"Theory of Particle Physics and Cosmology" Seminar
2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024
2024-09-02 (Monday)
room 1.02, Pasteura 5 at 12:15 
Abdur Rehman (University of Alberta)Radiative B meson decays at the NNLO in QCD for the physical charm quark mass
The inclusive radiative decay of the B meson is known to provide strong constraints on new particles and their interactions. In 2015, some of the important NNLO QCD corrections were determined using interpolation in the charm quark mass. An uncertainty due to such an interpolation in the predicted branching ratio was estimated at the +-3% level, which should be compared to around +-5% uncertainty in the experimental world average. In my talk, I will present yet unpublished preliminary results for the considered correction at the physical charm quark mass, which removes the need for interpolation and the associated uncertainty. I will discuss basic steps of the calculation that required evaluation of four-loop propagator diagrams with unitarity cuts in the presence of two mass scales. Next, I will discuss the phenomenological impact of the considered correction on the predicted branching ratio in the SM, as well as the resulting bounds on the charged Higgs boson mass in the Two-Higgs-Doublet Model II.
2024-06-13 (Thursday)
room 1.01, Pasteura 5 at 12:15
(NICPB, Tallinn)Metric-Affine Gravity as an Effective Field Theory: Expectations vs. Reality
Carlo Marzo
Eliminating ghosts and tachyons from the linear spectrum has long been a crucial criterion for establishing viable theories within the metric-affine paradigm. However, this initial step must be complemented by additional measures to ensure the development of a predictive quantum model. In this talk, we explore the one-loop structure for some ghost and tachyon-free vector theories, highlighting the significance of structural constraints in their interactions, even in the absence of gauge symmetries. Despite the presence of soft-breaking terms, we demonstrate that achieving a predictive framework for vector models within the realm of effective field theory depends critically on adopting a gauge-like approach to their interactions. Our findings provide a deeper understanding of the theoretical and practical challenges in advancing metric-affine gravity as a credible effective field theory.
2024-06-06 (Thursday)
room 1.01, Pasteura 5 at 12:15
Ignacy Nałęcz (IFT UW)Naturalness-Guided Search for the Origins of Matter
Twin Higgs (TH) models elegantly solve the little hierarchy problem of the Standard Model (SM) by introducing a twin (or mirror) copy of the SM. In my talk, I will review the EW phase transition in TH, demonstrating that it could be first-order, with a suitable source of asymmetry between the SM and twin sectors. This main result will be illustrated with concrete mechanisms of twin symmetry breaking that lead to the natural first-order phase transition (FOPT). I will discuss how the FOPT in TH can be embedded in a broader framework that explains the observed baryon asymmetry. Additionally, I will comment on the potential emission of stochastic gravitational waves that often accompany cosmological FOPTs.
2024-05-23 (Thursday)
room 1.01, Pasteura 5 at 12:15
Matthias Steinhauser (KIT, Karlsruhe)Higgs Boson Pair Production at the LHC
In the coming years, Higgs boson pair production will play an important role in the physics program of the LHC. It is the most prominent channel to measure the self coupling of the Higgs boson. For this purpose, precise theoretical predictions are important. In this talk, the state-of-the-art theory predictions are summarized with an emphasis on recent developments both for NLO electroweak and NNLO QCD corrections.
2024-05-09 (Thursday)
room 1.01, Pasteura 5 at 12:15
Oskar Grocholski (DESY)Production of like-sign W pairs via double parton scattering
Double parton scattering (DPS) is a mechanism in which two hard parton-level processes take place in a single collision. This can yield important contributions to search processes at the LHC, a prominent channel being like-sign lepton pair production in proton-proton collision via the production of two W bosons of equal charge. Indeed, the CMS collaboration recently announced the first observation of DPS in this channel (Phys. Rev. Lett. 131, 091803). In my talk, I will discuss the theoretical description of double parton scattering at large transverse momenta and will present the predictions for the transverse momentum-dependent differential crosssection of like-sign W production in the discussed process.
2024-04-18 (Thursday)
room 1.01, Pasteura 5 at 12:15
Mateusz Zych (IFT UW)Bubble-Wall Velocity from Hydrodynamical Simulations
Terminal velocity reached by bubble walls in cosmological first-order phase transitions is an important parameter determining both primordial gravitational wave spectrum and the production of baryon asymmetry in models of electroweak baryogenesis. We developed a numerical code to study the real-time evolution of expanding bubbles and investigate how their walls reach stationary states. In this talk I discuss the recent results for local thermal equilibrium approximation, for which we confirmed that pure hydrodynamic backreaction can lead to steady-state expansion and that bubble-wall velocity in such case agrees very well with the analytical estimates. However, this is not the generic outcome. Instead, it is much more common to observe runaways, as the early-stage dynamics right after the nucleation allow the bubble walls to achieve supersonic velocities before the heated fluid shell in front of the bubble is formed. This effect is not captured by other methods of calculation of the bubble-wall velocity which assume stationary solutions to exist at all times and would have a crucial impact on cosmological observables.
2024-04-11 (Thursday)
room 1.01, Pasteura 5 at 12:15
George Zahariade (UJ)Quantum formation and annihilation of topological defects
In this talk I will describe how topological defect formation and annihilation can be understood in a fully quantum formalism, albeit in a regime where self-interactions are negligible. This corresponds to the so-called spinodal instability phase of a quantum phase transition. I will introduce the relevant tools in a scalar 1+1 dimensional flat spacetime model where Z_2 symmetry is spontaneously broken, which generically leads to the formation of kinks and antikinks. I will calculate the number density of such objects as a function of time and show that it scales as t^{-1/2} in the late time limit (and independently of the details of the phase transition). This decay can be interpreted in terms of mutual annihilation of kink-antikink pairs. I will also discuss the extension of these methods to the case of asymmetric initial conditions, expanding and higher dimensional background spacetimes, as well as higher co-dimension topological defects.
2024-04-04 (Thursday)
room 1.01, Pasteura 5 at 12:15
Andrzej Hryczuk (NCBJ)Towards robust predictions for thermal production of multicomponent dark matter
The process of thermal freeze-out of multicomponent dark matter (DM) can be significantly more complex and richer than the usual simple single-WIMP scenario. In this talk I will discuss some of the recent progress in understanding the impact of non-equilibrium effects on dark matter production, in particular in multicomponent scenarios. First I will present a framework for performing calculations beyond kinetic equilibrium and then discuss the latest results regarding impact of processes affecting the momentum distribution, like semi-annihilation, cannibalization, conversions and also DM self-scatterings. Finally, I will comment on the status of the state-of-the-art multicomponent dark matter relic density calculations.
2024-03-26 (Tuesday)
room 1.01, Pasteura 5 at 12:15
Sebastian Trojanowski (NCBJ)New insights on neutrino interactions with dark matter from CMB data
In the talk, I will revisit the possibility of using cosmological observations to constrain models that involve interactions between neutrinos and dark matter. I will show that small-scale measurements of the cosmic microwave background with a few percent accuracy are critical to uncovering unique signatures from models with small couplings that would require a much higher sensitivity at lower multipoles. In order to test this, the currently available high-multipole data have been analyzed, both independently and in combination with low-multipole CMB and Baryon Acoustic Oscillation measurements, finding a preference for a non-vanishing coupling at 68% CL. This aligns with other CMB-independent probes, such as Lyman-α. I will illustrate how this coupling could be accounted for in dark matter interactions with a sterile neutrino.
2024-03-21 (Thursday)
room 1.01, Pasteura 5 at 12:15
Joanna Sobczyk (University of Mainz)Nuclear ab initio studies for neutrino oscillations (and beyond)
We are entering an era of high-precision neutrino oscillation experiments (T2HK, DUNE), which potentially hold answers to some of the most exciting questions in particle physics. Their scientific program requires a precise knowledge of neutrino-nucleus interactions coming from fundamental nuclear studies. Ab-initio many-body theory has made great advances in the last years and is able to give relevant predictions for medium-mass nuclei important for neutrino experiments. In my talk I will give an overview of the recent progress that has been made in describing electroweak nuclear processes within the ab-initio coupled-cluster framework. These techniques open the door to obtaining nuclear responses (and consequently cross-sections) for medium-mass nuclei starting from first principles.