4,635 research outputs found
Is the meson a dynamically generated resonance? -- a lesson learned from the O(N) model and beyond
O(N) linear model is solvable in the large limit and hence
provides a useful theoretical laboratory to test various unitarization
approximations. We find that the large limit and the
limit do not commute. In order to get the correct large spectrum one has
to firstly take the large limit. We argue that the meson may
not be described as generated dynamically. On the contrary, it is most
appropriately described at the same level as the pions, i.e, both appear
explicitly in the effective lagrangian. Actually it is very likely the
meson responsible for the spontaneous chiral symmetry breaking in a lagrangian
with linearly realized chiral symmetry.Comment: 15 pages, 3 figurs; references added; discussions slightly modified;
revised version accepted by IJMP
Evolving small-world networks with geographical attachment preference
We introduce a minimal extended evolving model for small-world networks which
is controlled by a parameter. In this model the network growth is determined by
the attachment of new nodes to already existing nodes that are geographically
close. We analyze several topological properties for our model both
analytically and by numerical simulations. The resulting network shows some
important characteristics of real-life networks such as the small-world effect
and a high clustering.Comment: 11 pages, 4 figure
Branching Ratio and CP Asymmetry of B_s \to K^*_0(1430)\pi Decays in the PQCD Approach
In the two-quark model supposition for , the branching ratios
and the direct CP-violating asymmetries for decays are studied by employing the
perturbative QCD factorization approach. We find that although these two decays
are both tree-dominated, the ratio of their penguin to tree contributions are
very different: there is only a few percent for the decay , while about 37% in scenario I, even 51% in scenario II
for the decay . It results that these two
decays have very different values in the branching ratios and the direct CP
asymmetries. The branching ratio of the decay is at the order of , and its direct CP asymmetry
is about (20-30)%. While for the decay , its
direct CP-violating asymmetry is very large and about 90%, but it is difficult
to measure it, because the branching ratio for this channel is small and only
order.Comment: 8pages, 2figure
Massive and Massless Neutrinos on Unbalanced Seesaws
The observation of neutrino oscillations requires new physics beyond the
standard model (SM). A SM-like gauge theory with p lepton families can be
extended by introducing q heavy right-handed Majorana neutrinos but preserving
its SU(2)_L x U(1)_Y gauge symmetry. The overall neutrino mass matrix M turns
out to be a symmetric (p+q) x (p+q) matrix. Given p>q, the rank of M is in
general equal to 2q, corresponding to 2q non-zero mass eigenvalues. The
existence of (p-q) massless left-handed Majorana neutrinos is an exact
consequence of the model, independent of the usual approximation made in
deriving the Type-I seesaw relation between the effective p x p light Majorana
neutrino mass matrix M_\nu and the q x q heavy Majorana neutrino mass matrix
M_R. In other words, the numbers of massive left- and right-handed neutrinos
are fairly matched. A good example to illustrate this seesaw fair play rule is
the minimal seesaw model with p=3 and q=2, in which one massless neutrino sits
on the unbalanced seesaw.Comment: RevTex 8 pages, 1 PS figure. Two crucial references adde
Updated Values of Running Quark and Lepton Masses
Reliable values of quark and lepton masses are important for model building
at a fundamental energy scale, such as the Fermi scale M_Z \approx 91.2 GeV and
the would-be GUT scale \Lambda_GUT \sim 2 \times 10^16 GeV. Using the latest
data given by the Particle Data Group, we update the running quark and
charged-lepton masses at a number of interesting energy scales below and above
M_Z. In particular, we take into account the possible new physics scale (\mu
\sim 1 TeV) to be explored by the LHC and the typical seesaw scales (\mu \sim
10^9 GeV and \mu \sim 10^12 GeV) which might be relevant to the generation of
neutrino masses. For illustration, the running masses of three light Majorana
neutrinos are also calculated. Our up-to-date table of running fermion masses
are expected to be very useful for the study of flavor dynamics at various
energy scales.Comment: 23 pages, 6 tables, 2 figures; version published in PR
Study of f_0(980) and f_0(1500) from B_s \to f_0(980)K, f_0(1500)K Decays
In this paper, we calculate the branching ratios and CP-violating asymmetries
for \bar B^0_s \to f_0(980)K, f_0(1500)K within Perturbative QCD approach based
on k_T factorization. If the mixing angle falls into the range of
25^\circ<\theta<40^\circ, the branching ratio of \bar B^0_s\to f_0(980)K is
2.0\times 10^{-6}<{\cal B}(\bar B^0_s\to f_0(980)K)<2.6\times 10^{-6}, while
lies in the range of 140^\circ<\theta<165^\circ, {\cal B}(\bar
B^0_s\to f_0(980)K) is about 6.5\times 10^{-7}. As to the decay {\cal B}(\bar
B^0_s\to f_0(1500)K), when the mixing scheme \mid f_0(1500)>=0.84\mid s\bar
s>-0.54\mid n\bar n> for f_0(1500) is used, it is difficult to determine which
scenario is more preferable than the other one from the branching ratios for
these two scenarios, because they are both close to 1.0\times10^{-6}. But there
exists large difference in the form factor F^{\bar B_s^0\to f_0(1500)} for two
scenarios.Comment: 14 pages, 3 figures, submitted to J. Phys.
Analysis of the as a baryonium state with Bethe-Salpeter equation
In this article, we take the X(1835) as a pseudoscalar baryonium state, and
calculate the mass spectrum of the baryon-antibaryon bound states ,
, , and in the
framework of the Bethe-Salpeter equation with a phenomenological potential. The
numerical results indicate the , and
bound states maybe exist, and the can be tentatively
identified as the bound state.Comment: 7 pages, 1 figure, published versio
Meta-analysis: The Effect of Muscle Strength Training on Walking Ability of Patients with Parkinson's Disease
Objective: This Meta-analysis was aimed to systematically studying the effects of muscle strength training on the walking ability like balance ability, mobility ability of Parkinson's disease patients and then provide useful theoretical reference to further researches on exercise treatments on Parkinson’s disease by retrieving and collecting articles about muscle strength training. Methods This literature review was finally determined on searching PubMed, Elsevier, Web of science, China Journal Full-text Database (CNKI), WanFang Data and other Chinese and foreign databases and combined with manual search. The limit of the search time was from the date when the literature was recorded to 2019. A comprehensive collection of randomly controlled trials of muscle strength training on the walking ability of Parkinson's patients was done. Researchers used the Cochrance risk assessment tool to evaluate the methodological quality of the selected articles, and the ReMan 5.3.5 software to statistically process the obtained data. Results A total of 13 RCTs and 627 samples were included in this study. Meta-analysis of BBS balance scale show that MD=4.67 (95%CI, I2=97%, P=0.52) between muscle strength training group and non-exercise intervention group; MD=-2.67 between muscle strength training group and exercise intervention control group (95%CI, I2=7%, P<0.00001); TUGT Meta-analysis show that MD=-1.06 (95%CI, I2=75%, P=0.10) between muscle strength training group and non-exercise intervention group; MD=0.09 (95%CI, I2=0%, P=0.31) between the muscle strength training group and the control group with exercise intervention; 10MWT Meta-analysis show MD=-0.28 (95%CI), I2=98%, P<0.29) between the muscle strength training group and the control group with exercise intervention; Stride length Meta-analysis show MD=-1.85 (95%CI, I2=68%, P=0.63) between the muscle strength training group and the control group without exercise intervention; MD=-1.75 (95%CI, I2=32%, P=0.56) between the muscle strength training group and the control group with exercise intervention; MD=-1.75 (95%CI, I2=32%, P=0.56). Meta-analysis of stride speed show MD=-0.02 (95%CI, I2=0%, P=0.46) between muscle strength training group and control group without exercise intervention; MD=-0.03 (95%CI, I2=35%, P=0.52) between the muscle strength training group and control group with exercise intervention. Conclusion Muscle strength training can significantly improve the balance ability, mobility, and walking ability of Parkinson's disease patients, but it has no significant benefits on improving stride length and walking speed
Neutrino Masses, Lepton Flavor Mixing and Leptogenesis in the Minimal Seesaw Model
We present a review of neutrino phenomenology in the minimal seesaw model
(MSM), an economical and intriguing extension of the Standard Model with only
two heavy right-handed Majorana neutrinos. Given current neutrino oscillation
data, the MSM can predict the neutrino mass spectrum and constrain the
effective masses of the tritium beta decay and the neutrinoless double-beta
decay. We outline five distinct schemes to parameterize the neutrino
Yukawa-coupling matrix of the MSM. The lepton flavor mixing and baryogenesis
via leptogenesis are investigated in some detail by taking account of possible
texture zeros of the Dirac neutrino mass matrix. We derive an upper bound on
the CP-violating asymmetry in the decay of the lighter right-handed Majorana
neutrino. The effects of the renormalization-group evolution on the neutrino
mixing parameters are analyzed, and the correlation between the CP-violating
phenomena at low and high energies is highlighted. We show that the observed
matter-antimatter asymmetry of the Universe can naturally be interpreted
through the resonant leptogenesis mechanism at the TeV scale. The
lepton-flavor-violating rare decays, such as , are also
discussed in the supersymmetric extension of the MSM.Comment: 50 pages, 22 EPS figures, macro file ws-ijmpe.cls included, accepted
for publication in Int. J. Mod. Phys.
A New Method to Calculate Electromagnetic Impedance Matching Degree in One-Layer Microwave Absorbers
A delta-function method was proposed to quantitatively evaluate the
electromagnetic impedance matching degree. Measured electromagnetic parameters
of {\alpha}-Fe/Fe3B/Y2O3 nanocomposites are applied to calculate the matching
degree by the method. Compared with reflection loss and quarter-wave principle
theory, the method accurately reveals the intrinsic mechanism of microwave
transmission and reflection properties. A possible honeycomb structure with
promising high-performance microwave absorption according to the method is also
proposed.Comment: 13 pages, 3 figure
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