Neutron Stars as Dark Matter Probes

We examine whether the accretion of dark matter onto neutron stars could ever have any visible external effects. Captured dark matter which subsequently annihilates will heat the neutron stars, although it seems the effect will be too small to heat close neutron stars at an observable rate whilst those at the galactic centre are obscured by dust. Non-annihilating dark matter would accumulate at the centre of the neutron star. In a very dense region of dark matter such as that which may be found at the centre of the galaxy, a neutron star might accrete enough to cause it to collapse within a period of time less than the age of the Universe. We calculate what value of the stable dark matter-nucleon cross section would cause this to occur for a large range of masses.Comment: 8 pages, 7 figure

Effects of voids on the reconstruction of the equation of state of Dark Energy

We quantify the effects of the voids known to exist in the Universe upon the reconstruction of the dark energy equation of state $w$. We show that the effect can start to be comparable with some of the other errors taken into account when analysing supernova data, depending strongly upon the low redshift cut-off used in the sample. For the supernova data alone, the error induced in the reconstruction of $w$ is much larger than the percent level. When the Baryonic Acoustic Oscillations and the CMB data are included in the fit, the effect of the voids upon the determination of $w$ is much lessened, but is not much smaller than some of the other errors taken into consideration when performing such fits.Comment: 6 pages, 4 figure

Early diagnosis and risk stratification of patients with syncope

Background: Syncope is a common and challenging problem in the Emergency Department (ED), representing about 1-2% of patients visits. Early detection of the underlying cause is critical as it defines treatment and prognosis. Cardiac syncope is associated with the highest mortality of all syncope etiologies and requires specific interventions such as implantation of a pacemaker or defibrillator. ED clinicians struggle to rapidly identify the underlying cause and the threat of a possible serious cardiac origin which leads to numerous diagnostics and high hospitalisation rates. In an attempt to improve diagnosis and risk-stratification in syncope patients in the ED, several rules and scores were derived, mostly of mono-centric and rather small studies. Additionally, their external validity has never been assessed and their complexity represent a problem for a rapid and efficient implementation in the ED. Similarly, the diagnostic and prognostic value of some readily available cardiac biomarkers (such as cardiac troponins or B-type Natriuretic peptides) has been investigated in some pilot studies but the small number of patients assessed and the use of poorly sensitive assays resulted in varying results and did not allow for any definitive conclusions. Aim and Hypothesis: The aim of this thesis is to assess the accuracy of diagnostic and prognostic accuracy of scores and biomarkers in a large international cohort of syncope patients presenting to the ED. First, the accuracy of existing syncope-specific diagnostic and risk-stratification rules will be compared and their complexity put in perspective through a comparison with the CHADS2 score. Second, the diagnostic and prognostic performance of cardiac troponins, as assessed by three different assays, and BNP will be investigated. We hypothesize that complex syncope-specific scores might not reliably diagnose or risk-stratify syncope patients and that both assessed biomarkers, at least in certain subgroups of patients for which the determination of a precise etiology appears particularly difficult, could be of specific interest to improve the diagnosis and risk stratification of patients presenting with syncope to the ED. Patients and Methods: BASEL IX is an ongoing prospective international multicenter diagnostic cohort study coordinated by the University Hospital Basel. Patients >40y presenting to the ED with a syncope within the 12 last hours are enrolled and blood is drawn for the blinded analysis of the investigational biomarkers. All patients underwent clinical assessment that included standardized and detailed assessment of predefined details of the medical history and syncopal event. The adjudication of the final diagnosis is performed by two independent cardiologists based on all available information after diagnostic work-up of patients as well as the clinical follow-up at 12 months. Patients are followed up to 5 years. The diagnostic endpoint is the diagnostic accuracy for cardiac syncope, the prognostic endpoints are the accuracy to predict death or major cardiovascular events (MACE). Results: Syncope diagnostic and risk stratification rules showed a moderate accuracy in patients presenting with syncope to the ED (with Area Under The Receiver Operating Curve (AUC) between 0.67 and 0.75 for diagnostic endpoints and between 0.57 and 0.79 for prognostic endpoints) and most of them were, not superior to a readily calculable CHADS2 score. Both assessed biomarkers performed with a moderate-to-good accuracy for the diagnosis and risk stratification of the overall cohort (AUC for diagnostic endpoints between 0.76 and 0.77, AUC for prognostic endpoints between 0.73 and 0.8 depending on the chosen time-point). When assessed in patients for whom the diagnosis stayed unclear despite initial ED evaluation, these biomarkers could provide guidance to the ED physician regarding his decision for hospitalization and further testing. Conclusion: Diagnosis and risk-stratification of patients with syncope is a challenging task and currently available structured clinical assessments scores do not sufficiently help with initial ED evaluation. Common and readily available cardiac biomarkers seem to represent a valuable tool, especially in patients for whom a first evaluation did not lead to a satisfactory diagnosis

Clinical Utility of D-Dimer for Rule-Out or Rule-In of Venous Thromboembolism in Syncope

Fig. 1 Diagnostic performance of D-dimer using two different assays in patients presenting with syncope. A Left: Receiver-operating characteristic curves quantifying the diagnostic performance of Innovance® D-dimer (blue) and hs-Loci-Innovance® D-dimer (red) for the diagnosis of venous thromboembolism (VTE). Right: Clinical application of D-dimer using the 2-level Wells-score with age-adjusted1 or fixed cutoffs versus the YEARS-algorithm with probability-adjusted cut offs2. B Left: Specificity for different cufoffs of Innovance® D-dimer (blue) and hs-Loci-Innovance® D-dimer (red) for the diagnosis of venous thromboembolism (VTE). Right: Percentage of patients ruled-in and correctly identified VTE patients for different cutoffs of Innovance® D-dimer (blue) and hs-Loci-Innovance® D-dimer (red). 1In patients 50 years or younger, D-dimer concentration < 0.5 mg/l was considered negative. For patients older than 50 years, we used the formula: age in years divided by 100. 2YEARS-algorithm: assessment of only three items from the Wells-score (clinical signs of deep vein thrombosis, hemoptysis, pulmonary embolism the most likely diagnosis) and using a D-dimer test threshold of 0.5 mg/l in presence, and 1.0 mg/l in absence of one of the YEARS-items. Keywords: Diagnostic testing; Pulmonary embolism; Syncop

Cosmology when living near the Great Attractor

If we live in the vicinity of the hypothesized Great Attractor, the age of the universe as inferred from the local expansion rate can be off by three per cent. We study the effect that living inside or near a massive overdensity has on cosmological parameters induced from observations of supernovae, the Hubble parameter and the Cosmic Microwave Background. We compare the results to those for an observer in a perfectly homogeneous LCDM universe. We find that for instance the inferred value for the global Hubble parameter changes by around three per cent if we happen to live inside a massive overdensity such as the hypothesized Great Attractor. Taking into account the effect of such structures on our perception of the universe makes cosmology perhaps less precise, but more accurate.Comment: 8 pages, 6 figures, Submitted to MNRA

Internal Heating of Old Neutron Stars: Contrasting Different Mechanisms

Context: The standard cooling models of neutron stars predict temperatures $T10^{7}$ yr. However, the likely thermal emission detected from the millisecond pulsar J0437-4715, of spin-down age $t_s \sim 7\times10^9$ yr, implies a temperature $T\sim 10^5$ K. Thus, a heating mechanism needs to be added to the cooling models in order to obtain agreement between theory and observation. Aims: Several internal heating mechanisms could be operating in neutron stars, such as magnetic field decay, dark matter accretion, crust cracking, superfluid vortex creep, and non-equilibrium reactions ("rotochemical heating"). We study these mechanisms in order to establish which could be the dominant source of thermal emission from old pulsars. Methods: We show by simple estimates that magnetic field decay, dark matter accretion, and crust cracking mechanism are unlikely to have a significant effect on old neutron stars. The thermal evolution for the other mechanisms is computed using the code of Fern\'andez and Reisenegger. Given the dependence of the heating mechanisms on the spin-down parameters, we study the thermal evolution for two types of pulsars: young, slowly rotating "classical" pulsars and old, fast rotating millisecond pulsars. Results: We find that magnetic field decay, dark matter accretion, and crust cracking do not produce detectable heating of old pulsars. Rotochemical heating and vortex creep can be important both for classical pulsars and millisecond pulsars. More restrictive upper limits on the surface temperatures of classical pulsars could rule out vortex creep as the main source of thermal emission. Rotochemical heating in classical pulsars is driven by the chemical imbalance built up during their early spin-down, and therefore strongly sensitive to their initial rotation period.Comment: 7 pages, 5 figures, accepted version to be published in A&

Towards the use of asteroseismology to investigate the nature of dark matter

The annihilation of huge quantities of captured dark matter (DM) particles inside low-mass stars has been shown to change some of the stellar properties, such as the star's effective temperature or the way the energy is transported throughout the star. While in the classical picture, without DM, a star of 1 M_sun is expected to have a radiative interior during the main sequence, the same star evolving in a halo of DM with a density rho_x > 10^8 GeV cm^-3 will develop a convective core in order to evacuate the energy from DM annihilation in a more efficient way. This convective core leaves a discontinuity in the density and sound-speed profiles that can be detected by the analysis of the stellar oscillations. In this paper we present an approach towards the use of asteroseismology to detect the signature produced by the presence of DM inside a star, and we propose a new methodology to infer the properties of a DM halo from the stellar oscillations (such as the product of the DM density and the DM particle-nucleon scattering cross-section).Comment: 6 pages, 4 figures. v2 matches published version in MNRA

Prohormones in the early diagnosis of cardiac syncope

Background--The early detection of cardiac syncope is challenging. We aimed to evaluate the diagnostic value of 4 novel prohormones, quantifying different neurohumoral pathways, possibly involved in the pathophysiological features of cardiac syncope: midregional-pro-A-type natriuretic peptide (MRproANP), C-terminal proendothelin 1, copeptin, and midregionalproadrenomedullin. Methods and Results--We prospectively enrolled unselected patients presenting with syncope to the emergency department (ED) in a diagnostic multicenter study. ED probability of cardiac syncope was quantified by the treating ED physician using a visual analogue scale. Prohormones were measured in a blinded manner. Two independent cardiologists adjudicated the final diagnosis on the basis of all clinical information, including 1-year follow-up. Among 689 patients, cardiac syncope was the adjudicated final diagnosis in 125 (18%). Plasma concentrations of MRproANP, C-terminal proendothelin 1, copeptin, and midregional-proadrenomedullin were all significantly higher in patients with cardiac syncope compared with patients with other causes (P < 0.001). The diagnostic accuracies for cardiac syncope, as quantified by the area under the curve, were 0.80 (95% confidence interval [CI], 0.76-0.84), 0.69 (95% CI, 0.64-0.74), 0.58 (95% CI, 0.52-0.63), and 0.68 (95% CI, 0.63-0.73), respectively. In conjunction with the ED probability (0.86; 95% CI, 0.82-0.90), MRproANP, but not the other prohormone, improved the area under the curve to 0.90 (95% CI, 0.87-0.93), which was significantly higher than for the ED probability alone (P=0.003). An algorithm to rule out cardiac syncope combining an MRproANP level of < 77 pmol/L and an ED probability of < 20% had a sensitivity and a negative predictive value of 99%. Conclusions--The use of MRproANP significantly improves the early detection of cardiac syncope among unselected patients presenting to the ED with syncope