School of Physics and Astronomy
https://qmro.qmul.ac.uk/handle/123456789/3479
20190116T07:46:16Z

First astrometric reduction of Cassini Imaging Science Subsystem images using an automatic procedure: application to Enceladus images 20132017
https://qmro.qmul.ac.uk/handle/123456789/54657
First astrometric reduction of Cassini Imaging Science Subsystem images using an automatic procedure: application to Enceladus images 20132017
Zhang, QF; Lainey, V; Cooper, NJ; Vienne, A; Peng, QY; Xiong, YT
20181101T00:00:00Z

Biadjoint wires
https://qmro.qmul.ac.uk/handle/123456789/54639
Biadjoint wires
BahjatAbbas, N; StarkMuchão, R; White, CD
© 2018 The Author(s) Biadjoint scalar field theory has been the subject of much recent study, due to a number of applications in field and string theory. The catalogue of exact nonlinear solutions of this theory is relatively unexplored, despite having a role to play in extending known relationships between gauge and gravity theories, such as the double copy. In this paper, we present new solutions of biadjoint scalar theory, corresponding to singular line configurations in four spacetime dimensions, with a powerlaw dependence on the cylindrical radius. For a certain choice of common gauge group (SU(2)), a family of infinitely degenerate solutions is found, whose existence can be traced to the global symmetry of the theory. We also present extended solutions, in which the pure powerlaw divergence is partially screened by a form factor.
20181120T00:00:00Z

The Magnetic Part of the Weyl Tensor, and the Expansion of Discrete Universes
https://qmro.qmul.ac.uk/handle/123456789/54508
The Magnetic Part of the Weyl Tensor, and the Expansion of Discrete Universes
Clifton, T; Gregoris, D; Rosquist, K
We examine the effect that the magnetic part of the Weyl tensor has on the largescale expansion of space. This is done within the context of a class of cosmological models that contain regularly arranged discrete masses, rather than a continuous perfect fluid. The natural set of geodesic curves that one should use to consider the cosmological expansion of these models requires the existence of a nonzero magnetic part of the Weyl tensor. We include this object in the evolution equations of these models by performing a Taylor series expansion about a hypersurface where it initially vanishes. At the same cosmological time, measured as a fraction of the age of the universe, we find that the influence of the magnetic part of the Weyl tensor increases as the number of masses in the universe is increased. We also find that the influence of the magnetic part of the Weyl tensor increases with time, relative to the leadingorder electric part, so that its contribution to the scale of the universe can reach values of ∼ 1%, before the Taylor series approximation starts to break down.
20170127T00:00:00Z

Decay of the Cosmic Vacuum Energy
https://qmro.qmul.ac.uk/handle/123456789/54506
Decay of the Cosmic Vacuum Energy
Clifton, T; Barrow, JD
In his 2005 review, Gravity and the Thermodynamics of Horizons, Paddy suggested that a vacuum in thermal equilibrium with a bath of radiation should have a gradually diminishing energy. We work through the consequences of this scenario, and find that a coupling between the vacuum and a bath of blackbody radiation at the temperature of the horizon requires the Hubble rate, $H$, to approach the same type of evolution as in the "intermediate inflation" scenario, with $H\propto t^{1/3}$, rather than as a constant. We show that such behaviour does not conflict with observations when the vacuum energy is described by a slowlyrolling scalar field, and when the fluctuations in the scalar field are treated as in the "warm inflation" scenario. It does, however, change the asymptotic states of the universe. We find that the existence of the radiation introduces a curvature singularity at early times, where the energy densities in both the radiation and the vacuum diverge. Furthermore, we show that the introduction of an additional noninteracting perfect fluid into the spacetime reveals that radiation can dominate over dust at late times, in contrast to what occurs in the standard cosmological model. Such a coupling can also lead to a negative vacuum energy becoming positive.
Book Chapter; 12 pages, 3 figures. Final version accepted for Padmanabhan birthday volume