Regular black holes with improved energy conditions and their analogues in fluids

On the premise of the importance of energy conditions for regular black holes, we propose a method to remedy those models that break the dominant energy condition, e.g., the Bardeen and Hayward black holes. We modify the metrics but ensure their regularity at the same time, so that the weak, null, and dominant energy conditions are satisfied, with the exception of the strong energy condition. Likewise, we prove a no-go theorem for conformally related regular black holes, which states that the four energy conditions can never be met in this class of black holes. In order to seek evidences for distinguishing regular black holes from singular black holes, we resort to analogue gravity and regard it as a tool to mimic realistic regular black holes in a fluid. The equations of state for the fluid are solved via an asymptotic analysis associated with a numerical method, which provides a modus operandi for experimental observations, in particular, the conditions under which one can simulate realistic regular black holes in the fluid.     

A simple expression for the ADM mass

We show by an almost elementary calculation that the ADM mass of an asymptotically flat space can be computed as a limit involving a rate of change of area of a closed 2-surface. The result is essentially the same as that given by David Brown and York (Phys. Rev. D 55, 1977–1984 1997; Phys. Rev. D 47, 1407–1419 1993). We will prove this result in two ways, first by direct calculation from the original formula as given by Arnowitt, Deser and Misner and second as a corollary of an earlier result by Brewin for the case of simplicial spaces.     

零势场中变质量粒子的束缚能谱

结合点正则变换(PCT)与分析转移矩阵(ATM)两种方法,得到了零势场中变质量粒子的束缚能谱.通过计算变质量粒子穿透零势场的概率,发现并解释了透射谱中共振峰与本征能量的一一对应关系.     

The null energy condition in wormholes with cosmological constant

Dynamic and static wormhole solutions of Einsteins equations with the cosmological constant are presented. The dynamic solutions can be interpreted as Friedmann–Robertson–Walker models with traversable wormholes. The null energy condition is checked for both dynamic and static wormholes and it is shown explicitly that the cosmological constant modifies the violation of this condition.     

ADM Mass for Asymptotically de Sitter Space-Time

In this paper, an ADM mass formula for asymptotically de Sitter（dS） space-time is derived from the energy-momentum tensor. We take the vacuum dS space as the background and investigate the ADM mass of the （d ＋ 3）-dimensional sphere-symmetric space with a positive cosmological constant, and find that the ADM mass of asymptotically dS space is based on the ADM mass of Schwarzschild field and the cosmological background brings some small mass contribution as well.     

Effect of vacuum energy on evolution of primordial black holes in Einstein gravity

We study the evolution of primordial black holes by considering present universe is no more matter dominated rather vacuum energy dominated. We also consider the accretion of radiation, matter and vacuum energy during respective dominance period. In this scenario, we found that radiation accretion efficiency should be less than 0.366 and accretion rate is much larger than previous analysis by Nayak et al. (2009) [1]. Thus here primordial black holes live longer than previous works Nayak and Singh (2011) [1]. Again matter accretion slightly increases the mass and lifetime of primordial black holes. However, the vacuum energy accretion is slightly complicated one, where accretion is possible only up to a critical time. If a primordial black hole lives beyond critical time, then its? lifespan increases due to vacuum energy accretion. But for presently evaporating primordial black holes, critical time comes much later than their evaporating time and thus vacuum energy could not affect those primordial black holes.     

On the possibility to determine neutrino mass hierarchy via supernova neutrinos with short-time characteristics

In this paper, we investigate whether it is possible to determine the neutrino mass hierarchy via a high-statistics and real-time observation of supernova neutrinos with short-time characteristics. The essential idea is to utilize distinct times-of-flight for different neutrino mass eigenstates from a core-collapse supernova to the Earth, which may significantly change the time distribution of neutrino events in the future huge water-Cherenkov and liquid-scintillator detectors. For illustration, we consider two different scenarios. The first case is the neutronization burst of emitted in the first tens of milliseconds of a core-collapse supernova, while the second case is the black hole formation during the accretion phase for which neutrino signals are expected to be abruptly terminated. In the latter scenario, it turns out only when the supernova is at a distance of a few Mpc and the fiducial mass of the detector is at the level of gigaton, might we be able to discriminate between normal and inverted neutrino mass hierarchies. In the former scenario, the probability for such a discrimination is even less due to a poor statistics.     

Quantifying energy condition violations in traversable wormholes

The ‘theoretical’ existence of traversable Lorentzian wormholes in the classical, macroscopic world is plagued by the violation of the well-known energy conditions of general relativity. In this brief article we show: (i) how the extent of violation can be quantified using certain volume integrals and (ii) whether this ‘amount of violation’ can be minimised for some specific cut-and-paste geometric constructions. Examples and possibilities are also outlined.     

经典Kerr黑洞和量子Kerr黑洞系统的微正则系综理论描述与统计“自举”条件

分别从Kerr黑洞的经典谱和量子谱出发，建立了一个居于微正则系综理论描述的系统态密度 的不等式，并由此证明了Kerr黑洞满足统计“自举(bootstrap)”条件.其主要结论是对于由 大量Kerr黑洞组成的体系，在高能极限下，最可能的构型是一个黑洞将获得系统所有的质量 和全部的角动量，而且转动不会破坏黑洞的“自举”性质. 关键词： Kerr黑洞 统计“自举”问题     

Hawking radiation via tunnelling from black holes with topological defects

In this paper, we extend Parikh's recent work to two kinds of the black holes whose ADM mass is no longer identical to its mass parameter, each with a topological defect, one being a global monopole black hole and another a cosmic string black hole. We view Hawking radiation as a tunnelling process across the event horizon and calculate the tunnelling probability. From the tunnelling probability we also find a leading correction to the semiclassical emission rate. The results are consistent with an underlying unitary theory.     

Rotating charged black holes in Einstein-Born-Infeld theories and their ADM mass

In this work, the solution of the Einstein equations for a slowly rotating black hole with Born-Infeld charge is obtained. Geometrical properties and horizons of this solution are analyzed. The conditions when the ADM mass (as in the nonlinear static cases) and the ADM angular momentum of the system have been modified by the non linear electromagnetic field of the black hole, are considered.     

Exploring neutrino mass and mass hierarchy in interacting dark energy models

We investigate how the dark energy properties impact the constraints on the total neutrino mass in interacting dark energy(IDE)models. In this study, we focus on two typical interacting dynamical dark energy models, i.e., the interacting w cold dark matter(IwCDM) model and the interacting holographic dark energy(IHDE) model. To avoid the large-scale instability problem in IDE models, we apply the parameterized post-Friedmann approach to calculate the perturbation of dark energy. We employ the Planck 2015 cosmic microwave background temperature and polarization data, combined with low-redshift measurements on baryon acoustic oscillation distance scales, type Ia supernovae, and the Hubble constant, to constrain the cosmological parameters. We find that the dark energy properties could influence the constraint limits on the total neutrino mass. Once dynamical dark energy is considered in the IDE models, the upper bounds of ∑mν will be changed. By considering the values of χ^2min , we find that in these IDE models the normal hierarchy case is slightly preferred over the inverted hierarchy case;for example, △χ^2= 2.720 is given in the IHDE+∑mν model. In addition, we also find that in the Iw CDM+∑mν model β = 0 is consistent with current observational data inside the 1σ range, and in the IHDE+∑mν model β > 0 is favored at more than 2σ level.     

Thermodynamics of noncommutative geometry inspired black holes based on Maxwell-Boltzmann smeared mass distribution

In order to further explore the effects of non-Gaussian smeared mass distribution on the thermodynamical properties of noncommutative black holes, we consider noncommutative black holes based on Maxwell-Boltzmann smeared mass distribution in (2+1)-dimensional spacetime. The thermodynamical properties of the black holes are investigated, including Hawking temperature, heat capacity, entropy and free energy. We find that multiple black holes with the same temperature do not exist, while there exists a possible decay of the noncommutative black hole based on Maxwell-Boltzmann smeared mass distribution into the rotating (commutative) BTZ black hole.     

Quasi-topological electromagnetism:Dark energy,dyonic black holes,stable photon spheres and hidden electromagnetic duality

We introduce the quasi-topological electromagnetism which is defined to be the squared norm of the topological 4-form F ∧ F. A salient property is that its energy-momentum tensor is of the isotropic perfect fluid with the pressure being precisely the opposite to its energy density. It can thus provide a model for dark energy. We study its application in both black hole physics and cosmology.The quasi-topological term has no effect on the purely electric or magnetic Reissner-Nordstr o¨m black holes, the dyonic solution is however completely modified. We find that the dyonic black holes can have four real horizons. For suitable parameters, the black hole can admit as many as three photon spheres, with one being stable. Another intriguing property is that although the quasitopological term breaks the electromagnetic duality, the symmetry emerges in the on-shell action in the Wheeler-De Witt patch. In cosmology, we demonstrate that the quasi-topological term alone is equivalent to a cosmological constant, but the model provides a mechanism for the dark energy to couple with other types of matter. We present a concrete example of the quasi-topological electromagnetism coupled to a scalar field that admits the standard FLRW cosmological solutions.     

磁场对黑洞吸积盘的能量提取及其天体物理应用

考虑到螺旋不稳定性的影响, 提出了一种黑洞磁层的新磁场位形(NCMF). 其中涉及到磁场提取能量的三种机制: (1) Blandford-Znajek (BZ)过程; (2)磁耦合(MC)过程; (3) 通过开磁力线联系吸积盘和天体物理负载,并提取吸积盘的旋转能量新机制(文中称为DL过程). 利用两类等效电路导出上述三种提能机制的功率和力矩的表达式. 结果表明,在新磁场位形中提能功率和效率比未考虑螺旋不稳定性的磁场位形有所增大,新磁场位形导出的非常陡的发射率指数可以拟合XMM-Newton天文卫星对邻近的明亮的Seyfert 1星系MCG-6-30-15的观测结果.     

Dark energy versus modified gravity: Impacts on measuring neutrino mass

In this paper,we make a comparison for the impacts of smooth dynamical dark energy,modified gravity,and interacting dark energy on the cosmological constraints on the total mass of active neutrinos.For definiteness,we consider theΛCDM model,the w CDM model,the f(R)model,and two typical interacting vacuum energy models,i.e.,the IΛCDM1 model with Q=βHρc and the IΛCDM2 model with Q=βHρΛ.In the cosmological fits,we use the Planck 2015 temperature and polarization data,in combination with other low-redshift observations including the baryon acoustic oscillations,the type Ia supernovae,the Hubble constant measurement,and the large-scale structure observations,such as the weak lensing as well as the redshift-space distortions.Besides,the Planck lensing measurement is also employed in this work.We find that,the w CDM model favors a higher upper limit on the neutrino mass compared to theΛCDM model,while the upper limit in the f(R)model is similar with that in theΛCDM model.For the interacting vacuum energy models,the IΛCDM1 model favors a higher upper limit on neutrino mass,while the IΛCDM2 model favors an identical neutrino mass with the case ofΛCDM.     

球对称动态黑洞视界附近的瞬时辐射能通量及瞬时辐射功率

采用黑洞的薄膜模型和局域热平衡的假定,研究球对称动态黑洞视界附近的瞬时辐射能通量和瞬时辐射功率,得到了当截断距离η取定后,Vaidya黑洞视界附近标量场的瞬时辐射能通量与黑洞的质量和视界变化率有关,其瞬时辐射功率仅与黑洞的视界变化率有关.Vaidya-Bonner黑洞的瞬时辐射能通量和瞬时辐射功率与黑洞的质量、电荷和视界变化率有关.表明黑洞周围的引力场、电磁场以及视界的变化均对黑洞的热辐射产生影响.     

Remarks on binding energy of fermions in Newtonian gravity

The clarifications made regarding the binding energy in connection with a model for the internal structure of black holes are shown to be incorrect.     

Impacts of dark energy on constraining neutrino mass after Planck 2018

Considering the mass splittings of three active neutrinos, we investigate how the properties of dark energy affect the cosmological constraints on the total neutrino mass $\sum {m}_{\nu }$ using the latest cosmological observations. In this paper, several typical dark energy models, including ΛCDM, wCDM, CPL, and HDE models, are discussed. In the analysis, we also consider the effects from the neutrino mass hierarchies, i.e. the degenerate hierarchy (DH), the normal hierarchy (NH), and the inverted hierarchy (IH). We employ the current cosmological observations to do the analysis, including the Planck 2018 temperature and polarization power spectra, the baryon acoustic oscillations (BAO), the type Ia supernovae (SNe), and the Hubble constant H₀ measurement. In the ΛCDM+$\sum {m}_{\nu }$ model, we obtain the upper limits of the neutrino mass $\sum {m}_{\nu }\lt 0.123\,\mathrm{eV}$ (DH), $\sum {m}_{\nu }\lt 0.156\,\mathrm{eV}$ (NH), and $\sum {m}_{\nu }\lt 0.185\,\mathrm{eV}$ (IH) at the 95% C.L., using the Planck+BAO+SNe data combination. For the wCDM+$\sum {m}_{\nu }$ model and the CPL+$\sum {m}_{\nu }$ model, larger upper limits of $\sum {m}_{\nu }$ are obtained compared to those of the ΛCDM+$\sum {m}_{\nu }$ model. The most stringent constraint on the neutrino mass, $\sum {m}_{\nu }\lt 0.080\,\mathrm{eV}$ (DH), is derived in the HDE+$\sum {m}_{\nu }$ model. In addition, we find that the inclusion of the local measurement of the Hubble constant in the data combination leads to tighter constraints on the total neutrino mass in all these dark energy models.     

Exploring neutrino mass and mass hierarchy in the scenario of vacuum energy interacting with cold dark matter

We investigate the constraints on total neutrino mass in the scenario of vacuum energy interacting with cold dark matter. We focus on two typical interaction forms, i.e., Q=βHρ_c and Q=βHρ_∧. To avoid the occurrence of large-scale instability in interacting dark energy cosmology, we adopt the parameterized post-Friedmann approach to calculate the perturbation evolution of dark energy. We employ observational data, including the Planck cosmic microwave background temperature and polarization data, baryon acoustic oscillation data, a JLA sample of type Ia supernovae observation, direct measurement of the Hubble constant, and redshift space distortion data. We find that, compared with those in the ∧CDM model, much looser constraints on ∑m_ν are obtained in the Q=βHρ_c model, whereas slightly tighter constraints are obtained in the Q=βHρ_∧ model. Consideration of the possible mass hierarchies of neutrinos reveals that the smallest upper limit of ∑m_ν appears in the degenerate hierarchy case. By comparing the values of χ_min², we find that the normal hierarchy case is favored over the inverted one. In particular, we find that the difference △χ_min² ≡ χ_{IH; min}²-χ_{NH; min}² > 2 in the Q=βHρ_c model. In addition, we find that β=0 is consistent with the current observations in the Q=βHρ_c model, and β < 0 is favored at more than the 1σ level in the Q=βHρ_∧ model.