118716363
Direct Production of Lightest Regge Resonances
Abstract We discuss direct production of Regge excitations in the collisions of massless four-dimensional superstring states, focusing on the first excited level of open strings ending on D-branes extending into higher dimensions. We construct covariant vertex operators and identify “universal” Regge states with the internal parts either trivial or determined by the world-sheet SCFT describing superstrings propagating on an arbitrary Calabi–Yau manifold. We evaluate the amplitudes involving one such massive state and up to three massless ones and express them in the helicity basis. The most important phenomenological applications of our results are in the context of low-mass string (and large extra dimensions) scenarios in which excited string states are expected to be produced at the LHC as soon as the string mass threshold is reached in the center-of-mass energies of the colliding partons. In order to facilitate the use of partonic cross sections, we evaluate them and tabulate for all production processes: gluon fusion, quark absorbing a gluon, quark–antiquark annihilation and quark–quark scattering.
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.
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.
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.
45682848
Wigglers for Control of Beam Characteristics in LEP
Eight three-block dipole wigglers will be used in LEP to maximize luminosity and control other beam parameters such as emittance, damping rates at injection, energy spread and polarization. The excitation law for constant emittance (chosen, for example, to fill the dynamic aperture) and damping partition numbers is given. In contrast to conventional wigglers where orbit perturbation is avoided by means of a series of equal fields of alternate polarity, the LEP wigglers will use unequal fields and pole lengths. This allows one to retain a high potential asymptotic polarisation level together with an increased polarisation rate. The choice of the degree of field asymmetry is imposed by limitations on the transverse dimensions of the magnets and field levels, by polarisation requirements and by cost. A practical design of the proposed wiggler is presented.
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.
122817793
Conceptual design of a 5 T/mm quadrupole for linear collider final focus
The luminosity required of a future linear e/sup +/e/sup -/ collider in the teraelectronvolt energy range puts high demands on the final focus elements. In particular, if a classical quadrupole arrangement is chosen, the last magnet should be capable of producing a gradient of several tesla per millimeter. The authors have studied the performance limits of a quadrupole having soft ferromagnetic poles of sufficiently simple geometry to allow fabrication to submicron tolerances, excited by blocks of commercial permanent magnet material. It is shown that it should be possible to obtain a good quality quadrupole of less than 1-mm aperture, with up to 1.4-T pole-tip field.<<ETX>>
115450618
A final focus design for the CERN linear collider CLIC
20721233
A design concept for the LHC insertion quadrupoles
It is noted that the low- beta insertion optics imposes severe constraints on the desired characteristics of the local quadrupoles. In order to obtain the necessary degree of focusing at the LHC (Large Hadron Collider), triplets made up of four 250 T/m superconducting quadrupoles, about 6- to 7-m long, are presently envisaged. The large value of the betatron functions through these magnets is such that, besides being the principal source of chromatic aberrations, errors in their gradient will also contribute significantly to the excitation of resonance in the circulating beams. The magnets should therefore provide a gradient field of very high quality. The relatively small number of quadrupoles involved means that the cost constraints are less binding on these than on the lattice magnets. Their single aperture also opens up the possibility of an approach different from that adopted for the regular twin-aperture quadrupoles. One of the design concepts being investigated involves the use of flat cable wound in rectangular blocks to approximate the required quadrupole producing current density. The characteristics of the magnet are described, as is the method of applying the required prestress to the winding.<<ETX>>