The European Physical Journal C最新文献

The Dymnikova black hole (BH) is a regular solution that interpolates between a de Sitter core near the origin and a Schwarzschild-like behavior at large distances. In this work, we investigate the properties of a Dymnikova BH immersed in a quintessential field, characterized by the state parameter (omega ) and a normalization constant c. We explore the thermodynamic behavior, null geodesics, scalar quasinormal modes and shadow profiles for this model. Our analysis shows that the presence of quintessence alters the Hawking temperature and specific heat, leading to parameter-dependent phase transitions. The null geodesics and corresponding black hole shadows are also found to be sensitive to the model parameters, especially (omega ) and c. This sensitivity influences light deflection and shadow size. Furthermore, we compute the scalar quasinormal modes and observe that quintessence tends to enhance the damping of the modes, indicating greater stability under perturbations.

Description of spin-dependent hadronic processes at high energies in terms of parton helicities is a both effective and technically convenient means. In the present paper, we obtain explicit expressions for the parton helicities when either collinear or KT forms of QCD factorization are used. Starting our studies with calculation of the helicities in the double-logarithmic approximation (DLA) in the region of small x and large (Q^2), we generalize the results in order to obtain formulae valid at arbitrary x and (Q^2). We argue against using collinear factorization, when the parton orbital angular momenta are accounted for, and prove that KT factorization should be used instead. We also consider in detail the small-x asymptotics of the parton helicities, compare them with the DGLAP-asymptotics in LO, NLO, etc. and prove that the DGLAP asymptotics are less singular at small x than the Regge asymptotics

We investigate the shadow properties in a recently proposed rotating wormhole spacetime in the presence of a cold and non magnetized plasma environment surrounding the wormhole throat. Using the Hamilton Jacobi formalism, we derive the orbit equation under specific plasma density profiles, where we consider plasma as a dispersive medium and disregard its influence on the background geometry. The electron density distribution is chosen to preserve a generalized Carter constant. We explore the shadow cast by this class of rotating wormhole in the presence of both homogeneous and non-homogeneous plasma as seen by an asymptotic observer. The photon regions are visualized, and the influence of geometric parameters, plasma parameters, and the observer’s inclination angle with the rotation axis on the resulting shadow morphology is analyzed. We tried to implement constraints on the plasma and the geometrical parameters of the wormhole such as the spin parameter and the deviation (from Kerr) parameter in the backdrop of recent observational bounds coming from the deviation from circularity of the shadow boundary ((Delta C)) and deviation of the average shadow radius from Schwarzschild ((delta )). The bound on (Delta C) is satisfied by the theoretically allowed range of parameters thus not found very useful to put any constraint; we could impose stringent constraints on the parameters based on the observed value of (delta ). Comparing the optical characteristics of the image of these wormholes with those of Kerr black holes, we identify the features that could serve as discriminants for similar types of compact objects.

In this paper, we investigate the production of primordial black holes (PBHs) during the radiation-dominated era. The collapse of significant density perturbations originating from large primordial scalar fluctuations generated during inflation can lead to the formation of primordial black holes. In our study, we adopt the Higgs hybrid metric-Palatini model as our framework, in which the inflaton field and the Palatini curvature are non-minimally coupled. To achieve our objective, we analyze the behavior of the primordial curvature power spectrum, which exhibits a large enhancement at small scales corresponding to large wavenumbers k. Furthermore, we examine the probability of PBHs formation by studying the mass variance, (sigma (M_{PBH})), and the mass fraction of the total energy density collapsing into PBHs, (beta (M_{PBH})). The evolution of both functions is consistent with current observational constraints. Finally, we investigate the abundance of primordial black holes as a dark matter candidate. We found that they can account for the totality or a fraction of the current dark matter content, depending primarily on the values of the coupling constant and the e-folds number.

We study frequentist confidence intervals based on graphical profile likelihoods (Wilks’ theorem, likelihood integration), and the Feldman–Cousins (FC) prescription, a generalisation of the Neyman belt construction, in a setting with non-Gaussian Markov chain Monte Carlo (MCMC) posteriors. Our simplified setting allows us to recycle the MCMC chain as an input in all methods, including mock simulations underlying the FC approach. We find all methods agree to within (10 %) in the close to Gaussian regime, but extending methods beyond their regime of validity leads to greater discrepancies. As a key consistency check, we recover a shift in cosmological parameters between low and high redshift cosmic chronometer data with the FC method, but only when one fits all parameters back to the mocks. We observe that fixing parameters, a common approach in the literature, risks underestimating confidence intervals.

We explore the structure and dynamics of compact stellar structures by assuming anisotropic fluid solutions within the framework of general relativity. Assuming that the interior geometry of compact stellar structures follows the Durgapal–Fuloria spacetime, we obtain exact analytic solutions of Einstein’s field equations under physically consistent boundary conditions. The resulting models satisfy all essential physical requirements, including regularity at the center, positive and decreasing pressure and density, energy and causality conditions, and dynamical stability criterion. To test the viability of our model, we examine ten well-known compact stellar structure candidates-LMC X-4, SMC X-1, Cen X-3, Vela X-1, 4U 1608-52, 4U 1820-30, SAX J1808.4-3658, Her X-1, PSR J1614-2230, and PSR J1903+327-assuming their interiors are described by the Durgapal-Fuloria geometry. Furthermore, we extending the analysis to the slow rotation regime, we incorporate first-order rotational effects to compute the moment of inertia and investigate its dependence on stellar mass and radii. The results confirm that the Durgapal-Fuloria spacetime provides physically acceptable and stable descriptions for realistic anisotropic compact stellar structures, consistent with observed systems.

We hereby address the cosmological singularity problem in a general gravitational theory invariant under Weyl conformal transformations. In particular, we focus on the Bianchi IX spacetime and we show that both the initial (big bang) and final (big crunch) singularities disappear in an infinite class of conformal frames naturally selected according to analyticity. It turns out that the past and future singularities are both unattainable within a finite affine parameter (for massless particles) or within a finite proper time (for massive and conformally coupled particles). In order to prove such a statement, we show the geodesic completion of the spacetime when probed by massless, massive, and conformally coupled particles. Finally, the chaotic behavior of the spacetime near the singularity is tamed by a conformal rescaling that turns the Bianchi IX metric into a quasi-FLRW spacetime.

This work analyzes the Darmois junction conditions matching an interior Alcubierre warp drive spacetime to an exterior Minkowski geometry. The joining hypersurface requires that the shift vector of the warp drive spacetime satisfy the solution of a particular inviscid Burgers equation, namely, the gauge where the shift vector is not a function of the y and z spacetime coordinates. Such a gauge connects the warp drive metric to shock waves via a Burgers-type equation, which was previously found to be an Einstein equation vacuum solution for the warp drive geometry. It is also shown that not all Ricci and Riemann tensor components are zero at the joining hypersurface; for that to happen, they depend on the shift vector solution of the inviscid Burgers equation at the joining wall. This means that the warp drive geometry is not globally flat.

We present the first-principles quantization of a damped scalar field within the framework of classical action principle of non-conservative systems using doubled dynamical variables. We consider a non-conservative potential term constructed to describe a linear damping of the scalar field for quantization using canonical and path-integral formalisms, and derive the two-point Green’s function along with the spectral function, which are consistent with known results from the well-known in-in formalism.

Within a framework requiring a well-defined event horizon and matter obeying the weak energy condition, we employ gravitational decoupling method to construct non-singular hairy black holes: spherically or axially symmetric. These solutions arise from a deformation of the Minkowski vacuum, where the maximum deformation can yield the Schwarzschild metric for the static case, and the Kerr geometry for the stationary case, respectively.