1,657 research outputs found
Light hadron production in decays
The article is devoted to Bc->Bs+n pi, Bc->Bs*+n pi decays with n=1, 2, 3, 4.
In the framework of factorization theorem the branching fractions of these
processes can be written as convolution of hard part, describing Bc->Bs W,
Bc->Bs* W vertices, and spectral functions, that correspond to transition of
virtual -boson into a final pi-meson system. These functions were obtained
from the fit of experimental data on -lepton decay and electron-positron
annihilation. Using different sets of Bc->Bs decay form-factors we present
branching fractions and distributions over the invariant mass of the final
pi-meson system.Comment: minor changes, some references adde
Pressure-driven metal-insulator transition in BiFeO from Dynamical Mean-Field Theory
A metal-insulator transition (MIT) in BiFeO under pressure was
investigated by a method combining Generalized Gradient Corrected Local Density
Approximation with Dynamical Mean-Field Theory (GGA+DMFT). Our paramagnetic
calculations are found to be in agreement with experimental phase diagram:
Magnetic and spectral properties of BiFeO3 at ambient and high pressures were
calculated for three experimental crystal structures , and
. At ambient pressure in the phase, an insulating gap of 1.2
eV was obtained in good agreement with its experimental value. Both and
phases have a metal-insulator transition that occurs simultaneously with
a high-spin (HS) to low-spin (LS) transition. The critical pressure for the
phase is 25-33 GPa that agrees well with the experimental observations.
The high pressure and temperature phase exhibits a metallic
behavior observed experimentally as well as in our calculations in the whole
range of considered pressures and undergoes to the LS state at 33 GPa where a
to transition is experimentally observed. The
antiferromagnetic GGA+DMFT calculations carried out for the structure
result in simultaneous MIT and HS-LS transitions at a critical pressure of 43
GPa in agreement with the experimental data
Doping-driven Mott transition in La_{1-x}Sr_xTiO_3 via simultaneous electron and hole doping of t2g subbands
The insulator to metal transition in LaTiO_3 induced by La substitution via
Sr is studied within multi-band exact diagonalization dynamical mean field
theory at finite temperatures. It is shown that weak hole doping triggers a
large interorbital charge transfer, with simultaneous electron and hole doping
of t2g subbands. The transition is first-order and exhibits phase separation
between insulator and metal. In the metallic phase, subband compressibilities
become very large and have opposite signs. Electron doping gives rise to an
interorbital charge flow in the same direction as hole doping. These results
can be understood in terms of a strong orbital depolarization.Comment: 4 pages, 5 figure
Role of Coulomb correlation on magnetic and transport properties of doped manganites: La0.5Sr0.5MnO3 and LaSr2Mn2O7
Results of LSDA and LSDA+U calculations of the electronic structure and
magnetic configurations of the 50% hole-doped pseudocubic perovskite
La0.5Sr0.5MnO3 and double layered LaSr2Mn2O7 are presented. We demonstrate that
the on-site Coulomb correlation (U) of Mn d electrons has a very different
influence on the (i) band formations, (ii) magnetic ground states, (iii)
interlayer exchange interactions, and (iv) anisotropy of the electrical
transport in these two manganites. A possible reason why the LSDA failures in
predicting observed magnetic and transport properties of the double layered
compound - in contrast to the doped perovskite manganite - is considered on the
basis of a p-d hybridization analysis.Comment: 11 pages, 3 figure
Non-leptonic two-body decays of the Bc meson in light-front quark model and QCD factorization approach
We study exclusive non-leptonic two-body
decays with (pseudoscalar or vector meson) being factored out in QCD
factorization approach. The non-leptonic decay amplitudes are related to the
product of meson decay constants and the form factors for semileptonic
decays. As inputs in obtaining the branching ratios for a large set of
non-leptonic decays, we use the weak form factors for the semileptonic
decays in the whole kinematical region and the
unmeasured meson decay constants obtained from our previous light-front quark
model. We compare our results of the branching ratios with those of other
theoretical studies.Comment: 11 pages, 3 figures, minor corrections, version to appear in PR
Post density functional theoretical studies of highly polar semiconductive Pb(TiNi)O solid solutions: The effects of cation arrangement on band gap
We use a combination of conventional density functional theory (DFT) and
post-DFT methods, including the local density approximation plus Hubbard
(LDA+), PBE0, and self-consistent to study the electronic properties of
Ni-substituted PbTiO (Ni-PTO) solid solutions. We find that LDA
calculations yield unreasonable band structures, especially for Ni-PTO solid
solutions that contain an uninterrupted NiO layer. Accurate treatment of
localized states in transition-metal oxides like Ni-PTO requires post-DFT
methods. -site Ni/Ti cation ordering is also investigated. The -site
cation arrangement alters the bonding between Ni and O, and therefore strongly
affects the band gap () of Ni-PTO. We predict that Ni-PTO solid
solutions should have a direct band gap in the visible light energy range, with
polarization similar to the parent PbTiO. This combination of properties
make Ni-PTO solid solutions promising candidate materials for solar energy
conversion devices.Comment: 19 pages, 6 figure
Branching ratios of Bc Meson Decays into Tensor Meson in the Final State
Two-body hadronic weak decays of Bc meson involving tensor meson in the final
state are studied by using Isgur- Scora-Grinstein-Wise (ISGW II) model. Decay
amplitudes are obtained using the factorization scheme in the Spectator Quark
Model. Branching ratios for the charm changing and bottom changing decay modes
are predicted.Comment: 18 pages. accepted in Physical Review
Visible Effects of the Hidden Sector
The renormalization of operators responsible for soft supersymmetry breaking
is usually calculated by starting at some high scale and including only visible
sector interactions in the evolution equations, while ignoring hidden sector
interactions. Here we explain why this is correct only for the most trivial
structures in the hidden sector, and discuss possible implications. This
investigation was prompted by the idea of conformal sequestering. In that
framework hidden sector renormalizations by nearly conformal dynamics are
critical. In the original models of conformal sequestering it was necessary to
impose hidden sector flavor symmetries to achieve the sequestered form. We
present models which can evade this requirement and lead to no-scale or anomaly
mediated boundary conditions; but the necessary structures do not seem generic.
More generally, the ratios of scalar masses to gaugino masses, the -term,
the -term, -terms, and the gravitino mass can be significantly
affected.Comment: 23 pages, no figure
Study of exclusive semileptonic and nonleptonic decays of B-c(-) in a nonrelativistic quark model
We present results for different observables measured in semileptonic and nonleptonic decays of the B-c(-) meson. The calculations have been done within the framework of a nonrelativistic constituent quark model. In order to check the sensitivity of all our results against the interquark interaction we use five different quark-quark potentials. We obtain form factors, decay widths, and asymmetry parameters for semileptonic B-c(-)-> c (c) over bar and B-c(-)->(B) over bar decays. In the limit of infinite heavy quark mass, our model reproduces the constraints of heavy quark spin symmetry. For the actual heavy quark masses we find nonetheless large corrections to that limiting situation for some form factors. We also analyze exclusive nonleptonic two-meson decay channels within the factorization approximation
First-principles dynamical CPA to finite-temperature magnetism of transition metals
We present here the first-principles dynamical CPA (coherent potential
approximation) combined with the tight-binding LMTO LDA+U method towards
quantitative calculations of the electronic structure and magnetism at finite
temperatures in transition metals and compounds. The theory takes into account
the single-site dynamical charge and spin fluctuations using the functional
integral technique as well as an effective medium. Numerical results for Fe,
Co, and Ni show that the theory explains quantitatively the high-temperature
properties such as the effective Bohr magneton numbers and the excitation
spectra in the paramagnetic state, and describes the Curie temperatures
semiquantitatively.Comment: ICM'09 Proceeding
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