arXiv subjects

Ruben Campos Delgado

Publications and source records attributed to Ruben Campos Delgado.

13 recordsLinked to original sources

arXiv2026

Frame dependence of Kochen-Specker contextuality for relativistic spin systems

We ask whether Kochen-Specker contextuality is Lorentz invariant. On the full Hilbert space, it is, since boosts act unitarily. Restricted to spin, it is not: momentum acts as an environment applying momentum-dependent Wigner rotations, leaving spin observables unsharp and breaking the operator identities behind state-independent contextuality. For spin $1/2$ one scalar governs the loss, the packet average $Δ$ of $\sin^2(θ_W/2)$ (where $θ_W$ is the Wigner angle); for any spin, a ray degrades at a rate set by its spin variance transverse to the boost. In the spin-only account, the Free Will Theorem's SPIN axiom fails for every $Δ>0$; the Yu-Oh set loses contextuality between $Δ\approx0.008$ and $0.016$, with state independence going first; the Peres-Mermin square loses contextuality at $Δ\approx0.059$ or $0.074$ by orientation; singlet CHSH loses nonlocality for $Δ\geq0.159$; and a GHZ-state OR gate loses Raussendorf's contextuality certificate at $Δ\approx0.206$. A $q$-plate implements the channel exactly on photon polarisation, with a retardation in place of the rapidity, so the nonlocality, GHZ and aimed-source results are testable without motion.

quant-ph↗

arXiv2025

Frame dependence of Spekkens' contextuality for relativistic spin systems

We show that the operational definition of contextuality introduced by Spekkens is, in general, not Lorentz invariant. Specifically, we consider an explicit example with particle states consisting of both spin and momentum, we apply a Lorentz transformation to obtain the states in a new inertial frame, and then trace out the momentum degrees of freedom in both frames. We find that, while an observer in the first inertial frame describes a contextual ontological model with respect to spin states and all possible spin measurements, an observer in the boosted frame describes a non-contextual model with respect to the transformed spin states and all transformed spin measurements. Hence, the Spekkens' notion of contextuality, when restricted to spin degress of freedom only, is a frame-dependent concept. We apply our results to predict a novel relativistic effect concerning the task of discriminating between two quantum states. We show that the probability of success for a moving observer exceeds that of an observer at rest.

quant-ph↗

arXiv2025

Ruling out nonlinear modifications of quantum theory with contextuality

Nonlinear modifications of quantum theory are considered potential candidates for the theory of quantum gravity, with the intuitive argument that since Einstein field equations are nonlinear, quantum gravity should be nonlinear as well. Contextuality is a property of quantum systems that forbids the explanation of prepare-and-measure experiments in terms of classical hidden variable models with suitable properties. We show that some well-known nonlinear modifications of quantum mechanics, namely the Deutsch's map, the Weinberg's model, and the Schrödinger - Newton equation, map a contextual set of states to a non-contextual one. That is, the considered nonlinear modifications of quantum theory allow for the existence of classical hidden variable models for certain experimental setups. This enables us to design experiments that would rule out the considered nonlinear modifications of quantum theory by verifying that the system remains contextual, or, equivalently, our results highlight a mechanism how nonlinear modification of quantum theory may lead to weak wave function collapse and ultimately to the solution of the measurement problem.

quant-ph↗

arXiv2024

Quantum gravitational corrections to the geometry of charged AdS black holes

We study the quantum gravitational corrections to the geometry of a four-dimensionalcharged (Reissner-Nordström) Anti de Sitter black hole starting from an effective field theory approach to quantum gravity. We use the expression of the modified horizon radius to compute the quantum corrected Wald entropy, whose expression reproduces the logarithmic behaviour found by other methods. We perform a thermodynamics analysis and compute the quantum gravitational corrections to the temperature, pressure, specific heat and Helmholtz free energy. All these quantities are renormalisation group invariant. We find that a quantum charged AdS black hole can exist only for a bounded range of masses and that it can undergo a second order phase transition as it moves from a state with positive specific heat to a negative one.

hep-th↗

arXiv2024

Traversable Wormholes in Constant Curvature Black Holes

This paper investigates the massive gauge field within spacetime context from a $\mathbb{Z}_2$ quotient of the constant curvature black hole. We investigate how the matter field's back reaction affects the spacetime geometry, considering perturbations in the metric up to the first order. The stress-energy tensor's expectation value can be precisely calculated by evaluating its pull-back onto the covering space. By appropriately selecting boundary conditions for the massive vector field along a non-contractible cycle of the quotient manifold, achieving a negative average energy along a null geodesic becomes feasible, enabling a traversable wormhole.

gr-qc↗

arXiv2024

Modified gravity theories from the Barrow hypothesis

Barrow proposed that quantum gravity effects might introduce fractal corrections to the area of the event horizon of black holes. The area law gets modified as $S \propto A^{1+Δ/2}$, with $0\leqΔ\leq 1$. It was so far unclear whether this assumption could lead to meaningful quantum gravity theories beyond general relativity. In this paper, we argue that this is indeed the case. In particular, assuming $Δ$ to be a radial function, we show that the Barrow hypothesis, together with the Jacobson's approach can generate non-trivial modified gravity theories.

gr-qc↗

arXiv2024

Einstein-Grisaru-Zanon gravity

The leading $(α')^3$-correction to the gravitational low-energy effective action of closed (type II) superstring theory in four-spacetime dimensions defines the Einstein-Grisaru-Zanon gravity action that is applied for a calculation of the leading corrections to the Schwarzschild solution and the Hubble function in the Friedmann-Lemaitre-Robertson-Walker universe, in the first order with respect to the effective string-generated coupling. The solutions found are compared to the corresponding solutions in the Einstein-Bel-Robinson gravity that also modifies the Einstein gravity by the terms quartic in the spacetime curvature. We consider the black hole shadows in the Einstein-Grisaru-Zanon gravity theory and derive the upper bound on the string coupling parameter from the Hawking temperature of a black hole.

hep-th↗

arXiv2023

Quantum Gravitational Corrections to the Entropy of a Reissner-Nordström Black Hole

Starting from an effective action for quantum gravity, we calculate the quantum gravitational corrections to the Wald entropy of a four dimensional non-extremal Reissner-Nordström (RN) black hole in the limit of small electric charge, generalising a previous calculation carried out by Calmet and Kuipers [1] for a Schwarzschild black hole. We show that, at second order in the Ricci curvature, the RN metric receives quantum corrections which shift the classical position of the event horizon. We apply the Wald entropy formula by integrating over the perimeter of the quantum corrected event horizon. We then compute the quantum gravitational corrections to the temperature and the pressure of the black hole.

hep-th↗

arXiv2023

Quantum gravitational corrected evolution equations of charged black holes

We explain how quantum gravity, treated as an effective field theory, might modify the evaporative evolution of a four-dimensional, non-extremal, non-rotating, charged black hole. With some approximations, we derive a set of coupled differential equations describing the charge and mass of the black hole as a function of time. These equations represent a generalisation of the analogous ones already present in the literature for classical black holes.

gr-qc↗

arXiv2023

Schwarzschild-type black holes in Starobinsky-Bel-Robinson gravity

We study physical properties of a Schwarzschild-type black hole in the framework of the recently proposed Starobinsky-Bel-Robinson (SBR) modified theory of gravity, working perturbatively in the new coupling constant. In particular, we compute the temperature, entropy, pressure and lifetime of a Schwarzschild-type black hole.

gr-qc↗

arXiv2022

Lyapunov exponents in $\mathbf{{\cal N}=2}$ supersymmetric Jackiw-Teitelboim gravity

We study $\mathcal{N}=2$ supersymmetric Jackiw-Teitelboim (JT) gravity at finite temperature coupled to matter. The matter fields are related to superconformal primaries by AdS/CFT duality. Due to broken super reparametrisation invariance in the SCFT dual, there are corrections to superconformal correlators. These are generated by the exchange of super-Schwarzian modes which is dual to the exchange of 2D supergravity modes. We compute corrections to four-point functions for superconformal primaries and analyse the behaviour of out-of-time-ordered correlators. In particular, four-point functions of two pairs of primaries with mutually vanishing two-point functions are considered. By decomposing the corresponding supermultiplet into its components, we find different Lyapunov exponents. The value of the Lyapunov exponents depends on whether the correction is due to graviton, gravitini or graviphoton exchange. If mutual two-point functions do not vanish all components grow with maximal Lyapunov exponent.

hep-th↗

arXiv2022

Cylinder quantum field theories at small coupling

We show that any 2D scalar field theory compactified on a cylinder and with a Fourier expandable potential $V$ is equivalent, in the small coupling limit, to a 1D theory involving a massless particle in a potential $V$ and an infinite tower of free massive Kaluza-Klein (KK) modes. Moving slightly away from the deep IR region has the effect of switching on interactions between the zero mode and the KK modes, whose strength is controlled by powers of the coupling, hence making the interactions increasingly suppressed. We take the notable example of Liouville field theory and, starting from its worldline version, we compute the torus (one-loop) partition function perturbatively in the coupling constant. The partition function at leading order is invariant under a T-duality transformation that maps the radius of the cylinder to its inverse and rescales it by the square of the Schwinger parameter of the cylinder. We show that this behavior is a universal feature of cylinder QFTs.

hep-th↗

arXiv2022

On the equivalence of two definitions of conformal primary fields in d > 2 dimensions

Conformal primary fields are of central importance in a conformal field theory with d > 2 spacetime dimensions. They can be defined in two ways. A first definition involves commutators between the field and the generators of the conformal group; a second definition characterizes a primary field according to its behavior under a finite conformal transformation. In the existing literature, the proof of the equivalence of the definitions is either omitted or carried out with little details. In this paper we present a clear and concise review of the two definitions and provide a simple and detailed proof for their equivalence, using some minimal results from quantum field theory and basic properties of conformal transformations. The paper is intended as a tutorial for an introductory lecture course in conformal field theory.

hep-th↗