24 research outputs found
Strong coupling constant to four loops in the analytic approach to QCD
The QCD analytic running coupling alpha_{an} which has no nonphysical
singularities for all Q^2>0 is considered for the initial perturbation theory
approximations up to four loop order. The finiteness of the analytic coupling
at zero is shown to be a consequence of the asymptotic freedom property of the
initial theory. The nonperturbative contributions to the analytic coupling are
extracted explicitly. For all Q>Lambda they are represented in the form of an
expansion in inverse powers of Euclidean momentum squared. The effective method
for a precise calculation of the analytic running coupling is developed on the
basis of the stated expansion. The energy scale evolution of the analytic
running coupling for the one- to four-loop cases is studied and the higher loop
stability and low dependence on the quark threshold matching conditions in
comparison with the perturbative running coupling were found. Normalizing the
analytic running coupling at the scale of the rest mass of the Z boson with the
world average value of the strong coupling constant,
alpha_{an}(M_Z^2)=0.1181^{+0.002}_{-0.002}, one obtains as a result of the
energy scale evolution of the analytic running coupling alpha_{an}(M_tau^2)=
0.2943^{+0.0111}_{-0.0106} that is notably lower than the estimations of the
coupling strength available at the scale of the mass of the tau lepton.Comment: 30 pages, LATEX, 4 tables, 8 figure
Nonperturbative Contributions in an Analytic Running Coupling of QCD
In the framework of analytic approach to QCD the nonperturbative
contributions in running coupling of strong interaction up to 4-loop order are
obtained in an explicit form. For all they are shown to be
represented in the form of an expansion in inverse powers of Euclidean momentum
squared. The expansion coefficients are calculated for different numbers of
active quark flavors and for different number of loops taken into
account. On basis of the stated expansion the effective method for precise
calculation of the analytic running coupling can be developed.Comment: 9 pages, LaTeX, 1 table, 1 eps figur
Analyticity and Minimality of Nonperturbative Contributions in Perturbative region for
It is shown, that the possibility of a freezing of QCD running coupling
constant at zero in the approach with "forced analyticity" can not be in accord
with Schwinger-Dyson equation for gluon propagator. We propose to add to the
analytic expression the well-known infrared singular term as well as
pole term corresponding to "excited gluon". With this example we formulate the
principle of minimality of nonperturbative contributions in perturbative
(ultraviolet) region, which allows us to fix ambiguities in introduction of
nonperturbative terms and maintain the finiteness of the gluon condensate. As a
result we obtain estimates of the gluon condensate, which quite agree with
existing data. The nonzero effective mass of the "excited gluon" leads also to
some interesting qualitative consequences.Comment: 11 pages, LATEX, 1 Table (calculation of gluon condensate corrected,
Table extended
Genome Characterization of a Pathogenic Porcine Rotavirus B Strain Identified in Buryat Republic, Russia in 2015
Citation: Alekseev, K.P.; Penin, A.A.; Mukhin, A.N.; Khametova, K.M.; Grebennikova, T.V.; Yuzhakov, A.G.; Moskvina, A.S.; Musienko, M.I.; Raev, S.A.; Mishin, A.M.; Kotelnikov, A.P.; Verkhovsky, O.A.; Aliper, T.I.; Nepoklonov, E.A.; Herrera-Ibata, D.M.; Shepherd, F.K.; Marthaler, D.G. Genome Characterization of a Pathogenic Porcine Rotavirus B Strain Identified in Buryat Republic, Russia in 2015. Pathogens 2018, 7, 46.An outbreak of enteric disease of unknown etiology with 60% morbidity and 8% mortality in weaning piglets occurred in November 2015 on a farm in Buryat Republic, Russia. Metagenomic sequencing revealed the presence of rotavirus B in feces from diseased piglets while no other pathogens were identified. Clinical disease was reproduced in experimentally infected piglets, yielding the 11 RVB gene segments for strain Buryat15, with an RVB genotype constellation of G12-P[4]-I13-R4-C4-M4-A8-N10-T4-E4-H7. This genotype constellation has also been identified in the United States. While the Buryat15 VP7 protein lacked unique amino acid differences in the predicted neutralizing epitopes compared to the previously published swine RVB G12 strains, this report of RVB in Russian swine increases our epidemiological knowledge on the global prevalence and genetic diversity of RVB
Challenges in QCD matter physics - The Compressed Baryonic Matter experiment at FAIR
Substantial experimental and theoretical efforts worldwide are devoted to
explore the phase diagram of strongly interacting matter. At LHC and top RHIC
energies, QCD matter is studied at very high temperatures and nearly vanishing
net-baryon densities. There is evidence that a Quark-Gluon-Plasma (QGP) was
created at experiments at RHIC and LHC. The transition from the QGP back to the
hadron gas is found to be a smooth cross over. For larger net-baryon densities
and lower temperatures, it is expected that the QCD phase diagram exhibits a
rich structure, such as a first-order phase transition between hadronic and
partonic matter which terminates in a critical point, or exotic phases like
quarkyonic matter. The discovery of these landmarks would be a breakthrough in
our understanding of the strong interaction and is therefore in the focus of
various high-energy heavy-ion research programs. The Compressed Baryonic Matter
(CBM) experiment at FAIR will play a unique role in the exploration of the QCD
phase diagram in the region of high net-baryon densities, because it is
designed to run at unprecedented interaction rates. High-rate operation is the
key prerequisite for high-precision measurements of multi-differential
observables and of rare diagnostic probes which are sensitive to the dense
phase of the nuclear fireball. The goal of the CBM experiment at SIS100
(sqrt(s_NN) = 2.7 - 4.9 GeV) is to discover fundamental properties of QCD
matter: the phase structure at large baryon-chemical potentials (mu_B > 500
MeV), effects of chiral symmetry, and the equation-of-state at high density as
it is expected to occur in the core of neutron stars. In this article, we
review the motivation for and the physics programme of CBM, including
activities before the start of data taking in 2022, in the context of the
worldwide efforts to explore high-density QCD matter.Comment: 15 pages, 11 figures. Published in European Physical Journal