Conveners
T02: Cosmology: Part 1
- Marko Simonovic (CERN)
T02: Cosmology: Part 2
- Camille Bonvin (University of Geneva)
T02: Cosmology: Part 3
- Thomas Konstandin (T (Cosmology))
Heavy QCD axion models are motivated by the so-called "quality problem", the sensitivity of the QCD axion to misaligned contributions to its potential.
In this talk I will show that despite the absence of axion relics today, these models can generically produce a large amount of gravitational waves, a non-vanishing theta angle and, in some cases, both signals simultaneously.
Therefore, I...
QCD Axions can be produced in various ways in the Early Universe by scatterings and decays from Standard Model particles, forming thus a Cosmic Axion Background that contributes to the abundance of relativistic relics (N_eff). We review in various setups how this is already constrained by present experiments and how it could be observed by future CMB experiments, in particular focusing on the...
Axion-like-particle (ALP) is a well-motivated candidate for dark matter, and it has been subject to extensive theoretical and experimental research in recent years. The most popular ALP production mechanism studied in the literature is the misalignment mechanism, where the ALP field has negligible kinetic energy initially, and it starts oscillating when its mass becomes comparable to the...
High energy embeddings of inflation often lead to departures from the single-field slow-roll paradigm, resulting in features in the primordial scalar power spectrum. Probing these features could, for instance, establish the existence of heavy particles beyond the reach of terrestrial experiments, and even test the inflationary paradigm or point to alternatives to it. To date, observational...
The Universe is homogeneous and isotropic on large scales, so on those scales it is usually modelled as a Friedmann-Lemaître-Robertson-Walker (FLRW) space-time. The non-linearity of the Einstein field equations raises concern over averaging over small-scale deviations form homogeneity and isotropy, with possible implications on the applicability of the FLRW metric to the Universe, even on...
Galaxy formation in the first billion years mark a time of great upheaval in the history of the Universe: as the first sources of light, these galaxies ended the 'cosmic dark ages' and produced the first photons that could break apart the hydrogen atoms suffusing all of space starting the process of cosmic reionization. As the earliest building blocks, the galaxies that formed in the first...
Due to the quantum origin of primordial perturbations, the early universe is an ideal setup for the interplay between gravity, quantum physics and thermodynamics. In this talk I will discuss results and ongoing work on the role that mutual information between distant regions play in cosmology.
Self-interaction among the neutrinos in the early Universe has been proposed as a solution to the Hubble tension, a discrepancy between the measured values of the Hubble constant from CMB and low-redshift data. However, flavor-universal neutrino self-interaction is highly constrained by BBN and several laboratory experiments such as, tau and K-meson decay, double-neutrino beta decay etc. In...
In this talk, we present a reconstruction of the neutrino mass as a function of redshift, $z$, from current cosmological data using both standard binned priors and linear spline priors with variable knots. Using Planck 2018 cosmic microwave background temperature, polarization and lensing data, in combination with distance measurements from baryonic acoustic oscillations and supernovae, we...
In first-order cosmological phase transitions, the asymptotic velocity of expanding bubbles is of crucial relevance for predicting observables like the spectrum of stochastic gravitational waves, or for establishing the viability of mechanisms explaining fundamental properties of the universe such as the observed baryon asymmetry. In these dynamic phase transitions, it is generally accepted...
The current experimentally measured parameters of the Standard Model (SM) suggest that our Universe lies in a metastable electroweak vacuum, where the Higgs field is prone to vacuum decay to a lower state with catastrophic consequences. Our measurements dictate that such an event has not taken place yet, despite the many different mechanisms that could have triggered it in our past light-cone....
A new class of inflationary attractors characterized by a strongly non-geodesic motion has been discovered in the past few years. I will describe how they naturally arise in negatively curved field space, allowing to inflate on potentials that are steep in Planck units. In these scenarios, primordial fluctuations often experience a transient tachyonic instability, akin to the one occurring in...
A fast-spinning axion can dominate the Universe at early times and generates the so-called kination era. The presence of kination imprints a smoking-gun spectral enhancement in the primordial gravitational-wave (GW) background. Current and future-planned GW observatories could constrain particle theories that generate the kination phase. Surprisingly, the viable parameter space allows for a...
In the model of low-energy quantum gravity by the author the
cosmological redshift and additional dimming of remote objects may
be interpreted as results of scattering of photons on gravitons of
the background. A tentative detection of a diffuse cosmic optical
background by the New Horizons mission may be connected with
non-forehead collisions of photons with gravitons, too....
