Nanoelectromechanics of Polarization Switching in Piezoresponse Force Microscopy

Nanoscale polarization switching in ferroelectric materials by Piezoresponse Force Microscopy (PFM) in weak and strong indentation limits is analyzed using exact solutions for electrostatic and coupled electroelastic fields below the tip. It is proposed that the tip-induced domain switching can be mapped on the Landau theory of phase transitions with the domain size as an order parameter. For a point charge interacting with a ferroelectric surface, switching of both first and second order is possible depending on the charge-surface separation. For a realistic tip shape, the domain nucleation process is first order in charge magnitude and polarization switching occurs only above a critical tip bias. In pure ferroelectric or ferroelastic switching, the late stages of the switching process can be described using point charge/force model and arbitrarily large domains can be created; however, the description of the early stages of nucleation process when domain size is comparable with the tip radius of curvature requires exact field structure to be taken into account.Comment: 16 pages, 3 figures, expanded version of paper submitted to PR

INFORMATIVE CAPACITY OF THE SARGAT CULTURE’S DISTURBED BURIALS: KURGAN NOVOPOKROVKA 16 IN THE MIDDLE IRTYSH RIVER BASIN 1

The article deals with a complex study of the materials obtained during archaeological excavation of the kurgan Novopokrovka 16 in the middle Irtysh river basin (Omsk region). The site, which is attributed to the Sargat culture (5th century BC – second half of the 3rd centuryAD), was located farmost on the right bank of the river Irtysh, nearby the group of “Princely kurgans”. Despite almost total disturbance by robbers and agricultural activity, common scholars’ efforts demonstrate high informative capacity of the multidisciplinary approach, while modern level of undertaken research is not just being declared but enables to reconstruct seemingly lost information. The kurgan erection stages and mound structure features have been decoded using the results of a geophysical survey and soil morphology data. The paleoanthropological study of the incomplete skeletal remains does not support multiple or inlet interment inside the central grave, and provides sexing and aging of the buried individuals as well as some paleopathological observations. Apart from species examination, archaeozoological data testify that a warm period from spring to early autumn was the season of animal slaughter. Characteristics of mortuary rituals and direction of intercultural contacts of the ancient forest-steppe groups have been completed by new details based on the results of strontium isotope analyses (dental enamel of humans and animals) and evidence non-local origin of the individual buried under the excavated kurgan, what is different from local origin of horses butchered for funereal feasts. The proposed hypothesis supports previously suggested archaeological, paleoanthropological and paleogenetic facts on the origin of the forest-steppe population, indicating an involvement of various population groups with notable external components. Based on the archaeological materials, the kurgan under study might be dated back to mid-4th – 3rd centuries BC. © 2023 The Author(s).Ministry of Education and Science of the Russian Federation, Minobrnauka: 075-15-2021-680The article was prepared in the framework of the state orders No. 121102500121-8, 123011800012-9, 1021061810416-7, АААА-А19-119013090163-2, RFBR grant No. 21-59-23003. Sr isotopic analyses were obtained in the Geoanalitik shared research facilities of the IGG UB RAS, whose re-equipment and comprehensive development is supported by a grant of the Ministry of Science and Higher Education of the Russian Federation (Agreement No. 075-15-2021-680)

Search for Yukawa Production of a Light Neutral Higgs Boson at LEP

Within a Two-Higgs-Doublet Model (2HDM) a search for a light Higgs boson in the mass range of 4-12 GeV has been performed in the Yukawa process e+e- -> b bbar A/h -> b bbar tau+tau-, using the data collected by the OPAL detector at LEP between 1992 and 1995 in e+e- collisions at about 91 GeV centre-of-mass energy. A likelihood selection is applied to separate background and signal. The number of observed events is in good agreement with the expected background. Within a CP-conserving 2HDM type II model the cross-section for Yukawa production depends on xiAd = |tan beta| and xihd = |sin alpha/cos beta| for the production of the CP-odd A and the CP-even h, respectively, where tan beta is the ratio of the vacuum expectation values of the Higgs doublets and alpha is the mixing angle between the neutral CP-even Higgs bosons. From our data 95% C.L. upper limits are derived for xiAd within the range of 8.5 to 13.6 and for xihd between 8.2 to 13.7, depending on the mass of the Higgs boson, assuming a branching fraction into tau+tau- of 100%. An interpretation of the limits within a 2HDM type II model with Standard Model particle content is given. These results impose constraints on several models that have been proposed to explain the recent BNL measurement of the muon anomalous magnetic moment.Comment: 24 pages, 9 figures, Submitted to Euro. Phys. J.

Search for the Standard Model Higgs Boson with the OPAL Detector at LEP

This paper summarises the search for the Standard Model Higgs boson in e+e- collisions at centre-of-mass energies up to 209 GeV performed by the OPAL Collaboration at LEP. The consistency of the data with the background hypothesis and various Higgs boson mass hypotheses is examined. No indication of a signal is found in the data and a lower bound of 112.7GeV/C^2 is obtained on the mass of the Standard Model Higgs boson at the 95% CL.Comment: 51 pages, 21 figure

Measurement of triple gauge boson couplings from WW production at LEP energies up to 189 GeV

A measurement of triple gauge boson couplings is presented, based on W-pair data recorded by the OPAL detector at LEP during 1998 at a centre-of-mass energy of 189 GeV with an integrated luminosity of 183 pb^-1. After combining with our previous measurements at centre-of-mass energies of 161-183 GeV we obtain k_g=0.97 +0.20 -0.16, g_1^z=0.991 +0.060 -0.057 and lambda_g=-0.110 +0.058 -0.055, where the errors include both statistical and systematic uncertainties and each coupling is determined by setting the other two couplings to their SM values. These results are consistent with the Standard Model expectations.Comment: 28 pages, 8 figures, submitted to Eur. Phys. J.

Measurement of the Hadronic Cross-Section for the Scattering of Two Virtual Photons at LEP

The interaction of virtual photons is investigated using the reaction e+e- -> e+e- hadrons based on data taken by the OPAL experiment at e+e- centre-of-mass energies sqrt(s_ee)=189-209 GeV, for W>5 GeV and at an average Q^2 of 17.9 GeV^2. The measured cross-sections are compared to predictions of the Quark Parton Model (QPM), to the Leading Order QCD Monte Carlo model PHOJET to the NLO prediction for the reaction e+e- -> e+e-qqbar, and to BFKL calculations. PHOJET, NLO e+e- -> e+e-qqbar, and QPM describe the data reasonably well, whereas the cross-section predicted by a Leading Order BFKL calculation is too large.Comment: 30 pages, 10 figures, Submitted to Eur.Phys.J.

Search for Nearly Mass-Degenerate Charginos and Neutralinos at LEP

A search was performed for charginos with masses close to the mass of the lightest neutralino in e+e- collisions at centre-of-mass energies of 189-209 GeV recorded by the OPAL detector at LEP. Events were selected if they had an observed high-energy photon from initial state radiation, reducing the dominant background from two-photon scattering to a negligible level. No significant excess over Standard Model expectations has been observed in the analysed data set corresponding to an integrated luminosity of 570pb-1. Upper limits were derived on the chargino pair-productin cross-section, and lower limits on the chargino mass were derived in the context of the Minimal Supersymmetric Extension of the Standard Model for the gravity and anomaly mediated Supersymmetry breaking scenarios.Comment: 26 pages, 9 figure

Measurement of the Hadronic Photon Structure Function F_2^gamma at LEP2

The hadronic structure function of the photon F_2^gamma is measured as a function of Bjorken x and of the factorisation scale Q^2 using data taken by the OPAL detector at LEP. Previous OPAL measurements of the x dependence of F_2^gamma are extended to an average Q^2 of 767 GeV^2. The Q^2 evolution of F_2^gamma is studied for average Q^2 between 11.9 and 1051 GeV^2. As predicted by QCD, the data show positive scaling violations in F_2^gamma. Several parameterisations of F_2^gamma are in agreement with the measurements whereas the quark-parton model prediction fails to describe the data.Comment: 4 pages, 2 figures, to appear in the proceedings of Photon 2001, Ascona, Switzerlan

A Measurement of Semileptonic B Decays to Narrow Orbitally-Excited Charm Mesons

The decay chain b -> Bbar -> D^{**0} l nu X, D^{**0} -> D^{*+} pi^-, D^{*+} -> D^0 pi^+, D^0 ->(Kpi or K3pi) is identified in a sample of 3.9 million hadronic Z decays collected with the OPAL detector at LEP. The branching ratio BR (b -> Bbar) x BR (Bbar -> D^0_1 l nu X) x BR (D^0_1 -> D^{*+} pi^-) is measured to be (2.64 +- 0.79 (stat) +- 0.39 (syst)) X 10^-3 for the J^P = 1^+ (D^0_1) state. For decays into the J^P = 2^+ (D^{*0}_2) state, an upper limit of 1.4 X 10^-3 is placed on the branching ratio at the 95% confidence level.Comment: 20 pages, 6 figure