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Yen Chin Ong

Publications and source records attributed to Yen Chin Ong.

At least 73 records · Page 4Linked to original sources
arXiv2019

Charged Particle Production Rate from Cosmic Censorship in Dilaton Black Hole Spacetimes

Hiscock and Weems showed that under Hawking evaporation, an isolated asymptotically flat Reissner-Nordstrom (RN) black hole evolves in a surprising manner: if it starts with a relatively small value of charge-to-mass ratio Q/M, then said value will temporarily increase along its evolutionary path, before finally decreases towards zero. This contrasts with highly charged ones that simply radiate away its charge steadily. The combination of these two effects is the cosmic censor at work: there exists an attractor that flows towards the Schwazschild limit, which ensures that extremality -- and hence naked singularity -- can never be reached under Hawking evaporation. We apply the scheme of Hiscock and Weems to model the evaporation of an asymptotically flat dilatonic charge black hole known as the Garfinkle-Horowitz-Strominger (GHS) black hole. We found that upholding the cosmic censorship requires us to modify the charged particle production rate, which remarkably agrees with the expression obtained independently via direct computation of charged particle production rate on curved spacetime background. This not only strengthens the case for cosmic censorship, but also provides an example in which cosmic censorship can be a useful principle to deduce other physics. We also found that the attractor behavior is not necessarily related to the specific heat, contrary to the claim by Hiscock and Weems.

gr-qc↗
arXiv2019

The Charge of Electron, Weak Gravity Conjecture and Black Hole Evolution

The charge of an electron is vastly larger than its mass. We found that black hole evolution under Hawking evaporation is very sensitive to the value of electron charge. If the electron charge is weakened by a mere one order of magnitude, then the evolutionary paths of Reissner-Nordström black holes under Hawking evaporation change substantially. In particular, weakening the electron charge causes some black holes that would otherwise immediately discharge towards Schwarzschild limit to first evolve towards extremality before turning around. We discuss the possible connections between the weak gravity conjecture, the cosmic censorship conjecture, and black hole evolution.

gr-qc↗
arXiv2019

The Attractor of Evaporating Reissner-Nordström Black Holes

Hiscock and Weems showed that there is an attractor behavior in the evolution of asymptotically flat Reissner-Nordström black hole under Hawking evaporation. If the initial charge-to-mass ratio $Q/M$ of the black hole is relatively small, then the ratio first increases until the black hole hits the attractor, and then starts to discharge towards the Schwarzschild limit. Sufficiently charged black holes, on the other hand, simply discharge steadily towards the Schwarzschild limit. In this work we further investigate the nature of the attractor, and found that it is characterized by the mass loss rate being equal to the charge loss rate. The attractor is not necessarily related to the specific heat in a general evaporating black hole spacetime, but for the Reissner-Nordström case part of the attractor lies very close to the boundary of the region where specific heat changes sign.

gr-qc↗
arXiv2019

A Complementary Third Law for Black Hole Thermodynamics

There are some examples in the literature, in which despite the fact that the underlying theory or model does not impose a lower bound on the size of black holes, the final temperature under Hawking evaporation is nevertheless finite and nonzero. We show that under some loose conditions, the black hole is necessarily an effective remnant, in the sense that its evaporation time is infinite. That is, the final state that there is nonzero finite temperature despite having no black hole remaining cannot be realized. We discuss the limitations, subtleties, and the implications of this result, which is reminiscent of the third law of black hole thermodynamics, but with the roles of temperature and size interchanged. We therefore refer to our result as the "complementary third law" for black hole thermodynamics.

gr-qc↗
arXiv2019

General Black Hole Solutions in (2+1)-dimensions with a Scalar Field Non-Minimally Coupled to Gravity

We discuss black hole solutions in (2+1)-dimensions with a scalar field non-minimally coupled to Einstein's gravity in the presence of a cosmological constant and a self-interacting scalar potential. Without specifying the form of the potential, we find a general solution of the field equations, which includes all the known asymptotically anti-de Sitter (AdS) black hole solutions in (2+1)-dimensions as special cases once values of the coupling constants are chosen appropriately. In addition, we obtain numerically new black hole solutions and for some specific choices of the coupling constants we derive new exact AdS black hole solutions. We also discuss the possibility of obtaining asymptotically de Sitter black hole solutions with or without an electromagnetic field.

gr-qc↗
arXiv2019

No Violation of the Second Law in Extended Black Hole Thermodynamics

Recently a number of papers have claimed that the horizon area - and thus the entropy - of near extremal black holes in anti-de Sitter spacetimes can be reduced by dropping particles into them. In this note we point out that this is a consequence of an underlying assumption that the energy of an infalling particle changes only the internal energy of the black hole, whereas a more physical assumption would be that it changes the enthalpy (mass). In fact, under the latter choice, the second law of extended black hole thermodynamics is no longer violated.

gr-qc↗
arXiv2019

A Note on Smarr Relation and Coupling Constants

The Smarr relation plays an important role in black hole thermodynamics. It is often claimed that the Smarr relation can be written down simply by observing the scaling behavior of the various thermodynamical quantities. We point out that this is not necessarily so in the presence of dimensionful coupling constants, and discuss the issues involving the identification of thermodynamical variables.

gr-qc↗
arXiv2018

Generalized Uncertainty Principle and White Dwarfs Redux: How Cosmological Constant Protects Chandrasekhar Limit

It was previously argued that generalized uncertainty principle (GUP) with a positive parameter removes the Chandrasekhar limit. One way to restore the limit is by taking the GUP parameter to be negative. In this work we discuss an alternative method that achieves the same effect: by including a cosmological constant term in the GUP (known as "extended GUP" in the literature). We show that an arbitrarily small but nonzero cosmological constant can restore the Chandrasekhar limit. We also remark that if the extended GUP is correct, then the existence of white dwarfs gives an upper bound for the cosmological constant, which -- while still large compared to observation -- is approximately 86 orders of magnitude smaller than the natural scale.

gr-qc↗
arXiv2018

GUP-Corrected Black Hole Thermodynamics and the Maximum Force Conjecture

We show that thermodynamics for an asymptotically flat Schwarzschild black hole leads to a force of magnitude $c^4/(2G)$. This remains true if one considers the simplest form of correction due to the generalized uncertainty principle. We comment on the maximum force conjecture, the subtleties involved, as well as the discrepancies with previous results in the literature.

gr-qc↗
arXiv2018

Generalized Uncertainty Principle, Black Holes, and White Dwarfs: A Tale of Two Infinities

It is often argued that quantum gravitational correction to the Heisenberg's uncertainty principle leads to, among other things, a black hole remnant with finite temperature. However, such a generalized uncertainty principle also seemingly removes the Chandrasekhar limit, i.e., it permits white dwarfs to be arbitrarily large, which is at odds with astrophysical observations. We show that this problem can be resolved if the parameter in the generalized uncertainty principle is negative. We also discuss the Planck scale physics of such a model.

gr-qc↗
arXiv2018

Counting Components in the Lagrange Multiplier Formulation of Teleparallel Theories

We investigate the Lagrange multiplier formulation of teleparallel theories, including f(T) gravity, in which the connection is not set to zero a priori and compare it with the pure frame theory. We show explicitly that the two formulations are equivalent, in the sense that the dynamical equations have the same content. One consequence is that the manifestly local Lorentz invariant f(T) theory cannot be expected to be free of pathologies, which were previously found to plague f(T) gravity formulated in the usual pure frame approach.

gr-qc↗
arXiv2018

Stephani Cosmology: Entropically Viable But Observationally Challenged

Inhomogeneous cosmological models such as the Stephani universes could, in principle, provide an explanation for the observed accelerated expansion of the Universe. Working with a concrete, popular model of the Stephani cosmology -- the Stephani-Dabrowski model, we found that it is entropically viable. We also comment on the energy conditions and the two-sheeted geometry of the spacetime. However, similar to the LTB models, despite satisfying the holographic principle, Stephani cosmology has difficulty satisfying all the constraints from observations.

gr-qc↗
arXiv2018

Giant Tortoise Coordinate

The giant tortoise coordinate is a moving mirror inspired generalization of the Regge-Wheeler counterpart that demonstrates a unitary evaporating black hole emitting a total finite energy.

gr-qc↗
arXiv2017

Lux in obscuro II: Photon Orbits of Extremal AdS Black Holes Revisited

A large class of spherically symmetric static extremal black hole spacetimes possesses a stable null photon sphere on their horizons. For the extremal Kerr-Newman family, the photon sphere only really coincides with the horizon in the sense clarified by Doran. The condition under which photon orbit is stable on an asymptotically flat extremal Kerr-Newman black hole horizon has recently been clarified; it is found that a sufficiently large angular momentum destabilizes the photon orbit, whereas electrical charge tends to stabilize it. We investigated the effect of a negative cosmological constant on this observation, and found the same behavior in the case of an extremal asymptotically Kerr-Newman-AdS black holes in (3+1)-dimensions. In (2+1)-dimensions, in the presence of electrical charge, the angular momentum never becomes large enough to destabilize the photon orbit. We comment on the instabilities of black hole spacetimes with a stable photon orbit.

gr-qc↗
arXiv2017

Lux in obscuro: Photon Orbits of Extremal Black Holes Revisited

It has been shown in the literature that the event horizon of an extremal asymptotically flat Reissner-Nordstrom black hole is also a stable photon sphere. We further clarify this statement and give a general proof that this holds for a large class of static spherically symmetric black hole spacetimes with an extremal horizon. In contrast, in the Doran frame, an extremal asymptotically flat Kerr black hole has an unstable photon orbit on the equatorial plane of its horizon. In addition, we show that an extremal asymptotically flat Kerr-Newman black hole exhibits two equatorial photon orbits if a < M/2, one of which is on the extremal horizon in the Doran frame and is stable, whereas the second one outside the horizon is unstable. For a > M/2, there is only one equatorial photon orbit, located on the extremal horizon, and it is unstable. There can be no photon orbit on the horizon of a non-extremal Kerr-Newman black hole.

gr-qc↗
arXiv2017

Entanglement Entropy and Complexity for One-Dimensional Holographic Superconductors

Holographic superconductor is an important arena for holography, as it allows concrete calculations to further understand the dictionary between bulk physics and boundary physics. An important quantity of recent interest is the holographic complexity. Conflicting claims had been made in the literature concerning the behavior of holographic complexity during phase transition. We clarify this issue by performing a numerical study on one-dimensional holographic superconductor. Our investigation shows that holographic complexity does not behave in the same way as holographic entanglement entropy. Nevertheless, the universal terms of both quantities are finite and reflect the phase transition at the same critical temperature.

hep-th↗
arXiv2017

Instanton Tunneling for De Sitter Space with Real Projective Spatial Sections

The physics of tunneling from one spacetime into another is often understood in terms of instantons. For some instantons, it was recently shown in the literature that there are two complementary "interpretations" for their analytic continuations. Dubbed "something-to-something" and "nothing-to-something" interpretations, respectively, the former involves situation in which the initial and final hypersurfaces are connected by a Euclidean manifold, whereas the initial and final hypersurfaces in the latter case are not connected in such a way. We consider a de Sitter space with real projective space $\mathbb{R}\text{P}^3$ spatial sections, as was originally understood by de Sitter himself. This original version of de Sitter space has several advantages over the usual de Sitter space with $\text{S}^3$ spatial sections. In particular, the interpretation of the de Sitter entropy as entanglement entropy is much more natural. We discuss the subtleties involved in the tunneling of such a de Sitter space.

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