Particle Production in the Early Universe

The paradigm of cosmic inflation explains our observations of the cosmic microwave background spectacularly well. To proceed in the quest of pinning down the particle physics model behind this very early phase of the Universe, multi-wavelength observations of the power spectra of the anisotropies generated during cosmic inflation are crucial. If the inflaton is a pseudo-Goldstone boson (a possible explanation for the required flatness of the inflaton potential), the couplings of this inflaton to the Standard Model may provide a window to probe inflation over a very wide range scales: as I will argue in this talk, different plausible couplings to gauge fields and fermions lead to unique signatures in the scalar and tensor power spectra at small scales. I will discuss possibilities to probe these scales, with a special focus on gravitational wave observatories

Gravitational Waves

4 x 90 minute

Probing the early Universe with gravitational waves

Gravitational waves are unique messengers to explore the very early universe, probing energy ranges far beyond the reach of photon or even neutrino astronomy. The holy grail in this context is to detect imprints left by cosmic inflation, which would shed light on the microphysics of inflation as well as on the entire subsequent cosmological history. In the simplest model of inflation such signals are however beyond the reach of current and planned gravitational wave interferometers. After reviewing this standard picture, I will discuss how considering a pseudoscalar inflaton (an axion-like particle) can be a real game-changer, boosting the primordial gravitational wave signal into the range accessible by experiments such as eLISA and LIGO/VIRGO and simultaneously generating a spectrum of primordial black holes, which can contribute to dark matter

Probing the early Universe with gravitational waves

Gravitational waves are unique messengers to explore the very early universe, probing energy ranges far beyond the reach of photon or even neutrino astronomy. The holy grail in this context is to detect imprints left by cosmic inflation, which would shed light on the microphysics of inflation as well as on the entire subsequent cosmological history. In the simplest model of inflation such signals are however beyond the reach of current and planned gravitational wave interferometers. After reviewing this standard picture, I will discuss how considering a pseudoscalar inflaton (an axion-like particle) can be a real game-changer, boosting the primordial gravitational wave signal into the range accessible by experiments such as eLISA and LIGO/VIRGO and simultaneously generating a spectrum of primordial black holes, which can contribute to dark matter

Baryogenesis from axion inflation

The coupling of an axion-like particle driving inflation to the Standard Model particle content through a Chern-Simons term generically sources a dual production of massless helical gauge fields and chiral fermions. We demonstrate that the interplay of these two components results in a highly predictive baryogenesis model, which requires no further ingredients beyond the Standard Model. If the helicity stored in the hyper magnetic field and the effective chemical potential induced by the chiral fermion production are large enough to avoid magnetic diffusion from the thermal plasma but small enough to sufficiently delay the chiral plasma instability, then the non-vanishing helicity survives until the electroweak phase transition and sources a net baryon asymmetry which is in excellent agreement with the observed value. If any of these two conditions is violated, the final baryon asymmetry vanishes. The observed baryon asymmetry can be reproduced if the energy scale of inflation is around $H_\text{inf} \sim 10^{9}$--$10^{13}$\, GeV with a moderate dependence on inflation model parameters