arXiv subjects

Marvin Sipp

Publications and source records attributed to Marvin Sipp.

4 recordsLinked to original sources

arXiv2025

Phase-space perturbation theory for cosmic large-scale structure

We consider a perturbative approach to the Vlasov-Poisson system for cosmic structure formation that does not rely on any truncation of the momentum-cumulant hierarchy. The generally non-trivial linear solution is computed by solving a Volterra-type integral equation and higher orders are obtained recursively. As expected, the results of Eulerian standard perturbation theory are recovered for perfectly cold initial conditions. Deviating slightly from the latter by introducing a homogeneous and isotropic initial velocity dispersion, we show that all higher momentum cumulants are generated dynamically at any perturbative order. We support our numerical solutions by an analytical large-scale approximation. Our approach serves as a basis for exploring different background-perturbation splits of the phase-space density and non-perturbative techniques.

astro-ph.CO↗

arXiv2025

Cosmic structure from the path integral of classical mechanics and its comparison to standard perturbation theory

We investigate cosmic structure formation in the framework of a path-integral formulation of an $N$-particle ensemble in phase space, dubbed Resummed Kinetic Field Theory (RKFT), up to one-loop perturbative order. In particular, we compute power spectra of the density contrast, the divergence and curl of the momentum density and arbitrary $n$-point cumulants of the stress tensor. In contrast to earlier works, we propose a different method of sampling initial conditions, with a Gaussian initial phase-space density. Doing so, we exactly reproduce the corresponding results from Eulerian standard perturbation theory (SPT) at one-loop order, showing that formerly found deviations can be fully attributed to inconsistencies in the previous sampling method. Since, in contrast to SPT, the full phase-space description does not assume a truncation of the Vlasov hierarchy, our findings suggest that nonperturbative techniques are required to accurately capture the physics of cosmic structure formation.

astro-ph.CO↗

arXiv2023

Scalar-Induced Gravitational Waves in a $Λ$CDM Cosmology

We reconsider the gravitational wave spectrum induced by scalar perturbations in spatially flat Friedmann-Lemaître-Robertson-Walker spacetimes, focusing on the matter- and $Λ$-dominated epochs. During matter domination, sub-horizon modes are not free and a commonly applied approximation for the derivative of the tensor perturbation is flawed. We show analytically that this leads to a significant overestimation of the energy density spectrum. In addition, we demonstrate that gauge-dependent non-oscillating tensor perturbations appear in the presence of a cosmological constant. Complementing the analytical calculations, we compute the according present-day spectrum numerically for a Planck-like $Λ$CDM cosmology, finding that non-oscillating growing modes appear during the transition between matter and $Λ$ domination in conformal Newtonian gauge.

astro-ph.CO↗

arXiv2020

Optimising tomography for weak gravitational lensing surveys

The subject of this paper is optimisation of weak lensing tomography: We carry out numerical minimisation of a measure of total statistical error as a function of the redshifts of the tomographic bin edges by means of a Nelder-Mead algorithm in order to optimise the sensitivity of weak lensing with respect to different optimisation targets. Working under the assumption of a Gaussian likelihood for the parameters of a $w_0 w_a$CDM-model and using Euclid's conservative survey specifications, we compare an equipopulated, equidistant and optimised bin setting and find that in general the equipopulated setting is very close to the optimal one, while an equidistant setting is far from optimal and also suffers from the ad hoc choice of a maximum redshift. More importantly, we find that nearly saturated information content can be gained using already few tomographic bins. This is crucial for photometric redshift surveys with large redshift errors. We consider a large range of targets for the optimisation process that can be computed from the parameter covariance (or equivalently, from the Fisher-matrix), extend these studies to information entropy measures such as the Kullback-Leibler-divergence and conclude that in many cases equipopulated binning yields results close to the optimum, which we support by analytical arguments.

astro-ph.CO↗