Realistic Anomaly-mediated Supersymmetry Breaking

TL;DR

This paper investigates realistic anomaly-mediated SUSY breaking (AMSB) in a sequestered hidden-sector framework where the soft terms are RG-determined by anomalous dimensions and $m_{3/2}$. It analyzes solutions to the notorious negative slepton masses intrinsic to AMSB, exploring three avenues: new lepton Yukawa couplings via extra Higgs doublets with flavor symmetries, compositeness scenarios for leptons at the weak scale, and horizontal gauge symmetries. To address the μ problem and achieve viable electroweak symmetry breaking, the authors develop a μ-term generated by the vacuum expectation value of a singlet, within an extended field content that preserves AMSB relations and yields a realistic superpartner spectrum with moderate fine-tuning. The resulting model predicts a rich phenomenology near the weak scale, including additional Higgs doublets, vector-like color triplets, and singlets, all tied to anomaly mediation and testable at colliders. Overall, the work provides a tightly constrained, predictive framework linking SUSY-breaking dynamics to weak-scale observables through anomaly mediation.

Abstract

We consider supersymmetry breaking communicated entirely by the superconformal anomaly in supergravity. This scenario is naturally realized if supersymmetry is broken in a hidden sector whose couplings to the observable sector are suppressed by more than powers of the Planck scale, as occurs if supersymmetry is broken in a parallel universe living in extra dimensions. This scenario is extremely predictive: soft supersymmetry breaking couplings are completely determined by anomalous dimensions in the effective theory at the weak scale. Gaugino and scalar masses are naturally of the same order, and flavor-changing neutral currents are automatically suppressed. The most glaring problem with this scenario is that slepton masses are negative in the minimal supersymmetric standard model. We point out that this problem can be simply solved by coupling extra Higgs doublets to the leptons. Lepton flavor-changing neutral currents can be naturally avoided by approximate symmetries. We also describe more speculative solutions involving compositeness near the weak scale. We then turn to electroweak symmetry breaking. Adding an explicit μterm gives a value for Bμthat is too large by a factor of order 100. We construct a realistic model in which the μterm arises from the vacuum expectation value of a singlet field, so all weak-scale masses are directly related to m_{3/2}. We show that fully realistic electroweak symmetry breaking can occur in this model with moderate fine-tuning.

Figures (3)

• Figure 1: Fig. 1. Diagrams that contribute to quartic terms in the Käh-ler potential connecting the hidden and observable sectors. The solid lines correspond to fields localized on the 3-branes, while the dashed lines correspond to SUGRA fields propagating in the bulk.
• Figure 2: Fig. 2. Top quark mass as a function of $y_t$ for different values of $\lambda_T$. From the upper curve to the lower, the values of $\lambda_T$ are = $0.35$, $0.25$, and $0.15$. The curves end at a finite value of $y_t$ because the model no longer breaks electroweak symmetry. The other parameters are $\lambda_H = 0.15$, $\lambda_T = 0.15$, $\lambda_{H}' = 0.15$, $\kappa = 0.3$, $a_d = 0$, $a_u = 0$, $b = 0$, $y'_e = 0.95$, $y_t = 1$. $y_b = 0.1$$y_\tau = 0.05$
• Figure 3: Fig. 3. Fine-tuning of electroweak symmetry breaking. The plot shows $v_u$ as a function of $y_t$ for values of $a_{u 3}$ ranging from $0.1$ (upper curve) to $0.8$ (lower curve). The values of the other coupling constants are as in the example in Section 4.