Supersymmetry beyond the TeV scale offers several theoretical and phenomenological advantages, such as accommodating the observed Higgs mass and alleviating the flavor and CP problems. However, flavor and CP observables still impose stringent constraints even at the PeV scale, motivating a systematic study of flavor symmetries in this regime. In this work, we investigate nucleon decay induced by dimension-five operators in supersymmetric standard models and examine how flavor symmetries, particularly of the Froggatt-Nielsen type, can suppress these operators. We perform a Bayesian analysis combining flavor, CP, and proton-decay observables to quantify the allowed parameter space and identify characteristic predictions. Our results demonstrate that a multi-messenger approach, integrating flavor, CP, and baryon-number-violating observables, is essential for probing the underlying structure of supersymmetry beyond the TeV scale.

Japan

Akifumi Chitose

Masahiro Ibe

Satoshi Shirai

Flavor symmetry and proton decay in PeV-scale supersymmetry

We investigate cosmic strings arising from a hierarchical gauge symmetry breaking sequence, SU(2) × U(1) → U(1) × U(1) → U(1)$\textit{′}$ → Nothing$\textit{.}$ This pattern gives rise to two distinct classes of cosmic strings: light, stable strings formed at a later stage, and heavy, metastable strings originating from an earlier stage. Our focus is on the heavy strings, which may decay either before or after the final U(1)$\textit{′}$ symmetry is broken. We analyze the internal structure of these strings and the magnetic flux sourced by monopole-like configurations that emerge at the endpoints of metastable string segments following their decay. Understanding the nature of the magnetic U(1) fluxes associated with these monopole-like objects is crucial for studying the post-decay evolution of the string network. The post-decay evolution influences the resulting gravitational wave signals. We show that the magnetic flux carried by string segments can be either confined or unconfined, depending on the specific sequence of symmetry breaking and string decay.

Yaxuan Wen

Cosmic strings in multi-step symmetry breaking

<p>We examine the minimal <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><mi mathvariant="normal">U</mi><mo stretchy="false">(</mo><mn>1</mn><msub><mrow><mo stretchy="false">)</mo></mrow><mrow><msub><mrow><mi>L</mi></mrow><mrow><mi>μ</mi></mrow></msub><mo>−</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>τ</mi></mrow></msub></mrow></msub></mrow></math> gauge model in light of the latest neutrino data, including neutrino oscillations, cosmological observations, direct mass measurements, and neutrinoless double-beta decay. Using the most conservative oscillation data, we find that normal ordering is excluded at approximately the 90% confidence level (CL). Incorporating cosmological constraints from cosmic microwave background observations strengthens this exclusion to about 95% CL, while further including baryon acoustic oscillation data increases it to nearly 99% CL. The inverted ordering is even more strongly disfavored. Our analysis is performed within a frequentist framework, minimizing sensitivity to prior assumptions inherent in Bayesian approaches. These results impose strong constraints on the viability of the minimal <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi mathvariant="normal">U</mi><mo stretchy="false">(</mo><mn>1</mn><msub><mo stretchy="false">)</mo><mrow><msub><mi>L</mi><mi>μ</mi></msub><mo>−</mo><msub><mi>L</mi><mi>τ</mi></msub></mrow></msub></math> gauge model.</p>

Keiichi Watanabe

Global neutrino constraints on the minimal <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mrow><msub><mrow><mi mathvariant="normal">U</mi><mo stretchy="false">(</mo><mn>1</mn><mo stretchy="false">)</mo></mrow><mrow><msub><mrow><mi>L</mi></mrow><mrow><mi>μ</mi></mrow></msub><mo>−</mo><msub><mrow><mi>L</mi></mrow><mrow><mi>τ</mi></mrow></msub></mrow></msub></mrow></math> model

The Froggatt-Nielsen (FN) mechanism successfully explains the hierarchical structure of fermion Yukawa couplings by introducing a U(1) flavor symmetry with distinct charge assignments for different fermion generations. While some FN charge assignments have been proposed, their evaluation has largely relied on heuristic approaches. This paper systematically investigates viable FN charge assignments within the Standard Model, including both the quark and lepton sectors, using Bayesian statistical analysis. The study explores scenarios involving both the seesaw mechanism and dimension-five operators for neutrino mass generation. A comprehensive parameter scan over FN charges reveals a wide range of charge assignments consistent with observed fermion masses and mixing angles. Interestingly, negative FN charges and significant generational differences in charges are found to be viable, contrary to conventional assumptions. The analysis also compares the seesaw mechanism and dimension-five operator scenarios, finding no strong preference between them for optimal charge assignments. Furthermore, predictions for the lightest neutrino mass and effective Majorana mass relevant for neutrinoless double-beta decay are presented, highlighting regions of parameter space accessible to upcoming experiments. Finally, implications for nucleon decay are studied, demonstrating that different FN charge assignments predict significantly different nucleon decay lifetimes and branching ratios, providing a potential experimental probe for FN models.

Comprehensive Bayesian exploration of Froggatt-Nielsen mechanism

This paper explores nucleon decay within the framework of a “fake Grand Unified Theory (GUT)” combined with the Froggatt-Nielsen (FN) mechanism. In this fake GUT framework, quarks and leptons may have distinct high-energy origins but fit into complete SU(5) multiplets at low energies without requiring force unification, setting it apart from conventional GUTs. By introducing flavor symmetry through the FN mechanism, the model addresses the flavor puzzle of quark and lepton mass hierarchies and mixing patterns. Our analysis demonstrates that nucleon decay rates and branching fractions in the fake GUT are sensitive to flavor symmetry, providing a means to distinguish it from conventional GUT predictions. These findings underscore the importance of nucleon decay searches in probing both baryon number violation and the underlying flavor structure.

Nucleon decay as a probe of flavor symmetry: the case of fake unification

This paper investigates the impact of small instanton effects on the axion mass in composite axion models. In particular, we focus on the Composite Accidental Axion (CAA) models, which are designed to address the axion quality problem, and where the Peccei-Quinn (PQ) symmetry emerges accidentally. In the CAA models, the QCD gauge symmetry is embedded in a larger gauge group at high energy. These models contain small instantons not included in low-energy QCD, which could enhance the axion mass significantly. However, in the CAA models, our analysis reveals that these effects on the axion mass are non-vanishing but are negligible compared to the QCD effects. The suppression of the small instanton effects originates from the global chiral U(1) symmetries which are not broken spontaneously and play a crucial role in eliminating θ-terms in the hidden sectors through anomalies. We find these U(1) symmetries restrict the impact of small instantons in hidden sectors on the axion mass. Our study provides crucial insights into the dynamics within the CAA models and suggests broader implications for understanding small instanton effects in other composite axion models.

Takafumi Aoki

Small instanton effects on composite axion mass

Metastable cosmic strings appear in models of new physics with a two-step symmetry breaking G → H → 1, where π 1(H) ≠ 0 and π 1(G) = 0. They decay via the monopole-antimonopole pair creation inside. Conventionally, the breaking rate has been estimated by an infinitely thin string approximation, which requires a large hierarchy between the symmetry breaking scales. In this paper, we reexamine it by taking into account the finite sizes of both the cosmic string and the monopole. We obtain a robust lower limit on the tunneling factor   <math> <msup> <mi>e</mi> <mrow> <mo>−</mo> <msub> <mi>S</mi> <mi>B</mi> </msub> </mrow> </msup> </math>  $$ {e}^{-{S}_B} $$  even for regimes the conventional estimate is unreliable. In particular, it is relevant to the cosmic string interpretation of the gravitational wave signals recently reported by pulsar timing array experiments.

Yuhei Nakayama

Revisiting metastable cosmic string breaking

Higgsinos and Winos in the supersymmetric Standard Model are prime candidates for dark matter due to their weakly interacting nature. The mass differences between their charged components (charginos) and neutral components (neutralinos) become degenerate when other superparticles are heavy, resulting in long-lived charginos. In the case of the Winos, the mass difference is approximately 160 MeV across a wide range of the parameter space. Consequently, the chargino decays into the lightest neutralino, emitting a single charged pion. For Higgsinos, however, mass differences ranging from O(0.1) GeV to O(1) GeV are possible, leading to a variety of decay channels. In this paper, we extend our previous analysis of Wino decay to the chargino with a larger mass difference. We emphasize characterizing its decay signatures through leptonic and hadronic modes. By utilizing the latest experimental data, we perform a comprehensive study of the decay rate calculations incorporating these hadronic modes to determine the impact on the predicted chargino lifetime. Additionally, we conduct next-to-leading order (NLO) calculations for the leptonic decay modes. Our NLO results can be applied to the case of more general fermionic electroweak multiplets, e.g., quintuplet dark matter.

Precise estimate of charged Higgsino/Wino decay rate

We consider a model of dark photon which appears as a result of the successive symmetry breaking <math><mrow><mi>SU</mi><mo>(</mo><mn>2</mn><mo>)</mo><mo>→</mo><mi>U</mi><mo>(</mo><mn>1</mn><mo>)</mo><mo>→</mo><msub><mrow><mi>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math>, where various types of topological defects appear in the dark sector. In this paper, we study the interactions between quantum electrodynamics (QED) charges and the dark topological defects through mixing between QED photon and dark photon. In particular, we extend our previous analysis by incorporating the magnetic mixing and <math><mi>θ</mi></math>-terms. We also consider the dyons and dyonic beads in the dark sector. Notably, dark magnetic/dyonic beads are found to induce a QED Coulomb potential through the magnetic mixing despite finite mass of the dark photon.

Interactions of electrical and magnetic charges and dark topological defects

The gauged   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  symmetry is the simplest possibility to explain the observed muon g − 2, while being consistent with the neutrino oscillations through the seesaw mechanism. In this paper, we investigate if leptogenesis can work at the same time. At first glance, leptogenesis seems challenging because the right-handed neutrino masses are related to the   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  breaking scale of 10 – 100 GeV as required from the muon g − 2. Contrary to this expectation, we find that non-thermal leptogenesis with the right-handed neutrino masses of   <math> <mi>O</mi> </math>  $$ \mathcal{O} $$ (107) GeV is possible. The successful scenario results in strict predictions on the neutrino oscillation parameters, which will be tested in future experiments.

Shintaro Eijima

Kai Murai

Muon g − 2 and non-thermal leptogenesis in   <math> <mi>U</mi> <msub> <mfenced> <mn>1</mn> </mfenced> <mrow> <msub> <mi>L</mi> <mi>μ</mi> </msub> <mo>−</mo> <msub> <mi>L</mi> <mi>τ</mi> </msub> </mrow> </msub> </math>  $$ \textrm{U}{(1)}_{L_{\mu }-{L}_{\tau }} $$  model