On tame ${\mathbb {Z}}/p{\mathbb {Z}}$-extensions with prescribed ramification
Canadian mathematical bulletin, Tome 67 (2024) no. 1, pp. 40-48
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The tame Gras–Munnier Theorem gives a criterion for the existence of a $ {\mathbb Z}/p{\mathbb Z} $-extension of a number field K ramified at exactly a tame set S of places of K, the finite $v \in S$ necessarily having norm $1$ mod p. The criterion is the existence of a nontrivial dependence relation on the Frobenius elements of these places in a certain governing extension. We give a short new proof which extends the theorem by showing the subset of elements of $H^1(G_S,{\mathbb {Z}}/p{\mathbb {Z}})$ giving rise to such extensions of K has the same cardinality as the set of these dependence relations. We then reprove the key Proposition 2.2 using the more sophisticated Greenberg–Wiles formula based on global duality.
Mots-clés :
Tame ramification, Z/pZ-extension, Gras–Munnier Theorem, Frobenius automorphism
Hajir, Farshid; Maire, Christian; Ramakrishna, Ravi. On tame ${\mathbb {Z}}/p{\mathbb {Z}}$-extensions with prescribed ramification. Canadian mathematical bulletin, Tome 67 (2024) no. 1, pp. 40-48. doi: 10.4153/S0008439523000498
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title = {On tame ${\mathbb {Z}}/p{\mathbb {Z}}$-extensions with prescribed ramification},
journal = {Canadian mathematical bulletin},
pages = {40--48},
year = {2024},
volume = {67},
number = {1},
doi = {10.4153/S0008439523000498},
url = {http://geodesic.mathdoc.fr/articles/10.4153/S0008439523000498/}
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AU - Maire, Christian
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