Effective Field Theory for Physics Beyond the Standard Model
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fective Field Theory for Physics Beyond the Standard Model E. E. Boos* Skobel’tsyn Institute of Nuclear Physics, Moscow State University, Moscow, 119991 Russia *e-mail: [email protected] Received December 20, 2019; revised January 16, 2020; accepted January 29, 2020
Abstract—While no significant deviations from Standard Model (SM) predictions have so far been detected by LHC experiments, much attention is currently paid to formulating an effective field theory in which all possible deviations are parametrized with a minimal complete set of gauge-invariant local operators with dimensions greater than four. In this paper, basic features of this formalism referred to as the Standard-Model Effective Field Theory (SMEFT) are briefly reviewed. DOI: 10.1134/S1063779620040176
INTRODUCTION Prior to the Higgs-boson discovery by LHC experiments in 2012, the so-called No-Lose Theorem was formulated by analyzing the high-energy behavior of transition amplitudes involving longitudinal components of the fields of massive gauge bosons. This stated that either a sufficiently light Higgs boson with mass below some 700 GeV should exist, or some “novel physics” should emerge on the TeV energy scale so as to maintain the unitarity of transition amplitudes at high energies. The 2012 discovery of the Higgs boson was a heyday for the Standard Model since, thereby, its basic concept of a spontaneously-broken gauge symmetry was validated experimentally. On the other hand, this discovery invalidated the arguments in favor of beyond-SM (BSM) physics on the TeV scale. New physics is generally expected to emerge on the gravitational (or Planck) energy scale of ~1019 GeV, and the curves of energy-dependent running coupling constants of all gauge interactions are expected to approximately intersect at an energy on the order of 1016 GeV, which corresponds to the so-called GrandUnification energy scale. Nonzero neutrino masses are possibly induced by novel-physics effects occurring on an energy scale of 1011–1012 GeV. At the same time, we still don’t know if any novel physics will reveal itself at energies on the order of ten and tens of TeV, which are accessible for the LHC and/or FCC colliders. Already today the limits on the masses of a number of new particles predicted in models beyond the SM surpass one or more TeV. Generally, BSM effects can be searched for in two different ways depending on their characteristic energy threshold. If the latter lies within the collider’s energy range, novel physics can be revealed by directly detect-
ing the production and decays of new particles provided that these interact with the Standard Model ones with sufficiently large coupling constants. (The existence of new particles is predicted by nearly all SM extensions.) If the production thresholds of new particles lie beyond the collider’s energy range, novel physics can still reveal itself in the form of deviations from SM predictions for the production cross sections, differential distributions, and decay widths and branching fractions of known parti
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