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Invisible's Journal Club

Past events

  • Date of the event: Tue, 16/12/2014 - 15:00
    Date: December 16th @ 15PM (CET)
    Title: Baryogenesis through Neutrino Oscillations: A Unified Perspective
    Presenter: Brian Shuve (Perimeter Institute)
    Abstract: The neutrino minimal Standard Model (nuMSM) is remarkable in its simplicity: with the addition of three sub-weak-scale sterile neutrinos to the Standard Model, the nuMSM can simultaneously resolve the questions of baryogenesis, dark matter, and neutrino masses. Focusing on baryogenesis, I give an overview of the dynamics of leptogenesis from sterile neutrino oscillations, showing that the sterile neutrinos in the minimal model are too sterile: their feeble interactions with Standard Model fields predict a baryon asymmetry that is too small unless model parameters are substantially tuned. I demonstrate that new leptonic interactions greatly enhance the predicted baryon asymmetry, eliminating the need for tuning, and giving concrete predictions for the LHC and other experiments. Other prospects for detecting the new states of the nuMSM will also be discussed.
  • Date of the event: Tue, 02/12/2014 - 15:00
    Date: December 2nd 2014 @ 15:00
    Title: Macro Dark Matter
    Presenter: David Jacobs (Case Western Reserve U.)
    Abstract: Dark matter is a vital component of the current best model of our universe, Lambda-CDM. There are leading candidates for what the dark matter could be (e.g. weakly-interacting massive particles, or axions), but no compelling observational or experimental evidence exists to support these particular candidates, nor any beyond-the-Standard-Model physics that might produce such candidates. This suggests that other dark matter candidates, including ones that might arise in the Standard Model, should receive increased attention. I will discuss the general class of dark matter candidates with characteristic masses and interaction cross-sections characterized in units of grams and square centimeters, respectively -- we refer to these macroscopic candidates as Macros. Such dark matter objects could potentially be assembled out of Standard Model particles (quarks and leptons) in the early universe. I will discuss the earth-based, astrophysical, and cosmological observations used to constrain part of the Macro parameter space. Large regions remain unconstrained, however, most notably for nuclear-dense objects with masses in the range between about 50 - 10^17 and 10^20 - 10^24 grams.
  • Date of the event: Tue, 25/11/2014 - 15:00
    Date: November 25th 2014 @ 15:00 (CET)
    Title: Planck dust polarization measurements, and impact on the BICEP2 gravitational waves result
    Presenter: F. Piacentini (U. Rome I)
    Abstract: In March 2014, the BICEP2 team sensationally claimed the first detection of primordial gravitational waves imprinted in the polarization of the Cosmic Microwave Background. It has soon been noted how that result lacked in control of possible contamination from inter-stellar dust in our Galaxy, due to absence of data. The Planck space telescope is now presenting the missing data: a map of the polarization generated by galactic dust, obtained by its unique 353 GHz polarization sensitive channel. This map is used to calculate the dust polarization angular power spectra. We show that even in the faintest dust-emitting regions there are no “clean” windows in the sky where primordial CMB B-mode polarization measurements could be made without subtraction of foreground emission. In particular, Planck team is measuring a possible contamination of the BICEP2 result as large as their detection. In this seminar, I present the last Planck result, and the status of this rapidly evolving research activity.
  • Date of the event: Tue, 11/11/2014 - 15:00
    Date: November 11th 2014 @ 15:00 (CET)
    Title: Re-Examining Astrophysical Constraints on the Dark Matter Model
    Presenter: Alyson Brooks (Rutgers University)
    Abstract: The cosmological model based on cold dark matter (CDM) and dark energy has been hugely successful in describing the observed evolution and large scale structure of our Universe.  However, at small scales (in the smallest galaxies and at the centers of larger galaxies), a number of observations seem to conflict with the predictions CDM cosmology, leading to recent interest in Warm Dark Matter (WDM) and Self-Interacting Dark Matter (SIDM) models. These small scales, though, are also regions dominated by the influence of baryons. I will present results from high resolution cosmological galaxy simulations that include both baryons and dark matter to show that baryonic physics can significantly alter the dark matter structure and substructure of galaxies, revolutionizing our expectations for galaxy structure and influencing our interpretation of the Dark Matter model.
  • Date of the event: Tue, 28/10/2014 - 15:00
    Date: October 28th 2014 @ 15:00 (CET)
    Title: Not-So-Sterile Neutrinos
    Presenter: Basudeb Dasgupta (ICTP Trieste)
    Abstract: We show that sterile neutrinos, as motivated by several short-baseline oscillation anomalies, can be consistent with cosmological constraints if they are charged under a hidden sector force mediated by a light boson. It is conceivable that the new gauge force also couples to dark matter, possibly ameliorating some of the small-scale structure problems associated with cold dark matter.
  • Date of the event: Tue, 14/10/2014 - 15:00

    Date and time: October 14th 2014 @ 15:00 (CET)

    Title: The 3.5 keV X-ray line saga

    Presenter: Stefano Profumo (UC Santa Cruz)

    Abstract: An X-ray line at an energy of 3.5 keV has been reported from several observations of galaxies and clusters of galaxies. The origin of the line might be related to the decay of dark matter, or to more complicated processes, possibly related to new physics, or more mundanely to atomic transitions. I will review the status of observations and of theoretical models, and outline future possible steps.

  • Date of the event: Tue, 24/06/2014 - 15:00

    Title:  Agravity

    Presenter:  Alberto Salvio (IFT-UAM)

    Abstract:  We will explore the possibility that the fundamental theory of nature does not contain any scale. This implies a renormalizable quantum gravity, which can be reinterpreted as a graviton minus an anti-graviton (agravity). We will show the super-Planckian renormalization group equations of gravity coupled to a generic matter sector. The Planck scale and a flat space can arise dynamically at quantum level provided that the quartic coupling of a scalar, which we call the Higgs of gravity, and its β function vanish at the Planck scale; for example, this is how the Higgs boson behaves for a Higgs mass Mh ≃ 125GeV and a top mass Mt ≃ 171GeV. We will also discuss the implementation of this general idea in specific models and discuss possible dark matter candidates. Within agravity, inflation is a generic phenomenon: the slow-roll parameters are given by the β-functions of the theory, and are small if couplings are perturbative. If the inflaton is identified with the Higgs of gravity the predictions for the scalar spectral index ns ≃0.967 and the tensor-to-scalar ratio r ≃ 0.13 arise. Furthermore, a small weak scale can be natural and is generated by agravity quantum corrections.

  • Date of the event: Tue, 10/06/2014 - 15:00

    Title: Thermal baryogenesis at low energies

    Presenter: Juan Racker (U. Valencia)

    Abstract: We will explain the problems and some solutions for having thermal baryogensis at low temperatures  (T<100 TeV).