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Invisible's Journal Club

Past events

  • Date of the event: Tue, 15/03/2016 - 15:00
    Date: 15 March 2016
    Presenter:  Sovan Chakraborty (MPP Munich)
    Title: Self-induced flavor conversion of supernova neutrinos
    Abstract: Neutrino flavor evolution in dense media such as core-collapse supernovae is dominated by neutrino–neutrino refraction, producing ``self-induced flavor conversion,” i.e., shuffling of flavor among momentum modes. This effect is driven by collective run-away modes of the coupled ``flavor oscillators” and can spontaneously break the initial symmetries (such as axial symmetry, homogeneity, isotropy, and even stationarity) of the neutrino flux and in particular can produce small-scale features. Another interesting feature of these unstable modes are that the growth rates can be of the order of the neutrino–neutrino interaction energy instead of the much smaller vacuum oscillation frequency: implying that the self-induced flavor conversion does not always require neutrino masses. However, the unavoidable ``multi-angle matter effect'' may shift these small-scale instabilities into regions of matter and neutrino density which are not encountered on the way out from a SN. We illustrate these newly found phenomena in terms of simple toy models, what happens in realistic astrophysical scenarios is remains to be understood.
  • Date of the event: Tue, 01/03/2016 - 15:00
    Date: 1 March 2016
    Presenter:  Cecilia Lunardini (Arizona S U)
    Title: Star formation and high energy neutrinos at IceCube: a correlation? 
    Abstract: The IceCube Neutrino Observatory has provided the first map of the high energy (~ 0.01 -- 1 PeV) sky in neutrinos. Since neutrinos propagate undeflected, their arrival direction is an important identifier for sources of high energy particle acceleration. Reconstructed arrival directions are consistent with an extragalactic origin, with possibly a galactic component, of the neutrino flux. We present a statistical analysis of positional coincidences of the IceCube neutrinos with known astrophysical objects from several catalogs. For the brightest gamma-ray emitting blazars and for Seyfert galaxies, the number of coincidences is consistent with the random, or "null", distribution. Instead, when considering starburst galaxies with the highest flux in gamma-rays and infrared radiation, up to n = 8 coincidences are found, representing an excess over the ~4 predicted for the null distribution. The probability that this excess is realized in the null case, the p-value, is p = 0.042. This value falls to p = 0.003 for a set of gamma-ray-detected starburst galaxies and star-forming regions in the galactic neighborhood. Therefore, it is possible that these might account for a subset of IceCube neutrinos. The physical plausibility of such correlation is discussed briefly.
  • Date of the event: Tue, 23/02/2016 - 15:00
    Date: 23 February 2016
    Speaker: Luca Merlo (IFT-UAM)
    Title: Determining the physical impact of operators in effective field theories
    Abstract: I will discuss a counting rule that allows to order effective operators in terms of their physical impact. It applies to weakly and strongly coupled theories. As title of examples, the Standard Model Effective Field Theory and the Higgs Effective Field Theory will be considered and compared. Some interesting observables will be discussed providing examples of analysis that could shed light on the Higgs nature.
  • Date of the event: Tue, 19/01/2016 - 15:00

    Speaker: Giovanni Villadoro (ICPT)

    Title: The QCD axion, precisely

    Abstract: The QCD axion is probably the most robust solution to the strong CP problem and a natural dark matter candidate. While its properties, such as the mass and the couplings, are mostly determined by non-perturbative QCD effects I will present recent computations demonstrating that they can be safely extracted with percent accuracy, which is important for the theory interpretation of experimental results. I will also present some recent lattice QCD results highlighting a large departure from the usual instanton estimates and changing substantially the prediction for the axion relic abundance.

  • Date of the event: Tue, 12/01/2016 - 15:00
    Date: 12 January 2016 15:00 CET
    Title: Signals of a 2 TeV W-prime boson
    Presenter: Bogdan Dobrescu (FNAL)
    Abstract: The LHC data analyzed by the CMS and ATLAS Collaborations includes some hints for the existence of a W-prime boson of mass near 2 TeV. I will show that an SU(2) x SU(2) x U(1) gauge theory can explain these hints by providing the correct cross sections in several channels. The CMS eejj events, in particular, are consistent with an interesting flavor symmetry in the leptonic sector. 
  • Date of the event: Tue, 24/11/2015 - 15:00

    Date:24 November 2015 15:00 CET

    Title: Dibosons at the LHC - Symmetry Restored?

    Presenter: Joachim Kopp (Mainz U)

    Abstract: "The ATLAS collaboration has recently reported a mild hint for a new resonance at around 2 TeV decaying to WW, WZ, and/or ZZ pairs. Intriguingly, similar though less significant excesses are also seen in other final states, for instance H+W and dijets. In this talk, we report results of a model-independent fit to all relevant ATLAS and CMS searches in this context. We discuss possible theoretical interpretations of the tentative signals, focusing in particular on left-right symmetric models with gauge group SU(2)_L x SU(2)_R x U(1), where the right-handed partner of the W can explain the excesses. We also comment on possible connections of such a scenario to the dark matter in the Universe."

  • Date of the event: Tue, 10/11/2015 - 15:00
    Date: 10 November 2015 15PM (CET)
    Title: Cutoff in the Lyman-alpha forest power spectrum: warm IGM or warm dark matter?
    Presenter: Antonella Garzilli, Lorentz Institute, Leiden University
    Abstract: We review how the Lyman-alpha forest, one of the observables of the intergalactic medium, can be used to constraint the warmness of dark matter. We re-analyse high redshift and high resolution Lyman-alpha forest spectra from (Viel et al 2013) seeking to constrain properties of warm dark matter particles.  Compared to the previous work we consider a wider range on thermal histories of the intergalactic medium and find that both warm and cold dark matter models can explain the cut-off observed in the flux power spectra of high-resolution observations equally well.  This implies, however, very different thermal histories and underlying re-ionisation models. We discuss the implication of our new constraints of warm dark matter on realistic sterile neutrino models. We illustrate a new method to constrain the intergalactic medium thermal history, and we discuss how to remove the degeneracy between temperature and the warmness of dark matter.
  • Date of the event: Tue, 27/10/2015 - 15:00

    Date: 27 October 2015 15PM (CET)

    Title: Neutrino Masses and Mixing Angles: a tribute to Guido Altarelli

    Presenter: Ferruccio Feruglio (Padova U.)

    Abstract: I present a personal recollection of Guido Altarelli, focused on his contribution to the problem of neutrino masses and mixing angles. I recap the main ideas in model building, following an historical path, from the discovery of neutrino oscillations in 1998 to the solution of the solar neutrino problem and the measurement of the reactor angle. I illustrate how the subject evolved from the study of neutrino mass textures to the implications of continuous-abelian and discrete-nonabelian flavour symmetries, emphasising the point of view of Guido on the subject. I conclude by commenting the present status of the field.