Quantum Theory of Fields (9781139633659) by Weinberg Steven

Author:Weinberg, Steven
Format: epub
Publisher: Cambridge Univ Pr

Figure 28.2. A one-loop diagram that can contribute to the ∆S = 2 effective interaction in both the, supersymmetric and non-supersymmetric standard models. Here solid lines are quarks and wavy lines are W± bosons.

Just as for the squarks, the sleptons of definite mass are expected to be non-diagonal linear combinations of the superpartners of the leptons. This leads to the decay process → e + through diagrams like Figure 28.3. The experimental upper bound 4.9 × 10–11 on the branching ratio of this process then sets a limit of about 10–3 on the fractional mass splitting of sleptons of the same charge but different generations for generic mixing angles, or on the mixing angles for non-degenerate sleptons.14

Attempts have been made to explain the degeneracy of the squarks and sleptons in terms of a gauge symmetry connecting the different generations.14a In Section 28.6 we will describe an approach to supersymmetry breaking in which this degeneracy appears without needing to impose such symmetries.

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