Thesis

Probing fundamental physics with scalar fields and cosmic defects using state of the art cosmological observations

• Call:

  IDPASC Portugal - PHD Programme 2016

• Academic Year:

  2016 / 2017

• Domains:

  Cosmology | Astrophysics

• Supervisor:

  Pedro Avelino

• Co-Supervisor:

  Lara Sousa

• Institution:

  Universidade do Porto

• Host Institution:

  Instituto de Astrofísica e Ciências do Espaço, CAUP

• Abstract:

  The recent discovery of the Higgs Boson at the Large Hadron Collider appears to support the idea that the universe underwent, in its early history, a series of symmetry-breaking phase transitions and that, as a consequence, networks of topological defects could have been generated. These defect networks, although formed in the early universe, are expected to survive throughout the cosmological history, potentially leaving behind a plethora of observational signatures. The study of cosmic defects and their signatures, then offers an insight into the physics of the early universe. Compellingly, the recent suggestion that fundamental strings and 1-dimensional Dirichlet branes – the fundamental objects of Superstring theory – may play the role of cosmic strings, extends this possibility towards very early cosmological times into energy scales far beyond the reach of current particle accelerators. Surveys of the cosmological 21cm signal – using SKA and LOFAR – will probe the matter distribution of the universe during the “dark ages”, potentially unveiling the role of small-scale density perturbations generated by cosmic strings and other cosmic defects in structure formation. On the other hand, the gravitational wave background will be probed with unprecedented sensitivity by a new generation of gravitational wave (e.g. eLISA) and Cosmic Microwave Background experiments (e.g. COrE+). Together these provide new observational windows for the study of cosmic defects and their associated vector and tensor perturbations which will be extensively explored in this project. The opportunities to gain information about the physics of the early universe through the search for topological defects are, thus, manifold. This PhD project aims at significantly improving current constraints on cosmic defects, by making use of the latest data and realistic numerical and semi-analytical models for defect network evolution. Particular emphasis will be given to the gravitational wave background generated by cosmic strings and domain walls and its potential impact on the B-mode polarization of the Cosmic Microwave Background (CMB), as well as to the characterization of specific string signatures on the 21cm background and their impact on reionization history. The potential role of domain walls as seeds of space-time variations of fundamental couplings shall also be investigated, taking full advantage of the window opened by a new generation of high-resolution ultra-stable spectrographs such as ESPRESSO and ELT-HIRES.