Theory Seminars WS 20/21

Thu 29.10.2020, 16.30 h

Coenraad Marinissen (NIKHEF and Utrecht University)

Efficient Hilbert Series for Effective Theories

Abstract:
The task of finding ope​rator bases for effective theories can be assisted by using the Hilbert series, which counts the number of independent operators at a given effective order. In this talk I will introduce the Hilbert series for Standard Model Effective Theory and some extensions, and present ECO, a FORM based implementation that can be used to efficiently establish the number of operators at effective orders as high as 20 (or more). I will discuss some applications, and give an outlook on interesting extensions to other effective theories.

Host: R. Harlander

 

Thu 05.11.2020, 16.30 h

Karsten Jedamzik (Montpellier U.)

On the Hubble tension and primordial magnetic fields

Abstract:
My talk will have three parts. First, I introduce the audience to the gross features of primordial magnetic field evolution before recombination. Then, I will show how primordial magnetic fields can help relieve the Hubble tension. Finally, I make some general statements about a large number of beyond LambdaCDM models proposed to solve the Hubble tension and why they usually do not completeley achieve this goal.

Host: J. Lesgourgues

 

Thu 12.11.2020, 16.30 h

Valentin Hirschi (ETH Zürich)

Local unitarity: a new paradigm for perturbative computations in QFT

Abstract:
The canonical approach for tackling higher-order computations involves splitting up a finite quantity into two separately divergent ones. First, multiloop amplitudes are evaluated using (mostly) analytical techniques. Second, phase-space integrals are computed using numerical Monte-Carlo techniques with ad-hoc subtraction terms for regularising soft and/or collinear infrared divergences. We will present our recent work, Local Unitarity, in which we propose a radically different technique whereby the singularities in real-emission and virtual degrees of freedom directly cancel without the use of any counterterms and at any perturbative order. On the practical side, this allows for the fully numerical computation of differential corrections, potentially alleviating the complexity bottleneck analytical alternatives are facing. From a theoretical standpoint, our proof of the local cancellation of infrared singularities sheds new light on the exact mechanism by which it is realised.

Host: M. Czakon

 

Thu 19.11.2020, 16.30 h

Ilias Cholis (Oakland University)

Scrutinizing Gamma-Ray Observations from Milky Way's Center in Search of Dark Matter Signals

Abstract:
The nature of dark matter is one of the most puzzling questions in physics. We observe its gravitational impact in many different astronomical systems and through cosmological measurements have now determined with great precision its abundance in the Universe. I will discuss how we search for possible signals of dark matter using observations at gamma-rays and how we address the challenges of both the astrophysical uncertainties and alternative astrophysical sources that can give signals mimicking those from dark matter. Using a recently released point source catalogue by the Fermi Large Area Telescope Collaboration and performing a template fit with my collaborators we have confirmed the presence of the previously claimed diffuse emission component known as the  ``Galactic Center Excess'' in gamma-ray observations at GeV energies. Moreover, through a wavelet-based search we have placed constraints on the properties of point sources that could possibly explain that diffuse emission seen in the template fit.

Host: P. Mertsch

 

Thu 26.11.2020, 16.30 h

Mathieu Pellen (Universität Freiburg)

Full NLO QCD corrections to off-shell ttbb production

Abstract:
The physics program of the LHC offers great opportunities to probe the fundamental structure of the Standard Model. To that end, precise theoretical predictions for both signal and background are required. A primary example of it is the measurement of the ttH signal which possesses the ttbb process as irreducible background. The physics and the challenges associated to it will be discussed in this talk. In particular I will present a new computation of the full NLO QCD corrections to off-shell ttbb production.

Host: M. Worek

 

Thu 03.12.2020, 16.30 h

Mauro Pieroni (Imperial College)

Future Gravitational Wave experiments: separating astrophysics and cosmology signals

Host: J. Lesgourgues

 

Thu 10.12.2020, 16.30 h

Marco Bonvini (INFN, Rome)

Probabilistic definition of the perturbative theoretical uncertainty from missing higher orders

Host: M. Worek

 

Thu 17.12.2020, 16.30 h

Tracy Slatyer (MIT)

Probing Dark Matter properties during the Dark Age of the universe

Host: J. Lesgourgues

 

Thu 07.01.2021, 16.30 h

Veronica Sanz (Valencia University)

TBA

Host: F. Kahlhoefer

 

Thu 14.01.2021, 16.30 h

Maria Petropolou (Athens University)

Reconnection models of blazars

Host: P. Mertsch

 

Thu 21.01.2021, 16.30 h

Asher Berlin (Chicago)

TBA

Host: F. Kahlhoefer

 

Thu 28.01.2021, 16.30 h

Tomer Volanski (Tel Aviv)

Millicharged Dark matter: model-building, bounds and EDGES anomaly

Host: J. Lesgourgues

 

Thu 04.02.2021, 9.00 h

Hiroshi Suzuki (Kyushu University)

TBA

Host: R. Harlander

 

Thu 11.02.2021, TBD

Andrea Thamm (Melbourne)

TBA

Host: F. Kahlhoefer