Supernatural Supersymmetry: Phenomenological Implications of Anomaly-Mediated Supersymmetry Breaking

TL;DR

The paper analyzes anomaly-mediated SUSY breaking (AMSB), where SUSY breaking is transmitted via the super-Weyl anomaly and is highly predictive through RG-invariant relations. To cure tachyonic sleptons, it adopts a minimal model with a universal scalar mass $m_0^2$, yielding a 3+1 parameter space $(M_{ ext{aux}}, m_0, \tan\beta, {\rm sign}(\mu))$ and revealing a novel RG focus-point behavior for $m_{H_u}^2$ that preserves naturalness even for multi-TeV scalar masses. The resulting spectrum features a degenerate Wino LSP in much of parameter space, with heavy first/second generation squarks and distinctive slepton degeneracies and mixings, leading to unique collider and low-energy signatures. Low-energy probes, including $b\to s\gamma$, the muon MDM, and EDMs, impose complementary constraints and can help distinguish AMSB from other SUSY-breaking scenarios. Overall, the work demonstrates that anomaly mediation with a small universal scalar mass can realize natural electroweak breaking while predicting testable collider phenomena and precise low-energy signals.

Abstract

We discuss the phenomenology of supersymmetric models in which supersymmetry breaking terms are induced by the super-Weyl anomaly. Such a scenario is envisioned to arise when supersymmetry breaking takes place in another world, i.e., on another brane. We review the anomaly-mediated framework and study in detail the minimal anomaly-mediated model parametrized by only 3+1 parameters: M_aux, m_0, \tanβ, and sign(μ). The renormalization group equations exhibit a novel "focus point" (as opposed to fixed point) behavior, which allows squark and slepton masses to be far above their usual naturalness bounds. We present the superparticle spectrum and highlight several implications for high energy colliders. Three lightest supersymmetric particle (LSP) candidates exist: the Wino, the stau, and the tau sneutrino. For the Wino LSP scenario, light Wino triplets with the smallest possible mass splittings are preferred; such Winos are within reach of Run II Tevatron searches. Finally, we study a variety of sensitive low energy probes, including b -> s gamma, the anomalous magnetic moment of the muon, and the electric dipole moments of the electron and neutron.

Figures (17)

• Figure 1: Contours of constant $\mu<0$ in GeV for $\tan\beta = 3$ (solid), 10 (dashed), and 30 (dotted). The value of $|\mu|$ is similar for $\mu>0$.
• Figure 2: The RG evolution of $m_{H_u}^2$ for fixed $M_{\text{aux}}=50 \text{ TeV}$, $\tan\beta=10$, and top quark mass (a) 174 GeV (b) 184 GeV. The GUT scale boundary conditions are for $m_0 = 0, 1, 2, 3 \text{ TeV}$, from the bottom. The RG behavior of $m_{H_u}^2$ exhibits a focus point (not a fixed point) near the weak scale, where $m_{H_u}^2$ takes its pure anomaly-mediated value, irrespective of $m_0$.
• Figure 3: Contours of $|\mu|$ in GeV for $\mu<0$, $M_{\text{aux}}=50 \text{ TeV}$, and $\tan\beta=10$. In the shaded region, electroweak symmetry cannot be broken radiatively.
• Figure 4: Parameters allowed by current constraints on particle masses and radiative symmetry breaking in the $(\mu, M_2)$ plane for $\mu < 0$ and $\tan\beta=3$ and 30. The contours are for constant $m_0 = 250$, 500, $\cdots$, 2000 GeV from the right. Similar results hold for $\mu > 0$.
• Figure 5: Contours of constant $m_{\tilde{\tau}_2} - m_{\tilde{\tau}_1}$ in GeV for $\mu < 0$ and $\tan\beta=3$ and 30. The shaded region is excluded by $m_{\tilde{\tau}_1}> 70\text{ GeV}$.