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A.6. Geometry over the hybrid circle [018N]

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A.6. Geometry over the hybrid circle

Let now XX be a scheme of finite type over ArA_{r}. We will associate to XX three kinds of analytic spaces.

First, since XX is obtained by gluing together finitely many affine schemes cut out by polynomials with coefficients holomorphic on 𝔻r∗⊂ℂ{\mathbb{D}}^{*}_{r}\subset{\mathbb{C}} and meromorphic at 00, we can associate to XX in a functorial way a complex analytic space XholX^{\operatorname{hol}} over 𝔻r∗{\mathbb{D}}^{*}_{r}, which we call its holomorphic analytification.

Second, since ArA_{r} is contained in ℂ⁡((t)){\mathbb{C}}(\!({t})\!), we may also consider the base change Xℂ⁡((t))X_{{\mathbb{C}}(\!({t})\!)} and its non-Archimedean analytification Xℂ⁡((t))anX^{\mathrm{an}}_{{\mathbb{C}}(\!({t})\!)} with respect to the non-Archimedean absolute value rord0r^{\operatorname{ord}_{0}} on ℂ⁡((t)){\mathbb{C}}(\!({t})\!).

Third, we denote by XhybX^{\mathrm{hyb}} the analytification of XX as a scheme of finite type over the Banach ring ArA_{r}, and call it the hybrid analytification of XX. In view of Proposition A.4, it comes with a continuous structure map

π:Xhyb→𝔻¯r≃ℳ⁡(Ar),\pi\colon X^{\mathrm{hyb}}\to\overline{{\mathbb{D}}}_{r}\simeq{\mathcal{M}}(A_{r}),

Recall further that XhybX^{\mathrm{hyb}} is locally compact, Hausdorff if XX is separated, and compact if XX is proper over ArA_{r}. The discussion above implies:

Lemma A.6.

We have canonical homeomorphisms

π−1​(0)≃Xℂ⁡((t))anandπ−1​(𝔻r∗)≃Xhol\pi^{-1}(0)\simeq X_{{\mathbb{C}}(\!({t})\!)}^{\mathrm{an}}{\quad\text{and}\quad}\pi^{-1}({\mathbb{D}}^{*}_{r})\simeq X^{\operatorname{hol}} (A.2)

compatible with the projection to 𝔻r{\mathbb{D}}_{r}.

In §4 we give a topological description of XhybX^{\mathrm{hyb}}.

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