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1. Semisimplification of contragredient Lie algebras

   https://doi.org/10.2140/om.2024.1.211  

   Angiono, Iván; Plavnik, Julia; Sanmarco, Guillermo (January 2025, Orbita Mathematicae)

   We describe the structure and different features of Lie algebras in the Verlinde category, obtained as semisimplification of contragredient Lie algebras in characteristic p with respect to the adjoint action of a Chevalley generator. In particular, we construct a root system for these algebras that arises as a parabolic restriction of the known root system for the classical Lie algebra. This gives a lattice grading with simple homogeneous components and a triangular decomposition for the semisimplified Lie algebra. We also obtain a non-degenerate invariant form that behaves well with the lattice grading. As an application, we exhibit concrete new examples of Lie algebras in the Verlinde category. 

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2. A Sequential Quadratic Programming Approach to Coupling‐Bounded Non‐Inertial Earthquake Cycle Kinematics With Distance‐Weighted Eigenmodes

   https://doi.org/10.1029/2025EA004229  

   Meade, Brendan J; Loveless, John P (July 2025, Earth and Space Science)

   Abstract Geologic and geodetic observations provide constraints on tectonic and earthquake cycle kinematics. Block models offer one approach to integrating the effects of plate rotations, elastic strain accumulation, applied basal displacements, internal block strain, and idealized pressure sources. Here, we describe the construction of block models where spatially variable slip rates are parameterized by distance‐weighted eigenmodes operating over meshes of triangular dislocation elements. This dimensionally reduced model is recast as a quadratic programming problem with upper and lower bounds on both geologic fault slip rates and spatially variable slip deficit rates. We propose iterating over successive quadratic programming estimates with evolving slip rate bounds to find a solution consistent with specified coupling at all points on geometrically complex fault surfaces. 

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3. Naturality and innerness for morphisms of compact groups and (restricted) Lie algebras

   https://doi.org/10.1090/bproc/164  

   Chirvasitu, Alexandru (July 2024, Proceedings of the American Mathematical Society, Series B)

   An extended derivation (endomorphism) of a (restricted) Lie algebra $L$is an assignment of a derivation (respectively) of $L^{\prime }$for any (restricted) Lie morphism $f:L\to <\#comment/>L^{\prime }$, functorial in $f$in the obvious sense. We show that (a) the only extended endomorphisms of a restricted Lie algebra are the two obvious ones, assigning either the identity or the zero map of $L^{\prime }$to every $f$; and (b) if $L$is a Lie algebra in characteristic zero or a restricted Lie algebra in positive characteristic, then $L$is in canonical bijection with its space of extended derivations (so the latter are all, in a sense, inner). These results answer a number of questions of G. Bergman. In a similar vein, we show that the individual components of an extended endomorphism of a compact connected group are either all trivial or all inner automorphisms. 

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4. ROOTS OF CHARACTERISTIC EQUATION FOR SYMPLECTIC GROUPOID

   Chekhov, L.; Shapiro, M.; Shibo, H. (July 2022, Uspehi matematičeskih nauk)

   We use the Darboux coordinate representation found by two of the authors (L.Ch. and M.Sh.) for entries of general symplectic leaves of the A_n-groupoid of upper-triangular matrices to express roots of the characteristic equation det(A−λA^T)=0, with A∈A_n, in terms of Casimirs of this Darboux coordinate representation, which is based on cluster variables of Fock--Goncharov higher Teichmüller spaces for the algebra sl_n. We show that roots of the characteristic equation are simple monomials of cluster Casimir elements. This statement remains valid in the quantum case as well. We consider a generalization of A_n-groupoid to a A_{Sp_2m}-groupoid. 

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5. Cluster algebra structures on Poisson nilpotent algebras

   https://doi.org/10.1090/memo/1445  

   Goodearl, K; Yakimov, M (October 2023, Memoirs of the American Mathematical Society)

   Various coordinate rings of varieties appearing in the theory of Poisson Lie groups and Poisson homogeneous spaces belong to the large, axiomatically defined class of symmetric Poisson nilpotent algebras, e.g. coordinate rings of Schubert cells for symmetrizable Kac–Moody groups, affine charts of Bott-Samelson varieties, coordinate rings of double Bruhat cells (in the last case after a localization). We prove that every symmetric Poisson nilpotent algebra satisfying a mild condition on certain scalars is canonically isomorphic to a cluster algebra which coincides with the corresponding upper cluster algebra, without additional localizations by frozen variables. The constructed cluster structure is compatible with the Poisson structure in the sense of Gekhtman, Shapiro and Vainshtein. All Poisson nilpotent algebras are proved to be equivariant Poisson Unique Factorization Domains. Their seeds are constructed from sequences of Poisson-prime elements for chains of Poisson UFDs; mutation matrices are effectively determined from linear systems in terms of the underlying Poisson structure. Uniqueness, existence, mutation, and other properties are established for these sequences of Poisson-prime elements. 

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