Hardy–Orlicz Spaces of Dirichlet Series: An Interpolation Problem on Abscissae of Convergence

The study of Hardy spaces of Dirichlet series denoted by $\mathscr{H}^p$ ($p\geq 1$) was initiated in [7] when $p=2$ and $p=\infty $, and in [2] for the general case. In this paper we introduce the Orlicz version of spaces of Dirichlet series $\mathscr{H}^\psi $. We focus on the case $\psi =\psi _q(t)=\exp (t^q)-1,$ and we compute the abscissa of convergence for these spaces. It turns out that its value is $\min \{1/q\,,1/2\}$ filling the gap between the case $\mathscr{H}^\infty $, where the abscissa is equal to $0$, and the case $\mathscr{H}^p$ for $p$ finite, where the abscissa is equal to $1/2$. The upper-bound estimate relies on an elementary method that applies to many spaces of Dirichlet series. This answers a question raised by Hedenmalm in [6].

Minkowski Dimension and Explicit Tube Formulas for p-Adic Fractal Strings

The theory of complex dimensions describes the oscillations in the geometry (spectra and dynamics) of fractal strings. Such geometric oscillations can be seen most clearly in the explicit volume formula for the tubular neighborhoods of a p-adic fractal string L p , expressed in terms of the underlying complex dimensions. The general fractal tube formula obtained in this paper is illustrated by several examples, including the nonarchimedean Cantor and Euler strings. Moreover, we show that the Minkowski dimension of a p-adic fractal string coincides with the abscissa of convergence of the geometric zeta function associated with the string, as well as with the asymptotic growth rate of the corresponding geometric counting function. The proof of this new result can be applied to both real and p-adic fractal strings and hence, yields a unifying explanation of a key result in the theory of complex dimensions for fractal strings, even in the archimedean (or real) case.

A possible new cosmological redshift effect due to Λ on traveling gravitational waves in Friedmann universes

In this paper, we continue the investigation concerning the propagation of gravitational waves in a cosmological background using Laplace transform. a We analyze the possible physical consequences of the result present in Ref. 19 where it is argued that a nonvanishing positive abscissa of convergence caused by the de Sitter expansion factor [Formula: see text] implies a shift in the frequencies domain of a traveling gravitational wave as measured by a comoving observer. In particular, we show that in a generic asymptotically de Sitter cosmological universe, this redshift effect does also arise. Conversely, in a universe expanding with, for example, a power law expansion, this phenomenon does not happen. This physically possible new redshift effect, although negligible for the actual very low value of [Formula: see text], can have interesting physical consequences concerning for example its relation with Bose–Einstein condensation or more speculatively with the nature of the cosmological constant in terms of gravitons, as recently suggested in Ref. 21 near a Bose–Einstein condensation phase.

WELL-ROUNDED SUBLATTICES

Given a lattice in the plane, we consider zeta-functions encoding the number of well-rounded sublattices of a given index. We are particularly interested in the abscissa of convergence of this function and show that the quality of convergence is related to arithmeticity questions concerning the ambient lattice. In particular, we discover that there are infinitely many similarity classes of well-rounded sublattices in a plane lattice if there is at least one. This generalizes results about the rings of Gaussian and of Eisenstein integers by Fukshansky and his coauthors.

The abscissa of convergence of the Laplace transform

Assume that we want to estimate – σ, the abscissa of convergence of the Laplace transform. We show that no non-parametric estimator of σ can converge at a faster rate than (log n)–1, where n is the sample size. An optimal convergence rate is achieved by an estimator of the form where xn = O(log n) and is the mean of the sample values overshooting xn. Under further parametric restrictions this (log n)–1 phenomenon is also illustrated by a weak convergence result.

The abscissa of convergence of the Laplace transform

Assume that we want to estimate – σ, the abscissa of convergence of the Laplace transform. We show that no non-parametric estimator of σ can converge at a faster rate than (log n)–1, where n is the sample size. An optimal convergence rate is achieved by an estimator of the form where xn = O(log n) and is the mean of the sample values overshooting xn. Under further parametric restrictions this (log n)–1 phenomenon is also illustrated by a weak convergence result.

Laurent expansion of Dirichlet series

Let 〈an〉 be an increasing sequence of real numbers and 〈bn a sequence of positive real numbers. We deal here with the Dirichlet series and its Laurent expansion at the abscissa of convergence, λ, say. When an and bn behave likeas N → ∞, where P2(x) is a certain polynomial, we obtain the Laurent expansion of f (s) at s = λ, namelywhere P1(x) is a polynomial connected with P2(x) above. Also, the connection between P1 and P2 is made intuitively transparent in the proof.