68,775 research outputs found
The low energy expansion of the one-loop type II superstring amplitude
The one-loop four-graviton amplitude in either of the type II superstring
theories is expanded in powers of the external momenta up to and including
terms of order s^4 log s R^4, where R^4 denotes a specific contraction of four
linearized Weyl tensors and s is a Mandelstam invariant. Terms in this series
are obtained by integrating powers of the two-dimensional scalar field theory
propagator over the toroidal world-sheet as well as the moduli of the torus.
The values of these coefficients match expectations based on duality relations
between string theory and eleven-dimensional supergravity.Comment: harvmac (b), 25 pages, 3 eps figures. v2: Factors of 2 corrected.
Conclusion unchange
The BIOSIS data base: Evaluation of its indexes and the STRATBLDR, CHEMFILE, STAIRS and DIALOG systems for on-line searching
An IBM-developed program, STAIRS, was selected for performing a search on the BIOSIS file. The evaluation of the hardware and search systems and the strategies used are discussed. The searches are analyzed by type of end user
Physics at COSY
The COSY accelerator in J\'ulich is presented together with its internal and
external detectors. The physics programme performed recently is discussed with
emphasis on strangeness physics.Comment: Invited talk given at the "10th International Symposium on
Meson-Nucleon Physics and the Structure of the Nucleon (MENU04)," IHEP,
Beijing, China, 30/Aug.-4/Sept./0
D-Instanton Corrections as (p,q)-String Effects and Non-Renormalization Theorems
We discuss higher derivative interactions in the type IIB superstring in ten
dimensions. From the fundamental string point of view, the non-perturbative
corrections are due to D-instantons. We argue that they can alternatively be
understood as arising from -strings. We derive a non-renormalization
theorem for eight-derivative bosonic interactions, which states that terms
involving either NS-NS or R-R fields occur at tree-level and one-loop only. By
using the symmetry of M-theory on , we show that in order for
the possible interactions in M-theory to have a
consistent perturbative expansion in nine dimensions, must be odd. Thus,
only terms can be present in M-theory and their string
theory counterparts arise at and loops. Finally, we treat an example
of fermionic term.Comment: 24 pages, latex, additional arguments for the perturbative form of
the eight-derivative interaction
Airborne Four-Dimensional Flight Management in a Time-based Air Traffic Control Environment
Advanced Air Traffic Control (ATC) systems are being developed which contain time-based (4D) trajectory predictions of aircraft. Airborne flight management systems (FMS) exist or are being developed with similar 4D trajectory generation capabilities. Differences between the ATC generated profiles and those generated by the airborne 4D FMS may introduce system problems. A simulation experiment was conducted to explore integration of a 4D equipped aircraft into a 4D ATC system. The NASA Langley Transport Systems Research Vehicle cockpit simulator was linked in real time to the NASA Ames Descent Advisor ATC simulation for this effort. Candidate procedures for handling 4D equipped aircraft were devised and traffic scenarios established which required time delays absorbed through speed control alone or in combination with path stretching. Dissimilarities in 4D speed strategies between airborne and ATC generated trajectories were tested in these scenarios. The 4D procedures and FMS operation were well received by airline pilot test subjects, who achieved an arrival accuracy at the metering fix of 2.9 seconds standard deviation time error. The amount and nature of the information transmitted during a time clearance were found to be somewhat of a problem using the voice radio communication channel. Dissimilarities between airborne and ATC-generated speed strategies were found to be a problem when the traffic remained on established routes. It was more efficient for 4D equipped aircraft to fly trajectories with similar, though less fuel efficient, speeds which conform to the ATC strategy. Heavy traffic conditions, where time delays forced off-route path stretching, were found to produce a potential operational benefit of the airborne 4D FMS
Piloted simulation of an air-ground profile negotiation process in a time-based Air Traffic Control environment
Historically, development of airborne flight management systems (FMS) and ground-based air traffic control (ATC) systems has tended to focus on different objectives with little consideration for operational integration. A joint program, between NASA's Ames Research Center (Ames) and Langley Research Center (Langley), is underway to investigate the issues of, and develop systems for, the integration of ATC and airborne automation systems. A simulation study was conducted to evaluate a profile negotiation process (PNP) between the Center/TRACON Automation System (CTAS) and an aircraft equipped with a four-dimensional flight management system (4D FMS). Prototype procedures were developed to support the functional implementation of this process. The PNP was designed to provide an arrival trajectory solution which satisfies the separation requirements of ATC while remaining as close as possible to the aircraft's preferred trajectory. Results from the experiment indicate the potential for successful incorporation of aircraft-preferred arrival trajectories in the CTAS automation environment. Fuel savings on the order of 2 percent to 8 percent, compared to fuel required for the baseline CTAS arrival speed strategy, were achieved in the test scenarios. The data link procedures and clearances developed for this experiment, while providing the necessary functionality, were found to be operationally unacceptable to the pilots. In particular, additional pilot control and understanding of the proposed aircraft-preferred trajectory, and a simplified clearance procedure were cited as necessary for operational implementation of the concept
Relativistic Harmonic Oscillator Revisited
The familiar Fock space commonly used to describe the relativistic harmonic
oscillator, for example as part of string theory, is insufficient to describe
all the states of the relativistic oscillator. We find that there are three
different vacua leading to three disconnected Fock sectors, all constructed
with the same creation-annihilation operators. These have different spacetime
geometric properties as well as different algebraic symmetry properties or
different quantum numbers. Two of these Fock spaces include negative norm
ghosts (as in string theory) while the third one is completely free of ghosts.
We discuss a gauge symmetry in a worldline theory approach that supplies
appropriate constraints to remove all the ghosts from all Fock sectors of the
single oscillator. The resulting ghost free quantum spectrum in d+1 dimensions
is then classified in unitary representations of the Lorentz group SO(d,1).
Moreover all states of the single oscillator put together make up a single
infinite dimensional unitary representation of a hidden global symmetry
SU(d,1), whose Casimir eigenvalues are computed. Possible applications of these
new results in string theory and other areas of physics and mathematics are
briefly mentioned.Comment: 41 pages, 2 figures, LaTe
Topological Black Holes of Einstein-Yang-Mills dilaton Gravity
We present the topological solutions of Einstein-dilaton gravity in the
presence of a non-Abelian Yang-Mills field. In 4 dimensions, we consider the
and semisimple group as the Yang-Mills gauge group, and
introduce the black hole solutions with spherical and hyperbolic horizons,
respectively. The solution in the absence of dilaton potential is
asymptotically flat and exists only with spherical horizon. Contrary to the
non-extreme Reissner-Nordstrom black hole, which has two horizons with a
timelike and avoidable singularity, here the solution may present a black hole
with a null and unavoidable singularity with only one horizon. In the presence
of dilaton potential, the asymptotic behavior of the solutions is neither flat
nor anti-de Sitter. These solutions contain a null and avoidable singularity,
and may present a black hole with two horizons, an extreme black hole or a
naked singularity. We also calculate the mass of the solutions through the use
of a modified version of Brown and York formalism, and consider the first law
of thermodynamics.Comment: 13 pages, 3 figure
Supersymmetry Constraints on Type IIB Supergravity
Supersymmetry is used to derive conditions on higher derivative terms in the
effective action of type IIB supergravity. Using these conditions, we are able
to prove earlier conjectures that certain modular invariant interactions of
order alpha' **3 relative to the Einstein-Hilbert term are proportional to
eigenfunctions of the Laplace operator on the fundamental domain of SL(2,Z). We
also discuss how these arguments generalize to terms of higher order in alpha',
as well as to compactifications of supergravity.Comment: 31 pages, harvmac (b); minor correction
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