118060107
New Stringy Instanton Effects And Neutrino Majorana Masses
D‐brane instantons can generate open string couplings in the superpotential which violate global abelian symmetries and are therefore perturbatively forbidden. After discussing the main ingredients, focussing for concretenes on Type IIA orientifold compactifications, we exemplify the computation of instanton‐induced Majorana mass terms for right‐handed neutrinos in a local SU(5) GUT‐like model. In particular, we show that the instanton allows for naturally engineering the intermediate scale of the Majorana masses, thereby realizing the seesaw mechanism for neutrinos.
118627385
Three- and four-point correlators of excited bosonic twist fields
A bstractWe compute three- and four-point correlation functions containing excited bosonic twist fields. Our results can be used to determine properties, such as lifetimes and production rates, of massive string excitations localised at D-brane intersections, which could be signatures of a low string scale even if the usual string resonances are inaccessible to the LHC.
118892007
Proton decay via dimension-six operators in intersecting D6-brane models
Abstract We analyze the proton decay via dimension six operators in supersymmetric SU ( 5 ) -grand unified models based on intersecting D6-brane constructions in type IIA string theory orientifolds. We include in addition to 10 ∗ 1010 ∗ 10 interactions also the operators arising from 5 ¯ ∗ 5 ¯ 10 ∗ 10 interactions. We provide a detailed construction of vertex operators for any massless string excitation arising for arbitrary intersecting D-brane configurations in type IIA toroidal orientifolds. In particular, we provide explicit string vertex operators for the 10 and 5 ¯ chiral superfields and calculate explicitly the string theory correlation functions for above operators. In the analysis we chose the most symmetric configurations in order to maximize proton decay rates for the above dimension six operators and we obtain a small enhancement relative to the field theory result. After relating the string proton decay rate to field theory computations the string contribution to the proton lifetime is τ p ST = ( 0.5 – 2.1 ) × 10 36  years , which could be up to a factor of three shorter than that predicted in field theory.
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.
11035127
Nonperturbative yukawa couplings from string instantons.
Nonperturbative D-brane instantons can generate perturbatively absent though phenomenologically relevant couplings for type II orientifold compactifications with D-branes. We discuss the generation of the perturbatively vanishing SU(5) GUT Yukawa coupling of type <10 10 5(H)>. Moreover, for a simple globally consistent intersecting D6-brane model, we discuss the generation of mass terms for matter fields. This can serve as a mechanism for decoupling exotic matter.
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.
110363376
Design and test of radiation hard p'n silicon strip detectors for the ATLAS SCT
Strip detectors covering radiation hardness and large-scale production ability are developed and produced for the ATLAS experiment at the Large Hadron Collider (LHC) at CERN (Switzerland). Capacitively coupled p‘n detectors (p-type strips on n-type substrate) were developed with implanted bias resistors in order to simplify the detector processing addressing the requirements of large-scale production. The detectors were irradiated with 24 GeV protons up to 3]1014 cm~2 in order to simulate a 10 years operation scenario at LHC. The presented static and signal measurements demonstrate the function of the device concept before and after irradiation. ( 2000 Elsevier Science B.V. All rights reserved.
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.
121450717
Development of Precision Muon Drift Tube Detectors for the High-Luminosity Upgrade of the LHC
For use at the future Super-LHC a new type of muon detector has been developed. It is based on the proven MDT drift tube design, but with tubes of half the diameter, leading to higher rate capabilities by an order of magnitude. We present test results on efficiency and position resolution at high background rates and describe the practical implementation in a real-size prototype.
108877301
Design and test of pixel sensors for operation in severe radiation environments
Abstract The inner detectors of LHC experiments will contain pixel detectors covering an area of several square meters. In addition they are facing the harsh radiation environment of the LHC. A first prototype sensor has been designed according to the requirements of the ATLAS experiment, produced and successfully tested with static measurements. Irradiation tests have also been performed with excellent results. The sensor is an n + n-device in order to allow partial depleted operation after bulk inversion and a guard ring scheme keeping the entire detector surface close to the electronic chip on ground potential. Further, a bias structure is introduced providing testability of the sensors prior to bump bonding and flip chipping.
121259350
Pulsed Heavy Ion Source for the Bevatron
A Phillips ion gauge source (Fig. 1) of the type used by the heavy ion accelerator in Berkeley has been adapted for use at the Bevatron. The objective was to achieve high charge state ions (4+, 5+) of carbon and nitrogen. All source parameters are pulsed. The ion source performance regarding linac acceleration is discussed. The light ion (deuteron, alpha) performance of the PIG source and duoplasmatron is compared.