arXiv subjects

Pham Thanh Tâm

Publications and source records attributed to Pham Thanh Tâm.

3 recordsLinked to original sources

arXiv2024

Logarithmic decomposition of connections on a relatively punctured disk

Let $R=C[[t]]$ be the ring of power series over an algebraically closed field $C$ of characteristic zero. We show that each connection on a finite flat $R((x))$-module is the sum of a regular singular connection and a diagonalizable $R((x))$-linear endomorphism when it admits a Turrittin-Levelt-Jordan form over $R((x))$. This decomposition is compatible with the limit of the logarithmic decompositions of the connections obtained by the reduction modulo $t^{k}$ of a given connection.

math.AG↗

arXiv2024

Prolongation of regular singular connections on punctured affine line over a Henselian ring

We generalize Deligne's equivalence between the categories of regular-singular connections on the formal punctured disk and on the punctured affine line to the case where the base is a strictly Henselian discrete valuation ring of equal characteristic 0. We also provide a weaker result when the base is higher dimensional.

math.AG↗

arXiv2023

Algebraic theory of formal regular-singular connections with parameters

This paper is divided into two parts. The first is a review, through categorical lenses, of the classical theory of regular-singular differential systems over $C((x))$ and $\mathbb P^1_C\smallsetminus\{0,\infty\}$, where $C$ is algebraically closed and of characteristic zero. It aims at reading the existing classification results as an equivalence between regular-singular systems and representations of the group $\mathbb Z$. In the second part, we deal with regular-singular connections over $R((x))$ and $\mathbb P_R^1\smallsetminus\{0,\infty\}$, where $R=C[[t_1,\ldots,t_r]]/I$. The picture we offer shows that regular-singular connections are equivalent to representations of $\mathbb Z$, now over $R$.

math.AG↗