452 research outputs found
ADE string vacua with discrete torsion
We complete the classification of (2,2) string vacua that can be constructed
by diagonal twists of tensor products of minimal models with ADE invariants.
Using the \LG\ framework, we compute all spectra from inequivalent models of
this type. The completeness of our results is only possible by systematically
avoiding the huge redundancies coming from permutation symmetries of tensor
products. We recover the results for (2,2) vacua of an extensive computation of
simple current invariants by Schellekens and Yankielowitz, and find 4
additional mirror pairs of spectra that were missed by their stochastic method.
For the model we observe a relation between redundant spectra and
groups that are related in a particular way.Comment: 13 pages (LaTeX), preprint CERN-TH.6931/93 and ITP-UH-20/93
(reference added
(0,2) Mirror Symmetry
We generalize the previously established (0,2) triality of exactly solvable
models, Landau-Ginzburg theories and Calabi-Yau manifolds to a number of
different classes of (0,2) compactifications derived from (2,2) vacua. For the
resulting models we show that the known (2,2) mirror constructions induce
mirror symmetry in the (0,2) context.Comment: plain TeX, harvmac incl., 38(b)/22(l) pp., 3 PS figs., epsf incl.,
references adde
A Note On ADE String Compactifications
We address the question whether so-called m-invariants of the N=2 super
Virasoro algebra can be used for the construction of reasonable
four-dimensional string models. It turns out that an infinite subset of those
are pathological in the sense that - although N=2 supersymmetric - the Ramond
sector is not isomorphic to the Neveu-Schwarz sector. Consequently, these two
properties are independent and only requiring both guarantees an N=1 space-time
supersymmetric string spectrum. However, the remaining 529 consistent spectra -
210 of them are mirrors of Gepner models and 76 real orbifolds - show exact
mirror symmetry and are contained in a recent classification of orbifolds of
Gepner models.Comment: 11 pages, plain TeX, no postscript figure
Heterotic Gauge Structure of Type II K3 Fibrations
We show that certain classes of K3 fibered Calabi-Yau manifolds derive from
orbifolds of global products of K3 surfaces and particular types of curves.
This observation explains why the gauge groups of the heterotic duals are
determined by the structure of a single K3 surface and provides the dual
heterotic picture of conifold transitions between K3 fibrations. Abstracting
our construction from the special case of K3 hypersurfaces to general K3
manifolds with an appropriate automorphism, we show how to construct Calabi-Yau
threefold duals for heterotic theories with arbitrary gauge groups. This
generalization reveals that the previous limit on the Euler number of
Calabi-Yau manifolds is an artifact of the restriction to the framework of
hypersurfaces.Comment: 15 pages, 3 eps figure
Some General Aspects of Coset Models and Topological Kazama-Suzuki Models
We study global aspects of N=2 Kazama-Suzuki coset models by investigating
topological G/H Kazama-Suzuki models in a Lagrangian framework based on gauged
Wess-Zumino-Witten models. We first generalize Witten's analysis of the
holomorphic factorization of bosonic G/H models to models with N=1 and N=2
supersymmetry. We also find some new anomaly-free and supersymmetric models
based on non-diagonal embeddings of the gauge group. We then explain the basic
properties (action, symmetries, metric independence, ...) of the topologically
twisted G/H Kazama-Suzuki models. We explain how all of the above generalizes
to non-trivial gauge bundles.
We employ the path integral methods of localization and abelianization (shown
to be valid also for non-trivial bundles) to establish that the twisted G/H
models can be localized to bosonic H/H models (with certain quantum
corrections), and can hence be reduced to an Abelian bosonic T/T model, T a
maximal torus of H. We also present the action and the symmetries of the
coupling of these models to topological gravity. We determine the bosonic
observables for all the models based on classical flag manifolds and the
bosonic observables and their fermionic descendants for models based on complex
Grassmannians.Comment: expanded version to appear in NPB: construction of wave functions,
proof of holomorphic factorization and localization extended to non-trivial
gauge bundles; 73 pages, LaTeX fil
Heterotic Weight Lifting
We describe a method for constructing genuinely asymmetric (2,0) heterotic
strings out of N=2 minimal models in the fermionic sector, whereas the bosonic
sector is only partly build out of N=2 minimal models. This is achieved by
replacing one minimal model plus the superfluous E_8 factor by a
non-supersymmetric CFT with identical modular properties. This CFT generically
lifts the weights in the bosonic sector, giving rise to a spectrum with fewer
massless states. We identify more than 30 such lifts, and we expect many more
to exist. This yields more than 450 different combinations. Remarkably, despite
the lifting of all Ramond states, it is still possible to get chiral spectra.
Even more surprisingly, these chiral spectra include examples with a certain
number of chiral families of SO(10), SU(5) or other subgroups, including just
SU(3) x SU(2) x U(1). The number of families and mirror families is typically
smaller than in standard Gepner models. Furthermore, in a large number of
different cases, spectra with three chiral families can be obtained. Based on a
first scan of about 10% of the lifted Gepner models we can construct, we have
collected more than 10.000 distinct spectra with three families, including
examples without mirror fermions. We present an example where the GUT group is
completely broken to the standard model, but the resulting and inevitable
fractionally charged particles are confined by an additional gauge group
factor.Comment: 19 pages, 1 figur
Entangled state quantum cryptography: Eavesdropping on the Ekert protocol
Using polarization-entangled photons from spontaneous parametric
downconversion, we have implemented Ekert's quantum cryptography protocol. The
near-perfect correlations of the photons allow the sharing of a secret key
between two parties. The presence of an eavesdropper is continually checked by
measuring Bell's inequalities. We investigated several possible eavesdropper
strategies, including pseudo-quantum non-demolition measurements. In all cases,
the eavesdropper's presence was readily apparent. We discuss a procedure to
increase her detectability.Comment: 4 pages, 2 encapsulated postscript files, PRL (tentatively) accepte
Topological String Amplitudes, Complete Intersection Calabi-Yau Spaces and Threshold Corrections
We present the most complete list of mirror pairs of Calabi-Yau complete
intersections in toric ambient varieties and develop the methods to solve the
topological string and to calculate higher genus amplitudes on these compact
Calabi-Yau spaces. These symplectic invariants are used to remove redundancies
in examples. The construction of the B-model propagators leads to compatibility
conditions, which constrain multi-parameter mirror maps. For K3 fibered
Calabi-Yau spaces without reducible fibers we find closed formulas for all
genus contributions in the fiber direction from the geometry of the fibration.
If the heterotic dual to this geometry is known, the higher genus invariants
can be identified with the degeneracies of BPS states contributing to
gravitational threshold corrections and all genus checks on string duality in
the perturbative regime are accomplished. We find, however, that the BPS
degeneracies do not uniquely fix the non-perturbative completion of the
heterotic string. For these geometries we can write the topological partition
function in terms of the Donaldson-Thomas invariants and we perform a
non-trivial check of S-duality in topological strings. We further investigate
transitions via collapsing D5 del Pezzo surfaces and the occurrence of free Z2
quotients that lead to a new class of heterotic duals.Comment: 117 pages, 1 Postscript figur
A Geometrical Construction of Rational Boundary States in Linear Sigma Models
Starting from the geometrical construction of special Lagrangian submanifolds
of a toric variety, we identify a certain subclass of A-type D-branes in the
linear sigma model for a Calabi-Yau manifold and its mirror with the A- and
B-type Recknagel-Schomerus boundary states of the Gepner model, by reproducing
topological properties such as their labeling, intersection, and the
relationships that exist in the homology lattice of the D-branes. In the
non-linear sigma model phase these special Lagrangians reproduce an old
construction of 3-cycles relevant for computing periods of the Calabi-Yau, and
provide insight into other results in the literature on special Lagrangian
submanifolds on compact Calabi-Yau manifolds. The geometrical construction of
rational boundary states suggests several ways in which new Gepner model
boundary states may be constructed.Comment: 45 pages, 8 Postscript figures, LaTeX2e. v2: the construction
reproduces a larger set of CFT boundary states; clarified discussion of
instanton contributions and moduli; other minor improvements; references
added . v3: version accepted for publication in Nuclear Physics B (minor
changes
First Measurement of the Transverse Spin Asymmetries of the Deuteron in Semi-Inclusive Deep Inelastic Scattering
First measurements of the Collins and Sivers asymmetries of charged hadrons
produced in deep-inelastic scattering of muons on a transversely polarized
6-LiD target are presented. The data were taken in 2002 with the COMPASS
spectrometer using the muon beam of the CERN SPS at 160 GeV/c. The Collins
asymmetry turns out to be compatible with zero, as does the measured Sivers
asymmetry within the present statistical errors.Comment: 6 pages, 2 figure
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