Seminários do CIF

 

Os seminários do CIF possuem caráter especializado e abordam um tema específico de cada vez. Eles são apresentados por pesquisadores credenciados no CIF ou por pesquisadores visitantes, e são marcados por amplas discussões acerca do tema apresentado com a plateia após o término.

 

4. Dr. Leonardo Giani (School of Mathematics and Physics, The University of Queensland, Australia)
The cosmic web and the gravity of the situation
17 de janeiro de 2025, 16:00
Resumo: Back in the time of Aristotle, scholars had decided that apples fall from the tree because they want to return to their "natural" place. Roughly 2000 years later, Galileo and Newton delivered better explanations for these phenomena based on simple empirical evidence: Gravity is an attractive force. However, at the dusk of the past century, we discovered that the expansion of the Universe has "recently" begun accelerating, rechallenging our understanding of gravity. Adding to the puzzle, the standard cosmological model seems incapable of explaining the disagreement between observations of the early Universe and of our cosmic environment, most notably the 5 sigma statistical tension on the value of the Hubble constant. In this talk, I will review the most recent attempts to address these questions and try to convince you that, beyond everything, gravity has never been more attractive. In particular, I will focus on the impact that our home in the cosmos, the supercluster of galaxies Laniakea, could have on our cosmological measurements by distorting the spacetime geometry.

 

3. Profa. Larissa Santos (Center for Gravitation and Cosmology, CGC, Yangzhou University - China)
Foreground removal in the upcoming CMB polarization data
16 de maio de 2024, 16:00
Resumo: Multi-frequency observations are needed to separate the CMB from foregrounds and accurately extract cosmological information from the data. In the past decades, many ground-based, balloon-borne and satellite experiments have been dedicated to CMB observations. The latest results from the Planck satellite achieved a precise measurement not only for temperature anisotropies, but also for CMB polarization E-modes. As an outcome of these experiments, much cosmological information has already been extracted from the CMB. Recently, much attention has been focused on the CMB polarization anisotropies, especially the B-modes, which are of particular interest as they are expected to probe inflation. However, a precise measurement of these B-modes strongly depends on our ability to separate the signal from the astrophysical foregrounds. In this seminar, I will discuss the foreground cleaning performance considering CMB polarization experiments, mainly in the context of the Chinese ground-based Ali CMB Polarization Telescope.

 

2. Prof. Aleksey Toporensky (Sternberg Astronomical Institute, Moscow University, Moscow - Russia)
General radially moving references frames in the black hole background
23 de abril de 2024, 16:00
Resumo: We consider general radially moving frames realized in the background of nonextremal black holes having causal structure similar to that of the Schwarzschild metric. In doing so, we generalize the Lemaître approach, constructing free-falling frames which are built from the reference particles with an arbitrary specific energy e0 including e0<0 and a special case e0=0 . The general formula of 3-velocity of a freely falling particle with the specific energy e with respect to a frame with e_0 is presented. We point out the relation between the properties of considered frames near a horizon and the Banados-Silk-West effect of an indefinite growth of energy of particle collisions. Using our radially moving frames, we also consider nonradial motion of test particles including the regions near the horizon and singularity. We also point out the properties of the Lemaître time at horizons depending on the frame and sign of particle energy.

 

1. Piotr Gładysz (Instituto de Física da Universidade Nicolau Copérnico, Polônia)
Nonlinear behavior of Rabi frequency in polar systems
8 de dezembro de 2022, 11:00

Seminário completo: https://www.youtube.com/live/QuOSBxzRhwM?feature=share