Public Thesis defense - IRMP


21 octobre 2022



Auditoire A04 SCES, place des Sciences - will also take place in video conference

Cosmic inhomogeneities in the early Universe: a numerical relativity approach by Cristian JOANA VELASCO

Pour l’obtention du grade de Docteur en sciences

Cosmic inflation is arguably the most favoured paradigm of the very early Universe. It postulates an early phase of fast, nearly exponential, and accelerated expansion. Inflationary models are capable of explaining the overall flatness and homogeneity of today's Universe at large spatial scales. Furthermore, their predictions give us an explanation of the observed statistical features of the primordial density fluctuations imprinted in both the cosmic microwave background (CMB) and the Universe's large scale structure. However, despite the wide acceptance in the physics community, these models are not absent from criticism. In scalar field inflation, a necessary condition to begin inflation is the requirement of a Universe dominated by the field's potential, which implies a subdominant contribution from the scalar field dynamics. This has given rise to large amounts of scientific debate and literature on the naturalness, and possible fine-tuning of the initial conditions for inflation. Another controversial issue concerns the ending of inflation, and the fact that a preheating mechanism is necessary to transfer the energy of the inflaton to the bath of highly energetic particles of the hot big bang plasma.

In this thesis, we present full general relativistic simulations to study these two problems, with a particular focus on the Starobinsky and Higgs models of inflation, being those the most favoured by the latest CMB observations. First, we consider the fine-tuning problem of beginning inflation from a highly dynamical and inhomogeneous "pre-inflation" epoch in the single-field case. In our second study, we approach the multi-field paradigm of inhomogeneous pre-inflation, together and consistently, with the preheating phase after inflation. These investigations further confirm the robustness of these types of models to highly inhomogeneous initial conditions, while putting in evidence the non-negligible effects of gravitational effects during the reheating. At the end of the thesis, we finalize by discussing some other potential applications of numerical simulations to study the early Universe, including our preliminary investigations on primordial black hole formation in asymmetric three-dimensional configurations and their potential observable features.

Jury members :

  • Prof. Christophe Ringeval (UCLouvain), supervisor
  • Prof. Sebastien Clesse (ULB), supervisor
  • Prof. Vincent Lemaitre (UCLouvain), chairperson
  • Prof. Jean-Marc Gerard (UCLouvain), secretary
  • Prof. Vincent Vennin (LPENS, France)
  • Dr. Katherine Clough (QMUL, United Kingdom)

Pay attention :

The public defense of Cristian Joana Velasco scheduled for Friday 21 October at 02:00 p.m. will also take place in the form of a video conference

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