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1. ADM mass for C 0 C^{0} metrics and distortion under Ricci–DeTurck flow

   https://doi.org/10.1515/crelle-2023-0085  

   Burkhardt-Guim, Paula (December 2023, Journal für die reine und angewandte Mathematik (Crelles Journal))

   Abstract We show that there exists a quantity, depending only on $C^0$C^{0}data of a Riemannian metric, that agrees with the usual ADM mass at infinity whenever the ADM mass exists, but has a well-defined limit at infinity for any continuous Riemannian metric that is asymptotically flat in the $C^0$C^{0}sense and has nonnegative scalar curvature in the sense of Ricci flow.Moreover, the $C^0$C^{0}mass at infinity is independent of choice of $C^0$C^{0}-asymptotically flat coordinate chart, and the $C^0$C^{0}local mass has controlled distortion under Ricci–DeTurck flow when coupled with a suitably evolving test function. 

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2. Curvature and sharp growth rates of log-quasimodes on compact manifolds

   https://doi.org/10.1007/s00222-025-01315-2  

   Huang, Xiaoqi; Sogge, Christopher D (March 2025, Inventiones mathematicae)

   Abstract We obtain new optimal estimates for the$$L^{2}(M)\to L^{q}(M)$$ $L^2\left(M\right)\to L^q\left(M\right)$,$$q\in (2,q_{c}]$$ $q\in (2,q_c]$,$$q_{c}=2(n+1)/(n-1)$$ $q_c=2(n+1)/(n-1)$, operator norms of spectral projection operators associated with spectral windows$$[\lambda ,\lambda +\delta (\lambda )]$$ $[\lambda ,\lambda +\delta (\lambda \left)\right]$, with$$\delta (\lambda )=O((\log \lambda )^{-1})$$ $\delta \left(\lambda \right)=O\left({(log\lambda )}^{-1}\right)$on compact Riemannian manifolds$$(M,g)$$ $(M,g)$of dimension$$n\ge 2$$ $n\ge 2$all of whose sectional curvatures are nonpositive or negative. We show that these two different types of estimates are saturated on flat manifolds or manifolds all of whose sectional curvatures are negative. This allows us to classify compact space forms in terms of the size of$$L^{q}$$ $L^q$-norms of quasimodes for each Lebesgue exponent$$q\in (2,q_{c}]$$ $q\in (2,q_c]$, even though it is impossible to distinguish between ones of negative or zero curvature sectional curvature for any$$q>q_{c}$$ $q>q_c$. 

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3. The Yamabe flow on asymptotically flat manifolds

   https://doi.org/10.1515/crelle-2023-0052  

   Chen, Eric; Wang, Yi (September 2023, Journal für die reine und angewandte Mathematik (Crelles Journal))

   Abstract We study the Yamabe flow starting from an asymptotically flat manifold $(M^n,g_0)$(M^{n},g_{0}).We show that the flow converges to an asymptotically flat, scalar flat metric in a weighted global sense if $Y(M,\left[g_0\right])>0$Y(M,[g_{0}])>0, and show that the flow does not converge otherwise.If the scalar curvature is nonnegative and integrable, then the ADM mass at time infinity drops by the limit of the total scalar curvature along the flow. 

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4. The Neumann problem on the domain in 𝕊 ³ bounded by the Clifford torus

   https://doi.org/10.1515/ans-2022-0072  

   Case, Jeffrey S; Chen, Eric; Wang, Yi; Yang, Paul; Yung, Po-Lam (January 2023, Advanced Nonlinear Studies)

   Abstract In this study, the solution of the Neumann problem associated with the CR Yamabe operator on a subset $\mathrm{\Omega }$\Omegaof the CR manifold ${\mathbb{S}}^3${{\mathbb{S}}}^{3}bounded by the Clifford torus $\mathrm{\Sigma }$\Sigmais discussed. The Yamabe-type problem of finding a contact form on $\mathrm{\Omega }$\Omegawhich has zero Tanaka-Webster scalar curvature and for which $\mathrm{\Sigma }$\Sigmahas a constant $p$p-mean curvature is also discussed. 

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5. Nonexistence of isoperimetric sets in spaces of positive curvature

   https://doi.org/10.1515/crelle-2024-0032  

   Antonelli, Gioacchino; Glaudo, Federico (May 2024, Journal für die reine und angewandte Mathematik (Crelles Journal))

   Abstract For every $d\ge 3$d\geq 3, we construct a noncompact smooth 𝑑-dimensional Riemannian manifold with strictly positive sectional curvature without isoperimetric sets for any volume below 1.We construct a similar example also for the relative isoperimetric problem in (unbounded) convex sets in ${\mathbb{R}}^d$\mathbb{R}^{d}.The examples we construct have nondegenerate asymptotic cone.The dimensional constraint $d\ge 3$d\geq 3is sharp.Our examples exhibit nonexistence of isoperimetric sets only for small volumes; indeed, in nonnegatively curved spaces with nondegenerate asymptotic cones, isoperimetric sets with large volumes always exist.This is the first instance of noncollapsed nonnegatively curved space without isoperimetric sets. 

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