Gr@v member António P. Morais gave a talk at Escola Secundária José Régio in Vila do Conde with title "Do Infinitamente Grande ao Infinitamente Pequeno - uma jornada pelas interações fundamentais na natureza". António was an invited speaker to participate in a sequence of seminars entitled "A Biblioteca convida...", and presented to 11th and 12th grade Science and Technology students the four fundamental interactions in nature and how have they shaped our Universe.

Abstract: I will present the influence of the chiral anomaly on the evolution of magnetohydrodynamics. In the early universe, before electroweak symmetry breaking, and in systems at high enough temperatures such that the electron mass can be ignored, the general description of a charged plasma needs to take into account the triangle anomaly. The interplay between turbulence and chiral magnetic effect can have important consequences on the evolution of magnetic fields, leading to the creation of maximally-helical fields from initially non-helical ones. Chiral effects can support a turbulent inverse cascade, causing a slower decrease of magnetic field with time and a faster growth of correlation length, when compared to the evolution predicted by the standard magnetohydrodynamical description. Using the weak anomaly approximation, specific solutions for the inverse cascade regime that show how chiral effects support it are derived.

Gr@v member Carlos Herdeiro was one of the invited speakers of the 5th UTQuest workshop, with the theme "Hidden Sector Physics and Cosmophysics", that took place at the Yukawa Insitute for Theoretical Physics, Kyoto University, Kyoto, Japan.

The article "Warm Little Inflaton", co-authored by Gr@v member João G. Rosa and collaborators Mar Bastero-Gil (Granada U.), Arjun Berera (Edinburgh U.) and Rudnei O. Ramos (U.E. Rio de Janeiro) has been published in Physical Review Letters and selected as one of the Editors' Suggestions (a distinction given to about 1 in 6 papers).

Abstract: We discuss the possibility that dark matter corresponds to an oscillating scalar field coupled to the Higgs boson. We argue that the initial field amplitude should generically be of the order of the Hubble parameter during inflation, as a result of its quasi-de Sitter fluctuations. This implies that such a field may account for the present dark matter abundance for masses in the range 10^−6–10^−4 eV, if the tensor-to-scalar ratio is within the range of planned CMB experiments. We show that such mass values can naturally be obtained through either Planck-suppressed non-renormalizable interactions with the Higgs boson or, alternatively, through renormalizable interactions within the Randall–Sundrum scenario, where the dark matter scalar resides in the bulk of the warped extra-dimension and the Higgs is confined to the infrared brane.

Abstract: In this talk, I will first discuss the challenges one faces when trying to explain the observed late-time acceleration of our Universe, due to the obstacles which the yet unkown physics of dark energy and dark matter place when we try to understand the true theory of gravity at large scales. In this context, I will further explain how model-independent observables have the potential to reveal whether gravity is truly modified at large scales, and will describe a fundamental, underlying relation between large-scale modifications of gravity and the (non-trivial) propagation of gravitational waves, as well as its observational implications for cosmology and astrophysics.

Abstract: Inflationary cosmology is the most successful explanation of the large scale features of our universe, such as the uniform tempertaure distribution of the Cosmic microwave background radiation (CMB) and the near flat global geometry of the universe. Satellite based measurements of the CMB in the past 2 decades by COBE, WMAP, and Planck have shown the predictions of inflation to be consistent with data. The most recent of these, the Planck Satellite, has provided the most precise measurement of the CMB ever and offers the best possibility to learn details about the dynamics during the early universe. I will first explain what sort of information can be obtained from measuring the CMB for understanding large scale structure and then review the results of measurement of the CMB made by these satellite experiments. Included in this discussion will be a summary on polarization and non-gaussianity measurements. I will then discuss the two dynamical descriptions of inflation, warm and cold, and present various models in both cases and their predictions for the CMB. I will then discuss how well CMB data has been able to discriminate between the different inflation models.

Abstract: The amplitude of primordial curvature perturbations is enhanced when a radiation bath at a temperature T>H is sustained during inflation by dissipative particle production, which is particularly significant when a non-trivial statistical ensemble of inflaton fluctuations is also maintained. This can be achieved during warm inflation, where the interactions of the inflaton field with other light degrees of freedom give rise to dissipative processes. We will review in this talk the basic of warm inflation, and how dissipation and viscous effects affect the spectrum of primordial fluctuations. Since gravitational modes are oblivious to dissipative dynamics, those generically lowers the tensor-to-scalar ratio and yields a modified consistency relation for warm inflation, as well as changing the tilt of the scalar spectrum. We show that this alters the landscape of observationally allowed inflationary models, with for example the quartic chaotic potential being in very good agreement with the Planck results for nearly-thermal inflaton fluctuations, whilst essentially ruled out for an underlying vacuum state.

Our group coordinated the "Numerical Relativity and High Energy Physics" IRSES network (2012-2015). Here is a list of the global network meetings organized: