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Free, publicly-accessible full text available February 1, 2026
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We show that for primes with , the class number of is divisible by . Our methods are via congruences between Eisenstein series and cusp forms. In particular, we show that when , there is always a cusp form of weight and level whose th Fourier coefficient is congruent to modulo a prime above , for all primes . We use the Galois representation of such a cusp form to explicitly construct an unramified degree- extension of .more » « less
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Abstract Given a profinite group G of finite p -cohomological dimension and a pro- p quotient H of G by a closed normal subgroup N , we study the filtration on the Iwasawa cohomology of N by powers of the augmentation ideal in the group algebra of H . We show that the graded pieces are related to the cohomology of G via analogues of Bockstein maps for the powers of the augmentation ideal. For certain groups H , we relate the values of these generalized Bockstein maps to Massey products relative to a restricted class of defining systems depending on H . We apply our study to prove lower bounds on the p -ranks of class groups of certain nonabelian extensions of $$\mathbb {Q}$$ and to give a new proof of the vanishing of Massey triple products in Galois cohomology.more » « less
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