69,768 research outputs found
The description of gravitational waves in geometric scalar gravity
It is investigated the gravitational waves phenomena in the geometric scalar
theory of gravity (GSG), a class of theories such that gravity is described by
a single scalar field. The associated physical metric describing the spacetime
is constructed from a disformal transformation of Minkowski geometry. In this
theory, a weak field approximation gives rise to a description similar to that
one obtained in general relativity, with the gravitational waves propagating at
the same speed as the light, although they have a characteristic longitudinal
polarization mode, besides others modes that are observer dependent. We also
analyze the energy carried by the gravitational waves as well as how their
emission affects the orbital period of a binary system. Observational data
coming from Hulse and Taylor binary pulsar is then used to constraint the
theory parameter.Comment: Revised version accepted for publication in EPJC; confrontation with
pulsar observational data added; abstract slightly changed. arXiv admin note:
substantial text overlap with arXiv:1607.0103
Free structures in division rings
Makar-Limanov's conjecture states that if a division ring D is finitely
generated and infinite dimensional over its center k then D contains a free
k-subalgebra of rank 2. In this work, we will investigate the existence of such
structures in D, the division ring of fractions of the skew polynomial ring
L[t;\sigma], where t is a variable and is a k-automorphism of L. For
instance, we prove Makar-Limanov's conjecture when either L is the function
field of an abelian variety or the function field of the n-dimensional
projective space.Comment: 12 page
Complex-mass shell renormalization of the higher-derivative electrodynamics
We consider a higher-derivative extension of QED modified by the addition of
a gauge-invariant dimension-6 kinetic operator in the U(1) gauge sector. The
Feynman diagrams at one-loop level are then computed. The modification in the
spin-1 sector leads the electron self-energy and vertex corrections diagrams
finite in the ultraviolet regime. Indeed, no regularization prescription is
used to calculate these diagrams because the modified propagator always occurs
coupled to conserved currents. Moreover, besides the usual massless pole in the
spin-1 sector, there is the emergence of a massive one, which becomes complex
when computing the radiative corrections at one-loop order. This imaginary part
defines the finite decay width of the massive mode. To check consistency, we
also derive the decay length using the electron--positron elastic scattering
and show that both results are equivalent. Because the presence of this
unstable mode, the standard renormalization procedures cannot be used and is
necessary adopt an appropriate framework to perform the perturbative
renormalization. For this purpose, we apply the complex-mass shell scheme (CMS)
to renormalize the aforementioned model. As an application of the formalism
developed, we estimate a quantum bound on the massive parameter using the
measurement of the electron anomalous magnetic moment and compute the Uehling
potential. At the end, the renormalization group is analyzed.Comment: 10 pages, 2 figures, replaced with published versio
Cities: Continuity, transformation and emergence
Book synopsis: This book applies ideas and methods from the complexity perspective to key concerns in the social sciences, exploring co-evolutionary processes that have not yet been addressed in the technical or popular literature on complexity. \ud
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Authorities in a variety of fields – including evolutionary economics, innovation and regeneration studies, urban modelling and history – re-evaluate their disciplines within this framework. The book explores the complex dynamic processes that give rise to socio-economic change over space and time, with reference to empirical cases including the emergence of knowledge-intensive industries and decline of mature regions, the operation of innovative networks and the evolution of localities and cities. Sustainability is a persistent theme and the practicability of intervention is examined in the light of these perspectives. \ud
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Specialists in disciplines that include economics, evolutionary theory, innovation, industrial manufacturing, technology change, and archaeology will find much to interest them in this book. In addition, the strong interdisciplinary emphasis of the book will attract a non-specialist audience interested in keeping abreast of current theoretical and methodological approaches through evidence-based and practical examples
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