151,526 research outputs found
Subleading Shape-Function Effects and the Extraction of |V_ub|
We derive a class of formulae relating moments of B -> Xu l nu to B -> Xs
gamma in the shape function region, where m_X^2 ~ m_b Lambda_QCD. We also
derive an analogous class of formulae involving the decay B -> Xs l+ l-. These
results incorporate Lambda_QCD/m_b power corrections, but are independent of
leading and subleading hadronic shape functions. Consequently, they enable one
to determine |V_ub|/|V_tb V_ts*| to subleading order in a model-independent
way.Comment: 23 page
Planetary companions orbiting M giants HD 208527 and HD 220074
Aims. The purpose of the present study is to research the origin of planetary
companions by using a precise radial velocity (RV) survey.
Methods. The high-resolution spectroscopy of the fiber-fed Bohyunsan
Observatory Echelle Spectrograph (BOES) at Bohyunsan Optical Astronomy
Observatory (BOAO) is used from September 2008 to June 2012.
Results. We report the detection of two exoplanets in orbit around HD 208527
and HD 220074 exhibiting periodic variations in RV of 875.5 +/- 5.8 and 672.1
+/- 3.7 days. The RV variations are not apparently related to the surface
inhomogeneities and a Keplerian motion of the planetary companion is the most
likely explanation. Assuming possible stellar masses of 1.6 +/- 0.4 and 1.2 +/-
0.3 M_Sun, we obtain the minimum masses for the exoplanets of 9.9 +/- 1.7 and
11.1 +/- 1.8 M_Jup around HD 208527 and HD 220074 with an orbital semi-major
axis of 2.1 +/- 0.2 and 1.6 +/- 0.1 AU and an eccentricity of 0.08 and 0.14,
respectively. We also find that the previously known spectral classification of
HD 208527 and HD 220074 was in error: Our new estimation of stellar parameters
suggest that both HD 208527 and HD 220074 are M giants. Therefore, HD 208527
and HD 220074 are so far the first candidate M giants to harbor a planetary
companion.Comment: 7 pages, 9 figures, 4 tables, accepted for publisation in Astronomy &
Astrophysic
The vibrational predissociation spectroscopy of hydrogen cluster ions
The first infrared spectra of protonated hydrogen clusters in the gas phase have been observed. Predissociation spectra were taken with a tandem mass spectrometer: mass selected hydrogen cluster ions were irradiated inside a rf ion trap by a tunable infrared laser, and the fragment ions created by photodissociation of the clusters were mass selected and detected. Spectra for each product channel were measured by counting fragment ions as a function of laser frequency. Low resolution spectra (Deltanu=10 cm^−1) in the region from 3800 to 4200 cm^−1 were observed for the ions H + 5, H + 7, and H + 9 at 3910, 3980, and 4020 cm−1, respectively. A band was also observed for H + 5 at 3532 cm^−1. No rotational structure was resolved. The frequencies of the band maxima agree well with the frequencies predicted by previous ab initio calculations for the highest modes
Quasiclassical Green function in an external field and small-angle scattering
The quasiclassical Green functions of the Dirac and Klein-Gordon equations in
the external electric field are obtained with the first correction taken into
account. The relevant potential is assumed to be localized, while its spherical
symmetry is not required. Using these Green functions, the corresponding wave
functions are found in the approximation similar to the Furry-Sommerfeld-Maue
approximation. It is shown that the quasiclassical Green function does not
coincide with the Green function obtained in the eikonal approximation and has
a wider region of applicability. It is illustrated by the calculation of the
small-angle scattering amplitude for a charged particle and the forward photon
scattering amplitude. For charged particles, the first correction to the
scattering amplitude in the non-spherically symmetric potential is found. This
correction is proportional to the scattering angle. The real part of the
amplitude of forward photon scattering in a screened Coulomb potential is
obtained.Comment: 20 pages, latex, 1 figur
Bloch-Nordsieck cancellations beyond logarithms in heavy particle decays
We investigate the one-loop radiative corrections to the semileptonic decay
of a charged particle at finite gauge boson mass. Extending the Bloch-Nordsieck
cancellation of infrared logarithms, the subsequent non-analytic terms are also
found to vanish after eliminating the pole mass in favor of a mass defined at
short distances. This observation justifies the operator product expansion for
inclusive decays of heavy mesons and implies that infrared effects associated
with the summation of the radiative corrections are suppressed by at least
three powers of the mass of the heavy decaying particle.Comment: LATEX, 7 pages, one figure appended as uu-encoded ps-file,
MPI-PhT/94-1
Charge ordering in doped manganese oxides: lattice dynamics and magnetic structure
Based on the Hamiltonian of small polarons with the strong nearest neighbor
repulsion, we have investigated the charge ordering phenomena observed in
half-doped manganites R_{1/2}A_{1/2}MnO_3. We have explored possible
consequences of the charge ordering phase in the half-doped manganites. First,
we have studied the renormalization of the sound velocity around ,
considering the acoustic phonons coupled to the electrons participating in the
charge ordering. Second, we have found a new antiferromagnetic phase induced by
the charge ordering, and discussed its role in connection with the specific
CE-type antiferromagnetic structure observed in half-doped manganites.Comment: 5 pages, 2 Postscript figures. To appear in Phys. Rev. B - Rapid
Comm. (01Jun97
Sandpiles on multiplex networks
We introduce the sandpile model on multiplex networks with more than one type
of edge and investigate its scaling and dynamical behaviors. We find that the
introduction of multiplexity does not alter the scaling behavior of avalanche
dynamics; the system is critical with an asymptotic power-law avalanche size
distribution with an exponent on duplex random networks. The
detailed cascade dynamics, however, is affected by the multiplex coupling. For
example, higher-degree nodes such as hubs in scale-free networks fail more
often in the multiplex dynamics than in the simplex network counterpart in
which different types of edges are simply aggregated. Our results suggest that
multiplex modeling would be necessary in order to gain a better understanding
of cascading failure phenomena of real-world multiplex complex systems, such as
the global economic crisis.Comment: 7 pages, 7 figure
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