arXiv subjects

Elizabeth Winstanley

Publications and source records attributed to Elizabeth Winstanley.

At least 19 recordsLinked to original sources

arXiv2026

Quantum effects of charged massive scalar fields on charged black hole space-times

We compute the renormalized expectation values of the scalar condensate, charge current and stress-energy tensor for a massive charged quantum scalar field on a Reissner-Nordstrom black hole. The mass of the scalar field is sufficiently large that classical superradiance is absent. We present results for the Boulware, Unruh and Hartle-Hawking states. Renormalized expectation values in the Hartle-Hawking state are computed using an efficient and accurate mode sum prescription, and for the other two states we employ state subtraction. The efficiency of our numerical method enables us to explore a large part of the parameter space, including near-extremal black hole charges and scalar field masses close to the superradiant limit.

hep-th↗

arXiv2025

Quantum-corrected three-dimensional AdS space-time

We study quantum-corrected solitons in global, three-dimensional, anti-de Sitter (AdS) space-time. These static solitons have a regular origin and arise as solutions of the linearized quantum-corrected Einstein equations (LQCEE). On the right-hand-side of the LQCEE is the renormalized expectation value of the stress-energy tensor operator for a massless, conformally coupled, quantum scalar field in a nonrotating thermal state, computed in quantum field theory (QFT), or using relativistic kinetic theory (RKT). We calculate the mass of the solitons and compare the results from QFT and RKT.

gr-qc↗

arXiv2025

Quantum effects in rotating thermal states on anti-de Sitter space-time

We study the stress-energy tensor of a massless, conformally coupled, quantum scalar field in a rigidly-rotating thermal state on three- and four-dimensional anti-de Sitter space-time. We first find the stress-energy tensor using relativistic kinetic theory, modelling the field as a thermal gas of massless bosons. We then compute the renormalized stress-energy tensor of the scalar field in quantum field theory and compare it with that resulting from relativistic kinetic theory.

hep-th↗

arXiv2025

Nonminimal coupling, quantum scalar field stress-energy tensor and energy conditions on global anti-de Sitter space-time

We compute the renormalized expectation value of the stress-energy tensor operator for a quantum scalar field propagating on three-dimensional global anti-de Sitter space-time. The scalar field has general mass and nonminimal coupling to the Ricci scalar curvature, and is subject to Dirichlet, Neumann or Robin boundary conditions at the space-time boundary. We consider both vacuum and thermal states, and explore whether the weak and null energy conditions are satisfied by the quantum stress-energy tensor. We uncover a rather complicated picture: compliance with these two energy conditions depends strongly on the mass and coupling of the scalar field to the curvature, and the boundary conditions applied.

hep-th↗

arXiv2025

Renormalized charged scalar current on a Reissner-Nordstrom black hole in the presence of charge superradiance

We compute the renormalized charge current for a massless, minimally coupled, charged quantum scalar field on a charged Reissner-Nordstrom black hole space-time, using the method of pragmatic mode-sum renormalization. Since the field exhibits superradiance, we consider the past Unruh, Boulware and Candelas-Chrzanowski-Howard states, and study how the renormalized current in these states depends on the charges of the black hole and scalar field. We also study the backreaction of the charge current on the electromagnetic field.

hep-th↗

arXiv2025

Quantum-corrected anti-de Sitter space-time

We study the back-reaction of a quantum scalar field on anti-de Sitter (AdS) space-time. The renormalized expectation value of the stress-energy tensor operator for a massless, conformally-coupled quantum scalar field on global AdS space-time in four space-time dimensions acts as a source term on the right-hand-side of the Einstein equations for the quantum-corrected metric. We solve the quantum-corrected Einstein equations numerically and find deviations from pure AdS which increase as the temperature of the quantum scalar field state increases. We interpret these quantum-corrected metrics as asymptotically-AdS solitons, and study the mass of these solitons as a function of the temperature of the quantum scalar field.

hep-th↗

arXiv2025

Quantum fermion superradiance and vacuum ambiguities on charged black holes

Unlike a classical charged bosonic field, a classical charged fermion field on a static charged black hole does not exhibit superradiant scattering. We demonstrate that the quantum analogue of this classical process is however present. We construct a vacuum state for the fermion field which has no incoming particles from past null infinity, but which contains, at future null infinity, a nonthermal flux of particles. This state describes both the discharge and energy loss of the black hole, and we analyze how the interpretation of this phenomenon depends on the ambiguities inherent in defining the quantum vacuum.

hep-th↗

arXiv2025

Quantum superposition of boundary condition in $\mathrm{PAdS}_2$

We explore the quantum superposition of boundary conditions in the context of the Poincaré patch of the two-dimensional Anti-de Sitter space ($\mathrm{PAdS}_2$). Focusing on Robin (mixed) boundary conditions (RBC), we investigate the response function of the Unruh-DeWitt (UDW) detector interacting with two or more scalar fields, each respecting a different boundary condition. The role of this quantum superposition is two-fold: i) it may represent different fields propagating on the same spacetime and interacting with an UDW detector or ii) it may describe an UDW detector on a superposition of spacetimes, each one with an inequivalent propagating field.

hep-th↗

arXiv2025

Mode-sum prescription for renormalized expectation values for a charged quantum scalar field on a charged black hole

We present a new mode-sum prescription for the efficient computation of renormalized expectation values for a massive, charged, quantum scalar field propagating on a curved space-time background. Our method is applicable to any static, spherically-symmetric, four-dimensional space-time with a time-independent, background electrostatic potential and can be used to find the renormalized scalar condensate, current and stress-energy tensor. As an explicit example, we present a calculation of these quantities for a charged scalar field in the Hartle-Hawking state on a Reissner-Nordstrom black hole background.

hep-th↗

arXiv2025

Some addition theorems for spin-weighted spherical harmonics

We present some addition theorems for spin-weighted spherical harmonics, generalizing previous results for scalar (spin-zero) spherical harmonics. These addition theorems involve sums over the azimuthal quantum number of products of two spin-weighted spherical harmonics at different points on the two-sphere, either (or both) of which are differentiated with respect to one of their arguments.

math-ph↗

arXiv2024

Quantum scalar field theory on equal-angular-momenta Myers-Perry-AdS black holes

We study the canonical quantization of a massive scalar field on a five dimensional, rotating black hole space-time. We focus on the case where the space-time is asymptotically anti-de Sitter and the black hole's two angular momentum parameters are equal. In this situation the geometry possesses additional symmetries which simplify both the mode solutions of the scalar field equation and the stress-energy tensor. When the angular momentum of the black hole is sufficiently small that there is no speed-of-light surface, there exists a Killing vector which is time-like in the region exterior to the event horizon. In this case classical superradiance is absent and we construct analogues of the usual Boulware and Hartle-Hawking quantum states for the quantum scalar field. We compute the differences in expectation values of the square of the quantum scalar field operator and the stress-energy tensor operator between these two quantum states.

hep-th↗

arXiv2024

Charge superradiance on charged BTZ black holes

We study superradiant scattering for a charged scalar field subject to Robin (mixed) boundary conditions on a charged BTZ black hole background. Scalar field modes having a real frequency do not exhibit superradiant scattering, independent of the boundary conditions applied. For scalar field modes with a complex frequency, no superradiant scattering occurs if the black hole is static. After exploring some regions of the parameter space, we provide evidence for the existence of superradiantly scattered modes with complex frequencies for a charged and rotating BTZ black hole. Most of the superradiantly scattered modes we find satisfy Robin (mixed) boundary conditions, but there are also superradiantly scattered modes with complex frequencies satisfying Dirichlet and Neumann boundary conditions. We explore the effect of the black hole and scalar field charge on the outgoing energy flux of these superradiantly scattered modes, and also investigate their stability.

hep-th↗

arXiv2024

Renormalized stress-energy tensor on global anti-de Sitter space-time with Robin boundary conditions

We study the renormalized stress-energy tensor (RSET) for a massless, conformally coupled scalar field on global anti-de Sitter space-time in four dimensions. Robin (mixed) boundary conditions are applied to the scalar field. We compute both the vacuum and thermal expectation values of the RSET. The vacuum RSET is a multiple of the space-time metric when either Dirichlet or Neumann boundary conditions are applied. Imposing Robin boundary conditions breaks the maximal symmetry of the vacuum state and results in an RSET whose components with mixed indices have their maximum (or maximum magnitude) at the space-time origin. The value of this maximum depends on the boundary conditions. We find similar behaviour for thermal states. As the temperature decreases, thermal expectation values of the RSET approach those for vacuum states and their values depend strongly on the boundary conditions. As the temperature increases, the values of the RSET components tend to profiles which are the same for all boundary conditions. We also find, for both vacuum and thermal states, that the RSET on the space-time boundary is independent of the boundary conditions and determined entirely by the trace anomaly.

hep-th↗

arXiv2023

Vacuum polarization on three-dimensional anti-de Sitter space-time with Robin boundary conditions

We study a quantum scalar field, with general mass and coupling to the scalar curvature, propagating on three-dimensional global anti-de Sitter space-time. We determine the vacuum and thermal expectation values of the square of the field, also known as the vacuum polarisation (VP). We consider values of the scalar field mass and coupling for which there is a choice of boundary conditions giving well-posed classical dynamics. We apply Dirichlet, Neumann and Robin (mixed) boundary conditions to the field at the space-time boundary. We find finite values of the VP when the parameter governing the Robin boundary conditions is below a certain critical value. For all couplings, the vacuum expectation values of the VP with either Neumann or Dirichlet boundary conditions are constant and respect the maximal symmetry of the background space-time. However, this is not the case for Robin boundary conditions, when both the vacuum and thermal expectation values depend on the space-time location. At the space-time boundary, we find that both the vacuum and thermal expectation values of the VP with Robin boundary conditions converge to the result when Neumann boundary conditions are applied, except in the case of Dirichlet boundary conditions.

hep-th↗

arXiv2023

Equivalence of the adiabatic expansion and Hadamard renormalization for a charged scalar field

We examine the relationship between three approaches (Hadamard, DeWitt-Schwinger and adiabatic) to the renormalization of expectation values of field operators acting on a charged quantum scalar field. First, we demonstrate that the DeWitt-Schwinger representation of the Feynman Green's function is a particular case of the Hadamard representation. Next, we restrict attention to a spatially flat Friedmann-Lemaitre-Robertson-Walker universe with time-dependent, purely electric, background electromagnetic field, considering two, three and four-dimensional space-times. Working to the order required for the renormalization of the stress-energy tensor (SET), we find the adiabatic and DeWitt-Schwinger expansions of the Green's function when the space-time points are spatially separated. In two and four dimensions, the resulting DeWitt-Schwinger and adiabatic expansions are identical. In three dimensions, the DeWitt-Schwinger expansion contains terms of adiabatic order four which are not necessary for the renormalization of the SET and hence absent in the adiabatic expansion. The equivalence of the DeWitt-Schwinger and adiabatic approaches to renormalization in the scenario considered is thereby demonstrated in even dimensions. In odd dimensions the situation is less clear and further investigation is required in order to determine whether adiabatic renormalization is a locally covariant renormalization prescription.

hep-th↗

arXiv2023

Superradiance and quantum states on black hole space-times

We consider the definition of the Boulware and Hartle-Hawking states for quantum fields on black hole space-times. The properties of these states on a Schwarzschild black hole have been understood for many years, but neither of these states has a direct analogue on a Kerr black hole. We show how superradiant modes play an important role in the definition of quantum states on Kerr. Superradiance is also present on static black hole space-times, in particular for a charged scalar field on a Reissner-Nordstrom black hole. We explore whether analogues of the Boulware and Hartle-Hawking states exist in this situation.

hep-th↗

arXiv2023

Quantization of a charged scalar field on a charged black hole background

We study the canonical quantization of a massless charged scalar field on a Reissner-Nordstrom black hole background. Our aim is to construct analogues of the standard Boulware, Unruh and Hartle-Hawking quantum states which can be defined for a neutral scalar field, and to explore their physical properties by computing differences in expectation values of the scalar field condensate, current and stress-energy tensor operators between two quantum states. Each of these three states has a non-time-reversal-invariant ``past'' and ``future'' charged field generalization, whose properties are similar to those of the corresponding ``past'' and ``future'' states for a neutral scalar field on a Kerr black hole. In addition, we present some tentative, time-reversal-invariant, equilibrium states. The first is a ``Boulware''-like state which is as empty as possible at both future and past null infinity. Second, we posit a ``Hartle-Hawking''-like state which may correspond to a thermal distribution of particles. The construction of both these latter states relies on the use of nonstandard commutation relations for the creation and annihilation operators pertaining to superradiant modes.

hep-th↗

arXiv2022

Vortical Effects for Free Fermions on Anti-De Sitter Space-Time

Here, we study a quantum fermion field in rigid rotation at finite temperature on anti-de Sitter space. We assume that the rotation rate $Ω$ is smaller than the inverse radius of curvature $\ell ^{-1}$, so that there is no speed of light surface and the static (maximally-symmetric) and rotating vacua coincide. This assumption enables us to follow a geometric approach employing a closed-form expression for the vacuum two-point function, which can then be used to compute thermal expectation values (t.e.v.s). In the high temperature regime, we find a perfect analogy with known results on Minkowski space-time, uncovering curvature effects in the form of extra terms involving the Ricci scalar $R$. The axial vortical effect is validated and the axial flux through two-dimensional slices is found to escape to infinity for massless fermions, while for massive fermions, it is completely converted into the pseudoscalar density $-i {\bar ψ} γ^5 ψ$. Finally, we discuss volumetric properties such as the total scalar condensate and the total energy within the space-time and show that they diverge as $[1 - \ell^2 Ω^2]^{-1}$ in the limit $Ω\rightarrow \ell ^{-1}$.

hep-th↗