Cosmological and astronomical observations indicate that the majority of mass and energy density of fields in the universe are in a form which interacts extremely weakly, if at all, with light. The standard interpretation is the existence of dark matter, commonly thought to be in the form of particles not part of the standard model of particle physics. At present a firm detection of such a particle is lacking, and moreover, all these observations concern a mismatch between the observed dynamics of visible matter with its gravitational influence.

Seminar of Philosophy of Science

Title: Replicability in cosmology: lessons to be drawn from the Hubble constant so called 'crisis'

Speaker: Dr Marie Gueguen, Center for the Philosophy of Science, University of Pittsburg

Date:
Friday the 20th of November, 11:00

Location:
Zoom: link communicated via e-mail

Details:
We are organising a cycle of seminars of philosophy of science this semester at the APC.

In the primordial Universe, neutrino decoupling occurs only slightly before electron-positron annihilations. This leads to an increased neutrino energy density with order 1% spectral distortions compared to the standard instantaneous decoupling approximation. A precise calculation of neutrino evolution is needed to assess its consequences on BBN, structure formation or on the CMB, and requires to take into account multiple effects such as neutrino oscillations, which represents a genuine numerical challenge. 

Understanding the cosmic-ray (CR) transport in the Milky Way magnetic field is fundamental to unveil their galactic factories. While we know now that they can be created in supernovas, there may be other sources available for CR acceleration. To trace back CR origins we can look at what they are made of. By weighing the different isotopes of elements that hit CR detectors, we can infer global properties as the galactic grammage and escape time.

In this talk I will discuss cosmological first-order phase transitions. These phase transitions which proceed through the nucleation and merger of bubbles on the new phase are known to source gravitational waves. If one of these events occurred in the early universe then upcoming space based gravitational wave detectors like LISA may be able to detect the resulting gravitational wave background that remains today. In this talk I will focus on transitions in which the bubble wall accelerates until collision.

Bonjour,

Publication par Virgo et LIGO du catalogue GWTC-2 contenant 39 détections

La classification et l’analyse finale des 39 événements détectés par
Virgo et LIGO lors de la prise de données « O3a » (1er avril – 1er
octobre 2019) ont été publiées le 29 octobre 2020. La plupart des
sources O3a sont des fusions de trous noirs. Une probable fusion d’un
système binaire d’étoiles à neutrons et deux possibles systèmes
« hybrides » – formés d’un trou noir et d’une étoile à neutrons –
figurent également au tableau de chasse de O3a. Si quatre de ces

The Gravitation Group is organising the following seminar on Thursday the 22nd of October, at 10:00 CEST.

Magnetic fields are observed on virtually all astrophysical scales of the modern Universe, from planets and stars to galaxies and galaxy clusters. Observations of blazars suggest that even the intergalactic medium is permeated by magnetic fields. Such large-scale fields were most likely generated very shortly after the Big Bang and therefore are a unique window into the physics of the very early Universe.