32,652 research outputs found
A Characterisation of the Weylian Structure of Space-Time by Means of Low Velocity Tests
The compatibility axiom in Ehlers, Pirani and Schild's (EPS) constructive
axiomatics of the space-time geometry that uses light rays and freely falling
particles with high velocity, is replaced by several constructions with low
velocity particles only. For that purpose we describe in a space-time with a
conformal structure and an arbitrary path structure the radial acceleration, a
Coriolis acceleration and the zig-zag construction. Each of these quantities
give effects whose requirement to vanish can be taken as alternative version of
the compatibility axiom of EPS. The procedural advantage lies in the fact, that
one can make null-experiments and that one only needs low velocity particles to
test the compatibility axiom. We show in addition that Perlick's standard clock
can exist in a Weyl space only.Comment: to appear in Gen.Rel.Gra
PhEMaterialist encounters with glitter: the materialisation of ethics, politics and care in arts-based research
This paper re-turns to a workshop we co-organised in London in 2018 as part of a series called ‘how to do sociology with...’ (Methods Lab, Sociology Department, Goldsmiths, University of London). The series aims to consider what happens when the materials, media, objects, devices and atmospheres of social research central to our practices are brought into focus. The specific material that we worked with and thought through in this workshop was glitter – a thing that is ubiquitous in early childhood and in wider feminine, gay and queer cultures. We draw on new materialist theories, methods and practice research, to consider how preparing and dismantling this workshop might be understood as a means of enacting feminist new materialism. We do this not to propose a blueprint for how new materialisms should be done so much as to offer a series of questions, reflections and diffractions on what unfolded and the affective and embodied traces that were left. In this sense, the paper understands arts-based practice to hold unanticipated pedagogical capacities which we attend to throughout the paper in terms of ethics, politics and care. We dwell upon ethics and politics by drawing on long-standing feminist arguments regarding what is often neglected in written accounts of doing research, and through focusing on the affective work involved in designing, choreographing and managing a workshop that asked participants to seriousplay (Haraway, 2016) with glitter and explore its material and affective properties. We discuss our own discomfort with, and uncertainty about, organising such a workshop and go on to outline what we see as the productive aspects and implications of orchestrating a glitter workshop for how we might conceive and do new materialist work. This includes a discussion about the response-ability of seriousplay with plastic in the contemporary climate, and more broadly about what new materialist methods and practice research might contribute to an understanding of educational and social research, and pedagogical and political practice. Throughout, photographs taken by us before, during and after the workshop (as jpeg images) are included, to not only illustrate the points we make and give readers/viewers a different sense of the workshop, but also extend what might count as academic knowledge production and circulation
Vacuum Decay in Theories with Symmetry Breaking by Radiative Corrections
The standard bounce formalism for calculating the decay rate of a metastable
vacuum cannot be applied to theories in which the symmetry breaking is due to
radiative corrections, because in such theories the tree-level action has no
bounce solutions. In this paper I derive a modified formalism to deal with such
cases. As in the usual case, the bubble nucleation rate may be written in the
form . To leading approximation, is the bounce action obtained by
replacing the tree-level potential by the leading one-loop approximation to the
effective potential, in agreement with the generally adopted {\it ad hoc}
remedy. The next correction to (which is proportional to an inverse power
of a small coupling) is given in terms of the next-to-leading term in the
effective potential and the leading correction to the two-derivative term in
the effective action. The corrections beyond these (which may be included in
the prefactor) do not have simple expressions in terms of the effective
potential and the other functions in the effective action. In particular, the
scalar-loop terms which give an imaginary part to the effective potential do
not explicitly appear; the corresponding effects are included in a functional
determinant which gives a manifestly real result for the nucleation rate.Comment: 39 pages, CU-TP-57
Space Time Foam: a ground state candidate for Quantum Gravity
A model of space-time foam, made by wormholes is considered. The Casimir
energy leading to such a model is computed by means of the phase shift method
which is in agreement with the variational approach used in Refs.[9-14]. The
collection of Schwarzschild and Reissner-Nordstr\"{o}m wormholes are separately
considered to represent the foam. The Casimir energy shows that the
Reissner-Nordstr\"{o}m wormholes cannot be used to represent the foam.Comment: 6 pages.RevTeX with package epsf and two eps figures. To be submitted
to the proceedings of the 4th Workshop of `Mysteries, Puzzles And Paradoxes
In Quantum Mechanics' Gargnano (Italy), 27 August-1 September 200
Resolution of the strong CP problem
It is shown that the quark mass aligns QCD vacuum in such a way that
the strong CP is conserved, resolving the strong CP problem.Comment: 9 pages;v2 slightly rewritten and expanded;v3 a few points
clarified;v4 minor changes, journal versio
Fate of the false monopoles: induced vacuum decay
We study a gauge theory model where there is an intermediate symmetry
breaking to a meta- stable vacuum that breaks a simple gauge group to a U (1)
factor. Such models admit the existence of meta-stable magnetic monopoles,
which we dub false monopoles. We prove the existence of these monopoles in the
thin wall approximation. We determine the instantons for the collective
coordinate that corresponds to the radius of the monopole wall and we calculate
the semi-classical tunneling rate for the decay of these monopoles. The
monopole decay consequently triggers the decay of the false vacuum. As the
monopole mass is increased, we find an enhanced rate of decay of the false
vacuum relative to the celebrated homogeneous tunneling rate due to Coleman
[1].Comment: 10 pages, 4 figure
Magnetic latitude effects in the solar wind
The Weber-Davis model of the solar wind is generalized to include the effects of latitude. The principal assumptions of high electrical conductivity, rotational symmetry, the polytropic relation between pressure and density, and a flow-alined field in a system rotating with the sun, are retained. An approximate solution to the resulting equations for spherical boundary conditions at the base of the corona indicates a small component of latitudinal flow toward the solar poles at large distances from the sun as result of latitudinal magnetic forces
On the relation between Euclidean and Lorentzian 2D quantum gravity
Starting from 2D Euclidean quantum gravity, we show that one recovers 2D
Lorentzian quantum gravity by removing all baby universes. Using a peeling
procedure to decompose the discrete, triangulated geometries along a
one-dimensional path, we explicitly associate with each Euclidean space-time a
(generalized) Lorentzian space-time. This motivates a map between the parameter
spaces of the two theories, under which their propagators get identified. In
two dimensions, Lorentzian quantum gravity can therefore be viewed as a
``renormalized'' version of Euclidean quantum gravity.Comment: 12 pages, 2 figure
Design of experiments for non-manufacturing processes : benefits, challenges and some examples
Design of Experiments (DoE) is a powerful technique for process optimization that has been widely deployed in almost all types of manufacturing processes and is used extensively in product and process design and development. There have not been as many efforts to apply powerful quality improvement techniques such as DoE to improve non-manufacturing processes. Factor levels often involve changing the way people work and so have to be handled carefully. It is even more important to get everyone working as a team. This paper explores the benefits and challenges in the application of DoE in non-manufacturing contexts. The viewpoints regarding the benefits and challenges of DoE in the non-manufacturing arena are gathered from a number of leading academics and practitioners in the field. The paper also makes an attempt to demystify the fact that DoE is not just applicable to manufacturing industries; rather it is equally applicable to non-manufacturing processes within manufacturing companies. The last part of the paper illustrates some case examples showing the power of the technique in non-manufacturing environments
High Density Preheating Effects on Q-ball Decays and MSSM Inflation
Non-perturbative preheating decay of post-inflationary condensates often
results in a high density, low momenta, non-thermal gas. In the case where the
non-perturbative classical evolution also leads to Q-balls, this effect shields
them from instant dissociation, and may radically change the thermal history of
the universe. For example, in a large class of inflationary scenarios,
motivated by the MSSM and its embedding in string theory, the reheat
temperature changes by a multiplicative factor of .Comment: 4 page
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