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Christoffel symbols of the Schwarzschild exterior metric in product charts

Statement

Let (M,g,N) be the Schwarzschild exterior datum of mass parameter m∗ with Schwarzschild radius s=2GNm∗/c2 and f(r)=1−s/r (The Schwarzschild exterior model datum: domain, metric, mass parameter and time orientation), and let ∇ be the metric-selected connection of g (Metric compatibility, torsion freedom and the metric-selected connection class, Existence and uniqueness of the metric-selected connection of a nondegenerate metric, and its extension to tensor fields). In every spherical-polar product chart (x0,r,ϑ,φ) with 0<ϑ<π and f′=dfdr=s/r2, the Christoffel symbols Γabc of ∇ (Christoffel symbols of an affine connection) are:

(a) Γ001=Γ010=f′2f, and Γ000=Γ011=Γ0ij=0 for all remaining index pairs;

(b) Γ100=ff′2, Γ111=−f′2f, Γ122=−rf, Γ133=−rfsin⁡2ϑ, and Γ101=Γ102=Γ103=Γ112=Γ113=Γ123=0;

(c) Γ212=Γ221=1r, Γ233=−sin⁡ϑcos⁡ϑ, and every other symbol with upper index 2 vanishes;

(d) Γ313=Γ331=1r, Γ323=Γ332=cot⁡ϑ, and every other symbol with upper index 3 vanishes.

All components not listed vanish; equivalently, the only nonzero symbols are those displayed. For the model value f(r)=1−s/r, so that f′=s/r2, the listed symbols read

Γ001=Γ010=s2r2f,Γ100=sf2r2,Γ111=−s2r2f,

Γ122=−rf,Γ133=−rfsin⁡2ϑ,Γ212=Γ313=1r,Γ233=−sin⁡ϑcos⁡ϑ,Γ323=cot⁡ϑ.

Facts & Assumptions

Given: The Schwarzschild exterior datum with Schwarzschild radius s, the metric g and its metric-selected connection ∇, and a product chart (x0,r,ϑ,φ) with 0<ϑ<π.

[L1]

In the product chart the metric components are g00=−f, g11=f−1, g22=r2, g33=r2sin⁡2ϑ and gab=0 for a≠b, with f=f(r)>0 smooth; the metric-selected connection exists and is the unique torsion-free g-compatible affine connection (The Schwarzschild exterior model datum: domain, metric, mass parameter and time orientation, The Schwarzschild exterior datum is a smooth time-oriented Lorentzian four-manifold, Metric compatibility, torsion freedom and the metric-selected connection class, Existence and uniqueness of the metric-selected connection of a nondegenerate metric, and its extension to tensor fields).

[L2]

The inverse-metric components are characterised by ∑bgabgbc=δac; for the diagonal matrix of [L1] they are g00=−f−1, g11=f, g22=r−2, g33=r−2sin⁡−2ϑ, all off-diagonal components vanishing (The inverse metric, musical isomorphisms and index raising, Tensor fields of type (r,s) on a Lorentzian four-manifold and their components).

[L3]

In every smooth chart the Christoffel symbols of the metric-selected connection are Γabc=12∑dgad(∂bgdc+∂cgbd−∂dgbc), and they are symmetric in the lower pair, Γabc=Γacb (Existence and uniqueness of the metric-selected connection of a nondegenerate metric, and its extension to tensor fields clause (a), Christoffel symbols of an affine connection, Torsion freedom and metric compatibility in chart components).

[L4]

All metric components of [L1] are independent of x0 and φ, so ∂0gbc=0 and ∂3gbc=0 for all indices; the coordinate partial derivatives of the components are those of Directional derivatives and partial derivatives of a map U⊆Rm→Rn, and ddrf=f′=sr2 for the model function f(r)=1−s/r by The derivative f′(c)=lim⁡x→cf(x)−f(c)x−c of f:A→R at a point c∈A that is a limit point of A, and differentiability on a set and the power rule.

[L5]

On the chart domain 0<ϑ<π, so sin⁡ϑ>0, sin⁡2ϑ>0 and r>s>0; the displayed expressions for Γ are smooth there (Rational powers ar of a positive base).

Proof

technique · substitute the metric components of [L1] and the inverse components of [L2] into the Koszul formula of [L3], organised by the upper index
1.1L1L2L4algebra

(Metric derivatives and inverse components.) The only nonconstant components of [L1] are g00=−f(r), g11=f(r)−1, g22=r2, g33=r2sin⁡2ϑ, and their nonzero coordinate derivatives are ∂1g00=−f′, ∂1g11=−f′/f2, ∂1g22=2r, ∂1g33=2rsin⁡2ϑ, ∂2g33=2r2sin⁡ϑcos⁡ϑ; by [L4] every ∂0 or ∂3 derivative vanishes. The inverse components are g00=−1/f, g11=f, g22=1/r2, g33=1/(r2sin⁡2ϑ), as the diagonal matrix inverse of [L2].

2.1L3step 1.1algebra

(The family Γ0⋅⋅.) By [L3], Γ0bc=12g00(∂bg0c+∂cg0b−∂0gbc). If {b,c} contains an index in {2,3} then g0c or g0b vanishes identically and ∂0gbc=0; the cases (b,c)=(0,0) and (1,1) give ∂0g00=0 and ∂0g11=0; hence only (b,c)∈{(0,1),(1,0)} can contribute, with value 12g00∂1g00=12(−1/f)(−f′)=f′/(2f). This is claim (a).

2.2L3step 1.1algebra

(The family Γ1⋅⋅.) By [L3], Γ1bc=12g11(∂bg1c+∂cg1b−∂1gbc). If g1c or g1b is nonzero the corresponding term contributes; since g1d=0 unless d=1, only b=c=1 retains a contribution and Γ111=12g11∂1g11=12f(−f′/f2)=−f′/(2f). The cases (b,c)=(0,0), (2,2) and (3,3) have Γ1bc=−12g11∂1gbc, giving Γ100=12ff′=ff′/2, Γ122=−12f(2r)=−rf and Γ133=−rfsin⁡2ϑ. Every mixed case (b≠c) has ∂bg1c+∂cg1b=0 and ∂1gbc=0 for the off-diagonal components, hence vanishes. This is claim (b).

2.3L3L4step 1.1algebra

(The families Γ2⋅⋅ and Γ3⋅⋅.) For the upper index 2, [L3] gives Γ2bc=12g22(∂bg2c+∂cg2b−∂2gbc) with g22=1/r2. The only nonzero g2c is c=2, so only b=c=2 and the pairs with gbc depending on ϑ contribute: Γ222=12r−2∂2g22=0 and Γ233=−12r−2∂2g33=−12r−2(2r2sin⁡ϑcos⁡ϑ)=−sin⁡ϑcos⁡ϑ, while Γ212=Γ221=12r−2∂1g22=r−2⋅r=1/r and the (0,0) case vanishes. For the upper index 3, g33=1/(r2sin⁡2ϑ) and only g33 is nonzero among the g3c: Γ313=Γ331=12(r2sin⁡2ϑ)−1∂1g33=12(r2sin⁡2ϑ)−1(2rsin⁡2ϑ)=1/r, Γ323=Γ332=12(r2sin⁡2ϑ)−1∂2g33=12(r2sin⁡2ϑ)−1(2r2sin⁡ϑcos⁡ϑ)=cot⁡ϑ, and Γ333=12g33∂3g33=0 by [L4]; all cases with an index 0 or 1 in b,c other than the displayed ones vanish because the corresponding g3c or gbc is constant. Together with the lower-pair symmetry of [L3], these are claims (c) and (d).

3.1L3L4L5step 2.1step 2.2step 2.3∎

(Exhaustiveness and the model values.) The index triples (a,b,c) with a,b,c∈{0,1,2,3} split into the families treated in step 1.1 and steps 2.1-2.3; each family was computed from the same unique connection ∇ of [L1], so the displays (a)-(d) list exactly the nonzero symbols of ∇ in the chart. Substituting f=1−s/r and f′=s/r2 of [L4] into the general expressions (a)-(d) gives the second display of the Statement. All symbols are smooth on the chart domain by [L5], and the expressions are those of the metric-selected connection, not of an arbitrary connection.

Remarks

  • Sign check at the leading order. For large r one has f=1−s/r+O(r−2) and f′=s/r2, so Γ100=12ff′=s2r2+O(r−3); this is the coefficient +c−2∂rΦ with the Newtonian potential Φ=−GNm∗/r of the flat and Newtonian bridge page, whose spatial acceleration reads −∂rΦ=−GNm∗/r2 and matches the geodesic acceleration −c2Γ100 computed in the weak-field bridge lemma of the flat-and-Newtonian page in the overlapping regime. The comparison is made with the round metric of the same chart and is not a statement of this lemma.

  • Distance to the Newtonian form. The symbols here are written with x0=ct as the time coordinate; in the coordinate t=x0/c the components acquire factors of c by the chain rule and the invariant statements of the following lemmas are used rather than the raw symbols.

Depends on

Dependency tree · 2 levels

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