Changes between Version 9 and Version 10 of dim6top

Timestamp:

Oct 14, 2019, 10:48:39 AM (5 years ago)

Author:

gdurieux

Comment:

--

dim6top

@@ -46 +46 @@
 - 2018-05-28: moved the definition of 'ctA' below that of 'sw' and 'cw' in parameters.py, to avoid "MadGraph5Error : Unable to evaluate mdl_ctA = (mdl_ctW-mdl_cw*mdl_ctZ)/mdl_sw: raise error: name 'mdl_cw' is not defined" (thanks to Marcel Vos)
 - 2018-05-21: corrected the Lorentz structure of Oledq operator from tensor to scalar (thanks to Ken Mimasu)
+
+==== Note on NLO QCD
+For NLO QCD simulation, the model authors recommend using the [wiki:SMEFTatNLO SMEFT@NLO] model which is mostly compatible with the baseline prescription of the LHC TOP WG. Few differences between the {{{dim6top}}} and [wiki:SMEFTatNLO SMEFT@NLO] (August 2019 version) models are to be noted:
+- [wiki:SMEFTatNLO SMEFT@NLO] includes Higgs and electroweak operators but does not include top-quark FCNCs.
+- [wiki:SMEFTatNLO SMEFT@NLO] is moreover restricted to CP-conserving operator coefficients.
+- [wiki:SMEFTatNLO SMEFT@NLO] imposes an enhanced U(2)q×U(2)u×U(3)d flavour symmetry in the quark sector, such that the right-handed bottom quark is treated on the same footing as other light down-type quarks. This is required for consistency with the five-flavour scheme at NLO QCD, where {{{MB=0}}}.
+- [wiki:SMEFTatNLO SMEFT@NLO] normalizes the top dipole operator (with coefficient {{{ctG}}}) with a factor of the strong coupling constant {{{G}}} for compatibility with MG 2.x series at NLO in QCD. The 3.x series does not requires it. This implies that {{{ctG_dim6top = G * ctG_SMEFTatNLO}}}. Note that {{{G}}} runs.
+
+Altogether, due to the enhanced quark flavour symmetry and to CP-conservation, [SMEFTatNLO] only includes a subset of 45 top-quark operator coefficients:
+cQQ1, cQQ8, cQd1, cQd8, cQe1, cQe2, cQe3, cQl31, cQl32, cQl33, cQlM1, cQlM2, cQlM3, cQq11, cQq13, cQq81, cQq83, cQt1, cQt8, cQu1, cQu8, cblS3, cdp, cpQ3, cpQM, cpt, ctG, ctW, ctZ, ctd1, ctd8, cte1, cte2, cte3, ctl1, ctl2, ctl3, ctlS3, ctlT3, ctp, ctq1, ctq8, ctt1, ctu1, ctu8
+and equates cQb1=cQd1, cQb8=cQd8, ctb1=ctd1, ctb8=ctd8.
+
+A high-precision comparison with {{{dim6top}}} has been performed at leading order following the prescription of [https://arxiv.org/abs/1906.12310 1906.12310], with the [https://bazaar.launchpad.net/~rwgtdim6/mg5amcnlo/plugin_eft_contrib/revision/ plugin_eft_contrib] of MG.
+
+The [wiki:SMEFTatNLO SMEFT@NLO] version dated from August 2019 does not include an implementation of four-fermion operators at NLO in QCD. Its validation is ongoing.