Research :: PhD Topics for 2017 :: Cosmology

Topics under the thematic line Unveiling the dynamics of the Universeavailable for the 2017 Call (8 PhD Topics):

  • 2017/426 – Spacetime singularities, cosmology and black holes beyond General Relativity
  • 2017/427 - Analytic Methods for Astrophysical Defect Fingerprinting
  • 2017/428 - Astrophysical and Local Tests of the Einstein Equivalence Principle
  • 2017/429 - Fundamental cosmology from precision spectroscopy: from ESPRESSO to the E-ELT
  • 2017/430 - New Maps of the Dark Side: Euclid and beyond
  • 2017/431 - Cosmic strings and other defects as probes of the (very) early universe
  • 2017/432 - Dark energy interactions
  • 2017/433c – Unveiling the Dark Side of the 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.

2017/426 – Spacetime singularities, cosmology and black holes beyond General Relativity

Advisors: Diego Rubiera-Garcia (IA U.Lisboa), Francisco Lobo (IA U.Lisboa)

Einstein’s deep insight on the relation between gravitation and geometry represents the culmination of scientific thinking on the nature of gravitation initiated with the pioneering works of Galileo. The idealization of a body as a point particle moving along geodesics of a spacetime determined by matter distributions leads to a number of astrophysical and cosmological predictions which are in excellent agreement with observations. There are, however, several issues that cast serious concerns on the limits and validity of this theory. From the observational side, we find the inability of General Relativity (GR) and the standard model of particle physics to account for astrophysical and cosmological observations, forcing the need to add dark matter/dark energy into the theory, of which we have no directly experimental evidence so far. From the theoretical side, the unavoidable existence inside GR of spacetime singularities deep inside black holes as well as in the early Universe, breaks the predictability and determinism of our physical theories. In this project, we shall address these questions from a broader perspective, where GR is taken as just an approximate theory that requires modifications both in the large curvature and large distance regions. More specifically, we will consider generalizations of GR by including additional geometrical elements not considered there, and study in detail the modifications in the predictions in astrophysics and cosmology with respect to the standard lore in the field. One fundamental goal of this project is the understanding of spacetime singularities, both inside black holes and in cosmology (early and late-time), as well as studying mechanisms for their resolution.

University: Lisboa

2017/427 – Analytic Methods for Astrophysical Defect Fingerprinting

Advisors: Carlos Martins (IA U.Porto)

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 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

2017/428 – Astrophysical and Local Tests of the Einstein Equivalence Principle

Advisors: Carlos Martins (IA U.Porto)

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.

In this thesis the student 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 the behaviour of GR on various scales. We will explore relevant paradigms (including scenarios with and without screening mechanisms), develop a taxonomy for the current and new 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 E-ELT instruments, as well as Euclid and the SKA.

University: Porto

2017/429 – Fundamental cosmology from precision spectroscopy: from ESPRESSO to the E-ELT

Advisors: Carlos Martins (IA U.Porto)

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 will be installed in the Combined Coudé Laboratory of the VLT in late 2017, 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, α.

In this thesis the student will be directly involved in the analysis and scientific exploration of the ESPRESSO fundamental physics GTO data, as well as 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 ongoing Phase A we are directly involved). Thus a second goal of the thesis is to use the ESPRESSO data to carry out detailed realistic simulations to assess the cosmology and fundamental physics impact of ELT-HIRES, inter alia exploring the feasibility of novel tests which are beyond the sensitivity of ESPRESSO, such as redshift drift measurements and molecular tests of composition-dependent forces.

University: Porto

2017/430 – New Maps of the Dark Side: Euclid and beyond

Advisors: Carlos Martins (IA U.Porto)

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 E-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

2017/431 – Cosmic strings and other defects as probes of the (very) early universe

Advisors: Lara Sousa (IA U.Porto), Pedro Pina Avelino (IA U.Porto & DFA/FCUP)

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.

The computation of the specific signatures left behind by topological defects is essential to use the data of present and upcoming observational infrastructures to their full potential. This project aims at improving the current estimates of these signatures, by making use of realistic semi-analytical and numerical models for the evolution of cosmic defect networks, with a particular emphasis on cosmic (super)string and domain wall networks. In particular, the associated gravitational wave background and its impact on the B-mode polarization of the Cosmic Microwave Background, their signatures on the reionization history of the universe and the 21cm background, and their potential role as seeds of variations in fundamental couplings, shall be investigated in detail. Detailed forecasts for upcoming probes, including eLISA (as part of our participation in the eLISA Cosmology Working Group), COrE+, SKA, ESPRESSO and E-ELT HIRES will be central to this PhD project.

University: Porto

2017/432 – Dark energy interactions

Advisors: Nelson Nunes (IA U.Lisboa)

This project tries to understand the nature of dark energy and how it interacts with the other particles, being dark matter, baryons, radiation or 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. This is both a theoretical and hands on data project.

University: Lisboa

2017/433c – Unveiling the Dark Side of the Universe

Advisors: Pedro Avelino (IA U.Porto)

Unveiling the nature of dark matter and dark energy, the main constituents of the Universe, is one of the most ambitious challenges of fundamental physics. The main goal of this project is to provide a contribution towards this major objective through the parameterization, characterization and constraining of coupled dark matter/dark energy models. This project contemplates both theoretical and numerical tasks, including the computation of the cosmological implications of coupled dark matter/dark energy models taking into account nonlinear backreaction effects.. Numerical simulations and semi-analytical methods will be employed in the modeling of the dark matter/dark energy interaction both at microscopic and macroscopic levels. State of the art cosmological observations, using type Ia supernovae, large scale clustering (including baryon acoustic oscillations), cosmic microwave background temperature and polarization anisotropies, and weak lensing, will be used to constrain the parameter space of coupled dark matter/dark energy scenarios. Forecasts of the results to be obtained with future missions, such as EUCLID and ESPRESSO, will also be performed.

University: Porto

Restriction: This is a closed topic.