20156101
Threshold Effects Beyond the Standard Model
In this contribution to the Festschrift celebrating Gabriele Veneziano on his 65th birthday, I discuss the threshold effects of extra dimensions and their applications to physics beyond the standard model, focusing on superstring theory.
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.
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.
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.
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.
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.
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.
115171795
Development of a superconducting insertion quadrupole model magnet for the Large Hadron Collider
37031481
Progress in the development of the 1-m model of the 70 mm aperture quadrupole for the LHC low-/spl beta/ insertions
Within the LHC magnet development program Oxford Instruments has built a one metre model of the 70 mm aperture low-/spl beta/ quadrupole. The magnet features a four layer coil wound from two 8.2 mm wide graded NbTi cables, and is designed for 250 T/m at 1.9 K. The magnet has previously been tested between 4.5 K and 23 K. In this paper we review the magnet rebuild and the subsequent tests. Results on magnet training at 43 K and 1.9 K are presented along with the results related to quench protection studies. We also present the first results of magnetic field measurements done at room and liquid nitrogen temperatures.
136548606
Analysis of the Performance of the Eight Superconducting Quadrupoles for the Lep Low-Beta Insertions
The LEP low-beta quadrupoles are iron-free superconducting magnets having a warm bore of 120 mm in diameter, an effective length of 2 m and a nominal gradient of 36 T m−l. The coils form a two-block approximation of the cosine 2θ distribution, and are wound from monolithic multifilamentary NbTi conductor; mechanical prestress is obtained by means of aluminium shrinking rings. Following manufacture and appraisal of a prototype magnet, eight series units have been produced by industry and thoroughly tested and measured prior to installation into LEP. In this paper, a brief description of the manufacturing technique is given, and the results of tests and measurements are presented and compared with the performance expected from calculations and previous experience. The analysis reveals the tolerances on field quality which can reasonably be obtained with this type of construction.
93472983
DESIGN OF THE LEP MAIN RING WIGGLERS