Séminaire

Exploring early-universe physics with stochastic gravitational-wave data

The stochastic gravitational-wave background is a superposition of many astrophysical and cosmological sources, such as unresolved compact binaries, cosmic strings, and phase transitions in the early Universe. We highlight the importance of source separation in the case of a detection. By separating the individual sources, we can reveal remnants of early-universe processes. We use the data from the third LVK observing run to explore the parameter space of first-order phase transition models. We then investigate signs of parity violation in gravitational-wave data.

Black hole perturbations in modified gravity

General relativity can be tested at many scales using various physical systems. A particularly interesting probe is the study of the ringdown phase of a binary black hole merger, during which the newly-formed black hole emits gravitational waves at given frequencies called its quasinormal modes. Such modes depend heavily on the theory of gravity underlying the solution and can thus be used to test GR and put constraints on modified gravity theories.

New ideas on quenching and detecting BH rotational superradiances

In this talk I’ll discuss two recent results on BH superradiance: first, I will describe how BH photon superradiance is typically quenched by interactions of the photon cloud with the ambient electrons. Second, I will explain how an axionic cloud may impact the CMB if it decays into low energy photons which quickly heat and ionise the surrounding medium to Mpc scales.

Cosmic String Interpretation of NANOGrav Pulsar Timing Data and its impact on Cosmic Archaeology with Gravitational Waves

The NANOGrav Collaboration has recently reported strong evidence for a stochastic common-spectrum process, which we interpret as a SGWB in the framework of cosmic strings. The possible NANOGrav signal would correspond to a string tension Gμ∈(4×10^{−11},10^{−10}) at the 68% confidence level, with a different frequency dependence from supermassive black hole mergers.

Gravitation seminar: Chiranjib Mondal, A flexible model for neutron star equation of state from nuclear physics

The gravitation group is inviting you to the following seminar:

A flexible model for neutron star equation of state from nuclear physics

Development in multi-messenger astronomy over the last few years has
opened new facets to the hadronic matter at densities beyond our terrestrial
reach. It provides new constraints to the theories of nuclear physics, where an
absolute energy density functional is desired from ab-initio mechanisms. Under
the realm of general relativity, there is a one-to-one correspondence between

New eyes on the X-ray sky: First Results from eROSITA on SRG

The emergence of the three-dimensional structure of the cosmic web over
the history of the Universe displays very distinctive features when
observed in X-rays, where both the most massive collapsed structure
(clusters of galaxies) and the most energetic events in the life of
galaxies (AGN and Quasars) reveal themselves unambiguously. The next
generation of wide-area, sensitive X-ray surveys designed to map the hot
and energetic Universe will be heralded by eROSITA (extended ROentgen

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