Dear Colleagues,

It gives me great pleasure to notify you of the publication of the above article in Classical and Quantum Gravity.

TITLE: Newtonian Gravity and the Bargmann Algebra
AUTHORS: Roel Andringa, Eric Bergshoeff, Sudhakar Panda and Mees de Roo

This article received very positive comments and a high quality rating from its referees. The article is available to download from IOPscience.

Please find below a summary by the authors of the developments made in this article:

‘Newton–Cartan gravity is a geometric formulation of Newtonian gravity, based on the nonrelativistic limit of general relativity. In our paper we confront this traditional view of Newton–Cartan gravity with a different approach that starts from the Bargmann algebra, a centrally extended version of the Galilei algebra. This approach emphasizes the analogy with the formulation of general relativity as a gauge theory of the Poincaré algebra. The algebraic method suggests a number of generalizations, for instance to conformal algebras, and to the Newton–Hooke algebra, which would lead to classical gravity induced by nonrelativistic strings.’

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Rachel Lawless
Publishing Editor
Classical and Quantum Gravity

Dear Colleagues,

TITLE: Lost in translation: topological singularities in group field theory
AUTHORS: Razvan Gurau

It gives me great pleasure to notify you of the publication of the above article in Classical and Quantum Gravity. This article received very positive comments and a high quality rating from its referees. The article is available to download here: http://herald.iop.org/link/4107

Please find a summary of the developments made in this article below:

Random matrix models generalize in higher dimensions to Group Field Theories (GFTs) whose Feynman graphs are dual to gluings of simplices. In this paper we prove that the effective behavior of generic GFTs is dominated by singular graphs, not dual to normal simplicial pseudo manifolds. This very serious problem brings into question their viability as quantum field theories. We prove however that, fortunately, the recently introduced “colored” GFT models circumvent this problem, generating only graphs dual to pseudo manifolds. We conclude that they are the correct starting point for the study of GFTs as quantum field theories.

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Adam Day
Publisher
Classical and Quantum Gravity

Dear Colleagues,

TITLE: Combining gravity with the forces of the standard model on a cosmological scale
AUTHORS: Claus Gerhardt

It gives me great pleasure to notify you of the publication of the above article in Classical and Quantum Gravity.

This article received very positive comments and a high quality rating from its referees. The article is available to download here:

http://herald.iop.org/branding/m19/rzl/$CONTACT_ID/link/3780

Please find a summary of the developments made in this article written by the authors below:

We prove the existence of a spectral resolution of the Wheeler-DeWitt equation when the underlying spacetime is a Friedman universe with flat spatial slices and where the matter fields are comprised of the strong interaction, with SU(3) replaced by a general SU(n), n >= 2, and the electro-weak interaction.

The wave functions are maps from R[4n+10] to a subspace of the antisymmetric Fock space, and one noteworthy result is that, whenever the electro-weak interaction is involved, the image of an eigenfunction is in general not one dimensional, i.e., in general it makes no sense specifying a fermion and looking for an eigenfunction the range of which is contained in the one dimensional vector space spanned by the fermion

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Adam Day
Publisher
Classical and Quantum Gravity

Dear Colleagues,

TITLE: Accurate light-time correction due to a gravitating mass
AUTHORS: Neil Ashby, Bruno Bertotti

It gives me great pleasure to notify you of the publication of the above article in Classical and Quantum Gravity.

This article received very positive comments and a high quality rating from its referees. Please find a summary of the developments made in this article below:

The time delay and deflection of light passing between two points near a spherical mass of gravitational radius m, are expressed to second order in m in terms of endpoint positions and angle subtended at the source by the endpoints, instead of unknown quantities such as the closest approach distance b. We minimize Fermat’s action functional and solve the eikonal equation for a null geodesic. In a close superior conjunction the second-order correction contains an enhanced part of order m²R/b², where R is of the order of the endpoint distances from the sun. We compare these results to previous calculations, in particular with the second-order terms introduced in NASA’s Orbit Determination Program. We use asymptotic series to determine which higher-order terms are important.

The results are significant for understanding the results of the Cassini light-time experiment, and for future missions whose purpose may include measuring the PPN parameter gamma.

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Adam Day
Publisher
Classical and Quantum Gravity

Dear Colleagues,

TITLE: Reduced Hamiltonian for next-to-leading order Spin-Squared Dynamics of General Compact Binaries
AUTHORS: Steven Hergt, Jan Steinhoff and Gerhard Schaefer

It gives me great pleasure to notify you of the publication of the above article in Classical and Quantum Gravity.

This article received very positive comments and a high quality rating from its referees.

Please find a summary of the developments made in this article below:

Fully reduced Hamiltonians belong to the most compact and elegant dynamical devices in physics. This particularly applies to spinning compact binaries in general relativity where approximate Hamiltonians are now available including spin-orbit, spin(1)spin(2), and spin-squared terms, all through next-to-leading order (NLO) in relativistic coupling counted in powers of the inverse of speed-of-light squared, called post-Newtonian expansion. The most complicated terms are the spin-squared ones which include information about the rotational deformation of black holes and, depending on a specific model, of neutron stars. For both a fully reduced NLO spin-squared Hamiltonian is derived and compared with former results from the Effective Field Theory approach where a nonreduced effective potential was obtained which is cast into Hamilton form under variable transformation applicable to all NLO spin terms. The result should have impact on the description of inspiralling binaries in gravitational wave astronomy.

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Adam Day
Publisher
Classical and Quantum Gravity

Iopscience.org/cqg