arxiv: 2605.08501 · v1 · submitted 2026-05-08 · ✦ hep-ph · hep-ex

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Lepton Flavor Violating Higgs decays at the Compact Linear Collider

Francisca Garay, Gabriel Vega, Philipp Roloff

Authors on Pith no claims yet

Pith reviewed 2026-05-12 01:26 UTC · model grok-4.3

classification ✦ hep-ph hep-ex

keywords lepton flavor violationHiggs decaysCLICbranching fractionssensitivity studyfuture collidersbeyond standard model

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The pith

The Compact Linear Collider could set 95% CL upper limits of 10^{-4} to 10^{-5} on branching fractions for lepton flavor violating Higgs decays.

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

This paper examines the reach of the proposed Compact Linear Collider for Higgs boson decays that convert one lepton flavor into another. Such processes do not occur in the Standard Model but can appear in many extensions that introduce new sources of flavor violation. The authors simulate the production of the Higgs boson at CLIC's two main operating energies together with the three decay channels h to e mu, h to tau mu, and h to e tau. Accounting for expected detector performance and background processes, they project that the planned data samples would allow upper limits in the 10^{-4} to 10^{-5} range if no signal appears. These sensitivities would test and potentially exclude regions of parameter space in beyond-Standard-Model scenarios that predict observable lepton flavor violation.

Core claim

In the absence of any observation, 95% CL upper limits in the region of 10^{-4} to 10^{-5} could be placed on the branching fractions of the processes h to e mu, h to tau mu, and h to e tau, assuming integrated luminosities of 4 ab^{-1} at sqrt(s) = 1.4 TeV and 5 ab^{-1} at sqrt(s) = 3 TeV.

What carries the argument

Monte Carlo simulation of signal and background events for Higgs production and the three lepton-flavor-violating decay modes, using the nominal CLIC detector performance at the two design collision energies.

Load-bearing premise

The projections assume that background processes are perfectly modeled and that detector efficiencies and resolutions match the design values used in the simulation.

What would settle it

Direct measurement of background rates in the signal regions that exceed the simulated predictions by more than the assumed uncertainties would prevent the quoted limits from being reached.

read the original abstract

Lepton flavor violating Higgs decays could appear in scenarios beyond the Standard Model of particle physics. In this article, we study the sensitivity of a future Compact Linear Collider (CLIC) to such processes, namely, $h\rightarrow e\mu$, $h\rightarrow\tau\mu$, and $h\rightarrow e\tau$. In the absence of any observation, 95\% CL\ upper limits in the region of $10^{-4}$ to $10^{-5}$ could be placed on the branching fractions of these processes, assuming integrated luminosities of $4$\,ab$^{-1}$ at $\sqrt{s}=1.4$ TeV and $5$\,ab$^{-1}$ at $\sqrt{s}=3$ TeV.

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.

Desk Editor's Note private letter to a colleague

Standard CLIC sensitivity projections for LFV Higgs decays using conventional Monte Carlo methods and idealized assumptions.

read the letter

The paper projects CLIC's sensitivity to lepton flavor violating Higgs decays h→eμ, h→τμ, and h→eτ. With the assumed luminosities of 4 ab^{-1} at 1.4 TeV and 5 ab^{-1} at 3 TeV, it claims 95% CL upper limits on the branching ratios in the 10^{-4} to 10^{-5} range if nothing is seen. This is not a new theoretical result or measurement. It is a standard fast-simulation study that takes the usual approach of generating signal and background events, applying cuts or efficiencies, and setting limits. Similar work exists for the LHC and ILC, so the novelty is mainly in plugging in CLIC's energies and luminosities. The paper does this part well. The limits are presented clearly for each channel and each energy stage. The assumptions are stated up front, and the statistical method for setting the limits is the conventional one. The main limitation is the idealized detector and background modeling. The projections assume backgrounds are perfectly known and that the detector performs exactly as designed. Any real-world deviations would make the actual limits weaker. This is a common feature of these studies rather than a unique flaw here. Readers who care about the physics reach of proposed linear colliders or who are building models with LFV in the Higgs sector will find the specific numbers useful. It is not essential reading for the broader community. I would take this to a reading group focused on collider phenomenology as a maybe. It is not something I would cite in my own work soon, since it does not introduce new ideas or data. But it is the kind of paper that deserves peer review to check the simulation details and confirm the numbers are correctly derived from the inputs.

Referee Report

1 major / 1 minor

Summary. The manuscript investigates the potential of the Compact Linear Collider (CLIC) to probe lepton flavor violating Higgs decays h→eμ, h→τμ, and h→eτ through a fast simulation study. It concludes that, in the absence of observation, 95% CL upper limits on the branching fractions could reach the 10^{-4} to 10^{-5} level with the assumed luminosities at 1.4 TeV and 3 TeV.

Significance. These projections are significant for the physics program of future linear colliders, as they demonstrate the potential to set stringent limits on LFV processes that are highly suppressed in the Standard Model. The work uses standard Monte Carlo techniques for sensitivity estimates, which is a strength for reproducibility in principle, but the lack of detailed documentation reduces the immediate impact.

major comments (1)

[Simulation and Analysis] The description of the Monte Carlo simulation, background modeling, detector efficiencies, and the statistical procedure for setting the 95% CL limits is insufficient. This prevents assessment of whether the projected limits in the abstract are supported by the setup.

minor comments (1)

The abstract could specify the detector model or simulation software used to allow better context for the assumed performance.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for the careful reading of our manuscript and for the constructive feedback. We address the major comment below and will revise the paper to improve clarity and completeness.

read point-by-point responses

Referee: [Simulation and Analysis] The description of the Monte Carlo simulation, background modeling, detector efficiencies, and the statistical procedure for setting the 95% CL limits is insufficient. This prevents assessment of whether the projected limits in the abstract are supported by the setup.

Authors: We agree that the current level of detail on the simulation chain is insufficient for full reproducibility and assessment. The study employs a fast simulation framework standard for CLIC projections, but the manuscript does not adequately document the specific generators, background samples, efficiency parametrizations, and limit-setting procedure. In the revised version we will expand the relevant sections to include: (i) the event generators and parton-level processes used for signal and all relevant backgrounds; (ii) the detector simulation and reconstruction assumptions, including any efficiency and resolution parametrizations; (iii) the selection cuts and background modeling approach; and (iv) the statistical method (including the treatment of systematic uncertainties) used to derive the 95% CL limits. These additions will directly support the quoted sensitivity numbers. revision: yes

Circularity Check

0 steps flagged

No circularity: standard Monte Carlo sensitivity projections

full rationale

The paper derives 95% CL upper limits on LFV Higgs branching fractions from forward simulation of signal and background events at specified CLIC energies and luminosities, followed by standard statistical limit-setting. No step reduces a claimed prediction to a fitted input by construction, no self-citation chain carries the central result, and no ansatz or uniqueness theorem is imported to force the outcome. The derivation remains self-contained against external benchmarks of detector performance and background modeling.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on standard Monte Carlo simulation of Standard Model backgrounds and assumed CLIC detector performance; no new free parameters, axioms beyond domain conventions, or invented entities are introduced.

axioms (2)

domain assumption Standard Model processes provide the dominant irreducible backgrounds for the rare LFV signals.
The upper-limit calculation assumes that any excess would be attributed to signal only after subtracting well-known SM backgrounds.
domain assumption CLIC detector performance matches the design values for efficiency and resolution used in the simulation.
Projected limits depend on the assumed reconstruction efficiencies and background rejection power of the future detector.

pith-pipeline@v0.9.0 · 5415 in / 1400 out tokens · 54970 ms · 2026-05-12T01:26:13.773869+00:00 · methodology

discussion (0)

Reference graph

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