Research
See iNSPIRE or arXiv for an up-to-date list of my papers
Some current areas of interest are:
Kosmic Field Theories — Holographic Duals to Cosmological Spacetimes
I work on developing holographic descriptions of cosmological spacetimes, with a particular focus on understanding quantum gravity in de Sitter space. This includes building frameworks where cosmological observables are computed from lower-dimensional dual theories, analogous to AdS/CFT, and exploring how such dualities encode physically measurable quantities like correlators and the Wavefunction of the Universe.
Cauchy Slice Holography
Cauchy Slice Holography is a program aimed at formulating holographic duals defined on spacelike slices, whether that be in static (e.g Anti-de Sitter space) or cosmological spacetimes (particularly de Sitter space). This approach emphasises wavefunctionals on constant time slices and their relationship to boundary data, seeking a non-perturbative description of bulk quantum gravity. The goal is to understand how bulk dynamics and constraints, such as diffeomorphism invariance and unitarity, are realised holographically.
Cosmological Correlators
The study of cosmological correlators lies at the intersection of modern field theory and observational cosmology. Cosmological correlators are expectation values of fluctuations (e.g., scalar and tensor modes) that are imprinted in the early universe. By applying tools from effective field theory, scattering amplitudes, and bootstrap techniques, we can extract model-independent signatures of fundamental physics during inflation or other early acceleration phases. These correlators provide powerful probes of unitarity, locality, and symmetry principles at energy scales (> 10^6 TeV) far beyond terrestrial colliders, and connect directly to observables like non-Gaussianities in the Cosmic Microwave Background.
Curvature Tension: Is our universe curved or flat?
I am also interested in questions related to the large-scale geometry of the universe, especially in understanding whether spatial curvature is truly zero within observational limits or whether there exist persistent hints of curvature. This includes developing analytical frameworks to treat primordial power spectra in curved backgrounds and assessing theoretical priors for curvature from fundamental physics.
Recent job talk explaining some of these cool concepts!
Summaries of my papers (which are hopefully pedagogical!) can be found below:
Analytical approximations for curved primordial tensor spectra
In this work, I (with my mentee, Ezra Msolla) developed analytical templates for how primordial gravitational waves (tensor perturbations) behave when the early universe had non-zero spatial curvature. These templates do not assume a specific inflation model, so they isolate the universal imprint of curvature on gravitational waves. We show that curvature changes the effective wave modes and leads to distinctive features — such as a modified spectrum at large angular scales and oscillatory behaviour — which could appear in the Cosmic Microwave Background (CMB)’s B-mode polarisation. This gives a way to use gravitational wave signatures to test spatial curvature in the early universe via future CMB observations.
Holographic Cosmology at Finite Time
This paper explores how Cauchy Slice Holography — a holographic description where the dual theory lives on spacelike slices — can work in de Sitter (inflation-like) spacetimes. We show that by deforming a candidate dual field theory with a specific operator (a so-called $T^2$ deformation), you get a boundary theory where time itself emerges as a renormalisation group scale. We compute two-point functions (for scalars and gravitons, as well as their conjugate momenta) in this deformed boundary theory and find exact agreement with wavefunction coefficients computed directly in the bulk spacetime at finite time; we simultaneously address some confusion in the literature regarding holographic renormalisation in cosmology and its relevance for obtaining the correct scaling of conjugate momentum correlators. This confirms that the deformation encodes finite-time cosmological dynamics, and sheds light on how holography might capture cosmology without relying on asymptotic boundaries at infinite time.
Kosmic Field Theories: Towards Holographic Duals for Unitary String Cosmologies
In this work, we proposed a new class of large-$N$ holographic theories, which we call Kosmic Field Theories (KFTs), as potential duals for cosmological spacetimes — including those that arise from string theory. Unlike traditional conformal theories, these allow complex phases in parameters like $N$ and the ’t Hooft coupling in such a way that their correlation functions match the unitarity reality conditions expected of cosmological wavefunctions. Crucially, these phases are not just mathematical artefacts, but are required if the holographic dual is to reproduce physical unitarity in the bulk. This provides a new route to building holographic descriptions of cosmology, where bulk unitarity and reality conditions — central to quantum physics — are respected.
Recent talk on arXiv:2510.21701
The Phase of the Cosmological Wavefunction (PhD thesis)
My thesis studies how fundamental principles like symmetry, unitarity, and locality constrain the wavefunction of the universe and cosmological correlators — particularly in inflationary (nearly de Sitter) spacetimes. The key idea is that these principles are so powerful that they not only help determine the magnitude and kinematic structure of cosmological observables, but also their complex phases, which encode qualitative features such as parity or time-reversal behaviour. I develop both perturbative and non-perturbative tools to extract these constraints, showing that discrete symmetries such as cosmological CPT and bulk unitarity severely restrict the allowed forms of wavefunction coefficients and correlators. The thesis builds an analytic understanding of how deep symmetry principles shape observable cosmological fluctuations, tying quantum gravity intuition to inflationary predictions.
No-go Theorem for Cosmological Parity Violation
This paper uses discrete symmetry constraints — especially those derived from the Cosmological CPT theorem — to show that in even spacetime dimensions, parity-odd cosmological correlators (signals that distinguish left- vs right-handedness) must vanish if the theory has only massless scalar and even-spin fields and starts in a standard vacuum state. That means many proposed mechanisms for generating parity violation in inflationary observables are ruled out by quite general symmetry and unitarity assumptions. The result establishes that any detected parity-violating signal in data would be an exceptionally sensitive probe of new physics beyond vanilla inflation.
Recent talk on arXiv:2501.06383
The Cosmological CPT Theorem
In this paper, written with Harry Goodhew and Aron Wall, we rederived the classic CPT theorem of quantum field theory — a foundational result in particle physics — in a way that allows for precise converse statements and a natural extension to cosmological spacetimes.
We showed that the usual CPT symmetry can be understood as emerging from three distinct ℤ₂ × ℤ₂ symmetries. Two of the nontrivial elements are:
- Reflection Reality, implied by unitarity, specifically any theory with an indefinite (not necessarily positive) norm.
- A 180-degree rotation, implied by Lorentz invariance.
The third symmetry is CRT, which resolves a longstanding conceptual puzzle:
How can CRT be antiunitary in Lorentzian signature while the 180-degree rotation is a linear symmetry? (See e.g. Appendix C of arXiv:2503.12771 by Edward Witten.)
The answer is that Reflection Reality is antiunitary, and when combined with the 180-degree rotation, it produces CRT. Similar logic applies to the other symmetry combinations. This clarifies the structural origin of CPT in a precise and group-theoretic way.
We then extended this structure to expanding cosmological spacetimes. In that setting, we showed that:
- Reflection Reality, implied by BULK Unitarity, specifically any theory where the bulk inner product has an indefinite (not necessarily positive) norm.
- A 180-degree rotation, implied by Scale/boost invariance.
together imply a cosmological version of CPT that fixes the phase of all late-time cosmological wavefunction coefficients, without requiring ad hoc analytic continuations.
This result is powerful because the phase of the wavefunction controls subtle effects such as parity properties and holographic duals to cosmological spacetimes. The converse statement of the Cosmological CPT Theorem also reveals how bulk unitarity manifests in cosmological spacetimes — a longstanding question in de Sitter holography and holographic cosmology
How does bulk unitarity manifest itself in the non-reflection positive holographic boundary theory, where the dual theory lacks an intrinsic notion of time and time is an emergent dimension? (See e.g. end of Section 6 of arXiv:1204.1057 by Gim Seng Ng and Andrew Strominger.)
In particular, we obtain a non-perturbative bulk unitarity constraint on the Wavefunction of the Universe, providing a foundational result for both inflationary cosmology and de Sitter holography. This work therefore connects deep structural aspects of quantum field theory to the fundamental physics of the early universe.
Recent talk on arXiv:2408.17406
On Graviton non-Gaussianities in the Effective Field Theory of Inflation
In this paper, with Giovanni Cabass, David Stefanyszyn, and Jakub Supeł, we systematically classify and compute parity-even three-point functions (bispectra) of gravitons within the Effective Field Theory of Inflation framework. We show that all possible cubic interactions that can contribute to graviton non-Gaussianities come from a small set of operators involving extrinsic curvature and its derivatives. By organising these contributions and using efficient tests like the Manifestly Local Test, we extract analytic forms for the bispectra and identify their physical signatures. This work clarifies which inflationary interactions can produce observable gravitational wave non-Gaussianities and helps connect theory with potential future measurements of tensor modes.
Recent talk on arXiv:2209.00677
Analytical approximations for curved primordial power spectra
In this paper, I (with Denis Werth and Will Handley) developed analytical expressions for primordial power spectra in inflationary models with spatial curvature. We showed how curvature modifies the scalar perturbation spectrum and provided approximations that match fully numerical calculations. These results help interpret how spatial curvature could leave imprints on large-scale CMB anisotropies, and provide tools to test curvature with observational data. This work also laid the groundwork for extensions to tensor modes (see arXiv:2511.10644) and connects to debates on whether our universe is exactly flat or slightly curved (see e.g. arXiv:1911.02087).