QCD Corrections to Electroweak Vector Boson Scattering at Small Scattering Angles

We investigate the role of a certain class of QCD corrections to electroweak vector boson scattering at small scattering angles and large energies. These are present since, from the perturbative analysis, the vector bosons may dissociate into quark-antiquark pairs giving rise to colour dipoles interacting through gluon exchanges. After the computation of the vector boson impact factors, we present expressions for the lowest order QCD scattering amplitude and for the leading logarithmic BFKL amplitude. Particularly we discuss numerical results for the process $\gamma\gamma\to ZZ$. The QCD corrections to the cross section resulting from the interference with the electroweak ones are estimated and compared with the leading pure electroweak part. Corrections resulting from the leading log BFKL amplitude are of the order of few percent already at the $0.5 - 1$ TeV energy range.Comment: 21 pages,9 figures, discussion on the helicity-flip impact factors added, typos correcte

Discovery of a ~7 Hz Quasi-Periodic Oscillation in the low-luminosity low-mass X-ray binary 4U 1820-30

We have discovered a 7.06+-0.08 Hz quasi-periodic oscillation (QPO) in the X-ray flux of the low-luminosity low-mass X-ray binary (LMXB) and atoll source 4U 1820-30. This QPO was only observable at the highest observed mass accretion rate, when the source was in the uppermost part of the banana branch, at a 2-25 keV luminosity of 5.4x10^37 erg/s (for a distance of 6.4 kpc). The QPO had a FWHM of only 0.5+-0.2 Hz during small time intervals (32-s of data), and showed erratic shifts in the centroid frequency between 5.5 and 8 Hz. The rms amplitude over the energy range 2-60 keV was 5.6%+-0.2%. The amplitude increased with photon energy from 3.7%+-0.5% between 2.8 and 5.3 keV to 7.3%+-0.6% between 6.8 and 9.3 keV, above which it remained approximately constant at ~7%. The time lag of the QPO between 2.8-6.8 and 6.8-18.2 keV was consistent with being zero (-1.2+-3.4 ms). The properties of the QPO (i.e., its frequency and its presence only at the highest observed mass accretion rate) are similar to those of the 5-20 Hz QPO observed in the highest luminosity LMXBs (the Z sources) when they are accreting near the Eddington mass accretion limit. If this is indeed the same phenomenon, then models explaining the 5-20 Hz QPO in the Z sources, which require the near-Eddington accretion rates, will not hold. Assuming isotropic emission, the 2-25 keV luminosity of 4U 1820-30 at the time of the 7 Hz QPOs is at maximum only 40% (for a companion star with cosmic abundances), but most likely ~20% (for a helium companion star) of the Eddington accretion limit.Comment: Accepted for publication in ApJ Letters (6 pages, including 3 figures

Type 2 Diabetes Mellitus and COVID-19: A Narrative Review

The pandemic of coronavirus disease (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has involved more than one hundred million individuals, including more than two million deaths. Diabetes represents one of the most prevalent chronic conditions worldwide and significantly increases the risk of hospitalization and death in COVID-19 patients. In this review, we discuss the prevalence, the pathophysiological mechanisms, and the outcomes of COVID-19 infection in people with diabetes. We propose a rationale for using drugs prescribed in patients with diabetes and some pragmatic clinical recommendations to deal with COVID-19 in this kind of patient

Suprathermal particle addition to solar wind pressure: possible influence on magnetospheric transmissivity of low energy cosmic rays?

Energetic (suprathermal) solar particles, accelerated in the interplanetary medium, contribute to the solar wind pressure, in particular during high solar activity periods. We estimated the effect of the increase of solar wind pressure due to suprathermal particles on magnetospheric transmissivity of galactic cosmic rays in the case of one recent solar event

Comment on Mie Scattering from a Sonoluminescing Bubble with High Spatial and Temporal Resolution [Physical Review E 61, 5253 (2000)]

A key parameter underlying the existence of sonoluminescence (SL)is the time relative to SL at which acoustic energy is radiated from the collapsed bubble. Light scattering is one route to this quantity. We disagree with the statement of Gompf and Pecha that -highly compressed water causes the minimum in scattered light to occur 700ps before SL- and that this effect leads to an overestimate of the bubble wall velocity. We discuss potential artifacts in their experimental arrangement and correct their description of previous experiments on Mie scattering.Comment: 10 pages, 2 figure

SOFIA/EXES Observations of Water Absorption in the Protostar AFGL 2591 at High Spectral Resolution

We present high spectral resolution (~3 km/s) observations of the nu_2 ro-vibrational band of H2O in the 6.086--6.135 micron range toward the massive protostar AFGL 2591 using the Echelon-Cross-Echelle Spectrograph (EXES) on the Stratospheric Observatory for Infrared Astronomy (SOFIA). Ten absorption features are detected in total, with seven caused by transitions in the nu_2 band of H2O, two by transitions in the first vibrationally excited nu_2 band of H2O, and one by a transition in the nu_2 band of H2{18}O. Among the detected transitions is the nu_2 1(1,1)--0(0,0) line which probes the lowest lying rotational level of para-H2O. The stronger transitions appear to be optically thick, but reach maximum absorption at a depth of about 25%, suggesting that the background source is only partially covered by the absorbing gas, or that the absorption arises within the 6 micron emitting photosphere. Assuming a covering fraction of 25%, the H2O column density and rotational temperature that best fit the observed absorption lines are N(H2O)=(1.3+-0.3)*10^{19} cm^{-2} and T=640+-80 K.Comment: 6 pages, 3 figures, 1 table, accepted for publication in ApJ

Mass and radius estimation for the neutron star in X-ray burster 4U 1820-30

We present a new method for determining masses and radii of neutron stars residing in thermo-nuclear X-ray burst sources. To illustrate this method we apply it to a burst from the source 4U 1820-30 recorded by the Rossi X-Ray Timing Explorer. Fits of the observed X-ray spectra to grids of Comptonised model atmospheres yield estimates for the mass and radius of the neutron star, M=1.3 \pm 0.6 M_sol and R=11^+3_-2 km, respectively.Comment: MNRAS in prin