Moduli interpretation of the integral anticanonical tower












4












$begingroup$


This question is related to my reading of On torsion in the cohomology of locally symmetric varieties by Scholze.



In chapter $3$, using the theory of canonical subgroup, he produces Frobenius maps defined over $text{Spf(}mathbb{Z}_p^{text{cycl}})$ between the integral models of strict neighborhoods of the ordinary locus for the modular curve. Then, he computes the projective limit along Frobenius of these maps, and he gets a formal scheme over $text{Spf}(mathbb{Z}_p^{text{cycl}})$, whose generic fiber is perfectoid and is called the anticanonical tower of modular curves. Later on in his exposition, he writes that the $(C,mathcal{O}_C)$-points of this perfectoid space (where $C$ is the completion of an algebraic closure of $mathbb{Q}_p$, and $mathcal{O}_C$ is its ring of integers) parametrize elliptic curves over $C$ with a trivialization of their Tate module.



First, I do not see why this construction provides a unique elliptic curve! First, I would like to say that the construction provides a projective system of elliptic curves over $C$, where every elliptic curve has $p^n$-torsion trivialized (for $n$ becoming bigger along the tower), where the maps defining the projective system are quotient by the canonical subgroup. But why is such a kind of system the same as a unique elliptic curve with Tate module trivialized?



Second question, does a similar description hold for the integral anticanonical tower? Is it true that an $R$ point of the anticanonical tower, where $R$ is a complete and flat (maybe normal) $mathbb{Z}_p^{text{cycl}}$-algebra, gives a family of elliptic curves over $R$ with a trivialization (at least a generic trivialization) of its Tate module seen as a sheaf? Thank you for any kind of suggestion!










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  • $begingroup$
    If nobody answers in the next day or two, you might consider cross-posting this to MathOverflow.
    $endgroup$
    – André 3000
    Dec 26 '18 at 19:59










  • $begingroup$
    Strange, I supposed to have posted it on Mathoverflow first! Let me do this, and thank you very much!
    $endgroup$
    – Zariski93
    Dec 28 '18 at 16:43
















4












$begingroup$


This question is related to my reading of On torsion in the cohomology of locally symmetric varieties by Scholze.



In chapter $3$, using the theory of canonical subgroup, he produces Frobenius maps defined over $text{Spf(}mathbb{Z}_p^{text{cycl}})$ between the integral models of strict neighborhoods of the ordinary locus for the modular curve. Then, he computes the projective limit along Frobenius of these maps, and he gets a formal scheme over $text{Spf}(mathbb{Z}_p^{text{cycl}})$, whose generic fiber is perfectoid and is called the anticanonical tower of modular curves. Later on in his exposition, he writes that the $(C,mathcal{O}_C)$-points of this perfectoid space (where $C$ is the completion of an algebraic closure of $mathbb{Q}_p$, and $mathcal{O}_C$ is its ring of integers) parametrize elliptic curves over $C$ with a trivialization of their Tate module.



First, I do not see why this construction provides a unique elliptic curve! First, I would like to say that the construction provides a projective system of elliptic curves over $C$, where every elliptic curve has $p^n$-torsion trivialized (for $n$ becoming bigger along the tower), where the maps defining the projective system are quotient by the canonical subgroup. But why is such a kind of system the same as a unique elliptic curve with Tate module trivialized?



Second question, does a similar description hold for the integral anticanonical tower? Is it true that an $R$ point of the anticanonical tower, where $R$ is a complete and flat (maybe normal) $mathbb{Z}_p^{text{cycl}}$-algebra, gives a family of elliptic curves over $R$ with a trivialization (at least a generic trivialization) of its Tate module seen as a sheaf? Thank you for any kind of suggestion!










share|cite|improve this question











$endgroup$












  • $begingroup$
    If nobody answers in the next day or two, you might consider cross-posting this to MathOverflow.
    $endgroup$
    – André 3000
    Dec 26 '18 at 19:59










  • $begingroup$
    Strange, I supposed to have posted it on Mathoverflow first! Let me do this, and thank you very much!
    $endgroup$
    – Zariski93
    Dec 28 '18 at 16:43














4












4








4


1



$begingroup$


This question is related to my reading of On torsion in the cohomology of locally symmetric varieties by Scholze.



In chapter $3$, using the theory of canonical subgroup, he produces Frobenius maps defined over $text{Spf(}mathbb{Z}_p^{text{cycl}})$ between the integral models of strict neighborhoods of the ordinary locus for the modular curve. Then, he computes the projective limit along Frobenius of these maps, and he gets a formal scheme over $text{Spf}(mathbb{Z}_p^{text{cycl}})$, whose generic fiber is perfectoid and is called the anticanonical tower of modular curves. Later on in his exposition, he writes that the $(C,mathcal{O}_C)$-points of this perfectoid space (where $C$ is the completion of an algebraic closure of $mathbb{Q}_p$, and $mathcal{O}_C$ is its ring of integers) parametrize elliptic curves over $C$ with a trivialization of their Tate module.



First, I do not see why this construction provides a unique elliptic curve! First, I would like to say that the construction provides a projective system of elliptic curves over $C$, where every elliptic curve has $p^n$-torsion trivialized (for $n$ becoming bigger along the tower), where the maps defining the projective system are quotient by the canonical subgroup. But why is such a kind of system the same as a unique elliptic curve with Tate module trivialized?



Second question, does a similar description hold for the integral anticanonical tower? Is it true that an $R$ point of the anticanonical tower, where $R$ is a complete and flat (maybe normal) $mathbb{Z}_p^{text{cycl}}$-algebra, gives a family of elliptic curves over $R$ with a trivialization (at least a generic trivialization) of its Tate module seen as a sheaf? Thank you for any kind of suggestion!










share|cite|improve this question











$endgroup$




This question is related to my reading of On torsion in the cohomology of locally symmetric varieties by Scholze.



In chapter $3$, using the theory of canonical subgroup, he produces Frobenius maps defined over $text{Spf(}mathbb{Z}_p^{text{cycl}})$ between the integral models of strict neighborhoods of the ordinary locus for the modular curve. Then, he computes the projective limit along Frobenius of these maps, and he gets a formal scheme over $text{Spf}(mathbb{Z}_p^{text{cycl}})$, whose generic fiber is perfectoid and is called the anticanonical tower of modular curves. Later on in his exposition, he writes that the $(C,mathcal{O}_C)$-points of this perfectoid space (where $C$ is the completion of an algebraic closure of $mathbb{Q}_p$, and $mathcal{O}_C$ is its ring of integers) parametrize elliptic curves over $C$ with a trivialization of their Tate module.



First, I do not see why this construction provides a unique elliptic curve! First, I would like to say that the construction provides a projective system of elliptic curves over $C$, where every elliptic curve has $p^n$-torsion trivialized (for $n$ becoming bigger along the tower), where the maps defining the projective system are quotient by the canonical subgroup. But why is such a kind of system the same as a unique elliptic curve with Tate module trivialized?



Second question, does a similar description hold for the integral anticanonical tower? Is it true that an $R$ point of the anticanonical tower, where $R$ is a complete and flat (maybe normal) $mathbb{Z}_p^{text{cycl}}$-algebra, gives a family of elliptic curves over $R$ with a trivialization (at least a generic trivialization) of its Tate module seen as a sheaf? Thank you for any kind of suggestion!







number-theory algebraic-geometry arithmetic-geometry






share|cite|improve this question















share|cite|improve this question













share|cite|improve this question




share|cite|improve this question








edited Dec 24 '18 at 19:17









André 3000

12.6k22243




12.6k22243










asked Dec 24 '18 at 18:24









Zariski93Zariski93

876




876












  • $begingroup$
    If nobody answers in the next day or two, you might consider cross-posting this to MathOverflow.
    $endgroup$
    – André 3000
    Dec 26 '18 at 19:59










  • $begingroup$
    Strange, I supposed to have posted it on Mathoverflow first! Let me do this, and thank you very much!
    $endgroup$
    – Zariski93
    Dec 28 '18 at 16:43


















  • $begingroup$
    If nobody answers in the next day or two, you might consider cross-posting this to MathOverflow.
    $endgroup$
    – André 3000
    Dec 26 '18 at 19:59










  • $begingroup$
    Strange, I supposed to have posted it on Mathoverflow first! Let me do this, and thank you very much!
    $endgroup$
    – Zariski93
    Dec 28 '18 at 16:43
















$begingroup$
If nobody answers in the next day or two, you might consider cross-posting this to MathOverflow.
$endgroup$
– André 3000
Dec 26 '18 at 19:59




$begingroup$
If nobody answers in the next day or two, you might consider cross-posting this to MathOverflow.
$endgroup$
– André 3000
Dec 26 '18 at 19:59












$begingroup$
Strange, I supposed to have posted it on Mathoverflow first! Let me do this, and thank you very much!
$endgroup$
– Zariski93
Dec 28 '18 at 16:43




$begingroup$
Strange, I supposed to have posted it on Mathoverflow first! Let me do this, and thank you very much!
$endgroup$
– Zariski93
Dec 28 '18 at 16:43










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