5 research outputs found
Spherical Casimir energies and Dedekind sums
Casimir energies on space-times having general lens spaces as their spatial
sections are shown to be given in terms of generalised Dedekind sums related to
Zagier's. These are evaluated explicitly in certain cases as functions of the
order of the lens space. An easily implemented recursion approach is used.Comment: 18 pages, 2 figures, v2:typos corrected, inessential equation in
Discussion altered. v3:typos corrected, 1 reference and comments added.
v4:typos corrected. Ancillary results added in an appendi
M-branes and N=2 Strings
The string field theory of N=(2,1) heterotic strings describes a set of
self-dual Yang-Mills fields coupled to self-dual gravity in 2+2 dimensions. We
show that the exact classical action for this field theory is a certain
complexification of the Green-Schwarz/Dirac-Born-Infeld string action, closely
related to the four dimensional Wess-Zumino action describing self-dual gauge
fields. This action describes the world-volume of a 2+2d ``M-brane'', which
gives rise upon different null reductions to critical strings and membranes. We
discuss a number of further properties of N=2 heterotic strings, such as the
geometry of null reduction, general features of a covariant formulation, and
possible relations to BPS and GKM algebras.Comment: 49 pages, harvmac; 1 figure (uses epsf.tex). References adde
Closed String Tachyon Condensation: An Overview
These notes are an expanded version of a review lecture on closed string
tachyon condensation at the RTN workshop in Copenhagen in September 2003. We
begin with a lightning review of open string tachyon condensation, and then
proceed to review recent results on localized closed string tachyon
condensation, focusing on two simple systems, C/Z_n orbifolds and twisted
circle compactifications.Comment: harvmac, 59 pages; references adde
Closed string tachyons, flips and conifolds
Following the analysis of tachyons and orbifold flips described in
hep-th/0412337, we study nonsupersymmetric analogs of the supersymmetric
conifold singularity and show using their toric geometry description that they
are nonsupersymmetric orbifolds of the latter. Using linear sigma models, we
see that these are unstable to localized closed string tachyon condensation and
exhibit flip transitions between their two small resolutions (involving
2-cycles), in the process mediating mild dynamical topology change. Our
analysis shows that the structure of these nonsupersymmetric conifolds as
quotients of the supersymmetric conifold obstructs the 3-cycle deformation of
such singularities, suggesting that these nonsupersymmetric conifolds decay by
evolving towards their stable small resolutions.Comment: Latex, 22 pgs, 2 figs. v4: matches JHEP version, 29 pgs, 3 figures,
more elaborate Introduction, various clarifications adde