We investigate the potential of gravitational-wave background searches to constrain cosmic histories characterised by a stiff equation of state, preceded by a period of matter domination. Such a scenario leads to a characteristic peak in the primordial gravitational-wave spectrum originating from cosmological inflation. Assuming instant transitions between distinct epochs, which allows an...
The recent adoption of the LISA mission by the European Space Agency marks a significant milestone for gravitational wave cosmology, offering unprecedented sensitivity to gravitational wave backgrounds emitted at temperatures around a few hundred GeV. Intriguingly, this temperature range not only corresponds to the electroweak epoch but also coincides with the scale at which the freeze-out of...
In recent years, wash-in leptogenesis has emerged as a new mechanism to explain the baryon asymmetry of the universe. In contrast to other leptogenesis scenarios it does not require CP-violation in the right handed neutrino sector (RHN). Instead it relies on primordial charge asymmetries generated at higher energies which are washed into a non vanishing B-L asymmetry via RHNs.
In this talk we...
Hot viscous plasmas unavoidably emit a stochastic gravitational wave background similar to electromagnetic black body radiation. Presenting work published in 2312.13855, we study the hidden particle contribution to the background emitted by the primordial plasma in the early universe. While this contribution can easily dominate over that from Standard Model particles, we find that both are...
We consider phase transitions with symmetry restoration, where particles
become massless inside the bubbles, and the leading order friction is
negative, causing the expanding bubble walls to accelerate, contrary to
standard phase transitions. We study the next to leading order
corrections arising from transition radiation in this case, which are
known to prevent runaway behavior in...
Isotropic Birefringence — all-sky rotation of linear polarization — of the cosmic microwave background (CMB) can be sourced by axion-like particle dark matter. We predict distinct signals from oscillating ultra-light axion dark matter present at recombination as well as locally. Using Planck CMB upper limits while incorporating allowed axion fractions of dark matter, we find strong constraints...
The Hubble Tension is the discrepancy between the measured value of the Hubble parameter $H_0$ and its $\Lambda$CDM model prediction using the Planck CMB data. New Early Dark Energy (NEDE) addresses this tension using a triggered phase transition in the dark sector. In this work we constrain the phenomenological fluid model properties of NEDE using recent datasets. We allow the equation of...
Gravity constrains the range of validity of quantum field theory. As has been pointed out by Cohen, Kaplan, and Nelson (CKN), such effects lead to interdependent ultraviolet and infrared cutoffs that may stabilize the dark energy of the universe against quantum corrections, if the infrared cutoff is set by the Hubble horizon. As a consequence of the cosmic expansion, this argument implies a...
The universe's current acceleration is a pretty recent phenomenon in cosmological time scales. This means that the modes that have left our horizon since the beginning of the contemporary acceleration phase, have not really reached the exact IR limit. Noting this observation, we reconsider the possibility of having a ghost condensate as dark energy with a sixth-order dispersion relation....
The existence of a relic neutrino backgorund (R$\nu$B) is a major prediction of the standard cosmological model, but its detection is one of the hardest tasks in neutrino physics. The main challenge arises because of its extremely low energy, as a consequence of its low temperature $T_\nu\simeq 1.67×10^{−4}$ eV. The most promising experimental technique to detect the R$\nu$B is that of...
Pulsar observations were the beginning of gravitational wave measurements. They recently came into the focus again with the publications from pulsar timing array organisations. But not only the transmission of gravitational waves, also their emission can be investigated using these systems. With the growing number of very precise observations of pulsars in binary systems it became possible to...
