15397236
Branes and instantons intersecting at angles
We study in detail the system of D6 branes and euclidean D2-brane instantons intersecting at angles in type IIA string theory. We find that in the absence of orientifolds the system does not contribute to the low energy superpotential, in agreement with expectations based on effective field theory arguments. We also comment on the implications of our results for dual string theory pictures.
5682028
Computation of D-brane instanton induced superpotential couplings: Majorana masses from string theory
We perform a detailed conformal field theory analysis of D2-brane instanton effects in four-dimensional type IIA string vacua with intersecting D6-branes. In particular, we explicitly compute instanton induced fermion two-point couplings which play the role of perturbatively forbidden Majorana mass terms for right-handed neutrinos or MSSM {mu} terms. These results can readily be extended to higher-dimensional operators. In concrete realizations of such nonperturbative effects, the Euclidean D2-brane has to wrap a rigid, supersymmetric cycle with strong constraints on the zero-mode structure. Their implications for type IIA compactifications on the T{sup 6}/(Z{sub 2}xZ{sub 2}) orientifold with discrete torsion are analyzed. We also construct a local supersymmetric GUT-like model allowing for a class of Euclidean D2-branes whose fermionic zero modes meet all the constraints for generating Majorana masses in the phenomenologically allowed regime. Together with perturbatively realized Dirac masses, these nonperturbative couplings give rise to the seesaw mechanism.
118063728
Mass Hierarchies versus proton Decay in MSSM Orientifold Compactifications
We review two systematic bottom-up analyses of MSSM quivers recently performed by the authors. We extend the analysis of arXiv:0905.3379 by including constraints arising from proton decay via dimension 5 operators and present all four-stack quivers in the Madrid embedding which satisfy this additional constraint. Furthermore, we investigate and make precise the interplay between mass hierarchies obtained via factorizable Yukawa textures and the presence of dimension 5 proton decay operators in MSSM orientifold compactifications. We discuss this issue in a five-stack quiver, first presented in arXiv:0909.4292, which exhibits proper mass hierarchies and no rapid proton decay.
117476620
On closed-string twist-field correlators and their open-string descendants
In a recent paper we have proposed the possibility that the lightest massive string states could be identified with open strings living at intersections of D-branes forming small angles. In this note, we reconsider the relevant twist-field correlation functions and perform the analysis of the sub-dominant physical poles in the various channels. Our derivation is new in that it is based on the algebraic procedure for the construction of open string models starting from their closed-string `parents' rather than on the stress-tensor method. We also indicate possible generalizations and diverse applications of our approach.
118374533
Dynamical supersymmetry breaking in intersecting brane models
In this paper we study dynamical supersymmetry breaking in absence of gravity with the matter content of the minimal supersymmetric standard model. The hidden sector of the theory is a strongly coupled gauge theory, realized in terms of microscopic variables which condensate to form mesons. The supersymmetry breaking scalar potential combines F, D terms with instanton generated interactions in the Higgs-mesons sector. We show that for a large region in parameter space the vacuum breaks in addition to supersymmetry also electroweak gauge symmetry. We furthermore present local D-brane configurations that realize these supersymmetry breaking patterns.
53533600
String constraints on discrete symmetries in MSSM type II quivers
A bstractWe study the presence of discrete gauge symmetries in D-brane semi-realistic compactifications. After establishing the constraints on the transformation behaviour of the chiral matter for the presence of a discrete gauge symmetry we perform a systematic search for discrete gauge symmetries within local semi-realistic D-brane realizations, based on four D-brane stacks, of the MSSM and the MSSM with three right-handed neutrinos. The systematic search reveals that Proton hexality, a discrete symmetry which ensures the absence of R-parity violating terms as well as the absence of dangerous dimension 5 proton decay operators, is only rarely realized. Moreover, none of the semi-realistic local D-brane configurations exhibit any family dependent discrete gauge symmetry.
120803754
Study of a DEPJFET pixel matrix with continuous clear mechanism
Abstract A new kind of silicon pixel detector with integrated amplification has been built and tested. Each pixel consists of a p -channel JFET located on a fully depleted substrate. The pixel size can be customized by using a drift-chamber-like transport mechanism in each pixel. The homogeneity of the signal response of a small matrix was investigated with a laser diode. The measured rise time and gain of the device are analyzed with a simple small signal model.
120631402
Characterization of silicon microstrip detectors using an infrared laser system
Abstract An infrared laser system with variable wavelength is used to study fundamental properties of silicon microstrip detectors. Results of measurements concerning charge sharing among adjacent readout strips and depletion mapping are presented. The results are interpreted in a model framework which describes the charge sharing with the help of the so-called η -function. The wavelength dependence of the η -function is studied. Surface effects important for short wavelengths are observed.
10893935
Measurement of Magnetic and Electric Field Inhomogeneities in a Time Projection Chamber Using Laser Tracks
In a model time projection chamber with a drift length of 1.3 m we study the track distortions caused by inhomogeneous or misaligned fields. The measured coordinate displacements are used to calculate the integrals over the transverse field components; these are found to be in agreement with the independently measured magnetic field.
111306145
Development of thin sensors and a novel interconnection technology for the upgrade of the ATLAS pixel system
To extend the discovery potential of the experiments at the LHC accelerator a luminosity upgrade towards the super LHC (sLHC) with an up to ten-fold peak luminosity is planned. Within this thesis a new module concept was developed and evaluated for the operation within an ATLAS pixel detector at the sLHC. This module concept utilizes a novel thin sensor production process for thin n-in-p silicon sensors which potentially allow for a higher radiation hardness at a reduced cost. Furthermore, the new 3D-integration technology ICV-SLID is explored which will allow for increasing the active area of the modules and hence, for employing the modules in the innermost layer of the upgraded ATLAS pixel detector.
124694239
Forward A2+ in Two-dimensions Production in $\pi^+ p \to K^+ \bar{K}(s$)0 $p$ at 12.7-{GeV}/$c$