115309009
Quench and Mechanical Behaviour of an LHC Low-$\beta$ Quadrupole Model
25983260
Conceptual design of a 70 mm aperture quadrupole for LHC insertions
Due to their detrimental effect on the Large Hadron Collider (LHC) dynamic aperture, the random multipole errors of the LHC insertion quadrupoles need to be lower by a factor of five than the corresponding errors in the lattice. For achieving this level of random errors, the authors propose to increase the aperture of the insertion quadrupoles. A novel approach for achieving a quadrupole strength of 250 T/m in an aperture of 70 mm, based on a graded multilayer coil wound from NbTi conductor cooled at 1.8 K, has been investigated. The design concept of the coil, which incorporates a shell-like structure composed of a high current density block imbedded in a low density shell, is developed. The coil design, parameters of the superconducting cable, and the yoke and collar design are described, both for a two-in-one and a single quadrupole geometries.<<ETX>>
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.
123424297
The Choice of Spectrometer Magnets for LEP
Many experiments at LEP will require matching spectrometer magnets. In this report, guidelines are established for providing a starting point in the iterative process of choosing the best device for a particular detector. Magnets are compared in terms of their resolving power based on measurements of sagitta. This approach draws attention to the importance of detector size, and also helps to define the preferred areas of application of normal and superconducting technology. Although most emphasis is placed on the solenoid, toroids and dipoles are also discussed.
118122719
DESIGN, TEST AND PERFORMANCE OF THE LIQUID HELIUM CRYOSTATS FOR THE LEP SUPERCONDUCTING QUADRUPOLE MAGNETS
The experimental areas of LEP, the high-energy electron-positron collider presently under construction at CERN, will be equipped with eight superconducting quadrupole magnets, housed in liquid helium cryostats embedded in the complex detector set-ups. To comply with transverse space restrictions, the 2.5 m-long slender cryostats feature a 130 mm diameter warm bore and a horizontally-oriented service funnel at one end, equipped with 2000 A current leads. The cryostats have been designed by CERN, manufactured and assembled by industry, and tested in the laboratory. Besides design principles and constructional features, results of tests and comparative performance data are presented.
107631253
AMPLITUDE DEPENDENT TUNE SPREAD AND FIELD ERRORS OF SUPERCONDUCTING LOW- QUADRUPOLES
The nonlinear effects in the lowinsertions are studied on the basis of the amplitude dependent tune spread. Several methods of estimating the tune spread in superconducting lowquadrupoles are compared. The main feature of these magnets is that the random errors dominate the multipole spectrum. The proposed methods allow an analysis of the final focus layout in the early stages of the insertion design, and point to the critical magnets and the dominant multipole errors.
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.
115161736
Non-commutative field theory with twistor-like coordinates
Abstract We consider quantum field theory in four-dimensional Minkowski spacetime, with the position coordinates represented by twistors instead of the usual world-vectors. Upon imposing canonical commutation relations between twistors and dual twistors, quantum theory of fields described by non-holomorphic functions of twistor variables becomes manifestly non-commutative, with Lorentz symmetry broken by a time-like vector. We discuss the free field propagation and its impact on the short- and long-distance behavior of physical amplitudes in perturbation theory. In the ultraviolet limit, quantum field theories in twistor space are generically less divergent than their commutative counterparts. Furthermore, there is no infrared–ultraviolet mixing problem.
42302696
Multigluon scattering in open superstring theory
We discuss the amplitudes describing $N$-gluon scattering in type I superstring theory, on a disk world sheet. After reviewing the general structure of amplitudes and the complications created by the presence of a large number of vertices at the boundary, we focus on the most promising case of maximally helicity violating (MHV) configurations because in this case, the zero Regge slope limit (${\ensuremath{\alpha}}^{\ensuremath{'}}\ensuremath{\rightarrow}0$) is particularly simple. We obtain the full-fledged MHV disk amplitudes for $N=4$, 5, and $N=6$ gluons, expressed in terms of one, two and six functions of kinematic invariants, respectively. These functions represent certain boundary integrals\char22{}generalized Euler integrals\char22{}which for $N\ensuremath{\ge}6$ correspond to multiple hypergeometric series (generalized Kamp\'e de F\'eriet functions). Their ${\ensuremath{\alpha}}^{\ensuremath{'}}$ expansions lead to Euler-Zagier sums. For arbitrary $N$, we show that the leading string corrections to the Yang-Mills amplitude, of order $\mathcal{O}({\ensuremath{\alpha}}^{\ensuremath{'}2})$, originate from the well-known ${\ensuremath{\alpha}}^{\ensuremath{'}2}\text{ }\mathrm{Tr}{F}^{4}$ effective interactions of four gauge field strength tensors. By using iteration based on the soft gluon limit, we derive a simple formula valid to that order for arbitrary $N$. We argue that such a procedure can be extended to all orders in ${\ensuremath{\alpha}}^{\ensuremath{'}}$. If nature gracefully picked a sufficiently low string mass scale, our results would be important for studying string effects in multijet production at the Large Hadron Collider (LHC).
15909902
GRAVITATIONAL MEDIATION OF SUPERSYMMETRY BREAKING IN SUPERSTRING THEORY
SUSY breaking and its mediation are among the most important problems of supersymmetric generalizations of the standard model. The idea of gravity-mediated SUSY breaking, proposed in 1982 by Arnowitt, Chamseddine and Nath, and independently by Barbieri, Ferrara and Savoy, fits naturally into superstring theory, where it can be realized at both classical as well as quantum levels. This talk is dedicated to Pran Nath on his 65th birthday.
121433390
Quantum gravity at large distances and the cosmological constant
Abstract The large-distance behaviour of quantum corrections to the gravitational field equations with a cosmological constant term is studied within the formalism of the gauge-invariant Vilkovisky-DeWitt effective action. Implications for a recently proposed Coleman-Weinberg type suppression of the cosmological constant are discussed.