Building a consistent parton shower

Modern parton showers are built using one of two models: dipole showers or angular ordered showers. Both have distinct strengths and weaknesses. Dipole showers correctly account for wide-angle, soft gluon emissions and track the leading flows in QCD colour charge but they are known to mishandle partonic recoil. Angular ordered showers keep better track of partonic recoil and correctly include large amounts of wide-angle, soft physics but azimuthal averaging means they are known to mishandle some correlations. In this paper, we derive both approaches from the same starting point; linking our under- standing of the two showers. This insight allows us to construct a new dipole shower that has all the strengths of a standard dipole shower together with the collinear evolution of an angular-ordered shower. We show that this new approach corrects the next-to-leading- log errors previously observed in parton showers and improves their sub-leading-colour accuracy.

Lie Groups and Quantum Chromodynamics

This article explores the mathematics of group theory, in particular Lie groups and their representations, and its connection to quantum field theory, specifically quantum chromodynamics. The first half discusses specific Lie groups and their Lie algebras and uses this information to describe the theory of the strong force, its particle constituents and a property of subatomic particles known as colour charge. This article emphasizes the importance of utilizing abstract algebra for the continued advancement of quantum physics in the modern era.

Evolution of Colour in QCD and Informational Approach to Quantum Measurement

Quantum chromodynamics (QCD) introduces the quantum characteristic of colour in order to satisfy the Pauli exclusion principle and symmetric considerations for wavefunctions of hadrons. However, the particles that possess colour charge (quarks and gluons) are not directly observed in experiment – the effect which is often referred to as confinement. Confinement of quarks and gluons represents a theoretical challenge, as the dynamics of underlying fields is non-perturbative and therefore is problematic to be described analytically. One possible way is to use non-perturbative approaches and derive analogies with other well-established branches of physics. In this work we describe the use of the method of vacuum correlators – to analyze the confinement and other non-perturbative dynamics of quarks. The discussion of the acquired results is then given on the basis of quantum information and measurement description. It is shown that the confinement of quarks might be associated with the decoherence of colour state due to the interaction of colour charges with the environment of colour fields (QCD stochastic vacuum).

Global symmetries and Noether’s theorem

Noethers theorem shows that continuous global symmetries lead classically to conservation laws. Such symmetries can be divided into spacetime and internal symmetries. The invariance of Minkowski space-time under global Poincaré transformations leads to the conservation of the four-momentum and the total angular momentum. Examples for conserved charges due to internal symmetries are electric and colour charge. The vacuum expectation value of a Noether current is shown to beconserved in a quantum field theory if the symmetry transformation keeps the path-integral measure invariant.

3. Powerful forces

Why do atomic nuclei exist at all? A large nucleus contains many protons in close proximity. Why do these protons, all with the same electrical charge, not mutually repel? ‘Powerful forces’ shows the answer: a strong attractive force that acts between neutrons and protons when they are in contact with one another. Further studies of atomic structure have revealed that protons and neutrons are not fundamental particles. They consist of smaller particles: pions, which are made up of quarks that possess a ‘colour’ charge. The relativistic quantum theory of colour, known as quantum chromo-dynamics (QCD), is described along with ‘quark–gluon plasma’.

Soot temperature and concentration measurements from colour charge coupled device camera images using a three-colour method

The three-colour method has been developed in order to turn chromatic information in charge coupled device (CCD) camera images of combustion into flame temperature and soot concentration measurements. The method showed the following advantages over the two-colour method from which it is derived: only one camera is needed; no further calibration is required once the response curve of the camera is known; it does not rely on light intensity but on ratios between colour components, making it easy to adapt to different operating points with different name brightness. The results on temperature evaluation were compared with a thermodynamic model, and better agreement was found in the late stages of the cycle, when the radiation from chemical reactions becomes negligible. The error analysis showed that the calculations for soot concentration are ill-conditioned, but when the results are integrated to give a soot loading the accuracy is improved and there is clear evidence of soot evolution and destruction during combustion.