Research :: PhD Topics for 2019 :: Cosmology

Topics under the thematic line Unveiling the dynamics of the Universeavailable for the 2019 Call (7 PhD Topics):

  • 2019/434 - Analytic Methods for Astrophysical Defect Fingerprinting
  • 2019/435 - Astrophysical and Local Tests of the Einstein Equivalence Principle
  • 2019/436 -Fundamental cosmology from precision spectroscopy: from ESPRESSO to the ELT
  • 2019/437 - New Maps of the Dark Side: Euclid and beyond
  • 2019/438 – Cosmological tests of gravity theory beyond General Relativity
  • 2019/439c – Testing cosmology in the non-linear regime in the Euclid era
  • 2019/440 – 2 Fast 2 Furious Universe

For details, please see below the abstract and advisors for each topic. Prospective candidates are welcome to contact directly the proposers of the topics for inquiries and further details.

2019/434 - Analytic Methods for Astrophysical Defect Fingerprinting

Advisors: Carlos J. A. P. Martins (IA U.Porto)

Abstract: 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.

Recent progress in CMB polarization and gravitational wave detection shows how some of these scenarios can be constrained by high-resolution data. However, to fully exploit the potential of ESA facilities such as CORE and LISA, one needs matching progress both in high-resolution HPC numerical simulations of defect networks and in the analytic modelling of key physical mechanisms underlying their evolution. This thesis will address the latter, using a series of novel mathematical and statistical techniques to develop more accurate analytic models for general defect evolution (building upon the successes of the current canonical VOS model) as well as for their astrophysical fingerprints, which is able to match the sensitivity of ongoing and future observational searches.

University: Porto

2019/435 - Astrophysical and Local Tests of the Einstein Equivalence Principle

Advisors: Carlos J. A. P. Martins (IA U.Porto)

Abstract: The Einstein Equivalence Principle (EEP, which Einstein formulated in 1907) is the cornerstone of General Relativity (only formulated in 1915) but also of a broader class known as metric theories of gravity. Although they are often confused, the two are conceptually distinct, and different experiments optimally constrain one or the other. Recent developments, including quantum interferometric tests and dedicated space missions, promise to revolutionize the field of local tests of the EEP and dramatically improve their current sensitivity.

This thesis will explore new synergies between these imminent new local tests of the EEP and ongoing or planned astrophysical and cosmological tests: some of these directly test the EEP, while others only test GR on various scales. We will explore relevant paradigms (including scenarios with and without screening mechanisms), develop a taxonomy for various model classes, and study how they are further constrained by experiments such as MicroSCOPE and ACES, in combination with astrophysical data from ESPRESSO, ALMA and other facilities. The work will also be directly relevant for the science case of several ELT instruments, as well as Euclid and the SKA.

University: Porto

2019/436 -Fundamental cosmology from precision spectroscopy: from ESPRESSO to the ELT

Advisors: Carlos J. A. P. Martins (IA U.Porto)

Abstract: ESPRESSO is the next generation spectrograph, combining the efficiency of a modern Echelle spectrograph with extreme radial velocity and spectroscopic precision, and including improved stability thanks to a vacuum vessel and wavelength calibration done with a Laser Frequency Comb. ESPRESSO has been installed in the Combined Coudé Laboratory of the VLT and linked to the four Unit Telescopes (UT) through optical Coudé trains, allowing operations either with a single UT or with up to four UTs for about a 1.5 magnitude gain. One of the key science drivers of ESPRESSO is to perform improved tests of the stability of nature’s fundamental couplings, and in particular to confirm or rule out the recent indications of dipole-like variations of the fine-structure constant, a.

In this thesis the student will be directly involved in the analysis and scientific exploration of the ESPRESSO fundamental physics GTO, and in the preparation of any follow-up observations. Apart from its obvious direct – and very significant – impact on cosmology and fundamental physics, the ESPRESSO data will also be important as the first reliable precursor of analogous high-resolution spectrographs for the next generation of Extremely Large Telescopes, and in particular of ELT- HIRES (in whose Phase B we are directly involved). A second goal of the thesis is to use the ESPRESSO data for detailed realistic simulations to assess the cosmology and fundamental physics impact of ELT-HIRES, also including tests beyond the sensitivity of ESPRESSO, such as redshift drift measurements and molecular tests of composition-dependent forces.

University: Porto

2019/437 - New Maps of the Dark Side: Euclid and beyond

Advisors: Carlos J. A. P. Martins (IA U.Porto)

Abstract: The growing amount of observational evidence for the recent acceleration of the universe unambiguously demonstrates that canonical theories of cosmology and particle physics are incomplete — if not incorrect — and that new physics is out there, waiting to be discovered. The most fundamental task for the next generation of astrophysical facilities is therefore to search for, identify and ultimately characterise this new physics. The acceleration is seemingly due to a dark component whose low-redshift gravitational behaviour is very similar to that of a cosmological constant. However, currently available data provides very little information about the high-redshift behaviour of this dark sector or its interactions with the rest of the degrees of freedom in the model.

It is becoming increasing clear that tackling the dark energy enigma will entail significantly extending the redshift range where its behaviour can be accurately mapped. A new generation of ESA and ESO facilities, such as Euclid, the ELT, and the SKA have dark energy characterization as a key science driver, and in addition to significantly increasing the range and sensitivity of current observational probes will allow for entirely new tests. The goal of this thesis will be to carry out a systematic exploration of the landscape of physically viable dark energy paradigms and provide optimal discriminating observational tests. The work will initially focus on Euclid (whose launch is fast approaching) and will gradually broaden to explore synergies and probe combination with the SKA and relevant ELT-HIRES instruments.

University: Porto

2019/43X - Cosmological tests of gravity theory beyond General Relativity

Advisors: Francisco Lobo (IA U.Lisboa), Noemi Frusciante (IA U.Lisboa)

Abstract: An outstanding problem faced by modern cosmology concerns cosmic acceleration, i.e. the phase of accelerated expansion recently entered by the Universe, for which we still lack a satisfactory theoretical explanation. Within the context of General Relativity, an accelerated expansion can be achieved adding an extra ingredient in the energy budget of the Universe, commonly referred to as dark energy. A different approach is to modify the law of gravity describing the Universe at large scales.A plethora of modified gravity models addressing the phenomenon of cosmic acceleration have been proposed and analyzed. The astronomical community has embarked on an intense observational effort to help exploring the real nature of the cosmic acceleration. Up and coming missions will deliver highly accurate data, offering an unprecedented insight into gravity on cosmological scales. This observational effort is not yet balanced by an equally focused effort at theoretical modeling. The ability to constrain various properties of cosmological models using observational data, such as the anisotropies of the cosmic microwave background, the large scale structure of the galaxy distribution, the expansion and acceleration rate of the universe and other such quantities, has become an essential part of modern cosmology.

The goal of the PhD project will be to unveil the real nature of the theory of gravity. To achieve this, the student will apply theoretical modeling and numerical methods to the best data available and perform forecasts for future next generation surveys.

Development of this project is required for several reasons 1) new theoretical models need to be built; 2) new numerical patches need to be developed which serve to test models against cosmological observations. The analysis tools developed by the student are expected to be used in the upcoming ESA Euclid mission in which the host institution has a leading role. In order to ensure a successful PhD,  this project contains theoretical and numerical elements that are flexible such that they can fit with the student’s skills and expertise.

University: Lisboa

2019/43Xc – Testing cosmology in the non-linear regime in the Euclid era

Advisors: Ismael Tereno (IA U.Lisboa), Alberto Rozas-Fernandez (IA U.Lisboa)

Abstract: Physical cosmology relies on two unknown substances – dark matter and dark energy – to provide a description of the Universe that is consistent with current observations. Many dark matter and dark energy hypotheses will soon become testable with data from the Euclid space mission. This project addresses one of those hypotheses: the unification of dark matter and dark energy (UDM).

The goals of this project are: (i) derive structure formation properties in UDM class of models and other related models, (ii) derive their signatures in Euclid’s gravitational lensing observables and (iii) forecast Euclid’s ability in testing this hypothesis. The theoretical derivations need to be done with high precision and accuracy to match the data quality. In particular, they need to address structure formation in the non-linear regime. To achieve these goals, this project will use existing numerical tools and develop new ones. In particular the project aims at producing N-body simulations of UDM models and the first detailed study of non- linear structure formation under the UDM hypothesis. Other tasks include assessment of model-dependent systematics, creation of lensing maps and statistical inference of model parameters.

University: Lisboa

Restriction: This is a closed topic.

2019/43X - 2 Fast 2 Furious Universe

Advisors: Nelson Nunes (IA U.Lisboa), Tiago Barreiro (IA U.Lisboa)

Abstract: The realization that the Universe is accelerating propels the idea of dark energy. This project aims to understand its nature and how it interacts with the other particles: dark matter, baryons, radiation and neutrinos. The crucial starting point is the most general scalar-tensor theory that leads to viable theoretical cosmologies. The student will test the free functions of the theory against current and forthcoming observational data (ESPRESSO, Euclid, Lisa). This is both a theoretical and hands on data project.

University: Lisboa