positive characteristic

Making use of topological periodic cyclic homology, we extend Grothendieck's standard conjectures of type C+ and D (with respect to crystalline cohomology theory) from smooth projective schemes to smooth proper dg categories in the sense of Kontsevich. As a first application, we prove Grothendieck's original conjectures in the new cases of linear sections of determinantal varieties. As a second application, we prove Grothendieck's (generalized) conjectures in the new cases of "low-dimensional" orbifolds. Finally, as a third application, we establish a far-reaching noncommutative generalization of Berthelot's cohomological interpretation of the classical zeta function and of Grothendieck's conditional approach to "half" of the Riemann hypothesis. Along the way, following Scholze, we prove that the topological periodic cyclic homology of a smooth proper scheme X agrees with the crystalline cohomologytheory of X (after inverting the characteristic of the base field).