SEMESTER 2024 - SUMMER




26.03.2024

Benjamin Knorr

Nordita, Stockholm University and KTH Royal Institute of Technology

Asymptotic Safety meets field redefinitions


Asymptotic Safety is an approach to quantum gravity that solely relies on quantum field theory - it posits that gravity can be quantised by a nonperturbative fixed point of its renormalisation group flow. This rather simple idea is complicated by the fact that in quantum field theory, field redefinitions can be performed without changing physical predictions, encoded for example in scattering amplitudes. As a consequence, only so-called essential couplings need to show such a fixed point - these are the combinations of couplings that are invariant under such redefinitions. In this talk, after a general introduction to Asymptotic Safety, I will discuss recent developments in how to treat the freedom of field redefinitions within nonperturbative renormalisation group flows. In particular, I will show how we can wield this freedom to simplify computations enormously so that more refined approximations can be investigated, consequently improving the accuracy of predictions.

Slides


09.04.2024

Rene Poncelet

Institute of Nuclear Physics PAN, Kraków

Precision phenomenology with heavy-flavour jets at the LHC


Jets are a staple of the research program at high-energy hadron colliders. As suitably defined sets of highly-energetic particles, they constitute a useful tool to establish a link between Quantum Chromodynamics (QCD) of quarks and gluons and the realm of actual strongly-interacting particles, baryons and mesons. Besides the general importance of jets for collider phenomenology, there is a growing interest in studying jet substructure in order to disentangle various QCD effects governing jet dynamics. Final states with jets identified to originate from heavy quarks play a vital role, for example, in understanding the process of heavy-quark fragmentation and the contents of protons at high energy. In this talk I will discuss fixed-order NNLO QCD phenomenology, comparisons thereof to data and infrared-safe flavoured jet algorithms, a non-trivial ingredient in defining useful collider observables.

Slides


23.04.2024

Nicolas Bernal

New York University Abu Dhabi

New Avenues For Dark Matter Production


The existence of nonbaryonic dark matter (DM) in the Universe is compelling, as suggested by astrophysical and cosmological observations. The most commonly assumed production mechanism for DM in the early universe corresponds to the weakly interacting massive particle (WIMP) paradigm, in which DM has mass and couplings at the electroweak scale. However, the current null experimental results and severe constraints on the natural parameter space are forcing us to search beyond the standard WIMP paradigm. In this talk, I will review alternative DM production mechanisms in the early universe, both thermal and non-thermal, like the FIMP and the SIMP paradigms. The possible impact of alternative non-standard cosmological scenarios will also be analyzed. Finally, experimental avenues for DM detection are discussed

Slides


07.05.2024

Oliver Newton

Center for Theoretical Physics PAN, Warsaw

Constraints on the properties of νMSM dark matter using the satellite galaxies of the Milky Way


Low-mass galaxies are powerful tools with which to investigate departures from the standard cosmological paradigm in models that suppress the abundance of small dark matter substructures. One of the simplest metrics that can be used to compare different models is the abundance of satellite galaxies in the Milky Way. Viable dark matter models must produce enough substructure to host the observed number of Galactic satellites. Here, we scrutinize the predictions of the neutrino Minimal Standard Model (νMSM), a well-motivated extension of the Standard Model of particle physics in which the production of sterile neutrino dark matter is resonantly enhanced by a lepton asymmetry in the primordial plasma. This process enables the model to evade current constraints associated with non-resonantly produced dark matter. Independently of assumptions about galaxy formation physics and the Milky Way halo mass we rule out, with at least 95 per cent confidence, all parametrizations of the νMSM with Ms < 1 keV. Incorporating physically motivated prescriptions of baryonic processes and modelling the effects of reionization strengthens our constraints and we exclude all models with Ms < 3 keV. Our fiducial constraints do not rule out the putative 3.55 keV X-ray line, if it is indeed produced by the decay of a sterile neutrino. In contrast with other work, we find that the constraints from satellite counts are substantially weaker than those reported from X-ray non-detections.

21.05.2024

Jaime Hoefken Zink

Università di Bologna

The dark in the white: Dark sectors in white dwarf cooling


White dwarfs constitute a fruitful environment to search for dark sectors, i.e. BSM physics. Their extreme conditions due to the high densities and temperatures in their cores together with the seemingly agreement in how to model them make them an ideal scenario for testing BSM models. Two specific models with dark photons will be shown: the Three portal model and Lμ - Lτ, both of which generate an extra contribution for the cooling of hot white dwarfs. For the latter, a first ever computed full calculation will be presented and discussed. Constraints found on the models will be also shown.