arXiv subjects

Francesco Scardino

Publications and source records attributed to Francesco Scardino.

At least 19 recordsLinked to original sources

arXiv2026

Rank matching in renormalization-group irreversibility: Exact defect and entropic tests

Why do local subtractions produce renormalization-group monotones in some settings but fail in others? We propose rank matching. Local counterterms fix how many scale derivatives scheme independence requires. Every derivative adds one connected insertion, while the available positivity inputs are bilinear forms or positive second variations and therefore control only quadratic data. Degree one is the last subtraction whose scale derivative stays within their direct reach. First-order subtractions can close when a Ward or entropic identity supplies a signed quadratic form. Higher orders need extra dynamics. Three exactly solvable tests exhibit both outcomes and show that the endpoint inequality can hold while running monotonicity fails. Massive scalars yield nonmonotone filtered free energies on every odd dimensional $p$-sphere with $p\geq3$. A generalized-free surface-defect $b$-function is strictly monotone when the defect-primary dimension $\widehatΔ$ satisfies $1/2\leq\widehatΔ<1$, and necessarily nonmonotone for $0<\widehatΔ<1/2$. At the threshold, its flow coefficient is completely monotone in the canonical spectral coordinate, with derivatives of every order alternating in sign. A local four-dimensional monodromy defect realizes the full transition. Under a stated assumption on the large-component entropy limit, disk entropy and sphere free energy share endpoints and total $F$ loss but distribute it differently over scale. Rank matching separates endpoint ordering, running monotonicity, and the distribution of loss over scale.

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arXiv2026

Nonadditivity in Quantum Field Theory: Replica Energies, Scaling Filters, and the Renormalization Group

Extensive systems have a simple thermodynamic signature: the dimensionless canonical free energy scales homogeneously with the size of the system. We show that the failure of this scaling, measured by the replica energy ${\cal E}$, provides a useful bridge between statistical mechanics and quantum field theory. The associated differential operator $(1-\frac1d L\partial_L)$ removes the leading bulk contribution to $\mathcal{F}=βF_{\rm can}=-\log Z$ and isolates the part that is sensitive to boundaries, topology, defects, long-range forces, or other sources of nonadditivity. In quantum field theory this thermodynamic idea has two closely related uses. For ordinary finite-volume or spherical partition functions, suitable higher-order versions of the same filter remove local counterterms and extract universal fixed-point data such as the central charge, the sphere free energy $F$, and the Euler anomaly coefficient $a$. For replica geometries with entangling defects, the same filtering principle gives the renormalized defect free energy. In $2+1$ dimensions, its $n\to1$ limit gives the entropic $F$-function, with the sign fixed below by the standard free-energy convention. We use this perspective to distinguish ordinary finite-size corrections, topology-dependent constants in gapped phases, subextensive fracton degeneracies, and genuinely nonextensive systems with long-range interactions such as self-gravitating thermal matter. Replica energy therefore offers a common thermodynamic language for additivity, defect free energies, and renormalization-group irreversibility.

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arXiv2026

Constrained Symplectic Quantization: Disclosing the Deterministic Framework Behind Quantum Field Theory

Symplectic quantization is a functional approach to quantum field theory that allows sampling of quantum fluctuations directly in Minkowski space time by means of a Hamiltonian dynamics in an intrinsic time $τ$ which samples a microcanonical ensemble, in close analogy with the standard microcanonical approach to lattice field theory. In this contribution we present constrained symplectic quantization for relativistic quantum field theory, generalizing from the quantum mechanical case. The method is based on the analytic continuation of fields and action from $\mathbb{R}$ to $\mathbb{C}$ and on constraints that select stable intrinsic time trajectories and that simultaneously define convergent integration cycles for the microcanonical partition function. In the continuum limit we recover the Feynman generating functional with the correct real time prescription. We test the construction for a free scalar field in $1+1$ dimensions on a periodic lattice by measuring real time two point functions and by verifying Dyson Schwinger identities with the correct contact term.

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arXiv2026

Constrained Symplectic Quantization II: The Free Scalar Field

Constrained symplectic quantization is a functional formulation of quantum field theory in which quantum fluctuations are sampled through a deterministic Hamiltonian flow in an auxiliary intrinsic time $τ$. In this paper we extend the quantum-mechanical framework introduced in [1] to a relativistic scalar quantum field theory in Minkowski space-time. The construction is based on the analytic continuation of fields and action from $\mathbb{R}$ to $\mathbb{C}$ together with constraints that select stable intrinsic-time trajectories and, at the same time, define convergent integration cycles for the corresponding microcanonical functional. We show that, in the continuum limit, the microcanonical generating functional reproduces the Feynman generating functional. For the free scalar field in $1+1$ dimensions we derive the constrained equations of motion, implement the resulting dynamics numerically, and verify real-time two-point correlators, equal-time commutator relations, and Dyson--Schwinger equations including the expected contact terms.

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arXiv2026

Constrained Symplectic Quantization I: the Quantum Harmonic Oscillator

Symplectic quantization is a functional approach to quantum field theory that allows sampling of quantum fluctuations directly in Minkowski space-time by means of a generalized microcanonical ensemble similar to the one of the standard microcanonical approach to lattice field theory. In a previous paper we showed that, for an interacting scalar field theory in 1+1-dimensions, this formalism allows to capture numerically some crucial real-time features inaccessible to any Euclidean approach to lattice field theory. Yet, the new approach was plagued by two main limitations: an ill-defined non-interacting limit and the absence of a direct formal correspondence between its correlation functions and those generated by the Feynman path integral approach. In this paper, we introduce the new \emph{"constrained symplectic quantization"} approach, for which the perfect equivalence with the Feynman path integral is proved and which is perfectly well defined for the free theory. This new approach is characterized by the analytical continuation of all fields and of the action from $\mathbb{R}$ to $\mathbb{C}$ and the presence of some constraints which guarantee the stability of the generalized Hamiltonian dynamics and the convergence of the corresponding generalized microcanonical partition function, hence the name of the theory. We show the application of this formalism to the quantum harmonic oscillator on a Minkowskian-time lattice, finding perfect agreement between one- and two-point numerical correlators and the exact quantum-mechanical results. We observe genuine real-time features such as the oscillatory propagator and the discrete excited-state energy spectrum. Our results provide strong numerical evidence that constrained symplectic quantization can sample real-time quantum-mechanical observables, offering a concrete route to overcome the limitations of Euclidean-time importance sampling.

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arXiv2026

The scheme independent 3-sphere free energy is not a monotone F-function

We study the natural scheme-independent quantity obtained from the three-sphere partition function of a $(2+1)$-dimensional quantum field theory by removing all local counterterm ambiguities. At conformal fixed points this quantity equals the standard $F$-theorem invariant. Conformal perturbation theory shows that it locally decreases at $O(g^2)$ under any relevant scalar deformation of a three-dimensional CFT. However, an exact analysis of the free massive scalar on $S^3$ shows that this sphere-free-energy interpolant is not monotone along the full renormalization-group flow: it dips below its infrared value and then returns to it. Thus the natural counterterm-subtracted quantity built from sphere thermodynamics is not, by itself, a monotone $F$-function. We trace the obstruction to the second-order differential operator required to eliminate the local ambiguities.

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arXiv2026

Update on the computation of the quenched $SU(6)$ Yang-Mills lattice spectrum

We report on our continued efforts to measure the glueball and meson spectra in SU($N$) Yang-Mills theory and QCD with the aim of extrapolating to the large-$N$ limit. In particular, we document the computation of the low-lying SU($6$) spectrum. We employ a multilevel sampling algorithm to measure glueball correlators to reduce statistical noise in the large-time separation limit. The gluon operator basis is composed of spatial Wilson loop measured at different levels of (APE) smearing, with vanishing momentum selected to maximise the orthonogality of the operators and their overlap with the lowest lying states. We also report on analogous computations for the $J=0,1$ non-singlet meson spectrum with two degenerate quark flavors.

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arXiv2026

Constrained Symplectic Quantization: Disclosing the Deterministic Framework Behind Quantum Mechanics

Symplectic quantization is a functional approach to quantum field theory that allows sampling of quantum fluctuations directly in Minkowski space time by means of a generalized Hamiltonian dynamics in an extra time variable $τ$ which, at large times, samples a microcanonical ensemble. In a previous work we showed that, for an interacting scalar theory in 1+1 dimensions, this framework captures genuine real time features that are inaccessible to Euclidean simulations. That original formulation suffers from two structural limitations, an ill defined non interacting limit and the lack of a direct correspondence between its correlation functions and those generated by the Feynman path integral. To solve these problems we introduced constrained symplectic quantization, a holomorphic reformulation in which fields and action are analytically continued and constraints are imposed on the intrinsic time Hamiltonian flow. The constraints select stable deterministic trajectories and they define convergent holomorphic integration cycles for the corresponding microcanonical measure. In the continuum limit we establish exact equivalence with the Feynman path integral at the level of the generating functional, thus providing a direct link between intrinsic time correlators and real time Green functions. In this contribution, we apply the method to the quantum harmonic oscillator on a real-time 1-dimensional lattice. Testing various observables, we find agreement between numerical and exact results for one- and two-point functions, and we reconstruct characteristic real-time features such as an oscillatory propagator, the discrete energy-gap spectrum, and the evolution of eigenstate probability densities. These tests provide numerical evidence that constrained symplectic quantization can sample real-time quantum observables and offers a practical route beyond Euclidean-time importance sampling.

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arXiv2025

Nonresonant renormalization scheme for twist-$2$ operators in $\mathcal{N}=1$ SUSY SU($N$) Yang-Mills theory

The short-distance asymptotics of the generating functional for $n$-point correlators of twist-$2$ operators in $\mathcal{N}=1$ supersymmetric (SUSY) SU($N$) Yang-Mills (SYM) theory were recently calculated in [1,2]. This calculation depends on a change of basis for renormalized twist-$2$ operators, in which $-γ(g)/ β(g)$ reduces to $γ_0/ (β_0\,g)$ at all orders in perturbation theory, where $γ_0$ is diagonal, $γ(g) = γ_0 g^2+\ldots$ is the anomalous-dimension matrix, and $β(g) = -β_0 g^3+\ldots$ is the beta function. The method is founded on a new geometric interpretation of operator mixing [3], assuming that the eigenvalues of the matrix $γ_0/ β_0$ meet the nonresonant condition $λ_i-λ_j\neq 2k$, with the eigenvalues $λ_i$ ordered nonincreasingly and $k\in \mathbb{N}^+$. This nonresonant condition was numerically verified for $i,j$ up to $10^4$ in [1,2]. In this work, we employ techniques initially developed in [4] to present a number-theoretic proof of the nonresonant condition for twist-$2$ operators, fundamentally based on the classic result that Harmonic numbers are not integers.

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arXiv2025

Symplectic Quantization: numerical results for the Feynman propagator on a 1+1 lattice and the theoretical relation with Quantum Field Theory

We present here the first lattice simulation of symplectic quantization, a new functional approach to quantum field theory which allows to define an algorithm to numerically sample the quantum fluctuations of fields directly in Minkowski space-time, at variance with all other present approaches. Symplectic quantization is characterized by a Hamiltonian deterministic dynamics evolving with respect to an additional time parameter $τ$ analogous to the fictious time of stochastic quantization. The difference between stochastic quantization and the present approach is that the former is well defined only for Euclidean field theories, while the latter allows to sample the causal structure of space-time. In this work we present the numerical study of a real scalar field theory on a 1+1 space-time lattice with a $λϕ^4$ interaction. We find that for $λ\ll1$ the two-point correlation function obtained numerically reproduces qualitatively well the shape of the free Feynman propagator. Within symplectic quantization the expectation values over quantum fluctuations are computed as dynamical averages along the dynamics in $τ$, in force of a natural ergodic hypothesis connecting Hamiltonian dynamics with a generalized microcanonical ensemble. Analytically, we prove that this microcanonical ensemble, in the continuum limit, is equivalent to a canonical-like one where the probability density of field configurations is $P[ϕ]\propto\exp(zS[ϕ]/\hbar)$. The results from our simulations correspond to the value $z=1$ of the parameter in the canonical weight, which in this case is a well-defined probability density for field configurations in causal space-time, provided that a lower bounded interaction potential is considered. The form proposed for $P[ϕ]$ suggests that our theory can be connected to ordinary quantum field theory by analytic continuation in the complex-$z$ plane.

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arXiv2025

On the structure of the large-$N$ expansion in SU($N$) Yang-Mills theory

Recently, we have computed the short-distance asymptotics of the generating functional of Euclidean correlators of single-trace twist-$2$ operators in the large-$N$ expansion of SU($N$) Yang-Mills (YM) theory to the leading-nonplanar order. Remarkably, it has the structure of the logarithm of a functional determinant, but with the sign opposite to the one that would follow from the spin-statistics theorem for the glueballs. In order to solve this sign puzzle, we have reconsidered the proof in the literature that in the 't Hooft topological expansion of large-$N$ YM theory the leading-nonplanar contribution to the generating functional consists of the sum over punctures of $n$-punctured tori. We have discovered that for twist-$2$ operators it contains -- in addition to the $n$-punctured tori -- the normalization of tori with $1 \leq p \leq n$ pinches and $n-p$ punctures. Once the existence of the new sector is taken into account, the violation of the spin-statistics theorem disappears. Moreover, the new sector contributes trivially to the nonperturbative $S$ matrix because -- for example -- the $n$-pinched torus represents nonperturbatively a loop of $n$ glueball propagators with no external leg. This opens the way for an exact solution limited to the new sector that may be solvable thanks to the vanishing $S$ matrix.

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arXiv2025

Superfield twist-$2$ operators in $\mathcal{N} = 1$ SCFTs and their renormalization-group improved generating functional in $\mathcal{N} = 1$ SYM theory

We provide a new construction of superfield collinear twist-$2$ operators as infinite-dimensional, irreducible representations of the collinear superconformal algebra in $\mathcal{N}=1$ superconformal field theories. As an application, we realize the above representations in terms of free superfields, in a manifestly gauge-invariant and supersymmetric-covariant fashion, in the zero coupling limit of $\mathcal{N}=1$ supersymmetric Yang-Mills (SYM) theory. This realization makes manifest their mixing and renormalization properties at one loop. We also extend to the superfield formalism the perturbative and nonperturbative techniques in [1-7] to a large class of supersymmetric theories that are superconformal in the zero-coupling limit. Specifically, we compute the generating functional of superfield twist-$2$ operators in $\mathcal{N}=1$ SU($N$) SYM theory in the zero coupling limit. We also work out in a closed form the corresponding asymptotic renormalization-group improved generating functional in Euclidean superspace and its planar and leading nonplanar large-$N$ expansion. We verify -- as originally predicted in [5] and verified in the component formalism [3, 4, 6, 7] -- that the leading nonplanar asymptotic RG-improved generating functional matches the structure of logarithm of a functional superdeterminant of the corresponding nonperturbative object, which it should be asymptotic to at short distances because of the asymptotic freedom. Hence, our large-$N$ computation sets strong ultraviolet asymptotic constraints on the nonperturbative solution of large-$N$ $\mathcal{N} = 1$ SYM theory that may be a pivotal guide for the search of such a solution.

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arXiv2025

Test of a two-level algorithm for the glueball spectrum in $SU(N_c)$ Yang-Mills theory

We present preliminary results obtained using a new code for $SU (N_c)$ Yang-Mills theory which performs a 2-level sampling of glueball correlators obtained from a suitably chosen basis of (APE) smeared and unsmeared operators. The code builds loop operators of any shape and length and classifies them according to the irreducible representations of the cubic group. We report on the performances of the algorithm and on the computation of the first low-lying glueball states choosing $N_c = 3$ as a reference to compare our results with the literature.

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arXiv2025

Generating functional of correlators of twist-$2$ operators in $\mathcal{N} = 1$ SUSY Yang-Mills theory, I

The present paper is the first installment where, extending our previous work in pure Yang-Mills (YM) theory, we compute the generating functional of correlators of collinear twist-$2$ operators that enter the components of balanced superfields -- i.e., superfields with an equal number of dotted and undotted indices in their spinor representation -- in $\mathcal{N} = 1$ SUSY SU($N$) YM theory in Minkowskian and Euclidean space-time, in the conformal limit and renormalization-group (RG) improved form, and to the leading and next-to-leading order in the large-$N$ expansion. Moreover, we compare our asymptotic RG-improved generating functional to the next-to-leading large-$N$ order with the corresponding nonperturbative object arising from the glueball/gluinoball one-loop effective action, which it should be asymptotic to at short distances because of the asymptotic freedom. Remarkably, we find that both have the structure of the logarithm of a functional superdeterminant. Hence, our large-$N$ computation sets strong ultraviolet asymptotic constraints on the nonperturbative solution of large-$N$ $\mathcal{N} = 1$ SUSY YM theory that may be a pivotal guide for the search of such a solution.

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arXiv2024

Symplectic Quantization and Minkowskian Statistical Mechanics: simulations on a 1+1 lattice

We introduce symplectic quantization, a novel functional approach to quantum field theory which allows to sample quantum fields fluctuations directly in Minkowski space-time, at variance with the traditional importance sampling protocols, well defined only for Euclidean Field Theory. This importance sampling procedure is realized by means of a deterministic dynamics generated by Hamilton-like equations evolving with respect to an auxiliary time parameter $τ$. In this framework, expectation values over quantum fluctuations are computed as dynamical averages along the trajectories parameterized by $τ$. Assuming ergodicity, this is equivalent to sample a microcanonical partition function. Then, by means of a large-M calculation, where M is the number of degrees of freedom on the lattice, we show that the microcanonical correlation functions are equivalent to those generated by a Minkowskian canonical theory where quantum fields fluctuations are weighted by the factor $\exp(S/\hbar )$, with $S$ being the original relativistic action of the system.

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arXiv2024

Nonresonant renormalization scheme for twist-$2$ operators in SU($N$) Yang-Mills theory

Recently, the short-distance asymptotics of the generating functional of $n$-point correlators of twist-$2$ operators in SU($N$) Yang-Mills (YM) theory has been worked out in [1]. The above computation relies on a basis change of renormalized twist-$2$ operators, where $-γ(g)/ β(g)$ reduces to $γ_0/ (β_0\,g)$ to all orders of perturbation theory, with $γ_0$ diagonal, $γ(g) = γ_0 g^2+\ldots$ the anomalous-dimension matrix and $β(g) = -β_0 g^3+\ldots$ the beta function. The construction is based on a novel geometric interpretation of operator mixing [2], under the assumption that the eigenvalues of the matrix $γ_0/ β_0$ satisfy the nonresonant condition $λ_i-λ_j\neq 2k$, with $λ_i$ in nonincreasing order and $k\in \mathbb{N}^+$. The nonresonant condition has been numerically verified up to $i,j=10^4$ in [1]. In the present paper we provide a number theoretic proof of the nonresonant condition for twist-$2$ operators essentially based on the classic result that Harmonic numbers are not integers. Our proof in YM theory can be extended with minor modifications to twist-$2$ operators in $\mathcal{N}=1$ SUSY YM theory, large-$N$ QCD with massless quarks and massless QCD-like theories.

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arXiv2023

UV asymptotics of $n$-point correlators of twist-$2$ operators in SU($N$) Yang-Mills theory

The generating functional $\mathcal{W}[J_{\mathcal O}]$ of Euclidean correlators of twist-$2$ operators in SU($N$) Yang-Mills theory admits the 't Hooft large-$N$ expansion: $\mathcal{W}[J_{\mathcal O}]=\mathcal{W}_{sphere}\,\,\,\,[J_{\mathcal O}]+\mathcal{W}_{torus} \,\,\,[J_{\mathcal O}]+ \cdots$. Nonperturbatively, $\mathcal{W}_{sphere} \,\,\,\,[J_{\mathcal O}]$ is a sum of tree diagrams involving glueball propagators and vertices, while $\mathcal{W}_{torus} \,\,\,[J_{\mathcal O}]$ is a sum of glueball one-loop diagrams. Moreover, it has been predicted that $\mathcal{W}_{torus } \,\,\,[J_{\mathcal O}]$ should admit the structure of the logarithm of a functional determinant summing glueball one-loop diagrams. We work out in a closed form the ultraviolet (UV) asymptotics of $\mathcal{W}_{sphere} \,\,\,\,[J_{\mathcal O},λ] \sim \mathcal{W}_{asym \, sphere} \,\,\,\,\,\,\,[J_{\mathcal O},λ]$ and $\mathcal{W}_{torus} \,\,\,[J_{\mathcal O},λ] \sim \mathcal{W}_{asym \, torus} \,\,\,\,\,\,[J_{\mathcal O},λ]$ in the coordinate representation as all the coordinates of the correlators are uniformly rescaled by a factor $λ\rightarrow 0$. Remarkably, we verify the above prediction that $\mathcal{W}_{asym \, torus} \,\,\,\,\,\,[J_{\mathcal O},λ]$ -- being asymptotic in the UV to $\mathcal{W}_{torus} \,\,\,[J_{\mathcal O}, λ]$ -- admits the structure of the logarithm of a functional determinant as well. Hence, the computation above sets strong UV asymptotic constraints on the nonperturbative solution of large-$N$ YM theory and it may be a pivotal guide for the search of such a solution.

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arXiv2021

$n$-point correlators of twist-$2$ operators in $SU(N)$ Yang-Mills theory to the lowest perturbative order

We compute, to the lowest perturbative order in $SU(N)$ Yang-Mills theory, $n$-point correlators in the coordinate and momentum representation of the gauge-invariant twist-$2$ operators with maximal spin along the $p_+$ direction, both in Minkowskian and -- by analytic continuation -- Euclidean space-time. We also construct the corresponding generating functionals. Remarkably, they have the structure of the logarithm of a functional determinant of the identity plus a term involving the effective propagators that act on the appropriate source fields.

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