The seminar of the Astro & Theory Section takes place Mondays (alternating with the Journal Club) in D3-114 (Onsager) 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 2021 2024 are
- 2206.01., Marco Stein Muzio (New York University): Closing in on the sources of UHECRs: A multimessenger approach
Abstract: Today ultrahigh energy cosmic rays (UHECRs), with energies in excess of an EeV (or 10^18 eV), provide us with a glimpse both into the most extreme astrophysical environments in the universe and into fundamental interactions beyond LHC energies. However, the source of these particles has long remained a mystery. In this talk, I will focus on progress made in characterizing the sources of UHECRs by combining a phenomenological model of these sources with multimessenger measurements. Recent elaborations of our model have allowed us to make more concrete statements about the types of environments required to explain UHECR data, and possibly astrophysical neutrino data. I will present these constraints and their implications for astrophysical sources.
slides19.02., Alessandro Mirizzi (INFN, U Bari): Axions: Bounds and Discovery Opportunities
Abstract: Axions have been introduced in relation to the strong CP problem of the QCD and are predicted in many extensions of the Standard Model of particle physics. Depending on the actual value of their mass, axions can play an important role in cosmology, acting as cold or hot dark matter. The coupling with photons allows for axion-photon mixing in external electromagnetic fields. This effect is exploited for direct searches of axions in laboratory experiments. Axions can be searched also through astrophysical observations. Notably they can be produced in stellar cores leading to an excessive energy loss, that would alter the standard stellar evolution. Furthermore, the two-photon vertex would also induce the mixing with axions for photons emitted by distant astrophysical sources, and propagating in the large-scale cosmic magnetic fields, leading to peculiar observational signature. In this talk I will present an overview of current bounds on axions and discovery opportunities in the planned laboratory and astrophysical experiments.
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19.03., Magdalena Eriksson (NTNU, UiS): Quantum corrections to inflation postponed - 16.04., Martin Mohajed (NTNU): Chiral perturbation theory at finite isospin
Abstract: Chiral perturbation theory (ChiPT) is a low-energy effective field theory of QCD. I will discuss the QCD phase diagram at finite isospin chemical potential and the application of ChiPT to the problem of pion condensation at zero temperature. Since QCD at finite isospin is free of the fermion sign problem, one can use lattice simulations. We compare our two- and three-flavor results for various condensates obtained using ChiPT with recent Monte Carlo data.
slides 30.04., Tomas Brauner (UiS): Topology of spontaneous symmetry breaking, emergent higher-form and higher-group symmetries - 07.05., Magnus Malmquist (NTNU): Polarization Sums and Unitarity in QCD
Abstract: One of the first techniques one encounters when learning quantum field theory is the method of replacing the sum over photon polarizations by minus the metric tensor. This is not an equality; instead the QED Ward identity ensures that the replacement gives the correct result. We ask the simple question of whether this replacement can be made in a non-abelian theory like QCD. The answer is "yes, we can". Using unitarity we explain how the method should be applied in QCD, which requires considering external Faddeev-Popov ghosts. Understanding the procedure of replacing the polarization sum by minus the metric tensor then leads us to Slavnov-Taylor identities which are a core stone of the mathematical consistency of QCD.
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Abstract: Spontaneous breaking of a continuous global symmetry implies as a rule the existence of new, emergent symmetries, associated with the topology of the vacuum manifold. These may take the form of ordinary symmetries associated to a conserved current and localized charged excitations, or higher-form symmetries, acting on extended topological defects. I will give a brief introduction to the above-mentioned concepts, and then show how higher-form symmetries can be combined into a more general mathematical structure still, referred to as higher-group symmetry. This is a concept that has recently attracted attention in the high-energy theory community. It however turns out to be also relevant for systems as mundane as superfluid mixtures.
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- 21.05., Magdalena Eriksson (NTNU, UiS): Quantum corrections to inflation
Abstract: The theory of cosmic inflation solves the problems of Big Bang cosmology and provides an explanation to the origin of the cosmic microwave background (CMB) radiation. Inflation is often modelled with a scalar field slowly rolling down some potential in FRLW spacetime. In cosmological perturbation theory one perturbs this inflaton field as well as the FRLW metric, and these perturbations can be related to the temperature fluctuations observed in the CMB. In this talk I give an introduction to inflationary cosmology and cosmological correlation functions. I introduce the concept of corrections to these correlation functions and how they can affect the inflationary dynamics. In particular I differentiate between corrections to cosmological observables, i.e. n-point correlation functions, and corrections to the evolving inflaton field and background metric. Corrections to the evolution equations can be viewed as corrections to the slow-rolling parameters, which also enter into observables.
- 02. Michael Unger (KIT and IFY, NTNU): 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. Summer break... - 06.09., Bjoern Eichmann (RUB, NTNU): Can radio galaxies solve the UHECR puzzle?
Abstract: The origin of the ultra-high-energy cosmic rays (UHECRs) is one of the great enigmas of modern astroparticle physics. Radio galaxies (RGs) - which were divided by Fanaroff and Riley into two classes (FR-I and FR-II) - show great potential to be the birthplace of these nuclei with energies above 1 EeV. In this talk some recent findings on the contribution of two individual, promising radio galaxies, Centaurus A and Cygnus A, will be discussed as well as the CR contribution from the bulk of these galaxies. Using the radio luminosity as a robust estimator for the CR luminosity, it is shown that the FR-I source Centaurus A is able to provide the dominant UHECR contribution at the highest energies. But there is an other contributor between 5 EeV and 30 EeV needed. The exceptionally bright radio source Cygnus A is a prominent source candidate, but it is shown in this talk, that the impact by the extragalactic magnetic field on the CR propagation causes some serious issues: Either the arrival directions of the CRs provide a high degree of anisotropy or the delay exceeds the source age. Alternatively, the low-energetic UHECRs can originate in the bulk of FR-I or FR-II sources. For such a scenario, the necessary jet dynamics of FR sources are discussed, showing that FR-I RGs can in principle provide the observed amount of UHECR energy as well as a proper spectral behavior. In contrast, the bulk of FR-II RGs most likely contribute less than 25%.
slides 28.10., Alexander Rothkopf (UiS): Open Quantum Systems: Thermometry at the Extremes - 15.11., David Garofalo (Kennesaw State University):
- Germano Nardini (UiS), Alexander Stasik (UiO)