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The recent experimental developments require a more precise theoretical study of weak decays of heavy baryon Λb0. In this work, we provide an updated and systematic analysis of both the semi-leptonic and nonleptonic decays of Λb0 into baryons Λc+, Λ, p, and n. The diquark approximation is adopted so that the methods developed in the B meson system can be extended into the baryon system. The baryon-to-baryon transition form factors are calculated in the framework of a covariant light-front quark model. The form factors f3, g3 can be extracted and are found to be non-negligible. The semileptonic processes of Λb0→Λc+(p)l−ν¯l are calculated and the results are consistent with the experiment. We study the nonleptonic processes within the QCD factorization approach. The decay amplitudes are calculated at the next-to-leading order in strong coupling constant αs. We calculate the nonleptonic decays of Λb0 into a baryon and a s-wave meson (pseudoscalar or vector) including 44 processes in total. The branching ratios and direct CP asymmetries are predicted. The numerical results are compared to the experimental data and those in the other theoretical approaches. Our results show validity of the diquark approximation and application of QCD factorization approach into the heavy baryon system.

The mixing of η−η′ or η−η′−G is of a great theoretical interest, because it concerns many aspects of the underlying dynamics and hadronic structure of pseudoscalar mesons and glueball. Determining the mixing parameters by fitting data is by no means trivial. In order to extract the mixing parameters from the available processes where hadrons are involved, theoretical evaluation of hadronic matrix elements is necessary. Therefore model dependence is somehow unavoidable. In fact, it is impossible to extract the mixing angle from a unique experiment because the model parameters must be obtained by fitting other experiments. Recently $\mathit{BR}(D\to\eta+\bar{l}+\nu_{l})$ and $\mathit{BR}(D_{s}\to\eta(\eta')+\bar{l}+\nu_{l})$ have been measured, thus we are able to determine the η−η′ mixing solely from the semileptonic decays of D-mesons where contamination from the final state interactions is absent. Thus we hope that the model dependence of the extraction can be somehow alleviated. Once $\mathit{BR}(D\to\eta'+\bar{l}+\nu_{l})$ is measured, we can further determine all the mixing parameters for η−η′−G. As more data are accumulated, the determination will be more accurate. In this work, we obtain the transition matrix elements of D (s)→η (′) using the light-front quark model whose feasibility and reasonability for such processes have been tested.

The lepton flavor violating process $J/\psi\to ll' (l\neq l')$ serves as an ideal place to probe the unparticle theory. Such process can only occur at loop level in the Standard model (SM), so that should be very suppressed, by contrast in unparticle scenario, it happens at tree level and its contribution may be sizable for practical measurement. Moreover, the BESIII will offer the largest database on $J/\psi$ which makes more accurate measurements possible. Furthermore, for such purely leptonic decays background is relatively low and signal would be cleaner. Our work carefully investigates the possibility of observing such processes from both theoretical and experimental aspects., Comment: 11 pages, 2 figures, revised version for publication

To testify the validity of the perturbative QCD (pQCD) and investigate its application range, one should look for a suitable process to do the job. $B\to J/\psi D$ is a promising candidate. The linear momentum of the products is relatively small, so that there may exist a region where exchanged gluons are soft and the perturbative treatment may fail, so that the non-perturbative effect would be significant. We attribute such non-perturbative QCD effects into the long-distance final state interaction (FSI) which is estimated in this work. We find that the contribution from the FSI to the branching ratio is indeed sizable and may span a rather wide range of $10^{-6}\sim 10^{-5}$, and cover a region where the pQCD prediction has the same order. A more accurate measurement on its branching ratio may provide important information about the application region of pQCD and help to clarify the picture of the inelastic rescattering (i.e. FSI) which is generally believed to play an important role in B decays., Comment: 6 pages, 3 figures, 1 table. More references added. Typos corrected

The concept of exact and broken scale invariance is discussed. We give a brief introduction to unparticle physics. The neutral meson mixing can be caused by exchange of unparticle at the tree level. The constraints on interaction between unparticle and SM quarks are discussed.

In our previous study, we calculated the transition from factors of $J/\psi\to D^{(*)}_{(s)}$ using the QCD sum rules. Based on the factorization approximation, the obtained form factors can be applied to evaluate the weak non-leptonic decay rates of $J/\psi\to D^{(*)}_{(s)}+M$, where $M$ stands for a light pseudoscalar or vector meson. We predict that the branching ratio for inclusive non-leptonic two-body weak decays of $J/\psi$ which are realized via the spectator mechanism, can be as large as $1.3 \times 10^{-8}$, in particular, the branching ratio of $J/\psi\to D^{*\pm}_s+\rho^\mp$ can reach $5.3 \times 10^{-9}$. Such values will be marginally accessed by the ability of BESIII which will begin running very soon., Comment: 16 pages, revTex4, 1 figure

The mixing of K 0 – K 0 ¯ , D 0 – D 0 ¯ and B ( s ) 0 – B ( s ) 0 ¯ provides a sensitive probe to explore new physics beyond the Standard Model. The scale invariant unparticle physics recently proposed by Georgi can induce flavor-changing neutral current and contribute to the mixing at tree level. We investigate the unparticle effects on B 0 – B 0 ¯ and D 0 – D 0 ¯ mixing. Especially, the newly observed D 0 – D 0 ¯ mixing sets the most stringent constraints on the coupling of the unparticle to quarks.

We provide a comprehensive test of factorization in the heavy-heavy $B$ decays motivated by the recent experimental data from BELLE and BABAR collaborations. The penguin effects are not negligible in the B decays with two pseudoscalar mesons. The direct CP asymmetries are found to be a few percent. We give estimates on the weak annihilation contributions by analogy to the observed annihilation-dominated processes. The $N_c$ insensitivity of branching ratios indicates that the soft final state interactions are not dominant. We also study the polarizations in $B\to D^*D_{(s)}^*$ decays. The power law shows that the transverse perpendicular polarization fraction is small. The effects of the heavy quark symmetry breaking caused by the perturbative QCD and power corrections on the transverse polarization are also investigated., 23 pages, 1 figure, published version, one reference added

The study of exclusive B decays in perturbative QCD are complicated by the endpoint problem. In order to perform the perturbative calculation, the Sudakov effects are introduced to regulate the endpoint singularity. We provide a systematic analysis with leading and next-to-leading twist corrections for $B\to\pi$ form factors in pQCD approach. The intrinsic transverse momentum dependence of hadronic wave function and threshold resummation effects are included in pQCD approach. There are two leading twist B meson distribution amplitudes (or generally wave functions) in general. The QCD equations of motion provide important constraints on B meson wave functions. The reliability of pQCD approach in \bpi form factors is discussed. 70% of the result comes from the region $\alpha_s(t)/\pi, Comment: 30 pages, latex, some typos corrected, to appear in Nucl. Phys. B

Cascade mixing provides an elegant place to study the $B^0-\bar{B^0}$ mixing. We use this idea to study the CPT violation caused by $B^0-\bar{B^0}$ mixing. An approximation method is adopted to treat the two complex $B^0-\bar{B^0}$ mixing parameters $\theta$ and $\phi$. A procedure to extract the parameters $\theta$ and $\phi$ is suggested. The feasibility of exploring the CPT violation and determining of $\theta$ and $\phi$ in the future B-factories and LHC-B is discussed., Comment: Latex, 17 pages, some errors modified

T violation should be tested independently of CP violation. Besides K system, B meson decays provide another good place to study T violation. In the Standard Model, T violation in $B^0 \rightleftharpoons \bar{B^0}$ oscillation is expected to be small. The angular distribution of $B\to VV$ decay permits one to extract the T-odd correlation. In the absence of final state interaction, T violation in $B\to J/\psi(l^+ l^-) K^*(K_S\pi^0)$ decay can reach $4-7%$ via $B^0-\bar{B^0}$ mixing., Comment: Latex, 11 pages, revised version will appear in PLB

We study the final-state interactions in B --> pi K decays through B --> VV --> pi K processes where the inelastic rescattering occurs via single pion exchange. The next-to-leading order low-energy effective Hamiltonian and Bauer-Stech-Wirbel (BSW) model are used to evaluate the weak transition matrix elements and final-state interactions. We found that the final-state interaction effects in B --> rho K* --> pi K processes are significant. The Fleischer-Mannel relation for the Cabibbo-Kobayashi-Maskawa (CKM) angle gamma can be significantly modified.

Assuming the newly observed $Z_c(3900)$ to be a molecular state of $D\bar D^*(D^{*} \bar D)$, we calculate the partial widths of $Z_c(3900)\to J/\psi+\pi;\; \psi'+\pi;\; \eta_c+\rho$ and $D\bar D^*$ within the light front model (LFM). $Z_c(3900)\to J/\psi+\pi$ is the channel by which $Z_c(3900)$ was observed, our calculation indicates that it is indeed one of the dominant modes whose width can be in the range of a few MeV depending on the model parameters. Similar to $Z_b$ and $Z_b'$, Voloshin suggested that there should be a resonance $Z_c'$ at 4030 MeV which can be a molecular state of $D^*\bar D^*$. Then we go on calculating its decay rates to all the aforementioned final states and as well the $D^*\bar D^*$. It is found that if $Z_c(3900)$ is a molecular state of ${1\over\sqrt 2}(D\bar D^*+D^*\bar D)$, the partial width of $Z_c(3900)\to D\bar D^*$ is rather small, but the rate of $Z_c(3900)\to\psi(2s)\pi$ is even larger than $Z_c(3900)\to J/\psi\pi$. The implications are discussed and it is indicated that with the luminosity of BES and BELLE, the experiments may finally determine if $Z_c(3900)$ is a molecular state or a tetraquark., Comment: 17 pages, 6 figures, 3 tables

The successful operation of the LHC provides a great opportunity to study the processes where heavy baryons are involved. In this work we mainly study the weak transitions of ${\ensuremath{\Sigma}}_{b}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}_{c}$. Assuming the reasonable quark-diquark structure, where the two light quarks constitute an axial vector, we calculate the widths of semileptonic decay ${\ensuremath{\Sigma}}_{b}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}_{c}e{\ensuremath{\nu}}_{e}$ and nonleptonic decay modes ${\ensuremath{\Sigma}}_{b}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}_{c}+M$ (light mesons) in terms of the light-front quark model. We first construct the vertex function for the concerned baryons and then deduce the form factors which are related to two Isgur-Wise functions for the ${\ensuremath{\Sigma}}_{b}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}_{c}$ transition under the heavy quark limit. Our numerical results indicate that $\ensuremath{\Gamma}({\ensuremath{\Sigma}}_{b}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}_{c}e{\ensuremath{\nu}}_{e})$ is about $1.60\ifmmode\pm\else\textpm\fi{}0.28\ifmmode\times\else\texttimes\fi{}{10}^{10}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ and $\ensuremath{\Gamma}({\ensuremath{\Sigma}}_{b}\ensuremath{\rightarrow}{\ensuremath{\Sigma}}_{c}+M)$ is slightly below $1\ifmmode\times\else\texttimes\fi{}{10}^{10}\text{ }\text{ }{\mathrm{s}}^{\ensuremath{-}1}$, which may be accessed at the LHCb detector. By the flavor SU(3) symmetry, we estimate the rates of ${\ensuremath{\Omega}}_{b}\ensuremath{\rightarrow}{\ensuremath{\Omega}}_{c}$. We suggest measuring weak decays of ${\ensuremath{\Omega}}_{b}\ensuremath{\rightarrow}{\ensuremath{\Omega}}_{c}$, because ${\ensuremath{\Omega}}_{b}$ does not decay via strong interactions, creating an obvious advantage.

The light-front quark model has been applied to calculate the transition matrix elements of heavy hadron decays. However, it is noted that using the traditional wave functions of the light-front quark model given in the literature, the theoretically determined decay constants of the {Upsilon}(nS) obviously contradict the data. This implies that the wave functions must be modified. Keeping the orthogonality among the nS states and fitting their decay constants, we obtain a series of the wave functions for {Upsilon}(nS). Based on these wave functions and by analogy with the hydrogen atom, we suggest a modified analytical form for the {Upsilon}(nS) wave functions. Using the modified wave functions, the obtained decay constants are close to the experimental data. Then we calculate the rates of radiative decays of {Upsilon}(nS){yields}{eta}{sub b}+{gamma}. Our predictions are consistent with the experimental data on decays {Upsilon}(3S){yields}{eta}{sub b}+{gamma} within the theoretical and experimental errors.

In this work we calculate the branching ratios of semileptonic and nonleptonic decays of {lambda}{sub b} into light baryons (p and {lambda}), as well as the measurable asymmetries which appear in the processes, in the light-front quark model. In the calculation, we adopt the diquark picture and discuss the justifiability of applying the picture in our case. Our result on the branching ratio of {lambda}{sub b}{yields}{lambda}+J/{psi} is in good agreement with the data. More predictions are made in the same model and the results will be tested in the future experiments which will be conducted at the Large Hadron Collider beauty and even the International Linear Collider.

Only two isospin-singlet scalar mesons f{sub 0}(600) ({sigma}) and f{sub 0}(980) exist below 1 GeV, so that it is natural to suppose that they are two energy eigenstates which are mixtures of (1/{radical}(2))(uu+dd) and ss. Is this picture right? Generally, it is considered that f{sub 0}(600) mainly consists of (1/{radical}(2))(uu+dd); if so, the dominant component of f{sub 0}(980) should be ss. The recent measurement of the CLEO Collaboration on the branching ratio of D{sub s}{yields}f{sub 0}(980)e{sup +}{nu}{sub e} provides an excellent opportunity to test the structure of f{sub 0}(980), namely, whether the data can be understood as long as it consists of mainly the conventional qq structure. We calculate the form factors of D{sub s}{yields}f{sub 0}(980) in the light-front quark model and the corresponding branching ratio of the semileptonic decay. By fitting the data, we obtain the mixing angle {phi}. The obtained mixing angle shows that the ss component in f{sub 0}(980) may not be dominant.

The recent measurement on the decay constant of D{sub s} shows a discrepancy between theory and experiment. We study the leptonic and semileptonic decays of D and D{sub s} simultaneously within the standard model by employing a light-front quark model. There is space by tuning phenomenological parameters which can explain the 'f{sub D{sub s}} puzzle' and do not contradict other experiments on the semileptonic decays. We also investigate the leptonic decays of D and D{sub s} with a new physics scenario, unparticle physics. The unparticle effects induce a constructive interference with the standard model contribution. The nontrivial phase in unparticle physics could produce direct CP violation which may distinguish it from other new physics scenarios.

In this work, we calculate the form factors for $J/\psi\to \bar{D}^{(*)0}$ induced by the flavor changing neutral currents (FCNC) in terms of the QCD sum rules. Making use of these form factors, we further calculate the branching fractions of semileptonic decays $J/\psi \to \bar{D}^{(*)0} l ^+ l^-$ ($l=e, \mu$). In particular, we formulate the matrix element $$ with $T_{\mu\nu}$ being a tensor current, which was not fully discussed in previous literature. Our analysis indicates that if only the standard model (SM) applies, the production of single charmed mesons at the present electron-positron colliders is too small to be observed even the resonance effects are included, therefore if an anomalous production rates are observed, it would be a hint of new physics beyond SM. Even though the predicted branching ratios are beyond the reach of present facilities which can be seen from a rough order estimate, the more accurate formulation of the three point correlation function derived in this work has theoretical significance and the technique can also be applied to other places. In analog to some complicated theoretical derivations which do not have immediate phenomenological application yet, if the future experiments can provide sufficient luminosity and accuracy, the results would be helpful., Comment: 27 pages, 7 figures

In this review, we discuss some interesting issues in charm physics which is full with puzzles and challenges. So far in the field there exist many problems which have not obtained satisfactory answers yet and more unexpected phenomena have been observed at the present facilities of high energy physics. Charm physics may become an ideal place for searching new resonances and studying non-perturbative QCD effects, moreover probably is an area to explore new physics beyond the Standard Model. More data will be available at BESIII, B-factories, LHC and even future ILC which may open a wide window to a better understanding of the nature., 50 pages, 3 figures, minor modifications, several references added

It is interesting to search for new physics beyond the standard model at Large Hadron Collider beauty (LHCb). We suggest that weak decays of doubly charmed baryon such as ${\ensuremath{\Xi}}_{cc}(3520{)}^{+}$, ${\ensuremath{\Xi}}_{cc}^{++}$ to charmless final states would be a possible signal for new physics. In this work we consider two models, i.e. the unparticle and ${Z}^{\ensuremath{'}}$ as examples to study such possibilities. We also discuss the cases for ${\ensuremath{\Xi}}_{bb}^{0}$, ${\ensuremath{\Xi}}_{bb}^{\ensuremath{-}}$ which have not been observed yet, but one can expect to find them when LHCb begins running. Our numerical results show that these two models cannot result in sufficiently large decay widths, therefore if such modes are observed at LHCb, there must be a new physics other than the unparticle or ${Z}^{\ensuremath{'}}$ models.

Within the Standard Model, we investigate the semi-leptonic weak decays of $J/\psi$. The various form factors of $J/\psi$ transiting to a single charmed meson ($D^{(*)}_{(d,s)}$) are studied in the framework of the QCD sum rules. These form factors fully determine the rates of the weak semi-leptonic decays of $J/\psi$ and provide valuable information about the non-perturbative QCD effects. Our results indicate that the decay rate of the semi-leptonic weak decay mode $J/\psi \to D^{(*)-}_{s}+e^{+}+\nu_{e}$ is at order of $10^{-10}$., Comment: 28 pages, 6 figures, revised version to be published in Eur.Phys.J.C

The light cone method provides a convenient non-perturbative tool to study the heavy-to-light form factors. We construct a light cone quark model utilizing the soft collinear effective theory. In the leading order of effective theory, the ten $B$ to light physical form factors are reduced to three universal form factors which can be calculated as overlaps of hadron light front wave functions in the light cone quark model. The numerical results show that the leading contribution is close to the results from other approaches. The $q^2$ dependence of the heavy-to-light form factors are also presented., 25 pages, 4 figures

We study unparticle effects on particle and antiparticle osillations in meson-antimeson, and muonium-antimuonium systems. Unlike usual tree level contributions to meson oscillations from heavy particle exchange with small $\Gamma_{12}$, the unparticle may have sizeable contributions to both $M_{12}$ and $\Gamma_{12}$ due to fractional dimension $d_\U$ of the unparticle. We find that very stringent constraints on the unparticle and particle interactions can be obtained. If unparticle effect dominates the contributions (which may happen in $D^0-\bar D^0$ mixing) to meson mixing parameters $x$ and $y$, we find that $x/y =\cot(\pi d_\U)$. Interesting constraints on unparticle and particle interactions can also be obtained using muonion and antimuonion oscillation data. We also comment on unparticle effects on CP violation in meson oscillations., Comment: 14 pages, 4 figures

We study the productions of $p$-wave mesons ${K}_{0}^{*}(1430)$, ${K}_{1}(1270)$, and ${K}_{1}(1400)$ in $B$ decays. By the generalized factorization approach, we find that the branching ratios of $B\ensuremath{\rightarrow}{K}_{0}^{*}(1430)\ensuremath{\phi}$ are similar to those of $B\ensuremath{\rightarrow}K\ensuremath{\phi}$ while the branching ratios of $B\ensuremath{\rightarrow}{K}_{1}(1270)\ensuremath{\phi}$ and $B\ensuremath{\rightarrow}{K}_{1}(1400)\ensuremath{\phi}$ are $O({10}^{\ensuremath{-}5})$ and $O({10}^{\ensuremath{-}6})$, respectively. In terms of the observation of $B\ensuremath{\rightarrow}{K}_{1}(1270)\ensuremath{\gamma}$ by BELLE, we can remove the sign ambiguity in the mixing angle for physical states ${K}_{1}(1270)$ and ${K}_{1}(1400)$. In addition, we analyze annihilation contributions in the decays $B\ensuremath{\rightarrow}{K}_{1}\ensuremath{\phi}$ and we conclude that they could be neglected.

We reformulate the soft-collinear effective theory which includes the collinear quark and soft gluons. The quark form factor is used to prove that SCET$_{\rm II}$ reproduces the IR physics of the full theory. We give a factorization proof in deep inelastic lepton-hadron scattering by use of the position space formulation., 14 pages. The revised version which modifies largely will appear in PLB

The pion electromagnetic form factor with leading and next-to-leading twist corrections is studied in the framework of the pQCD approach. We find that the Sudakov effects provide a weak suppression of the nonperturbative contributions at the experimental accessible energy region. We also find a large twist-3 contribution. Our conclusion is that the prediction of the pion form factor in the pQCD approach is not precise.

It is believed that the production rate of $D^0\to K^0\bar K^0$ is almost solely determined by final state interactions (FSI) and hence provides an ideal place to test FSI models. Here we examine model calculations of the contributions from s-channel resonance $f_J(1710)$ and t-channel exchange to the FSI effects in $D^0\to K^0\bar K^0$. The contribution from s-channel $f_0(1710)$ is sma$ For the t-channel FSI evaluation, we employ the one-particle-exchange (OPE) model and Regge model respecti$ The results from two methods are roughly consistent with each other and can reproduce the large rate of $D^0\to K^0\bar K^0$ reasonably well$

The space-like penguin contributions to branching ratios and CP asymmetries in charmless decays of $B_{c}$ to two pseudoscalar mesons are studied using the next-to-leading order low energy effective Hamiltonian and factorization approximation. Both the gluonic penguin and the electroweak penguin diagrams are considered. In addition the annihilation diagram contributions are also taken in account. We find that the space-like penguin effects are significant., Latex, 13 pages, with 2 figures and 2 tables

The end-point singularity is an unsolved problem in BBNS approach. Incorporating the partonic transverse momentum and the Sudakov form factor, this problem can be solved model-independently. We discuss the Sudakov effects in BBNS approach. The BBNS approach is compared with the modified PQCD approach. The main idea of Sudakov form factor is briefly discussed. Our conclusion is that the twist-3 contribution for the hard spectator scattering is numerically not important in $B\to \pi\pi$ decays, compared with the twist-2 contribution., Comment: 16 pages, Latex, two figures, some typos corrected

With only the tree level operator, the decay of $\Lambda_b\rightarrow pK$ is predicted to be one order smaller than the experimental data. The QCD penguin effects should be taken into account. In this paper, we explore the one-loop QCD corrections to the decay of $\Lambda_b\to pK$ within the framework of QCD factorization approach. For the baryon system, the diquark approximation is adopted. The transition hadronic matrix elements between $\Lambda_b$ and $p$ are calculated in the light front quark model. The branching ratio of $\Lambda_b\rightarrow pK$ is predicted to be about $4.85\times 10^{-6}$ which is consistent with experimental data $(4.9\pm 0.9)\times 10^{-6}$. The CP violation is about 5\% in theory.