Nonexistence of quantum black and white hole horizons in an improved dynamic approach

In this paper,we study the quantum geometric effects near the locations where classical black hole horizons used to appear in Einstein's classical theory,within the framework of an improved dynamic approach,in which the internal region of a black hole is modeled by the Kantowski-Sachs(KS)spacetime and the two polymerization parameters are functions of the phase space variables.Our detailed analysis shows that the effects are so strong that black and white hole horizons of the effective quantum theory do not exist at all and instead are replaced by transition surfaces,across which the metric coefficients and their inverses are smooth and remain finite,as are the corresponding curvatures,including the Kretschmann scalar.These surfaces always separate trapped regions from anti-trapped regions.The number of such surfaces is infinite,so the corresponding KS spacetimes become geodesically complete,and no black and white hole-like structures exist in this scheme.

On the improved dynamics approach in loop quantum black holes

In this paper,we consider the B?hmer–Vandersloot(BV)model of loop quantum black holes obtained from the improved dynamics approach.We adopt the Saini–Singh gauge,in which it was found analytically that the BV spacetime is geodesically complete.We show that black/white hole horizons do not exist in this geodesically complete spacetime.Instead,there exists only an infinite number of transition surfaces,which always separate trapped regions from anti-trapped ones.Comments on the improved dynamics approach adopted in other models of loop quantum black holes are also given.

Scalar induced gravitational waves in light of Pulsar Timing Array data

The power-law parametrization for the energy density spectrum of gravitational wave(GW)background is a useful tool to study its physics and origin.While scalar induced secondary gravitational waves(SIGWs)from some particular models fit the signal detected by NANOGrav,Parkers Pulsar Timing Array,European Pulsar Timing Array,and Chinese Pulsar Timing Array collaborations better than GWs from supermassive black hole binaries(SMBHBs),we test the consistency of the data with the infrared part of SIGWs which is somewhat independent of models.Through Bayesian analysis,we show that the infrared parts of SIGWs fit the data better than GW background from SMBHBs.The results give tentative evidence for SIGWs.

引引力波偏振

引力波的直接观测不但开启了一扇探测引力本质的全新窗口,而且使我们进入了多信使引力波天文学时代.引力波不影响单个检验粒子的测地线运动,其偏振态由两个相邻检验粒子的相对运动,即测地线偏离运动所决定.测地线偏离方程中只出现黎曼张量的电分量,它有6个独立分量,所以在最一般的度规引力理论中,引力波最多可以有6种偏振模式.这6种偏振模式分别为:"+"偏振态、"×"偏振态、呼吸偏振态、矢量-x偏振态、矢量-y偏振态及纵振态.爱因斯坦广义相对论中的引力波只有"+"与"×"两个张量偏振态,Brans-Dicke理论中的引力波除了"+"与"×"偏振态外,还有一个呼吸偏振态.在Horndeski及f(R)理论中,引力波除了"+"与"×"两个张量偏振态外,还有一个由呼吸模与纵振模混合而成的标量偏振态.在爱因斯坦-以太理论中,非零矢量场的出现破坏了局域洛伦兹对称性,该理论中的引力波以非光速传播,且具有5个独立偏振态.张量-矢量-标量理论中的引力波传播速度与光速不同,且该理论中的引力波具有6个独立偏振态.因为不同引力理论中的引力波偏振态不同,所以引力波偏振态的测量可用于探究引力本质.

The upper bound on the tensor-to-scalar ratio consistent with quantum gravity

We consider the polynomial inflation with the tensor-to-scalar ratio as large as possible which can be consistent with the quantum gravity(QG) corrections and effective field theory(EFT). To get a minimal field excursion ΔΦ for enough e-folding number N, the inflaton field traverses an extremely flat part of the scalar potential, which results in the Lyth bound to be violated. We get a CMB signal consistent with Planck data by numerically computing the equation of motion for inflaton Φ and using Mukhanov–Sasaki formalism for primordial spectrum. Inflation ends at Hubble slow-roll parameter ε_(1)^(H)=1 or a=0. Interestingly, we find an excellent practical bound on the inflaton excursion in the format a+b√r, where a is a tiny real number and b is at the order 1. To be consistent with QG/EFT and suppress the high-dimensional operators, we show that the concrete condition on inflaton excursion is M_(PI)/△_(Ф)<0.2×√10≈0.632. For n_(s)= 0.9649,N_(e)= 55, and M_(PI)/△_(Ф)<0.632 MPl, we predict that the tensor-to-scalar ratio is smaller than 0.0012 for such polynomial inflation to be consistent with QG/EFT.

Thermodynamics of general scalar-tensor theory with non-minimally derivative coupling

With the usual definitions for the entropy and the temperature associated with the apparent horizon, we discuss the first law of the thermodynamics on the apparent in the general scalar-tensor theory of gravity with the kinetic term of the scalar field nonminimally coupling to Einstein tensor. We show the equivalence between the first law of thermodynamics on the apparent horizon and Friedmann equation for the general models, by using a mass-like function which is equal to the Misner-Sharp mass on the apparent horizon. The results further support the universal relationship between the first law of thermodynamics and Friedmann equation.