Theorie-Seminare SS 22

Do. 28.04.2022, 16.30 Uhr

Ke Fang (U Wisconsin, Madison)

Multi-messenger Astrophysics: Probing Compact Objects with Cosmic Particles

The study of compact objects such as black holes and neutron stars is an important component of modern astrophysics. Recent detections of astrophysical neutrinos, gamma-rays, ultrahigh energy cosmic rays, and gravitational waves open up opportunities to study compact objects with multi-messengers. In this talk, we first review the latest progress in Astroparticle Physics, including some surprising puzzles revealed by new observations of neutrinos and gamma rays. We then demonstrate that the key to Multi-messenger Astrophysics is to understand and establish the link between the messengers. We show that high-energy particle propagation in the vicinity of compact objects may play an important role in connecting multi-wavelength observation and source physics.

Host: P. Mertsch


Do. 12.05.2022, 16.30 Uhr

Federico Urban (FZU, Prague)

Harmonic correlators for UHECRs

I will review the applications, advantages and limitations of harmonic techniques to detect anisotropies in the UHECR arrival direction distribution. In particular I will focus on the harmonic cross-correlation between UHECRs and galaxies, where the latter are taken as proxies for the locations of UHECR sources. This type of harmonic cross-correlation shows very promising complementarities with the well-known harmonic UHECR auto-correlation. I will show how the combination of UHECR harmonic auto-correlation and cross-correlations with large-scale structures can disentangle different UHECR primaries and could reverse-engineer some of the effects of the galactic magnetic field to a much better degree than the auto-correlation alone. I will conclude with an outlook on applications to other data sets, such as astrophysical neutrinos.

Host: J. Lesgourgues


Do. 19.05.2022, 16.30 Uhr (MBP2 117)

Ramon Winterhalder (CP3, UC Louvain)

Targeting Multi-Loop Integrals with Neural Networks

Achieving high-precision in HEP theory predictions requires the evaluation of scattering amplitudes beyond leading order. These (multi)-loop amplitudes can contain complicated integrals where an analytic solution is not feasible. In this case, they have to be evaluated numerically, and a careful treatment of possible singularities of the integrand is required. After isolating and factorizing the UV and IR poles of the integrand, using sector decomposition, only threshold singularities remain, which can be avoided by a deformation of the integration contour into the complex plane. While valid contours are easy to construct, the numerical precision for a multi-loop integral can depend critically on the chosen contour. We present methods to optimize this contour using a combination of optimized, global complex shifts and a normalizing flow. These methods can lead to a significant gain in precision.

Host: C. Brancaccio


Do. 02.06.2022, 16.30 Uhr

Carmelo Evoli (GSSI, L'Aquila)

Phenomenology and theory of galactic cosmic-ray propagation

Cosmic rays are the most energetic particles in the local Universe as they are known to reach energies above few Joules. How and where they are produced have been a science puzzle for several decades now, whose solution has been driving the rising of multi-messenger astrophysics as well as novel theoretical approaches. Of particular interest is the energy range below ~PeV as we expect that these particles have been all accelerated in the most extreme objects in our own Galaxy. Additionally, the past decade has seen an unprecedented improvement in the quality and quantity of data about their energy spectrum and chemical composition, allowing us to infer global properties as the galactic grammage and the average residence time. These quantities are crucial to test any more fundamental description of the transport of charged particles in the interstellar plasma. Even more thrilling, these new measurements, together with a deeper scrutiny of the diffuse gamma-ray emission from the Galactic plane, have revealed unexpected new features in the cosmic-ray elemental spectra that are challenging the commonly accepted scenario of how these particles are energized and propagate through interstellar space. In my talk I will provide an overview of these recent findings, and discuss some of the new ideas proposed to explain these anomalies.

Host: P. Mertsch


Do. 30.06.2022, 16.30 Uhr

Irene Tamborra (NBI Kopenhagen)

Messengers from the Universe

Neutrinos are fascinating elementary particles heralding the dawn of the multi-messenger astronomy era. Neutrinos affect the stellar dynamics, drive the formation of the heavy elements, and carry signatures of the yet mysterious physics ruling the most powerful cosmic fireworks. Recent developments on the role of neutrinos in cosmic sources will be reviewed together with the most exciting detection prospects.

Host: S. Manconi


Do. 07.07.2022, 16.30 Uhr

Sven Heinemeyer (UA Madrid)

New Physics around the corner?!

We discuss two recent measurements that disagree with the SM prediction at the level of ~4 sigma: the first one are three independent excesses in the search for light Higgs bosons around 95 GeV, the second one is the measurement of the mass of the W boson. We show how these excesses can be described by physics beyond the SM, and how these excesses can be explained simultaneously by one BSM model.

Host: R.Harlander


Do. 14.07.2022, 16.30 Uhr

Vivian Poulin (U. Of Montpellier)

Towards resolving the Hubble and sigma8 cosmic tensions

In recent years, high precision cosmological data have revealed a number of `cosmic tensions’, i.e. a mismatch between the prediction of certain quantities in the `Lambda Cold Dark Matter’ model calibrated onto cosmic microwave background data (probing early times) and their direct measurement at low redshift (probing late times). In particular, tensions in the determination of `H0’ (the expansion rate today) and `sigma8’ (the local amplitude of fluctuation) have attracted a lot of theoretical (and experimental) attention, as they could be the first signs of the nature of a rich dark sector.  In this talk, I will review promising theoretical efforts to resolve these tensions. I will show that resolving the H0 tension most likely require new physics in the early universe, but that current models generally cannot resolve the sigma8 tension, sometimes even slightly exacerbating it. I will then discuss guidelines to resolving the sigma8 tension. I will argue that the low-sigma8 values may indicate that cold Dark Matter is not stable on cosmological time-scales, decaying with a lifetime of ~15Gyrs, and leading to the creation of a dark matter component with large velocity (representing roughly 30% of the total Dark Matter today). Future DESI and Euclid data will be able to detect (or exclude) this model.

Host: J. Lesgourgues