2021 Highlights

IR-conformal dynamics in SU(2) gauge theories with adjoint fermions

An urgent question in Particle Physics is related to the possible existence of new interactions beyond the Standard Model. The existence of those interactions is strongly suggested by currently open problems such as the nature of Dark Matter and the naturalness of the measured value of the Higgs mass.…

The Occam’s razor equation

This equation is science in a nutshell. On the left-hand-side it has the Bayesian Evidence. This is the quantity which is responsible for updating our belief in a scientific model in light of data (for example, how much we believe in the concordance model of cosmology in light of…

Nested sampling beyond Bayesian statistics

Nested sampling is a numerical tool widely used in cosmology for performing Bayesian data analysis: using astrophysical data and models of the universe to extract parameters such as its age and its size, as well as to numerically determine which model is preferred by the data. This paper [2105.13923]…

Composite Higgs Phenomenology at the LHC

Understanding the nature of the Standard Model Higgs boson is still an open problem. An appealing possibility is that the Higgs boson be a composite particle resulting from a novel strong interaction. The lack of observation of otherwise unexplained particles interacting through this conjectured novel force and with mass…

Likelihood-free inference with Dark Energy Survey Y3 data

Project summary: Using optimised “active learning’’ to efficiently sample the cosmological model space, we will generate a suite of simulated catalogues of mock Dark Energy Survey (DES) data. These mock data are the primary input (along with the actual observed data) to the DES likelihood-free inference pipeline. This pipeline…

Solar Energetic Particle propagation in the 3D heliosphere

diffusion-based model (Laitinen et al 2016) of SEP propagation from the Sun (yellow dot in the middle) as guided by Parker spiral (black curve). During solar eruptions, charged particles are accelerated to relativistic energies. These solar energetic particles (SEPs) propagate through the interplanetary space to Earth and cause a…

Tracing the small-scale structure of the cosmic web over 12 billion years

The intergalactic medium (IGM) is the rarefied material that spans the vast distances between galaxies in the Universe.   In our DiRAC thematic project, we model the ionisation and thermal structure of the IGM using a combination of hydrodynamical structure formation simulations and GPU accelerated radiative transfer.  The results form…

Transport properties of finite-density SU(2) lattice gauge theory

Quantum Chromodynamics (QCD) is a fundamental theory of nuclear interactions, describing nucleons as composite states of quarks and gluons. Heavy-ion collision experiments create a very hot and dense phase of nuclear matter, in which nucleons melt into a quark-gluon plasma. With more than 100 nucleons participating in each collision,…

Spontaneous Symmetry Breaking in the 3d Thirring Model

PI: Simon Hands, University of Liverpool The Thirring Model describes relativistic fermions moving in a two-dimensional plane and interacting via a contact term between covariantly conserved currents. The physical system it most resembles is that of low-energy electronic excitations in graphene. For free electrons at half-filling on a honeycomb…

Kinematic signatures of gravitational instability

Young stars are born surrounded by cold discs or dust and gas. These discs act as a conduit for accretion of mass on to the central star, and also provide the raw material for planet formation. At early times these discs are thought to be sufficiently massive that they…

Decays of an exotic 1-+ hybrid meson resonance in QCD

Using cutting-edge lattice Quantum Chromodynamics (QCD) methods, in a recent calculation [Phys. Rev. D103, 054502 (2021), arXiv:2009.10034] we demonstrated the presence of an exotic hybrid meson resonance for the first time. The results suggest that it is related to the  resonance observed by the COMPASS experiment at CERN. Most…

Fundamental Physics from Strong Gravity

This project continues our work to characterise the behaviour of light fields in strong gravity environments, in particular focussing on the potential for gravitational wave signatures from dark matter, exotic compact objects and the possible formation of primordial black holes. A key highlight this year was an investigation of…

Proving a 40-year-old conjecture using lattice simulations

This project is focused on the study of field theories relevant for building holographic cosmological models. These models propose to use hypothetical theories dual to the unknown laws of gravity in the early universe and predict observable phenomena such as the cosmic microwave background (CMB). This allows to provide…

Exoplanet Science at Imperial

Project – Exoplanet Demographics In recent years, a bimodal distribution has been observed in the sizes of small, close-in exoplanets, often referred to as the ‘radius gap’. Currently there are two atmospheric evolution models which can provide explanations as to how the radius gap may arise, namely XUV photoevaporation and…

Understanding the Galaxy-Halo Connection Using the Simba Simulation

Romeel Davé, PI The Concordance Cosmological Model predicts the properties and distribution of dark matter halos with exceptional precision.  However, how these halos come to be populated with the diversity of galaxies that we observe remains unclear.  A curious recent observational result shows that at a given halo mass,…

Collisional ionisation and recombination effects in partially ionised plasma

Project dp050 PI: A. Hillier, Research by G. Murtas Plasmoid-mediated fast magnetic reconnection plays a fundamental role in driving explosive dynamics such as chromospheric jets (Shibata et al. 2007, Singh et al. 2012) and heating in the solar chromosphere, but relatively little is known about how it develops in…

Ionisation by non-thermal particles in thermonuclear supernovae

Luke Shingles, Stuart Sim, Christine CollinsAstrophysics Research Centre, Queen’s University Belfast, Northern Ireland Type Ia supernovae (SNe Ia) originate from the thermonuclear explosions of white dwarf stars. Understanding these events is important to astronomy since their brightness means they can be used to study cosmological expansion, and they are…

HPQCD: the charming strangeness of the W boson

Figure 1. When the D meson emits a W boson to become a K meson, the underlying process is a charm quark transition to a strange quark. The coupling between c, s and W is called Vcs. Theorists in the HPQCD collaboration have pinned down Vcs, a key parameter…

Quantum Electrodynamics meets Quantum Chromodynamics

The Standard Model (SM) of Elementary Particles has been extremely successful in correctly predicting and describing the properties of elementary particles studied at experimental facilities all around the world. The SM itself covers elementary particles such as quarks and electrons, for instance, and their anti-particles, which interact by means…

(π0,η,η’) mass splittings and mixings

A particularly challenging topic in the phenomenological study of QCD is the (π0,η,η’) particle mass splittings and mixings. With exact SU(3) flavour symmetry of the u, d and s quarks, the decomposition of the familiar eigenstates of the π0,η,η’ is known. However, when SU(3) and isospin are broken due…

Model independent modified gravity N-body simulations

The assumption that General Relativity is the fundamental law of gravity requires an extrapolation of many orders of magnitude from solar system length scales where the theory is well tested. This uncertainty undergirds explorations of modified gravity theories, which are further motivated by the possibility of explaining dark energy…