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Bott Residue Formula


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2025 年 4 月
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We make the same assumptions as in previous section. Let i1,,ik be k positive even integers. For any pzero(K) and 1jk, set
λij(p)=λij1++λijl.By following theorem, we reduce the computation of characteristic numbers of TM to quantities on zero(K).

Theorem 1. If i1++ik=l, then
Mtr[(RTM)i1]tr[(RTM)ik]=(2π1)lpzero(K)2kλi1(p)λik(p)λ(p),where RTM is the curvature of the Levi-Civita connection TM. And, if i1++ik<l, then
pzero(K)2kλi1(p)λik(p)λ(p)=0.

Proof . We define a operator
LK=TMKLK|Γ(TM).Obviously, for any YΓ(TM)
LKY=TMKY[K,L]=(TMK)(Y).i.e., LK=(TMK)Γ(End(TM))=Ω0(M,End(TM)). We need to find a ωΩ(M) satisfied dKω=0 and
Mω=Mtr[(RTM)i1]tr[(RTM)ik].
Of course, it is necessary that we can calculate Mω.
For any integer h, if we have dKtr[(RTM+LK)h]=0. Since
[tr[(RTM+LK)i1]tr[(RTM+LK)ik]][top]=tr[(RTM)i1]tr[(RTM)ik],it means
Mtr[(RTM)i1]tr[(RTM)ik]=Mtr[(RTM+LK)i1]tr[(RTM)ik+LK].
By the Berline-Vergne localization formula, one can easily obtain
Mtr[(RTM)i1]tr[(RTM)ik]=(2π)lpzero(K)tr[(LK(p))i1]tr[(LK(p))ik]λ(p)On the local coordinate system (Up,(x1,,x2l)) from the previous section,
K=li=1λi(x2ix2i1x2i1x2i).And, we know LK=TMK is a anti-symmetry operator. So on Up,
LK(p)=(0λ1λ100λlλl0),then (LK(p))2=diag{λ21,λ21,,λ2l,λ2l}.
Thus, for each 1jk, tr[(LK(p))ij]=2(1)ij/2λij(p). From this result,
Mtr[(RTM)i1]tr[(RTM)ik]=(2π1)lpzero(K)2kλi1(p)λik(p)λ(p).
Otherwise, we have
(d+iK)tr[(RTM+LK)h]=dtr[(RTM+LK)h]+iKtr[(RTM+LK)h]=tr[TM,(RTM+LK)h]+tr[iK(RTM+LK)h]=tr[TM,(RTM+LK)h]+tr[iK,(RTM+LK)h]=tr[TM+iK,(RTM+LK)h];
(TM+iK)2=()2+(iK)2+TMiK+iKTM=RTM+0+TMiK+iKTM=RTM+0+TMiK+iK(TM)TMiK=RTM+TMK=RTM+LK+LK;
i.e.,RTM+LK=(TM+iK)2LK. By Bianchi identity, one can obtain
[TM+iK,RTM+LK]=[TM+iK,(TM+iK)2LK]=[TM+iK,LK].
Since both TM and K are S1-invariant, one has
[TM,LK]=0,[iK,LK]=0.Hence [TM+iK,RTM+LK]=0. It shows
dKtr[(RTM+LK)h]=tr[TM+iK,RTM+LK]=0.

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