42 research outputs found
Electroerosive Powder Obtained from Alloy VK8 Waste into Butanol
The results of studies of the properties of the powders obtained by electroerosive dispersing of the hard alloy
wastes of mark VK8 in butanol. It is found that the powder particles obtained by electroerosive dispersing
of waste carbide grade VK8 in butyl alcohol, consist of the following major elements: W, Co, Fe, C and O
Electron Spin Relaxation in a Semiconductor Quantum Well
A fully microscopic theory of electron spin relaxation by the
D'yakonov-Perel' type spin-orbit coupling is developed for a semiconductor
quantum well with a magnetic field applied in the growth direction of the well.
We derive the Bloch equations for an electron spin in the well and define
microscopic expressions for the spin relaxation times. The dependencies of the
electron spin relaxation rate on the lowest quantum well subband energy,
magnetic field and temperature are analyzed.Comment: Revised version as will appear in Physical Review
Extraction of Kaon Formfactors from K^- -> mu^- nu_mu gamma Decay at ISTRA+ Setup
The radiative decay K->mu nu gamma has been studied at ISTRA+ setup in a new
kinematical region. About 22K events of K^- -> mu^- nu_mu gamma have been
observed. The sign and value of Fv-Fa have been measured for the first time.
The result is Fv-Fa=0.21(4)(4).Comment: 11 pages, 21 figures, submitted to Phys. Lett.
Possible violation of the spin-statistics relation for neutrinos: cosmological and astrophysical consequences
We assume that the Pauli exclusion principle is violated for neutrinos, and
consequently, neutrinos obey the Bose-Einstein statistics. Cosmological and
astrophysical consequences of this assumption are considered. Neutrinos may
form cosmological Bose condensate which accounts for all (or a part of) the
dark matter in the universe. ``Wrong'' statistics of neutrinos could modify big
bang nucleosynthesis, leading to the effective number of neutrino species
smaller than three. Dynamics of the supernova collapse would be influenced and
spectra of the supernova neutrinos may change. The presence of neutrino
condensate would enhance contributions of the Z-bursts to the flux of the UHE
cosmic rays and lead to substantial refraction effects for neutrinos from
remote sources. The Pauli principle violation for neutrinos can be tested in
the two-neutrino double beta decay.Comment: 13 pages; a reference on BBN bound is added, more accurate result of
the work in progress on BBN is presented; a minor typo in eq. (4) is
correcte
Search for light pseudoscalar sgoldstino in K- decays
A search for the light pseudoscalar sgoldstino production in the three body
K- decay K-->pipi0P has been performed with the ISTRA+ detector exposed to the
25 GeV negative secondary beam of the U70 proton synchrotron. No signal is
seen. An upper limit for the branching ratio Br(K->pipi0P), at 90% confidence
level, is found to be around 9*10**-6 in the effective mass m(P) range from 0
till 200 MeV, excluding the region near m(pi0) where it degrades to 3.5*10**-5.Comment: 10 pages, LATEX, 8 EPS figures, revised version, to be published in
Phys.Lett.
High statistic measurement of the K- -> pi0 e- nu decay form-factors
The decay K- -> pi0 e- nu is studied using in-flight decays detected with the
ISTRA+ spectrometer. About 920K events are collected for the analysis. The
lambda+ slope parameter of the decay form-factor f+(t) in the linear
approximation (average slope) is measured: lambda+(lin)= 0.02774 +-
0.00047(stat) +- 0.00032(syst). The quadratic contribution to the form-factor
was estimated to be lambda'+ = 0.00084 +- 0.00027(stat) +- 0.00031(syst). The
linear slope, which has a meaning of df+(t)/dt|_{t=0} for this fit, is lambda+
= 0.02324 +- 0.00152(stat) +- 0.00032(syst). The limits on possible tensor and
scalar couplings are derived: f_{T}/f_{+}(0)=-0.012 +- 0.021(stat) +-
0.011$(syst), f_{S}/f_{+}(0)=-0.0037^{+0.0066}_{-0.0056}(stat) +- 0.0041(syst).Comment: 11 pages, 8 figures. Accepted by Phys.Lett.
Search for Heavy Neutrino in K->mu nu_h(nu_h-> nu gamma) Decay at ISTRA+ Setup
Heavy neutrino nu_h with m_h < 300MeV/c^2 can be effectively searched for in
kaon decays. We put upper limits on mixing matrix element |U_mu_h}|^2 for
radiatively decaying nu_h from K->mu nu_h (nu_h -> nu gamma) decay chain in the
following parameter region: 30MeV/c^2 < m_h < 80MeV/c^2; 10^{-11}sec < tau_h <
10^{-9}sec. For the whole region |U_{mu h}|^2 < 5 x 10^{-5} for Majorana type
of nu_h and | U_{\mu h}|^2 < 8 x 10^{-5} for the Dirac case.Comment: Published in Phys. Lett.
Measurement of the Dalitz plot slope parameters for K- -> pi0 pi0 pi- decay using ISTRA+ detector
The Dalitz plot slope parameters g, h and k for the K- -> pi0 pi0 pi- decay
have been measured using in-flight decays detected with the ISTRA+ setup
operating in the 25 GeV negative secondary beam of the U-70 PS. About 252 K
events with four-momenta measured for the pi- and four involved photons were
used for the analysis. The values obtained g=0.627+/-0.004(stat)+/-0.010(syst),
h=0.046+/-0.004(stat)+/-0.012(syst), k=0.001+/-0.001(stat)+/-0.002(syst) are
consistent with the world averages dominated by K+ data, but have significantly
smaller errors.Comment: LaTeX, 10 pages, 8 eps-figures, update of IHEP 2002-1
Two-loop N=4 Super Yang Mills effective action and interaction between D3-branes
We compute the leading low-energy term in the planar part of the 2-loop
contribution to the effective action of SYM theory in 4 dimensions,
assuming that the gauge group is broken to by a
constant scalar background . While the leading 1-loop correction is the
familiar term, the 2-loop expression starts with . The 1-loop constant is known to be equal to the coefficient
of the term in the Born-Infeld action for a probe D3-brane separated by
distance from a large number of coincident D3-branes. We show that
the same is true also for the 2-loop constant : it matches the coefficient
of the term in the D3-brane probe action. In the context of the AdS/CFT
correspondence, this agreement suggests a non-renormalization of the
coefficient of the term beyond two loops. Thus the result of
hep-th/9706072 about the agreement between the term in the D0-brane
supergravity interaction potential and the corresponding 2-loop term in the 1+0
dimensional reduction of SYM theory has indeed a direct generalization
to 1+3 dimensions, as conjectured earlier in hep-th/9709087. We also discuss
the issue of gauge theory -- supergravity correspondence for higher order
(, etc.) terms.Comment: 33 pages, late
Properties of heavy quarkonia and B_c mesons in the relativistic quark model
The mass spectra and electromagnetic decay rates of charmonium, bottomonium
and B_c mesons are comprehensively investigated in the relativistic quark
model. The presence of only heavy quarks allows the expansion in powers of
their velocities. All relativistic corrections of order v^2/c^2, including
retardation effects and one-loop radiative corrections, are systematically
taken into account in the computations of the mass spectra. The obtained wave
functions are used for the calculation of radiative magnetic dipole (M1) and
electric dipole (E1) transitions. It is found that relativistic effects play a
substantial role. Their account and the proper choice of the Lorentz structure
of the quark-antiquark interaction in a meson is crucial for bringing
theoretical predictions in accord with experimental data. A detailed comparison
of the calculated decay rates and branching fractions with available
experimental data for radiative decays of charmonium and bottomonium is
presented. The possibilities to observe the currently missing spin-singlet S
and P states as well as D states in bottomonium are discussed. The results for
B_c masses and decays are compared with other quark model predictions.Comment: 31 pages, 2 figures, minor correction