Measurement of light mesons at RHIC by the PHENIX experiment

The PHENIX experiment at RHIC has measured a variety of light neutral mesons ($\pi^{0}$, K$_{S}^{0}$, $\eta$, $\omega$, $\eta^{\prime}$, $\phi$) via multi-particle decay channels over a wide range of transverse momentum. A review of the recent results on the production rates of light mesons in p+p and their nuclear modification factors in d+Au, Cu+Cu and Au+Au collisions at different energies is presented.Comment: 5 pages, 4 figures, talk given at Hard Probes 2008 conference in La Toja, Spain. submitted to EPJ

Impulsive acceleration of strongly magnetized relativistic flows

The definitive version can be found at: http://onlinelibrary.wiley.com/ Copyright Royal Astronomical SocietyThe strong variability of magnetic central engines of active galactic nuclei (AGNs) and gamma-ray bursts (GRBs) may result in highly intermittent strongly magnetized relativistic outflows. We find a new magnetic acceleration mechanism for such impulsive flows that can be much more effective than the acceleration of steady-state flows. This impulsive acceleration results in kinetic-energy-dominated flows that are conducive to efficient dissipation at internal magnetohydrodynamic shocks on astrophysically relevant distances from the central source. For a spherical flow, a discrete shell ejected from the source over a time t0 with Lorentz factor Γ∼ 1 and initial magnetization σ0=B20/4πρ0c2≫ 1 quickly reaches a typical Lorentz factor Γ∼σ1/30 and magnetization σ∼σ2/30 at the distance R0≈ct0. At this point, the magnetized shell of width Δ∼R0 in the laboratory frame loses causal contact with the source and continues to accelerate by spreading significantly in its own rest frame. The expansion is driven by the magnetic pressure gradient and leads to relativistic relative velocities between the front and back of the shell. While the expansion is roughly symmetric in the centre of the momentum frame, in the laboratory frame, most of the energy and momentum remains in a region (or shell) of width Δ∼R0 at the head of the flow. This acceleration proceeds as Γ∼ (σ0R/R0)1/3 and σ∼σ2/30 (R/R0)-1/3 until reaching a coasting radius Rc∼R0σ20, where the kinetic energy becomes dominant: Γ∼σ0 and σ∼ 1 at Rc. The shell then starts coasting and spreading (radially), its width growing as Δ∼R0(R/Rc), causing its magnetization to drop as σ∼Rc/R at R > Rc. Given the typical variability time-scales of AGNs and GRBs, the magnetic acceleration in these sources is a combination of the quasi-steady-state collimation acceleration close to the source and the impulsive (conical or locally quasi-spherical) acceleration farther out. The interaction with the external medium, which can significantly affect the dynamics, is briefly addressed in the discussion.Peer reviewe

Soft end-point and mass corrections to the eta' g*g* vertex function

Power-suppressed corrections arising from end-point integration regions to the space-like vertex function of the massive eta'-meson virtual gluon transition eta' - g*g* are computed. Calculations are performed within the standard hard-scattering approach (HSA) and the running coupling method supplemented by the infrared renormalon calculus. Contributions to the vertex function from the quark and gluon contents of the eta' -meson are taken into account and the Borel resummed expressions for F_{eta' g*g*}(Q2,\omega ,\eta), as well as for F_{eta' g g*}}(Q^{2},\omega =\pm 1,\eta) and F_{eta' g*g*}(Q^{2},\omega =0,\eta) are obtained. It is demonstrated that the power-suppressed corrections \sim (\Lambda ^{2}/Q^{2})^{n}, in the explored range of the total gluon virtuality 1 <Q2 < 25 GeV2, considerably enhance the vertex function relative to the results found in the framework of the standard HSA with a fixed coupling. Modifications generated by the eta ' -meson mass effects are discussed

Power corrections to the π0γ\pi^0\gamma transition form factor and pion distribution amplitudes

Employing the standard hard-scattering approach and the running coupling method we calculate a class of power-suppressed corrections $\sim 1/Q^{2n},n=1,2,3,...$ to the electromagnetic $\pi^0\gamma$ transition form factor (FF) $Q^2F_{\pi\gamma}(Q^2)$ arising from the end-point $x \to 0,1$ integration regions. In the investigations we use a hard-scattering amplitude of the subprocess $\gamma+\gamma^{*} \to q +\bar{q}$, symmetrized under exchange $\mu_R^2 \leftrightarrow \bar{\mu}_R^2$ important for exclusive processes containing two external photons. In the computations the pion model distribution amplitudes (DA's) with one and two non-asymptotic terms are employed. The obtained predictions are compared with the CLEO data and constraints on the DA parameters $b_2(\mu_0^2)$ and $b_4(\mu_0^2)$ at the normalization point $\mu_0^2=1 GeV^2$ are extracted. Further restrictions on the pion DA's are deduced from the experimental data on the electromagnetic FF $F_{\pi}(Q^2)$.Comment: 23 pages, 6 figures; the version published in Phys. Rev. D69, 094010 (2004

Continuous star cluster formation in the spiral NGC 45

We determined ages for 52 star clusters with masses < 10^6 solar masses in the low surface brightness spiral galaxy NGC 45. Four of these candidates are old globular clusters located in the bulge. The remaining ones span a large age range. The cluster ages suggest a continuous star/cluster formation history without evidence for bursts, consistent with the galaxy being located in a relatively unperturbed environment in the outskirts of the Sculptor group.Comment: 4 pages, 3 figures. To appear in "Island Universes - Structure and Evolution of Disk Galaxies", Terschelling (Netherlands), July 200

The gauge-string duality and heavy ion collisions

I review at a non-technical level the use of the gauge-string duality to study aspects of heavy ion collisions, with special emphasis on the trailing string calculation of heavy quark energy loss. I include some brief speculations on how variants of the trailing string construction could provide a toy model of black hole formation and evaporation. This essay is an invited contribution to "Forty Years of String Theory" and is aimed at philosophers and historians of science as well as physicists.Comment: 21 page

An unusual cause of acute cardiogenic shock in the operating room

A 51-year-old man with a renal carcinoma with inferior vena cava (IVC) invasion was referred to our hospital for the performance of a radical nephrectomy with IVC thrombus excision. To prevent embolism, an IVC filter was implanted the day before surgery below the suprahepatic veins. On nephrectomy completion, the clinical status of the patient started to deteriorate and an unsuccessful attempt was made to excise the IVC thrombus. The patient developed profound refractory hypotension without significant bleeding and worsening splanchnic stasis was noted. A transesophageal echocardiogram was immediately performed in the operating room, revealing a hemispheric mass protruding from the IVC ostium to the right atrium, completely blocking all venous return. Volume depletion was evident by low left and right atrial volumes and increased septum mobility. No other abnormalities were found that could explain the shock, namely ventricular dysfunction or valvular disease. Cardiac surgery consultation was immediately obtained, ultimately deciding to perform a median sternotomy with direct exploration of right atrium. Under cardiopulmonary bypass, a 6-cm long thrombotic mass was identified, involving the IVC filter, blocking all lower body venous return; the removal of the mass reversed the shock. The patient had an uneventful recovery. Adverse outcomes associated with IVC filters are common. Our case highlights the importance of a team approach to rapid changes in hemodynamic status in the operating room, including the surgeon, the anesthesiologist, and the cardiologist. It also emphasizes the pivotal role of transesophageal echocardiogram in the clinical evaluation of severely unstable patien

Robustness of Sound Speed and Jet Quenching for Gauge/Gravity Models of Hot QCD

We probe the effectiveness and robustness of a simple gauge/gravity dual model of the QCD fireball that breaks conformal symmetry by constructing a family of similar geometries that solve the scalar/gravity equations of motion. This family has two parameters, one of which is associated to the temperature. We calculate two quantities, the speed of sound and the jet-quenching parameter. We find the speed of sound to be universal and robust over all the geometries when appropriate units are used, while the jet-quenching parameter varies significantly away from the conformal limit. We note that the overall structure of the jet-quenching depends strongly on whether the running scalar is the dilaton or not. We also discuss the variation of the scalar potential over our family of solutions, and truncate our results to where the associated error is small.Comment: 21 pages, 9 figures, LaTeX. v2:references added, minor correction to speed of sound; conclusions unchange

The impact of type 2 diabetes and Microalbuminuria on future cardiovascular events in patients with clinically manifest vascular disease from the Second Manifestations of ARTerial Disease (SMART) study

Aims Type 2 diabetes mellitus and microalbuminuria are important risk factors for cardiovascular disease (CVD). Whether these two complications are important and independent risk factors for future CVD events in a high-risk population with clinically manifest vascular disease is unknown. The objectives of this study were to examine the impact of Type 2 diabetes and microalbuminuria on future CVD events. Methods Patients with clinically manifest vascular disease (coronary, cerebral and peripheral vascular disease) from the Second Manifestation of Arterial disease study were followed up for 4 years. Data obtained from 1996–2006 were analysed. At baseline, there were 804 patients with Type 2 diabetes mellitus (mean age 60 years) and 2983 patients without. Incident CVD (n = 458) was defined as hospital-verified myocardial infarction, stroke, vascular death and the composite of these vascular events. Results Both Type 2 diabetes [hazard ratio (HR) 1.42, 95% confidence interval (CI) 1.16, 1.75] and microalbuminuria (HR 1.86, 95% CI 1.49, 2.33) increased the risk of new cardiovascular events in univariate analyses. From multivariable models, presence of diabetes remained significantly and independently related to incident CVD (HR 1.42, 95% CI 1.11, 1.80). Presence of microalbuminuria also remained significantly independently related to incident CVD (HR 1.38, 95% CI 1.07, 1.77). In diabetes-stratified analyses, the effect of microalbuminuria on CVD risk was observed only in patients with diabetes. In microalbuminuria-stratified analyses, the significant and independent effect of diabetes on CVD risk was shown only in the non-microalbuminuric group. Conclusions In this high-risk population, both microalbuminuria and Type 2 diabetes are important and independent risk factors for future CV

Quantum Hall Effect induced by electron-electron interaction in disordered GaAs layers with 3D spectrum

It is shown that the observed Quantum Hall Effect in epitaxial layers of heavily doped n-type GaAs with thickness (50-140 nm) larger the mean free path of the conduction electrons (15-30 nm) and, therefore, with a three-dimensional single-particle spectrum is induced by the electron-electron interaction. The Hall resistance R_xy of the thinnest sample reveals a wide plateau at small activation energy E_a=0.4 K found in the temperature dependence of the transverse resistance R_xx. The different minima in the transverse conductance G_xx of the different samples show a universal temperature dependence (logarithmic in a large range of rescaled temperatures T/T_0) which is reminiscent of electron-electron-interaction effects in coherent diffusive transport.Comment: 6 pages, 3 figures, 1 tabl