183 research outputs found
The strength of small-instanton amplitudes in gauge theories with compact extra dimensions
We study instanton effects in theories with compact extra dimensions. We
perform an instanton calculation in a 5d theory on a circle of radius R, with
gauge, scalar, and fermion fields in the bulk of the extra dimension. We show
that, depending on the matter content, instantons of size rho << R can dominate
the amplitude. Using deconstruction as an ultraviolet definition of the theory
allows us to show, in a controlled approximation, that for a small number of
bulk fermions, the amplitude for small size instantons exponentially grows as
e^{O(1)R/rho}.Comment: Title modified, references added, typos corrected. Version to appear
in JHEP. 24 pages, 1 figur
Amplification of Magnetooptical Response in the «Nanocomposite-Bismuth Telluride» Multilayer System
The presented work is devoted to the study of magneto-optical properties of «nanocompositesemiconductor
» ((Co40Fe40B20)33.9(SiO2)66.1/Te3Bi2)) multilayer structures. It has been found, that the adding
of Te3Bi2 spacer regardless of composite’s compound increases a magneto-optical response and the amplification
of it is the biggest among the other spacers such as Si, SiC and Cu. There has also been established
a good correlation between thickness dependencies of magnetooptical (MO) and magnetotransport properties.
This correlation is related to the peculiarities of interface forming at the «FM-granule - semiconductor
» edge and to percolation process in multilayer structures.
When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3533
Domain Walls Zoo in Supersymmetric QCD
Solving numerically the equations of motion for the effective lagrangian
describing supersymmetric QCD with the SU(2) gauge group, we find a menagerie
of complex domain wall solutions connecting different chirally asymmetric
vacua. Some of these solutions are BPS saturated walls; they exist when the
mass of the matter fields does not exceed some critical value m < m* <
4.67059... There are also sphaleron branches (saddle points of the ebergy
functional). In the range m* < m < m** \approx 4.83, one of these branches
becomes a local minimum (which is not a BPS saturated one). At m > m*, the
complex walls disappear altogether and only the walls connecting a chirally
asymmetric vacuum with the chirally symmetric one survive.Comment: 23 pages, LaTeX, 11 figure
Analysis of the selective value of promising Melissa officinalis L. subsp. altissima (Smith.) Arcang variety
The aim of this research was to study a promising MD 1–17 Melissa officinalis L.
subsp. altissima (Smith.) Arcang. variety sample obtained in the collection of the gene pool of
the Research Institute of Agriculture of Crimea (RIAC) in comparison with Krymchanka
(selected in the RIAC) and Lada (selected in the All-Russian research Institute of medicinal and
aromatic plants(VILAR) varieties of lemon balm M. officinalis L. subsp. officinalis. In 2017–
2019, in the Department of Essential Oil and Medicinal Plants of the RIAC,a competitive variety
trial of lemon balm varieties was conducted in accordance with the methodological
recommendations for the selection of essential-oil plants. A territory where this study was
conducted belongs to one of the five agroclimatic regions – the upper piedmont, warm, not
enough humid; to the northern subarea with moderately mild winters. Weather conditions during
the years of competitive variety trial varied significantlya fact that allowed assessing the
adaptability of studied variety samples and forecasting the nature of productivity potential
realization in different growing conditions. As a result, it was found that MD 1–17 variety sample
significantly exceeds other varieties in terms of yield of fresh raw materials, on average, by 62.2
and 77.4%, and in yield of air-dried raw materials, on average, by 32.2 and 52.2%, respectively.
In terms of obtaining essential oil from air-dried raw materials, this variety sample exceeds the
best in this parameter Crimean variety Krymchanka by 56.3%. Basic components of its essential
oil are caryophyllene (25.3–35.9%) and germacrene D (17.7–31.2%) with almost complete
absence or insignificant amount of citral (0.1–7.3%); the proportion of latter in essential oils of
Krymchanka and Lada varieties can reach 36.6% or more. Novelty of this study includes the
creation of the first variety of a new promising essential oil plant –M. altissima. Raw materials
of this variety and products of its processing may be of interest for different ways of use, including
the perfumery and cosmetics industry, for food purposes as a component of tea compositions, etc
Nonperturbative Corrections to Inclusive Beauty and Charm Decays: QCD versus Phenomenological Models
We present a selfconsistent method for treating nonperturbative effects in
inclusive nonleptonic and semileptonic decays of heavy flavour hadrons. These
effects give rise to powerlike corrections , with
denoting the heavy quark mass.The leading correction to the semileptonic
branching ratio occurs for n=2. It is expressed in terms of the
vector-pseudoscalar mass splitting: \delta BR\ind{sl}/BR\ind{sl} \simeq
BR\ind{nl}\, \cdot \,6\,(\,(M_V^2-M_P^2)/m_Q^2)\cdot (c_+^2 - c_-^2)/2N_c and
yields a {\it reduction} of BR\ind{sl}. This nonperturbative correction
contributes to the nonleptonic width with a sign opposite to that of the
perturbative terms that are non-leading in . In beauty decays the former
reduces the latter by 20 \% whereas in charm decays they more or less cancel.
This leads to a {\it reduction} of BR\ind{sl} by no more than 10 \% in beauty
decays and by a factor of roughly two in charm decays. We confront these
results with those obtained from phenomenological models of heavy flavour
decays and find that such models are unable to mimic these leading corrections
by a specific choice of quark masses or by invoking Fermi motion.Comment: 11 pages (2 figs are not included), Latex file, FERMILAB-PUB-92/158-T
UND-HEP-92-BIG04 TPI-MINN-92/30-
Pion form factor and QCD sum rules: case of pseudoscalar current
We present an analysis of QCD sum rules for pion form factor in
next-to-leading order of perturbation theory for the case of pseudoscalar pion
currents. The essential instanton contribution is reanalysed with account for
present more accurate values of parameters entering Single Instanton
Approximation (SIA). The theoretical curve obtained for Q^2 dependence of pion
form factor is in a good agreement with existing experimental data. To
calculate NLO corrections for double spectral densities we developed an
effective computational technic. The details of the method together with the
results for pion form factor in a more theoretically clean case of axial
interpolating currents will be presented elsewhere.Comment: LaTeX file, 12 pages, 5 figures, uses axodraw.st
Spectral representation and QCD sum rules for nucleon at finite temperature
We examine the problem of constructing spectral representations for two point
correlation functions, needed to write down the QCD sum rules in the medium. We
suggest constructing them from the Feynman diagrams for the correlation
functions. As an example we use this procedure to write the QCD sum rules for
the nucleon current at finite temperature
The type numbers of closed geodesics
A short survey on the type numbers of closed geodesics, on applications of
the Morse theory to proving the existence of closed geodesics and on the recent
progress in applying variational methods to the periodic problem for Finsler
and magnetic geodesicsComment: 29 pages, an appendix to the Russian translation of "The calculus of
variations in the large" by M. Mors
Can Theta/N Dependence for Gluodynamics be Compatible with 2 pi Periodicity in Theta ?
In a number of field theoretical models the vacuum angle \theta enters
physics in the combination \theta/N, where N stands generically for the number
of colors or flavors, in an apparent contradiction with the expected 2 \pi
periodicity in \theta. We argue that a resolution of this puzzle is related to
the existence of a number of different \theta dependent sectors in a finite
volume formulation, which can not be seen in the naive thermodynamic limit V ->
\infty. It is shown that, when the limit V -> \infty is properly defined,
physics is always 2 \pi periodic in \theta for any integer, and even rational,
values of N, with vacuum doubling at certain values of \theta. We demonstrate
this phenomenon in both the multi-flavor Schwinger model with the bosonization
technique, and four-dimensional gluodynamics with the effective Lagrangian
method. The proposed mechanism works for an arbitrary gauge group.Comment: minor changes in the discussion, a few references are adde
- …