Project Supervisor

Professor Konstantinos Dimopoulos

Description

Cosmic Inflation in the early Universe Cosmic Inflation is a period of superluminal expansion of space just after the Big Bang. It is fixing the initial conditions of the Universe history, in that it makes the Universe large and uniform. Additionally, inflation generates quantum-mechanically the controlled violation of uniformity necessary for the build-up of structures such as galaxies and galactic clusters. Inflation is under new light due to the recent cosmological data, such as the Planck CMB observations. Several families of inflationary models are now excluded, while new research on the favoured models overlaps with concerns over the stability of the electroweak vacuum (Higgs inflation) and the UV completion of gravity (R^2 inflation). The discovery of gravitational waves has ignited new interest in detecting primordial gravitational waves, quantum generated during inflation, which are a smoking gun for inflation theory, and motivates forthcoming observations (e.g. the Einstein Telescope). Observations of primordial gravitational waves may reveal the history of the early Universe, especially if there are periods when the Universe is dominated by a stiff fluid, which enhance the primordial gravitational radiation. Such a period is a natural ingredient of quintessential inflation scenarios.

Quintessential Inflation and Dark Energy Observations suggest that the Universe at present is engaging anew in a period of late time inflation, determined by a mysterious substance called dark energy, which makes up about 70% of the density budget of the Universe today. Dark energy can be modelled similarly to primordial inflation, through a substance called quintessence. Quintessential inflation is the effort to economically treat dark energy and primordial inflation in a common theoretical framework. As such, quintessential inflation connects not only with primordial inflation data but also with imminent future dark energy observations (e.g. EUCLID), which can provide information on early Universe physics at very high energies, well beyond the reach of Earth based experiments. Moreover, quintessential inflation can exploit the famous scale mystery, whereby the scale of electroweak physics, which is explored in collider experiments such as the LHC, is roughly the geometric mean of the Planck energy scale, which is associated with gravity, and the dark energy scale. This implies that observations in the early and late Universe can be used to shed some light on particle physics phenomenology.

Primordial Black Holes are a natural outcome of many inflationary scenarios, as they can be formed by rare spikes in the spectrum of primordial density perturbations, generated by inflation. Primordial Black Holes can be the Dark Matter in the Universe, which makes up about 25% of the Universe budget at present. They could also seed the supermassive black holes which reside at the centres of galaxies and are responsible for Active Galactic Nuclei. Their formation depends not only on the details of inflation but also on the conditions in the post-inflation Universe. If they are small enough, they are expected to evaporate through the emission of Hawking radiation, which could heat the Universe after inflation but might also have many other effects on the CMB radiation. After the direct observations of binary black hole mergers, there is intense interest in exploring the cosmology of Primordial Black Holes.

Funding is available on a competitive basis. To be considered for a funded studentship, please submit your application by 31^st January 2025.

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