A
bstract
Recent works have suggested that the entanglement wedge of Hawking radiation coming from an AdS black hole will include an island inside the black hole interior after the Page time. In this ...paper, we propose a concrete way to extract the information from the island by acting only on the radiation degrees of freedom, building on the equivalence between the boundary and bulk modular flow. We consider examples with black holes in JT gravity coupled to baths. In the case that the bulk conformal fields contain free massless fermion field, we provide explicit bulk picture of the information extraction process, where we find that one can almost pull out an operator from the island to the bath with modular flow.
A
bstract
We investigate the spectral form factor in two different systems, free large
N
gauge theories and highly excited string gas. In both cases, after a rapid decay of the spectral form factor ...at early time, new contributions come in, preventing the spectral form factor from ever becoming exponentially small. We consider U(
N
) gauge theories with only adjoint matter and compute the spectral form factor using a matrix integral of the thermal holonomy
U
. The new saddles differ from the early time saddle by preserving certain subgroups of the center symmetry. For a gas of strings, the short time decay of the spectral form factor is governed by the continuous Hagedorn density of states, which can be associated to the thermal winding mode with winding number ±1. We show that the rise of the spectral form factor comes from other winding modes that also carry momentum along the time direction. We speculate on the existence of a family of classical solutions for these string modes, similar to the Horowitz-Polchinski solution.
We review a similar problem for black holes. In particular, we examine the Kontsevich-Segal criterion on complex black holes that contribute to the spectral form factor. In the canonical ensemble quantity
Z
(
β
+
it
), the black hole becomes unallowed at
t
~
O
(
β
). A way to avoid this is to consider the microcanonical ensemble, where the black hole stays allowable.
A
bstract
We consider two dimensional CFT states that are produced by a gravitational path integral.
As a first case, we consider a state produced by Euclidean AdS
2
evolution followed by flat space ...evolution. We use the fine grained entropy formula to explore the nature of the state. We find that the naive hyperbolic space geometry leads to a paradox. This is solved if we include a geometry that connects the bra with the ket, a bra-ket wormhole. The semiclassical Lorentzian interpretation leads to CFT state entangled with an expanding and collapsing Friedmann cosmology.
As a second case, we consider a state produced by Lorentzian dS
2
evolution, again followed by flat space evolution. The most naive geometry also leads to a similar paradox. We explore several possible bra-ket wormholes. The most obvious one leads to a badly divergent temperature. The most promising one also leads to a divergent temperature but by making a projection onto low energy states we find that it has features that look similar to the previous Euclidean case. In particular, the maximum entropy of an interval in the future is set by the de Sitter entropy.
This study explores the mechanical properties of geopolymers derived from construction and demolition waste exposed to high temperatures. Geopolymers were exclusively crafted from waste bricks or ...ceramic tiles, activated with potassium hydroxide/sodium silicate solution. We assessed compressive deformation during 850°C − 1050°C exposure and residual strength post 600°C − 1050°C exposure (simulating ISO 834 curve). Microstructure and bulk properties were also examined.Both geopolymers exhibitecd consistent post-fire behavior. Compressive strength decreased between 600°C and 800°C but rebounded at 1050°C, surpassing initial levels. At 1050°C, density dropped by 8–9%, with a 7–10% mass loss. In fire tests, ceramic tile-based geopolymers displayed plastic deformation at all tested temperatures without macro-fractures, whereas brick-based geopolymers remained elastic up to 1000°C with evident macro-fractures.These findings suggest the potential of both geopolymers as fire-resistant building materials, contributing to advancements in construction materials.
String scale black holes at large D Chen, Yiming; Maldacena, Juan
The journal of high energy physics,
01/2022, Letnik:
2022, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A
bstract
We study aspects of black holes near the Hagedorn temperature. The large dimension expansion introduced by Soda, Emparan, Grumiller and Tanabe connects them to the well studied two ...dimensional black hole based on SL(2)
k
/
U(1). This allows us to explore black holes at string scale temperatures. We argue that the black hole can surpass the Hagedorn temperature, but at a somewhat larger temperature it is likely to turn over to a highly excited string.
A
bstract
It is widely believed that exact global symmetries do not exist in theories that admit quantum black holes. Here we propose a way to quantify the degree of global symmetry violation in the ...Hawking radiation of a black hole by using certain relative entropies. While the violations of global symmetry that we consider are non-perturbative effects, they nevertheless give
O
(1) contributions to the relative entropy after the Page time. Furthermore, using “island” formulas, these relative entropies can be computed within semi-classical gravity, which we demonstrate with explicit examples. These formulas give a rather precise operational sense to the statement that a global charge thrown into an old black hole will be lost after a scrambling time.
The relative entropies considered here may also be computed using a replica trick. At integer replica index, the global symmetry violating effects manifest themselves as charge flowing through the replica wormhole.
A
bstract
In this paper, we study the entanglement entropy between two SYK systems with bilinear coupling. We use the replica trick to calculate the entanglement entropy in the ground state. In ...parallel, we calculate the entanglement entropy through the Ryu-Takayanagi formula in gravity. For the ground state that is dual to an eternal traversable wormhole in AdS
2
, the bulk quantum correction to the entanglement entropy is of the same order as the minimal surface area. The ground state of the coupled system is close to a thermofield double state with particular temperature and they have the same entanglement entropy. From the gravity point of view, we explain why the two states have the same entanglement entropy. We also study a case with time-dependent coupling, which involves finding the quantum extremal surface in the bulk.
The rapid development of modern industry and excessive consumption of petroleum‐based polymers have triggered a double crisis presenting a shortage of nonrenewable resources and environmental ...pollution. However, this has provided an opportunity to stimulate researchers to harness native biobased materials for novel advanced materials and applications. Nanocellulose‐based aerogels, using abundant and sustainable cellulose as raw material, present a third‐generation of aerogels that combine traditional aerogels with high porosity and large specific surface area, as well as the excellent properties of cellulose itself. Currently, nanocellulose aerogels provide a highly attention‐catching platform for a wide range of functional applications in various fields, e.g., adsorption, separation, energy storage, thermal insulation, electromagnetic interference shielding, and biomedical applications. Here, the preparation methods, modification strategies, composite fabrications, and further applications of nanocellulose aerogels are summarized, with additional discussions regarding the prospects and potential challenges in future development.
Nanocellulose aerogels are summarized in terms of their preparation methods, modification strategies, properties, and their inclusion in composites with various other compounds. Their applications with recent advancements in various fields are also presented. Finally, some conclusions and brief future prospects regarding nanocellulose aerogels are discussed.
A
bstract
Motivated by recent studies of the information paradox in (1+1)-D anti-de Sitter spacetime with a bath described by a (1+1)-D conformal field theory, we study the dynamics of second Ŕenyi ...entropy of the Sachdev-Ye-Kitaev (SYK) model (
χ
) coupled to a Majorana chain bath (
ψ
). The system is prepared in the thermofield double (TFD) state and then evolved by
H
L
+
H
R
. For small system-bath coupling, we find that the second Rényi entropy
S
χ
L
,
χ
R
2
of the SYK model undergoes a first order transition during the evolution. In the sense of holographic duality, the long-time solution corresponds to a “replica wormhole”. The transition time corresponds to the Page time of a black hole coupled to a thermal bath. We further study the information scrambling and retrieval by introducing a classical control bit, which controls whether or not we add a perturbation in the SYK system. The mutual information between the bath and the control bit shows a positive jump at the Page time, indicating that the entanglement wedge of the bath includes an island in the holographic bulk.
The Sachdev-Ye-Kitaev (SYK) model is a concrete solvable model to study non-Fermi liquid properties, holographic duality, and maximally chaotic behavior. In this work, we consider a generalization of ...the SYK model that contains two SYK models with a different number of Majorana modes coupled by quadratic terms. This model is also solvable, and the solution shows a zero-temperature quantum phase transition between two non-Fermi liquid chaotic phases. This phase transition is driven by tuning the ratio of two mode numbers, and a nonchaotic Fermi liquid sits at the critical point with an equal number of modes. At a finite temperature, the Fermi liquid phase expands to a finite regime. More intriguingly, a different non-Fermi liquid phase emerges at a finite temperature. We characterize the phase diagram in terms of the spectral function, the Lyapunov exponent, and the entropy. Our results illustrate a concrete example of the quantum phase transition and critical behavior between two non-Fermi liquid phases.
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