How cosmology can help and benefit from other areas of physics
- Autores: David Valcin
- Directores de la Tesis: Licia Verde (dir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2021
- Idioma: inglés
- Tribunal Calificador de la Tesis: Viviana Acquaviva (presid.), Mark Gieles (secret.), Matteo Viel (voc.)
- Programa de doctorado: Programa Oficial de Doctorado en Física
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
Context The current ΛCDM cosmological paradigm has seen remarkable success in recent decades (whether it is the discovery of the CMB, the formation of large-scale structures, the expansion of the universe etc.). Like any paradigm, there comes a point when the theory reaches its limits and the question arises as to whether it is simply due to the incompleteness of the theory or whether it should be questioned. In this thesis, I focused particularly on two aspects of the ΛCDM theory: how to effectively include massive neutrinos in the formation of structures and find a methodology to bring a new perspective in the tension surrounding the expansion of the universe.
Aims Our objective for this thesis is to show how cosmology can help and benefit from other areas of physics because there is a mutual interest in tackling problems at the interface between cosmology and other areas of physics. Methods In the first part of the thesis, I devoted myself to the development of an emulator in order to be able to quickly and easily implement the effect of massive neutrinos on the clustering of dark matter halos. For that I used the HADES numerical simulations to calibrate the bias (a very useful quantity in cosmology which describes the relation between the clustering of dark matter and the different observables). By combining the result of these calibrations with a software which makes it possible to calculate the perturbative terms of the power spectrum, I was able to develop a competitive emulator up to non-linear scales. Secondly, I devoted myself to the study of globular clusters in a cosmological context. I used a catalog of clusters provided by the HST telescope in the F606W and F814 filters. After removing the clusters with poor photometry, I performed a Bayesian analysis which allowed me to constrain the various parameters common to stars in the same cluster. Models that describe stellar evolution, like the ones I used for the analysis, are often defined for a given set of parameters that vary from model to model. Therefore to reduce the systematic errors due to the use of a specific stellar model, I studied the influence of the parameters governing the different evolutionary phases of stars with the MESA software.
Results The work carried out within the framework of the realization of an emulator, allowed us to highlight important results such as: even if the shape of the bias must be calibrated using numerical simulations, its amplitude can be simply rescaled by a factor proportional to the mass of the neutrinos or the combination of pre-computed coefficients with a software calculating the perturbative terms can be fast enough to be implemented in Monte Carlo sampling softwares. On the other hand, the estimate of the age of the globular clusters that we obtained, coupled with some hypotheses on the time of galaxy formation makes it possible to put a lower limit on the age of the universe. After the reduction of the systematic errors, the age of the universe is thus compared to those obtained from the inference of cosmological parameters of various surveys. With our current precision it is not yet possible to discard any of the measurements at odds (namely Planck or SHOES) in the H0 tension but the results are very promising.
Conclusion Through this thesis I wanted to show that physics and more particularly cosmology could benefit from its interplay with other fields. With a better modeling of the effect of massive neutrinos it will be possible to both improve the inference of cosmological parameters and precisely constrain the mass of neutrinos (for the moment inaccessible to particle physics). A rigorous analysis of globular clusters also offers an estimate of the age of the universe almost independent of a cosmological model which is very valuable in this period of tension when the cosmological paradigm is questioned and challenged.
