Colóquios

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.

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.

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".

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.