Research :: PhD Topics for 2014 :: Cosmology

Topics under the thematic line Unveiling the dynamics of the Universeavailable for the 2014 Call (7 PhD Topics):

  • 2014/401 - The nature of the accelerating Universe
  • 2014/402 - Fundamental Physics with Euclid
  • 2014/403 - Mapping the Dark Universe with Fundamental Couplings
  • 2014/404 - Cosmic Paleontology: Searching for Superstrings
  • 2014/405 - Probing fundamental physics with scalar fields and cosmic defects using state of the art cosmological observations
  • 2014/406 - Cosmological weak lensing and galaxy formation effects with Euclid
  • 2014/407 - Polarisation of the Cosmic Microwave Background Radiation

For further details, please see the listing below for the abstract and advisors.

2014/401 - The nature of the accelerating Universe

Advisors: Nelson Nunes (CAAUL)

Over a decade has passed since supernova observations first indicated a remarkable property of our Universe: it is currently undergoing a period of accelerated expansion. In the intervening time, this acceleration has been confirmed by a range of complementary observational probes, such as those of the cosmic microwave background and of large scale structure and baryonic acoustic oscillations. Yet despite this plethora of observational evidence, the theoretical model that explains this phase of evolution remains unknown.

In this project we aim to take a step towards determining the theoretical model of present-day acceleration by analysing an extremely general class of models, which can have intriguing theoretical properties, to evaluate if they can also be observationally consistent. This investigation has both a theoretical and a hands on data component. A combination of analytical and numerical methods is, therefore, required to construct and test these models against current and forthcoming data.

This study is extremely timely given the current push to understand theoretical models concerning dark energy and the cosmological constant in time for them to be confronted by the data of the Euclid mission.

2014/402 - Fundamental Physics with Euclid

Advisors: Carlos Martins (CAUP)

Euclid is an ESA medium-class mission, due to be launched in 2020, whose main goal is to understand the physical origin of the accelerated expansion of the universe.
CAUP is an affiliated institute of the Euclid Consortium and is actively involved both in the technical preparation and in the scientific exploitation of the mission. This project will contribute to the latter. Its main goal will be to carry out a detailed assessment of Euclid as a precision tool for consistency tests of the LambdaCDM paradigm and for searches for new physics giving a special attention to the variation of fundamental constants. Inter alia, we will explore possible synergies with ground-based spectrographs such as ESPRESSO and HIRES (a proposed CODEX-like spectrograph for the E-ELT). The work will be done in the context of the Euclid Science Working Groups.

2014/403 - Mapping the Dark Universe with Fundamental Couplings

Advisors: Carlos Martins (CAUP)

Tests of the spacetime stability of nature’s fundamental couplings recently became an extremely active area of research, and are listed among ESA and ESO’s science drivers for the next generation of facilities. While a detection of variations will be direct evidence of Equivalence Principle violations and a fifth force in Nature, any such measurements (even null results) can provide tight constraints on additional dynamical degrees of freedom (such as fundamental scalar fields) that are known to be among Nature’s building blocks. The thesis will explore the role of these astrophysical tests on fundamental physics, with some emphasis on dynamical dark energy. Initially the work will be done in the context of a UVES Large Program (whose data analysis is ongoing), but forthcoming facilities such as ESPRESSO and ELT-HIRES will also be relevant.

2014/404 - Cosmic Paleontology: Searching for Superstrings

Advisors: Carlos Martins (CAUP)

Cosmic strings arise naturally in many proposed theories of new physics beyond the standard model unifying the electroweak and strong interactions, as well as in many superstring inspired inflation models. In the latter case, fundamental superstrings produced in the very early universe may have stretched to macroscopic scales, in which case they are known as cosmic superstrings. If observed, these objects thus provide a unique window into the early universe and possibly string theory. The goal of this thesis will be to study the evolution and astrophysical consequences of these objects, in the context of ongoing and forthcoming observational searches.

2014/405 - Probing fundamental physics with scalar fields and cosmic defects using state of the art cosmological observations

Advisors: Pedro Avelino (CAUP) and Lara Sousa (CAUP)

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 experiments (e.g. eLISA, LIGO) and the Cosmic Microwave Background B-mode polarization power spectrum will be determined with unprecedented precision by present and future missions such as Planck and CMBPol. 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.

2014/406 - Cosmological weak lensing and galaxy formation effects with Euclid

Advisors: Ismael Tereno (CAAUL) and António da Silva (CAUP)

Cosmological weak lensing is a powerful probe of gravity, geometry and mass in the Universe, and is in the core of the forthcoming Euclid space mission.  Weak lensing cosmological measurements are however contaminated by astrophysical effects originated by mechanisms that operate during the galaxy formation process. In order to achieve highly precise constraints in the parameters of the dark universe, the contamination must be mitigated. For this, the effects need to be studied and modelled and their impact on the cosmological signal understood.

This project aims to investigate the process of angular momentum acquisition of galaxies using dedicated state-of-the-art N-body simulations of large-scale structure. With this investigation we will be able to design effective models for intrinsic alignments and to estimate their effects in weak lensing data. Finally, we will define estimators to efficiently combine the modelled effects with forecasted Euclid cosmic shear data, in order to mitigate the impact of intrinsic alignments of galaxies in cosmological parameters constraints.

2014/407 - Polarisation of the Cosmic Microwave Background Radiation

Advisors: C. Sofia Carvalho (CAAUL) and António da Silva ( CAUP)

Cosmology is presently a very active field because of the large number of observations that are becoming available and that will allow us to characterize with great precision the nature and physical origin of the primordial cosmological perturbations, as well as of dark matter and dark energy. The cosmic microwave background (CMB) radiation provides a wealth of cosmological information that has led to major advances on our knowledge about the origin and evolution of the Universe. One of the ultimate challenges for CMB observations is to fully probe the CMB polarisation spectrum, from large to small angular scales, and to decipher the information encoded in the polarisation signal.

This project is centred on cosmological data analysis and modelling in the context of the Planck and Euclid ESA satellite missions. It comprises two main objectives.

The first objective consists in developing and implementing a novel estimator of the primary polarisation signal of the CMB. This signal can be measured from the gravitational lensing field to be extracted from CMB maps. This type of analysis will be particularly important in the sequence of the public release of CMB polarisation data by the Planck Collaboration (due by the end of 2014) and in the context of the tasks of the CMB Cross-Correlations Science Working Group of the Euclid Consortium.

The second objective consists in assessing the robustness of the estimator of the primary CMB with respect to contamination by secondary CMB polarisation effects, which is not being considered in the current CMB data analysis. This requires the development of a detailed model of the secondary polarisation signals, such as the CMB quadrupole and double-scattering induced polarisations, which act as contaminants in the detection of the primary signal. This topic is related to the detection of CMB secondary polarisation by galaxy clusters with the ALMA interferometer. Another interesting topic of research that may be addressed within this project is the development of methods for the separation of the different polarisation components at the ALMA frequencies.