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The program AutoEFT is described. It allows one to generate Effective Field Theories (EFTs) from a given set of fields and symmetries. Allowed fields include scalars, spinors, gauge bosons, and gravitons. The symmetries can be local or global Lie groups based on U (1) and S U (N). The mass dimension of the EFT is limited only by the available computing resources. The operators are stored in a compact, human and machine-readable format. Aside from the program itself, we provide input files for EFTs based on the Standard Model and a number of its extensions. These include additional particles and symmetries, EFTs with minimal flavor violation, and gravitons. Program title: AutoEFT CPC Library link to program files: https://doi.org/10.17632/z8xm2hpbsp.1 Developer's repository link: https://gitlab.com/auto%5feft/autoeft Licensing provisions: MIT license Programming language: Python Nature of problem: The bottom-up construction of an Effective Field Theory (EFT) which describes physics below a certain energy scale Λ requires obtaining a set of operators, composed of fields with mass m ≪ Λ , that are invariant under certain symmetries. One is primarily interested in complete sets of independent operators, called operator bases. Their construction for a given mass dimension of the operators is nontrivial due to algebraic and kinematic relations that may render different operators redundant. Except for the lowest mass dimensions, the number of operators is so large that the task of constructing an explicit EFT operator basis requires a high degree of automation on a computer. In addition, an automated approach will allow one to immediately take into account newly postulated or discovered light particles beyond the Standard Model. Solution method: Based on the group theoretical techniques and concepts established in Refs. [1–9] and in particular Refs. [10,11], we developed the program AutoEFT, capable of constructing a non-redundant on-shell operator basis for general EFTs and arbitrary mass dimension. Provided a suitable model file , the respective operator basis is generated explicitly, including contractions of the symmetry group indices, in a fully automated fashion. Due to the generality of the algorithm, it can be applied to a variety of low-energy scenarios. The underlying low-energy theory is encoded in a model file which defines the symmetries and the field content. The fairly simple format enables the user to compose their own model files and to construct the respective operator basis with minimal effort. Additional comments including restrictions and unusual features: In its current form, AutoEFT is restricted to theories including particles with spin 0, 1/2, 1, and 2, where the latter two are considered massless. In addition, AutoEFT only constructs operators that mediate proper interactions, meaning that any operator must be composed of at least three fields. The internal symmetries must be given as factors of U (1) and S U (N) groups. In principle, operator bases can be generated for any mass dimension, which is, however, limited by the available computing resources. [1] Y. Shadmi, Y. Weiss, Effective field theory amplitudes the on-shell way: scalar and vector couplings to gluons, J. High Energy Phys. 02 (2019) 165, arXiv:1809.09644 [hep-ph]. [2] B. Henning, T. Melia, Conformal-helicity duality & the Hilbert space of free CFTs, arXiv:1902.06747 [hep-th]. [3] T. Ma, J. Shu, M.-L. Xiao, Standard model effective field theory from on-shell amplitudes, Chin. Phys. C 47 (2023) 023105, arXiv:1902.06752 [hep-ph]. [4] B. Henning, T. Melia, Constructing effective field theories via their harmonics, Phys. Rev. D 100 (2019) 016015, arXiv:1902.06754[hep-ph]. [5] R. Aoude, C.S. Machado, The Rise of SMEFT on-shell amplitudes, J. High Energy Phys. 12 (2019) 058, arXiv:1905.11433 [hep-ph]. [6] R.M. Fonseca, Enumerating the operators of an effective field theory, Phys. Rev. D 101 (2020) 035040, arXiv:1907.12584 [hep-ph]. [7] G. Durieux, T. Kitahara, Y. Shadmi, Y. Weiss, The electroweak effective field theory from on-shell amplitudes, J. High Energy Phys. 01 (2020) 119, arXiv:1909.10551 [hep-ph]. [8] A. Falkowski, Bases of massless EFTs via momentum twistors, arXiv:1912.07865[hep-ph]. [9] G. Durieux, C.S. Machado, Enumerating higher-dimensional operators with on-shell amplitudes, Phys. Rev. D 101 (2020) 095021, arXiv:1912.08827 [hep-ph]. [10] H.-L. Li, Z. Ren, J. Shu, M.-L. Xiao, J.-H. Yu, Y.-H. Zheng, Complete set of dimension-eight operators in the standard model effective field theory, Phys. Rev. D 104 (2021) 015026, arXiv:2005.00008[hep-ph]. [11] H.-L. Li, Z. Ren, M.-L. Xiao, J.-H. Yu, Y.-H. Zheng, Complete set of dimension-nine operators in the standard model effective field theory, Phys. Rev. D 104 (2021) 015025, arXiv:2007.07899 [hep-ph]. [ABSTRACT FROM AUTHOR]

We consider a mechanism for neutrino mass generation, based on a local B - L extension of the standard model, which becomes a linear seesaw regime for light neutrinos after spontaneous symmetry breaking. The spectrum of extra particles includes heavy neutrinos with masses near the TeV scale and a heavy Z' boson, as well as three extra neutral scalars and a charged scalar pair. We study the production and decays of these heavy particles at the LHC. Z' will decay mainly into heavy neutrino pairs or charged lepton pairs, similar to other low scale seesaw scenarios with local B - L, while the phenomenology of the extra scalars is what distinguishes the linear seesaw from the previous models. One of the neutral scalars is produced by Z'Z' fusion and decays mainly into vector boson pairs, the other two neutral scalars are less visible as they decay only into heavy or light neutrino pairs, and finally the charged scalars will decay mainly into charged leptons and missing energy. [ABSTRACT FROM AUTHOR]

Neutral diboson processes are precise probes of the Standard Model (SM) of particle physics, which entails high sensitivity to new physics effects. We identify in terms of dimension-8 effective operators the leading departures from the SM that survive in neutral diboson processes at high energy and that interfere with the unsuppressed SM helicity contributions. We describe symmetries and selection rules that single out those operators, both for weakly and strongly coupled physics beyond the SM. Finally, we show that unitarity and causality enforce, via dispersion relations, positivity constraints on the coefficients of these effective operators, reducing the parameter space which is theoretically allowed. [ABSTRACT FROM AUTHOR]