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arxiv: 2308.10890 · v2 · submitted 2023-08-21 · 🌀 gr-qc · hep-th

Dust collapse in asymptotic safety: a path to regular black holes

Alfio Bonanno , Daniele Malafarina , Antonio Panassiti This is my paper

Pith reviewed 2026-05-24 06:58 UTC · model grok-4.3

classification 🌀 gr-qc hep-th
keywords asymptotic safetyregular black holesdust collapsequantum gravityReuter fixed pointsingularity resolutionjunction conditions
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0 comments X

The pith

Asymptotic safety gravity yields singularity-free spacetimes from dust collapse.

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

The paper models the interior of a collapsing dust cloud with an effective Lagrangian from quantum Einstein gravity in which the dust interacts with the metric through a multiplicative coupling function χ. The functional form of χ is fixed by asymptotic safety under the assumption that the Reuter fixed point is only minimally altered by matter, causing the gravitational coupling to vanish at high energies. The exterior geometry is fixed by junction conditions at the surface, producing a global spacetime that remains regular at every stage of the collapse. A sympathetic reader would care because the construction supplies an explicit dynamical route by which regular black holes can arise from classical matter without ever encountering a singularity.

Core claim

In the effective theory the gravitational coupling is driven to zero at high curvatures by the matter-geometry interaction χ derived from the Reuter fixed point. The resulting interior solution matched to a static exterior via junction conditions produces a global geometry free of singularities throughout the entire collapse process.

What carries the argument

The multiplicative coupling function χ between the dust fluid and the geometry, whose explicit form is obtained from asymptotic safety by assuming the Reuter fixed point is minimally affected by matter.

If this is right

  • The gravitational coupling vanishes at high energies inside the collapsing matter.
  • The global spacetime geometry stays regular at all times during collapse.
  • The static exterior geometry is completely fixed by the junction conditions alone.
  • Regular black holes can form dynamically from the collapse of ordinary dust.

Where Pith is reading between the lines

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

  • The same coupling construction could be applied to other collapsing matter models such as perfect fluids or scalar fields.
  • If the assumption on the Reuter fixed point holds, the model supplies a concrete mechanism that could be tested by comparing predicted horizon formation times against classical general-relativity expectations.
  • The approach suggests that singularity resolution in collapse may be a generic consequence of asymptotic safety rather than an ad-hoc choice of metric.

Load-bearing premise

The Reuter fixed point in asymptotic safety remains minimally affected by the presence of matter, so that the functional form of χ can be deduced directly from the fixed-point structure.

What would settle it

A computation demonstrating that matter fields appreciably shift the location or existence of the Reuter fixed point would invalidate the derived χ and therefore the claimed absence of singularities.

Figures

Figures reproduced from arXiv: 2308.10890 by Alfio Bonanno, Antonio Panassiti, Daniele Malafarina.

Figure 1
Figure 1. Figure 1: FIG. 1: The thick line shows the potential [PITH_FULL_IMAGE:figures/full_fig_p003_1.png] view at source ↗
Figure 3
Figure 3. Figure 3: FIG. 3: The behavior the metric function [PITH_FULL_IMAGE:figures/full_fig_p004_3.png] view at source ↗
Figure 4
Figure 4. Figure 4: Our solution represents a significant alternative to present models of regular black holes. It is built upon the assumption that black hole solutions observed in Nature are sourced by a matter interior whose evo￾lution is non-singular due to the antiscreening of the gravitational constant at small distances [22], accord￾ing to a specific renormalization group trajectory ter￾minating at the Reuter fixed poi… view at source ↗
read the original abstract

Regular black hole spacetimes are obtained from an effective Lagrangian for Quantum Einstein Gravity. The interior matter is modeled as a dust fluid, which interacts with the geometry through a multiplicative coupling function denoted as $\chi$. The specific functional form of $\chi$ is deduced from Asymptotically Safe gravity, under the key assumption that the Reuter fixed point remains minimally affected by the presence of matter. As a consequence the gravitational coupling vanishes at high energies. The static exterior geometry of the black hole is entirely determined by the junction conditions at the boundary surface. Consequently, the resulting global spacetime geometry remains devoid of singularities at all times. This outcome offers a new perspective on how regular black holes are formed through gravitational collapse.

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

2 major / 0 minor

Summary. The paper constructs an effective Lagrangian for dust collapse in asymptotically safe gravity. Interior dust couples to geometry via a multiplicative function χ whose form is fixed by assuming the Reuter fixed point of pure gravity is only minimally shifted by matter; this forces the gravitational coupling to vanish at high energies. Junction conditions at the collapsing surface then fix the static exterior, yielding a globally singularity-free spacetime at all times.

Significance. If the central modeling assumption can be independently justified, the construction supplies an explicit mechanism by which asymptotic safety can resolve singularities during collapse and produce regular black holes, with the exterior geometry determined solely by matching rather than by an ad-hoc choice of metric.

major comments (2)
  1. [Derivation of the coupling χ (abstract and § on effective Lagrangian)] The functional form of χ is deduced directly from the assumption that the Reuter fixed point remains minimally affected by the presence of dust matter. No renormalization-group computation that includes matter degrees of freedom is supplied to support or quantify this assumption; consequently the high-energy suppression of G (and therefore the regularity of the junction-matched geometry) is conditional on an input that is not derived within the manuscript.
  2. [Junction conditions and global geometry] The claim that the global spacetime remains devoid of singularities at all times follows from the specific high-energy behavior engineered by χ. If the Reuter-fixed-point assumption is relaxed, the junction conditions no longer guarantee regularity, so the central result is not robust against plausible variations of the modeling choice.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful reading of the manuscript and for highlighting both its potential significance and the central modeling assumptions. We respond to the major comments below.

read point-by-point responses

  1. Referee: [Derivation of the coupling χ (abstract and § on effective Lagrangian)] The functional form of χ is deduced directly from the assumption that the Reuter fixed point remains minimally affected by the presence of dust matter. No renormalization-group computation that includes matter degrees of freedom is supplied to support or quantify this assumption; consequently the high-energy suppression of G (and therefore the regularity of the junction-matched geometry) is conditional on an input that is not derived within the manuscript.

    Authors: We agree that the functional form of χ is introduced via the assumption that the Reuter fixed point experiences only minimal shifts from the inclusion of dust. This modeling choice is adopted to isolate the dynamical consequences for collapse within asymptotic safety, consistent with indications in the literature that matter contributions remain subdominant near the fixed point. A complete renormalization-group analysis including matter degrees of freedom would provide additional support but constitutes a separate, technically demanding study outside the scope of the present work, which instead examines the resulting spacetime geometry. We will revise the manuscript to expand the discussion of this assumption, its motivation, and its limitations in both the introduction and the concluding section. revision: partial

  2. Referee: [Junction conditions and global geometry] The claim that the global spacetime remains devoid of singularities at all times follows from the specific high-energy behavior engineered by χ. If the Reuter-fixed-point assumption is relaxed, the junction conditions no longer guarantee regularity, so the central result is not robust against plausible variations of the modeling choice.

    Authors: The referee is correct that singularity resolution in the constructed spacetime is a direct consequence of the high-energy vanishing of G induced by our choice of χ. The manuscript presents an explicit mechanism, within the stated assumption, by which junction conditions alone determine a globally regular geometry. We will add a clarifying paragraph that explicitly states the dependence of regularity on the Reuter-fixed-point assumption and notes that different behaviors could arise under alternative modeling choices, thereby framing the result as a concrete illustration rather than a fully assumption-independent theorem. revision: partial

Circularity Check

1 steps flagged

Central claim rests on unverified assumption that Reuter fixed point is minimally affected by dust matter when deducing χ

specific steps
  1. other [Abstract]
    "The specific functional form of χ is deduced from Asymptotically Safe gravity, under the key assumption that the Reuter fixed point remains minimally affected by the presence of matter. As a consequence the gravitational coupling vanishes at high energies. [...] Consequently, the resulting global spacetime geometry remains devoid of singularities at all times."

    The functional form of χ (which suppresses G at high energies inside the dust) is obtained by assuming the Reuter fixed point is minimally shifted by matter. The no-singularity result then follows automatically from the junction conditions once this χ is adopted. Without an independent verification of the assumption via RG computation with dust, the regularity outcome reduces to the input modeling choice.

full rationale

The paper deduces the functional form of the coupling χ directly from the assumption that the Reuter fixed point of pure gravity is only minimally affected by matter. This choice forces the gravitational coupling to vanish at high energies, which then guarantees (via junction conditions) a globally regular geometry. No independent RG flow computation including dust is provided, so the singularity-free outcome is a direct consequence of the modeling assumption rather than an independent derivation. This matches the pattern of a load-bearing input assumption that forces the central result.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 1 invented entities

The construction depends on the domain assumption that the Reuter fixed point is minimally affected by matter and on the effective Lagrangian of quantum Einstein gravity; no explicit free parameters are named, but the coupling χ is introduced to enforce vanishing gravitational strength at high energies.

axioms (1)
  • domain assumption Reuter fixed point remains minimally affected by the presence of matter
    Explicitly invoked in the abstract to deduce the functional form of χ
invented entities (1)
  • multiplicative coupling function χ no independent evidence
    purpose: To encode the interaction between dust and geometry so that the gravitational coupling vanishes at high energies
    Introduced as the central modeling device; no independent evidence outside the assumption is provided

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