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From: HUFNAGEL Marco <marco.hufnagel@ulb.be> Subject: JC/Seminar tomorrow by Fabrizio Rompineve Date: 8 February 2023 at 12:07:09 GMT+1 To: GRP_ULB_PhysTh <GRP_phys_th@ulb.be>, GRP_ULB_JC_Add <GRP_physth_jc@ulb.be>, "fabrizio.rompineve@cern.ch" <fabrizio.rompineve@cern.ch> Resent-From: <alberto.mariotti@vub.be>

Dear all,

it is a pleasure to announce that tomorrow -- instead of our usual JC -- we will have a special seminar by Fabrizio Rompineve from CERN, who is visiting VUB at the moment. The seminar will take place at 12:30 in the room 2NO.708 on the 7th floor of the NO building at ULB.

Fabrizio will talk about

QCD axion production in the early Universe

with the following abstract:

A population of relativistic QCD axions can be produced in the early Universe, via scatterings with Standard Model particles. This can be searched for in cosmological datasets, which therefore provide the opportunity to discover/constrain the QCD axion, independently of astrophysical and/or laboratory probes. In this talk, after reviewing the subject, I present an improved calculation of the relic abundance of such “hot” axions from scatterings with pions below the QCD crossover, as well as the resulting upper bound on the QCD axion mass. I then discuss the exciting outlook of upcoming cosmological surveys, which may probe otherwise unexplored regions of the QCD axion parameter space. I highlight the need of a non-perturbative calculation of axion production rates throughout the QCD crossover, to fully exploit the reach of such datasets.

I am very much looking forward to seeing you there!

Best, Marco

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