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 our observables are part of a much larger system. Thus, we need an open quantum system approach to study early-universe dynamics. More generally, gravity creates boundaries of spacetime, which restrict our observables while still allowing the flow of information and energy across it, known as "horizons". We need an open EFT in such scenarios, going beyond standard treatments of QFT in flat space, to account for the interesting physics resulting from such dissipative (and diffusive) effects due to such exchanges between the 'system' and the 'environment'. Restricted to the observable 'system' modes alone, the evolution equations are non-unitary in nature which can be handled by importing techniques from Quantum Information Theory.
One of our recent findings have shown that not only are there non-unitary effects present in the open EFT of inflation (or, more generally, of any accelerating backgrounds), these dissipative effects are often non-local as well. The main goal of this project would be to treat the early universe as an open quantum system and to discover hitherto unexplored (time) non-local effects on the dynamics of the system observables. We have seen that, in toy models, late-time infrared divergences in de Sitter space can arise from time non-local terms in the so-called memory kernel but, more importantly, they can still be non-perturbatively resummed using new techniques giving us new insights for such systems.
The benefits of such a program are manifold. Firstly, it would help establish the quantum origins of structure in our universe and find a smoking gun for it by finding new observable signatures for the power spectrum, bispectrum and other higher order correlation functions. Moreover, such dissipative/thermal effects can significantly influence predictions for primordial magnetic fields or the abundance of primordial black holes. 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 stochastic inflation. This will lead to new constraints on allowed models in the parameter space of inflation. Finally, studying the entanglement of quantum fields in inflationary backgrounds have deep implications for the lifetime of quasi-de Sitter spacetimes and for understanding how information backflow might happen between localized regions of spacetime for non-Markovian systems. This last step will be crucial in 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.