- 2016/418 - Coding the Cosmos: A New Generation of Superstring Simulations
- 2016/419 - New Maps of the Dark Side
- 2016/420c – Unveiling the Dark Side of the Universe
- 2016/421 - Late-time cosmic acceleration and modified theories of gravity
- 2016/422 - Astrophysical and Local Tests of the Einstein Equivalence Principle
- 2016/423 - Cosmological Simulations for a full exploitation of the Euclid mission Weak Lensing data
- 2016/424 - Generalised scalar-tensor theories of gravity in cosmology
- 2016/425 - Non-linear structure formation in 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.
2016/418 – Coding the Cosmos: A New Generation of Superstring Simulations
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 highlights how some of these scenarios can be constrained by high-resolution data. However, they also show that the current bottleneck is the lack of accurate high-resolution simulations of defect networks that can be used as templates for robust statistical analysis. This is expected to be an even bigger problem for next-generation facilities such as COrE+ and eLisa. This thesis will go significantly beyond the state-of-the-art and develop and implement a new generation of high-scalability HPC defect codes that will be able to match the sensitivity of ongoing and forthcoming observational searches.
2016/419 - New Maps of the Dark Side
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 (in which the dark side team is more directly involved) and will gradually broaden to explore synergies with the SKA and relevant ELT-HIRES instruments.
2016/420c - Unveiling the Dark Side of the Universe
Advisors: Pedro P. 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.
Note: This is a closed topic.
2016/421 -Late-time cosmic acceleration and modified theories of gravity
Advisors: Francisco Lobo (IA U.Lisboa), Diego Rubiera-Garcia (IA U.Lisboa)
The late-time cosmic accelerated expansion is one of the most important and challenging current problems in cosmology. Although models of dark energy are the most popular candidates responsible for the cosmic expansion, the latter may be due to modifications of General Relativity, which introduce new degrees of freedom to the gravitational sector itself. This research project will explore the viability of a plethora of modified gravity models, consistently analysing the reproduction of all the cosmological epochs. More specifically, we will consider generalizations of the Einstein- Hilbert action by including non-linear curvature invariants and Lagrangians that also include curvature couplings to the matter sector. Another class of theories under our scrutiny will be generalised scalar-tensor or vector-tensor gravity theories, where scalar or vector fields play gravitational roles that can also be perceived as couplings to matter in an appropriate frame. One fundamental goal of this project is to study the theoretical issues of the extra degrees of freedom of the theory and to analyse its astrophysical applications.
2016/422 – 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) and study how they will be further constrained by experiments such as MicroSCOPE and ACES, in combination with astrophysical data. The project may have a theoretical or an observational focus, depending on the student’s preference and skills. In any case the work will be directly relevant for the science case of several ELT instruments, and to a lesser extent for ALMA, Euclid and the SKA.
2016/423 - Cosmological Simulations for a full exploitation of the Euclid mission Weak Lensing data
Advisors: Ismael Tereno (IA U.Lisboa), António da silva (IA U.Lisboa)
The Euclid cosmological space mission is designed to explore the “Dark Universe” and is expected to produce a full sky map of the dark matter distribution in the universe and explain the accelerated expansion of the universe.
The spacecraft will be launched in 2020 and until then all the scientific pipelines need to be ready. In order to fully exploit the high-precision upcoming data, during the next 4 years there will be a large international effort to improve the precision of the theoretical cosmological modeling and the accuracy of the corrections of systematic effects. To tackle both of these aspects, realistic simulations of large volumes of the large-scale structure are needed.
In this project, the student will join this international effort and work on dedicated state-of-the-art N-body simulations of large-scale structure. The project aims to produce precise theoretical modelling of weak gravitational lensing observables, focusing on higher order correlation functions of the cosmological structure and their covariances, and on the impact of intrinsic alignments systematics.
2016/424 - Generalised scalar-tensor theories of gravity in cosmology
Advisors: Nelson Nunes (IA U.Lisboa), Ippocratis Saltas (IA U.Lisboa)
This PhD project concerns the model building and associated phenomenology of gravitational theories beyond the standard paradigm of General Relativity, focusing on general theories constructed out of a scalar field, known as generalised scalar-tensor theories. The student will learn and apply analytical and numerical tools, such as cosmological perturbation theory and statistical methods to make phenomenological predictions for the dynamics and structure of the Universe at very large scales, with the aim of testing the concordance cosmological model with current and future observational surveys like Euclid and Planck. On the same time, the student will have the opportunity to explore the implications of these theories for the Universe at its very first moments after the Big Bang, where quantum-gravitational effects become important.
2016/425 - Non-linear structure formation in the Universe
Advisors: José Pedro Mimoso (IA U.Lisboa 6 DF/FCUL), Ippocratis Saltas (IA U.Lisboa)
This project will investigate the cosmological and astrophysical implications of non-linear structure formation within General Relativity as well as generalisations of it. The student will have the opportunity to understand modern approaches of gravitational collapse at the non-linear level and beyond, with the aim of testing the concordance cosmological paradigm, by combining analytical and numerical tools. The techniques mastered in this project can be applied to a variety of physical setups, from star formation to the formation of non-linear structures in the Universe.