arXiv subjects

Kai Lin

Publications and source records attributed to Kai Lin.

120 records · Page 7Linked to original sources

arXiv2014

Universal horizons and black holes in gravitational theories with broken Lorentz symmetry

In this paper, we first show that the definition of the universal horizons studied recently in the khrononmetric theory of gravity can be straightforwardly generalized to other theories that violate the Lorentz symmetry, by simply considering the khronon as a probe field and playing the same role as a Killing vector field. As an application, we study static charged ($D+1$)-dimensional spacetimes in the framework of the healthy (non-projectable) Horava-Lifshitz (HL) gravity in the infrared limit, and find various solutions. Some of them represent Lifshitz space-times with hyperscaling violations, and some have black hole structures. In the latter universal horizons always exist inside the Killing horizons. The surface gravity on them can be either larger or smaller than the surface gravity on the Killing horizons, depending on the space-times considered. Although such black holes are found only in the infrared, we argue that black holes with universal horizons also exist in the full theory of the HL gravity. A simple example is the Schwarzschild solution written in the Painleve-Gullstrand coordinates, which is also a solution of the full theory of the HL gravity and has a universal horizon located inside the Schwarzschild Killing horizon.

gr-qc↗

arXiv2014

Holographic Superconductors in a Rotating Spacetime

We consider holographic superconductors in a rotating black string spacetime. In view of the mandatory introduction of the $A_φ$ component of the vector potential we are left with three equations to be solved. Their solutions show that the effect of the rotating parameter $a$ influences the critical temperature $T_c$ and the conductivity $σ$ in a simple but not trivial way.

hep-th↗

arXiv2014

Holographic Superconductors in Horava-Lifshitz Gravity

We consider holographic superconductors related to the Schwarzschild black hole in the low energy limit of Hořava-Lifshitz spacetime. The non-relativistic electromagnetic and scalar fields are introduced to construct a holographic superconductor model in Hořava-Lifshitz gravity and the results show that the $α_2$ term plays an important role, modifying the conductivity curve line by means of an attenuation the conductivity.

hep-th↗

arXiv2014

Lifshitz spacetimes, solitons, and generalized BTZ black holes in quantum gravity at a Lifshitz point

In this paper, we study static vacuum solutions of quantum gravity at a fixed Lifshitz point in (2+1) dimensions, and present all the diagonal solutions in closed forms in the infrared limit. The exact solutions represent spacetimes with very rich structures: they can represent generalized BTZ black holes, Lifshitz space-times or Lifshitz solitons, in which the spacetimes are free of any kind of space-time singularities, depending on the choices of the free parameters of the solutions. We also find several classes of exact static non-diagonal solutions, which represent similar space-time structures as those given in the diagonal case. The relevance of these solutions to the non-relativistic Lifshitz-type gauge/gravity duality is discussed.

hep-th↗

arXiv2014

Post-Newtonian approximations in the Hořava-Lifshitz gravity with extra U(1) symmetry

In this paper, we first propose a universal coupling between the gravity and matter in the framework of the Hořava-Lifshitz theory of gravity with an extra U(1) symmetry for both the projectable and non-projectable cases. Then, using this universal coupling we study the post-Newtonian approximations and obtain the parameterized post-Newtonian (PPN) parameters in terms of the coupling constants of the theory. Contrary to the previous works in which only two PPN parameters were calculated, we obtain {\it all} PPN parameters. We then, for the first time in either projectable or non-projectable case, find that all the solar system tests carried out so far are satisfied in a large region of the parameters space. In particular, the same results obtained in general relativity can be easily realized here. A remarkable feature is that the solar system tests impose no constraint on the parameter $λ$ appearing in the kinetic part of the action. As a result, the solar system tests, when combined with the condition for avoidance of strong coupling, do not lead to an upper bound on the energy scale $M_{*}$ that suppresses higher dimensional operators in the theory. This is in sharp contrast to other versions of the HL theory.

hep-ph↗

arXiv2014

Lorentz Invariance Violation and Modified Hawking Fermions Tunneling from Black Strings

Recently the modified Dirac equation with Lorentz invariance violation has been proposed, which would be helpful to resolve some issues in quantum gravity theory and high energy physics. In this paper, the modified Dirac equation has been generalized in curved spacetime, and then fermion tunneling of black strings is researched under this correctional Dirac field theory. We also use semi-classical approximation method to get correctional Hamilton-Jacobi equation, so that the correctional Hawking temperature and correctional black hole's entropy are derived.

hep-th↗

arXiv2013

Dirac quasinormal modes in spherically symmetric regular black holes

Using the WKB approximation, massless and massive Dirac quasinormal modes (QNMs) are studied in spherically symmetric regular spacetimes. We analyze the relationships between QNM frequencies and the parameters (angular momentum number $l$, magnetic monopole charge $β$ and the mass of the field $m$), and discuss the extreme charge of magnetic monopole $β_{e}$ for spherically symmetric regular black holes (BHs). Furthermore, we apply an expansion method to expand QNMs in inverse powers of $L=l+1/2$, and confirm good precision with $l>n$. Finally, we improve traditional finite difference method to be available in massive Dirac case, and illuminate the dynamical evolution of massive Dirac field.

gr-qc↗

arXiv2013

Static post-Newtonian limits in non-projectable Hořava-Lifshitz gravity with an extra U(1) symmetry

In this paper, we study static post-Newtonian limits in non-projectable Hořava-Lifshitz gravity with an extra U(1) symmetry. After obtaining all static spherical solutions in the infrared, we apply them to the solar system tests, and obtain the Eddington-Robertson-Schiff parameters in terms of the coupling constants of the theory. These parameters are well consistent with observations for the physically viable coupling constants. In contrast to the projectable case, this consistence is achieved without taking the gauge field and Newtonian prepotential as part of the metric.

hep-th↗

arXiv2013

Solar system tests and interpretation of gauge field and Newtonian prepotential in general covariant Hořava-Lifshitz gravity

We study spherically symmetric, stationary vacuum configurations in general covariant theory (U(1) extension) of Hořava-Lifshitz gravity with the projectability condition and an arbitrary coupling constant $λ$, and obtain all the solutions in closed forms. If the gauge field $A$ and the Newtonian prepotential $φ$ do not directly couple to matter fields, the theory is inconsistent with solar system tests for $λ\not=1$, no matter how small $|λ-1|$ is. This is shown to be true also with the most general ansatz of spherical (but not necessarily stationary) configurations. Therefore, to be consistent with observations, one needs either to find a mechanism to restrict $λ$ precisely to $λ_{GR}=1$, or to consider $A$ and/or $φ$ as parts of the 4-dimensional metric on which matter fields propagate. In the latter, requiring that the line element be invariant not only under the foliation-preserving diffeomorphism but also under the local U(1) transformations, we propose the replacements, $N \rightarrow N - \upsilon(A - {\cal{A}})/c^2$ and $N^i \rightarrow N^i+N\nabla^{i}φ$, where $\upsilon$ is a dimensionless coupling constant to be constrained by observations, $N$ and $N^i$ are, respectively, the lapse function and shift vector, and ${\cal{A}} \equiv - \dotφ + N^i\nabla_{i}φ+ N(\nabla_{i}φ)^2/2$. With this prescription, we show explicitly that the aforementioned solutions are consistent with solar system tests for both $λ=1$ and $λ\not=1$, provided that $|\upsilon-1|<10^{-5}$. From this result, the physical and geometrical interpretations of the fields $A$ and $φ$ become clear. However, it still remains to be understood how to obtain such a prescription from the action principle.

hep-th↗

arXiv2012

Static electromagnetic fields and charged black holes in general covariant theory of Horava-Lifshitz gravity

In this paper, we study electromeganetic static spacetimes in the nonrelativisitc general covariant theory of the Horava-Lifshitz (HL) gravity, proposed recently by Horava and Melby-Thompson, and present all the electric static solutions, which represent the generalization of the Reissner-Nordstrom solution found in Einstein's general relativity (GR). The global/local structures of spacetimes in the HL theory in general are different from those given in GR, because the dispersion relations of test particles now contain high-order momentum terms, so the speeds of these particles are unbounded in the ultraviolet (UV). As a result, the conception of light-cones defined in GR becomes invalid and test particles do not follow geodesics. To study black holes in the HL theory, we adopt the geometrical optical approximations, and define a horizon as a (two-closed) surface that is free of spacetime singularities and on which massless test particles are infinitely redshifted. With such a definition, we show that some of our solutions give rise to (charged) black holes, although the radii of their horizons in general depend on the energies of the test particles.

hep-th↗

arXiv2011

On strong coupling in nonrelativistic general covariant theory of gravity

We study the strong coupling problem in the Horava-Melby-Thompson setup of the Horava-Lifshitz gravity with an arbitrary coupling constant $λ$, generalized recently by da Silva, where $λ$ describes the deviation of the theory in the infrared from general relativity that has $λ_{GR} = 1$. We find that a scalar field in the Minkowski background becomes strong coupling for processes with energy higher than $Λ_ω [\equiv (M_{pl}/c_1)^{3/2} M_{pl}|λ- 1|^{5/4}]$, where generically $c_1 \ll M_{pl}$. However, this problem can be cured by introducing a new energy scale $M_{*}$, so that $M_{*} < Λ_ω$, where $M_{*}$ denotes the suppression energy of high order derivative terms of the theory.

hep-th↗

arXiv2011

Detailed balance condition and ultraviolet stability of scalar field in Horava-Lifshitz gravity

Detailed balance and projectability conditions are two main assumptions when Horava recently formulated his theory of quantum gravity - the Horava-Lifshitz (HL) theory. While the latter represents an important ingredient, the former often believed needs to be abandoned, in order to obtain an ultraviolet stable scalar field, among other things. In this paper, because of several attractive features of this condition, we revisit it, and show that the scalar field can be stabilized, if the detailed balance condition is allowed to be softly broken. Although this is done explicitly in the non-relativistic general covariant setup of Horava-Melby-Thompson with an arbitrary coupling constant $λ$, generalized lately by da Silva, it is also true in other versions of the HL theory. With the detailed balance condition softly breaking, the number of independent coupling constants can be still significantly reduced. It is remarkable to note that, unlike other setups, in this da Silva generalization, there exists a master equation for the linear perturbations of the scalar field in the flat Friedmann-Robertson-Walker background.

hep-th↗