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Harald Grobner

Publications and source records attributed to Harald Grobner.

13 recordsLinked to original sources

On divergence related to Riemann--von Mangoldt's explicit formula of the prime-counting function

An explicit formula for the prime-counting function $\pi(x)$, usually attributed to Riemann and von Mangoldt, is prominently stated as the equation $\pi(x)=R(x)-\sum_\rho R(x^\rho)$, where the sum runs over all zeros $\rho$ of the Riemann $\zeta$-function, the non-trivial ones being ordered by increasing absolute value of their imaginary parts and counted with multiplicity. This particularly entails the claim that the partial sums over the non-trivial zeros, $\Sigma R_T(x):=\sum_{0<|\Im m(\rho)|\le T} R(x^\rho)$ converge as ${T\to\infty}$. Writing $\Theta:=\sup\{\Re e(\rho):\ \zeta(\rho)=0,\ 0<\Re e(\rho)<1\},$ for what has recently been called ``Riemann's constant'', we prove that, for every fixed $x>1$ and every $\theta<\Theta$, the sums $\Sigma R_T(x)$ are not $O(T^\theta)$. As a consequence, $\limsup_{{T\to\infty}}|\Sigma R_T(x)|=\infty$ and $\sum_\rho R(x^\rho)$ diverges. We conclude the paper by showing that an adapted, but simpler strategy also gives the divergence of the contribution of the trivial zeros to $\sum_\rho R(x^\rho)$.

math.NT

On the residual Eisenstein cohomology of unitary groups

We investigate the residual Eisenstein cohomology of an arbitrary unitary group $U(V)$ attached to an arbitrary quadratic extension of number fields $E/F$. Our focus lies on the contribution of the maximal parabolic $F$-subgroups of $U(V)$, for which we identify the cohomologically relevant poles of Eisenstein series and prove that the resulting residues all survive as non-trivial classes in automorphic cohomology in an explicit degree. To illustrate the range of phenomena involved, we study in detail the case of a unitary group over $F=\mathbb{Q}(\sqrt[3]{2})$ of $F$-rank $3$, for which we explicitly construct cuspidal automorphic representations, which satisfy all the assumptions of our main theorem and hence explicitly construct non-zero residual Eisenstein cohomology classes for this unitary group. The methods used in this construction are paradigmatic however, i.e., generalize to other unitary groups over other ground fields $F$ by the use of base change.

math.NT

Uniformity of Consistency in Arithmetic and G\"odel's Second Incompleteness Theorem: Ein M\"archen

In much discussed work Artemov has recently argued that, for $\mathrm{PA}$, the consistency schema admits a form of uniform verification via selector-proofs, despite the unprovability of the corresponding uniform consistency sentence $\mathrm{Con}(\mathrm{PA})$. In this note, we show that this phenomenon extends to all sufficiently strong, uniformly reflexive arithmetizable theories, including $\mathrm{ZF}$ and many of their extensions: For such theories $T$, there exists a primitive recursive selector which, given a derivation code $d$, extracts a finite fragment $T_d\subseteq T$ containing the non-logical axioms occurring in $d$, uses a reflexivity proof of $\mathrm{Con}(T_d)$, and produces a $T$-proof that $d$ is not a derivation of $0=1$. As a dictum, one obtains a $T$-verification of the consistency of $T$ in a uniform way, despite the fact that it cannot be internalized as the single universal consistency sentence prohibited by G\"odel's Second Incompleteness Theorem. We further analyze this latter discrepancy and locate selector-proofs within the broader framework of provability and reflection.

math.LO

A Functorial Refinement of the Franke Filtration and the Jacquet--Langlands Correspondence for Spaces of Automorphic Forms

The global Jacquet--Langlands correspondence is an instance of Langlands functoriality, namely the expected lifting of the irreducible automorphic representations of an inner form of the general linear group to the split form via the identity morphism of $L$-groups. It is established, by the work of Badulescu, in the case of irreducible components of the discrete spectrum. The purpose of this paper is to extend this correspondence beyond the discrete spectrum. To this end, the point of view of the Franke filtration of spaces of automorphic forms is taken. In fact, our technical key ingredient is a functorial refinement of the Franke filtration, which allows us to establish the Jacquet--Langlands correspondence between consecutive quotients of this refined filtration on the general linear group and its inner form. As a result, our extended Jacquet--Langlands correspondence properly extends Badulescu's correspondence and contains the full functorial lift, predicted by Langlands functoriality.

math.NT

Factorization of periods, construction of automorphic motives and Deligne's conjecture over CM-fields

The present paper is devoted to the relations between Deligne's conjecture on critical values of motivic $L$-functions and the multiplicative relations between periods of arithmetically normalized automorphic forms on unitary groups. As an application of our main result, we establish Deligne's conjecture for a class of CM-automorphic motives, which we construct in this paper. Our proof uses the results of our recent joint work with Raghuram in combination with the Ichino--Ikeda--Neal-Harris (IINH) formula for unitary groups -- which is now a theorem -- and an analysis of cup products of coherent cohomological automorphic forms on Shimura varieties to establish relations between certain automorphic periods and critical values of Rankin-Selberg and Asai $L$-functions of $\GL(n)\times\GL(m)$ over CM fields. By reinterpreting these critical values in terms of automorphic periods of holomorphic automorphic forms on unitary groups, we show that the automorphic periods of holomorphic forms can be factored as products of coherent cohomological forms, compatibly with a motivic factorization predicted by the Tate conjecture. All of these results are stated under a certain regularity condition and an hypothesis of rationality on archimedean zeta-integrals.

math.NT

On the notion of the parabolic and the cuspidal support of smooth-automorphic forms and smooth-automorphic representations

In this paper we describe several new aspects of the foundations of the representation theory of the space of smooth-automorphic forms (i.e., not necessarily $K_\infty$-finite automorphic forms) for general connected reductive groups over number fields. Our role model for this space of smooth-automorphic forms is a ''smooth version'' of the space of automorphic forms, whose internal structure was the topic of a famous paper of Franke. We prove that the important decomposition along the parabolic support, and the even finer - and structurally more important - decomposition along the cuspidal support of automorphic forms transfer in a topologized version to the larger setting of smooth-automorphic forms. In this way, we establish smooth-automorphic versions of the main results of a paper of Franke-Schwermer and of Moeglin-Waldspurger's book, III.2.6.

math.NT

On the arithmetic of Shalika models and the critical values of $L$-functions for ${\rm GL}(2n)$

Let $Π$ be a cohomological cuspidal automorphic representation of ${\rm GL}_{2n}(\mathbb A)$ over a totally real number field $F$. Suppose that $Π$ has a Shalika model. We define a rational structure on the Shalika model of $Π_f$. Comparing it with a rational structure on a realization of $Π_f$ in cuspidal cohomology in top-degree, we define certain periods $ω^ε(Π_f)$. We describe the behaviour of such top-degree periods upon twisting $Π$ by algebraic Hecke characters $χ$ of $F$. Then we prove an algebraicity result for all the critical values of the standard $L$-functions $L(s, Π\otimes χ)$; here we use the work of B. Sun on the non-vanishing of a certain quantity attached to $Π_\infty$. As an application, we obtain new algebraicity results in the following cases: Firstly, for the symmetric cube $L$-functions attached to holomorphic Hilbert modular cusp forms; we also discuss the situation for higher symmetric powers. Secondly, for Rankin-Selberg $L$-functions for ${\rm GL}_3 \times {\rm GL}_2$; assuming Langlands Functoriality, this generalizes to Rankin-Selberg $L$-functions of ${\rm GL}_n \times {\rm GL}_{n-1}$. Thirdly, for the degree four $L$-functions for ${\rm GSp}_4$. Moreover, we compare our top-degree periods with periods defined by other authors. We also show that our main theorem is compatible with conjectures of Deligne and Gross.

math.NT

Deligne's conjecture for automorphic motives over CM-fields

The present paper is devoted to the relations between Deligne's conjecture on critical values of motivic $L$-functions and the multiplicative relations between periods of arithmetically normalized automorphic forms on unitary groups. In the first place, we combine the Ichino--Ikeda--Neal-Harris (IINH) formula -- which is now a theorem -- with an analysis of cup products of coherent cohomological automorphic forms on Shimura varieties to establish relations between certain automorphic periods and critical values of Rankin-Selberg and Asai $L$-functions of ${\rm GL}(n)\times{\rm GL}(m)$ over CM fields. By reinterpreting these critical values in terms of automorphic periods of holomorphic automorphic forms on unitary groups, we show that the automorphic periods of holomorphic forms can be factored as products of coherent cohomological forms, compatibly with a motivic factorization predicted by the Tate conjecture. All of these results are conditional on a conjecture on non-vanishing of twists of automorphic $L$-functions of ${\rm GL}(n)$ by anticyclotomic characters of finite order, and are stated under a certain regularity condition.

math.NT

Special values of $L$-functions and the refined Gan-Gross-Prasad conjecture

We prove explicit rationality-results for Asai- $L$-functions, $L^S(s,\Pi',{\rm As}^\pm)$, and Rankin-Selberg $L$-functions, $L^S(s,\Pi\times\Pi')$, over arbitrary CM-fields $F$, relating critical values to explicit powers of $(2\pi i)$. Besides determining the contribution of archimedean zeta-integrals to our formulas as concrete powers of $(2\pi i)$, it is one of the advantages of our approach, that it applies to very general non-cuspidal isobaric automorphic representations $\Pi'$ of ${\rm GL}_n(\mathbb A_F)$. As an application, this enables us to establish a certain algebraic version of the Gan--Gross--Prasad conjecture, as refined by N.\ Harris, for totally definite unitary groups. As another application we obtain a generalization of a result of Harder--Raghuram on quotients of consecutive critical values, proved by them for totally real fields, and achieved here for arbitrary CM-fields $F$ and pairs $(\Pi,\Pi')$ of relative rank one.

math.NT

A rationality result for the exterior and the symmetric square $L$-function

Let $G={\rm GL}_{2n}$ over a totally real number field $F$ and $n\geq 2$. Let $Π$ be a cuspidal automorphic representation of $G(\mathbb A)$, which is cohomological and a functorial lift from SO$(2n+1)$. The latter condition can be equivalently reformulated that the exterior square $L$-function of $Π$ has a pole at $s=1$. In this paper, we prove a rationality result for the residue of the exterior square $L$-function at $s=1$ and also for the holomorphic value of the symmetric square $L$-function at $s=1$ attached to $Π$. On the way, we also show a rationality result for the residue of the Rankin--Selberg $L$-function at $s=1$, which is very much in the spirit of our recent joint paper with Harris and Lapid, as well as of one of the main results in a recent article of Balasubramanyam--Raghuram.

math.NT

Whittaker rational structures and special values of the Asai $L$-function

Let $F$ be a totally real number field and $E/F$ a totally imaginary quadratic extension of $F$. Let $Π$ be a cohomological, conjugate self-dual cuspidal automorphic representation of $GL_n(\mathbb A_E)$. Under a certain non-vanishing condition we relate the residue and the value of the Asai $L$-functions at $s=1$ with rational structures obtained from the cohomologies in top and bottom degrees via the Whittaker coefficient map. This generalizes a result in Eric Urban's thesis when $n = 2$, as well as a result of the first two named authors, both in the case $F = \mathbb Q$.

math.NT

Whittaker periods, motivic periods, and special values of tensor product L-functions

Let $\mathcal K$ be an imaginary quadratic field. Let $Π$ and $Π'$ be irreducible generic cohomological automorphic representation of $GL(n)/{\mathcal K}$ and $GL(n-1)/{\mathcal K}$, respectively. Each of them can be given two natural rational structures over number fields. One is defined by the rational structure on topological cohomology, the other is given in terms of the Whittaker model. The ratio between these rational structures is called a {\it Whittaker period}. An argument presented by Mahnkopf and Raghuram shows that, at least if $Π$ is cuspidal and the weights of $Π$ and $Π'$ are in a standard relative position, the critical values of the Rankin-Selberg product $L(s,Π\times Π')$ are essentially algebraic multiples of the product of the Whittaker periods of $Π$ and $Π'$. We show that, under certain regularity and polarization hypotheses, the Whittaker period of a cuspidal $Π$ can be given a motivic interpretation, and can also be related to a critical value of the adjoint $L$-function of related automorphic representations of unitary groups. The resulting expressions for critical values of the Rankin-Selberg and adjoint $L$-functions are compatible with Deligne's conjecture.

math.NT

Automorphic Forms, Cohomology and CAP Representations. The Case $GL_2$ over a definite quaternion algebra

In this paper we fully describe the cuspidal and the Eisenstein cohomology of the group $G=GL_2$ over a definite quaternion algebra $D/\Q$. Functoriality is used to show the existence of residual and cuspidal automorphic forms, having cohomology in degree 1. The latter ones turn out to be CAP-representations, though $G$ satisfies Strong Multiplicity One. A non-vanishing result on intertwining operators of induced representations will serve as a starting point for further investigations concerning rationality of critical $L$-values.

math.NT