arXiv subjects

Bai-Cian Ke

Publications and source records attributed to Bai-Cian Ke.

18 recordsLinked to original sources

arXiv2026

A Class of Exact Single-Field Inflationary Solutions beyond Slow Roll

We construct exact solutions for single-field inflaton dynamics without invoking the slow-roll approximation. A suitable change of variables reduces the background equation to an Abel equation of the first kind. Although a generic Abel equation is not analytically solvable, we identify a class of inflaton potentials for which the transformed equation admits exact solutions. The resulting framework contains constant-roll inflation as a special case and also accommodates solutions with a constant second Hubble-flow parameter. We analyze the linear local attractor behavior and superhorizon evolution of these rolling backgrounds. Using the public joint CMB likelihood contours in the $(n_s,r)$ plane, we identify compatible parameter regions and show that one rolling branch can also yield $50\leq N_*<60$. Direct numerical evolution of the scalar and tensor modes at representative points validates the local-index predictions to better than $7\times10^{-4}$ in $n_s$ and $2\times10^{-6}$ in $r$. The exact family extends beyond slow roll, although the observationally selected regions displayed here lie close to the slow-roll regime.

astro-ph.CO↗

arXiv2026

Angular and invariant-mass observables in the four-body Higgs decay $h\to\ell\barν_\ell\bar{\ell}^\primeν_{\ell^\prime}$

We study the angular distribution of the Higgs boson decay $h\to\ell\barν_\ell\bar{\ell}^\primeν_{\ell^\prime}$ with $\ell\neq\ell^\prime$. Due to the presence of two undetected neutrinos, a complete angular analysis is not experimentally feasible. To overcome this, we reorganize the kinematics from the conventional lepton-neutrino pairs into a charged-lepton pair and a neutrino pair, i.e.~$\ell\bar{\ell}^\prime$ and $\barν_\ellν_{\ell^\prime}$. This allows us to express the differential decay rate in terms of experimentally accessible variables, including the invariant mass squared of the neutrino pair. Using the effective field theory framework, we derive this rate and integrate over the neutrino-associated angles. This parametrization provides a clean and measurable angular distribution, offering a new probe of the $hWW$ coupling and possible beyond-the-Standard-Model contributions.

hep-ph↗

arXiv2026

Amplitude analysis for charmed meson decays at BESIII

Amplitude analysis bridges the gap between experimental measurements of multibody charmed-meson decays and theoretical predictions of intermediate two-body processes. This work presents a comprehensive overview of the amplitude-analysis methodology employed by the BESIII Collaboration, emphasizing practical implementation. We detail the construction of the probability density function and likelihood function for unbinned maximum-likelihood fits. This encompasses Monte Carlo integration techniques for normalization, the incorporation of detection efficiency and resolution effects, and multidimensional background modeling utilizing XGBoost classifiers. Furthermore, we describe the amplitude formalism for both hadronic and semileptonic decays, incorporating standard resonance-propagator parametrizations. Key analytical aspects, including the evaluation of fit fractions, the generation of kinematic projections, and the estimation of statistical uncertainties, are also discussed.

hep-ex↗

arXiv2026

Power-Law Inflation Survives Observational Constraints

Power-law inflation has stood as a classical model in inflationary cosmology since the early 1980s, prized for its exact analytical solutions and ability to naturally resolve the Big Bang theory's horizon and flatness problems through exponential expansion. However, its simplest form appears incompatible with modern precision observations, motivating increasingly complex alternatives. In this work, we demonstrate how previous predictions with power-law inflation considered only a particular solution of the field equations, and derive the complete set of general analytical solutions that satisfy current theoretical and observational constraints. This finding revitalizes power-law inflation as a viable framework, offering new possibilities for cosmological model-building while preserving its original mathematical elegance.

astro-ph.CO↗

arXiv2026

Testing Non-Standard Neutrinos in Purely Leptonic Lepton Decays

We propose a method to probe sterile neutrinos using polarization observables in the purely leptonic decays $\ell^{\prime-} \to \ell^{-} \barν_{\ell} ν_{\ell^{\prime}}$. By analyzing angular distributions and asymmetries derived from polarized decay rates, we identify distinctive signatures of sterile neutrino mixing. In particular, we demonstrate that sterile neutrinos can induce singularities in certain asymmetry parameters as functions of the invariant mass squared of the neutrino pair. These singularities occur for sterile neutrino masses $m_{4ν}$ satisfying $m_{4ν}^2 < m_{\ell^{\prime}}^2 / 2$, providing a clear target for experimental investigation. Our results motivate the incorporation of polarized beam sources at future colliders to enhance sensitivity to sterile neutrinos and other new physics.

hep-ph↗

arXiv2025

Novel Model-Independent Approach to Explore New Physics in Five-body Semileptonic Decays

Substantial contribution of the tensor current in semileptonic decays is regarded as a clear signal for new physics. In this work, we propose a model-independent approach to unambiguously test contribution of the tensor current in semileptonic five-body decays $\bar{D}_{(s)}/\bar{B}_{(s)}\to V\ell\barν_{\ell}\,(\ell=e,μ,τ)$ with $V\to π^0π^+π^-$, where $V$ denotes vector particles. We derive three parameters associated with the angular asymmetry, which are always equal to one in the Standard Model regardless the data of form factor but will deviate if contribution of the tensor current doesn't vanish. The outcomes have potential applications in precisely testing the Standard Model and searching for new physics. Relevant measurements can be performed using data collected by BESIII, Belle~II, and LHCb.

hep-ph↗

arXiv2025

Roles of the scalar $f_0(500)$ and $f_0(980)$ in the process $D^0\to π^0π^0 \bar{K}^0$

Motivated by the near-threshold enhancement and the dip structure around 1~GeV in the $π^0π^0$ invariant mass distribution of the process $D^0\to π^0π^0\bar{K}^0$ observed by the CLEO Collaboration, we have investigated this process by taking into account the contribution from the $S$-wave pseudoscalar meson-pseudoscalar meson interactions within the chiral unitary approach, and also the one from the intermediate resonance $K^{*}(892)$. Our results are in good agreement with the CLEO measurements, which implies that, the near-threshold enhancement near the $π^0π^0$ threshold is mainly due to the contributions from the scalar meson $f_0(500)$ and the intermediate $K^*$, and the cusp structure around 1~GeV in the $π^0π^0$ invariant mass distribution should be associated with the scalar meson $f_0(980)$.

hep-ph↗

arXiv2025

A phenomenological estimate of rescattering effects in $B_s\to K^{0}\bar{K}^{0}$

The measurements in $b\to s$ penguin-dominated decays are widely recognized as a powerful test for searching for New Physics by studying the deviation from theoretical estimations within the Standard Model. We examine the final-state rescattering effects on the decay $B_s\to K^{*0}\bar{K}^{*0}$ and provide estimations of the branching ratio and longitudinal polarization of $B_s\to K^{*0}\bar{K}^{*0}$, which is consistent with experimental observations. Our conclusion is that both short- and long-distance interactions contribute significantly in this decay. The small longitudinal polarization in $B\to VV$ modes may not be a signal for New Physics.

hep-ph↗

arXiv2025

Testing the light scalar meson as a non-$q\bar q$ state in semileptonic $D$ decays

While the light scalar mesons ($S_0$) are considered to be either ordinary $q\bar q$ or exotic tetraquark states, we investigate the semileptonic decays $D\to S_0 e^+ν_e$, by taking into account the resonant effects of $S_0\to M_1 M_2$, where $S_0=a_0(980)$, $f_0(980)$, and $f_0(500)/σ_0$, and $M_{1(2)}$ represents a pseudoscalar meson. For the first time, the $D\to S_0$ form factors in the two quark structures are both presented. Subsequently, we calculate ${\cal B}(D_s^+\to σ_0 e^+ν_e,σ_0\toπ^+π^-)=(20.3\pm 1.8\pm 0.5)\times 10^{-4}$ in the $q\bar q$ structure, showing significant $9σ$ deviations from the experimental upper limit of $3.3\times 10^{-4}$. In contrast, ${\cal B}(D_s^+\to σ_0 e^+ν_e,σ_0\toπ^+π^-)=(0.58^{+1.43}_{-0.57}\pm 0.01)\times 10^{-4}$ in the $q^2\bar q^2$ structure is within the allowed experimental range. Clearly, the light scalar meson is tested as a non-$q\bar q$ state. We hence demonstrate a highly sensitive new approach for exploring the true nature of scalar mesons, which can be extended to non-leptonic $D$ decays as well as $B$ meson decays.

hep-ph↗

arXiv2024

Five-body $D\to V$ Semileptonic Decays

Our main objective is to derive the decay rate for the semileptonic decays $D\to V\ell^+ν_{\ell}\,(\ell=e,μ)$, where $V$ represents a vector particle. In these decays, the vector particle $V$ decays into three pseudo-scalar particles. To accomplish this, we evaluate the phase-space factor for the five-body decay with a set of eight independent variables which uniquely define a point in the phase space. We further conduct a detailed investigation of the $D\to ω\ell^+ν_{\ell}$, where $ω$ subsequently decays into $π^+π^-π^0$, within the Standard Model and in a general effective field theory description of the weak interactions at low energies. The outcomes of this study have potential applications in the measurement of $D\to ω$ form factors. These measurements can be performed using data obtained from BESIII.

hep-ph↗

arXiv2024

Muon mass correction in partial wave analyses of charmed meson semi-leptonic decays

We derive the parameterization formula for partial wave analyses of charmed meson semi-leptonic decays with consideration of the effects caused by the lepton mass. As the proposed super-tau-charm factory will reach much enhanced luminosity and BESIII is taking $ψ(3770)\to D\bar{D}$ data, our results are helpful to improve the measurement precision of future partial wave analyses of charmed meson semi-muonic decays.

hep-ph↗

arXiv2023

Investigating $Z_{cs}(3985)$ and $Z_{cs}(4000)$ exotic states in $Λ_b\to Z^-_{cs}p$ decays

We study the $Z_{cs}(3985)$ and $Z_{cs}(4000)$ exotic states in the decays of $Λ_b$ baryons through a molecular scenario. In the final state interaction, the $Λ_b\to Λ_c^+ D_s^{(*)-}$ decays are followed by the $Λ_c^+ D_s^{(*)-}$ to $Z^-_{cs}p$ rescatterings via exchange of a $D^{(*)}$ meson. We predict a branching fraction of $(3.1^{+1.4}_{-2.6})\times 10^{-4}$ for $Λ_b\to Z^-_{cs}p$, which can be measured in the $Λ_b\to J/ψK^{(*)-}p$ decay. This study proposes a new approach to test the molecular model, and guides future experimental searches for the $Z_{cs}(3985)$ and $Z_{cs}(4000)$.

hep-ph↗

arXiv2023

Recent Progress in Leptonic and Semileptonic Decays of Charmed Hadrons

We present a comprehensive review of purely leptonic and semileptonic decays of $D^{0(+)}$, $D_s^{+}$, and charmed baryons (including $Λ_c^{+}$, $Ξ_c$ and $Ω_c$). The precise studies of these decays help deepen our understanding and knowledge of quantum chromodynamics via measuring decay constants and form factors, and test the Standard Model through examining the unitarity of Cabibbo-Kobayashi-Maskawa matrix and lepton flavor universality. We give an overview of the theoretical and experimental tools before discussing the recent progress. The data sets collected by BESIII near the production thresholds of $D\bar{D}$, $D_s^{(*)+}D_s^{(*)-}$ and $Λ_c^{+}\barΛ_c^{-}$ offer important opportunities for studies of charm physics.

hep-ex↗

arXiv2023

Investigating $η^\prime_{1}(1855)$ exotic states in $J/ψ\toη^\prime_{1}(1855)η^{(\prime)}$ decays

An analysis of the $J/ψ\to ηη^\primeγ$ decay by the BESIII collaboration claims the observation of an exotic state $η_1(1855)$ with $I^GJ^{PC}=0^+1^{-+}$. To establish its C-parity partner $η^\prime_{1}(1855)$ in the picture of the $K \bar{K}_1(1400)$ molecular state, we propose that $J/ψ\toη^\prime_{1}(1855)η^{(\prime)}$ receives the main contributions from the final state interaction of $KK^*$($K^+ K^{*-}$, $K^- K^{*+}$, $K^0 \bar{K}^{*0}$, and $\bar{K}^0 K^{*0}$). Specifically, $K$ and $K^*$ in $J/ψ\to KK^*$ decays transform as $η^\prime_{1}(1855)η^{(\prime)}$, by exchanging a $K_1(1400)$. We predict ${\cal B}(J/ψ\to η^{\prime}_1(1855)η)=(6.3^{+12.6}_{-3.5})\times 10^{-6}$, and ${\cal B}(J/ψ\to η^{\prime}_1(1855)η^{\prime}) =(6.5^{+6.6}_{-4.6})\times 10^{-6}$, which can be studied in the $J/ψ\to K^*\bar{K}^*η^{(\prime)}$ decays.

hep-ph↗

arXiv2023

Photo-production of lowest $Σ^*_{1/2^-}$ state within the Regge-effective Lagrangian approach

Since the lowest $Σ^{*}$ state, with quantum numbers spin-parity $J^{P} =1/2^{-}$, is far from established experimentally and theoretically, we have performed a theoretical study on the $Σ^*_{1/2^-}$ photo-production within the Regge-effective Lagrangian approach. Taking into account that the $Σ^*_{1/2^-}$ couples to the $\bar{K}N$ channel, we have considered the contributions from the $t$-channel $K$ exchange diagram. Moreover, these contributions from $t$-channel $K^*$ exchange, $s$-channel nucleon pole, $u$-channel $Σ$ exchange, and the contact term, are considered. The differential and total cross sections of the process $γn \to K^{+}Σ^{*-}_{1/2^-}$ are predicted with our model parameters. The results should be helpful to search for the $Σ^*_{1/2^-}$ state experimentally in future.

hep-ph↗

arXiv2022

Distinguishing (Dirac or Majorana) neutrinos in purely leptonic decays of leptons

We investigate purely leptonic decays of leptons $ł^{\prime-}\to l^-\barν_lν_{l^{\prime}}$ to distinguish Dirac or Majorana neutrinos. We derive the differences of the decay width (and associated quantities) between the two neutrino hypotheses by the effect of identical particles. Evidence from experimental data makes the hypothesis of Majorana neutrinos very unlikely and our results strongly favor the hypothesis of Dirac neutrinos (in the standard three-neutrino theory). Moreover, our exploration for decay widths can be extended to the polarization angles of leptons, which will inspire new information for experimental and theoretical studies.

hep-ph↗

arXiv2021

Study of the $D_s^+\to a_0(980) ρ$ and $a_0(980) ω$ decays

We study $D_{s}^{+}\toρ^{0(+)}a^{+(0)}_{0}$, $D_{s}^{+}\toωa^{+}_{0}$, and the resonant $D_{s}^{+}\toρa_0$,$a_{0}\to ηπ(KK)$ decays. In the final state interaction, where $D_s^+\to (η^{(\prime)}π^+,K^+\bar K^0)$ are followed by the $(η^{(\prime)}π^+,K^+\bar K^0)$ to $ρ^{0(+)}a^{+(0)}_{0}$ rescatterings, we predict ${\cal B}(D_{s}^{+}\toρ^{0(+)}a^{+(0)}_{0})=(3.0\pm 0.3\pm 1.0)\times 10^{-3}$. Due to the cancellation of the rescattering effects and the suppressed short-distance $W$ annihilation contribution, we expect that ${\cal B}(D_{s}^{+}\toωa^{+}_{0}) \simeq {\cal B}(D_s^+\toπ^+π^0)<3.4\times 10^{-4}$. In our calculation, ${\cal B}(D_{s}^{+}\toρ^{0}(a^{+}_{0}\to)ηπ^{+}) =(1.6^{+0.2}_{-0.3}\pm 0.6)\times 10^{-3}$ agrees with the data, whereas ${\cal B}(D_{s}^{+}\toρ^{+}(a^{0}_{0}\to)K^+K^-)$ is 10 times smaller than the observation, which requires a careful examination.

hep-ph↗

arXiv2020

Resonant $a_0(980)$ state in triangle rescattering $D_s^+\to π^+π^0η$ decays

We study the $D_s^+\to π^+(a_0(980)^0\to)π^0η$, $π^0(a_0(980)^+\to)π^+η$ decays, which have been recently measured by the BESIII collaboration. We propose that $D_s^+\to π^{+(0)}(a_0(980)^{0(+)}\to)π^{0(+)}η$ receives the contributions from the triangle rescattering processes, where $M^0$ and $ρ^+$ in $D_s^+\to M^0 ρ^+$, by exchanging $π^{0(+)}$, are formed as $a_0(980)^{0(+)}$ and $π^{+(0)}$, respectively, with $M^0=(η,η')$. Accordingly, we calculate that ${\cal B}(D_s^+\to a_0(980)^{0(+)}π^{+(0)})=(1.7\pm 0.2\pm 0.1)\times 10^{-2}$ and ${\cal B}(D_s^+\to π^{+(0)}(a_0(980)^{0(+)}\to)π^{0(+)}η)=(1.4\pm 0.1\pm 0.1)\times 10^{-2}$, being consistent with the data.

hep-ph↗