arXiv subjects

Lucas Buzaglo

Publications and source records attributed to Lucas Buzaglo.

8 recordsLinked to original sources

arXiv2026

On the boundary Carrollian conformal algebra

We initiate the mathematical study of the boundary Carrollian conformal algebra (BCCA), an infinite-dimensional Lie algebra recently discovered in the context of Carrollian physics. The BCCA is an intriguing object from both physical and mathematical perspectives, since it is a filtered but not graded Lie algebra. In this paper, we first construct some modules for the BCCA and one of its subalgebras, which we call $\mathcal{O}$, by restriction of well-known modules of the BMS$_3$ and Witt algebras respectively. Along the way, we prove the irreducibility criteria for the so-called ``induced modules'' of the BMS$_3$ algebra (which we prefer to call massive modules to avoid ambiguity) and show that this is the same criteria for the irreducibility of the Verma modules of the BMS$_3$ algebra. Interestingly, the modules generated by the action of the BCCA on the generating vector of the massive modules are also irreducible under the same criteria. When this criteria holds, every massive module decomposes into a direct sum of two BCCA-submodules, each of which we conjecture to be indecomposable. Meanwhile, restricting Verma modules to the BCCA and $\mathcal{O}$ leads to free or ``almost free'' modules, which are not particularly interesting from a representation-theoretic viewpoint. This motivates the construction of BCCA modules intrinsically. To do this, we go through some structure theory on the BCCA to define a new basis and a decreasing filtration on the algebra, using which we construct Whittaker modules over the BCCA and the subalgebra $\mathcal{O}$ and prove criteria for their irreducibility.

math.RT↗

arXiv2026

Lie subalgebras of vector fields on curves

We study the subalgebra structure of Krichever-Novikov algebras, which are Lie algebras of vector fields on smooth affine curves. Our main result is that every infinite-dimensional subalgebra of a Krichever-Novikov algebra is isomorphic to a finite-codimensional subalgebra of another Krichever-Novikov algebra. We then present some applications of our main result. First, we show that the universal enveloping algebra of any such infinite-dimensional subalgebra is not noetherian. We then prove that all Krichever-Novikov algebras satisfy the Dixmier property that all their nonzero endomorphisms are automorphisms, except for the Witt algebra of vector fields on the once-punctured affine line. Finally, we provide an explicit classification of the infinite-dimensional subalgebras of the Witt algebra.

math.RA↗

arXiv2026

Coactions of cocommutative Hopf algebras on skew polynomial rings

We classify the cocommutative Hopf algebras which coact inner-faithfully on (one-parameter) skew polynomial rings $A_q(n) = \Bbbk \langle x_1,\dots,x_n \rangle/(x_j x_i - q x_i x_j \mid i < j)$ for $n = 2$ and $3$. As a direct corollary, we obtain a classification of group gradings on two- and three-variable skew polynomial rings, recovering a result of Crawford in the two-variable case. Our results are achieved via Manin's universal coacting Hopf algebra construction, often denoted $\underline{\operatorname{aut}}(A_q(n))$, by classifying all its cocommutative quotients. We therefore also give an explicit presentation of $\underline{\operatorname{aut}}(A_q(n))$ for arbitrary $q \in \Bbbk^*$ and $n \in \mathbb{N}$.

math.RA↗

arXiv2025

Central extensions, derivations, and automorphisms of semi-direct sums of the Witt algebra with its intermediate series modules

Lie algebras formed via semi-direct sums of the Witt algebra $\text{Der}(\mathbb{C}[t,t^{-1}])$ and its modules have become increasingly prominent in both physics and mathematics in recent years. In this paper, we complete the study of (Leibniz) central extensions, derivations and automorphisms of the Lie algebras formed from the semi-direct sum of the Witt algebra and its indecomposable intermediate series modules (that is, graded modules with one-dimensional graded components). Our techniques exploit the internal grading of the Witt algebra, which can be applied to a wider class of graded Lie algebras.

math.RA↗

arXiv2024

Maximal dimensional subalgebras of general Cartan type Lie algebras

Let $\Bbbk$ be a field of characteristic zero and let $\mathbb{W}_n = \operatorname{Der}(\Bbbk[x_1,\cdots,x_n])$ be the $n^{\text{th}}$ general Cartan type Lie algebra. In this paper, we study Lie subalgebras $L$ of $\mathbb{W}_n$ of maximal Gelfand-Kirillov (GK) dimension, that is, with $\operatorname{GKdim}(L) = n$. For $n = 1$, we completely classify such $L$, proving a conjecture of the second author. As a corollary, we obtain a new proof that $\mathbb{W}_1$ satisfies the Dixmier conjecture, in other words, $\operatorname{End}(\mathbb{W}_1) \setminus \{0\} = \operatorname{Aut}(\mathbb{W}_1)$, a result first shown by Du. For arbitrary $n$, we show that if $L$ is a GK-dimension $n$ subalgebra of $\mathbb{W}_n$, then $U(L)$ is not (left or right) noetherian.

math.RA↗

arXiv2024

Enveloping algebras of derivations of commutative and noncommutative algebras

Let $\Bbbk$ be a field of characteristic zero. Motivated by the fundamental question of whether it is possible for the universal enveloping algebra of an infinite-dimensional Lie algebra to be noetherian, we study Lie algebras of derivations of associative algebras. The main result of this paper is that the universal enveloping algebra of the Lie algebra of derivations of a finitely generated $\Bbbk$-algebra is not noetherian. This extends a result of Sierra and Walton on the Witt algebra, as well as a result of the second author on Krichever-Novikov algebras. We highlight that the result applies to derivations of both commutative and noncommutative algebras without restriction on their growth.

math.RA↗

arXiv2023

Derivations, extensions, and rigidity of subalgebras of the Witt algebra

Let $\Bbbk$ be an algebraically closed field of characteristic 0. We study some cohomological properties of Lie subalgebras of the Witt algebra $W = \operatorname{Der}(\Bbbk[t,t^{-1}])$ and the one-sided Witt algebra $W_{\geq -1} = \operatorname{Der}(\Bbbk[t])$. In the first part of the paper, we consider finite codimension subalgebras of $W_{\geq -1}$. We compute derivations and one-dimensional extensions of such subalgebras. These correspond to $\operatorname{Ext}_{U(L)}^1(M,L)$, where $L$ is a subalgebra of $W_{\geq -1}$ and $M$ is a one-dimensional representation of $L$. We find that these subalgebras exhibit a kind of rigidity: their derivations and extensions are controlled by the full one-sided Witt algebra. As an application of these computations, we prove that any isomorphism between finite codimension subalgebras of $W_{\geq -1}$ extends to an automorphism of $W_{\geq -1}$. The second part of the paper is devoted to explaining the observed rigidity. We define a notion of "completely non-split extension" and prove that $W_{\geq -1}$ is the universal completely non-split extension of any of its subalgebras of finite codimension. In some sense, this means that even when studying subalgebras of $W_{\geq -1}$ as abstract Lie algebras, they remember that they are contained in $W_{\geq -1}$. We also consider subalgebras of infinite codimension, explaining the similarities and differences between the finite and infinite codimension situations. Almost all of the results above are also true for subalgebras of the Witt algebra. We summarise results for $W$ at the end of the paper.

math.RA↗

arXiv2022

Enveloping algebras of Krichever-Novikov algebras are not noetherian

This work is part of the overarching question of whether it is possible for the universal enveloping algebra of an infinite-dimensional Lie algebra to be noetherian. The main result of this paper is that the universal enveloping algebra of any Krichever-Novikov algebra is not noetherian, extending a result of Sierra and Walton on the Witt (or classical Krichever-Novikov) algebra. As a subsidiary result, which may be of independent interest, we show that if $\mathfrak{h}$ is a Lie subalgebra of $\mathfrak{g}$ of finite codimension, then the noetherianity of $U(\mathfrak{h})$ is equivalent to the noetherianity of $U(\mathfrak{g})$. The second part of the paper focuses on Lie subalgebras of $W_{\geq -1} = \operatorname{Der}(\Bbbk[t])$. In particular, we prove that certain subalgebras of $W_{\geq -1}$ (denoted by $L(f)$, where $f \in \Bbbk[t]$) have non-noetherian universal enveloping algebras, and provide a sufficient condition for a subalgebra of $W_{\geq -1}$ to have a non-noetherian universal enveloping algebra. Furthermore, we make significant progress on a classification of subalgebras of $W_{\geq -1}$ by showing that any infinite-dimensional subalgebra must be contained in some $L(f)$ in a canonical way.

math.RA↗