Cosmology News & Events

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A no-go theorem for exotic alternatives to black holes as LIGO/Virgo sources

Five of the ground-breaking gravitational wave detections by the LIGO/Virgo collaboration have been interpreted as black hole collisions forming a more massive black hole. It is hard to demonstrate conclusively that these objects are indeed black holes, and there is a lively debate on the intriguing possibility that other, more exotic alternatives could explain the observations. In an article to appear in Physical Review Letters, Gr@v members P.

From Infinitely Large to Infinitely Small

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.

Chiral Magnetohydrodynamic Turbulence

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Speaker
Natacha Leite (DESY, U. Hamburg)
Event date
Venue
GAP room
Event type
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.

Scalar field dark matter and the Higgs field

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Speaker
Catarina Cosme (Porto U.)
Event date
Venue
GAP room
Event type
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.