اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدGravity with Explicit Diffeomorphism Breaking
64
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
Modified theories of gravity that explicitly break diffeomorphism invariance have been used for over a decade to explore open issues related to quantum gravity, dark energy, and dark matter. At the same time, the Standard-Model Extension (SME) has been widely used as a phenomenological framework in investigations of spacetime symmetry breaking. Until recently, it was thought that the SME was suitable only for theories with spontaneous spacetime symmetry breaking due to consistency conditions stemming from the Bianchi identities. However, it has recently been shown that, particularly with matter couplings included, the consistency conditions can also be satisfied in theories with explicit breaking. An overview of how this is achieved is presented, and two examples are examined. The first is massive gravity, which includes a nondynamical background tensor. The second is a model based on a low-energy limit of Hov rava gravity, where spacetime has a physically preferred foliation. In both cases, bounds on matter--gravity interactions that explicitly break diffeomorphisms are obtained using the SME.
قيم البحث
اقرأ أيضاً
We construct a Weyl transverse diffeomorphism invariant theory of symmetric teleparallel gravity by employing the Weyl compensator formalism. The low-energy dynamics has a single spin two gravition without a scalar degree of freedom. By construction,
it is equivalent to the unimodular gravity (as well as the Einstein gravity) at the non-linear level.
We present, in an explicit form, the metric for all spherically symmetric Schwarzschild-Bach black holes in Einstein-Weyl theory. In addition to the black hole mass, this complete family of spacetimes involves a parameter that encodes the value of th
e Bach tensor on the horizon. When this additional non-Schwarzschild parameter is set to zero the Bach tensor vanishes everywhere and the Schwa-Bach solution reduces to the standard Schwarzschild metric of general relativity. Compared with previous studies, which were mainly based on numerical integration of a complicated form of field equations, the new form of the metric enables us to easily investigate geometrical and physical properties of these black holes, such as specific tidal effects on test particles, caused by the presence of the Bach tensor, as well as fundamental thermodynamical quantities.
Lorentz and diffeomorphism violations are studied in linearized gravity using effective field theory. A classification of all gauge-invariant and gauge-violating terms is given. The exact covariant dispersion relation for gravitational modes involvin
g operators of arbitrary mass dimension is constructed, and various special limits are discussed.
We present a detailed study of the spherically symmetric solutions in Lorentz breaking massive gravity. There is an undetermined function $mathcal{F}(X, w_1, w_2, w_3)$ in the action of St{u}ckelberg fields $S_{phi}=Lambda^4int{d^4xsqrt{-g}mathcal{F}
}$, which should be resolved through physical means. In the general relativity, the spherically symmetric solution to the Einstein equation is a benchmark and its massive deformation also play a crucial role in Lorentz breaking massive gravity. $mathcal{F}$ will satisfy the constraint equation $T_0^1=0$ from the spherically symmetric Einstein tensor $G_0^1=0$, if we maintain that any reasonable physical theory should possess the spherically symmetric solutions. The St{u}ckelberg field $phi^i$ is taken as a hedgehog configuration $phi^i=phi(r)x^i/r$, whose stability is guaranteed by the topological one. Under this ans{a}tz, $T_0^1=0$ is reduced to $dmathcal{F}=0$. The functions $mathcal{F}$ for $dmathcal{F}=0$ form a commutative ring $R^{mathcal{F}}$. We obtain a general expression of solution to the functional differential equation with spherically symmetry if $mathcal{F}in R^{mathcal{F}}$. If $mathcal{F}in R^{mathcal{F}}$ and $partialmathcal{F}/partial X=0$, the functions $mathcal{F}$ form a subring $S^{mathcal{F}}subset R^{mathcal{F}}$. We show that the metric is Schwarzschild, AdS or dS if $mathcal{F}in S^{mathcal{F}}$. When $mathcal{F}in R^{mathcal{F}}$ but $mathcal{F} otin S^{mathcal{F}}$, we will obtain some new metric solutions. Using the general formula and the basic property of function ring $R^{mathcal{F}}$, we give some analytical examples and their phenomenological applications. Furthermore, we also discuss the stability of gravitational field by the analysis of Komar integral and the results of QNMs.
The Randall-Sundrum scenario, with a 1+3-dimensional brane in a 5-dimensional bulk spacetime, can be generalized in various ways. We consider the case where the Z2-symmetry at the brane is relaxed, and in addition the gravitational action is generali
zed to include an induced gravity term on the brane. We derive the complete set of equations governing the gravitational dynamics for a general brane and bulk, and identify how the asymmetry and the induced gravity act as effective source terms in the projected field equations on the brane. For a Friedmann brane in an anti de Sitter bulk, the solution of the Friedmann equation is given by the solution of a quartic equation. We find the perturbative solutions for small asymmetry, which has an effect at late times.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
