Bartomeu Fiol
Current Organizations / Institutes
The organizations/institutes from the scholar's latest article
Previous Organizations / Institutes
The organizations / institutes from the scholar's other articles in the past ten years
Research Subjects
Bartomeu Fiol has a total of 47 co-authors. Here are the top co-authors by number of shared publications:
- Alan Rios Fukelman
King’s College London
10 shared publications - Blai Garolera
Universitat de Barcelona
8 shared publications - Genís Torrents
Departament de Física Fonamental i Institut de Ciències del Cosmos Universitat de Barcelona Marti i Franquès 1 08028 Barcelona Catalonia Spain
7 shared publications - Jairo Martínez-Montoya
Departament de Física Quàntica i Astrofísica i Institut de Ciències del Cosmos Universitat de Barcelona Martí i Franquès 1 08028 Barcelona Catalonia Spain
7 shared publications - Nadav Drukker
Department of Mathematics King's College London WC2R 2LS London United Kingdom
4 shared publications - Aitor Lewkowycz
Perimeter Institute for Theoretical Physics, Waterloo, Canada
3 shared publications
Latest Publications
- Open Access
- 10 February 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (2) , 111
Schwinger-Dyson approximants
A bstract: We revisit the solution to the Schwinger-Dyson equations in the simple case of the 0-dimensional $$ \frac{1}{2}{m}^2{\phi}^2+\frac{\lambda }{4}{\phi}^4 $$ theory with m 2 > 0 and λ ≥ 0. We argue that the truncated Schwinger-Dyson equations are solved by rational approximants to all n-point functions ⟨ ϕ 2 k ⟩, and provide strikingly simple recursive relations for them. These rational approximants are constructed without any reference to ordinary perturbative expansions. They turn out to be Padé approximants for ⟨ ϕ 2 ⟩ and for half of the truncations in the case of ⟨ ϕ 4 ⟩, but they are not Padé approximants for higher n-point functions. This difference is related to the fact that ⟨ ϕ 2 ⟩ and ⟨ ϕ 4 ⟩ are Stieltjes functions, while higher n-point functions are not. We prove that as the size of the truncation tends to infinity, these rational approximants converge to the full non-perturbative n-point functions for all positive values of the coupling λ . Thus, in the example studied in this work, these new rational approximants are much easier to derive than the usual Padé approximants, and when different, they are better suited to approximate the full non-perturbative n-point functions.- 10 February 2026
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2026 (2) , 111
Open AccessSchwinger-Dyson approximants
A bstract: We revisit the solution to the Schwinger-Dyson equations in the simple case of the 0-dimensional $$ \frac{1}{2}{m}^2{\phi}^2+\frac{\lambda }{4}{\phi}^4 $$ theory with m 2 > 0 and λ ≥ 0. We argue that the truncated Schwinger-Dyson equations are solved by rational approximants to all n-point functions ⟨ ϕ 2 k ⟩, and provide strikingly simple recursive relations for them. These rational approximants are constructed without any reference to ordinary perturbative expansions. They turn out to be Padé approximants for ⟨ ϕ 2 ⟩ and for half of the truncations in the case of ⟨ ϕ 4 ⟩, but they are not Padé approximants for higher n-point functions. This difference is related to the fact that ⟨ ϕ 2 ⟩ and ⟨ ϕ 4 ⟩ are Stieltjes functions, while higher n-point functions are not. We prove that as the size of the truncation tends to infinity, these rational approximants converge to the full non-perturbative n-point functions for all positive values of the coupling λ . Thus, in the example studied in this work, these new rational approximants are much easier to derive than the usual Padé approximants, and when different, they are better suited to approximate the full non-perturbative n-point functions. - Open Access
Schwinger-Dyson approximants
We revisit the solution to the Schwinger-Dyson equations in the simple case of the 0-dimensional $\frac{1}{2}m^2 φ^2 +\fracλ{4} φ^4$ theory with $m^2>0$ and $λ\geq 0$. We argue that the truncated Schwinger-Dyson equations are solved by rational approximants to all n-point functions $\langle φ^{2k} \rangle$, and provide strikingly simple recursive relations for them. These rational approximants are constructed without any reference to ordinary perturbative expansions. They turn out to be Padé approximants for $\langle φ^2 \rangle$ and for half of the truncations in the case of $\langle φ^4 \rangle$, but they are not Padé approximants for higher n-point functions. This difference is related to the fact that $\langle φ^2 \rangle$ and $\langle φ^4 \rangle$ are Stieltjes functions, while higher n-point functions are not. We prove that as the size of the truncation tends to infinity, these rational approximants converge to the full non-perturbative n-point functions for all positive values of the coupling $λ$. Thus, in the example studied in this work, these new rational approximants are much easier to derive than the usual Padé approximants, and when different, they are better suited to approximate the full non-perturbative n-point functions.Open AccessSchwinger-Dyson approximants
We revisit the solution to the Schwinger-Dyson equations in the simple case of the 0-dimensional $\frac{1}{2}m^2 φ^2 +\fracλ{4} φ^4$ theory with $m^2>0$ and $λ\geq 0$. We argue that the truncated Schwinger-Dyson equations are solved by rational approximants to all n-point functions $\langle φ^{2k} \rangle$, and provide strikingly simple recursive relations for them. These rational approximants are constructed without any reference to ordinary perturbative expansions. They turn out to be Padé approximants for $\langle φ^2 \rangle$ and for half of the truncations in the case of $\langle φ^4 \rangle$, but they are not Padé approximants for higher n-point functions. This difference is related to the fact that $\langle φ^2 \rangle$ and $\langle φ^4 \rangle$ are Stieltjes functions, while higher n-point functions are not. We prove that as the size of the truncation tends to infinity, these rational approximants converge to the full non-perturbative n-point functions for all positive values of the coupling $λ$. Thus, in the example studied in this work, these new rational approximants are much easier to derive than the usual Padé approximants, and when different, they are better suited to approximate the full non-perturbative n-point functions. - Open Access
- 15 January 2025
- Published by Stichting SciPost in SciPost Physics
- Vol. 18 (1) , 018
Conformal line defects at finite temperature
We study conformal field theories at finite temperature in the presence of a temporal conformal line defect, wrapping the thermal circle, akin to a Polyakov loop in gauge theories. Although several symmetries of the conformal group are broken, the model can still be highly constrained from its features at zero temperature. In this work we show that the defect and bulk one and two-point correlators can be written as functions of zero-temperature data and thermal one-point functions (defect and bulk). The defect one-point functions are new data and they are induced by thermal effects of the bulk. For this new set of data we derive novel sum rules and establish a bootstrap problem for the thermal defect one-point functions from the KMS condition. We also comment on the behaviour of operators with large scaling dimensions. Additionally, we relate the free energy and entropy density to the OPE data through the one-point function of the stress-energy tensor. Our formalism is validated through analytical computations in generalized free scalar field theory, and we present new predictions for the O(N) O ( N ) model with a magnetic impurity in the \varepsilon ε -expansion and the large N N limit.
- 15 January 2025
- Published by Stichting SciPost in SciPost Physics
- Vol. 18 (1) , 018
Open AccessConformal line defects at finite temperature
We study conformal field theories at finite temperature in the presence of a temporal conformal line defect, wrapping the thermal circle, akin to a Polyakov loop in gauge theories. Although several symmetries of the conformal group are broken, the model can still be highly constrained from its features at zero temperature. In this work we show that the defect and bulk one and two-point correlators can be written as functions of zero-temperature data and thermal one-point functions (defect and bulk). The defect one-point functions are new data and they are induced by thermal effects of the bulk. For this new set of data we derive novel sum rules and establish a bootstrap problem for the thermal defect one-point functions from the KMS condition. We also comment on the behaviour of operators with large scaling dimensions. Additionally, we relate the free energy and entropy density to the OPE data through the one-point function of the stress-energy tensor. Our formalism is validated through analytical computations in generalized free scalar field theory, and we present new predictions for the O(N) O ( N ) model with a magnetic impurity in the \varepsilon ε -expansion and the large N N limit.
- Open Access
- 1 April 2024
- Published by IOP Publishing in Journal of Cosmology and Astroparticle Physics
- Vol. 2024 (04)
A novel approach to cosmological particle production
In this work we present a novel approach to the study of cosmological particle production in asymptotically Minkowski spacetimes. We emphasize that it is possible to determine the amount of particle production by focusing on the mathematical properties of the mode function equations, i.e. their singularities and monodromies, sidestepping the need to solve those equations. We consider in detail creation of scalar and spin 1/2 particles in four dimensional asymptotically Minkowski flat FLRW spacetimes. We explain that when the mode function equation for scalar fields has only regular singular points, the corresponding scale factors are asymptotically Minkowski. For Dirac spin 1/2 fields, the requirement of mode function equations with only regular points is more restrictive, and picks up a subset of the aforementioned scale factors. For the scalar case, we argue that there are two different regimes of particle production; while most of the literature has focused on only one of these regimes, the other regime presents enhanced particle production. On the other hand, for Dirac fermions we find a single regime of particle production. Finally, we very briefly comment on the possibility of studying particle production in spacetimes that don't asymptote to Minkowski, by considering mode function equations with irregular singular points.
- 1 April 2024
- Published by IOP Publishing in Journal of Cosmology and Astroparticle Physics
- Vol. 2024 (04)
Open AccessA novel approach to cosmological particle production
In this work we present a novel approach to the study of cosmological particle production in asymptotically Minkowski spacetimes. We emphasize that it is possible to determine the amount of particle production by focusing on the mathematical properties of the mode function equations, i.e. their singularities and monodromies, sidestepping the need to solve those equations. We consider in detail creation of scalar and spin 1/2 particles in four dimensional asymptotically Minkowski flat FLRW spacetimes. We explain that when the mode function equation for scalar fields has only regular singular points, the corresponding scale factors are asymptotically Minkowski. For Dirac spin 1/2 fields, the requirement of mode function equations with only regular points is more restrictive, and picks up a subset of the aforementioned scale factors. For the scalar case, we argue that there are two different regimes of particle production; while most of the literature has focused on only one of these regimes, the other regime presents enhanced particle production. On the other hand, for Dirac fermions we find a single regime of particle production. Finally, we very briefly comment on the possibility of studying particle production in spacetimes that don't asymptote to Minkowski, by considering mode function equations with irregular singular points.
- Open Access
A novel approach to cosmological particle production
In this work we present a novel approach to the study of cosmological particle production in asymptotically Minkowski spacetimes. We emphasize that it is possible to determine the amount of particle production by focusing on the mathematical properties of the mode function equations,i.e. their singularities and monodromies, sidestepping the need to solve those equations. We consider in detail creation of scalar and spin 1/2 particles in four dimensional asymptotically Minkowski flat FLRW spacetimes. We explain that when the mode function equation for scalar fields has only regular singular points, the corresponding scale factors are asymptotically Minkowski. For Dirac spin 1/2 fields, the requirement of mode function equations with only regular points is more restrictive, and picks up a subset of the aforementioned scale factors. For the scalar case, we argue that there are two different regimes of particle production; while most of the literature has focused on only one of these regimes, the other regime presents enhanced particle production. On the other hand, for Dirac fermions we find a single regime of particle production. Finally, we very briefly comment on the possibility of studying particle production in spacetimes that don't asymptote to Minkowski, by considering mode function equations with irregular singular points.
Open AccessA novel approach to cosmological particle production
In this work we present a novel approach to the study of cosmological particle production in asymptotically Minkowski spacetimes. We emphasize that it is possible to determine the amount of particle production by focusing on the mathematical properties of the mode function equations,i.e. their singularities and monodromies, sidestepping the need to solve those equations. We consider in detail creation of scalar and spin 1/2 particles in four dimensional asymptotically Minkowski flat FLRW spacetimes. We explain that when the mode function equation for scalar fields has only regular singular points, the corresponding scale factors are asymptotically Minkowski. For Dirac spin 1/2 fields, the requirement of mode function equations with only regular points is more restrictive, and picks up a subset of the aforementioned scale factors. For the scalar case, we argue that there are two different regimes of particle production; while most of the literature has focused on only one of these regimes, the other regime presents enhanced particle production. On the other hand, for Dirac fermions we find a single regime of particle production. Finally, we very briefly comment on the possibility of studying particle production in spacetimes that don't asymptote to Minkowski, by considering mode function equations with irregular singular points.
- Open Access
- 8 November 2023
- Published by Sissa Medialab Srl
- Vol. 436, 133
From von Neumann algebras to quantum de Sitter
In this talk we review recent progress in translating heuristic considerations about quantum properties of de Sitter space into rigorous statements in the framework of Algebraic Quantum Field Theory.
- 8 November 2023
- Published by Sissa Medialab Srl
- Vol. 436, 133
Open AccessFrom von Neumann algebras to quantum de Sitter
In this talk we review recent progress in translating heuristic considerations about quantum properties of de Sitter space into rigorous statements in the framework of Algebraic Quantum Field Theory.
- Open Access
- 12 July 2023
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2023 (7) , 1-24
The planar limit of integrated 4-point functions
We study the planar limit of integrated 4-point functions of moment map operators of 𝒩 = 2 SU(N) SQCD. We do so by considering the planar free energy on S4 of the massive deformation of this theory, and taking advantage of the exact relation between this free energy and the integrated 4-point function. For this planar free energy we derive all the terms with maximal and next-to-maximal transcendentality, and present a procedure to compute terms of lower transcendentality. We also derive the first non-planar corrections, as all order series in the ’t Hooft coupling, and to all orders in transcendentality. Finally, we also apply our approach to the better studied example of 𝒩 = 4 SU(N) SYM integrated 4-point functions, and reproduce their known planar limit.
- 12 July 2023
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2023 (7) , 1-24
Open AccessThe planar limit of integrated 4-point functions
We study the planar limit of integrated 4-point functions of moment map operators of 𝒩 = 2 SU(N) SQCD. We do so by considering the planar free energy on S4 of the massive deformation of this theory, and taking advantage of the exact relation between this free energy and the integrated 4-point function. For this planar free energy we derive all the terms with maximal and next-to-maximal transcendentality, and present a procedure to compute terms of lower transcendentality. We also derive the first non-planar corrections, as all order series in the ’t Hooft coupling, and to all orders in transcendentality. Finally, we also apply our approach to the better studied example of 𝒩 = 4 SU(N) SYM integrated 4-point functions, and reproduce their known planar limit.
- Open Access
The planar limit of integrated 4-point functions
We compute the planar limit, as all-order power series in the 't Hooft coupling, of various integrated 4-point functions of chiral primary operators of ${\cal N}=4$ SU(N) super Yang-Mills, and of moment map operators of ${\cal N}=2$ SU(N) SQCD. We do so by computing the planar free energy on $S^4$ of the respective massive deformations of these theories, and then taking advantage of the exact relation between these free energies and the integrated 4-point functions.Open AccessThe planar limit of integrated 4-point functions
We compute the planar limit, as all-order power series in the 't Hooft coupling, of various integrated 4-point functions of chiral primary operators of ${\cal N}=4$ SU(N) super Yang-Mills, and of moment map operators of ${\cal N}=2$ SU(N) SQCD. We do so by computing the planar free energy on $S^4$ of the respective massive deformations of these theories, and then taking advantage of the exact relation between these free energies and the integrated 4-point functions. - Open Access
- 7 November 2022
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2022 (11) , 1-19
A derivation of the planar limit of $ \mathcal{N} $ = 2 chiral correlatorsWe derive analytically the terms of maximal transcendentality of the planar 2- and 3-point functions of single-trace chiral primary operators of $$ \mathcal{N} $$ = 2 SQCD on ℝ4, to all orders in the ’t Hooft coupling. These results prove two conjectures we formulated in previous work. Furthermore, we also provide an explicit expression for the terms in the planar 2-point functions of these operators that contain products of two values of the ζ function.- 7 November 2022
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2022 (11) , 1-19
Open AccessA derivation of the planar limit of $ \mathcal{N} $ = 2 chiral correlatorsWe derive analytically the terms of maximal transcendentality of the planar 2- and 3-point functions of single-trace chiral primary operators of $$ \mathcal{N} $$ = 2 SQCD on ℝ4, to all orders in the ’t Hooft coupling. These results prove two conjectures we formulated in previous work. Furthermore, we also provide an explicit expression for the terms in the planar 2-point functions of these operators that contain products of two values of the ζ function. - Open Access
- 10 February 2022
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2022 (2) , 1-22
On the planar free energy of matrix models
- 10 February 2022
- Published by Springer Nature in Journal of High Energy Physics
- Vol. 2022 (2) , 1-22
Open AccessOn the planar free energy of matrix models