WIMP Dark Matter and Baryogenesis

In the present universe visible and dark matter contribute comparable energy density although they have different properties. This coincidence can be elegantly explained if the dark matter relic density, originating from a dark matter asymmetry, is fully determined by the baryon asymmetry. Thus the dark matter mass is not arbitrary, rather becomes predictive. We realize this scenario in baryon(lepton) number conserving models where two or more neutral singlet scalars decay into two or three baryonic(leptonic) dark matter scalars, and also decay into quarks(leptons) through other on-shell and/or off-shell exotic scalar bilinears. The produced baryon(lepton) asymmetries in the dark matter scalar and in the standard model quarks(leptons) are thus equal and opposite. The dark matter mass can be predicted in a range from a few GeV to a few TeV depending on the baryon(lepton) numbers of the decaying scalars and the dark matter scalar. The dark matter scalar can interact with the visible matter through the exchange of the standard model Higgs boson, opening a window for the dark matter direct detection experiments. These models also provide testable predictions in the searches for the exotic scalar bilinears at LHC.Comment: 5 pages, 1 figur

External uniform electric field removing flexoelectric effect in epitaxial ferroelectric thin films

Using the modified Landau-Ginsburg-Devonshire thermodynamic theory, it is found that the coupling between stress gradient and polarization, or flexoelectricity, has significant effect on ferroelectric properties of epitaxial thin films, such as polarization, free energy profile and hysteresis loop. However, this effect can be completely eliminated by applying an optimized external, uniform electric field. The role of such uniform electric field is shown to be the same as that of an ideal gradient electric field which can suppress the flexoelectricty effect completely based on the present theory. Since the uniform electric field is more convenient to apply and control than gradient electric field, it can be potentially used to remove the flexoelectric effect induced by stress gradient in epitaxial thin films and enhance the ferroelectric properties.Comment: 5 pages, 3 figure