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.

  • Dr. Hajime Sotani (Kochi University and RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS), Japan)
    Neutron star mass and radius of FRB 20240114A by identification of crustal oscillations
    3 de fevereiro de 2026, 16:00
    Resumo: By identifying quasi-periodic oscillations reported in FRB 20240114A (from the Five-hundred-meter Aperture Spherical Telescope) with neutron star crustal torsional oscillations, together with experimental constraints on the nuclear saturation parameter, the incompressibility, we constrain the mass and radius of an extragalactic neutron star at redshift z=0.13. Identifying the low-order QPO frequencies as fundamental oscillations, and frequencies of 567.7 Hz or 655.5 Hz (rest frame) as first overtone candidates imply neutron star mass ranges of 1.00-1.55 solar mass or 1.17-1.76 solar mass, respectively. Additionally, accounting for the nuclear parameter dependence of low-mass neutron star structure yields an estimated radius of 12.5-13.5 km. Simultaneously, we also constrain the nuclear saturation parameter, namely the density dependence of the nuclear symmetry energy, L, and determine it to be L=59.5-96.8 MeV, which is broadly consistent with the previous constraints on L obtained from the experiments and astronomical observations. Thus, a mapping of FRB QPOs to crustal torsional modes seems reasonable. This can be investigated with upcoming FRB surveys over a broad range of redshifts and more elaborate data analyses.
    Youtube: https://www.youtube.com/live/sO-XzmPQdik?si=JmUTuR_pJSZ6sd93 

leo

 

  • Dr. Riccardo Sturani (IFT - UNESP)
    Gravitational Wave Astronomy and waveform modeling
    4 de dezembro de 2025, 16:00
    Resumo: The gravitational two-body problem attracted revived interest since the direct detection of gravitational waves from coalescing binaries over ten years ago. I'll give an overview of the current understanding of the perturbative expansions of the two body dynamics within different approximation schemes emphasizing the relations between the oldest (post-Newtonian) and the one which is more actively developed at the moment (post-Minkowskian).
    Youtube: https://www.youtube.com/live/bGzCfCedLVw?si=GAP2nWlJv1Bkw_x6 

leo

 

  • Dr. Oleg Zaslavskii (Kharkiv National University - Ucraine)
    High Energy particle colisions near black holes
    12 de junho de 2025, 16:00
    Resumo: If two particles move towards a black hole and collide in the vicinity of the horizon, under certain conditions their energy Ec.m. in the center of mass frame can grow unbounded. This is the Banados-Silk-West (BSW) effect. Usually, this effect is considered for extremal horizons and geodesic (or electrogedesic) trajectories. Simple explanation of this effect from the geometric and kinematic viewpoints is considered.
    We review this effect for different types of horizon and take into account a force acting on a particle. We also give general classification of possible trajectories that include so-called usual, subcritical, critical and ultracritical ones depending on the near-horizon behavior of the radial component of the four-velocity..
    Youtube: https://www.youtube.com/watch?v=5aghuGOu-gM 

leo

 

  • 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.

leo

 

  • 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.
    larissa

 

  • 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.
    seminar

  • O poder das ideias: propriedade intelectual e empreendedorismo na UnB
    Youtube: https://www.youtube.com/watch?v=SZUbKcpcgfc&list=PLukZFARoEvIZ1iZ3_rMLc0u-jZutkgv3L&index=7