Colóquios

  • Cosmic Photons from Mass Splitting in the Dark Sector

    Data: 
    27/11/2018 - 11:00
    Palestrante: 
    Francesco D'Eramo (University of Padova)
    Resumo: 

    In this talk, I will present two dark matter frameworks where a mass splitting in the dark sector dramatically alters the expectations for indirect detection rates. In the first case, the presence of a quasi-degenerate metastable state, where the dark matter number is stored, allows for sub-GeV relics with large s-wave annihilation cross section and not excluded by CMB bounds. In the second case, dark matter particles inelastically up-scatter in the interstellar plasma to a quasi-degenerate heavier partner, whose subsequent decays generate X-ray lines with unique spectrum and morphology.

  • From the Largest Spectroscopic Galaxy Survey to the Lightest Neutrino Mass

    Data: 
    21/11/2018 - 11:00
    Palestrante: 
    Arthur Loureiro
    Resumo: 

    Since the late 90's we have known that neutrinos oscillate between their three leptonian flavours, which lead to the 2015 Nobel Prize conclusion that these particles are massive. However, particle physics experiments can only tell us about the mass difference between some neutrino species and, consequently, their minimum mass. The neutrino mass hierarchy and the maximum value for the sum of their masses are still unknown. Cosmology, on the other hand, is sensitive to different aspects of neutrino physics since the number of massive neutrino species and the total sum of neutrino masses influence the evolution and formation of structure in the Universe. In this talk, I will present how a spherical harmonic analysis of the Baryon Oscillation Spectroscopic Survey (BOSS) large-scale structure galaxy sample can help set constraints on the sum of neutrino masses, their mass hierarchy and the mass of the lightest neutrino family. When combining the BOSS sample with Cosmic Microwave Background data from the Planck Satellite, Big Bang Nucleosynthesis constraints, and the latest SNe Type Ia data from the Pantheon compilation, we are able to obtain reliable neutrino mass constraints using physically motivated prior models.

     

  • Spontaneous Momentum Dissipation and Coexistence of Phases in Holographic Horndeski Theory

    Data: 
    10/10/2018 - 11:00
    Palestrante: 
    Prof. Dr. Eleftherios Papantonopoulos
    Resumo: 

    We discuss the possible phases dual to the AdS hairy black holes in Horndeski theory. In the probe limit breaking the translational invariance, we study the conductivity and we find a non-trivial structure indicating a collective excitation of the charge carriers. Going beyond the probe limit, we investigate the spontaneous breaking of translational invariance near the critical temperature and discuss the stability of the theory. We consider the backreaction of the charged scalar field to the metric and we construct numerically the hairy black hole solution. To determine the dual phases of a hairy black hole, we compute the conductivity. When the wave number of the scalar field is zero, the DC conductivity is divergent due to the conservation of translational invariance. For nonzero wave parameter with finite DC conductivity, we find two phases in the dual theory. For low temperatures and for positive couplings, as the temperature is lower, the DC conductivity increases therefore the dual theory is in metal phase, while if the coupling is negative we have the opposite behavior and it is dual to an insulating phase. We argue that this behavior of the coupling of the scalar field to Einstein tensor can be attributed to its role as an impurity parameter in the dual theory.

    *Local: Sala Jayme Tiomno*

  • Harmonic high-order statistics in cosmology

    Data: 
    21/09/2018 - 11:00
    Palestrante: 
    Dr. Antonino Troja (ICTP-SAIFR)
    Resumo: 
    With the developing of precision cosmology, high-order statistics started to play a key role in the analysis of incoming data. Especially in the case of spherical distributed data, where harmonic statistics help to get tighter constraints on cosmological parameters. My work is focused on bispectrum and trispectrum, showing how it is possible to lift degeneracies and improve the cosmological results.
     
    Local: Sala Jayme Tiomno
  • Primordial Regular Black Holes and Dark Matter

    Data: 
    05/09/2018 - 11:00
    Palestrante: 
    Prof. Jose A. de Freitas Pacheco (Observatoire de la Côte d'Azur)
    Resumo: 

    Dark matter is an indispensable component to explain the large scale structure of the universe. However, some theoretical expectations are still in contradiction with observations as, for instance, the large number of predicted satellites, the central mass distribution of galaxies, the presence of massive galaxies and clusters at redshift z > 2. Moreover, LHC data do not indicate detection of supersymmetric particles, posing problems to the nature of dark matter. I will discuss an alternative scenario in which dark matter particles are primordial extreme regular black holes formed at the end of inflation, during the reheating era.

    Local: Sala Jayme Tyomno

     

  • Flavourful roads to New Physics

    Data: 
    27/08/2018 - 11:00
    Palestrante: 
    Dr. Rafael Silva Coutinho (University of Zurich)
    Resumo: 

    The family of decays mediated by b -> sl+l- transitions provide a rich laboratory to search for effects of physics beyond the Standard Model. In recent years LHCb has found hints of deviations from theoretical predictions both in the rates and angular distributions of such processes. In addition, hints of lepton flavour non-universality have been seen when comparing B+ -> K+ mu+mu- and B+ -> K+ e+e- decay rates, with the so-called RK ratio. Similar observables in different decays, such as RK* = BR(B0 -> K*0mu+mu-)/BR(B0->K*0e+e-), have recently become available and indicate the same anomalous pattern. In this talk, an overview of the latest results in this sector and further avenues to test the effectiveness of lepton flavour universality will be presented.

    Local: Sala Jayme Tiomno

  • Matrix Models for Zeta Functions

    Data: 
    30/07/2018 - 11:00
    Palestrante: 
    Prof. Debashis Ghoshal (School of Physical Sciences, Jawaharlal Nehru University, New Delhi, India)
    Resumo: 

    Riemann hypothesized that the zeta function ζ(s) has (non-trivial) zeroes only on the line Re(s) = 1/2 in the complex s-plane. Hilbert and Polya suggested that the position of these zeroes might be related to the spectrum of a `Hamiltonian'. It has been known for some time that the statistical properties of the eigenvalue distribution of an ensemble of random matrices resemble those of the zeroes of the zeta function. We construct a unitary matrix models (UMM) for the zeta function, however, our approach to the problem is `piecemeal'. That is, we consider each factor in the Euler product representation of the zeta function to get a UMM for each prime. This suggests a Hamiltonian (of the type proposed by Berry and Keating) from its phase space description. We attempt to combine this to get a matrix model for the full zeta function.

    Local: Sala Jayme Tiomno

  • Entanglement entropy production and the Kolmogorov-Sinai rate

    Data: 
    30/05/2018 - 11:00
    Palestrante: 
    Prof. Nelson de Oliveira Yokomizo (UFMG)
    Resumo: 

    The rate of entropy production in a classical dynamical system is characterized by the Kolmogorov-Sinai entropy rate given by the sum of all positive Lyapunov exponents of the system. I will present a quantum version of this result valid for bosonic systems with unstable quadratic Hamiltonians: the entanglement entropy of squeezed coherent states grows linearly for large times, with a rate determined by the Lyapunov exponents and the choice of the subsystem. I will discuss the application of this result to quantum field theory and its conjectured implications for the behaviour of chaotic quantum systems prepared in a semiclassical state.

    *Local: Sala Jayme Tyomno

  • Modelos Ferromagnéticos: transições de fase, campos decaindo e g-medidas

    Data: 
    23/05/2018 - 11:00
    Palestrante: 
    Prof. Rodrigo Bissacot (IME-USP)
    Resumo: 

    Descreverei, de maneira não técnica, resultados que obtive com diversos co-autores nos últimos anos, explorando a ideia de que modelos ferromagnéticos, quando na presença de campos externos, podem ter o comportamento do mesmo modelo com campo nulo ou com campo uniforme não-nulo, dependendo da velocidade com que este decai a zero. O exemplos são modelos de Ising na rede e em árvores, e, também, modelos de Dyson na rede unidimensional Z. Neste último caso, obtemos o primeiro exemplo de uma medida de Gibbs que não é uma g-medida.

    Local: Sala Jayme Tiomno

  • Ausência de transporte para sistemas discretos unidimensionais sob campos elétricos

    Data: 
    07/05/2018 - 11:00
    Palestrante: 
    Prof. César Rogério de Oliveira (UFScar)
    Resumo: 

    Discutir-se-á localização dinâmica para perturbações de operadores de Schrödinger discretos unidimensionais com campos elétricos uniformes. Os principais argumentos são baseados no processo iterativo KAM.

    Local: Sala Jayme Tiomno

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