We study neutrinoless double-beta decay in extensions of the Standard Model that include $\textit{n}$ right-handed neutrino singlets, with masses $\textit{m}$ below the GeV scale. Generalizing recently developed matching methods, we determine the $\textit{m}$ dependence of the short-range $\textit{nn}$ → $\textit{pp}$ couplings that appear to leading order in the chiral effective field theory description of neutrinoless double beta decay. We focus on two scenarios, corresponding to the minimal $\textit{ν}$SM and left-right symmetric models. We illustrate the impact of our new results in the case of the $\textit{ν}$SM, showing a significant impact on the neutrinoless double-beta decay half-life when $\textit{m}$ is in the 200–800 MeV range.

United States

Vincenzo Cirigliano

Wouter Dekens

Sebastián Quiroga

Neutrinoless double $\textit{β}$ decay with light sterile neutrinos: the contact terms

The accuracy of <math><mrow><msub><mrow><mi>V</mi></mrow><mrow><mi>u</mi><mi>d</mi></mrow></msub></mrow></math> determinations from superallowed <math><mi>β</mi></math> decays critically hinges on control over radiative corrections. Recently, substantial progress has been made on the single-nucleon, universal corrections, while nucleus-dependent effects, typically parametrized by a quantity <math><msub><mi>δ</mi><mi>NS</mi></msub></math>, are much less well constrained. Here, we lay out a program to evaluate this correction from effective field theory (EFT), highlighting the dominant terms as predicted by the EFT power counting. Moreover, we compare the results to a dispersive representation of <math><msub><mi>δ</mi><mi>NS</mi></msub></math> and show that the expected momentum scaling applies even in the case of low-lying intermediate states. Our EFT framework paves the way toward ab initio calculations of <math><msub><mi>δ</mi><mi>NS</mi></msub></math> and thereby addresses the dominant uncertainty in <math><msub><mi>V</mi><mrow><mi>u</mi><mi>d</mi></mrow></msub></math>.

Netherlands

Jordy de Vries

Stefano Gandolfi

Switzerland

Martin Hoferichter

Emanuele Mereghetti

Radiative Corrections to Superallowed <math><mi>β</mi></math> Decays in Effective Field Theory

We perform a loop-level analysis of charged-current (CC) processes involving light leptons and quarks within the Standard Model Effective Field Theory (SMEFT). This work is motivated by the high precision reached in experiment and Standard Model calculations for CC decays of mesons, neutron, and nuclei, and by a lingering tension in the Cabibbo universality test. We identify the SMEFT operators that induce the largest loop-level contributions to CC processes. These include four-quark and four-fermion semileptonic operators involving two third-generation quarks. We discuss the available constraints on the relevant effective couplings and along the way we derive new loop-level bounds from K →   <math> <mi>πν</mi> <mover> <mi>ν</mi> <mo>¯</mo> </mover> </math>  $$ \pi \nu \overline{\nu} $$  on four-quark operators involving two top quarks. We find that low-energy CC processes are quite competitive with other probes, set constraints that do not depend on flavor-symmetry assumptions, and probe operators involving third-generation quarks up to effective scales of Λ ≃ 8 TeV. Finally, we briefly discuss single-field ultraviolet completions that could induce the relevant operators.

Maria Dawid

One-loop analysis of β decays in SMEFT

Recent developments in the Standard Model analysis of semileptonic charged-current processes involving light quarks have revealed ~ 3σ tensions in Cabibbo universality tests involving meson, neutron, and nuclear beta decays. In this paper, we explore beyond the Standard Model explanations of this so-called Cabibbo Angle Anomaly in the framework of the Standard Model Effective Field Theory (SMEFT), including not only low-energy charged current processes (‘L’), but also electroweak precision observables (‘EW’) and Drell-Yan collider processes (‘C’) that probe the same underlying physics across a broad range of energy scales. The resulting ‘CLEW’ framework not only allows one to test explanations of the Cabibbo Angle Anomaly, but is set up to provide near model-independent analyses with minimal assumptions on the flavor structure of the SMEFT operators. Besides the global analysis, we consider a large number of simpler scenarios, each with a subset of SMEFT operators, and investigate how much they improve upon the Standard Model fit. We find that the most favored scenarios, as judged by the Akaike Information Criterion, are those that involve right-handed charged currents. Additional interactions, namely oblique operators, terms modifying the Fermi constant, and operators involving right-handed neutral currents, play a role if the CDF determination of the W mass is included in the analysis.

Jordy Vries

Germany

Tom Tong

Anomalies in global SMEFT analyses. A case study of first-row CKM unitarity

We investigate neutrinoless double-beta decay (<math><mrow><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></mrow></math>) in the minimal extension of the standard model of particle physics, the <math><mrow><mi>ν</mi><mi>SM</mi></mrow></math>, where gauge-singlet right-handed neutrinos give rise to Dirac and Majorana neutrino mass terms. We focus on the associated sterile neutrinos and argue that the usual evaluation of their contributions to <math><mrow><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></mrow></math>, based on mass-dependent nuclear matrix elements, is missing important contributions from neutrinos with ultrasoft and hard momenta. We identify the hadronic and nuclear matrix elements that enter the new contributions, and calculate all relevant nuclear matrix elements for <math><mmultiscripts><mi>Xe</mi><mprescripts></mprescripts><none></none><mn>136</mn></mmultiscripts></math> using the nuclear shell model. Finally, we illustrate the impact on <math><mrow><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></mrow></math> rates in specific neutrino mass models and show that the new contributions significantly alter the <math><mrow><mn>0</mn><mi>ν</mi><mi>β</mi><mi>β</mi></mrow></math> rate in most parts of the <math><mrow><mi>ν</mi><mi>SM</mi></mrow></math> parameter space.

Spain

Javier Menéndez

Pablo Soriano

China

Guanghui Zhou

Neutrinoless double-<math><mi>β</mi></math> decay in the neutrino-extended standard model

We study radiative corrections to low-energy charged-current processes involving nucleons, such as neutron beta decay and (anti)neutrino-nucleon scattering within a top-down effective-field-theory approach. We first match the Standard Model to the low-energy effective theory valid below the weak scale and, using renormalization group equations with anomalous dimensions of <math><mrow><mi>O</mi><mo>(</mo><mi>α</mi><mo>,</mo><mi>α</mi><msub><mrow><mi>α</mi></mrow><mrow><mi>s</mi></mrow></msub><mo>,</mo><msup><mrow><mi>α</mi></mrow><mrow><mn>2</mn></mrow></msup><mo>)</mo></mrow></math>, evolve the resulting effective coupling down to the hadronic scale. Here, we first match to heavy-baryon chiral perturbation theory and subsequently, below the pion-mass scale, to a pionless effective theory, evolving the effective vector coupling with anomalous dimensions of <math><mi>O</mi><mo>(</mo><mi>α</mi><mo>,</mo><msup><mi>α</mi><mn>2</mn></msup><mo>)</mo></math> all the way down to the scale of the electron mass, relevant for beta decays. We thus provide a new evaluation of the “inner” radiative corrections to the vector coupling constant and to the neutron decay rate, discussing differences with the previous literature. Using our new result for the radiative corrections, we update the extraction of the Cabibbo-Kobayashi-Maskawa matrix element <math><msub><mi>V</mi><mrow><mi>u</mi><mi>d</mi></mrow></msub></math> from the neutron decay.

Oleksandr Tomalak

Effective field theory for radiative corrections to charged-current processes: Vector coupling

Peter Stoffer

Erratum to: Low-energy effective field theory below the electroweak scale: matching at one loop

We point out the necessity to consider <math><mi>β</mi></math>-decay observables in resolutions of the <math><mi>W</mi></math>-boson anomaly in the Standard Model Effective Field Theory that go beyond pure oblique corrections. We demonstrate that present global analyses that explain the <math><mi>W</mi></math>-boson mass anomaly predict a large, percent-level, violation of first-row Cabibbo Kobayashi Maskawa unitarity. We investigate what solutions to the <math><mrow><mi>W</mi></mrow></math>-boson mass anomaly survive after including <math><mrow><mi>β</mi></mrow></math>-decay constraints.

Beta-decay implications for the <math><mrow><mi>W</mi></mrow></math>-boson mass anomaly

Axions are introduced to explain the observed smallness of the   <math> <mover> <mi>θ</mi> <mo>¯</mo> </mover> </math>  $$ \overline{\theta} $$  term of QCD. Standard Model extensions typically contain new sources of CP violation, for instance to account for the baryon asymmetry of the universe. In the presence of additional CP-violating sources a Peccei-Quinn mechanism does not remove all CP violation, leading to CP-odd interactions among axions and Standard Model fields. In this work, we use effective field theory to parametrize generic sources of beyond-the-Standard-Model CP violation. We systematically compute the resulting CP-odd couplings of axions to leptons and hadrons by using chiral perturbation theory. We discuss in detail the phenomenology of the CP-odd axion couplings and compare limits from axion searches, such as fifth force and monopole-dipole searches and astrophysics, to direct limits on the CP-violating operators from electric dipole moment experiments. While limits from electric dipole moment searches are tight, the proposed ARIADNE experiment can potentially improve the existing constraints in a window of axion masses.

Sachin Shain

CP-violating axion interactions in effective field theory

We investigate contributions to the anomalous magnetic moments of charged leptons in the neutrino-extended Standard Model Effective Field Theory (νSMEFT). We discuss how νSMEFT operators can contribute to a lepton’s magnetic moment at one- and two-loop order. We show that only one operator can account for existing electronic and muonic discrepancies, assuming new physics appears above 1 TeV. In particular, we find that a right-handed charged current in combination with minimal sterile-active mixing can explain the discrepancy for sterile neutrino masses of   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (100) GeV while avoiding direct and indirect constraints. We discuss how searches for sterile neutrino production at the (HL-)LHC, measurements of h → μ + μ  −  and searches for h → e + e  − , neutrinoless double beta decay experiments, and improved unitarity tests of the CKM matrix can further probe the relevant parameter space.