arXiv subjects

Chun-Khiang Chua

Publications and source records attributed to Chun-Khiang Chua.

At least 19 recordsLinked to original sources

arXiv2026

Revisiting two-body charmed anti-charmed baryonic $B$ decays

The study of two-body charmed anti-charmed baryonic $\overline B\to {\bf B}_c \overline {\bf B}_c$ decays using the topological amplitude approach is revisited. We include the $b\to u\bar u q$ contributions, in addition to the $b\to c\bar c q$ contributions, to these decays. The topological decomposition of $\overline B\to {\bf B}_c(\bf {\bar 3_f}) \overline {\bf B}_c(\bf { 3_f})$, ${\bf B}_c(\bf 6_f) \overline {\bf B}_c(\bf { 3_f})$, ${\bf B}_c(\bf {\bar 3_f}) \overline {\bf B}_c(\bf {\bar 6_f})$ and ${\bf B}_c(\bf 6_f) \overline {\bf B}_c(\bf {\bar 6_f})$ decay amplitudes are updated accordingly. Although the $b\to u\bar u q$ contributions are Cabibbo-Kobayashi-Maskawa (CKM) suppressed in $ΔS=-1$ transitions, their effects are significantly amplified in $ΔS=0$ transitions, as the relative size of the CKM factors in $b\to u\bar u q$ and $b\to c\bar c q$ contributions in $ΔS=0$ transitions is enlarged by $λ^{-2}$, roughly a factor of 20, from the one in $ΔS=-1$ transitions. Present data in $\overline B\to {\bf B}_c(\bf {\bar 3_f}) \overline {\bf B}_c(\bf { 3_f})$ decay rates allow or even slightly prefer non-negligible $b\to u\bar u q$ contributions. These $b\to u\bar u q$ contributions can allow much larger rates for $B^-\to Ξ_c^0 \bar Ξ_c^{-}$, $\overline B{}_s^0\to Λ_c^+ \bar Ξ_c^{-}$ and $\overline B{}^0\to Ξ_c^+ \bar Ξ_c^{-}$ decays than those only have $b\to c\bar c d$ contributions. Several modes containing only $b\to u\bar u q$ contributions in $\overline B\to {\bf B}_c(\bf 6_f) \overline {\bf B}_c(\bf { 3_f})$, ${\bf B}_c(\bf {\bar 3_f}) \overline {\bf B}_c(\bf {\bar 6_f})$ decays are also identified. Measuring these decays will be interesting and useful in clarifying the role of $b\to u\bar u q$ contributions in two-body charmed anti-charmed baryonic $\overline B$ decays.

hep-ph↗

arXiv2026

Two-body charmed anti-charmed baryonic $B$ decays

We study the rates of two-body charmed anti-charmed baryonic $\overline B\to {\bf B}_c \overline {\bf B}_c$ decays using the topological amplitude approach. All amplitudes of $\overline B\to {\bf B}_c(\bf {\bar 3_f}) \overline {\bf B}_c(\bf { 3_f})$, ${\bf B}_c(\bf 6_f) \overline {\bf B}_c(\bf { 3_f})$, ${\bf B}_c(\bf {\bar 3_f}) \overline {\bf B}_c(\bf {\bar 6_f})$ and ${\bf B}_c(\bf 6_f) \overline {\bf B}_c(\bf {\bar 6_f})$ decays are decomposed topologically. SU(3) breaking effects on these amplitudes, depending on the position of the $s$-quark line, are modeled. Using existing data as inputs, we obtained the following results. (i) In the low-lying $\overline B\to {\bf B}_c(\bf {\bar 3_f}) \overline {\bf B}_c(\bf { 3_f})$ decays, we find that the exchange diagram is sizable. Furthermore, there is a large cancellation between internal $W$-tree and exchange $W$-tree amplitudes. The SU(3) breaking is sizable, 35% SU(3) breaking effects are needed, and they work differently in different amplitudes. The rates of $\overline B\to {\bf B}_c(\bf {\bar 3_f}) \overline {\bf B}_c(\bf { 3_f})$ decays with some excited ${\bf B}_c(\bf {\bar 3_f})$ are also studied. (ii) The $\overline B\to {\bf B}_c(\bf 6_f) \overline {\bf B}_c(\bf { 3_f})$ decays, with low-lying $ \overline {\bf B}_c(\bf { 3_f})$ and low-lying and some excited ${\bf B}_c(\bf 6_f)$ baryons are studied with some predictions on rates obtained. (iii) The $\overline B\to {\bf B}_c(\bf {\bar 3_f}) \overline {\bf B}_c(\bf {\bar 6_f})$ decays with low-lying charmed anti-charmed baryons are studied with some predictions on rates obtained. (iv) Uncertainties in most predicted rates are large, reflecting our current poor understanding of the related SU(3) breaking effects. Measuring these rates can provide very useful information about these effects.

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arXiv2025

Heavy Mesons to Open-Charmed Tetraquark Decays

Motivated by the recent observations of $T^*_{cs0}(2870)^0$, $T^*_{c\bar s 0}(2900)^0$ and $T^*_{c\bar s 0}(2900)^{++}$ open-charmed tetraquark states by LHCb, we study the decays of heavy mesons to these open-charmed tetraquark states ($T$) using a topological amplitude approach. We first obtain the $T\to DP$ and $DS$ strong decay amplitudes by decomposing them into several topological amplitudes, where $P$ is a light pseudo-scalar particle and $S$ is a low-lying scalar particle. Subsequently, weak decay amplitudes of $\overline B\to D\overline T$, $\overline D T$ and $\overline B\to TP$, $TS$ decays are decomposed topologically. In addition, $B^-_c\to T\overline T$ decays are also discussed. Using these results, modes with an unambiguous exotic interpretation in flavor are highlighted.

hep-ph↗

arXiv2023

Charmless Semileptonic Baryonic $B_{u,d,s}$ Decays

We study $\bar B_q\to {{\rm\bf B}\bar{\rm\bf B}}' l \barν$ and $\bar B_q\to {{\rm\bf B}\bar{\rm\bf B}}' ν\barν$ decays with all low lying octet and decuplet baryons using a topological amplitude approach. In tree induced $\bar B_q\to {{\rm\bf B}\bar{\rm\bf B}}' l \barν$ decay modes, we need 2 tree and 1 annihilation amplitudes in octet-anti-octet decay modes, 1 tree amplitude in octet-anti-decuplet decay modes, 1 tree amplitude in decuplet-anti-octet decay modes and 1 tree and 1 annihilation amplitudes in decuplet-anti-decuplet decay modes. In loop induced $\bar B_q\to {{\rm\bf B}\bar{\rm\bf B}}' ν\barν$ decay modes, similar numbers of penguin-box and penguin-box-annihilation amplitudes are needed. Relations on these semileptonic baryonic $B_q$ decay amplitudes are found. Furthermore, the ratios of loop topological amplitudes and tree topological amplitudes are fixed by known CKM factors and loop functions. The observed $B^-\to p\bar p μ^-\barν$ differential rate exhibits threshold enhancement, which is expected to hold in all other semileptonic baryonic modes. The threshold enhancement squeezes the phase space and leads to very large SU(3) breaking effects in the decay rates. They are estimated using the measured $B^-\to p\bar p μ^-\barν$ differential rate and model calculations. Modes with relatively unsuppressed rates and good detectability are identified. These modes can be searched experimentally in near future and the rate estimations can be improved when more modes are discovered. Ratios of rates of some loop induced $\bar B_q\to {{\rm\bf B}\bar{\rm\bf B}}' ν\barν$ decays and tree induced $\bar B_q\to {{\rm\bf B}\bar{\rm\bf B}}' l \barν$ decays are predicted and can be checked experimentally. They can be tests of the SM. Some implications on $\bar B_{q}\to {{\rm\bf B}\bar{\rm\bf B}}' l^+ l^-$ decays are also given.

hep-ph↗

arXiv2022

Two-body Baryonic $B_{u,d,s}$ and $B_c$ to Charmless Final State Decays

We study the rates and direct CP violations of two-body baryonic $\bar B_{u,d,s}\to {{\rm\bf B}\overline{\rm\bf B}}'$ and $B^-_c\to{{\rm\bf B}\overline{\rm\bf B}}'$ decays, where the final state baryons include low-lying octet and decuplet baryons. We incorporate topological amplitude formalism and the factorization approach. Asymptotic relations at large $m_b$ are used to simplify decay amplitudes. Using the most up-to-date data on $\bar B^0\to p\bar p$ and $B^-\toΛ\bar p$ decay rates as inputs, rates and direct CP violations of $\bar B_{u,d,s}\to {{\rm\bf B}\overline{\rm\bf B}}'$ decays are revised and predicted. It is interesting that the results on rates satisfy all existing experimental bounds and some are close to the bounds. Factorization diagrams contribute to penguin-exchange, exchange, annihilation and penguin-annihilation amplitudes. Although the resulting penguin-exchange factorization amplitudes are sizable, the rest suffer from severe chiral suppression and are sensitive to non-factorizable contributions. The $\bar B_s\to p\bar p$ decay rate predicted in factorization calculation is very rare, but it can be enhanced by including non-factorizable contributions. The case where the rate is enhanced to saturate the present experimental bound is discussed. As annihilation modes $B^-_c\to{{\rm\bf B}\overline{\rm\bf B}}'$ decays from factorization calculation are found to be very rare, but they can be enhanced by including non-factorizable contributions as well. Small direct CP violations of pure penguin modes in $ΔS=-1$ $\bar B_{u,d,s}\to{{\rm\bf B}\overline{\rm\bf B}}'$ decays are robust predictions of the SM, while vanishing direct CP violations of exchange modes in $\bar B_{u,d,s}\to{{\rm\bf B}\overline{\rm\bf B}}'$ decays and in all $B^-_c\to{{\rm\bf B}\overline{\rm\bf B}}'$ decay modes are null tests of the SM.

hep-ph↗

arXiv2021

Finite-Width Effects in Three-Body B Decays

It is customary to apply the so-called narrow width approximation $Γ(B\to RP_3\to P_1P_2P_3)=Γ(B\to RP_3)Br(R\to P_1P_2)$ to extract the branching fraction of the quasi-two-body decay $B\to RP_3$, with $R$ and $P_3$ being an intermediate resonant state and a pseudoscalar meson, respectively. However, the above factorization is valid only in the zero width limit. We consider a correction parameter $η_R$ from finite width effects. Our main results are: (i) We present a general framework for computing $η_R$ and show that it can be expressed in terms of the normalized differential rate and determined by its value at the resonance. (ii) We introduce a form factor $F(s_{12},m_R)$ for the strong coupling involved in the $R(m_{12})\to P_1P_2$ decay when $m_{12}$ is away from $m_R$. We find that off-shell effects are small in vector meson productions, but prominent in the $K_2^*(1430)$, $σ/f_0(500)$ and $K_0^*(1430)$ resonances. (iii) We evaluate $η_R$ in the theoretical framework of QCD factorization (QCDF) and in the experimental parameterization (EXPP) for three-body decay amplitudes. In general, $η_R^{\rm QCDF}$ and $η_R^{\rm EXPP}$ are similar for vector mesons, but different for tensor and scalar resonances. A study of the differential rates enables us to understand the origin of their differences. (iv) Finite-width corrections to $Br(B^-\to RP)_{\rm NWA}$ obtained in the narrow width approximation are generally small, less than 10\%, but they are prominent in $B^-\toσ/f_0(500)π^-$ and $B^-\to \overline K_0^{*0}(1430)π^-$ decays. The EXPP of the normalized differential rates should be contrasted with the theoretical predictions from QCDF calculation as the latter properly takes into account the energy dependence in weak decay amplitudes.

hep-ph↗

arXiv2020

Width effects in resonant three-body decays: $B$ decay as an example

For three-body hadron decays mediated by intermediate resonances with large widths, we show how to properly extract the quasi-two-body decay rates for a meaningful comparison with the corresponding theoretical estimates, using several $B$ decays as explicit examples. We compute the correction factor from finite width effects in the QCD factorization approach, and make a comparison with that using the experimental parameterization in which the momentum dependence in the weak dynamics is absent. Although the difference is generally less than $10\%$ for tensor and vector resonances, it can be as large as $(25-40)\%$ for scalar resonances. Our finding can in fact be applied to general quasi-two-body decays.

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arXiv2020

Data-driven study of the implications of anomalous magnetic moments and lepton flavor violating processes of $e$, $μ$ and $τ$

We study anomalous magnetic moments and flavor violating processes of $e$, $μ$ and $τ$ leptons. We use a data driven approach to investigate the implications of the present data on the parameters of a class of models, which has spin-0 scalar and spin-1/2 fermion fields. We compare two different cases, which has or does not have a built-in cancelation mechanism. Our findings are as following. Chiral interactions are unable to generate large enough $Δa_e$ and $Δa_μ$ to accommodate the experimental results. Sizable $Δa_e$ and $Δa_μ$ can be generated from non-chiral interactions, but they are not contributed from the same source. The upper limit of $μ\to eγ$ decay gives the most severe constraints on photonic penguin contributions in $μ\to e$ transitions, but the situation may change in considering future experimental sensitivities. The $Z$-penguin diagrams can constrain chiral interaction better than photonic penguin diagrams in $μ\to e$ transitions. In most of the parameter space, box contributions to $μ\to 3e$ decay are subleading. In $τ\to e$ $(μ)$ transitions, the present $τ\to eγ$ $(μγ)$ upper limit constrains the photonic penguin contribution better than the $τ\to 3 e$ $(3μ)$ upper limit, and $Z$-penguin amplitudes constrain chiral interaction better than photonic penguin amplitudes. Box contributions to $τ\to 3e$ and $τ\to 3μ$ decays can sometime be comparable to $Z$-penguin contributions. The $τ^-\to e^- μ^+ e^-$ and $τ^-\to μ^- e^+ μ^-$ rates are highly constrained by $τ\to eγ$, $μ\to eγ$ and $τ\to μγ$, $μ\to eγ$ upper limits, respectively. We compare the current experimental upper limits, future sensitivities and bounds from consistency on various muon and tau LFV processes.

hep-ph↗

arXiv2020

Branching Fractions and CP Violation in $B^-\to K^+K^-π^-$ and $B^-\to π^+π^-π^-$ Decays

We present in this work a study of tree-dominated charmless three-body decays of $B$ mesons, $B^-\to K^+K^-π^-$ and $B^-\toπ^+π^-π^-$, within the factorization approach. The main results are: (i) There are two distinct sources of nonresonant contributions: one arises from the $b\to u$ tree transition and the other from the nonresonant matrix element of scalar densities $\langle M_1M_2|\bar q_1 q_2|0\rangle^{\rm NR}$. It turns out that even for tree-dominated three-body decays, dominant nonresonant contributions originate from the penguin diagram rather than from the $b\to u$ tree process, as implied by the large nonresonant component observed recently in the $π^- K^+$ system which accounts for one third of the $B^-\to K^+K^-π^-$ rate. (ii) The calculated branching fraction of $B^-\to f_2(1270)π^-\to K^+K^-π^-$ is smaller than the LHCb by a factor of $\sim 7$ in its central value, but the predicted $\B(B^-\to f_2(1270)π^-\toπ^+π^-π^-)$ is consistent with the data. Branching fractions of $B^-\to f_2(1270)π^-$ extracted from the LHCb measurements of these two processes also differ by a factor of seven! Therefore, it is likely that the $f_2(1270)$ contribution to $B^-\to K^+K^-π^-$ is largely overestimated experimentally. Including $1/m_b$ power corrections from penguin annihilation inferred from QCD factorization (QCDF), a sizable CP asymmetry of 32\% in the $f_2(1270)$ component agrees with experiment. (iii) A fraction of 5\% for the $ρ(1450)$ component in $B^-\toπ^+π^-π^-$ is in accordance with the theoretical expectation. However, a large fraction of 30\% in $B^-\to K^+K^-π^-$ is entirely unexpected. This issue needs to be clarified in the future.

hep-ph↗

arXiv2019

Color-allowed Bottom Baryon to $s$-wave and $p$-wave Charmed Baryon non-leptonic Decays

We study color allowed bottom baryon to $s$-wave and $p$-wave charmed baryon non-leptonic decays in this work. The charmed baryons include spin-1/2 and spin-3/2 states. Explicitly, we consider $Λ_b\to Λ^{(*,**)}_c M^-$, $Ξ_b\toΞ_c^{(**)} M^-$ and $Ω_b\toΩ^{(*,**)}_c M^-$ decays with $M=π, K, ρ, K^*, a_1, D, D_s, D^*, D^*_s$, $Λ^{(*,**)}_c=Λ_c, Λ_c(2595), Λ_c(2625), Λ_c(2765), Λ_c(2940)$, $Ξ_c^{(**)}=Ξ_c, Ξ_c(2815), Ξ_c(2790)$ and $Ω^{(*,**)}_c=Ω_c, Ω_c(2770), Ω_c(3050), Ω_c(3090), Ω_c(3120)$. There are six types of transitions, namely, (i) ${\cal B}_b({\bf \bar 3_f},1/2^+)$ to ${\cal B}_c({\bf \bar 3_f},1/2^+)$, (ii) ${\cal B}_b({\bf 6_f},1/2^+)$ to ${\cal B}_c({\bf 6_f},1/2^+)$, (iii) ${\cal B}_b({\bf 6_f},1/2^+)$ to ${\cal B}_c({\bf 6_f},3/2^+)$, (iv) ${\cal B}_b({\bf 6_f},1/2^+)$ to ${\cal B}_c({\bf 6_f},3/2^-)$, (v) ${\cal B}_b({\bf \bar 3_f},1/2^+)$ to ${\cal B}_c({\bf \bar 3_f},1/2^-)$, and (vi) ${\cal B}_b( {\bf \bar 3_f},1/2^+)$ to ${\cal B}_c({\bf \bar 3_f},3/2^-)$ transitions. Types (i) to (iii) involve spin 1/2 and 3/2 $s$-wave charmed baryons, while types (iv) to (vi) involve spin 1/2 and 3/2 $p$-wave charmed baryons. The transition form factors are calculated in the light-front quark model approach. All of the form factors in the $1/2\to 1/2$ and $1/2 \to 3/2$ transitions are extracted, and they are found to reasonably satisfy the relations obtained in the heavy quark limit, as we are using heavy but finite $m_b$ and $m_c$. Using naïve factorization, decay rates and up-down asymmetries of the above modes are predicted and can be checked experimentally. The study on these decay modes may shed light on the quantum numbers of $Λ_c(2765)$, $Λ_c(2940)$ $Ω_c(3050)$, $Ω_c(3090)$ and $Ω_c(3120)$.

hep-ph↗

arXiv2018

Color-allowed Bottom Baryon to Charmed Baryon non-leptonic Decays

We study color allowed $Λ_b\to Λ^{(*,**)}_c M^-$, $Ξ_b\toΞ_c^{(**)} M^-$ and $Ω_b\toΩ^{(*)}_c M^-$ decays with $M=π, K,ρ, K^*, D, D_s, D^*, D^*_s, a_1$, $Λ^{(*,**)}_c=Λ_c$, $Λ_c(2595)$, $Λ_c(2765)$, $Λ_c(2940)$, $Ξ_c^{(**)}=Ξ_c, Ξ_c(2790)$ and $Ω^{(*)}_c=Ω_c, Ω_c(3090)$, in this work. There are three types of transitions, namely ${\cal B}_b({\bf \bar 3_f},1/2^+)$ to ${\cal B}_c({\bf \bar 3_f},1/2^+)$, ${\cal B}_b({\bf 6_f},1/2^+)$ to ${\cal B}_c({\bf 6_f},1/2^+)$ and ${\cal B}_b({\bf \bar 3_f},1/2^+)$ to ${\cal B}_c({\bf \bar 3_f},1/2^-)$ transitions. The bottom baryon to charmed baryon form factors are calculated using the light-front quark model. Decay rates and up-down asymmetries are predicted using naïve factorization and can be checked experimentally. We find that in ${\cal B}_b\to {\cal B}_cP$ decays, rates in type~(ii) transition are smaller than those in type (i) transition, but similar to those in type (iii) transition, while in ${\cal B}_b\to{\cal B}_c V, {\cal B}_c A$ decays, rates in type~(ii) transition are much smaller than those in type (i) transition and are also smaller than those in type (iii) transition. For the up-down asymmetries, the signs are mostly negative, except for those in the type (ii) transition. All of these asymmetries are large in sizes. The study on these decay modes may shed light on the quantum numbers of some of the charmed baryons as the decays depend on the bottom baryon to charmed baryon form factors, which are sensitive to the configurations of the final state charmed baryons.

hep-ph↗

arXiv2018

Obtaining Hydrogen energy wave functions using the Runge-Lenz vector

The Pauli method of quantizing the Hydrogen system using the Runge-Lenz vector is ingenious. It is well known that the energy spectrum is identical with the one obtained from the Schrödinger equation and the consistency contributed significantly to the development of Quantum Mechanics in the early days. Since the Runge-Lenz vector is a vector and it commutes with the Hamiltonian, it is natural to use it to connect energy eigenstate $|n,l,m\rangle$ with other degenerate states $|n, l\pm 1,m'\rangle$. Recursive relations can be obtained and the wave functions of the whole spectrum can be obtained easily. Note that the recursive relations are consistent with those used in factorizing the Schrödinger equation. Nevertheless, the present analysis provide a better reasoning originated from the conserved vector, the Runge-Lenz vector. As in the Pauli analysis, group theory or symmetry plays a prominent role in the present analysis, while the rest of the derivations are mostly elementary.

quant-ph↗

arXiv2018

Revisiting Final State Interaction in Charmless $B_q\to P P$ Decays

Various new measurements in charmless $B_{u,d,s}\to PP$ modes, where $P$ is a low lying pseudoscalar meson, are reported by Belle and LHCb. These include the rates of $B^0\toπ^0π^0$, $ηπ^0$, $B_s\toη'η'$, $B^0\to K^+K^-$ and $B^0_s\toπ^+π^-$ decays. Some of these modes are highly suppressed and are among the rarest $B$ decays. Direct CP asymmetries on various modes are constantly updated. It is well known that direct CP asymmetries and rates of suppressed modes are sensitive to final state interaction (FSI). As new measurements are reported and more data will be collected, it is interesting and timely to revisit the rescattering effects in $B_{u,d,s}\to PP$ states. We perform a $χ^2$ analysis with all available data on CP-averaged rates and CP asymmetries in $\overline B{}_{u,d,s}\to PP$ decays. Our numerical results are compared to data and those from factorization approach. The quality of the fit is improved significantly from the factorization results in the presence of rescattering. The relations on topological amplitudes and rescattering are explored and they help to provide a better understanding of the effects of FSI. As suggested by U(3) symmetry on topological amplitudes and FSI, a vanishing exchange rescattering scenario is considered. The exchange, annihilation, $u$-penguin, $u$-penguin annihilation and some electroweak penguin amplitudes are enhanced significantly via annihilation and total annihilation rescatterings. In particular, the $u$-penguin annihilation amplitude is sizably enhanced by the tree amplitude via total annihilation rescattering. These enhancements affect rates and CP asymmetries. Predictions can be checked in the near future.

hep-ph↗

arXiv2017

Time-independent Green's Function of a Quantum Simple Harmonic Oscillator System and Solutions with Additional Generic Delta-Function Potentials

The one-dimensional time-independent Green's function $G_0$ of a quantum simple harmonic oscillator system ($V_0(x)=m ω^2 x^2/2$) can be obtained by solving the equation directly. It has a compact expression, which gives correct eigenvalues and eigenfunctions easily. The Green's function $G$ with an additional delta-function potential can be obtained readily. The same technics of solving the Green's function $G_0$ can be used to solve the eigenvalue problem of the simple harmonic oscillator with an generic delta-function potential at an arbitrary site, i.e. $V_1(x)\propto δ(x-a)$. The Wronskians play an important and interesting role in the above studies. Furthermore, the approach can be easily generalized to solve the quantum system of a simple harmonic oscillator with two or more generic delta-function potentials. We give the solutions of the case with two additional delta-functions for illustration.

quant-ph↗

arXiv2017

Confronting Dirac Fermionic Dark Matter with Recent Data

We study Dirac fermionic dark matter (DM, $χ^0$) and confront it with recent data. To evade the stringent direct search limits from PandaX-II, XENON1T and LUX experiments, the quantum numbers of the Dirac DM are taken to be $I_3=Y=0$ to remove the tree-level $Z$-exchange diagram. Loop amplitudes can contribute to the elastic scattering cross section. We find that there are cancellations in the one-loop diagrams, which largely reduce the cross section and make the Dirac DM viable in the direct search. For a generic isospin $I$, we survey the Dirac DM mass constrained by the latest results of PandaX-II, XENON1T and LUX experiments, the observed DM relic density, and the H.E.S.S. and the Fermi-LAT astrophysical observations. Sommerfeld enhancement effects on DM annihilation processes are investigated. We find that the cross section of $χ^0\barχ^0$ annihilating to the standard model (SM) gauge bosons are in general significantly enhanced, and the Fermi-LAT, the H.E.S.S. upper limits on $\langleσv\rangle({W^+W^-,γγ})$ and the observed relic density become serious constraints on the Dirac DM mass. The $I<4$ cases are ruled out and for $I\geq 4$, the lower bound on Dirac DM mass are forced to be $\gtrsim$ 60 TeV. The elastic scattering cross section for $m_χ$ of few tens TeV with a generic $I$ is found to be $σ^{SI}\simeq I^2(I+1)^2\times7\times10^{-49}$~cm$^2$. The predicted $\langleσ(χ^0\barχ^0\to Z^0Z^0, Z^0γ, γγ)v\rangle$ and $σ^{SI}$ are sizable and they will be useful to search for DM in astrophysical observation and in direct search in near future.

hep-ph↗

arXiv2017

Rates and $CP$ asymmetries of Charmless Two-body Baryonic $B_{u,d,s}$ Decays

With the experimental evidences of $\overline B {}^0\to p \overline{p}$ and $B^-\toΛ\overline p$ decays, it is now possible to extract both tree and penguin amplitudes of the charmless two-body baryonic $B$ decays for the first time. The extracted penguin-tree ratio agrees with the expectation. Using the topological amplitude approach with the experimental results on $\overline B {}^0\to p \overline{p}$ and $B^-\toΛ\bar p$ decay rates as input, predictions on all other $\overline B_q\to {\cal B} \overline {\cal B}$, ${\cal B} \overline {\cal D}$, ${\cal D} \overline {\cal B}$ and ${\cal D} \overline {\cal D}$ decay rates, where ${\mathcal B}$ and ${\cal D}$ are the low lying octet and decuplet baryons, respectively, are given. It is non-trivial that the results do not violate any existing experimental upper limit. From the analysis it is understandable that why $\overline B {}^0\to p \overline{p}$ and $B^-\toΛ\bar p$ modes are the first two modes with experimental evidences. Relations on rates are verified using the numerical results. We note that the predicted $B^-\to p\overline{Δ^{++}}$ rate is close to the experimental bound, which has not been updated in the last ten years. Direct $CP$ asymmetries of all $\overline B_q\to {\cal B} \overline {\cal B}$, ${\cal B} \overline {\cal D}$, ${\cal D} \overline {\cal B}$ and ${\cal D} \overline {\cal D}$ modes are explored. Relations on $CP$ asymmetries are examined using the numerical results. The direct $CP$ asymmetry of $\overline B {}^0\to p \overline{p}$ decay can be as large as $\pm 50\%$. The $CP$ asymmetries of $ΔS=-1$ pure penguin modes are constrained to be of few $\%$. These modes are expected to be sensitive to New Physics contributions and are good candidates to be added to the list of the tests of the Standard Model.

hep-ph↗

arXiv2016

Direct CP Violation in Charmless Three-body Decays of $B$ Mesons

Direct CP violation in charmless three-body hadronic decays of $B$ mesons is studied within the framework of a simple model based on the factorization approach. Three-body decays of heavy mesons receive both resonant and nonresonant contributions. Dominant nonresonant contributions to tree-dominated and penguin-dominated three-body decays arise from the $b\to u$ tree transition and $b\to s$ penguin transition, respectively. The former can be evaluated in the framework of heavy meson chiral perturbation theory with some modification, while the latter is governed by the matrix element of the scalar density $\langle M_1M_2|\bar q_1 q_2|0\rangle$. Strong phases in this work reside in effective Wilson coefficients, propagators of resonances and the matrix element of scalar density. In order to accommodate the branching fraction and CP asymmetries observed in $B^-\to K^-π^+π^-$, the matrix element $\langle Kπ|\bar sq|0\rangle$ should have an additional strong phase, which might arise from some sort of power corrections such as final-state interactions. We calculate inclusive and regional CP asymmetries and find that nonresonant CP violation is usually much larger than the resonant one and that the interference effect is generally quite significant. If nonresonant contributions are turned off in the $K^+K^-K^-$ mode, the predicted CP asymmetries due to resonances will be wrong in sign when confronted with experiment. In our study of $B^-\to π^-π^+π^-$, we find that ${\cal A}_{C\!P}(ρ^0π^-)$ should be positive in order to account for CP asymmetries observed in this decay. However, all theories predict a large and negative CP violation in $B^-\to ρ^0π^-$. Measurements of CP-asymmetry Dalitz distributions put very stringent constraints on the theoretical models. We check the magnitude and the sign of violation in some (large) invariant mass regions to test our model.

hep-ph↗

arXiv2016

Study of Majorana Fermionic Dark Matter

We construct a generic model of Majorana fermionic dark matter (DM). Starting with two Weyl spinor multiplets $η_{1,2}\sim (I,\mp Y)$ coupled to the Standard Model (SM) Higgs, six additional Weyl spinor multiplets with $(I\pm 1/2, \pm(Y\pm 1/2))$ are needed in general. It has 13 parameters in total, five mass parameters and eight Yukawa couplings. The DM sector of the minimal supersymmetric standard model (MSSM) is a special case of the model with $(I,Y)=(1/2,1/2)$. Therefore, this model can be viewed as an extension of the neutralino DM sector. We consider three typical cases: the neutralino-like, the reduced and the extended cases. For each case, we survey the DM mass $m_χ$ in the range of $(1,2500)$ GeV by random sampling from the model parameter space and study the constraints from the observed DM relic density, the direct search of LUX, XENON100 and PICO experiments, and the indirect search of Fermi-LAT data. We investigate the interplay of these constraints and the differences among these cases. It is found that the direct detection of spin-independent DM scattering off nuclei and the indirect detection of DM annihilation to $W^+W^-$ channel are more sensitive to the DM searches in the near future. The allowed mass for finding $\tilde H$-, $\tilde B$-, $\tilde W$- and non neutralino-like DM particles and the predictions on $\langleσ(χχ\rightarrow ZZ, ZH, t{\bar t}) v\rangle$ in the indirect search are given.

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