Colóquios

  • Probes of ultralight dark matter and primordial black holes with gravitational-wave detectors | Colóquio DFMA

    Data: 
    sexta-feira, 1 Março, 2024 - 16:00 até 17:30
    Palestrante: 
    Dr. Andrew Miller
    Resumo: 

    Resumo: Gravitational-wave interferometers can be used to probe the existence of dark matter. Different types of dark matter, such as sub-solar primordial black holes, axions and dark photons, could leave different imprints on gravitational-wave detectors. While arising from physically different sources, such signals share common traits, and can be searched for with similar methods. In this talk, I will explain how persistent, quasi-monochromatic signals in ground-based detectors could arise from each of the aforementioned dark matter candidates. I also describe some of our search methods and summarize results from the most recent observing runs of Advanced LIGO, Virgo, and KAGRA. 

     
  • The observer-dependence of the Hubble parameter: a covariant perspective | Colóquio DFMA

    Data: 
    quarta-feira, 29 Novembro, 2023 - 16:00 até 17:00
    Palestrante: 
    Dra. Jessica Santiago
    Resumo: 

    Resumo: Given the exponential growth on the upcoming supernovae data available, the possibilities of rigorously testing the cosmological principle becomes ever more real. One of the ways to do so is by measuring the multipole decomposition of the Hubble and deceleration parameters. In this presentation, I will discuss the observational-theoretical approach, initially introduced by Kristian & Sachs, which allows for the interpretation of data in non-homogeneous and anisotropic universes. I will also explore the effects introduced by the relative motion between the observer and the reference frame defined by galaxies (the matter frame), demonstrating that the luminosity distance should be corrected in such cases.

  • Scattering Amplitudes and Classical Observables | Colóquio DFMA

    Data: 
    sexta-feira, 24 Novembro, 2023 - 16:00 até 17:00
    Palestrante: 
    Prof. Gabriel Santos Menezes
    Resumo: 

    Resumo: Scattering experiments play a key role in the understanding of the fundamental aspects of nature. In this respect, scattering amplitudes have a paramount physical significance through their contribution in the calculation of scattering cross-sections, the primary observables in this context. On the other hand, amplitudes have also been applied successfully to assess features of general-relativistic problems. In this talk I will review some basic techniques which are important in the modern research on scattering amplitudes as well as discussing some current trends and future perspectives, with a particular focus on the black-hole binary dynamics and classical observables.

  • What can we learn from the full (three-dimensional) kinematic dipole? | Colóquios DFMA

    Data: 
    sexta-feira, 10 Novembro, 2023 - 16:00 até 17:00
    Palestrante: 
    Dra. Caroline Guandalin
    Resumo: 

    Resumo: Recent studies of our motion with respect to the distribution of matter on large scales have found discrepancies in our peculiar velocity with respect to results obtained from the cosmic microwave background (CMB). These findings raise questions about the Cosmological Principle, a fundamental concept that suggests our velocity should be the same in both the CMB and matter reference frames. In this talk, I will explore the quasar luminosity function (QLF), which describes how quasars are distributed in terms of distance and brightness, and how different QLF models impact the strength of the kinematic dipole. I will also discuss how ignoring the dipole evolution over time leads to different results for our peculiar velocity. Finally, I will explain how this time evolution may provide opportunities to constrain cosmological parameters, with a particular focus on dark energy.

  • Cosmology with gravitational lensing of the Cosmic Microwave Background | Colóquios DFMA

    Data: 
    sexta-feira, 27 Outubro, 2023 - 16:00 até 17:00
    Palestrante: 
    Prof. Louis Legrand
    Resumo: 

    Resumo:
     
    The Cosmic Microwave Background (CMB) is the most distant light that we can observe today. Since its emission roughly 380.000 years after the Big Bang it crossed all the Universe while coming to us. During their travel, the photons of the CMB have been deflected by the matter they crossed along their path, an effect called gravitational lensing. This deflection field of the CMB is a powerful observable, proportional to the integral of the matter distribution up to the early Universe. I will introduce how we can reconstruct this lensing field from CMB observations. I will then demonstrate how CMB lensing can put tight constraints on the content of the Universe, on the sum of the neutrino masses, and help us discover cosmic inflation. Lastly, I will introduce a new CMB lensing estimator, which will reconstruct optimally the lensing field for the next generation of CMB surveys. 

     

  • "Dipoles" | Colóquio DFMA

    Data: 
    terça-feira, 11 Julho, 2023 - 17:00 até 18:00
    Palestrante: 
    Prof. Dr. Enrico Bertuzzo - FISMAT IFUSP
    Resumo: 

    Resumo: Electric and magnetic dipoles play an important role in classical electromagnetism and quantum mechanics. They are even more significant in quantum field theory, since the first successful loop prediction of QED is precisely the anomalous (dipole) magnetic moment of the electron. More broadly, dipole operators frequently appear in theories beyond the standard model, where they can be probed using different techniques. In this colloquium, I will first summarize the important role that dipoles play in classical electromagnetism, quantum mechanics and quantum field theory; I will then describe two examples of theories beyond the Standard Model in which dipole operators are important for the phenomenology: "sterile dipoles" and "dark dipoles".

  • "Transição espectral do tipo Anderson em modelos esparsos multidimensionais: novos rumos e diretrizes | Colóquio DFMA"

    Data: 
    terça-feira, 27 Junho, 2023 - 17:00 até 18:00
    Palestrante: 
    Prof. Dr. Domingos Humberto Urbano Marchetti - FGE IFUSP
    Resumo: 

    Resumo: Proposto por Anderson em 1959 para descrever a mobilidade de elétrons em uma rede cristalina na presença de impurezas (contexto Físico: semicondutores, por exemplo, Si dopados com P), o modelo de Anderson é descrito por uma Hamiltoniana Hω = ∆ + V ω em l2 (Zd) onde ∆ é o Laplaciano discreto e V ω é um potencial aleatório (para cada sítio nV ω (n) é uma variável aleatória independente e igualmente distribuída F(x) = µ ( : Vω (n) ≤ x}) com um parâmetro v que controla a desordem. Anderson conjecturou a existência de um valor crítico 0 < vc < ∞ tal que, para v ≥ vo espectro de Hω é puro ponto (p.p.), µ quase certamente, e para v < vc medida espectral de Hω contém duas componentes separadas pela chamada fronteira de mobilidade (“mobility edges”) λ±: se λ ∈ [λ, λ+] o espectro de Hω  é puramente absolutamente contínuo (a.c.) e puro ponto no complemento, trazendo à Física dos materiais o importante e novo fenômeno de localização. Nossa atenção restringe-se aos últimos desenvolvimentos relativos a elusiva existência de espectro a.c., estabelecida em 1998 por A. Klein para o modelo de Anderson na rede de Bethe. Daremos nesta apresentaçãênfase as ideias e resultados empregados na trabalho em colaboração com W. F. Wreszinski sobre uma transição do tipo Anderson em uma classe de modelos esparsos em d ≥ 2

  • Quantum Bit Commitment - Colóquio DFMA

    Data: 
    terça-feira, 13 Junho, 2023 - 17:00 até 18:00
    Palestrante: 
    Profa. Bárbara Lopes Amaral
    Resumo: 

    Resumo: Bit commitment is a cryptographic protocol between two mistrusting parties, Alice and Bob, in which Alice wants to commit to a bit while keeping it hidden from Bob. Bit commitment is an important primitive in cryptography since it can serve as a building block to achieve various cryptographic tasks, such as secure coin flipping, zero knowledge proofs, secure computation, user authentication, signature schemes, and verifiable secret sharing.  It was accepted that exemplary valid quantum protocols for bit commitment were available, but the optimism in the development of secure quantum bit commitment protocols was put into very serious doubt in works by Mayers and by Lo and Chau were it was shown, or so was it believed for over 20 years, that all proposed quantum bit commitment protocols are insecure. In this seminar I will talk about  the development of the project Unconditionally Secure Quantum Bit Commitment, developed in partnership with Prof. Paulo Nussenzveig (USP) and Prof. Charles Tresser (IMPA), and funded by the Call 04/2020 of Instituto Serrapilheira, in which our goal is to understand the assumptions in Mayers and Lo and Chau results and search for a quantum protocol that evades these assumptions and thus accomplishes unconditionally secure quantum bit commitment. If successful, this will be a major contribution to the field, not only for the practical applications of a bit commitment scheme but also for our understanding of the limits of quantum cryptography and quantum information, changing our perspective of what can or can not be done with quantum systems.

  • "Are we there yet?" | Colóquio DFMA

    Data: 
    terça-feira, 16 Maio, 2023 - 17:00 até 18:00
    Palestrante: 
    Prof. Dr. Oscar Eboli
    Resumo: 


    Resumo: The standard model (SM) passed with flying colors all the tests it has been subjected to. More than a decade ago the Cern Large Hadron Collider (LHC) started probing a new energy scale, leading to the discovery of the last SM building block, the Higgs boson. However, the SM is not the final theory since it leaves many questions answered. The LHC has been searching for signals of extensions of the SM. Let's analyze the present results and answer the question whether we are there yet!

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