Analytic torsion

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In mathematics, Reidemeister torsion (or R-torsion, or Reidemeister-Franz torsion) is a topological invariant of manifolds introduced by Reidemeister (1935) for 3-manifolds and generalized to higher dimensions by Franz (1935) and de Rham (1936). Analytic torsion (or Ray-Singer torsion) is an invariant of Riemannian manifolds defined by Ray and Singer (1971, 1973a, 1973b) as an analytic analogue of Reidemeister torsion. Cheeger (1977, 1979) and Müller (1978) proved Ray and Singer's conjecture that Reidemeister torsion and analytic torsion are the same for compact Riemannian manifolds.

Reidemeister torsion was the first invariant in algebraic topology that could distinguish between spaces which are homotopy equivalent but not homeomorphic. It can be used to classify lens spaces.

Reidemeister torsion is closely related to Whitehead torsion; see (Milnor 1966). For later work on torsion see the books (Turaev 2002), (Nicolaescu 2002, 2003).

[edit] Definition of analytic torsion

If M is a Riemannian manifold and E an orthogonal bundle over M, then there is a Laplacian operator acting on the i-forms with values in E. If the eigenvalues on i-forms are λ_j then the zeta function ζ_i is defined to be

$\zeta_i(s) = \sum_{\lambda_j>0}\lambda_j^{-s}$

for s large, and this is extended to all complex s by analytic continuation. The zeta regularized determinant of the Laplacian acting on i-forms is

$\Delta_i=\exp(-\zeta^\prime_i(0))$

which is formally the product of the positive eigenvalues of the laplacian acting on i-forms. The analytic torsion T(M,E) is defined to be

$T(M,E) = \exp\left(\sum_i (-1)^ii \zeta^\prime_i(0)/2\right) = \prod_i\Delta_i^{-(-1)^ii/2}.$

[edit] Definition of Reidemeister torsion

Let X be a finite connected CW-complex with fundamental group π := π₁(X) and U an orthogonal finite-dimensional π-representation. Suppose that

$H^\pi_n(X;U) := H_n(U \otimes_{\mathbf{Z}[\pi]} C_*({\tilde X})) = 0$

for all n. If we fix a cellular basis for $C_*({\tilde X})$ and an orthogonal R-basis for U, then $D_* := U \otimes_{\mathbf{Z}[\pi]} C_*({\tilde X})$ is a contractible finite based free R-chain complex. Let $\gamma_*: D_* \to D_{*+1}$ be any chain contraction of D_*, i.e. $d_{n+1} \circ \gamma_n + \gamma_{n-1} \circ d_n = id_{D_n}$ for all n. We obtain an isomorphism $(d_* + \gamma_*)_{odd}: D_{odd} \to D_{even}$ with $D_{odd} := \oplus_{n \, odd} \, D_n$ , $D_{even} := \oplus_{n \, even} \, D_n$ . We define the Reidemeister torsion

$\rho(X;U) := |\mathop{det}(A)| \in \mathbf{R}^{>0}$

where A is the matrix of (d_* + γ_*)_odd with respect to the given bases. The Reidemeister torsion $ρ(X; U)$ is independent of the choice of the cellular basis for $C_*({\tilde X})$ , the orthogonal basis for U and the chain contraction γ_*.

[edit] Examples

Reidemeister torsion was first used to classify 3-dimensional lens spaces. The classification includes examples of homotopy equivalent 3-dimensional manifolds which are not homeomorphic -- at the time (1935) the classification was only up to PL homeomorphism, but later (1960) E.J.Brody showed that this was in fact a classification up to homeomorphism.

[edit] References

Cheeger, Jeff (1977), "Analytic Torsion and Reidemeister Torsion", PNAS 74 (7): 2651–2654, doi:10.1073/pnas.74.7.2651, MR 0451312, http://www.pnas.org/cgi/content/abstract/74/7/2651
Cheeger, Jeff (1979), "Analytic torsion and the heat equation", Ann. Of Math. (2) 109 (2): 259–322, doi:10.2307/1971113, MR 0528965, http://links.jstor.org/sici?sici=0003-486X%28197905%292%3A109%3A2%3C259%3AATATHE%3E2.0.CO%3B2-2
Franz, W. (1935), "Ueber die Torsion einer Ueberdeckung", J. Reine Angew. Math. 173: 245–254
Milnor, J. (1966), "Whitehead torsion.", Bull. Amer. Math. Soc. 72: 358–426, doi:10.1090/S0002-9904-1966-11484-2, MR 0196736 , http://www.ams.org/bull/1966-72-03/S0002-9904-1966-11484-2/home.html
Mishchenko, A.S. (2001), "Reidemeister torsion", in Hazewinkel, Michiel, Encyclopaedia of Mathematics, Kluwer Academic Publishers, ISBN 978-1556080104
Müller, Werner (1978), "Analytic torsion and R-torsion of Riemannian manifolds.", Adv. In Math. 28 (3): 233–305, doi:10.1016/0001-8708(78)90116-0, MR 0498252
Nicolaescu, Liviu I. (2002), Notes on the Reidemeister torsion, http://www.nd.edu/~lnicolae/Torsion.pdf Online book
Nicolaescu, Liviu I. (2003), The Reidemeister torsion of 3-manifolds, de Gruyter Studies in Mathematics, 30, Berlin: Walter de Gruyter & Co., pp. xiv+249, MR 1968575, ISBN 3-11-017383-2
Ray, D. B.; Singer, I. M. (1973a), "Analytic torsion for complex manifolds.", Ann. Of Math. (2) 98: 154–177, doi:10.2307/1970909, MR 0383463, http://links.jstor.org/sici?sici=0003-486X%28197307%292%3A98%3A1%3C154%3AATFCM%3E2.0.CO%3B2-G
Ray, D. B.; Singer, I. M. (1973b), "Analytic torsion.", Partial differential equations, Proc. Sympos. Pure Math., XXIII, Providence, R.I.: Amer. Math. Soc., pp. 167–181, MR 0339293
Ray, D. B.; Singer, I. M. (1971), "R-torsion and the Laplacian on Riemannian manifolds.", Advances in Math. 7: 145–210, doi:10.1016/0001-8708(71)90045-4, MR 0295381
Reidemeister, K. (1935), "Homotopieringe und Linsenräume", Abh. Math. Sem. Univ. Hamburg 11: 102–109, doi:10.1007/BF02940717
de Rham, G. (1936), "Sur les nouveaux invariants de M. Reidemeister", Mat. Sb. , 1 (5): 737–743
Turaev, Vladimir (2002), Torsions of 3-dimensional manifolds, Progress in Mathematics, 208, Basel: Birkhäuser Verlag, pp. x+196 ISBN= 3–7643–6911–6, MR 1958479

Analytic torsion

From Wikipedia, the free encyclopedia

Contents

[edit] Definition of analytic torsion

[edit] Definition of Reidemeister torsion

[edit] Examples

[edit] References

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