Highlights
• Studies of the 2α and 3α channels of the 12C+12C reaction in the range of Ec.m.=8.9 MeV to 21 MeV using the active target Time Projection Chamber
2022, 46(10): 104001. doi: 10.1088/1674-1137/ac7a1d
The 12C+12C fusion reaction was studied in the range of Ec.m.=8.9 to 21 MeV using the active-target Time Projection Chamber. With full information on all tracks of the reaction products, cross sections of the 12C(12C,8Be)16Og.s. channel and the 12C(12C,3α)12C channel could be measured down to the level of a few milibarns. The 12C(12C,8Be)16Og.s. reaction channel was determined to be 10 $_{-8}^{+24}$ mb at Ec.m.=11.1 MeV, supporting the direct α transfer reaction mechanism. The 12C(12C,3α)12C reaction channel was studied for the first time using an exclusive measurement. Our result does not confirm the anomaly behavior reported in the previous inclusive measurement by Kolata et al. [Phys. Rev. C 21, 579 (1980)]. Our comparisons with statistical model calculations suggest that the 3α channel is dominated by the fusion evaporation process at Ec.m. > 19 MeV. The additional contribution of the 3α channel increases the fusion reaction cross section by 10% at energies above 20 MeV. We also find that an additional reaction mechanism is needed to explain the measured cross section at Ec.m. < 15 MeV at which point the statistical model prediction vanishes.
• Nonextensive effects on QCD chiral phase transition with a chiral chemical potential
2022, 46(10): 103107. doi: 10.1088/1674-1137/ac5dbc
In this study, we investigate the QCD chiral phase diagram in the presence of a chiral chemical potential $\mu_{5}$ based on nonextensive statistical mechanics. A feature of this new statistic is a dimensionless nonextensivity parameter q, which summarizes all possible effects violating the assumptions of Boltzmann-Gibbs (BG) statistics (when $q\rightarrow1$, it returns to the BG case). Within the nonextensive Polyakov-Nambu-Jona-Lasinio model, we find that as $\mu_{5}$ increases, the critical end point (CEP) in the $T-\mu$ plane continues to $\mathrm{CEP}_{5}$ in the $T-\mu_{5}$ plane, and nonextensive effects have a significant impact on the evolution from the CEP to $\mathrm{CEP}_{5}$. Generally, with an increase in q, both the CEP and $\mathrm{CEP}_{5}$ move in the direction of a lower temperature T and larger chemical potential μ ($\mu_{5}$). In addition, we find that chiral charge density $n_{5}$ generally increases with T, μ, $\mu_{5}$, and q. Our study may provide useful hints about lattice QCD and relativistic heavy-ion collision experiments.
• A unique gravitational wave signal from phase transition during inflation
2022, 46(10): 101001. doi: 10.1088/1674-1137/ac76a7
We study the properties of gravitational wave (GW) signals produced by first-order phase transitions during the inflation era. We show that the power spectrum of a GW oscillates with its wave number. This signal can be observed directly by future terrestrial and spatial GW detectors and through the B-mode spectrum in the CMB. This oscillatory feature of the GW is generic for any approximately instantaneous sources occurring during inflation and is distinct from the GW from phase transitions after inflation. The details of the GW spectrum contain information about the scale of the phase transition and the later evolution of the universe.
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• Effects of a global monopole on the thermodynamic phase transition of a charged AdS black hole
Published: 2022-09-28, doi: 10.1088/1674-1137/ac878b
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We study the dynamical properties of the thermodynamic phase transition (PT) of a charged AdS black hole (BH) with a global monopole via the Gibbs free energy landscape and reveal the effects of the global monopole on the kinetics of thermodynamic PTs. First, we briefly review the thermodynamics of a charged AdS BH with a global monopole. Then, we introduce the Gibbs free energy landscape to investigate the thermodynamic stability of the BH states. Because of thermal fluctuations, the small black hole (SBH) state can transit to a large black hole (LBH) state, and vice versa. Further, we use the Fokker-Planck equation with the reflecting boundary condition to study the probability evolution of the BH state with and without a global monopole separately. It is found that for both the SBH and LBH states, the global monopole could slow down the evolution of the BH state. In addition, we obtain the relationship between the first passage time and the monopole parameter η. The result shows that as the monopole parameter η increases, the mean first passage time becomes longer for both the SBH and LBH states.
• Probing top-quark operators with precision electroweak measurements
Published: 2022-09-27, doi: 10.1088/1674-1137/ac82e1
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In the standard model effective field theory, operators involving the top quark are generally difficult to probe and can generate sizable loop contributions to electroweak precision observables measured by past and future lepton colliders. Could the high precision of electroweak measurements compensate for loop suppression and provide competitive reaches on these operators? Would the inclusion of these contributions introduce too many additional parameters for a meaningful global electroweak analysis to be performed? In this paper, we perform a detailed phenomenological study to address these two important questions. Focusing on eight dimension-6 operators that generate anomalous couplings between electroweak gauge bosons and third-generation quarks, we calculate their one loop contributions to $e^+e^- \to f\bar{f}$ processes, both on and off the Z-pole, and the $e^-e^+ \to WW$ process. A global analysis is performed with these eight operators and those that contribute to the above processes at tree level using measurements at the LEP, SLC, and several low energy experiments. We find that although current electroweak precision measurements are sensitive to the one-loop effects of top-quark operators, it is difficult to separate them from the operators that contribute at tree level, making a global analysis rather challenging. Under further assumptions (for instance, new physics contributes to only third generation quark operators and the S and T parameters), competitive reaches may be obtained in a global fit. Another important finding of our study is that the two operators that generate the dipole interactions of the bottom quark have a significant impact on the Z-pole measurements and should not be omitted. We also discuss the implications of the recently reported W-boson mass measurement at the CDF for our results. Finally, we estimate the reaches of future lepton colliders in probing top-quark operators with precision electroweak measurements.
• Shadow thermodynamics of non-linear charged Anti-de Sitter black holes
Published: 2022-09-27, doi: 10.1088/1674-1137/ac87f1
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It is well known that when vacuum polarization emerges in quantum electrodynamics, the non-linear interaction between electromagnetic fields should be considered. Moreover, the corresponding field of non-linear electrodynamics can have important effects on black hole physics. In this work, we focus on the relationship between an observable quantity, that is, the shadow radius, and the first-order phase transition of non-linear charged AdS black holes in the framework of Einstein-power-Yang-Mills gravity. The results show that, under a certain condition, there exists a first-order phase transition from the viewpoint of both the shadow radius and horizon radius, which depend on temperature (or pressure). From the viewpoint of the shadow radius, the phase transition temperature is higher than that from the viewpoint of the horizon radius under the same condition. This may be due to the non-linear Yang Mills charge and the gravitational effect. This indicates that the shadow radius can be regarded as a probe to reveal the thermodynamic phase transition information of black holes. The thermal profiles of coexistent large and small black hole phases when the system is undergoing the phase transition are presented for two different values of the non-linear Yang Mills charge parameter: $\gamma=1,\; 1.5$. Furthermore, the effects of the non-linear Yang Mills charge parameter on the shadow radius and thermal profile are investigated.
Current Issued
2022 Vol. 46, No. 10
Published: 21 September 2022
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