440 research outputs found
Factorization Approach for Inclusive Production of Doubly Heavy Baryon
We study inclusive production of doubly heavy baryon at a collider
and at hadron colliders through fragmentation. We study the production by
factorizing nonpertubative- and perturbative effects. In our approach the
production can be thought as a two-step process: A pair of heavy quarks can be
produced perturbatively and then the pair is transformed into the baryon. The
transformation is nonperturbative. Since a heavy quark moves with a small
velocity in the baryon in its rest frame, we can use NRQCD to describe the
transformation and perform a systematic expansion in the small velocity. At the
leading order we find that the baryon can be formed from two states of the
heavy-quark pair, one state is with the pair in state and in color
, another is with the pair in state and in color . Two matrix elements are defined for the transformation from the two
states, their perturbative coefficients in the contribution to the
cross-section at a collider and to the function of heavy quark
fragmentation are calculated. Our approach is different than previous
approaches where only the pair in state and in color is
taken into account. Numerical results for colliders at the two
-factories and for hadronic colliders LHC and Tevatron are given.Comment: Add results for large p_t, minor change
Large Lepton Mixings from Continuous Symmetries
Within the broad context of quark-lepton unification, we investigate the
implications of broken continuous family symmetries which result from requiring
that in the limit of exact symmetry, the Dirac mass matrices yield hierarchical
masses for the quarks and charged leptons, but lead to degenerate light
neutrino masses as a consequence of the seesaw mechanism, without requiring
hierarchical right-handed neutrino mass terms. Quark mixing is then naturally
small and proportional to the size of the perturbation, but lepton mixing is
large as a result of degenerate perturbation theory, shifted from maximal
mixing by the size of the perturbation. Within this approach, we study an
illustrative two-family prototype model with an SO(2) family symmetry, and
discuss extensions to three-family models.Comment: 23 page
S_3 Symmetry and Neutrino Masses and Mixings
Based on a universal seesaw mass matrix model with three scalars \phi_i, and
by assuming an S_3 flavor symmetry for the Yukawa interactions, the lepton
masses and mixings are investigated systematically. In order to understand the
observed neutrino mixing, the charged leptons (e, \mu, \tau) are regarded as
the 3 elements (e_1, e_2, e_3) of S_3, while the neutrino mass-eigenstates are
regarded as the irreducible representation (\nu_\eta, \nu_\sigma, \nu_\pi) of
S_3, where (\nu_\pi, \nu_\eta) and \nu_\sigma are a doublet and a singlet,
respectively, which are composed of the 3 elements (\nu_1, \nu_2, \nu_3) of
S_3.Comment: 16 pages, no figure, version to appear in EPJ-
The newly observed open-charm states in quark model
Comparing the measured properties of the newly observed open-charm states
D(2550), D(2600), D(2750), D(2760), D_{s1}(2710), D_{sJ}(2860), and
D_{sJ}(3040) with our predicted spectroscopy and strong decays in a constituent
quark model, we find that: (1) the D(2\,^1S_0) assignment to D(2550) remains
open for its too broad width determined by experiment; (2) the D(2600) and
can be identified as the 2\,^3S_1-1\,^3D_1 mixtures; (3) if
the D(2760) and D(2750) are indeed the same resonance, they would be the
D(1\,^3D_3); otherwise, they could be assigned as the D(1\,^3D_3) and
, respectively; (4) the could be either the
's partner or the D_s(1\,^3D_3); and (5) both the
and interpretations for the seem likely. The
and radiative decays of these sates are also studied. Further
experimental efforts are needed to test the present quarkonium assignments for
these new open-charm states.Comment: 26 pages,7 figures, journal versio
A supernova constraint on bulk majorons
In models with large extra dimensions all gauge singlet fields can in
principle propagate in the extra dimensional space. We have investigated
possible constraints on majoron models of neutrino masses in which the majorons
propagate in extra dimensions. It is found that astrophysical constraints from
supernovae are many orders of magnitude stronger than previous accelerator
bounds. Our findings suggest that unnatural types of the "see-saw" mechanism
for neutrino masses are unlikely to occur in nature, even in the presence of
extra dimensions.Comment: Minor changes, matches the version to appear in PR
Pilot Testing of Assessment of Capacity for Myoelectric Control (ACMC) in Evaluating Myoelectric Hand Function in Chinese Population
Upper limb amputations cause marked functional disability and lower the individualâs self-body image, with severepsychological implications. Many rehabilitation parameters are involved in the successful rehabilitation of upper limbamputations. The aim of this study was to examine the validity and reliability of the Chinese version of Assessment ofCapacity for Myoelectric Control (Chinese-ACMC) in upper limb amputated subjects and with a myo-electric-poweredprosthetic hand.To validate the Chinese version of Assessment of Capacity for Myoelectric Control (Chinese-ACMC) in upper limbamputee subjects (children and adults) with a myo-electric-powered prosthetic hand. A sample of convenience samplingof 22 subjects (11 males, 11 females) with upper limb amputation and myoelectric prosthetic hands were recordedduring a regular clinical visit for ACMC. Each subject was evaluated according to four criteria: (a) Upper Limb Amputationincluding all levels of amputation; (b) No specific pain type â no matter phantom or pain in the stump; (c) With intactcognitive function; (d) Age ranged from 12 to 40 years. With instruction, occupational therapists and prosthetic-orthoticswith at least twenty yearsâ clinical experience of myoelectric prosthesis training would conduct the 30-items ChineseACMC for each subject. A serial of errand tasks of activities of daily living were designed for evaluation. Individualsâratings were repeated after 4 weeks. Through test-retest reliability, internal consistency testing, factor analysis, intra andinter factor correlation analysis. A four-factor structure, namely, âGrippingâ, âHoldingâ, âReleasingâ and âCoordinatingâare identified
S4 Flavor Symmetry and Fermion Masses: Towards a Grand Unified theory of Flavor
Pursuing a bottom-up approach to explore which flavor symmetry could serve as
an explanation of the observed fermion masses and mixings, we discuss an
extension of the standard model (SM) where the flavor structure for both quarks
and leptons is determined by a spontaneously broken S4 and the requirement that
its particle content is embeddable simultaneously into the conventional SO(10)
grand unified theory (GUT) and a continuous flavor symmetry G_f like SO(3)_f or
SU(3)_f. We explicitly provide the Yukawa and the Higgs sector of the model and
show its viability in two numerical examples which arise as small deviations
from rank one matrices. In the first case, the corresponding mass matrix is
democratic and in the second one only its 2-3 block is non-vanishing. We
demonstrate that the Higgs potential allows for the appropriate vacuum
expectation value (VEV) configurations in both cases, if CP is conserved. For
the first case, the chosen Yukawa couplings can be made natural by invoking an
auxiliary Z2 symmetry. The numerical study we perform shows that the best-fit
values for the lepton mixing angles theta_12 and theta_23 can be accommodated
for normal neutrino mass hierarchy. The results for the quark mixing angles
turn out to be too small. Furthermore the CP-violating phase delta can only be
reproduced correctly in one of the examples. The small mixing angle values are
likely to be brought into the experimentally allowed ranges by including
radiative corrections. Interestingly, due to the S4 symmetry the mass matrix of
the right-handed neutrinos is proportional to the unit matrix.Comment: 27 pages, published version with minor change
Can lepton flavor violating interactions explain the LSND results?
If the atmospheric and the solar neutrino problem are both explained by
neutrino oscillations, and if there are only three light neutrinos, then all
mass-squared differences between the neutrinos are known. In such a case,
existing terrestrial neutrino oscillation experiments cannot be significantly
affected by neutrino oscillations, but, in principle there could be an anomaly
in the neutrino flux due to new neutrino interactions. We discuss how a
non-standard muon decay would modify the
neutrino production processes of these experiments. Since violation
is small for New Physics above the weak scale one can use related
flavor-violating charged lepton processes to constrain these decays in a model
independent way. We show that the upper bounds on ,
muonium-antimuonium conversion and rule out any observable
effect for the present experiments due to
for , respectively. Applying similar arguments to
flavor-changing semi-leptonic reactions we exclude the possibility that the
"oscillation signals" observed at LSND are due to flavor-changing interactions
that conserve total lepton number.Comment: 21 pages, 6 figures, Latex; minor correction
The development of pharyngeal taste buds in Hucho taimen (Pallas, 1773) larvae
This study aims to investigate the relationship between the development of pharyngeal taste buds (TBs) and first feeding of Hucho taimen. Larvae were fed with live food (water flea and tubifex) for 8 weeks. TBs of larval pharynx were histologically examined using light microscopy during the rearing experiment. The results showed that the first few TBs primordia were visible within the pharynx 27 days after hatch (DAH), which coincides with the onset of feeding, and the first few TBs with open receptor areas appear 45 DAH. TBs of pharynx were well developed 76 DAH. The number and size of TBs were quantiïŹed during larval development. The average number of pharynx was 8.63±1.15, 11.29±0.50, 14.50±1.06, and 17.78±0.47 TBs at 27, 36, 45, and 76 DAH, respectively. The number of TBs increased in both the upper and lower pharynx. The ratio of height to width of TBs showed an increase tendency, ranging from 0.81 to 1.11. The height of TBs showed an increase tendency after 29 DAH during the development. However, the width of TBs exhibited a low at 35 DAH. In conclusion, the development of pharyngeal TBs coincides with the first feeding, and this should lead to a better understanding of improvement of larval rearing in H. taimen hatcheries
Sensitivity of deexcitation energies of superdeformed secondary minima to the density dependence of symmetry energy with the relativistic mean-field theory
The relationship between deexcitation energies of superdeformed secondary
minima relative to ground states and the density dependence of the symmetry
energy is investigated for heavy nuclei using the relativistic mean field (RMF)
model. It is shown that the deexcitation energies of superdeformed secondary
minima are sensitive to differences in the symmetry energy that are mimicked by
the isoscalar-isovector coupling included in the model. With deliberate
investigations on a few Hg isotopes that have data of deexcitation energies, we
find that the description for the deexcitation energies can be improved due to
the softening of the symmetry energy. Further, we have investigated
deexcitation energies of odd-odd heavy nuclei that are nearly independent of
pairing correlations, and have discussed the possible extraction of the
constraint on the density dependence of the symmetry energy with the
measurement of deexcitation energies of these nuclei.Comment: 14 pages, 3 figure
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