{"title":"Three-torsion subgroups and wild conductor exponents of plane quartics.","authors":"Elvira Lupoian, James Rawson","doi":"10.1007/s40993-025-00672-4","DOIUrl":"https://doi.org/10.1007/s40993-025-00672-4","url":null,"abstract":"<p><p>In this paper we give an algorithm to find the 3-torsion subgroup of the Jacobian of a smooth plane quartic curve with a marked rational point. We describe <math><mrow><mn>3</mn> <mo>-</mo></mrow> </math> torsion points in terms of cubics which triply intersect the curve, and use this to define a system of equations whose solution set corresponds to the coefficients of these cubics. We compute the points of this zero-dimensional, degree 728 scheme first by approximation, using homotopy continuation and Newton-Raphson, and then using continued fractions to obtain accurate expressions for these points. We describe how the Galois structure of the field of definition of the 3-torsion subgroup can be used to compute local wild conductor exponents, including at <math><mrow><mi>p</mi> <mo>=</mo> <mn>2</mn></mrow> </math> .</p>","PeriodicalId":43826,"journal":{"name":"Research in Number Theory","volume":"11 4","pages":"92"},"PeriodicalIF":0.8,"publicationDate":"2025-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC12496290/pdf/","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145240026","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}