Chiral Superconducting Strings and Nambu-Goto Strings in Arbitrary Dimensions

We present general solutions to the equations of motion for a superconducting relativistic chiral string that satisfy the unit magnitude constraint in terms of products of rotations. From this result we show how to construct a general family of odd harmonic superconducting chiral loops. We further generalise the product of rotations to an arbitrary number of dimensions.Comment: 6 pages, RevTex. Replaced with version accepted for publication in J. Math. Phy

The stochastic background: scaling laws and time to detection for pulsar timing arrays

We derive scaling laws for the signal-to-noise ratio of the optimal cross-correlation statistic, and show that the large power-law increase of the signal-to-noise ratio as a function of the the observation time $T$ that is usually assumed holds only at early times. After enough time has elapsed, pulsar timing arrays enter a new regime where the signal to noise only scales as $\sqrt{T}$. In addition, in this regime the quality of the pulsar timing data and the cadence become relatively un-important. This occurs because the lowest frequencies of the pulsar timing residuals become gravitational-wave dominated. Pulsar timing arrays enter this regime more quickly than one might naively suspect. For T=10 yr observations and typical stochastic background amplitudes, pulsars with residual RMSs of less than about $1\,\mu$s are already in that regime. The best strategy to increase the detectability of the background in this regime is to increase the number of pulsars in the array. We also perform realistic simulations of the NANOGrav pulsar timing array, which through an aggressive pulsar survey campaign adds new millisecond pulsars regularly to its array, and show that a detection is possible within a decade, and could occur as early as 2016.Comment: Submitted to Classical and Quantum Gravity for Focus Issue on Pulsar Timing Arrays. 15 pages, 5 figure

New limits on cosmic strings from gravitational wave observation

We combine new analysis of the stochastic gravitational wave background to be expected from cosmic strings with the latest pulsar timing array (PTA) limits to give an upper bound on the energy scale of the possible cosmic string network, $G\mu < 1.5\times 10^{-11}$ at the 95% confidence level. We also show bounds from LIGO and to be expected from LISA and BBO. Current estimates for the gravitational wave background from supermassive black hole binaries are at the level where a PTA detection is expected. But if PTAs do observe a background soon, it will be difficult in the short term to distinguish black holes from cosmic strings as the source, because the spectral indices from the two sources happen to be quite similar. If PTAs do not observe a background, then the limits on $G\mu$ will improve somewhat, but a string network with $G\mu$ substantially below $10^{-11}$ will produce gravitational waves primarily at frequencies too high for PTA observation, so significant further progress will depend on intermediate-frequency observatories such as LISA, DECIGO and BBO.Comment: 9 pages, updated link to companion pape

Reparations and Oil in the Cold War: British Perspectives on the Luxembourg Agreement of 1952

This article analyses the British perspectives on the Luxembourg Reparations Agreement between Israel and the Federal Republic of Germany from 1952. Short-term economic interests were of central importance when it came to assessing the consequences of this deal for the United Kingdom. Her Majesty’s Government welcomed West German reparations as a means of securing Israel\u27s ability to pay for oil supplied by British companies, but at the same time saw them as a threat to its economic and political interests in the Middle East. British diplomats underestimated the long-term political value of the Luxembourg Agreement precisely because they read it verbatim. They recognised the reservations on both sides but did not expect that working relations between Israel and the Federal Republic would improve rapidly after the Agreement was ratified, limiting in turn the UK\u27s political and economic room for manoeuvre in the region. By examining a hitherto little-noticed chapter of British foreign policy in the post-war years, the article foregrounds the commercial aspects of diplomacy in the early 1950s and contributes to a better understanding of international relations in the Cold War

The reaction pi N -> pi pi N in chiral effective field theory with explicit Delta(1232) degrees of freedom

The reaction pi N -> pi pi N is studied at tree level up to next-to-leading order in the framework of manifestly covariant baryon chiral perturbation theory with explicit Delta(1232) degrees of freedom. Using total cross section data to determine the relevant low-energy constants, predictions are made for various differential as well as total cross sections at higher energies. A detailed comparison of results based on the heavy-baryon and relativistic formulations of chiral perturbation theory with and without explicit Delta degrees of freedom is given.Comment: 30 pages, 13 figure

Implementation of barycentric resampling for continuous wave searches in gravitational wave data

We describe an efficient implementation of a coherent statistic for continuous gravitational wave searches from neutron stars. The algorithm works by transforming the data taken by a gravitational wave detector from a moving Earth bound frame to one that sits at the Solar System barycenter. Many practical difficulties arise in the implementation of this algorithm, some of which have not been discussed previously. These difficulties include constraints of small computer memory, discreteness of the data, losses due to interpolation and gaps in real data. This implementation is considerably more efficient than previous implementations of these kinds of searches on Laser Interferometer Gravitational Wave (LIGO) detector data.Comment: 10 pages, 3 figure

Elastic pion-nucleon scattering in chiral perturbation theory: A fresh look

Elastic pion-nucleon scattering is analyzed in the framework of chiral perturbation theory up to fourth order within the heavy-baryon expansion and a covariant approach based on an extended on-mass-shell renormalization scheme. We discuss in detail the renormalization of the various low-energy constants and provide explicit expressions for the relevant $\beta$-functions and the finite subtractions of the power-counting breaking terms within the covariant formulation. To estimate the theoretical uncertainty from the truncation of the chiral expansion, we employ an approach which has been successfully applied in the most recent analysis of the nuclear forces. This allows us to reliably extract the relevant low-energy constants from the available scattering data at low energy. The obtained results provide a clear evidence that the breakdown scale of the chiral expansion for this reaction is related to the $\Delta$-resonance. The explicit inclusion of the leading contributions of the $\Delta$-isobar is demonstrated to substantially increase the range of applicability of the effective field theory. The resulting predictions for the phase shifts are in an excellent agreement with the ones from the recent Roy-Steiner-equation analysis of pion-nucleon scattering