# Dr Ricardo Monteiro

## Royal Society University Research Fellow

Email: ricardo.monteiro@qmul.ac.uk

Telephone: 0207 882 7813

Room Number: G. O. Jones Building, Room 225

## Profile

I joined the Centre for Research in String Theory in 2017. Previously, I held research positions at CERN, at the Mathematical Institute in Oxford, and at the Niels Bohr Institute in Copenhagen. I did my graduate studies at DAMTP in Cambridge, and my undergraduate studies at IST in Lisbon.

## Teaching

I currently teach the 3rd-year course Spacetime and Gravity. The course is a basic introduction to Einstein's theory of general relativity.

I also supervise undergraduate, master and PhD projects.

## Research

### Research Interests:

I have a broad interest in high-energy theoretical physics. My recent work focuses on perturbative aspects of quantum field theory, quantum gravity and string theory.

One of my main areas of activity has been the perturbative description of gravity as a double copy of gauge theory. This idea appeared in the study of scattering amplitudes, which are notoriously complicated in theories of gravity if traditional methods are used. The double-copy technique allows us to perform certain gravity computations using much simpler computations in gauge theory. My goals here are two-fold: to investigate the mathematical structure behind the double copy, including at loop level (quantum effects), and to apply this technique to a wider set of problems, including the study of classical solutions (perturbative or exact) in gravity theories.

My other major line of work is the description of certain quantum field theories in terms of worldsheet models inspired by string theory, known as ambitwistor strings. These models underlie a new mathematical formalism for the scattering amplitudes of massless particles, based on scattering equations that relate the kinematic invariants to the moduli space of a sphere. My main focus here has been the extension of this very promising formalism to loop level, which opens the possibility of a much wider application. Both gauge theory and gravity admit this type of formalism, and this is also a promising avenue to understand the double-copy relation at a more fundamental level.

Apart from these topics, I maintain my interest for areas in which I have worked in the past. These include black holes in general relativity and in string theory, and the AdS/CFT correspondence between a theory of gravity (string theory) and a lower-dimensional (conformal) field theory.

## Funding

Significant grants held at QMUL:

Co-PI in STFC Consolidated Grant "Amplitudes, Strings and Duality" ST/T000686/1 [A Brandhuber (PI), M Buican, MB Green, RJF Monteiro, MG Perry, S Ramgoolam, R Russo, G Travaglini, C White], £890,210 (2020-2023).

PI in Royal Society Grant supporting a PhD Studentship, £85,992 (2018-2022).

PI in Royal Society Grant supporting a PhD Studentship, £85,492 (2017-2021).

PI in Royal Society University Research Fellowship, £452,148 (2017-2021)

## Supervision

**Scattering Amplitudes and Ambitwistor Strings**

This project focuses on a new approach to describe quantum field theory, and in particular to calculate scattering amplitudes, which is inspired by string theory. A new and intriguing breed of “string-like” theories, known as ambitwistor strings, is actually a class of well-known particle theories in disguise, including gravity and gauge theory. While these theories are formulated as two-dimensional conformal field theories, similarly to string theory, they do not possess the infinite tower of massive states that characterises string theory, but possess only a massless spectrum perturbatively. My recent research has opened the way to make these theories a serious tool to calculate scattering amplitudes at loop level in theories of physical interest.

The major goal of the project will be to understand the nature and the applicability of ambitwistor strings. There are plenty of questions. How does the all-loop expansion work? What is the most general class of theories that these models can describe? How can we make the calculations more efficient? Beyond scattering amplitudes, what other quantities can we calculate? Can they bring a new light into the connections between theories, such as those between gauge theory and gravity? And how does standard string theory fit into this picture?

Requirements: knowledge of Quantum Field Theory, General Relativity and String Theory at the level of a Master course.

**Gravity as a Double Copy of Gauge Theory**

This project explores a powerful connection between gauge theory and gravity, two fundamental ingredients in our understanding of Nature. It is clear that there is a close mathematical analogy between the two theories, with gauge theory describing "spin-1" particles and gravity describing "spin-2" particles. In recent years, that relationship has been shown to be much closer than previously recognised. It turns out that gravity can be expressed as a "double copy" of gauge theory, at least perturbatively. Using this technique, fiendish calculations in gravity can be substituted by much simpler calculations in gauge theory. One of the applications of the technique is to study in detail the ultraviolet divergences in a variety of theories of gravity, a problem at the heart of quantum gravity. More recently, there is a new programme to study classical solutions (either perturbative or exact) in general relativity using the double copy.

The aims of the project are (1) to understand at a more fundamental level the mathematical structure behind the double-copy relation, (2) to develop an efficient formalism for loop-level amplitudes, (3) to investigate the connection between the spaces of solutions to the Einstein equations and to the Yang-Mills equations, and (4) to explore the application of the double copy in gravitational phenomenology, namely to problems of astrophysical interest involving gravitational waves.

Requirements: knowledge of Quantum Field Theory and General Relativity at the level of a Master course.

## Public Engagement

I have outreach experience, both as a scientist and as an organiser, including Pint of Science (UK), Folkeuniversitetet (Denmark), Associacao Juvenil de Ciencia and Ciencia Viva (Portugal). I am also involved in the outreach activities of the researcher training network SAGEX.

I am available to give public talks on topics related to my work, and I am also open to other public engagement suggestions.