We are currently investigating several aspects of some of the most interesting topics in Theoretical Cosmology. Here is just a short summary of some of these topics.
Cosmic strings are topological defects that may have been created in the early universe. They typically form in a phase transition that gives rise to a complicated network of long strings that stretch across the horizon. One of the most important questions that one needs to address in order to extract predictions on these theories is to understand the cosmological evolution of these networks and its statistical properties. One of the most interesting methods to tackle these questions is the use of computer simulations that evolve the strings from some initial conditions. We are one of the leading research groups on cosmic strings simulations being involved in the largest simulations of a network of strings ever performed.
We are currently involved in several different projects that aim to extract information about Cosmology and BSM physics from GW observations. The work is mainly focused on the accurate calculation of the signal expected in current and future observatories from cosmological sources of primordial GWs. In particular, the group is one of the leading research teams in the computation of the stochastic background of GWs from cosmological cosmic string networks. These cosmological scenarios are predicted in many extensions of the Standard Model and therefore learning about their GW signatures is of paramount importance in order to put reliable constraints in these models. Furthermore, these GW signals extend over a very large range of frequencies covering the sensitivity of several different observatories. This is why some of our members have recently joined the NANOGrav Collaboration and they are also part of the Cosmology Working Group in the LISA collaboration as well as the ET. In all these collaborations they are actively participating in estimating the power of those instruments to probe specific scenarios of high energy physics in particular GUT models and String Theory cosmological scenarios. Finally, the group is also interested in the computation of the GW signals from other cosmological sources such as PBH, inflation, preheating, etc…
Several cosmological observations suggest that our universe underwent a period of accelerated expansion in its early stages. On the other hand the precise underlying physics of inflation and in particular its embedding within a fundamental theory are still a mystery. In many models inflation is in fact eternal. This would lead to the formation of “pocket universes” that would rise to universes like ours. This view of the universe give some interesting predictions for cosmological observables that allow us to distinguish this scenario from other ones. We are currently following several lines of research to further investigate these issues.
String Theory Cosmology.
String Theory is today one of the leading candidates for a fundamental theory. It is therefore natural to look for ways to link String Theory and Cosmology. Recent avances on String Theory compactification have allowed us to find some of the most detailed descriptions of Inflation in String Theory. Our group is mainly interested in extracting the observational consequences of the novel ways inflation can occur in String Theory.
The Landscape of String Theory.
String Theory suggests that there is a large number of ways that one can compactify the original 10d spacetime down to four dimensions. This compactification process gives rise to a complicated multidimensional potential that fixes all the possible degrees of freedom that specify, for example, the geometry of the internal space. Some of the minima of this potential would have a positive value of the cosmological constant and therefore one would expect to have patches of an eternally inflating spacetime. This is an interesting new take on the idea of cosmology within string theory and it is paramount to extract the observational consequences of a multiverse of this kind.
Our group is currently working on several avenues to explore the consequences of this radical new picture of the spacetime suggested by the existence of a String Theory Landscape.