Theory Seminars SS 20

Thu 16.04.2020, 16.30 h

T. Linden (Stockholm)

Thermal WIMPs on the Brink

Weakly Interacting Dark Matter Particles (WIMPs) are among the most well-motivated models for particle dark matter. While these particles can be detected through direct, indirect, and collider experiments, only their indirect annihilation cross-section is guaranteed within the confines of a thermal model. Intriguingly, experimental searches using both gamma-rays and cosmic-rays are beginning to close in on the coveted "thermal annihilation cross-section". More intriguingly, several excesses in Galactic center gamma-rays and cosmic-ray antiprotons have been discovered. Even more intriguingly, these excesses are potentially consistent with each other. In this talk, I will summarize the current state of the field, and argue that there is hope of resolving this puzzle within the next five years.

Host: P. Mertsch


Thu 23.04.2020, 16.30 h

M. Diehl (DESY Hamburg)

Double parton scattering

Double parton scattering can give important contributions to high-multiplicity final states in proton-proton collisions.  I review the status of the theory for this mechanism, with a focus on recent developments regarding higher-order calculations.

Host: M. Czakon


Thu 07.05.2020, 16.30 h

L. Lellouch (CNRS & Aix-Marseille U.)

New lattice QCD calculation of the hadronic vacuum polarization contribution to the muon magnetic moment

Charged-lepton magnetic moments play a special role in probing the standard model (SM) of particle physics, which is complementary to direct searches for new physics at the energy frontier. In particular, the
experimental value of the anomalous contribution to the muon magnetic moment, a_\mu=(g_\mu-2)/2, has exhibited a persistent discrepancy of over 3 standard deviations with the SM prediction, ever since the very precise measurement made at Brookhaven National Lab in the early 2000s. This is particularly enticing, because it could indicate the presence new, fundamental physics.  At present, theoretical and experimental uncertainties are comparable in size. However, a new experiment underway at Fermilab, and another one planned at J-PARC, are aiming to reduce the error on the measurement of a_\mu by a factor of 4. To fully leverage these future measurements, and possibly claim the presence of new fundamental physics, it is imperative to check the SM prediction with independent methods and to reduce its uncertainties. After an introduction and a discussion of the current experimental and theoretical status of a_\mu, I will present a new lattice QCD calculation of the contribution to this quantity that most limits the precision of its SM prediction.  Surprisingly, our result eliminates the need to invoke new physics to explain the current measurement of a_\mu.

Host: R. Harlander


Thu 14.05.2020, 16.30 h

C. Pitrou (Institut d’Astrophysique de Paris)

Global cosmological anisotropy as a long wavelength perturbation

The current concordance model of cosmology has been extremely successful in constraining the global properties of the universe. However, it is based on the assumption of statistical homogeneity and isotropy, and we are thus lead to test this global geometry. In this webinar, I will review how a global anisotropy can imprint the various observables. In particular, an early anisotropic phase during inflation is imprinted in a direction-dependent initial power spectrum, whereas a late phase is imprinted in the evolution of cosmological perturbations and in the CMB radiative transfer. In practice, it is sufficient to constrain mild anisotropies, and I will show how anisotropy can be considered as a special long-wavelength perturbation around a Friedmann-Lemaître space-time. Within this framework, the same tools can be used to compute the anisotropic and non-stochastic perturbation, and the statistically isotropic and stochastic ones, allowing to test late anisotropy from all cosmological observables.

Host: J. Lesgourgues


Thu 04.06.2020, 16.30 h

O. Hahn (Nice)


Host: J. Lesgourgues


Thu 18.06.2020, 16.30 h

T. Hambye (Brussels)


Host: F. Kahlhoefer


Thu 25.06.2020, 16.30 h

P. Schwaller (Mainz)


Host: M. Krämer


Thu 02.07.2020, 16.30 h

M. Zaro (Milano/Amsterdam)


Host: M. Worek


Thu 09.07.2020, 16.30 h

K. Petraki (LPTHE, Jussieu)


Host: F. Kahlhoefer