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Irreducible symplectic varieties of dimensions 4 to 20 arise as terminalisations of finite symplectic quotients of Beauville-Mukai systems on K3-del Pezzo double covers.

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2026-06-26 22:20 UTC pith:YD7VFVT6

load-bearing objection This paper constructs new irreducible symplectic varieties in dimensions 4-20 with b2 16-24 via K3-del Pezzo double covers, Beauville-Mukai systems, and terminalised quotients.

arxiv 2606.18357 v1 pith:YD7VFVT6 submitted 2026-06-16 math.AG

Irreducible symplectic varieties via K3-del Pezzo double covers

Riccardo Carini This is my paper
classification math.AG
keywords irreducible symplectic varietiesK3-del Pezzo double coversBeauville-Mukai systemssymplectic quotientsterminalisationshyperkahler manifoldssecond Betti numberalgebraic geometry
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved

The pith

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

The paper constructs a family of irreducible symplectic varieties in even dimensions from 4 up to 20. These examples are produced by forming finite symplectic quotients of certain moduli spaces called Beauville-Mukai systems that live on very general double covers of del Pezzo surfaces by K3 surfaces, then taking minimal resolutions of the resulting singularities. The second Betti numbers of the varieties fall in the range 16 to 24. A reader would care because the construction supplies explicit new instances of these higher-dimensional hyperkähler-type objects in a range where concrete examples have been limited.

Core claim

We construct a series of irreducible symplectic varieties of dimension 2n, for 2≤n≤10, with second Betti numbers 16≤b2≤24. They arise as non-trivial terminalisations of finite symplectic quotients of Beauville-Mukai systems on very general K3-del Pezzo double covers.

What carries the argument

non-trivial terminalisations of finite symplectic quotients of Beauville-Mukai systems on very general K3-del Pezzo double covers

Load-bearing premise

The finite symplectic quotients of the Beauville-Mukai systems on very general K3-del Pezzo double covers admit non-trivial terminalisations that remain irreducible symplectic varieties.

What would settle it

An explicit computation for any single n between 2 and 10 showing that the terminalisation either fails to be symplectic, introduces non-terminal singularities, or yields a variety whose second Betti number lies outside 16-24.

Watch this falsifier — get emailed when new claim-graph text bears on it.

If this is right

  • Examples exist in every even dimension from 4 through 20.
  • The second Betti numbers of these varieties lie between 16 and 24 inclusive.
  • The source objects are Beauville-Mukai systems on very general K3 surfaces that double-cover del Pezzo surfaces.
  • The group actions used to form the quotients are finite and symplectic.
  • The terminalisations are non-trivial, meaning they differ from the original quotients.

Where Pith is reading between the lines

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

  • These varieties may supply test cases for conjectures on the possible values of b2 for irreducible symplectic varieties in each dimension.
  • Further Hodge numbers or the Fujiki relation constant could be computed directly from the construction for small n.
  • The same quotient-and-terminalise method might apply to other families of surfaces carrying Beauville-Mukai systems.
  • The resulting moduli spaces of these new varieties could be compared with known deformation types.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit.

Referee Report

0 major / 1 minor

Summary. The manuscript constructs a series of irreducible symplectic varieties of dimension 2n for 2 ≤ n ≤ 10, with second Betti numbers satisfying 16 ≤ b₂ ≤ 24. These varieties are obtained as non-trivial terminalisations of finite symplectic quotients of Beauville-Mukai systems on very general K3-del Pezzo double covers.

Significance. If the central construction holds, the work supplies new examples of irreducible symplectic varieties in dimensions up to 20 whose Betti numbers lie in a previously sparsely populated range. The approach via K3-del Pezzo double covers and controlled symplectic quotients offers a systematic geometric source that could be compared with existing deformation classes of hyperkähler varieties and their singular analogues.

minor comments (1)
  1. The abstract states the dimension range and Betti-number bounds but does not indicate whether the terminalisation process is shown to preserve the symplectic form or the irreducibility of the resulting variety; a dedicated section or proposition establishing these preservation properties would strengthen the exposition.

Simulated Author's Rebuttal

0 responses · 0 unresolved

We thank the referee for their summary of the manuscript and for noting its potential significance in providing new examples of irreducible symplectic varieties. No specific major comments were provided in the report.

Circularity Check

0 steps flagged

No significant circularity; construction is self-contained

full rationale

The paper is a geometric construction claiming existence of certain irreducible symplectic varieties as terminalisations of quotients of Beauville-Mukai systems on K3-del Pezzo double covers. No equations, fitted parameters, or predictions are present that reduce by construction to the paper's own inputs. The central claim is an existence result relying on standard algebraic geometry techniques (quotients, terminalisations, symplectic forms) without self-definitional loops, self-citation load-bearing premises, or renaming of known results. The reader's assessment of score 1.0 aligns with this; the derivation chain does not collapse to tautology.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

Only the abstract is supplied, so the ledger records the background assumptions explicitly invoked by the construction claim. No free parameters or invented entities are mentioned.

axioms (2)
  • domain assumption Very general K3-del Pezzo double covers exist and carry Beauville-Mukai systems admitting finite symplectic quotients.
    Invoked in the abstract as the starting point for the quotients and terminalisations.
  • domain assumption Non-trivial terminalisations of these quotients remain irreducible symplectic varieties.
    This is the load-bearing step that produces the claimed objects.

pith-pipeline@v0.9.1-grok · 5563 in / 1456 out tokens · 36169 ms · 2026-06-26T22:20:11.333824+00:00 · methodology

0 comments
read the original abstract

We construct a series of irreducible symplectic varieties of dimension $2n$, for $2\leq n\leq 10$, with second Betti numbers $16\leq b_2\leq 24$. They arise as non-trivial terminalisations of finite symplectic quotients of Beauville-Mukai systems on very general K3-del Pezzo double covers.

Figures

Figures reproduced from arXiv: 2606.18357 by Riccardo Carini.

Figure 3.1
Figure 3.1. Figure 3.1: Polystable-type Hasse diagram for Mv(S, H), with T ∼= P 2 . Here v = 3v0, with v0 := (0, f ∗h, −3). Nodes are polystable types; an upward arrow labelled k means that the lower stratum is contained in the closure of the upper one with codimension k. Note that Mv0 (S, H) is a smooth hyper-K¨ahler fourfold of K3[2]-type. from the non-primitivity of v, while the last two splittings define the same non-zero w… view at source ↗
Figure 3.2
Figure 3.2. Figure 3.2: Polystable-type Hasse diagram for Mv(S, H), with T ∼= Bl1P 2 . Here v = 2v1+3v2 as in (3.7). Nodes are polystable types; an upward arrow labelled k means that the lower stratum is contained in the closure of the upper one with codimension k. The proof of Proposition 3.5 also gives an integral identification of transcendental lat￾tices T(S) −→∼ T(Mv(S, H)). (3.6) For d = 1 and d = 9, in the absence of v-w… view at source ↗
Figure 3.3
Figure 3.3. Figure 3.3: Polystable-type Hasse diagram for Mv(S, H), with T ∼= P 1 × P 1 . Here v = 2v1 + 2v2 as in (3.8). Nodes are polystable types; an upward arrow labelled k means that the lower stratum is contained in the closure of the upper one with codimension k. so that v = (0, H, −8) = 2v1+3v2 ∈ Healg(S,Z). Both classes v1 and v2 are admissible, in the sense that the associated moduli spaces have non-empty stable loci.… view at source ↗

discussion (0)

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