318 research outputs found
Constraining the Higgs self couplings at colliders
We study the sensitivity to the shape of the Higgs potential of single,
double, and triple Higgs production at future colliders. Physics
beyond the Standard Model is parameterised through the inclusion of
higher-dimensional operators
with , which allows a consistent treatment of independent deviations of
the cubic and quartic self couplings beyond the tree level. We calculate the
effects induced by a modified potential up to one loop in single and double
Higgs production and at the tree level in triple Higgs production, for both
boson associated and boson fusion production mechanisms. We consider two
different scenarios. First, the dimension six operator provides the dominant
contribution (as expected, for instance, in a linear
effective-field-theory(EFT)); we find in this case that the corresponding
Wilson coefficient can be determined at accuracy by just
combining accurate measurements of single Higgs cross sections at 240-250 GeV and double Higgs production in boson fusion at higher
energies. Second, both operators of dimension six and eight can give effects of
similar order, i.e., independent quartic self coupling deviations are present.
Constraints on Wilson coefficients can be best tested by combining measurements
from single, double and triple Higgs production. Given that the sensitivity of
single Higgs production to the dimension eight operator is presently unknown,
we consider double and triple Higgs production and show that combining their
information colliders at higher energies will provide first coarse constraints
on the corresponding Wilson coefficient.Comment: minor changes, version accepted for publication in JHE
Associated production of a top-quark pair with vector bosons at NLO in QCD: impact on searches at the LHC
We study the production of a top-quark pair in association with one and two
vector bosons, and with , at the
LHC. We provide predictions at next-to-leading order in QCD for total cross
sections and top-quark charge asymmetries as well as for differential
distributions. A thorough discussion of the residual theoretical uncertainties
related to missing higher orders and to parton distribution functions is
presented. As an application, we calculate the total cross sections for this
class of processes (together with and
production) at hadron colliders for energies up to 100 TeV. In addition, by
matching the NLO calculation to a parton shower, we determine the contribution
of and to final state signatures (two-photon and
two-same-sign-, three- and four-lepton) relevant for analyses at
the Run II of the LHC.Comment: 44 pages, 23 figures. Version published on JHEP, typos in Table 5
have been correcte
On cascade decays of squarks at the LHC in NLO QCD
In this paper we present an analysis at NLO of the contribution from
squark-squark production to the experimental signature 2j + 2l + missing E_T
(+X) with opposite-sign same flavor leptons, taking into account decays and
experimental cuts. We consider the case in which one squark decays directly
into the lightest neutralino chi^0_1 and the other one into the second lightest
neutralino and subsequently into l^+l^-chi^0_1 via an intermediate slepton. On
one hand we study effects of the NLO corrections on invariant mass
distributions which can be used for future parameter determination. On the
other hand we analyze the impact on predictions for cut-and-count searches
using this experimental signature.Comment: 21 pages, 10 figure
Trilinear Higgs coupling determination via single-Higgs differential measurements at the LHC
We study one-loop effects induced by an anomalous Higgs trilinear coupling on
total and differential rates for the decay and some of the main
single-Higgs production channels at the LHC, namely, VBF, , and
. Our results are based on a public code that calculates these effects by
simply reweighting samples of Standard-Model-like events for a given production
channel. For and production, where differential effects are
particularly relevant, we include Standard Model electroweak corrections, which
have similar sizes but different kinematic dependences. Finally, we study the
sensitivity of future LHC runs to determine the trilinear coupling via
inclusive and differential measurements, considering also the case where the
Higgs couplings to vector bosons and the top quark is affected by new physics.
We find that the constraints on the couplings and the relevance of differential
distributions critically depend on the expected experimental and theoretical
uncertainties.Comment: 31 pages, 15 figures, 5 tables; Matches the journal versio
On the Impact of Lepton PDFs
In this paper we discuss the effect of the complete leading-order QED
corrections to the DGLAP equations in the perturbative evolution of parton
distribution functions (PDFs). This requires the extension of the purely QCD
DGLAP evolution, including a PDF for the photons and, consistently, also for
the charged leptons , and . We present the
implementation of the QED-corrected DGLAP evolution in the presence of photon
and lepton PDFs in the APFEL program and, by means of different assumptions for
the initial scale PDFs, we produce for the first time PDF sets containing
charged lepton distributions. We also present phenomenological studies that aim
to assess the impact of the presence of lepton PDFs in the proton for some
relevant SM (and BSM) processes at the LHC at 13 TeV and the FCC-hh at 100 TeV.
The impact of the photon PDF is also outlined for those processes.Comment: 32 pages, 19 figures, matches published version in JHE
Probing the Higgs self coupling via single Higgs production at the LHC
We propose a method to determine the trilinear Higgs self coupling that is
alternative to the direct measurement of Higgs pair production total cross
sections and differential distributions. The method relies on the effects that
electroweak loops featuring an anomalous trilinear coupling would imprint on
single Higgs production at the LHC. We first calculate these contributions to
all the phenomenologically relevant Higgs production (, VBF, ,
, ) and decay (, , ,
) modes at the LHC and then estimate the sensitivity to the
trilinear coupling via a one-parameter fit to the single Higgs measurements at
the LHC 8 TeV. We find that the bounds on the self coupling are already
competitive with those from Higgs pair production and will be further improved
in the current and next LHC runs.Comment: 34 pages, 13 figures, 5 tables; V2: New appendix A added on the
comparison with the Effective Field Theory approach; V3: Journal versio
Electroweak corrections to squark-antisquark production at the LHC
We present the calculation of the electroweak corrections for
squark-antisquark pair production at the LHC within the Minimal Supersymmetric
Standard Model. Taking into account all possible chirality and light-flavor
configurations, we evaluate the NLO EW corrections, which are of O(a_s^2 a), as
well as the subleading tree-level contributions of O(a_s a) and O(a^2).
Numerical results are presented for several scans in the SUSY parameter space
and relevant differential distributions are investigated. The impact of the
electroweak corrections is nonnegligible and strongly depends on the chirality
configuration of the produced squarks. Our analysis includes a discussion of
photon-gluon initiated processes with a focus on the impact of the
corresponding large PDF uncertainties.Comment: 33 pages, 12 figures; V2: Original results unchanged. Various minor
modifications. Matches version published in JHE
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