1,071 research outputs found
Analytical evaluation of certain on-shell two-loop three-point diagrams
An analytical approach is applied to the calculation of some
dimensionally-regulated two-loop vertex diagrams with essential on-shell
singularities. Such diagrams are important for the evaluation of QED
corrections to the muon decay, QCD corrections to top quark decays t->W^{+}b,
t->H^{+}b, etc.Comment: 2 pages, LaTeX, contribution to proceedings of ACAT2002 (Moscow, June
2002
Spin-resonance modes of the spin-gap magnet TlCuCl_3
Three kinds of magnetic resonance signals were detected in crystals of the
spin-gap magnet TlCuCl_3.
First, we have observed the microwave absorption due to the excitation of the
transitions between the singlet ground state and the excited triplet states.
This mode has the linear frequency-field dependence corresponding to the
previously known value of the zero-field spin-gap of 156 GHz and to the closing
of spin-gap at the magnetic field H_c of about 50 kOe.
Second, the thermally activated resonance absorption due to the transitions
between the spin sublevels of the triplet excitations was found. These
sublevels are split by the crystal field and external magnetic field.
Finally, we have observed antiferromagnetic resonance absorption in the
field-induced antiferromagnetic phase above the critical field H_c. This
resonance frequency is strongly anisotropic with respect to the direction of
the magnetic field.Comment: v.2: typo correction (one of the field directions was misprinted in
the v.1
NIR Microscopy Possibilities for the Visualization of Silicon Microelectronic Structure Topology through the Substrate
AbstractExperimental setup based on visible and NIR spectral range microscope with laser port and picosecond laser is developed for silicon integrated circuit (IC) failure analysis. The possibility of visualizing the topology of the submicron technology silicon structures from the back side of the crystal through the substrate is shown. Main features of new setup are demonstrated by some results of backside focused pulsed laser beam initiated latchup effect study. The possibility of the localization of the latchup sensitive areas under focused laser irradiation is shown. NIR light emission accompanying the latchup effect is observed and analyzed. The practical aspects of NIR microscopy for failure analysis under backside laser irradiation are discussed
P-matrix and J-matrix approaches. Coulomb asymptotics in the harmonic oscillator representation of scattering theory
The relation between the R- and P-matrix approaches and the harmonic
oscillator representation of the quantum scattering theory (J-matrix method) is
discussed. We construct a discrete analogue of the P-matrix that is shown to be
equivalent to the usual P-matrix in the quasiclassical limit. A definition of
the natural channel radius is introduced. As a result, it is shown to be
possible to use well-developed technique of R- and P-matrix theory for
calculation of resonant states characteristics, scattering phase shifts, etc.,
in the approaches based on harmonic oscillator expansions, e.g., in nuclear
shell-model calculations. P-matrix is used also for formulation of the method
of treating Coulomb asymptotics in the scattering theory in oscillator
representation.Comment: Revtex, 57 pages including 15 figures; to be published in Annals of
Physic
Small-threshold behaviour of two-loop self-energy diagrams: some special cases
An algorithm to construct analytic approximations to two-loop diagrams
describing their behaviour at small non-zero thresholds is discussed. For some
special cases (involving two different-scale mass parameters), several terms of
the expansion are obtained.Comment: 7 pages, plain latex; talk given at DESY-Zeuthen Workshop "QCD and
QED in Higher Order", Rheinsberg, April 1996, to appear in Proceeding
Investigation of thermal and magnetic properties of defects in a spin-gap compound NaV2O5
The specific heat, magnetic susceptibility and ESR signals of a Na-deficient
vanadate Na_xV_2O_5 (x=1.00 - 0.90) were studied in the temperature range 0.07
- 10 K, well below the transition point to a spin-gap state. The contribution
of defects provided by sodium vacancies to the specific heat was observed. It
has a low temperature part which does not tend to zero till at least 0.3 K and
a high temperature power-like tail appears above 2 K. Such dependence may
correspond to the existence of local modes and correlations between defects in
V-O layers. The magnetic measurements and ESR data reveal S=1/2 degrees of
freedom for the defects, with their effective number increasing in temperature
and under magnetic field. The latter results in the nonsaturating magnetization
at low temperature. No long-range magnetic ordering in the system of defects
was found. A model for the defects based on electron jumps near vacancies is
proposed to explain the observed effects. The concept of a frustrated
two-dimensional correlated magnet induced by the defects is considered to be
responsible for the absence of magnetic ordering.Comment: 6 pages, 8 figure
Electromagnetic Neutrino Properties and Neutrino Oscillations in Electromagnetic Fields
The presence of medium and external magnetic field change electromagnetic
properties of neutrino. In this article the behavior of neutrino magnetic
moment in electromagnetic field is considered. On the basis the
Bargmann-Michel-Telegdi equation for the case of models with CP invariance and
P nonconservation the new type of neutrino resonances in the electromagnetic field is predicted.Comment: 6 page
Factorizing the hard and soft spectator scattering contributions for the nucleon form factor F_1 at large Q^2
We investigate the soft spectator scattering contribution for the FF .
We focus our attention on factorization of the hard-collinear scale corresponding to transition from SCET-I to SCET-II. We compute the
leading order jet functions and find that the convolution integrals over the
soft fractions are logarithmically divergent. This divergency is the
consequence of the boost invariance and does not depend on the model of the
soft correlation function describing the soft spectator quarks. Using as
example a two-loop diagram we demonstrated that such a divergency corresponds
to the overlap of the soft and collinear regions. As a result one obtains large
rapidity logarithm which must be included in the correct factorization
formalism. We conclude that a consistent description of the factorization for
implies the end-point collinear divergencies in the hard and soft
spectator contributions, i.e. convolution integrals with respect to collinear
fractions are not well-defined. Such scenario can only be realized when the
twist-3 nucleon distribution amplitude has specific end-point behavior which
differs from one expected from the evolution of the nucleon distribution
amplitude. Such behavior leads to the violation of the collinear factorization
for the hard spectator scattering contribution. We suggest that the soft
spectator scattering and chiral symmetry breaking provide the mechanism
responsible for the violation of collinear factorization in case of form factor
.Comment: 25 pages, 6 figures, text is improved, few typos corrected, one
figure added, statement about end-point behavior of the nucleon DA is
formulated more accuratel
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