107 research outputs found
Off-shell scattering amplitudes in the double-logarithmic approximation
When scattering amplitudes are calculated in the double-logarithmic
approximation, it is possible to relate the double-logarithmic on-shell and
off-shell amplitudes. Explicit relations are obtained for scattering amplitudes
in QED, QCD, and the ElectroWeak Standard Model. The off-shell amplitudes are
considered in the hard and the Regge kinematic limits. We compare our results
in both the Feynman and Coulomb gauges.Comment: 15 pages, 3 figures; RevTeX
Asymptotic high energy behavior of the deeply virtual Compton scattering amplitude
We compute the deeply virtual Compton scattering (DVCS) amplitude for forward
and backward scattering in the asymptotic limit. Since this calculation does
not assume ordering of the transverse momenta, it includes important
logarithmic contributions that are beyond those summed by the DGLAP evolution.
These contributions lead to a power-like behavior for the forward DVCS
amplitude.Comment: Latex, 22 pages, 5 Figures; references enhanced; typos correcte
Resummation of double logarithms in electroweak high energy processes
At future linear collider experiments in the TeV range, Sudakov
double logarithms originating from massive boson exchange can lead to
significant corrections to the cross sections of the observable processes.
These effects are important for the high precision objectives of the Next
Linear Collider. We use the infrared evolution equation, based on a gauge
invariant dispersive method, to obtain double logarithmic asymptotics of
scattering amplitudes and discuss how it can be applied, in the case of broken
gauge symmetry, to the Standard Model of electroweak processes. We discuss the
double logarithmic effects to both non-radiative processes and to processes
accompanied by soft gauge boson emission. In all cases the Sudakov double
logarithms are found to exponentiate. We also discuss double logarithmic
effects of a non-Sudakov type which appear in Regge-like processes.Comment: 26 pages, 3 figures, Latex2
The heat capacity of nitrogen chains in grooves of single-walled carbon nanotube bundles
The heat capacity of bundles of closed-cap single-walled carbon nanotubes
(SWNT) with one-dimensional chains of nitrogen molecules adsorbed in the
grooves has been first experimentally studied at temperatures from 2K to 40K
using an adiabatic calorimeter. The contribution of nitrogen C(T) to the total
heat capacity has been separated. In the region 2-8K the behaviour of the curve
C(T) is qualitatively similar to the theoretical prediction of the phonon heat
capacity of 1D chains of krypton (Kr) atoms localized in the grooves of SWNT
bundles. Below 3K the dependence C(T) is linear. Above 8K the dependence C(T)
becomes steeper in comparison with the case of Kr atoms. This behaviour of the
heat capacity C(T) is due to the contribution of the rotational degrees of
freedom of the nitrogen molecules.Comment: 15 pages, 4 figure
Giant and tunable excitonic optical anisotropy in single-crystal CsPbX halide perovskites
During the last years, giant optical anisotropy demonstrated its paramount
importance for light manipulation which resulted in numerous applications
ranging from subdiffraction light guiding to switchable nanolasers. In spite of
recent advances in the field, achieving continuous tunability of optical
anisotropy remains an outstanding challenge. Here, we present a solution to the
problem through chemical alteration of the ratio of halogen atoms (X = Br or
Cl) in single-crystal CsPbX halide perovskites. It turns out that the
anisotropy originates from an excitonic resonance in the perovskite, which
spectral position and strength are determined by the halogens composition. As a
result, we manage to continually modify the optical anisotropy by 0.14. We also
discover that the halide perovskite can demonstrate optical anisotropy up to
0.6 in the visible range -- the largest value among non-van der Waals
materials. Moreover, our results reveal that this anisotropy could be in-plane
and out-of-plane, depending on perovskite shape -- rectangular and square.
Hence, it can serve as an additional degree of freedom for anisotropy
manipulation. As a practical demonstration, we created perovskite anisotropic
nanowaveguides and show a significant impact of anisotropy on high-order
guiding modes. These findings pave the way for halide perovskites as a
next-generation platform for tunable anisotropic photonics.Comment: 18 pages, 3 figure
Unusual congenital polydactyly in mini-pigs from the breeding group of the Institute of Cytology and Genetics (Novosibirsk, Russia)
The article describes a new phenomenon in the breeding group of mini-pigs at the Institute of Cytology and Genetics (ICG, Novosibirsk): polydactyly (extra digits), which is unusual because the additional digits are situated at the lateral surface of legs or at the lateral and medial ones. This anomaly was first found here in 2017 in adult animals intended for culling due to incorrect positioning of the legs caused by flexor tendon laxity and resulting in weight-bearing on the palmar surface of the proximal phalanges (“bear’s paw”). Therefore, the polydactyly of mini-pigs has a pronounced negative selection effect. A visual survey of the livestock was conducted, and a description of the detected anomaly was compiled. The polydactyly in mini-pigs is a stand-alone trait and is not part of any syndromes. Individuals with polydactyly may have extra digits either on pectoral or on pectoral and pelvic limbs. On thoracic limbs, there may be either one lateral digit or a lateral digit and a medially located rudimentary hooflet. On pelvic limbs, only lateral extra digits can occur. Anatomical and morphological analyses showed that the lateral extra digit is an anatomically complete (“mature”) structure, whereas the medial rudimentary digit consists of only a hooflet without other structures characteristic of normal digits. Cytological examination revealed no specific karyotypic features, except for Robertsonian translocation Rb 16;17 previously reported for the mini-pigs of the same livestock. Cytological findings indicated that the polydactyly and Robertsonian translocation are not linked genetically. Genealogical analysis and results of crosses are consistent with a working hypothesis of recessive inheritance of the trait. Overall, the study shows that this type of polydactyly is anatomically and morphologically unique and not typical of Sus scrofa. In this species, only polydactyly types with medial accessory toes have been described and are usually inherited as a dominant trait with incomplete penetrance. In our case, the results of test crosses indicate recessive inheritance of the trait with varying expression and incomplete penetrance, because of which poorly expressed phenotypes are not visually detectable
Small x behavior of parton distributions. A study of higher twist effects
Higher twist corrections to the structure function F_2 at small x are studied
for the case of a flat initial condition for the twist-two QCD evolution in the
next-to-leading order approximation. We present an analytical parameterization
of the contributions from the twist-two and higher twist operators of the
Wilson operator product expansion. Higher twist terms are evaluated using two
different approaches, one motivated by BFKL and the other motivated by the
renormalon formalism. The results of the latter approach are in very good
agreement with deep inelastic scattering data from HERA.Comment: 46 pages, 9 figures, typeset using REVTeX. Misprints corrected, new
results, discussions, references and acknowledgements added, 2 pictures
replaced. The conclusions remain unchange
Assessment of oral mucosa in persons with pathology of the gastrointestinal tract
The article analyzes the features of the oral mucosa in patients with diseases of the gastrointestinal tract in persons aged 25 to 45 years. The study of their prevalence showed that in this category of persons, recurrent oral afts are most often prevalent in 36% of cases of examinations. Timely diagnosis of pathology of the oral mucosa as a whole contributes to the development of effective pathogenetically justified complex diagnostic and therapeutic and preventive measures that reduce the risk of their development and progression and improve the quality of lifeВ статье проведен анализ особенностей состояния слизистой оболочки рта у пациентов с заболеваниями желудочно-кишечного тракта у лиц в возрасте от 25 до 45 лет. Изучение их распространенности показало, что у данной категории лиц чаще всего превалируют рецидивирующие афты полости рта в 36% случаев обследований. Своевременная диагностика патологии слизистой оболочки рта в целом способствует разработке эффективных патогенетически обоснованных комплексных диагностических и лечебно-профилактических мероприятий, которые снижают риск их развития и прогрессирования и улучшают качество жизни
Spin asymmetry A_1^d and the spin-dependent structure function g_1^d of the deuteron at low values of x and Q^2
We present a precise measurement of the deuteron longitudinal spin asymmetry
A_1^d and of the deuteron spin-dependent structure function g_1^d at Q^2 < 1
GeV^2 and 4*10^-5 < x < 2.5*10^-2 based on the data collected by the COMPASS
experiment at CERN during the years 2002 and 2003. The statistical precision is
tenfold better than that of the previous measurement in this region. The
measured A_1^d and g_1^d are found to be consistent with zero in the whole
range of x.Comment: 17 pages, 10 figure
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