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Effect of Mn-doping on the low temperature magnetic phase transitions of
No full textIn the present work, we have carried out a comparative study of the low temperature phase transitions using dc magnetization (M (T)) and ac susceptibility (χ (ω, T)) measurements on undoped and 0.3 wt% MnO doped BiFeO3 samples in the 2–300 K temperature range. It is shown that MnO doping increases the resistivity and decreases the dielectric loss as a result of reduced oxygen vacancy concentration as confirmed by iodometry and x-ray photoelectron spectroscopy (XPS) studies. A comparative study of the dc M (T) and ac χ (ω, T) results on two types of samples reveal that the transitions around 25 K, 110 to 150 K and 260 K are intrinsic to BiFeO. The widely reported transition at 50 K is argued to be defect induced, as it is absent in the doped samples. We also show that the spin-glass transition temperature (T) ∼20 K, determined from an analysis of χ (ω, T), is less than the spin-glass freezing temperature (T) ∼25 K in marked contrast to T > T reported by earlier workers
Lattice calculation of the hadronic leading order contribution to the muon
No full textThe persistent discrepancy of about 3.5 standard deviations between the experimental measurement and the Standard Model prediction for the muon anomalous magnetic moment, , is one of the most promising hints for the possible existence of new physics. Here we report on our lattice QCD calculation of the hadronic vacuum polarisation contribution , based on gauge ensembles with flavours of O() improved Wilson quarks. We address the conceptual and numerical challenges that one encounters along the way to a sub-percent determination of the hadronic vacuum polarisation contribution. The current status of lattice calculations of is presented by performing a detailed comparison with the results from other groups
Search for Light Bosons in Exotic Decays of the 125 GeV Higgs Boson
No full textA search for pairs of light bosons produced from decays of the 125 GeV Higgs boson is presented. The search covers the light boson mass region where the particle could have an enhanced decay rate to a pair of τ leptons, according to different models and scenarios.The leptonic decay channels corresponding to the 4τ and 2μ2τ final states are used. The search is based on proton-proton collisions collected by the CMS experiment in 2016 at a center-of-mass energy of 13 TeV. This dataset corresponds to an integrated luminosity of 35.9 fb^{-1} .The analysis is motivated by many theories beyond the Standard Model that suggest modifications in the Higgs sector. The prevailing tendency among these new models is to extend the group structure of the scalar sector, thus resulting in an increased number of physical states in their spectrum. The additional bosons could couple to both the 125 GeV Higgs boson and the rest of the particles in the theory, which allows their detection through different production and decay mechanisms.Two different approaches used for the analysis of the data are presented. The first strategy targets boosted event topologies, occurring for light bosons with masses between 4 and 15 GeV. The second method employs a modified event selection technique combined with a more powerful final discriminant to be able to extend the mass range up to 21 GeV. In both approaches, no significant deviation beyond the expectation from the Standard Model is observed. Observed and expected upper limits at 95% confidence level on the product of the Higgs boson production cross-section relative to that in the Standard Model and the branching fraction into the 4τ final state are set. Interpretations of the experimental results in the context of a specific theoretical model are also provided
Patterns in the multi-wavelength behavior of candidate neutrino blazars
No full textMotivated by the identification of the blazar TXS 0506+056 as the first promising high-energy neutrino counterpart candidate, we search for additional neutrino blazars candidates among the Fermi-LAT detected blazars. We investigate the multi-wavelength behavior from radio to GeV gamma rays of blazars found to be in spatial coincidence with single high-energy neutrinos and lower-energy neutrino flare candidates. In addition, we compare the average gamma-ray emission of the potential neutrino-emitting sources to the entire sample of gamma-ray blazars. We find that neutrino-emitting blazar candidates are statistically compatible with both hypothesis of a linear correlation and of no correlation between neutrino and gamma-ray energy flux
LOFAR 144-MHz follow-up observations of GW170817
No full textWe present low-radio-frequency follow-up observations of AT 2017gfo, the electromagnetic counterpart of GW170817, which was the first binary neutron star merger to be detected by Advanced LIGO-Virgo. These data, with a central frequency of 144 MHz, were obtained with LOFAR, the Low-Frequency Array. The maximum elevation of the target is just 13.7 degrees when observed with LOFAR, making our observations particularly challenging to calibrate and significantly limiting the achievable sensitivity. On time-scales of 130-138 and 371-374 days after the merger event, we obtain 3 upper limits for the afterglow component of 6.6 and 19.5 mJy beam, respectively. Using our best upper limit and previously published, contemporaneous higher-frequency radio data, we place a limit on any potential steepening of the radio spectrum between 610 and 144 MHz: the two-point spectral index . We also show that LOFAR can detect the afterglows of future binary neutron star merger events occurring at more favourable elevations
Enhancement of light extraction in YAlO: thin films through nanopatterning
No full textLight extraction is a key parameter to improve the performances of optical devices. Nanopatterned YAlO: luminescent coatings usable in such devices have been elaborated and have shown enhanced emission efficiency compared to their unpatterned counterparts. These nanostructured films were obtained by using the colloidal lithography combined with the Langmuir-Blodgett technique. It is the first time to our knowledge that this patterning technique is directly applied on YAG matrix. Resulting nanostructuring is a hexagonal network capable of modifying the light travelling path within the substrate. Conventional and angular-resolved photoluminescence were investigated on both unpatterned and patterned samples. Due to the nanostructuring, the extraction efficiency is improved by 26% and 131% depending on the crystallinity of the sample. Noticeably, nanostructuring is found to have an influence on the angular distribution of photoluminescence whose intensity has been evaluated to its maximum normal to the film surface
Texture transition in friction stir processed Al powder compact
No full textGreen Al powder compacts of commercial purity with random orientation were subjected to single pass frictionstir processing (FSP) with different tool rotational and traverse speeds. The evolution of crystallographic textureobtained from large area electron back scattered diffraction were compared with the bulk texture of the nuggetzone characterized using synchrotron diffraction. Evolution of different deformation and recrystallization texturecomponents were discussed. While the grain size distributions were found to be independent of processparameters, the texture components and their strength of the FSPed samples were strongly influenced by theprocess parameters. Continuous dynamic recrystallization (CDRx) was found to be the primary restorationmechanism for most of the processing conditions leading to a bi-modal misorientation distribution. The possiblerelations between different texture components and the appearance or suppression of bimodal misorientationdistributions were discussed. Restoration mechanism changed to discontinuous dynamic recrystallization(DDRx) with the evolution of cube component at the stir zone along with random misorientation distribution.Dominance of a particular restoration mechanism depends on strain, strain rate and temperature attained duringthe processing
Precision luminosity measurement with proton-proton collisions at the CMS experiment in Run 2
No full textPrecision luminosity calibration is critical to determine fundamental parameters of the standard model and to constrain or to discover beyond-the-standard-model phenomena at LHC. The luminosity determination at the LHC interaction point 5 with the CMS detector, using proton-proton collisions at 13 and 5.02 TeV during Run 2 of the LHC (2015–2018), is reported. The absolute luminosity scale is obtained using beam-separation (``van der Meer'') scans. The dominant sources of systematic uncertainty are related to the knowledge of the scale of the beam separation provided by LHC magnets and the nonfactorizability between the spatial components of the proton bunch density distributions in the transverse direction. When applying the van der Meer calibration to the entire data-taking period, a substantial contribution to the total uncertainty in the integrated luminosity originates from the measurement of the detector linearity and stability. The reported integrated luminosity in 2015–2016 is among the most precise luminosity measurements at bunched-beam hadron colliders
Occurrence of Tachyonic Preheating in the Mixed Higgs- Model
No full textIt has recently been suggested that at the post-inflationary stage of the mixed Higgs- model of inflation there can arise an efficient particle production from the tachyonic instability of the Higgs field. It might complete the preheating of the Universe, if appropriate conditions are satisfied, especially in the Higgs-like regime. In this paper, we study this behavior in more depth, including the conditions of occurrence, analytical estimates for the maximal efficiency, and the necessary degree of fine-tuning of model parameters to complete preheating by this effect. We find that the parameter sets that cause the most efficient tachyonic instabilities obey simple laws in both the Higgs-like regime and -like regime, respectively. We then estimate the efficiency of this instability. In particular, even in the deep -like regime with a small non-minimal coupling, this effect is strong enough to complete preheating although a severe fine-tuning is required among the model parameters. We also estimate how much fine-tuning is needed to complete preheating by this effect. It is shown that the fine-tuning of parameters for the sufficient particle production is at least in the deep Higgs-like regime with a large scalaron mass, while it is more severe in the -like regime with a small non-minimal coupling
Lattice distortion and stability of (CoCuMgNiZnO high-entropy oxide under high pressure
No full textHigh-entropy oxides (HEOs) stabilize multiple cations in a single solid solution phase, providing a new opportunity for property engineering in almost infinite compositional space. The structural stability and tunability of HEO are of great interest and importance but has not been well understood, especially under pressure. Here, we studied the structure evolution of a rock salt phase (Co0.2Cu0.2Mg0.2Ni0.2Zn0.2)O HEO using in situ synchrotron X-ray diffraction, pair distribution function, Raman spectroscopy up to ~43 GPa, and ex situ transmission electron microscopy, a pressure-induced reversible rock salt to highly distorted cubic phase transition was observed. These results suggest highly tunable lattice distortion in HEOs under pressure, which could promote the fundamental understanding and also guide applications of HEOs