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Interference effects in BSM processes with a generalised narrow-width approximation.

Fuchs E, Thewes S, Weiglein G - Eur Phys J C Part Fields (2015)

Bottom Line: It is demonstrated that interference effects of this kind arising in BSM models can be very large, leading to drastic modifications of predictions based on the standard NWA.The generalised NWA, based on on-shell matrix elements or their approximations leading to simple weight factors, is shown to produce UV- and IR-finite results which are numerically close to the result of the full process at tree level and at one-loop order, where an agreement of better than [Formula: see text] is found for the considered process.The most accurate prediction for this process based on the generalised NWA, taking into account also corrections that are formally of higher orders, is briefly discussed.

View Article: PubMed Central - PubMed

Affiliation: DESY, Deutsches Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg, Germany.

ABSTRACT

A generalisation of the narrow-width approximation (NWA) is formulated which allows for a consistent treatment of interference effects between nearly mass-degenerate particles in the factorisation of a more complicated process into production and decay parts. It is demonstrated that interference effects of this kind arising in BSM models can be very large, leading to drastic modifications of predictions based on the standard NWA. The application of the generalised NWA is demonstrated both at tree level and at one-loop order for an example process where the neutral Higgs bosons h and H of the MSSM are produced in the decay of a heavy neutralino and subsequently decay into a fermion pair. The generalised NWA, based on on-shell matrix elements or their approximations leading to simple weight factors, is shown to produce UV- and IR-finite results which are numerically close to the result of the full process at tree level and at one-loop order, where an agreement of better than [Formula: see text] is found for the considered process. The most accurate prediction for this process based on the generalised NWA, taking into account also corrections that are formally of higher orders, is briefly discussed.

No MeSH data available.


Related in: MedlinePlus

2-body decay widths of a and c with  (blue) and H (green) at the tree level (dashed) or at the 1-loop level (solid), and the relative effect of the loop contributions (b), (d)
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Fig12: 2-body decay widths of a and c with (blue) and H (green) at the tree level (dashed) or at the 1-loop level (solid), and the relative effect of the loop contributions (b), (d)

Mentions: The triangle corrections appearing at the -vertex are renormalised by the counterterm129\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\begin{aligned} \delta C_{ijk}^{R/L}&=\frac{e}{2c_{W}s_{W}}\delta c^{(*)}_{ijk} + \left( \delta Z_e - \frac{\delta s_{W}}{s_{W}}- \frac{\delta c_{W}}{c_{W}}\right) C_{ijk}^{R/L}\nonumber \\&\quad +\, \frac{1}{2}\sum _{l=1}^{4}(\delta Z_{li}^{R/L}\,C_{ljk}^{R/L}+\delta \bar{Z}_{jl}^{L/R}\,C_{ilk}^{R/L} +\delta Z_{h_kh_l}C_{ijk}^{R/L}) \end{aligned}$$\end{document}δCijkR/L=e2cWsWδcijk(∗)+δZe-δsWsW-δcWcWCijkR/L+12∑l=14(δZliR/LCljkR/L+δZ¯jlL/RCilkR/L+δZhkhlCijkR/L)in the on-shell scheme, see Ref. [64] and references therein. In Eq. (129), for denote the neutral Higgs and Goldstone bosons. The parameters are related to the choice of the three electroweakinos which are renormalised on-shell and thus define the choice for the on-shell renormalisation scheme for the neutralino-chargino sector, as mentioned in Sect. 4.2. In our scenario, we identify as the most bino-like, as the most higgsino-like and as the most wino-like state and hence renormalise these three neutralinos on-shell. By this choice of an NNN scheme, we avoid large mass corrections to the remaining neutralino and the charginos. Alternatively, instead of could be identified as the most wino-like state because the two corresponding elements in the matrix N, which diagonalises the neutralino mass matrix (see Sect. 4.2), have nearly the same magnitude. Thus, this alternative choice would lead to a comparable sensitivity to the three parameters of this sector and thereby also to a stable renormalisation scheme. But since is involved in our process as an external particle, we prefer to set it on-shell. The 1-loop effect on the 2-body decay widths is shown in Fig. 12.


Interference effects in BSM processes with a generalised narrow-width approximation.

Fuchs E, Thewes S, Weiglein G - Eur Phys J C Part Fields (2015)

2-body decay widths of a and c with  (blue) and H (green) at the tree level (dashed) or at the 1-loop level (solid), and the relative effect of the loop contributions (b), (d)
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4464706&req=5

Fig12: 2-body decay widths of a and c with (blue) and H (green) at the tree level (dashed) or at the 1-loop level (solid), and the relative effect of the loop contributions (b), (d)
Mentions: The triangle corrections appearing at the -vertex are renormalised by the counterterm129\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\begin{aligned} \delta C_{ijk}^{R/L}&=\frac{e}{2c_{W}s_{W}}\delta c^{(*)}_{ijk} + \left( \delta Z_e - \frac{\delta s_{W}}{s_{W}}- \frac{\delta c_{W}}{c_{W}}\right) C_{ijk}^{R/L}\nonumber \\&\quad +\, \frac{1}{2}\sum _{l=1}^{4}(\delta Z_{li}^{R/L}\,C_{ljk}^{R/L}+\delta \bar{Z}_{jl}^{L/R}\,C_{ilk}^{R/L} +\delta Z_{h_kh_l}C_{ijk}^{R/L}) \end{aligned}$$\end{document}δCijkR/L=e2cWsWδcijk(∗)+δZe-δsWsW-δcWcWCijkR/L+12∑l=14(δZliR/LCljkR/L+δZ¯jlL/RCilkR/L+δZhkhlCijkR/L)in the on-shell scheme, see Ref. [64] and references therein. In Eq. (129), for denote the neutral Higgs and Goldstone bosons. The parameters are related to the choice of the three electroweakinos which are renormalised on-shell and thus define the choice for the on-shell renormalisation scheme for the neutralino-chargino sector, as mentioned in Sect. 4.2. In our scenario, we identify as the most bino-like, as the most higgsino-like and as the most wino-like state and hence renormalise these three neutralinos on-shell. By this choice of an NNN scheme, we avoid large mass corrections to the remaining neutralino and the charginos. Alternatively, instead of could be identified as the most wino-like state because the two corresponding elements in the matrix N, which diagonalises the neutralino mass matrix (see Sect. 4.2), have nearly the same magnitude. Thus, this alternative choice would lead to a comparable sensitivity to the three parameters of this sector and thereby also to a stable renormalisation scheme. But since is involved in our process as an external particle, we prefer to set it on-shell. The 1-loop effect on the 2-body decay widths is shown in Fig. 12.

Bottom Line: It is demonstrated that interference effects of this kind arising in BSM models can be very large, leading to drastic modifications of predictions based on the standard NWA.The generalised NWA, based on on-shell matrix elements or their approximations leading to simple weight factors, is shown to produce UV- and IR-finite results which are numerically close to the result of the full process at tree level and at one-loop order, where an agreement of better than [Formula: see text] is found for the considered process.The most accurate prediction for this process based on the generalised NWA, taking into account also corrections that are formally of higher orders, is briefly discussed.

View Article: PubMed Central - PubMed

Affiliation: DESY, Deutsches Elektronen-Synchrotron, Notkestr. 85, 22607 Hamburg, Germany.

ABSTRACT

A generalisation of the narrow-width approximation (NWA) is formulated which allows for a consistent treatment of interference effects between nearly mass-degenerate particles in the factorisation of a more complicated process into production and decay parts. It is demonstrated that interference effects of this kind arising in BSM models can be very large, leading to drastic modifications of predictions based on the standard NWA. The application of the generalised NWA is demonstrated both at tree level and at one-loop order for an example process where the neutral Higgs bosons h and H of the MSSM are produced in the decay of a heavy neutralino and subsequently decay into a fermion pair. The generalised NWA, based on on-shell matrix elements or their approximations leading to simple weight factors, is shown to produce UV- and IR-finite results which are numerically close to the result of the full process at tree level and at one-loop order, where an agreement of better than [Formula: see text] is found for the considered process. The most accurate prediction for this process based on the generalised NWA, taking into account also corrections that are formally of higher orders, is briefly discussed.

No MeSH data available.


Related in: MedlinePlus