Non-linear Matter Spectra in Coupled Quintessence

We consider cosmologies in which a dark-energy scalar field interacts with cold dark matter. The growth of perturbations is followed beyond the linear level by means of the time-renormalization-group method, which is extended to describe a multi-component matter sector. Even in the absence of the extra interaction, a scale-dependent bias is generated as a consequence of the different initial conditions for baryons and dark matter after decoupling. The effect is enhanced significantly by the extra coupling and can be at the 2-3 percent level in the range of scales of baryonic acoustic oscillations. We compare our results with N-body simulations, finding very good agreement.Comment: 20 pages, 6 figures, typo correcte

Shifting the Universe: Early Dark Energy and Standard Rulers

The presence of dark energy at high redshift influences both the cosmic sound horizon and the distance to last scattering of the cosmic microwave background. We demonstrate that through the degeneracy in their ratio, early dark energy can lie hidden in the CMB temperature and polarization spectra, leading to an unrecognized shift in the sound horizon. If the sound horizon is then used as a standard ruler, as in baryon acoustic oscillations, then the derived cosmological parameters can be nontrivially biased. Fitting for the absolute ruler scale (just as supernovae must be fit for the absolute candle magnitude) removes the bias but decreases the leverage of the BAO technique by a factor 2.Comment: 6 pages, 3 figure

Early Dark Energy Cosmologies

We propose a novel parameterization of the dark energy density. It is particularly well suited to describe a non-negligible contribution of dark energy at early times and contains only three parameters, which are all physically meaningful: the fractional dark energy density today, the equation of state today and the fractional dark energy density at early times. As we parameterize Omega_d(a) directly instead of the equation of state, we can give analytic expressions for the Hubble parameter, the conformal horizon today and at last scattering, the sound horizon at last scattering, the acoustic scale as well as the luminosity distance. For an equation of state today w_0 < -1, our model crosses the cosmological constant boundary. We perform numerical studies to constrain the parameters of our model by using Cosmic Microwave Background, Large Scale Structure and Supernovae Ia data. At 95% confidence, we find that the fractional dark energy density at early times Omega_early < 0.06. This bound tightens considerably to Omega_early < 0.04 when the latest Boomerang data is included. We find that both the gold sample of Riess et. al. and the SNLS data by Astier et. al. when combined with CMB and LSS data mildly prefer w_0 < -1, but are well compatible with a cosmological constant.Comment: 6 pages, 3 figures; references added, matches published versio

Averaging Robertson-Walker Cosmologies

The cosmological backreaction arises when one directly averages the Einstein equations to recover an effective Robertson-Walker cosmology, rather than assuming a background a priori. While usually discussed in the context of dark energy, strictly speaking any cosmological model should be recovered from such a procedure. We apply the Buchert averaging formalism to linear Robertson-Walker universes containing matter, radiation and dark energy and evaluate numerically the discrepancies between the assumed and the averaged behaviour, finding the largest deviations for an Einstein-de Sitter universe, increasing rapidly with Hubble rate to a 0.01% effect for h=0.701. For the LCDM concordance model, the backreaction is of the order of Omega_eff~4x10^-6, with those for dark energy models being within a factor of two or three. The impacts at recombination are of the order of 10^-8 and those in deep radiation domination asymptote to a constant value. While the effective equations of state of the backreactions in Einstein-de Sitter, concordance and quintessence models are generally dust-like, a backreaction with an equation of state w_eff<-1/3 can be found for strongly phantom models.Comment: 18 pages, 11 figures, ReVTeX. Updated to version accepted by JCA

Intracoronary infusion of mononuclear cells after PCI-treated myocardial infarction and arrhythmogenesis: is it safe?

To reduce long-term morbidity after revascularised acute myocardial infarction, different therapeutic strategies have been investigated. Cell therapy with mononuclear cells from bone marrow (BMMC) or peripheral blood (PBMC) has been proposed to attenuate the adverse processes of remodelling and subsequent heart failure. Previous trials have suggested that cell therapy may facilitate arrhythmogenesis. In the present substudy of the HEBE cell therapy trial, we investigated whether intracoronary cell therapy alters the prevalence of ventricular arrhythmias after 1 month or the rate of severe arrhythmogenic events (SAE) in the first year. In 164 patients of the trial we measured function and infarct size with cardiovascular magnetic resonance (CMR) imaging. Holter registration was performed after 1 month from which the number of triplets (3 successive PVCs) and ventricular tachycardias (VT, ≥4 successive PVCs) was assessed. Thirty-three patients (20%) showed triplets and/or VTs, with similar distribution amongst the groups (triplets: control n = 8 vs. BMMC n = 9, p = 1.00; vs. PBMC n = 10, p = 0.67. VT: control n = 9 vs. BMMC n = 9, p = 0.80; vs. PBMC n = 11, p = 0.69). SAE occurred in 2 patients in the PBMC group and 1 patient in the control group. In conclusion, intracoronary cell therapy is not associated with an increase in ventricular arrhythmias or SAE

Cosmological Backreaction from Perturbations

We reformulate the averaged Einstein equations in a form suitable for use with Newtonian gauge linear perturbation theory and track the size of the modifications to standard Robertson-Walker evolution on the largest scales as a function of redshift for both Einstein de-Sitter and Lambda CDM cosmologies. In both cases the effective energy density arising from linear perturbations is of the order of 10^-5 the matter density, as would be expected, with an effective equation of state w ~ -1/19. Employing a modified Halofit code to extend our results to quasilinear scales, we find that, while larger, the deviations from Robertson-Walker behaviour remain of the order of 10^-5.Comment: 15 pages, 8 figures; replaced by version accepted by JCA

Intra-observer and interobserver variability of biventricular function, volumes and mass in patients with congenital heart disease measured by CMR imaging

Cardiovascular magnetic resonance (CMR) imaging provides highly accurate measurements of biventricular volumes and mass and is frequently used in the follow-up of patients with acquired and congenital heart disease (CHD). Data on reproducibility are limited in patients with CHD, while measurements should be reproducible, since CMR imaging has a main contribution to decision making and timing of (re)interventions. The aim of this study was to assess intra-observer and interobserver variability of biventricular function, volumes and mass in a heterogeneous group of patients with CHD using CMR imaging. Thirty-five patients with CHD (7–62 years) were included in this study. A short axis set was acquired using a steady-state free precession pulse sequence. Intra-observer and interobserver variability was assessed for left ventricular (LV) and right ventricular (RV) volumes, function and mass by calculating the coefficient of variability. Intra-observer variability was between 2.9 and 6.8% and interobserver variability was between 3.9 and 10.2%. Overall, variations were smallest for biventricular end-diastolic volume and highest for biventricular end-systolic volume. Intra-observer and interobserver variability of biventricular parameters assessed by CMR imaging is good for a heterogeneous group of patients with CHD. CMR imaging is an accurate and reproducible method and should allow adequate assessment of changes in ventricular size and global ventricular function

Identification of patients at risk of sudden cardiac death in congenital heart disease:The PRospEctiVE study on implaNTable cardlOverter defibrillator therapy and suddeN cardiac death in Adults with Congenital Heart Disease (PREVENTION-ACHD)

BACKGROUND Sudden cardiac death (SCD) is the main preventable cause of death in patients with adult congenital heart disease (ACHD). Since robust risk stratification methods are lacking, we developed a risk score model to predict SCD in patients with ACHD: the PRospEctiVE study on implaNTable cardlOverter defibrillator therapy and suddeN cardiac death in Adults with Congenital Heart Disease (PREVENTION-ACHD) risk score model. OBJECTIVE The purpose of this study was to prospectively study predicted SCD risk using the PREVENTION-ACHD risk score model and actual SCD and sustained ventricular tachycardia/ventricular fibrillation (VT/VF) rates in patients with ACHD. METHODS The PREVENTION-ACHD risk score model assigns 1 point each to coronary artery disease, New York Heart Association class II/III heart failure, supraventricular tachycardia, systemic ejection fraction = 120 ms, and QT dispersion >= 70 ms. SCD risk was calculated for each patient. An annual predicted risk of >= 3% constituted high risk. The primary outcome was SCD or VT/VF after 2 years. The secondary outcome was SCD. RESULTS The study included 783 consecutive patients with ACHD (n=239 (31%) left-sided lesions; n=138 (18%) tetralogy of Fallot; n=108 (14%) dosed atrial septal defect; median age 36 years; interquartile range 28-47 years; n=401 (51%) men). The PREVENTION-ACHD risk score modelidentified 58 high-risk patients. Eight patients (4 at high risk) experienced the primary outcome. The Kaplan-Meier estimates were 7% (95% confidence interval [CI] 0.1%-13.3%) in the high-risk group and 0.6% (95% CI 0.0%-1.1%) in the low-risk group (hazard ratio 12.5; 95% CI 3.1-50.9; P < .001). The risk score model's sensitivity was 0.5 and specificity 93, resulting in a C-statistic of 0.75 (95% CI 0.57-0.90). The hazard ratio for SCD was 12.4 (95% CI 1.8-88.1) (P = .01); the sensitivity and specificity were 0.5 and 0.92, and the C-statistic was 0.81 (95% CI 0.67-0.95). CONCLUSION The PREVENTION-ACHD risk score model provides greater accuracy in SCD or VT/VF risk stratification as compared with current guideline indications and identifies patients with ACHD who may benefit from preventive implantable cardioverterdefibrillator implantation