Sgoldstino inflation

TL;DR

Sgoldstino inflation leverages the decoupling of the sgoldstino from SUSY-preserving sectors to deliver a robust two-field effective description (the real and imaginary sgoldstino components) that can emulate single-field inflation while accounting for turns and heavy-field stabilization. By formulating the dynamics in terms of the Kähler invariant function $G = K + \ln|W|^2$, the authors derive a block-diagonal mass structure and explicit stability conditions for the spectator sector, clarifying when heavy fields can be integrated out. They analyze large-field, small-field, and hybrid sgoldstino inflation, finding large-field realizations untenable, hybrid inflation as the most natural embedding, and small-field inflation feasible only with substantial fine-tuning and careful SUSY-breaking embedding; they also critique recent low-tuning proposals as lacking robustness. Overall, sgoldstino inflation provides a compelling, symmetry-guided pathway to inflation in supergravity, with practical implications for how SUSY breaking is connected to the inflationary sector and how spectator fields influence observables.

Abstract

We discuss the possibility that inflation is driven by the sgoldstino, the superpartner of the goldstino. Unlike in generic supergravity scenarios, the sgoldstino decouples from all other fields in the theory, which allows for a simple and robust inflationary model. We argue that the two-field model given by this single complex scalar correctly captures the full multifield inflationary phenomenology. On the other hand, the assumption of stability, along the entire inflationary trajectory, of the supersymmetry-preserving sector that is integrated out leads to supplementary constraints on the parent supergravity. We investigate small field, large field and hybrid sgoldstino inflation scenarios and provide some working examples. They are subject to the usual fine-tuning issues that are common to all supergravity models of inflation. We comment on some other recently proposed sgoldstino inflation models.

Figures (3)

• Figure 1: (Figure adapted from Kepa1Kepa3.) Stability diagram for the separable case $G = g(X,\bar{X}) + \tilde{g}(z,\bar{z})$. The variables on the axes $b,\, x$ are defined in (\ref{['defx']}), with $x$ one of the degenerate eigenvalues of the $x^{\bar{i}}_j$ matrix. The masses of the spectator fields are positive in the shaded region, while the unstable region signals a tachyonic mode. The black arrow represents the inflationary trajectory for the proposed hybrid set-up, which ends when one of the spectator fields (the waterfall fields) becomes tachyonic. Also shown are possible inflationary trajectories for small field inflation (red arrows).
• Figure 2: Scalar potential for small field inflation corresponding to the first solution (\ref{['example1']}).
• Figure 3: Stability plot of the spectator $z$-fields for a separable Kähler function $G = g(X,\bar{X})+\tilde{g}(z,\bar{z})$. The trajectories for small field inflation are vertical lines, going upward (red) to infinity for solution (\ref{['example1']}) which has a susy preserving vacuum, and downward (black) to zero for (\ref{['example2']}) which has a susy breaking vacuum. Dashed lines indicate unstable trajectories. The position on the horizontal axis depends on the specifics of the spectator sector. Solution (\ref{['example1']}) always leads to an instability for $|x| >1$.