Category Archives: Views on high quality CQG papers

Towards quantum asymptotic flatness

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Miguel and Madhavan

Miguel, a postdoc at the Raman Research Institute (RRI), enjoying a traditional south Indian dish: masala dosa.
Madhavan (professor at RRI) not enjoying traditional South American drink: mate.

It is of great physical interest to construct a canonical quantization of asymptotically flat spacetimes. The classical phase space variables are subject to delicate boundary conditions at spatial infinity and the first challenge is to construct a quantum kinematics which carries an imprint of these boundary conditions.

This work is one of a series of papers which seeks to construct such a Continue reading →

New hair on black rings

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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 →

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 →

Isolated systems are asymptotically… flat

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Martin Reiris is Junior Scientist at the Max Planck Institute for Gravitational Physics (Golm-Germany) since 2009. He received the PHD in pure math in 2005 at SUNYSB, and held a Moore Instructor in Math at MIT from 2006 to 2009. His interests are mainly in geometry and the mathematical structure of general relativity

In the extraordinary manuscript The Foundation of the Generalised Theory of Relativity, printed in 1916 in Annalen der Physics, Einstein begins addressing what he calls an epistemological defect of classical mechanics, (as well as of special relativity), whose dignity he attributes to E Mach. He imagined two bodies, A and B, made of the same fluid material and sufficiently separated from each other that none of the properties of one could be attributed to the existence of the other. Observers at rest in one body, he continues, see the other body rotating at a constant angular velocity, yet these same observers measure a perfect round surface in one case and an ellipsoid of rotation in the other case. It is then asked: “Why is this difference between the two bodies?”. Continue reading →

Why are complete compact-binary-coalescence waveforms so important for compact-object astrophysics?

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Marie-Anne Bizouard is a research fellow at CNRS, Laboratoire de l’Accélérateur Linéaire, Orsay, France.
She is an experimental physicist working on gravitational wave searches with ground based interferometric detectors.

The numerical relativity breakthrough in 2005 has provided waveforms of the gravitational wave signal emitted by a compact binary sources that describe the coalescence, the merger of the two compact objects and the ring-down of the newborn object. These waveforms are now more and more often used in gravitational wave searches carried out with interferometric detectors (LIGO, Virgo, GEO and eventually KAGRA), instead of analytical waveforms from Post Newtonian expansion that Continue reading →

The Weyl curvature and the Cosmic Censorship conjecture

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Parampreet Singh

Parampreet Singh is an Assistant Professor of Physics at Louisiana State University

Whether the gravitational collapse of an astrophysical object leads to a black hole or a naked singularity is one of the most intriguing issues in Einstein’s theory of General Relativity. In many astrophysical situations, the initial conditions are such that a trapped region forms and the gravitational collapse ends in a black hole, in confirmation with the Cosmic Censorship conjecture. However, in recent years Continue reading →

Symmetry operators

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Thomas Bäckdahl

Thomas Bäckdahl is a Post-Doctoral Research Assistant in the School of Mathematics at the University of Edinburgh.

Conserved quantities, for example energy and momentum, play a fundamental role in the analysis of dynamics of particles and fields. For field equations, one manifestation of conserved quantities in a broad sense is the existence of symmetry operators, i.e. linear differential operators which take solutions to solutions. A well-known example of a symmetry operator for the scalar wave equation is provided by the Lie derivative along a Killing vector field.

It is important to note that other kinds of objects Continue reading →

Testing the weak equivalence principle with atom interferometry in space

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Clifford Will

Clifford Will is the Editor-in-Chief of Classical and Quantum Gravity

The Weak Equivalence Principle (WEP) is one of the three pillars that support all metric theories of gravity, and testing it to high precision has occupied experimentalists for over 100 years. Although many successful tests have been performed, there is still room for new experiments (see this recent CQG focus issue on tests of WEP).

This paper describes in detail a concept called STE-QUEST for testing WEP in space. What makes this different from other space experiments, such as MICROSCOPE, due for launch in 2016, and STEP, still only a design concept, is that those experiments use macroscopic bodies, while STE-QUEST will use fundamentally quantum-mechanical systems: Bose-Einstein condensates of rubidium isotopes. Using atom Continue reading →