# Cosmological model with running vacuum energy and warm dark matter

Name: Jhonny Andres Agudelo Ruiz

Type: PhD thesis

Publication date: 28/01/2021

Advisor:

Name | Role |
---|---|

Ilia Chapiro | Advisor * |

Examining board:

Name | Role |
---|---|

Patrick Peter | External Examiner * |

Oliver Fabio Piattella | Internal Examiner * |

Manuel Asorey Carballeira | External Examiner * |

Júlio César Fabris | Internal Examiner * |

Ilia Chapiro | Advisor * |

Celia del Carmen Escamilla Rivera | External Examiner * |

Alan Miguel Velasquez Toribio | Internal Examiner * |

Summary: The core of the present thesis is the possibility of the change with the energy scale (running) of the cosmological constant. Theoretically, this running in the IR region is not ruled out. On the other hand, from the Quantum Field Theory (QFT) viewpoint, the energy released due to the variation of the cosmological constant in the late Universe cannot go to the matter sector. For this reason, the phenomenolog- ical bounds on such a running are not sufficiently restrictive. The situation can be different in the early Universe when the gravitational field was sufficiently strong to provide an efficient creation of particles from the vacuum. We develop a framework for systematically exploring this possibility. It is supposed that the running occurs in the epoch when the Dark Matter (DM) already decoupled and is expanding adia- batically, while the usual matter should be regarded approximately massless and can be abundantly created from vacuum due to the decay of vacuum energy. By using the handy model of Reduced Relativistic Gas (RRG) for describing the Warm Dark Matter (WDM), we consider the dynamics of both cosmic background and linear perturbations and evaluate the impact of the vacuum decay on the matter power spectrum and to the first CMB peak. Additionally, using the combined SNIa+BAO data, we find the best-fit values for the free parameters of the model.

Additionally, it is known than the inclusion of spatial curvature can modify the evolution of matter perturbations and affect the Large Scale Structure (LSS) formation. We quantify the effects of the non-zero space curvature in terms of LSS formation for a cosmological model with a RCC and a WDM component. The evolution of density perturbations and the modified shape of its power spectrum are also reconstructed and analyzed in this context.

Finally, it is analytically constructed the scalar field actions minimally and non- minimally coupled to gravity, which are equivalent to RRG (describing the WDM component) in the sense they produce the same cosmological solutions for the con- formal factor of the metric. In particular, we construct the scalar theory which corresponds to the model of an ultra-relativistic ideal gas of spinless particles pos- sessing conformal symmetry. The possibility of supplementing our scalar field model for WDM with dynamical dark energy in the form of a RCC is also considered.