Continuous metrics [01IS]
Original official author HTML, exact retained edition. Historical TeX conversion verdicts remain unchanged. Cited-edition alignment and mathematical self-containment are not assessed.
Complete original source context · Original author HTML
Continuous metrics
Let be a -analytic space in the sense of Berkovich [11]. For simplicity, we will assume that is the analytic space associated to a proper scheme over . In that context, the general definition of continuous metrized line bundles given above makes sense.
Let us detail the example of the line bundle on the projective space . A point possesses a complete residue field which is a complete extension of and homogeneous coordinates in the field . As in complex geometry, the projective space is obtained by glueing copies of the affine space , where corresponds to those points such that . Recall also that is the space of multiplicative semi-norms on the -algebra which induce the given absolute value on , together with the coarsest topology such that for any semi-norm , the map defined by is continuous. The kernel of a semi-norm is a prime ideal of and induces a norm on the quotient ring , hence on its field of fractions . The completion of with respect to this norm is denoted and is called the complete residue field of . The images in of the intederminates are denoted , more generally, the image in of any polynomial is denoted ; one has .
Let be a rational function on , that is an element of . It defines an actual function on the open set of where its denominator does not vanish ; its value at a point is an element of . More generally, Berkovich defines an analytic function on an open set of as a function on such that for any , and such that any point possesses a neighbourhood such that is a uniform limit of rational functions without poles on .
The line bundle can also be defined in a similar way to the classical case ; by a similar GAGA theorem, its global sections are exactly the same as in algebraic geometry and are described by homogeneous polynomials of degree with coefficients in . If is such a polynomial and the corresponding section, then
where is a system of homogeneous coordinates in for the point . The function is continuous on , by the very definition of the topology on . Using the fact that is generated by its global sections, one deduces the existence of a continuous metric on satisfying the previous formula.