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Events for October 2025 – February 2026

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Thu, Oct. 30 5pm (CSU)	Algebraic Geometry Multiple speakers X 3rd installment of Front Range Algebraic Geometry (FRAG) day happening at CSU in Weber 201 1:00-5:00 https://sites.google.com/colorado.edu/front-range-ag/home FRAG Day
Thu, Oct. 2 11:15am (MATH …	Algebraic Geometry Daniel Lyness X In this talk we will be continuing where we left off last week, having just introduced the Hilbert-Mumford Numerical Criterion. Now we will see how to use this powerful computational tool to do GIT on the space of plane cubic curves. There will be lots of pictures! Then we’ll kick it up a notch to my research question: How to use GIT to find a moduli space for pairs (Q,C) of a conic and cubic plane curve, and how our moduli space will change depending on the ample line bundle used for our embedding in projective space. GIT on plane curves
Thu, Oct. 2 2:30pm (MATH 3…	Functional Analysis Alonso Delfín (CU Boulder) X The main goal of this set of talks is to introduce twisted crossed products of Banach algebras by locally compact groups. Both talks will be accessible to anyone with basic Functional Analysis knowledge, but Part II will assume familiarity with Part I. Classical crossed products of Banach algebras have been extensively studied for different classes of representations, including contractive representations on L^p-spaces. Part I: We give a general formulation for Banach algebras associated with twisted dynamical systems. Recent developments in L^p-twisted crossed products have mostly focused on situations where either the algebra is the complex numbers or when the group is discrete (more generally for étale groupoids). We present a universal characterization of the twisted crossed product when the acting group is locally compact and the Banach algebra has a contractive approximate identity. Part II: We now focus on the case when the representations are contractive ones acting on L^p spaces. We briefly discuss a reduced version for L^p-operator algebras. We present a generalization of the so called Packer–Raeburn trick to the L^p-setting, showing that the universal L^p twisted crossed product is ``stably'' isometrically isomorphic to an untwisted one. This is joint work with Carla Farsi and Judith Packer. Twisted Crossed Products of Banach Algebras (Part I)
Fri, Oct. 3 10:10am (Math …	Math Edu Joseph Timmer & Rebekah Jones X In this workshop, we'll analyze examples of teaching statements and discuss what makes a successful teaching statement. We'll also hear directly from faculty who've served on hiring committees about their evaluation process and priorities. Participants can bring their own teaching statements to receive more targeted guidance and feedback. Teaching Statement Workshop
Tue, Oct. 7 1:25pm (online)	Algebra/Logic Andrew Moorhead (TU Dresden, Germany) View Online:https://cuboulder.zoom.us/j/96896272260 X A strong Maltsev class of varieties is a class of varieties for which there exists a finitely presented variety (i.e. a variety in a finite signature satisfying finitely many identities) whose interpretability class is a lower bound to every variety in the interpretability order, while a Maltsev class of varieties is a class for which there exists a countably infinite descending chain of finitely presented varieties and each variety in the Maltsev class is bounded below by some of the chain. A Maltsev term is the original example of a strong Maltsev condition and the identities that define it define the class of congruence permutable varieties. On the other hand, the classes of congruence distributive and congruence modular varieties are not strong Maltsev classes, but rather Maltsev classes (the terms for distributivity were discovered by Jónsson and the terms for modularity were discovered by Day). There has been for some years a fertile area of research which connects Universal Algebra to the complexity theory of constraint satisfaction. While many of these results are largely important for complexity theory, some of them have been important for algebra. In particular, Siggers discovered that the class of locally finite Taylor varieties is captured by a finite package of identities. In 2015, Olsak made the surprising discovery that in fact the class of all Taylor algebras is strong Maltsev. A natural next question was: what about the class of congruence meet semidistributive varieties? This is an important class in fixed template finite domain CSP, since the class of locally finite congruence meet semidistributive varieties is exactly the class of varieties which correspond to CSP templates which can be solved with local consistency methods. Actually, Kozik, Krokhin, Valeriote, and Willard proved that locally finite congruence meet semidistributive varieties are characterized by a finite package of identities. We show that, unlike the class of Taylor varieties, this finiteness does not lift to the general case, that is, there does not exist a strong Maltsev condition that captures every congruence meet semidistirbutive variety. The class of congruence meet semidistributive varieties is not strong Maltsev
Tue, Oct. 7 2:30pm (MATH 2…	Grad Algebra/Logic Omar Al - Khazali (CU Boulder) Graph algebras
Tue, Oct. 7 2:30pm (MATH 3…	Lie Theory Richard Green (CU) X Every permutation is associated to a classical combinatorial object called a Rothe diagram, where the number of points in the diagram is equal to the number of inversions in the permutation. In this talk, we generalize this notion by associating a Rothe diagram to a set of positive orthogonal roots for a finite simply-laced Weyl group. This construction turns out to have many applications to algebraic combinatorics and to the theory of invariant polynomials. This is based on joint work with Tianyuan Xu (University of Richmond). Orthogonal roots and generalized Rothe diagrams
Thu, Oct. 9 11:15am (MATH …	Algebraic Geometry Matt Watson X TBA TBA
Thu, Oct. 9 2:30pm (MATH 3…	Functional Analysis Alonso Delfín (CU Boulder) X The main goal of this set of talks is to introduce twisted crossed products of Banach algebras by locally compact groups. Both talks will be accessible to anyone with basic Functional Analysis knowledge, but Part II will assume familiarity with Part I. Classical crossed products of Banach algebras have been extensively studied for different classes of representations, including contractive representations on L^p-spaces. Part I: We give a general formulation for Banach algebras associated with twisted dynamical systems. Recent developments in L^p-twisted crossed products have mostly focused on situations where either the algebra is the complex numbers or when the group is discrete (more generally for étale groupoids). We present a universal characterization of the twisted crossed product when the acting group is locally compact and the Banach algebra has a contractive approximate identity. Part II: We now focus on the case when the representations are contractive ones acting on L^p spaces. We briefly discuss a reduced version for L^p-operator algebras. We present a generalization of the so called Packer–Raeburn trick to the L^p-setting, showing that the universal L^p twisted crossed product is ``stably'' isometrically isomorphic to an untwisted one. This is joint work with Carla Farsi and Judith Packer. Twisted Crossed Products of Banach Algebras (Part II)
Thu, Oct. 9 3:30pm (Math 3…	Probability Ewan Davies (Colorado State University) X The hard-core model is a well-studied probability distribution in statistical physics and algorithms since it exhibits interesting behavior from probabilistic and algorithmic perspectives. We will survey the underlying mathematical phenomena that drive this interesting behavior and uncover some surprises. A first-order phase transition in the hard-core model
Fri, Oct. 10 10:10am (Math …	Math Edu Hilary Freeman (Colorado State University) X Math 160 Calculus I for Engineers at Colorado State University has been using a version of standards-based grading since Fall of 2020. In this talk I will discuss why I made the change to alternative grading and how I’ve been implementing this grading system and the changes we’ve gone through. I’ll address the particular challenges of coordinating multiple sections with a large total enrollment and what technology I’ve found helpful or not so helpful. Five Years of Standards-Based Grading in a First Semester Calculus Course
Tue, Oct. 14 12:10pm (MATH …	Kempner Constantin Dorin Dumitrascu (Adrian College) X We take a combinatorial approach to the classical problem of random walks in the d-dimensional Euclidean lattice Z^d, where the walker takes steps {-1, +1}^d, each with equal probability 1/(2d). We give precise asymptotics for the number of closed walks or excursions (the walks of a given length that return to the starting point). We also discuss the more complicated case of first-time returns. Recall that a sequence (f_n)_n is called P-recursive if it admits a recurrence relation with coefficients polynomials in n. This property is equivalent with holonomicity (or D-finiteness) of the generating function, meaning that the vector space of its formal derivatives is finite dimensional. We show that, in dimension greater or equal to 2, the sequence of excursions is P-recursive, while the sequence of first-time returns is not P-recursive. Techniques from the theory of Legendre polynomials, analytic combinatorics, holonomic functions, and Fuchsian ODEs are employed in the proofs. This presentation reports on joint work with Liviu Suciu. On the non-holonomic character of first time returns in the Euclidean lattice
Tue, Oct. 14 2:30pm (MATH 2…	Grad Algebra/Logic Nick Jamesson (CU Boulder) Categorical Perspective on Constraint Satisfaction (Part 4)
Tue, Oct. 14 2:30pm (MATH 3…	Lie Theory Richard Green (CU) X We explore further applications of the generalized Rothe diagrams associated to sets of orthogonal positive roots of simply laced root systems. We will discuss examples arising from labelled Fano planes and from the representation theory of simple Lie algebras. This talk is based on joint work with Tianyuan Xu (University of Richmond), and is a continuation of last week's talk. Orthogonal roots and generalized Rothe diagrams, part 2
Tue, Oct. 14 3:30pm (MATH 3…	Topology Taylor Rogers X Recently, higher categorical generalizations of semiadditivity have proven useful in stable homotopy theory; in particular, they demonstrate that certain localizations of the category of spectra are exceedingly well-behaved. Understanding higher semiadditivity has also produced an interesting theory of ambidextrous adjunctions, that may be useful in the study of other stable infinity categories. In this talk, we will introduce semiadditivity and ambidexterity in a general categorical setting. We will then specialize to the context of stable homotopy theory and discuss how the theory of higher semiaddtivity gives a proof of May's nilpotence conjecture. Ambidexterity and Nilpotence
Tue, Oct. 14 3:35pm (MATH 2…	PDE/Analysis Fernando Charro (Wayne State University) X In recent years there has been an increasing interest in whether a mean value property, known to characterize harmonic functions, can be extended in some weak form to solutions of nonlinear equations. This question has been partially motivated by the surprising connection between Random Tug-of-War games and the normalized p-Laplacian discovered some years ago by Peres et al., where a nonlinear asymptotic mean value property for solutions of a PDE is related to a dynamic programming principle for an appropriate game. In this talk, we discuss asymptotic mean value formulas for a class of nonlinear second-order equations that includes the classical Monge-Ampère and k-Hessian equations among other examples. Asymptotic Mean Value Formulas for Nonlinear Equations Sponsored by the Meyer Fund
Thu, Oct. 16 11:15am (MATH …	Algebraic Geometry Matt Watson X TBA TBA
Thu, Oct. 16 2:30pm (MATH 3…	Functional Analysis Gregory Berkolaiko (Texas A&M) X Duistermaat index is a symplectic invariant defined for triples of Lagrangian subspaces. We discuss its concise axiomatic definition, its relation to the Maslov index of paths of Lagrangian subspaces and its surprising application to eigenvalue interlacing for differential operators with different sets of boundary conditions. Based on joint work with Graham Cox, Yuri Latushkin and Selim Sukhtaiev. Duistermaat index and its application to eigenvalue interlacing
Tue, Oct. 21 2:30pm (MATH 3…	Lie Theory Andrew Reimer-Berg (Colorado State University) TBD
Tue, Oct. 21 3:30pm (MATH 3…	Topology Alex LaJeunesse TBD
Thu, Oct. 23 11:15am (MATH …	Algebraic Geometry Yota Maeda (TU Darmstadt) X See https://sites.google.com/view/fragmentseminar/ On the Kodaira dimension of even-dimensional ball quotients Sponsored by the Meyer Fund
Thu, Oct. 30 10am (Math 350)	Number Theory Wissam Ghantous (University of Central Florida) TBD
Thu, Oct. 30 1:20pm (MATH 3…	Number Theory Gabrielle Scullard (University of Georgia) TBD
Thu, Oct. 30 2:30pm (MATH 3…	Functional Analysis Maggie Reardon (CU Boulder) X Matui’s HK-conjecture proposes a connection between the homology of a nice enough étale groupoid and the -theory of the associated reduced -algebra. The HK-conjecture is not true in general and there are a number of counterexamples. The related AH-conjecture predicts an exact sequence involving the zeroth and first homology groups together with the abelianization of the topological full group. Unlike the HK-conjecture, no counterexamples are known for the AH-conjecture, though it remains unproven. Both conjectures are verified for a number of natural classes of groupoids, including AF groupoids. Putnam introduced a new class of groupoids in the paper titled “Some classifiable groupoid -algebras with prescribed -theory”. These new groupoids are related to AF groupoids and this prompts a natural question: does this new class of groupoids satisfy the HK- and AH-conjectures? The HK- and AH-conjectures for certain groupoids constructed by Putnam
Tue, Nov. 4 3:30pm (MATH 3…	Topology Ben Knudsen (Colorado State University) TBD
Thu, Nov. 6 11:15am (MATH …	Algebraic Geometry Lisa Marquand (NYU) TBD Sponsored by the Meyer Fund
Thu, Nov. 6 2:30pm (MATH 3…	Functional Analysis James Woodcock (CU Boulder) X Minimal homeomorphisms of topological spaces provide a source of simple C-algebras whose structure and K-theory can be understood through dynamical systems. I will present results on the existence of minimal homeomorphisms of flat manifolds with positive first Betti number. When the flat manifold has a spin^c structure we will show that the resulting cross product satisfies Poincare Duality for C-algebras. Finally, I will describe ongoing work toward constructing explicit KK-cycle representatives in the presence of minimal flows, in analogy with the classical case of irrational rotation algebras. Flat manifolds, C*-algebras, and duality
Tue, Nov. 11 1:25pm (online)	Algebra/Logic George Metcalfe (University Bern) View Online:https://cuboulder.zoom.us/j/96896272260 X This talk will be about idempotent semifields, which, from a purely algebraic perspective are just lattice-ordered groups formulated in a restricted language with the group multiplication, neutral element, and lattice-join operation. We will see that although countably infinitely many equational theories of lattice-ordered groups have a finite equational basis, no non-trivial equational theory of idempotent semifields has this property. On the other hand, as in the case of lattice-ordered groups, there are continuum-many equational theories of classes of idempotent semifields. Finally, we will relate the problem of deciding equations in the class of idempotent semifields to the problem of deciding if there exists a right order on a free group satisfying a given finite set of inequalities, and show that these problems are, respectively, co-NP-complete and NP-complete. This is joint work with Simon Santschi. Equational Theories of Idempotent Semifields
Wed, Nov. 12 4:30pm (TBD)	Algebraic Geometry Zhijia Zhang (NYU) X TBD TBD - Note the unusual time and date Sponsored by the Meyer Fund
Tue, Nov. 18 1:25pm (MATH 2…	Algebra/Logic Simon Santschi (University Bern) View Online:https://cuboulder.zoom.us/j/96896272260 TBA
Tue, Nov. 18 3:30pm (MATH 3…	Topology Rick TBD
Wed, Nov. 19 4:40pm (MATH 3…	Grad Student Seminar Basia Klos (CU Boulder) X TBD What even is a VOA?
Tue, Dec. 2 3:30pm (MATH 3…	Topology Stephanie TBD

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