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26 pages, 1599 KiB

Open AccessReview

The Standard Model Theory of Neutron Beta Decay

by Mikhail Gorchtein and Chien-Yeah Seng

Universe 2023, 9(9), 422; https://doi.org/10.3390/universe9090422 - 19 Sep 2023

Cited by 13 | Viewed by 2361

We review the status of the Standard Model theory of neutron beta decay. Particular emphasis is put on the recent developments in the electroweak radiative corrections. Given that some existing approaches give slightly different results, we thoroughly review the origin of discrepancies, and provide our recommended value for the radiative correction to the neutron and nuclear decay rates. The use of dispersion relation, lattice Quantum Chromodynamics, and an effective field theory framework allows for high-precision theory calculations at the level of

10^{- 4}

, turning neutron beta decay into a powerful tool to search for new physics, complementary to high-energy collider experiments. We offer an outlook to the future improvements. Full article

(This article belongs to the Special Issue Neutron Lifetime)

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41 pages, 1172 KiB

Open AccessFeature PaperReview

On Instabilities Caused by Magnetic Background Fields

by Michael Bordag

Symmetry 2023, 15(6), 1137; https://doi.org/10.3390/sym15061137 - 23 May 2023

Cited by 1 | Viewed by 1538

Abstract

We review instabilities that appear from the coupling of spin-one fields to a magnetic background in a non-Abelian theory. Such coupling results, due to asymptotic freedom in a negative quantum, contribute to the effective potential. In QCD, the Savvidy vacuum results. However, due to the tachyonic mode, such a state is not stable, and the question about the true ground state of QCD is still open. In the electroweak model, the corresponding instability is postponed to very large background fields and may be of relevance in the early universe, at best. We start with an introduction to the topic and display the necessary formulas and methods. Then, we consider the one-particle spectra of the fields in a magnetic background and the related Euler–Heisenberg Lagrangians. In addition, we discuss the potential instability connected with the anomalous moment of the electron. The main part is on the quantum correction to the energy in non-Abelian fields, including massive ones. Here, the focus is on so-called electroweak magnetism and the search for a classical solution of the field equations and their approximations by a lattice of flux tubes. Finally, we review approaches with non-homogeneous background fields and the background of an

A_{0}

-field. Full article

(This article belongs to the Special Issue Review on Quantum Field Theory)

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15 pages, 540 KiB

Open AccessFeature PaperArticle

Non-Minimal Approximation for the Type-I Seesaw Mechanism

by Mikhail Dubinin and Elena Fedotova

Symmetry 2023, 15(3), 679; https://doi.org/10.3390/sym15030679 - 8 Mar 2023

Cited by 4 | Viewed by 1855

Abstract

A non-minimal approximation for effective masses of light and heavy neutrinos in the framework of a type-I seesaw mechanism with three generations of sterile Majorana neutrinos which recover the symmetry between quarks and leptons is considered. The main results are:

(a)

[...] Read more.

(a)

the next-order corrections to the effective mass matrix of heavy neutrinos due to terms

O (θ M_{D})

are obtained, which modify the commonly used representation for the effective mass (

M_{D}

is a Dirac neutrino mass when the electroweak symmetry is spontaneously broken); and

(b)

the general form of the mixing matrix is found in non-minimal approximation parametrized by a complex

3 \times 3

matrix satisfying a nontrivial constraint. Numerical analysis within the

ν

MSM framework demonstrates the very small effect of new contributions of direct collider observables as opposed to their possible significance for cosmological models. Full article

(This article belongs to the Special Issue Symmetry in Experimental Physics of High Energies)

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6 pages, 266 KiB

Open AccessCommunication

W-Boson Mass Anomaly as a Manifestation of Spontaneously Broken Additional SU(2) Global Symmetry on a New Fundamental Scale

by Sergey Afonin

Universe 2022, 8(12), 627; https://doi.org/10.3390/universe8120627 - 28 Nov 2022

Cited by 8 | Viewed by 1334

Abstract

Recently, the CDF Collaboration has announced a new precise measurement of the W-boson mass M_W that deviates from the Standard Model (SM) prediction by 7σ. The discrepancy in M_W is about Δ_W ≃ 70 MeV and is probably caused by a beyond the SM physics. Within a certain scenario of extension of the SM, we obtain the relation Δ_W ≃

\frac{3 α}{8 π}

M_W ≃ 70 MeV, where α is the electromagnetic fine structure constant. The main conjecture is the appearance of longitudinal components of the W-bosons as the Goldstone bosons of a spontaneously broken additional SU(2) global symmetry at distances much smaller than the electroweak symmetry breaking scale r_EWSB. We argue that within this scenario, the masses of charged Higgs scalars can obtain an electromagnetic radiative contribution which enhances the observed value of M_W^± with respect to the usual SM prediction. Our relation for Δ_W follows from the known one-loop result for the corresponding effective Coleman–Weinberg potential in combination with the Weinberg sum rules. Full article

(This article belongs to the Special Issue Research on Physics beyond the Standard Model)

71 pages, 2928 KiB

Open AccessEditor’s ChoiceReview

Radiative Corrections to Semileptonic Beta Decays: Progress and Challenges

by Chien-Yeah Seng

Particles 2021, 4(4), 397-467; https://doi.org/10.3390/particles4040034 - 28 Sep 2021

Cited by 18 | Viewed by 4910

Abstract

We review some recent progress in the theory of electroweak radiative corrections in semileptonic decay processes. The resurrection of the so-called Sirlin’s representation based on current algebra relations permits a clear separation between the perturbatively-calculable and incalculable pieces in the [...] Read more.

O (G_{F} α)

radiative corrections. The latter are expressed as compact hadronic matrix elements that allow systematic non-perturbative analysis such as dispersion relation and lattice QCD. This brings substantial improvements to the precision of the electroweak radiative corrections in semileptonic decays of pion, kaon, free neutron and

J^{P} = 0^{+}

nuclei that are important theory inputs in precision tests of the Standard Model. Unresolved issues and future prospects are discussed. Full article

(This article belongs to the Special Issue Beta-Decay Processes in Nuclear Systems)

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14 pages, 332 KiB

Open AccessArticle

Electroweak Effects in e⁺e⁻→ZH Process

by Andrej Arbuzov, Serge Bondarenko, Lidia Kalinovskaya, Renat Sadykov and Vitaly Yermolchyk

Symmetry 2021, 13(7), 1256; https://doi.org/10.3390/sym13071256 - 13 Jul 2021

Cited by 4 | Viewed by 2248

Abstract

Electroweak radiative corrections to the cross-section of the process

e^{+} e^{-} \to Z H

Electroweak radiative corrections to the cross-section of the process

e^{+} e^{-} \to Z H

are considered. The complete one-loop electroweak radiative corrections are evaluated with the help of the SANC system. Higher-order contributions of the initial-state radiation are computed in the QED structure function formalism. Numerical results are produced by a new version of the ReneSANCe event generator and MCSANCee integrator for the conditions of future electron-positron colliders. The resulting theoretical uncertainty in the description of this process is estimated. Full article

(This article belongs to the Special Issue Symmetry in Particle Physics II)

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15 pages, 416 KiB

Open AccessArticle

Asymmetries in Processes of Electron–Positron Annihilation

by Andrej Arbuzov, Serge Bondarenko and Lidia Kalinovskaya

Symmetry 2020, 12(7), 1132; https://doi.org/10.3390/sym12071132 - 7 Jul 2020

Cited by 5 | Viewed by 4001

Abstract

Processes of electron–positron annihilation into a pair of fermions were considered. Forward–backward and left–right asymmetries were studied, taking into account polarization of initial and final particles. Complete 1-loop electroweak radiative corrections were included. A wide energy range including the Z boson peak and [...] Read more.

e^{+} e^{-}

colliders was covered. Sensitivity of observable asymmetries to the electroweak mixing angle and fermion weak coupling was discussed. Full article

(This article belongs to the Special Issue Symmetry in Particle Physics)

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