66,348 research outputs found
Spacetime and orbits of bumpy black holes
Our universe contains a great number of extremely compact and massive objects
which are generally accepted to be black holes. Precise observations of orbital
motion near candidate black holes have the potential to determine if they have
the spacetime structure that general relativity demands. As a means of
formulating measurements to test the black hole nature of these objects,
Collins and Hughes introduced "bumpy black holes": objects that are almost, but
not quite, general relativity's black holes. The spacetimes of these objects
have multipoles that deviate slightly from the black hole solution, reducing to
black holes when the deviation is zero. In this paper, we extend this work in
two ways. First, we show how to introduce bumps which are smoother and lead to
better behaved orbits than those in the original presentation. Second, we show
how to make bumpy Kerr black holes -- objects which reduce to the Kerr solution
when the deviation goes to zero. This greatly extends the astrophysical
applicability of bumpy black holes. Using Hamilton-Jacobi techniques, we show
how a spacetime's bumps are imprinted on orbital frequencies, and thus can be
determined by measurements which coherently track a small orbiting body's
orbital phase. We find that weak-field orbits of bumpy black holes are modified
exactly as expected from a Newtonian analysis of a body with a prescribed
multipolar structure, reproducing well-known results from the celestial
mechanics literature. The impact of bumps on strong-field orbits is especially
strong, suggesting that this framework will allow observations to set robust
limits on the extent to which a spacetime's multipoles deviate from the black
hole expectation.Comment: 24 pages, 3 figures, accepted to Phys. Rev. D. This version corrects
some typos and incorporates suggested edit
Sound insulation design of modular construction housing
This paper provides an insight into the acoustic issues of modular housing using the Verbus System of construction. The paper briefly summarises the history of the development of Verbus modular housing and the acoustic design considerations of the process. Results are presented from two sound insulation tests conducted during the course of the project. The results are discussed in terms of compliance with Approved Document E1 and increased performance standards such as EcoHomes2
Matter couplings in partially broken extended supersymmetry
We use nonlinear realizations to describe the spontaneous breaking of
supersymmetry to in four dimensions. We identify the Goldstone multiplet
with an chiral superfield, and show that chiral matter is
consistent with the partially broken supersymmetry. We find that the
chiral matter can be in any representation of the gauge group; no mirror
particles are required. We present the Goldstone action and the general
couplings to matter to the first nontrivial order in the scale of
symmetry breaking.Comment: JHU-TIPAC-94011, 9 pages. References adde
Weak-Field Gravity of Circular Cosmic Strings
A weak-field solution of Einstein's equations is constructed. It is generated
by a circular cosmic string externally supported against collapse. The solution
exhibits a conical singularity, and the corresponding deficit angle is the same
as for a straight string of the same linear energy density. This confirms the
deficit-angle assumption made in the Frolov-Israel-Unruh derivation of the
metric describing a string loop at a moment of time symmetry.Comment: 15 page
Photometric Metallicities in Bootes I
We present new Stromgren and Washington data sets for the Bootes I dwarf
galaxy, and combine them with the available SDSS photometry. The goal of this
project is to refine a ground-based, practical, accurate method to determine
age and metallicity for individual stars in Bootes I that can be selected in an
unbiased imaging survey, without having to take spectra. We produce photometric
metallicities from Stromgren and Washington photometry, for stellar systems
with a range of . To avoid the decrease in sensitivity of the
Stromgren metallicity index on the lower red-giant branch, we replace the
Stromgren v-filter with the broader Washington C-filter; we find that
is the most successful filter combination, for individual stars with
, to maintain ~0.2 dex -resolution over the whole
red-giant branch. We demonstrate that we can break the isochrones'
age-metallicity degeneracy with these filters, using stars with log g=2.5-3.0,
which have less than a 2% change in their -colour due to age, over a
range of 11-14 Gyr.Comment: 24 pages, 18 figures, accepted by MNRA
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