The European Physical Journal C最新文献

The present work deals with a complex scalar field in scalar tensor gravity theory in the background of spatially flat Friedmann–Lema({hat{i}})tre–Robertson–Walker (FLRW) geometry. Noether symmetry analysis has been used to determine the classical cosmological solution of a scalar field in scalar–tensor theory with the scalar field as a nonminimally coupled complex field. Noether symmetry analysis is not only used to find a symmetry vector and potential but also it helps in finding an appropriate transformation ((a,~phi ,~theta )rightarrow (u,~v,~theta )) in the augmented space so that one of the new variables becomes cyclic. In quantum cosmology, the Wheeler–DeWitt (WD) equation has been formed in the minisuperspace and its solution i.e. the wave function of the universe has been evaluated by using the operator version of the conserved (Noether) charge. Finally, the nature of the classical solution has been discussed from the observational point of view and the cosmological singularity has been examined both classically and quantum mechanically.

The concept of dark energy can be used as a possible option to prevent the gravitational collapse of compact objects into singularities. It affects the universe on the largest scale, as it is responsible for our universe’s accelerated expansion. As a consequence, it seems possible that dark energy will interact with any compact astrophysical stellar object [Phys. Rev. D 103, 084042 (2021)]. In this work, our prime focus is to develop a simplified model of a charged strange star coupled to anisotropic dark energy in Tolman–Kuchowicz spacetime (Tolman in Phys Rev 55:364, 1939; Kuchowicz in Acta Phys Pol 33:541, 1968) within the context of general relativity. To develop our model, here we consider a particular strange star object, Her X-1 with observed values of mass (=(0.85 pm 0.15)M_{odot }) and radius (= 8.1_{-0.41}^{+0.41}) km. respectively. In this context, we initially started with the equation of state (EoS) to model the dark energy, in which the dark energy density is proportional to the isotropic perfect fluid matter-energy density. The unknown constants present in the metric have been calculated by using the Darmois–Israel condition. We perform an in-depth analysis of the stability and force equilibrium of our proposed stellar configuration as well as multiple physical attributes of the model such as metric function, pressure, density, mass–radius relation, and dark energy parameters by varying dark energy coupling parameter (alpha ). Thus after a thorough theoretical analysis, we found that our proposed model is free from any singularity and also satisfies all stability criteria to be a stable and physically realistic stellar model.

The (SU(3)_Lotimes U(1)_X) symmetry actually studied is directly broken to the electroweak symmetry (SU(2)_Lotimes U(1)_Y) by a Higgs triplet, predicting a relevant new physics at TeV scale. This work argues, by contrast, that the higher weak isospin (SU(3)_L) might be broken at a high energy scale, much beyond 1 TeV, by a Higgs octet to an intermediate symmetry (SU(2)_Lotimes U(1)_{T_8}) at TeV, before the latter (U(1)_{T_8}) recombined with (U(1)_X) defines (i.e., broken to) (U(1)_Y) by a Higgs singlet. The new physics coupled to (SU(3)_L) breaking phase is decoupled, whereas what remains is a novel family-nonuniversal abelian model, (U(1)_{T_8}otimes U(1)_X), significantly overhauling the standard model as well as yielding consistent results for neutrino mass, dark matter, W-mass anomaly, and FCNC, differently from the usual 3-3-1 model.

In this paper, we investigate the possible parameter space of Palatini–Horndeski theory with gravitational waves in a spatially flat Universe. We develop a general method for obtaining the speed of gravitational waves in the Palatini formalism in the cosmological background and we find that if the theory satisfies the following condition: in any spatially flat cosmological background, the tensor gravitational wave speed is the speed of light c, then only (S = int d^4x sqrt{-g} big [K(phi ,X)-G_{3}(phi ,X){{tilde{Box }}}phi +G_{4}(phi ){tilde{R}}big ]) is left as the possible action in Palatini–Horndeski theory. We also find that when (G_{5}(phi ,X)ne 0), the tensor part of the connection will propagate and there are two different tensor gravitational wave speeds.

Many physically inspired general relativity (GR) modifications predict significant deviations in the properties of spacetime surrounding massive neutron stars. Among these modifications is (f({mathcal {R}}, {mathbb {T}})), where ({mathcal {R}}) is the Ricci scalar, ( {mathbb {T}}) is the trace of the energy–momentum tensor, the gravitational theory that is thought to be a neutral extension of GR. Neutron stars with masses above 1.8 (M_{odot }) expressed as radio pulsars are precious tests of fundamental physics in extreme conditions unique in the observable universe and unavailable to terrestrial experiments. We obtained an exact analytical solution for anisotropic perfect-fluid spheres in hydrostatic equilibrium using the frame of the linear form of (f({mathcal {R}},{mathbb {T}})={mathcal {R}}+beta {mathbb {T}}) where (beta ) is a dimensional parameter. We show that the dimensional parameter (beta ) and the compactness, (C=frac{2GM}{Rc^2}) can be used to express all physical quantities within the star. We fix the dimensional parameter (beta ) to be at most (beta _1=frac{beta }{kappa ^2}= 0.1) in positive values through the use of observational data from NICER and X-ray Multi-Mirror telescopes on the pulsar ({textit{PSR J0740+6620}}), which provide information on its mass and radius. The mass and radius of the pulsar ({textit{PSR J0740+6620}}) were determined by analyzing data obtained from NICER and X-ray Multi-Mirror telescopes. It is important to mention that no assumptions about equations of state were made in this research. Nevertheless, the model demonstrates a good fit with linear patterns involving bag constants. Generally, when the dimensional parameter (beta ) is positive, the theory predicts that a star of the same mass will have a slightly larger size than what is predicted by GR. It has been explained that the hydrodynamic equilibrium equation includes an additional force resulting from the coupling between matter and geometry. This force partially reduces the effect of gravitational force. As a result, we compute the maximum compactness allowed by the strong energy condition for (f({mathcal {R}}, {mathbb {T}})={mathcal {R}}+beta {mathbb {T}}) and for GR, which are (C = 0.757) and 0.725, respectively. These values are approximately 3% higher than the prediction made by GR.. Furthermore, we estimate the maximum mass (Mapprox 4.26 M_{odot }) at a radius of (Rapprox 15.9) km for the surface density at saturation nuclear density (rho _{text {nuc}} = 2.7times 10^{14})?g/cm(^3).

In this work, we have studied the quasinormal modes of a black hole in a model of the type (f(Q)=underset{n}{sum }a_{n}left( Q-Q_{0}right) ^{n} ) in f(Q) gravity by using a recently introduced method known as Bernstein spectral method and confirmed the validity of the method with the help of well known Padé averaged higher order WKB approximation method. Here we have considered scalar perturbation and electromagnetic perturbation in the black hole spacetime and obtained the corresponding quasinormal modes. We see that for a non-vanishing nonmetricity scalar (Q_0), quasinormal frequencies in scalar perturbation are greater than those in electromagnetic perturbation scenarios. On the other hand, the damping rate of gravitational waves is higher for electromagnetic perturbation. To confirm the quasinormal mode behaviour, we have also investigated the time domain profiles for both types of perturbations.

We study a class of homogeneous and anisotropic geometries with affine equation of state (EoS) for different physically plausible scenarios of the universe evolution using dynamical system technique. We analyze the locally rotationally symmetric Bianchi I (LRS BI), Bianchi III (LRS BIII) and Bianchi V (LRS BV) geometry for the exhibition of the effects of affine EoS in the model. The model exhibits stable attractor which is also isotropic and thus, it may explain the late-time accelerated expansion of the universe. The model also possess stiff matter-, radiation- and matter-dominated phases prior to the dark energy assisted accelerating phase which are confirmed by the behaviours of effective equation of state and deceleration parameters. We use the statefinder diagnostic which is a geometrical diagnostic to explore model independent features of the cosmological dynamical system. The LRS BI, BIII and BV geometry based dynamical systems exhibit (r=1,s=0) ((Lambda ) cold dark matter model) at late-times, which is compatible with the observations. The dynamical system for the Kantowski–Sachs model yields synchronous bounce on the basis of the model parameters. It also yields a late-time attractor which may explain the accelerated expansion of the universe in the model. The qualitative differences between LRS BIII and BV cosmological dynamical systems have also been discussed.

We discuss the effect of QED corrections in the evolution of polarized parton distributions. We solve the corresponding evolution equations exactly to ({mathcal {O}}(alpha )) and ({mathcal {O}}(a_{textrm{S}}^2)) in Mellin N-space, extending the available techniques for pure QCD evolution. To accomplish this, we introduce, for the first time, the Altarelli–Parisi polarized kernels at LO in QED. Furthermore, we perform a phenomenological analysis of the QED effects on polarized parton distributions (pPDFs), proposing different scenarios for the polarized photon density. Finally, we quantify the impact of the corresponding QED contributions to the polarized structure function (g_1). We show that the relative corrections to both the pPDFs and the (g_1) structure function are approximately at the few percent level, which is the order of magnitude expected considering the value of (alpha ).

The phenomenologically emergent dark energy (PEDE) model is a varying dark energy model with no extra degrees of freedom proposed by Li and Shafieloo (Astrophys J 883(1):L3, 2019) to alleviate the Hubble tension. The statistical consistency of the model has been discussed by many authors. Since the model depicts a phantom dark energy that increases with redshift, its cosmic evolution, particularly during the late phase, must be examined. We discover that the model’s Hubble and deceleration parameters display unusual behaviour in the future, which differs from (varLambda )CDM cosmology. We find the model also follows a distinct evolution in the statefinder plane. The phantom nature of the model leads to the violation of the null energy condition and a decrease in horizon entropy. The asymptotic future epoch also seems to be unstable based on our dynamical system analysis as well as the stability analysis based on dark energy sound speed.

We show that it is possible to steer clear of a spacetime singularity during gravitational collapse by considering time-variation of a fundamental coupling, in this case, the fine structure constant (alpha ). We study a spherical distribution of cold dark matter coexisting with other fluid elements, collapsing under its own gravity. The dark matter is written as a scalar field interacting with electrically charged matter. This leads to a time variation of (alpha ) and as a consequence, a breakdown of local charge conservation within the sphere. The exterior has no such field and therefore, Einstein’s GR and standard equivalence principles remain valid. We derive the lowest possible bound on the collapse of this sphere beyond which there is a bounce and dispersal of most of the accumulated matter. We discuss the critical behavior of the system around this point and show that the bound is connected to a length scale of the order of Planck, introduced in the theory for dimensional requirements.