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Institut d'Astrophysique et
de Géophysique (Bât. B5c)

Quartier Agora
Allée du 6 août, 19C
B-4000 Liège 1 (Sart-Tilman)
Belgique

Tel.: 04.366.9774
Fax: 04.366.9729

Seminars

Seminars are regularly held to enable department's researchers as well as external scientists to present the latest findings in their fields. You are most welcome to join us:

27/08/2019 :
16h00  
Clusters of primordial black holes
Konstantin Belotsky
28/08/2019 :
16h00  
The local positron flux: what do pulsars have to say about it?
Ruben Lopez-Coto
12/09/2019 :
16h00  
Configuration mixing of excited baryons in the large Nc limit of QCD
Cintia T. Willemyns
03/10/2019 :
16h00  
TBA
Gautier Mathys
11/10/2019 :
11h00  
TBA
Steve Ertel
Archives: 2019 - 2018 - 2017 - 2016 - 2015 - 2014 - 2013 - 2012 - 2011 - 2010
2009 - 2008 - 2007 - 2006 - 2005 - 2004 - 2003 - 2002 - 2001
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Next seminar Tuesday 27 august, 16h00 (13th Seminar 2019 - poster)
Attention: unusual day!
Clusters of primordial black holes
Konstantin Belotsky (NRNU MEPhI)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)


Primordial black holes (PBHs) are a well-established probe of new physics in the very early Universe. I am going to discuss the possibility of PBH agglomeration into clusters that may have several interesting observable features. The clusters can form due to the production of closed domain walls in the natural and hybrid inflation models whose subsequent evolution leads to PBH formation. Such model inherits all the advantages of uniformly distributed PBHs -- it can possibly explain the early formation of quasars and the rate of binary black hole mergers registered by LIGO/Virgo, these clusters can contribute to the reionization of the Universe. The model also potentially alleviates the existing constraints on the abundance of uniformly distributed PBH, thus allowing clusters of PBH to be a viable dark matter candidate. I am going to show that most of the existing constraints on uniform PBH density should be reconsidered in the case of PBH clustering.
Previous seminar Next seminar Wednesday 28 august, 16h00 (14th Seminar 2019 - poster)
The local positron flux: what do pulsars have to say about it?
Ruben Lopez-Coto (INFN Padova)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)


Pulsars and their associated nebulae are the most commonly invoked astrophysical sources to explain the highest energy local cosmic ray positrons. However, a recent measurement of particle propagation around nearby pulsars by HAWC combined with the latest measurement of the local cosmic all-electron spectrum up to 20 TeV by HESS seemed to exclude this possibility. I will show in this presentation the latest experimental results on the Very-High-Energy gamma-ray emission surrounding Geminga and PSR B0656+14 by HAWC and discuss their implications. I will also show that the new observational facts can be reconciled with a pulsar origin, even in the case of a low diffusion close to the Earth, if an undiscovered nearby pulsar is the sole contributor to the local electron spectrum at the highest energies. Furthermore, I will give the predicted characteristics of this pulsar and show that the existence of such a pulsar with the required properties is not unlikely taking into account the properties of the pulsar population.
Previous seminar Next seminar Thursday 12 september, 16h00 (15th Seminar 2019 - poster)
Configuration mixing of excited baryons in the large Nc limit of QCD
Cintia T. Willemyns (Nuclear and Subnuclear Physics Department, University of Mons)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)


The asymptotic freedom in QCD allows for accurate calculations at high energy using perturbation theory. At low energies, typical of hadronic systems, a perturbative approach using the coupling constant as the expansion parameter is not appropriate. Baryon spectroscopy has been essential for our understanding of QCD in the low-energy, strong-coupling regime. In this context, the quark model which is based on the spin-flavor group O(3)×SU(2Nf) has since a long time been a useful tool to analyze the spectrum and properties of excited baryons. This symmetry is not something that follows from the fundamental QCD theory. An analytic scheme to study the phenomenology of baryons and their excited states, whose connection with QCD is clearly stated, can be obtained by generalizing QCD from three colors and an SU(3) gauge group to Nc colors and an SU(Nc) gauge group. In this talk, I will present a complete analysis of the masses of the positive parity excited baryons in the quark model O(3)×SU(6) multiplets contained in the N=2 band in the large Nc limit. We find that the mixing of the spin-flavor states is much simpler than what is naively expected in the quark model. The obtained mass degeneracies and mixing pattern constitute a signature of the contracted spin-flavor symmetry for baryons in this limit.
Previous seminar Next seminar Thursday 03 october, 16h00 (16th Seminar 2019 - poster)
TBA
Gautier Mathys (ESO)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)



Coffee, tea and cookies will be served after the seminar...
Previous seminar Friday 11 october, 11h00 (17th Seminar 2019 - poster) 
TBA
Steve Ertel (Université d’Arizona.)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)
University of Liège > Faculty of Sciences > Department of Astrophysics, Geophysics and Oceanography : CoWebAGO, June 2009.