# Nathan Moynihan

# ABOUT ME

My research is focussed on two main areas:

- Modern formulations of scattering amplitudes and what they can teach us about gravity,
- Entanglement entropy & Complexity (and other information theoretic quantities) in QFT and how it can be used to learn about dualities between field theories and gravity.

If you want to know more about my research, head over to my research or check out my up to date CV. In addition to studying physics, I am also a keen photographer, and if you would like you can check out some of my work below. I am mostly interested in Landscape, Animal, Portrait, Fashion and Artistic Nude photography, but frankly i’ll dabble in anything. At some point I would love to get into astrophotography, but I never seem to find the time…

# PHOTOGRAPHY

A selection of my most recent photography is below. For more of my work, check out my profile on 500px.

# MY RESEARCH

# Amplitudes

Scattering events are common areas of interest in many different areas of physics. In Quantum Field Theory (QFT), one of the most fundamental quantities calculated is a scattering amplitude – the square of which gives you the probability of a given scattering event occurring. In the last two decades, scattering amplitudes in QFT have had a bit of a revolution, partially initiated with introduction of twistor variables to the field in 2004. I am interested in how we can use this modern formulation to understand theories of gravity and to understand any dualities that may exist between those theories and well known gauge theories (for example, the BCJ duality). One key idea of the amplitudes programme that is particularly interesting is that spacetime is *not *the best place to do quantum field theory calculations. Working in an auxilliary space (such as twistor space) seems to in some sense be more natural, showing an underlying mathematical structure that is otherwise obscured. I am interested in attempting to understand how deformations of general relativity behave in these auxillary spaces, specifically using the structure of the amplitudes programme.

In their most basic form, dualities are mappings between theories. They allow you to calculate quantities of interest in one theory by first mapping them to another (hopefully simpler) theory, doing the the calculation there and then mapping back to see the answer in the original theory. This has proven to be an immensely useful tool in modern physics, allowing deep insights to be made that might have otherwise remained hidden. I am interested in dualities in low-dimensional field theories, for example the bosonization of theories involving fermions. In particular, I am interested in using the tools of information theory to probe dualities (3D Bosonization, AdS/CFT) in QFT and in turn to use dualities to understand the role of information theoretic quantities in characterising those theories. I am also interested in dualities between gravity and field theories that exist both classically (known in the literature as the classical double copy) and quantum mechanically (i.e. loops) at the amplitude level (the BCJ duality). So far, these dualities have been formulated for GR and Yang Mills type gauge theories, but it might be interesting to find out if deformations of these theories produce similar dualities.

Gravity is one of the most fascinating forces of nature. On one hand, from the lofty perspective of general relativity, it’s very well understood. On the other hand, when looked at quantum mechanically, it just doesn’t work properly and often leads to baffling paradoxes. My interest is in how Gravity can be understood through the lens of Quantum Field Theory, and whether certain dualities between gauge theories and gravity can tell us something interesting. Using the tools of information theory, a precise paradox can be formulated that seems to require that either quantum mechanics or general relativity needs to be reformulated. In the last few years, some interesting progress has been made on this front in the form of firewalls, complementarity and ER = EPR, but each formulation doesn’t quite seem to fit the bill and in my opinion is still a very open arena filled with interesting questions. Using the tools of quantum information and AdS/CFT, we are able to probe some aspects of quantum gravity in an interesting way. Sharpening our understanding of these tools is an important step in the direction of a quantum theory of gravity.

Information theory is really a branch of computer science, and yet in the last few years it has found itself a comfortable home in theoretical physics. I am interested in *quantum* information theoretic quantities – things like computational complexity, entanglement entropy, mutual information etc, attempting to understand what these quantities can tell us about quantum field theories.

Information seems to be a deep concept in physics, and while some stuff is known about the role it plays, there is a lot left to find out. One particularly interesting idea is the connection between information and gravity, as there is emerging evidence that both gravity and spacetime itself may well be a manifestation of quantum information in a way that we have yet to fully understand.

### SAY HELLO

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