arXiv subjects

Victor Franken

Publications and source records attributed to Victor Franken.

11 recordsLinked to original sources

arXiv2026

The endless journey towards the horizon of a quantum black hole

It is a problem of great importance in quantum gravity whether quantum effects lead to nontrivial structure near black hole horizons, and if their interiors are emergent features of a large $N$ limit. We show that the strongly chaotic nature of black holes, captured by random matrix statistics of their spectrum, makes it so that a suitably gravitationally dressed infalling observer takes an infinite amount of proper time to reach the horizon. This makes the black hole interior operationally inaccessible to any outside observer, marking a sharp breakdown of the large $N$ causal structure of black holes in quantum gravity. To model the experience of an infalling observer, we study the response of an infalling particle detector coupled to a matter field in a 2d quantum black hole background, finding a peak in the detector's excitation probability as it enters an infinitely long non-perturbative journey close to the black hole horizon.

hep-th↗

arXiv2026

Falling through the horizon of a quantum black hole

We study quantum-gravitational effects on the response of an infalling detector as it crosses the horizon of a near-extremal black hole in the framework of quantum JT gravity. These effects are incorporated via the gravitational dressing needed to define both the infalling trajectory and the local observables probed by the detector in a diffeomorphism-invariant way. In the black hole exterior, a preferred choice of dressing to the Schwarzian mode of JT gravity can be motivated in connection to geometric modular flow. We show how to extend this dressing to the black hole interior, defining local observables that are gravitationally dressed to both boundaries in the thermofield double state. The gravitational dressing connects the near-horizon region to the IR sector of the Schwarzian theory, leading to measurable effects as the horizon is approached. We find that the infalling detector is able to locally determine the location of the horizon and its temperature, violating the equivalence principle, but without encountering a firewall.

hep-th↗

arXiv2025

Ordering-Independent Wheeler-DeWitt Equation for Flat Minisuperspace Models

We consider minisuperspace models with two-derivative kinetic terms, assuming a flat target space and a closed Universe. We show that, upon canonical quantization of the Hamiltonian, only a restricted class of operator orderings is compatible with the path-integral formulation. Remarkably, these orderings are physically equivalent to all orders in $\hbar$. More precisely, each choice of path-integral measure in the definition of the wavefunction path integral uniquely determines an operator ordering, and hence a corresponding Wheeler-DeWitt equation. These orderings are in one-to-one correspondence with the Jacobians arising from field redefinitions of a set of canonical fields. For each operator ordering consistent with a path-integral measure, we identify a positive definite Hilbert-space inner product. All such prescriptions define the same quantum theory, in the sense that they yield identical physical observables. We illustrate our formalism by applying it to de Sitter Jackiw-Teitelboim gravity and to the Starobinsky model.

hep-th↗

arXiv2025

Information-theoretic constraints in quantum gravity and cosmology

In this dissertation, we review results on quantum information constraints in gravity that are relevant to cosmological models and demonstrate how this approach sheds light on cosmological holography. Using Jackiw-Teitelboim gravity as a toy model, we establish the validity of the quantum Bousso bound and prove the restricted quantum focusing conjecture (rQFC), which is a central assumption in semiclassical gravity and holography. Interestingly, we find violations of the original QFC in this model. Building on these results, we introduce a covariant prescription for computing holographic entanglement entropy in the static patch holography description of de Sitter space and explore a generalization to closed FLRW spacetimes. This leads us to a formulation of subregion-subregion duality, where entanglement between complementary holographic theories gives rise to bulk connectivity. Causality considerations imply that entanglement wedges are bounded by surfaces that are not extremal in the usual sense, but instead satisfy an extremization with constraint. Finally, we discuss the connected wedge theorem, which establishes a relation between the causal structure of spacetime and information-theoretic constraints in the holographic dual. We argue that maintaining the consistency of static patch holography with this theorem leads to constraints on the causal structure of the dual theory. Our results suggest a novel relationship between static patch holography and the dS/CFT correspondence.

hep-th↗

arXiv2025

Tests of restricted Quantum Focusing and a new CFT bound

The restricted quantum focusing conjecture (rQFC) plays a central role in an axiomatic formulation of semiclassical gravity. Since much hinges on its validity, it is imperative to subject the rQFC to rigorous tests in novel settings. Here we do so in two independent directions. First, we prove rQFC in a class of spacetime dimension $d=2$ toy models, JT gravity coupled to a QFT. We also construct explicit counter-examples to the original and stronger Quantum Focusing Conjecture in a regime where matter quantum effects are comparable to the total dilaton value. Second, for $d>2$, we derive from the rQFC a constraint stronger than the Quantum Null Energy Condition (QNEC). In a broad class of states, this bound forbids the QNEC from saturating faster than $O(\mathcal{A})$ as the transverse area $\mathcal{A}$ of a certain null deformation shrinks to zero. We speculate about a universal strengthened QNEC holding across all QFT states.

hep-th↗

arXiv2024

Horizon causality from holographic scattering in asymptotically dS$_3$

In the AdS/CFT correspondence, a direct scattering in the bulk may not have a local boundary analog. A nonlocal implementation on the boundary requires $O(1/G_N)$ mutual information. This statement is formalized by the connected wedge theorem, which can be proven using general relativity within AdS$_3$ but also argued for using quantum information theory on the boundary, suggesting that the theorem applies to any holographic duality. We examine scattering within the static patch of asymptotically dS$_3$ spacetime, which is conjectured to be described by a quantum theory on the stretched horizon in static patch holography. We show that causality on the horizon induced from null infinities $\mathcal{I}^{\pm}$ is consistent with the theorem. Specifically, signals propagating in the static patch are associated with local operators at $\mathcal{I}^{\pm}$. Our results suggest a novel connection between static patch holography and the dS/CFT correspondence.

hep-th↗

arXiv2024

Closed FRW holography: A time-dependent ER=EPR realization

We extend a recent de Sitter holographic proposal and entanglement entropy prescription to generic closed FRW cosmologies in arbitrary dimensions, and propose that for large classes of bouncing and Big Bang/Big Crunch cosmologies, the full spacetime can be encoded holographically on two holographic screens, associated to two antipodal observers. In the expanding phase, the two screens lie at the apparent horizons. In the contracting phase, there is an infinite number of possible trajectories of the holographic screens, which can be grouped in equivalence classes. In each class the effective holographic theory can be derived from a pair of ``parent'' screens on the apparent horizons. A number of cases including moduli dominated cosmologies escape our discussion, and it is expected that two antipodal observers and their associated screens do not suffice to reconstruct these cosmologies. The leading contributions to the entanglement entropy between the screens arise from a minimal extremal trapped or anti-trapped surface lying in the region between them. This picture entails a time-dependent realization of the ER=EPR conjecture, where an effective geometrical bridge connecting the screens via the minimal extremal surface emerges from entanglement. For the Big Crunch contracting cases, the screens disentangle and the geometrical bridge closes off when the minimal extremal trapped sphere hits the Big Crunch singularity at a finite time before the collapse of the Universe. Semiclassical, thermal corrections are incorporated in the cases of radiation dominated cosmologies.

hep-th↗

arXiv2024

On the Quantum Bousso Bound in JT gravity

We prove the Strominger-Thompson quantum Bousso bound in the infinite class of conformal vacua in semiclassical JT gravity, with postive or negative cosmological constant. The Bousso-Fisher-Leichenauer-Wall quantum Bousso bound follows from an analogous derivation, requiring only initial quantum non-expansion. In this process, we show that the quantity ${2πk^μk^ν<:T_{μν}:>-S''-\frac{6}{c}(S')^2}$ vanishes in any vacuum state, entailing a stronger version of Wall's quantum null energy condition. We derive an entropy formula in the presence of a generic class of two reflecting boundaries, in order to apply our argument to the half reduction model of de Sitter JT gravity.

hep-th↗

arXiv2024

de Sitter Connectivity from Holographic Entanglement

Considering two antipodal observers in de Sitter space, we illustrate how spacetime connectivity between the holographic screens located on the (stretched) horizons emerges from holographic entanglement. To do so, we construct a covariant holographic entanglement entropy prescription in de Sitter space, including quantum corrections. While this prescription is inspired by the bilayer proposal, we argue that the monolayer proposal appears to be inconsistent. Entanglement wedge reconstruction implies an extension of static patch holography where the exterior region connecting the static patches is included, and reconstructible from the two screens. A phase transition occurs where there is an exchange of dominance between two competing quantum extremal surfaces, leading to a transfer of the encoding of the exterior region from one screen to the other. The effects in the bulk of integrating out degrees of freedom from the screens are discussed.

hep-th↗

arXiv2023

Bridging the static patches: de Sitter holography and entanglement

In the context of de Sitter static-patch holography, two prescriptions have been put forward for holographic entanglement entropy computations, the monolayer and bilayer proposals. In this paper, we reformulate both prescriptions in a covariant way and extend them to include quantum corrections. We argue that the bilayer proposal is self-consistent, while the monolayer proposal exhibits contradictory behavior. In fact, the bilayer proposal leads to a stronger holographic description, in which the full spacetime is encoded on two screens at the cosmological horizons. At the classical level, we find large degeneracies of minimal extremal homologous surfaces, localized at the horizons, which can be lifted by quantum corrections. The entanglement wedges of subregions of the screens exhibit non-trivial behaviors, hinting at the existence of interesting phase transitions and non-locality in the holographic theory. In particular, while each screen encodes its corresponding static patch, we show that the entanglement wedge of the screen with the larger quantum area extends and covers the causal diamond between the screens, with a phase transition occurring when the quantum areas of the screens become equal. We argue that the capacity of the screens to encode the region between them is lost, when these are pushed further in the static patches of the observers and placed on stretched horizons.

hep-th↗

arXiv2022

Pseudo-Nambu-Goldstone bosons and tachyons in flux compactification

In a six-dimensional gauge theory compactified on a torus with magnetic flux, translational symmetry in the extra dimensions is broken. As a result, a massless Nambu-Goldstone boson appears in the four-dimensional effective Lagrangian. We show that a model with two $U(1)$ gauge symmetries includes a pseudo-Nambu-Goldstone scalar boson, whose mass is finite but shielded from large quantum corrections. This opens the door to achieving scalar masses in the TeV range. Additionally, we explore the presence of tachyons in the effective Lagrangian for $SU(2)$ gauge theories. By introducing a scalar field in the adjoint representation of $SU(2)$ with a finite vacuum expectation value, we demonstrate that tachyonic modes can be eliminated for sufficiently large values of the coupling constant, while preserving fermion chirality in the model.

hep-th↗