Fuzzy Euclidean wormholes in anti-de Sitter space

This paper is devoted to an investigation of Euclidean wormholes made by fuzzy instantons. We investigate the Euclidean path integral in anti-de Sitter space. In Einstein gravity, we introduce a scalar field with a potential. Because of the analyticity, there is a contribution of complex-valued instantons, so-called fuzzy instantons. If we have a massless scalar field, then we obtain Euclidean wormholes, where the probabilities become smaller and smaller as the size of the throat becomes larger and larger. If we introduce a non-trivial potential, then in order to obtain a non-zero tunneling rate, we need to tune the shape of the potential. With the $O(4)$ symmetry, after the analytic continuation to the Lorentzian time, the wormhole throat should expand to infinity. However, by adding mass, one may obtain an instant wormhole that should eventually collapse to the event horizon. The existence of Euclidean wormholes is related to the stability or unitarity issues of anti-de Sitter space. We are not conclusive yet, but we carefully comment on these physical problems.Comment: 20 pages, 9 figure

Tunneling from the past horizon

We investigate a tunneling and emission process of a thin-shell from a Schwarzschild black hole, where the shell was initially located beyond the Einstein-Rosen bridge and finally appears at the right side of the Penrose diagram. In order to obtain such a solution, we should assume that the areal radius of the black hole horizon increases after the tunneling. Hence, there is a parameter range such that the tunneling rate is exponentially enhanced, rather than suppressed. We may have two interpretations regarding this. First, such a tunneling process from the past horizon is improbable by physical reasons; second, such a tunneling is possible in principle, but in order to obtain a stable Einstein-Rosen bridge, one needs to restrict the parameter spaces. If such a process is allowed, this can be a non-perturbative contribution to Einstein-Rosen bridges as well as eternal black holes.Comment: 13 pages, 6 figure

Causal structures and dynamics of black-hole-like solutions in string theory

We investigate spherically symmetric solutions in string theory. Such solutions depend on three parameters, one of which corresponds to the asymptotic mass while the other two are the dilaton and two-form field amplitudes, respectively. If the two-form field amplitude is non-vanishing, then this solution represents a trajectory of a singular and null hypersurface. If the dilaton and two-form field amplitudes are non-vanishing but very close to zero, then the solution is asymptotically the same as the Schwarzschild solution, while only the near horizon geometry will be radically changed. If the dilaton field diverges toward the weak coupling regime, this demonstrates a firewall-like solution. If the dilaton field diverges toward the strong coupling limit, then as we consider quantum effects, this spacetime will emit too strong Hawking radiation to preserve semi-classical spacetime. However, if one considers a junction between the solution and the flat spacetime interior, this can allow a stable star-like solution with reasonable semi-classical properties. We discuss possible implications of these causal structures and connections with the information loss problem.Comment: 17 pages, 11 figure

Demonstration of the Hayden-Preskill protocol via mutual information

We construct the Hayden-Preskill protocol by using a system of spin-1/2 particles and demonstrate information flows of this system which can mimic black holes. We first define an analogous black hole $A$ as a collection of such particles. Second, we take the particles from inside to outside the black hole to define an analogous system of Hawking radiation $B$ as outside particles. When the black hole and the radiation have the maximum entanglement at the Page time, we take an entangled pair system $C$ and $D$. The particles of $C$ fall into the black hole while their counterparts of $D$ remain outside. If we assume rapid mixing of the particle states in the black hole $A \cup C$, can the information of $C$ rapidly escape from the black hole like a mirror? We numerically show that if we turn on the rapid mixing in the black hole, the original information of $C$ rapidly escapes from the black hole to outside in the form of the mutual information between $B$ and $D$. On the other hand, if the mixing between $A$ and $C$ is not enough, the information escapes slowly. Hence, we explicitly demonstrate the original conjecture of Hayden and Preskill. We emphasize that enough mixing is an essential condition to make the Hayden-Preskill protocol functionally work.Comment: 12 pages, 4 figure

Causal structures and dynamics of black-hole-like solutions in string theory

AbstractWe investigate spherically symmetric solutions in string theory. Such solutions depend on three parameters, one of which corresponds to the asymptotic mass while the other two are the dilaton and two-form field amplitudes, respectively. If the two-form field amplitude is non-vanishing, then this solution represents a trajectory of a singular and null hypersurface. If the dilaton and two-form field amplitudes are non-vanishing but very close to zero, then the solution is asymptotically the same as the Schwarzschild solution, while only the near horizon geometry will be radically changed. If the dilaton field diverges toward the weak coupling regime, this demonstrates a firewall-like solution. If the dilaton field diverges toward the strong coupling limit, then as we consider quantum effects, this spacetime will emit too strong Hawking radiation to preserve semi-classical spacetime. However, if one considers a junction between the solution and the flat spacetime interior, this can allow a stable star-like solution with reasonable semi-classical properties. We discuss possible implications of these causal structures and connections with the information loss problem.</jats:p

Diphoton channel at the LHC experiments to find a hint for a new heavy gauge boson

Recently there has been a buge interest in the diphoton excess around 750 GeV reported by both ATLAS and CMS collaborations, although the newest analysis with more statis-tics does not seem to support the excess. Nevertheless, the diphoton channel at the LHC experiments are a powerful tool to probe a new physics. One of the most natural explana-tions of a diphoton excess, if it occurs, could be a new scalar boson with exotic colored particles. In this setup, it would be legitimate to ask what is the role of this new scalar in nature. A heavy neutral gauge boson (Z′) is one of the traditional targets of the dis-covery at the collider experiments with numerous motivations. While the Landau-Yang theorem dictates the diphoton excess cannot be this spin-1 gauge boson, there is a strong correlation of a new heavy gauge boson and a new scalar boson which provides a mass to the gauge boson being at the same mass scale. In this paper, we point out a simple fact that a new scalar with a property similar th the recently highlighted 750GeV would suggest an existence of a TeV scale Z′ gauge boson that might be within the reach of the LHC Run 2 experiments. We take a scenario of the well-motivated and popular gauged B-L symmetry and require the gauge coupling unification to predict the mass and other properties of the Z′ and illustrate the discovery of the Z′ would during the LHC experiments. (c) World Scientific Publishing Company3211Nsciescopu

Novel Phenomena of the Hartle–Hawking Wave Function

We find a novel phenomenon in the solution to the Wheeler–DeWitt equation by solving numerically the equation assuming O(4)-symmetry and imposing the Hartle–Hawking wave function as a boundary condition. In the slow-roll limit, as expected, the numerical solution gives the most dominant steepest-descent that describes the probability distribution for the initial condition of a universe. The probability is consistent with the Euclidean computations, and the overall shape of the wave function is compatible with analytical approximations, although there exist novel differences in the detailed probability computation. Our approach gives an alternative point of view for the no-boundary wave function from the wave function point of view. Possible interpretations and conceptual issues of this wave function are discussed