arXiv subjects

Chao-Qiang Geng

Publications and source records attributed to Chao-Qiang Geng.

At least 55 records · Page 3Linked to original sources

arXiv2023

Resolving puzzle in $Ξ_c^0\to Ξ^-e^+ν_e$ with $Ξ_c-Ξ_c'$ mixing

We study the ratio of $R=2 Γ(Ξ_c^0 \to Ξ^- e^+ ν_e )/3Γ(Λ_c^+ \to Λe^+ ν_e )$, which is found to be $R= 1 (0.8)$ from the exact (broken) $SU(3)$ flavor symmetry, in sharp contrast to the average value of $R_{av}=0.59\pm 0.10 $ from the ALICE collaboration and lattice QCD results. We propose to use the mixing of $Ξ_c-Ξ_c'$ to resolve the puzzle. With the model-independent mass relations, we find that the mixing angle is $|θ_c| = 0.137(5)π$, which suppresses $Ξ_c\to Ξe^+ ν_e$ about $20\%$ model-independently, resulting in $R\approx 0.6$ with the $SU(3)$ flavor breaking effect. We explicitly demonstrate that $R= 0.70 \pm 0.09$ from the bag model, which is also consistent with $R_{av}$. To test the mixing mechanism, we recommend the experiments to measure the decays of $Ξ_c \to Ξ'(1530) e^+ ν_e$, whose branching fractions are determined to be $ ( 4.4\sim 8.7)\times 10^{-3}$ and $(1.3\sim 2.6 )\%$ for $Ξ_c^0$ and $Ξ_c^+$, respectively, but vanish without the mixing. In addition, nonvanishing values of ${\cal B}(Ξ_c^+\to Ξ^{\prime 0} (1530)π^+ )$ and ${\cal B}(Ξ_c^+\to Σ^{\prime +} (1530) \overline{K}^0 )$ will also be evidences of the mixing based on the Köner-Pati-Woo theorem, which are calculated as $(3.8\sim 7.5)\times 10^{-3}$ and $(6.6\sim 13)\times 10 ^{-4}$, respectively. We emphasize that $θ_c$ is sizable and should be given serious considerations in future studies on the heavy baryon systems.

hep-ph↗

arXiv2023

Nonleptonic decays of $Ξ_{cc}\to Ξ_c π$ with $Ξ_c-Ξ_c'$ mixing

Aiming on testing the $Ξ_c-Ξ_c'$ mixing, we study the decays of $Ξ_{cc}\to Ξ_c π$ with $Ξ_{cc} = (Ξ_{cc}^{++} , Ξ_{cc} ^+ )$, $Ξ_c = (Ξ_c^{(\prime)+},Ξ_c^{(\prime)0})$ and $π= (π^+ , π^0)$. The soft-meson limit is considered along with the pole model, and the baryon matrix elements are evaluated by the bag model with and without removing the center-of-mass motion (CMM). We find that the four-quark operator matrix elements are about twice larger once the unwanted CMM is removed. We obtain that ${\cal R} = {\cal B}(Ξ_{cc}^+ \to Ξ_c^{\prime +} π^+ )/ {\cal B}(Ξ_{cc}^+ \to Ξ_c^{ +} π^+ ) = 0.87^{+0.17}_{-0.11} $ and $1.45$ with and without removing the CMM, where the former is close to the lower bound and the later is well consistent with ${\cal R} = 1.41 \pm 0.17 \pm 0.10$ measured at LHCb. In addition, we show that after including the mixing, the up-down asymmetry of $α( Ξ_{cc}^+ \to Ξ_c^{(\prime)0 } π^+)$ flips sign. Explicitly, we obtain that $α(Ξ_{cc}^{+} \to Ξ_c^{\prime +} π^0) = 0.52$ and $α(Ξ_{cc}^{+} \to Ξ_c^{ 0 } π^+) = 0.31$ with and without the CMM corrections, respectively, which are all negative if the mixing is absence. As a bonus, a positive value of $α(Ξ_{cc}^{+} \to Ξ_c^{\prime 0} π^+)$ in experiments can also serve as the evidence of the $W$-exchange contributions.

hep-ph↗

arXiv2022

Bottomed baryon decays with invisible Majorana fermions

We study the invisible Majorana fermions of $χ$ in bottomed baryon decays with flavor-changing neutral currents (FCNCs) based on the model-independent effective Lagrangian between the quarks and invisible particles. From the bounds of the coupling constants extracted from the experiments, we examine the decay branching ratios of $Λ_b\toΛχχ$, $Ξ_b^{0(-)}\toΞ^{0(-)}χχ$, $Λ_b\to n χχ$, $Ξ_b^{-}\to Σ^{-} χχ$, $Ξ_b^{0}\to Σ^{0} χχ$, and $Ξ_b^{0}\to Λχχ$, which can be as large as $6.3,~9.2,~5.7,~5.8,~2.7$, and $1.0\times10^{-5}$ for $m_χ=2$ GeV, respectively. Some of these decays are accessible to the future experimental searches, such as Belle II.

hep-ph↗

arXiv2022

Time-reversal asymmetries in $Λ_b \to Λ(\to p π^-)\ell^+\ell^-$

We study the decays of $Λ_b \to Λ(\to p π^-) \ell ^+ \ell^-$ with $\ell = (e, μ, τ)$. In particular, we examine the full angular distributions with polarized $Λ_b$ and identify the time-reversal asymmetries or T-odd observables. By using the homogeneous bag model, we find that the decay branching fractions of $Λ_b \to Λ\ell^+\ell^-$ are $(9.1\pm 2.5,7.9\pm 1.8, 2.1\pm 0.2)\times 10^{-7}$ for $\ell =(e, μ,τ)$, respectively. In addition, we obtain that $A_{FB}^{\ell} = -0.369\pm 0.007$ and $A_{FB}^{h}=-0.333\pm 0.004$, averaged in the range of $15 \leq q^2 \leq 20~ \text{GeV}^2$. These results are well consistent with the current experimental data. We also explore the T-odd observables in $Λ_b \to Λ(\to p π^-) μ^+ μ^-$, which are sensitive to new physics~(NP). Explicitly, we illustrate that the current experimental measurement from one of the T-odd observables favors the existence of NP, such as the extra $Z$-boson model.

hep-ph↗

arXiv2022

Semileptonic decays of doubly charmed baryons with $Ξ_c-Ξ_c'$ mixing

We study the $Ξ_c- Ξ_c'$ mixing effects in the semileptonic decays the doubly charm baryons of $Ξ_{cc}$. We focus on the ratio of ${\cal R}(θ_c) \equiv {\cal B}( Ξ_{cc} \to Ξ_c' e^+ ν_e)/ {\cal B}( Ξ_{cc} \to Ξ_c e^+ ν_e) $ and find that $({\cal R}(θ_0),{\cal R}(- θ_0)) =(0.46 \pm 0.01,7.33 \pm 0.23)$ with $θ_0 = 0.137π$, which are in sharp contrast to ${\cal R}(0)=2.15\pm0.11$ without the mixing. The ratio is enhanced~(suppressed) by a factor of four for a negative~(positive) $θ_c$. In addition, the polarization asymmetries of $Ξ_c^{(\prime)}$ are found to be $α(-θ_0) = 0.32 ~(-0.76)$ and $α(θ_0) = -0.82~(-0.38)$. As ${\cal R}$ and $α$ are highly sensitive to $θ_c$ and unaffected by the $W$-exchange contributions, they provide excellent opportunities to determine $θ_c$ in the ongoing experiments.

hep-ph↗

arXiv2022

Semileptonic decays of doubly charmed baryons with bag model

We study the semileptonic decays of $B_{cc}$ ${\rightarrow}$ $B_c\ell^+ν_\ell$ with the bag model, where $\ell$ = $(e, μ)$, $B_{cc}$ = $(Ξ_{cc}^{++}$, $Ξ_{cc}^+$, $Ω_{cc}^+$), and $ B_c$ are the singly charmed baryons with $J^P= 1/2^+$. We obtain the decay widths of $Γ(Ξ_{cc}^{++}{\rightarrow}Ξ_c^+e^+ν_e, Ξ_c^{\prime+}e^+ν_e, Λ_c^+e^+ν_e, Ω_c^+ e^+ν_e) =(5.1\pm 0.1 , 11\pm 1, 0.34\pm 0.06, 0.76\pm 0.06)\times 10^{-14}$~GeV, $Γ(Ξ_{cc}^+\rightarrow Ξ_c^0e^+ν_e, Ξ_c^{\prime0}e^+ν_e , Σ_c^0e^+ν_e) = (5.1\pm 0.6, 11\pm 1, 1.5\pm 0.1) \times 10^{-14}$~GeV, and $Γ(Ω_{cc}^+\rightarrow Ω_c^0 e^+ν_e, Ξ_c^0e^+ν_e , Ξ_c^{\prime0} e^+ν_e) = (22\pm 2, 0.32 \pm 0.04, 0.77\pm 0.06)\times 10^{-14}$~GeV. We also get that $Γ$($B_{cc}$ ${\rightarrow}$ $B_cμ^+ν_μ$)/$Γ$($B_{cc}$ ${\rightarrow}$ $B_ce^+ν_e$) = $0.97\sim 1.00$. In addition, we discuss the $SU(3)$ flavor breaking effects, classified into three aspects: phase space differences, spectator quarks, and overlappings of the transited quarks. In particular, we show that the breaking effects are dominated by the phase space differences, which can be as large as 25\%. Explicitly, we find that $Γ(Ξ_{cc}^{++} \to Λ_c ^+ e^+ ν_e) V_{cs}^2/Γ(Ξ_{cc}^{++} \to Ξ_c ^+ e^+ ν_e )V_{cd}^2 = 1.24$, which is expected as $1$ under the exact $SU(3)$ flavor symmetry.

hep-ph↗

arXiv2022

Center of mass motion in bag model

Despite the great success on the mass spectra, the reputation of the bag model has been closely followed by the embarrassment from the center of mass motion. It leads to severe theoretical inconsistencies. For instance, the masses and the decay constants would no longer be independent of the momentum. In this work, we provide a systematical approach to resolve this problem. The meson decay constants as well as the baryon transition form factors can be computed consistently in our framework. Notably, the form factors in the neutron $β$ decays do not depend on any free parameters, and are determined to be $F^V_1 =1 $ and $F^A_1 = 1.31$ or $F_1^A/F_1^V= 1.31$, which is close the experimental value of $F^A_1/F^V_1 = 1.27$. In addition, we find that ${\cal B} (Λ_b \to Λγ) = (6.8 \pm 3.3 ) \times 10^{-6} $, which agrees to the experimental value of $(7.1\pm 1.7)\times 10^{-6}$.

hep-ph↗

arXiv2022

Time-reversal asymmetries in $Λ_b$ semileptonic decays

We study the decays of $Λ_b \to Λ_c(\to B_n f) \ell ^- \overlineν$ with $\ell = e, μ, τ$, where $B_n$ and $f$ are the daughter baryons and the rest of the particles in $Λ_c$ cascade decays, respectively. In particular, we examine the full angular distributions with polarized $Λ_b$ and lepton mass effects, in which the time-reversal asymmetries are identified. We concentrate on the decay modes of $Λ_b \to Λ_c(\to p K^- π^+) \ell ^- \overlineν$ to demonstrate their experimental feasibility. We show that the observables associated with the time-reversal asymmetries are useful to search for new physics as they vanish in the standard model. Explicitly, we find that they are sensitive to the right-handed current from new physics, and possible to be observed at LHCb.

hep-ph↗

arXiv2022

New extraction of CP violation in b-baryon decays

We study CP violation in b-baryon decays of $Ξ_b^- \to Ξ^- D$ with $D = D^0, \bar{D}^0$ and $D_i~(i=1,2)$. We find that these baryonic decay processes provide an ideal opportunity to measure the weak phase due to the absence of the relative strong phase. Explicitly, we relate $\barρ$ and $\barη$ the CKM elements with the decay rate ratios of $R_i= Γ(Ξ_b^- \to Ξ^-D_{i} ) / Γ( Ξ_b^- \to Ξ^-D^0 )$ without the charge conjugate states. As a complementary, we also examine the decay distributions of $Λ_b \to Λ(\to p π^- ) D$. There are in total 32 decay observables, which can be parameterized by 9 real parameters, allowing the experiments to extract the angle $γ\equiv \arg(-V_{ud}V_{ub}^*/V_{cd}V_{cb}^*)$ in the CKM unitarity triangle. In addition, the feasibilities of the experimental measurements are discussed. We find that $\barρ$ and $\barη$ can be extracted at LHCb Run3 from $Ξ_b^- \to Ξ^- D$, and a full analysis of $Λ_b \to Λ(\to p π^-)D$ is available at LHCb Run4.

hep-ph↗

arXiv2022

Unitarity Bounds on the Massive Spin-2 Particle Explanation of Muon $g-2$ Anomaly

Motivated by the long-standing discrepancy between the Standard Model prediction and the experimental measurement of the muon magnetic dipole moment, we have recently proposed to interpret this muon $g-2$ anomaly in terms of the loop effect induced by a new massive spin-2 field $G$. In the present paper, we investigate the unitarity bounds on this scenario. We calculate the $s$-wave projected amplitudes for two-body elastic scatterings of charged leptons and photons mediated by $G$ at high energies for all possible initial and final helicity states. By imposing the condition of the perturbative unitarity, we obtain the analytic constraints on the charged-lepton-$G$ and photon-$G$ couplings. We then apply our results to constrain the parameter space relevant to the explanation of the muon $g-2$ anomaly.

hep-ph↗

arXiv2022

Weak Radiative Decays of Anti-triplet Bottomed Baryons in Light-Front Quark Model

We study the weak radiative decays of ${\bf B}_b \to {\bf B}_n γ$ with ${\bf B}_{b(n)} $ the anti-triplet-bottom (octet) baryons in the light front quark model. We obtain that ${\cal B}(Λ_b \to Λγ)= (7.1 \pm 0.3 )\times 10 ^{-6}$, which agrees well with the current experimental value of $(7.1 \pm 1.7 )\times 10 ^{-6}$. We predict that ${\cal B}(Ξ_b^0 \to Ξ^0 γ)= (1.0 \pm 0.1 )\times 10 ^{-5}$ and ${\cal B}(Ξ_b^- \to Ξ^- γ) = (1.1 \pm 0.1) \times 10^{-5}$, which are consistent with the latest upper limits set by the LHCb collaboration. In addition, we find that the $SU(3)_F$ flavor symmetry breaking effects for the modes related to the $b\to d γ$ transition can be as large as $20\%$.

hep-ph↗

arXiv2022

Study of charmless two-body baryonic $B$ decays

We study the charmless two-body decays of $B\to {\bf B}_n \overline{\bf B}_n^\prime$ with $B = ( B^+ , B^0 , B^0_s)$ and ${\bf B}_n^{(\prime)}$ the low-lying octet baryons. The factorizable amplitudes are calculated by the modified bag model, while the nonfactorizable ones are extracted from the experimental data with the $SU(3)_F$ flavor symmetry. We are able to explain all current experimental measurements and provide predictions on the decay branching ratios in $B\to {\bf B}_n \overline{\bf B}_n^\prime$. Particularly, we find that ${\cal B}(B_s^0 \to Ξ^0 \overlineΞ^0) = (19.3\pm 2.7 )\times 10^{-7}$ and ${\cal B}(B_s^0 \to Ξ^- \overlineΞ^-) = (19.4\pm 2.7 )\times 10^{-7}$, which are sizable and able to be observed in the ongoing experiments at LHCb and BELLE-II. Furthermore, the decay branching ratios of $B_s^0 \to (p\overline{p}, n\overline{n})$ and $B^0 \to (Ξ^0 \overlineΞ^0 ,Σ^+\overlineΣ^+)$ are expected to be $O(10^{-10})$, which are suppressed due to the angular momentum conservation and chiral symmetry.

hep-ph↗

arXiv2022

Sizable Time-reversal violating effects in bottom baryon decays

We study time-reversal~(T) asymmetries in the charmless two-body decays of antitriplet bottom baryons. We find that in ${\bf B}_b \to {\bf B}_n P$ with ${\bf B}_b = (Ξ_b ^- , \,Ξ_b^0, \,Λ_b)$ and ${\bf B}_n(P)$ a octet baryon (pseudoscalar meson), the positive and negative helicity amplitudes are both sizable, resulting in the large T-violating effects. Particularly, the T-odd parameters, $β_w$, for the color-enhanced channels are expected to be around $40\%$ and $-25\%$ in $b\to s $ and $b\to d $ transitions for the standard model, which can be measured by the experiments at LHCb, respectively. On the other hand, in ${\bf B}_b \to {\bf B}_n V(γ)$ with $V(γ)$ a vector meson~(photon), the decays are predominated by a single helicity amplitude, and the T violating effects by the correlations among spins are suppressed. We also explore the T violating observables for the $Ξ_b$ decays based on the angular distributions.

hep-ph↗

arXiv2021

Cosmological Constraints on Non-flat Exponential $f(R)$ Gravity

We explore the viable $f(R)$ gravity models in FLRW backgrounds with a free spatial curvature parameter $Ω_{K}$. In our numerical calculation, we concentrate on the exponential $f(R)$ model of $f(R) = R - λR_{ch}(1-\exp{(-R/R_{ch}}))$, where $R_{ch}$ is the characteristic curvature scale, which is independent of $Ω_K$, and $λ$ corresponds to the model parameter, while $R_{ch}λ=2Λ$ with $Λ$ the cosmological constant. In particular, we study the evolutions of the dark energy density and equation of state for exponential $f(R)$ gravity in open, flat and closed universe, and compare with those for $Λ$CDM. From the current observational data, we find that $λ^{-1}=0.42927^{+0.39921}_{-0.32927}$ at 68$\%$ C.L and $Ω_K=-0.00050^{+0.00420}_{-0.00414}$ at 95$\%$ C.L. in the exponential $f(R)$ model. By using Akaike information criterion (AIC), Bayesian information criterion (BIC) and Deviance Information Criterion (DIC), we conclude that there is no strong preference between the exponential $f(R)$ gravity and $Λ$CDM models in the non-flat universe.

astro-ph.CO↗

arXiv2021

Time-reversal asymmetries and angular distributions in $Λ_b \to ΛV$

We study the spin correlations to probe time-reversal~(T) asymmetries in the decays of $Λ_b \to ΛV ~(V=ϕ, ρ^0, ω, K^{*0})$. The eigenstates of the T-odd operators are obtained along with definite angular momenta. We obtain the T-odd spin correlations from the complex phases among the helicity amplitudes. We give the angular distributions of $Λ_b \to Λ(\to p π^-)V(\to PP')$ and show the corresponding spin correlations, where $P^{(\prime)}$ are the pseudoscalar mesons. Due to the helicity conservation of the $s$ quark in $Λ$, we deduce that the polarization asymmetries of $Λ$ are close to $-1$. Since the decay of $Λ_b \to Λϕ$ in the standard model~(SM) is dictated by the single weak phase from the product of CKM elements, $V_{tb}V_{ts}^*$, the true T and CP asymmetries are suppressed, providing a clean background to test the SM and search for new physics. In the factorization approach, as the helicity amplitudes in the SM share the same complex phase, T-violating effects are absent. Nonetheless, the experimental branching ratio of $Br(Λ_b \to Λϕ) = (5.18\pm 1.29 )\times 10^{-6}$ suggests that the nonfactorizable effects or some new physics play an important role. By parametrizing the nonfactorizable contributions with the effective color number, we calculate the branching ratios and direct CP asymmetries. We also explore the possible T-violating effects from new physics.

hep-ph↗

arXiv2021

Scalar Gravitational Wave Signals from Core Collapse in Massive Scalar-Tensor Gravity with Triple-Scalar Interactions

The spontaneous scalarization during the stellar core collapse in the massive scalar-tensor theories of gravity introduces extra polarizations (on top of the plus and cross modes) in gravitational waves, whose amplitudes are determined by several model parameters. Observations of such scalarization-induced gravitational waveforms therefore offer valuable probes into these theories of gravity. Considering a triple-scalar interactions in such theories, we find that the self-coupling effects suppress the magnitude of the scalarization and thus reduce the amplitude of the associated gravitational wave signals. In addition, the self-interacting effects in the gravitational waveform are shown to be negligible due to the dispersion throughout the astrophysically distant propagation. As a consequence, the gravitational waves observed on the Earth feature the characteristic inverse-chirp pattern. Although not with the on-going ground-based detectors, we illustrate that the scalarization-induced gravitational waves may be detectable at a signal-to-noise ratio level of ${\cal O}(100)$ with future detectors, such as Einstein Telescope and Cosmic Explorer.

gr-qc↗

arXiv2021

A Dark Energy model from Generalized Proca Theory

We consider a specific dark energy model, which only includes the Lagrangian up to the cubic order in terms of the vector field self-interactions in the generalized Proca theory. We examine the cosmological parameters in the model by using the data sets of CMB and CMB+HST, respectively. In particular, the Hubble constant is found to be $H_0=71.80^{+1.07}_{-0.72}$ ($72.48^{+0.72}_{-0.60}$) $\rm kms^{-1}Mpc^{-1}$ at $68\%$~C.L. with CMB (CMB+HST), which would alleviate the Hubble constant tension. We also obtain that the reduced $χ^2$ values in our model are close to unity when fitting with CMB and CMB+HST, illustrating that our model is a good candidate to describe the cosmological evolutions of the universe.

gr-qc↗

arXiv2020

Probing new physics with the kaon decays $K\toππ\!\not\!\!E$

The latest search for the rare kaon decay $K^+\toπ^+ν\barν$ by the NA62 experiment has produced evidence for it with a branching fraction consistent with the prediction of the standard model. The new result implies that in this decay, with the $ν\barν$ pair appearing as missing energy ($\not\!\!E$), the room for possible new physics is no longer sizable and that therefore its contributions to underlying four-particle $s\to d\!\not\!\!E$ operators with parity-even $ds$ quark bilinears have become significantly constrained. Nevertheless, we point out that appreciable manifestations from beyond the standard model induced by the corresponding operators with mainly parity-odd $ds$ quark bilinears could still occur in $K\toππ\!\not\!\!E$ modes, on which there are only minimal empirical details at present. We find in particular that new physics of this kind may enhance the branching fraction of $K_L\toπ^0π^0\!\not\!\!E$ to values reaching its current experimental upper limit and the branching fractions of $K^+\toπ^+π^0\!\not\!\!E$ and $K_L\toπ^+π^-\!\not\!\!E$ to the levels of $10^{-7}$ and $10^{-6}$, respectively. Thus, quests for these decays in existing kaon facilities such as KOTO and NA62 or future ones could provide valuable information complementary to that gained from $K\toπ\!\not\!\!E$.

hep-ph↗