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Di-Higgs production as a probe of flavor changing neutral Yukawa couplings
Shi-Ping He
Published:   , doi: 10.1088/1674-1137/abfb50
Abstract:
Top partners are well motivated in many new physics models. Usually, vector like quarks \begin{document}$T_{L,R}$\end{document} are introduced to avoid the quantum anomaly. It is crucial to probe their interactions with the standard model particles. However, flavor changing neutral couplings are always difficult to detect directly in the current and future experiments. In this paper, we will show how to constrain the flavor changing neutral Yukawa coupling \begin{document}$Tth$\end{document} through the di-Higgs production indirectly. We consider the simplified model including a pair of gauge singlet \begin{document}$T_{L,R}$\end{document}. Under the perturbative unitarity and experimental constraints, we choose \begin{document}$m_T=400~{\rm{GeV}},s_L=0.2$\end{document} and \begin{document}$m_T=800~{\rm{GeV}},s_L=0.1$\end{document} as benchmark points. After the analysis of amplitude and evaluation of the numerical cross sections, we find that the present constraints from di-Higgs production have already surpassed the unitarity bound because of the \begin{document}$(y_{L,R}^{tT})^4$\end{document} behavior. For the case of \begin{document}$m_T=400~{\rm{GeV}}$\end{document} and \begin{document}$s_L=0.2$\end{document}, \begin{document}${\rm{Re}}y_{L,R}^{tT}$\end{document} and \begin{document}${\rm{Im}}y_{L,R}^{tT}$\end{document} can be bounded optimally in the range \begin{document}$(-0.4, 0.4)$\end{document} at HL-LHC with \begin{document}$2\sigma$\end{document} CL. For the case of \begin{document}$m_T=800~{\rm{GeV}}$\end{document} and \begin{document}$s_L=0.1$\end{document}, \begin{document}${\rm{Re}}y_{L,R}^{tT}$\end{document} and \begin{document}${\rm{Im}}y_{L,R}^{tT}$\end{document} can be bounded optimally in the range \begin{document}$(-0.5, 0.5)$\end{document} at HL-LHC with \begin{document}$2\sigma$\end{document} CL. The anomalous triple Higgs coupling \begin{document}$\delta_{hhh}$\end{document} can also affect the constraints on \begin{document}$y_{L,R}^{tT}$\end{document}. Finally, we find that the top quark electric dipole moment can give stronger bounds of \begin{document}$y_{L,R}^{tT}$\end{document} in the off-axis regions for some scenarios.
Chiral symmetry restoration and deconfinement in the contact interaction model of quarks with a parallel electric and magnetic fields
Aftab Ahmad
Published:  
Abstract:
We study the impact of steady, homogeneous, and external parallel electric and magnetic field strengths (\begin{document}$ eE\parallel eB $\end{document}) on the chiral symmetry breaking-restoration and confinement-deconfinement phase transition. We also sketch the phase diagram of quantum chromodynamics (QCD) at finite temperature T and in the presence of background fields. Our unified formalism for this study is based on the Schwinger-Dyson equations, symmetry preserving vector-vector contact interaction model of quarks, and the proper time regularization scheme. At \begin{document}$ T = 0 $\end{document}, in the purely magnetic case (i.e., \begin{document}$ eE\rightarrow 0 $\end{document}), we observe the well-known magnetic catalysis effect. On the other hand, in the pure electric field background (\begin{document}$ eB\rightarrow 0 $\end{document}), the electric field tends to restore the chiral symmetry and deconfinement above the pseudo-critical electric field \begin{document}$ eE^{\chi, C}_c $\end{document}. In the presence of both \begin{document}$ eE $\end{document} and \begin{document}$ eB $\end{document}, we found the magnetic catalysis effect in the particular region where \begin{document}$ eB $\end{document} dominated over \begin{document}$ eE $\end{document}, whereas we observe the chiral inhibition (or electric chiral rotation) effect when \begin{document}$ eE $\end{document} stands over \begin{document}$ eB $\end{document}. At finite T, in the pure electric field case, the phenomenon of inverse electric catalysis appears to exist in our model. On the other hand for pure magnetic field background, we notice the magnetic catalysis effect in the mean-field approximation and inverse magnetic catalysis with \begin{document}$ eB $\end{document}-dependent coupling. The combined effect of both \begin{document}$ eE $\end{document} and \begin{document}$ eB $\end{document} on the pseudo-critical \begin{document}$ T^{\chi, C}_c $\end{document} yields the inverse electromagnetic catalysis with and without \begin{document}$ eB- $\end{document}dependent effective coupling of the model. Our findings are satisfactory in agreement with already predicted results by lattice simulations and other reliable effective models of QCD.
Theoretical uncertainties on the extraction of in-medium NN cross sections by different Pauli blocking algorithms
Xiang Chen, Yingxun Zhang, Zhuxia Li
Published:   , doi: 10.1088/1674-1137/abfb51
Abstract:
Three typical algorithms of Pauli blocking in the quantum molecular dynamics type models are investigated in the nuclear matter, the nucleus and the heavy ion collisions. The calculations in nuclear matter show that the blocking ratios obtained with the three algorithms are underestimated 13-25% compared to the analytical values of blocking ratios. For the finite nucleus, the spurious collisions occur around the surface of the nucleus owing to the defects of Pauli blocking algorithms. In the simulations of heavy ion collisions, the uncertainty of stopping power from different Pauli blocking algorithms is less than 5%. Furthermore, the in-medium effects of nucleon-nucleon (NN) cross sections on the nuclear stopping power are discussed. Our results show that the transport model calculations with free NN cross sections result in the stopping power decreasing with the beam energy at the beam energy less than 300 MeV/u. To increase or decrease the values of stopping power, the transport model calculations need an enhanced or suppressed model dependent in-medium NN cross sections which are expected to be smaller than the true in-medium NN cross sections.
Explore the halo phenomena of medium-mass nuclei near Z=40 with point-coupled parameters in complex momentum representation
Yao-Wu Chu, Tai-Hua Heng
Published:   , doi: 10.1088/1674-1137/abfa84
Abstract:
For exploring the properties of neutron-rich nuclei with protons near 40, the density-dependent point coupling (DD-PC1) effective interaction parameter is adopted in the relativistic mean-field theory with the complex momentum representation (RMF-CMR). The calculated two-neutron separation energy (S2n), root-mean-square (rms) radii support the halo structure appear in Mo and Ru isotopic chain. Besides, the neutron skin structures appear for Kr, Sr isotopes. The conclusions are also supported by the single-particle energy levels and their occupancy probability, density distribution. Especially, the energy levels which reduce to bound state or close to 0 MeV with a small orbital angular momentum are suggested to give the main contribution to increase the neutron radius. Moreover, the single-particle energy levels clearly reflect the shell structure. In addition, the neutron drip line nuclei for Kr, Sr, Mo, Ru elements are proposed through the changes of S2n.
Improved macroscopic microscopic mass formula
Tian Liang Zhao, Xiao Jun Bao, Hong Fei Zhang
Published:   , doi: 10.1088/1674-1137/abfaf2
Abstract:
A nuclear mass formula based on the macroscopic microscopic approach is proposed, the number of model parameters is reduced compared with other macroscopic microscopic models. The root mean square (RMS) deviation with respect to 2314 training set (measured nuclear masses) is reduced to 0.447 MeV, and the calculated value of each nucleus is no more than 0.8% different from the experimental value. The single and two nucleon separation energy, and the shell gaps are calculated to test the model. The shell corrections and double magic number of superheavy nuclei are also analyzed.
Analysis of the Zcs(3985) as the axialvector tetraquark state
Zhi-Gang Wang
Published:  
Abstract:
In this paper, we choose the scalar and axialvector diquark operators in the color antitriplet as the fundamental building blocks to construct the four-quark currents and investigate the diquark-antidiquark type axialvector tetraquark states \begin{document}$ c\bar{c}u\bar{s} $\end{document} in the framework of the QCD sum rules. The predicted tetraquark mass \begin{document}$ M_Z = 3.99\pm0.09\;\rm{GeV} $\end{document} is in excellent agreement with the experimental value \begin{document}$ 3985.2^{+2.1}_{-2.0}\pm1.7\;\rm{MeV} $\end{document} from the BESIII collaboration, which supports identifying the \begin{document}$ Z_{cs}(3985) $\end{document} as the cousin of the \begin{document}$ Z_c(3900) $\end{document} with the quantum numbers \begin{document}$ J^{PC} = 1^{+-} $\end{document}. We take into account the light flavor \begin{document}$ SU(3) $\end{document} mass-breaking effect to estimate the mass spectrum of the diquark-antidiquark type hidden-charm tetraquark states having the strangeness according to the previous works.
Dark sector production and baryogenesis from not quite black holes
Ufuk Aydemir, Jing Ren
Published:  
Abstract:
Primordial black holes have been considered as an attractive dark matter candidate, whereas some of the predictions heavily rely on the near-horizon physics that remains to be tested experimentally. As a concrete alternative, thermal 2-2-holes closely resemble black holes without event horizons. Being a probable endpoint of gravitational collapse, they not only provide a resolution to the information loss problem, but also naturally give rise to stable remnants. Previously, we have considered primordial 2-2-hole remnants as dark matter. Due to the strong constraints from a novel phenomenon associated with remnant mergers, only small remnants with close to the Planck mass can constitute all of dark matter. In this paper, we examine the scenario that the majority of dark matter consists of particles produced by the evaporation of primordial 2-2-holes, whereas the remnant contribution is secondary. The products with light enough mass may contribute to the number of relativistic degrees of freedom in the early universe, which we also calculate. Moreover, 2-2-hole evaporation can produce particles that are responsible for the baryon asymmetry. We find that baryogenesis through direct B-violating decays or through leptogenesis can both be realized. Overall, the viable parameter space for the Planck remnant case is similar to primordial black holes with Planck remnants. Heavier remnants, on the other hand, lead to different predictions, and the viable parameter space remains large even when the remnant abundance is small.
The coexistence of isospin I = 0 and I = 1 pairings in asymmetric nuclear matter
Yi-Jun Yan, Xin-Le Shang, Jian-Min Dong, Wei Zuo
Published:  
Abstract:
The coexistence of neutron-neutron (n-n), proton-proton (p-p), and neutron-proton (n-p) pairings is investigated by adopting an effective density-dependent contact pairing potential. These three types of pairings can coexist only if the n-p pairing is stronger than the n-n and p-p ones for isospin asymmetric nuclear matter. In addition, the existence of n-n and p-p pairs might enhance n-p pairings in asymmetric nuclear matter when the n-p pairing strength is much larger than the n-n and p-p ones. Contrarily, the n-p pairing is reduced by the n-n and p-p pairs when n-p pairing interaction get close to n-n and p-p ones.
Neutrons in the classically forbidden region in neutron-rich nucleus 68Ca
Shiwen Zhu, Ying Zhang
Published:  
Abstract:
The neutrons tunneling to the classically forbidden (CF) region in the neutron-rich nucleus \begin{document}$ ^{68} {\rm{Ca}}$\end{document} are investigated in the Skyrme Hartree-Fock (HF) and Hartree-Fock-Bogoliubov (HFB) models. The definition of the CF region is examined in the HF model by using different single-particle potentials for the bound states. In the HFB model, the weakly bound and continuum states could also contribute to the neutrons in the CF region due to the pairing correlation. Their asymptotic wave functions are carefully calculated by the Green’s function method.
Crust-core transition and dynamical instabilities in neutron stars for model with point-coupling interactions
Yan-jun Chen, Zi-peng Cheng, Bin-guang He
Published:   , doi: 10.1088/1674-1137/abf99b
Abstract:
We explore the effects of the density dependence of symmetry energy on the crust-core phase transition and dynamical instabilities in the cold and warm neutron stars in the RMF theory with point-coupling interactions using the Vlasov approach. The role of neutrino trapping has also been considered. The crust-core transition density and pressure, distillation effect, the cluster size and growth rates have been discussed. The present work shows that the slope of symmetry energy at saturation, temperature, and neutrino trapping have non-negligible effects.
Exact relations for two-photon-exchange effect in elastic ep scattering by dispersion relation and hadronic model
Hui-Yun Cao, Hai-Qing Zhou
Published:   , doi: 10.1088/1674-1137/abf913
Abstract:
The two-photon-exchange (TPE) effect plays a key role to extract the form factors (FFs) of the proton. In this work, we discuss some exact properties on the TPE effect in the elastic \begin{document}$ep$\end{document} scattering. By taking four low energy interactions as examples, we analyze the kinematical singularities, the asymptotic behaviors and the branch cuts of the TPE amplitudes. The analytical expressions clearly indicate some exact relations between the dispersion relation (DR) method and the hadronic model (HM) method. It suggests that the two methods should be modified to general forms and the new forms give the same results. After the modification the new DRs include a non-trivial term with two singularities. Furthermore, the new DRs automatically include the contributions due to the seagull interaction, the meson-exchange effect, the contact interactions and the off-shell effect. To analyze the elastic \begin{document}$e^{\pm}p$\end{document} scattering data sets, the new forms should be used.
QCD chiral phase transition and critical exponents within the nonextensive Polyakov-Nambu-Jona-Lasinio model
Ya-Peng Zhao, Shu-Yu Zuo, Cheng-Ming Li
Published:   , doi: 10.1088/1674-1137/abf8a2
Abstract:
We present a nonextensive version of the Polyakov-Nambu-Jona-Lasinio model which is based on the nonextentive statistical mechanics. This new statistics is characterized by a dimensionless nonextensivity parameter q that accounts for all possible effects violating the assumptions of the Boltzmann-Gibbs (BG) statistics (when \begin{document}$q\rightarrow1$\end{document}, it returns to the BG case). Based on the nonextensive Polyakov-Nambu-Jona-Lasinio model, we discussed the influence of the nonextensive effects on the curvature of the phase diagram at \begin{document}$\mu=0$\end{document}, and especially on the location of the critical end point (CEP). A new and interesting phenomenon we found is that with the increase of q, the CEP position initially shifts toward the direction of larger chemical potential and lower temperature. But then, when q is larger than a critical value \begin{document}$q_{c}$\end{document}, the CEP position moves in the opposite direction. In other words, as q increases, the CEP position moves in the direction of smaller chemical potential and higher temperature. This U-turn phenomenon may be important for the search of CEP in relativistic heavy-ion collisions, in which the validity of BG statistics is questioned due to strong fluctuations and long-range correlations, and the nonextensive effects begin to manifest itself. In addition, we calculated the influence of the nonextensive effects on the critical exponents and found that they remain almost constant with q.
The dependence of overlap topological charge density on Wilson mass parameter
Zhen Cheng, Jian-bo Zhang
Published:   , doi: 10.1088/1674-1137/abf827
Abstract:
In this paper, we analyze the dependence of the topological charge density from the overlap operator on the Wilson mass parameter in the overlap kernel by the symmetric multi-probing source (SMP) method. We observe that the non-trivial topological objects are removed as the Wilson mass is increased. A comparison of topological charge density calculated by the SMP method using fermionic definition with that of gluonic definition by the Wilson flow method is shown. A matching procedure for these two methods is used. We find that there is a best match for topological charge density between gluonic definition with varied Wilson flow time and fermionic definition with different Wilson mass. By using the matching procedure, the proper flow time of Wilson flow in the calculation of topological charge density can be estimated. As the lattice spacing a decreases, the proper flow time also decreases, as expected.
Effective field theory approach to lepton number violating τ decays
Yi Liao, Xiao-Dong Ma, Hao-Lin Wang
Published:   , doi: 10.1088/1674-1137/abf72e
Abstract:
We continue our endeavor to investigate lepton number violating (LNV) processes at low energy in the framework of effective field theory (EFT). In this work we study the LNV tau decays \begin{document}$\tau^+\rightarrow \ell^-P_i^{+}P_j^{+}$\end{document}, where \begin{document}$\ell=e,~\mu$\end{document} and \begin{document}$P^+_{i,j}$\end{document} are the lowest-lying charged pseudoscalars \begin{document}$\pi^+,~K^+$\end{document}. We analyze the dominant contributions in a series of EFTs from high to low energy scales, namely, the standard model effective field theory (SMEFT), the low-energy effective field theory (LEFT), and the chiral perturbation theory (\begin{document}$\chi{\rm{PT}}$\end{document}). The decay branching ratios are expressed in terms of the Wilson coefficients of dimension-five and -seven operators in SMEFT and hadronic low energy constants. These Wilson coefficients involve the first and second generations of quarks and all generations of leptons and thus cannot be explored in low energy processes such as nuclear neutrinoless double decay or LNV kaon decays. Unfortunately, the current experimental upper limits on the branching ratios are too weak to set useful constraints on those coefficients. Or, if we assume the new physics scale is larger than 1~TeV, the branching ratios are well below the current experimental bounds. We also estimate hadronic uncertainties incurred in applying \begin{document}$\chi{\rm{PT}}$\end{document} to τ decays by computing one-loop chiral logarithms and attempt to improve convergence of chiral perturbation by employing dispersion relations in the short-distance part of the decay amplitudes.
Black holes in asymptotic safety with higher derivatives: accretion and stability analysis
Fabián H. Zuluaga, Luis A. Sánchez
Published:   , doi: 10.1088/1674-1137/abf72d
Abstract:
We review the issue of steady spherically symmetric accretion onto a renormalization group improved Schwarzschild space-time which is solution to an asymptotically safe theory (AS) containing high-derivative terms. We use a Hamiltonian dynamical system approach for the analysis of the accretion of four types of isothermal test fluids: ultra-stiff fluid, ultra-relativistic fluid, radiation fluid, and sub-relativistic fluid. An important outcome of our study is that, contrary to what claimed in a recent work, there exist physical solutions for the accretion of an ultra-relativistic fluid in AS which include subsonic, supersonic and transonic regimes. We also study quantum corrections to the known stability of the accretion in general relativity (GR). To this end we use a perturbative procedure based on the continuity equation with the mass accretion rate being the perturbed quantity. Two classes of perturbations are studied: standing waves and travelling waves. We find that quantum gravity effects either enhance or diminish the stability of the accretion depending on the type of test fluid and depending on the radial distance to the central object.
Same-Sign Dilepton Signature in the Inert Doublet Model
Fa-Xin Yang, Zhi-Long Han, Yi Jin
Published:   , doi: 10.1088/1674-1137/abf828
Abstract:
In this paper, we perform a detailed analysis on the same-sign dilepton signature in the inert doublet model. Focusing on the low dark matter mass region, we randomly scan the corresponding parameter space. Viable samples allowed by various constraints are obtained, among which twenty benchmark points are selected for further collider signature study. At hadron colliders, the same-sign dilepton signature is produced via \begin{document}$pp\to W^{\pm *}W^{\pm *}jj \to H^\pm H^\pm jj$\end{document} with the leptonic decay mode \begin{document}$ H^\pm \to HW^\pm (\to l^\pm \nu)$\end{document}, where H is the dark matter candidate. We investigate the testability of this signal at the high-luminosity LHC (HL-LHC) and the proposed 27 TeV high-energy LHC (HE-LHC). According to our simulation, the HL-LHC with \begin{document}${\cal{L}}=3\;{\rm{ab}}^{-1}$\end{document} can hardly probe this signal. Meanwhile, for the HE-LHC with \begin{document}${\cal{L}}=15\;{\rm{ab}}^{-1}$\end{document}, it is promising to obtain a \begin{document}$5\sigma$\end{document} significance when \begin{document}$250\;{\rm{GeV}}\lesssim m_{H^\pm}-m_H\lesssim 300$\end{document} GeV with dark matter mass \begin{document}$m_H\sim 60$\end{document} or 71 GeV.
Detecting anomaly in vector boson scattering
Jinmian Li, Shuo Yang, Rao Zhang
Published:   , doi: 10.1088/1674-1137/abf829
Abstract:
Measuring the vector boson scattering (VBS) precisely is an important step towards understanding the electroweak symmetry breaking of the standard model (SM) and detecting new physics beyond the SM. We propose a neural network which compress the features of the VBS into three dimensional latent space. The consistency of the SM prediction and the experimental data is tested by the binned log-likelihood analysis in the latent space. We will show that the network is capable of distinguish different polarization modes of WWjj production in both dileptonic channel and semi-leptonic channel. The method is also applied to constrain the effective field theory and two Higgs Doublet Model. The results demonstrate that the method is sensitive to generic new physics contributing to the VBS.
Phase Structures and Transitions of Quintessence Surrounding RN Black Holes in a Grand Canonical Ensemble
Yuchen Huang, Hongmei Jing, Jun Tao, Feiyu Yao
Published:  
Abstract:
Considering a grand canonical ensemble, we study the phase structures and transitions of RN black holes surrounded by quintessence dark energy on two different boundary conditions, namely AdS space and a Dirichlet wall. For AdS space, under the condition of fixed temperature and potential, as the temperature increases for lower potential, the black hole undergoes a first-order phase transition, while for higher potential, no phase transition occurs. There are two different regions in the parameter space. For the Dirichlet wall, on which the temperature and potential are fixed and the state parameter of quintessence \begin{document}$ \omega=-2/3$\end{document} is analyzed in detail. Then, three different physically allowed regions in the parameter space of the black hole are well studied. As the temperature rises, a first-order phase transition and a second-order phase transition may occur. In this case, there are nine regions in the parameter space, which is obviously distinct from the case of AdS space.
Spectroscopic investigation of light strange S = −1 Λ, Σ and S = −2 Ξ baryons
Chandni Menapara, Ajay Kumar Rai
Published:   , doi: 10.1088/1674-1137/abf4f4
Abstract:
The present study is dedicated to light-strange \begin{document}$\Lambda$\end{document} with strangeness S = −1, isospin I = 0; \begin{document}$\Sigma$\end{document} with S = −1, I = 1 and \begin{document}$\Xi$\end{document} baryon with S = −2 and \begin{document}$I=\dfrac{1}{2}$\end{document} . In this article, hypercentral Constituent Quark Model with linear confining potential has been employed along with first order correction term to obtain the resonance masses for nearly upto 4 GeV. The calculated states include 1S-5S, 1P-4P, 1D-3D, 1F-2F and 1G (in few case) along with all the possible spin-parity assignments. Regge Trajectories have been explored for the linearly of the calculated masses for \begin{document}$(n,M^{2})$\end{document} and \begin{document}$(J,M^{2})$\end{document} respectively. Magnetic moments have been intensively studied for ground state spin \begin{document}$\dfrac{1}{2}$\end{document} and \begin{document}$\dfrac{3}{2}$\end{document} , in addition to the configuration mixing for first negative parity state for \begin{document}$\Xi$\end{document} . Lastly, transition magnetic moment and radiative decay width have been presented.
Factorization of radiative leptonic D-meson decay with sub-leading power corrections
Long-Sheng Lu
Published:  
Abstract:
In this work, we calculate the sub-leading power contributions to the radiative leptonic \begin{document}$ D\to\gamma \,\ell \,\nu $\end{document} decay. For the first time, we provide the analytic expressions of next-to-leading power contributions and the error estimation associated with the power expansion of \begin{document}$ {\cal O}(\Lambda_{\rm QCD}/m_c) $\end{document}. In our calculation, we adopt two different models of the D-meson distribution amplitudes \begin{document}$ \phi_{D,\rm I}^+ $\end{document} and \begin{document}$ \phi_{D,\rm II}^+ $\end{document}. Within the framework of the QCD factorization as well as the dispersion relation, we evaluate the soft contribution up to the next-to-leading logarithmic accuracy, and the higher-twist contribution from the two-particle and three-particle distribution amplitudes is also considered. Finally, we find that all the sub-leading power contributions are significant at \begin{document}$ \lambda_D(\mu_0) = 354\,\rm MeV $\end{document}, and the next-to-leading power contributions will lead to 143% in \begin{document}$ \phi_{D,\rm I}^+ $\end{document} and 120% in \begin{document}$ \phi_{D,\rm II}^+ $\end{document} corrections to leading power vector form factors with \begin{document}$ E_{\gamma} = 0.5\,\rm GeV $\end{document}. As the corrections from the higher-twist and local sub-leading power contributions will be enhanced with the growing of the inverse moment, it is difficult to extract an appropriate inverse moment of the D-meson distribution amplitude. The predicted branching fractions are \begin{document}$ (1.88_{-0.29}^{+0.36})\times10^{-5} $\end{document} for \begin{document}$ \phi_{D,\rm I}^+ $\end{document} and \begin{document}$ (2.31_{-0.54}^{+0.65})\times10^{-5} $\end{document} for \begin{document}$ \phi_{D,\rm II}^+ $\end{document}, respectively.