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Width effects of broad new resonances in loop observables and application to (g−2)μ


Crivellin, Andreas; Hoferichter, Martin (2023). Width effects of broad new resonances in loop observables and application to (g−2)μ. Physical review D, 108(1):013005.

Abstract

In the phenomenology of strong interactions most physical states acquire a substantial width, and thus can only be defined in a model-independent way by pole positions and residues of the S-matrix. This information is incorporated in the Källén-Lehmann representation, whose spectral function characterizes the shape of the resonance and can be constrained by the dominant decay channels. Here, we argue that similar effects become important whenever beyond-the-Standard-Model particles possess a sizable decay width—as possible for instance in cases with a large branching fraction to a dark sector or strongly coupled scenarios—and show how their widths can be incorporated in the calculation of loop observables. As an application, we consider the anomalous magnetic moment of the muon, including both the direct effect of new physics and the possible indirect impact of a broad light Z′ on e+e−→hadrons cross sections. Throughout, we provide results for a general spectral function and its reconstruction from the one-loop imaginary part, where the latter captures the leading two-loop effects.

Abstract

In the phenomenology of strong interactions most physical states acquire a substantial width, and thus can only be defined in a model-independent way by pole positions and residues of the S-matrix. This information is incorporated in the Källén-Lehmann representation, whose spectral function characterizes the shape of the resonance and can be constrained by the dominant decay channels. Here, we argue that similar effects become important whenever beyond-the-Standard-Model particles possess a sizable decay width—as possible for instance in cases with a large branching fraction to a dark sector or strongly coupled scenarios—and show how their widths can be incorporated in the calculation of loop observables. As an application, we consider the anomalous magnetic moment of the muon, including both the direct effect of new physics and the possible indirect impact of a broad light Z′ on e+e−→hadrons cross sections. Throughout, we provide results for a general spectral function and its reconstruction from the one-loop imaginary part, where the latter captures the leading two-loop effects.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Physics Institute
Dewey Decimal Classification:530 Physics
Scopus Subject Areas:Physical Sciences > Nuclear and High Energy Physics
Language:English
Date:17 July 2023
Deposited On:29 Dec 2023 10:13
Last Modified:28 Jun 2024 03:31
Publisher:American Physical Society
ISSN:2470-0010
OA Status:Hybrid
Publisher DOI:https://doi.org/10.1103/physrevd.108.013005
Project Information:
  • : FunderAspen Center for Physics
  • : Grant ID
  • : Project Title
  • Content: Published Version
  • Language: English
  • Licence: Creative Commons: Attribution 4.0 International (CC BY 4.0)