arXiv subjects

Chiang-Mei Chen

Publications and source records attributed to Chiang-Mei Chen.

At least 55 records · Page 3Linked to original sources

arXiv2016

Gravity: a gauge theory perspective

The evolution of a generally covariant theory is under-determined. One hundred years ago such dynamics had never before been considered; its ramifications were perplexing, its future important role for all the fundamental interactions under the name gauge principle could not be foreseen. We recount some history regarding Einstein, Hilbert, Klein and Noether and the novel features of gravitational energy that led to Noether's two theorems. Under-determined evolution is best revealed in the Hamiltonian formulation. We developed a covariant Hamiltonian formulation. The Hamiltonian boundary term gives covariant expressions for the quasi-local energy, momentum and angular momentum. Gravity can be considered as a gauge theory of the local Poincaré group. The dynamical potentials of the Poincaré gauge theory of gravity are the frame and the connection. The spacetime geometry has in general both curvature and torsion. Torsion naturally couples to spin; it could have a significant magnitude and yet not be noticed, except on a cosmological scale where it could have significant effects.

gr-qc↗

arXiv2015

Pair Production In Near Extremal Charged Black Holes

We study the spontaneous pair production, including the Schwinger mechanism and the Hawking radiation, of charged scalar and spinor particles from the near horizon region of (near) extremal charged black holes in the probe field limit. The pair production rate and the absorption cross section, as well as the retarded Green's functions of the probe fields are analytically computed. Moreover, the holographic description dual to the pair production is discussed.

hep-th↗

arXiv2015

Gravitational Energy for GR and Poincare Gauge Theories: a Covariant Hamiltonian Approach

Our topic concerns a long standing puzzle: the energy of gravitating systems. More precisely we want to consider, for gravitating systems, how to best describe energy-momentum and angular momentum/center-of-mass momentum (CoMM). It is known that these quantities cannot be given by a local density. The modern understanding is that (i) they are quasi-local (associated with a closed 2-surface), (ii) they have no unique formula, (iii) they have no reference frame independent description. In the first part of this work we review some early history, much of it not so well known, on the subject of gravitational energy in Einstein's general relativity (GR), noting especially Noether's contribution. In the second part we review (including some new results) much of our covariant Hamiltonian formalism and apply it to Poincaré gauge theories (GR is a special case). The key point is that the Hamiltonian boundary term has two roles, it determines the quasi-local quantities, and, furthermore it determines the boundary conditions for the dynamical variables. Energy-momentum and angular momentum/CoMM are associated with the geometric symmetries under Poincaré transformations. They are best described in a local Poincaré gauge theory. The type of spacetime that naturally has this symmetry is Riemann-Cartan spacetime, with a metric compatible connection having, in general, both curvature and torsion. Thus our expression for the energy-momentum of physical systems is obtained via our covariant Hamiltonian formulation applied to Poincaré gauge theories.

gr-qc↗

arXiv2014

Spinor Particle Creation in Near Extremal Reissner-Nordstrom Black Holes

The pair production of spinor particles, which can be captured by the solution of the Dirac equation with an appropriate boundary condition, in charged black holes is investigated. We obtain the closed form of the production rate in the near extremal limit of the Reissner-Nordstrom black holes. The cosmic censorship conjecture is seemingly guaranteed by the pair production process. Moreover, the absorption cross section ratio and retarded Green's functions of the spinor fields calculated from the gravity side match well with those of spinor operators in the dual CFT side.

hep-th↗

arXiv2014

Bertotti-Robinson and soliton string solutions of $D=5$ minimal supergravity

We report on a series of new solutions to five-dimensional minimal supergravity. Our method applies to space-times with two commuting Killing symmetries and consists in combining dimensional reduction on two-spaces of constant curvature with reduction on a two-torus. The first gives rise to various generalized Bertotti-Robinson solutions supported by electric and magnetic fluxes, which presumably describe the near-horizon regions of black holes and black rings (strings). The second provides generating techniques based on U-duality of the corresponding three-dimensional sigma model. We identify duality transformations relating the above solutions to asymptotically flat ones and obtain new globally regular dyonic solitons. Some new extremal asymptotically flat multi-center solutions are constructed too. We also show that geodesic solutions of three-dimensional sigma models passing through the same target space point generically split into disjoint classes which cannot be related by the isotropy subgroup of U-duality.

hep-th↗

arXiv2013

Bertotti-Robinson solutions of D=5 Einstein-Maxwell-Chern-Simons-Lambda theory

We present a series of new solutions in five-dimensional Einstein-Maxwell-Chern-Simons theory with an arbitrary Chern-Simons coupling $γ$ and a cosmological constant $Λ$. For general $γ$ and $Λ$ we give various generalizations of the Bertotti-Robinson solutions supported by electric and magnetic fluxes, some of which presumably describe the near-horizon regions of black strings or black rings. Among them there is a solution which could apply to the horizon of a topological AdS black ring in gauged minimal supergravity. Others are horizonless and geodesically complete. We also construct extremal asymptotically flat multi-string solutions for $Λ=0$ and arbitrary $γ$.

gr-qc↗

arXiv2013

A Reference for the Gravitational Hamiltonian Boundary Term

The Hamiltonian for physical systems and dynamic geometry generates the evolution of a spatial region along a vector field. It includes a boundary term which not only determines the value of the Hamiltonian, but also, via the boundary term in the variation of the Hamiltonian, the boundary conditions. The value of the Hamiltonian comes from its boundary term; it gives the quasi-local quantities: energy-momentum and angular-momentum/center-of-mass. This boundary term depends not only on the dynamical variables but also on their reference values; these reference values determine the ground state---the state having vanishing quasi-local quantities. Here our concern is how to select on the two-boundary the reference values. To determine the "best matched" reference metric and connection values for our preferred boundary term for Einstein's general relativity, we propose on the boundary two-surface (i) \emph{four dimensional} isometric matching, and (ii) extremizing the value of the energy.

gr-qc↗

arXiv2013

An Optimal Choice of Reference for the Quasi-Local Gravitational Energy and Angular Momentum

The boundary term of the gravitational Hamiltonian can be used to give the values of the quasi-local quantities as long as one can provide a suitable evolution vector field and an appropriate reference. On the two-surface boundary of a region we have proposed using {\em four dimensional isometric matching} between the dynamic spacetime and the reference geometry along with energy extremization to find both the optimal reference matching and the appropriate quasi-Killing vectors. Here we consider the axisymmetric spacetime case. For the Kerr metric in particular we can explicitly solve the equations to find the best matched reference and quasi-Killing vectors. This leads to the exact expression for the quasi-local boundary term and the values of our optimal quasi-local energy and angular momentum.

gr-qc↗

arXiv2012

A reference for the covariant Hamiltonian boundary term

The Hamiltonian for dynamic geometry generates the evolution of a spatial region along a vector field. It includes a boundary term which determines both the value of the Hamiltonian and the boundary conditions. The value gives the quasi-local quantities: energy-momentum, angular-momentum/center-of-mass. The boundary term depends not only on the dynamical variables but also on their reference values; the latter determine the ground state (having vanishing quasi-local quantities). For our preferred boundary term for Einstein's GR we propose 4D isometric matching and extremizing the energy to determine the reference metric and connection values.

gr-qc↗

arXiv2012

Quasi-local Energy for Spherically Symmetric Spacetimes

We present two complementary approaches for determining the reference for the covariant Hamiltonian boundary term quasi-local energy and test them on spherically symmetric spacetimes. On the one hand, we isometrically match the 2-surface and extremize the energy. This can be done in two ways, which we call programs I (without constraint) and II (with additional constraints). On the other hand, we match the orthonormal 4-frames of the dynamic and the reference spacetimes. Then, if we further specify the observer by requiring the reference displacement to be the timelike Killing vector of the reference, the result is the same as program I, and the energy can be positive, zero, or even negative. If, instead, we require that the Lie derivatives of the two-area along the displacement vector in both the dynamic and reference spacetimes to be the same, the result is the same as program II, and it satisfies the usual criteria: the energies are non-negative and vanish only for Minkowski (or anti-de Sitter) spacetime.

gr-qc↗

arXiv2012

Spontaneous Pair Production in Reissner-Nordstrom Black Holes

We investigate the spontaneous pair production, including the Schwinger mechanism and the Hawking thermal radiation, of charged scalar particles from the near horizon region of a (near) extremal Reissner-Nordström black hole. The paradigm is equivalent to the dynamics of the charged scalar field in a specific AdS$_2 \times S^2$ spacetime with a constant electric field. Two possible boundary conditions are adopted to explicitly compute the corresponding production rate and absorption cross section. It is shown that the Schwinger production rate can be eventually suppressed by the increasing attractive gravitational force as the geometry changes from the extremal to the near extremal black hole. Consequently, the Schwinger mechanism and the Hawking radiation are generically indistinguishable for the near extremal black holes. The holographic description dual to the pair production is also briefly discussed.

hep-th↗

arXiv2012

The Kerr-Newman/CFTs Correspondence

In this article, we review recent studies on multiple dual 2D CFT descriptions of the Kerr-Newman black hole, in terms of the Kerr/CFT and Reissner-Nordström/CFT correspondences. A microscopic hair conjecture is suggested.

hep-th↗

arXiv2011

Optimal Choices of Reference for a Quasi-local Energy: Spherically Symmetric Spacetimes

For a given timelike displacement vector the covariant Hamiltonian quasi-local energy expression requires a proper choice of reference spacetime. We propose a program for determining the reference by embedding a neighborhood of the two-sphere boundary in the dynamic spacetime into a Minkowski reference, so that the two sphere is embedded isometrically, and then extremizing the energy to determine the embedding variables. Applying this idea to Schwarzschild spacetime, we found that for each given future timelike displacement vector our program gives a unique energy value. The static observer measures the maximal energy. Applied to the Friedmann-Lemaitre-Robertson-Walker spacetime, we find that the maximum energy value is nonnegative; the associated displacement vector is the unit dual mean curvature vector, and the expansion of the two-sphere boundary matches that of its reference image. For these spherically symmetric cases the reference determined by our program is equivalent to isometrically matching the geometry at the two-sphere boundary and taking the displacement vector to be orthogonal to the spacelike constant coordinate time hypersurface, like the timelike Killing vector of the Minkowski reference.

gr-qc↗

arXiv2011

Quasi-local energy and the choice of reference

A quasi-local energy for Einstein's general relativity is defined by the value of the preferred boundary term in the covariant Hamiltonian formalism. The boundary term depends upon a choice of reference and a time-like displacement vector field (which can be associated with an observer) on the boundary of the region. Here we analyze the spherical symmetric cases. For the obvious analytic choice of reference based on the metric components, we find that this technique gives the same quasi-local energy values using several standard coordinate systems and yet can give different values in some other coordinate systems. For the homogeneous-isotropic cosmologies, the energy can be non-positive, and one case which is actually flat space has a negative energy. As an alternative, we introduce a way to determine the choice of both the reference and displacement by extremizing the energy. This procedure gives the same value for the energy in different coordinate systems for the Schwarzschild space, and a non-negative value for the cosmological models, with zero energy for the dynamic cosmology which is actually Minkowski space. The timelike displacement vector comes out to be the dual mean curvature vector of the two-boundary.

gr-qc↗

arXiv2011

An Analytic Analysis of Phase Transitions in Holographic Superconductors

Using a simple analytic approach, we study the universal properties of second-order phase transition in holographic superconductor models. We explore a general model in arbitrary dimensions in which the condensation occurs via the Stückelberg spontaneous symmetry breaking mechanism. All the possible second-order phase transitions and their universal characteristics can be identified analytically. The relationship between the critical temperature and charge density is generic, and the critical exponents can be greater than the typical mean field value 1/2. In addition, the related numerical factors can also be computed qualitatively.

hep-th↗

arXiv2011

Holographic Q-picture of Kerr-Newman-AdS-dS Black Hole

In this article, we show that a four-dimensional Kerr-Newman-AdS-dS black hole could be described by two different holographic two-dimensional conformal field theories. The first description, in view of the angular momentum, has been well discussed in (arXiv:1006.0157). The other alternative dual picture, however, is somehow overlooked. This new description, in view of the charge, provides another holographic correspondence. This picture again is supported not only by the match of the macroscopic entropy with the counting of microscopic degrees of freedom via the Cardy formula and also by the agreement on the real-time correlator in the superradiant scattering.

hep-th↗

arXiv2011

Holographic Dual of the Reissner-Nordström Black Hole

In this article we give a brief, nevertheless, comprehensive review on recent studies in the quantum gravity description of the Reissner-Nordström (RN) black hole from the perspective of the AdS/CFT correspondence. We survey the known evidence supporting a two-dimensional conformal field theory (CFT) description holographically dual to the RN black hole.

hep-th↗

arXiv2010

On Holographic Dual of the Dyonic Reissner-Nordström Black Hole

It is shown that the hidden conformal symmetry, namely $SO(2,2) \sim SL(2,R)_L \times SL(2,R)_R$ symmetry, of the non-extremal dyonic Reissner-Nordström black hole can be probed by a charged massless scalar field at low frequencies. The existence of such hidden conformal symmetry suggests that the field theory holographically dual to the 4D Reissner-Nordström black hole indeed should be a 2D CFT. Although the associated AdS$_3$ structure does not explicitly appear in the near horizon geometry, the primary parameters of the dual CFT$_2$ can be exactly obtained without the necessity of embedding the 4D Reissner-Nordström black hole into 5D spacetime. The duality is further supported by comparing the absorption cross sections and real-time correlators obtained from both the CFT and the gravity sides.

hep-th↗