"Theory of Particle Physics and Cosmology" Seminar
2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024
2021-11-04 (Thursday)
room 1.01, Pasteura 5 at 12:15 
Marco Merchand and Mateusz Zych (IFT UW)Electroweak bubble wall expansion: gravitational waves and baryogenesis in Standard Model-like thermal plasma
According to the Higgs mechanism, violation of the electroweak symmetry is the reason particles we observe have non-zero masses. In the early universe thermal corrections restore this symmetry and we investigate the dynamics of its breaking. We focus on models predicting a first order phase transition proceeding through nucleation of bubbles. Such transitions are known to be able to facilitate production of the observed baryon asymmetry through electroweak baryogenesis as well as leaving a gravitational wave signal which will be one of the prime targets of upcoming GW experiments.We find that only weak transitions can result in slow expansion of the symmetry breaking bubbles for which we can test baryogenesis. For stronger transitions we never find the plasma is able to slow down the wall sufficiently to predict successful baryogenesis as the fluid approximation we employ breaks down. We find the weak transitions typically produce GW signals too weak to be observed in LISA which leads us to conclude that visible signals are likely to only be produced in strong transitions with highly relativistic wall velocities thus despite progress the tension between baryogenensis and strong GW signal remains. Finally, we also provide a simple analytical approximation for the wall velocity which only requires calculation of the strength and temperature of the transition and works reasonably well in all models tested.
slides: https://mycloud.fuw.edu.pl/index.php/s/5EfkZpMqWDJo6AK
2021-10-28 (Thursday)
join us at 12:15
Monica Pepe Altarelli (CERN)Review of recent results on rare decays and tests of Lepton Flavour Universality at LHCb
I will review recent results from LHCb with emphasis on recent precise measurements of rare decays and tests of Lepton Flavour Universality (LFU) at LHCb. Any violation of LFU would be a clear sign of physics beyond the SM. I will mainly focus on flavour-changing b → sll transitions, which are exceptionally sensitive to NP effects and in particular to NP particles that are too massive to be directly produced at present colliders. These particles can appear as virtual contributions that may induce significant effects on branching fractions and angular observables. In the last few years, hints of LFU violation have been observed, mainly by LHCb, in both loop-level b → sll and tree-level b → clν transitions. These measurements, combined with the tensions observed in angular observables and branching fractions of rare semileptonic b decays, have generated considerable interest in the community and, if confirmed, open up interesting prospects for the future.
slides: https://mycloud.fuw.edu.pl/index.php/s/QfkPw7Kw2EzeMzb
2021-10-21 (Thursday)
room 1.01, Pasteura 5 at 12:15
Anish Ghoshal (IFT UW)Dynamical Generation of Dark Matter and Electroweak Scales
The Standard Model (SM) of particle physics suffers from the hierarchy problem which can be ameliorated if all the scales that we observe in nature are considered not to be fundamental but generated dynamically in nature. As examples, we will discuss freeze-out and freeze-in production of vector dark matter (DM) in a classically scale invariant theory, where the Standard Model (SM) is augmented with an extended gauge symmetries that are spontaneously broken due to the non-zero vacuum expectation value (VEV) of a scalar. Generating the SM Higgs mass at 1-loop level, it leaves only two parameters in the dark sector, namely, the DM mass mX and the gauge coupling gX as independent. For freeze-in, which require very feeble coupling to satisfy the relic, the scenario is testable in several light dark sector searches (e.g., in DUNE and in FASER-II) as well as direct detection probes in a complementary manner courtesy to the underlying scale invariance of the theory.
slides: https://mycloud.fuw.edu.pl/index.php/s/58K9ZRWYYQyW8kw
2021-10-14 (Thursday)
join us at 12:15
Nazila Mahmoudi (Lyon University and CERN)New Physics Implications and prospects of LHCb flavour anomalies
We present new physics implications of LHCb measurements of bsll observables within a model-independent approach and make projections for future measurements that indicate that LHCb will have the potential to discover lepton non-universality with the Run 3 data in a single observable. Moreover, we present global fits of rare B-decays within multidimensional fits involving up to all the relevant 20 Wilson coefficients and compare different scenarios via likelihood ratio tests, applying Wilks’ theorem.
slides: https://mycloud.fuw.edu.pl/index.php/s/2JWTkJp4NHiXyGG
2021-10-07 (Thursday)
join us at 12:15
Monica Pepe Altarelli (CERN)Review of recent results on rare decays and tests of Lepton Flavour Universality at LHCb
I will review recent results from LHCb with emphasis on recent precise measurements of rare decays and tests of Lepton Flavour Universality (LFU) at LHCb. Any violation of LFU would be a clear sign of physics beyond the SM. I will mainly focus on flavour-changing b → sll transitions, which are exceptionally sensitive to NP effects and in particular to NP particles that are too massive to be directly produced at present colliders. These particles can appear as virtual contributions that may induce significant effects on branching fractions and angular observables. In the last few years, hints of LFU violation have been observed, mainly by LHCb, in both loop-level b → sll and tree-level b → clν transitions. These measurements, combined with the tensions observed in angular observables and branching fractions of rare semileptonic b decays, have generated considerable interest in the community and, if confirmed, open up interesting prospects for the future.