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Riemann–Roch theorem for smooth manifolds
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Riemann–Roch theorem for smooth manifolds : ウィキペディア英語版
Riemann–Roch theorem for smooth manifolds
In mathematics, a Riemann–Roch theorem for smooth manifolds is a version of results such as the Hirzebruch–Riemann–Roch theorem or Grothendieck–Riemann–Roch theorem (GRR) without a hypothesis making the smooth manifolds involved carry a complex structure. Results of this kind were obtained by Michael Atiyah and Friedrich Hirzebruch in 1959, reducing the requirements to something like a spin structure.
==Formulation==

Let ''X'' and ''Y'' be oriented smooth closed manifolds,
and ''f'': ''X'' → ''Y'' a continuous map.
Let ''v''''f''=''f''
*
(''TY'') − ''TX'' in the K-group
K(X).
If dim(X) ≡ dim(Y) mod 2, then
:\mathrm(f_(x)) = f_(\mathrm(x) e^\hat(v_f)),
where ch is the Chern character, d(vf) an element of
the integral cohomology group ''H''2(''Y'', ''Z'') satisfying
''d''(''v''''f'') ≡ ''f''
*
''w''2(T''Y'')-''w''2(T''X'') mod 2,
fK
*
the Gysin homomorphism for K-theory,
and fH
*
the Gysin homomorphism for cohomology
.〔M. Karoubi, ''K-theory, an introduction'', Springer-Verlag, Berlin (1978)〕
This theorem was first proven by Atiyah and Hirzebruch.〔M. Atiyah and F. Hirzebruch, ''Riemann–Roch theorems for differentiable manifolds'' (Bull. Amer. Math. Soc. 65 (1959) 276–281)〕
The theorem is proven by considering several special cases.〔M. Karoubi, ''K-theory, an introduction'', Springer-Verlag, Berlin (1978)〕
If ''Y'' is the Thom space of a vector bundle ''V'' over ''X'',
then the Gysin maps are just the Thom isomorphism.
Then, using the splitting principle, it suffices to check the theorem via explicit computation for line
bundles.
If ''f'': ''X'' → ''Y'' is an embedding, then the
Thom space of the normal bundle of ''X'' in ''Y'' can be viewed as a tubular neighborhood of ''X''
in ''Y'', and excision gives a map
:u:H^
*(B(N), S(N)) \to H^
*(Y, Y-B(N)) \to H^
*(Y)
and
:v:K(B(N), S(N)) \to K(Y, Y-B(N)) \to K(Y).
The Gysin map for K-theory/cohomology is defined to be the composition of the Thom isomorphism with these maps.
Since the theorem holds for the map from ''X'' to the Thom space of ''N'',
and since the Chern character commutes with ''u'' and ''v'', the theorem is also true for embeddings.
''f'': ''X'' → ''Y''.
Finally, we can factor a general map ''f'': ''X'' → ''Y''
into an embedding
:i: X \to Y \times S^
and the projection
:p: Y \times S^ \to Y.
The theorem is true for the embedding.
The Gysin map for the projection is the Bott-periodicity isomorphism, which commutes with the Chern character,
so the theorem holds in this general case also.

抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)
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