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Quantum Gravity and Particle Physics
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PHASE CONTOURS AND BOOTSTRAPS. I.
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N=4 Yang-Mills and N=8 Supergravity as Limits of String Theories
The formulation of supersymmetric string theories in ten dimensions is generalized to incorporate compactified dimensions. Expressions for the one-loop four-particle S -matrix elements of N = 4 Yang-Mills and N = 8 supergravity in four dimensions are obtained by studying the string-theory loop amplitudes in the limit that the radii of the compactified dimensions and the Regge slope parameter simultaneously approach zero. If certain patterns that emerge should persist in the higher orders of perturbation theory, then N = 4 Yang-Mills in four dimensions would be ultraviolet finite to all orders, whereas N = 8 supergravity in four dimensions would have ultraviolet divergences starting at three loops.
123230985
Off-shell states in the dual model
Abstract We present a class of Lorentz invariant, gauge invariant off-shell amplitudes for the ordinary Veneziano and Ramond-Neveu-Schwarz dual models. They correspond to interactions with the string which are local in space-time.
9607753
Anomalous creation of branes
In certain circumstances when two branes pass through each other a third brane is produced stretching between them. We explain this phenomenon by the use of chains of dualities and the inflow of charge that is required for the absence of chiral gauge anomalies when pairs of D-branes intersect.
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Anomaly cancellations in supersymmetric D = 10 gauge theory and superstring theory☆
Abstract Supersymmetric ten-dimensional Yang-Mills theory coupled to N = 1, D = 10 supergravity has gauge and gravitational anomalies that can be partially cancelled by the addition of suitable local interactions. The remaining pieces of all the anomalies cancel if the gauge group is SO(32) or E 8 × E 8 . These cancellations are automatically incorporated in the type I superstring theory based on SO(32). A superstring theory for E 8 × E 8 has not yet been constructed.
119852414
Superconducting dipole moment correction coils for a free-flying version of ASTROMAG
Abstract ASTROMAG is a particle astrophysics experiment which will operate in space for a period of two years or more. Momentum and charge resolution of cosmic rays is achieved using particle detectors in a magnetic field. In the ASTROMAG experiment, this magnetic field is provided by a pair of superconducting solenoids. The ASTROMAG superconducting magnet is supposed to have a zero net magnetic dipole moment so that magnetic torques introduced to the space craft are kept at a low level. Dipole moment correction coils, which can provide up to 11,000 Am 2 of correction in the Z direction and 7,000 Am 2 of correction in the X and Y directions, appear to be practical using superconducting correction coils which are mounted on the superfluid helium tank in a region 0.5 meters wide halfway between the main ASTROMAG coils. The superconducting dipole moment correction coils should be capable of reducing the ASTROMAG magnet net dipole moment to 100 Am −2 or lower.
54880209
The effect of low temperature cryocoolers on the development of low temperature superconducting magnets
The commercial development of reliable 4 K cryocoolers improves the future prospects for magnets made from low temperature superconductors (LTS). The hope of the developers of high temperature superconductors (HTS) has been to replace liquid helium cooled LTS magnets with HTS magnets that operate at or near liquid nitrogen temperature. There has been limited success in this endeavor, but continued problems with HTS conductors have greatly slowed progress toward this goal. The development of cryocoolers that reliably operate below 4 K will allow magnets made from LTS conductor to remain very competitive for many years to come. A key enabling technology for the use of low temperature cryocoolers on LTS magnets has been the development of HTS leads. This report describes the characteristics of LTS magnets that can be successfully melded to low-temperature cryocoolers. This report also shows when it is not appropriate to consider the use of low-temperature cryocoolers to cool magnets made with LTS conductor. A couple of specific examples of LTS magnets where cryocoolers can be used are given.
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Helium cooling systems for large superconducting physics detector magnets
Abstract The large superconducting detector magnets used for high energy physics experiments are virtually all indirectly cooled. In general, these detector magnets are not cryogenically stabilized. Therefore, there are a number of choices for cooling large indirectly cooled detector magnets. These choices include; 1) forced two-phase helium cooling driven by the helium refrigerator J-T circuit, 2) forced two-phase helium cooling driven by a helium pump, and 3) a peculation gravity feed cooling system which uses liquid helium from a large storage dewar. The choices for the cooling of a large detector magnet are illustrated by applying these concepts to a 4.2 meter diameter 0.5 tesla thin superconducting solenoid for an experiment at the Relativistic Heavy Ion Collider (RHIC).
21404619
The Cold Mass Support System and the Helium Cooling System for the MICE Focusing Solenoid
The heart of the absorber focus coil (AFC) module for the muon ionization cooling experiment (MICE) is the two-coil superconducting solenoid that surrounds the muon absorber. The superconducting magnet focuses the muons that are cooled using ionization cooling, in order to improve the efficiency of cooling. The coils of the magnet may either be run in the solenoid mode (both coils operate at the same polarity) or the gradient (the coils operate at opposite polarity). The AFC magnet cold mass support system is designed to carry a longitudinal force up to 700 kN. The AFC module will be cooled using three pulse tube coolers that produce 1.5 W of cooling at 4.2 K. One of the coolers will be used to cool the liquid (hydrogen or helium) absorber used for ionization cooling. The other two coolers will cool the superconducting solenoid. This report will describe the MICE AFC magnet. The cold mass supports will be discussed. The reasons for using a pulsed tube cooler to cool this superconducting magnet will also be discussed.
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The two-coil toroid magnet, an option for ASTROMAG
The ASTROMAG particle astrophysics experiment for the US space station requires a magnetic field in order to determine the energy and momentum of charged particles of various momenta. A second concept for generating magnetic field for ASTROMAG is presented. This magnet configuration consists of two D-shaped coils which form a two-coil toroid. The two coils are located within a paddle connected to a spherical helium tank. The physics detectors would be located on either side of the flat paddle. The particles travel toward the tank in a direction approximately parallel to the paddle surface. A description is given of the two-coil toroid, the magnet cryostat, and the helium II cryogenic system, which keeps the magnet cold for up to two years without refilling. >