arXiv subjects

Chun-Khiang Chua

Publications and source records attributed to Chun-Khiang Chua.

At least 37 records · Page 2Linked to original sources

arXiv2015

Revisiting Scalar Glueballs

It is commonly believed that the lowest-lying scalar glueball lies somewhere in the isosinglet scalar mesons $f_0(1370), f_0(1500)$ and $f_0(1710)$ denoted generically by $f_{0}$. In this work we consider lattice calculations and experimental data to infer the glue and $q\bar q$ components of $f_0$. These include the calculations of the scalar glueball masses in quenched and unquenched lattice QCD, measurements of the radiative decays $J/ψ\toγf_{0}$, the ratio of $f_{0}$ decays to $ππ$ and $K\bar K$, the ratio of $J/ψ$ decays to $f_0(1710)ω$ and $f_0(1710)ϕ$, the $f_0$ contributions to $B_s\to J/ψπ^+π^-$, and the near mass degeneracy of $a_0(1450)$ and $K_0^*(1430)$. All analyses suggest the prominent glueball nature of $f_0(1710)$ and the flavor octet structure of $f_0(1500)$.

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arXiv2015

Strong Decays of Charmed Baryons in Heavy Hadron Chiral Perturbation Theory: An Update

We first give a brief overview of the charmed baryon spectroscopy and discuss their possible structure and spin-parity assignments in the quark model. With the new Belle measurement of the widths of $Σ_c(2455)$ and $Σ_c(2520)$ and the recent CDF measurement of the strong decays of $Λ_c(2595)$ and $Λ_c(2625)$, we give updated coupling constants in heavy hadron chiral perturbation theory. We find $g_2=0.565^{+0.011}_{-0.024}$ for $P$-wave transitions between $s$-wave and $s$-wave baryons, and $h_2$, one of the couplings responsible for $S$-wave transitions between $s$-wave and $p$-wave baryons, is extracted from $Λ_c(2595)^+\toΛ_c^+ππ$ to be $0.63\pm0.07$. It is substantially enhanced compared to the old value of order 0.437. With the help from the quark model, two of the couplings $h_{10}$ and $h_{11}$ responsible for $D$-wave transitions between $s$-wave and $p$-wave baryons are determined from $Σ_c(2880)$ decays. There is a tension for the coupling $h_2$ as its value extracted from $Λ_c(2595)^+\to Λ_c^+ππ$ will imply $Ξ_c(2790)^0\toΞ'_cπ$ and $Ξ_c(2815)^+\toΞ_c^*π$ rates slightly above the current limits. It is conceivable that SU(3) flavor symmetry breaking can help account for the discrepancy.

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arXiv2015

Bottom Baryon Decays to Pseudoscalar Meson and Pentaquark

Based on SU(3) flavor symmetry, we decompose the decay amplitudes of bottom baryon decays to a pseudoscalar meson and an octet (a decuplet) pentaquark in terms of three (two) invariant amplitudes $T_1$ and $T_{2,3}$ ($\tilde T_1$ and $\tilde T_2$) corresponding to external $W$-emission and internal $W$-emission diagrams, respectively. For antitriplet bottom baryons $Λ_b^0,Ξ_b^0$ and $Ξ_b^-$, their decays to a decuplet pentaquark proceed only through the internal $W$-emission diagram. Assuming the dominance from the external $W$-emission amplitudes, we present an estimate of the decay rates relative to $Λ_b^0\to P_p^+K^-$, where $P_p^+$ is the hidden-charm pentaquark with the same light quark content as the proton. Hence, our numerical results will provide a very useful guideline to the experimental search for pentaquarks in bottom baryon decays. For example, $Ξ_b^0\to P_{Σ^+}K^-$, $Ξ_b^-\to P_{Σ^-}\bar K^0$, $Ω_b^-\to P_{Ξ^-}\bar K^0$ and $Ω_b^-\to P_{Ξ^0}K^-$ may have rates comparable to that of $Λ_b^0\to P_p^+K^-$ and these modes should be given the higher priority in the experimental searches for pentaquarks.

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arXiv2014

On the smallness of Tree-dominated Charmless Two-body Baryonic $B$ Decay Rates

The long awaited baryonic $B$ decay $\bar B{}^0\to p\bar p$ was recently observed by LHCb with a branching fraction of order $10^{-8}$. All the earlier model predictions are too large compared with experiment. In this work, we point out that for a given tree operator $O_i$, the contribution from its Fiertz transformed operator, an effect often missed in the literature, tends to cancel the internal $W$-emission amplitude induced from $O_i$. The wave function of low-lying baryons are symmetric in momenta and the quark flavor with the same chirality, but antisymmetric in color indices. Using these symmetry properties and the chiral structure of weak interactions, we find that half of the Feynman diagrams responsible for internal $W$-emission cancel. Since this feature holds in the charmless modes but not in the charmful ones, we advocate that the partial cancellation accounts for the smallness of the tree-dominated charmless two-body baryonic $B$ decays. This also explains why most previous model calculations predicted too large rates as the above consideration was not taken into account. Finally, we emphasize that, contrary to the claim in the literature, the internal $W$-emission tree amplitude should be proportional to the Wilson coefficient $c_1+c_2$ rather than $c_1-c_2$.

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arXiv2014

Charmless Three-body Decays of B_s Mesons

Branching fractions and CP-violating asymmetries of charmless $B_s\to PPP$ decays with $P=K,π$ are studied using a simple model based on the factorization approach. The penguin-dominated modes $B_s\to \bar K^0 K^+π^-$ and $K^0K^-π^+$ have the largest rates among the three-body $B_s$ decays and they are dominated by the $K_0^*(1430)$ resonances and nonresonant contributions. The branching fraction of $B_s\to K^0K^+K^-$ is predicted to be $1.4\times 10^{-6}$, which is close to the high end of the measured result $(0.2-3.4)\times 10^{-6}$ obtained by LHCb. We find sizable CP violation in $K^0π^+π^-$, $K^0π^0π^0$, $K^0K^+K^-$ and $K_SK_SK_S$ channels. Just as the $B_u$ sector, the correlation of CP asymmetries $A_{CP}(B_s\to K^0π^+π^-)\approx -A_{CP}(B_s\to K^0K^+K^-)$ holds in $B_s$ decays. Several model-independent relations based on $U$-spin symmetry for CP asymmetries are derived. Although they cannot be tested by the present available data, they can be checked by the dynamical calculations. Since the $U$-spin symmetry which relates various matrix elements of scalar densities, for example, $ $ and $<\bar K^0π|\bar sq|0>$, is badly broken, the derived $U$-spin relations are generally not well respected.

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arXiv2014

Charmless Two-body Baryonic $B_{u,d,s}$ Decays Revisited

We study charmless two-body baryonic $B$ decays using the topological amplitude approach. We extend a previous work to include all ground state octet and decuplet final states with full topological amplitudes. Relations on rates and CP asymmetries are obtained. The number of independent topological amplitudes is significantly reduced in the large $m_B$ asymptotic limit. With the long awaited $\overline B{}^0\to p\bar p$ data, we can finally extract information on the topological amplitudes and predict rates of all other modes. The predicted rates are in general with uncertainties of a factor of two by including corrections to the asymptotic relations and from sub-leading contributions. We point out some modes that will cascadely decay to all charged final states and have large decay rates. For example, $\overline B {}^0_s\toΩ^-\overline{Ω^-}$, $B^-\to p\overline{Δ^{++}}$, $B^-\to Λ\bar p$ and $\overline B{}^0_s\to Λ\overlineΛ$ decays are interesting modes to search for. We find that the $\overline B{}^0\to p\bar p$ mode is the most accessible one among octet-anti-octet final states in the $ΔS=0$ transition. It is not surprise that it is the first one being found. With the detection of $π^0$ and/or $γ$ many other unsuppressed modes can be searched for. The predicted $\overline B{}^0_s\to p\bar p$ rate is several order smaller than the present experimental result. The central value of the experimental result can be reproduced only with unnaturally scaled up "subleading contributions", which will affect other modes including the $\overline B{}^0\to p\bar p$ decay. We need more data to clarify the situation. The analysis presented in this work can be systematically improved when more measurements on decay rates become available.

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arXiv2013

Branching Fractions and Direct CP Violation in Charmless Three-body Decays of B Mesons

Charmless three-body decays of B mesons is studied using a simple model based on the framework of the factorization approach. Hadronic three-body decays receive both resonant and nonresonant contributions. Dominant nonresonant contributions to tree-dominated three-body decays arise from the $b\to u$ tree transition which can be evaluated using heavy meson chiral perturbation theory valid in the soft meson limit. For penguin-dominated decays, nonresonant signals come mainly from the penguin amplitude governed by the matrix elements of scalar densities $ $. We use the measurements of $\bar B^0\to K_SK_SK_S$ to constrain the nonresonant component of $ $. The intermediate vector meson contributions to three-body decays are identified through the vector current, while the scalar meson resonances are mainly associated with the scalar density. While the calculated direct CP violation in $B^-\to K^+K^-K^-$ and $B^-\to π^+π^-π^-$ decays agrees well with experiment in both magnitude and sign, the predicted CP asymmetries in $B^-\to π^- K^+K^-$ and $B^-\to K^-π^+π^-$ are wrong in signs when confronted with experiment. It has been conjectured recently that a possible resolution to this CP puzzle may rely on final-state rescattering of $π^+π^-$ and $K^+K^-$. Assuming a large strong phase associated with the matrix element $ $ arising from some sort of power corrections, we fit it to the data of $K^-π^+π^-$ and find a correct sign for $π^- K^+K^-$.

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arXiv2013

A Study of Dirac Fermionic Dark Matters

We study pure weak eigenstate Dirac fermionic dark matters (DM). We consider WIMP with renormalizable interaction. According to results of direct searches and the nature of DM (electrical neutral and being a pure weak eigenstate), the quantum number of DM is determined to be $I_3=Y=0$. There are only two possible cases: either DM has non-vanishing weak isospin ($I\neq 0$) or it is an isosinglet (I=0). In the first case, the Sommerfeld enhancement is sizable for large $I$, producing large $χ^0\bar{χ^0}\to VV$ rates. In particular, we obtain large $χ\barχ\to W^+ W^-$ cross section, which is comparable to the latest bounds from indirect searches and $m_χ$ is constrained to be larger than few hundred GeV to few TeV. It is possible to give correct relic density with $m_χ$ higher than these lower bounds. In the second case, to couple DM to standard model (SM) particles, a SM-singlet vector mediator $X$ is required from renormalizability and the SM gauge quantum numbers. To satisfy the latest bounds of direct searches and to reproduce the DM relic density at the same time, resonant enhancement in DM annihilation diagram is needed. Thus, the masses of DM and the mediator are related. Furthermore, this model is not sufficient to explain the deviation in muon $g-2$.

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arXiv2013

Revisiting charmless hadronic B decays to scalar mesons

Hadronic charmless B decays to scalar mesons are studied within the framework of QCD factorization (QCDF). Considering two different scenarios for scalar mesons above 1 GeV, we find that the data favor the scenario in which the scalars $a_0(1450)$ and $K_0^*(1430)$ are the lowest lying $q\bar q$ bound states. This in turn implies a preferred four-quark nature for light scalars below 1 GeV. Assuming $K_0^*(1430)$ being a lowest lying $q\bar s$ state, we show that the data of $B\to K_0^*(1430)η^{(')}$ and $B\to K_0^*(1430)(ρ,ω,ϕ)$ can be accommodated in QCDF without introducing power corrections induced from penguin annihilation, while the predicted $B^-\to \ov K_0^{*0}(1430)π^-$ and $\ov B^0\to K_0^{*-}(1430)π^+$ are too small compared to experiment. In principle, the data of $K_0^*(1430)π$ modes can be explained if penguin-annihilation induced power corrections are taken into account. However, this will destroy the agreement between theory and experiment for $B\to K_0^*(1430)(η^{(')},ρ,ω,ϕ)$. Contrary to the pseudoscalar meson sector where $B\to Kη'$ has the largest rate in 2-body decays of the $B$ meson, we show that $Br(B\to K_0^*η')<\B(B\to K_0^*η)$. The decay $\ov B^0\to a_0(980)^+K^-$ is found to have a rate much smaller than that of $\ov B^0\to a_0(980)^+π^-$ in QCDF, while it is the other way around in pQCD. Experimental measurements of these two modes will help discriminate between these two different approaches. Assuming 2-quark bound states for $f_0(980)$ and $f_0(500)$, the observed large rates of $f_0(980)K$ and $f_0(980)K^*$ modes can be explained in QCDF with the $f_0(980)\!-\!f_0(500)$ mixing angle $θ$ in the vicinity of $20^\circ$.

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arXiv2012

Implications of Br(μ-> e γ) and Δa_mu on Muonic Lepton Flavor Violating Processes

We study the implications of the experimental results on the μ-> eγdecay rate and the muon anomalous magnetic moment, on muonic lepton flavor violating processes, such as μ-> 3 e and μN -> e N. We use a model independent approach in this analysis, where these processes are considered to be loop induced by exchanging spin 1/2 and spin 0 particles. We explore two complementary cases, which has no or has an internal (built-in) cancellation mechanism in amplitudes. Our main results are as following. (a) Bounds from rates are used to constrain parameters, such as coupling constants and masses. These constraints can be easily updated by simple scalings, if the experimental situations change. (b) The muon g-2 data favors non-chiral interactions. (c) In μ-> 3 e and μN -> e N processes, Z-penguin diagrams may play some role, while box diagrams contributions are usually highly constrained. (d) In the first case (without any built-in cancellation mechanism), using the recent μ-> eγbound, we find that μ-> 3e and μN -> e N rates are bounded below the present experimental limits by two to three orders of magnitudes in general. Furthermore, by comparing Δa_μand Br(μ->eγ) data, the couplings of μand e are found to be highly hierarchical. Additional suppression mechanism should be called for. (e) In the second case (with a built-in cancellation mechanism), mixing angles can provide additional suppression factors to satisfy the Δa_μand Br(μ-> eγ) bounds. While the μ-> 3 e rate remains suppressed, the bounds on μN -> e N rates, implicated from the latest μ-> eγbound, can be relaxed significantly and can be just below the present experimental limits.

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arXiv2011

Long-Distance Contribution to ΔΓs/Γs of the $B_s-\bar{B}_s$ System

We estimate the long-distance contribution to the ΔΓs of B_s system, based mainly on two-body D^(*)_s\Dbar^(*)_s modes and three-body D^(*)_s\Dbar^(*)\Kbar^(*) modes (and their CP conjugates). Some higher c\bar{s} resonances are also considered. The contribution to ΔΓs/Γs by two-body modes is 10.2+-3.0%, slightly smaller than the short-distance result of 13.3+-3.2%. The contribution to width difference by D*_s0(2317), D_s1(2460), and D_s1(2536) resonances is negligible. For the three-body modes, we adopt the factorization formalism and model the form factors with off-shell D^(*)_s poles, the D_{sJ}(2700) resonance, and non-resonant (NR) contributions. These three-body modes can arise through current-produced or transition diagrams, but only SU(3)-related D^(*)_{u,d} \Dbar^(*)\Kbar modes from current diagram have been measured so far. The pole model results for D^*_{u,d} \Dbar^(*)\Kbar agree well with data, while D_{u,d} \Dbar^(*)\Kbar rates agree with data only within a factor of 2 to 3. All measured three-body rates can be reproduced by including NR contribution. The total ΔΓs/Γs obtained is 16.7+-8.5%, which agrees with the short-distance result within uncertainties. For illustration, we also demonstrate the effect of D_{sJ}(2700) in modes with D^(*)K^*. In all scenarios, the total width difference remain consistence to the short-distance result. Our result indicates that (a) the operator product expansion (OPE) in short-distance picture is a valid assumption, (b) approximating the two-body decays to saturate width difference has a large correction, (c) the effect of three-body modes cannot be neglected, and (d) in addition to D^(*)_s poles, the D_{sJ}(2700) resonance also plays an important role in three-body modes. Future experiments are necessary to improve the estimation of ΔΓs from long-distance picture.

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arXiv2011

Phenomenological constraints on minimally coupled exotic lepton triplets

By introducing a set of new triplet leptons (with nonzero hypercharge) that can Yukawa couple to their Standard Model counterparts, new sources of tree-level flavor changing currents are induced via mixing. In this work, we study some of the consequences of such new contributions on processes such as the leptonic decays of gauge bosons, $\ell \rightarrow 3\ell'$ and $\ell \rightarrow \ell' γ$ which violate lepton flavor, and mu-e conversion in atomic nuclei. Constraints are then placed on the parameters associated with the exotic triplets by invoking the current low-energy experimental data. Moreover, the new physics contribution to the lepton anomalous magnetic moments is calculated.

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arXiv2010

The B-CP Puzzles in QCD Factorization

Within the framework of QCD factorization (QCDF), power corrections due to penguin annihilation can account for theobserved rates of penguin-dominated two-body decays of $B$ mesons and direct CP asymmetries $A_{CP}(K^-π^+)$, $A_{CP}((K^{*-}π^+)$, $A_{CP}((K^-ρ^0)$ and $A_{CP}((π^+π^-)$. However, the predicted direct CP-violating effects in QCDF for $B^-\to K^-π^0,K^-η,π^-η$ and $\bar B^0\toπ^0π^0$ are wrong in signs when confronted with experiment. We consider two different types of power correction effects in order to resolve the CP puzzles and rate deficit problems with penguin-dominated two-body decays of $B$ mesons and color-suppressed tree-dominated $π^0π^0$ and $ρ^0π^0$ modes: penguin annihilation and soft corrections to the color-suppressed tree amplitude.

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arXiv2010

B to V, A, T Tensor Form Factors in the Covariant Light-Front Approach: Implications on Radiative B Decays

We reanalyze the $B\to M$ tensor form factors in a covariant light-front quark model, where $M$ represents a vector meson $V$, an axial-vector meson $A$, or a tensor meson $T$. The treatment of masses and mixing angles in the $K_{1A,1B}$ systems is improved, where $K_{1A}$ and $K_{1B}$ are the $^3P_1$ and $^1P_1$ states of the axial-vector meson $K_1$, respectively. Rates of $B\to Mγ$ decays are then calculated using the QCD factorization approach. The updated $B\to K^*γ$, $B\to K_1(1270)γ$, $K_1(1400)γ$ and $K_2γ$ rates agree with the data. The $K_1(1270)$--$K_1(1400)$ mixing angle is found to be about $51^\circ$. The sign of the mixing angle is fixed by the observed relative strength of $B\to K_1(1270)γ$ and $K_1(1400)γ$. The formalism is then applied to $B_s\to M$ tensor form factors. We find that the calculated $B_s\to ϕγ$ rate is consistent with experiment, though in the lower end of the data. The branching fractions of $B_s\to f_1(1420)γ$ and $f'_2(1525)γ$ are predicted to be of order $10^{-5}$ and it will be interesting to search for these modes. Rates on $B_s\to f_1(1285)γ$, $h_1(1380)γ$, $h_1(1170)γ$, $f_2(1270)γ$ decays are also predicted.

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arXiv2010

On Charmless $B\to K_hη^{(')}$ Decays with $K_h=K,K^,K_0^(1430),K_2^*(1430)$

We study the charmless decays $B\to K_hη$ and $B\to K_hη'$ within the framework of QCD factorization (QCDF) for $K_h= K,K^*,K_0^*(1430)$ and naive factorization for $K_h=K_2^*(1430)$. There are three distinct types of penguin contributions: (i) $b\to sq\bar q\to sη_{q}$, (ii) $b\to ss\bar s\to sη_s$, and (iii) $b\to s q\bar q\to q \bar K_h$, where $η_q=(u\bar u+d\bar d)/\sqrt{2}$ and $η_s=s\bar s$. $B\to K^{(*)}η^{(')}$ decays are dominated by type-II and type-III penguin contributions. The interference, constructive for $Kη'$ and $K^*η$ and destructive for $Kη$ and $K^*η'$, between type-II and type-III diagrams explains the pattern of $Γ(B\to Kη')\ggΓ(B\to Kη)$ and $Γ(B\to K^*η')\llΓ(B\to K^*η)$. Within QCDF, the observed large rate of the $Kη'$ mode can be naturally explained without invoking flavor-singlet contributions or something exotic. The decay pattern for $B\to K_0^*(1430)η^{(')}$ decays depends on whether the scalar meson $K_0^*(1430)$ is an excited state of $κ$ or a lowest-lying $P$-wave $q\bar q$ state. Hence, the experimental measurements of $B\to K_0^*(1430)η^{(')}$ can be used to explore the quark structure of $K_0^*(1430)$. If $K_0^*(1430)$ is a low-lying $q\bar q$ bound state, we find that $K_0^*η$ has a rate slightly larger than $K_0^*η'$ owing to the fact that the $η$-$η'$ mixing angle in the $η_q,η_s$ flavor basis is less than $45^\circ$, in agreement with experiment. Type-III penguin diagram does not contribute to $B\to K_2^*η^{(')}$ under the factorization hypothesis and type-II diagram dominates.

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arXiv2009

QCD Factorization for Charmless Hadronic B_s Decays Revisited

Branching fractions and CP-violating asymmetries of charmless $\bar B_s\to PP, VP, VV$ decays (P and V denoting pseudoscalar and vector mesons, respectively) are re-examined in the framework of QCD factorization (QCDF). We take into account subleading power corrections to the penguin annihilation topology and to color-suppressed tree amplitudes that are crucial for resolving the CP puzzles and rate deficit problems with penguin-dominated two-body decays and color-suppressed tree-dominated $π^0π^0$ and $ρ^0π^0$ modes in the $B_{u,d}$ sector. Many of the $B_s\to h_1h_2$ decays can be related to $B_d\to h_1h_2$ ones via U-spin or SU(3) symmetry. Some useful model-independent relations can be derived and tested. Mixing-induced CP asymmetries for many of the penguin-dominated decays are predicted to be very small in the standard model. They are sensitive to New Physics and offer rich possibilities of new discoveries. Measurements of direct CP-violating asymmetries can be used to discriminate QCDF from other competing approaches such as pQCD and soft-collinear effective theory.

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arXiv2009

Resolving B-CP Puzzles in QCD Factorization

Within the framework of QCD factorization (QCDF), power corrections due to penguin annihilation can account for the observed rates of penguin-dominated two-body decays of $B$ mesons and direct CP asymmetries $A_{CP}(K^-π^+)$, $A_{CP}(K^{*-}π^+)$, $A_{CP}(K^-ρ^0)$ and $A_{CP}(π^+π^-)$. However, the predicted direct CP-violating effects in QCDF for $B^-\to K^-π^0,K^-η,π^-η$ and $\bar B^0\toπ^0π^0$ are wrong in signs when confronted with experiment. We show that subleading $1/m_b$ power corrections to the color-suppressed tree amplitude due to spectator scattering or final-state interactions will yield correct signs for aforementioned CP asymmetries and accommodate the observed $π^0π^0$ and $ρ^0π^0$ rates simultaneously. Implications are discussed.

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arXiv2009

Revisiting Charmless Hadronic B_{u,d} Decays in QCD Factorization

Within the framework of QCD factorization (QCDF), we consider two different types of power correction effects in order to resolve the CP puzzles and rate deficit problems with penguin-dominated two-body decays of B mesons and color-suppressed tree-dominated $π^0π^0$ and $ρ^0π^0$ modes: penguin annihilation and soft corrections to the color-suppressed tree amplitude. We emphasize that the electroweak penguin solution to the $B\to Kπ$ CP puzzle via New Physics is irrelevant for solving the CP and rate puzzles related to tree-dominated decays. While some channels e.g. $K^-π^+,K^-ρ^0,π^+π^-,ρ^\pmπ^\mp$ need penguin annihilation to induce the correct magnitudes and signs for their CP violation, some other decays such as $B^-\to K^-π^0,π^-η, K^-η$ and $\bar B^0\to \bar K^{*0}η,π^0π^0$ require the presence of both power corrections to account for the measured CP asymmetries. In general, QCDF predictions for the branching fractions and direct CP asymmetries of $\bar B\to PP,VP,VV$ decays are in good agreement with experiment. The predictions of pQCD and soft-collinear effective theory are included for comparison.

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