arXiv subjects

Arian L. von Blanckenburg

Publications and source records attributed to Arian L. von Blanckenburg.

5 recordsLinked to original sources

arXiv2026

Pulsar timing array analysis in a Legendre polynomial basis

We use Legendre polynomials, previously employed in this context by Lee et al., van Haasteren and Levin, and Pitrou and Cusin, to model signals in pulsar timing arrays. These replace the (Fourier mode) basis of trigonometric functions normally used for data analysis. The Legendre basis makes it simpler to incorporate pulsar modeling effects, which remove constant-, linear-, and quadratic-in-time terms from pulsar timing residuals. In the Legendre basis, this zeroes the amplitudes of the the first three Legendre polynomials. We use this basis to construct an optimal quadratic cross-correlation estimator $\widehatμ$ of the Hellings and Downs (HD) correlation and compute its variance $σ^2_{\widehatμ}$ in the way described by Allen and Romano. Remarkably, if the gravitational-wave background (GWB) and pulsar noise power spectra are (sums of) power laws in frequency, then in this basis one obtains analytic closed forms for many quantities of interest.

gr-qc↗

arXiv2026

The trace-free Einstein tensor is not variational for the metric as field variable

It is well-known that the trace-free Einstein tensor of a pseudo-Riemannian metric cannot arise by variation of a local diffeomorphism-invariant action functional with the (inverse) metric as field variable. We show that this statement remains true even for general local actions, without the assumption of diffeomorphism invariance.

gr-qc↗

arXiv2025

The Newtonian limit of orthonormal frames in metric theories of gravity

We extend well-known results on the Newtonian limit of Lorentzian metrics to orthonormal frames. Concretely, we prove that, given a one-parameter family of Lorentzian metrics that in the Newtonian limit converges to a Galilei structure, any family of orthonormal frames for these metrics converges pointwise to a Galilei frame, assuming that the two obvious necessary conditions are satisfied: the spatial frame must not rotate indefinitely as the limit is approached, and the frame's boost velocity with respect to some fixed reference observer needs to converge.

gr-qc↗

arXiv2025

On gauge transformations in twistless-torsional Newton--Cartan geometry

Twistless-torsional Newton--Cartan (TTNC) geometry exists in two variants, type I and type II, which differ by their gauge transformations. In TTNC geometry there exists a specific locally Galilei-invariant function, called by different names in existing literature, that we dub the `locally Galilei-invariant potential'. We show that in both types of TTNC geometry, there always exists a local gauge transformation that transforms the locally Galilei-invariant potential to zero. For type I TTNC geometry, we achieve this due to the corresponding equation for the gauge parameter taking the form of a Hamilton--Jacobi equation. In the case of type II TTNC geometry, we perform subleading spatial diffeomorphisms. In both cases, our arguments rigorously establish the existence of the respective gauge transformation also in case of only finite-degree differentiability of the geometric fields. This improves upon typical arguments for `gauge fixing' in the literature, which need analyticity. We consider two applications of our result. First, it generalises a classical result in standard Newton--Cartan geometry. Second, it allows to (locally) parametrise TTNC geometry in two new ways: either in terms of just the space metric and a unit timelike vector field, or in terms of the distribution of spacelike vectors and a positive-definite cometric.

gr-qc↗

arXiv2024

Comment on `The Classical Limit of Teleparallel Gravity'

We critically discuss the claims of a recent article regarding the Newtonian limit of the teleparallel equivalent of general relativity (TEGR) in pure-tetrad formulation (arXiv:2406.17594). In particular, we refute this article's purported main result that if a regular Newtonian limit exists, the torsion of the limiting derivative operator (i.e., connection) necessarily vanishes.

gr-qc↗