Wydział Fizyki UW > Badania > Seminaria i konwersatoria > Seminarium "Teoria cząstek elementarnych i kosmologia"

Seminarium "Teoria cząstek elementarnych i kosmologia"

2017/2018 | 2018/2019 | 2019/2020 | 2020/2021 | 2021/2022 | 2022/2023 | 2023/2024 | 2024/2025

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Tom Zlosnik (University of Gdańsk)

Removing spurious degrees of freedom from EFT of gravity

In the effective field theory approach to gravity, the Lagrangian density for general relativity is supplemented by generally covariant terms of higher order in the Riemann tensor and its derivatives. At face value, these terms will result in higher derivative equations of motion and additional degrees of freedom beyond those of general relativity. This is seemingly at odds with the goal of effective field theory which is to encode ultraviolet corrections in terms of existing low energy degrees of freedom. An action-based procedure for the removal of spurious degrees of freedom is considered for the case of general relativity in the presence of such additional terms, resulting in an extension to general relativity that does not introduce new degrees of freedom in the gravitational sector.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Piotr Toczek (IFT UW)

The complicated story of Primordial Black Hole production in cosmological Phase Transitions

Among all the possible candidates for Dark Matter, one appealing example is a population of Primordial Black Holes, which could have been borne by various processes in the early stages of the Universe. In this talk, I will investigate the formation of such objects as the result of the collapse of energy density fluctuations originating from supercooled first-order phase transitions. I will present the results of a simplified approach, where the energy density fluctuations are evolved within the limit of flat FRW Universe. These results let us identify how the parameters of the phase transition, such as temperature and transition speed, influence the spectrum and total population of Primordial Black Holes. Additionally, I will show how energy density fluctuations modify the Gravitational Wave signals as the production of secondary Gravitational Waves is induced. Finally, we will discuss the latest results, where the full covariant formalism of cosmological perturbation is introduced and show how it impacts the production of Primordial Black Holes and Gravitational Waves.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Miguel Vanvlasselaer (Vrije Universiteit Brussel & The International Solvay Institutes)

Bubble wall dynamics from nonequilibrium quantum field theory

In this talk, we derive the coupled dynamics between the bubble wall and the plasma from first principles using nonequilibrium quantum field theory. The commonly used equation of motion of the bubble wall in the kinetic approach is shown to be incomplete. In the language of the two-particle-irreducible effective action, the conventional equation misses higher-loop terms generated by the condensate-particle type vertices (e.g.,~ φϕχ2, where φ is the background field describing the bubble wall, ϕ the corresponding particle excitation and χ another particle species in the plasma). From the missing terms, we identify an additional dissipative friction which is contributed by particle production processes from the condensate-particle type vertices. We also show how other transmission processes beyond the 1-to-1 elementary transmission studied in the literature for ultrarelativistic bubble walls, e.g., 1-to-1 mixing and 1-to-2 transition radiation, can be understood from the kinetic approach.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Mateusz Zych (IFT UW)

Bubble wall velocity from hydrodynamics

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. In this talk I discuss the recent results for local thermal equilibrium approximation for which, using hydrodynamic simulations, we have confirmed that pure hydrodynamic backreaction can lead to steady-state expansion. 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. In order to capture this effect, we generalized the analytical methods beyond the local thermal equilibrium and find a qualitative way to predict whether the runaway is physical, which has a crucial impact on cosmological observables.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Björn Garbrecht (TUM)

CP conservation in the strong interactions

We examine possible effects of the topological term in the QCD-Lagrangian. For the path integral in zero-temperature Euclidean space, topological quantization only emerges in the infinite-volume limit, so that it must be taken prior to summing over winding numbers. This procedure is consistent with the construction of the path-integral contour from steepest-descent flows. As a result, CP violation is absent from observables, in contrast to calculations that rely on singular deformations leading to an inequivalent integration contour with the opposite order of limits. We also address theta-vacua in temporal gauge, which in the conventional picture are not properly normalizable, in contradiction with the axioms of quantum mechanics. However, we show that the possible wave-functionals, given the canonical commutation relations and without introducing extra gauge constraints, are properly normalizable states that do not exhibit CP violation.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Philipp Schicho (University of Geneva)

Limits and limitations of perturbative approaches to cosmological phase transitions

Scale hierarchies are required to reliably describe the thermodynamics of cosmological first-order phase transitions using perturbation theory. At finite temperature, such a hierarchy is provided naturally. One can then use this hierarchy to construct a three-dimensional effective field theory (EFT) that systematically includes thermal resummations to all orders.Using this EFT setup, I discuss completing the perturbative program for equilibrium thermodynamics of cosmological first-order phase transitions by determining the finite-temperature effective potential of gauge-Higgs theories at their perturbative limit, reaching next-to-next-to-next-to-next-to-leading order (N4LO) [1].I then explore the limitations of thermal EFTs, discussing their regime of validity and the conditions under which thermally induced higher-dimensional operators become relevant for gravitational-wave predictions. [1] A. Ekstedt, P. Schicho, and T. V. I. Tenkanen, Cosmological phase transitions at three loops: The final verdict on perturbation theory, Phys. Rev. D 110, 096006 (2024), [2405.18349].

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Nicklas Ramberg (SISSA)

Bubble Nucleation and Gravitational Waves from Strongly Coupled QFT's

Gravitational waves (GWs) emitted during the first-order phase transitions (FOPTs) of strongly coupled quantum field theories (QFTs) present a significant challenge for accurate prediction due to the nature of the strong coupling. In this talk, we will demonstrate a method for predicting the GW spectra of strongly coupled QFTs by combining holography with lattice data from pure SU(N) Yang-Mills theory. We will explore how holography can be employed to construct an effective action and, with this action in hand, investigate bubble nucleation as a means of estimating the gravitational wave spectra. Finally, we will discuss the broader phenomenological implications of our findings.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 12:15

Tomasz Krajewski (IPPT PAN)

Hydrodynamic studies of accretion in Reissner-Nordström spacetime

Even though, naked singularities are perceived by many scientists only as strictly academic curiosities, solutions of the Einstein equation representing them are not hard to obtain. The well-known Reissner-Nordström (RN) metric is an example that can model black holes as well as naked singularities. It turns out that the RN metric is not only the solution of the Einstein equation coupled to the Maxwell electrodynamics, as it was obtained for the first time more than a century ago, but is also the solution in certain modified theories of gravity.In this talk we will go beyond well-studied accretion onto black holes described by the Kerr metric and investigate the analogous process in the background of the RN one. We will consider both regimes, i.e. when the charge parameter Q is smaller than the mass M of the black hole or when it is greater than M and the metric describes the naked singularity. We will discover new, exciting phenomena like repulsive gravity, levitating atmospheres and much more. Our findings may have applications to astrophysics of the active galactic nuclei (AGNs) with their powerful jets and outflows.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 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.

Zapraszamy do sali 1.01, ul. Pasteura 5 o godzinie 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.

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