Recent Writings

This web page contains information about my recent writings. For some, only meant to be circulated within a restricted circle for the time being, passwords are needed. If you are interested in, please write me.

Zeta Functions

Zeta Functions of Reductive Groups and Their Zeros


Part 1. Non-Abelian Zeta Functions

Part 2. Rank Two Zeta Functions

Part 3. Eisenstein Periods and Multiple Zeta Functions

Part 4. Zeta Functions for Reductive Groups

Part 5. Algebraic, Analytic Structures and the Riemann Hypothesis

Part 6. Geometric Structures and the Riemann Hypothesis

Part 7. Five Essays on Arithmetic Cohomology (with K. Sugahara)

To be published in Feb 2018

L. WENG and D. Zagier
Non-abelian zeta function is defined for any smooth curve $X$ over a finite field $\mathbb F_q$ and any integer $n\ge 1$ by $$ \zeta_{X/\mathbb F_q,n}(s) \,=\, \sum_{[\mathcal E]}\frac{|H^0(X,\mathcal E)\!\smallsetminus\!\{0\}|} {|\mathrm{Aut}(\mathcal E)|}\;q^{-\text{deg}(\mathcal E)s} \qquad(\Re(s)>1)\,,$$ where the sum is over moduli stack of $\mathbb F_q$-rational semi-stable vector bundles $\mathcal E$ of rank $n$ on $X$ with degree divisible by $n$. This function, which agrees with the usual Artin zeta function of $X/\mathbb F_q$ if $n=1$, is a rational function of $q^{-s}$ with denominator $(1-q^{-ns})(1-q^{n-ns})$ and conjecturally satisfies the Riemann hypothesis. In this paper we study the case of genus 1 curves in detail. We show that in that case the Dirichlet series $$\mathcal Z_{X/\mathbb F_q}(s) \,=\, \sum_{[\mathcal E]}\frac1{|\mathrm{Aut}(\mathcal E)|}\;q^{-\text{rank}(\mathcal E)s} \qquad(\Re(s)>0)\,,$$ where the sum is now over isomorphism classes of $\mathbb F_q$-rational semi-stable vector bundles $\mathcal E$ of degree 0 on $X$, is equal to $\prod_{k=1}^\infty\zeta_{X/\mathbb F_q}(s+k)\,$, and use this fact to deduce the validity of the Riemann hypothesis for $\zeta_{X,n}(s)$ for all $n$.

L. WENG and D. Zagier
A different approach to zeta functions for curves leads to the so-called group zeta function ${\widehat\zeta}_X^{G/P}(s)$ associated to a connected split algebraic reductive group $G$ and its maximal parabolic subgroup $P$. We will be interested in the $SL_n$-zeta ${\widehat\zeta}_X^{\mathrm{SL}_n}(s):={\widehat\zeta}_X^{SL_n/P_{n-1,1}}(s)$. Our main result will be a proof of the following theorem on the conjecture of special uniformity of zetas: $$\widehat\zeta_{X,n}(s)\,=\,{\widehat\zeta}_X^{\mathrm{SL}_n}(s).$$ This theorem should be seen as a joint result of the present authors and of Mozgovoy and Reineke, because it is proved by comparing a formula established here for the $\mathrm{SL}_n$-zeta with a formula given in their work for rank $n$ non-abelian zeta using Hall algebra and wall-crossing.

Zeros of Zeta Functions for Exceptional Groups of Type $E$
A selection of 128 elements form Weyl groups for exceptional groups of type $E_8$ with 696,729,600 elements is given. As a direct consequence, we then prove the weak Riemann Hypothesis for the so-called Weng zeta functions of $E_8$. Moreover, we explain what is the meaning of these $128\,(=2^7)$ elements in terms of the masses of semi-stable principal $E_8$-lattices, following our earlier conjecture on Stability, Parabolic Reduction, and the Masses.

To be appeared as Chapter 13 of Part 5 in Zeta Functions of Reductive Groups and Their Zeros

Short version w/ limited data, Long version

Distributions of Zeros for Non-Abelian Zeta Functions
Two levels of fine structures on distributions of non-abelian zeta zeros are exposed. For pair correlations of zeros for rank $n$ non-abelian zeta $\widehat\zeta_{\mathbb Q,n}(s)$ $\ (n\geq 2)$, we have, for $\gamma_{n,k}$ the $k$-th zero, $$ \gamma_{n,k}=\frac{2\,\pi}{n}\frac{k}{\log k}\big(1+O\big(\frac{1}{\log k}\big)\big),\ \ \qquad \delta_{n,k}=1+O\big(\frac{1}{\log k}\big), $$ where $ \delta_{n,k} :=\big(\frac{n}{2\,\pi}(\gamma_{n,k+1}-\gamma_{n,k})\big)\cdot \log \big(\frac{n}{2\,\pi}\gamma_{n,k}\big). $ For GUE, we introduce $$ \Delta_{n,k}:=\big(\delta_{n,k}-1 \big)\cdot\log\big(\frac{n}{2\,\pi}\gamma_{n,k}\big), $$ and conjecture that distributions of these big Delta are closely related with GUE. Supportive evidences from numerical calculations are provided. Also treated are zeta functions for reductive groups and their maximal parabolic subgroups. Paper with pictures.

To be appeared as Chapter 18 of Part 6 in Zeta Functions of Reductive Groups and Their Zeros

In memory of Gang XIAO.

Motivic Euler Product and Its Aplications
We begin with a construction of non-abelian motivic zeta functions for curves over any base field, using moduli stacks of semi-stable bundles. As an application, we define motivic Euler products. Then, we introduce genuine zeta functions for Riemann surfaces and establish their convergences, based on the theory of Ray-Singer analytic torsions. To understand common features of these zetas, we next introduce natural motivic measures for the associated adelic spaces and hence obtain a motivic Siegel-Weil formula for the total mass of $\mathcal G$-torsors in terms of special values of motivic zetas, using the newly defined motivic Euler product. Moreover, we, using parabolic reduction and stability, obtain natural decompositions for moduli stacks of $\mathcal G$-torsors, and prove the parabolic reduction, stability and the mass conjecture for $\mathcal G$-torsors relating the total mass and the semi-stable masses. Finally, with Atiyah-Bott's analogue between Riemann surfaces and curves over finite fields and the conformal field theory in mind, we conjecture that our analytic zeta functions for Riemann surfaces are motivic, and hence unify our algebraic and analytic zetas.

Arithmetic Cohomology Theory

Arithmetic central extensions and tame reciprocity laws for arithmetic surfaces
K. Sugahara and L. WENG

About 50 years ago, Tate developed a theory of residues for curves using traces and adelic cohomologies. In 1989, Tate's work was integrated with the $K_2$ central extensions by Arbarello-De Concini-Kac. Later, in 2003, Osipov, based on Kapranov's dimension theory, constructed dimension two central extensions and hence established the reciprocity law for algebraic surfaces using Parshin's adelic theory. In essence, Osipov's construction may be viewed as $K_2$ type theory of central extensions developed by Brylinski-Deligne. However, for arithmetic surfaces, $K_2$ theory does not work. Instead, we first develop a new theory of central extensions based on Arakelov theory, then we use our adelic cohomology theory to establish the reciprocity law for arithmetic surfaces.

Reciprocity Law version, Reciprocty Law+Central Extension version

To be appeared as Appendix E in Zeta Functions of Reductive Groups and Their Zeros

Arithmetic Cohomology Groups
K. Sugahara and L. WENG

We first introduce global arithmetic cohomology groups for quasi-coherent sheaves on arithmetic varieties, adopting an adelic approach. Then, we establish fundamental properties, such as topological duality and inductive long exact sequences, for these cohomology groups on arithmetic surfaces. Finally, we expose basic structures for ind-pro topologies on adelic spaces of arithmetic surfaces. In particular, we show that these adelic spaces are topologically self-dual.

This is a revised version dated on 27 November, 2014. Newly developed is a theory of ind-pro topologies over adelic spaces for arithmetic surfaces.

To be appeared as Appendix A in Zeta Functions of Reductive Groups and Their Zeros

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Last update: June 21, 2013 18:00:00 PM