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- 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%.
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- 25.10., Jonas Tjemsland (NTNU): The Almighty Axion
The Standard Model of particle physics has had immense success over the years. Yet, it has several shortcomings that illustrate its incompleteness, including for example the strong CP problem. However, already back in 1977 Peccei and Quinn postulated the existence of the so-called axion—a hypothetical, light pseudo-scalar boson—as a solution to the strong CP problem. Not only that, the axion and axion-like particles turn out to be potential miracle cures for many of the biggest problems humanity has ever faced: identifying dark matter, explaining dark energy, explaining inflation and ending world hunger. First, though, one must address the elephant in the room: the axion has not yet been detected. In this talk, I will give a theoretical introduction to the axion and its potential importance to modern physics, and I will discuss how the characteristic two-photon coupling enables the detection of axion-like particles. In particular, I will explain how axion-like particles can be detected by measuring photons from distant gamma-ray sources by exploiting a phenomenon known as ``photon-axion oscillation'' that occurs as photons propagate through astrophysical environments.
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- 28.10., Alexander Rothkopf (UiS): Open Quantum Systems: Thermometry at the Extremes
The study of quantum systems coupled to an environment plays a vital role in how we measure temperatures of the coldest and hottest matter in the universe. The strategy relies on introducing impurities into the system of interest and on observing how these probe particles evolve towards or in equilibrium with their surroundings, from which we may in turn deduce the thermal properties of that environment. Originally studied in the context of condensed matter physics, open quantum systems nowadays provide a common language to research spanning multiple orders of magnitude in temperature, ranging from Bose Einstein condensates made of ultracold atoms to the Quark-Gluon plasma created in ultra-relativistic collisions of heavy ions. This talk builds a bridge from polaron impurities in the former to quarkonium particles in the latter as two manifestations of quantum Brownian motion, a phenomenon ideally described by open quantum systems.
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- 15.11., David Garofalo (Kennesaw State University): Radio galaxies and their supermassive black holes
Despite the universe being only a few hundred million years old, a merger between two gas-rich galaxies produces a rapidly spinning massive black hole weighing 4 billion solar masses. But the bright disk of gas that settles around this black hole does so in an unusual way, with the direction of gas flow opposite to black hole rotation. A powerful jet emerges from the hole that enhances star formation in the galaxy for 400 million years. But as the black hole spin decreases, the jet turns off and remains so for about a billion years, after which a new jet emerges, but with a fundamentally different feature, its orientation tilted with respect to the previous jet. This allows the jet energy to couple directly to the ISM, heating it and suppressing star formation. Despite 10 billion years of accretion, the black hole fails to spin rapidly again, reaching only about 50% of its maximum possible when it is observed with the EHT. This is the black hole at the center of M87. I will describe the theoretical framework that accounts for this story.
Germano Nardini (UiS), Alexander Stasik (UiO)
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