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.
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.
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.
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.
126243744
Measurement of the reaction π−p→π+π−n on a transversely polarized target at 17.2 GeV
Preliminary results from a high statistics measurement (1 M events) of the reaction π−p→π+π−n on strong polarization effects which must be attributed to amplitudes corresponding to ’’A1’’ exchange.
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.
122005953
Improvement of the L1 trigger for the ATLAS muon spectrometer at high luminosity
Abstract When the peak luminosity of 10 34 cm − 2 s − 1 of the LHC will be increased by a factor of 5–7 in about a decade from now (“SLHC”), the selectivity of the ATLAS Level-1 (L1) triggering system will have to be improved in order to cope with the maximum allowed trigger rate of about 100 kHz. For the L1 trigger of the ATLAS Muon Spectrometer this calls for an increase of the p T -threshold for single muons. In the present L1 muon trigger system, however, the effective p T -threshold is not very sharp due to the limited spatial resolution of the trigger chambers, resulting in a majority of L1 triggers from muons below threshold. We describe a new, high-speed readout system of the Monitored Drift Tube chambers, which allows to supply the precision coordinates of the candidate muon to the L1 trigger, resulting in an accurate momentum determination, a sharpened p T -threshold and an efficient rejection of unwanted L1 triggers from low-p T muons.
125139430
Measurement of the Reactions $\bar{P} P \to \bar{\Lambda} \Lambda$, $\bar{p} p \to \bar{\Lambda} \Sigma^0$ and $\bar{P} P \to \bar{\Lambda}$ (Missing Mass) at 6-{GeV}
120597551
Influence of the magnetic field on the gating of a time projection chamber
A large cylindrical time projection chamber (TPC 90), 60 cm in diameter, a driftlength of 130 cm, as well as a smaller test-chamber of 30 × 30 × 15 cm3 have been used to investigate the effects of the magnetic field on the operation of a gated grid. The magnetic field is found to affect strongly the drifting electrons, but not for the positive ions. The results can be well explained by the specific configuration of the combined EandB fields near the gating grid wires and in the region of the proportional wires.