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Universe
Special Issues
CP Violation and Flavor Physics
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CP Violation and Flavor Physics

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "High Energy Nuclear and Particle Physics".

Deadline for manuscript submissions: 28 February 2025 | Viewed by 6635

Special Issue Editors

Dr. Andreas Trautner

E-Mail Website
Guest Editor
Max-Planck-Institut für Kernphysik, Saupfercheckweg 1, 69117 Heidelberg, Germany
Interests: CP violation; flavor physics; neutrino interactions; physics beyond the standard model; particle cosmology; strong CP problem; symmetries and outer automorphisms
Prof. Dr. Celso C. Nishi

E-Mail Website
Guest Editor
Centro de Matemática, Computação e Cognição, Universidade Federal do ABC, Av. dos Estados, 5001, 09.210-170, Santo André, SP, Brasil
Interests: CP violation; neutrino physics; flavor physics; flavor symmetries; physics beyond the standard model

Special Issue Information

Dear Colleagues,

All charge parity (CP)-violating phenomena detected so far can be described by a single phase that originates from the Standard Model (SM) Cabibbo–Kobayashi–Maskawa (CKM) mixing matrix, linking the three families of up-type quarks with the three families of down-type quarks. Hence, measurable CP violation in the SM only manifests itself in flavor-changing phenomena and not in flavor-conserving ones. Despite this huge theoretical success, there exist many unresolved issues in connection with CP violation and flavor.

Firstly, the leptonic sector with massive neutrinos allows for an analogous CP-violating phase in the PMNS mixing matrix, which has not been observed yet but is eagerly searched for in present and near-future experiments.

Secondly, the theta term of QCD, a possible source of flavor-preserving CP violation which is already present in the SM and related to the vacuum structure of strong interactions, does not show its effect in experiments. It can be most prominently observed in the form of the absence of a neutron electric dipole moment. Understanding why this parameter is so small constitutes the strong CP problem.

Thirdly, an explanation of the matter–antimatter asymmetry of the Universe requires more CP violation than is present in the SM, thus suggesting the existence of new sources of CP violation beyond the SM.

At the same time, CP violation in the SM is of a very specific kind, and new physics (NP) often introduces new sources that easily overwhelms the known SM contribution if not properly suppressed. Understanding such a suppression is one of the questions of the flavor puzzle.

This Special Issue is dedicated to (a) reviewing the current status of the various problems concerning flavor and CP violation; (b) exploring new links between these topics; and (c) exploring new directions to solve these problems. Topics of interest for this Special Issue include (but are not limited to) the keywords summarized below. We welcome both original submissions and review papers.

Dr. Andreas Trautner
Prof. Dr. Celso C. Nishi
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • CP violation
  • flavor physics
  • flavor puzzle
  • strong CP problem
  • flavor symmetries
  • spontaneous CP violation
  • baryogenesis
  • leptogenesis

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Published Papers (5 papers)

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Research

Jump to: Review

11 pages, 330 KiB  
Article
Predictions for the Rare Kaon Decays KS,L → π0ℓ+ℓ− from QCD in the Limit of a Large Number of Colours
by Giancarlo D’Ambrosio and Marc Knecht
Universe 2024, 10(12), 457; https://doi.org/10.3390/universe10120457 - 13 Dec 2024
Viewed by 434
Abstract
The long-distance and non-local parts of the form factors describing the single-photon-mediated KS,L→π0γ*→π0ℓ+ℓ− (ℓ=e,μ) transitions in the standard model are addressed in [...] Read more.
The long-distance and non-local parts of the form factors describing the single-photon-mediated KS,L→π0γ*→π0ℓ+ℓ− (ℓ=e,μ) transitions in the standard model are addressed in QCD regarding the limit where the number Nc of colours becomes infinite. It is shown that this provides a suitable theoretical framework to study these decay modes and that it enables predicting the decay rates for KS→π0ℓ+ℓ−. It also unambiguously predicts that the interference between the direct and indirect CP-violating contributions to the decay rate for KL→π0ℓ+ℓ− is constructive. Full article
(This article belongs to the Special Issue CP Violation and Flavor Physics)
16 pages, 506 KiB  
Article
On Quark–Lepton Mixing and the Leptonic CP Violation
by Alessio Giarnetti, Simone Marciano and Davide Meloni
Universe 2024, 10(9), 345; https://doi.org/10.3390/universe10090345 - 28 Aug 2024
Viewed by 490
Abstract
In the absence of a Grand Unified Theory framework, connecting the values of the mixing parameters in the quark-and-lepton sector is a difficult task, unless one introduces ad hoc relations among the matrices that diagonalize such different kinds of fermions. In this paper, [...] Read more.
In the absence of a Grand Unified Theory framework, connecting the values of the mixing parameters in the quark-and-lepton sector is a difficult task, unless one introduces ad hoc relations among the matrices that diagonalize such different kinds of fermions. In this paper, we discuss in detail the possibility that the PMNS matrix is given by the product UPMNS=VCKM★T★, where T comes from the diagonalization of a see-saw like mass matrix that can be of a Bimaximal (BM), Tri-Bimaximal (TBM) and Golden Ratio (GR) form, and identify the leading corrections to such patterns that allow for a good fit to the leptonic mixing matrix as well as to the CP phase. We also show that the modified versions of BM, TBM and GR can easily accommodate the solar and atmospheric mass differences. Full article
(This article belongs to the Special Issue CP Violation and Flavor Physics)
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37 pages, 1405 KiB  
Article
CP Conservation in the Strong Interactions
by Wen-Yuan Ai, Björn Garbrecht and Carlos Tamarit
Universe 2024, 10(5), 189; https://doi.org/10.3390/universe10050189 - 23 Apr 2024
Cited by 1 | Viewed by 1044
Abstract
We discuss matters related to the point that topological quantization in the strong interaction is a consequence of an infinite spacetime volume. Because of the ensuing order of limits, i.e., infinite volume prior to summing over topological sectors, CP is conserved. Here, [...] Read more.
We discuss matters related to the point that topological quantization in the strong interaction is a consequence of an infinite spacetime volume. Because of the ensuing order of limits, i.e., infinite volume prior to summing over topological sectors, CP is conserved. Here, we show that this reasoning is consistent with the construction of the path integral from steepest-descent contours. We reply to some objections that aim to support the case for CP violation in strong interactions that are based on the role of the CP-odd theta-parameter in three-form effective theories, the correct sampling of all configurations in the dilute instanton gas approximation and the volume dependence of the partition function. We also show that the chiral effective field theory derived from taking the volume to infinity first is in no contradiction with analyses based on partially conserved axial currents. Full article
(This article belongs to the Special Issue CP Violation and Flavor Physics)
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25 pages, 1702 KiB  
Article
Neutrino Mixing Sum Rules and the Littlest Seesaw
by Francesco Costa and Stephen F. King
Universe 2023, 9(11), 472; https://doi.org/10.3390/universe9110472 - 31 Oct 2023
Cited by 5 | Viewed by 1748
Abstract
In this work, we study the neutrino mixing sum rules arising from discrete symmetries and the class of Littlest Seesaw (LS) neutrino models. These symmetry-based approaches all offer predictions for the cosine of the leptonic CP phase cosδ in terms of the [...] Read more.
In this work, we study the neutrino mixing sum rules arising from discrete symmetries and the class of Littlest Seesaw (LS) neutrino models. These symmetry-based approaches all offer predictions for the cosine of the leptonic CP phase cosδ in terms of the mixing angles, θ13, θ12, θ23, while the LS models also predict the sine of the leptonic CP phase sinδ, as well as making other predictions. In particular, we study the solar neutrino mixing sum rules, arising from charged lepton corrections to tri-bimaximal (TB), bimaximal (BM), golden ratio (GR) and hexagonal (HEX) neutrino mixing, and the atmospheric neutrino mixing sum rules, arising from preserving one of the columns of these types of mixing—for example, the first or second column of the TB mixing matrix (TM1 or TM2)—and we confront them with an up-to-date global fit of the neutrino oscillation data. We show that some mixing sum rules, such as an atmospheric neutrino mixing sum rule arising from a version of neutrino golden ratio mixing (GRa1), are already excluded at 3σ, and we determine the remaining models allowed by the data. We also consider the more predictive LS models (which obey the TM1 sum rules and offer further predictions) based on constrained sequential dominance CSD(n) with n≈3. We compare for the first time the three cases n=2.5, n=3 and n=1+6≈3.45, which are favored by theoretical models, using a new type of analysis to accurately predict the observables θ12, θ23 and δ. We study all the above approaches, solar and atmospheric mixing sum rules and LS models, together so that they may be compared and to give an up-to-date analysis of the predictions of all of these possibilities, when confronted with the most recent global fits. Full article
(This article belongs to the Special Issue CP Violation and Flavor Physics)
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Review

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22 pages, 617 KiB  
Review
Neutrino Flavor Model Building and the Origins of Flavor and CP Violation
by Yahya Almumin, Mu-Chun Chen, Murong Cheng, Víctor Knapp-Pérez, Yulun Li, Adreja Mondol, Saúl Ramos-Sánchez, Michael Ratz and Shreya Shukla
Universe 2023, 9(12), 512; https://doi.org/10.3390/universe9120512 - 12 Dec 2023
Cited by 14 | Viewed by 1991
Abstract
The neutrino sector offers one of the most sensitive probes of new physics beyond the Standard Model of Particle Physics (SM). The mechanism of neutrino mass generation is still unknown. The observed suppression of neutrino masses hints at a large scale, conceivably of [...] Read more.
The neutrino sector offers one of the most sensitive probes of new physics beyond the Standard Model of Particle Physics (SM). The mechanism of neutrino mass generation is still unknown. The observed suppression of neutrino masses hints at a large scale, conceivably of the order of the scale of a rand unified theory (GUT), which is a unique feature of neutrinos that is not shared by the charged fermions. The origin of neutrino masses and mixing is part of the outstanding puzzle of fermion masses and mixings, which is not explained ab initio in the SM. Flavor model building for both quark and lepton sectors is important in order to gain a better understanding of the origin of the structure of mass hierarchy and flavor mixing, which constitute the dominant fraction of the SM parameters. Recent activities in neutrino flavor model building based on non-Abelian discrete flavor symmetries and modular flavor symmetries have been shown to be a promising direction to explore. The emerging models provide a framework that has a significantly reduced number of undetermined parameters in the flavor sector. In addition, such a framework affords a novel origin of CP violation from group theory due to the intimate connection between physical CP transformation and group theoretical properties of non-Abelian discrete groups. Model building based on non-Abelian discrete flavor symmetries and their modular variants enables the particle physics community to interpret the current and anticipated upcoming data from neutrino experiments. Non-Abelian discrete flavor symmetries and their modular variants can result from compactification of a higher-dimensional theory. Pursuit of flavor model building based on such frameworks thus also provides the connection to possible UV completions: in particular, to string theory. We emphasize the importance of constructing models in which the uncertainties of theoretical predictions are smaller than, or at most compatible with, the error bars of measurements in neutrino experiments. While there exist proof-of-principle versions of bottom-up models in which the theoretical uncertainties are under control, it is remarkable that the key ingredients of such constructions were discovered first in top-down model building. We outline how a successful unification of bottom-up and top-down ideas and techniques may guide us towards a new era of precision flavor model building in which future experimental results can give us crucial insights into the UV completion of the SM. Full article
(This article belongs to the Special Issue CP Violation and Flavor Physics)
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