{"title":"Applications of representation theory and of explicit units to Leopoldt's conjecture.","authors":"Fabio Ferri, Henri Johnston","doi":"10.1007/s40993-026-00717-2","DOIUrl":"https://doi.org/10.1007/s40993-026-00717-2","url":null,"abstract":"<p><p>Let <i>L</i>/<i>K</i> be a Galois extension of number fields and let <math><mrow><mi>G</mi> <mo>=</mo> <mtext>Gal</mtext> <mo>(</mo> <mi>L</mi> <mo>/</mo> <mi>K</mi> <mo>)</mo></mrow> </math> . We show that under certain hypotheses on <i>G</i>, for a fixed prime number <i>p</i>, Leopoldt's conjecture at <i>p</i> for certain proper intermediate fields of <i>L</i>/<i>K</i> implies Leopoldt's conjecture at <i>p</i> for <i>L</i>. We also obtain relations between the Leopoldt defects of intermediate fields of <i>L</i>/<i>K</i>. By applying a result of Buchmann and Sands together with an explicit description of units and a special case of the above results, we show that given any finite set of prime numbers <math><mi>P</mi></math> , there exists an infinite family <math><mi>F</mi></math> of totally real <math><msub><mi>S</mi> <mn>3</mn></msub> </math> -extensions of <math><mi>Q</mi></math> such that Leopoldt's conjecture for <i>F</i> at <i>p</i> holds for every <math><mrow><mi>F</mi> <mo>∈</mo> <mi>F</mi></mrow> </math> and <math><mrow><mi>p</mi> <mo>∈</mo> <mi>P</mi></mrow> </math> .</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"12 2","pages":"32"},"PeriodicalIF":0.8,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12995976/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147487823","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Wild Galois representations: elliptic curves with wild cyclic reduction.","authors":"Nirvana Coppola","doi":"10.1007/s40993-026-00730-5","DOIUrl":"https://doi.org/10.1007/s40993-026-00730-5","url":null,"abstract":"<p><p>In 1990, Kraus [12] classified all possible inertia images of the <math><mi>ℓ</mi></math> -adic Galois representation attached to an elliptic curve over a non-archimedean local field. In [1, 2], the author computed explicitly the Galois representation of elliptic curves having non-abelian inertia image, a phenomenon which only occurs when the residue characteristic of the field of definition is 2 or 3 and the curve attains good reduction over some non-abelian ramified extension. In this work, the computation of the Galois representation in all the remaining \"wild\" cases, i.e. when the residue characteristic is <math><mrow><mi>p</mi> <mo>=</mo> <mn>2</mn></mrow> </math> or 3 and the curve attains good reduction over an extension whose ramification degree is divisible by <i>p</i> (without assuming the condition on the image of inertia being non-abelian), is completed. This is based on Chapter V of the author's PhD thesis [4].</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"12 2","pages":"49"},"PeriodicalIF":0.8,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13139269/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147844056","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"<ArticleTitle xmlns:ns0=\"http://www.w3.org/1998/Math/MathML\">Adjoint <i>L</i>-functions, congruence ideals, and Selmer groups over <ns0:math><ns0:msub><ns0:mtext>GL</ns0:mtext> <ns0:mi>n</ns0:mi></ns0:msub></ns0:math>.","authors":"Ho Leung Fong","doi":"10.1007/s40993-026-00721-6","DOIUrl":"https://doi.org/10.1007/s40993-026-00721-6","url":null,"abstract":"<p><p>The study of special values of adjoint <i>L</i>-functions and congruence ideals is gradually becoming a classical theme in number theory, driven by the Bloch-Kato conjecture and generalisations of Wiles-Lenstra's numerical criterion. In this paper, we relate <math><mrow><mi>L</mi> <mo>(</mo> <mn>1</mn> <mo>,</mo> <mi>π</mi> <mo>,</mo> <msup> <mrow><mrow><mspace></mspace> <mtext>Ad</mtext> <mspace></mspace></mrow> </mrow> <mo>∘</mo></msup> <mo>)</mo></mrow> </math> to the congruence ideals for cohomological cuspidal automorphic representations <math><mi>π</mi></math> of <math><msub><mtext>GL</mtext> <mi>n</mi></msub> </math> over any number field. We then use this result to deduce relationships between the congruences of automorphic forms and adjoint <i>L</i>-functions. For CM fields, using the existence of Galois representations, we apply the result to obtain a lower bound on the cardinality of certain Selmer groups in terms of <math><mrow><mi>L</mi> <mo>(</mo> <mn>1</mn> <mo>,</mo> <mi>π</mi> <mo>,</mo> <msup> <mrow><mrow><mspace></mspace> <mtext>Ad</mtext> <mspace></mspace></mrow> </mrow> <mo>∘</mo></msup> <mo>)</mo></mrow> </math> . This can be viewed as partial progress on the Bloch-Kato conjecture. The main technical ingredients are a careful study of the cohomology associated with the locally symmetric space of <math><msub><mtext>GL</mtext> <mi>n</mi></msub> </math> , its relation to automorphic representations, and the establishment of some algebraic properties of the congruence ideals. We anticipate that the methods developed here will find further applications in related problems, particularly in the study of congruence modules and their relation to the arithmetic of automorphic forms.</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"12 1","pages":"20"},"PeriodicalIF":0.8,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12948911/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147327608","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Endomorphism algebras of abelian varieties with large cyclic 2-torsion field over a given field.","authors":"Pip Goodman","doi":"10.1007/s40993-026-00722-5","DOIUrl":"10.1007/s40993-026-00722-5","url":null,"abstract":"<p><p>In this article we study the endomorphism algebras of abelian varieties <i>A</i> defined over a given number field <i>K</i> with large cyclic 2-torsion fields. A key step in doing so is to provide criteria for all the endomorphisms of <i>A</i> to be defined over <i>K</i>(<i>A</i>[2]), the field extension generated by its 2-torsion. When <math><mrow><mi>K</mi> <mo>=</mo> <mi>Q</mi></mrow> </math> and <math><mrow><mtext>Gal</mtext> <mo>(</mo> <mi>Q</mi> <mo>(</mo> <mi>A</mi> <mo>[</mo> <mn>2</mn> <mo>]</mo> <mo>)</mo> <mo>/</mo> <mi>Q</mi> <mo>)</mo></mrow> </math> is cyclic of prime order <math><mrow><mi>p</mi> <mo>=</mo> <mn>2</mn> <mo>dim</mo> <mo>(</mo> <mi>A</mi> <mo>)</mo> <mo>+</mo> <mn>1</mn></mrow> </math> , we prove that there are only finitely many possibilities for the geometric endomorphism algebra <math><mrow><mtext>End</mtext> <mo>(</mo> <mi>A</mi> <mo>)</mo> <mo>⊗</mo> <mi>Q</mi></mrow> </math> . In fact, when <math><mrow><mo>dim</mo> <mo>(</mo> <mi>A</mi> <mo>)</mo> <mo>∉</mo> <mo>{</mo> <mn>3</mn> <mo>,</mo> <mn>5</mn> <mo>,</mo> <mn>9</mn> <mo>,</mo> <mn>21</mn> <mo>,</mo> <mn>33</mn> <mo>,</mo> <mn>81</mn> <mo>}</mo></mrow> </math> , we show <math><mrow><mtext>End</mtext> <mo>(</mo> <mi>A</mi> <mo>)</mo> <mo>⊗</mo> <mi>Q</mi></mrow> </math> is a proper subfield of the <i>p</i>-th cyclotomic field. In particular, when <math><mrow><mi>g</mi> <mo>=</mo> <mn>2</mn></mrow> </math> , <math><mrow><mtext>End</mtext> <mo>(</mo> <mi>A</mi> <mo>)</mo> <mo>⊗</mo> <mi>Q</mi></mrow> </math> is isomorphic to either <math><mi>Q</mi></math> or <math><mrow><mi>Q</mi> <mo>(</mo> <msqrt><mn>5</mn></msqrt> <mo>)</mo></mrow> </math> .</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"12 2","pages":"34"},"PeriodicalIF":0.8,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC13009002/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147515610","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Moments of derivatives of quadratic Dirichlet <i>L</i>-functions with prime conductor.","authors":"Christopher G Best","doi":"10.1007/s40993-026-00704-7","DOIUrl":"https://doi.org/10.1007/s40993-026-00704-7","url":null,"abstract":"<p><p>We compute an asymptotic formula for the mixed second moment of the <math><mi>μ</mi></math> -th and <math><mi>ν</mi></math> -th derivatives of quadratic Dirichlet <i>L</i>-functions over monic, irreducible polynomials in the function field setting.</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"12 1","pages":"14"},"PeriodicalIF":0.8,"publicationDate":"2026-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12882857/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"146150898","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Transcendental Brauer-Manin obstructions on singular K3 surfaces.","authors":"Mohamed Alaa Tawfik, Rachel Newton","doi":"10.1007/s40993-024-00580-z","DOIUrl":"10.1007/s40993-024-00580-z","url":null,"abstract":"<p><p>Let <i>E</i> and <math><msup><mi>E</mi> <mo>'</mo></msup> </math> be elliptic curves over <math><mi>Q</mi></math> with complex multiplication by the ring of integers of an imaginary quadratic field <i>K</i> and let <math><mrow><mi>Y</mi> <mo>=</mo> <mrow><mspace></mspace> <mtext>Kum</mtext> <mspace></mspace></mrow> <mo>(</mo> <mi>E</mi> <mo>×</mo> <msup><mi>E</mi> <mo>'</mo></msup> <mo>)</mo></mrow> </math> be the minimal desingularisation of the quotient of <math><mrow><mi>E</mi> <mo>×</mo> <msup><mi>E</mi> <mo>'</mo></msup> </mrow> </math> by the action of <math><mrow><mo>-</mo> <mn>1</mn></mrow> </math> . We study the Brauer groups of such surfaces <i>Y</i> and use them to furnish new examples of transcendental Brauer-Manin obstructions to weak approximation.</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"11 1","pages":"16"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC11655618/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142878096","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A Fourier-Jacobi Dirichlet series for cusp forms on orthogonal groups.","authors":"Rafail Psyroukis","doi":"10.1007/s40993-025-00668-0","DOIUrl":"https://doi.org/10.1007/s40993-025-00668-0","url":null,"abstract":"<p><p>We investigate a Dirichlet series involving the Fourier-Jacobi coefficients of two cusp forms <i>F</i>, <i>G</i> for orthogonal groups of signature <math><mrow><mo>(</mo> <mn>2</mn> <mo>,</mo> <mi>n</mi> <mo>+</mo> <mn>2</mn> <mo>)</mo></mrow> </math> . In the case when <i>F</i> is a Hecke eigenform and <i>G</i> is a Maass lift of a Poincaré series, we establish a connection with the standard <i>L</i>-function attached to <i>F</i>. What is more, we find explicit choices of orthogonal groups, for which we obtain a clear-cut Euler product expression for this Dirichlet series. Through our considerations, we recover a classical result for Siegel modular forms, first introduced by Kohnen and Skoruppa, but also provide a range of new examples, which can be related to other kinds of modular forms, such as paramodular, Hermitian, and quaternionic.</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"11 4","pages":"90"},"PeriodicalIF":0.8,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12449435/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145114578","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Traces of partition Eisenstein series and almost holomorphic modular forms.","authors":"Kathrin Bringmann, Badri Vishal Pandey","doi":"10.1007/s40993-025-00615-z","DOIUrl":"10.1007/s40993-025-00615-z","url":null,"abstract":"<p><p>Recently, Amdeberhan, Griffin, Ono, and Singh started the study of \"traces of partition Eisenstein series\" and used it to give explicit formulas for many interesting functions. In this note we determine the precise spaces in which they lie, find modular completions, and show how they are related via operators.</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"11 2","pages":"49"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12018508/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143989987","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Constructing families of 3-Selmer companions.","authors":"Harry Spencer","doi":"10.1007/s40993-025-00647-5","DOIUrl":"https://doi.org/10.1007/s40993-025-00647-5","url":null,"abstract":"<p><p>Mazur and Rubin introduced the notion of <i>n</i>-Selmer companion elliptic curves and gave several examples of pairs of non-isogenous Selmer companions. We construct several pairs of families of elliptic curves, each parameterised by <math><mrow><mi>t</mi> <mo>∈</mo> <mi>Z</mi></mrow> </math> , such that the two curves in a pair corresponding to a given <i>t</i> are non-isogenous 3-Selmer companions, possibly provided that <i>t</i> satisfies a simple congruence condition.</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"11 3","pages":"67"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12227473/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144576602","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Daniel Barrera Salazar, Andrew Graham, Chris Williams
{"title":"<ArticleTitle xmlns:ns0=\"http://www.w3.org/1998/Math/MathML\">On <i>p</i>-refined Friedberg-Jacquet integrals and the classical symplectic locus in the <ns0:math> <ns0:msub><ns0:mrow><ns0:mspace /> <ns0:mtext>GL</ns0:mtext> <ns0:mspace /></ns0:mrow> <ns0:mrow><ns0:mn>2</ns0:mn> <ns0:mi>n</ns0:mi></ns0:mrow> </ns0:msub> </ns0:math> eigenvariety.","authors":"Daniel Barrera Salazar, Andrew Graham, Chris Williams","doi":"10.1007/s40993-025-00631-z","DOIUrl":"https://doi.org/10.1007/s40993-025-00631-z","url":null,"abstract":"<p><p>Friedberg-Jacquet proved that if <math><mi>π</mi></math> is a cuspidal automorphic representation of <math> <mrow><msub><mtext>GL</mtext> <mrow><mn>2</mn> <mi>n</mi></mrow> </msub> <mrow><mo>(</mo> <mi>A</mi> <mo>)</mo></mrow> </mrow> </math> , then <math><mi>π</mi></math> is a functorial transfer from <math><msub><mtext>GSpin</mtext> <mrow><mn>2</mn> <mi>n</mi> <mo>+</mo> <mn>1</mn></mrow> </msub> </math> if and only if a global zeta integral <math><msub><mi>Z</mi> <mi>H</mi></msub> </math> over <math><mrow><mi>H</mi> <mo>=</mo> <msub><mtext>GL</mtext> <mi>n</mi></msub> <mo>×</mo> <msub><mtext>GL</mtext> <mi>n</mi></msub> </mrow> </math> is non-vanishing on <math><mi>π</mi></math> . We conjecture a <i>p</i>-refined analogue: that any <i>P</i>-parahoric <i>p</i>-refinement <math> <msup><mover><mi>π</mi> <mo>~</mo></mover> <mi>P</mi></msup> </math> is a functorial transfer from <math><msub><mtext>GSpin</mtext> <mrow><mn>2</mn> <mi>n</mi> <mo>+</mo> <mn>1</mn></mrow> </msub> </math> if and only if a <i>P</i>-twisted version of <math><msub><mi>Z</mi> <mi>H</mi></msub> </math> is non-vanishing on the <math> <msup><mover><mi>π</mi> <mo>~</mo></mover> <mi>P</mi></msup> </math> -eigenspace in <math><mi>π</mi></math> . This twisted <math><msub><mi>Z</mi> <mi>H</mi></msub> </math> appears in all constructions of <i>p</i>-adic <i>L</i>-functions via Shalika models. We connect our conjecture to the study of classical symplectic families in the <math><msub><mtext>GL</mtext> <mrow><mn>2</mn> <mi>n</mi></mrow> </msub> </math> eigenvariety, and-by proving upper bounds on the dimensions of such families-obtain various results towards the conjecture.</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"11 2","pages":"51"},"PeriodicalIF":0.6,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12031854/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144028936","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}