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An hypersphere model of the universe – the dismissal of dark matter
"... Abstract. One can make the very simple hypothesis that the Universe is the inside of an hypersphere in 4 dimensions, where our 3dimensional world consists of hypersurfaces at different radii. Based on this assumption it is possible to show that Universe expansion at a rate corresponding to flat com ..."
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Abstract. One can make the very simple hypothesis that the Universe is the inside of an hypersphere in 4 dimensions, where our 3dimensional world consists of hypersurfaces at different radii. Based on this assumption it is possible to show that Universe expansion at a rate corresponding to flat comes as a direct geometrical consequence without intervening critical density; any mass density is responsible for opening the Universe and introduces a cosmological constant. Another consequence is the appearance of inertia swirls of expanding matter, which can explain observed velocities around galaxies, again without the intervention of dark matter. When restricted to more everyday situations the model degenerates in what has been called 4dimensional optics; in the paper this is shown to be equivalent to general relativity in all static isotropic metric situations. In the conclusion some considerations bring the discussion to the realm of 4D wave optics.
ASPECTS OF MODULI STABILISATION IN STRING AND MTHEORY
"... I thank the tax paying citizens of the United Kingdom whose money has made my studies possible. I thank the University of Sussex for providing a comfortable and stimulating environment to work in, and Edmund Copeland, Mark Hindmarsh and Paul Saffin for guidance during my studies here. One of the mos ..."
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I thank the tax paying citizens of the United Kingdom whose money has made my studies possible. I thank the University of Sussex for providing a comfortable and stimulating environment to work in, and Edmund Copeland, Mark Hindmarsh and Paul Saffin for guidance during my studies here. One of the most enjoyable features of research in physics are
New Regions for a Chameleon to Hide
, 2006
"... Abstract: We show that inclusion of an extremely small quartic coupling constant in the potential for a nearly massless scalar field greatly increases the experimentally allowed region A large number of speculative theoretical ideas suggest the existence of new scalar fields, as reviewed in [1–3]. A ..."
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Abstract: We show that inclusion of an extremely small quartic coupling constant in the potential for a nearly massless scalar field greatly increases the experimentally allowed region A large number of speculative theoretical ideas suggest the existence of new scalar fields, as reviewed in [1–3]. A sufficiently light scalar will produce a new macroscopic force. Such forces may lead to violations of the equivalence principle (EP) and the inverse square law (ISL). For recent discussions of experimental searches for violation of the EP see ref. [4–8], while recent
Current tests of alternative gravity theories: the Modified Newtonian Dynamics case
, 2006
"... We address the possibility of taking advantage of high accuracy gravitational space experiments in the Solar System and complementary cosmological tests to distinguish between the usual general relativistic theory from the alternative modified Newtonian dynamics paradigm. Key words: ..."
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We address the possibility of taking advantage of high accuracy gravitational space experiments in the Solar System and complementary cosmological tests to distinguish between the usual general relativistic theory from the alternative modified Newtonian dynamics paradigm. Key words:
On the Multiple Deaths of Whitehead’s Theory of Gravity
, 2006
"... Whitehead’s 1922 theory of gravitation continues to attract the attention of philosophers, despite evidence presented in 1971 that it violates experiment. We demonstrate that the theory strongly fails five quite different experimental tests, and conclude that, notwithstanding its meritorious philoso ..."
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Whitehead’s 1922 theory of gravitation continues to attract the attention of philosophers, despite evidence presented in 1971 that it violates experiment. We demonstrate that the theory strongly fails five quite different experimental tests, and conclude that, notwithstanding its meritorious philosophical underpinnings, Whitehead’s theory is truly dead. 1. Introduction and
On the motion of matter in spacetime
 Proceedings of the Conference on Symmetries in Gravity and Field Theory
, 2003
"... We argue that the geodesic hypothesis based on autoparallels of the LeviCivita connection may need refinement in theories of gravity with additional scalar fields. This argument is illustrated with a reformulation of the BransDicke theory in terms of a spacetime connection with torsion determined ..."
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We argue that the geodesic hypothesis based on autoparallels of the LeviCivita connection may need refinement in theories of gravity with additional scalar fields. This argument is illustrated with a reformulation of the BransDicke theory in terms of a spacetime connection with torsion determined dynamically in terms of the gradient of the BransDicke scalar field. The perihelion shift in the orbit of Mercury is calculated on the alternative hypothesis that its worldline is an autoparallel of such a connection. If scalar fields couple significantly to matter and spinless test particles move on such worldlines, current time keeping methods based on the conventional geodesic hypothesis may need refinement. 1 Einstein’s formulation of interacting classical fields in spacetime with a preferred geometry and his identification of gravitation as a consequence of such a geometry is arguably one of the most elegant mathematical descriptions
Analogue Models for Emergent Gravity
, 2009
"... Gravity stands out among the fundamental interactions because of its apparent incompatibility with having a quantum description. Moreover, thermodynamic aspects of gravitation theory appears as puzzling features of some classical solutions such as black holes. These and other aspects of gravitationa ..."
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Gravity stands out among the fundamental interactions because of its apparent incompatibility with having a quantum description. Moreover, thermodynamic aspects of gravitation theory appears as puzzling features of some classical solutions such as black holes. These and other aspects of gravitational theories have recently lead to the proposal that gravity might not be a fundamental interaction but rather an emergent phenomenon, a sort of hydrodynamic limit of some more fundamental theory. In order to further explore this possibility we shall here discuss two systems where such emergence of a gravitational dynamics is observed. We shall consider first the case of a nonrelativistic BoseEinstein condensate and then a more abstract model based on scalar fields living on a Riemannian manifold. This will allow us to put in evidence the general issues related to emergent gravity scenarios with a particular attention to the role and nature of Lorentz and diffeomorphism invariance.
CPTHRR0710707 Toward metastable string vacua from magnetized branes
, 708
"... The scalar potential of recombination fields of magnetized branes in Type IIB orientifold compactifications is analyzed in the absence of any closed string fluxes. Considering its perturbative F and Dterm contributions in a quadratic approximation, we present the conditions for which its minima are ..."
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The scalar potential of recombination fields of magnetized branes in Type IIB orientifold compactifications is analyzed in the absence of any closed string fluxes. Considering its perturbative F and Dterm contributions in a quadratic approximation, we present the conditions for which its minima are supersymmetric. We show that for reasonable conditions on the spectrum, both metric moduli and recombination fields can be stabilized. We then provide explicit examples of compact manifolds where a Minkowski vacuum is realized in a Higgs phase. The vacuum energy is zero and some charged scalars acquire a vev. We then address the question of supersymmetry breaking. The scalar potential for recombination fields is analyzed when supersymmetry is broken by F and Dterm. We show that locally stable vacua can exist at the classical level. These are formed by a hidden supersymmetric sector that fixes metric moduli and recombination fields and a visible sector where supersymmetry is spontaneously broken.
Chaotic diffusion in the Solar System
 Icarus
, 2008
"... Abstract The discovery of the chaotic behavior of the planetary orbits in the Solar System [Laskar, J., 1989. Nature 338, 237238; Laskar, J., 1990. Icarus 88, 266291] was obtained using numerical integration of averaged equations. In [Laskar, J., 1994. Astron. Astrophys. 287, L9L12], these sam ..."
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Abstract The discovery of the chaotic behavior of the planetary orbits in the Solar System [Laskar, J., 1989. Nature 338, 237238; Laskar, J., 1990. Icarus 88, 266291] was obtained using numerical integration of averaged equations. In [Laskar, J., 1994. Astron. Astrophys. 287, L9L12], these same equations are integrated over several Gyr and show the evidence of very large possible increase of the eccentricity of Mercury through chaotic diffusion. On the other hand, in the direct numerical integration of Ito and Tanikawa [Ito, T., Tanikawa, K., 2002. Mon. Not. R. Astron. Soc. 336, 483500] performed without general relativity over ±4 Gyr, the eccentricity of Mercury presented some chaotic diffusion, but with a maximal excursion smaller than about 0.35. In the present work, a statistical analysis is performed over more than 1001 different integrations of the secular equations over 5 Gyr. This allows to obtain for each planet, the probability for the eccentricity to reach large values. In particular, we obtain that the probability of the eccentricity of Mercury to increase beyond 0.6 in 5 Gyr is about 1 to 2%, which is relatively large. In order to compare with Ito and Tanikawa [Ito, T., Tanikawa, K., 2002. Mon. Not. R. Astron. Soc. 336, 483500], we have performed the same analysis without general relativity, and obtained even more orbits of large eccentricity for Mercury. In order to clarify these differences, we have performed as well a direct integration of the planetary orbits, without averaging, for a dynamical model that do not include the Moon or general relativity with 10 very close initial conditions over 3 Gyr. The statistics obtained with this reduced set are comparable to the statistics of the secular equations, and in particular we obtain two trajectories for which the eccentricity of Mercury increases beyond 0.8 in less than 1.3 and 2.8 Gyr, respectively. These strong instabilities in the orbital motion of Mercury results from secular resonance between the perihelion of Jupiter and Mercury that are facilitated by the absence of general relativity. The statistical analysis of the 1001 orbits of the secular equations also provides probability density functions (PDF) for the eccentricity and inclination of the terrestrial planets (Mercury, Venus, the Earth and Mars) that are very well approximated by Rice PDF. This provides a very simple representation of the planetary PDF over 5 Gyr. On this timescale the evolution of the PDF of the terrestrial planets is found to be similar to the one of a diffusive process. As shown in Laskar [Laskar, J., 1994. Astron. Astrophys. 287, L9L12], the outer planets orbital elements do not present significant diffusion, and the PDFs of their eccentricities and inclinations are well represented by the PDF of quasiperiodic motions with a few periodic terms.