arXiv subjects

Yan-Liang Shi

Publications and source records attributed to Yan-Liang Shi.

14 recordsLinked to original sources

arXiv2024

Study on the mixing of $Ξ_c$ and $Ξ'_c$ by the transition $Ξ_{b}\toΞ^{(')}_c$

Recently, the LHCb collaboration has observed the decays $Ξ^0_{b}\toΞ^+_{c}D^-_s$ and $Ξ^-_{b}\toΞ^0_{c}D^-_s$. They measured the relative branching fractions times the ratio of beauty-baryon production cross-sections $\mathcal{R}(\frac{Ξ^0_b}{Λ_b})\equiv\frac{σ(Ξ_b^0)}{σ(Λ^0_b)}\times\frac{B(Ξ^0_{b}\toΞ^+_{c}D^-_s)}{B(Λ^0_{b}\toΛ^+_{c}D^-_s)}$ and $\mathcal{R}(\frac{Ξ^-_b}{Λ_b})\equiv\frac{σ(Ξ^-_b)}{σ(Λ^0_b)}\times\frac{B(Ξ^-_{b}\toΞ^0_{c}D^-_s)}{B(Λ^0_{b}\toΛ^+_{c}D^-_s)}$. Once the ratio $\frac{σ(Ξ_b^0)}{σ(Λ^0_b)}$ or $\frac{σ(Ξ_b^-)}{σ(Λ^0_b)}$ is known, one can determine the relative branching fractions which can be used to exam the mixing of $Ξ_c$ and $Ξ'_c$. In previous literature, $Ξ_c$ and $Ξ'_c$ were assumed to belong to SU(3)$_F$ antitriple and sextet, respectively. However, recent experimental measurements such as the ratio $Γ(Ξ_{cc}\toΞ_cπ^+)/Γ(Ξ_{cc}\toΞ'_cπ^+)$ indicate the spin-flavor structures of $Ξ_{c}$ and $Ξ'_{c}$ are a mixture of $Ξ^{\bar 3}_{c}$ and $Ξ^{6}_{c}$. The exact value of mixing angle $θ$ is still under debate. In theoretical models, the mixing angle was fitted to be about $16.27^\circ\pm2.30^\circ$ or $85.54^\circ\pm2.30^\circ$ based on decay channels $Ξ_{cc} \toΞ^{(')}_{cc} $. While in lattice calculation, a small angle ($1.2^\circ\pm0.1^\circ$) is preferred. To address such discrepancy and test the mixing of $Ξ_c$ and $Ξ'_c$, here we propose the analysis of semileptonic and non-leptonic decays of $Ξ_{b}\toΞ_{c}$ and $Ξ_{b}\toΞ^{'}_{c}$. We calculate the decay rate of $Ξ_{b}\toΞ_{c}$ and $Ξ_{b}\toΞ^{'}_{c}$ based on light-front quark model and study the effect of the mixing angle on the ratios of weak decays $Ξ_{b}\toΞ_{c}$ and $Ξ_{b}\toΞ^{'}_{c}$.....

hep-ph↗

arXiv2023

Study on the weak decay between two heavy baryons $ \mathcal{B}_i(\frac{1}{2}^+)\to \mathcal{B}_f(\frac{3}{2}^+)$ in the light-front quark model

In this work, we study the weak decay between two heavy baryons $ \mathcal{B}_i(\frac{1}{2}^+)\to \mathcal{B}_f(\frac{3}{2}^+)$ in the light-front quark model where three-quark picture is employed for baryon. We derive general form of transition amplitude of $ \mathcal{B}_i(\frac{1}{2}^+)\to \mathcal{B}_f(\frac{3}{2}^+)$, and analyze two specific cases of transitions: the weak decays of single heavy baryon $Σ_{b} \to Σ_{c}^*$ and the decays of double-charmed baryon $Ξ_{cc}\to Σ_{c}^*(Ξ_{c}^*)$. We compute the hadronic form factors for the transitions and apply them to study the decay widths of the semi-leptonic $\mathcal B_i(\frac{1}{2}^+)\to\mathcal B_f(\frac{3}{2}^+) l\barν_l$ and non-leptonic $\mathcal B_i(\frac{1}{2}^+)\to\mathcal B_f(\frac{3}{2}^+)M$. Previously we studied the transition $Σ_{b} \to Σ_{c}^*$ with the quark-diquark picture of baryon in the light-front quark model. Here we revisit this transition with three-quark picture of baryon. At the quark level, the transition $Σ_{b} \to Σ_{c}^*$ is induced by the $b\rightarrow c$ transition.The subsystem of the two unchanged light quarks which possesses definite and same spin in initial and final state can be viewed as a spectator, so the spectator approximation can be applied directly. For the weak decay of doubly charmed baryon $Ξ_{cc}$, a $c$ quark decays to a light quark $q_1$, so both the initial state $cc$ and final state $q_1q_2$ ($q_1$ and the original $q_2$ in initial state may be the same flavor quarks) which possess definite spin are no longer spectators. A rearrangement of quarks for initial and final states is adopted to isolate the unchanged subsystem $cq_2$ which can be viewed as the spectator approximately. Future measurements on these channels will constrain the nonperturbative parameter in the wavefunctions and test the model predictions.

hep-ph↗

arXiv2022

Spatial and temporal correlations in neural networks with structured connectivity

Correlated fluctuations in the activity of neural populations reflect the network's dynamics and connectivity. The temporal and spatial dimensions of neural correlations are interdependent. However, prior theoretical work mainly analyzed correlations in either spatial or temporal domains, oblivious to their interplay. We show that the network dynamics and connectivity jointly define the spatiotemporal profile of neural correlations. We derive analytical expressions for pairwise correlations in networks of binary units with spatially arranged connectivity in one and two dimensions. We find that spatial interactions among units generate multiple timescales in auto- and cross-correlations. Each timescale is associated with fluctuations at a particular spatial frequency, making a hierarchical contribution to the correlations. External inputs can modulate the correlation timescales when spatial interactions are nonlinear, and the modulation effect depends on the operating regime of network dynamics. These theoretical results open new ways to relate connectivity and dynamics in cortical networks via measurements of spatiotemporal neural correlations.

q-bio.NC↗

arXiv2022

The study of possible molecular states of $D_s^{()}D_s^{()}$ and $B_s^{()}B_s^{()}$

Recently the LHCb collaboration reported a new exotic state $T^+_{cc}$ which is conjectured to be a molecular state of $D^0D^{*+}$ (or $D^{*0}D^{+}$) theoretically. Belle Collaboration also searched for tetraquark state $X_{ccss}$ in $D_sD_s (D^*_sD^*_s )$ final states but no significant signals were observed, which did not rule out the possibility of $X_{ccss}$ to be a molecular state of $D_sD_s (D^*_sD^*_s )$. Inspired by these experimental results on double charmed exotic state, in this paper we study whether the molecular bound states of $D_s^{(*)}D_s^{(*)}$ and $B_s^{(*)}B_s^{(*)}$ can exist with the Bethe-Salpeter (B-S) equation approach. We employ heavy meson chiral perturbation theory with one boson-exchange approximation to calculate the interaction kernels in the B-S equations. Our numerical results suggest that two $B_s^{*}$ mesons perhaps form a $0^+$ molecular state. Future experimental search for $X_{ccss}$ states in other decay channels may shed light on the structure of double charmed exotic state.

hep-ph↗

arXiv2021

Tetraquark state $X(6900)$ and the interaction between diquark and antidiquark

Recently LHCb declared a new structure $X(6900)$ in the final state di-$J/ψ$ which is popularly regarded as a $cc$-$\bar c\bar c$ tetraquark state. %popularly. Within the Bethe-Salpeter (B-S) frame we study the possible $cc$-$\bar c\bar c$ bound states and the interaction between diquark ($cc$) and antidiquark ($\bar c\bar c$). In this work $cc$ ($\bar c\bar c$) is treated as a color anti-triplet (triplet) axial-vector so the quantum numbers of $cc$-$\bar c\bar c$ bound state are $0^+$, $1^+$ and $2^+$. Learning from the interaction in meson case and using the effective coupling we suggest the interaction kernel for diquark and antidiquark system. Then we deduce the B-S equations for different quantum numbers. Solving these equations numerically we find the spectra of some excited states can be close to the mass of $X(6900)$ when we assign appropriate values for parameter $κ$ introduced in the interaction (kernel).We also briefly calculate the spectra of $bb$-$\bar b\bar b$ bound states. Future measurement of $bb$-$\bar b\bar b$ state will help us to determine the exact form of effective interaction.

hep-ph↗

arXiv2018

Lifetimes of Doubly Charmed Baryons

The lifetimes of doubly charmed hadrons are analyzed within the framework of the heavy quark expansion (HQE). Lifetime differences arise from spectator effects such as $W$-exchange and Pauli interference. The $Ξ_{cc}^{++}$ baryon is longest-lived in the doubly charmed baryon system owing to the destructive Pauli interference absent in the $Ξ_{cc}^+$ and $Ω_{cc}^+$. In the presence of dimension-7 contributions, its lifetime is reduced from $\sim5.2\times 10^{-13}s$ to $\sim3.0\times 10^{-13}s$. The $Ξ_{cc}^{+}$ baryon has the shortest lifetime of order $0.45\times 10^{-13}s$ due to a large contribution from the $W$-exchange box diagram. It is difficult to make a precise quantitative statement on the lifetime of $Ω_{cc}^+$. Contrary to $Ξ_{cc}$ baryons, $τ(Ω_{cc}^+)$ becomes longer in the presence of dimension-7 effects and the Pauli interference $Γ^{\rm int}_+$ even becomes negative. This implies that the subleading corrections are too large to justify the validity of the HQE. Demanding the rate $Γ^{\rm int}_+$ to be positive for a sensible HQE, we conjecture that the $Ω_c^0$ lifetime lies in the range of $(0.75\sim 1.80)\times 10^{-13}s$. The lifetime hierarchy pattern is $τ(Ξ_{cc}^{++})>τ(Ω_{cc}^+)>τ(Ξ_{cc}^+)$ and the lifetime ratio $τ(Ξ_{cc}^{++})/τ(Ξ_{cc}^+)$ is predicted to be of order 6.7.

hep-ph↗

arXiv2016

Revisiting radiative decays of $1^{+-}$ heavy quarkonia in the covariant light-front approach

We revisit the calculation of the width for the radiative decay of a $1^{+-}$ heavy $Q \bar Q$ meson via the channel $1^{+-} \to 0^{-+} +γ$ in the covariant light-front quark model. We carry out the reduction of the light-front amplitude in the non-relativistic limit, explicitly computing the leading and next-to-leading order relativistic corrections. This shows the consistency of the light-front approach with the non-relativistic formula for this electric dipole transition. Furthermore, the theoretical uncertainty in the predicted width is studied as a function of the inputs for the heavy quark mass and wavefunction structure parameter. We analyze the specific decays $h_{c}(1P) \to η_{c}(1S) + γ$ and $h_{b}(1P) \to η_{b}(1S) + γ$. We compare our results with experimental data and with other theoretical predictions from calculations based on non-relativistic models and their extensions to include relativistic effects, finding reasonable agreement.

hep-ph↗

arXiv2016

Radiative decays of $1^{++}$ heavy mesons in the covariant light-front approach

We calculate the predicted width for the radiative decay of a $1^{++}$ heavy meson via the channel $1^{++} \to 1^{--} +γ$ in the covariant light-front quark model. Specifically, we compute the decay widths for $χ_{c1}(1P) \to J/ψ+ γ$ and $χ_{b1}(nP) \to Υ(n'S) + γ$. The results are compared with experimental data and with predictions from calculations based on nonrelativistic models and their extensions to include relativistic effects.

hep-ph↗

arXiv2016

Dynamical Symmetry Breaking in Chiral Gauge Theories with Direct-Product Gauge Groups

We analyze patterns of dynamical symmetry breaking in strongly coupled chiral gauge theories with direct-product gauge groups $G$. If the gauge coupling for a factor group $G_i \subset G$ becomes sufficiently strong, it can produce bilinear fermion condensates that break the $G_i$ symmetry itself and/or break other gauge symmetries $G_j \subset G$. Our comparative study of a number of strongly coupled direct-product chiral gauge theories elucidates how the patterns of symmetry breaking depend on the structure of $G$ and on the relative sizes of the gauge couplings corresponding to factor groups in the direct product.

hep-th↗

arXiv2015

$A_k \bar F$ Chiral Gauge Theories

We study asymptotically free chiral gauge theories with an SU($N$) gauge group and chiral fermions transforming according to the antisymmetric rank-$k$ tensor representation, $A_k \equiv [k]_N$, and the requisite number, $n_{\bar F}$, of copies of fermions in the conjugate fundamental representation, $\bar F \equiv \overline{[1]}_N$, to render the theories anomaly-free. We denote these as $A_k \, \bar F$ theories. We take $N \ge 2k+1$ so that $n_{\bar F} \ge 1$. The $A_2 \, \bar F$ theories form an infinite family with $N \ge 5$, but we show that the $A_3 \, \bar F$ and $A_4 \,\bar F$ theories are only asymptotically free for $N$ in the respective ranges $7 \le N \le 17$ and $9 \le N \le 11$, and that there are no asymptotically free $A_k \, \bar F$ theories with $k \ge 5$. We investigate the types of ultraviolet to infrared evolution for these $A_k \, \bar F$ theories and find that, depending on $k$ and $N$, they may lead to a non-Abelian Coulomb phase, or may involve confinement with massless gauge-singlet composite fermions, bilinear fermion condensation with dynamical gauge and global symmetry breaking, or formation of multifermion condensates that preserve the gauge symmetry. We also show that there are no asymptotically free, anomaly-free SU($N$) $S_k \, \bar F$ chiral gauge theories with $k \ge 3$, where $S_k$ denotes the rank-$k$ symmetric representation.

hep-th↗

arXiv2015

Renormalization-Group Evolution and Nonperturbative Behavior of Chiral Gauge Theories with Fermions in Higher-Dimensional Representations

We study the ultraviolet to infrared evolution and nonperturbative behavior of a simple set of asymptotically free chiral gauge theories with an SU($N$) gauge group and an anomaly-free set of $n_{S_k}$ copies of chiral fermions transforming as the symmetric rank-$k$ tensor representation, $S_k$, and $n_{\bar A_\ell}$ copies of fermions transforming according to the conjugate antisymmetric rank-$\ell$ tensor representation, $\bar A_\ell$, of this group with $k, \ \ell \ge 2$. As part of our study, we prove a general theorem guaranteeing that a low-energy effective theory resulting from the dynamical breaking of an anomaly-free chiral gauge theory is also anomaly-free. We analyze the theories with $k=\ell=2$ in detail and show that there are only a finite number of these. Depending on the specific theory, the ultraviolet to infrared evolution may lead to a non-Abelian Coulomb phase, or may involve confinement with massless composite fermions, or fermion condensation with dynamical gauge and global symmetry breaking. We show that $S_k \bar A_k$ chiral gauge theories with $k \ge 3$ are not asymptotically free. We also analyze theories with fermions in $S_k$ and $\bar A_\ell$ representations of SU($N$) with $k \ne \ell$ and $k, \ \ell \ge 2$.

hep-th↗

arXiv2014

Renormalization-Group Evolution of Chiral Gauge Theories

We calculate the ultraviolet to infrared evolution and analyze possible types of infrared behavior for several asymptotically free chiral gauge theories with gauge group SU($N$) and massless chiral fermions transforming according to a symmetric rank-2 tensor representation $S$ and $N+4$ copies (flavors) of a conjugate fundamental representation $\bar F$, together with a vectorlike subsector with chiral fermions in higher-dimensional representation(s). We construct and study three such chiral gauge theories. These have respective vectorlike subsectors comprised of (a) $p$ copies of fermions in the adjoint representation, (b) $N = 2k$ even and $p$ copies of fermions in the antisymmetric rank-$k$ tensor representation, and (c) $p$ copies of $\{S + \bar S\}$ fermions. Results are presented for beta functions, their infrared zeros, and predictions from the most-attractive-channel approach for the formation of bilinear fermion condensates. Importantly, we show that for these theories, the expected ultraviolet to infrared evolution obeys a conjectured inequality concerning the field degrees of freedom for all values of the parameters $N$ and $p$ characterizing each theory.

hep-th↗

arXiv2013

The radiative decays of $0^{++}$ and $1^{+-}$ heavy mesons

The radiative decay is believed to be an ideal lab to study hadronic structure of newly observed resonances because the reactions are governed by only the electromagnetic interaction (tree level). However, to obtain correct theoretical values, one has to properly deal with the non-perturbative QCD effects in the wavefunction and hadronization. In this work we derive the formulas for the radiative decays of $0^{++}$ and $1^{-+}$ heavy mesons in the light front quark model (LFQM). Because $\mathcal{B}(χ_{c0}\rightarrow J/ψγ)$ is well measured, the theoretical evaluation of the transition rate can be used to test our approach. Within this theoretical framework, the width of $χ_{b0}\rightarrow Υ(1S)γ$ is evaluated. The formulas can be applied to identify the inner structures of new resonances, for example the isospin of $h_{c(b)}$ and the structure of $D_s(2317)$, via processes $h_c\rightarrow η_cγ$, $h_b\rightarrow η_bγ$ and $D_s(2317)\rightarrow D_s^*+γ$.

hep-ph↗

arXiv2012

Is $Z_b(10610)$ a Molecular State?

Whether molecular states indeed exist in nature has been disputed for a long time. Several new resonances have been observed in the recent experiments and they seem to be of exotic structures and some of them have been proposed to be molecular states. The very recent observation of $Z_b(10610)[(10608.4\pm 2.0)$ MeV] and $Z_b(10650)[(10653.2\pm 1.5)$ MeV] encourages the interpretation of multi-quark states. In the Beter-Salpeter (BS) approach, we study the possibility if two heavy mesons can form a molecular state by exchanging light mesons. Our results indicate that two heavy mesons can form an isospin singlet (I=0) bound state but cannot form an isospin triplet (I=1) when the contribution of $σ-$ exchange is reasonably small, i.e. as the coupling of $σ$ with mesons $g_σ$ takes the value given in previous literatures. Thus we conclude that the newly observed $Z_b(10610)$ should not be a molecular state, but a tetraquark state instead, at most, the fraction of the molecular state in the physical resonance $Z_b(10610)$ is tiny.

hep-ph↗