arXiv subjects

Jianwei Mei

Publications and source records attributed to Jianwei Mei.

69 records · Page 4Linked to original sources

arXiv2011

Towards A Possible Fluid Flow Underlying the Kerr Spacetime

Based on the idea of emergent spacetime, we consider the possibility that the material underlying our spacetime is modelled by a fluid. We are particularly interested in possible connections between the geometrical properties of the emergent spacetime and the properties of the underlying fluid. We find some partial results that support this possibility. By using the Kerr spacetime as an example, we construct from the Riemann curvature tensor a vector field, which behaves just like the speculated fluid flow.

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arXiv2010

Intrinsic Deviation from the Tri-bimaximal Neutrino Mixing in a Class of A_4 Flavor Models

It is well known that the tri-bimaximal neutrino mixing pattern V_0 can be derived from a class of flavor models with the non-Abelian A_4 symmetry. We point out that small corrections to V_0, which are inherent in the A_4 models and arise from both the charged-lepton and neutrino sectors, have been omitted in the previous works. We show that such corrections may lead the 3 \times 3 neutrino mixing matrix V to a non-unitary deviation from V_0, but they cannot result in a nonzero value of θ_13 or any new CP-violating phases. Current experimental constraints on the unitarity of V allow us to constrain the model parameters to some extent.

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arXiv2010

The Entropy for General Extremal Black Holes

We use the Kerr/CFT correspondence to calculate the entropy for all known extremal stationary and axisymmetric black holes. This is done with the help of two ansatzs that are general enough to cover all such known solutions. Considering only the contribution from the Einstein-Hilbert action to the central charge(s), we find that the entropy obtained by using Cardy's formula exactly matches with the Bekenstein-Hawking entropy.

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arXiv2009

Solutions to Horava Gravity

Recently Horava proposed a non-relativistic renormalisable theory of gravitation, which reduces to Einstein's general relativity at large distances, and that may provide a candidate for a UV completion of Einstein's theory. In this paper, we derive the full set of equations of motion, and then we obtain spherically symmetric solutions and discuss their properties. We also obtain solutions for the Friedman-Lemaitre-Robertson-Walker cosmological metric.

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arXiv2009

GL(n,R) Wormholes and Waves in Diverse Dimensions

We construct the most general Ricci-flat metrics in (D+n) dimensions that preserve the R^{1,n-1}\times SO(D) isometry. The equations of motion are governed by the system of a GL(n,\R)/SO(1,n-1) scalar coset coupled to D-dimensional gravity. Among the solutions, we find a large class of smooth Lorentzian wormholes that connect two asymptotic flat spacetimes. In addition, we obtain new vacuum tachyonic wave solutions in D\ge 4 dimensions, which fit the general definition of pp-waves in that there exists a covariantly constant null vector. The momenta of the tachyon waves are larger than their ADM masses. The world-volume of the tachyon wave is R^{1,2}, instead of R^{1,1} for the usual vacuum pp-wave. We show that the tachyon wave solutions admit no Killing spinors, except in D=4, in which case it preserves half of the supersymmetry. We also obtain a general class of p-brane wormhole and tachyon wave solutions where the R^{1,n-1} part of the spacetime lies in the the world-volume of the p-branes. These include examples of M-branes and D3-brane. Furthermore, we obtain AdS tachyon waves in D\ge 4 dimensions.

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arXiv2009

Extremal Static AdS Black Hole/CFT Correspondence in Gauged Supergravities

A recently proposed holographic duality allows the Bekenstein-Hawking entropy of extremal rotating black holes to be calculated microscopically, by applying the Cardy formula to the two-dimensional chiral CFTs associated with certain reparameterisations of azimuthal angular coordinates in the solutions. The central charges are proportional to the angular momenta of the black hole, and so the method degenerates in the case of static (non-rotating) black holes. We show that the method can be extended to encompass such charged static extremal AdS black holes by using consistent Kaluza-Klein sphere reduction ansatze to lift them to exact solutions in the low-energy limits of string theory or M-theory, where the electric charges become reinterpreted as angular momenta associated with internal rotations in the reduction sphere. We illustrate the procedure for the examples of extremal charged static AdS black holes in four, five, six and seven dimensions.

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arXiv2008

Kerr-AdS/CFT Correspondence in Diverse Dimensions

It was proposed recently that the near-horizon states of an extremal four-dimensional Kerr black hole could be identified with a certain chiral conformal field theory whose Virasoro algebra arises as an asymptotic symmetry algebra of the near-horizon Kerr geometry. Supportive evidence for the proposed duality came from the equality of the microscopic entropy of the CFT, calculated by means of the Cardy formula, and the Bekenstein-Hawking entropy of the extremal Kerr black hole. In this paper we examine the proposed Kerr/CFT correspondence in a broader context. In particular, we show that the microscopic entropy and the Bekenstein-Hawking entropy agree also for the extremal Kerr-AdS metric in four dimensions, and also for the extremal Kerr-AdS metrics in dimensions 5, 6 and 7. General formulae for all higher dimensions are also presented.

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arXiv2008

AdS Wormholes

We obtain a large class of smooth Lorentzian p-brane wormholes in supergravities in various dimensions. They connect two asymptotically flat spacetimes. In cases where there is no dilaton involved in the solution, the wormhole can connect an AdS_n\times S^m in one asymptotic region to a flat spacetime in the other. We obtain explicit examples for (n,m)=(4,7), (7,4), (5,5), (3,3), (3,2). These geometries correspond to field theories with UV conformal fixed points, and they undergo decompactification in the IR region. In the case of AdS_3, we compute the central charge of the corresponding conformal field theory.

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arXiv2008

Ricci-Flat and Charged Wormholes in Five Dimensions

We construct stationary Ricci-flat inter-universe Lorentzian wormhole solutions in all D\ge 5 dimensions that connect two flat asymptotic spacetimes. Such a solution can be viewed as the gravity dual of a string tachyon state whose linear momentum is larger than its tension. We focus our analysis on the D=5 wormholes which are not traversable for the timelike and null geodesics; however, we demonstrate that there exist accelerated timelike trajectories that traverse from one asymptotic region to the other. We further study the minimally-coupled scalar wave equation and demonstrate that the quantum tunnelling between two worlds must occur. We also obtain charged wormholes in five-dimensional supergravities. With appropriate choice of parameters, these wormholes connect AdS$_3\times S^2$ in one asymptotic region to flat Minkowskian spacetime in the other.

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arXiv2008

New Charged Black Holes in Five Dimensions

We obtain new stationary charged solutions of five-dimensional minimal supergravity. We first obtain purely dipole charged solutions, by extending a technique that we developed for five-dimensional Ricci-flat metrics in a previous paper, which could be viewed as being analogous to a four-dimensional construction by Demianski and Plebanski. The further introduction of electric charge is achieved by means of a solution-generating technique, which exploits the global SL(2,R) symmetry of five-dimensional minimal supergravity reduced on a timelike direction to four dimensions. We present this procedure in detail, since it provides a particularly simple general way of adding charge to any stationary solution of five-dimensional minimal supergravity. The new charged solutions we obtain limit in special cases to black rings carrying electric and magnetic dipole charge, or to charged Myers-Perry rotating black holes. We analyse the general solutions in detail, showing that they can describe asymptotically locally flat black holes whose horizon is a lens space L(n;m)=S^3/Γ(n;m). At infinity they approach Minkowski_5/Γ(m;n).

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arXiv2008

New Black Holes in Five Dimensions

We construct new stationary Ricci-flat metrics of cohomogeneity 2 in five dimensions, which generalise the Myers-Perry rotating black hole metrics by adding a further non-trivial parameter. We obtain them via a construction that is analogous to the construction by Plebanski and Demianski in four dimensions of the most general type D metrics. Limiting cases of the new metrics contain not only the general Myers-Perry black hole with independent angular momenta, but also the single rotation black ring of Emparan and Reall. In another limit, we obtain new static metrics that describe black holes whose horizons are distorted lens spaces L(n;m)= S^3/Γ(n;m), where m\ge n+2\ge 3. They are asymptotic to Minkowski spacetime factored by Γ(m;n). In the general stationary case, by contrast, the new metrics describe spacetimes with an horizon and with a periodicity condition on the time coordinate; these examples can be thought of as five-dimensional analogues of the four-dimensional Taub-NUT metrics.

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arXiv2007

New Rotating Non-Extremal Black Holes in D=5 Maximal Gauged Supergravity

We obtain new non-extremal rotating black hole solutions in maximal five-dimensional gauged supergravity. They are characterised by five parameters, associated with the mass, the two angular momenta, and two independently-specifiable charge parameters. Two of the three charges associated with the U(1)^3 Cartan subgroup of the SO(6) gauge group are equal, whilst the third can be independently specified. These new solutions generalise all the previously-known rotating solutions in five-dimensional gauged supergravity with independent angular momenta. They describe regular black holes, provided the parameters lie in appropriate ranges so that naked singularities and closed-timelike curves (CTCs) are avoided. We also construct the BPS limit, and show that regular supersymmetric black holes or topological solitons arise if the parameters are further restricted in an appropriate manner.

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arXiv2005

Radiative Generation of Leptonic CP Violation

Three CP-violating phases of the $3\times 3$ lepton flavor mixing matrix $V$ are entangled with one another in the renormalization-group evolution from the seesaw scale ($Λ_{\rm SS} \sim 10^{14}$ GeV) to the electroweak scale ($Λ_{\rm EW} \sim 10^2$ GeV). Concerning the Dirac phase $δ$, we show that $δ=90^\circ$ at $Λ_{\rm EW}$ can be radiatively generated from $δ=0^\circ$ at $Λ_{\rm SS}$ in the minimal supersymmetric standard model, if three neutrino masses are nearly degenerate. As for the Majorana phases $ρ$ and $σ$, it is also possible to radiatively generate $ρ=90^\circ$ or $σ= 90^\circ$ at $Λ_{\rm EW}$ from $ρ=0^\circ$ or $σ= 0^\circ$ at $Λ_{\rm SS}$. The one-loop renormalization-group equations for the Jarlskog invariant and two off-diagonal asymmetries of $V$ are derived, and their running behaviors from $Λ_{\rm SS}$ to $Λ_{\rm EW}$ are numerically illustrated.

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arXiv2005

Radiative Corrections to Democratic Lepton Mixing

A new ansatz of democratic lepton mixing is proposed at the GUT scale and the radiative corrections to its phenomenological consequences are calculated at the electroweak scale. We demonstrate that it is possible to obtain the experimentally favored results for both neutrino masses and lepton flavor mixing angles from this ansatz, provided the neutrino Yukawa coupling matrix takes a specific nontrivial pattern. The seesaw threshold effects play a significant role in the running of relevant physical quantities.

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arXiv2005

Running Neutrino Masses, Leptonic Mixing Angles and CP-Violating Phases: From $M_{\rm Z}$ to $Λ_{\rm GUT}$

We derive renormalization group equations for neutrino masses, leptonic mixing angles and CP-violating phases running at energies above the seesaw threshold, both in the Standard Model and in the Minimal Supersymmetric Standard Model extended with three right-handed neutrinos. With these equations, we carry out a systematic study of the radiative correction that may arise to neutrino parameters, via their renormalization group evolution from the electroweak scale ($M_{\rm Z}$) to the scale of Grand Unified theories ($Λ_{\rm GUT}$). We study in detail three typically interesting neutrino mass patterns: normal hierarchy, near degeneracy and inverted hierarchy. Magnitudes of possible corrections in each case are carefully investigated. We also emphasize the significance of CP-violating phases in controlling the evolution behavior of all neutrino parameters.

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