118484883
Relational Quadrilateralland Interpretation of CP^2 and Quotients
I investigate qualitatively significant regions of the configuration space for the classical and quantum mechanics of the relational quadrilateral in 2-d. This is relational in the sense that only relative ratios of separations, relative angles and relative times are significant. Such relational particle mechanics models have many analogies with the geometrodynamical formulation of general relativity. Thus, they are suitable as toy models for studying 1) problem of time in quantum gravity strategies, in particular timeless, semiclassical and histories theory approaches and combinations of these. 2) Various other quantum-cosmological issues, such as structure formation/inhomogeneity and the significance of uniform states. The relational quadrilateral is more useful in these respects than previously investigated simpler RPM's as it possesses linear constraints, nontrivial subsystems and its configuration space is a nontrivial complex-projective space. In this paper, I investigate the submanifold of collinear configurations, the submanifolds with a single-particle collision, the square configurations and regions of the configuration space for which such as approximate collinearity, approximate squareness and approximate triangularity hold. I consider both mirror image identified and unidentified shapes, as well as both distinguishable and indistinguishable particle labels. I find the following CP^2 coordinate systems to be useful to these ends. 1) Kuiper's coordinates, which, for quadrilateralland, are magnitudes of the Jacobi vectors and anisoscelesnesses of the triangles formed between them. 2) Gibbons-Pope type coordinates, which, for quadrilateralland, are the sum and difference of relative angles between subsystems, the ratio of size of 2 subsystems and the proportion of universe model occupied by the subsystems.
17420273
Seminar on Records Theory
In quantum gravity, one seeks to combine quantum mechanics and general relativity. In attempting to do so, one comes across the `problem of time' impasse: the notion of time is conceptually different in each of these theories. In this seminar, I consider the timeless records approach toward resolving this. Records are localized, information-containing subconfigurations of a single instant. Records theory is the study of these and of how science (or history) is to be abstracted from correlations between them. I explain how to motivate this approach, provide a ground-level structure for it and discuss what kind of further tools are needed. For a more comprehensive account with many more references, see [1].
14733645
The Campbell--Magaard Theorem is inadequate and inappropriate as a protective theorem for relativistic field equations
Given a particular prescription for the Einstein field equations (EFE's), it is important to have general protective theorems that lend support to it. The prescription of data on a timelike hypersurface for the (n + 1)-d EFE's arises in `noncompact Kaluza--Klein theory', and in certain kinds of braneworlds and low-energy string theory. The Campbell--Magaard (CM) theorem, which asserts local existence (and, with extra conditions, uniqueness) of analytic embeddings of completely general n-d manifolds into vacuum (n + 1)-d manifolds, has often recently been invoked as a protective theorem for such prescriptions. But in this paper I argue that there are problems with loosening the CM thoerem of restrictive meanings in its statement, which is worthwhile thing to do in pursuit of the proposed applications. While I remedy some problems by identifying the required topology, delineating what `local' can be taken to mean, and offering a new, more robust and covariant proof, other problems remain unsurmountable. The theorem lends only inadequate support, both because it offers no guarantee of continuous dependence on the data and because it disregards causality. Furthermore, the theorem is only for the analytic functions which renders it inappropriate for the study of the relativistic equations of modern physics. Unfortunately, there are no known general theorems that offer adequate protection to the proposed applications' prescription. I conclude by making some suggestions for more modest progress.
118832557
Geometrodynamics: Spacetime or Space ?
This thesis concerns the split of Einstein's field equations (EFE's) with respect to nowhere null hypersurfaces. Areas covered include A) the foundations of relativity, deriving geometrodynamics from relational first principles and showing that this form accommodates a sufficient set of fundamental matter fields to be classically realistic, alternative theories of gravity that arise from similar use of conformal mathematics. B) GR Initial value problem (IVP) methods, the badness of timelike splits of the EFE's and studying braneworlds under guidance from GR IVP and Cauchy problem methods.
119109018
Approaching the problem of time with a combined semiclassical-records-histories scheme
I approach the problem of time and other foundations of quantum (QM) cosmology using a combined histories, timeless and semiclassical approach. This approach is along the lines pursued by Halliwell. It involves the timeless probabilities for dynamical trajectories entering regions of configuration space, which are computed within the semiclassical regime. Moreover, the objects that Halliwell uses in this approach commute with the Hamiltonian constraint, H. This approach has not hitherto been considered for models that also possess nontrivial linear constraints, Lin. This paper carries this out for some concrete relational particle mechanics (RPMs). If there is also commutation with Lin—the Kuchař observables condition—the constructed objects are Dirac observables. Moreover, this paper shows that the problem of Kuchař observables is explicitly resolved for 1D and 2D RPMs. Then as a first route to Halliwell’s approach for nontrivial linear constraints that is also a construction of Dirac observables, I consider theories for which Kuchař observables are formally known, giving the relational triangle as an example. As a second route, I apply an indirect method that generalizes both group averaging and Barbour’s best matching. For conceptual clarity, my study involves the simpler case of Halliwell 2003 sharp-edged window function. I leave the elsewise-improved softened case of Halliwell 2009 for a subsequent paper II. Finally, I provide comments on Halliwell’s approach and how well it fares as regards the various facets of the problem of time and as an implementation of QM propositions.
17821899
Records Theory
In quantum gravity, one seeks to combine quantum mechanics and general relativity. In attempting to do so, one comes across the ‘problem of time’ impasse: the notion of time is conceptually different in each of these theories. In this paper, I consider the timeless records approach toward resolving this. Records are localized, information-containing subconfigurations of a single instant. Records theory is the study of these and of how science (or history) is to be abstracted from correlations between them. I critically evaluate motivations for this approach that have previously appeared in the literature. I provide a ground-level structure for records theory and discuss what kind of further tools are needed, illustrated with some toy models: ordinary mechanics, relatonal particle dynamics, detector models and inhomogeneous perturbations about homogeneous cosmology. PACS numbers 04.60-m, 04.60.Ds
122864304
Direct measurement of the lifetime of the neutral pion
Abstract The lifetime of the neutral pion ( π 0 ) has been directly measured. The lifetime has been found to be τ π 0 = (0.897±0.022±0.017) × 10 −16 s. The systematic error results from uncertainties in the momentum spectrum of the π 0 used for the measurement. This measurement yields a decay width of the π 0 of (7.34±0.18±0.11) eV. An axial anomaly calculation, which neglects the finite mass of the π 0 , predicts a value of 7.87 eV.
122807269
Observation of increasing charged multiplicity as a function of transverse momentum in 28.5-GeV/c pp interactions
121752579
Precision Lifetime Measurements on Positive and Negative Muons
An experiment to measure and compare the free decay rates of positive and negative muons is described. Muons from the Nevis synchrocyclotron were stopped in a liquid-hydrogen target containing less than 1 ppm ${\mathrm{D}}_{2}$ and less than 1 part in ${10}^{9}$ of other impurities. In this situation, the rate of ${\ensuremath{\mu}}^{\ensuremath{-}}$ capture in ${\mathrm{H}}_{2}$ was the only significant correction to the free decay rate of ${\ensuremath{\mu}}^{\ensuremath{-}}$ and was measured in a separate experiment. The lifetimes were monitored by measuring the time intervals between muon stops and decay electrons using a transistorized digitron of 30-nsec channel width. Electronic circuitry of the "interference remover" type was employed to eliminate time-dependent background. ${\ensuremath{\mu}}^{\ensuremath{-}}$ and ${\ensuremath{\mu}}^{+}$ lifetimes were measured with the same apparatus and under essentially the same conditions of rate and geometry. The ratio of the lifetimes is expected to be particularly insensitive to any systematic errors. We have obtained: ${\ensuremath{\tau}}_{{\ensuremath{\mu}}^{\ensuremath{-}}}=2.198\ifmmode\pm\else\textpm\fi{}0.002$ \ensuremath{\mu}sec (hydrogen correction made), ${\ensuremath{\tau}}_{{\ensuremath{\mu}}^{+}}=2.197\ifmmode\pm\else\textpm\fi{}0.002$ \ensuremath{\mu}sec, $R=\frac{{\ensuremath{\tau}}_{{\ensuremath{\mu}}^{\ensuremath{-}}}}{{\ensuremath{\tau}}_{{\ensuremath{\mu}}^{+}}}=1.000\ifmmode\pm\else\textpm\fi{}0.001$.
119158624
Block Diagonalization using SRG Flow Equations
Here s is a flow parameter and the flow operator Gs specifies the type of SRG [4]. Decoupling between low-energy and high-energy matrix elements is naturally achieved in a momentum basis by choosing a momentum-diagonal flow operator such as the kinetic energy Trel or the diagonal of Hs; either drives the Hamiltonian toward banddiagonal form. This decoupling leads to dramatically improved variational convergence in few-body nuclear systems compared to unevolved phenomenological or chiral EFT potentials [5, 6]. Renormalization Group (RG) methods that evolve NN interactions with a sharp or smooth cutoff in relative momentum, known generically as Vlow k, rely on the invariance of the two-nucleon T matrix [7, 8]. These approaches achieve a block-diagonal form characterized by a cutoff Λ (see left plots in Figs. 1 and 2). As usually implemented they set the high-momentum matrix elements to zero but this is not required. Block-diagonal decoupling of the sharp Vlow k form can
121981552
Observation and study of centrally produced pion clusters in 28. 5-GeV/c p-p interactions
A double-arm spectrometer is used to identify a pion cluster produced in central p-p collisions at 28.5 GeV/c. Cluster properties studied are angular momentum, quantum statistics, multiplicity, and effective mass. There is some speculation on the production mechanism. (AIP)