Colóquios

  • O sistema solar distante visto pelo Dark Energy Survey / Colóquio DFMA

    Data: 
    segunda-feira, 8 Novembro, 2021 - 16:00 até 17:00
    Palestrante: 
    Prof. Pedro Bernardinelli
    Resumo: 

    Transmissão ao vivo via YouTube

    Resumo: Nesta apresentação, discutiremos os resultados de uma busca por objetos no sistema solar distante realizada com o Dark Energy Survey (DES). Esta busca levou à identificação de mais de 800 objetos, sendo 600 deles novos, incluindo C/2014 UN271 (Bernardinelli-Bernstein), o maior e mais distante cometa originário da Nuvem de Oort já identificado. Apresentaremos o processo de descoberta desses objetos que, dada a estratégia observacional do DES, foi uma tarefa com uma exigência computacional extrema, necessitando de 15 a 20 milhões de horas de CPU. Também caracterizaremos o cometa B-B, detalhando os argumentos observacionais que indicam seu tamanho incomum, além de sua história dinâmica e propriedades de sua superfície, comparando-o a outros cometas distantes. Por fim, discutiremos também como os objetos descobertos pelo DES se encaixam na história dinâmica da formação dos planetas gigantes e enfraquecem a hipótese da existência de um nono planeta ainda não descoberto no Sistema Solar.

  • Cosmological perturbations in closed universes and the CMB / Colóquio DFMA

    Data: 
    segunda-feira, 25 Outubro, 2021 - 16:00 até 17:00
    Palestrante: 
    Prof. Nelson de Oliveira Yokomizo (Departamento de Física da UFMG)
    Resumo: 

     

    Transmissão ao vivo via YouTube

    Resumo: We investigate the evolution of gauge invariant quantum perturbations in the closed FLRW model in the
    presence of an inflationary potential. We first determine initial conditions for the background dynamics which lead to a desired slow-roll phase that is compatible with observations. Providing the initial conditions for the quantized perturbations at the onset of inflation we study the influence of the spatial curvature on the scalar and tensor power spectra at the end of inflation. We determine the implications of the modifications of the primordial power spectra due to the presence of spatial curvature to the CMB spectra and compare our results with the Planck data. We highlight the main differences from the standard inflationary scenario in a flat FLRW model.

     

  • QCD parameters for Standard Model precision physics | Colóquio DFMA

    Data: 
    segunda-feira, 4 Outubro, 2021 - 16:00 até 17:00
    Palestrante: 
    Prof. Diogo Boito (IFSC-USP/ University of Vienna)
    Resumo: 

    Transmissão ao vivo via YouTube

    Resumo: The theoretical precision of many crucial observables in the Standard Model is nowadays limited by our knowledge of QCD parameters. This is the case, for example, in Higgs physics. Determining the strong coupling and quark masses with smaller uncertainties is therefore a fundamental task in order to match the reduced errors expected on the experimental side with the advent of future facilities, such as the FCC-ee and HL-LHC. Obtaining the QCD parameters is not a straightforward task, since they are not physical
    observables, as they depend on renormalization conventions: theory input is as important as experimental data. I will discuss recent developments in the precise determination of the strong coupling and heavy-quark masses, with emphasis on taming the intrinsic error associated with the truncation of the perturbative series in QCD and its interplay with non-perturbative physics.

     

  • An update on phenomenological constraints of properties of the quark-gluon plasma | Colóquio DFMA

    Data: 
    segunda-feira, 27 Setembro, 2021 - 16:00 até 17:00
    Palestrante: 
    Prof. Matthew Luzum (DFMA, IFUSP)
    Resumo: 

    Transmissão ao vivo via YouTube

    Resumo:
    At extremely high temperature, there exists a deconfined state of matter known as the quark-gluon plasma (QGP), where color degrees of freedom are liberated.  In order to achieve the necessary temperature to study the QGP experimentally, heavy nuclei are collided at ultrarelativistic energies, and measurements made.  In this colloquium I review recent progress in determining properties of the QGP from relativistic heavy ion collision data -- specifically,  a recent verification of deconfinement and the liberation of color degrees of freedom via the QGP equation of state, and recent developments using Bayesian inference to extract the shear and bulk viscosities of the QGP.

    Referências:
    Nature Phys. 16 (2020) 6, 615-619 (arXiv:1908.09728)
    Phys.Rev.C 103 (2021) 5, 054904 (arXiv:2011.01430)
    Phys.Rev.Lett. 126 (2021) 24, 242301 (arXiv:2010.03928)

     

  • CHAOS AND COMPLEXITY | Colóquio DFMA

    Data: 
    segunda-feira, 20 Setembro, 2021 - 16:00 até 17:00
    Palestrante: 
    Prof. Celso Grebogi (Institute for Complex Systems and Mathematical Biology, King’s College, University of Aberdeen)
    Resumo: 

     

     

    Transmissão via YouTube

    Resumo: Many simple nonlinear deterministic systems can behave in an apparently unpredictable and chaotic manner. This realisation has broad implications for many fields of science. Some basic concepts and properties in the field of chaotic dynamics of dissipative systems will be reviewed in this talk. I will use some of these properties in application topics, including the control of chaos in the heart and in the brain. I will then go a step further by arguing that a complex system are made up of many states that are interrelated in a complicated manner. The ability of a complex system to access those different states, combined with its sensitivity, offers great flexibility in manipulating the system’s dynamics to select a desired behaviour. Another important issue is the question of mathematical modelling of chaotic and complex systems, including complex networks. Mathematical modellers of such systems need to understand and take seriously the question of their own limitations.

    Controlling complexity, L. Poon and C. Grebogi, Phys. Rev. Lett. 75, 4023 (1995).
    Controlling Chaotic Dynamical Systems, C. Grebogi and Y. C. Lai, Systems Control Lett. 31, 307 (1997).
    Data Based Identification and Prediction of Nonlinear and Complex Dynamical Systems, W.-X. Wang, Y.-C. Lai, and C. Grebogi, Phys. Reports. 644, 1-76 (2016).
    Relativistic Quantum Chaos, L. Huang, H.-Y. Xu, C. Grebogi, and Y.-C. Lai, Phys. Reports 753 1-128 (2018).
    Sudden Regime Shifts After Apparent Stasis, C. Grebogi, Phys. of Life Reviews 32, 41-43 (2020).
    Tipping Point and Noise-induced Transients in Ecological Networks, Y. Meng, Y.-C. Lai, and C. Grebogi, J. Royal Soc. Interface 17, 20200645 (2020).
    Machine Learning Prediction of Critical Transition and System Collapse, L.-W.Long, H. Fan, C. Grebogi, and Y.-C. Lai, Phys. Rev. Research 3, 013090(1-14)
    (2021).

  • Where is String Theory? | Colóquio DFMA

    Data: 
    sexta-feira, 23 Julho, 2021 - 16:00 até 17:00
    Palestrante: 
    Prof. Pedro Vieira (ICTP-SAIFR-IFT-UNESP & Perimeter Institute, Canadá)
    Resumo: 

    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.

     

  • Effective momentum-momentum coupling in a correlated electronic system: the diamagnetism of benzene | Colóquio DFMA

    Data: 
    sexta-feira, 16 Julho, 2021 - 16:00 até 17:00
    Palestrante: 
    Prof. Amir Ordacgi Caldeira (IFGW, Unicamp)
    Resumo: 

    Transmissão ao vivo via YouTube e Zoom

    Resumo: A well-known property of aromatic molecules is their highly anisotropic response to an external magnetic field. This intriguing phenomenon is rationalized as a consequence of the delocalization of the itinerant electrons that populate the aromatic ring.

    In this presentation, we revisit the magnetism of aromatic molecules through the study of simple Hubbard – rings, and argue that if the itinerant electrons are described by an extended Hubbard Hamiltonian with an effective momentum – momentum interaction between them, a large enhancement of the molecule diamagnetic response takes place.

    We show that the presence of this new term is due to the reincorporation of part of the effects of the localized bonding electrons on the dynamics of their itinerant counterparts in Hubbard – like Hamiltonians. Going beyond the adiabatic approximation, we show that the net effect of virtual transitions of bonding electrons between their ground and excited states is to furnish the itinerant electrons with an effective interelectronic momentum – momentum interaction.

    Although we have applied these ideas to the specific case of rings, our assumptions can be generalized to higher-dimensional systems sharing the required properties of which we have made use herein.

  • Acceleration of Cosmic Rays by Magnetic Reconnection and the Origin of Very High Energy Emission from Black Holes and Relativistic Jets of Active Galaxies | Colóquio DFMA

    Data: 
    sexta-feira, 2 Julho, 2021 - 16:00 até 17:00
    Palestrante: 
    Profa. Elisabete M. de Gouveia Dal Pino (IAG-USP)
    Resumo: 

    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).

  • Lições do Run II do Large Hadron Collider | Colóquio DFMA

    Data: 
    sexta-feira, 25 Junho, 2021 - 16:00 até 17:00
    Palestrante: 
    Prof. Oscar José Pinto Éboli (DFMA-IFUSP)
    Resumo: 

    Transmissão ao vivo via YouTube e Zoom.

    Resumo: Desde a descoberta do Higgs em 2012 o Large Hadron Collider do CERN acumulou uma grande quantidade de dados. Discutiremos o impacto destes resultados na Física de Partículas.

     

  • Estrelas de nêutrons na era da astronomia multimensageira | Colóquio DFMA

    Data: 
    sexta-feira, 18 Junho, 2021 - 16:00 até 17:00
    Palestrante: 
    Profa. Débora Peres Menezes (Departamento de Física, UFSC)
    Resumo: 

    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.

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