12 research outputs found
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 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 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 as outside
particles. When the black hole and the radiation have the maximum entanglement
at the Page time, we take an entangled pair system and . The particles
of fall into the black hole while their counterparts of remain outside.
If we assume rapid mixing of the particle states in the black hole ,
can the information of 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 rapidly escapes from the black hole to outside in
the form of the mutual information between and . On the other hand, if
the mixing between and 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
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
Multiscale Modulation of Nanocrystalline Cellulose Hydrogel via Nanocarbon Hybridization for 3D Neuronal Bilayer Formation
Bacterial biopolymers have drawn much attention owing to their unconventional three-dimensional structures and interesting functions, which are closely integrated with bacterial physiology. The nongenetic modulation of bacterial (Acetobacter xylinum) cellulose synthesis via nanocarbon hybridization, and its application to the emulation of layered neuronal tissue, is reported. The controlled dispersion of graphene oxide (GO) nanoflakes into bacterial cellulose (BC) culture media not only induces structural changes within a crystalline cellulose nanofibril, but also modulates their 3D collective association, leading to substantial reduction in Young's modulus (approximate to 50%) and clear definition of water-hydrogel interfaces. Furthermore, real-time investigation of 3D neuronal networks constructed in this GO-incorporated BC hydrogel with broken chiral nematic ordering revealed the vertical locomotion of growth cones, the accelerated neurite outgrowth (approximate to 100 mu m per day) with reduced backward travel length, and the efficient formation of synaptic connectivity with distinct axonal bifurcation abundancy at the approximate to 750 mu m outgrowth from a cell body. In comparison with the pristine BC, GO-BC supports the formation of well-defined neuronal bilayer networks with flattened interfacial profiles and vertical axonal outgrowth, apparently emulating the neuronal development in vivo. We envisioned that our findings may contribute to various applications of engineered BC hydrogel to fundamental neurobiology studies and neural engineering
Graphene Potentiates the Myocardial Repair Efficacy of Mesenchymal Stem Cells by Stimulating the Expression of Angiogenic Growth Factors and Gap Junction Protein
Stem cell therapy has emerged as a potential modality for myocardial infarction treatment. Mesenchymal stem cells (MSCs) exert reparative actions in the injured myocardium mainly through the secretion of paracrine factors. In addition, the overexpression of connexin 43 (Cx43), a gap junction protein, promotes cardiac repair and function restoration. It is known that MSCs in a spheroid form, which have enhanced cell-cell interaction, exhibit enhanced expression of paracrine factors and Cx43. However, cell-extracellular matrix (ECM) interactions, which also contribute to growth factor expression, are very limited in MSC spheroids. Reduced graphene oxide (RGO) shows high affinity toward ECM proteins, such as fibronectin (FN), and high electrical conductivity. In this study, by incorporating FN-adsorbed RGO flakes into MSC spheroids, it is possible to enhance the cell-ECM interactions and, subsequently, the paracrine factor expression in the MSCs in spheroids. Cx43 is also upregulated likely due to the enhanced paracrine factor expression and electrical conductivity of RGO. The injection of MSC-RGO hybrid spheroids into the infarcted hearts enhances cardiac repair compared with the injection of RGO flakes or MSC spheroids. This study demonstrates that RGO can effectively improve the therapeutic efficacy of MSCs for ischemic heart diseases
Tension-controlled single-crystallization of copper foils for roll-to-roll synthesis of high-quality graphene films
It has been known that the crystalline orientation of Cu substrates plays a crucial role in chemical vapor deposition (CVD) synthesis of high-quality graphene. In particular, Cu (1 1 1) surface showing the minimum lattice mismatch with graphene is expected to provide an ideal catalytic reactivity that can minimize the formation of defects, which also induces larger single-crystalline domain sizes of graphene. Usually, the Cu (1 1 1) substrates can be epitaxially grown on single-crystalline inorganic substrates or can be recrystallized by annealing for more than 12 h, which limits the cost and time-effective synthesis of graphene. Here, we demonstrate a new method to optimize the crystalline orientations of vertically suspended Cu foils by tension control during graphene growth, resulting in large-area recrystallization into Cu (1 1 1) surface as the applied tension activates the grain boundary energy of Cu and promotes its abnormal grain growth to single crystals. In addition, we found a clue that the formation of graphene cooperatively assists the recrystallization into Cu (1 1 1) by minimizing the surface energy of Cu. The domain sizes and charge carrier mobility of graphene grown on the single-crystalline Cu (1 1 1) are 5 times and similar to 50% increased, respectively, in comparison with those of graphene from Cu (1 0 0), indicating that the less lattice mismatch and the lower interaction energy between Cu (1 1 1) and graphene allows the growth of larger single-crystalline graphene with higher charge carrier mobility. Thus, we believe that our finding provides a crucial idea to design a roll-to-roll (R2R) graphene synthesis system where the tension control is inevitably involved, which would be of great importance for the continuous production of high-quality graphene in the future.