"Theory of Particle Physics and Cosmology" Seminar
2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025
2025-03-06 (Thursday)
room 1.01, Pasteura 5 at 12:15 
Giovanni Grilli di Cortona (Gran Sasso)Atoms as electron accelerators
Resonant positron annihilation on atomic electrons is a powerful technique for searching for light new particles that couple to electrons. Precise estimates of production rates require a detailed characterisation of atomic electron momentum distributions. I will present a general method that leverages the Compton profile of the target material to accurately account for electron velocity effects in resonant annihilation cross-sections. Additionally, I will discuss the implications of this precise computation for new physics searches and explore how high Z atoms can effectively serve as electron accelerators, significantly extending the experimental mass reach. Finally, I will demonstrate that by harnessing the relativistic velocities of electrons in the inner atomic shells, a high-intensity 12 GeV positron beam — such as the one planned at JLab — can enable precise measurements of the hadronic cross section, from the two-pion threshold to a center-of-mass energy exceeding 1 GeV.
2025-02-27 (Thursday)
room 1.01, Pasteura 5 at 12:15
Bogumiła Świeżewska (IFT UW)Observable gravitational waves from the early Universe
The discovery of gravitational waves and the advent of space-borne detector LISA makes early Universe cosmology, in particular electroweak symmetry breaking, experimentally testable. In this talk, I will discuss supercooled phase transitions, associated with radiative symmetry breaking, which generically source strong gravitational-wave signal. I will cover a wide range of aspects from the construction of models with radiative symmetry breaking, their renormalisation, through the construction of high-temperature effective field theories needed for accurate treatment of thermal effects to the phenomenological predictions and the prospects of probing fundamental physics models via gravitational waves.
2025-01-23 (Thursday)
join us at 12:15
Viatcheslav Mukhanov (Ludwig Maximilian University, Munich)Gravitationally dominated instantons
We study the decay of the false vacuum in the regime where the quantum field theory analysis is not valid, since gravitational effects become important. This happens when the height of the barrier separating the false and the true vacuum is large, and it has implications for the instability of de Sitter, Minkowski and anti-de Sitter vacua. We carry out the calculations for a scalar field with a potential coupled to gravity, and work within the thin-wall approximation, where the bubble wall is thin compared to the size of the bubble. We show that the false de Sitter vacuum is unstable, independently of the height of the potential and the relative depth of the true vacuum compared to the false vacuum. The false Minkowski and anti-de Sitter vacua can be stable despite the existence of a lower energy true vacuum. However, when the relative depth of the true and false vacua exceeds a critical value, which depends on the potential of the false vacuum and the height of the barrier, then the false Minkowski and anti-de Sitter vacua become unstable. We calculate the probability for the decay of the false de Sitter, Minkowski and anti-de Sitter vacua, as a function of the parameters characterizing the field potential.
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2025-01-16 (Thursday)
room 1.01, Pasteura 5 at 12:15
Daniele Perri (IFT UW)Magnetic monopoles in cosmic magnetic fields: acceleration and constraints
Magnetic monopoles are intriguing hypothetical particles and inevitable predictions of theories of Grand Unification. They should be produced during phase transitions in the early universe, but mechanisms like the Schwinger effect in strong magnetic fields could also contribute to the monopole number density. I will show how we can infer additional bounds on the magnetic monopole flux from detecting intergalactic magnetic fields, and how even well-established limits, such as Parker bounds and limits from terrestrial experiments, strongly depend on the acceleration in cosmic magnetic fields. I will also discuss the implications of these bounds for minicharged monopoles and magnetic black holes as dark matter candidates. Finally, we apply our primordial bounds to monopoles produced by the primordial magnetic fields themselves through the Schwinger effect, deriving necessary conditions for the survival of the primordial fields.
2024-12-19 (Thursday)
join us at 12:15
Oleg Lebedev (Helsinki U.)Predictive freeze-in
Non-thermal dark matter models suffer from the ever-presentgravitational particle production background, which marspredictivity of the framework altogether. I will discuss a classof freeze-in dark matter models with a low reheating temperaturethat are free of such problems and are directly testable.
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2024-12-12 (Thursday)
room 1.01, Pasteura 5 at 12:15
Theodoros Papanikolaou (SSM & INFN Napoli)Primordial black holes and induced gravitational waves
Primordial black holes (PBHs) can generically form through the collapse of enhanced cosmological perturbations, constituting in some specific mass ranges a viable candidate for dark matter. Interestingly enough, the enhanced cosmological perturbations which collapse to form PBHs as well as the PBH energy density perturbations themselves can produce a stochastic gravitational-wave (GW) background induced by second-ordergravitational interactions, which can be detectable in GW observatories. In this talk, afterintroducing initially the motivation for the physics of PBHs and the associated to them GWsignals I will focus afterwards on the ultra-light PBH mass range and its induced GWsignatures through which one can probe the physics of the primordial Universe, theunderlying gravity theory testing as well fundamental high-energy physics theories.
2024-12-05 (Thursday)
room 1.01, Pasteura 5 at 12:15
Maxim Laletin (IFT UW)Revisited axion contribution to dark radiation using momentum-dependent evolution
Axions can be produced via the interactions in the thermal plasma of the early Universe and their contribution to dark radiation can modify the cosmological observables and constrain the axion couplings to SM particles. In my talk I am going to outline an approach to calculate the axion cosmological abundance that goes beyond the approximations widely used in the literature on the topic and demonstrate how it affects the bounds on axion couplings on the example of axion interactions with leptons.
2024-11-28 (Thursday)
join us at 12:15
Pedro Schwaller (University of Mainz)Gravitational wave probes of dark sectors
Gravitational waves offer a new window into the early and dark universe. I will review sources of gravitational waves that can be searched for with current and future GW experiments, discuss interpretations of the recent observation of a stochastic GW background with PTAs, and explore new ideas for GW searches at utra-high frequencies using microwave cavities.
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2024-11-21 (Thursday)
join us at 12:15
Kai Schmitz (Münster U.)Gravitational waves from low-scale cosmic strings
(on-line)
Cosmic strings are a common prediction in many grand unified theories and a promising source of stochastic gravitational waves (GWs) from the early Universe. If strings are produced at a comparatively low energy scale, v ≲ 10^9 GeV, their GW signal exhibits, as I will discuss in this talk, several novel features that are not present in the case of high-scale cosmic strings, including: (i) a sharp cutoff frequency f_cut in the GW spectrum from the fundamental oscillation mode on closed string loops and (ii) an oscillating pattern in the total GW spectrum from all oscillation modes whose local minima are located at integer multiples of f_cut. I will explain the physical origin of these features and illustrate how they can be leveraged to directly probe the discrete spectrum of oscillation modes on closed string loops with future GW observatories such as BBO and DECIGO.
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2024-11-14 (Thursday)