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Isospin-sensitive observables as a probe of proton transition momentum in the HMT
Fang Zhang, Hai-Bo Peng, Jiang-Tao Zhao
Published:   , doi: 10.1088/1674-1137/43/11/114106
Abstract:
Based on the IBUU transport model, the effect of proton transition momentum on the collective flows is studied in 40Ca + 40Ca,112Sn + 112Sn and 197Au + 197Au collisions at incident beam energy of 400 MeV/A with impact parameter \begin{document}$ b = 6 fm $\end{document}. It is found that in neutron rich system, the difference of neutron and proton elliptic flow is largely affected by the proton transition momentum. At beam energy around pion production threshold, especially below pion production threshold, the \begin{document}$ \pi^{-}/\pi^{+} $\end{document} ratio is greatly sensitive to the proton transition momentum in asymmetric nuclear matter. These studies may help us to understand the nucleon momentum distribution in nuclei which is important for the equation of state of asymmetric nuclear matter such as neutron star.
Non-relativistic expansion of single-nucleon Dirac equation: Comparison between Foldy-Wouthuysen transformation andsimilarity renormalization group
Yixin Guo, Haozhao Liang
Published:   , doi: 10.1088/1674-1137/43/11/114105
Abstract:
By following the Foldy-Wouthuysen (FW) transformation of the Dirac equation, we work out the exact analytic expressions up to the 1/M4 order for the general cases in the covariant density functional theory. These results are further compared with the corresponding ones derived from another novel non-relativistic expansion method, the similarity renormalization group (SRG). Based on that, the origin of the difference between the results obtained by the FW transformation and SRG method is explored.
Simplified dark matter models with loop effects in direct detection and the constraints from indirect detection and collider search
Tong Li, Peiwen Wu
Published:   , doi: 10.1088/1674-1137/43/11/113102
Abstract:
We reexamine the simplified dark matter (DM) models with fermionic DM particle and spin-0 mediator. The DM-nucleon scattering cross sections of these models are low-momentum suppressed at tree-level, but receive sizable loop-induced spin-independent contribution. We perform one-loop calculation for scalar-type and twist-2 DM-quark operators and complete two-loop calculation for scalar-type DM-gluon operator. By analyzing the loop-level contribution from new operators, we find that future direct detection experiments can be sensitive to a fraction of parameter space. The indirect detection and collider search also provide complementary constraints on these models.
Drag force on heavy quarks from holographic QCD
Yuanhui Xiong, Xingzheng Tang, Zhongjie Luo
Published:   , doi: 10.1088/1674-1137/43/11/113103
Abstract:
We study the drag force of a relativistic heavy quark using a holographic QCD model with conformal invariance broken by a background dilaton. We analyze the effects of chemical potential and confining scale on this quantity, respectively. It is shown that the drag force in this model is larger than that of \begin{document}${\cal N}=4$\end{document} supersymmetric Yang-Mills (SYM) plasma. In particular, the inclusion of the chemical potential and confining scale both enhance the drag force, in agreement with earlier findings. Also, we discuss how chemical potential and confining scale influence the diffusion coefficient.