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.normally on Wednesdays in D5-106, starting at 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@ntnuRaphael.Mignon-Risse@ntnu.no).
A list of seminars in the previous and the current years can be accessed in the sidebar; the The (planned) seminars in 2022 2024 are
- 1706.02. , Marco Turchetta ( Michael Unger (KIT and 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
- 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.
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.
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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.
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- 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 :-)
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- 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.
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- News from the Galactic Magntic Field (...and the Origin of the Amaterasu Particle)
Abstract: Galaxies are known to be permeated by large-scale magnetic fields with energy densities comparable to the turbulent and thermal energy densities of the interstellar medium. A good knowledge of the global structure of these fields is important to understand their origin and to infer their effect on galactic dynamics and the propagation of charged particles in galaxies. In this talk I will present new studies of the global structure of the magnetic field of our Galaxy based on the analysis of recent new full-sky data of extragalactic rotation measures and the final polarized intensity maps from WMAP and Planck. The analysis employs the latest models for the thermal electron density tuned to the dispersion measures of Galactic pulsars and state-of-the-art cosmic-ray electrons models, needed to predict the rotation measures and synchrotron emission from the Galaxy, respectively. As a result, I will present a major revision of the widely-used Jannson-Farrar 2012 model of the magnetic field of the Galaxy. In addition to a fiducial magnetic field model, a suite of alternative models was studied that fit the data with similar quality, but use different model assumption. This suite of models is then used to place a lower limit on the model uncertainties. As an application, I will discuss the uncertainties of the predicted deflection of ultrahigh-energy cosmic rays in the Galaxy, in particular the origin of the extremely energetic "Amaterasu particle" recently reported by the Telescope Array Collaboration.
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- 13.02. Lena Saurenhaus (MPP Muenchen): Seyfert Galaxies as Astrophysical Neutrino Sources
Abstract: Active galactic nuclei (AGNs) are among the most powerful objects in the Universe and are suspected to be sources of astrophysical neutrinos. Recently, the IceCube Collaboration reported an excess of neutrino events with energies between 1.5 and 15 TeV associated with NGC 1068, a nearby Seyfert galaxy with an extraordinarily high intrinsic X-ray flux. The lack of observable gamma rays in this energy range indicates that these neutrinos are likely to be produced in the AGN corona, which is opaque to high-energy gamma rays. I will give an overview over existing neutrino emission models for NGC 1068-like sources and talk about our current project, which explores the prospects of observing other hidden neutrino sources with similar neutrino production mechanisms and aims to constrain their contribution to astrophysical neutrino observations.
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- 05.03. Triantafyllos Kormpakis (IFY, NTNU): The Particle in Cell method: Theory and astrophysical applications
Abstract: The Particle in Cell (PIC) numerical method (first developed in the 1950s) aims to simulate the behavior of plasmas in the presence of electric and magnetic fields. With it's unique architecture, moving particles on a Langrangian frame and depositing their charge and current densities on a fixed eulerian mesh, it tracks the evolution of systems where high densities of charged particles (mainly electron-positron pairs) and/or strong electromagnetic fields are present. In the parameter space where the Force free magnetic field approximation is valid, such as the magnetospheres of pulsars, magnetars and active galactic nuclei (AGN) jets, the PIC scheme accurately simulates features such as magnetic reconnection phenomena, enables the study of shock acceleration, particle flows and emission regions. In this talk I will first give a basic overview of the PIC method, particularly in its implementation on the Zeltron code. This will lead to the discussion of my application and qualitative reproduction of existing results, in magnetic reconnection in ABC magnetic fields (particular eulerian flows with stable as well as chaotic flow regimes). Lastly, I will also describe my application and results of PIC methodology to a test case: an axially symmetric magnetic field, representing a magnetic field topology present in an AGN jet.s.
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- 14.03. Rita C. Anjos (U Parana): The nature of high-energy multi-messenger sources
Abstract: In this seminar, I will present the main results of high-energy physics, considering charged particles and gamma radiation as multi-messengers. In this context, the primary sources of these particles will be discussed, along with significant challenges in the field and some results from my research group in Brazil. I will also introduce some diversity/outreach initiatives developed by the group to foster the inclusion of children and youth in the subatomic universe.
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- 19.03. Ellis Owen (U Osaka): Cosmic Ray feedback in galaxy evolution
Abstract: Cosmic rays go hand-in-hand with violent and energetic astrophysical conditions. They are an active agent within galactic and circumgalactic ecosystems, where they can deposit energy and momentum, modify the circulation of baryons, and even have the potential to regulate star-formation on local and galactic scales. Their influence in galaxies can be probed using observable signatures across the electromagnetic spectrum, with high energy radiation being particularly important to determine their energy budget, feedback power and hydrodynamic effects. In this talk, I will discuss some of the astrophysical impacts hadronic and leptonic cosmic rays can have in and around galaxies, how their influence can be probed using signatures in X-rays and gamma-rays, and the opportunities soon to open-up that will allow us to map-out the multi-scale effects of cosmic rays in galaxies near and far.
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- 21.03. Dmitri Semikoz (APC Paris): Multi-messenger signatures of astrophysical neutrino sources
Abstract: In this talk I’ll review recent observations of galactic and extragalactic neutrino sources comparing them to the predictions of theoretical models. At multi-TeV energies dominant contribution to the neutrino flux of Milky Way is expected from Galactic Ridge, brightest region of our Galaxy, where cosmic rays interact with interstellar gas and produce secondary gamma-rays and neutrinos. In neutrinos first hint of Galactic Ridge was found in ANTARES in 2022. In 2023 IceCube detected it in cascade channel with 4 sigma significance. I’ll discuss perspectives of detection of Galactic Ridge by future neutrino telescopes and by LHAASO, SWGO and CTA in gamma-rays. Also I’ll review recent gamma-ray and neutrino observations from Pevatron source in Cygnus region.For extragalactic neutrino sources I’ll focus on Seyfert galaxies. In addition to well known NGC 1068 only two other sources, based on their hard X-ray properties, NGC 4151 and NGC 3079 are expected to be detectable in 10 years of IceCube data. We find an evidence for neutrino signal from both sources in publicly available ten-year IceCube dataset. The chance coincidence probability to find the observed neutrino count excesses in the directions of the two out of two expected sources, in addition to the previously reported brightest source, is p<2.6e-7. This corresponds to the detection of Seyfert galaxies as a neutrino source class.
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- 25.06. Paul Lai (University College London): Tracking the gas distribution in the Galactic Centre using neutrinos and Alisha Roberts (IFY, NTNU): Investigating Neutrino Emissions from Blazar 3C 454.3
- tbd. Jens Oluf Andersen (IFY, NTNU): Pion condensation and pion stars
Abstract: In this talk I will discuss pion condensation in the context of two and three-flavor chiral perturbation theory. I will present results for quark and pion condensates as functions of the isospin chemical potential. The results compare favorably to those of lattice QCD. As an application, I will discuss pion condensation in a dense neutrino cloud and the possibility of pion stars. These are compact objects with a mass up to 20 solar masses and radii of up to 140km.
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