Forskning ved Københavns Universitet - Københavns Universitet


Lifts of projective congruence groups, II

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We continue and complete our previous paper ``Lifts of projective congruence groups'' concerning the question of whether there exist noncongruence subgroups of  that are projectively equivalent to one of the groups  or . A complete answer to this question is obtained: In case of  such noncongruence subgroups exist precisely if  and we additionally have either that  or that  is divisible by an odd prime congruent to  modulo . In case of  these noncongruence subgroups exist precisely if .

As in our previous paper the main motivation for this question is the fact that the above noncongruence subgroups represent a fairly accessible and explicitly constructible reservoir of examples of noncongruence subgroups of  that can serve as the basis for experimentation with modular forms on noncongruence subgroups.

TidsskriftProceedings of the American Mathematical Society
Udgave nummer11
Sider (fra-til)3761-3770
Antal sider10
StatusUdgivet - 2014

ID: 122608744