Klein Bottles and Simple Currents

The standard Klein bottle coefficient in the construction of open descendants is shown to equal the Frobenius-Schur indicator of a conformal field theory. Other consistent Klein bottle projections are shown to correspond to simple currents. These observations enable us to generalize the standard open string construction from C-diagonal parent theories to include non-standard Klein bottles. Using (generalizations of) the Frobenius-Schur indicator we prove positivity and integrality of the resulting open and closed string state multiplicities for standard as well as non-standard Klein bottles.Comment: 11 pages, LaTeX. References added, minor error correcte

Crosscaps, Boundaries and T-Duality

Open descendants with boundaries and crosscaps of non-trivial automorphism type are studied. We focus on the case where the bulk symmetry is broken to a Z_2 orbifold subalgebra. By requiring positivity and integrality for the open sector, we derive a unique crosscap of automorphism type g \in Z_2 and a corresponding g-twisted Klein bottle for a charge conjugation invariant. As a specific example, we use T-duality to construct the descendants of the true diagonal invariant with symmetry preserving crosscaps and boundaries.Comment: Latex, 14 page

Deuteron frozen spin polarized target for nd experiements at the VdG accelerator of Charles University

A frozen spin polarized deuteron target cooled by the 3He/4He dilution refrigerator is described. Fully deuterated 1,2-propanediol was used as a target material. Deuteron vector polarization about 40% was obtained for the target in the shape of a cylinder of 2 cm diameter and 6 cm length. The target is intended for a study of 3N interactions at the polarized neutron beam generated by the Van de Graaff accelerator at the Charles University in Prague

Permutation Orbifold of N=2 Supersymmetric Minimal Models

In this paper we apply the previously derived formalism of permutation orbifold conformal field theories to N=2 supersymmetric minimal models. By interchanging extensions and permutations of the factors we find a very interesting structure relating various conformal field theories that seems not to be known in literature. Moreover, unexpected exceptional simple currents arise in the extended permuted models, coming from off-diagonal fields. In a few situations they admit fixed points that must be resolved. We determine the complete CFT data with all fixed point resolution matrices for all simple currents of all Z_2-permutations orbifolds of all minimal N=2 models with k\neq 2 mod 4.Comment: 48 page

Geotomography with solar and supernova neutrinos

We show how by studying the Earth matter effect on oscillations of solar and supernova neutrinos inside the Earth one can in principle reconstruct the electron number density profile of the Earth. A direct inversion of the oscillation problem is possible due to the existence of a very simple analytic formula for the Earth matter effect on oscillations of solar and supernova neutrinos. From the point of view of the Earth tomography, these oscillations have a number of advantages over the oscillations of the accelerator or atmospheric neutrinos, which stem from the fact that solar and supernova neutrinos are coming to the Earth as mass eigenstates rather than flavour eigenstates. In particular, this allows reconstruction of density profiles even over relatively short neutrino path lengths in the Earth, and also of asymmetric profiles. We study the requirements that future experiments must meet to achieve a given accuracy of the tomography of the Earth.Comment: 35 pages, 7 figures; minor textual changes in section

Fixed Point Resolution in Extensions of Permutation Orbifolds

We determine the simple currents and fixed points of the orbifold theory $CFT\otimes CFT/\mathbb{Z}_2$, given the simple currents and fixed point of the original $CFT$. We see in detail how this works for the $SU(2)_k$ WZW model, focusing on the field content (i.e. $h$-spectrum of the primary fields) of the theory. We also look at the fixed point resolution of the simple current extended orbifold theory and determine the $S^J$ matrices associated to each simple current for $SU(2)_2$ and for the $B(n)_1$ and $D(n)_1$ series.Comment: 35 pages, no figure

Permutation orbifolds of heterotic Gepner models

We study orbifolds by permutations of two identical N=2 minimal models within the Gepner construction of four dimensional heterotic strings. This is done using the new N=2 supersymmetric permutation orbifold building blocks we have recently developed. We compare our results with the old method of modding out the full string partition function. The overlap between these two approaches is surprisingly small, but whenever a comparison can be made we find complete agreement. The use of permutation building blocks allows us to use the complete arsenal of simple current techniques that is available for standard Gepner models, vastly extending what could previously be done for permutation orbifolds. In particular, we consider (0,2) models, breaking of SO(10) to subgroups, weight-lifting for the minimal models and B-L lifting. Some previously observed phenomena, for example concerning family number quantization, extend to this new class as well, and in the lifted models three family models occur with abundance comparable to two or four.Comment: 49 pages, 4 figure

Search for composite and exotic fermions at LEP 2

A search for unstable heavy fermions with the DELPHI detector at LEP is reported. Sequential and non-canonical leptons, as well as excited leptons and quarks, are considered. The data analysed correspond to an integrated luminosity of about 48 pb^{-1} at an e^+e^- centre-of-mass energy of 183 GeV and about 20 pb^{-1} equally shared between the centre-of-mass energies of 172 GeV and 161 GeV. The search for pair-produced new leptons establishes 95% confidence level mass limits in the region between 70 GeV/c^2 and 90 GeV/c^2, depending on the channel. The search for singly produced excited leptons and quarks establishes upper limits on the ratio of the coupling of the excited fermio

Search for charginos in e+e- interactions at sqrt(s) = 189 GeV

An update of the searches for charginos and gravitinos is presented, based on a data sample corresponding to the 158 pb^{-1} recorded by the DELPHI detector in 1998, at a centre-of-mass energy of 189 GeV. No evidence for a signal was found. The lower mass limits are 4-5 GeV/c^2 higher than those obtained at a centre-of-mass energy of 183 GeV. The (\mu,M_2) MSSM domain excluded by combining the chargino searches with neutralino searches at the Z resonance implies a limit on the mass of the lightest neutralino which, for a heavy sneutrino, is constrained to be above 31.0 GeV/c^2 for tan(beta) \geq 1.Comment: 22 pages, 8 figure

Search for lightest neutralino and stau pair production in light gravitino scenarios with stau NLSP

Promptly decaying lightest neutralinos and long-lived staus are searched for in the context of light gravitino scenarios. It is assumed that the stau is the next to lightest supersymmetric particle (NLSP) and that the lightest neutralino is the next to NLSP (NNLSP). Data collected with the Delphi detector at centre-of-mass energies from 161 to 183 \GeV are analysed. No evidence of the production of these particles is found. Hence, lower mass limits for both kinds of particles are set at 95% C.L.. The mass of gaugino-like neutralinos is found to be greater than 71.5 GeV/c^2. In the search for long-lived stau, masses less than 70.0 to 77.5 \GeVcc are excluded for gravitino masses from 10 to 150 \eVcc . Combining this search with the searches for stable heavy leptons and Minimal Supersymmetric Standard Model staus a lower limit of 68.5 \GeVcc may be set for the stau mas