714 research outputs found
Absorption cross section in de Sitter space
We study the wave equation for a minimally coupled massive scalar in
three-dimensional de Sitter space. We compute the absorption cross section to
investigate its cosmological horizon in the southern diamond. Although the
absorption cross section is not defined exactly, we can be determined it from
the fact that the low-energy -wave absorption cross section for a
massless scalar is given by the area of the cosmological horizon. On the other
hand, the low-temperature limit of -mode absorption cross section is
useful for extracting information surrounding the cosmological horizon. Finally
we mention a computation of the absorption cross section on the CFT-side using
the dS/CFT correspondence.Comment: 13 pages, version to appear in MPL
N=4 Supersymmetry and the BPST Instanton
In this paper we construct the Lagrangian and Hamiltonian formulations of N=4
supersymmetric systems describing the motion of an isospin particle on a
conformally flat four-manifold with SO(4) isometry carrying the non-Abelian
field of a BPST instanton. The conformal factor can be specified to yield
various particular systems, such as superconformally invariant mechanics as
well as a particle on the four-sphere, the pseudosphere or on R x S^3. The
isospin degrees of freedom arise as bosonic components of an additional
fermionic N=4 supermultiplet, whose other components are rendered auxiliary by
a nonlocal redefinition. Our on-shell component action coincides with the one
recently proposed in arXiv:0912.3289.Comment: 1+8 pages; v2: two references added, published versio
Dynamical Cobordisms in General Relativity and String Theory
We describe a class of time-dependent solutions in string- or M-theory that
are exact with respect to alpha-prime and curvature corrections and interpolate
in physical space between regions in which the low energy physics is
well-approximated by different string theories and string compactifications.
The regions are connected by expanding "domain walls" but are not separated by
causal horizons, and physical excitations can propagate between them. As
specific examples we construct solutions that interpolate between oriented and
unoriented string theories, and also between type II and heterotic theories.
Our solutions can be weakly curved and under perturbative control everywhere
and can asymptote to supersymmetric at late times.Comment: 35 pages, 5 figures, LaTeX v2: reference adde
On a Matrix Model of Level Structure
We generalize the dimensionally reduced Yang-Mills matrix model by adding d=1
Chern-Simons term and terms for a bosonic vector. The coefficient, \kappa of
the Chern-Simons term must be integer, and hence the level structure. We show
at the bottom of the Yang-Mills potential, the low energy limit, only the
linear motion is allowed for D0 particles. Namely all the particles align
themselves on a single straight line subject to \kappa^2/r^2 repulsive
potential from each other. We argue the relevant brane configuration to be
D0-branes in a D4 after \kappa of D8's pass the system.Comment: 1+6 pages, No figure, LaTeX; Minor changes; To appear in Class.
Quant. Gra
Cluster decomposition, T-duality, and gerby CFT's
In this paper we study CFT's associated to gerbes. These theories suffer from
a lack of cluster decomposition, but this problem can be resolved: the CFT's
are the same as CFT's for disconnected targets. Such theories also lack cluster
decomposition, but in that form, the lack is manifestly not very problematic.
In particular, we shall see that this matching of CFT's, this duality between
noneffective gaugings and sigma models on disconnected targets, is a worldsheet
duality related to T-duality. We perform a wide variety of tests of this claim,
ranging from checking partition functions at arbitrary genus to D-branes to
mirror symmetry. We also discuss a number of applications of these results,
including predictions for quantum cohomology and Gromov-Witten theory and
additional physical understanding of the geometric Langlands program.Comment: 61 pages, LaTeX; v2,3: typos fixed; v4: writing improved in several
sections; v5: typos fixe
On fluctuations of closed string tachyon solitons
We discuss fluctuations on solitons in the dilaton/graviton/tachyon system
using the low energy effective field theory approach. It is shown that closed
string solitons are free of tachyons in this approximation, regardless of the
exact shape of the tachyon potential.Comment: 13 pages, 1 figure, uses JHEP3.cl
Sums over topological sectors and quantization of Fayet-Iliopoulos parameters
In this paper we discuss quantization of the Fayet-Iliopoulos parameter in
supergravity theories with altered nonperturbative sectors, which were recently
used to argue a fractional quantization condition. Nonlinear sigma models with
altered nonperturbative sectors are the same as nonlinear sigma models on
special stacks known as gerbes. After reviewing the existing results on such
theories in two dimensions, we discuss examples of gerby moduli `spaces'
appearing in four-dimensional field theory and string compactifications, and
the effect of various dualities. We discuss global topological defects arising
when a field or string theory moduli space has a gerbe structure. We also
outline how to generalize results of Bagger-Witten and more recent authors on
quantization issues in supergravities from smooth manifolds to smooth moduli
stacks, focusing particular attention on stacks that have gerbe structures.Comment: 52 pages, LaTeX; v2: typo fixe
Non-Abelian statistics versus the Witten anomaly
This paper is motivated by prospects for non-Abelian statistics of deconfined
particle-like objects in 3+1 dimensions, realized as solitons with localized
Majorana zeromodes. To this end, we study the fermionic collective coordinates
of magnetic monopoles in 3+1 dimensional spontaneously-broken SU(2) gauge
theories with various spectra of fermions. We argue that a single Majorana
zeromode of the monopole is not compatible with cancellation of the Witten
SU(2) anomaly. We also compare this approach with other attempts to realize
deconfined non-Abelian objects in 3+1 dimensions.Comment: 11 pages, 3 figures; v2: added refs, minor corrections, published
versio
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