arXiv subjects

Damien A. Easson

Publications and source records attributed to Damien A. Easson.

At least 19 recordsLinked to original sources

arXiv2026

Black Hole Interiors as a Laboratory for Time-Dependent Classical Double Copy

The classical double copy relates gravity and gauge theory, but its most explicit realizations remain concentrated in stationary or highly symmetric settings. We show that trapped regions of black-hole geometries provide an exact setting for time-dependent classical double copy. More generally, a class of Kantowski--Sachs cosmologies admits an intrinsic double-copy construction: the Kerr--Schild scalar and single-copy field are uniquely reconstructible from the cosmological metric alone, without prior knowledge that the spacetime is a black-hole interior or reference to any exterior completion. The reconstructed field admits both the standard flat-background Kerr--Schild realization and a complementary Maxwell realization on the Kantowski--Sachs geometry, where it describes a homogeneous, time-dependent electric field. We prove that this class is characterized by a relation between the Kantowski--Sachs scale factors equivalent to $p_{\parallel}=-ρ$. For Schwarzschild, the single-copy electric field diverges along the interior evolution, whereas for the regular Bardeen solution it remains finite throughout the trapped region and extends smoothly into the regular static core. The Bardeen geometry violates the strong energy condition in a compact central region, whereas the corresponding single-copy Maxwell field remains regular and satisfies the standard classical energy conditions. We further show that the Bardeen horizon phase structure is encoded in the single-copy scalar. Thus trapped Kerr--Schild interiors provide an exact local realization of time-dependent classical double copy.

hep-th↗

arXiv2026

The Double Copy of the Black Ring

We construct an exact Weyl double copy of the singly spinning five-dimensional Emparan--Reall black ring. Its complete nonlinear Weyl curvature is the sum of two scalar-weighted Maxwell squares. One field is generated by the stationary Killing vector; the other carries topological magnetic flux through a sphere linking the ring. Both are source-free Maxwell fields on the black-ring spacetime, with corresponding scalar partners obeying a common sourced wave equation. This extends exact five-dimensional Weyl doubling beyond the type-$\mathrm D$ and type-$\mathrm N$ examples to a black hole whose exterior contains both type-$\mathrm G$ and type-$\mathrm{I}_i$ regions. The Weyl polynomial factorizes into two distinct irreducible quadratics, establishing genuine De Smet type $22$, thereby ruling out a reduction to a single Maxwell square.

hep-th↗

arXiv2026

Obstructions to Minimal Regular Black Hole Cosmologies

We derive an obstruction to Friedmann--Lemaître--Robertson--Walker (FLRW) daughter cosmologies from static, asymptotically flat regular black holes. The trapped region of such a parent is Kantowski--Sachs rather than FLRW, so the daughter must be introduced as a separate matched region. For closed daughters, the angular Darmois condition is controlled by the Misner--Sharp mass: asymptotic flatness and finite ADM mass force the induced density to decay as $A^{-3}$, while the $k=+1$ curvature term scales as $A^{-2}$. The minimal closed branch is therefore bounded rather than indefinitely expanding. Flat and open daughters avoid this boundedness mechanism. For their maximal homogeneous FLRW continuations, the regular-end affine-ANEC theorem excludes simultaneous non-staticity, curvature regularity, null geodesic completeness, and ANEC consistency. For Bardeen, the parent source does not naturally supply the late-time support needed for an unbounded closed daughter. Within these criteria, a viable FLRW daughter therefore requires additional structure, such as modified asymptotics, nonminimal matching, non-FLRW evolution, or an additional stress-energy component.

gr-qc↗

arXiv2026

Anomaly-driven evaporation endpoints of a two-dimensional regular black hole

Spherical reduction of four-dimensional minimally coupled matter yields a two-dimensional theory with dilaton-coupled matter rather than minimally coupled conformal matter. We use this distinction to revisit the backreacted late-time endpoint problem for the regular two-dimensional Bardeen-like black hole considered by Barenboim, Frolov, and Kunstatter. Replacing the Polyakov quantum sector by the dilaton-coupled anomaly model of Fabbri, Farese, and Navarro-Salas (FFN), we derive the corresponding semiclassical field equations and classify the asymptotically allowed late branches at finite radius. For any quiescent finite-radius branch with finite nonzero conformal factor, the late-time mixed equation enforces $J'(r_\infty)=0$, and hence $r_\infty=\sqrt{2}\,\ell$, independently of the local dilaton-anomaly convention. For finite-radius null branches satisfying the stated state-tail assumptions, the ordinary strong-cosmic-censorship-restoring exponential null boundary is excluded. Generic power-law branches $e^{2ρ}\sim v^{-p}$ with $p>1$ are likewise excluded, except for the borderline case $p=2$, which is the only remaining null loophole of this type. In the FFN model, the settled realization of this loophole carries finite affine flux and requires the stronger state-tail decay $s_ϕ=O(v^{-2})$. The natural finite-radius outcome is remnant-like, while the surviving null branch is a highly constrained soft-null alternative.

hep-th↗

arXiv2026

Geodesically Complete Curvature-Bounce Inflation

The early universe need not be described by an incomplete inflationary phase connected to a separate, more exotic prehistory. Recent results show that, within non-static FRW cosmology, only positive spatial curvature permits a nonsingular, geodesically complete universe with ANEC-respecting matter. We construct a geodesically complete closed $k=+1$ bounce-plus-inflation cosmology in ordinary general relativity, sourced by a single canonical scalar field with a positive vacuum offset. The bounce is supported by curvature rather than exotic stress energy: the matter content satisfies the NEC throughout and violates only the strong energy condition, as in any accelerated expansion. The solved branch remains sub-Planckian and evolves onto a curvature-diluted slow-roll phase with inflationary observables consistent with current constraints. The pivot-scale predictions are $n_s=0.9617$, $r=0.0045$ at $N_*=55$ and $n_s=0.9650$, $r=0.0037$ at $N_*=60$. Direct evolution of closed-universe infrared perturbations shows regular tensor and scalar propagation through the bounce and inflationary era, with the physical curvature perturbation freezing in the standard way. This gives a minimal explicit realization of a complete early-universe cosmology in the closed FRW branch selected by completeness and ANEC compatibility.

astro-ph.CO↗

arXiv2026

Resonant delay in a stationary quantum clock: Lifting the threshold mask

Quantum transit times have a long history of inequivalent definitions, including phase times, dwell times, and quantum-clock constructions. In this context we revisit the Salecker--Wigner--Peres stationary quantum clock as a phase-sensitive scattering observable, with clock time defined by the energy derivative of the transmission phase shift across the interaction region. For real compactly supported one-dimensional potentials, we show that the raw stationary Peres clock generically contains a universal $1/\sqrt{E}$ continuum-edge term whose coefficient is fixed by low-energy scattering data. For the attractive square well, this threshold singularity is inherited from the vanishing exterior momentum and the associated scattering matching, rather than from resonant delay itself. We derive the exact stationary clock time for the square well and introduce a new threshold-subtracted clock observable. Away from exceptional zero-energy tuning, the subtraction removes the universal low-energy term and isolates the resonant contribution. Comparison with the dwell time and the transmission Wigner phase delay shows that the threshold-subtracted clock acquires the expected local Lorentzian form near isolated transmission resonances. Near the continuum edge, if $\varepsilon$ denotes the detuning from threshold, the resonant peak grows only as $\varepsilon^{-1/2}$, whereas the unsubtracted threshold background grows as $\varepsilon^{-3/2}$. A symmetric barrier--well--barrier cavity and a numerical asymmetric two-step attractive well provide complementary controls. The result is a new threshold-subtracted stationary-clock candidate that separates universal threshold kinematics from pole-sensitive resonant delay.

quant-ph↗

arXiv2026

The fate of Schwarzschild--de Sitter black holes: nonequilibrium evaporation

We present a fully analytic treatment of Schwarzschild--de~Sitter (SdS) black-hole evaporation in two-dimensional dilaton gravity with anomaly-induced backreaction. Starting from the spherical reduction of four-dimensional Einstein gravity with a cosmological constant, we construct an exactly solvable 2D model that captures the full causal and thermodynamic structure of the SdS static patch, including both black-hole and cosmological horizons. Incorporating the trace anomaly of $N$ conformal matter fields via the Polyakov action, we determine the evolution of the black-hole mass and geometry in the Unruh--de~Sitter state, track the steady nonequilibrium Hawking flux, and compute local thermodynamic observables for static observers. The conserved Killing energy flux drives an irreversible heat current from the black hole to the cosmological horizon whenever their surface gravities differ, ensuring monotonic entropy growth and satisfaction of the generalized second law. We prove that $κ_b>κ_c$ throughout the physical static patch, so the only zero-flux configuration is the Nariai limit where the horizons coincide. Extending the framework to the quantum-information regime, we construct a thermo-controlled estimate of the Page curve and show how quantum extremal surfaces and entanglement islands emerge naturally within the anomaly-induced steady state. These results constitute a fully analytic, backreacted solution for SdS evaporation that unifies semiclassical thermodynamics and information flow in a cosmological setting, thereby elucidating the ultimate fate of evaporating black holes in de~Sitter space.

hep-th↗

arXiv2026

Cauchy-horizon flux coefficients in the reduced Polyakov model

We derive the leading Cauchy-horizon flux coefficient in the stationary reduced Polyakov sector of spherically symmetric charged black holes. For a nonextremal inner horizon with affine coordinate $V_-=-e^{-κ_-v}$, a finite late-time Eddington--Finkelstein flux $F_-^{(\infty)}=\lim_{v\to+\infty}\langle T_{vv}\rangle$ is amplified as $\langle T_{V_-V_-}\rangle\sim F_-^{(\infty)}/(κ_-^2V_-^2)$. In the stationary reduced Polyakov model, $F_-^{(\infty)}=t_v-Nκ_-^2/(48π)$. Thus the leading pure $V_-^{-2}$ Polyakov coefficient is absent precisely on the inner-horizon cancellation surface $t_v=Nκ_-^2/(48π)$. The future event horizon determines the distinct outgoing condition $t_u=Nκ_+^2/(48π)$, so the two horizons select different loci in the stationary $(t_u,t_v)$ state space. Standard outer prescriptions, such as the asymptotically flat Unruh prescription and the outer-horizon thermal/KMS prescription, generically lie away from the inner-horizon cancellation surface and generate nonzero inner-horizon coefficients. We then analyze the total flux hierarchy $T_{vv}^{\rm tot}=F_0+Av^{-p}+o(v^{-p})$: cancellation of the pure quadratic coefficient is the constant-level condition $F_0=0$, while nonzero Price-tail terms give logarithmically weakened divergences. This state-space formulation gives an exact characterization of Cauchy-horizon flux amplification in the anomaly-induced radial sector and shows that, when the total coefficient is nonzero, the corresponding radial null curvature diverges.

gr-qc↗

arXiv2026

The fate of Reissner--Nordström--de Sitter black holes: nonequilibrium discharge and evaporation

We develop a semiclassical description of Reissner--Nordström--de Sitter (RN--dS) evaporation by combining a spherically reduced two-dimensional dilaton gravity model with Polyakov anomaly backreaction. The framework captures the causal and thermodynamic structure of the static patch and yields closed adiabatic evolution equations for the mass and charge. With an outward-oriented flux convention, the anomaly-induced Killing-energy flux is $\mathcal F=(N_{\rm eff}/48π)(κ_b^2-κ_c^2)$, while the full mass evolution is $\dot M=-\mathcal F+Φ_b\dot Q$, with $Φ_b=Q/r_b$. We prove analytically that along the entire sub-Nariai neutral Schwarzschild--de Sitter branch $κ_b>κ_c$, so neutral black holes lose mass monotonically. Schwinger pair production provides the discharge channel. In the rapid-discharge regime, controlled charged trajectories become effectively neutral on a timescale short compared with the anomaly-driven Hawking mass-loss time and then follow the neutral SdS channel toward empty de Sitter space. The classical lukewarm locus $T_b=T_c$ is only the nullcline of the anomaly-induced heat flux: the electromagnetic work term tilts the full semiclassical vector field away from this curve, so it is not an invariant trajectory. When sufficiently light charged species provide a rapid-discharge channel, the classical cold/extremal, charged Nariai, ultracold, and lukewarm loci are not semiclassical attractors for controlled nondegenerate trajectories. These results give an adiabatically backreacted derivation of the RN--dS evaporation endpoint in the regime controlled by anomaly-induced flux and rapid charge discharge, and provide the semiclassical background for generalized-second-law monotonicity and conservative quantum-extremal-surface/island estimates.

hep-th↗

arXiv2026

Affine ANEC selects the closed FRW branch for geodesically complete cosmology

We study the relation between geodesic completeness, the averaged null energy condition (ANEC), and spatial curvature in Friedmann--Robertson--Walker (FRW) cosmology within classical general relativity. Using the affinely parameterized ANEC along radial null geodesics, we prove that non-static flat or open FRW spacetimes in the regular classes considered here cannot be both null geodesically complete and ANEC-satisfying. Bounded oscillatory or cyclic flat/open models do not circumvent the obstruction: the negative affine-ANEC bulk term accumulates over infinitely many cycles, giving $I_{\rm ANEC}=-\infty$ for non-static periodic cases. Equivalently, within these classes, non-static ANEC-satisfying flat or open models are null incomplete. The sign obstruction is absent in closed $(k=+1)$ FRW geometry, where the positive curvature term enters the affine ANEC identity with the opposite sign and can support nonsingular, geodesically complete cosmologies with ordinary NEC-respecting matter. We give explicit closed-FRW scalar-field constructions, including a fully analytic quadratic reconstruction and a cubic-root reconstruction in closed quadrature, and contrast them with their flat realizations, which require NEC-violating support. Furthermore, we quantify how positive curvature can bias flat-model reconstructions toward an effective phantom equation of state, finding only a percent-level effect under current curvature bounds. The result is a curvature classification of ANEC-compatible eternal FRW cosmology: flat and open branches are obstructed, while the closed branch admits explicit complete realizations, with global de Sitter appearing as the vacuum limiting representative.

gr-qc↗

arXiv2026

Open case for a closed universe

We establish a new no-go theorem for cosmology: spatially flat ($k=0$) and open ($k=-1$) Friedmann--Robertson--Walker (FRW) non-static spacetimes cannot be simultaneously nonsingular, geodesically complete, and consistent with the averaged null energy condition (ANEC). Equivalently, any dynamic flat or open universe that is complete must violate the ANEC. By contrast, closed universes ($k=+1$) uniquely admit nonsingular, geodesically complete, ANEC-consistent solutions, with global de Sitter space as the canonical realization that saturates the ANEC. Furthermore, we analytically demonstrate that positive spatial curvature naturally mimics the phenomenology of phantom dark energy ($w<-1$), biasing flat-model reconstructions of $w(z)$ at the $\sim 1\%$ level. These results augment the classical singularity theorems, establish a new classification of eternal cosmologies, and motivate renewed scrutiny of spatial curvature in both theory and observation.

hep-th↗

arXiv2026

Untwisting the double copy: the zeroth copy as an optical seed

We present a historical optical foundation for stationary vacuum Kerr--Schild spacetimes on a flat background and interpret it in modern double-copy language. In this setting, a complex optical seed $ρ=-θ-iω$, built from the expansion and signed twist of the Kerr--Schild congruence, is harmonic, while its inverse obeys an eikonal equation and reconstructs the congruence algebraically. Thus the local stationary geometry is organized by a single complex seed. In the overlap of the stationary Kerr--Schild and Petrov type--D Weyl double-copy framework, this seed furnishes a normalized representative of the zeroth-copy data, while its real part yields the Kerr--Schild profile and its gradient generates the single-copy gauge-field strength. The construction provides, without recourse to twistor methods, a spacetime realization of how a single complex seed builds the congruence, organizes the associated spacetime and gauge fields, and encodes the geometric content of the zeroth copy.

hep-th↗

arXiv2026

Inflationary resolution of the initial singularity

The inflationary paradigm has transformed our understanding of the early universe; yet most inflationary models are considered geodesically past-incomplete, suggesting a beginning of time or a primordial Big Bang singularity. The Borde-Guth-Vilenkin (BGV) theorem is often cited as demonstrating that all eternally inflating spacetimes must be past-incomplete. Utilizing a new theorem establishing geodesic completeness in generalized cosmologies, we present a simple, explicit class of inflationary solutions that are smooth, nonsingular, and geodesically complete for all time, including into the past. These models exhibit localized NEC violation but remain globally well-behaved in both temporal directions. The NEC violation is confined and controlled: the averaged null energy condition (ANEC) is satisfied in the strongest sense, while violations of smeared null energy conditions (SNEC) are uniformly bounded and become nonnegative under sufficiently wide smearings. Our results suggest that eternal inflation can arise from controlled NEC-violating dynamics, offering a new, nonsingular, and past-eternal picture of the universe.

hep-th↗

arXiv2025

Eternal Universes

We consider the possibility of a past and future eternal universe, constructing geodesically complete inflating, loitering, and bouncing spacetimes. We identify the constraints energy conditions in General Relativity place on the building of eternal cosmological models. Inflationary and bouncing behavior are shown to be essential ingredients in all significant examples. Non-trivial complete flat spacetimes are shown to violate the null energy condition (NEC) for at least some amount of time. Ignoring the intractable subtleties introduced by quantum considerations, such as rare tunneling events and Boltzmann brains, we demonstrate that these universes need not have had a beginning or an end.

hep-th↗

arXiv2025

Nonsingular black holes as dark matter

It is commonly assumed that low-mass primordial black holes cannot constitute a significant fraction of the dark matter in our universe due to their predicted short lifetimes from the conventional Hawking radiation and evaporation process. Assuming physical black holes are nonsingular--likely due to quantum gravity or other high-energy physics--we demonstrate that a large class of nonsingular black holes have finite evaporation temperatures. This can lead to slowly evaporating low-mass black holes or to remnant mass states that circumvent traditional evaporation constraints. As a proof of concept, we explore the limiting curvature hypothesis and the evaporation process of a nonsingular black hole solution in two-dimensional dilaton gravity. We identify generic features of the radiation profile and compare them with known regular black holes, such as the Bardeen solution in four dimensions. Remnant masses are proportional to the fundamental length scale, and we argue that slowly evaporating low-mass nonsingular black holes, or remnants, are viable dark matter candidates.

hep-th↗

arXiv2024

Isometries and the double copy

In the standard derivation of the Kerr-Schild double copy, the geodicity of the Kerr-Schild vector and the stationarity of the spacetime are presented as assumptions that are necessary for the single copy to satisfy Maxwell's equations. However, it is well known that the vacuum Einstein equations imply that the Kerr-Schild vector is geodesic and shear-free, and that the spacetime possesses a distinguished vector field that is simultaneously a Killing vector of the full spacetime and the flat background, but need not be timelike with respect to the background metric. We show that the gauge field obtained by contracting this distinguished Killing vector with the Kerr-Schild graviton solves the vacuum Maxwell equations, and that this definition of the Kerr-Schild double copy implies the Weyl double copy when the spacetime is Petrov type D. When the Killing vector is taken to be timelike with respect to the background metric, we recover the familiar Kerr-Schild double copy, but the prescription is well defined for any vacuum Kerr-Schild spacetime and we present new examples where the Killing vector is null or spacelike. While most examples of physical interest are type D, vacuum Kerr-Schild spacetimes are generically of Petrov type II. We present a straightforward example of such a spacetime and study its double copy structure. Our results apply to real Lorentzian spacetimes as well as complex spacetimes and real spacetimes with Kleinian signature, and provide a simple correspondence between real and self-dual vacuum Kerr-Schild spacetimes. This correspondence allows us to study the double copy structure of a self-dual analog of the Kerr spacetime. We provide evidence that this spacetime may be diffeomorphic to the self-dual Taub-NUT solution.

gr-qc↗

arXiv2024

Kleinian black holes

We prove there is a unique vacuum solution in split-signature spacetimes with Kleinian SO(2,1) spherical symmetry. We extend our analysis to accommodate a positive or negative cosmological constant and we prove the Kleinian spherically symmetric solutions to Einstein's equation are locally isomorphic to the split-signature analogues of Schwarzschild-(Anti)-de Sitter or Nariai spacetimes. Our analysis provides a Kleinian extension of Birkhoff's theorem to metrics with split-signature. Axisymmetric vacuum solutions are also considered, including (2,2) signature formulations of the Kerr and Taub-NUT metrics.

hep-th↗

arXiv2022

Einstein-Maxwell theory and the Weyl double copy

The Weyl double copy relates vacuum solutions in general relativity to Abelian gauge fields in Minkowski spacetime. In a previous work, we showed how the Weyl double copy can be extended to provide a treatment of external gravitational sources consistent with the classical Kerr-Schild double copy. Using this generalization, here we provide a complete double copy analysis of electrovacuum Petrov type D spacetimes. This includes the first analysis of the charged C-metric, whose single copy interpretation invokes the two-potential formalism of electrodynamics. We also present the first double copy prescription for the Ricci spinor, which for non-accelerating spacetimes, takes a form similar to the original double copy relation for the Weyl spinor.

gr-qc↗