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The first chip identifies the source of the statement or construction; the second identifies the source of its local proof or verification.
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Planck coefficient from unwarped and warped products
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 , let , , take to be a declared -dimensional Einstein-frame metric, and let be the coupling in that frame's Einstein–Hilbert action, with . Assume that action is and take either a fixed product metric , where is smooth Lorentzian and is smooth, compact, Riemannian, and boundaryless, or the following internal-only warped metric with smooth : For the fixed product, and the coefficient of the -dimensional Einstein–Hilbert term is For , define the reduced Planck scale by , taking the positive root when . In this gives under the convention , and hence . The internal-curvature integral contributes a separate term without external curvature.
For the warped metric, the coefficient of the external Einstein–Hilbert term is
For a block-diagonal variable-volume product metric , let be a smooth Lorentzian metric and let be a smooth family of positive-definite metrics on the compact boundaryless , with no mixed components. Define The coefficient of is in the Jordan metric. If , is positive and smooth, and is a fixed reference volume, the Weyl rescaling makes the coefficient constant, , and also produces modulus-derivative terms. All metrics and couplings in each formula are in the same declared frame.
Statement references
Facts & Assumptions
Given: A smooth compact boundaryless , the stated Einstein–Hilbert action and product metric, or the displayed warped metric; is a fixed reference volume.
Kaluza–Klein product and warped reduction data: the fixed product, internal-only warped, and block-diagonal variable-volume ansätze are defined, including and the Weyl rescaling for .
Supergravity Conventions And Normalizations: in ten dimensions and, when the constant asymptotic dilaton is absorbed, with . The coupling convention is not changed during a frame conversion.
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.
When varies, it is positive and smooth, , and the external Weyl factor is smooth; its boundary term is discarded under the stated boundary conditions.
For the constant-dilaton frame conversion in step 3.1, set , , , constant, and use . This conversion does not include derivatives or dynamics of the dilaton.
Proof
For , block diagonality gives and hence . The mixed Christoffel symbols vanish because the two blocks depend on separate coordinates; the remaining Christoffel symbols are those of and . Contracting their block-diagonal curvature gives .
For the internal-only warped metric, block determinants give . The external-curvature part of is ; warp-derivative terms carry no factor . Multiplication therefore leaves , proving the warped coefficient.
For the block-diagonal variable-volume metric , its determinant gives . In the scalar curvature, the term containing the external scalar curvature is ; terms involving -derivatives of contain no . Integrating the coefficient over therefore gives .
Put and . The curvature transformation has and . Thus the coefficient of is ; derivatives of remain as scalar kinetic terms after the boundary term is treated.
Substituting these identities into and integrating over yields The first term is the stated external Einstein coefficient; the second contains no external curvature and is a separate potential/cosmological contribution. For , matching to gives the Planck formula.
Under [A3], put and let be the volume in the string metric. The constant rescaling gives and . Consequently, for the fixed coupling in the adopted Einstein action, its external curvature density obeys . In particular, if that action uses , then is the string-frame coefficient. Converting its external density back gives the Einstein-frame coefficient . If the adopted Einstein action instead uses , its string-frame coefficient is ; the coupling is held fixed in each conversion. A varying dilaton adds terms and is excluded.