On measuring the Galactic dark matter halo with hypervelocity stars

Hypervelocity stars (HVSs) travel from the Galactic Centre across the dark matter halo of the Milky Way, where they are observed with velocities in excess of the Galactic escape speed. Because of their quasi-radial trajectories, they represent a unique probe of the still poorly constrained dark matter component of the Galactic potential. In this paper, we present a new method to produce such constraints. Our likelihood is based on the local HVS density obtained by back-propagating the observed phase space position and quantifies the ejection probability along the orbit. To showcase our method, we apply it to simulated Gaia samples of $\sim200$ stars in three realistic Galactic potentials with dark matter components parametrized by spheroidal NFW profiles. We find that individual HVSs exhibit a degeneracy in the scale mass-scale radius plane ($M_s-r_s$) and are able to measure only the combination $\alpha = M_s/r_s^2$. Likewise, a degeneracy is also present between $\alpha$ and the spheroidal axis-ratio $q$. In the absence of observational errors, we show the whole sample can nail down both parameters with {\it sub-per cent} precision (about $1\%$ and $0.1\%$ for $\alpha$ and $q$ respectively) with no systematic bias. This remarkable power to constrain deviations from a symmetric halo is a consequence of the Galactocentric origin of HVSs. To compare our results with other probes, we break the degeneracy in the scale parameters and impose a mass-concentration relation. The result is a competitive precision on the virial mass $M_{200}$ of about $10\%$.Comment: See Fig. 8 for a summar

Spontaneous rotating vortex rings in a parametrically driven polariton fluid

We present the theoretical prediction of spontaneous rotating vortex rings in a parametrically driven quantum fluid of polaritons -- coherent superpositions of coupled quantum well excitons and microcavity photons. These rings arise not only in the absence of any rotating drive, but also in the absence of a trapping potential, in a model known to map quantitatively to experiments. We begin by proposing a novel parametric pumping scheme for polaritons, with circular symmetry and radial currents, and characterize the resulting nonequilibrium condensate. We show that the system is unstable to spontaneous breaking of circular symmetry via a modulational instability, following which a vortex ring with large net angular momentum emerges, rotating in one of two topologically distinct states. Such rings are robust and carry distinctive experimental signatures, and so they could find applications in the new generation of polaritonic devices.Comment: 6 pages, 4 figure

Bench-to-bedside review: Candida infections in the intensive care unit.

Invasive mycoses are life-threatening opportunistic infections and have emerged as a major cause of morbidity and mortality in critically ill patients. This review focuses on recent advances in our understanding of the epidemiology, diagnosis and management of invasive candidiasis, which is the predominant fungal infection in the intensive care unit setting. Candida spp. are the fourth most common cause of bloodstream infections in the USA, but they are a much less common cause of bloodstream infections in Europe. About one-third of episodes of candidaemia occur in the intensive care unit. Until recently, Candida albicans was by far the predominant species, causing up to two-thirds of all cases of invasive candidiasis. However, a shift toward non-albicans Candida spp., such as C. glabrata and C. krusei, with reduced susceptibility to commonly used antifungal agents, was recently observed. Unfortunately, risk factors and clinical manifestations of candidiasis are not specific, and conventional culture methods such as blood culture systems lack sensitivity. Recent studies have shown that detection of circulating beta-glucan, mannan and antimannan antibodies may contribute to diagnosis of invasive candidiasis. Early initiation of appropriate antifungal therapy is essential for reducing the morbidity and mortality of invasive fungal infections. For decades, amphotericin B deoxycholate has been the standard therapy, but it is often poorly tolerated and associated with infusion-related acute reactions and nephrotoxicity. Azoles such as fluconazole and itraconazole provided the first treatment alternatives to amphotericin B for candidiasis. In recent years, several new antifungal agents have become available, offering additional therapeutic options for the management of Candida infections. These include lipid formulations of amphotericin B, new azoles (voriconazole and posaconazole) and echinocandins (caspofungin, micafungin and anidulafungin)

Predicting the hypervelocity star population in Gaia

Hypervelocity stars (HVSs) are amongst the fastest objects in our Milky Way. These stars are predicted to come from the Galactic center (GC) and travel along unbound orbits across the Galaxy. In the coming years, the ESA satellite Gaia will provide the most complete and accurate catalogue of the Milky Way, with full astrometric parameters for more than $1$ billion stars. In this paper, we present the expected sample size and properties (mass, magnitude, spatial, velocity distributions) of HVSs in the Gaia stellar catalogue. We build three Gaia mock catalogues of HVSs anchored to current observations, exploring different ejection mechanisms and GC stellar population properties. In all cases, we predict hundreds to thousands of HVSs with precise proper motion measurements within a few tens of kpc from us. For stars with a relative error in total proper motion below $10 \%$, the mass range extends to ~$10 M_{\odot}$ but peaks at ~$1$ $M_\odot$. The majority of Gaia HVSs will therefore probe a different mass and distance range compared to the current non-Gaia sample. In addition, a subset of a few hundreds to a few thousands of HVSs with $M$ ~ $3$ $M_\odot$ will be bright enough to have a precise measurement of the three-dimensional velocity from Gaia alone. Finally, we show that Gaia will provide more precise proper motion measurements for the current sample of HVS candidates. This will help identifying their birthplace narrowing down their ejection location, and confirming or rejecting their nature as HVSs. Overall, our forecasts are extremely encouraging in terms of quantity and quality of HVS data that can be exploited to constrain both the Milky Way potential and the GC properties.Comment: 17 pages, 18 figures, accepted for publication in MNRA

Models of plastic depinning of driven disordered systems

Two classes of models of driven disordered systems that exhibit history-dependent dynamics are discussed. The first class incorporates local inertia in the dynamics via nonmonotonic stress transfer between adjacent degrees of freedom. The second class allows for proliferation of topological defects due to the interplay of strong disorder and drive. In mean field theory both models exhibit a tricritical point as a function of disorder strength. At weak disorder depinning is continuous and the sliding state is unique. At strong disorder depinning is discontinuous and hysteretic.Comment: 3 figures, invited talk at StatPhys 2

Driven depinning of strongly disordered media and anisotropic mean-field limits

Extended systems driven through strong disorder are modeled generically using coarse-grained degrees of freedom that interact elastically in the directions parallel to the driving force and that slip along at least one of the directions transverse to the motion. A realization of such a model is a collection of elastic channels with transverse viscous couplings. In the infinite range limit this model has a tricritical point separating a region where the depinning is continuous, in the universality class of elastic depinning, from a region where depinning is hysteretic. Many of the collective transport models discussed in the literature are special cases of the generic model.Comment: 4 pages, 2 figure

Stellar density profile and mass of the Milky Way Bulge from VVV data

We present the first stellar density profile of the Milky Way bulge reaching latitude $b=0^\circ$. It is derived by counting red clump stars within the colour\--magnitude diagram constructed with the new PSF-fitting photometry from VISTA Variables in the V\'\i a L\'actea (VVV) survey data. The new stellar density map covers the area between $|l|\leq 10^\circ$ and $|b|\leq 4.5^\circ$ with unprecedented accuracy, allowing to establish a direct link between the stellar kinematics from the Giraffe Inner Bulge Spectroscopic Survey (GIBS) and the stellar mass density distribution. In particular, the location of the central velocity dispersion peak from GIBS matches a high overdensity in the VVV star count map. By scaling the total luminosity function (LF) obtained from all VVV fields to the LF from Zoccali et al.(2003), we obtain the first fully empirical estimate of the mass in stars and remnants of the Galactic bulge. The Milky Way bulge stellar mass within ($|b|<9.5^\circ$, $|l|<10^\circ$) is $2.0\pm0.3\times 10^{10}M_{\odot}$.Comment: 4 pages, 5 figures, accepted for publication on A&