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arxiv: 1907.11013 · v1 · pith:3XMDEKQVnew · submitted 2019-07-25 · ⚛️ nucl-th

Studies of quasiclassical approach applicability to true three-body decays

Pith reviewed 2026-05-24 16:00 UTC · model grok-4.3

classification ⚛️ nucl-th
keywords three-body decaysquasiclassical approximationhyperspherical harmonicstwo-proton decay17Nenuclear resonancescoupled channels
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The pith

Reducing three-body hyperspherical equations to a single channel overestimates the two-proton decay width.

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

The paper applies the hyperspherical harmonics method to true three-body decays, where the three-body problem reduces to motion of one effective particle in a strongly deformed field treated in coupled channels. It shows that the quasiclassical formula itself works well on the resulting effective potentials, yet the further step of collapsing the coupled channels into a single-channel Schrödinger equation produces a clear overestimate of the two-proton width. The overestimate is quantified for the first excited 3/2- state in 17Ne. The result indicates that this common simplification cannot be trusted for accurate width calculations in genuine three-body systems.

Core claim

The reduction of the hyperspherical equations set to a single-channel Schrödinger equation leads to significant overestimation of the two-proton width Γ_{2p}, demonstrated by the example of the 17Ne first excited 3/2- state decay.

What carries the argument

The coupled-channel hyperspherical harmonics reduction of the three-body problem to an effective single-particle motion, followed by its collapse to a single-channel Schrödinger equation for quasiclassical width evaluation.

If this is right

  • The quasiclassical formula remains accurate when applied directly to the three-body effective potentials.
  • Single-channel reduction produces widths larger than the coupled-channel treatment for the studied 17Ne state.
  • The single-channel approximation cannot be assumed valid for other true three-body decays without separate verification.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Accurate widths for other Borromean or three-body decaying nuclei will require retaining the full coupled-channel structure.
  • Methods that avoid the single-channel reduction step may be needed for reliable predictions in similar systems.
  • The size of the overestimate could be mapped across a range of three-body potentials to identify when the approximation is least harmful.

Load-bearing premise

The full multi-channel hyperspherical problem can be replaced by one effective potential whose quasiclassical width reproduces the coupled-channel result.

What would settle it

A full coupled-channel hyperspherical calculation of the 17Ne 3/2- width that matches the single-channel quasiclassical value would falsify the claimed overestimate.

Figures

Figures reproduced from arXiv: 1907.11013 by D.A. Kostyleva, L.V. Grigorenko, M.V. Zhukov, O.M. Sukhareva.

Figure 1
Figure 1. Figure 1: Decay width calculations for dineutron+dineutron system with radius r0 = 4 fm and diffuseness a = 0.001 fm for different angular momenta by integral formula and quasiclassical approximation. so, in contrast with a two-body case, the centrifugal barrier in the three-body case is never equal to zero. The hyperspherical potentials are matrix elements of the pairwise intercluster potentials over hyperspherical… view at source ↗
Figure 2
Figure 2. Figure 2: Decay width calculations for 15F → 14O + p system with r0 = 2.96 fm and diffuseness a = 0.001 fm for different angular momenta by integral formula and quasiclassical approximation. These equations contain the effective adiabatic potentials, which take the form Veff(ρ) = λn(ρ) + 15/4 2M ρ 2 + V3b(ρ) . (12) The adiabatic terms λn(ρ) in this approach have complicated radial behavior: they may intersect. For w… view at source ↗
Figure 3
Figure 3. Figure 3: Decay width calculations for 15F → 14O + p system with r0 = 2.96 fm and angular momentum l = 0 for different diffusenesses a by integral formula and quasiclassical approximation. formfactor to reproduce the Q2p = 0.34 MeV in the integral formula formalism. The potentials V3b were also selected in such a way, that for ET > 0 they do not affect the Veff behavior in the barrier region. The long-range behavior… view at source ↗
Figure 4
Figure 4. Figure 4: Several lowest terms of the diagonalized potentia [PITH_FULL_IMAGE:figures/full_fig_p008_4.png] view at source ↗
Figure 5
Figure 5. Figure 5: Effective single channel potentials Veff for quasi-classical calculations of two-proton width of the 17Ne 3/2 − state. The two-proton decay energy ET is indicated by horizontal dashed line. Our hyperspherical harmonics potentials (gray and orange curves) are obtained by trivial diagonalization of the HH potential matrix from [2]. The dotted, solid and dashed black lines are from [3, 6]. They were obtained … view at source ↗
read the original abstract

Within the hyperspherical harmonics approach the three-body problem is reduced to a motion of one effective particle in a "strongly deformed" field, which is described in coupled-channel formalism. This method is especially suited to studies of phenomena characterized by genuine three-body dynamics, e.g. Borromean haloes and true three-body decays. The reduction of the hyperspherical equations set to a single-channel Schr\"odinger equation provides the basis for the use of the standard quasiclassical expression for calculations of widths for true three-body decays. We demonstrate that the quasiclassical approach by itself is quite precise in application to typical profiles of the three-body effective potentials. However, the reduction to single-channel formalism leads to significant overestimation of the two-proton width $\Gamma_{2p}$. This is demonstrated by the example of the $^{17}$Ne first excited $3/2^-$ state decay, questioning, however, the applicability of such an approximation in general.

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 / 0 minor

Summary. The paper investigates the applicability of the quasiclassical approach to true three-body decays within the hyperspherical harmonics method. It states that the quasiclassical approximation is precise for typical three-body effective potentials, but that reducing the coupled-channel hyperspherical equations to a single-channel Schrödinger equation leads to significant overestimation of the two-proton width Γ_{2p}, demonstrated explicitly for the first excited 3/2^- state in 17Ne.

Significance. If the numerical comparison holds, the result is significant for nuclear few-body physics because it identifies a concrete limitation of the single-channel reduction step that is often used to enable quasiclassical width formulas. This targeted observation can inform methodological choices for Borromean systems and true three-body decays without requiring a general theorem.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for the careful review and the positive recommendation to accept the manuscript. The referee's summary accurately captures the main results concerning the precision of the quasiclassical approximation versus the overestimation arising from single-channel reduction.

Circularity Check

0 steps flagged

No significant circularity

full rationale

The paper performs a numerical comparison within the hyperspherical harmonics method between the full coupled-channel treatment and the reduced single-channel quasiclassical approximation for three-body decay widths. The central result—that the single-channel reduction overestimates Γ_{2p} for the ^{17}Ne 3/2^- state—is an empirical observation from explicit calculations on specific effective potentials, not a derivation that reduces to fitted inputs or self-citations by construction. No self-definitional steps, fitted parameters renamed as predictions, or load-bearing self-citations appear in the abstract or described logic; the work is self-contained against external benchmarks via direct numerical comparison.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on the validity of the hyperspherical reduction to an effective potential and the subsequent single-channel collapse; no explicit free parameters or invented entities are named in the abstract.

axioms (2)
  • domain assumption The three-body problem can be reduced to motion of one effective particle in a strongly deformed field via hyperspherical harmonics.
    Stated in the first sentence of the abstract as the starting point for the method.
  • domain assumption Reduction of the coupled hyperspherical equations to a single-channel Schrödinger equation is a valid approximation whose accuracy can be tested by comparison to the full treatment.
    This reduction is the step whose consequences are being examined.

pith-pipeline@v0.9.0 · 5711 in / 1484 out tokens · 27041 ms · 2026-05-24T16:00:40.565631+00:00 · methodology

discussion (0)

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Reference graph

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