New phenomenological and theoretical perspective on anomalous ZZ and Zγ processes

Abstract

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.

Sum rules in the standard model effective field theory from helicity amplitudes

“…Such relations, often denoted as sum rules, can be classified in terms of the energy expansion of the amplitudes analogous to the EFT operator expansion. In previous works, the main focus has been at the level of dimension-8 operators for which the sum rules can be interpreted as positivity bounds on certain operator coefficients (or combinations of them) [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. This remarkable finding suggests that the possible parameter space in an EFT is already constrained by the fundamental properties of quantum field theory, i.e.…”

“…can be imposed by requiring the isospins of f to satisfy either 12) which are exactly the same conditions in ref. [59] for protecting the SM Zff coupling.…”

“…, but is obtained with much less effort with the help of the sum rules. 12 It is also interesting to note that by combining eq. (5.5) and eq.…”

Towards the ultimate differential SMEFT analysis

“…The reason for this is that only a finite number of helicity amplitudes get corrections up to the given EFT order, see for instance refs. [45,46]. The coefficients of these basis functions, the so called angular moments [47][48][49][50], and their energy dependance, thus, contain the full differential information available in a process.…”

A new precision process at FCC-hh: the diphoton leptonic Wh channel

“…It has been shown that, at the LHC, several simple two-body production channels can be exploited to obtain precision measurements [1][2][3][4][5][6][7][8]. Among them, diboson production processes, featuring EW gauge bosons or the Higgs boson, play a privileged role since they can be used to indirectly test the high-energy Higgs dynamics [5,6,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27].…”