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Antonio Ferreiro

Publications and source records attributed to Antonio Ferreiro.

At least 19 recordsLinked to original sources
arXiv2025

Deflating the Spacetime-Matter Dichotomy

In this paper we analyse scalar-tensor theories-specific instances of which include mainstream inflation and dark energy models-in light of the spacetime-matter dichotomy. We argue that it is difficult to categorise the scalar fields as either a pure aspect of the spacetime structure or a pure form of matter, by focusing on the Jordan vs Einstein frames of these theories. We present and evaluate various interpretational options available, concluding that the spacetime-matter dichotomy becomes untenable in this context. At the same time, the ontological and conceptual category of spacetime can be decoupled from that of gravity, with the latter remaining viable in the context of scalar-tensor theories.

physics.hist-ph↗
arXiv2025

The Birth of Gravitational Particle Creation: the Enduring Legacy of Leonard Parker's 1966 Thesis

This paper offers a historical overview of the origins and enduring significance of gravitational particle creation, a groundbreaking discovery first formulated in Leonard Parker's 1966 doctoral thesis at Harvard University. By tracing the context in which Parker developed this idea and examining its subsequent influence, the paper highlights how the concept of gravitational particle creation advanced the study of quantum field theory in curved spacetime and profoundly shaped modern cosmology, as well as the quantum theory of black holes.

physics.hist-ph↗
arXiv2024

Physical scale adiabatic regularization in cosmological spacetimes

We develop a new regularization method for the stress-energy tensor and the two-point function of free quantum scalar fields propagating in cosmological spacetimes. We proceed by extending the adiabatic regularization scheme with the introduction of two additional mass scales. By setting them to the order of the physical scale of the studied scenario, we obtain ultraviolet-regularized quantities that do not distort the power spectra amplitude at the infrared scales amplified by the expansion of the universe. This is not ensured by the standard adiabatic approach. We also show how our proposed subtraction terms can be interpreted as a renormalization of coupling constants in the Einstein equations. We finally illustrate our proposed regularization method in two scenarios of cosmological interest: de Sitter inflation and geometric reheating.

gr-qc↗
arXiv2023

Comment on "Gravitational Pair Production and Black Hole Evaporation"

We scrutinize the recent Letter "Gravitational pair production and black hole evaporation" by M.F. Wondrak, W.D. van Suijlekom and H. Falcke [Phys. Rev. Lett. 130, 221502 (2023); arXiv:2305.18521]. We show that some consequences based on the proposed imaginary part of the lowest order effective action are in sharp tension with exact results on pair creation in electrodynamics and cosmology. This casts serious doubt on their claims for particle production in a Schwarzschild spacetime.

gr-qc↗
arXiv2023

Adiabatic regularization and preferred vacuum state for the $λϕ^4$ field theory in cosmological spacetimes

We extend the method of adiabatic regularization by introducing an arbitrary parameter $μ$ for a scalar field with quartic self-coupling in a Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime at one-loop order. The subtraction terms constructed from this extended version allow us to define a preferred vacuum state at a fixed time $η= η_0$ for this theory. We compute this vacuum state for two commonly used background fields in cosmology. We also give a possible prescription for an adequate value for $μ$.

gr-qc↗
arXiv2023

Ultraviolet-regularized power spectrum without infrared distortions in cosmological spacetimes

We reexamine the regularization of the two-point function of a scalar field in a Friedmann-Lemaitre-Robertson-Walker (FLRW) spacetime. Adiabatic regularization provides a set of subtraction terms in momentum space that successfully remove its ultraviolet divergences at coincident points, but can significantly distort the power spectrum at infrared scales, especially for light fields. In this work we propose, by using the intrinsic ambiguities of the renormalization program, a new set of subtraction terms that minimize the distortions for scales $k \lesssim M$, with $M$ an arbitrary mass scale. Our method is consistent with local covariance and equivalent to general regularization methods in curved spacetime. We apply our results to the regularization of the power spectrum in de Sitter space: while the adiabatic scheme yields exactly $Δ_ϕ^{\rm (reg)} = 0$ for a massless field, our proposed prescription recovers the standard scale-invariant result $Δ_ϕ^{\rm (reg)} \simeq H^2 /(4π^2)$ at super-horizon scales.

gr-qc↗
arXiv2021

Renormalization and decoupling for the Yukawa model in curved spacetime

We consider the renormalization of the one-loop effective action for the Yukawa interaction. We compute the beta functions in the generalized DeWitt-Schwinger subtraction scheme. For the quantized scalar field we obtain that all the beta functions exhibit decoupling for heavy fields as stated by the Appelquist-Carazzone theorem including also the gravitational couplings. For the quantized Dirac field, decoupling appears for almost all of them. We obtain the atypical result that the mass parameter of the background scalar field does not decouple.

gr-qc↗
arXiv2021

Renormalization, running couplings and decoupling for the Yukawa model in curved spacetime

The decoupling of heavy fields as required by the Appelquist-Carazzone theorem plays a fundamental role in the construction of any effective field theory. However, it is not a trivial task to implement a renormalization prescription that produces the expected decoupling of massive fields, and it is even more difficult in curved spacetime. Focused on this idea, we consider the renormalization of the one-loop effective action for the Yukawa interaction with a background scalar field in curved space. We compute the beta functions within a generalized DeWitt-Schwinger subtraction procedure and discuss the decoupling in the running of the coupling constants. For the case of a quantized scalar field, all the beta function exhibit decoupling, including also the gravitational ones. For a quantized Dirac field, decoupling appears almost for all the beta functions. We obtain the anomalous result that the mass of the background scalar field does not decouple.

gr-qc↗
arXiv2020

Instantaneous vacuum for Dirac fields with a Yukawa interaction in cosmological space-times

We propose a suitable vacuum state for a quantized Dirac field interacting with a classical scalar field in a Friedman-Robertson-Walker-Lemaitre spacetime. This state is constructed from an extended version of the adiabatic expansion of the associated Fourier modes of the field. We compute the full renormalized stress-energy tensor. For any given initial time, this instantaneous vacuum can always be chosen to have vanishing Fourier modes for the renormalized stress-energy tensor. We check the consistency of the solution for several inflationary models.

gr-qc↗
arXiv2020

Running gravitational couplings, decoupling, and curved spacetime renormalization

We propose to slightly generalize the DeWitt-Schwinger adiabatic renormalization subtractions in curved space to include an arbitrary renormalization mass scale $μ$. The new predicted running for the gravitational couplings are fully consistent with decoupling of heavy massive fields. This is a somewhat improvement with respect to the more standard treatment of minimal (DeWitt-Schwinger) subtractions via dimensional regularization. We also show how the vacuum metamorphosis model emerges from the running couplings.

gr-qc↗
arXiv2020

R-summed form of adiabatic expansions in curved spacetime

The Feynman propagator in curved spacetime admits an asymptotic (Schwinger-DeWitt) series expansion in derivatives of the metric. Remarkably, all terms in the series containing the Ricci scalar R can be summed exactly. We show that this (non-perturbative) property of the Schwinger-DeWitt series has a natural and equivalent counterpart in the adiabatic (Parker-Fulling) series expansion of the scalar modes in an homogeneous cosmological spacetime. The equivalence between both R-summed adiabatic expansions can be further extended when a background scalar field is also present.

gr-qc↗
arXiv2019

Breaking of adiabatic invariance in the creation of particles by electromagnetic fields

Particles are spontaneously created from the vacuum by time-varying gravitational or electromagnetic backgrounds. It has been proven that the particle number operator in an expanding universe is an adiabatic invariant. In this paper we show that, in some special cases, the expected adiabatic invariance of the particle number fails in presence of electromagnetic backgrounds. In order to do this, we consider as a prototype a Sauter-type electric pulse. Furthermore, we also show a close relation between the breaking of the adiabatic invariance and the emergence of the axial anomaly.

hep-th↗
arXiv2019

Adiabatic regularization with a Yukawa interaction

We extend the adiabatic regularization method for an expanding universe to include the Yukawa interaction between a quantized Dirac field and a homogeneous time-dependent scalar field. We present the renormalized semiclassical equations that are needed in order to take into account the backreaction of the produced Dirac fermions in both gravitational and scalar background fields.

gr-qc↗
arXiv2019

Pair creation in electric fields, renormalization, and backreaction

We consider pair production phenomena in spatially homogeneous strong electric fields. We focus on spinor QED in two-dimensions and discuss the potential ambiguity in the adiabatic order assignment for the electromagnetic potential required to fix the renormalization subtractions. This ambiguity can be univocally fixed by imposing, at the semiclassical level, stress-energy conservation when both electric and gravitational backgrounds are present.

gr-qc↗
arXiv2019

Running couplings from adiabatic regularization

We extend the adiabatic regularization method by introducing an arbitrary mass scale $μ$ in the construction of the subtraction terms. This allows us to obtain, in a very robust way, the running of the coupling constants by demanding $μ$-invariance of the effective semiclassical (Maxwell-Einstein) equations. In particular, we get the running of the electric charge of perturbative quantum electrodynamics. Furthermore, the method brings about a renormalization of the cosmological constant and the Newtonian gravitational constant. The running obtained for these dimensionful coupling constants has new relevant (non-logarithmic) contributions, not predicted by dimensional regularization.

gr-qc↗
arXiv2018

Adiabatic expansions for Dirac fields, renormalization, and anomalies

We introduce an iterative method to univocally determine the adiabatic expansion of the modes of Dirac fields in spatially homogeneous external backgrounds. We overcome the ambiguities found in previous studies and use this new procedure to improve the adiabatic regularization/renormalization scheme. We provide details on the application of the method for Dirac fields living in a four-dimensional Friedmann-Lemaitre-Robertson-Walker spacetime with a Yukawa coupling to an external scalar field. We check the consistency of our proposal by working out the conformal anomaly. We also analyze a two-dimensional Dirac field in Minkowski space coupled to a homogeneous electric field and reproduce the known results on the axial anomaly. The adiabatic expansion of the modes given here can be used to properly characterize the allowed physical states of the Dirac fields in the above external backgrounds.

gr-qc↗
arXiv2018

Role of gravity in the pair creation induced by electric fields

We analyze the pair production induced by homogenous, time-dependent electric fields in an expanding space-time background. We point out that, in obtaining the semiclassical Maxwell equations, two distinct notions of adiabatic renormalization are possible. In Minkowski space the two recipes turn out to be equivalent. However, in the presence of gravity only the recipe requiring an adiabatic hierarchy between the gravitational and the gauge field is consistent with the conservation of the energy-momentum tensor.

gr-qc↗