"Theory of Particle Physics and Cosmology" Seminar
2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2023-11-23 (Thursday)
room 1.01, Pasteura 5 at 12:15 
Peter Matak (Comenius University, Bratislava)Diagrammar for the early universe
The CP asymmetries necessary for explaining the observed baryon asymmetry of the universe require irreducible complex phases in couplings and imaginary kinematics from loop diagrams. Furthermore, they must obey the so-called CPT and unitarity constraints - for a particular initial state, summing the asymmetries over all possible final states yields zero. In this seminar, we use unitarity and holomorphic cutting rules to reformulate these constraints diagrammatically in any perturbative order. As a result, the number of terms to be evaluated is reduced and tracking the asymmetry cancellations is simplified. After briefly commenting on handling the s- and t-channel singularities within the same framework, we approach the inclusion of thermal corrections in the Boltzmann equation. Studying the density matrix evolution, we argue that, surprisingly, thermal effects enter via modified cutting rules while still using zero-temperature Feynman rules for the matrix elements.
slides: https://mycloud.fuw.edu.pl/index.php/s/6ZdkfYCkZcXTfwA
2023-11-16 (Thursday)
room 1.01, Pasteura 5 at 12:15
Krzysztof Rolbiecki (IFT UW)LHC searches beyond simplified models
In this talk I will discuss a concept of simplified models which is used for interpretation of searches for new physics at the LHC. I will discuss limitations of this approach and the need for reinterpretation of results. Then I will introduce several computer programs that are used to reinterpret ATLAS and CMS searches beyond Standard Model physics. Finally I will show recent examples of reinterpretation efforts from the theory community.
slides: https://mycloud.fuw.edu.pl/index.php/s/QW5HbCA4eYRyjZo
2023-11-09 (Thursday)
room 1.01, Pasteura 5 at 12:15
Ayuki Kamada (IFT UW)Self-interacting dark matter: strong or resonant interaction
According to the lack of signals in conventional dark-matter (DM) searches, gravitational probes have been attracting growing interests. Structure formation of the Universe is also a unique way to examine the possibility that dark matter has a sizable self-interaction (SIDM). Observations of DM halos in a wide range of masses, from ultra-faint dwarf galaxies to galaxy clusters, may indicate that the SIDM cross section strongly depends on the velocity. In this talk, after reviewing the current status of SIDM, we introduce two interesting possibilities, which appear to be compatible with current observations: self-interaction is very strong or resonant. We discuss the evolution of these DM halos and possible observational signatures.
slides: https://mycloud.fuw.edu.pl/index.php/s/c9eN4i4ZPwDYAAo
2023-10-26 (Thursday)
room 1.01, Pasteura 5 at 12:15
Bogumiła Świeżewska (IFT UW)Supercooled phase transitions and how to find them
This talk will discuss various aspects of supercooled phase transitions in the early Universe. A working example will be a model with classical scale invariance. I will highlight special features of supercooled transitions and show the predictions for the resulting gravitational-wave signals. Moreover, I will mention the interplay with the dark matter abundance. Subsequently, I will reverse the problem and discuss what we can learn about the underlying model if a signal characteristic of a supercooled phase transition is observed. Finally, I will examine the reliability of presented results and sketch ways to improve the accuracy of theoretical predictions.
slides: https://mycloud.fuw.edu.pl/index.php/s/z9nWmL5EK7kqdsY
2023-10-19 (Thursday)
room 1.01, Pasteura 5 at 12:15
Anish Ghoshal (IFT UW)Testing high-scale and weakly coupled BSM via CMB, gravitational waves and non-Gaussianity
Beyond Standard Model (BSM) physics addresses puzzles like neutrino mass generation mechanism, dark matter, matter-antimatter asymmetry and the strong CP problem, etc.. Current severe constraints from LHC and dark matter experiments point towards BSM that is either (i) weakly coupled to the SM or (ii) its energy scale is beyond the reach of terrestrial experiments. Faced with this challenge of testing such BSM we try to show that cosmological observables like the inflationary spectral indices, detection of primordial gravitational waves, primordial blackholes and non-Gaussianity provide sometimes an alternate avenue and sometime complementary avenues to test BSM theories. We overview such attempts and in particular we show scenarios involving Higgs-portal dark matter, baryogengesis via leptogenesis and axion physics in early universe that may lead to testable predictions for such observables to complement the laboratory observables.
slides: https://mycloud.fuw.edu.pl/index.php/s/8qiCMDywLwqeNbX
2023-10-12 (Thursday)
room 1.01, Pasteura 5 at 12:15
Kamila Kowalska (NCBJ)Naturally small neutrino mass from trans-Planckian asymptotic safety
There is growing theoretical evidence for the existence of an interactive UV fixed point in the renormalization group flow of the dimensionless couplings of the gravitational effective action. In the Standard Model and/or in models of New Physics embedded in the framework of trans-Planckian asymptotic safety, the presence of such a fixed point imposes Planck-scale boundary conditions on the gauge, Yukawa and scalar couplings. The ensuing fixed-point analysis often allows one to derive specific predictions for the IR phenomenology. Interestingly, it can also lead to the dynamical generation of arbitrarily small quantities, like for example the Yukawa couplings of Dirac neutrinos.In my talk I will briefly review the methods of the Functional Renormalization Group and the arguments which support the existence of a trans-Planckian fixed point of the gravitational action. I will then demonstrate how minuscule Yukawa couplings can be dynamically generated in this framework, both in the Standard Model with right-handed neutrinos and in its simple extension, the gauged B-L model. Finally, I will discuss possible phenomenological signatures of this scenario, in particular in the detection of gravitational waves from first-order phase transitions.
slides: https://mycloud.fuw.edu.pl/index.php/s/R27HNxRSzqkB8yN
2023-10-05 (Thursday)
room 1.01, Pasteura 5 at 12:15
Agnieszka Pollo (NCBJ & UJ)Evolving (baryonic) galaxies as tracers of (dark) cosmic web
Galaxies are known to be good but biased tracers of the underlying dark matter field. This bias is driven mainly by the history of hierarchical clustering and galaxy/halo assembly history but is also affected by other factors regulating galaxy evolution, usually environment-dependent. Moreover, the global picture is easily blurred by observational biases unavoidably present in the data. This combination complicates modeling the relations between galaxy physical properties and the underlying dark cosmic web. At the same time, all cosmological tests are necessarily based on baryonic tracers. Thus, using galaxies for tests of cosmological models relies on our understanding of the relations between a galaxy, its DM halo, its large-scale environment, their co-evolution, and observational biases in the data we use. In my talk, I will present briefly these dependencies between galaxy evolution and their environment and challenges, I will illustrate them with recent results from our group, and discuss the prospects – and challenges – arising with (very) near-future large cosmological surveys.
slides: https://mycloud.fuw.edu.pl/index.php/s/qkfX59Ct3ctwn9B