Moments for positivity: using Drell-Yan data to test positivity bounds and reverse-engineer new physics

Abstract

Moments of the leptonic angular distribution in the Drell-Yan process have recently been shown to be sensitive probes of a specific class of dimension-8, four-fermion operators in the Standard Model Effective Field Theory, involving a pair of quarks and leptons. The same operators are also subject to positivity bounds, when requiring the associated (unknown) UV completion to obey basic principles of quantum field theory. We perform a phenomenological study to quantify the sensitivity of the high-luminosity LHC to this set of operators and, by extension, the positivity bounds. We further extend the angular basis of moments and consider double differential information to improve the ability to disentangle the different operators, leading to a sensitivity to new physics scales up to 3 TeV. We use this information to explore the violation of positivity at the LHC as a way to test the underlying principles of quantum field theory. Finally, we present a case study which combines our results with information from other (current and prospective) experiments, as well as the positivity cone to infer the properties of possible tree-level UV completions. The data lead to robust, model-independent lower bounds on the $$ M/\sqrt{g} $$ M / g combination of the particle mass and coupling, for states that couple to right-handed leptons and/or up quarks.

Constraints on anomalous dimensions from the positivity of the S-matrix

“…This assumption is supported by substantial evidence in the literature[44,49,50]. Let us focus, for example, on φ 4 D 4 operators.…”

Positivity bounds on Higgs-Portal dark matter

“…In particular, such consistency conditions give rise to positivity conditions in the forward limit of the scattering amplitudes at low energies [1][2][3]. Recently, positivity bounds have been applied to the SMEFTs [4][5][6][7][8][9][10][11] and the Higgs-portal derivative interactions for scalar dark matter [12]. In the latter work, it has been shown that the positivity bounds can constrain the parameter space further for explaining the relic density for Weakly Interacting Massive Particles [12].…”

Triple crossing positivity bounds, mass dependence and cosmological scalars: Horndeski theory and DHOST

“…These positivity bounds have been used to constrain Horndeski theory and related models and confront with cosmological data [44, 49-51, 57, 59-64]. Other fruitful phenomenological applications of positivity bounds include constraining the enormous parameter space of the Standard Model EFT (SMEFT) (see, e.g., [69][70][71][72][73][74][75][76][77][78][79][80][81][82][83]). The SMEFT…”