Let
and
be vector bundles over a compact manifold
. If a
differential operator
is elliptic, then
and
are finite-dimensional vector spaces and we can
define the *index* of
to be the virtual vector space

Now suppose a Lie group acts on , and and are -equivariant vector bundles over . Then acts on by

for , . The -action is said to

If the multiple is positive, then is the trivial representation of dimension of . If is negative, the is a virtual representation and the rigidity of implies that the trivial representation occurs more often in than in .

For a circle action on a compact oriented Riemannian manifold, it is well known that the Hodge operator and the signature operator are both rigid.

An oriented Riemannian manifold of dimension
has an atlas whose transition
functions take values in
. The manifold is called a *spin
manifold* if it is possible to lift the transition functions to the double cover
of
.

Inspired by physics, Witten discovered infinitely many rigid elliptic operators on a compact spin manifold with a circle action. They are typically of the form , where is the signature operator and is some combination of the exterior and the symmetric powers of the tangent bundle. In [91] Bott and Taubes found a proof, more accessible to mathematicians, of Witten's results, by recasting the rigidity theorem as a consequence of the Atiyah-Bott fixed point theorem.

The idea of [91] is as follows. To decompose a representation, one needs to know only its trace, since the trace determines the representation. By assumption, the action of on the elliptic complex commutes with . This means each element in is an endomorphism of the elliptic complex. It therefore induces an endomorphism in the cohomology of the complex. But and . The alternating sum of the trace of in cohomology is precisely the left-hand side of the Atiyah-Bott fixed point theorem. It then stands to reason that the fixed point theorem could be used to decompose the index of into irreducible representations.

**Papers of Raoul Bott discussed in this article**

- [1]
- (with R. J. Duffin) Impedance synthesis without use of
transformers, J. Appl. Phys.,
**20**(1949), 816. - [8]
- On torsion in Lie groups, Proc. NAS,
**40**(1954), 586-588. - [9]
- Nondegenerate critical manifolds, Ann. of Math.
**60**(1954), 248-261. - [12]
- (with H. Samelson) The cohomology ring of
,
Proc. NAS,
**41**(1955), 490-493. - [14]
- On the iteration of closed geodesics and the Sturm
Intersection theory, Comm. Pure Appl. Math.
**IX**(1956), 171-206. - [15]
- Homogeneous vector bundles, Ann. of Math.
**66**(1957), 933-935. - [24]
- The stable homotopy of the classical groups, Ann. of Math.
**70**(1959), 313-337. - [33]
- (with M. F. Atiyah and A. Shapiro) Clifford modules,
Topology
**3**(1965), 3-38. - [37]
- The index theorem for homogeneous differential operators, in:
*Differential and Combinatorial Topology: A Symposium in Honor of Marston Morse*, Princeton, (1964), 167-186. - [38]
- (with S. Chern) Hermitian vector bundles and the
equidistribution of the zeroes of their holomorphic sections, Acta
Mathematics
**114**(1964), 71-112. - [41]
- Vector fields and characteristic numbers, Mich. Math.
Jour.
**14**(1967), 231-244. - [42]
- (with M. F. Atiyah) A Lefschetz fixed point formula for
elliptic complexes: I, Ann. of Math.
**86**(1967), 374-407. - [43]
- A residue formula for holomorphic vector fields, J.
Differential Geom.
**1**(1967), 311-330. - [44]
- (with M. F. Atiyah) A Lefschetz fixed point formula for
elliptic complexes: II, Ann. of Math.
**88**(1968), 451-491. - [51]
- On a topological obstruction to integrability, in:
*Global Analysis*, Proceedings of Symposia in Pure Math.**XVI**(1970), 127-131. - [71]
- (with G. Segal) The cohomology of the vector fields on a
manifold, Topology
**16**(1977), 285-298. - [81]
- (with M. F. Atiyah) The Yang-Mills equations over Riemann
surfaces, Phil. Trans. R. Soc. Lond.
**A 308**(1982), 524-615. - [82]
- (with M. F. Atiyah) The moment map and equivariant
cohomology, Topology
**23**(1984), 1-28. - [91]
- (with C. Taubes) On the rigidity theorem of Witten,
Jour. of the Amer. Math.
Soc.
**2**(1989), 137-186.

**Update to the Bibliography of Raoul Bott**

Raoul Bott's Bibliography in his Collected Papers [B5]
is not complete.
This update completes the Bibliography as of June 2000.

- [20]
- In memoriam Sumner B. Myers, Mich. Math. Jour.,
**5**(1958), 1-4. - [79]
- (with L. Tu)
*Differential Forms in Algebraic Topology*, Springer-Verlag, (1982), 1-331. - [94]
- Georges de Rham: 1901-1990,
*Notices Amer. Math. Soc.***38**(1991), 114-115. - [95]
- Stable bundles revisited, Surveys in Differential Geometry,
**1**(1991), 1-18. - [96]
- On E. Verlinde's formula in the context of stable bundles,
Internat. J. Modern Phys. A
**6**(1991), 2847-2858. - [97]
- Nomination for Stephen Smale,
*Notices Amer. Math. Soc.*,**38**(1991), 758-760.. - [98]
- On knot and manifold invariants, in:
*New Symmetry Principles in Quantum Field Theory (Cargèse, 1991)*, NATO Adv. Sci. Inst. Ser. B Phys. 295, Plenum, (1992), 37-52. - [99]
- Topological aspects of loop groups, in:
*Topological Quantum Field Theories and Geometry of Loop Spaces (Budapest, 1989)*, World Sci. Publishing, (1992), 65-80. - [100]
- For the Chern volume, in:
*Chern--a Great Geometer of the Twentieth Century*, Internat. Press, (1992), 106-108. - [101]
- Reflections on the theme of the poster, in:
*Topological Methods in Modern Mathematics (Stony Brook, NY, 1991)*, Publish or Perish (1993), 125-135. - [102]
- Luncheon talk and nomination for Stephen Smale, in:
*From Topology to Computation: Proceedings of the Smalefest (Berkeley, CA, 1990)*, Springer, (1993), 67-72. - [103]
- (with C. Taubes) On the self-linking of knots, J. Math.
Phys.
**35**(1994), 5247-5287. - [104]
- On invariants of manifolds, in:
*Modern Methods in Complex Analysis (Princeton, NJ, 1992)*, Ann. of Math. Stud., 137, Princeton Univ. Press, (1995), 29-39. - [105]
- Configuration spaces and imbedding invariants, Turkish J.
Math.
**20**(1996), 1-17. - [106]
- Configuration spaces and imbedding problems, in:
*Geometry and Physics (Aarhus, 1995)*, Lecture Notes in Pure and Appl. Math.,**184**, Dekker (1997), 135-140. - [107]
- Critical point theory in mathematics and in mathematical
physics, Turkish J. Math.
**21**(1997), 9-40. - [108]
- (with A. Cattaneo) Integral invariants of
-manifolds, J.
Differential Geom.
**48**(1998), 91-133. - [109]
- An introduction to equivariant cohomology, in:
*Quantum Field Theory: Perspective and Prospective*, Kluwer Academic Publishers, (1999), 35-57. - [110]
- (with A. Cattaneo) Integral invariants of -manifolds, II, to appear in J. Differential Geom.