GW day at CERN

Wednesday 22 Nov 2023, 09:30 → 17:00 Europe/Zurich

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

1 Thermal contributions to the production of gravitational waves in the earliest universe

The simplest models of inflation predict a flat gravitational wave signal,
whose contribution to a stochastic background from the early universe
might be negligible. However, during and after inflation, gravitational
waves are sourced also by the thermal processes that lead to a heating-up
period after inflation. We derive a general framework to estimate the
production of gravitational waves for the case where the inflaton field is
embedded within a thermal plasma. The shape of the corresponding signal is
mostly model-independent, while the amplitude depends peculiarly on the
constituents of the plasma and the interactions between them. To evaluate
benchmark results we consider non-Abelian axion inflation.

Speaker: Simona Procacci (University of Geneva)

2 Constraints on new physics with pulsar timing arrays: the case of induced gravitational waves and primordial black holes

Recent pulsar timing array (PTA) data strongly supports the existence of a stochastic gravitational wave background (SGWB) in the nano-Hz frequency range. While supermassive black hole mergers are the primary candidate to explain the observations, it is also possible that a cosmological SGWB contributes to the signal. In this talk, we will discuss the case of gravitational waves induced at second order in the early universe, a scenario that can be accompanied by the formation of a sizeable abundance of primordial black holes. We will review some recent progress on the characterization of such a signal and discuss the constraints PTA observations could set on this scenario, as well as on the inflationary dynamics underlying these models.

Speaker: Gabriele Franciolini (CERN)

11:00 coffee break

3 Detecting nano-Hertz gravitational waves with Pulsar Timing Arrays

Around the world, several groups are working to detect a stochastic background of very low frequency gravitational waves using "pulsar timing arrays". Such gravitational waves are generated by orbiting pairs of extremely massive black holes at cosmological distances from Earth. The "detector" operates at a Galactic-scale, by exploiting radio pulsars (very stable rapidly-spinning neutron stars) as high precision clocks. I'll explain how these detectors operate -- the gravitational waves leave detectable imprints on the radio pulses -- and review the current state of the field and its prospects. I'll also describe some recent work (arXiv:2205.05637, arXiv:2208.07230) on properties of the "Hellings and Downs correlation". This pattern of pulsar timing correlations is the "smoking gun" that should reveal the presence of gravitational waves.

https://indico.cern.ch/event/1326135/

Speaker: Bruce Allen (Max Planck Society/Albert Einstein Institute Hannover)

13:00 lunch break

4 Free discussion or attendance to TH Colloquium

https://indico.cern.ch/event/1324271/

5 Common discussion