In this paper, we study the Jeans analysis in the context of energy-momentum-squared gravity (EMSG). More specifically we find the new Jeans mass for non-rotating infinite mediums as the smallest mass scale for local perturbations that can be stable against its own gravity. Furthermore, for rotating mediums, specifically for rotating thin disks in the context of EMSG, we find a new Toomre-like criterion for the local gravitational stability. Finally, the results are applied to a hyper-massive neutron star, as an astrophysical system. Using a simplified toy model we have shown that, for a positive (negative) value of the EMSG parameter $α$, the system is stable (unstable) in a wide range of $α$. On the other hand, no observational evidence has been reported on the existence of local fragmentation in HMNS. Naturally, this means that EMSG with positive $α$ is more acceptable from the physical point of view.
We present a quantum treatment of the Jeans gravitational instability in the Newtonian limit of the non-minimal matter-curvature coupling gravity model. By relying on Wigner functions, allowing for the representation of quantum states in a classical phase space, we formulate a quantum kinetic treatment of this problem, generalizing the classical kinetic approach [C. Gomes, Eur. Phys. J. C 80, 633 (2020)]. This allows us to study the interplay between non-minimal matter-curvature coupling effects, quantum effects, and kinetic (finite-temperature) effects, on the Jeans criterion. We study in det…
The generalized and extended uncertainty principles affect the Newtonian gravity and also the geometry of the thermodynamic phase space. Under the influence of the latter, the energy-temperature relation of ideal gas may change. Moreover, it seems that the Newtonian gravity is modified in the framework of the Rényi entropy formalism motivated by both the long-range nature of gravity, and the extended uncertainty principle. Here, the consequences of employing the generalized and extended uncertainty principles, instead of the Heisenberg uncertainty principle, on the Jeans mass are studied. The …
The weak field limit of the nonminimally coupled Boltzmann equation is studied, and relations between the invariant Bardeen scalar potentials are derived. The Jean's criterion for instabilities is found through the modified dispersion relation. Special cases are scrutinised and considerations on the model parameters are discussed for Bok globules.
We examine the effects of $f(R)$ gravity on Jeans analysis of collapsing dust clouds. We provide a method for testing modified gravity models by their effects on star formation as the presence of $f(R)$ gravity is found to modify the limit for collapse. In this analysis we add perturbations to a de Sitter background. Depending on the characteristics of a chosen $f(R)$ model, the appearance of new limits is possible. The physicality of these limits is further examined. We find the asymptotic Jeans masses for $f(R)$ theories compared to standard Jeans mass. Through this ratio, the effects of the…
We analyze the stability of self-gravitating systems which dynamics is investigated using the collisionless Boltzmann equation, and the modified Poisson equation of Eddington-inspired Born-Infield gravity. These equations provide a description of the Jeans paradigm used to determine the critical scale above which such systems collapse. At equilibrium, the systems are described using the time-independent Maxwell- Boltzmann distribution function $f_0(v)$. Considering small perturbations to this equilibrium state, we obtain a modified dispersion relation, and we find a new characteristic scale le…
Corda, Mosquera Cuesta and Lorduy Gomez have shown that spherically symmetric stationary states can be used as a model for galaxies in the framework of the linearized R^2 gravity. Those states could represent a partial solution to the Dark Matter Problem. Here we discuss an improvement of this work. In fact, as the star density is a functional of the invariants of the associated Vlasov equation, we show that any of these invariants is in its turn a functional of the local energy and the angular momentum. As a consequence, the star density depends only on these two integrals of the Vlasov syste…
This paper investigates static wormhole solutions through Noether symmetry approach in the context of energy-momentum squared gravity. This newly developed proposal resolves the singularity of big-bang and yields feasible cosmological results in the early times. We consider the particular model of this theory to establish symmetry generators and corresponding conserved quantities. For constant and variable red-shift functions, we examine the presence of viable traversable wormhole solutions for both dust as well as non-dust matter distributions and analyze the stable state of these solutions. …
We consider a gravitational theory with an additional non-minimal coupling between baryonic matter fields and geometry. The coupling is second order in the energy momentum tensor and can be seen as a generalization of the energy-momentum squared gravity model. We will add a constraint through a Lagrange multiplier to ensure the conservation of the energy-momentum tensor. Background cosmological implications together with its dynamical system analysis will be investigated in details. Also we will consider the growth of matter perturbation at first order, and estimate the model parameter from ob…
In this paper, we introduce the post-Minkowskian approximation of Energy-Momentum-Squared Gravity (EMSG). This approximation is used to study the gravitational energy flux in the context of EMSG. As an application of our results, we investigate the EMSG effect on the first time derivative of the orbital period of the binary pulsars. Utilizing this post-Keplerian parameter, the free parameter of the EMSG theory, $f_0'$, is estimated for six known binary pulsars. Taking the binaries that have the most accurate observations, it turns out that $-6\times 10^{-37}\text{m}\,\text{s}^2\text{kg}^{-1}<f…
This paper analyzes the stability of the closed Einstein static universe by using linear homogeneous perturbations in the framework of energy-momentum squared gravity. This newly developed proposal resolves the primordial singularity and yields feasible cosmological results in the early times. For this purpose, we consider the closed Friedmann-Robertson-Walker universe with isotropic matter configuration and adopt small perturbations on the matter parameters and scale factor. Further, we establish equations of motion for static as well as perturbed systems and analyze the stable regions for pa…
We study the structure of quark stars (QSs) adopting homogeneously confined matter inside the star with a 3-flavor neutral charge and a fixed strange quark mass $m_s$. We explore the internal structure, and the physical properties of specific classes of QSs in the recently proposed energy-momentum squared gravity (EMSG). Also, we obtain the mass-radius $(M-R)$ and mass-central energy density $(M-ρ_c)$ relations for QS using the QCD motivated EoS. The maximum mass for QSs in EMSG is investigated depending on the presence and absence of the free parameter $α$. Furthermore, the stability of stars…
Wormholes are tunnels connecting two different points in space-time. In Einstein's General Relativity theory, wormholes are expected to be filled by exotic matter, i.e., matter that does not satisfy the energy conditions and may have negative density. We propose, in this paper, the achievement of wormhole solutions with no need for exotic matter. In order to achieve so, we consider quadratic terms in the trace of the energy-momentum tensor as corrections to the effective energy-momentum tensor of the underlined theory of gravity. We show that by following this formalism, it is possible, indeed…
This paper investigates some physical features that give rise to complexity within the self-gravitating static cylindrical structure coupled with anisotropic distribution in the energy-momentum squared gravity. To accomplish this, we formulate the modified field equations and explore the structure of the astronomical body. The C-energy and Tolman mass are also calculated to discuss the matter distribution. We then obtain some structure scalars via orthogonal splitting of the Riemann tensor. Since, the complexity of the considered structure is influenced by a variety of variables, including ani…
We study the generalized version of energy-momentum squared gravity (EMSG) in the Palatini formalism. This theory allows the existence of a scalar constructed with energy-momentum tensor as $T_{αβ}T^{αβ}$ in the generic action of the theory. We study the most general form of this theory in the Palatini framework and present the underlying field equations. The equations of motion of a massive test particle have been derived. The weak field limit of the theory is explored and the generalized version of the Poisson equation is obtained. Moreover, we explore the cosmological behavior of the theory…
In this work we present a few simple cosmological models under the modified theory of gravity in the particular form of $f(R,\mathcal{T})=R+2f(\mathcal{T})$, where $R$ is the Ricci Scalar and $\mathcal{T}$ is the trace of the energy-momentum tensor. Two special cosmological models are studied with (i) hyperbolic scale factor and (ii) specific form of the Hubble parameter. The models are observed to predict relevant cosmological parameters closer to the observational values. Both the models reduce to overlap with the $Λ$CDM model at late times. We have discussed some interesting results related…
Rotating Fermion-Boson Stars in $R$-squared Gravity
Universitat de València（瓦伦西亚大学）；Universidad Nacional Autónoma de México（墨西哥国立自治大学）；Sofia University “St. Kliment Ohridski”（索非亚大学（圣克利门特·奥赫里斯基））；Bulgarian Academy of Sciences（保加利亚科学院）
Damghan University（达姆甘大学）；Mangalore Institute of Technology & Engineering（曼格洛尔理工工程学院）；Sri Siddhartha Institute of Technology（斯里西达塔理工大学）；Kuvempu University（库文普大学）；Pacif Institute of Cosmology and Selfology (PICS)（帕西夫宇宙学与自我学研究所（PICS））；Khazar University（哈萨尔大学）；Fukushima University（福岛大学）
Several attempts have been made in the past decades to search for the true ground state of the dense matter at sufficiently large densities and low temperatures via compact astrophysical objects. Focusing on strange stars, we derive the hydrostatic equilibrium assuming a maximally symmetric phase of homogeneous superconducting quark matter called the \textit{color-flavor-locked} (CFL) phase in the background of energy-momentum squared gravity (EMSG). Theoretical and experimental investigations show that strange quark matter (SQM) in a CFL state can be the true ground state of hadronic matter a…
In this paper, we investigate the newly developed $f(R,\mathbf{T}^2)$ theory ($R$ is the Ricci scalar and $\mathbf{T}^2=T_{αβ}T^{αβ},~T _{αβ}$ demonstrates the energy-momentum tensor) to explore some viable cosmological models. For this purpose, we use the Noether symmetry approach in the context of flat Friedmann-Robertson-Walker (FRW) universe. We solve the Noether equations of this modified theory for two types of models and obtain the symmetry generators as well as corresponding conserved quantities. We also evaluate exact solutions and investigate their physical behavior via different cos…
In this work we perform an observational data analysis on the energy momentum squared gravity model. Possible solutions for matter density are obtained from the model and their cosmological implications are studied. Some recent observational data is used to constrain model parameters using statistical techniques. We have used the cosmic chronometer and SNe Type-Ia Riess (292) $H(z)-z$ data-sets in our study. Along with the data-sets we have also used baryon acoustic oscillation (BAO) peak parameter and cosmic microwave background (CMB) peak parameter to obtain bounds on the model parameters. J…
In this work we propose the $f(Q,T_{μν}T^{μν})$ gravity as a further extension of the $f(Q)$ and $f(Q,T)$ gravity theories. The action involves an arbitrary function of the non-metricity $Q$ and $T_{μν}T^{μν}$ in the gravity Lagrangian. The field equations for the theory are derived in the metric-affine formalism by varying the action with respect to the metric. The theory involves a non-minimal coupling between the geometric and the matter sectors, and hence the covariant divergence of the energy-momentum tensor is non-zero, thus implying the non-conservation of the same. The vacuum solutions…
Quantum gravity corrections to the conformally coupled scalar self-mass-squared on de Sitter background
我们评估了局部de Sitter背景下共形耦合（CC）标量自质量平方的单圈量子引力修正。在本文中，我们只考虑自质量平方的共形-共形相互作用部分。这是对前一篇文章[E. O. Kahya和R. P. Woodard，Phys.Rev.D76，124005（2007），arXiv：0709.0536]，并且我们将在后续论文中添加最小共形部分以完成一个循环阶的完整自质量平方。计算使用维度正则化进行，并通过吸收带有反项的发散来完全重正化结果。有限的结果可以引起量子修正的CC标量模式功能，因此，他们的功率谱。
This paper investigates the influence of charge on physical features of gravastars in the framework of energy-momentum squared gravity. A gravastar is an alternate model to a black hole that comprises of three distinct regions, namely the intermediate shell, inner and outer sectors. Different values of the barotropic equation of state parameter provide the mathematical formulation for these regions. We construct the structure of a gravastar admitting conformal motion for a specific model of energy-momentum squared gravity. The field equations are formulated for a spherically symmetric spacetim…
A simple generalization to Einstein's general relativity (GR) was recently proposed which allows a correction term $T_{αβ}T^{αβ}$ in the action functional of the theory. This theory is called Energy-Momentum Squared Gravity (EMSG) and introduces a new coupling parameter $η$. EMSG resolves the big bang singularity and has a viable sequence of cosmological epochs in its thermal history. {Interestingly, in the vacuum EMSG is equivalent to GR, and its effects appear only inside the matter-energy distribution. More specifically, its consequences appear in high curvature regime. Therefore it is natu…
In the present work, we derive the motion of light in the weak-field limit of energy-momentum-squared gravity (EMSG). To do so, we introduce the post-Newtonian (PN) expansion of this modified theory of gravity. It is shown that in addition to the Newtonian potential, a new EMSG potential affects the trajectory of photons. As a result, in this theory, photons do not behave as predicted by general relativity (GR). To evaluate the EMSG theory by the solar system tests, we study light deflection and Shapiro time delay. Regarding the results obtained in \cite{bertotti2003test,shapiro2004measurement…
The present work is the second part of a series of computations for the self-mass-squared of the conformally coupled (CC) scalar interacting with gravitons. This work includes the kinetic-kinetic and kinetic-conformal parts, and thus completes the full scalar self-mass squared at one loop order in de Sitter background when combined with the conformal-conformal part previously evaluated. We use dimensional regularization and renormalize the results by subtracting appropriate counterterms. The self-mass squared is finally ready to quantum-correct the CC scalar field equation so that one can stud…
We study the Gauss-Bonnet (GB) term as the leading higher-curvature correction to pure Einstein gravity. Assuming a tree-level ultraviolet completion free of ghosts or tachyons, we prove that the GB term has a nonnegative coefficient in dimensions greater than four. Our result follows from unitarity of the spectral representation for a general ultraviolet completion of the GB term.
The Becchi-Rouet-Stora-Tyutin (BRST) transformations and equations of motion of a gravity-two-form-dilaton system are derived from the product of two Yang-Mills theories in a BRST covariant form, to linear approximation. The inclusion of ghost fields facilitates the separation of the graviton and dilaton. The gravitational gauge fixing term is uniquely determined by those of the Yang-Mills factors which can be freely chosen. Moreover, the resulting gravity-two-form-dilaton Lagrangian is anti-BRST invariant and the BRST and anti-BRST charges anti commute as a direct consequence of the formalism…
Bessel-Hagen currents for linearised Weyl-squared gravity
Astrophysics Group, Cavendish Laboratory（卡文迪许实验室天体物理组）；Institute of Physics of the Czech Academy of Sciences（捷克科学院物理研究所）；Kavli Institute for Cosmology（卡弗里宇宙学研究所）
In this paper, we investigate AdS/BCFT for curvature-squared gravity. To warm up, we start with Gauss-Bonnet gravity. We derive the one point function of stress tensor and show that the central charge related to the norm of displacement operator is positive for the couplings obeying causality constraints. Furthermore, by imposing the null energy condition on the end-of-the-world brane, we prove the holographic g-theorem for Gauss-Bonnet gravity. This corrects a wrong point of view in the literature, which claims that the holographic g-theorem is violated for Gauss-Bonnet gravity. As a by-produ…
This work is concerned to study the bouncing nature of the universe for an isotropic configuration of fluid $\mathcal{T}_{αβ}$ and Friedmann-Lemaître-Robertson-Walker metric scheme. This work is carried out under the novel $f(\mathcal{G},\mathcal{T}_{αβ} \mathcal{T}^{αβ})$ gravitation by assuming a specific model i.e, $f(\mathcal{G},\mathcal{T}^2)=\mathcal{G}+α\mathcal{G}^2+2λ\mathcal{T}^2$ with $α$ and $λ$ are constants, serving as free parameters. {The terms $\mathcal{G}$ and $\mathcal{T}^2$ served as an Gauss-Bonnet invariant and square of the energy-momentum trace term as an inclusion in t…
We analyse configurations of compact stars in the so-called R-squared gravity in the Palatini formalism. Using a realistic equation of state we show that the mass-radius configurations are lighter than their counterparts in General Relativity. We also obtain the internal profiles, which run in strong correlation with the derivatives of the equation of state, leading to regions where the mass parameter decreases with the radial coordinate in a counter-intuitive way. In order to analyse such correlation, we introduce a parametrisation of the equation of state given by multiple polytropes, which …
