Geometry and Unitarity of Scalar Fields Coupled to Gravity.

We formulate scalar field theories coupled nonconformally to gravity in a manifestly frame-independent fashion. Physical quantities such as the S matrix should be invariant under field redefinitions, and hence can be represented by the geometry of the target space. This elegant geometric formulation, however, is obscured when considering the coupling to gravity because of the redundancy associated with the Weyl transformation.

New Constraint on Primordial Lepton Flavor Asymmetries.

A chiral chemical potential present in the early Universe can source helical hypermagnetic fields through the chiral plasma instability. If these hypermagnetic fields survive until the electroweak phase transition, they source a contribution to the baryon asymmetry of the Universe. In this Letter, we demonstrate that lepton flavor asymmetries above |μ|/T∼9×10^{-3} trigger this mechanism even for vanishing total lepton number.

Baryon Asymmetry of the Universe from Lepton Flavor Violation.

Charged-lepton flavor violation (CLFV) is a smoking-gun signature of physics beyond the standard model. The discovery of CLFV in upcoming experiments would indicate that CLFV processes must have been efficient in the early Universe at relatively low temperatures. In this Letter, we point out that such efficient CLFV interactions open up new ways of creating the baryon asymmetry of the Universe.

Wash-In Leptogenesis.

We present a leptogenesis mechanism based on the standard type-I seesaw model that successfully operates at right-handed-neutrino masses as low as a few hundred TeV. This mechanism, which we dub wash-in leptogenesis, does not require any CP violation in the neutrino sector and can be implemented even in the regime of strong wash-out. The key idea behind wash-in leptogenesis is to generalize standard freeze-out leptogenesis to a nonminimal cosmological background in which the chemical potentials of all particles not in chemical equilibrium at the temperature of leptogenesis are allowed to take arbitrary values.

NANOGrav Results and LIGO-Virgo Primordial Black Holes in Axionlike Curvaton Models.

We discuss a possible connection between the recent NANOGrav results and the primordial black holes (PBHs) for the LIGO-Virgo events. In particular, we focus on the axionlike curvaton model, which provides a sizable amount of PBHs and gravitational waves (GWs) induced by scalar perturbations around the NANOGrav frequency range. The inevitable non-Gaussianity of this model suppresses the induced GWs associated with PBHs for the LIGO-Virgo events to be compatible with the NANOGrav results.

Rapid Bound State Formation of Dark Matter in the Early Universe.

The formation and decay of dark matter (DM) bound states deplete the thermal relic density during the chemical decoupling process, allowing for larger DM masses. While so far the bound state formation (BSF) has been described via the emission of an on-shell mediator, we point out that this particular process does not have to be the dominant one in general. If the mediator is coupled in a direct way to any relativistic species present in the early Universe, we demonstrate that BSF can much more efficiently occur through particle scattering.