80 research outputs found
Top and Higgs: Recent Theory developments
I review recent theory developments in the computation of Higgs production in
association with top quarks, as well as the modelling of the corresponding
backgrounds. In addition to progress within the Standard model I discuss
higher-order corrections for the process in the presence of new
interactions.Comment: Talk given at the 10th International Workshop on Top Quark Physics
(TOP 2017), 17th-22nd September, Braga, Portugal, to appear in the
proceeding
Higgs production in association with a top-antitop pair in the Standard Model Effective Field Theory at NLO in QCD
We present the results of the computation of the next-to-leading order QCD
corrections to the production cross section of a Higgs boson in association
with a top-antitop pair at the LHC, including the three relevant dimension-six
operators () of the standard model
effective field theory. These operators also contribute to the production of
Higgs bosons in loop-induced processes at the LHC, such as inclusive Higgs,
and production, and modify the Higgs decay branching ratios for which
we also provide predictions. We perform a detailed study of the cross sections
and their uncertainties at the total as well as differential level and of the
structure of the effective field theory at NLO including renormalisation group
effects. Finally, we show how the combination of information coming from
measurements of these production processes will allow to constrain the three
operators at the current and future LHC runs. Our results lead to a significant
improvement of the accuracy and precision of the deviations expected from
higher-dimensional operators in the SM in both the top-quark and the
Higgs-boson sectors and provide a necessary ingredient for performing a global
EFT fit to the LHC data at NLO accuracy.Comment: typos in figures 7 & 12 correcte
Scalar production and decay to top quarks including interference effects at NLO in QCD in an EFT approach
Scalar and pseudo-scalar resonances decaying to top quarks are common
predictions in several scenarios beyond the standard model (SM) and are
extensively searched for by LHC experiments. Challenges on the experimental
side require optimising the strategy based on accurate predictions. Firstly,
QCD corrections are known to be large both for the SM QCD background and for
the pure signal scalar production. Secondly, leading order and approximate
next-to-leading order (NLO) calculations indicate that the interference between
signal and background is large and drastically changes the lineshape of the
signal, from a simple peak to a peak-dip structure. Therefore, a robust
prediction of this interference at NLO accuracy in QCD is necessary to ensure
that higher-order corrections do not alter the lineshapes. We compute the exact
NLO corrections, assuming a point-like coupling between the scalar and the
gluons and consistently embedding the calculation in an effective field theory
within an automated framework, and present results for a representative set of
beyond the SM benchmarks. The results can be further matched to parton shower
simulation, providing more realistic predictions. We find that NLO corrections
are important and lead to a significant reduction of the uncertainties. We also
discuss how our computation can be used to improve the predictions for physics
scenarios where the gluon-scalar loop is resolved and the effective approach is
less applicable.Comment: 32 pages, 17 figures; accepted versio
Higgs pair production via gluon fusion in the Two-Higgs-Doublet Model
We study the production of Higgs boson pairs via gluon fusion at the LHC in
the Two-Higgs-Doublet Model. We present predictions at NLO accuracy in QCD,
matched to parton showers through the MC@NLO method. A dedicated reweighting
technique is used to improve the NLO calculation upon the infinite top-mass
limit. We perform our calculation within the MadGraph5_aMC@NLO framework, along
with the 2HDM implementation based on the NLOCT package. The inclusion of the
NLO corrections leads to large K-factors and significantly reduced theoretical
uncertainties. We examine the seven 2HDM Higgs pair combinations using a number
of representative 2HDM scenarios. We show how the model-specific features
modify the Higgs pair total rates and distribution shapes, leading to trademark
signatures of an extended Higgs sector.Comment: 39 pages, 10 figures, 11 tables, matching published versio
NLO QCD+EW predictions for and production at the LHC
In this work we calculate the cross sections for the hadroproduction of a
single top quark or antiquark in association with a Higgs () or boson
() at NLO QCD+EW accuracy. In the case of production we consider
both the case of the boson undecayed and the complete final state , including off-shell and non-resonant effects. We perform our
calculation in the five-flavour-scheme (5FS), without selecting any specific
production channel (-, - or associated). Moreover, we provide a more
realistic estimate of the theory uncertainty by carefully including the
differences between the four-flavour-scheme (4FS) and 5FS predictions. The
difficulties underlying this procedure in the presence of EW corrections are
discussed in detail. We find that NLO EW corrections are in general within the
NLO QCD theory uncertainties only if the flavour scheme uncertainty (4FS
vs.~5FS) is taken into account. For the case of production
we also investigate differences between NLO QCD+EW predictions and NLO QCD
predictions matched with a parton shower simulation including multiple photon
emissions.Comment: 29 pages, 10 figures, 3 table
Complete SMEFT predictions for four top quark production at hadron colliders
We study four top quark production at hadron colliders in the Standard Model
Effective Field Theory (SMEFT). We perform an analysis at the tree-level,
including all possible QCD- and EW-coupling orders and relevant dimension-six
operators. We find several cases where formally subleading terms give rise to
significant contributions, potentially providing sensitivity to a broad class
of operators. Inclusive and differential predictions are presented for the LHC
and a future circular collider operating at TeV. We estimate the
sensitivity of different operators and perform a simplified chi-square fit to
set limits on SMEFT Wilson coefficients. In so doing, we assess the importance
of including subleading terms and differential information in constraining new
physics contributions. Finally, we compute the SMEFT predictions for the double
insertion of dimension-six operators and scrutinise the possible enhancements
to the sensitivity induced by a specific class of higher order terms in the EFT
series.Comment: 32 pages with tables and figures, v2: version accepted by JHE
Renormalisation group effects on SMEFT interpretations of LHC data
We explore the impact of Renormalisation Group (RG) effects in the Standard
Model Effective Field Theory (SMEFT) interpretations of LHC measurements. We
implement the RG running and mixing for the Wilson coefficients as obtained
from the one-loop anomalous dimension matrix in the SMEFT into a Monte Carlo
generator. This allows to consistently predict and combine in global fits
collider observables characterised by different scales. As a showcase, we
examine the impact of RG running in the strong coupling on the SMEFT
predictions for production cross sections and differential
distributions as well as on the bounds on the Wilson coefficients that can be
obtained from current LHC data.Comment: 25 pages, 9 figures; 2 appendice
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