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Thom–Sebastiani Theorem

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In complex analysis, a branch of mathematics, the Thom–Sebastiani Theorem states: given the germ f : ( C n 1 + n 2 , 0 ) ( C , 0 ) {\displaystyle f:(\mathbb {C} ^{n_{1}+n_{2}},0)\to (\mathbb {C} ,0)} defined as f ( z 1 , z 2 ) = f 1 ( z 1 ) + f 2 ( z 2 ) {\displaystyle f(z_{1},z_{2})=f_{1}(z_{1})+f_{2}(z_{2})} where f i {\displaystyle f_{i}} are germs of holomorphic functions with isolated singularities, the vanishing cycle complex of f {\displaystyle f} is isomorphic to the tensor product of those of f 1 , f 2 {\displaystyle f_{1},f_{2}} . Moreover, the isomorphism respects the monodromy operators in the sense: T f 1 T f 2 = T f {\displaystyle T_{f_{1}}\otimes T_{f_{2}}=T_{f}} .

The theorem was introduced by Thom and Sebastiani in 1971.

Observing that the analog fails in positive characteristic, Deligne suggested that, in positive characteristic, a tensor product should be replaced by a (certain) local convolution product.

References

  1. Fu, Lei (30 December 2013). "A Thom-Sebastiani Theorem in Characteristic p". arXiv:1105.5210. {{cite journal}}: Cite journal requires |journal= (help)
  2. ^ Illusie 2016, § 0.
  3. Sebastiani, M.; Thom, R. (1971). "Un résultat sur la monodromie". Inventiones Mathematicae. 13 (1–2): 90–96. Bibcode:1971InMat..13...90S. doi:10.1007/BF01390095. S2CID 121578342.


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