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Journal articles on the topic 'Perturbative computations'

Author: Grafiati

Published: 9 March 2023

Last updated: 28 July 2025

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1

Shindler, Andrea. "Gradient Flow: Perturbative and Non-Perturbative Renormalization." EPJ Web of Conferences 274 (2022): 01005. http://dx.doi.org/10.1051/epjconf/202227401005.

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We review the gradient flow for gauge and fermion fields and its applications to lattice gauge theory computations. Using specific examples, we discuss the interplay between perturbative and non-perturbative calculations in the context of renormalization with the gradient flow.

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Debbio, Luigi Del, Francesco Di Renzo, and Gianluca Filaci. "High-order perturbative expansions in massless gauge theories with NSPT." EPJ Web of Conferences 175 (2018): 11023. http://dx.doi.org/10.1051/epjconf/201817511023.

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We investigate the possibility of using numerical stochastic perturbation theory (NSPT) to probe high orders in the perturbative expansion of lattice gauge theories with massless Wilson fermions. Twisted boundary conditions are used to regularise the gauge zero-mode; the extension of these boundary conditions to include fermions in the fundamental representation requires to introduce a smell degree of freedom. Moreover, the mass of Wilson fermions is affected by an additive renormalisation: we study how to determine the mass counterterms consistently in finite volume. The knowledge of the crit

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3

Lüscher, M., and P. Weisz. "Efficient numerical techniques for perturbative lattice gauge theory computations." Nuclear Physics B 266, no. 2 (1986): 309–56. http://dx.doi.org/10.1016/0550-3213(86)90094-5.

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4

Bern, Z. "Perturbative gravity from gauge theory." Modern Physics Letters A 29, no. 32 (2014): 1430036. http://dx.doi.org/10.1142/s0217732314300365.

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Here, we describe a recently conjectured duality between color and kinematics for gauge-theory amplitudes. Whenever this duality is manifest, the integrands of loop-level gravity scattering amplitudes can be obtained from corresponding gauge-theory amplitudes via a double-copy relation. This duality has been used to enormously simplify a number of explicit multiloop supergravity calculations. The results of these computations is that supergravity theories have a surprisingly tame ultraviolet behavior, and in some cases may even be finite. As an example, we summarize a recent calculation showin

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5

DEMETERFI, KRESIMIR, ANTAL JEVICKI, and JOĀO P. RODRIGUES. "PERTURBATIVE RESULTS OF COLLECTIVE STRING FIELD THEORY." Modern Physics Letters A 06, no. 35 (1991): 3199–212. http://dx.doi.org/10.1142/s0217732391003699.

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We present a summary of perturbative results obtained in the framework of collective string field theory. We discuss computations of tree-level scattering amplitudes, loop corrections to tachyon self-energy, ground state energy and finite temperature free energy. A comparison with results obtained in different approaches is given. We also discuss the physical implications of our results.

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Reyes, Edilson, and Raffaele Fazio. "High-Precision Calculations of the Higgs Boson Mass." Particles 5, no. 1 (2022): 53–73. http://dx.doi.org/10.3390/particles5010006.

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In this paper, we review the status of the computations of the perturbative quantum corrections to the Higgs boson mass in the Standard Model and in its supersymmetric extensions. In particular, supersymmetric theories require a very accurate computation of the Higgs boson mass, which includes corrections even up to the three-loop level, since their predictions are limited by theoretical uncertainties. A discussion about these uncertainties in the context of the Minimal and Next To Minimal Supersymmetric Standard Model is included.

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MANIN, YURI I. "Renormalisation and computation II: time cut-off and the Halting Problem." Mathematical Structures in Computer Science 22, no. 5 (2012): 729–51. http://dx.doi.org/10.1017/s0960129511000508.

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This is the second instalment in the project initiated in Manin (2012). In the first Part, we argued that both the philosophy and technique of perturbative renormalisation in quantum field theory could be meaningfully transplanted to the theory of computation, and sketched several contexts supporting this view.In this second part, we address some of the issues raised in Manin (2012) and develop them further in three contexts: a categorification of the algorithmic computations; time cut-off and anytime algorithms; and, finally, a Hopf algebra renormalisation of the Halting Problem.

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SURGULADZE, LEVAN R. "COMPUTER PROGRAMS FOR ANALYTICAL PERTURBATIVE CALCULATIONS IN HIGH ENERGY PHYSICS." International Journal of Modern Physics C 05, no. 06 (1994): 1089–101. http://dx.doi.org/10.1142/s0129183194001161.

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A short review of the present status of computer packages for the high order analytical perturbative calculations is presented. The mathematical algorithm and the quantum field theory methods used are briefly discussed. The most recent computer package HEPLoops for analytical computations in high energy physics up to four-loops is also discussed.

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9

Krmar, Marija, та Miljenko Peric. "Interplay between vibronic and spin-orbit couplings in 3П states of triatomic molecules using as an example the A3Пu electronic state of NCN". Journal of the Serbian Chemical Society 66, № 9 (2001): 613–30. http://dx.doi.org/10.2298/jsc0109613k.

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A systematic study of various effects on the structure of the spectra of linear triatomic molecules in the 3P electronic states has been carried out. Paricular attention was paid to the interplay between the vibronic and spin-orbit couplings. Variational and perturbative computations at various levels of sophistication were performed for the A3Pu state of the NCN radical.

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10

Karanikas, A. I., and C. N. Ktorides. "Polyakov's spin factor and new algorithms for efficient perturbative computations in QCD." Physics Letters B 500, no. 1-2 (2001): 75–86. http://dx.doi.org/10.1016/s0370-2693(01)00062-4.

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11

Creedon, Ryan, Bernard Deconinck, and Olga Trichtchenko. "High-Frequency Instabilities of a Boussinesq–Whitham System: A Perturbative Approach." Fluids 6, no. 4 (2021): 136. http://dx.doi.org/10.3390/fluids6040136.

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We analyze the spectral stability of small-amplitude, periodic, traveling-wave solutions of a Boussinesq–Whitham system. These solutions are shown numerically to exhibit high-frequency instabilities when subject to bounded perturbations on the real line. We use a formal perturbation method to estimate the asymptotic behavior of these instabilities in the small-amplitude regime. We compare these asymptotic results with direct numerical computations.

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12

Lin, Ying-Tsong. "Higher-order perturbative parabolic-equation solutions for reduced-order sound propagation modeling." Journal of the Acoustical Society of America 152, no. 4 (2022): A156. http://dx.doi.org/10.1121/10.0015871.

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The parabolic-equation (PE) approximation to the Helmholtz equation has been shown to be one of the most effective and efficient numerical methods for sound propagation modeling. In this talk, a recursive and iterative algorithm will be introduced to compute the PE solutions due to perturbations in the medium wavenumber, which is a function of frequency and sound speed. This algorithm is developed based on perturbation theory with higher-order nonlinear terms, and it can efficiently compute higher-order derivatives of the sound pressure field with respect to changes in the local wavenumber. Th

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13

Garcia, Marcos A. G., and Aline Pereyra-Flores. "Impact of dark sector preheating on CMB observables." Journal of Cosmology and Astroparticle Physics 2024, no. 08 (2024): 043. http://dx.doi.org/10.1088/1475-7516/2024/08/043.

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Abstract The prediction of a nearly scale-invariant spectrum of curvature and tensor fluctuations is among the main features of cosmic inflation. The current measurements of the primordial fluctuations in the cosmic microwave background (CMB) provide tight constraints on the amplitude of the scalar and tensor spectra, and the scalar tilt. However, the precise connection between these observables and a given inflationary model, depends on the expansion history between the end of inflation and the beginning of the radiation dominated era, which corresponds to the reheating epoch. This mapping be

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14

Parisi, Giorgio. "Scientific and personal recollections of Roberto Petronzio." EPJ Web of Conferences 175 (2018): 01001. http://dx.doi.org/10.1051/epjconf/201817501001.

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This paper aims to recall some of the main contributions of Roberto Petronzio to physics, with a particular regard to the period we have been working together. His seminal contributions cover an extremely wide range of topics: the foundation of the perturbative approach to QCD, various aspects of weak interaction theory, from basic questions (e.g. the mass of the Higgs) to lattice weak interaction, lattice QCD from the beginning to most recent computations.

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BJERRUM-BOHR, N. E. J., and PIERRE VANHOVE. "SURPRISING SIMPLICITY OF $\mathcal{N}=8$ SUPERGRAVITY." International Journal of Modern Physics D 18, no. 14 (2009): 2295–301. http://dx.doi.org/10.1142/s0218271809015874.

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Gravity amplitudes are, via the Kawai–Lewellen–Tye relations intimately linked to products of Yang–Mills amplitudes. Explicitly, this shows up in computations of [Formula: see text] supergravity where the perturbative expansion and ultraviolet behavior of this theory is akin to [Formula: see text] super-Yang–Mills at least through three loops. Full persistence to all loop orders would be truly remarkable and imply finiteness of [Formula: see text] supergravity in four dimensions.

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Jeszenszki, Péter, Dávid Ferenc, and Edit Mátyus. "Variational Dirac–Coulomb explicitly correlated computations for atoms and molecules." Journal of Chemical Physics 156, no. 8 (2022): 084111. http://dx.doi.org/10.1063/5.0075096.

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The Dirac–Coulomb equation with positive-energy projection is solved using explicitly correlated Gaussian functions. The algorithm and computational procedure aims for a parts-per-billion convergence of the energy to provide a starting point for further comparison and further developments in relation with high-resolution atomic and molecular spectroscopy. Besides a detailed discussion of the implementation of the fundamental spinor structure, permutation, and point-group symmetries, various options for the positive-energy projection procedure are presented. The no-pair Dirac–Coulomb energy con

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17

Gracey, J. A. "Large Nf quantum field theory." International Journal of Modern Physics A 33, no. 35 (2018): 1830032. http://dx.doi.org/10.1142/s0217751x18300326.

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We review the development of the large [Formula: see text] method, where [Formula: see text] indicates the number of flavours, used to study perturbative and nonperturbative properties of quantum field theories. The relevant historical background is summarized as a prelude to the introduction of the large [Formula: see text] critical point formalism. This is used to compute large [Formula: see text] corrections to [Formula: see text]-dimensional critical exponents of the universal quantum field theory present at the Wilson–Fisher fixed point. While pedagogical in part the application to gauge

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18

MAMEDOVA, YEGANA V. "INFRARED RENORMALON EFFECTS ON LIGHT MESONS ELECTROMAGNETIC TRANSITION FORM FACTOR FMγ*(Q2, ω)". International Journal of Modern Physics A 18, № 07 (2003): 1023–50. http://dx.doi.org/10.1142/s0217751x03013806.

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The light pseudoscalar π0, η and η′ mesons electromagnetic transition γ* + γ* → M form factors FMγ*(Q2,ω) are calculated, applying the perturbative QCD factorization formula and the frozen coupling constant approximation. In the computations the O(αS) order expression for FMγ*(Q2,ω) and the mesons' infrared renormalon corrected distribution amplitudes are used. In the case of the η and η′ mesons, the SUf(3) ordinary octet-singlet mixing scheme is utilized. Comparisons are made with the results obtained, employing the mesons' ordinary distribution amplitudes and with γ + γ* → M transition form

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19

Arsie, Alessandro, Paolo Lorenzoni, and Antonio Moro. "On integrable conservation laws." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 471, no. 2173 (2015): 20140124. http://dx.doi.org/10.1098/rspa.2014.0124.

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We study normal forms of scalar integrable dispersive (not necessarily Hamiltonian) conservation laws, via the Dubrovin–Zhang perturbative scheme. Our computations support the conjecture that such normal forms are parametrized by infinitely many arbitrary functions that can be identified with the coefficients of the quasi-linear part of the equation. Moreover, in general, we conjecture that two scalar integrable evolutionary partial differential equations having the same quasi-linear part are Miura equivalent. This conjecture is also consistent with the tensorial behaviour of these coefficient

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20

Heitger, Jochen, Fabian Joswig, Anastassios Vladikas, and Christian Wittemeier. "Non-perturbative determination of cV, ZV and ZS/ZP in Nf = 3 lattice QCD." EPJ Web of Conferences 175 (2018): 10004. http://dx.doi.org/10.1051/epjconf/201817510004.

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We report on non-perturbative computations of the improvement coefficient cV and the renormalization factor ZV of the vector current in three-flavour O(a) improved lattice QCD with Wilson quarks and tree-level Symanzik improved gauge action. To reduce finite quark mass effects, our improvement and normalization conditions exploit massive chiral Ward identities formulated in the Schrödinger functional setup, which also allow deriving a new method to extract the ratio ZS/ZP of scalar to pseudoscalar renormalization constants. We present preliminary results of a numerical evaluation of ZV and cV

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21

Grats, Yuri V., and Pavel Spirin. "Vacuum Polarization in a Zero-Width Potential: Self-Adjoint Extension." Universe 7, no. 5 (2021): 127. http://dx.doi.org/10.3390/universe7050127.

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The effects of vacuum polarization associated with a massless scalar field near pointlike source with a zero-range potential in three spatial dimensions are analyzed. The “physical” approach consists in the usage of direct delta-potential as a model of pointlike interaction. We use the Perturbation theory in the Fourier space with dimensional regularization of the momentum integrals. In the weak-field approximation, we compute the effects of interest. The “mathematical” approach implies the self-adjoint extension technique. In the Quantum-Field-Theory framework we consider the massless scalar

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22

Fraidenraich, A., P. M. Jacovkis, and F. R. de A. Lima. "Sensitivity computations using first and second orders perturbative methods for the advection-diffusion-reaction model of pollutant transport." Journal of the Brazilian Society of Mechanical Sciences and Engineering 25, no. 1 (2003): 23–29. http://dx.doi.org/10.1590/s1678-58782003000100004.

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23

Lahoche, Vincent, Dine Ousmane Samary, and Mohamed Tamaazousti. "Generalized scale behavior and renormalization group for data analysis." Journal of Statistical Mechanics: Theory and Experiment 2022, no. 3 (2022): 033101. http://dx.doi.org/10.1088/1742-5468/ac52a6.

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Abstract Some recent results showed that the renormalization group (RG) can be considered as a promising framework to address open issues in data analysis. In this work, we focus on one of these aspects, closely related to principal component analysis (PCA) for the case of large dimensional data sets with covariance having a nearly continuous spectrum. In this case, the distinction between ‘noise-like’ and ‘non-noise’ modes becomes arbitrary and an open challenge for standard methods. Observing that both RG and PCA search for simplification for systems involving many degrees of freedom, we aim

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24

Kurtadikar, M. L., and S. C. Mehrotra. "Collision-Induced Rotational Excitations of Interstellar Molecules due to He and H2." Symposium - International Astronomical Union 120 (1987): 47–48. http://dx.doi.org/10.1017/s007418090015377x.

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An Effective Straight-line Trajectory (EST) approach by introducing a parameter RX has been proposed for computations of collision-induced rotational line widths (HWHM) and excitation rates in case of atom-molecule systems under the frame work of Smith, Giraud and Cooper (1976) and molecule-molecule systems under the frame work of normalized semi-classical perturbative approach. An optimised parameter RX, which is a measure of significance of the curved trajectories of the colliding molecules, can be determined from the temperature dependence of collision-induced line widths. the EST approach

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BERAKDAR, J. "SCATTERING PATH FORMALISM FOR THE PROPAGATION OF INTERACTING COMPOUNDS IN ORDERED AND DISORDERED MATERIALS." Surface Review and Letters 07, no. 03 (2000): 205–10. http://dx.doi.org/10.1142/s0218625x00000257.

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This study presents a theoretical framework for the propagation of a compound consisting of N interacting particles in a multicenter potential. A novel Green operator approach is proposed that disentangles the geometrical and dynamical properties of the scatterers from the internal evolution of the projectile compound. Furthermore, the transition operator for the scattering from the multicenter potential is expanded in terms of many-body scattering path operators, which in turn are expressed in terms of single site transition operators that are amenable to computations. To deduce the correlate

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26

Czernek, Jiří, and Jiří Brus. "On the Intermolecular Interactions in Thiophene-Cored Single-Stacking Junctions." International Journal of Molecular Sciences 24, no. 17 (2023): 13349. http://dx.doi.org/10.3390/ijms241713349.

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There have been attempts, both experimental and based on density-functional theory (DFT) modeling, at understanding the factors that govern the electronic conductance behavior of single-stacking junctions formed by pi-conjugated materials in nanogaps. Here, a reliable description of relevant stacked configurations of some thiophene-cored systems is provided by means of high-level quantum chemical approaches. The minimal structures of these configurations, which are found using the dispersion-corrected DFT approach, are employed in calculations that apply the coupled cluster method with singles

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27

Noriega, Hernán E., Alejandro Aviles, Sebastien Fromenteau, and Mariana Vargas-Magaña. "Fast computation of non-linear power spectrum in cosmologies with massive neutrinos." Journal of Cosmology and Astroparticle Physics 2022, no. 11 (2022): 038. http://dx.doi.org/10.1088/1475-7516/2022/11/038.

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Abstract We compute 1-loop corrections to the redshift space galaxy power spectrum in cosmologies containing additional scales, and hence kernels different from Einstein-de Sitter (EdS). Specifically, our method is tailored for cosmologies in the presence of massive neutrinos and some modified gravity models; in this article we concentrate on the former case. The perturbative kernels have contributions that we notice appear either from the logarithmic growth rate f(k,t), which is scale-dependent because of the neutrino free-streaming, or from the failure of the commonly used approximation f 2

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Kevrekidis, P. G., R. Carretero-González, and D. J. Frantzeskakis. "Stability of single and multiple matter-wave dark solitons in collisionally inhomogeneous Bose–Einstein condensates." International Journal of Modern Physics B 31, no. 10 (2017): 1742013. http://dx.doi.org/10.1142/s0217979217420139.

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We examine the spectral properties of single and multiple matter-wave dark solitons in Bose–Einstein condensates confined in parabolic traps, where the scattering length is periodically modulated. In addition to the large density limit picture previously established for homogeneous nonlinearities, we explore a perturbative analysis in the vicinity of the linear limit, which provides good agreement with the observed spectral modes. Between these two analytically tractable limits, we use numerical computations to fill in the relevant intermediate regime. We find that the scattering length modula

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Gerlach, Marvin. "Three-loop topology analysis of neutral B-meson mixing with tapir." Journal of Physics: Conference Series 2438, no. 1 (2023): 012156. http://dx.doi.org/10.1088/1742-6596/2438/1/012156.

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Abstract Modern advances in particle physics depend strongly on the usage of reliable computer programs. In this context two issues become important: The usage of powerful algorithms to handle the amount of evaluated data properly, and a software architecture capable of overcoming the problems of maintainability and extendability. We present our approach to such a computer program, called tapir. This tool assists computations in perturbative quantum field theory in many ways. Such calculations often involve the evaluation of a large amount of Feynman diagrams with multiple loops. tapir helps i

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Boyd, John P., and Zhengjie Xu. "Numerical and perturbative computations of solitary waves of the Benjamin–Ono equation with higher order nonlinearity using Christov rational basis functions." Journal of Computational Physics 231, no. 4 (2012): 1216–29. http://dx.doi.org/10.1016/j.jcp.2011.10.004.

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Bhattacharya, Sourav. "Massless minimal quantum scalar field with an asymmetric self interaction in de Sitter spacetime." Journal of Cosmology and Astroparticle Physics 2022, no. 09 (2022): 041. http://dx.doi.org/10.1088/1475-7516/2022/09/041.

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Abstract Massless minimally coupled quantum scalar field with an asymmetric self interaction, V(ϕ) = λϕ 4/4! + βϕ 3/3! (with λ > 0) is considered in the (3+1)-dimensional inflationary de Sitter spacetime. This potential is bounded from below irrespective of the sign of β. Earlier computations mostly considered the quartic part. Our chief motivation behind this study is to assess the vacuum expectation values of V(ϕ) and ϕ, both of which can be negative, and hence may lead to some screening of the inflationary cosmological constant value. First using the in-in formalism, the renormalised qua

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Xhako, Dafina, Valbona Muda, Niko Hyka, and Elda Spahiu. "Using QCDLAB2 to Define Lattice Parameter." WSEAS TRANSACTIONS ON SYSTEMS 24 (March 18, 2025): 59–65. https://doi.org/10.37394/23202.2025.24.7.

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Lattice Quantum Chromodynamics (LQCD) may be studied in low-energy regimes where non-perturbative approaches are useful because of their computational methods. Determining the lattice parameter, sometimes referred to as the lattice scale or lattice parameter, is a crucial objective in LQCD computations. The best way to get this parameter is to examine the quark-antiquark potential's behavior, which in LQCD simulations may be obtained by first computing the Wilson loops. We used an improved version of QCDLAB 2.0, a program specifically designed for lattice QCD simulations, in this paper. We con

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JOHNSON, CLIFFORD V. "THE ENHANÇON, MULTIMONOPOLES AND FUZZY GEOMETRY." International Journal of Modern Physics A 16, no. 05 (2001): 990–1001. http://dx.doi.org/10.1142/s0217751x01004062.

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The presentation at Strings 2000 was intended to be in two main parts, but there was only time for part one. However both parts appeared on the online proceedings, and are also included in this document. The first part concerns an exploration of the connection between the physics of the "enhançon" geometry arising from wrapping N D6–branes on the K3 manifold in Type IIA string theory and that of a charge N BPS multi–monopole. This also relates to the physics of 2+1 dimensional SU(N) gauge theory with eight supercharges. The main results uncovered by this exploration are: a) better insight into

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Baglioni, Paolo, and Francesco Di Renzo. "Large fluctuations in NSPT computations: a lesson from O(N) non-linear sigma models." European Physical Journal C 85, no. 2 (2025). https://doi.org/10.1140/epjc/s10052-025-13887-7.

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Abstract In the last three decades, numerical stochastic perturbation theory (NSPT) has proven to be an excellent tool for calculating perturbative expansions in theories such as Lattice QCD, for which standard, diagrammatic perturbation theory is known to be cumbersome. Despite the significant success of this stochastic method and the improvements made in recent years, NSPT apparently cannot be successfully implemented in low-dimensional models due to the emergence of huge statistical fluctuations: as the perturbative order gets higher, the signal to noise ratio is simply not good enough. Thi

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Cristofoli, Andrea, Asaad Elkhidir, Anton Ilderton, and Donal O’Connell. "Large gauge effects and the structure of amplitudes." Journal of High Energy Physics 2023, no. 6 (2023). http://dx.doi.org/10.1007/jhep06(2023)204.

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Abstract We show that large gauge transformations modify the structure of momentum conservation leading to non-vanishing three-point amplitudes in a simple toy model of a gravitational wave event. This phenomenon resolves an apparent tension between perturbative scattering amplitude computations and exact methods in field theory. The tension is resolved to all orders of perturbation theory once large gauge effects are included via a modified LSZ prescription; if they are omitted, perturbative methods only recover a subset of terms in the full non-perturbative expression. Although our results a

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Schenk, Sebastian. "The breakdown of resummed perturbation theory at high energies." Journal of High Energy Physics 2022, no. 3 (2022). http://dx.doi.org/10.1007/jhep03(2022)100.

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Abstract Calculations of high-energy processes involving the production of a large number of particles in weakly-coupled quantum field theories have previously signaled the need for novel non-perturbative behavior or even new physical phenomena. In some scenarios, already tree-level computations may enter the regime of large-order perturbation theory and therefore require a careful investigation. We demonstrate that in scalar quantum field theories with a unique global minimum, where suitably resummed perturbative expansions are expected to capture all relevant physical effects, perturbation t

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Hirvonen, Joonas, Johan Löfgren, Michael J. Ramsey-Musolf, Philipp Schicho, and Tuomas V. I. Tenkanen. "Computing the gauge-invariant bubble nucleation rate in finite temperature effective field theory." Journal of High Energy Physics 2022, no. 7 (2022). http://dx.doi.org/10.1007/jhep07(2022)135.

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Abstract A gauge-invariant framework for computing bubble nucleation rates at finite temperature in the presence of radiative barriers was presented and advocated for model-building and phenomenological studies in an accompanying article [1]. Here, we detail this computation using the Abelian Higgs Model as an illustrative example. Subsequently, we recast this approach in the dimensionally-reduced high-temperature effective field theory for nucleation. This allows for including several higher order thermal resummations and furthermore delineate clearly the approach’s limits of validity. This a

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Damour, Yann, Alejandro Gallo, and Anthony Scemama. "Stochastically accelerated perturbative triples correction in coupled cluster calculations." Journal of Chemical Physics 161, no. 3 (2024). http://dx.doi.org/10.1063/5.0220730.

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We introduce a novel algorithm that leverages stochastic sampling techniques to compute the perturbative triples correction in the coupled-cluster framework. By combining elements of randomness and determinism, our algorithm achieves a favorable balance between accuracy and computational cost. The main advantage of this algorithm is that it allows for the calculation to be stopped at any time, providing an unbiased estimate, with a statistical error that goes to zero as the exact calculation is approached. We provide evidence that our semi-stochastic algorithm achieves substantial computationa

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Thim, Oliver, Andreas Ekström, and Christian Forssén. "Perturbative computations of neutron-proton scattering observables using renormalization-group invariant chiral effective field theory up to N3LO." Physical Review C 109, no. 6 (2024). http://dx.doi.org/10.1103/physrevc.109.064001.

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We predict neutron-proton scattering cross sections and polarization observables up to next-to-next-to-next-to-leading order in a renormalization-group invariant description of the strong nucleon-nucleon interaction. Low-energy constants are calibrated to phase shifts, subleading corrections are computed in distorted-wave perturbation theory, and we employ momentum-cutoff values 500 and 2500 MeV. We find a steady order-by-order convergence and realistic descriptions of scattering observables up to a laboratory scattering energy of approximately 100 MeV. We also compare perturbative and nonpert

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Pesando, Igor. "On the breakdown of the perturbative interaction picture in Big Crunch/Big Bang or the true reason why perturbative string amplitudes on temporal orbifolds diverge." European Physical Journal C 82, no. 12 (2022). http://dx.doi.org/10.1140/epjc/s10052-022-11096-0.

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AbstractWe discuss how the perturbative particle paradigm fails in certain background with space-like singularity but asymptotically flat which should admit a S-matrix. The Feynman approach relies on the interaction picture. This approach means that we can interpret interactions as exchanges of particles. Particles are the modes of the quadratic part of the Lagrangian. In certain backgrounds with space-like singularity the interaction Hamiltonian is well defined but the perturbative expansion of the evolution operator through the singularity and the perturbative S matrix do not exist. On the o

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Bliard, Gabriel James Stockton. "Notes on n-point Witten diagrams in AdS₂." Journal of Physics A: Mathematical and Theoretical, July 7, 2022. http://dx.doi.org/10.1088/1751-8121/ac7f6b.

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Abstract Witten diagrams provide a perturbative framework for calculations in Anti-de-Sitter space, and play an essential role in a variety of holographic computations. In the case of this study in AdS2, the one-dimensional boundary allows for a simple setup, in which we obtain perturbative analytic results for correlators with the residue theorem. This elementary method is used to ﬁnd all scalar n-point contact Witten diagrams for external operators of conformal dimension ∆ = 1 and ∆ = 2, and to determine topological correlators of Yang-Mills in AdS2. Another established method is applied to

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Benaych-Georges, Florent, Nathanaël Enriquez, and Alkéos Michaïl. "Eigenvectors of a matrix under random perturbation." Random Matrices: Theory and Applications, May 28, 2020, 2150023. http://dx.doi.org/10.1142/s2010326321500234.

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In this text, based on elementary computations, we provide a perturbative expansion of the coordinates of the eigenvectors of a Hermitian matrix of large size perturbed by a random matrix with small operator norm whose entries in the eigenvector basis of the first one are independent, centered, with a variance profile. This is done through a perturbative expansion of spectral measures associated to the state defined by a given vector.

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Gould, Oliver, Anna Kormu, and David J. Weir. "Nonperturbative test of nucleation calculations for strong phase transitions." Physical Review D 111, no. 5 (2025). https://doi.org/10.1103/physrevd.111.l051901.

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Nucleation rate computations are of broad importance in particle physics and cosmology. Perturbative calculations are often used to compute the nucleation rate Γ, but these are incomplete. We perform nonperturbative lattice simulations of nucleation in a scalar field theory with a tree-level barrier, computing a final result extrapolated to the thermodynamic and continuum limits. Although the system in question should be well described by a complete one-loop perturbative calculation, we find only qualitative agreement with the full perturbative result, with a 20% discrepancy in |logΓ|. Our res

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Li, Xinyu, Lam Hui, and Greg L. Bryan. "Numerical and perturbative computations of the fuzzy dark matter model." Physical Review D 99, no. 6 (2019). http://dx.doi.org/10.1103/physrevd.99.063509.

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Kousvos, Stefanos Robert, and Andreas Stergiou. "CFTs with $\mathbf{U(m)\times U(n)}$ global symmetry in 3D and the chiral phase transition of QCD." SciPost Physics 15, no. 2 (2023). http://dx.doi.org/10.21468/scipostphys.15.2.075.

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Conformal field theories (CFTs) with U(m)\times U(n)U(m)×U(n) global symmetry in d=3d=3 dimensions have been studied for years due to their potential relevance to the chiral phase transition of quantum chromodynamics (QCD). In this work such CFTs are analyzed in d=4-\varepsilond=4−ε and d=3d=3. This includes perturbative computations in the \varepsilonε and large-nn expansions as well as non-perturbative ones with the numerical conformal bootstrap. New perturbative results are presented and a variety of non-perturbative bootstrap bounds are obtained in d=3d=3. Various features of the bounds ob

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Gould, Oliver, and Tuomas V. I. Tenkanen. "On the perturbative expansion at high temperature and implications for cosmological phase transitions." Journal of High Energy Physics 2021, no. 6 (2021). http://dx.doi.org/10.1007/jhep06(2021)069.

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Abstract We revisit the perturbative expansion at high temperature and investigate its convergence by inspecting the renormalisation scale dependence of the effective potential. Although at zero temperature the renormalisation group improved effective potential is scale independent at one-loop, we show how this breaks down at high temperature, due to the misalignment of loop and coupling expansions. Following this, we show how one can recover renormalisation scale independence at high temperature, and that it requires computations at two-loop order. We demonstrate how this resolves some of the

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Nelson, Philip M., Zachary L. Glick, and C. David Sherrill. "Approximating large-basis coupled-cluster theory vibrational frequencies using focal-point approximations." Journal of Chemical Physics 159, no. 9 (2023). http://dx.doi.org/10.1063/5.0168608.

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The focal-point approximation can be used to estimate a high-accuracy, slow quantum chemistry computation by combining several lower-accuracy, faster computations. We examine the performance of focal-point methods by combining second-order Møller–Plesset perturbation theory (MP2) with coupled-cluster singles, doubles, and perturbative triples [CCSD(T)] for the calculation of harmonic frequencies and that of fundamental frequencies using second-order vibrational perturbation theory (VPT2). In contrast to standard CCSD(T), the focal-point CCSD(T) method approaches the complete basis set (CBS) li

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Iskakov, Sergei, Mikhail I. Katsnelson, and Alexander I. Lichtenstein. "Perturbative solution of fermionic sign problem in quantum Monte Carlo computations." npj Computational Materials 10, no. 1 (2024). http://dx.doi.org/10.1038/s41524-024-01221-w.

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AbstractWe have developed a strong-coupling perturbation scheme for a general doped Hubbard model around a particle-hole-symmetric reference system, which is free from the fermionic sign problem. Our approach is based on the lattice determinantal Quantum Monte Carlo (QMC) method in both continuous and discrete time versions for large periodic clusters in a fermionic bath. By considering the first-order perturbation in the shift of the chemical potential and the second-neighbor hopping, we are able to obtain an accurate electronic spectral function for a range of parameters that correspond to o

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Di Pietro, Lorenzo, Victor Gorbenko, and Shota Komatsu. "Analyticity and unitarity for cosmological correlators." Journal of High Energy Physics 2022, no. 3 (2022). http://dx.doi.org/10.1007/jhep03(2022)023.

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Abstract We study the fundamentals of quantum field theory on a rigid de Sitter space. We show that the perturbative expansion of late-time correlation functions to all orders can be equivalently generated by a non-unitary Lagrangian on a Euclidean AdS geometry. This finding simplifies dramatically perturbative computations, as well as allows us to establish basic properties of these correlators, which comprise a Euclidean CFT. We use this to infer the analytic structure of the spectral density that captures the conformal partial wave expansion of a late-time four-point function, to derive an

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Curko, Arpad, and G. Cynolter. "Unitarity in multi-Higgs production using the Schwinger-Dyson equation." Journal of Physics G: Nuclear and Particle Physics, August 16, 2022. http://dx.doi.org/10.1088/1361-6471/ac8a07.

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Abstract In spontaneuosly broken scalar theories perturbative and semi-classical calculations show that multi-particle production grows rapidly with the number of scalar particles at sufficiently high energies. According to recent computations, for $ \lambda n \gg 1 $, where $ n $ is the multiplicity and $ \lambda $ is the self-coupling, the amplitude grows exponentially with the energy, resulting in a divergent propagator and predicting the violation of perturbative unitarity. In this paper in the scalar theory the self-consistent Schwinger-Dyson equation is solved in the spectral representat

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