Date: June 9th 15 PM (CET)
Presenter: M. Laine (Bern U)
Title: Gravitational wave background from Standard Model physics
Abstract: Apart from CMB photons and neutrinos, another principal carrier of information from very early epochs in the history of the universe are gravitational waves. Besides inflation, they have been proposed to contain features originating from post-inflationary phenomena such as preheating or thermal phase transitions. However, a gravitational wave background, akin to blackbody radiation, is also being emitted from a plasma without any phase transition. In this talk the general properties of the thermal background are discussed. The absence of additional relativistic degrees of freedom in Planck data sets an upper bound on the total energy density carried by gravitational waves and thereby on the highest temperature of the radiation epoch. Theoretically it might even be possible to observe the thermal background with future generations of GHz range detectors.
Date: March 24th @ 15:00 (CET)
Presenter: M. Lisanti (Princeton U)
Title: Bringing Dark Matter into Focus
Abstract: Although dark matter comprises the vast majority of the matter in the universe, its properties remain elusive. Direct detection experiments are a promising avenue for discovering and characterizing the dark sector. These experiments seek toidentify dark matter particles as they scatter off nuclei in underground detectors.The standard picture since the 1980s is that the scattering rate modulates annually due to the Earth's orbit around the Sun. We have recently discovered a new modulation effect: Unbound dark-matter particles are focused by the Sun's gravitational potential, affecting their phase-space density in the lab frame. This 'gravitational focusing' results in a significant overall shift in the phase of the annual modulation and provides a powerful new tool for characterizing the properties of the dark matter particle. Gravitational focusing has additional applications to relic neutrino searches, providing the only source of annual modulation in that case.
Date: February 24th @ 15:00 (CET)
Presenter: Andrea Wulzer (Padova U.)
Title: Robust collider limits on heavy-mediator dark matter
Abstract: We explain how to consistently use Effective Field Theories (EFTs) to set universal bounds on heavy-mediator Dark Matter at colliders, without prejudice on the model underlying a given effective interaction. We illustrate the method for a Majorana fermion, universally coupled to the Standard Model quarks via a dimension-6 axial-axial four-fermion operator. We recast the ATLAS mono-jet analysis and show that a considerable fraction of the parameter space, seemingly excluded by a na\"ive EFT interpretation, is actually still unexplored. Consistently set EFT limits can be reinterpreted in any specific underlying model. We provide two explicit examples for the chosen operator and compare the reach of our model-independent method with that obtainable by dedicated analyses.