54,382 research outputs found
A unique distant submillimeter galaxy with an X-ray-obscured radio-luminous active galactic nucleus
We present a multiwavelength study of an atypical submillimeter galaxy in the
GOODS-North field, with the aim to understand its physical properties of
stellar and dust emission, as well as the central AGN activity. Although it is
shown that the source is likely an extremely dusty galaxy at high redshift, its
exact position of submillimeter emission is unknown. With the new NOEMA
interferometric imaging, we confirm that the source is a unique dusty galaxy.
It has no obvious counterpart in the optical and even NIR images observed with
HST at lambda~<1.4um. Photometric-redshift analyses from both stellar and dust
SED suggest it to likely be at z~>4, though a lower redshift at z~>3.1 cannot
be fully ruled out (at 90% confidence interval). Explaining its unusual
optical-to-NIR properties requires an old stellar population (~0.67 Gyr),
coexisting with a very dusty ongoing starburst component. The latter is
contributing to the FIR emission, with its rest-frame UV and optical light
being largely obscured along our line of sight. If the observed fluxes at the
rest-frame optical/NIR wavelengths were mainly contributed by old stars, a
total stellar mass of ~3.5x10^11Msun would be obtained. An X-ray spectral
analysis suggests that this galaxy harbors a heavily obscured AGN with
N_H=3.3x10^23 cm^-2 and an intrinsic 2-10 keV luminosity of L_X~2.6x10^44
erg/s, which places this object among distant type 2 quasars. The radio
emission of the source is extremely bright, which is an order of magnitude
higher than the star-formation-powered emission, making it one of the most
distant radio-luminous dusty galaxies. The combined characteristics of the
galaxy suggest that the source appears to have been caught in a rare but
critical transition stage in the evolution of submillimeter galaxies, where we
are witnessing the birth of a young AGN and possibly the earliest stage of its
jet formation and feedback.Comment: 13 pages in printer format, 10 figures, 1 table, accepted for
publication in the A&
Helicity Probabilities For Heavy Quark Fragmentation Into Excited Mesons
In the fragmentation of a heavy quark into a heavy meson whose light degrees
of freedom have angular momentum , all the helicity probabilities are
completely determined in the heavy quark limit up to a single probability
. We point out that this probability depends on the longitudinal
momentum fraction of the meson and on its transverse momentum
relative to the jet axis. We calculate as a function of scaling
variables corresponding to and for the heavy quark limit of the
perturbative QCD fragmentation functions for quark to fragment into mesons. In this model, the light degrees of freedom prefer to have
their angular momentum aligned transverse to, rather than along, the jet axis.
Implications for the production of excited heavy mesons, like and
, are discussed.Comment: 10 pages, Latex file plus 3 figures with postscript files appended at
the en
Search for via the transition at LHCb and factory
It is interesting to study the characteristics of the whole family of
which contains two different heavy flavors. LHC and the proposed factory
provide an opportunity because a large database on the family will be
achieved. and its excited states can be identified via their decay modes.
As suggested by experimentalists, is not easy to be
clearly measured, instead, the trajectories of and occurring in
the decay of () can be unambiguously
identified, thus the measurement seems easier and more reliable, therefore this
mode is more favorable at early running stage of LHCb and the proposed
factory. In this work, we calculate the rate of
in terms of the QCD multipole-expansion and the numerical results indicate that
the experimental measurements with the luminosity of LHC and factory are
feasible.Comment: 12 pages, 1 figures and 4 tables, acceptted by SCIENCE CHINA Physics,
Mechanics & Astronomy (Science in China Series G
The magnetic dipole transitions in the binding system
The magnetic dipole transitions between the vector mesons and their
relevant pseudoscalar mesons (, , , ,
and etc, the binding states of system) of
the family are interesting. To see the `hyperfine' splitting due to
spin-spin interaction is an important topic for understanding the spin-spin
interaction and the spectrum of the the binding system. The
knowledge about the magnetic dipole transitions is also very useful for
identifying the vector boson mesons experimentally, whose masses are
just slightly above the masses of their relevant pseudoscalar mesons
accordingly. Considering the possibility to observe the vector mesons via the
transitions at factory and the potentially usages of the theoretical
estimate on the transitions, we fucus our efforts on calculating the magnetic
dipole transitions, i.e. precisely to calculate the rates for the transitions
such as decays and , and particularly
work in the Behte-Salpeter framework. In the estimate, as a typical example, we
carefully investigate the dependance of the rate
on the mass difference as well.Comment: 10 pages, 2 figures, 1 tabl
Towards a CPT Invariant Quantum Field Theory on Elliptic de Sitter Space
Consequences of Schr\"{o}dinger's antipodal identification on quantum field
theory in de Sitter space are investigated. The elliptic
identification provides observers with complete information. We show that a
suitable confinement on dimension of the elliptic de Sitter space guarantees
the existence of globally defined spinors and orientable
manifold. In Beltrami coordinates, we give exact solutions of scalar and spinor
fields. The CPT invariance of quantum field theory on the elliptic de Sitter
space is presented explicitly.Comment: 16 pages, some references have been added, the structure of paper
have been revised, accepted for publication in Int. J. Mod. Phys.
Testing systems of identical components
We consider the problem of testing sequentially the components of a multi-component reliability system in order to figure out the state of the system via costly tests. In particular, systems with identical components are considered. The notion of lexicographically large binary decision trees is introduced and a heuristic algorithm based on that notion is proposed. The performance of the heuristic algorithm is demonstrated by computational results, for various classes of functions. In particular, in all 200 random cases where the underlying function is a threshold function, the proposed heuristic produces optimal solutions
The Domination Number of Grids
In this paper, we conclude the calculation of the domination number of all
grid graphs. Indeed, we prove Chang's conjecture saying that for
every , .Comment: 12 pages, 4 figure
Hadronic Production of S-wave and P-wave Charmed Beauty Mesons via Heavy Quark Fragmentation
At hadron colliders the dominant production mechanism of mesons
with large transverse momentum is due to parton fragmentation. We compute the
rates and transverse momentum spectra for production of S-wave and P-wave
mesons at the Tevatron via the direct fragmentation of the bottom
antiquark as well as the Altarelli-Parisi induced gluon fragmentation. Since
all the radially and orbitally excited mesons below the
flavor threshold will cascade into the pseudoscalar ground state through
electromagnetic and/or hadronic transitions, they all contribute to the
inclusive production of . The contributions of the excited S-wave and
P-wave states to the inclusive production of are 58 and 23\%,
respectively, and hence significant.Comment: Changes are made in the Discussio
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