P. Valtancoli
We study the propagation of a gravitational wave in an Ads spacetime. We find that, in presence of the cosmological constant, the graviton mass cannot be measured with higher precision than the square root of the cosmological constant.
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We show that solitonic cosmological gravitational waves propagated through the Friedmann universe and generated by the inhomogeneities of the gravitational field near the Big Bang can be responsible for increase of cosmological distances.
Exact Cosmological Solutions of Gravitational Theories
一个全球性的图片被绘制在一起的引力理论在四维或四维以上的时空维度的最精确的宇宙学解决方案。
Cosmological Models with Variable Gravitational and Cosmological constants in $R^{2}$ Gravity
我们考虑了在高阶导数理论中，在引力和宇宙学常数可变的情况下，包含Einstein-Hilbert作用量的$αR^{2}$项的平坦Friedmann-Roberstson-Walker宇宙的演化.本文研究了在辐射和物质支配宇宙时代的引力常数和宇宙学常数的演化。我们在这里提出了新的宇宙学的解决方案，这是物理上有趣的模型建设。
Remarks on a solvable cosmological model
在空间平坦的Robertson-Walker度规下，给出了具有宇宙学常数的爱因斯坦方程的精确解析解.这被解释为宇宙学弗里德曼模型的各向同性勒梅特型版本。最近发现的宇宙加速和宇宙暴胀模型理论的影响是在视图中。这个解决方案的一些性质指出作为一个结果的模型的数值研究。
The asymptotic form of the Bel-Robinson tensor in the gravitational radiation-zone is obtained in terms of the mass quadrupole of the source. A comparison is made with the standard formula for the gravitational power emission. The problem of a fully covariant description of gravitational radiation in terms of this tensor is discussed with some detail.
Gravitational dust collapse with cosmological constant
我们研究了存在宇宙学常数时引力坍缩的命运。推导了静态时空与非静态时空的连接条件。形成了三个视视界，但只有两个具有物理意义，其中一个是黑洞视界，另一个是宇宙学视界。宇宙学常数项减缓了物质的坍缩，也限制了黑洞的大小。
Some Remarks on the Neutrino Oscillation Phase in a Gravitational Field
本文对弱引力场展开法解释引力诱导的中微子振荡效应进行了严格的考察。结果表明，中微子相分裂为“运动学”相和"引力“相并不总是可能的，因为相对论因子改变了引力场中粒子干涉相分裂的条件.
Higher-order gravity and the cosmological background of gravitational waves
通过对引力拉氏量的高阶修正，可以调谐引力波的宇宙学背景。特别是，它可以表明，假设$R^{1+ε}$，其中$ε$表示一个通用的（最终很小）修正的希尔伯特-爱因斯坦作用在里奇标量$R$，给出了一个参数化的方法来控制演化和生产机制的引力波在早期宇宙。
We derive a formula for the total canonical energy, and its flux, of weak gravitational waves on a de Sitter background.
A remark on Ma's "Cosmic gravitational background radiation"
本文对马广文最近的一封信[Phys.Lett. A239，（1998）209]包含一个很容易发现的错误，使他的结论无关紧要。
We analyze propagation equations for the polar modes of gravitational waves in cosmological space-times. We prove that polar gravitational waves must perturb the density and non-azimuthal components of the velocity of material medium of the Friedman-Lemaitre-Robertson-Walker spacetimes. Axial gravitational waves can influence only the azimuthal velocity, leading to local cosmological rotation. The whole gravitational dynamics reduces to the single "master equation" that has the same form for polar and axial modes. That allows us to conclude that the status of the Huygens principle is the same …
Within the framework of Bianchi type-II (BII) cosmological model the behavior of matter distribution has been considered. It is shown that the non-zero off-diagonal component of Einstein tensor implies some severe restriction on the choice of matter distribution. In particular for a locally rotationally symmetric Bianchi type-II (LRS BII) space-time it is proved that the matter distribution should be strictly isotropic if the corresponding matter field possesses only non-zero diagonal components of the energy-momentum tensor.
Gravitational waves are inevitably produced by second order terms in cosmological perturbation theory. Most notably, the so-called induced gravitational waves are a window to the small scales part of the primordial spectrum of fluctuations and a key counterpart to the primordial black hole scenario. However, semi-analytical solutions are only known for matter and radiation domination eras. In this paper, we present new analytic integral formulas for the induced gravitational waves on subhorizon scales in a general cosmological background with a constant equation of state. We also discuss appli…
We give a very short proof that the vacuum Einstein equations in 4+1 dimensions have no cohomogeneity-two Bianchi IX continuously self-similar solutions.
Gravitational entropy in cosmological models
我们讨论了一个适当定义的无量纲标量函数是否可能是一个可接受的候选人的引力熵，明确考虑Szekeres和Bianchi VI型$_{h}$模型，承认各向同性奇异性。我们还简要讨论了其他可能的引力熵函数，包括适当的测量速度依赖的贝尔-罗宾逊张量。
Gravitational Collapse of Massless Scalar Field with Negative Cosmological Constant in (2+1) Dimensions
找到了具有负宇宙学常数的Einstein无质量标量场方程的2+1维测地圆对称解，并研究了它们的局部和整体性质.发现其中一个代表引力坍缩，那里总是形成黑洞。
In the middle of last century, Bondi and his coworkers proposed an out going boundary condition for the Einstein equations. Based on such boundary condition the authors theoretically solved the puzzle of the existence problem of gravitational wave. Currently many works on gravitational wave source modeling use Bondi's result to do the analysis including the gravitational wave calculation in numerical relativity. Recently more and more observations imply that the Einstein equations should be modified with an nonzero cosmological constant. In this work we use Bondi's original method to treat the…
Evolution of high-frequency gravitational waves in some cosmological models
我们研究了Isaacson的高频引力波在一些相关的宇宙学模型，特别是FRW时空中的传播。对于各种度规形式的（反）de Sitter宇宙，得到了它们在Fourier空间中的时间演化.高频波在各向异性Kasner时空中的行为也被描述。
An infinite tower of gravitational memories was proposed in \cite{Compere:2019odm} by considering the matter-induced vacuum transition in the impulsive limit. We give an alternative realization of the infinite towers of gravitational memories in Newman-Penrose formalism. We also demonstrate that the memories at each order can be associated to the same supertranslation instead of infinite towers of supertranslations or superrotations.
Some Remarks on Gravitational Global Monopoles
本文主要用解析的方法导出了静态引力球单极子中希格斯场最大真空值的精确关系式$η_{max}=\sqrt{3/8π}$。对于这个值，全局解与在Higgs场为零时得到的de Sitter解分叉。此外，我们还分析了解的稳定性。
In this paper, we calculate the one-loop quantum cosmological corrections to the kink energy in the closed Friedmann-Robertson-Walker universe in which the fluctuation potential $V^{\prime\prime}$ has a shape invariance property. We use the generalized zeta function regularization method to implement our setup for describing quantum kink-like states. It is conjectured that the corrections lead to the renormalized gravitational constant.
A remark on Brans-Dicke dust cosmological solutions with negative $ω$
分析Brans迪克解决方案的尘埃阶段，我们表明，为负值的$ω$，他们包含的情况下，显示初始的亚光速膨胀，随后的通货膨胀阶段。本文结合高红移超新星的观测结果以及年龄问题和结构形成问题讨论了这些解。我们建立这些解决方案与那些新兴的字符串有效的模型可能的连接。
Dirac Spinor in Bianchi-I Universe with Time Dependent Gravitational and Cosmological Constants
本文研究了非线性旋量场与Bianchi I（BI）引力场的自洽系统，该系统的引力常量（$G$）和宇宙学常数（$Λ$）随时间变化.对场函数和度量场函数的初始性态和渐近性态进行了深入的研究。给定$Λ= Λ_0/τ^2$，使用$τ= \sqrt{-g}$，已将$G$估计为$τ$的函数。阐明了理想流体在初始各向异性宇宙的膨胀和渐近各向同性过程中的作用。
The solution of the null non-radial geodesic in a Schwarzschild-de Sitter background is revisited. The gravitational bending of a light ray is affected by the cosmological constant, in agreement with the findings of some previous investigations. The present study confirms that the leading correction term depends directly not only on the cosmological constant but also on the impact parameter and on the angular distance to the source. Using the resulting lens equation, the projected mass of the lens was estimated for several systems displaying Einstein rings. Corrections on masses due to the cos…
Cosmological Gravitational Wave in a Gravity with Quadratic Order Curvature Couplings
本文给出了一组描述引力理论中宇宙引力波的方程，其中包含了在量子修正过程中自然产生的二阶引力耦合项。引力理论中的引力波方程在作用量中含有一般的$f(R)$项，导出了一个二阶微分方程，其唯一的修正因子出现在阻尼项中。$R^{ab} R_{ab}$术语的情况完全不同。引力波在时间和空间上都可以用一个四阶微分方程来描述。然而，奇怪的是，我们发现，对背景演化的贡献是定性的两项相同。
Causal Bulk Viscous Dissipative Isotropic Cosmologies with Variable Gravitational and Cosmological Constants
我们考虑了一个平坦的Friedmann-Robertson-Walker宇宙的演化，宇宙中充满了一种因果性的粘性宇宙流体，存在可变的引力常数和宇宙学常数。在宇宙总能量守恒的补充假设下，导出了哈勃参数的基本方程，它是引力耦合和宇宙学项为常数时的演化方程的推广。在假设宇宙学常数与哈勃参数的平方成正比，体粘滞系数、温度和弛豫时间与宇宙流体的能量密度呈幂律关系的条件下，得到了场方程的两类精确解.在第一类解中，宇宙在暴胀时代结束，而在第二类解中，宇宙的膨胀在任何时候都是非暴胀的。在这两个模型中，宇宙学常数是时间的递减函数，而引力常数在宇宙演化的早期阶段增加，在大的时间限制中趋于恒定值。
In the framework of 10-dimensional "Friedmann-Calabi-Yau" cosmology of superstring origin we show that the time variation of either Newton's gravitational constant or Yang-Mills one is unavoidable in the present epoch.
We study cosmological gravitational waves generated during inflation under the influence of a decaying cosmological "constant", in the Transverse-Traceless (TT) gauge. In our approach we consider a non-perturbative contribution of the dynamical cosmological "constant" to the tensor modes. As an application of the model we study the well-known cases $Λ(t)=σH^2$ and $Λ(t) =\vartheta H$. The spectrum of gravitational waves for the first case results scale invariant at the end of inflation, whereas for the second case scale invariance is not achieved, leaving this to new proposals of the form: $Λ(…
The gravitational lensing of gravitational waves might cause beat patterns detectable by interferometers. The feature of this kind of signal is the existence of the beat pattern in the early inspiral phase, followed by a seemingly randomly changing profile. After the strain peaks for the first time, the signal takes the usual waveform and the strain peaks for the second time. Once this signal is detected, the actual magnification factors can be obtained, so the true luminosity distance of the binary system is known. If the lens can be described by a point mass or a singular isothermal sphere, …
Causal Bulk Viscous LRS Bianchi I Models With Variable Gravitational and Cosmological "Constant"
本文研究了LRS Bianchi I各向异性宇宙学模型，采用全因果非平衡态热力学描述的体粘流体源时变$G$和$Λ$.我们得到了一个宇宙学常数作为时间的递减函数，对于$m, n > 0$，这个模型的宇宙学"常数“的值被发现是小的和积极的，这是支持的结果，从最近的超新星观测。
We deal with a dynamical mechanism in which a large cosmological constant, as suggested by inflationary scenarios, decays due to expansion of the universe. This mechanism has its origin in the gravitational coupling of the vacuum density. We assume that the vacuum couples anomalously to gravity that is the metric tensor that appears the gravitational part is not the same as that appears the matter part as suggested by weak equivalence principle. Instead, the two metric tensors are taken to be conformally related. We show that this provides a dynamical mechanism which works during expansion of …
Detecting the Cosmological Stochastic Background of Gravitational Waves with FastICA
我们证明了宇宙学早期产生的引力波的随机背景严格依赖于假设的引力理论。特别是函数f（R）的具体形式，其中R是Ricci标量，与引力波的演化和产生机制有关。使用神经网络算法，它只需要非高斯性质和输入信号的独立性，我们得出结论，为了检测CSB信号，像处女座的探测器的干涉灵敏度将得到改善。
In this paper, we show the equivalence between a classical static scalar field theory and the (closed) de Sitter cosmological model whose potential represents shape invariance property. Based on this equivalence, we calculate the one-loop quantum cosmological correction to the ground state energy of the kink-like solution in the (closed) de Sitter cosmological model in which the fluctuation potential $V^{\prime\prime}$ has a shape invariance property. It is shown that this type of correction, which yields a renormalized mass in the case of scalar field theory, may be {\it interpreted} as a ren…
A technique is given to derive the well known Bell-Szekeres solution of the Einstein-Maxwell vacuum field equations describing the space-time and the Maxwell field following the head-on collision of two homogeneous, plane, electromagnetic shock waves. The analogue of this technique is then utilized to construct the space-time model of the gravitational field following the head-on collision of two homogeneous, plane, gravitational shock waves. The latter collision, which is followed by a pair of impulsive gravitational waves and a pair of light like shells traveling away from each other, provid…
We present a space--time model of the collision of two homogeneous, plane impulsive gravitational waves (each having a delta function profile) propagating in a vacuum before collision and for which the post collision space--time has constant curvature. The profiles of the incoming waves are $k\,δ(u)$ and $l\,δ(v)$ where $k, l$ are real constants and $u=0, v=0$ are intersecting null hypersurfaces. The cosmological constant $Λ$ in the post collision region of the space--time is given by $Λ=-6\,k\,l$.
Instability of cosmological event horizons of nonstatic global cosmic strings II: perturbations of gravitational waves and massless scalar field
研究了一类非静态整体宇宙弦在引力波和无质量标量场扰动下的宇宙学事件视界的稳定性。结果表明，引力波的微扰总是使CEH变为非标量弱时空曲率奇点，而无质量标量场的微扰则使CEH变为非标量弱奇点或标量奇点.对试验无质量标量场的微扰也作了研究，发现它们并不总是给出正确的预言。
Inferring the cosmological constant in early Universe only by gravitational waves
本研究通过分析LISA探测到的原始黑洞双星引力波信号，利用费雪信息矩阵，证明可有效约束早期宇宙的宇宙学常数。
We present a method to calculate the gravitational energy when asymptotic boundary conditions for the space-time are not given. This is the situation for most of the cosmological models. The expression for the gravitational energy is obtained in the context of the teleparallel equivalent of general relativity. We apply our method first to the Schwarzschild-de Sitter solution of Einstein's equation, and then to the Robertson-Walker Universe. We show that in the first case our method leads to an average energy density of the vacuum space-time, and in latter case the energy vanishes in the case o…
A mathematical model is formulated for the evolution of plane perturbations in a cosmological two-component statistical system of completely degenerate scalarly charged fermions with an asymmetric scalar Higgs interaction. A complete closed system of differential equations describing the unperturbed state of a homogeneous and isotropic system and a system of self-consistent evolution equations of small perturbations are constructed.
Perturbations of rotating cosmological black holes
在存在宇宙学常数的情况下，研究了带电旋转黑洞引力方程的解。导出了一对控制电磁扰动和引力扰动的波动方程。
Remarks on (super-)accelerating cosmological models in general scalar-tensor gravity
我们考虑Friedmann-Lemaitre-Robertson-Walker宇宙学模型的框架内的一般标量张量理论的重力（STG）与任意耦合函数，设置在约旦框架。首先，我们描述了正压物质流体和标量场势在任意空间曲率（平坦、球面、双曲）下相空间的一般性质。然后，我们解决的问题，在何种条件下，时代的加速和超加速膨胀是可能的STG。对于充满尘埃物质（和零势）的平坦模型，我们给出了标量场的耦合函数的一个必要条件，该条件必须满足才允许加速和超加速。这是通过一个具体的例子来说明。
We propose a definition of mass for characteristic hypersurfaces in asymptotically vacuum space-times with non-vanishing cosmological constant $Λ\in {\mathbb R}^*$, generalising the definition of Trautman and Bondi for $Λ=0$. We show that our definition reduces to some standard definitions in several situations. We establish a balance formula linking the characteristic mass and a suitably defined renormalised volume of the null hypersurface, generalising the positivity identity of one of us (PTC) and Paetz proved when $Λ=0$.
Gravitational Perfect Fluid Collapse With Cosmological Constant
本文研究了正宇宙学常数对理想流体球对称坍缩的影响。在存在宇宙学常数的情况下，给出了静态外部时空与非静态内部时空的匹配条件。我们还研究了视视界及其物理意义。得出结论：宇宙学常数减缓了物质的坍缩，从而限制了黑洞的大小。这一分析将尘埃情况推广到理想流体。我们恢复了$p=0$的尘埃情况的结果。
Nonexpanding impulsive gravitational waves with an arbitrary cosmological constant
利用“剪切粘贴”方法构造了宇宙学常数非零背景中非膨胀脉冲波的精确解。这些解决方案是使用统一的方法，其中包括的情况下，德西特，反德西特和闵可夫斯基背景。度量以连续和分布的形式给出，这两种形式都与脉冲pp波的相应度量共形，并且可以明确地将其限制为$Λ\to 0$。
In this work we investigate the stochastic gravitational wave background generated during the f\/irst-order cosmological QCD phase transition of the early universe in the framework of the Barrow entropy. We f\/irst derived the Barrow corrections to the expression of stochastic gravitational wave background spectrum in presence of trace anomaly. Then, by taking account of Bubble wall collisions, sound waves and magnetohydrodynamic turbulence as the sources of stochastic gravitational wave, an analysis of the influence of Barrow entropy on the total energy density and the peak signal of stochast…
Gravitational waves in vacuum spacetimes with cosmological constant. I. Classification and geometrical properties of non-twisting type N solutions
总结了具有宇宙学常数λ的真空爱因斯坦场方程的所有无扭Petrov-type N解。它们要么属于非扩张的Kundt类，要么属于扩张的Robinson-Trautman类。每个类的不变子类的定义和相应的度量给出明确的合适的规范坐标。分析了子类与几何性质之间的关系。在随后的论文中，这些解被解释为在德西特或反德西特时空中传播的精确引力波。
Through averaging the Einstein equations over transverse gravitational perturbations it is obtained a closed system of two ordinary differential equations describing macroscopic cosmological evolution of the isotropic space-flat Universe filled with gravitational radiation. It is found an asymptotic solution of evolution equation for gravitational perturbation amplitude. Making the substitution of this solution into Einstein equation averaged over gravitational perturbations, the single evolution non-linear ordinary differential second-order equation relative to macroscopic scale factor is obt…
Gravitational waves during inflation in presence of a decaying cosmological parameter from a 5D vacuum theory of gravity
在黎曼平坦的5维几何背景下，研究了宇宙学参数衰减时暴胀时期产生的引力波。两个例子被认为是，一个恒定的宇宙学参数和第二个减少。
Cosmological Constant and Gravitational Repulsion Effect: 1. Homogeneous models with radiation
在Riemann-Cartan时空中最小二次庞加莱引力规范理论的框架内，我们研究了引力真空能量密度（一个宇宙学常数）对各种引力系统动力学的影响。结果表明，宇宙学项的引入会导致引力排斥。对于一些简单的辐射空间齐次宇宙模型，我们得到了初等函数和椭圆积分形式的非奇异解。
Gravitational waves have been directly detected and astronomical observations indicate that our Universe has a positive cosmological constant $Λ$. Nevertheless, a theoretical gauge-invariant notion of gravitational waves arriving at infinity (escaping from the space-time) in the presence of a positive $Λ$ has been elusive. We find the answer to this long-standing gravitational puzzle and present a geometric, gauge-invariant radiation condition at infinity.
Does Cosmological Term Influence Gravitational Lensing?
我们分析了在宇宙学项存在下星系或星系团对光的弯曲。转到Friedmann-Robertson-Walker坐标系，实际上用于描述实际观测，我们证明了宇宙学常数实际上不影响透镜效应。
Constraining the Cosmological Evolution of Post-Newtonian Parameters with Gravitational Wave Signals from Compact Binary Inspirals
本文利用致密双星旋近引力波的高精度观测，提出理论无关方法约束引力耦合参数的宇宙学时间演化，为修正引力研究提供新途径。
We briefly review the need to perform renormalization of inflationary perturbations to properly work out the physical power spectra. We also summarize the basis of (momentum-space) renormalization in curved spacetime and address several misconceptions found in recent literature on this subject.
Remarks on the Theory of Cosmological Perturbation
指出同步规范定义的功率谱不能直接用于计算宇宙学模型对宇宙大尺度结构的预言，而应直接用合适的规范不变功率谱或牛顿规范定义的功率谱来计算。
The issue of the gauge invariance of gravitational waves arises if they are produced in the early universe at second-order in perturbation theory. We address it by dividing the discussion about the gauge invariance in three parts: the production of gravitational waves, their propagation in the real universe, and their measurement.
Gravitational Collapse of Dust with a Cosmological Constant
Markovic和Shapiro最近关于宇宙学常数对球对称均匀尘埃球演化的影响的分析被推广到包括非均匀和简并的情况。通过有效势和Penrose-Carter图的方式显示的历史。
Given spherically symmetric characteristic initial data for the Einstein-scalar field system with a positive cosmological constant, we provide a criterion, in terms of the dimensionless size and dimensionless renormalized mass content of an annular region of the data, for the formation of a future trapped surface. This corresponds to an extension of Christodoulou's classical criterion by the inclusion of the cosmological term.
Positive Definite Gravitational Action, Cosmological Constant and Superstring Theory
利用最近发现的一阶爱因斯坦方程的普适性，提出了一个正定的欧几里德作用量。可能的影响量子引力被认为是。利用新作用量讨论了Hawking和Coleman关于宇宙学常数为零的方法，发现宇宙学常数可能为零.讨论了从超弦场论中获得这种作用的一种可能方案。
Gravitational wave standard sirens can be used to arbitrate the $H_0$ tension within the following several years. In the future, the observation of gravitational wave standard sirens would be developed into a powerful new cosmological probe because they can play an important role in breaking parameter degeneracies formed by other observations. Therefore, gravitational wave standard sirens are of great importance for the future accurate measurement of cosmological parameters.
Birefringence of light induced not by matter, but by the gradient of an electric field, has been predicted in 1955 and observed in 2008. Here we replace the electric field by the gravitional field of our expanding universe.
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