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.
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.
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.
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.
122734759
Measurement and Optimization of the Emittance of a 300-ns 250-A 3.4-MeV Electron Beam
Author(s): Allison, R.W.; Beal, J.W.; Everett, W.L.; Guggemos, J.R.; Lamb, W.A.S.; Richter, R.M.; Sherwood, W.A.; Spoerlein, R.L.; Tanabe, J.; Wright, R.E.; Zajec, E.
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.
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.
122599029
High energy proton damage effects in thin high resistivity FZ silicon detectors
Abstract The proposed luminosity upgrade of the Large Hadron Collider (S-LHC) will demand the inner most layers of the vertex detector to sustain fluences of about 10 16 charged hadrons/cm 2 . Due to the high multiplicity of tracks, the required spatial resolution and the extremely harsh radiation field thin silicon detector assemblies are proposed as a possible solution for this challenge. The radiation tolerance of 50 μm thin high resistivity float zone (FZ) devices has been studied for 24 GeV/ c protons in the fluence range between 4×10 13  cm −2 and 8.6×10 15  cm −2 . For the manufacturing of such thin devices, a technology based on direct wafer bonding and deep anisotropic etching was used. Annealing measurements at 80 °C have shown that the introduction rate g C in the stable damage component is about the same as observed for oxygen enriched FZ detectors and that the fluence dependence of the reverse annealing amplitude N Y exhibits a saturating function. It is also demonstrated that the annealing behavior of the reverse current related damage parameter α is independent on the fluence and the silicon material parameters. Charge collection efficiency (CCE) measurements were performed using 5.8 MeV α-particles. After fully annealing for about 31 days at 80 °C CCE was determined by extrapolation to be 66% at 10 16  p/cm 2 .
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.