Highlights
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The images of Brans-Dicke-Kerr type naked singularities
2026, 50(2): 025108. doi: 10.1088/1674-1137/ae2f50
We have studied the images of the Brans-Dicke-Kerr spacetime with a dimensionless Brans-Dicke parameter ω, which belongs to axisymmetric rotating solutions in the Brans-Dicke theory. Our results show that the Brans-Dicke-Kerr spacetime with the parameter $ \omega>-3/2 $ represents naked singularities with distinct structures. For the case with $ a \leqslant M $, the shadow in the Brans-Dicke-Kerr spacetime persists, gradually becomes flatter and smaller as ω decreases. Especially when $ \omega<1/2 $, the shadow in the image exhibits a very special "jellyfish" shape and possesses a self-similar fractal structure. For the case with $ a > M $, a distinct gray region consisting of two separate patches appears in the image observed by equatorial observers. This indicating that the Brans-Dicke-Kerr spacetime can be distinguished from the Kerr and Kerr-de Sitter cases based on its image. These effects of the Brans-Dicke parameter could help us to reveal the intrinsic structure of the Brans-Dicke-Kerr spacetimes and provide a foundation for testing Brans-Dicke theory through future high-precision observations. -
New constraints on cosmological gravitational waves from CMB and BAO in light of dynamical dark energy
2026, 50(2): 025105. doi: 10.1088/1674-1137/ae167c
In this work, we derive upper limits on the physical energy-density fraction today of cosmological gravitational waves, denoted by $ \Omega_{\rm{gw}}h^{2} $, by analyzing Planck, ACT, SPT CMB, and DESI BAO data combinations. In the standard cosmological model, we establish 95% CL upper limits of $ \Omega_{\rm{gw}}h^{2} < 1.0 \times 10^{-6} $ for adiabatic initial conditions and $ \Omega_{\rm{gw}}h^{2} < 2.7 \times 10^{-7} $ for homogeneous initial conditions, assuming a uniform prior for $ \Omega_{\rm gw}h^{2} $. In light of dynamical dark energy, we obtain $ \Omega_{\rm{gw}}h^{2} < 7.2 \times 10^{-7} $ (adiabatic) and $ \Omega_{\rm{gw}}h^{2} < 2.4 \times 10^{-7} $ (homogeneous). In contrast, if a log-uniform prior is assumed for $ \Omega_{\rm gw}h^{2} $, these constraints become tighter by a factor of approximately 4, suggesting the results are prior-sensitive. Furthermore, we project the sensitivity achievable with LiteBIRD and CMB Stage-IV measurements of CMB and CSST observations of BAO, forecasting 68% CL uncertainties of $ \sigma = 2.5 \times 10^{-7} $ (adiabatic) and $ \sigma = 1.0 \times 10^{-7} $ (homogeneous) for $ {\Omega_{\rm{gw}}h^{2}} $. The constraints obtained in this work provide critical benchmarks for exploring the cosmological origins of gravitational waves within the frequency band $ f \gtrsim 10^{-15} $ Hz and potentially enable joint analysis with direct gravitational-wave detection sensitive to this regime. -
Dynamic shadow of a black hole with a self-interacting massive complex scalar hair
2026, 50(2): 025102. doi: 10.1088/1674-1137/ae1442
We investigate the dynamic shadows of a black hole with a self-interacting massive complex scalar hair. The complex scalar field $\psi$ evolves with time t, and its magnitude on the apparent horizon $|\psi_{\rm h}|$ starts from zero, undergoes a sharp rise followed by rapid oscillations, and eventually converges to a constant value. The variation in the photon sphere radius $r_{\rm ps}$ is similar to that of the magnitude $|\psi_{\rm h}|$. Owing to the emergence of the complex scalar hair $\psi$, the apparent horizon radius $r_{\rm h}$ starts increasing sharply and then smoothly approaches a stable value eventually. The shadow radius $R_{\rm sh}$ of the black hole with an accretion disk increases with time $t_{\rm o}$ at the observer's position. In the absence of an accretion disk, the shadow radius $R_{\rm sh}$ is larger and also increases as $t_{\rm o}$ increases. Furthermore, we slice the dynamical spacetime into spacelike hypersurfaces for all time points $t$. For the case with an accretion disk, the variation in $R_{\rm sh}$ is similar to that in the apparent horizon $r_{\rm h}$, because the inner edge of the accretion disk extends to the apparent horizon. In the absence of an accretion disk, the variation in $R_{\rm sh}$ is similar to that in the photon sphere radius $r_{\rm ps}$, because the black hole shadow boundary is determined by the photon sphere. As the variation in $r_{\rm ps}$ is induced by $\psi$, it can be stated that the variation in the size of the shadow is similarly caused by the change in $\psi$. Regardless of the presence or absence of the accretion disk, the emergence of the complex scalar hair $\psi$ causes the radius $R_{\rm sh}$ of the shadow to start changing. Moreover, we investigate the time delay $\Delta t$ of light propagating from light sources to the observer. These findings not only enrich the theoretical models of dynamic black hole shadows but also provide a foundation for testing black hole spacetime dynamics.
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Exploring Thermalization and Multi-Freeze-Out Effects in Pb–Pb Collisions Based on Tsallis pT Distributions
Published: 2026-01-22
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Fusion Reaction of 19O + 12C Studied with an Active-Target Time Projection Chamber in the Energy Range 9.7 < Ec.m. < 16.9 MeV
Published: 2026-01-22, doi: 10.1088/1674-1137/ae368b
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Dynamical System and Statefinder Analysis of Cosmological Models in f(T, B) Gravity
Published: 2026-01-18
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Searching for the toponium ${{\boldsymbol\eta}_{\boldsymbol t}}$ with the ${{\boldsymbol\eta}_{\boldsymbol t}}$ ${\boldsymbol\to}$ ${{\boldsymbol W}^{\bf +}{\boldsymbol W}^{\bf -}}$ decay
2026, 50(3): 033101-033101-5. doi: 10.1088/1674-1137/ae18aaShow AbstractInspired by the observation of the ${\eta}_{t}$ meson at the LHC and the promising prospect of the ${\eta}_{t}$ meson available at the approaching HL-LHC, branching ratios for the ${\eta}_{t}$ ${\to}$ $f\bar{f}$, $gg$, ${\gamma}{\gamma}$, $W^{+}W^{-}$, $Z^{0}Z^{0}$, $Z^{0}{\gamma}$, and $Z^{0}H$ decays are roughly estimated. It is found that tens of opposite-charge dilepton events from the ${\eta}_{t}$ ${\to}$ $W^{+}W^{-}$ decay and hundreds of events from the ${\eta}_{t}$ ${\to}$ $Z^{0}H$ ${\to}$ ${\ell}^{+}{\ell}^{-}H$ decay using the single $Z^{0}$ boson tagging method are expected to be accessible. This estimation provides a reference for future experimental study on the ${\eta}_{t}$ meson.
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One texture zero for Dirac neutrinos in a diagonal charged lepton basis
2026, 50(3): 033111-033111-9. doi: 10.1088/1674-1137/ae2b5cShow AbstractAn analytical and numerical systematic study of the neutrino mass matrix with one texture zero is presented in a basis where the charged leptons are diagonal. Under the assumption that neutrinos are Dirac particles, the analysis is conducted in detail for the normal and inverted hierarchy mass spectra. Our study is performed without any approximations, first analytically and then numerically, using current neutrino oscillation data. The analysis constrains the parameter space in such a way that, among the six possible one-texture-zero patterns, only four are favored in the normal hierarchy and one in the inverted hierarchy by current oscillation data at the $3 \sigma$ level. Phenomenological implications for the lepton CP-violating phase and neutrino masses are also explored.
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Search potential for direct slepton pair production at the CEPC with ${ \sqrt{\boldsymbol s}}$ = 360 GeV
2026, 50(3): 033001-033001-12. doi: 10.1088/1674-1137/ae2f4eShow AbstractThe Circular Electron Positron Collider (CEPC) is designed to operate at key center-of-mass energies: 91.2 GeV as a Z factory for precision Z boson studies, ≈ 160 GeV at the threshold for W boson pair production, and 240 GeV as a Higgs factory for copious Higgs boson production. It can be upgraded to 360 GeV (CEPC-360 GeV) for enabling top quark-antiquark ($ t\bar{t}$) pair production. Beyond enabling high-precision measurements of the Standard Model (SM), CEPC-360 GeV is uniquely positioned to perform searches for new physics beyond the SM (BSM), serving as a valuable complement to hadron colliders. This paper presents a sensitivity study on the direct pair production of staus and smuons at the CEPC with $ \sqrt{s}$ = 360 GeV, conducted via full Monte Carlo simulation. Under the assumptions of 1.0 ab−1 integrated luminosity and a flat 5% systematic uncertainty, CEPC-360 GeV could potentially discover the combined production of left-handed and right-handed staus up to a mass of 170 GeV (if they exist) or up to 169 for pure left-handed staus and 162 GeV for pure right-handed staus. For direct smuon production, the discovery potential reaches up to 178 GeV under the same conditions.
Current Issued
2026 Vol. 50, No. 2
Published: 02 February 2026
Published: 02 February 2026
Archive
IF: 3.1
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ISSN 1674-1137 CN 11-5641/O4
Original research articles, Ietters and reviews Covering theory and experiments in the fieids of
- Particle physics
- Nuclear physics
- Particle and nuclear astrophysics
- Cosmology
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Cover Story
- Cover Story (Issue 2, 2026) |The images of Brans-Dicke-Kerr type naked singularities
- Cover Story (Issue 1, 2026) A focused review of quintom cosmology: from quintom dark energy to quintom bounce
- Cover Story (Issue 11, 2025) The Earth-Magnet Assists DAMPE in Studying Cosmic Anti-Electrons
- Cover Story (Issue 9, 2025): Precise measurement of χc0 resonance parameters and branching fractions of χc0,c2→π＋π－/ K+K-
- Cover Story (Issue 8, 2025) A Novel Perspective on Spacetime Perturbations: Bridging Riemannian and Teleparallel Frameworks
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