Monthly Archives: August 2014

New hair on black rings

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Simon Ross

Simon Ross is a professor in the department of mathematical sciences at Durham University, and a member of the university’s Centre for Particle Theory.

Relating different charge densities gives black rings with non-trivial profiles with smooth horizons.

There is a rich space of solutions in five-dimensional supergravity, including smooth horizonless supertube solutions and black ring solutions. Supertubes can have arbitrary profiles, and varying charge densities along the profile, but previously-known black ring solutions required a constant charge density along the ring to have a smooth horizon.

Recently, we discovered a new kind of supersymmetric horizonless object which generalizes the supertube, which we dubbed the magnetube. They carry coordinated electric charge densities with Continue reading →

Three-dimensional massive gravity and AdS/CFT

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Alasdair Routh and Wout Merbis

Alasdair Routh (left) is a Ph.D. student in the Department of Applied Mathematics and Theoretical Physics at the University of Cambridge. Wout Merbis (right) is a Ph.D. student at the Centre for Theoretical Physics of the University of Groningen.

Einstein’s gravitational field equations, which relate the geometry of spacetime to the matter in it, can also be applied to a spacetime of three dimensions (3D) but in this case the matter completely determines the geometry, so there is no “room” for gravitational waves: gravitons in the quantum theory. However, in 3D there is a simple extension of Einstein’s second-order equations to the third-order equations of “Topologically-Massive Gravity” (TMG), which propagates a single massive spin-2 mode; i.e. a massive graviton.

In the context of asymptotically anti-de Sitter (AdS) space times, both 3D Einstein gravity and TMG are potentially semi-classical approximations to some consistent 3D quantum gravity theory defined, via the AdS/CFT correspondence, in terms of a 2D conformal field theory (CFT). However, Continue reading →

Noisy surface charges on gravitational wave detector optics

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Paul Campsie

Paul Campsie completed his Ph.D. in the Institute for Gravitational Research at the University of Glasgow. He now works as a Product & Test Engineer for Freescale Semiconductor.

A direct measurement of the fluctuating force noise created by surface charge on dielectrics

It has been known that future interferometric gravitational wave detectors could have their low frequency sensitivity limited by excess surface charges on the detector optics. Though it is suspected that the limiting effects of this noise source have been observed in initial detectors, this was never directly verified because there was no measurement of the charge on the optic.

In our recent CQG article we present a direct measurement of the fluctuating force noise created by excess surface charges (charging noise) on a dielectric. This measurement is Continue reading →

Video: A look at the Square Kilometre Array (SKA)

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James DACEY

James Dacey is multimedia projects editor for Physics World

The Square Kilometre Array (SKA) promises to usher in a new era in radio astronomy. Astronomers will use the telescope to probe the early universe by looking as far back in time as the first 100 million years after the Big Bang. It will also be employed to search for life and planets, as well as to study the nature of dark energy, and to examine theories of gravity and general relativity.

I recently travelled to the global headquarters of the SKA Organisation at the Jodrell Bank observatory in the north of England, along with a small film crew. We met scientists and engineers involved with the SKA, and we produced this short film about what the project is designed to achieve. The video takes you on a tour of the sites in Australia and southern Africa that will host the SKA, featuring artists’ impressions of the impressive telescope equipment.

It was inspiring to hear the SKA representatives talk about the unprecedented scale of the project and the range of scientific fields that stand to benefit from the new tool. But it was also interesting to learn about the economic and social considerations that underpin a scientific project of such vast scale. The hope is that it can inspire the next generation of scientists and engineers in Australia and the African continent.

We produced the film in connection with the July issue of Physics World, a special issue devoted to dark matter and dark energy. Physics World is published by the Institute of Physics, which also publishes CQG and CQG+.

Attempting to quantize geometry

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Jan Ambjørn is professor of theoretical high energy physics at the Niels Bohr Institute, University of Copenhagen and at IMAPP, Radboud University.

Jan Ambjørn is professor of theoretical high energy physics at the Niels Bohr Institute, University of Copenhagen and at IMAPP, Radboud University.

The Standard Model of particle physics is a quantum theory. It is born quantum. The observations of the weak and the strong interactions were from the beginning linked to quantum phenomena. For gravity the situation is different. Because the gravitational coupling constant is so small compared to coupling constants in the Standard Model, any observations of quantum aspects of gravity have been ruled out so far. Here we will assume that gravity is a quantum theory. However, quantizing gravity has so far turned out to be difficult. That Continue reading →