# PhD project: Quantum entanglement in the early universe

## Project description

The main goal of this project would be to establish the quantum origins of inflation, and find observational signatures for it. The structure of galaxy distributions we see in the sky today is said to have its origins in the quantum vacuum fluctuations during inflation. Therefore, if the large scale structure of our universe originates from quantum fluctuations, we should be able to see evidence of quantum entanglement between these fluctuations from observational data.

The early universe presents a unique arena for us to apply quantum mechanics, one in which the 'system' and 'environment' do not remain fixed. This is known as an 'open quantum system' -- one in which there is exchange of information between the system and environment degrees of freedom, typically leading to interesting physics in the form of dissipative effects, although the latter is often ignored in standard QFT treatments. The main goal of this project would be to treat the early universe as an open quantum system and to discover hitherto unobserved signatures of quantum corrections resulting from entanglement between system and environment modes. Although common in other branches of physics, open quantum systems have remained largely unexplored in cosmology.

The benefits of such a program are manifold. Firstly, it would help establish the quantum origins of inflation and find a smoking gun for it vis a vis alternate mechanisms of the early-universe (such as bouncing models), by finding new observable signatures for the power spectrum, bispectrum and other higher order correlation functions. Secondly, this will start a new line of enquiry into the standard assumptions (e.g., of the Markovian nature of the quantum system) which are often invoked for studying quantum corrections during inflation. We will quantify the effects of relaxing these oft-used approximations on observable predictions of inflation. Finally, studying the momentum-space entanglement of quantum fields in inflationary backgrounds have deep implications for the lifetime of quasi-de Sitter spacetimes and for understanding (the analogue of) the Page curve for de Sitter. This last step is thought to be crucial is understanding the UV-completion of de Sitter space within some quantum gravity theory (such as string theory).

## Project supervisor

- Dr Suddhasattwa Brahma (School of Physics & Astronomy, University of Edinburgh)

The project supervisor welcomes informal enquiries about this project.

## Find out more about this research area

The links below summarise our research in the area(s) relevant to this project:

- Find out more about Fundamental Theory.
- Find out more about Particle Cosmology.
- Find out more about Particle Physics Theory.
- Find out more about the Institute for Particle and Nuclear Physics.

## What next?

- Find out how to apply for our PhD degrees.
- Find out about fees and funding and studentship opportunities.
- View and complete the application form (on the main University website).
- Find out how to contact us for more information.