1,133 research outputs found
Of Higgs, Unitarity and other Questions
On the verge of conclusive checks on the Standard Model by the LHC, we
discuss some of the basic assumptions. The reason for this analysis stems from
a recent proposal of an Electroweak Model based on a nonlinearly realized gauge
group SU(2) X U(1), where, in the perturbative approximation, there is no Higgs
boson. The model enjoys the Slavnov-Taylor identities and therefore the
perturbative unitarity. On the other hand, it is commonly believed that the
existence of the Higgs boson is entangled with the property of unitarity, when
high energy processes are considered. The argument is based mostly on the
Froissart bound and on the Equivalence Theorem. In this talk we briefly review
some of our objections on the validity of such arguments. Some open questions
are pointed out, in particular on the limit of zero mass for the vector mesons
and on the fate of the longitudinal polarizations.Comment: 23 pages, 1 figure, presented by Ruggero Ferrari at the International
Conference "Gauge Fields. Yesterday, Today, Tomorrow" in honor of A.A.
Slavnov. Moscow, January 19-24 201
The Algebra of Physical Observables in Nonlinearly Realized Gauge Theories
We classify the physical observables in spontaneously broken nonlinearly
realized gauge theories in the recently proposed loopwise expansion governed by
the Weak Power-Counting (WPC) and the Local Functional Equation. The latter
controls the non-trivial quantum deformation of the classical nonlinearly
realized gauge symmetry, to all orders in the loop expansion. The
Batalin-Vilkovisky (BV) formalism is used. We show that the dependence of the
vertex functional on the Goldstone fields is obtained via a canonical
transformation w.r.t. the BV bracket associated with the BRST symmetry of the
model. We also compare the WPC with strict power-counting renormalizability in
linearly realized gauge theories. In the case of the electroweak group we find
that the tree-level Weinberg relation still holds if power-counting
renormalizability is weakened to the WPC condition.Comment: 20 pages, 1 figur
Synchrotron radiation study of interconfigurational 5d-4f luminescence of Pr3+ in KLuP2O7
The double phosphate KLuP2O7 doped with Pr 3+ ions was prepared by solid-state reaction. The material obtained was characterized by powder X-ray diffraction. The luminescence spectroscopy and the excited state dynamics of this material were studied upon excitation with VUV synchrotron radiation. The 5d-4f emission of Pr3+ upon both direct and band gap excitation was detected and assigned. The decay kinetics of the Pr3+ 5d-4f emission is characterized by a decay time of about 20 ns and is nearly temperature independent within the range 8-300 K. Both dynamics and energy transfer peculiarities revealed in the study suggested good potentials for application of KLuP2O7:Pr3+ as a fast scintillator material. © 2014 Verlag der Zeitschrift für Naturforschung, Tübingen
High-density linkage mapping and QTL identification of black rot resistance towards marker-assisted breeding in grapevine
Today sustainability is a pivotal objective for viticulture, but it also presents us with new challenges. The decrease in treatments has in fact changed grapevine-pathogen interactions and dynamics causing the reaffirmation of diseases previously considered secondary. This is the case of black rot (BR, caused by Phyllosticta ampelicida), which is spreading with increasing pressure in warm-humid regions causing the loss of entire crops. The interinstitutional DAMAGE project between Edmund Mach Foundation (FEM) and the Institute for Grapevine Breeding (JKI-Geilweilerhof) aims to characterize BR resistance and to develop a toolkit of molecular markers (MM) to be routinely used in marker-assisted breeding for the introgression of this trait into mildew resistant backgrounds. The first fungal strain was isolated from infected leaves collected in Trentino-Italy and mixed with a second strain isolated in southwestern Germany. This inoculum has been used to screen a segregating population derived from 'Merzling' (V. rupestris × V. lincecumii, mid-resistant) × 'Teroldego' (V. vinifera, susceptible). BR resistance phenotyping consisted of a newly developed inoculation protocol on potted plants. The F1 individuals were genotyped with the Vitis18KSNP chip and a high-density genetic map has been constructed, following the integration of 190 informative SSRs. Moreover, explorative QTL analyzes have been conducted on phenotypic data of 2020 and 2021 seasons. Finally, upon the genomic interval characterization, new MM will be designed, tested and validated on various segregating populations with different genetic backgrounds
Bandgap behavior and singularity of the domain-induced light scattering through the pressure-induced ferroelectric transition in relaxor ferroelectric A(x)Ba(1-x)Nb(2)O(6) (A: Sr,Ca)
[EN] In this letter, we have investigated the electronic structure of A(x)Ba(1-x)Nb(2)O(6) relaxor ferroelectrics on the basis of optical absorption spectroscopy in unpoled single crystals with A = Sr and Ca under high pressure. The direct character of the fundamental transition could be established by fitting Urbach's rule to the photon energy dependence of the absorption edge yielding bandgaps of 3.44(1) eV and 3.57(1) eV for A = Sr and Ca, respectively. The light scattering by ferroelectric domains in the pre-edge spectral range has been studied as a function of composition and pressure. After confirming with x-ray diffraction the occurrence of the previously observed ferroelectric to paraelelectric phase transition at 4 GPa, the light scattering produced by micro-and nano-ferroelectric domains at 3.3 eV in Ca0.28Ba0.72Nb2O6 has been probed. The direct bandgap remains virtually constant under compression with a drop of only 0.01 eV around the phase transition. Interestingly, we have also found that light scattering by the polar nanoregions in the paraelectric phase is comparable to the dispersion due to ferroelectric microdomains in the ferroelectric state. Finally, we have obtained that the bulk modulus of the ferroelectric phase of Ca0.28Ba0.72Nb2O6 is B-0 = 222(9) GPa. Published by AIP Publishing.J.R.-F. acknowledges the Spanish MINECO for the Juan de la Cierva (IJCI-2014-20513) Program and Dr. Bayarjargal from the Goethe-Universitat Frankfurt for providing the CBN28 samples. This work was supported by Spanish MINECO under Grant No. MAT2016-75586-C4-1-P/2-P. The high pressure x-ray diffraction experiments were performed at MSPD beamline at ALBA Synchrotron (Project 2016021588) with the collaboration of ALBA staff.Ruiz-Fuertes, J.; Gomis, O.; Segura, A.; Bettinelli, M.; Burianek, M.; Muehlberg, M. (2018). Bandgap behavior and singularity of the domain-induced light scattering through the pressure-induced ferroelectric transition in relaxor ferroelectric A(x)Ba(1-x)Nb(2)O(6) (A: Sr,Ca). Applied Physics Letters. 112(4). https://doi.org/10.1063/1.5012111S112
Strukturna i dielektrična svojstva nanostrukturnih prahova BaTiO3 punjenih ionima Eu3+ I pripremljenih sol-gel procesom
Nano-structure BaTiO3 powders doped with Eu3+ ions have been prepared by a sol-gel technique. X-ray diffraction (XRD) results indicate that BaTiO3 gel powders crystallize into tetragonal symmetry on heat treatment at 750 ◦C. Particle sizes as small as 3.5 nm were measured for pure BaTiO3 powders. The XRD data were confirmed by transmission electron microscope. Room-temperature luminescence spectra of BaTiO3:0.5% Eu3+, BaTiO3:1% Eu3+ and BaTiO3:2% Eu3+ powders have been measured. The luminescence spectra of prepared ultrafine powders are dominated by the 5D0 →7F2 transition in Eu3+, suggesting a strong distortion of the Eu3+ sites. The foreign ions are mainly accommodated in Ba2+ tetragonal sites, which are then distorted by the occurrence of different ionic charge of the two cations Ba2+ and Eu3+. The dielectric constant, ε, of BaTiO3, BaTiO3:0.5% Eu3+, BaTiO3:1% Eu3+ and BaTiO3:2% Eu3+ powders at frequency 100 Hz was found to be equal to 1000, 1211, 1455 and 1800, respectively. This high dielectric constant is believed to arise from the increase of the crystallite size, when increasing the concentration of Eu3+ ions. After annealing in argon at 400 ◦C for two hours, at 100 Hz, the dielectric constant of the pure sample was 625 and the AC resistivity also decreased. The room temperature (RT) AC resistivity of the samples depends on the concentration of Eu3+ ions in BaTiO3 powders, and was found to decrease as the concentration of Eu3+ ions increased.Pripremali smo sol-gel metodom nanostrukturne prahove BaTiO3 punjene Eu3+ ionima. Difrakcija X-zračenja (DXZ) pokazuje da se gel prahovi BaTiO3 kristaliziraju u tetragonalnoj simetriji zagrijavanjem na 750 ◦C. Utvrdili smo veličine zrna od samo 3.5 nm u čistom prahu BaTiO3. Podatke od DXZ potvrdili smo prolaznom elektronskom mikroskopijom. Mjerili smo fotoluminescentne spektre prahova BaTiO3:0.5% Eu3+, BaTiO3:1% Eu3+ i BaTiO3:2% Eu3+ na sobnoj temperaturi. U luminescentnim spektrima pripremljenih ultrafinih prahova prevladava prijelaz 5D0 →7F2 u Eu3+, što ukazuje na snažna izobličenja na mjestima Eu3+ iona. Ugrađeni se ioni Eu3+ uglavnom smještaju na tetragonalne položaje Ba2+, a velika razlika ionskih naboja dvaju kationa, Ba2+ i Eu3+, uzrokuje snažne promjene oko tog defekta. Dielektrične konstante, ε, prahova BaTiO3, BaTiO3:0.5% Eu3+, BaTiO3:1% Eu3+ i BaTiO3:2% Eu3+ na frekvenciji 100 Hz prema našim mjerenjima iznose 1000, 1211, 1455 odn. 1800. Smatramo da su tako velike vrijednosti dielektrične konstante posljedica povećanih veličina kristalita za veća punjenja ionima Eu3+. Nakon opuštanja u argonu na 400 ◦C tijekom dva sata, dielektrična konstanta čistog praha bila je 625, a otpornost se također smanjila. Izmjenična otpornost prahova BaTiO3 ovisi o punjenju ionima Eu3+ i nalazi se da se smanjuje kada se poveća sadržaj iona Eu3+
The star formation history of the Sextans dwarf spheroidal galaxy: a true fossil of the pre-reionization era
We present the star formation history (SFH) of the Sextans dwarf spheroidal
galaxy based on deep archive , photometry taken with Suprime-Cam at
Subaru telescope focusing our analysis on the inner region of the galaxy, fully
located within the core radius. Within the errors of our SFH we have not
detected any metallicity gradient along the considered radial distance
interval. As a main result of this work we can state that the Sextans dwarf
spheroidal stopped forming stars less than Gyr after Big Bang in
correspondance to the end of the reionization epoch. We have been able to
constrain the duration of the main burst of star formation to Gyr.
From the calculation of the mechanical luminosity released from supernovae
(SNe) during the brief episode of star formation, there are strong indications
that SNe could have played an important role in the fate of Sextans, by
removing almost completely the gas component, so preventing a prolonged star
formation.Comment: 11 pages, 10 figures. Accepted for publication in MNRA
High pressure Raman, optical absorption, and resistivity study of SrCrO4
We studied the electronic and vibrational properties of monazite-type SrCrO4 under compression. The study extended the pressure range of previous studies from 26 to 58 GPa. The existence of two previously reported phase transitions was confirmed at 9 and 14 GPa, and two new phase transitions were found at 35 and 48 GPa. These transitions involve several changes in the vibrational and transport properties with the new high-pressure phases having a conductivity lower than that of the previously known phases. No evidence of chemical decomposition or metallization of SrCrO4 was detected. A tentative explanation for the reported observations is discussed
Random lasing in Nd:LuVO4 crystal powder
Room temperature random lasing action is demonstrated for the first time in a low concentrated neodymium doped vanadate crystal powder. Laser threshold and emission efficiency are comparable to the ones obtained in stoichiometric borate crystal powders. The present investigation provides a complete picture of the random lasing characteristics of Nd-doped vanadate powder both in the spectral and temporal domain, together with a simplified model which accounts for the most relevant features of the random laser. © 2011 Optical Society of America.Peer Reviewe
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