Semináre Katedry teoretickej fyziky - Peter Čišovský, Vladimír Kráľovič (31.5.2022)

v utorok 31.5.2022 o 14:00 a 14:30 hod. v miestnosti F2/125

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Prednášajúci: Peter Čišovský

Názov: Cosmological perturbations in universe with dark energy

Termín: 31.5.2022, 14:00 hod., miestnosť F2/125

Abstrakt:
Dark energy with pressure to energy density ratio $w=-1$, or close to $-1$, is an essential component of our universe, but its nature is still a matter of research. When cosmological perturbations are studied, perturbations of all components in the universe must be considered. However, it turns out that if the dark energy is described as a perfect fluid, then perturbations in it cannot be formed. Dark energy perturbations are then usually omitted. A prominent exception is cosmological inflation in which expansion of the universe is driven by matter with pressure to energy density ratio w not equal to but close to $-1$. Violation of the condition $w=-1$ is needed to avoid eternal inflation, and also leads to perturbations of the matter driving it. The goal is to study cosmological perturbations in models slightly different from the model with ideal fluid with $w=-1$, such as model with shear stress, or models combining simpler ones.

Prednášajúci: Vladimír Kráľovič

Názov: Infrared finiteness of the NLO corrections to leptogenesis

Termín: 31.5.2022, 14:30 hod., miestnosť F2/125

Abstrakt:
Infrared divergences appear in quantum theories involving massless particles and complicate evaluation of the reaction rates. Therefore, it is crucial to somehow remove these divergences from our calculations. In this thesis we explore how we can use the S-matrix unitarity constraints for the cancelation of infrared divergences. Then we will use this approach to evaluate some reaction rates for the type-I seesaw model. This model involves only one type of massive particles at the relevant energetic scale (the right-handed Majorana neutrinos) and all standard model particles are considered massless.

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