Chinese Physics C

Chromomagnetic and chromoelectric dipole moments of quarks in the reduced 331 model

A. I. Hernández-Juárez, G. Tavares-Velasco, A. Moyotl

Published: , doi: 10.1088/1674-1137/ac1b9a

Abstract:
The one-loop contributions to the chromomagnetic dipole moment $\hat\mu_t(q^2)$ and electric dipole moment $\hat d_t(q^2)$ of the top quark are calculated within the reduced 331 model (RM331) for non-zero $q^2$. It is argued that the results are gauge independent and thus represent valid observable quantities. In the RM331, $\hat \mu_t(q^2)$ receives new contributions from two heavy gauge bosons, namely $Z'$ and $V^\pm$, and one neutral scalar boson $h_2$, along with a new contribution from the standard model's Higgs boson via flavor changing neutral currents. The latter, which is also mediated by the $Z'$ gauge boson and the scalar boson $h_2$, can provide a non-vanishing $\hat d_t(q^2)$ if there is a $CP$-violating phase. The analytical results are presented in terms of both Feynman parameter integrals and Passarino-Veltman scalar functions, which are useful to cross-check the numerical results. Both $\hat\mu_t(q^2)$ and $\hat d_t(q^2)$ are numerically evaluated for parameter values still allowed by the constraints from experimental data. It is found that the new one-loop contributions of the RM331 to the real (imaginary) part of $\hat \mu_t(q^2)$ are of the order of $10^{-5}$ ($10^{-6}$), which means at least three orders of magnitude smaller than the standard model prediction but larger than the predictions of other models of new physics. In the RM331, the dominant contribution arises from the $V^\pm$ gauge boson for $\|q\|$ in the 30-1000 GeV interval and a mass $m_{V}$ of the order of a few hundreds of GeV. As for $\hat d_t(q^2)$, it receives its largest contribution from $h_2$ exchange and can reach values of the order of $10^{-19}$, i.e., smaller than the contributions predicted by other standard model extensions.

Cosmological implications of a B − L charged hidden scalar: leptogenesis and gravitational waves

Ligong Bian, Wei Cheng, Huai-Ke Guo, Yongchao Zhang

Published: , doi: 10.1088/1674-1137/ac1e09

Abstract:
In this study, we investigated the cosmological implications of a complex singlet scalar $ {\cal{S}}$ with non-trivial $ B-L$ charges in the conformal $ U(1)_{B-L}$ theory. It was found that, in a sizable region of parameter space, $ {\cal{S}}$ may disturb the resonant leptogenesis mechanism, which is used to generate baryon asymmetry, and affect the symmetry breaking dynamics in the strong first order phase transition. The stochastic gravitational waves (GWs) produced at the phase transition can be probed in future GW experiments. The GW searches prefer a relatively light $ {\cal{S}}$ at the TeV-scale; however, this is difficult to detect directly at future high-energy colliders.

Description of elastic scattering induced by the unstable nuclei ^{9,10,11,13,14}C

Yong-Li Xu, Yin-Lu Han, Xin-Wu Su, Xiao-Jun Sun, Hai-Ying Liang, Hai-Rui Guo, Chong-Hai Cai

Published: , doi: 10.1088/1674-1137/ac1fe1

Abstract:
The elastic-scattering angular distributions and total reaction cross sections of $^{9,10,11,13,14}{\rm{C}}$ projectiles were predicted using the obtained $^{12}{\rm{C}}$ and $^{9}{\rm{Be}}$ global optical model potentials, respectively. The predictions were analyzed in detail by comparison with the available experimental data. The results indicate that the $^{12}{\rm{C}}$ and $^{9}{\rm{Be}}$ global optical model potentials provide a satisfactory description of the elastic scattering data for the reactions induced by the $^{9,10,11,13}{\rm{C}}$. For the neutron-rich carbon isotope $^{14}{\rm{C}}$, the elastic scattering can be well described by changing the real part radius parameter of the $^{12}{\rm{C}}$ global optical model potential. Possible physical explanations for the observed differences are further discussed.

Energy conditions in the new model of loop quantum cosmology

Gaoping Long, Yunlong Liu, Xiangdong Zhang

Published: , doi: 10.1088/1674-1137/ac1e83

Abstract:
Recently, a de-Sitter epoch has been found in the new model of loop quantum cosmology, which is governed by the scalar constraint with both Euclidean and Lorentz terms. The singularity free bounce in the new LQC model and the emergent cosmology constant strongly suggest that the effective stress-energy tensor induced by quantum corrections must violate the standard energy conditions. In this study, we perform an explicit calculation to analyze the behaviors of specific representative energy conditions, i.e., average null, strong, and dominant energy conditions. We reveal that the average null energy condition is violated at all times, while the dominant energy condition is violated only at a period around the bounce point. The strong energy condition is violated not only at a period around the bounce point but also in the whole period from the bounce point to the classical phase corresponding to the de Sitter period. Our results will shed some light on the construction of a wormhole and time machine, which usually require exotic matter to violate energy conditions.

Proca equation and vector field quantization in a rotating system

Tian Xu, Yin Jiang

Published: , doi: 10.1088/1674-1137/ac1d9c

Abstract:
A strong background field drastically changes the vacuum structure and proper basis of a system in both classical and quantum mechanics, e.g., the Landau levels in a background magnetic field. This is true even for a rotating system. In such a system, the usual set of plane-wave states would no longer be suitable as a starting point of perturbation. Alternatively and straightforwardly, in a rapidly and globally rotating system, it is better to reformulate the perturbation computation in principle. In this study, we completed the first step for the spin-1 field, which includes solving the Proca equation in the presence of a background rotation and completing its canonical quantization. We show that because of the symmetry, the eigen states are actually the same as those of Maxwell equations in cylindrical coordinates. The propagator as well as the near-central approximation were obtained by assuming that the vorticity areas are very small in the relativistic QGP.

Matrix elements in the SU(1,1) ${\otimes}$ SO(6) limit of the proton-neutron symplectic model

H. G. Ganev

Published: , doi: 10.1088/1674-1137/ac1c67

Abstract:
The matrix elements along the reduction chain Sp(12,R) $ \supset $ SU(1,1) $ \otimes $ SO(6) $ \supset $ U(1) $ \otimes $ SU$ _{pn} $(3) $ \otimes $ SO(2) $ \supset $ SO(3) of the proton-neutron symplectic model (PNSM) are considered. Closed analytical expressions are obtained for the matrix elements of the basic building blocks of the PNSM and the Sp(12,R) symplectic generators, allowing the computation of matrix elements of other physical operators as well. The computational technique developed in the present study generally provides us with the required algebraic tool for performing realistic symplectic-based shell-model calculations of nuclear collective excitations. Utilizing two simple examples, we illustrate the application of the theory.

Particles accelerated in Hertzian magnetic dipole field of a pulsar

Zhe Chang, Qing-Hua Zhu

Published: , doi: 10.1088/1674-1137/ac1c65

Abstract:
Supernova remnants are supposed to be the most possible sources of cosmic rays. However, alternative sources of cosmic rays, such as an active galactic nucleus, gamma-ray bursts, and pulsars, have not be excluded. In this study, we investigate the possibility of cosmic rays being generated by pulsars. The pulsar is simply described as a rotational magnetic dipole, the so-called Hertzian magnetic dipole, an exact solution of the d'Alembert equations. In the rotational magnetic dipole field, charged particles experience an accelerated electric field with their radiation reaction. The particles, which are initially static out of the light cylinder radius, can be accelerated up to a high energy.

Reanalysis of the top-quark pair hadroproduction and a precise determination of the top-quark pole mass at the LHC

Sheng-Quan Wang, Xing-Gang Wu, Jian-Ming Shen, Stanley J. Brodsky

Published: , doi: 10.1088/1674-1137/ac1bfd

Abstract:
In this study, we calculate the $t\bar{t}$ pQCD production cross-section at the NNLO and determine the top-quark pole mass from recent measurements at the LHC at the center-of-mass energy $\sqrt{S}=13$ TeV to a high precision by applying the principle of maximum conformality (PMC). The PMC provides a systematic method that rigorously eliminates QCD renormalization scale ambiguities by summing the nonconformal $\beta$ contributions into the QCD coupling constant. The PMC predictions satisfy the requirements of renormalization group invariance, including renormalization scheme independence, and the PMC scales accurately reflect the virtuality of the underlying production subprocesses. By using the PMC, an improved prediction for the $t\bar{t}$ production cross-section is obtained without scale ambiguities, which in turn provides a precise value for the top-quark pole mass. Moreover, the prediction of PMC calculations that the magnitudes of higher-order PMC predictions are well within the error bars predicted from the known lower-order has been demonstrated for the top-quark pair production. The resulting determination of the top-quark pole mass, $m_t^{\rm{pole}}=172.5\pm1.4$ GeV, from the LHC measurement at $\sqrt{S}=13$ TeV agrees with the current world average cited by the Particle Data Group (PDG). The PMC prediction provides an important high-precision test of the consistency of pQCD and the SM at $\sqrt{S}=13$ TeV with previous LHC measurements at lower CM energies.

Weak decays of ${\boldsymbol \Xi^{(')}_{\boldsymbol c}\to \boldsymbol\Xi }$ in the light-front quark model

Hong-Wei Ke, Qing-Qing Kang, Xiao-Hai Liu, Xue-Qian Li

Published: , doi: 10.1088/1674-1137/ac1c66

Abstract:
Without contamination from the final state interactions, the calculation of the branching ratios of semileptonic decays $ \Xi^{(')}_{c}\to\Xi+e^+\nu_e $ may provide further information about the inner structure of charmed baryons. Moreover, by studying such processes, one can better determine the form factors of $ \Xi_c\to\Xi $ that can be further applied to relevant estimates. In this study, we used the light-front quark model to carry out computations where the three-body vertex functions for $ \Xi_c $ and $ \Xi $ are employed. To fit the new data of the Belle II, we re-adjusted the model parameters to obtain $ \beta_{s[sq]} = 1.07 $ GeV, which is 2.9 times larger than $ \beta_{s\bar s} = 0.366 $ GeV. This value may imply that the $ ss $ pair in $ \Xi $ constitutes a more compact subsystem. Furthermore, we investigated the non-leptonic decays of $ \Xi^{(')}_c\to \Xi $, which will be experimentally measured soon. Thus, our model will be tested in terms of consistency with the new data.

Pattern for flavor-dependent quark-antiquark interaction

Muyang Chen, Lei Chang

Published:

Abstract:
A flavor-dependent kernel is constructed based on the rainbow-ladder truncation of the Dyson-Schwinger and Bethe-Salpeter equation approach of quantum chromodynamics. The quark-antiquark interaction is composed of a flavor-dependent infrared part and a flavor-independent ultraviolet part. Our model gives a successful and unified description of the light, heavy, and heavy-light ground pseudoscalar and vector mesons. For the first time, our model shows that the infrared-enhanced quark-antiquark interaction is stronger and wider for lighter quarks.

In Press