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Weekly Seminars for December 2016 Print E-mail
Monday December 5th, 2016 - 4:00pm
ICRANet Pescara 
Piazza della Repubblica 10, 65122 - Pescara (Italy) 

ICRANet Seminars
Speaker: Wilmer Daniel Alfonso Pardo 
Institution: Institute of Physics, University of Antioquia, Medellín, Colombia
Title"Spectral analysis of the gravitational waves emitted by two interacting binary systems in an hierarchical arrangement." 
The study of (N > 2)-body systems as sources of gravitational waves (GWs), seems to be an interesting next step after the recent reported detections by LIGO. Firstly, because those systems can allow a wider use of this radiation in the newborn field of astronomy with GWs, and secondly, because the GWs they emit could bring us fundamental knowledge related with the wavelike behaviour of the gravitational radiation. To clarify this point, it is important to realize that when analyzing the spiral phase of a binary system in the common point-like, circular, and quadrupolar approximations, the GWs it emits have a well defined frequency with a value of twice the system’s orbital frequency. However, it is reasonable to think that in dense star environments, like star clusters, encounters of two binary systems could be possible and some of them could evolve as a closed 4-body system which stability depends on the hierarchical structure it develops. Assuming than the two binaries evolve in such a way that each center of mass orbits in a perturbed keplerian orbit, without any interchange between their components, the expected GW signal will have at least three frequencies that could change with time because of their correlated dynamics. In this work we are exploring the aforementioned situations and studying the relevance that it could have in the so called inverse problem, where from the GW spectrum it is expected to recognize the astrophysical information of the source. A review of these ideas and other perspectives to be explored will be presented during this talk.
Speaker: Alexander Gallego Cadavid
Institution: Institute of Physics, University of Antioquia, Medellín, Colombia
Title: "Effects of local features of the inflaton potential on the spectrum and bispectrum of primordial perturbations"

We study the effects of a class of features of the potential of slow-roll inflationary models corresponding to a step symmetrically dumped by an even power negative exponential factor, which we call local features. Local-type features differ from other branch-type features considered previously, because the potential is only affected in a limited range of the scalar field value, and they are symmetric with respect to the location of the feature. This type of feature only affects the spectrum and bispectrum in a narrow range of scales which leave the horizon during the time interval corresponding to the modification of the potential. On the contrary branch-type features have effects on all the perturbation modes leaving the horizon when the field value is within the interval de fining the branch, introducing for example differences in the power spectrum between large and small scale which are absent in the case of local-type features. The spectrum and bispectrum of primordial curvature perturbations are affected by oscillations around the scale k0 exiting the horizon at the time T0 corresponding to the feature. We also compute the effects of the features on the CMB temperature and polarization spectra, showing the effects of different choices of parameters.  
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