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.
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.
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.
120821170
Breakdown protection and long-term stabilisation for Si-detectors
Abstract Normally, guardrings are used to shield the sensitive part of detectors from surface and edge leakage currents. We propose a structure which in addition provides a gradual drop of the potential from the detector rim towards the bulk potential. Different structures were measured and also simulated with the two-dimensional semiconductor analysis package TOSCA. The possibilities of this package are briefly discussed. The agreement between the measurements and the simulation is very good. Based on these simulations, a layout of a detector protection structure with optimized performance is proposed.
23063408
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.
13052670
Prospects of using silicon photomultipliers for the astroparticle physics experiments EUSO and MAGIC
We discuss the silicon photomultiplier as a novel photon detector for the Major Atmospheric Gamma Imaging Cerenkov Telescope and the Extreme Universe Space Observatory. For these astroparticle experiments we pursue two different developments of the SiPM. One development is pursued at MEPhI, where prototypes are available. In the course of this paper we will describe some characteristics of these devices. The second development, which is using the back illumination principle is at present in its design phase.
109933860
Upgrade of the ATLAS Muon Trigger for the SLHC
The outer shell of the ATLAS experiment at the LHC consists of a system of toroidal air-core magnets in order to allow for the precise measurement of the transverse momentum (pT) of muons, which in many physics channels are a signature of interesting physics processes [1,2]. For the precise determination of the muon momentum Monitored Drift Tube chambers (MDT) with high position accuracy are used, while for the fast identification of muon tracks chambers with high time resolution are used, able to select muons above a predefined pT threshold for use in the first Level of the ATLAS triggering system (Level-1 trigger). When the LHC peak luminosity of 1034 cm−2s−1 will be increased by a factor of 4–5 in about a decade from now (''SLHC''), an improvement of the selectivity of the ATLAS Level-1 triggering system will be mandatory in order to cope with the maximum allowed trigger rate of 100 kHz. For the Level-1 trigger of the ATLAS muon spectrometer this means an increase of the pT threshold for single muons. Due to the limited spatial resolution of the trigger chambers, however, the selectivity for tracks above ~ 20 GeV/c is insufficient for an effective reduction of the Level-1 rate. We describe how the track coordinates measured in the MDT precision chambers can be used to decisively improve the selectivity for high momentum tracks. The resulting increase in latency will also be discussed.
59503820
Design and technology of DEPFET pixel sensors for linear collider applications
The performance requirements of vertex detectors for future linear collider experiments is very challenging especially for the detector's innermost sensor layers. The DEPleted Field Effect Transistor (DEPFET) combining detector and amplifier operation is capable to meet these requirements. A silicon technology is presented which allows production of large sensor arrays consisting of linear DEPFET detector structures. The envisaged pixel array offers a low noise and low power operation. To ensure a high radiation length a thinning technology based on direct wafer bonding is proposed.