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Zhong Chao Wu

Publications and source records attributed to Zhong Chao Wu.

At least 19 recordsLinked to original sources
arXiv2017

How is a Black Hole Created from Nothing?

Using the synchronous coordinates, the creation of a Schwarzschild black hole immersed in a de Sitter spacetime can be viewed as a coherent creation of a collection of timelike geodesics. The previously supposed conical singularities do not exist at the horizons of the constrained instan- ton. Instead, the unavoidable irregularity is presented as a non-vanishing second fundamental form elsewhere at the quantum transition 3-surface. The same arguments can be applied to charged, topological or higher dimensional black hole cases.

gr-qc↗
arXiv2014

Quantization of (1+1)-dimensional Hořava-Lifshitz theory of gravity

In this paper, we study the quantization of the (1+1)-dimensional projectable Hořava-Lifshitz (HL) gravity, and find that, when only gravity is present, the system can be quantized by following the canonical Dirac quantization, and the corresponding wavefunction is normalizable for some orderings of the operators. The corresponding Hamilton can also be written in terms of a simple harmonic oscillator, whereby the quantization can be carried out quantum mechanically in the standard way. When the HL gravity minimally couples to a scalar field, the momentum constraint is solved explicitly in the case where the fundamental variables are functions of time only. In this case, the coupled system can also be quantized by following the Dirac process, and the corresponding wavefunction is also normalizable for some particular orderings of the operators. The Hamilton can be also written in terms of two interacting harmonic oscillators. But, when the interaction is turned off, one of the harmonic oscillators has positive energy, while the other has negative energy. A remarkable feature is that orderings of the operators from a classical Hamilton to a quantum mechanical one play a fundamental role in order for the Wheeler-DeWitt equation to have nontrivial solutions. In addition, the space-time is well quantized, even when it is classically singular.

hep-th↗
arXiv2010

Spacetime Singularities in String and its Low Dimensional Effective Theory

Spacetime singularities are studied in both the $D+d$-dimensional string theory and its $D$-dimensional effective theory, obtained by the Kaluza-Klein compactification. It is found that spacetime singularities in the low dimensional effective theory may or may not remain after lifted to the $D+d$-dimensional string theory, depending on particular solutions. It is also found that there exist cases in which spacetime singularities appearing in high/low dimensional spacetimes do not necessarily happen on the same surfaces.

hep-th↗
arXiv2009

Commutativity of Substitution and Variation in Actions of Quantum Field Theory

There exists a paradox in quantum field theory: substituting a field configuration which solves a subset of the field equations into the action and varying it is not necessarily equivalent to substituting that configuration into the remaining field equations. We take the $S^4$ and Freund-Rubin-like instantons as two examples to clarify the paradox. One must match the specialized configuration field variables with the corresponding boundary conditions by adding appropriate Legendre terms to the action. Some comments are made regarding exceptional degenerate cases.

hep-th↗
arXiv2009

Inverse Temperature 4-vector in Special Relativity

There exist several prescriptions for identifying the notion of temperature in special relativity. We argue that the inverse temperature 4-vector $\bf β$ is the only viable option from the laws of thermodynamics, and $\bf β$ is a future-directed timelike 4-vector. Using a superfluidity thought experiment, one can show that $\bf β$ is not necessarily along the time direction of the comoving frame of the system, as is usually thought. It is conjectured that, for an isolated system, the 4-vector is determined from the entropy-maximum principle.

gr-qc↗
arXiv2009

Colliding branes and formation of spacetime singularities in string theory

Colliding branes without $Z_{2}$ symmetry and the formation of spacetime singularities in string theory are studied. After developing the general formulas to describe such events, we study a particular class of exact solutions first in the 5-dimensional effective theory, and then lift it to the 10-dimensional spacetime. In general, the 5-dimensional spacetime is singular, due to the mutual focus of the two colliding 3-branes. Non-singular cases also exist, but with the price that both of the colliding branes violate all the three energy conditions, weak, dominant, and strong. After lifted to 10 dimensions, we find that the spacetime remains singular, whenever it is singular in the 5-dimensional effective theory. In the cases where no singularities are formed after the collision, we find that the two 8-branes necessarily violate all the energy conditions.

hep-th↗
arXiv2008

A Proposal of Testing Imaginary Time in a Total Reflection

All paradoxes concerning faster-than-light signal propagation reported in recent experiments can be dispelled by using imaginary time in a quantum framework. I present a proposal of testing imaginary time in a total reflection.

quant-ph↗
arXiv2008

The Imaginary Time in the Tunneling Process

By using techniques developed in quantum cosmology, it is found that a tunneling particle spends purely imaginary time on a barrier region. The {\it imaginary} time is associated with the stochastic acausal behaviour of a state, while the {\it real} time is associated with the deterministic causal evolution of a state. For the tunneling case the nonzero imaginary time is associated with the transmission rate of the tunneling process, which is related to the thickness of the barrier. The physical meaning of the zero real time is that the particle instantly jumps from one side of the barrier to the other regardless of the thickness. This leads to the illusion that tunneling particles could actually travel faster than light. The results of recent experiments in quantum optics concerning tunneling time can be thought of as the first experimental confirmation of the existence of imaginary time. Relativity is not violated.

quant-ph↗
arXiv2005

Creation of Kerr-de Sitter Black Hole in All Dimensions

We discuss the quantum creation scenario of a Kerr-de Sitter black hole in all dimensions. We show that its relative creation probability is the exponential to the entropy of the black hole, using a topological argument. The action of the regular Euclidean instanton can be calculated in the same way.

gr-qc↗
arXiv2005

No-boundary Codimension-two Braneworld

The quantum creation probability and entropy of a 2-codimensional braneworld are calculated in the framework of no-boundary universe. The entropy can take an arbitrarily large value as the brane tensions increase, in violation of the conjectured "N-bound" in quantum gravity, even for a 4-dimensional ordinary universe.

hep-th↗
arXiv2004

Self-Similar Collapse of Scalar Field with Plane Symmetry

Plane symmetric self-similar solutions to Einstein's four-dimensional theory of gravity are studied and all such solutions are given analytically in closed form. The local and global properties of these solutions are investigated and it is shown that some of the solutions can be interpreted as representing gravitational collapse of the scalar field. During the collapse, trapped surfaces are never developed. As a result, no black hole is formed. Although the collapse always ends with spacetime singularities, it is found that these singularities are spacelike and not naked.

gr-qc↗
arXiv2004

Dimensionality in the Freund-Rubin Cosmology

In the $n-$dimensional Freund-Rubin model with an antisymmetric tensor field of rank $s-1$, the dimension of the external spacetime we live in must be $min(s, n-s)$. This result is a generalization of the previous result in the $d=11$ supergravity case, where $s = 4$.

hep-th↗
arXiv2001

Quantum Kaluza-Klein Cosmologies (V)

In the No-boundary Universe with $d=11$ supergravity, under the $S_n \times S_{11-n}$ Kaluza-Klein ansatz, the only seed instanton for the universe creation is a $S_7 \times S_4$ space. It is proven that for the Freund-Rubin, Englert and Awada-Duff-Pope models the macroscopic universe in which we are living must be 4- instead of 7-dimensional without appealing to the anthropic principle.

hep-th↗
arXiv2000

The Topological Origin of Black Hole Entropy

In gravitational thermodynamics, the origin of a black hole's entropy is the topology of its instanton or constrained instanton. We prove that the entropy of an arbitrary nonrotating black hole is one quarter the sum of the products of the Euler characteristics of its horizons with their respective areas. The Gauss-Bonnet-like form of the action is not only crucial for the evaluation, but also for the existence of the entropy. This result covers all previous results on the entropy of a nonrotating black hole with a regular instanton. The argument can be readily extended into the lower or higher dimensional model. The problem of quantum creation of such a black hole is completely resolved.

gr-qc↗
arXiv1999

Can Black Hole be Created at the Birth of the Universe?

We study the quantum creation of black hole pairs in the (anti-)de Sitter space background. These black hole pairs in the Kerr-Newman family are created from constrained instantons. At the $WKB$ level, for the chargeless and nonrotating case, the relative creation probability is the exponential of (the negative of) the entropy of the universe. Also for the remaining cases of the family, the creation probability is the exponential of (the negative of) one quarter of the sum of the inner and outer black hole horizon areas. In the absence of a general no-boundary proposal for open universes, we treat the creations of the closed and the open universes in the same way.

gr-qc↗
arXiv1999

Entropy of a Black Hole with Distinct Surface Gravities

In gravitational thermodynamics, the entropy of a black hole with distinct surface gravities can be evaluated in a microcanonical ensemble. At the $WKB$ level, the entropy becomes the negative of the Euclidean action of the constrained instanton, which is the seed for the black hole creation in the no-boundary universe. Using the Gauss-Bonnet theorem, we prove the quite universal formula in Euclidean quantum gravity that the entropy of a nonrotating black hole is one quarter the sum of the products of the Euler characteristics and the areas of the horizons. For Lovelock gravity, the entropy and quantum creation of a black hole are also studied.

gr-qc↗