The European Physical Journal C最新文献

In this work we highlight the impact of shear on Weyl stresses and complexity within a collapsing stellar core which dissipates heat to the exterior spacetime. We adopt a radiating stellar model first presented by Thirukkanesh et al. (J Math Phys. 53:032506, 2012) which has many salient features including a means of switching off the shear. We demonstrate for the first time the impact of shear on the complexity and its components in a radiating star. We find that for early times, as the fluid loses hydrostatic equilibrium, the evolution of the complexity factor, both at the stellar center and boundary are indistinguishable in the shear-free and shearing cases. For late times, the complexity in the shear-free and shearing regimes differ significantly with shear-free collapse dominating its shearing counterpart. Our investigation into the evolution of the Weyl stresses highlight the connection between the Weyl tensor components and the contributions to the overall complexity arising from pressure anisotropy, density inhomogeneities and heat dissipation. We believe that this is the first exposition which highlights the influence of shear on stellar complexity during dissipative gravitational collapse.

Noncommutative (NC) geometry may open an alternative route to quantum gravity. We study the signatures that quantum structure of spacetime may leave on Dirac quasinormal mode spectrum in the setting defined by a common astrophysical background. For that purpose we examine the influence of spacetime noncommutativity on the Dirac quasinormal modes in modified Reissner–Nordström black hole spacetime. The framework for the latter study is provided by the effective model of NC gravity coupled to fermions introduced in Dimitrijević Ćirić et al. (Eur Phys J C 83:387, 2023). This model describes a classical Dirac field coupled to a modified Reissner–Nordström geometry where the corresponding metric acquires an additional nonvanishing (r-varphi ) component. As the earlier study shows, this model appears to be equivalent to a model of semiclassical NC gauge theory in which a NC gauge field is coupled to a NC fermion field on the one side and the classical Reissner–Nordström background on the other. We compute the resulting Dirac quasinormal modes and compare them with those of the undeformed Reissner–Nordström spacetime. The results show that spacetime noncommutativity modifies both the oscillation frequencies and damping rates, and induces features in the effective potential and quasinormal mode spectrum reminiscent of a Zeeman-like splitting. Since such geometric modifications are expected to become relevant only near the Planck scale, these effects are more naturally associated with microscopic rather than astrophysical black holes.

We investigate cosmology-driven modifications to Schwarzschild-like black hole spacetimes and analyze their impact on photon propagation, gravitational lensing, and shadow observation. The gravitational deflection angle is computed using the Rindler–Is-hak method, which incorporates finite-distance corrections and provides a consistent framework for non-asym-ptotically flat spacetimes. The effective potential for null geodesics exhibits a single unstable maximum corresponding to the photon sphere, and we study photon orbits classified according to the critical impact parameter into capture, escape, and unstable circular trajectories. Our analysis shows that the deflection angle decreases with increasing model parameter ((alpha )), resulting in weaker light bending compared to the Schwarzschild case. In addition, we examine the angular diameter of the black hole shadow as measured by a static observer, highlighting its dependence on the cosmological modification parameters. These results suggest that high-precision astrometric and lensing observations can place meaningful constraints on cosmology-inspired modifications to gravity, thereby linking astrophysical black holes with cosmic expansion and offering a novel probe of gravitational physics in strong-field regimes.

We systematically investigate the production of (J/psi + gamma ) in (gamma gamma ) collisions within nonrelativistic QCD (NRQCD) factorization, with the direct-photon channel calculated specifically up to the next-to-leading order in (alpha _s). Calculations for CEPC energy region show the resolved photon contribution is negligible, while the direct photon process dominates, yielding substantial annual (J/psi ) yields. Significant modifications to (J/psi ) polarization parameters emerge from color-octet mechanisms, and different NRQCD long distance matrix elements (LDMEs) further yield distinct polarization patterns. Furthermore, the polarization predictions are highly sensitive to the ³(P_J^{[8]}) LDME, while being insensitive to the ¹(S_0^{[8]}) and ³(S_1^{[8]}) LDMEs. Leveraging the cleaner environment of (e^+e^-) collisions versus hadronic processes, the production of (J/psi ) associated with a photon in (gamma gamma ) collisions provides a high-precision platform to test LDMEs universality and resolve longstanding (J/psi ) polarization puzzles.

We construct an exact spinning generalisation of the Morris–Thorne traversable wormhole supported by an anisotropic fluid. Within the Teo wormhole ansatz with unit lapse and Morris–Thorne shape function, we solve analytically for the frame-dragging function and obtain a two-parameter family of asymptotically flat solutions labelled by the throat radius (r_0) and total angular momentum J. Curvature scalars and stress–energy components are given in closed form, showing a regular throat, equatorial reflection symmetry, and violations of all standard energy conditions, as required for traversable wormholes. We analyse the causal structure and show that, despite the presence of an ergoregion for sufficiently large |J|,  the coordinate time defines a global temporal function, so the spacetime is stably causal and free of closed timelike curves. The optical appearance is studied via photon trajectories. The resulting shadows are smaller than Kerr’s and depend on the wormhole shape. Finally, we compute the Geroch–Hansen multipole moments and find a massless but spinning configuration with distinctive higher multipoles that encode the throat scale.

In a recent analysis (Misra et al. in npj Quantum Inf 10:34, 2024. 10.1038/s41534-024-00817-w), it has been shown that Hawking radiation is the main source of energy to empower a coherent signal pulse. In this work, we have explored the same effect for a case where the time derivative of the scalar field mode of the redirected Hawking radiation appears explicitly in the interaction Hamiltonian. We have considered a stream of two-level atoms falling freely towards the event horizon of a black hole. The Hawking radiation redirected from an orbiting mirror interacts with the atoms which make a transition between the ground state and the excited state through the emission of a signal photon. The signal pulse is amplified by the mechanical work done by the redirected Hawking mode. The whole set up works as a black hole powered quantum heat engine. We have shown that this amplification depends on the frequency of both the signal mode and the Hawking mode, the flux of the redirected Hawking mode and the lapse function of the black hole. In contrast to the result obtained in Misra et al. (npj Quantum Inf 10:34, 2024. 10.1038/s41534-024-00817-w), we observe in our analysis, that due to the coupling of the momentum degrees of freedom of the Hawking radiation modes with the freely falling detector, the power output depends inversely with the lapse function of the black hole and is proportional to the frequency of the emitted Hawking radiation. As a result the maximum output power enhances significantly if the atom is very close to the event horizon of the black hole. We have analyzed this effect for two types of detectors attached to the cavity. At first we considered a point-like detector and then we have done the analysis from the perspective of a detector with smearing.

We investigate the orbital dynamics and gravitational wave signatures of neutral extreme mass ratio inspirals (EMRIs) in the spacetime of a Kerr black hole immersed in an asymptotically uniform magnetic field, described by the exact Kerr–Bertotti–Robinson (Kerr–BR) solution (Podolsky and Ovcharenko in Phys Rev Lett 135:181401, 2025). Unlike the widely used Kerr–Melvin metric, the Kerr–BR solution is of algebraic type D, allowing for a rigorous analysis of geodesics and possessing a clear asymptotic structure. By analyzing the Innermost Stable Circular Orbit (ISCO), we confirm that the external magnetic field consistently pushes the ISCO to larger radii. However, contrary to Newtonian intuition, this radial expansion is accompanied by a systematic magnetically induced hardening of the spectrum, where the ISCO frequency is blue-shifted relative to the vacuum case. Notably, in the strong-field regime, we identify a non-monotonic frequency evolution, where the orbital frequency initially decreases before rising rapidly near the horizon, fundamentally altering the chirp character. We further demonstrate that retrograde orbits are significantly more sensitive to magnetic fields than prograde orbits, leading to frequency crossover phenomena where magnetic effects can invert the usual spin-frequency hierarchy. Finally, employing a semi-analytic adiabatic evolution scheme, we quantify the dephasing accumulated during the final year of inspiral. Our results demonstrate that space-borne detectors like LISA can distinguish magnetic environments from vacuum spacetimes for field strengths as low as (B sim 10^{-4}), suggesting that environmental magnetic fields could introduce systematic biases in parameter estimation if not properly modeled.

We explore a supergravity model based on the modified Kähler potential (hat{K} = -3 ln left( Phi + Phi ^dagger - beta , mathcal {R} bar{mathcal {R}} -right. left. gamma , (mathcal {R}bar{mathcal {R}})^2 right) ),where (Phi ) is a chiral superfield containing the dilaton and (mathcal {R}) is the chiral curvature superfield. The quartic term (-gamma (mathcal {R}bar{mathcal {R}})^2) ensures stabilization of the curvature sector, in line with recent proposals in modified supergravity, while the linear term (-beta mathcal {R}bar{mathcal {R}}) yields a dilaton-modulated contribution to the effective (R^2) coefficient. As clarified via the superfield Legendre transform, the model is equivalent to Einstein supergravity coupled to three chiral superfields ((Phi ), S, T), yielding six physical scalars. Full stability requires both the curvature–sector stabilization (via (gamma )) and a non-vanishing dilaton VEV. When the extra scalars are stabilized and (langle phi rangle = mathcal {O}(M_P)), the kinetic mixing is exponentially suppressed during inflation ((Z propto e^{-sigma /sqrt{6}})), reducing the dynamics to an effectively single-field Starobinsky model. Thus, cosmological viability is inherited conditionally from the established success of Starobinsky inflation. To the best of our knowledge, this represents the first explicit realization of dilaton-coupled modified supergravity, where a physical scalar (the dilaton) directly influences the curvature sector through the Kähler geometry. While chiral matter couplings to modified supergravity have been studied in the literature, the explicit coupling of the dilaton remains unexplored. The framework is presented as a phenomenological ansatz for exploring scalar–curvature unification in supersymmetry, with the understanding that a UV completion remains an open challenge.

We perform a unified description of the experimental data of the (pi ^+pi ^-) invariant mass spectra of (B_s^0 rightarrow psi (2S) pi ^+pi ^-), the (pi ^+pi ^-) and (K^+ K^-) invariant mass spectra of (B_s^0 rightarrow X(3872) pi ^+pi ^- (K^+ K^-)), and the ratio of branch fractions (mathcal {B}[B_s^0 rightarrow X(3872)(K^+K^-)_{mathrm{non-}phi }]/ mathcal {B}[B_s^0 rightarrow X(3872)pi ^+ pi ^-]). The strong final state interactions between the two pseudoscalars are taken into account using a parametrization fulfilling unitarity and analyticity. We find that there is universality in the coupling constants for (B_s^0 rightarrow psi (2S) pi ^+pi ^-) and (B_s^0 rightarrow J/psi pi ^+pi ^-) processes. While the couplings of (B_s^0 rightarrow X(3872) pi ^+pi ^-) are about half of magnitude smaller than the couplings of (B_s^0 rightarrow psi (2S) pi ^+pi ^-), which indicates that the X(3872) is different from a pure charmonium state. Furthermore, we find that the (f_0(1500)) plays an important role in the (B_s^0 rightarrow psi (2S) pi ^+pi ^-) and the (B_s^0 rightarrow X(3872) pi ^+pi ^- (K^+ K^-)) processes, though the phase space of (B_s^0 rightarrow X(3872) f_0(1500)) is small. Also we predict the ratio of branch fractions (mathcal {B}[B_s^0 rightarrow psi (2S)(K^+K^-)_{mathrm{non-}phi }]/ mathcal {B}[B_s^0 rightarrow psi (2S)pi ^+ pi ^-]) and the (K^+ K^-) invariant mass distribution of (B_s^0 rightarrow psi (2S)K^+K^-).

In this article we present a numerical code, based on the collocation or pseudospectal method, which integrates the equations of the BSSN formalism in cylindrical coordinates. In order to validate the code, we carried out a series of tests, using three groups of initial data: (i) pure gauge evolution; (ii) Teukolsky quadrupole solution for low amplitudes and (iii) Brill and Teukolsky solutions with higher amplitudes, which account for a deviation from the linear regime when compared to the case of low amplitudes. In practically all cases, violations of the Hamiltonian and momentum constraints were analyzed. We also analyze the behavior of the lapse function, which can characterize the collapse of gravitational waves into black holes. Furthermore, all three groups of tests used different computational mesh resolutions and different gauge choices, thus providing a general scan of most of the numerical solutions adopted.