According to the nonuniqueness principle, the homogeneous scalar field Lagrangian can be expressed in various forms both standard and nonstandard ones. Therefore, the standard and all possible nonstandard Lagrangians can be linearly combined while the Klein-Gordon equation is still intact. This linear combination of Lagrangians is used to demonstrate that the energy density of homogeneous phantom field can possibly be bounded from below. The applications of this new Lagrangian in the nature of the ghost condensate and the equation of state with $w<-1$ are discussed.
Scale Factor Dependent Equations of State for Curvature Inspired Dark Energy, Phantom Barrier and Late Cosmic Acceleration
在这里，我们发现如果在Einstein-Hilbert拉氏量中加入标量曲率的非线性项，那么暗能量和暗物质将从引力扇区中产生。暗能量的状态方程，具有形式$p_{\rm de} = - ρ_{\rm de} + f(a) (with $ p_{\rm de}（ρ_{ \rm de}）$ being the pressure(density) for dark energy, $ f（a）$ being a function of scale feactor $ a（t）$ and $ t $ being the cosmic time) is explored. Interestingly, this equation of state leads to a phantom barrier $ {\rm w}_{ \rm de} = \rm MATHABMN/ρ_{ \rm de} =-1 $ at $ a = a_{\rm w} $. It is found that when $ a < a_{\rm w}，{ \rm w}_{\rm de} > - 1 $ and $ { \rm w}_{ \rm de} < - 1 $ for $ a >a_{\rm w}，$ showing a transition from non-phantom to phantom phas…
Spherical systems in models of nonlocally corrected gravity
在S。Deser和R.伍达德，物理修订信函663，111301（2007）和S. Capozziello等人，Phys. Lett. B 671，193（2009）。对于第一种情况，非局部原点的拉格朗日量表示具有两个无质量标量的标量-张量理论，发现了一个明确的条件，在该条件下，两个标量都是正则的（非幻影）。如果此条件不成立，则其中一个字段显示幻像行为。标量真空组态的行为方式，然后已知的标量张量理论。在第二种情况下，非局部原点的拉格朗日量表现为与Gauss-Bonnet（GB）不变量相互作用的标量场，并且包含任意的标量场势。结果发现，GB项，在一般情况下，导致违反著名的不去定理有效的最小耦合标量场在广义相对论。然而，它示出，一些感兴趣的配置仍然是禁止的，无论是标量场势和GB-标量耦合函数，即“无力”虫洞（这样g_{tt} =常数）和黑洞与高阶视界。
Simpson and Visser recently proposed a phenomenological way to avoid some kinds of space-time singularities by replacing a parameter whose zero value corresponds to a singularity (say, $r$) with the manifestly nonzero expression $r(u) = \sqrt{u^2 + b^2}$, where $u$ is a new coordinate, and $b =$ \const $>0$. This trick, generically leading to a regular minimum of $r$ beyond a black hole horizon (called a "black bounce"), may hopefully mimic some expected results of quantum gravity, and was previously applied to regularize the Schwarzschild, Reissner-Nordström, Kerr and some other metrics. In t…
In this work, we consider the full Horndeski Lagrangian applied to wormhole geometries and present the full gravitational field equations. We analyse the general constraints imposed by the flaring-out conditions at the wormhole throat and consider a plethora of specific subclasses of the Horndeski Lagrangian, namely, quintessence/phantom fields, $k$-essence, scalar-tensor theories, covariant galileons, nonminimal kinetic coupling, kinetic gravity braiding, and the scalar-tensor representation of Gauss-Bonnet couplings, amongst others. The generic constraints analysed in this work serve as a co…
Black Bounce Solutions from a Self-Interacting 3-Form Field in General Relativity
Institute of Astrophysics and Space Sciences, Faculty of Sciences, University of Lisbon（里斯本大学理学院天体物理与空间科学研究所）；Department of Physics, Faculty of Sciences, University of Lisbon（里斯本大学理学院物理学系）；Faculty of Physics, Graduate Program in Physics, Federal University of Pará（帕拉联邦大学物理学院物理研究生项目）；Faculty of Exact Sciences and Technology, Federal University of Pará（帕拉联邦大学精确科学与技术学院）
