437 research outputs found
Quasifission at extreme sub-barrier energies
With the quantum diffusion approach the behavior of the capture cross-section
is investigated in the reactions Mo + Mo, Ru +
Ru, Pd + Pd, and Kr + Sn at deep
sub-barrier energies which are lower than the ground state energies of the
compound nuclei. Because the capture cross section is the sum of the complete
fusion and quasifission cross sections, and the complete fusion cross section
is zero at these sub-barrier energies, one can study experimentally the unique
quasifission process in these reactions after the capture.Comment: 3 pages, 3 figure
Azimuthal asymmetries in QCD hard scattering: infrared safe but divergent
We consider high-mass systems of two or more particles that are produced by
QCD hard scattering in hadronic collisions. We examine the azimuthal
correlations between the system and one of its particles. We point out that the
perturbative QCD computation of such azimuthal correlations and asymmetries can
lead to divergent results at fixed perturbative orders. The fixed-order
divergences affect basic (and infrared safe) quantities such as the total cross
section at fixed (and arbitrary) values of the azimuthal-correlation angle
. Examples of processes with fixed-order divergences are heavy-quark
pair production, associated production of vector bosons and jets, dijet and
diboson production. A noticeable exception is the production of high-mass
lepton pairs through the Drell--Yan mechanism of quark-antiquark annihilation.
However, even in the Drell--Yan process, fixed-order divergences arise in the
computation of QED radiative corrections. We specify general conditions that
produce the divergences by discussing their physical origin in fixed-order
computations. We show lowest-order illustrative results for
asymmetries (with ) in top-quark pair production and associated
production of a vector boson and a jet at the LHC. The divergences are removed
by a proper all-order resummation procedure of the perturbative contributions.
Resummation leads to azimuthal asymmetries that are finite and computable. We
present first quantitative results of such a resummed computation for the
asymmetry in top-quark pair production at the LHC.Comment: 43 pages, 5 eps figure
Geometrically nonlinear static theory of micropolar elastic thin shallow shells
Abstract Micropolar thin shallow shells are considered, the elastic deflections are comparable to their thickness and at the same time are small in relation to the basic size, at the same time as the small angles of relation of the normal to the middle surface before deformation, and their free rotations. Thus, in the deformation tensor and bending-torsion tensor takes into account not only linear but also the nonlinear terms in the gradients of displacements. The hypothesis method is developed and on this base static applied theory of micropolar elastic flexible shallow shells are constructed. Some practical problems are solved
Sub-barrier capture reactions with O and Ca beams
Various sub-barrier capture reactions with beams O and Ca
are treated within the quantum diffusion approach. The role of neutron transfer
in these capture reactions is discussed. The quasielastic and capture barrier
distributions are analyzed and compared with the recent experimental data.Comment: 8 pages, 9 figures, will be published in EPJA. arXiv admin note:
substantial text overlap with arXiv:1211.433
Sub-barrier capture reactions with O beams
Various sub-barrier capture reactions with beams O are treated
within the quantum diffusion approach. The role of neutron transfer in these
capture reactions is discussed.Comment: 3 pages, 4 figure
To the center of cold spot with Planck
The structure of the cold spot, of a non-Gaussian anomaly in the cosmic
microwave background (CMB) sky first detected by Vielva et al. is studied using
the data by Planck satellite. The obtained map of the degree of stochasticity
(K-map) of CMB for the cold spot, reveals, most clearly in 100 GHz band, a
shell-type structure with a center coinciding with the minima of the
temperature distribution. The shell structure is non-Gaussian at a 4\sigma
confidence level. Such behavior of the K-map supports the void nature of the
cold spot. The applied method can be used for tracing voids that have no
signatures in redshift surveys.Comment: A & A (in press), 4 pages, 5 figures; to match the published versio
Threshold energy for sub-barrier fusion hindrance phenomenon
The relationship between the threshold energy for a deep sub-barrier fusion
hindrance phenomenon and the energy at which the regime of interaction changes
(the turning-off of the nuclear forces and friction) in the sub-barrier capture
process, is studied within the quantum diffusion approach. The quasielastic
barrier distribution is shown to be a useful tool to clarify whether the slope
of capture cross section changes at sub-barrier energies.Comment: 4 pages, 4 figures (accepted in Eur. Phys. J. A
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