# Nicola PinamontiUniversità degli Studi di Genova | UNIGE · Dipartimento di Matematica (DIMA)

Nicola Pinamonti

PhD

## About

86

Publications

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Introduction

Additional affiliations

January 2011 - present

February 2010 - December 2010

January 2007 - January 2010

## Publications

Publications (86)

We discuss the scaling of the effective action for the interacting scalar quantum field theory on generic spacetimes with Lorentzian signature and in a generic state (including vacuum and thermal states, if they exist). This is done constructing a flow equation, which is very close to the renown Wetterich equation, by means of techniques recently d...

The linearization of semiclassical theories of gravity is investigated in a toy model, consisting of a quantum scalar field in interaction with a second classical scalar field which plays the role of a classical background. This toy model mimics also the evolution induced by semiclassical Einstein equations, such as the one which describes the earl...

We study the evaporation of a four-dimensional spherically symmetric black hole formed in a gravitational collapse. We analyze the back-reaction of a massless quantum scalar field conformally coupled to the scalar curvature by means of the semiclassical Einstein equations. We show that the evaporation is linked to an ingoing negative energy flux at...

We consider spherically symmetric spacetimes with an outer trapping horizon. Such spacetimes are generalizations of spherically symmetric black hole spacetimes where the central mass can vary with time, like in black hole collapse or black hole evaporation. While these spacetimes possess in general no timelike Killing vector field, they admit a Kod...

We prove existence and uniqueness of solutions of the semiclassical Einstein equation in flat cosmological spacetimes driven by a quantum massive scalar field with arbitrary coupling to the scalar curvature. In the semiclassical approximation, the backreaction of matter to curvature is taken into account by equating the Einstein tensor to the expec...

In this paper we investigate the massive Sine-Gordon model in the ultraviolet finite regime in thermal states over the two-dimensional Minkowski spacetime. We combine recently developed methods of perturbative algebraic quantum field theory with techniques developed in the realm of constructive quantum field theory over Euclidean spacetimes to cons...

In this paper we study the evaporation of a four-dimensional spherically symmetric black hole formed during a gravitational collapse, analyzing the backreaction of a massless conformally coupled quantum scalar field by means of the semiclassical Einstein equation. We link the evaporation and the corresponding black hole mass loss to an ingoing nega...

We consider spherically symmetric spacetimes with an outer trapping horizon. Such spacetimes are generalizations of spherically symmetric black hole spacetimes where the central mass can vary with time, like in black hole collapse or black hole evaporation. These spacetimes possess in general no timelike Killing vector field, but admit a Kodama vec...

As discussed in Bahns et al. (2015) fundamental physical principles suggests that, close to cosmological singularities, the effective Planck length diverges, hence a “quantum point” becomes infinitely extended. We argue that, as a consequence, at the origin of times spacetime might reduce effectively to a single point and interactions disappear. Th...

We construct states describing Bose–Einstein condensates at finite temperature for a relativistic massive complex scalar field with $$|\varphi |^4$$ | φ | 4 -interaction. We start with the linearized theory over a classical condensate and construct interacting fields by perturbation theory. Using the concept of thermal masses, equilibrium states at...

The quantum structure of Spacetime at the Planck scale suggests the use, in defining interactions between fields, of the Quantum Wick product. The resulting theory is ultraviolet finite, but subject to an adiabatic cutoff in time which seems difficult to remove. We solve this problem here by another strategy: the fields at a point in the interactio...

We prove existence and uniqueness of solutions of the semiclassical Einstein equation in flat cosmological spacetimes driven by a quantum massive scalar field with arbitrary coupling to the scalar curvature. In the semiclassical approximation, the backreaction of matter to curvature is taken into account by equating the Einstein tensor to the expec...

As discussed in arXiv:1501.03298, Physics suggests that, close to cosmological singularities, the effective Planck length diverges, hence a "quantum point" becomes infinitely extended. We argue that, as a consequence, at the origin of times spacetime might reduce effectively to a single point and interactions disappear. This last point is supported...

We construct states describing Bose Einstein condensates at finite temperature for a relativistic massive complex scalar field with $|\varphi|^4$-interaction. We start with the linearized theory over a classical condensate and construct interacting fields by perturbation theory. Using the concept of thermal masses, equilibrium states at finite temp...

We compare the construction of equilibrium states at finite temperature for self-interacting massive scalar quantum field theories on Minkowski spacetime proposed by Fredenhagen and Lindner (Commun Math Phys 332:895, 2014) with results obtained in ordinary thermal field theory, by means of real-time and Matsubara (or imaginary time) formalisms. In...

States of a generic quantum field theory on a curved spacetime are considered which satisfy the KMS condition with respect to an evolution associated with a complete (Killing) vector field. It is shown that at any point where the vector field is spacelike, such states cannot satisfy a certain microlocal condition which is weaker than the microlocal...

The quantum structure of Spacetime at the Planck scale suggests the use, in defining interactions between fields, of the Quantum Wick product. The resulting theory is ultraviolet finite, but subject to an adiabatic cutoff in time which seems difficult to remove. We solve this problem here by another strategy: the fields at a point in the interactio...

In this paper we compare the construction of equilibrium states at finite temperature for self-interacting massive scalar quantum field theories on Minkowski spacetime proposed by Fredenhagen and Lindner with results obtained in ordinary thermal field theory, by means of real time and Matsubara formalisms. In the construction of this state, even if...

Quantum field theory (QFT) on non-stationary spacetimes is well understood from the side of the algebra of observables. The state space, however, is largely unexplored, due to the non-existence of distinguished states (vacuum, scattering states, thermal states). Project C7 of the SFB 676 was focused on characterisations of states by asymptotic cond...

States of a generic quantum field theory on a curved spacetime are considered, which satisfy the KMS condition with respect to an evolution associated with a complete (Killing) vector field. It is shown that at any point where the vector field is spacelike, such states cannot satisfy a certain microlocal regularity condition, which is weaker than t...

For any number $h$ such that $\hbar :=h/2\pi $ is irrational and any skew-symmetric, non-degenerate bilinear form $\sigma :{{\mathbb{Z}}}^{2g}\times{{\mathbb{Z}}}^{2g} \to{{\mathbb{Z}}}$, let be ${{\mathcal{A}}}^h_{g,\sigma }$ be the twisted group *-algebra ${{\mathbb{C}}}[{{\mathbb{Z}}}^{2g}]$ and consider the ergodic group of *-automorphisms of $...

We analyze the stability properties shown by KMS states for interacting massive scalar fields propagating over Minkowski spacetime, recently constructed in the framework of perturbative algebraic quantum field theories by Fredenhagen and Lindner \cite{FredenhagenLindner}. In particular, we prove the validity of the return to equilibrium property wh...

In this paper we analyze the relative entropy of certain KMS states for scalar self-interacting quantum field theories over Minkowski backgrounds that have been recently constructed by Fredenhagen and Lindner in [FL14] in the framework of perturbative algebraic quantum field theory. The definition we are using is a generalization of the Araki relat...

In the introduction to this work, we explained that the algebraic approach to quantum field theory is a two-step procedure. The first consists of the assignment to a physical system of a suitable complex unital \(^*\)-algebra of observables which encompasses structural properties ranging from dynamics, to causality and locality. In the previous cha...

Goal of this section is to discuss the geometric background on which our investigation is based.

The goal of this chapter is twofold. On the one hand we will review how the algebra of observables for a real scalar field on globally hyperbolic spacetimes is built. We will show in addition that a similar construction exists when one consider a suitable class of null manifolds of which future and past null infinity, discussed in the previous chap...

Goal of this chapter is to discuss the interplays between the bulk-to-boundary correspondence outlined in the previous chapters and the extension of the algebra of observables to include also the Wick polynomials.

This book provides a rather self-contained survey of the construction of Hadamard states for scalar field theories in a large class of notable spacetimes, possessing a (conformal) light-like boundary. The first two sections focus on explaining a few introductory aspects of this topic and on providing the relevant geometric background material. The...

In physically motivated models of quantum spacetime, a U(1) gauge theory turns into a U(∞) gauge theory; hence, free classical electrodynamics is no longer free and neutral fields may have electromagnetic interactions. We discuss the last point for scalar fields, as a way to possibly describe dark matter; we have in mind the gravitational collapse...

This book provides a rather self-contained survey of the construction of Hadamard states for scalar field theories in a large class of notable spacetimes, possessing a (conformal) light-like boundary. The first two sections focus on explaining a few introductory aspects of this topic and on providing the relevant geometric background material. The...

A U(1) gauge theory turns, on physically motivated models of Quantum Spacetime, into a U($\infty$) gauge theory, hence free classical electrodynamics is no longer free and neutral fields may have electromagnetic interactions. We discuss the last point for scalar fields, possibly describing dark matter; we have in mind the gravitational collapse of...

We consider a region of Minkowski spacetime bounded either by one or by two
parallel, infinitely extended plates orthogonal to a spatial direction and a
real Klein-Gordon field satisfying Dirichlet boundary conditions. We quantize
these two systems within the algebraic approach to quantum field theory using
the so-called functional formalism. As a...

It is shown how cosmological perturbation theory arises from a fully quantized perturbative theory of quantum gravity. Central for the derivation is a non-perturbative concept of gauge-invariant local observables by means of which perturbative invariant expressions of arbitrary order are generated. In particular, in the linearised theory, first ord...

A new condition, called "Local KMS Condition", characterizing states of a
quantum field to which one can ascribe, at a given spacetime point, a
temperature, is introduced in this article. It will be shown that the Local KMS
Condition (LKMS condition) is equivalent to the Local Thermal Equilibrium (LTE)
condition, proposed previously by Buchholz, Oj...

We develop a renormalisation scheme for time--ordered products in interacting
field theories on curved spacetimes which consists of an analytic
regularisation of Feynman amplitudes and a minimal subtraction of the resulting
pole parts. This scheme is directly applicable to spacetimes with Lorentzian
signature, manifestly generally covariant, invari...

We present an extension of the semiclassical Einstein equations which couples
n-point correlation functions of a stochastic Einstein tensor to the n-point
functions of the quantum stress-energy tensor. We apply this extension to
calculate the quantum fluctuations during an inflationary period, where we take
as a model a massive conformally coupled...

During solar flares a large amount of electrons are accelerated within the
plasma present in the solar atmosphere. Accurate measurements of the motion of
these electrons start becoming available from the analysis of hard X-ray
imaging-spectroscopy observations. In this paper, we discuss the linearized
perturbations of the Boltzmann kinetic equation...

The Principle of Perturbative Agreement, as introduced by Hollands and Wald,
is a renormalisation condition in quantum field theory on curved spacetimes.
This principle states that the perturbative and exact constructions of a field
theoretic model given by the sum of a free and an exactly tractable interaction
Lagrangean should agree. We develop a...

We study the solutions of the semiclassical Einstein equation in flat cosmological spacetimes driven by a massive conformally coupled scalar field. In particular, we show that it is possible to give initial conditions at finite time to get a state for the quantum field which gives finite expectation values for the stress–energy tensor. Furthermore,...

The Spectrometer/Telescope for Imaging X-rays (STIX) is a hard X-ray imaging
spectroscopy device to be mounted in the Solar Orbiter cluster with the aim of
providing images and spectra of solar flaring regions at different photon
energies in the range from a few keV to around 150 keV. The imaging modality of
this telescope is based on the Moire pat...

A mixture model of tumour microenvironment is considered, which consists of a solid phase for the tumour cells, a liquid phase for the interstitial fluid, and a nutrient phase. The balance equations for the three phases take into account exchange of mass between tumour and nutrients, and exchange of drag forces between the constituents. Under rathe...

We study the passive influence of quantum matter fluctuations on the
expansion parameter of a congruence of timelike geodesics in a semiclassical
regime. In particular, we show that, the perturbations of this parameter can be
considered to be elements of the algebra of matter fields at all perturbative
order. Hence, once a quantum state for matter...

According to a standard ohmic perspective, the injection of accelerated
electrons into the flaring region violates local charge equilibrium and
therefore, in response, return currents are driven by an electric field to
equilibrate such charge violation. In this framework, the energy loss rate
associated to these local currents has an ohmic nature a...

Tunnelling processes through black hole horizons have recently been investigated in the framework of WKB theory discovering interesting interplay with the Hawking radiation. A more precise and general account of that phenomenon has been subsequently given within the framework of QFT in curved spacetime by two of the authors of the present paper. In...

We present electron images of an extended solar flare source, deduced from RHESSI hard X-ray imaging spectroscopy data. We apply the electron continuity equation to these maps in order to determine empirically the form of the energy loss rate for the bremsstrahlung-emitting electrons. We show that this form is consistent with an energy transport mo...

In the special case of a spherically symmetric solution of Einstein equations
coupled to a scalar massless field, we examine the consequences on the exact
solution imposed by a semiclassical treatment of gravitational interaction when
the scalar field is quantized. In agreement with the work of Doplicher,
Fredenhagen and Roberts (DFR), imposing the...

We construct and discuss Hadamard states for both scalar and Dirac spinor fields in a large class of spatially flat Friedmann–Robertson–Walker spacetimes characterised by an initial phase either of exponential or of power-law expansion. The states we obtain can be interpreted as being in thermal equilibrium at the time when the scale factor a has a...

In the framework of the algebraic formulation, we discuss and analyse some
new features of the local structure of a real scalar quantum field theory in a
strongly causal spacetime. In particular we use the properties of the
exponential map to set up a local version of a bulk-to-boundary correspondence.
The bulk is a suitable subset of a geodesic ne...

The discovery of the radiation properties of black holes prompted the search
for a natural candidate quantum ground state for a massless scalar field theory
on Schwarzschild spacetime, here considered in the Eddington-Finkelstein
representation. Among the several available proposals in the literature, an
important physical role is played by the so-...

Tunnelling processes through black hole horizons have recently been investigated in the framework of WKB theory, discovering
an interesting interplay with Hawking radiation. In this paper, we instead adopt the point of view proper of QFT in curved
spacetime, namely, we use a suitable scaling limit towards a Killing horizon to obtain the leading ord...

We study the backreaction of free quantum fields on a flat Robertson-Walker spacetime. Apart from renormalization freedom, the vacuum energy receives contributions from both the trace anomaly and the thermal nature of the quantum state. The former represents a dynamical realisation of dark energy, while the latter mimics an effective dark matter co...

In this paper we shall discuss the backreaction of a massive quantum scalar
field on the curvature, the latter treated as a classical field. Furthermore,
we shall deal with this problem in the realm of cosmological spacetimes by
analyzing the Einstein equations in a semiclassical fashion. More precisely, we
shall show that, at least on small interv...

We focus on quantization of the metric of a black hole restricted to the Killing horizon with universal radius r0. After imposing spherical symmetry and after restriction to the Killing horizon, the metric is quantized employing the chiral currents formalism. Two "components of the metric" are indeed quantized: The former behaves as an affine scala...

We discuss from scratch the classical structure of Dirac spinors on an arbitrary globally hyperbolic, Lorentzian spacetime, their formulation as a locally covariant quantum field theory, and the associated notion of a Hadamard state. Eventually, we develop the notion of Wick polynomials for spinor fields, and we employ the latter to construct a cov...

As a starting point, we state some relevant geometrical properties enjoyed by the cosmological horizon of a certain class of Friedmann-Robertson-Walker backgrounds. Those properties are generalised to a larger class of expanding spacetimes M admitting a geodesically complete cosmological horizon \({{\Im^-}}\) common to all co-moving observers. This...

In a recent paper, we proved that a large class of spacetimes, not necessarily homogeneous or isotropous and relevant at a cosmological level, possesses a preferred codimension one submanifold, i.e., the past cosmological horizon, on which it is possible to encode the information of a scalar field theory living in the bulk. Such bulk-to-boundary re...

In this paper we generalize the construction of generally covariant quantum theories given in the work of Brunetti, Fredenhagen and Verch to encompass the conformal covariant case. After introducing the abstract framework, we discuss the massless conformally coupled Klein Gordon field theory, showing that its quantization corresponds to a functor b...

In the mathematically rigorous analysis of semiclassical Einstein's equations, the renormalisation of the stress-energy tensor plays a crucial role. We address such a topic in the case of a scalar field with both arbitrary mass and coupling with gravity in the hypothesis that the underlying algebraic quantum state is of Hadamard type. Particularly,...

Some years ago it was shown that, in some cases, a notion of locality can arise from the group of symmetry enjoyed by the theory, thus in an intrinsic way. In particular, when Moebius covariance is present, it is possible to associate some particular transformations to the Tomita Takesaki modular operator and conjugation of a specific interval of a...

Scalar QFT on the boundary J+ at null infinity of a general asymptotically flat 4D spacetime is constructed using the algebraic approach based on Weyl algebra associated to a BMSinvariant symplectic form. The constructed theory turns out to be invariant under a suitable strongly continuous unitary representation of the BMS group with manifest meani...

We focus on quantization of the metric of a black hole restricted to the
Killing horizon with universal radius $r_0$. After imposing spherical symmetry
and after restriction to the Killing horizon, the metric is quantized employing
the chiral currents formalism. Two ``components of the metric'' are indeed
quantized: The former behaves as an affine...

Exploiting results recently proved in a technical paper (and some of them are reviewed herein in the language of theoretical physicists) we focus on quantization of the metric of a black hole restricted to the Killing horizon with universal radius r0. The metric is represented in a suitable manner after imposing spherical symmetry and, after restri...

We show here how it is possible to build a QFT on the horizon of a Schwarzschild-like spacetime. That theory, found by restricting bulk quantum elds on the horizon, is equivalent to QFT on the bulk. That fact is called Holography. Moreover the hidden conformal symmetry (SL(2;R)) found for the bulk theory becomes manifest on the horizon in terms of...

Local scalar QFT (in Weyl algebraic approach) is constructed on degenerate semi-Riemannian manifolds corresponding to Killing horizons in spacetime. Covariance properties of the $C^*$-algebra of observables with respect to the conformal group $PSL(2,\bR)$ are studied.It is shown that, in addition to the state studied by Guido, Longo, Roberts and Ve...

In this paper we first show that within the Hamiltonian description of general relativity, the central charge of a near horizon asymptotic symmetry group is zero, and therefore that the entropy of the system cannot be estimated using Cardy’s formula. This is done by mapping a static black hole to a two dimensional space. We explain how such a charg...

It is shown that it is possible to define quantum field theory of a massless scalar free field on the Killing horizon of a 2D-Rindler spacetime. Free quantum field theory on the horizon enjoys diffeomorphism invariance and turns out to be unitarily and algebraically equivalent to the analogous theory of a scalar field propagating inside Rindler spa...

Using the holographic machinery built up in a previous work, we show that the hidden SL(2,R) symmetry of a scalar quantum field propagating in a Rindler spacetime admits an enlargement in terms of a unitary positive-energy representation of Virasoro algebra, with central charge c=1, defined in the Fock representation. The Virasoro algebra of operat...

It is shown that it is possible to define quantum field theory of a massless scalar free field on the Killing horizon of a 2D Rindler space-time. Free quantum field theory on the horizon enjoys diffeomorphism invariance and turns out to be unitarily and algebraically equivalent to the analogous theory of a scalar field propagating inside Rindler sp...

Using the holographic machinery built up in a previous work, we show that the hidden SL(2,R) symmetry of a scalar quantum field propagating in a Rindler space-time admits an enlargement in terms of a unitary positive-energy representation of Virasoro algebra defined in the Fock representation. That representation has central charge c=1. The Virasor...

It is shown that it is possible to define quantum field theory of a massless scalar free field on the event horizon of a 2D-Rindler spacetime. Free quantum field theory on the horizon enjoys diffeomorfism invariance and turns out to be unitarily and algebraically equivalent to the analogous theory of a scalar field prapogating inside Rindler spacet...

It is argued that free QFT can be defined on the event horizon of a Schwarzschild-like spacetime and that that theory is unitarily and algebraically equivalent to QFT in the bulk (near the horizon). Under that unitary equivalence the bulk hidden SL(2,R) symmetry found in a previous work becomes manifest on the event horizon, it being induced by a g...

In this article we compute the black hole entropy by finding a classical central charge of the Virasoro algebra of a Liouville theory using the Cardy formula. This is done by performing a dimensional reduction of the Einstein Hilbert action with the ansatz of spherical symmetry and writing the metric in conformally flat form. We obtain two coupled...

The invariance under unitary representations of the conformal group SL(2,R) of a quantum particle is rigorously investigated in two-dimensional spacetimes containing Killing horizons using DFF model. The limit of the near-horizon approximation is considered. If the Killing horizon is bifurcate the conformal symmetry is hidden, i.e. it does not aris...

We study the positive-operator-valued measures (POVMs) on the
projective real line covariant with respect to the projective
group. We interpret the projective line as a compactified time
axis and we assume that the energy is a positive operator. This
formalism may describe a time-of-arrival observable for a free
particle covariant with respect to l...

We study the positive-operator-valued measures on the projective real line covariant with respect to the projective group, assuming that the energy is a positive operator. This problem is similar to the more complicated problem of finding the positive-operator-valued measures on the compactified Minkowski space-time covariant with respect to the co...

The discovery of the radiation properties of black holes prompted the search for a natural candidate quantum ground state for a massless scalar field theory on the Schwarzschild spacetime. Among the several available proposals in the literature, an important physical role is played by the so-called Unruh state which is supposed to be appropriate to...