{"title":"Equivariant algebraic concordance of strongly invertible knots","authors":"Alessio Di Prisa","doi":"10.1112/topo.70006","DOIUrl":"https://doi.org/10.1112/topo.70006","url":null,"abstract":"<p>By considering a particular type of invariant Seifert surfaces we define a homomorphism <span></span><math>\u0000 <semantics>\u0000 <mi>Φ</mi>\u0000 <annotation>$Phi$</annotation>\u0000 </semantics></math> from the (topological) equivariant concordance group of directed strongly invertible knots <span></span><math>\u0000 <semantics>\u0000 <mover>\u0000 <mi>C</mi>\u0000 <mo>∼</mo>\u0000 </mover>\u0000 <annotation>$widetilde{mathcal {C}}$</annotation>\u0000 </semantics></math> to a new equivariant algebraic concordance group <span></span><math>\u0000 <semantics>\u0000 <msup>\u0000 <mover>\u0000 <mi>G</mi>\u0000 <mo>∼</mo>\u0000 </mover>\u0000 <mi>Z</mi>\u0000 </msup>\u0000 <annotation>$widetilde{mathcal {G}}^mathbb {Z}$</annotation>\u0000 </semantics></math>. We prove that <span></span><math>\u0000 <semantics>\u0000 <mi>Φ</mi>\u0000 <annotation>$Phi$</annotation>\u0000 </semantics></math> lifts both Miller and Powell's equivariant algebraic concordance homomorphism (<i>J. Lond. Math. Soc</i>. (2023), no. 107, 2025-2053) and Alfieri and Boyle's equivariant signature (<i>Michigan Math. J. 1</i> (2023), no. 1, 1–17). Moreover, we provide a partial result on the isomorphism type of <span></span><math>\u0000 <semantics>\u0000 <msup>\u0000 <mover>\u0000 <mi>G</mi>\u0000 <mo>∼</mo>\u0000 </mover>\u0000 <mi>Z</mi>\u0000 </msup>\u0000 <annotation>$widetilde{mathcal {G}}^mathbb {Z}$</annotation>\u0000 </semantics></math> and obtain a new obstruction to equivariant sliceness, which can be viewed as an equivariant Fox–Milnor condition. We define new equivariant signatures and using these we obtain novel lower bounds on the equivariant slice genus. Finally, we show that <span></span><math>\u0000 <semantics>\u0000 <mi>Φ</mi>\u0000 <annotation>$Phi$</annotation>\u0000 </semantics></math> can obstruct equivariant sliceness for knots with Alexander polynomial one.</p>","PeriodicalId":56114,"journal":{"name":"Journal of Topology","volume":"17 4","pages":""},"PeriodicalIF":0.8,"publicationDate":"2024-11-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1112/topo.70006","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664938","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Metrics of positive Ricci curvature on simply-connected manifolds of dimension \u0000 \u0000 \u0000 6\u0000 k\u0000 \u0000 $6k$","authors":"Philipp Reiser","doi":"10.1112/topo.70007","DOIUrl":"https://doi.org/10.1112/topo.70007","url":null,"abstract":"<p>A consequence of the surgery theorem of Gromov and Lawson is that every closed, simply-connected 6-manifold admits a Riemannian metric of positive scalar curvature. For metrics of positive Ricci curvature, it is widely open whether a similar result holds; there are no obstructions known for those manifolds to admit a metric of positive Ricci curvature, while the number of examples known is limited. In this article, we introduce a new description of certain <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>6</mn>\u0000 <mi>k</mi>\u0000 </mrow>\u0000 <annotation>$6k$</annotation>\u0000 </semantics></math>-dimensional manifolds via labeled bipartite graphs and use an earlier result of the author to construct metrics of positive Ricci curvature on these manifolds. In this way, we obtain many new examples, both spin and nonspin, of <span></span><math>\u0000 <semantics>\u0000 <mrow>\u0000 <mn>6</mn>\u0000 <mi>k</mi>\u0000 </mrow>\u0000 <annotation>$6k$</annotation>\u0000 </semantics></math>-dimensional manifolds with a metric of positive Ricci curvature.</p>","PeriodicalId":56114,"journal":{"name":"Journal of Topology","volume":"17 4","pages":""},"PeriodicalIF":0.8,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://onlinelibrary.wiley.com/doi/epdf/10.1112/topo.70007","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142664918","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"数学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}