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.
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.
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.
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.
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.
15415835
A Low Noise Pwc Cathode Readout System
A system has been developed, primarily to detect the induced charge deposited on PWC cathodes, which is versatile, fast and has a good signal to noise ratio for signals of ¿ 10-14 Coulomb input. The amplifier system, which is completely separated from the detector by 95¿ coaxial cables, is followed by a new charge integrating, version of the SHAM/BADC system developed at SLAC. This SHAM IV system is CAMAC based, allowing for computer calibration of the entire system from amplifier through ADC.
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.
37405387
Power supply system for the ATLAS muon spectrometer: design specifications and test
In this paper, the problem of the low-voltage (LV) and high-voltage (HV) power supply distribution of the monitored drift tubes (MDT) detector is addressed. Due to the high number of channels (1168 for low voltage and twice for high voltage) involved and to the dimension of the apparatus, these power supply systems are very complicated. Both systems are made of three different parts: a power generator, a system controller, and an active distributor. The first two parts will be localized in the cavern close to the experimental area, so they are subjected to standard environmental conditions. The third part (the active distributor) will be placed in the experimental area on the platforms just outside the detector, where the environmental conditions are more severe, due to the presence of magnetic field (about 0.08 T) and radiations. In the paper, we present the design specifications and tests for the power supply systems.
110963059
Use of Triple Modular Redundancy (TMR) technology in FPGAs for the reduction of faults due to radiation in the readout of the ATLAS Monitored Drift Tube (MDT) chambers
The Triple Modular Redundancy (TMR) technology allows protection of the functionality of FPGAs against single event upsets (SEUs). Each logic block is implemented three times with a 2-out-of-3 voter at the output. Thus, the correct logical value is available even if there is an upset bit in one location. We applied TMR to the configuration code of a Virtex-II-2000 FPGA, which serves as the on-chamber readout processor of the ATLAS monitored drift tubes (MDTs). We describe the code implementation, results of performance measurements and discuss several limitations of the method. Finally, we present a supplementary technology called ``scrubbing''. It permanently checks the configuration memory while the FPGA is operating, and corrects upset configuration bits when necessary.
121460348
Irradiation tests of double-sided silicon strip detectors optimized for the ATLAS-inner-detector-region
Abstract Silicon detectors, which will be used as tracking detectors in LHC-experiments, face special requirements; one major challenge is the long term operation of the detectors in very intense radiation fields. This paper describes a design for double-sided strip detectors, which takes these requirements into account. Irradiation tests have been carried out using 24 GeV protons. The change of detector characteristics in particular guardring-behaviour, punchthrough biasing and interstrip isolation has been studied.