Adrián Andrada, María Laura Barberis, Beatrice Brienza
{"title":"Holonomy of the Obata connection on 2-step hypercomplex nilmanifolds","authors":"Adrián Andrada, María Laura Barberis, Beatrice Brienza","doi":"10.1112/blms.70338","DOIUrl":"https://doi.org/10.1112/blms.70338","url":null,"abstract":"<p>We study the holonomy of the Obata connection on 2-step hypercomplex nilmanifolds. By explicitly computing the curvature tensor, we determine the conditions under which the Obata connection is flat, showing that this depends on the nilpotency step of each complex structure. In particular, we show that for 2-step hypercomplex nilmanifolds, the holonomy algebra of the Obata connection is always an abelian subalgebra of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>sl</mi>\u0000 <mo>(</mo>\u0000 <mi>n</mi>\u0000 <mo>,</mo>\u0000 <mi>H</mi>\u0000 <mo>)</mo>\u0000 </mrow>\u0000 <annotation>$mathfrak {sl}(n, mathbb {H})$</annotation>\u0000 </semantics></math> and we prove that the <span></span><math>\u0000 <semantics>\u0000 <mi>H</mi>\u0000 <annotation>$mathbb {H}$</annotation>\u0000 </semantics></math>-solvable conjecture holds in this case. Furthermore, we provide new examples of <span></span><math>\u0000 <semantics>\u0000 <mi>k</mi>\u0000 <annotation>$k$</annotation>\u0000 </semantics></math>-step nilpotent hypercomplex nilmanifolds, with arbitrary <span></span><math>\u0000 <semantics>\u0000 <mi>k</mi>\u0000 <annotation>$k$</annotation>\u0000 </semantics></math>, which are not Obata flat.</p>","PeriodicalId":55298,"journal":{"name":"Bulletin of the London Mathematical Society","volume":"58 4","pages":""},"PeriodicalIF":0.9,"publicationDate":"2026-03-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147569058","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"O-minimal total harmonic functions are polynomial","authors":"Chris Miller","doi":"10.1112/blms.70278","DOIUrl":"https://doi.org/10.1112/blms.70278","url":null,"abstract":"<p>If <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>h</mi>\u0000 <mo>:</mo>\u0000 <msup>\u0000 <mi>R</mi>\u0000 <mi>n</mi>\u0000 </msup>\u0000 <mo>→</mo>\u0000 <mi>R</mi>\u0000 </mrow>\u0000 <annotation>$hcolon mathbb {R}^n rightarrow mathbb {R}$</annotation>\u0000 </semantics></math> is harmonic and definable in an o-minimal expansion of the real field, then <span></span><math>\u0000 <semantics>\u0000 <mi>h</mi>\u0000 <annotation>$h$</annotation>\u0000 </semantics></math> is polynomial.</p>","PeriodicalId":55298,"journal":{"name":"Bulletin of the London Mathematical Society","volume":"58 4","pages":""},"PeriodicalIF":0.9,"publicationDate":"2026-03-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147568270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Quasibounded solutions to the complex Monge–Ampère equation","authors":"Mårten Nilsson","doi":"10.1112/blms.70340","DOIUrl":"https://doi.org/10.1112/blms.70340","url":null,"abstract":"<p>We study the Dirichlet problem for the complex Monge–Ampère operator on B-regular domains in <span></span><math>\u0000 <semantics>\u0000 <msup>\u0000 <mi>C</mi>\u0000 <mi>n</mi>\u0000 </msup>\u0000 <annotation>$mathbb {C}^n$</annotation>\u0000 </semantics></math>, allowing boundary data that is singular or unbounded. We extend the concept of pluri-quasibounded functions on the domain to functions on the boundary, defined by the existence of plurisuperharmonic majorants that dominate their absolute value in a strong sense—that is, the ratio of the function to the majorant tends to zero as the function tends to infinity. For such boundary data, we prove existence and uniqueness of pluri-quasibounded solutions in the Błocki–Cegrell class, the largest class for which the complex Monge–Ampère operator is well-behaved. In the unit disk, our approach recovers harmonic functions represented as Poisson integrals of <span></span><math>\u0000 <semantics>\u0000 <msup>\u0000 <mi>L</mi>\u0000 <mn>1</mn>\u0000 </msup>\u0000 <annotation>$L^1$</annotation>\u0000 </semantics></math> boundary data with respect to harmonic measure, and our characterization extends to all regular domains in <span></span><math>\u0000 <semantics>\u0000 <msup>\u0000 <mi>R</mi>\u0000 <mi>n</mi>\u0000 </msup>\u0000 <annotation>$mathbb {R}^n$</annotation>\u0000 </semantics></math>, when the boundary data is continuous almost everywhere. We also describe how boundary singularities propagate into the interior via a refined pluripolar hull.</p>","PeriodicalId":55298,"journal":{"name":"Bulletin of the London Mathematical Society","volume":"58 4","pages":""},"PeriodicalIF":0.9,"publicationDate":"2026-03-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://londmathsoc.onlinelibrary.wiley.com/doi/epdf/10.1112/blms.70340","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147567943","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"A computer-free property (T) proof for high-rank \u0000 \u0000 \u0000 Aut\u0000 (\u0000 \u0000 F\u0000 n\u0000 \u0000 )\u0000 \u0000 $mathrm{Aut}(F_n)$","authors":"Martin Nitsche","doi":"10.1112/blms.70334","DOIUrl":"https://doi.org/10.1112/blms.70334","url":null,"abstract":"<p>Existing property (T) proofs for <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>Aut</mi>\u0000 <mo>(</mo>\u0000 <msub>\u0000 <mi>F</mi>\u0000 <mi>n</mi>\u0000 </msub>\u0000 <mo>)</mo>\u0000 </mrow>\u0000 <annotation>$mathrm{Aut}(F_n)$</annotation>\u0000 </semantics></math>, <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>n</mi>\u0000 <mo>⩾</mo>\u0000 <mn>4</mn>\u0000 </mrow>\u0000 <annotation>$ngeqslant 4$</annotation>\u0000 </semantics></math>, rely crucially on extensive computer calculations. We give a new proof that <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>Aut</mi>\u0000 <mo>(</mo>\u0000 <msub>\u0000 <mi>F</mi>\u0000 <mi>n</mi>\u0000 </msub>\u0000 <mo>)</mo>\u0000 </mrow>\u0000 <annotation>$mathrm{Aut}(F_n)$</annotation>\u0000 </semantics></math> has property (T) for all but finitely many <span></span><math>\u0000 <semantics>\u0000 <mi>n</mi>\u0000 <annotation>$n$</annotation>\u0000 </semantics></math>, which is inspired by the semidefinite programming approach but does not use the computer in any step. More specifically, we prove property (T) for a certain extension <span></span><math>\u0000 <semantics>\u0000 <msub>\u0000 <mi>Γ</mi>\u0000 <mi>n</mi>\u0000 </msub>\u0000 <annotation>$Gamma _n$</annotation>\u0000 </semantics></math> of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>SAut</mi>\u0000 <mo>(</mo>\u0000 <msub>\u0000 <mi>F</mi>\u0000 <mi>n</mi>\u0000 </msub>\u0000 <mo>)</mo>\u0000 </mrow>\u0000 <annotation>$mathrm{SAut}(F_n)$</annotation>\u0000 </semantics></math> as <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mi>n</mi>\u0000 <mo>→</mo>\u0000 <mi>∞</mi>\u0000 </mrow>\u0000 <annotation>$nrightarrow infty$</annotation>\u0000 </semantics></math>.</p>","PeriodicalId":55298,"journal":{"name":"Bulletin of the London Mathematical Society","volume":"58 4","pages":""},"PeriodicalIF":0.9,"publicationDate":"2026-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"147567410","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}