131,730 research outputs found
Amplitudes and Resonances from an Energy-Dependent Analysis of pbar+p -> pi+pi
The amplitudes at a series of discrete energies obtained from a previuos
analysis of pbar+p -> pi+pi have been used as input to a global energy-
dependent analysis of data in the momentum range 360 - 1550 MeV/c. The results
confirm the previous analysis and yield refined values for meson resonance
parameters in this energy region.Comment: 8 pages, LaTex, 2 postscript figures, a reference is correcte
Induced Gravity II: Grand Unification
As an illustration of a renormalizable, asymptotically-free model of induced
gravity, we consider an gauge theory interacting with a real scalar
multiplet in the adjoint representation. We show that dimensional transmutation
can occur, spontaneously breaking to while
inducing the Planck mass and a positive cosmological constant, all proportional
to the same scale . All mass ratios are functions of the values of coupling
constants at that scale. Below this scale (at which the Big Bang may occur),
the model takes the usual form of Einstein-Hilbert gravity in de Sitter space
plus calculable corrections. We show that there exist regions of parameter
space in which the breaking results in a local minimum of the effective action,
and a {\bf positive} dilaton from two-loop corrections
associated with the conformal anomaly. Furthermore, unlike the singlet case we
considered previously, some minima lie within the basin of attraction of the
ultraviolet fixed point. Moreover, the asymptotic behavior of the coupling
constants also lie within the range of convergence of the Euclidean path
integral, so there is hope that there will be candidates for sensible vacua.
Although open questions remain concerning unitarity of all such renormalizable
models of gravity, it is not obvious that, in curved backgrounds such as those
considered here, unitarity is violated. In any case, any violation that may
remain will be suppressed by inverse powers of the reduced Planck mass.Comment: 44 pages, 5 figures, 2 tables. v2 has new discussion concerning
stability of SSB plus related appendix. Additional references added. v3 is
version to be published; contains minor revision
Zero modes in de Sitter background
There are five well-known zero modes among the fluctuations of the metric of
de~Sitter (dS) spacetime. For Euclidean signature, they can be associated with
certain spherical harmonics on the sphere, viz., the vector
representation of the global isometry. They appear, for example,
in the perturbative calculation of the on-shell effective action of dS space,
as well as in models containing matter fields. These modes are shown to be
associated with collective modes of corresponding to certain coherent
fluctuations. When dS space is embedded in flat five dimensions they may
be seen as a legacy of translation of the center of the sphere. Rigid
translations of the -sphere on leave the classical action invariant
but are unobservable displacements from the point of view of gravitational
dynamics on Thus, unlike similar moduli, the center of the sphere is not
promoted to a dynamical degree of freedom. As a result, these zero modes do not
signify the possibility of physically realizable fluctuations or flat
directions for the metric of dS space. They are not associated with Killing
vectors on but can be with certain non-isometric, conformal Killing forms
that locally correspond to a rescaling of the volume element
For convenience, we frame our discussion in the context of renormalizable
gravity, but the conclusions apply equally to the corresponding zero modes in
Einstein gravity. We expect that these zero modes will be present to all orders
in perturbation theory. They will occur for Lorentzian signature as well, so
long as the hyperboloid is locally stable, but there remain certain
infrared issues that need to be clarified. We conjecture that they will appear
in any gravitational theory having dS background as a locally stable solution
of the effective action, regardless of whether additional matter is included.Comment: v4, 28pages, no figures; final journal form, minor changes in text
and refs from v
Wind-tunnel acoustic results of two rotor models with several tip designs
A three-phase research program has been undertaken to study the acoustic signals due to the aerodynamic interaction of rotorcraft main rotors and tail rotors. During the first phase, two different rotor models with several interchangeable tips were tested in the Langley 4- by 7-Meter Tunnel on the U.S. Army rotor model system. An extensive acoustic data base was acquired, with special emphasis on blade-vortex interaction (BVI) noise. The details of the experimental procedure, acoustic data acquisition, and reduction are documented. The overall sound pressure level (OASPL) of the high-twist rotor systems is relatively insensitive to flight speed but generally increases with rotor tip-path-plane angle. The OASPL of the high-twist rotors is dominated by acoustic energy in the low-frequency harmonics. The OASPL of the low-twist rotor systems shows more dependence on flight speed than the high-twist rotors, in addition to being quite sensitive to tip-path-plane angle. An integrated band-limited sound pressure level, limited by 500 to 3000 Hz, is a useful metric to quantify the occurrence of BVI noise. The OASPL of the low-twist rotors is strongly influenced by the band-limited sound levels, indicating that the blade-vortex impulsive noise is a dominant noise source for this rotor design. The midfrequency acoustic levels for both rotors show a very strong dependence on rotor tip-path-plane angle. The tip-path-plane angle at which the maximum midfrequency sound level occurs consistently decreases with increasing flight speed. The maximum midfrequency sound level measured at a given location is constant regardless of the flight speed
Labour-market in a border-area; searching for jobs and the influence of borders
At the moment borders, border-related problems, and the process of tearing down borders are very much in the centre of interest. Especially in Europe a lot of scientific work is done with regard to borders of countries, to determine their role in the ongoing integration process. In this respect border-regions are considered to be able to play a catalytic role. The borderland economies on both sides of a national border in this view have to be changed into one transborder economy. Initiatives to encourage cross-border integration however are not always successful. To our opinion, one of the main reasons lies in the fact that the border has many faces. The effect of a border differs, depending on the type of interaction (e.g. economic, social-cultural or institutional) and the nature of the region it defines. This paper tries to formulate a conceptual framework, within which the different properties of borders and border-regions are taken into account. Next this model is applied to the regional labour-market in the Nijmegen-Arnhem border-area in the eastern part of the Netherlands. The most important questions to be answered are: - Are there effects stemming from the fact the regional labour-market in the Arnhem-Nijmegen is part of a (peripheral) borderland economy? - What are the effects of the border with regard to the interaction of the region Arnhem-Nijmegen with the neighbouring region in Germany? - Is a part of the "natural" labour-market cut off by the national border, or put in other words, what would happen if the Dutch-German border would disappear completely? Keywords: Borders, Regional labour-markets, Transition
A local moment approach to the degenerate Anderson impurity model
The local moment approach is extended to the orbitally-degenerate [SU(2N)]
Anderson impurity model (AIM). Single-particle dynamics are obtained over the
full range of energy scales, focussing here on particle-hole symmetry in the
strongly correlated regime where the onsite Coulomb interaction leads to
many-body Kondo physics with entangled spin and orbital degrees of freedom. The
approach captures many-body broadening of the Hubbard satellites, recovers the
correct exponential vanishing of the Kondo scale for all N, and its universal
scaling spectra are found to be in very good agreement with numerical
renormalization group (NRG) results. In particular the high-frequency
logarithmic decays of the scaling spectra, obtained here in closed form for
arbitrary N, coincide essentially perfectly with available numerics from the
NRG. A particular case of an anisotropic Coulomb interaction, in which the
model represents a system of N `capacitively-coupled' SU(2) AIMs, is also
discussed. Here the model is generally characterised by two low-energy scales,
the crossover between which is seen directly in its dynamics.Comment: 23 pages, 7 figure
Protein search for multiple targets on DNA
Protein-DNA interactions are crucial for all biological processes. One of the
most important fundamental aspects of these interactions is the process of
protein searching and recognizing specific binding sites on DNA. A large number
of experimental and theoretical investigations have been devoted to uncovering
the molecular description of these phenomena, but many aspects of the
mechanisms of protein search for the targets on DNA remain not well understood.
One of the most intriguing problems is the role of multiple targets in protein
search dynamics. Using a recently developed theoretical framework we analyze
this question in detail. Our method is based on a discrete-state stochastic
approach that takes into account most relevant physical-chemical processes and
leads to fully analytical description of all dynamic properties. Specifically,
systems with two and three targets have been explicitly investigated. It is
found that multiple targets in most cases accelerate the search in comparison
with a single target situation. However, the acceleration is not always
proportional to the number of targets. Surprisingly, there are even situations
when it takes longer to find one of the multiple targets in comparison with the
single target. It depends on the spatial position of the targets, distances
between them, average scanning lengths of protein molecules on DNA, and the
total DNA lengths. Physical-chemical explanations of observed results are
presented. Our predictions are compared with experimental observations as well
as with results from a continuum theory for the protein search. Extensive Monte
Carlo computer simulations fully support our theoretical calculations
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