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arxiv: 2606.30910 · v1 · pith:YO5DLILGnew · submitted 2026-06-29 · ✦ hep-ph

Phenomenology of Long-Lived Dark Photons and Axion-Like Particles in a Mixed Portal Framework

Caglar Zorbilmez , Beyhan Tatar , Azmi Ali Altintas This is my paper

Pith reviewed 2026-07-01 01:07 UTC · model grok-4.3

classification ✦ hep-ph
keywords dark photonaxion-like particlemixed portallong-lived particlesdisplaced verticesmulti-photon decayslepton colliders
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The pith

A mixed portal between dark photons and axion-like particles allows exotic cascades that convert long-lived states into displaced multi-photon events.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper examines how a dark photon and an axion-like particle linked through a mixed portal can decay either to ordinary fermion pairs or via an exotic path through the ALP to three photons. A dominance parameter D tracks when the exotic channel overtakes the standard one, changing the particles' effective lifetimes and producing new signatures. Analysis of both light and heavy mass ranges shows these cascades create displaced multi-photon events and allow the ALP itself to appear as a long-lived diphoton source. The resulting phenomenology opens additional search channels at future high-luminosity lepton colliders.

Core claim

In the mixed portal framework the dark photon A' possesses two competing decay modes, the conventional A' to f f-bar and the cascade A' to a gamma to 3 gamma, whose relative strength is set by the dominance parameter D equal to the ratio of the exotic width to the Standard Model width. When D exceeds one the cascade dominates, shortening the boosted decay length and converting otherwise stable or invisible states into observable displaced multi-photon final states; the ALP can likewise behave as a long-lived particle yielding displaced diphoton signatures.

What carries the argument

The dominance parameter D = Gamma(A' to a gamma)/Gamma_SM that marks the boundary between Standard Model-dominated and cascade-dominated regimes in the mixed portal.

Load-bearing premise

The mixed portal is assumed to let both the ordinary visible decay and the exotic three-photon cascade occur at comparable or dominant rates without extra constraints that would suppress one channel.

What would settle it

Absence of displaced three-photon or diphoton vertices in the predicted mass and lifetime windows at a high-luminosity lepton collider such as the FCC-ee would falsify the mixed-portal long-lived-particle predictions.

Figures

Figures reproduced from arXiv: 2606.30910 by Azmi Ali Altintas, Beyhan Tatar, Caglar Zorbilmez.

Figure 1
Figure 1. Figure 1: FIG. 1. Exotic branching ratio Br( [PITH_FULL_IMAGE:figures/full_fig_p010_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: FIG. 2. Light Dark Photon parameter space for D=1 Boundary [PITH_FULL_IMAGE:figures/full_fig_p011_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3. Constant Decay Length Contours in Light Dark Photon Parameter Space ( [PITH_FULL_IMAGE:figures/full_fig_p012_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: FIG. 4. Exotic branching ratio Br( [PITH_FULL_IMAGE:figures/full_fig_p013_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: FIG. 5 [PITH_FULL_IMAGE:figures/full_fig_p014_5.png] view at source ↗
Figure 6
Figure 6. Figure 6: FIG. 6. Constant Decay Length Contours in Heavy Dark Photon Parameter Space ( [PITH_FULL_IMAGE:figures/full_fig_p015_6.png] view at source ↗
Figure 7
Figure 7. Figure 7: FIG. 7. ALP laboratory decay length [PITH_FULL_IMAGE:figures/full_fig_p016_7.png] view at source ↗
read the original abstract

We investigate the phenomenology of a dark photon \(A'\) and an axion-like particle (ALP) ,\(a\), connected through a mixed portal framework which simultaneously allows the conventional visible decay $(A'\rightarrow f\bar f)$ and the exotic cascade process $(A'\rightarrow a\gamma\rightarrow3\gamma)$. We derive the relevant decay widths, branching ratios, and Lorentz-boosted decay lengths, and introduce a dominance parameter \(D=\Gamma(A'\to a\gamma)/\Gamma_{\rm SM}\) to distinguish Standard Model-dominated and cascade-dominated regions, with the transition occurring at $(D=1)$. A detailed analysis of both light $(0.1\leq m_{A'}\leq10~{\rm GeV})$ and heavy $(10\leq m_{A'}\leq100~{\rm GeV})$ dark-photon scenarios shows that the exotic channel can substantially modify the expected dark-photon signatures, transforming otherwise long-lived or detector-stable states into experimentally accessible displaced multi-photon events. In addition, the ALP sector itself may exhibit long-lived particle behavior, leading to distinct displaced diphoton signatures. Our results show that mixed dark-photon-ALP portals offer a rich LLP phenomenology that can be explored at future high-luminosity lepton colliders such as the FCC-ee.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

0 major / 2 minor

Summary. The manuscript investigates the phenomenology of a dark photon A' and an axion-like particle a in a mixed portal framework permitting both the conventional visible decay A' → f f-bar and the exotic cascade A' → a γ → 3γ. It derives the relevant decay widths, branching ratios, and Lorentz-boosted decay lengths via standard QFT techniques, introduces a dominance parameter D = Γ(A' → a γ)/Γ_SM to delineate SM-dominated (D < 1) and cascade-dominated (D > 1) regimes, and analyzes both light (0.1–10 GeV) and heavy (10–100 GeV) mass ranges, concluding that the exotic channel can convert otherwise long-lived or stable states into displaced multi-photon signatures while the ALP itself may yield displaced diphoton signals, all accessible at future lepton colliders such as the FCC-ee.

Significance. If the central claims hold, the work supplies a compact phenomenological parameterization that expands the LLP search space for dark-photon models by incorporating mixed ALP portals. The use of standard effective-field-theory methods for widths and boosted lengths, together with the explicit D-based regime separation, supplies a transparent and falsifiable framework that could directly inform experimental strategies at high-luminosity e+e− colliders.

minor comments (2)
  1. Abstract: the statement that the transition occurs at D=1 is clear, yet the manuscript should verify that the same numerical definition of D is applied uniformly when quoting boosted decay lengths in both the light and heavy mass regimes.
  2. The abstract refers to the 'mixed portal framework' without a one-sentence reminder of the underlying operators; adding this would improve accessibility for readers outside the immediate sub-field.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the positive summary, significance assessment, and recommendation of minor revision. No major comments were listed in the report, so we provide no point-by-point responses below. We will incorporate any minor suggestions during revision.

Circularity Check

0 steps flagged

No significant circularity detected

full rationale

The paper sets up a phenomenological mixed-portal framework, derives standard EFT decay widths and boosted lengths, and defines the dominance parameter D explicitly as the ratio of partial widths to label SM-dominated vs. cascade-dominated regimes. All central claims about modified LLP signatures follow directly from these definitions plus Lorentz boosts, with no reduction of predictions to fitted inputs, no self-citation load-bearing steps, and no uniqueness theorems or ansatze smuggled in. The analysis remains self-contained within the assumed effective theory.

Axiom & Free-Parameter Ledger

1 free parameters · 1 axioms · 1 invented entities

The central claims rest on the existence of a mixed portal Lagrangian that simultaneously generates both visible and exotic decay channels; no independent evidence for the portal strength or the relative size of the two channels is supplied beyond the model definition itself.

free parameters (1)
  • dominance parameter D
    Defined as the ratio of exotic to SM partial widths; its value determines the transition between regimes and is treated as a free dial in the analysis.
axioms (1)
  • domain assumption The mixed portal allows both A' to f f-bar and A' to a gamma decays to be present at comparable rates without additional suppression mechanisms.
    Invoked in the abstract when stating that the exotic channel can substantially modify signatures.
invented entities (1)
  • mixed portal framework no independent evidence
    purpose: To connect dark photon and ALP while permitting both conventional and cascade decays.
    The framework is postulated to enable the phenomenology described; no independent evidence or falsifiable prediction outside the model is given.

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discussion (0)

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Reference graph

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