Gravitational power from cosmic string loops with many kinks

We investigate the effect of a large number of kinks on the gravitational power radiated by cosmic string loops. We show that the total power radiated by a loop with N left-moving and right-moving kinks is proportional to N and increases with the typical kink angle. We then apply these results to loops containing junctions which give rise to a proliferation of the number of sharp kinks. We show that the time of gravitational decay of these loops is smaller than previously assumed. In light of this we revisit the gravitational wave burst predictions from a network containing such loops. We find there is no parameter regime in which the rate of individual kink bursts is enhanced with respect to standard networks. By contrast, there remains a region of parameter space for which the kink-kink bursts dominate the stochastic background. Finally, we discuss the order of magnitude of the typical number of sharp kinks resulting from kink proliferation on loops with junctions.Comment: 20 pages, 1 figur

Exponentially sensitive internal layer solutions of one-side and their asymptotic expansions

We consider a singularly perturbed boundary value problem with Dirichlet conditions and study the sensitivity of the internal layers solutions with respect to small changes in the boundary data. Our approach exploits the existence of smooth invariant manifolds and their asymptotic expansions in the small parameter of perturbation. We show that the phenomenon is extremely sensitive since the shock layers are only obtained by exponentially small perturbations of the boundary data

La cooperación: un mundo lleno de contradicciones

Aquest estiu 2007 vaig tenir la gran oportunitat de treballar per l’ONG Universitat Sense Fronteres (USF), i portar a terme un dels seus projectes en la zona de la Chiquitània (Bolívia), on fa deu anys que realitzen cooperació. En concret, es tractava de construir l’ampliació d’una guarderia en el poble de San José de Chiquitos. La primera part es va construir entre els anys 2003 i 2005, i una representació de l’Alcaldia del poble va venir a Barcelona per demanar l’ampliació de la mateixa, degut a que el primer mòdul s’havia quedat petit per acollir el nombre creixent de nens.Este verano 2007 tuve la gran oportunidad de trabajar para ONG Universidad Sin Fronteras (USF), y llevar a cabo uno de sus proyectos en la zona de la Chiquitánia (Bolivia), dónde hace diez años que realizan cooperación. En concreto, se trataba de construir la ampliación de una guardería en el pueblo de San José de Chiquitos. La primera parte se construyó entre los años 2003 y 2005, y una representación de la Alcaldía del pueblo vino a Barcelona para pedir la ampliación de la misma, debido a que el primer módulo se había quedado pequeño para acoger el número creciente de niños.Peer Reviewe

Conservative Dynamics of Binary Systems of Compact Objects at the Fourth Post-Newtonian Order

We review our recent derivation of a Fokker action describing the conservative dynamics of a compact binary system at the fourth post-Newtonian (4PN) approximation of general relativity. The two bodies are modeled by point particles, which induces ultraviolet (UV) divergences that are cured by means of dimensional regularization combined with a renormalization of the particle's wordlines. Associated with the propagation of wave tails at infinity is the appearance of a non-local-in-time conservative tail effect at the 4PN order in the Lagrangian. In turn this implies the appearance of infrared (IR) divergent integrals which are also regularized by means of dimensional regularization. We compute the Noetherian conserved energy and periastron advance for circular orbits at 4PN order, paying special attention to the treatment of the non-local terms. One ambiguity parameter remaining in the current formalism is determined by comparing those quantities, expressed as functions of the orbital frequency, with self-force results valid in the small mass ratio limit.Comment: 7 pages; contribution to the proceedings of the 52nd Rencontres de Moriond, "Gravitation

Dimensional regularization of the IR divergences in the Fokker action of point-particle binaries at the fourth post-Newtonian order

The Fokker action of point-particle binaries at the fourth post-Newtonian (4PN) approximation of general relativity has been determined previously. However two ambiguity parameters associated with infra-red (IR) divergencies of spatial integrals had to be introduced. These two parameters were fixed by comparison with gravitational self-force (GSF) calculations of the conserved energy and periastron advance for circular orbits in the test-mass limit. In the present paper together with a companion paper, we determine both these ambiguities from first principle, by means of dimensional regularization. Our computation is thus entirely defined within the dimensional regularization scheme, for treating at once the IR and ultra-violet (UV) divergencies. In particular, we obtain crucial contributions coming from the Einstein-Hilbert part of the action and from the non-local tail term in arbitrary dimensions, which resolve the ambiguities.Comment: 25 pages, published versio

Fokker action of non-spinning compact binaries at the fourth post-Newtonian approximation

The Fokker action governing the motion of compact binary systems without spins is derived in harmonic coordinates at the fourth post-Newtonian approximation (4PN) of general relativity. Dimensional regularization is used for treating the local ultraviolet (UV) divergences associated with point particles, followed by a renormalization of the poles into a redefinition of the trajectories of the point masses. Effects at the 4PN order associated with wave tails propagating at infinity are included consistently at the level of the action. A finite part procedure based on analytic continuation deals with the infrared (IR) divergencies at spatial infinity, which are shown to be fully consistent with the presence of near-zone tails. Our end result at 4PN order is Lorentz invariant and has the correct self-force limit for the energy of circular orbits. However, we find that it differs from the recently published result derived within the ADM Hamiltonian formulation of general relativity [T. Damour, P. Jaranowski, and G. Sch\"afer, Phys. Rev. D 89, 064058 (2014)]. More work is needed to understand this discrepancy.Comment: 47 pages; references added; Sec. VD enhanced; a few more minor improvement

Relation between respiratory variations in pulse oximetry plethysmographic waveform amplitude and arterial pulse pressure in ventilated patients.

IntroductionRespiratory variation in arterial pulse pressure is a reliable predictor of fluid responsiveness in mechanically ventilated patients with circulatory failure. The main limitation of this method is that it requires an invasive arterial catheter. Both arterial and pulse oximetry plethysmographic waveforms depend on stroke volume. We conducted a prospective study to evaluate the relationship between respiratory variation in arterial pulse pressure and respiratory variation in pulse oximetry plethysmographic (POP) waveform amplitude.MethodThis prospective clinical investigation was conducted in 22 mechanically ventilated patients. Respiratory variation in arterial pulse pressure and respiratory variation in POP waveform amplitude were recorded simultaneously in a beat-to-beat evaluation, and were compared using a Spearman correlation test and a Bland-Altman analysis.ResultsThere was a strong correlation (r2 = 0.83; P < 0.001) and a good agreement (bias = 0.8 +/- 3.5%) between respiratory variation in arterial pulse pressure and respiratory variation in POP waveform amplitude. A respiratory variation in POP waveform amplitude value above 15% allowed discrimination between patients with respiratory variation in arterial pulse pressure above 13% and those with variation of 13% or less (positive predictive value 100%).ConclusionRespiratory variation in arterial pulse pressure above 13% can be accurately predicted by a respiratory variation in POP waveform amplitude above 15%. This index has potential applications in patients who are not instrumented with an intra-arterial catheter

Enriching the Symphony of Gravitational Waves from Binary Black Holes by Tuning Higher Harmonics

For the first time, we construct an inspiral-merger-ringdown waveform model within the effective-one-body formalism for spinning, nonprecessing binary black holes that includes gravitational modes beyond the dominant $(\ell,|m|) = (2,2)$ mode, specifically $(\ell,|m|)=(2,1),(3,3),(4,4),(5,5)$. Our multipolar waveform model incorporates recent (resummed) post-Newtonian results for the inspiral and information from 157 numerical-relativity simulations, and 13 waveforms from black-hole perturbation theory for the (plunge-)merger and ringdown. We quantify the improved accuracy including higher-order modes by computing the faithfulness of the waveform model against the numerical-relativity waveforms used to construct the model. We define the faithfulness as the match maximized over time, phase of arrival, gravitational-wave polarization and sky position of the waveform model, and averaged over binary orientation, gravitational-wave polarization and sky position of the numerical-relativity waveform. When the waveform model contains only the $(2,2)$ mode, we find that the averaged faithfulness to numerical-relativity waveforms containing all modes with $\ell \leq$ 5 ranges from $90\%$ to $99.9\%$ for binaries with total mass $20-200 M_\odot$ (using the Advanced LIGO's design noise curve). By contrast, when the $(2,1),(3,3),(4,4),(5,5)$ modes are also included in the model, the faithfulness improves to $99\%$ for all but four configurations in the numerical-relativity catalog, for which the faithfulness is greater than $98.5\%$. Using our results, we also develop also a (stand-alone) waveform model for the merger-ringdown signal, calibrated to numerical-relativity waveforms, which can be used to measure multiple quasi-normal modes. The multipolar waveform model can be extended to include spin-precession, and will be employed in upcoming observing runs of Advanced LIGO and Virgo.Comment: 28 page

Frequency-domain gravitational waves from non-precessing black-hole binaries. II. A phenomenological model for the advanced detector era

We present a new frequency-domain phenomenological model of the gravitational-wave signal from the inspiral, merger and ringdown of non-precessing (aligned-spin) black-hole binaries. The model is calibrated to 19 hybrid effective-one-body--numerical-relativity waveforms up to mass ratios of 1:18 and black-hole spins of $|a/m| \sim 0.85$ ($0.98$ for equal-mass systems). The inspiral part of the model consists of an extension of frequency-domain post-Newtonian expressions, using higher-order terms fit to the hybrids. The merger-ringdown is based on a phenomenological ansatz that has been significantly improved over previous models. The model exhibits mismatches of typically less than 1\% against all 19 calibration hybrids, and an additional 29 verification hybrids, which provide strong evidence that, over the calibration region, the model is sufficiently accurate for all relevant gravitational-wave astronomy applications with the Advanced LIGO and Virgo detectors. Beyond the calibration region the model produces physically reasonable results, although we recommend caution in assuming that \emph{any} merger-ringdown waveform model is accurate outside its calibration region. As an example, we note that an alternative non-precessing model, SEOBNRv2 (calibrated up to spins of only 0.5 for unequal-mass systems), exhibits mismatch errors of up to 10\% for high spins outside its calibration region. We conclude that waveform models would benefit most from a larger number of numerical-relativity simulations of high-aligned-spin unequal-mass binaries.Comment: 27 pages, 21 figures, Updated coefficients tabl