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Physics theoremStatement: Literature-sourcedProof: AI-adaptedPipeline-generatedprecheck passverified 2026-11-04 (gpt-6.1-sol)
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Planck coefficient from unwarped and warped products

Physical scope

Coefficient of the two-derivative Einstein–Hilbert term for fixed product, fixed internal-only warped, or block-diagonal variable-volume product metrics. Flux/source actions, higher-curvature terms, loop corrections, and dynamical dilaton terms are excluded. A constant dilaton appears only in the stated ten-dimensional frame conversion.

Statement

In natural units ℏ=c=1, let d,n≥1, D=d+n, take GD to be a declared D-dimensional Einstein-frame metric, and let κD>0 be the coupling in that frame's Einstein–Hilbert action, with [κD2]=(length)D−2. Assume that action is SD=12κD2∫Md×Yndd+nX−G R[G], and take either a fixed product metric GD=gd⊕hY, where Md is smooth Lorentzian and Yn is smooth, compact, Riemannian, and boundaryless, or the following internal-only warped metric with smooth A,B:Yn→R: dsD2=e2A(y)gd+e2B(y)g^Y. For the fixed product, Vol⁡E(Y):=∫Ydny det⁡hY and the coefficient of the d-dimensional Einstein–Hilbert term is 12κd2=Vol⁡E(Y)2κD2,κd−2=Vol⁡E(Y)κD−2. For d>2, define the reduced Planck scale by Md,Pld−2:=κd−2, taking the positive root when κd−2>0. In d=4 this gives M4,Pl2=κ4−2=(8πGN)−1 under the convention κ42=8πGN, and hence M4,Pl2=Vol⁡E(Y)/κD2. The internal-curvature integral contributes a separate term without external curvature.

For the warped metric, the coefficient of the external Einstein–Hilbert term is 12κD2∫Ydnydet⁡g^Y e(d−2)A+nB.

For a block-diagonal variable-volume product metric GD(x,y)=gJ(x)⊕γY(x,y), let gJ be a smooth Lorentzian metric and let γY(x,⋅) be a smooth family of positive-definite metrics on the compact boundaryless Yn, with no mixed components. Define VJ(x):=∫Ydny det⁡γY(x,y). The coefficient of R[gJ] is VJ(x)/(2κD2) in the Jordan metric. If d>2, VJ is positive and smooth, and V∗>0 is a fixed reference volume, the Weyl rescaling gE=(VJ/V∗)2/(d−2)gJ makes the coefficient constant, V∗/(2κD2), and also produces modulus-derivative terms. All metrics and couplings in each formula are in the same declared frame.

Facts & Assumptions

Given: A smooth compact boundaryless Yn, the stated Einstein–Hilbert action and product metric, or the displayed warped metric; V∗>0 is a fixed reference volume.

[F1]

Kaluza–Klein product and warped reduction data: the fixed product, internal-only warped, and block-diagonal variable-volume ansätze are defined, including VJ(x) and the Weyl rescaling for d>2.

[F2]

Supergravity Conventions And Normalizations: in ten dimensions G(E)=e−Φ/2G(s) and, when the constant asymptotic dilaton is absorbed, κ10,phys2=e2Φ∞κ02 with 2κ02=(2π)7α′4. The coupling convention is not changed during a frame conversion.

[A1]

Each coefficient calculation uses the displayed Einstein–Hilbert action and metrics in one common frame; other action terms are excluded. External boundary terms vanish or are discarded under the declared boundary conditions.

[A2]

When VJ varies, it is positive and smooth, d>2, and the external Weyl factor is smooth; its boundary term is discarded under the stated boundary conditions.

[A3]

For the constant-dilaton frame conversion in step 3.1, set D=10, d=4, n=6, Φ=Φ0=Φ∞ constant, and use κ10,phys2=e2Φ0κ02. This conversion does not include derivatives or dynamics of the dilaton.

Proof

1.1givenF1A1algebra

For GD=gd⊕hY, block diagonality gives det⁡GD=(det⁡gd)(det⁡hY) and hence −det⁡GD=−det⁡gddet⁡hY. The mixed Christoffel symbols vanish because the two blocks depend on separate coordinates; the remaining Christoffel symbols are those of gd and hY. Contracting their block-diagonal curvature gives R[GD]=R[gd]+R[hY].

1.2givenF1A1algebra

For the internal-only warped metric, block determinants give −det⁡GD=edA+nB−det⁡gddet⁡g^Y. The external-curvature part of R[GD] is e−2AR[gd]; warp-derivative terms carry no factor R[gd]. Multiplication therefore leaves e(d−2)A+nB, proving the warped coefficient.

1.3givenF1A1A2algebra

For the block-diagonal variable-volume metric GD(x,y)=gJ(x)⊕γY(x,y), its determinant gives −det⁡GD=−det⁡gJdet⁡γY. In the scalar curvature, the term containing the external scalar curvature is R[gJ]; terms involving x-derivatives of γY contain no R[gJ]. Integrating the coefficient over Y therefore gives VJ(x)/(2κD2).

2.1givenA2step 1.3algebra

Put Ω=(VJ/V∗)1/(d−2) and gE=Ω2gJ. The curvature transformation has R[gJ]=Ω2(R[gE]+terms with derivatives of Ω) and −det⁡gJ=Ω−d−det⁡gE. Thus the coefficient of R[gE] is VJΩ2−d=V∗; derivatives of Ω remain as scalar kinetic terms after the boundary term is treated.

2.2givenA1step 1.1algebra

Substituting these identities into SD and integrating over Y yields SD=Vol⁡E(Y)2κD2∫Md−gdR[gd]+12κD2(∫YhYR[hY])∫Md−gd. The first term is the stated external Einstein coefficient; the second contains no external curvature and is a separate potential/cosmological contribution. For d=4, matching 1/(2κ42) to M4,Pl2/2 gives the Planck formula.

3.1givenF2A3algebra∎

Under [A3], put VE:=Vol⁡E(Y) and let Vs be the volume in the string metric. The constant rescaling gives Vs=e3Φ0/2VE and −det⁡g4,sR[g4,s]=eΦ0/2−det⁡g4,ER[g4,E]. Consequently, for the fixed coupling κ10 in the adopted Einstein action, its external curvature density obeys VE2κ102−det⁡g4,ER[g4,E]=Vse−2Φ02κ102−det⁡g4,sR[g4,s]. In particular, if that action uses κ10=κ0, then Vse−2Φ0/(2κ02)=Vs/(2κ10,phys2) is the string-frame coefficient. Converting its external density back gives the Einstein-frame coefficient VseΦ0/2/(2κ10,phys2)=VE/(2κ02). If the adopted Einstein action instead uses κ10=κ10,phys, its string-frame coefficient is Vse−2Φ0/(2κ10,phys2); the coupling is held fixed in each conversion. A varying dilaton adds terms and is excluded.

Depends on

Dependency tree · 2 levels

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