Colóquios

  • Wavepackets on de Sitter spacetime: first step towards a Haag-Ruelle scattering theory

    Data: 
    21/11/2017 - 10:00
    Palestrante: 
    Dr. Marcus Brum, Instituto de Física da USP
    Resumo: 

    In this colloquium, we want to present the first steps of the formulation of a scattering theory on a curved spacetime, in the Haag-Ruelle approach. This approach determines the S-matrix without specifying a particular interaction, it is rather based on the asymptotic behaviour of massive solutions of the wave equation, which can be estimated with great generality. We will show the construction of wavepackets on de Sitter spacetime, whose masses are consistently defined from the structure of the Lorentz algebra, and estimate its asymptotic behaviour. Furthermore, we show that, in the limit as the de Sitter radius tends to infinity, the wavepackets tend to the wavepackets of Minkowski spacetime and the plane waves arising after contraction have support sharply located on the mass shell. We will also show how to construct (scalar) field operators from these wavepackets. Besides, we will argue that the equilibrium state is not a thermal state, thus avoiding known issues of scattering theory at finite temperatures, and we will discuss possible interpretations of the in- and out-states.

  • The phase diagram in T-muB-Nc space

    Data: 
    27/05/2014 - 11:00
    Palestrante: 
    Prof. Giorgio Torrieri (UNICAMP)
    Resumo: 

    I will discuss the phase structure of Yang-Mills matter at moderate temperature and chemical potential. Motivated by large Nc physics, I will argue that the non-perturbative structure of QCD can give rise to hitherto little explored phenomena, such as the coexistence of confinement with perturbative quark degrees of freedom. I will however show that this "quarkyonic phase" is defined by a percolation-type phase transition line which curves in "number of colors", as well as density and temperature. Given theoretical uncertainities in dealing with matter at this regime, therefore, a phenomenological and experimental investigation of matter at high chemical potential might be decisive to determine if the quarkyonic phase does in fact exist. I will conclude discussing possible experimental signatures of this new state of matter, concentrating on electromagnetic signals, as well as proposals for studying this matter using Gauge/Gravity duality.

  • Cosmological information and bias from lensing of point sources

    Data: 
    19/05/2014 - 11:00
    Palestrante: 
    Dr. Valerio Marra
    Resumo: 

    My seminar will be about cosmological gravitational lensing of point sources by matter structures along the line of sight. I will first introduce the sGL method, an approach to quickly compute the lensing PDF for point sources. I will then show various applications. When analyzing supernova datasets lensing is usually treated as a noise which changes the error budget and can bias the results (if selection effects are present). This is an important topic for accurate cosmology and I will show how sGL can contribute to it.  On the other hand, if a good modeling of SN lensing is available, one can invert the problem and transform noise into signal and I will show which cosmological information can be extracted from future SN surveys. Finally, I will discuss ongoing work on constraining the inner halo profile with strong lensing.

  • A Física da Consciência

    Data: 
    13/05/2014 - 11:00
    Palestrante: 
    Prof. Osvaldo Pessoa Jr. (USP)
    Resumo: 

    Uma grande revolução na neurociência cognitiva poderá ocorrer nas próximas décadas, transformando a concepção que temos de nós mesmos. É possível que o chamado “problema difícil” da consciência seja esclarecido, o que provavelmente  envolverá um novo estilo de se fazer ciência. Qual o papel que a abordagem das ciências físicas desempenhará nessas transformações? Neste seminário, discutirei em primeiro lugar os limites que a metodologia científica encontra no esclarecimento da natureza da consciência e da subjetividade, explorando o argumento filosófico conhecido como “o quarto de Mary”. A discussão ajudará a definir o que é uma explicação física do mundo, o que é o mundo “físico” e qual é a natureza das qualidades subjetivas (qualia). Em seguida, de uma perspectiva materialista, após apresentar algumas definições de “consciência” e o papel da seleção natural em sua evolução, nos lançaremos na questão de qual é a natureza física dos processos que são essenciais para a consciência. Exploraremos em especial uma tradição (Penfield, Bogen etc.) que considera que o cerne da consciência envolve processos subcorticais ocorrendo no tálamo.

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