207 research outputs found
Non-minimal electrodynamics and resonance interactions in relativistic plasma
A three-parameter toy-model, which describes a non-minimal coupling of
gravity field with electromagnetic field of a relativistic two-component
electrically neutral plasma, is discussed. Resonance interactions between
particles and transversal waves in plasma are shown to take place due to the
curvature coupling effect.Comment: 6 pages, no figures, the short version of the talk at RUSGRAV-13, to
be published in Gravitation and Cosmology, 2009, No.
Non-minimal Wu-Yang wormhole
We discuss exact solutions of three-parameter non-minimal Einstein-Yang-Mills
model, which describe the wormholes of a new type. These wormholes are
considered to be supported by SU(2)-symmetric Yang-Mills field, non-minimally
coupled to gravity, the Wu-Yang ansatz for the gauge field being used. We
distinguish between regular solutions, describing traversable non-minimal
Wu-Yang wormholes, and black wormholes possessing one or two event horizons.
The relation between the asymptotic mass of the regular traversable Wu-Yang
wormhole and its throat radius is analysed.Comment: 9 pages, 2 figures, typos corrected, 2 references adde
Non-minimal coupling of photons and axions
We establish a new self-consistent system of equations accounting for a
non-minimal interaction of gravitational, electromagnetic and axion fields. The
procedure is based on a non-minimal extension of the standard
Einstein-Maxwell-axion action. The general properties of a ten-parameter family
of non-minimal linear models are discussed. We apply this theory to the models
with pp-wave symmetry and consider propagation of electromagnetic waves
non-minimally coupled to the gravitational and axion fields. We focus on exact
solutions of electrodynamic equations, which describe quasi-minimal and
non-minimal optical activity induced by the axion field. We also discuss
empirical constraints on coupling parameters from astrophysical birefringence
and polarization rotation observations.Comment: 31 pages, 2 Tables; replaced with the final version published in
Classical and Quantum Gravit
Notes on wormhole existence in scalar-tensor and F(R) gravity
Some recent papers have claimed the existence of static, spherically
symmetric wormhole solutions to gravitational field equations in the absence of
ghost (or phantom) degrees of freedom. We show that in some such cases the
solutions in question are actually not of wormhole nature while in cases where
a wormhole is obtained, the effective gravitational constant G_eff is negative
in some region of space, i.e., the graviton becomes a ghost. In particular, it
is confirmed that there are no vacuum wormhole solutions of the Brans-Dicke
theory with zero potential and the coupling constant \omega > -3/2, except for
the case \omega = 0; in the latter case, G_eff < 0 in the region beyond the
throat. The same is true for wormhole solutions of F(R) gravity: special
wormhole solutions are only possible if F(R) contains an extremum at which
G_eff changes its sign.Comment: 7 two-column pages, no figures, to appear in Grav. Cosmol. A misprint
corrected, references update
Gradient models of the axion-photon coupling
We establish an extended version of the Einstein - Maxwell - axion model by
introducing into the Lagrangian cross-terms, which contain the gradient
four-vector of the pseudoscalar (axion) field in convolution with the Maxwell
tensor. The gradient model of the axion-photon coupling is applied to
cosmology: we analyze the Bianchi-I type Universe with an initial magnetic
field, electric field induced by the axion-photon interaction, cosmological
constant and dark matter, which is described in terms of the pseudoscalar
(axion) field. Analytical, qualitative and numerical results are presented in
detail for two distinguished epochs: first, for the early Universe with
magnetic field domination; second, for the stage of late-time accelerated
expansion.Comment: 26 pages, 5 figures, accepted for publication in The European
Physical Journal
Novel potent pyridoxine-based inhibitors of AChE and BChE, structural analogs of pyridostigmine, with improved in vivo safety profile
© 2016 Elsevier LtdWe report a novel class of carbamate-type ChE inhibitors, structural analogs of pyridostigmine. A small library of congeneric pyridoxine-based compounds was designed, synthesized and evaluated for AChE and BChE enzymes inhibition in vitro. The most active compounds have potent enzyme inhibiting activity with IC50 values in the range of 0.46–2.1 μM (for AChE) and 0.59–8.1 μM (for BChE), with moderate selectivity for AChE comparable with that of pyridostigmine and neostigmine. Acute toxicity studies using mice models demonstrated excellent safety profile of the obtained compounds with LD50 in the range of 22–326 mg/kg, while pyridostigmine and neostigmine are much more toxic (LD50 3.3 and 0.51 mg/kg, respectively). The obtained results pave the way to design of novel potent and safe cholinesterase inhibitors for symptomatic treatment of neuromuscular disorders
Observation of Plasma Focusing of a 28.5 GeV Positron Beam
The observation of plasma focusing of a 28.5 GeV positron beam is reported.
The plasma was formed by ionizing a nitrogen jet only 3 mm thick. Simultaneous
focusing in both transverse dimensions was observed with effective focusing
strengths of order Tesla per micron. The minimum area of the beam spot was
reduced by a factor of 2.0 +/- 0.3 by the plasma. The longitudinal beam
envelope was measured and compared with numerical calculations
Evidence for Factorization in Three-body B --> D(*) K- K0 Decays
Motivated by recent experimental results, we use a factorization approach to
study the three-body B --> D(*) K- K0 decay modes. Two mechanisms are proposed
for kaon pair production: current-produced (from vacuum) and transition (from B
meson). The Bbar0 --> D(*)+ K- K0 decay is governed solely by the
current-produced mechanism. As the kaon pair can be produced only by the vector
current, the matrix element can be extracted from e+ e- --> K Kbar processes
via isospin relations. The decay rates obtained this way are in good agreement
with experiment. Both current-produced and transition processes contribute to
B- --> D(*)0 K- K0 decays. By using QCD counting rules and the measured B- -->
D(*)0 K- K0 decay rates, the measured decay spectra can be understood.Comment: 17 pages, 6 figure
The combination of traditional cardiorespiratory markers during treadmill testing “to failure” in athletes, depending on professional activity
Exercise tolerance test with the use of the spiroergometry technique is a reliable diagnostic method which provides objective information about cardiorespiratory system condition when performing physical activity. Both new and traditional, well-proven cardiorespiratory markers obtained in the process of treadmill testing “to failure”, are described in this article. The nature of the influence of physical exertion on the indicators of cardiorespiratory system functional activity is presented. The interpretation for planning and subsequent monitoring of the training process in athletes of various professional activities is proposed
Sensitive Search for a Permanent Muon Electric Dipole Moment
We are proposing a new method to carry out a dedicated search for a permanent
electric dipole moment (EDM) of the muon with a sensitivity at a level of
10^{-24} e cm. The experimental design exploits the strong motional electric
field sensed by relativistic particles in a magnetic storage ring. As a key
feature, a novel technique has been invented in which the g-2 precession is
compensated with radial electric field. This technique will benefit greatly
when the intense muon sources advocated by the developers of the muon storage
rings and the muon colliders become available.Comment: 16 pages, 3 figures. Submitted for publication in Proceedings of the
International Workshop on High Intensity Muon Sources (HIMUS99), KEK, Japan,
December 1-4 199
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