Given a chord-generic, horizontally displaceable Legendrian submanifold
with
the property that its characteristic algebra admits a finite-dimensional matrix
representation, we prove an Arnold-type lower bound for the number of Reeb chords
on
.
This result is a generalization of the results of Ekholm, Etnyre, Sabloff and Sullivan,
which hold for Legendrian submanifolds whose Chekanov–Eliashberg algebras
admit augmentations. We also provide examples of Legendrian submanifolds
of
,
, whose
characteristic algebras admit finite-dimensional matrix representations but whose
Chekanov–Eliashberg algebras do not admit augmentations. In addition, to show the
limits of the method of proof for the bound, we construct a Legendrian submanifold
with the property that the characteristic algebra of
does
not satisfy the rank property. Finally, in the case when a Legendrian submanifold
has a non-acyclic Chekanov–Eliashberg algebra, using rather elementary
algebraic techniques we obtain lower bounds for the number of Reeb chords
of .
These bounds are slightly better than the number of Reeb chords it is possible to
achieve with a Legendrian submanifold whose Chekanov–Eliashberg algebra is
acyclic.
Keywords
Legendrian contact homology, characteristic algebra, linear
representation, Arnold-type inequality
Department of Pure Mathematics and
Mathematical Statistics
Centre for Mathematical Sciences
University of Cambridge
Wilberforce Road
Cambridge CB3 0WB
UK