48 research outputs found
Resumming double logarithms in the QCD evolution of color dipoles
The higher-order perturbative corrections, beyond leading logarithmic
accuracy, to the BFKL evolution in QCD at high energy are well known to suffer
from a severe lack-of-convergence problem, due to radiative corrections
enhanced by double collinear logarithms. Via an explicit calculation of Feynman
graphs in light cone (time-ordered) perturbation theory, we show that the
corrections enhanced by double logarithms (either energy-collinear, or double
collinear) are associated with soft gluon emissions which are strictly ordered
in lifetime. These corrections can be resummed to all orders by solving an
evolution equation which is non-local in rapidity. This equation can be
equivalently rewritten in local form, but with modified kernel and initial
conditions, which resum double collinear logs to all orders. We extend this
resummation to the next-to-leading order BFKL and BK equations. The first
numerical studies of the collinearly-improved BK equation demonstrate the
essential role of the resummation in both stabilizing and slowing down the
evolution.Comment: 16 pages, 5 figure
Quark contribution to the gluon Regge trajectory at NLO from the high energy effective action
The two loop (NLO) diagrams with quark content contributing to the gluon
Regge trajectory are computed within the framework of Lipatov's effective
action for QCD, using the regularization procedure for longitudinal
divergencies recently proposed by two of us in
http://arXiv.org/abs/arXiv:1110.6741. Perfect agreement with previous results
in the literature is found, providing a robust check of the regularization
prescription and showing that the high energy effective action is a very useful
computational tool in the quasi-multi-Regge limit.Comment: 12 page, many figure
Continuous population-level monitoring of SARS-CoV-2 seroprevalence in a large European metropolitan region.
Effective public health measures against SARS-CoV-2 require granular knowledge of population-level immune responses. We developed a Tripartite Automated Blood Immunoassay (TRABI) to assess the IgG response against three SARS-CoV-2 proteins. We used TRABI for continuous seromonitoring of hospital patients and blood donors (n = 72'250) in the canton of Zurich from December 2019 to December 2020 (pre-vaccine period). We found that antibodies waned with a half-life of 75 days, whereas the cumulative incidence rose from 2.3% in June 2020 to 12.2% in mid-December 2020. A follow-up health survey indicated that about 10% of patients infected with wildtype SARS-CoV-2 sustained some symptoms at least twelve months post COVID-19. Crucially, we found no evidence of a difference in long-term complications between those whose infection was symptomatic and those with asymptomatic acute infection. The cohort of asymptomatic SARS-CoV-2-infected subjects represents a resource for the study of chronic and possibly unexpected sequelae
The CARMENES search for exoplanets around M dwarfs: Two planets on opposite sides of the radius gap transiting the nearby M dwarf LTT 3780
We present the discovery and characterisation of two transiting planets observed by the Transiting Exoplanet Survey Satellite (TESS) orbiting the nearby (dâ â 22 pc), bright (J â 9 mag) M3.5 dwarf LTT 3780 (TOI-732). We confirm both planets and their association with LTT 3780 via ground-based photometry and determine their masses using precise radial velocities measured with the CARMENES spectrograph. Precise stellar parameters determined from CARMENES high-resolution spectra confirm that LTT 3780 is a mid-M dwarf with an effective temperature of Teff = 3360 ± 51 K, a surface gravity of log gâ = 4.81 ± 0.04 (cgs), and an iron abundance of [Fe/H] = 0.09 ± 0.16 dex, with an inferred mass of Mâ = 0.379 ± 0.016M· and a radius of Râ = 0.382 ± 0.012R·. The ultra-short-period planet LTT 3780 b (Pb = 0.77 d) with a radius of 1.35-0.06+0.06 R·, a mass of 2.34-0.23+0.24 M·, and a bulk density of 5.24-0.81+0.94 g cm-3 joins the population of Earth-size planets with rocky, terrestrial composition. The outer planet, LTT 3780 c, with an orbital period of 12.25 d, radius of 2.42-0.10+0.10 R·, mass of 6.29-0.61+0.63 M·, and mean density of 2.45-0.37+0.44 g cm-3 belongs to the population of dense sub-Neptunes. With the two planets located on opposite sides of the radius gap, this planetary system is anexcellent target for testing planetary formation, evolution, and atmospheric models. In particular, LTT 3780 c is an ideal object for atmospheric studies with the James Webb Space Telescope (JWST)
Particle production with rapidity correlations in proton-nucleus collisions
We illustrate how a generalization of the JIMWLK formalism which treats independently the direct and complex conjugate amplitudes can be used to describe semi-inclusive multiparticle production with rapidity correlations in pA collisions. The evolution equations that are obtained with this formalism are susceptible of numerical implementation as a Langevin process
Collinearly-improved BK evolution meets the HERA data
In a previous publication, we have established a collinearly-improved version of the Balitsky-Kovchegov (BK) equation, which resums to all orders the radiative corrections enhanced by large double transverse logarithms. Here, we study the relevance of this equation as a tool for phenomenology, by confronting it to the HERA data. To that aim, we first improve the perturbative
accuracy of our resummation, by including two classes of single-logarithmic corrections: those generated by the first non-singular terms in the DGLAP splitting functions and those expressing the one-loop running of the QCD coupling. The equation thus obtained includes all the next-to-leading order corrections to the BK equation which are enhanced by (single or double) collinear logarithms. We then use numerical solutions to this equation to fit the HERA data for the electron-proton reduced cross-section at small Bjorken x. We obtain good quality fits for physically acceptable initial conditions. Our best fit, which shows a good stability up to virtualities as large as Q^2=400 GeV^2 for the exchanged photon, uses as an initial condition the running-coupling version of the McLerran-Venugopalan model, with the QCD coupling running according to the smallest dipole prescription