Gravitation, Cosmology and Astrophysics Physicist (PhD)

## About the work

**CritPt** is a public benchmark of research-level physics challenges, built to test whether frontier AI models can carry out genuine physics research reasoning rather than textbook problem solving. The benchmark paper is [**arXiv:2509.26574**](https://arxiv.org/abs/2509.26574) and we recommend reading it before applying. It will tell you quickly whether this work interests you.

We are engaging physicists to work on research-level physics problems in their own subfield. Depending on where your publication record fits, that can mean creating problems, solving them, reviewing completed work, or auditing it. We agree the specific assignment with you once you are matched to an area.

This is research-grade work rather than volume work. Whatever you produce has to be complete enough for another specialist in your subfield to follow and verify independently, so written reasoning is part of every assignment.

## Research areas in this panel

Four areas, three in torsionful gravity and axion inflation and one in high-energy astrophysics. We match narrowly: you need to have published on one of these specific phenomena, not in gravitation broadly. Each area lists the methods it requires.

**1\. Einstein-Cartan and Nieh-Yan axion inflation: perturbations and power spectrum:** Einstein-Cartan-Palatini first-order gravity, Nieh-Yan topological invariant, spacetime torsion in the tetrad formalism, pseudoscalar axion inflation, natural inflation potentials, cosmological perturbation theory, Mukhanov-Sasaki mode equation, primordial curvature power spectrum, slow-roll approximation.

**2\. Einstein-Cartan and Nieh-Yan axion inflation: FRW background dynamics:** First-order Palatini formulation of gravity, tetrad and spin-connection variables, Einstein-Cartan gravity with torsion, Nieh-Yan topological term, axionic natural inflation potential, FRW background cosmological dynamics, numerical integration of background field equations.

**3\. Dynamical Chern-Simons gravity in Palatini formalism, parity-violating inflation:** First-order Palatini and Einstein-Cartan formulations of gravity, tetrad and spin-connection variables, spacetime torsion and contorsion decomposition, gravitational Chern-Simons coupling of a pseudoscalar to the Pontryagin density, parity violation in the gravitational sector, FRW background cosmology and slow-roll inflation, numerical integration of coupled cosmological field equations.

**4\. High-energy astrophysics: blazar jets, photohadronic emission, multimessenger constraints:** Relativistic jet beaming and Doppler boosting, photopion production at the Delta resonance, photohadronic interaction optical depth, electromagnetic cascade emission, synchrotron target photon fields, one-zone blazar emission modeling, variability-based causality constraints, multimessenger X-ray constraints.

## Methods we expect to find in your own publications

You should be able to point to your own papers demonstrating **at least one** of the following families:

• First-order gravity: Einstein-Cartan-Palatini formalism, tetrad and spin-connection variables, spacetime torsion and contorsion decomposition
• Topological terms in gravity: Nieh-Yan topological invariant, gravitational Chern-Simons coupling to the Pontryagin density
• Cosmological perturbation theory: Mukhanov-Sasaki mode equation, primordial curvature power spectrum, slow-roll approximation
• Numerical cosmology: integration of coupled background field equations in modified gravity
• Astroparticle modelling: relativistic beaming and Doppler boosting, photohadronic processes, electromagnetic cascades, one-zone emission models

## Who we are looking for

**A PhD in gravitation, cosmology, astroparticle physics or a closely related field.** This is a hard requirement. Postdoctoral researchers, research scientists and junior faculty are the strongest fit. Senior PhD students with a strong first-author record are welcome to apply.

**Pu