A. Alves, O. Bertolami
We consider unparticle inspired corrections of the type ${(\frac{R_{G}}{r})}^β$ to the Newtonian potential in the context of the gravitational quantum well. The new energy spectrum is computed and bounds on the parameters of these corrections are obtained from the knowledge of the energy eigenvalues of the gravitational quantum well as measured by the GRANIT experiment.
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Based on astrophysical constraints derived from Chandrasekhar's mass limit for white-dwarfs, we study the effects of the model on the parameters of unparticle-inspired gravity, on scales $Λ_U > 1 \; TeV$ and $d_U \approx 1$.
We use big bang nucleosynthesis bounds on the variation of the gravitational coupling to derive constraints on the strength of the deviation from the gravitational inverse-square law due to tensor and vector unparticle exchange.
Interest has focussed recently on low energy implications of a nontrivial scale invariant sector of an effective field theory with an IR fixed point, manifest in terms of ``unparticles'' with peculiar properties. If unparticle stuff exists it could couple to the stress tensor and mediate a new 'fifth' force which we call 'ungravity' arising from the exchange of unparticles between massive particles, which in turn could modify the inverse square law. Under the assumption of strict conformal invariance in the hidden sector down to low energies, we compute the lowest order ungravity correction to…
Addressing the discrepancy between the late and early time measurements of the Hubble parameter, $H_0$, and the so-called $S_8$ parameter has been a challenge in precision cosmology. Several models are present to address these tensions, but very few of them can do so simultaneously. In the past, we have suggested Banks-Zaks/Unparticles as an emergent Dark Energy model and claimed that it can ameliorate the Hubble tension. In this work, we test this claim and perform a likelihood analysis of the model and its parameters are given current data and compare it to $Λ$CDM. The model offers a possibl…
A novel mechanism of baryogenesis is proposed on the basis of the phase transition from the conformal invariant space-time to the Einstein space-time in quantum gravity. Strong-coupling gravitational excitations with dynamical mass about 10^17 GeV are generated at the transition. They eventually decay into ordinary matters. As a realization of unparticle physics we show that the low energy effective interactions between the gravitational potential describing the excitation and the non-conserving matter currents by the axial anomalies can explain matter asymmetry out of thermal equilibrium.
Gravitational lensing in a topologically charged Eddington-inspired Born-Infeld spacetime
本文研究拓扑荷磁单极/虫洞在弱场与强场极限下的引力透镜，计算光线偏折并确定观测物理量，发现拓扑荷使观测结果区别于广义相对论虫洞情形。
In this paper we review the EiBI gravity in the presence of a cosmological constant and its tensor perturbations analysis. We show the existence of gravitational waves in the past-time, seeing as a result the smooth transition between high-energy densities (where the EBI dynamics plays its role) and low-energy densities (GR). We obtain the fluctuation spectrum for the graviton in this theory, where for small values of k the fluctuations are strongly suppressed and for large values of k these fluctuations vanish during the De Sitter expansion.
Light deflection and gravitational lensing effects inspired by loop quantum gravity
该研究针对圈量子引力修正的两种规则时空，解析推导弱场与强场下的光线偏折展开式，用于研究引力透镜可观测量，并给出第二个模型可观测量的可探测合理值。
In this work we calculate the angular deflection of light in the strong field limit in two spacetimes which were previously studied within the Eddington-inspired Born-Infeld gravity (EiBI), namely, a black hole and a wormhole, both with topological charge. We show that the presence of the parameters characterizing EiBI and the topological charge promote significant changes in the angular deflection of light with respect to that one obtained in Schwarzschild spacetime. Using the expression for angular deflection in the strong field limit, we calculate the position and magnification of the respe…
Gravitational Wave Signatures from Periodic Orbits around a non-commutative inspired black hole surrounded by quintessence
研究非交换启发黑洞周围暗能量的周期轨道引力波信号，发现非交换参数和暗能量显著改变轨道结构和波形，为未来空间引力波探测提供新的探测途径。
I review a string-inspired cosmological model with gravitational anomalies in its early epochs, which is based on fields from the (bosonic) massless gravitational multiplet of strings, in particular gravitons and Kalb Ramond (KR), string-model independent, axions (the dilaton is assumed constant). I show how condensation of primordial gravitational waves, which are generared at the very early eras immediately after the big bang, can lead to inflation of the so called running vacuum model (RVM) type, without external inflatons. The role of the slow-roll field is played by the KR axion, but it d…
Condensate-Induced Inflation from Primordial Gravitational Waves in String-Inspired Chern-Simons Gravity
本研究基于弦启发的Chern-Simons引力模型，利用动力系统方法首次详细考察了从刚性轴子物质时代向运行真空模型暴胀的过渡，发现原初引力波诱发的CS引力反常项凝聚体会产生线性轴子单值势从而驱动暴胀，并验证了先前研究的定性结论。
The formation of primordial black hole (PBH) dark matter and the generation of scalar induced secondary gravitational waves (SIGWs) have been studied in the generic no-scale supergravity inflationary models. By adding an exponential term to the Kähler potential, the inflaton experiences a period of ultraslow-roll and the amplitude of primordial power spectrum at small scales is enhanced to $\mathcal{O}(10^{-2})$. The enhanced power spectra of primordial curvature perturbations can have both sharp and broad peaks. A wide mass range of PBHs can be produced in our model, and the frequencies of th…
We systematically examine the properties of null geodesics around an electrically charged, asymptotically flat black hole in Eddington-inspired Born-Infeld gravity, varying the electric charge of black hole and the coupling constant in the theory. We find that the radius of the unstable circular orbit for massless particle decreases with the coupling constant, if the value of the electrical charge is fixed. Additionally, we consider the strong gravitational lensing around such a black hole. We show that the deflection angle, the position angle of the relativistic images, and the magnification …
We study here the gravitational collapse of dust in $(2+1)$-dimensional spacetimes for the formation of black holes (BH) and naked singularities (NS) as final states in a modified theory of gravity, with vanishing cosmological constant. From the perspective of cosmic censorship, we investigate the collapse of a dust cloud in Eddington-inspired Born-Infeld gravity (EiBI) and compare the results with those of general relativity (GR). It turns out that, as opposed to the general relativistic situation, where the outcome of dust collapse in $(2+1)$ dimensions is always a naked singularity, the EiB…
In this paper, we address the implications when a homogeneous dust model is considered for a scenario of gravitational collapse in the context of Eddington-inspired Born-Infeld (EiBI) theory. In order to describe the dynamical evolution of the collapse, we present an effective equation, which constitutes the first order corrections, in EiBI coupling parameter $κ$, to Einstein's field equations. The geometry outside the collapsing object is derived by imposing the standard Darmois-Israel junction conditions at the boundary surface of the dust. This induces an effective matter source in the oute…
The extreme-gravity collisions between black holes allow us to probe the underlying theory of gravity. We apply the theory-agnostic inspiral-merger-ringdown consistency test to an example theory beyond general relativity for the first time. Here we focus on the string-inspired Einstein-dilaton Gauss-Bonnet gravity and modify the inspiral, ringdown, and remnant black hole properties of the gravitational waveform. We found that future multiband observations allow us to constrain the theory stronger than current observations by an order of magnitude. The formalism developed here can easily be app…
Stability and localization of the gravitational perturbations for a special brane system in Eddington-inspired Born-Infeld (EiBI) gravity were studied in [Phys. Rev. D 85, 124053 (2012)]. In this paper, we show that the gravitational perturbations for a general brane system are stable, the four-dimensional graviton (massless KK graviton) can be localized on the brane, and the mass spectrum of massive KK gravitons are gapless and continuous. Two models are constructed as examples. In the first model, which is a generalization of [Phys. Rev. D 85, 124053 (2012)], the brane has no inner structure…
Gravitational lensing of the wormhole in the Eddington-inspired Born-Infeld spacetime with a cosmic string
研究EiBI时空中含宇宙弦虫洞的引力透镜，发现宇宙弦增强强场光线偏折，影响像的角分离与亮度，深化对拓扑缺陷虫洞结构的理解。
Within the framework of the recent Eddington-inspired Born-Infeld (EiBI) theory we study gravitational field around an $SO(3)$ global monopole. The solution also suffers from the deficit solid angle as in the Barriola-Vilenkin metric but shows a distinct feature that cannot be transformed away unless in the vanishing EiBI coupling constant, $κ$. When seen as a black hole eating up a global monopole, the corresponding Schwarzschild horizon is shrunk by $κ$. The deficit solid angle makes the space is globally not Euclidean, and to first order in $κ$ (weak-field limit) the deflection angle of lig…
In this letter, we elaborate further on a Cosmological "Running-Vacuum" type model for the Universe, suggested previously by the authors within the context of a string-inspired effective theory in the presence of a Kalb-Ramond (KR) gravitational axion field which descends from the antisymmetric tensor of the massless gravitational string multiplet. In the presence of this field, which has anomalous CP violating interactions with the gravitons, primordial gravitational waves induce gravitational anomalies, which in turn are responsible for the appearance of $H^2$ and $H^4$ contributions to the …
We study a mechanism to produce the circular polarization of primordial gravitational waves. The circular polarization is generated during the super-inflation driven by the Gauss-Bonnet term in the string-inspired cosmology. The instability in the tensor mode caused by the Gauss-Bonnet term and the parity violation due to the gravitational Chern-Simons term are the essential ingredients of the mechanism. We also discuss detectability of the produced circular polarization of gravitational waves. It turns out that the simple model of single-field inflation contradicts CMB observations. To circum…
Gravitational Effects of Sources Inspired by ideal Electromagnetic Fields in Spherical Painlevé-Gullstrand Coordinates
本文通过构建静态球对称时空，研究了由理想电磁场启发的源对引力的影响，分析了能量条件与奇点行为。
We study the evolution of gravitational waves for non-singular cosmological solutions within the framework of Born-Infeld inspired gravity theories, with special emphasis on the Eddington-inspired Born-Infeld theory. We review the existence of two types of non-singular cosmologies, namely bouncing and asymptotically Minkowski solutions, from a perspective that makes their features more apparent. We study in detail the propagation of gravitational waves near these non-singular solutions and carefully discuss the origin and severity of the instabilities and strong coupling problems that appear. …
In this talk, I review briefly a scenario for the evolution of a string-inspired cosmological model, in which condensates of primordial gravitational waves (GW), formed at the very early eras after the Big Bang, are considered responsible for inducing inflation and then a smooth exit to a radiation dominated epoch. Primordial axion fields, that exist in the fundamental massless gravitational (bosonic) string multiplet, couple to the non-trivial GW-induced anomalies. As a result of this coupling, there exist axion background configurations which violate (spontaneously) Lorentz symmetry, and rem…
Gravitational lensing in a space-time with cosmic string within the Eddington-inspired Born-Infeld gravity
本文在EiBI引力背景时空中引入宇宙弦，推导了类光与类时测地线的有效势及光子偏转角，揭示了宇宙弦对这些物理量的修正效应。
We calculate the covariant one-loop quantum gravitational effective action for a scalar field model inspired by the recently proposed nonminimal natural inflation model. Our calculation is perturbative, in the sense that the effective action is evaluated in orders of background field, around a Minkowski background. The effective potential has been evaluated taking into account the finite corrections. An order-of-magnitude estimate of the one-loop corrections reveals that gravitational and non-gravitational corrections have same or comparable magnitudes.
Exploration of features in the black hole mass spectrum inspired by non-parametric analyses of gravitational wave observations
本文受非参数分析启发，提出两种修改的PowerLaw+Peak模型分析引力波目录，支持黑洞质量函数存在两个红移演化不同的子种群，并指出对称双星质量比分布形状仍难确定。
In a modest attempt to present potentially new paradigms in Cosmology, including its inflationary epoch, and initiate discussions, I review in this article some novel, string-inspired cosmological models, which entail a purely geometrical origin of the Dark sector of the Universe but also of its observed matter-antimatter asymmetry. The models contain gravitational (string-model independent, Kalb-Ramond (KR)) axion fields coupled to primordial gravitational anomalies via CP-violating interactions. The anomaly terms are four-space-time-dimensional remnants of the Green-Schwarz counterterms appe…
In the present work we search for a new wormhole solution inspired by noncommutative geometry with the additional condition of allowing conformal Killing vectors (CKV). A special aspect of noncommutative geometry is that it replaces point-like structures of gravitational sources with smeared objects under Gaussian distribution. However, the purpose of this paper is to obtain wormhole solutions with noncommutative geometry as a background where we consider a point-like structure of gravitational object without smearing effect. It is found through this investigation that wormhole solutions exist…
Wave and particle probes of a regular T-duality-inspired black hole with gravitational self-energy
研究具有引力自能的正则 T 对偶启发黑洞对大质量标量场振荡及粒子和光运动的影响，通过改变零点长度，发现其在波传播、黑洞阴影和圆轨道物理中留下相关印记。
Accretion, greybody factor, quasinormal modes, power spectrum, sparsity of Hawking radiation, and weak gravitational lensing of a minimum measurable length inspired Schwarzchild black hole
该研究针对线性-二次GUP启发的量子修正史瓦西黑洞，通过解析与数值方法分析其阴影、拟正模、霍金辐射及弱引力透镜特性，揭示了量子修正带来的一系列观测差异。
A new theory of gravity called Eddington-inspired Born-Infeld (EiBI) gravity was recently proposed by Bañados and Ferreira. This theory leads to some exciting new features, such as free of cosmological singularities. In this paper, we first obtain a charged EiBI black hole solution with a nonvanishing cosmological constant when the electromagnetic field is included in. Then based on it, we study the strong gravitational lensing by the asymptotic flat charged EiBI black hole. The strong deflection limit coefficients and observables are shown to closely depend on the additional coupling paramete…
We investigate gravitational collapses of charged black holes in string-inspired gravity models, including dilaton gravity and braneworld model, as well as f(R) gravity and the ghost limit. If we turn on gauge coupling, the causal structures and the responses of the Brans-Dicke field depend on the coupling between the charged matter and the Brans-Dicke field. For Type IIA inspired models, a Cauchy horizon exists, while there is no Cauchy horizon for Type I or Heterotic inspired models. For Type IIA inspired models, the no-hair theorem is satisfied asymptotically, while it is biased to the weak…
Inspired by the recent progress in the field of scattering amplitudes, we discuss hypothetical particles which can be characterised as the double copies of fermions -- in the same way gravitons can be viewed as double copies of gauge bosons. As the gravitons, these hypothetical particles interact only through gravitational interactions. We present two equivalent methods for the computation of the relevant scattering amplitudes. The hypothetical particles can be massive and non-relativistic.
Investigation of the gravitational dust collapse of the LQG-inspired effective asymmetric bounce model
本文研究了LQG启发的有效非对称 bounce模型中引力尘坍缩的现象，发现奇点解决和视界形成的关键质量阈值，揭示了pre-和post-bounce动态的差异。
We elaborate further on the compatibility of the "vacuumon potential" that characterises the inflationary phase of the Running Vacuum Model (RVM) with the Swampland criteria. The work is motivated by the fact that, as demonstrated recently by the authors [1-3], the RVM framework can be derived as an effective gravitational field theory stemming from underlying microscopic (critical) string theory models with gravitational anomalies, involving condensation of primordial gravitational waves. Although believed to be a classical scalar field description, not representing a fully fledged quantum fi…
Gravitational perturbations of a regular T-duality inspired black hole: Quasinormal modes, excitation factors, and time-domain evolution
研究正则 T 对偶启发的黑洞轴向引力微扰，用高阶 WKB - Padé 方法计算准正则模等，通过时域演化验证主导模。发现开启零点长度时，特定引力模式频率实部增加、阻尼率变化有特点，且激发因子大小变化相对准正则频率较小。
Post-Newtonian theory-inspired framework for characterizing eccentricity in gravitational waveforms
提出一种基于后牛顿理论的框架，利用引力波球谐模的调制特征一致地表征非旋进偏心双黑洞合并的偏心率，并验证其与数值相对论模拟的平滑连接。
Dark Universe inspired by the Kaluza-Klein gravity and impact on Primordial Gravitational Waves
本文基于卡鲁扎-克莱因引力，通过维度约化引入额外场，类比超导理论赋予自旋-1引力子质量，提出环境依赖质量模型解释暗物质现象，并研究其对原初引力波谱的影响，为测试理论提供观测机会。
We consider general relativistic homogeneous gravitational collapses for dust and radiation. We show that replacing the density profile with an effective density justified by some quantum gravity framework leads to the avoidance of the final singularity. The effective density acts on the collapsing cloud by introducing an isotropic pressure, which is negligible at the beginning of the collapse and becomes negative and dominant in the strong field regime. Event horizons never form and therefore the outcome of the collapse is not a black hole, in the sense that there are no regions causally disc…
In this work an extension to Eddington's gravitational action is analyzed. We consider the tensor perturbations of a FLRW space-time in the Eddington regime in where the tensor mode is linearly unstable deep and the resulting modifications to Einstein regime are quite strong.
Eddington-inspired Born-Infeld gravity: Constraints from the generalized parton distributions (GPDs)
本文利用由GPDs的QCD分析得到的质子内部压力分布约束EiBI引力参数$κ$，发现压力模型影响显著，并给出$|κ|\leq0.10\text{--}0.3\\,\text{m}^5\\,\text{kg}^{-1}\\,\text{s}^{-2}$的最强限制。
The recent years witnessed a surge of interest of the lensing of the black holes arising from general as well as other modified theories of gravity due to the experimental data available from the EHT results. The EHT may open a new door indicating the possible existence of the rotating black hole solutions in modified theories of gravity in the strong field regime. With this motivation, we investigate in the present paper the equatorial lensing $(θ=π/2)$ by a recently obtained exact rotating black holes solution in EiBI theory in both the strong and weak field limits. Such black holes are the …
An eikonal-inspired approach to the gravitational scattering waveform
本文用受程函启发的两粒子切割处理 KMOC 框架，证明其对应渐近参考系变换，并给出含 ω log ω 的软极限 PM 波形，使其与 PN 结果在 G^3/c^5 阶一致。
Quasinormal modes of noncommutative geometry-inspired dirty black holes
本文用 Chebyshev 谱方法计算非对易几何“脏”黑洞在标量、电磁和引力微扰下的 QNMs，发现近极端区的过阻尼模及大质量极限向 Schwarzschild 的收敛。
The energy-momentum for a gravitating system can be considered by the tetard teleparalle gauge current in orthonormal frames. Whereas the Einstein pseudotensor used holonomic frames. Tetrad expression itself gives a better result for gravitational energy than Einstein's. Inspired by an idea of Deser, we found a gravitational energy expression which enjoys the positive energy property by combining the tetrad expression and the Einstein pseudotensor, i.e., the connection coefficient has a form appropriate to a suitable intermediate between orthonormal and holonomic frames.
I review several aspects of torsion in string-inspired cosmologies. In particular, I discuss its connection with fundamental, string-model independent, axion fields associated with the massless gravitational multiplet of the string. I argue in favour of the role of primordial gravitational anomalies coupled to such axions in inducing inflation of a type encountered in the "running-vacuum-model (RVM)" cosmological framework, without fundamental inflaton fields. The gravitational-anomaly terms owe their existence to the Green-Schwarz mechanism for the (extra-dimensional) anomaly cancellation, an…
We consider the density profile of pressureless dark matter in Eddington-inspired Born-Infeld (EiBI) gravity. The gravitational field equations are investigated for a spherically symmetric dark matter galactic halo, by adopting a phenomenological tangential velocity profile for test particles moving in stable circular orbits around the galactic center. The density profile and the mass distribution, as well as the general form of the metric tensor is obtained by numerically integrating the gravitational field equations, and in an approximate analytical form by using the Newtonian limit of the t…
Gravitational Lensing and Image Distortion by Buchdahl Inspired Metric in $\mathcal{R}^2$ Gravity
本文研究 $\mathcal{R}^2$ 引力中受 Buchdahl 启发度规的透镜效应，解析推导强弱偏转极限偏转角，并利用 Sgr A*、M87* 与 Canarias 爱因斯坦环约束参数。
Black Holes Surrounded by Perfect Fluid Dark Matter in Eddington-inspired Born-Infeld Gravity
本文研究了在埃德蒙顿启发布林-伊尔德引力中，周围由完美流体暗物质包围的黑洞的引力场解及其稳定性特性。
Geodesics and Light Deflection in Schwarzschild-like Spacetime from Cosmology-Inspired Modified Gravity
本文研究了宇宙学启发的修改引力对类史瓦西黑洞时空的影响，利用 Rindler-Ishak 方法计算光线偏折角并分析光子轨道与黑洞阴影，发现偏折角随模型参数增大而减小，表明高精度观测可约束引力修改。
Ground State and Collective Modes of Bose-Einstein Condensates in Newtonian and MOND-inspired gravitational potentials
研究牛顿和MOND引力势中玻色-爱因斯坦凝聚体的基态和集体模式，发现MOND势下存在束缚态且尺寸随β^{1/3}标度，频率与β^{-1/3}相关。
Effective LQG-inspired dynamics of a thin shell and the fate of a collapsing star
本文研究了受圈量子引力启发的薄壳动力学，探讨了坍缩星在量子引力反弹后的发展及壳交叉奇点之外的时空扩展。
The recent direct detection of gravitational waves has highlighted the huge importance of the tensorial modes in any extended gravitational theory. One of the most appealing approaches to extend gravity beyond general relativity is the Eddington-inspired-Born-Infeld gravity which is formulated within the Palatini approach. This theory can avoid the Big Bang singularity in the physical metric although a Big Bang intrinsic to the affine connection is still there, which in addition couples to the tensorial sector and might jeopardize the viability of the model. In this paper, we suggest that a qu…
Catenoid Inspired Hyperbolic Wormhole Geometry
受悬链面极小曲面结构启发，提出一类精确球对称可穿越双曲虫洞，推导其曲率、张量性质，分析能量条件、可穿越性等特性，证明其为有界空间范围的有限虫洞。
In this paper we consider an extension to Eddington's proposal for the gravitational action. We study tensor perturbations of a homogeneous and isotropic space-time in the Eddington regime, where modifications to Einstein gravity are strong. We find that the tensor mode is linearly unstable deep in the Eddington regime and discuss its cosmological implications.
Quantum corrections in general relativity explored through a GUP-inspired maximal acceleration analysis
通过GUP启发的最大加速度分析，发现广义相对论的量子修正发生在施瓦茨希尔德尺度而非普朗克尺度，禁止黑洞奇点的无限加速度。
It is believed that primordial black holes (PBHs), if they exist, can serve as a powerful tool to probe the early stage of the cosmic history. Essentially, in the radiation dominated universe, PBHs could form by the gravitational collapse of overdense primordial perturbations produced during inflation. In this picture, one important ingredient is the threshold of density contrast, which defines the onset of PBH formation. In the literature, most of the estimations of threshold, no matter numerically or analytically, are implemented in the framework of general relativity (GR). In this paper, by…
Gravitational wave observations of the near-horizon region of black holes lend insight into the quantum nature of gravity. In particular, gravitational wave echoes have been identified as a potential signature of quantum gravity-inspired structure near the horizon. In this paper, we connect such observables to the language of black hole microstates in string theory and holography. To that end, we propose a toy model describing the AdS$_3$ near-horizon region of five-dimensional black holes, inspired by earlier work of Solodukhin. This model captures key features of recently constructed microst…
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