## Precision Phenomenology of Elementary Particles at Colliders

The Large Hadron Collider (LHC) at CERN probes the basic laws governing the interactions among elementary particles and offers the widest range of physics opportunities in the exploration of unprecedented energy regimes. The discovery of a Higgs boson-like particle in 2012 marks the end of a decades-long search and has fortified the Standard Model (SM) of particle physics as the best description of nature at the fundamental level.

At the same time, the SM is known to be theoretically incomplete and can therefore be considered valid only in a limited range of energies. However, striking signals of physics beyond the SM still remain absent to date. Elusive new-physics phenomena are therefore likely hiding in small and subtle effects, which need to be pinned down through detailed studies that confront the experimental data with theoretical predictions. Precision measurements of so-called “standard-candle processes” as well as the determination of the properties of the Higgs boson are therefore among the highest priorities of the LHC programme and possible future colliders.

Such studies, however, critically rely on our ability to predict both signal and background processes with high precision. Possible PhD projects will focus on precision calculations within the SM and their phenomenological applications and will be closely aligned with the physics programme of the LHC and possible future colliders. Those projects requite the application and development of analytical and numerical techniques, as well as the use of high-performance computing resources.

## Electroweak symmetry breaking, flavour physics and ultralight Dark Matter

The mass spectrum of known elementary particles spans 12 orders of magnitude from sub eV neutrino masses to the heavy flavours and the Higgs whereas the unknown, particle dark matter, could be orders of magnitude heavier than the top quark or lighter than neutrinos by almost 20 orders of magnitude. Yet the highest of these masses still lies 15 orders of magnitude below the Planck mass where new states should arise to render gravity consistent. Is there a hidden structure behind this disparity of scales or within any of these sectors? The big picture however can only be addressed starting small and so PhD students would begin dedicated to any of the following projects: i) electroweak symmetry breaking and the nature of the Higgs; characterize the scalar particle found at LHC with the incoming data and making use of effective field theory to determine how closely it behaves as elementary ii) the flavour of standard model particles; study possible underlying symmetries to explain the generational structure of fermions and derive phenomenological consequences be it with effective field theory or models of gauged flavour iii) searches for ultralight dark-matter; study the reach of very precise quantum devices like co-magnetometers and atomic clocks in the search for dark matter so light that it behaves like a background field around us iv) the UV completion of gravity; making use of the basis for amplitudes of on-shell spin J exchange search numerically for solutions to the unitarization of gravity, as well as using a bottom-up approach in deriving consistency constraints on the spectrum of new states.

## Effective Quantum Field Theories for the LHC

Effective field theories are a powerful tool for tacking problems in quantum field theory characterised by two or more disparate energy scales. Expertise in effective theories can be applied to many areas of particle physics phenomenology, from generating all-orders perturbative results (i.e. resummation) for scattering cross sections, to searching for signs of new physics through non-standard interactions of Standard Model particles. A PhD project in this direction will thus involve becoming familiar with effective-field theory machinery in general, and then applying it to a specific directions in LHC phenomenology, which can be shaped according to the interests of the student. As concrete examples, my current PhD students are developing techniques for calculating quantum corrections to Higgs boson decays in the “Standard Model Effective Field Theory” on the one hand, and using machine learning and deep neural networks in order to search for new interactions at the LHC on the other.

## Searching for Dark Matter and fifth forces with Ultracold H Atoms

It is conventionally accepted that there are four fundamental forces in nature: gravitational, electromagnetic, strong nuclear and weak nuclear forces. However, the existence of dark matter and dark energy have led many to postulate a “fifth” force that acts over a range anywhere from nanometres to cosmological distances. For very light masses, Dark Matter is also predicted to act like a fifth force, but can be distinguished by the time-dependence of the signal.

In this PhD project, you will develop a source of ultracold (μK) hydrogen or deuterium atoms that you will use for making precision spectroscopic measurements of Rydberg states that may reveal a fifth force acting on atomic length scales. Such a force would be carried by a new dark-matter boson with rest mass on the order of eV to keV.

This PhD project is experimental, but tightly integrated in the quantum sensors for fundamental science project between the IPPP and the Quantum, Light and Matter groups in Durham. Regular meeting and shared lecture courses with the theory group will provide a background in the particle physics theory underpinning this experiment and the candidate will be involved in publications produced between the experimental and theory groups. If you apply for a PhD position at the IPPP, please indicate whether you are interested in this position.