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# Astro&Theory Seminar

The seminar of the Astro & Theory Section takes place Thursdays (alternating with the Journal Club)  in E3-128   and on zoom, starting normally at 14.15. If you would like to suggest a seminar speaker or want to be added to the email list, please contact the organizer (Michael.Kachelriess@ntnu.no).

A list of seminars in the previous and the current years can be accessed in the sidebar;  the (planned) seminars in 2022 are

• 17.02., Marco Turchetta  (IFY, NTNU): Searches and characterisation of optical and X-ray pulsations from candidate millisecond pulsars
Abstract:   In recent years three transitional millisecond pulsars (tMSPs) have been identified, showing transitions between rotation and accretion-powered pulsar state. In 2016 the SiFAP2/TNG (INAF) optical photometer unveiled for the first time optical pulsations from one of these systems, PSR J1023 + 0038 (J1023). The issues in explaining this phenomenon in terms of emission fed by either rotation or accretion power have fostered the formulation of new models, in which both the two mechanisms conspire to yield the emission of optical pulsations. During this talk I will present the results obtained in my master thesis work, which was aimed to gain insight into the nature of these optical pulsations. At this purpose, I have performed periodicity searches in optical and X-ray band from five candidate tMSPs, all showing the same multi-wavelength emission features observed in both the two states of J1023.

• 21.02.,  Patrick Reichherzer (RUB Bochum):   !postponed!

• 10.03., Petter Taule (TU Munich): Non-linear structure formation in cosmologies with non-trivial time- and scale-dependence
Abstract: Mapping out the large-scale structure (LSS) of the Universe is one of the key advances driving precision cosmology. Current and near-future large-scale surveys offers the prospect of testing deviations of the LambdaCDM model, such as measuring the absolute neutrino mass scale or probing properties of dark energy or dark matter. Major efforts have been devoted to describing non-linear scales perturbatively, and in this talk I discuss a framework for computing loop corrections in cosmological perturbation theory for cosmologies with non-trivial time- and scale-dependence. I apply this framework to cosmologies with massive neutrinos taking neutrino perturbations beyond the linear level into account. Finally, I discuss the bispectrum in the context of the effective field theory of LSS, going to next-to-next-to-leading order in perturbation theory.
slides

• 17.03., Robert Plantey (NTNU): Renormalization group evolution analysis of the gauged Froggatt-Nielsen mechanism in 2HDMs
Abstract: There are many free parameters in the flavour sector of the Standard Model which exhibit hierarchies. From a theoretical point of view this situation, known as the flavour puzzle, is not satisfying and the Froggatt-Nielsen mechanism aims to partially address it. In this model, hierarchies in the flavour parameters can be removed at the cost of introducing a new scalar field and heavy vector-like fermions. In this talk, I will present my master thesis which focused on building a realistic, theoretically consistent 2-Higgs-doublet model equipped with the Froggatt-Nielsen mechanism.

• 23.03., Gabriela Barcenas Enrique (Universidad de Guanajuato; NTNU): Self-gravitating Scalar Field Dark Matter
Abstract: Diverse evidence has proved the existence of dark matter in the universe, with the arrival of accurate cosmological and astrophysical observations, some as part of the scientific community consider it the most interesting problem in modern physics. We are no able to discard the existence of new particles with properties that may look exotic in comparison with the particles that constitute all that we know as ordinary matter. The scalar field dark matter is a model that considers the existence of a scalar field, in which the principal parameter is a very small mass. This model has displayed consequences in the formation of cosmological structure. Furthermore, scalar field dark matter presents a solution to galactic scales. We review a particular configuration of self-gravitating scalar field dark matter with the aim of presenting a viable candidate to describe the behaviour of the galactic centre. We present an approach to test this configuration with recent observations from the closest stellar cluster to Sgr A*, moreover, we expect to find new constrictions for the exact quantity for the mass of the scalar field.
slides

• 30.03. Yan-Chuan Cai (University of Edinburgh, NTNU): Astrophysics and Cosmology with the Cosmic Web
Abstract:  On large scales of our observable Universe, the distribution of matter follows a web-like pattern, consisting of knots, filaments, sheets and voids. The cosmic-web is non-Gaussian, containing valuable information about astrophysics and cosmology. I will summarise recent research activities in trying to extract some of this information, and how we can use observations of the cosmic-web to tackle some of the major problems in cosmology.

• 07.04. Inga Strumke (AI Lab, NTNU): Introduction to machine learning - a guided tour with examples from particle physics
Abstract:  Inga will give us a crash course in machine learning, how it's done and which forms exist. She will take us through a a few examples from HEPP, demonstrating current applications and their challenges. Finally, the million dollar question of how to explain machine learning models - also referred to as the "black box problem" - is disseminated and an overview of the status of explainable AI (XAI) is given.  The talk is open for everybody, and intellectually available to anyone comfortable with arithmetic and the existence of the Higgs boson :-)

• 12.05.,  Patrick Reichherzer (RUB Bochum):  Influence of diffusive cosmic-ray transport on multimessenger observables
Abstract: Cosmic-ray transport in astrophysical environments is often dominated by diffusion in a magnetic field with a turbulent component. The diffusion properties of charged particles directly influence observable properties, such as the spectrum of cosmic rays and their secondaries produced in interactions. In many diffusion scenarios, the simplified assumption of fully resonant Kolmogorov diffusion in the quasi-linear limit results in a parallel diffusion coefficient D ~ E^(1/3). A quantitative investigation of the scattering regimes, however, shows that the diffusion coefficient tensor can deviate significantly from this behaviour. In this talk, the complex dependencies of charged particle diffusion on the turbulence level of the magnetic field are presented. Examples of how this affects observational signatures will be shown in the context of galaxies or the transient sky, i.e., flaring Blazars.

• 4.5. Karri Koljonen (IFY): Shocking news - a polarizing study of a tidal disruption event
Abstract: Supermassive black holes have been known to disrupt passing stars producing outbursts called tidal disruption events (TDEs) offering a unique view on the early stages of the accretion disk and jet formation. The advent of large-scale optical time-domain surveys has significantly increased the number of known events and challenged our understanding of their dynamics and emission processes. Especially, the so-called optical TDEs have shown late-time X-ray and radio emission years after the optical peak emission indicating delayed accretion disk formation and long timescales for the circularization process. In this seminar, I will present our study on the most polarized TDE up-to-date without any indication of contribution from a jet to the emission. Our observations demonstrate that optical TDE emission can be powered by tidal stream shocks.

• 19.5. Sven Heinemeyer (IFT (CSIC), Madrid):  New Physics around the corner?!
Abstract:  Three recent experimental results will be reviewed that deviate from the Standard Model (SM) prediction by $\sim 4 \sigma$. These are the anomalous magnetic moment of the muon, excesses in the searches for light Higgs bosons at the LHC and the measurement of the W-boson mass by CDF. The implications for new physics beyond the SM as well as corresponding
prospects for future experiments will be discussed.

• 25.05. Inga Strumke (AI Lab, NTNU): Introduction to machine learning - a guided tour with examples from particle physics -- PART II

• 8.9. Tim Ruhe (TU Dortmund):

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