COVID-19 transmission risk factors.

We analyze risk factors correlated with the initial transmission growth rate of the recent COVID-19 pandemic in different countries. The number of cases follows in its early stages an almost exponential expansion; we chose as a starting point in each country the first day di with 30 cases and we fitted for 12 days, capturing thus the early exponential growth. We looked then for linear correlations of the exponents α with other variables, for a sample of 126 countries. We find a positive correlation, i.e. faster spread of COVID-19, with high confidence level with the following variables, with respective p-value: low Temperature (4⋅10-7), high ratio of old vs. working-age people (3⋅10-6), life expectancy (8⋅10-6), number of international tourists (1⋅10-5), earlier epidemic starting date di (2⋅10-5), high level of physical contact in greeting habits (6⋅10-5), lung cancer prevalence (6⋅10-5), obesity in males (1⋅10-4), share of population in urban areas (2⋅10-4), cancer prevalence (3⋅10-4), alcohol consumption (0.0019), daily smoking prevalence (0.0036), and UV index (0.004, 73 countries). We also find a correlation with low Vitamin D serum levels (0.002-0.006), but on a smaller sample, ∼50 countries, to be confirmed on a larger sample. There is highly significant correlation also with blood types: positive correlation with types RH- (3⋅10-5) and A+ (3⋅10-3), negative correlation with B+ (2⋅10-4). We also find positive correlation with moderate confidence level (p-value of 0.02∼0.03) with: CO2/SO emissions, type-1 diabetes in children, low vaccination coverage for Tuberculosis (BCG). Several of the above variables are correlated with each other, and so they are likely to have common interpretations. We thus performed a Principal Component Analysis, to find the significant independent linear combinations of such variables. The variables with loadings of at least 0.3 on the significant PCA are: greeting habits, urbanization, epidemic starting date, number of international tourists, temperature, lung cancer, smoking, and obesity in males. We also analyzed the possible existence of a bias: countries with low GDP-per capita might have less intense testing, and we discuss correlation with the above variables.

Mass hierarchy in identified particle distributions in proton-lead collisions.

We study the mass dependence for identified particle average transverse momentum and harmonic flow coefficients in proton-lead (p-Pb) collisions, recently measured at the LHC. The collective mechanism in the p-Pb system predicts a specific mass ordering in these observables: the growth of the average transverse momentum with the particle mass and a mass splitting of the elliptic flow coefficient, i.e., smaller differential elliptic flow of protons than pions for p(T)<2 GeV. This provides an opportunity to distinguish between the collective scenario and the mechanism based on the initial gluon dynamics in the evolution of the p-Pb system.

Photon signals from quarkyonic matter.

We calculate the bremsstrahlung photon spectrum emitted from dynamically evolving "quarkyonic" matter and compare this spectrum with that of a high chemical potential quark-gluon plasma as well as to a hadron gas. We find that the transverse momentum distribution and the harmonic coefficient is markedly different in the three cases. The transverse momentum distribution of quarkyonic matter can be fit with an exponential but is markedly steeper than the distribution expected for the quark-gluon plasma or a hadron gas, even at the lower temperatures expected in the critical point region. The quarkyonic elliptic flow coefficient fluctuates randomly from event to event and within the same event at different transverse momenta. The latter effect, which can be explained by the shape of quark wave functions within quarkyonic matter, might be considered as a quarkyonic matter signature, provided that the initial temperature is low enough that the quarkyonic regime dominates over deconfinement effects and the reaction-plane flow can be separated from the fluctuating component.

Percolation transition in Yang-Mills matter at a finite number of colors.

We examine baryonic matter at a quark chemical potential of the order of the confinement scale µ(q)∼Λ(QCD). In this regime, quarks are supposed to be confined but baryons are close to the "tightly packed limit" where they nearly overlap in configuration space. We show that this system will exhibit a percolation phase transition when varied in the number of colors N(c): at high N(c), large distance correlations at the quark level are possible even if the quarks are essentially confined. At low N(c), this does not happen. We discuss the relevance of this for dense nuclear matter, and argue that our results suggest a new "phase transition," varying N(c) at constant µ(q).

Universal flow-driven conical emission in ultrarelativistic heavy-ion collisions.

The double-peak structure observed in soft-hard hadron correlations is commonly interpreted as a signature for a Mach cone generated by a supersonic jet interacting with the hot and dense medium created in ultrarelativistic heavy-ion collisions. We show that it can also arise due to averaging over many jet events in a transversally expanding background. We find that the jet-induced away-side yield does not depend on the details of the energy-momentum deposition in the plasma, the jet velocity, or the system size. Our claim can be experimentally tested by comparing soft-hard correlations induced by heavy-flavor jets with those generated by light-flavor jets.

Di-jet conical correlations associated with heavy quark jets in anti-de sitter space/conformal field theory correspondence.

We show that far zone Mach and diffusion wake "holograms" produced by supersonic strings in anti-de Sitter space/conformal field theory (AdS/CFT) correspondence do not lead to observable conical angular correlations in the strict N_{c}-->infinity supergravity limit if Cooper-Frye hadronization is assumed. However, a special nonequilibrium "neck" zone near the jet is shown to produce an apparent sonic boom azimuthal angle distribution that is roughly independent of the heavy quark's velocity. Our results indicate that a measurement of the dependence of the away-side correlations on the velocity of associated identified heavy quark jets at the BNL Relativistic Heavy Ion Collider and CERN LHC will provide a direct test of the nonperturbative dynamics involved in the coupling between jets and the strongly coupled quark-gluon plasma implied by AdS/CFT correspondence.