General Relativity and Gravitation最新文献

We study the general relativistic transonic accretion flow around the primary black hole, which forms the circumprimary disc (CPD), within a binary black hole (BBH) system. The BBH spacetime is characterized by the mass ratio (q) and the separation distance ((z_2)) between the two black holes. We numerically solve the radial momentum and energy equations to obtain the accretion solutions. It is observed that the CPD can exhibit shock solutions, which exist for a wide range parameter space spanned by flow specific angular momentum ((lambda )) and energy (E). We find that the shock parameter space is modified by q and (z_2). Investigations show that q and (z_2) also affect various shock properties, such as density compression and temperature compression across the shock fronts. Moreover, we calculate the spectral energy distributions (SEDs) of the CPD and examine how the SEDs are modified by q and (z_2) for both shock-free and shock-induced accretion solutions. SED is found to be nearly independent of the binary parameters. We essentially show that although q and (z_2) alter the effective horizon area of the primary black hole located at the center of the CPD, they have a minimal impact on the dynamical and spectral properties of the accretion flow around the primary black hole.

We show that general relativistic time dilation can act as a controllable source of non-Markovianity in the dynamics of delocalized quantum clocks coupled to structured environments. As a concrete setting, we model a delocalized quantum clock, a two-level Unruh-DeWitt detector interacting with a thermal scalar field with finite correlation time in a weak, static gravitational field. The gravitational redshift between spatially separated branches leads to a path-dependent sampling of the bath correlation functions and to an effective spectral mismatch between the arms of the interferometer. Within a second-order time-convolutionless (TCL2) expansion we derive a time-local master equation whose time-dependent rates depend explicitly on the redshift parameter and reduce to the usual Markovian Gorini-Kossakowski-Sudarshan-Lindblad generator when gravity is switched off or the bath becomes memoryless. Numerical evaluation for an Ohmic environment reveals gravitationally induced coherence revivals and information backflow, providing a genuine non-Markovian signature that can be quantified by standard trace-distance measures. We identify a resonance-like regime in which the gravitational detuning becomes comparable to the dominant bath frequencies, leading to suppressed decoherence and longer entanglement lifetimes in the two-clock scenario considered below (two initially entangled Unruh–DeWitt detectors), relative to the flat-space Markovian case. Finally, by comparing the size of the gravity-induced deviations to quantum projection noise (QPN) in state-of-the-art optical clocks, we derive an analytic signal-to-noise ratio and show that, within our model, engineered low-frequency reservoirs could allow gravity-controlled memory effects to be resolved above the shot-noise limit on few-hour integration times, whereas for fast thermal baths the effect remains QPN-limited and effectively unobservable.

We develop extended black-hole thermodynamics on a Dvali–Gabadadze–Porrati (DGP) brane by promoting the brane tension (sigma ) to a thermodynamic variable within the extended Iyer–Wald framework. The brane tension acts as a localized vacuum energy with pressure (P_sigma equiv -sigma ), yielding a new work term (V_sigma ,textrm{d}P_sigma ) in the first law and the corresponding Smarr relation. For static, spherically symmetric black holes we show that the conjugate volume equals the geometric volume (V_sigma =tfrac{4pi }{3}r_h^3); for stationary, axisymmetric solutions it admits a covariant, slice-independent definition and evaluates to (V_sigma =tfrac{4pi }{3}!left( r_+^3+a^2 r_+right) ). Working on the ghost-free normal branch, the brane is asymptotically flat with a single horizon, so the construction avoids de Sitter obstructions. Along a flat-brane path, asymptotic flatness is preserved by co-varying the bulk cosmological constant, and induced-gravity effects are suppressed by (r_h/r_c). These results establish a consistent flat-braneworld realization of black-hole chemistry in which brane tension provides the physically motivated pressure variable.

The current cosmological paradigm, (Lambda hbox {CDM}), is characterized its expansive description of the history of the Universe, its deep connections to particle physics and the large amounts of data that support it. Nonetheless, (Lambda hbox {CDM})’s critics and boosters alike agree on one thing: it is the not the final cosmological theory and they are anxious to see it replaced by something better! However, given its successes and the absence of a worthy competitor, this replacement is not likely to happen soon. Nonetheless, after reviewing the impactful events in cosmology since the last Lemaître Workshop, I discuss the role that the recent evidence for evolving dark energy might play in getting cosmology to that better theory.

We prove that every open connected region of relativistic spacetime ((M,{textbf {g}})) that encloses a b-incomplete half-curve has an open connected subregion that encloses a b-incomplete half-curve and is also ‘small’ in the following sense: it is the image, under the bundle projection map, of some open region in the (connected) orthonormal frame bundle (O^+M) over that spacetime which is bounded, and whose closure is Cauchy incomplete, with respect to any ‘natural’ distance function on (O^+M). As a corollary, it follows that every b-incomplete half-curve can be covered by a sequence of singular regions which are images of a sequence of bounded subsets of (O^+M) whose diameter, with respect to any ‘natural’ distance function on (O^+M), tends to zero. We discuss to what extent these results can be interpreted in favour of the claim that singular structure in classical general relativity is ‘localizable’.

Bianchi I cosmological solutions in f(T) gravity are discussed. We start from diagonal metrics and tetrads and show that their dynamical equations are pretty much tractable analytically, with a possible arena for physical applications. Then we derive a very bad unpredictability of the teleparallel connection in these configurations. Namely, even for the simple isotropic Friedmann universes, one might apply an arbitrary time-dependent spatial rotation to the standard tetrad of Weitzenböck gauge without changing anything in the cosmological equations.

This manuscript presents a detailed investigation of the complexity of cylindrically symmetric fluid distributions influenced by an electric field in the formalism of (f(R, L_{m}, T)) theory. The analysis begins with the consideration of an anisotropic charged fluid configuration, where modified field equations are formulated after using the relations between internal curvature and the conformal tensor. We explore the mathematical structure of the C-energy and Tolman mass and examine their connection with the conformal tensor. The impact of anisotropic pressures and varying energy densities is thoroughly assessed. Furthermore, the orthogonal splitting of the Riemann curvature tensor yields structure scalars, with particular focus on the scalar factor, which serves as a measure of complexity associated with anisotropic matter. It is shown that for homogeneous energy density, the complexity factor vanishes. Significant conclusions are drawn regarding the behavior of the Weyl scalar, Tolman mass, and complexity factor under the influence of the more degrees of freedom in our considered gravity. The role of the vanishing complexity condition is also emphasized in obtaining physically viable solutions.

In this work, we systematically present a new dynamical systems approach to nonstandard inflationary processes as constant-roll inflation and ultraslow-roll inflation. Using the techniques presented in our work one can in general investigate the attractor nature of the inflationary models in the phase space. We have compactified the phase space coordinates, wherever necessary, and regulated the nonlinear differential equations, constituting the autonomous system of equations defining the dynamical system, at the cost of a new redefined time variable which is a monotonic increasing function of the standard time coordinate. We have shown that in most of the relevant cases the program is executable although the two time coordinates may show different durations of cosmological events. Our methods of analysis differs slightly in different models but we have always emphasized on the nature of the initial conditions leading to stable inflationary phases in different cases. We have provided a universal language in terms of which various nonstandard inflationary models can be studied.

In this work we study the structure of the future causal completion (hat{M}) of a globally hyperbolic GRW spacetime (mathbb {R}times _alpha M) using the novel notion of Lorentzian pre-length spaces. As our main result, we prove that the causal completion of a GRW spacetime is a globally hyperbolic pre-length space provided the chronological topology is Hausdorff.

Finslerian gravity extends classical general relativity, enabling a more generalized description of cosmic dynamics. In this study we explore the cosmological evolution of the FLRW model modified by an anisotropic Finslerian parameter ((eta )), constructed within the context of Kropina-Barthel spacetime. This spacetime represents a specific class of Finsler geometry that extends Riemannian geometry by incorporating a metric that depends on both the spacetime coordinates and a vector field. Such a formulation provides greater flexibility in modeling spacetime structure, making it particularly valuable for addressing anisotropies in cosmology and investigating the nature of dark energy. This study investigates bouncing cosmology within the framework of Finsler-Kropina geometry by incorporating anisotropic corrections through the geometric function (eta (t)). Standard Riemannian cosmological models, which assume isotropy, often result in singularities and do not account for directional dependencies in the early universe. Our Finslerian approach here introduces anisotropy into the spacetime structure, enabling a richer modeling of cosmic evolution. We first obtain the Finslerian Einstein field equations and the energy conservation equation, and explore how anisotropic-effects influence the dynamics of the universe during the bounce phase. Then, using a barotropic equation of state ( p = (gamma - 1)rho ) and the form of the scale factor we derive the corresponding form of (eta (t)), capturing its role in shaping the anisotropic geometry. Applied to various bouncing models, the results demonstrate that Finslerian parameters ensure stability, regulate energy conditions, and avoid singularities, offering an alternative to inflationary paradigms. Additionally, we develop a new set of cosmographic parameters termed anisotropic cosmographic parameters that extend conventional Hubble, deceleration, jerk, and snap parameters to include the impact of anisotropy. In addition to exploring the Finsler-Kropina framework and its impact on cosmological dynamics, the study incorporates a scalar field description to analyze the interplay between quintessence and phantom fields. The stability of the proposed models is evaluated using perturbation analysis, ensuring their physical viability.