Transmissão ao vivo via YouTube e Zoom

Resumo: At low energies we have gravity. What could be the space of UV completions? The S-matrix bootstrap is a tool which might help shedding light into this important questions. I will review how so.

Transmissão ao vivo via YouTube e Zoom.

Resumo: Black Holes (BHs) and Relativistic Jets from active galaxies are among the most extreme particle accelerators and very high energy (VHE) emitters in the universe. Only lately, combining theory, numerical simulations, and observations, we have started to understand the potential physical processes that prevail in the surrounds of these sources in order to explain major puzzles, like  the origin of  their VHE flares in gamma-rays. In regions of these sources where magnetic fields are dynamically dominating, fast magnetic reconnection is expected and thus particle acceleration driven by this process. In this seminar, I will discuss what is magnetic reconnection and present recent results that combine multidimensional magnetohydrodynamical relativistic simulations with the injection of test particles, which demonstrate how particles can be stochastically accelerated in relativistic jets and accretion flows around BHs by magnetic reconnection. We find that for jets with magnetic fields B ~ 10 G, the particles can be accelerated up to observed ultra-high energies ~10^20 eV. I will also show that these ultra-high-energy-cosmic-rays (UHECRs) are able to explain the VHE flares and the associated neutrino emission observed in the relativistic jets from active galaxies. Finally, I will discuss the implications of these results in predictions for forthcoming high energy astrophysical observatories like the Cherenkov Telescope Array (CTA).

Transmissão ao vivo via YouTube e Zoom.

Resumo: A primeira detecção de uma estrela de nêutrons ocorreu em 1967. Sabe-se hoje que essas estrelas são objetos muito compactos com raios da ordem de 10 km e massas que vão de 1,4 a mais de 2 massas solares. Na verdade, são remanescentes estelares de estrelas massivas, uma espécie de zumbis estelares (morrem, mas não completamente). Nas últimas décadas, observações astronômicas geraram vários vínculos para massas das estrelas de nêutrons. Finalmente, em 2017, as primeiras ondas gravitacionais geradas pela fusão de duas estrelas de nêutrons que faziam parte de um sistema binário, foram detectadas pela colaboração LIGO-Virgo, e também por meio de emissão de raios-X, raios-gama, ultravioleta, infravermelho, no rádio e até no visível, dando início a era da astronomia multimensageira.  Para entender as estrelas de nêutrons, equações de estado que satisfazem propriedades nucleares bem definidas são necessárias. E agora, elas podem ser calibradas por meio de vínculos observacionais que delimitam também os raios desses pequenos objetos compactos.

Nesse seminário, vou tentar mostrar como o minúsculo mundo da física nuclear e seus modelos pode ser útil no entendimento do cosmos, por meio de remanescentes estelares que geram, ao se fundir, ondas gravitacionais, por fim, detectáveis.

Transmissão ao vivo via YouTube e Zoom

Resumo: Heavy-ion collision experiments have provided overwhelming evidence that quarks and gluons, the elementary particles within protons and neutrons, can flow as a nearly frictionless, strongly interacting relativistic liquid over distance scales not much larger than the size of a proton. On the other hand, with the dawn of the multi-messenger astronomy era marked by the detection of a binary neutron star merger, it became imperative to understand how extremely dense fluids behave under very strong gravitational fields. Therefore, three of the most cutting-edge experimental apparatus in modern science, the Relativistic Heavy Ion Collider (RHIC), the Large Hadron Collider (LHC), and the Laser Interferometer Gravitational-Wave Observatory (LIGO) are now taking data whose description requires a major overhaul of our current understanding of fluid dynamics. In this colloquium I will discuss the new developments that have contributed to redefine the onset of relativistic fluid dynamics and its extension towards the far-from-equilibrium regime. New results involving viscous fluids and their coupling to general relativity will also be presented. These results pave the way for the inclusion of viscous effects in neutron star merger simulations.