Strong CP problem

The strong CP problem is a question in particle physics, which brings up the following quandary: why does quantum chromodynamics (QCD) seem to preserve CP-symmetry? In particle physics, CP stands for the combination of charge conjugation symmetry (C) and parity symmetry (P). According to the current mathematical formulation of quantum chromodynamics, a violation of CP-symmetry in strong interactions could occur. However, no violation of the CP-symmetry has ever been seen in any experiment involving only the strong interaction. As there is no known reason in QCD for it to necessarily be conserved, this is a "fine tuning" problem known as the strong CP problem. The strong CP problem is sometimes regarded as an unsolved problem in physics, and has been referred to as "the most underrated puzzle in all of physics." There are several proposed solutions to solve the strong CP problem. The most well-known is Peccei–Quinn theory, involving new pseudoscalar particles called axions. Theo

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CP violation

In particle physics, CP violation is a violation of CP-symmetry (or charge conjugation parity symmetry): the combination of C-symmetry (charge symmetry) and P-symmetry (parity symmetry). CP-symmetry

Axion

An axion (ˈæksiɒn) is a hypothetical elementary particle originally postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics (QCD). If axions exist an

Dark matter

Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe. Dark matter is called "dark" because it does not appear to interact with the elect

A minimal scale invariant axion solution to the strong CP-problem

Anna Tokareva

2018

Effective Field Theories for New and Old Physics

Alfredo Glioti

Effective Field Theories have changed our understanding of Quantum Field Theories. This thesis shows several applications of this powerful tool in the context of the Standard Model and for searches of New Physics.The thesis starts with a review of the Standard Model and its open questions and is followed by an updated and systematic study of models of flavor in the context of Partial Compositeness in Composite Higgs theories. Following that, the question on how to measure the Wilson coefficients of the Standard Model effective operators at present and future experiments is addressed: first by using modern Machine Learning techniques by studying angular distributions for diboson production, followed then by a study on ElectroWeak radiation at a future Muon Collider and how to use it to better probe the new physics parameter space.The fourth chapter deals instead with applying Non-Relativistic Effective Theories to the study of exotic mesons in the Standard Model. The two competing interpretations, a molecule formed of two mesons or a compact tetraquark state, and their consequences are studied. In particular this study is done on the X(3872) exotic charmonium and the consequences of the two accidental tunings of this system are discussed.The last chapter addresses the problem of baryogenesis from the ElectroWeak phase transition. A new scalar sector is introduced that decouples the physics responsible for the generation of the baryon asymmetry from the weak scale. This helps solving the main problems that ElectroWeak baryogenesis models face, namely the large modifications to the Higgs physics and the need of large CP violating new effects.

EPFL2022

Strong CP violation, electroweak baryogenesis and axionic dark matter

Igor Tkachev

We discuss the influence of strong CP-violating effects in invisible-axion models on electroweak baryogenesis. We find that they can be important only if the electroweak phase transition (EPT) occurs simultaneously with the chirality-breaking phase transition in QCD. The predicted baryon asymmetry of the Universe (BAU) might be of order of the observable one only if there is no entropy production in the EPT. At the same time the dark-matter constraints put a lower bound on the temperature after the EPT, so that it is impossible to satisfy simultaneously both requirements (BAU and axion dark matter). We conclude that possible strong CP violation plays no role in electroweak baryogenesis, unless there exists some yet unknown mechanism for the BAU generation, producing baryons at a rate which has to be at least 3 orders of magnitude higher than the sphaleron-induced rate. In this kind of hypothetical scenario there is a prediction of the axionic dark matter in the Universe from the very existence of the baryon excess while the dark-matter density is generally of order or greater than that of the observed baryonic matter. © 1992 The American Physical Society.

1992

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