639 research outputs found
Bordism, rho-invariants and the Baum-Connes conjecture
Let G be a finitely generated discrete group. In this paper we establish
vanishing results for rho-invariants associated to
(i) the spin-Dirac operator of a spin manifold with positive scalar curvature
(ii) the signature operator of the disjoint union of a pair of homotopy
equivalent oriented manifolds with fundamental group G.
The invariants we consider are more precisely
- the Atiyah-Patodi-Singer rho-invariant associated to a pair of finite
dimensional unitary representations.
- the L2-rho invariant of Cheeger-Gromov
- the delocalized eta invariant of Lott for a finite conjugacy class of G.
We prove that all these rho-invariants vanish if the group G is torsion-free
and the Baum-Connes map for the maximal group C^*-algebra is bijective. For the
delocalized invariant we only assume the validity of the Baum-Connes conjecture
for the reduced C^*-algebra.
In particular, the three rho-invariants associated to the signature operator
are, for such groups, homotopy invariant. For the APS and the Cheeger-Gromov
rho-invariants the latter result had been established by Navin Keswani. Our
proof re-establishes this result and also extends it to the delocalized
eta-invariant of Lott. Our method also gives some information about the
eta-invariant itself (a much more saddle object than the rho-invariant).Comment: LaTeX2e, 60 pages; the gap pointed out by Nigel Higson and John Roe
is now closed and all statements of the first version of the paper are proved
(with some small refinements
Rho-classes, index theory and Stolz' positive scalar curvature sequence
In this paper, we study the space of metrics of positive scalar curvature
using methods from coarse geometry.
Given a closed spin manifold M with fundamental group G, Stephan Stolz
introduced the positive scalar curvature exact sequence, in analogy to the
surgery exact sequence in topology. It calculates a structure group of metrics
of positive scalar curvature on M (the object we want to understand) in terms
of spin-bordism of BG and a somewhat mysterious group R(G).
Higson and Roe introduced a K-theory exact sequence in coarse geometry which
contains the Baum-Connes assembly map, with one crucial term K(D*G) canonically
associated to G. The K-theory groups in question are the home of interesting
index invariants and secondary invariants, in particular the rho-class in
K_*(D*G) of a metric of positive scalar curvature on a spin manifold.
One of our main results is the construction of a map from the Stolz exact
sequence to the Higson-Roe exact sequence (commuting with all arrows), using
coarse index theory throughout.
Our main tool are two index theorems, which we believe to be of independent
interest. The first is an index theorem of Atiyah-Patodi-Singer type. Here,
assume that Y is a compact spin manifold with boundary, with a Riemannian
metric g which is of positive scalar curvature when restricted to the boundary
(and with fundamental group G). Because the Dirac operator on the boundary is
invertible, one constructs a delocalized APS-index in K_* (D*G). We then show
that this class equals the rho-class of the boundary.
The second theorem equates a partitioned manifold rho-class of a positive
scalar curvature metric to the rho-class of the partitioning hypersurface.Comment: 39 pages. v2: final version, to appear in Journal of Topology. Added
more details and restructured the proofs, correction of a couple of errors.
v3: correction after final publication of a (minor) technical glitch in the
definition of the rho-invariant on p6. The JTop version is not correcte
The surgery exact sequence, K-theory and the signature operator
The main result of this paper is a new and direct proof of the natural
transformation from the surgery exact sequence in topology to the analytic
K-theory sequence of Higson and Roe.
Our approach makes crucial use of analytic properties and new index theorems
for the signature operator on Galois coverings with boundary. These are of
independent interest and form the second main theme of the paper. The main
technical novelty is the use of large scale index theory for Dirac type
operators that are perturbed by lower order operators.Comment: 29 pages, AMS-LaTeX; v2: small corrections and (hopefully) improved
exposition, as suggested by the referee. Final version, to appear in Annals
of K-Theor
Different amplitude and time distribution of the sound of light and classical music
Several pieces of different musical kinds were studied measuring , the
output amplitude of a peak detector driven by the electric signal arriving to
the loudspeaker. Fixed a suitable threshold , we considered ,
the number of times that , each of them we named event and
, the distribution of times between two consecutive events. Some
and distributions are displayed in the reported logarithmic
plots, showing that jazz, pop, rock and other popular rhythms have
noise-distribution, while classical pieces of music are characterized by more
complex statistics. We pointed out the extraordinary case of the aria
``\textit{La calunnia \`{e} un venticello}'', where the words describe an
avalanche or seismic process, calumny, and the rossinian music shows and
distribution typical of earthquakes.Comment: 3 pages with 4 figures, to be published in The European Physical
Journal
Eta cocycles, relative pairings and the Godbillon-Vey index theorem
We prove a Godbillon-Vey index formula for longitudinal Dirac operators on a
foliated bundle with boundary; in particular, we define a Godbillon-Vey eta
invariant on the boundary-foliation; this is a secondary invariant for
longitudinal Dirac operators on type-III foliations. Moreover, employing the
Godbillon-Vey index as a pivotal example, we explain a new approach to higher
index theory on geometric structures with boundary. This is heavily based on
the interplay between the absolute and relative pairings of K-theory and cyclic
cohomology for an exact sequence of Banach algebras which in the present
context takes the form , with J dense and
holomorphically closed in the C^*-algebra of the foliation and B depending only
on boundary data. Of particular importance is the definition of a relative
cyclic cocycle for the pair ;
is a cyclic cochain on A defined through a regularization, \`a la Melrose, of
the usual Godbillon-Vey cyclic cocycle ; is a cyclic
cocycle on B, obtained through a suspension procedure involving and
a specific 1-cyclic cocycle (Roe's 1-cocycle). We call the eta
cocycle associated to . The Atiyah-Patodi-Singer formula is obtained
by defining a relative index class \Ind (D,D^\partial)\in K_* (A,B) and
establishing the equality =<\Ind (D,D^\partial),
[\tau^r_{GV}, \sigma_{GV}]>\eta_{GV}\sigma_{GV}$.Comment: 86 pages. This is the complete article corresponding to the
announcement "Eta cocycles" by the same authors (arXiv:0907.0173
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