14287005
Superstring threshold corrections to Yukawa couplings
Abstract A general method of computing string corrections to the Kahler metric and Yukawa couplings is developed at the one-loop level for a general compactification of the heterotic superstring theory. It also provides a direct determination of the so-called Green-Schwarz term. The matter metric has an infrared divergent part which reproduces the field-theoretical anomalous dimensions, and a moduli-dependent part which gives rise to threshold corrections in the physical Yukawa couplings. Explicit expressions are derived for symmetric orbifold compactifications.
62835109
Lectures on heterotic-type I duality
In the last couple of years, there has been remarkable progress in understanding non-perturbative aspects of string theories. The new ingredient is the discovery of various duality symmetries; these, in particular, invert the coupling constant and exchange perturbative states with non-perturbative solitonic excitations. Since inversion of the coupling involves the Planck constant ħ, duality symmetries can be realized only at the quantum level. Once the dual models are identified, non-perturbative dynamics of one model can be studied by means of the standard perturbative techniques in the other model.
120574302
Stability of supersymmetric ground state in chiral theories
Abstract The effective action for the scalar propagator is studied in supersymmetric chiral gauge theories. The form of the scalar potential ensures the stability of the supersymmetric ground state, even for large values of the coupling constant. It is found however, that the gluino condensation tends to destabilize the system. This may signal dynamical supersymmetry breaking.
14387997
N = 2 HETEROTIC SUPERSTRING AND ITS DUAL THEORY IN FIVE DIMENSIONS
Abstract We study quantum effects in five dimensions in heterotic superstring theory compactified on K 3 × S 1 and analyze the conjecture that its dual effective theory is eleven-dimensional supergravity compactified on a Calabi-Yau threefold. This theory is also equivalent to type II superstring theory compactified on the same Calabi-Yau manifold, in an appropriate large volume limit. In this limit the conifold singularity disappears and is replaced by a singularity associated to enhanced gauge symmetries, as naively expected from the heterotic description. Furthermore, we exhibit the existence of additional massless states which appear in the strong coupling regime of the heterotic theory and are related to a different type of singular points on Calabi-Yau threefolds.
120318508
Low-energy softly-broken supersymmetry
Abstract We consider supersymmetric low-energy lagrangians based on the gauge group SU(3) × SU(2) × U(1) × Ũ(1), where Ũ(1) is an additional axial group a la Fayet. Models with explicit soft breaking of supersymmetry are considered as an alternative to models with axial anomalies. We argue that soft breaking can be very efficient and illustrate this with a simple example in which the introduction of a negative mass squared term for only one scalar field leads to a phenomenologically interesting model.
120401055
Dilaton Couplings at Large Distances
Abstract The large-distance behaviour of dilaton couplings is studied within the framework of four-dimensional heterotic superstring theories. String loop corrections violate universality of dilaton and graviton couplings, increasing dilaton couplings at large distances. This implies a serious problem for string theories, unless a non-zero dilaton mass is generated.
54553106
Quench performance and field quality measurements of the first LHC low-/spl beta/ quadrupole model
As part of the LHC magnet development program, CERN in collaboration with Oxford Instruments has designed, built and tested a one metre model of a 70 mm aperture low-/spl beta/ quadrupole. The magnet features a four layer coil, and is designed for 250 T/m at 1.9 K. We review the results of the magnet training and quench propagation studies performed at 4.3 K and 1.9 K, and report on the magnetic field measurements.
118159983
The LHC:: a new hadron collider for experimental physics
Abstract The Large Hadron Collider is now under construction at CERN. This accelerator will be by far the most powerful ever built, and will provide the current generation of experimental physicists with an extraordinary opportunity to make new discoveries. It will also provide accelerator scientists with a tool to test current theory and refine studies of possible future accelerators going to even higher energies. The environment of a collider is such that experts of both disciplines have to collaborate closely, and this will surely continue to be to the long-term advantage of our whole field of science.
121851945
Design, test and performance of the prototype superconducting quadrupole for the LEP low-beta insertions
The prototype of the superconducting quadrupoles for the low-beta insertions at the Large Electron-Positron collider has been tested successfully. This industry-built quadrupole, which has a warm bore of 130 mm and a magnetic length of 2 m, is required to provide a gradient of 36 T/m over a field aperture of 1000 mm diameter. It achieved its maximum operating current without training. While retaining the main characteristics of its ISR predecessors, the design of this magnet incorporates several novel features, due to constraints imposed by the environment of the LEP experiments. In particular the quadrupole is slender and ironless, and has a horizontally oriented cryogenic service funnel. Following a description of the major aspects of the design, the results are given of the magnetic and cryogenic tests and measurements. >
44644796
Technological Aspects of the LEP Low-Beta Insertions
In order to obtain the highest luminosity at LEP, it is necessary to use superconducting quadrupoles for the final vertical focusing of the beams. The low-beta structure is such that these quadrupoles must be virtually integrated into the experiments, imposing severe constraints on their design. In particular, at LEP these magnets must be iron-free, occupy minimum space in the transverse direction, and be supported together with other beam- and experiment-related equipment on mobile cantilever girders. The constraints are analyzed, and the proposed system is described.
117897317
Mechanical Design and Characteristics of a Superconducting Insertion Quadrupole Model Magnet for The Large Hadron Collider
Abstract ---A superconducting insertion quadruple is being developed by KEK in collaboration with CERN for the Large Hadron Collider (LHC) project. The mechanical design of the magnet in which the pre-stress is applied to the coil through thin stainless steel collars inside the yoke, the two halves of which are held together by means of keys, has been validated experimentally by measurements on a short model. The 140 mm long model was assembled from real magnet components in order to simulate the magnet assembly and to evaluate the change in coil pre-stress during assembly and cool-down. A new technique using capacitance pressure transducers was used, which has enabled measurements of the stress distributions in the coil with high accuracy. This paper describes the mechanical design of the quadrupole magnet and results obtained from the short mechanical model. I. I NTRODUCTION A cooperative program to develop the low-β quadrupole magnets has been established between KEK and CERN as part of the Japanese contribution to the LHC accelerator project which is being built at CERN [1-5]. KEK will provide half of the 32 quadrupole magnets required for the inner triplets. These quadrupoles are key components that are necessary for strong focusing of the high energy proton beams and high luminosity collisions in the physics experiments. The main design goal for the magnet is to provide a field gradient of 240 T/m in a coil aperture of 70 mm, corresponding to a nominal operational field gradient of 200 to 205 T/m at 1.9 K with a superconductor load line ratio of not more than 80 %. The lost particle showers from the colliding beams will deposit a power of several watts per meter into the coil windings, and this has to be allowed by the coil design. The design optimization has been based on the use of NbTi superconductor cooled with pressurized superfluid helium at 1.9 K. In this paper, we discuss the reasons for building and testing of a140 mm thick “slice” of the straight part of the quadrupole, shown in Fig. 1, and describe the assembly of the mechanical short model.. The “slice” was built using real magnet components, and was instrumented with capacitance pressure transducers [6]. The model was assembled and cooled to liquid nitrogen temperature. The internal coil pressures were measured and the results compared with the design values [3]. Finally, we compare two techniques of coil modulus measurements, and comment on the choice of the material for the yoke, which has to provide support for the assembly and magnetic forces.