⚛️ phenomenology

Higgsino dark matter in the Starobinsky supergravity with the MSSM in light of the LUX-ZEPLIN event

This paper proposes a nearly pure 1 TeV higgsino dark matter candidate within the Minimal Supersymmetric Standard Model coupled to Starobinsky supergravity, demonstrating that the model's predicted Higgs boson mass aligns with experimental observations for bino-induced mass splittings while excluding wino-induced scenarios, all in light of the recent LUX-ZEPLIN event.

Original authors: Daniel Frolovsky, Sergei V. Ketov

Published 2026-09-11

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CC BY 4.0

Original authors: Daniel Frolovsky, Sergei V. Ketov

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

The universe is filled with invisible matter that holds galaxies together, yet we have never seen it directly. Scientists call this "dark matter," and while we know it exists through its gravitational pull, its true identity remains one of the biggest mysteries in physics. One leading idea suggests that this hidden substance is made of particles that are partners to the ones we know, a concept rooted in a theory called supersymmetry. This theory proposes that for every known particle, there is a heavier, invisible twin. If these twins exist, the lightest one could be stable and fill the cosmos, acting as the dark matter we search for. Recently, a sensitive experiment deep underground detected a single, puzzling signal that some researchers believe could be a dark matter particle bumping into an atomic nucleus. This event has sparked a fresh wave of investigation into what these particles might be and how they fit into the grand story of the universe, from the first moments after the Big Bang to the present day.

In a new study, researchers have taken this recent signal and connected it to a specific theory of how the universe began. They focused on a candidate for dark matter called the "higgsino," a heavy particle that is a partner to the Higgs boson, the particle responsible for giving other particles their mass. The team worked within a framework that links the physics of these tiny particles to the massive expansion of the early universe, known as cosmic inflation. By combining two different ways of generating the mass for these particles, they created a model where a nearly pure higgsino with a mass of about one trillion electron volts could exist as the stable dark matter particle. This specific mass and the way the particle splits into slightly different energy states were chosen to match the recent detection reported by the LUX-ZEPLIN collaboration, an experiment designed to catch dark matter in a tank of liquid xenon.

The researchers did not just propose this particle; they tested whether it could coexist with everything else we know about the universe. They ran detailed computer simulations to see if this higgsino dark matter model would produce the correct mass for the Higgs boson, which has been measured by other experiments to be roughly 125 GeV. The study found that the model works, but only under very specific conditions. When the dark matter particle interacts with a specific type of partner particle known as a "bino," the predicted mass of the Higgs boson matches the observed value within the margin of error. However, when the model relies on a different partner called a "wino," the predicted mass comes out several GeV higher than what is actually observed. This result effectively rules out the wino version of this theory, leaving the bino version as the only viable path forward in this specific framework.

The study also addressed a major hurdle in interpreting the recent LUX-ZEPLIN signal. While a single event detected could be explained by a higgsino with a very small energy difference between its states, other experiments looking for neutrinos from the Sun have set strict limits on how small that difference can be. The new analysis confirms that these solar neutrino constraints, which were previously shown to exclude the specific interpretation of the LUX-ZEPLIN event as a thermal higgsino dark matter signal due to the required energy splitting being too small, do not question the viability of higgsino dark matter itself. However, the researchers calculated that for the bino version of the model, the Higgs boson mass comes out to align with the measured value when all known uncertainties are taken into account. In contrast, the wino version predicts a mass around 131 GeV, which is too high to be correct.

This work ties together three distinct areas of physics: the origin of the universe, the breaking of fundamental symmetries, and the nature of dark matter. By showing that a specific type of dark matter particle can explain a recent experimental hint while also correctly predicting the mass of the Higgs boson, the study offers a coherent picture of how the invisible sector of the universe might be structured, provided the specific interpretation of the LUX-ZEPLIN event is set aside in favor of larger energy splittings. It suggests that if the recent underground signal is indeed dark matter, it is likely a heavy higgsino interacting with a bino, a scenario that fits neatly into a theory of the early universe that has long been favored for its ability to explain cosmic inflation. The findings do not prove the existence of this particle, but they demonstrate that such a particle is a mathematically consistent and physically plausible candidate that deserves further scrutiny as experiments continue to search for the invisible building blocks of our reality.

Technical Summary: Higgsino Dark Matter in Starobinsky Supergravity with the MSSM

Problem Statement
The particle nature of Dark Matter (DM) remains unknown. While the Minimal Supersymmetric Standard Model (MSSM) with conserved R-parity offers a stable Lightest Supersymmetric Particle (LSP) candidate, specific scenarios face phenomenological challenges. Pure thermal wino DM requires a mass of approximately 3 TeV to match the observed relic abundance, a value excluded by gamma-ray observations. Conversely, a nearly pure higgsino LSP with a mass of roughly 1 TeV is a viable thermal DM candidate but is typically degenerate, leading to a small mass splitting between the neutralino states.

Recent reports of a 248 keV nuclear-recoil event by the LUX-ZEPLIN (LZ) collaboration have renewed interest in inelastic higgsino interpretations. However, constraints from the non-observation of high-energy solar neutrinos by IceCube suggest that for thermal higgsinos constituting all DM, the mass splitting must exceed 566 keV, potentially excluding the direct higgsino interpretation of the LZ event. Furthermore, connecting the parameters of such a DM candidate (specifically the higgsino mass and its splitting) to the fundamental scale of cosmic inflation and the observed Higgs boson mass within a consistent supergravity framework has not been fully established.

Methodology
The authors utilize a framework coupling the MSSM to Starobinsky supergravity, as previously proposed in Ref. [1]. In this setup:

Inflation and SUSY Breaking: The hidden sector responsible for Starobinsky inflation and spontaneous supersymmetry (SUSY) breaking emerges from the Einstein-frame description. The amplitude of primordial scalar perturbations fixes the inflationary scale, which in turn sets the scale of MSSM soft terms via gravitational mediation.
The $\mu$ Term: The model employs a combined $\mu$ term containing both a "bare" mass contribution ( $\mu_0$ ) and a dynamical contribution ( $\mu_{dyn}$ ) generated by interactions between the Higgs sector and the goldstino superfield. This allows for a tuned cancellation, resulting in a light higgsino mass ( $\sim 1$ TeV) while preserving the successful description of inflation.
Boundary Conditions: The model derives boundary conditions at the high matching scale ( $m_0 \approx 1.53 \times 10^{13}$ GeV) determined by the gravitino mass ( $m_{3/2}$ ) and the vacuum expectation value of the goldstino field ( $s_0$ ). These conditions include universal scalar masses ( $m_0$ ), specific trilinear couplings ( $A$ ), and gaugino masses determined by holomorphic gauge kinetic functions.
Renormalization Group Evolution (RGE): To test compatibility with low-energy observables, the authors evolve the higgsino and gaugino mass parameters from the low-energy scale (where the mass splitting $\delta$ is defined) up to the matching scale $m_0$ . They then match these to the supergravity boundary conditions and run the parameters back down to the electroweak scale to calculate the physical Higgs boson mass.
Computational Tools: The calculations utilize SARAH and FlexibleSUSY, adapted for SplitMSSM effective field theory (EFT) towers. The analysis includes two-loop RGE evolution, one-loop matching of renormalizable parameters, and selected higher-loop threshold corrections for the Higgs quartic coupling and neutral splitting operators.

Key Contributions and Results
The paper investigates two specific scenarios for the mass splitting $\delta \approx 350$ keV (motivated by the LZ event), corresponding to two different gaugino hierarchies:

Light Bino Case: The splitting is induced by a light bino ( $M_1$ ), with the wino and gluino heavy ( $M_2 = M_3 = m_0$ ).
Light Wino Case: The splitting is induced by a light wino ( $M_2$ ), with the bino and gluino heavy ( $M_1 = M_3 = m_0$ ).

The study yields the following results regarding the predicted Higgs boson mass ( $M_h$ ):

Light Bino Scenario: The predicted Higgs mass is $M_h = 126.64 \pm 0.50 \text{ (th)} \pm 0.65 (\alpha_s) \pm 0.62 (M_t)$ GeV. When uncertainties are added linearly, this result is consistent with the measured value of $125.13 \pm 0.11$ GeV.
Light Wino Scenario: The predicted Higgs mass is $M_h = 131.37 \pm 0.47 \text{ (th)} \pm 0.58 (\alpha_s) \pm 0.56 (M_t)$ GeV. This value is approximately 5 GeV higher than the measured value and is therefore excluded within the quoted uncertainties.

The analysis demonstrates that the wino triplet contributes more strongly to the running of the Higgs quartic coupling than the bino, leading to the higher predicted mass in the wino-induced splitting case. The light-bino scenario remains compatible with the measured Higgs mass even for larger splittings up to $\delta = 1$ MeV.

Significance and Claims
The paper claims to realize a nearly pure higgsino dark matter candidate with a mass of about 1 TeV within a unified framework that connects particle phenomenology to cosmic inflation. The primary significance lies in demonstrating that:

A combined "bare" and dynamical $\mu$ term allows for the necessary tuning to achieve a light higgsino LSP while maintaining the Starobinsky inflationary scenario.
The particle spectrum, including the Higgs mass and higgsino splitting, is not arbitrary but is connected to inflation observables via gravitational mediation and RGE.
The model successfully predicts a Higgs boson mass consistent with experimental data specifically in the light-bino induced splitting scenario, whereas the light-wino scenario is ruled out.

The authors note that while recent solar-capture bounds (IceCube) exclude the higgsino interpretation of the specific LZ event for thermal higgsinos constituting all DM (due to the required splitting being larger than 566 keV), this does not invalidate higgsino DM itself. The light-bino case remains a viable realization of higgsino DM within the Starobinsky supergravity framework, consistent with inflation, spontaneous SUSY breaking, and the observed Higgs mass.

Technical Summary: Higgsino Dark Matter in Starobinsky Supergravity with the MSSM

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