Wochenübersicht – nächste Woche

The measurement of the mixing-induced CP-violating phase phi_s in the Bs − B̄s system is one of the key goals of the LHCb experiment. It has been measured at the LHCb collaboration with several decay channels. Thanks to the precise prediction of the phi_s value in the frame of the Standard Model, it represents an excellent probe to search for new physics.

Using the quantum chromodynamics (QCD) equation of state (EoS) from lattice calculations we investigated QCD effects on the first order primordial gravitational waves (PGWs) produced during the inflationary era. We also considered the cases for vanishing and nonvanishing lepton asymmetry where the latter one is constrained by cosmic microwave background experiments. Also, we investigated scenarios that inflation is succeeded by a phase where the energy density of the Universe was dominated by a scalar component with a general equation of state. Then we evaluated the spectrum of primordial gravitational waves induced in the post-inflationary Universe. We showed that if the energy density of the Universe was dominated by some specific fluid 𝜙 before Big Bang Nucleosynthesis (BBN), its equation of state could be constrained by gravitational wave experiments. Moreover, we studied the effect of QCD and electroweak transitions on the induced (or second order) PGW from scalar perturbations which is different from the first order PGW spectrum. Finally, I briefly discuss the production of dark matter (DM) in an early matter era dominated by a heavy long lived scalar field.

Over many years the experimental programme to search for dark matter has been guided by the so-called freeze-out paradigm, which assumes that interactions between the dark matter and Standard Model particles are comparable in strength to weak interactions. The non-observation of any dark matter signal has challenged this idea and led to a shift of focus towards dark matter models with even weaker interactions. At first sight, the chance of discovering such particles appears very low, but there are a number of exciting cases where potentially observable signals are predicted in spite of tiny couplings. I will present cosmological and phenomenological aspects of these models and discuss how existing and planned experiments can be used to search for such hidden particles.

Domain walls naturally arise whenever a symmetry is spontaneously broken. They interconnect regions with different realizations of the broken symmetry, promoting structure formation from cosmological length scales to the atomic level. In my talk, I will present domain walls with unique functionalities which emerge in spin-spiral multiferroics and chiral magnets and which hold great promise for nanoelectronics and spintronics applications. In particular, I will discuss that a wide variety of new domain walls occurs in the presence of spatially modulated domain states. In contrast to domain walls in conventional ferroics, such domain walls exhibit a well-defined inner structure, which — analogous to cholesteric liquid crystals — consists of topological disclination and dislocation defects. Similar to the magnetic skyrmions, the domain walls can carry a finite topological charge, permitting an efficient coupling to spin currents and contributions to a topological Hall effect. Our studies establish domain walls in chiral magnets as functional nano-objects with non-trivial topology, opening the door to innovative device concepts in information and communication nanotechnology.

Ultrathin optical fibres, with diameters on the order of the propagating light wavelength, have already proven their versatility across a variety of different areas, such as sensing, particle manipulation, cold atom physics, and as optical couplers. The intense evanescent field at the fibre waist is one of the main advantages offered by these systems as it allows us to achieve ultrahigh light intensities that may otherwise not be attainable in a standard laboratory. In this talk, I will present work conducted at OIST with particular focus on our work on optical nanofibre-mediated multiphoton processes for the generation of highly excited Rydberg atoms and for exploring some other effects, such as quadrupole transitions and stimulated emission from Rb atoms. Overall, the versatility of these fibres for many different experimental platforms particularly if one goes beyond the basic, single mode fibre design will be promoted.