GW day at CERN

Wednesday 16 Oct 2024, 10:00 → 15:00 Europe/Zurich

4/3-006 - TH Conference Room (CERN)

10:00 → 10:30 Forecasting Pulsar Timing Array Sensitivity to Gravitational Wave Anisotropies

Recent Pulsar Timing Array (PTA) data show substantial evidence for a gravitational wave background (GWB) in the nHz range. Detecting anisotropies would play a crucial role in identifying its source, whether astrophysical or cosmological. We will present estimates of current and future PTA sensitivity to these anisotropies. While the constraining power of the current PTA dataset is limited, upcoming improvements could achieve percent-level precision for low multipoles. We also show that GWB anisotropies and the Hellings-Downs angular correlation can be independently reconstructed due to their minimal correlation.

Speaker: Mr Gabriele Franciolini

Talk_GWDay.pdf

10:30 → 10:45 discussion

10:45 → 11:15 Wave optics lensing of gravitational waves in LISA-band triple systems

One of the major predictions of Einstein’s general relativity is gravitational lensing, the deflection or amplification of light by mass distributions. In my talk, I focus on gravitational wave lensing in wave optics (very long wavelength), as opposed to the standard geometric optics. I show how a supermassive black hole acts as a wave optics lens, for triple systems in the regime of the LISA mission. Keeping track of the tensorial structure of the signal, the lensing process shows rich physical features in wave optics, such as non-preservation of the GW helicity and polarization content. This makes black holes a particularly interesting gravitational lens that may be probed in the next decades.

Speaker: Martin Pijnenburg

Talk_MP_GWdayCERN.pdf

11:15 → 11:30 discussion

11:30 → 11:45 coffee break

11:45 → 12:15 The impact of large-scale galaxy clustering on the Hellings-Downs correlation

While pulsar timing array experiments have recently found compelling evidence for the existence of a stochastic gravitational wave (GW) background, its origin is still unclear. If this background is of astrophysical nature, we expect the distribution of GW sources to follow the one of galaxies. This leads to an intrinsic anisotropy in the distribution of GW sources due to galaxy clustering at cosmological scales. In this talk, I present how this anisotropy can be modelled when evaluating the expected signal of pulsar arrival time correlations. I will describe a two-step averaging procedure, taking the stochasticity both of the GW background and of the galaxy distribution into account. We find that galaxy clustering introduces a new contribution to the variance of the Hellings-Downs correlation. Employing realistic astrophysical models to obtain numerical results, I will show that this new variance remains below the percent level, thus not polluting the measurement of pulsar arrival time correlations. I will conclude by discussing possible future directions to exploit synergies between galaxy clustering and pulsar timing arrays.

Speaker: Nastassia Grimm

Nastassia_Presentation_GWdays.pdf

12:15 → 12:30 discussion

12:30 → 13:30 lunch

13:30 → 15:00 discussion (council chamber)