Abstract
Gluon-gluon to photon-photon scattering gg→γγ offers to the LHC experiments a uniquely powerful probe of dimension-8 operators in the standard model effective field theory that are quadratic in both the electromagnetic and gluonic field-strength tensors, such as would appear in the Born-Infeld extension of the standard model. We use 13-TeV ATLAS data on the production of isolated photon pairs to set lower limits on the scales of dimension-8 operators M≳1 TeV and discuss the prospective sensitivities of possible future hadron colliders.
Highlights
Theoretical Particle Physics and Cosmology Group, Physics Department, King’s College London, London WC2R 2LS, United Kingdom, National Institute of Chemical Physics and Biophysics, Rävala 10, 10143 Tallinn, Estonia, and Theoretical Physics Department, CERN, CH-1211 Geneva 23, Switzerland
Introduction.—A model-independent way to constrain possible extensions of the standard model (SM) with high-scale new physics that decouples at low energies is provided by the standard model effective field theory (SMEFT) [1], which employs a systematic expansion in the effective mass dimensions of the new operators generated by high-scale physics beyond the SM
Apart from the dimension-5 operators that may contribute to neutrino masses and oscillations [2], the most prominent operators are those of dimension 6, whose coefficients scale as 1=Λ2, where Λ represents a generic new-physics scale
Summary
Since the electromagnetic field strength tensor Fμν is a specific combination of W3μν and Bμν, the gg → γγ scattering process is sensitive to just 4 combinations of these dimension-8 operators One of these combinations is of particular interest, as it arises in the Born-Infeld (BI) extension of the SM with the following Lagrangian LBISM:. Born and Infeld proposed a similar nonlinear extension of QED in 1934 [6], motivated by a “unitarian” idea that there should be an upper limit on the strength of the electromagnetic field This theory remained largely a curiosity until Fradkin and Tseytlin [7] showed in 1985 that it appears in models inspired by M theory, e.g., in which vector fields are coupled to matter particles that are localized on lower-dimensional “branes” [8]. It was pointed out in Ref. [10] that a measurement of light-by-light scattering in heavy-ion collisions at the LHC by the ATLAS Collaboration [11] imposes a constraint on the BI extension of QED that is orders of magnitude
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