Time-symmetric initial data for binary black holes in numerical relativity

We look for physically realistic initial data in numerical relativity which are in agreement with post-Newtonian approximations. We propose a particular solution of the time-symmetric constraint equation, appropriate to two momentarily static black holes, in the form of a conformal decomposition of the spatial metric. This solution is isometric to the post-Newtonian metric up to the 2PN order. It represents a non-linear deformation of the solution of Brill and Lindquist, i.e. an asymptotically flat region is connected to two asymptotically flat (in a certain weak sense) sheets, that are the images of the two singularities through appropriate inversion transformations. The total ADM mass M as well as the individual masses m_1 and m_2 (when they exist) are computed by surface integrals performed at infinity. Using second order perturbation theory on the Brill-Lindquist background, we prove that the binary's interacting mass-energy M-m_1-m_2 is well-defined at the 2PN order and in agreement with the known post-Newtonian result.Comment: 27 pages, to appear in Phys. Rev.

Detection of the ultranarrow temporal correlation of twin beams via sum-frequency generation

We demonstrate the ultranarrow temporal correlation (6 fs full width half maximum) of twin beams generated by parametric down-conversion, by using the inverse process of sum-frequency generation. The result relies on an achromatic imaging of a huge bandwith of twin beams and on a careful control of their spatial degrees of freedom. The detrimental effects of spatial filtering and of imperfect imaging are shown toghether with the theoretical model used to describe the results

Perturbative effects of spinning black holes with applications to recoil velocities

Recently, we proposed an enhancement of the Regge-Wheeler-Zerilli formalism for first-order perturbations about a Schwarzschild background that includes first-order corrections due to the background black-hole spin. Using this formalism, we investigate gravitational wave recoil effects from a spinning black-hole binary system analytically. This allows us to better understand the origin of the large recoils observed in full numerical simulation of spinning black hole binaries.Comment: Proceedings of Theory Meets Data Analysis at Comparable and Extreme Mass Ratios (NRDA/Capra 2010), Perimeter Institute, June 2010 - 12 page

Relating leptogenesis parameters to light neutrino masses

We obtain model independent relations among neutrino masses and leptogenesis parameters. We find exact relations that involve the CP asymmetries $\epsilon_{N_\alpha}$, the washout parameters $\tilde m_\alpha$ and $\theta_{\alpha\beta}$, and the neutrino masses $m_i$ and $M_\alpha$, as well as powerful inequalities that involve just $\tilde m_\alpha$ and $m_i$. We prove that the Yukawa interactions of at least two of the heavy singlet neutrinos are in the strong washout region ($\tilde m_\alpha\gg10^{-3} eV$).Comment: 5 pages, 1 figur

Gravitational-Wave Recoil from the Ringdown Phase of Coalescing Black Hole Binaries

The gravitational recoil or "kick" of a black hole formed from the merger of two orbiting black holes, and caused by the anisotropic emission of gravitational radiation, is an astrophysically important phenomenon. We combine (i) an earlier calculation, using post-Newtonian theory, of the kick velocity accumulated up to the merger of two non-spinning black holes, (ii) a "close-limit approximation" calculation of the radiation emitted during the ringdown phase, and based on a solution of the Regge-Wheeler and Zerilli equations using initial data accurate to second post-Newtonian order. We prove that ringdown radiation produces a significant "anti-kick". Adding the contributions due to inspiral, merger and ringdown phases, our results for the net kick velocity agree with those from numerical relativity to 10-15 percent over a wide range of mass ratios, with a maximum velocity of 180 km/s at a mass ratio of 0.38.Comment: 9 pages, 5 figures; to appear in Class. Quant. Gra

Health care workers' influenza vaccination: motivations and mandatory mask policy

Background Vaccination of health care workers (HCW) against seasonal influenza (SI) is recommended but vaccination rate rarely reach >30%. Vaccination coverage against 2009 pandemic influenza (PI) was 52% in our hospital, whilst a new policy requiring unvaccinated HCW to wear a mask during patient care duties was enforced. Aims To investigate the determinants of this higher vaccination acceptance for PI and to look for an association with the new mask-wearing policy. Methods A retrospective cohort study, involving HCW of three critical departments of a 1023-bed, tertiary-care university hospital in Switzerland. Self-reported 2009-10 SI and 2009 PI vaccination statuses, reasons and demographic data were collected through a literature-based questionnaire. Descriptive statistics, uni- and multivariate analyses were then performed. Results There were 472 respondents with a response rate of 54%. Self-reported vaccination acceptance was 64% for PI and 53% for SI. PI vaccination acceptance was associated with being vaccinated against SI (OR 9.5; 95% CI 5.5-16.4), being a physician (OR 7.7; 95% CI 3.1-19.1) and feeling uncomfortable wearing a mask (OR 1.7; 95% CI 1.0-2.8). Main motives for refusing vaccination were: preference for wearing a surgical mask (80% for PI, not applicable for SI) and concerns about vaccine safety (64%, 50%) and efficacy (44%, 35%). Conclusions The new mask-wearing policy was a motivation for vaccination but also offered an alternative to non-compliant HCW. Concerns about vaccine safety and efficiency and self-interest of health care workers are still main determinants for influenza vaccination acceptance. Better incentives are needed to encourage vaccination amongst non-physician HC

Particle approximation of the one dimensional Keller-Segel equation, stability and rigidity of the blow-up

We investigate a particle system which is a discrete and deterministic approximation of the one-dimensional Keller-Segel equation with a logarithmic potential. The particle system is derived from the gradient flow of the homogeneous free energy written in Lagrangian coordinates. We focus on the description of the blow-up of the particle system, namely: the number of particles involved in the first aggregate, and the limiting profile of the rescaled system. We exhibit basins of stability for which the number of particles is critical, and we prove a weak rigidity result concerning the rescaled dynamics. This work is complemented with a detailed analysis of the case where only three particles interact

Three-body equations of motion in successive post-Newtonian approximations

There are periodic solutions to the equal-mass three-body (and N-body) problem in Newtonian gravity. The figure-eight solution is one of them. In this paper, we discuss its solution in the first and second post-Newtonian approximations to General Relativity. To do so we derive the canonical equations of motion in the ADM gauge from the three-body Hamiltonian. We then integrate those equations numerically, showing that quantities such as the energy, linear and angular momenta are conserved down to numerical error. We also study the scaling of the initial parameters with the physical size of the triple system. In this way we can assess when general relativistic results are important and we determine that this occur for distances of the order of 100M, with M the total mass of the system. For distances much closer than those, presumably the system would completely collapse due to gravitational radiation. This sets up a natural cut-off to Newtonian N-body simulations. The method can also be used to dynamically provide initial parameters for subsequent full nonlinear numerical simulations.Comment: 8 pages, 9 figure

Baryogenesis via Leptogenesis in Adjoint SU(5)

The possibility to explain the baryon asymmetry in the Universe through the leptogenesis mechanism in the context of Adjoint SU(5) is investigated. In this model the neutrino masses are generated through the Type I and Type III seesaw mechanisms, and the field responsible for the Type III seesaw, called rho_3, generates the B-L asymmetry needed to satisfy the observed value of the baryon asymmetry in the Universe. We find that the CP asymmetry originates only from the vertex correction, since the self-energy contribution is not present. When neutrino masses have a normal hierarchy, successful leptogenesis is possible for 10^{11} GeV < M_{\rho_3}^{NH} < 4 10^{14} GeV. When the neutrino hierarchy is inverted, the allowed mass range changes to 2 10^{11} GeV < M_{\rho_3}^{IH} < 5 10^{11} GeV. These constraints make possible to rule out a large part of the parameter space in the theory which was allowed by the unification of gauge interactions and the constraints coming from proton decay.Comment: 15 pages, 3 figures, minor corrections, to appear in JCA

Application of asymptotic expansions of maximum likelihood estimators errors to gravitational waves from binary mergers: the single interferometer case

In this paper we describe a new methodology to calculate analytically the error for a maximum likelihood estimate (MLE) for physical parameters from Gravitational wave signals. All the existing litterature focuses on the usage of the Cramer Rao Lower bounds (CRLB) as a mean to approximate the errors for large signal to noise ratios. We show here how the variance and the bias of a MLE estimate can be expressed instead in inverse powers of the signal to noise ratios where the first order in the variance expansion is the CRLB. As an application we compute the second order of the variance and bias for MLE of physical parameters from the inspiral phase of binary mergers and for noises of gravitational wave interferometers . We also compare the improved error estimate with existing numerical estimates. The value of the second order of the variance expansions allows to get error predictions closer to what is observed in numerical simulations. It also predicts correctly the necessary SNR to approximate the error with the CRLB and provides new insight on the relationship between waveform properties SNR and estimation errors. For example the timing match filtering becomes optimal only if the SNR is larger than the kurtosis of the gravitational wave spectrum