arXiv subjects

Gabriel Abellán

Publications and source records attributed to Gabriel Abellán.

9 recordsLinked to original sources

arXiv2026

Zero expansion is not free: the sharp minimum of Eulerian negative energy in Natário warp drives

Natário's warp drive replaces the contraction and expansion of the Alcubierre bubble by a divergence-free shift. We determine exactly how much Eulerian negative energy this construction requires. For the Lobo-Visser volume integral $\mathcal{E}_{\rm LV}=-\int_{Σ_t}ρ_{\rm E}\,d^3x$ on the standard flat slice, with unit lapse, a flat interior of radius $R$, and exact matching to a uniform exterior stream of speed $v$ at $R+Δ$, we prove a lower bound for every admissible shift and find the exact minimum in closed form at every aspect ratio. As the wall thins, $\mathcal{E}_{\min}\sim v^2R^4/(4Δ^3)$ with sharp constant $1/4$, two powers of $R/Δ$ above the earlier estimate $v^2R^2/Δ$ applied to both Natário and Alcubierre bubbles. Incompressibility forces the flux displaced by the bubble to return through the wall, and the tangential shear of this return current dominates the energy. The full variational problem is equivalent to classical Stokes flow between concentric spheres. Its unique minimizer tends to a minimal-curvature cubic in the thin-wall limit. An exact flux identity and independent quadrature support the analytic result. The bounded quantity is slice and observer dependent and is distinct from the ADM mass.

gr-qc↗

arXiv2026

Transient Coherence and Multiscale Spectral Structure after a Mass Quench in a 1+1-Dimensional Scalar Field

A mass quench generates anomalous pair correlations that are absent from the final particle occupations. For a free real scalar field in $1+1$ dimensions, we define a bilocal observable by smearing the statistical Keldysh correlator with a Morlet kernel on the finite post-quench relative-time interval. Its excess over the dephased correlator gives a dimensionless relative coherence weight. At fixed momentum, this weight is exactly independent of the initial temperature for Gaussian thermal states evolved with the same free Hamiltonian: the common thermal amplitude cancels between numerator and denominator. The cancellation is not a purity criterion and is not exclusive to wavelets. We derive the finite-window response and show that the anomalous signal depends essentially on the observation window; an admissible zero-mean wavelet annihilates the relative-time-constant anomalous term on the full line. We compare this response with the signed finite-time Wigner spectrum and derive a distinct Gaussian-extension positivity bound. Exact smooth-quench occupations provide an independent dynamical reference. Finally, we formulate a renormalized Hartree extension and delimit the oscillatory and nonoscillatory regimes of a scalar mode on a fixed two-dimensional de Sitter background.

hep-th↗

arXiv2026

Boundary Obstructions and Lapse Freedom in Static Spherical Hollow Cores

We analyze a sharply delimited comparison problem for a static spherical hollow core: an empty, flat cavity surrounded by a positive matter wall. In the unit-lapse, flat-slice radial Painleve--Gullstrand (PG) class the Type-I source obeys $p_r=-ρ$ and $p_\perp=-ρ-rρ'/2$. A regular nonnegative density that rises out of the cavity must therefore violate the transverse null and weak energy conditions. We quantify this boundary obstruction by an exact weighted onset budget and a depth--width bound, and show that the sharp limit has the same negative tangential pressure as its symmetry-invariant regularized Israel layer. We then close the adjacent unit-lapse, curved-slice route under a monotone areal-radius hypothesis. Finally, when only the lapse is released, an incomplete-beta family gives regular hollow shells with flat cavities, Schwarzschild exteriors, no thin shells, and NEC/WEC/SEC/DEC on an explicit compactness interval. The family is conditionally characterized in the minimum-degree and $p_r=0$ sectors and admits a fixed-ADM-mass cavity redshift benchmark. The result is a static boundary theorem and construction, not a general hollow-shell existence theorem, a transport result, or an experimental feasibility claim.

gr-qc↗

arXiv2026

Covariance-Driven Momentum Rectification at Liquid-Vapor Interfaces Near Wetting Transitions

Zero-mean forcing can generate directed transport when a medium responds in a spatially structured way and the relevant symmetries are broken. Liquid-vapor interfaces are a useful setting for this problem because surface-tension gradients, wetting dynamics, vapor exchange, capillary and acoustic waves, electro-ionic screening, thermal noise, and boundary compliance can all carry momentum. We develop a conservative continuum model in which the central object is the covariance between a local response field and a zero-mean tangential drive, $\langle Mf\rangle-\langle M\rangle\langle f\rangle$, embedded in an explicit momentum ledger. In a minimal diffuse-interface realization, this covariance gives the phase-selective drift law $U\proptoε_hΘ\sinφ$ for a Marangoni-driven liquid-vapor interface above a structured wall, with exact nulls when the symmetry is restored. Wetting susceptibility then acts as a bounded gain factor: first-order spinodal conditions provide the useful amplification regime, critical wetting saturates because interfacial unbinding removes the short-range drive, and bulk criticality suppresses the channel as the interface disappears. Additional reservoirs - phase change, waves, thermal transport, electro-ionic coupling, compliance, and fluctuations - are treated as compensating channels to be isolated by sign reversals, scaling laws, and budget closure. The result is neither a new microscopic force nor an apparatus-level claim, but a symmetry-constrained accounting scheme for rectified momentum transfer in water-based interfacial systems. Reduced numerical calculations illustrate the phase-selection rules, bounded spinodal gain, momentum-budget closure, transverse chirality, and grid convergence.

cond-mat.soft↗

arXiv2023

A Generalized Double Chaplygin Model for Anisotropic Matter: The Newtonian Case

In this work, we investigate astrophysical systems in a Newtonian regime using anisotropic matter. For this purpose, we considered that both radial and tangential pressures satisfy a generalized Chaplygin-type equation of state. Using this model, we found the Lane--Emden equation for this system and solved it numerically for several sets of parameters. Finally, we explored the mass supported by this physical system and compared it with the Chandrasekhar mass.

gr-qc↗

arXiv2023

Warp drive solutions in spherical coordinates with anisotropic matter configurations

In this work we study the influence of isotropic and anisotropic fluids on the spherically symmetric warp metric. We evaluate the energy conditions and the influence of including a cosmological constant type term. We find that, considering this term, there is a trade-off between the weak and strong energy conditions. The obtained solutions are numerical and we solve the system for both the stationary and the full regime. The influence of imposing the zero expansion condition has been explored. We find a wide diversity of behaviours for the solutions. In general there are regions of spacetime where the energy conditions can be at least partially satisfied. Finally, we calculate the value of the total mass using the density found in the numerical simulations, finding examples where it remains positive during the entire evolution of the system.

gr-qc↗

arXiv2020

Anisotropic 2+1 dimensional black holes by gravitational decoupling

In the present paper, we analyze the well-known 2+1 dimensional black holes (assuming a non-vanishing cosmological constant) in light of the gravitational decoupling by the minimal geometric deformation approach. To illustrate our results, we consider the BTZ geometry as the seed solution to generate new anisotropic ones. To complement the study, the curvature scalars and the energy conditions are analyzed.

gr-qc↗

arXiv2020

Beyond classical anisotropy and a new look to relativistic stars: a gravitational decoupling approach

In this article, we propose a physical condition to extend interior isotropic solutions to anisotropic domains by gravitational decoupling in the framework of the Minimal Geometric Deformation approach. In particular, it is found that by using an expression reminiscent of the classical anisotropy factor, we can close the decoupling system of equations and a new anisotropic solution can be found. As an example, we extend the well--known Tolman IV.

gr-qc↗

arXiv2020

Regularity condition on the anisotropy induced by gravitational decoupling in the framework of MGD

We use gravitational decoupling to establish a connection between the minimal geometric deformation approach and the standard method for obtaining anisotropic fluid solutions. Motivated by the relations that appear in the framework of minimal geometric deformation, we give an anisotropy factor that allows us to solve the quasi--Einstein equations associated to the decoupler sector. We illustrate this by building an anisotropic extension of the well known Tolman IV solution, providing in this way an exact and physically acceptable solution that represents the behavior of compact objects. We show that, in this way, it is not necessary to use the usual mimic constraint conditions. Our solution is free from physical and geometrical singularities, as expected. We have presented the main physical characteristics of our solution both analytically and graphically and verified the viability of the solution obtained by studying the usual criteria of physical acceptability.

gr-qc↗