SEMESTER 2020 - SUMMER




Seminars are broadcast online at meet.google.com

02.06.2020

Martin Stref

LAPTH, Annecy

Predicting the dark matter velocity distribution : test against hydrodynamical simulations


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The knowledge of the dark matter (DM) velocity distribution is an important element of several types of DM searches e.g. direct detection, p-wave-suppressed or Sommerfeld-enhanced annihilating DM. Many predictions for these signals rely on a Maxwell-Boltzmann approximation for the velocity distribution, however a more refine calculation can be obtained using the Eddington inversion method. I will review the theoretical foundations of this technique as well as some of its shortcomings, then present a recent test of its reliability against hydrodynamical cosmological simulations.

19.05.2020

Kodai Sakurai

Institute for Theoretical Physics, Karlsruhe

Precise calculations to Higgs branching ratios in extended Higgs models


We have calculated next-to-leading order corrections to branching ratios of the discovered Higgs boson in various extended Higgs models, such as the Higgs singlet model, 4 types of two Higgs doublet models and the inert doublet model. All analytical results have been implemented in our computation program for the discovered Higgs boson, H-COUP. In this talk, I will describe the impact of loop contributions of additional Higgs bosons for the decay branching ratios. Also, I will discuss whether above extended Higgs models are discriminated by precise measurements at future collider experiments or not.

Slides


05.05.2020

Evangelos Sfakianakis

Nikhef & Lorentz Institute for Theoretical Physics, Leiden University

Preheating on Curved Field-Space Manifolds


I will discuss preheating in multi-field models of inflation with a curved field-space manifold. In case of multi-field models with non-minimal couplings, where the field-space in the Einstein frame is highly curved near the origin, I will describe recent lattice simulations that have been used to capture significant nonlinear effects like backreaction and rescattering. I will show how we can we extract the effective equation of state and typical time-scales for the onset of thermalization, quantities that could affect the usual mapping between predictions for primordial perturbation spectra and measurements of anisotropies in the cosmic microwave background radiation. For large values of the nonminimal coupling constants, efficient particle production gives rise to nearly instantaneous preheating. Moreover, the strong single-field attractor behavior that was identified for these models in linearized analyses remains robust in the full theory, and in all cases considered the attractor persists until the end of preheating. Furthermore, I will discuss the implications for Higgs inflation. In the case of two-field generalizations of alpha-attractor models with is a highly curved hyperbolic field-space manifold, analytical progress can be made for preheating using the WKB approximation and Floquet analysis. I will show the emergence of a simple scaling behavior of the Floquet exponents for large values of the field-space curvature, that enables a quick estimation of the reheating efficiency for any large value of the field-space curvature. In this regime one can observe and explain universal preheating features that arise for different values of the potential steepness. In general preheating is faster for larger negative values of the field-space curvature and steeper potentials. For very highly curved field-space manifolds preheating is essentially instantaneous.

21.04.2020

Tobias Binder

Kavli IPMU, Tokyo

Aspects of Dark Matter long-range effects at finite temperature


If Dark Matter (DM) is realized at around the TeV-mass region or above, even the heaviest electroweak force carriers could act as attractive long-range forces, leading to the existence of meta-stable DM bound states. The formation and subsequent decay of the latter further deplete the relic density during the freeze-out process on top of the Sommerfeld enhancement, allowing for larger WIMP masses. While the relic abundance computation is well understood in the context of vacuum amplitudes, it is less clear how thermal corrections arising from the primordial plasma environment could modify the long-range force effects and eventually altering the prediction. The talk focuses on the thermal field theoretical description of how to deal with long-range interactions at finite temperature. Collective phenomena like the melting of dark matter bound states at high temperature, as well as surprisingly large next-to-leading order corrections to the bound-state formation cross section at the decoupling from ionization equilibrium and temperatures below are discussed.

Slides


07.04.2020

Yue-Lin Sming Tsai

Institute of Physics, Academia Sinica, Taipei

Detecting a DM lighter than proton: Majorana DM and scalar mediator


We study a light fermionic weakly interacting massive particle (WIMP) dark matter and its minimal renormalizable model, where it requires a scalar mediator to have an interaction between the WIMP and standard model particles. A comprehensive analysis of the model involving the latest but robust constraints as well as those in the near future is performed. We show that near-future experiments and observations such as low-mass direct dark matter detections, flavor experiments, and CMB observations play important roles to test the model. Still, a wide parameter region will remain even if no WIMP and mediator signals are detected there. Finally, as a future prospect, we propose two directions to further probe such an inaccessible parameter space. The first one is a strongly self-interacting DM (SIDM) scenario if such a WIMP owns features of SIDM but the second one is to detect DM and cosmic ray up-scattering.

Slides


03.03.2020

Marco Fedele

Universitat de Barcelona

The status of b to s anomalies before Moriond 2020


Flavour Changing Neutral Currents (FCNC) are an excellent probe for the search of New Physics. Therefore, LHCb has put a particular care in the study of B decays mediated by FCNC. Tensions between present data and Standard Model predictions have been found in some of these channels, hinting at a possible violation of Lepton Flavour Universality. I will review the status of these tensions after the results presented last year at Moriond 2019, assessing with particular care the theoretical cleanness of the observables displaying such tensions. Then, I'll discuss the possible explanations for such a pattern of anomalies both within and beyond the Standard Model, employing a model independent EFT framework. Finally, I'll review a possible loop model capable to address such anomalies.

Slides