Resonant production of Wh and Zh at the LHC Dobado, Antonio; Llanes-Estrada, Felipe J.; Sanz-Cillero, Juan J.
The journal of high energy physics,
03/2018, Volume:
2018, Issue:
3
Journal Article
Peer reviewed
Open access
A
bstract
We examine the production of
Wh
and
Zh
pairs at the LHC in the context of a Strongly Interacting Symmetry Breaking Sector of the Standard Model. Our description is based on a non-linear ...Higgs Effective Theory, including only the Standard Model particles. We focus on its scalar sector (Higgs boson
h
and electroweak Goldstones associated to
W
L
±
and
Z
L
), which is expected to give the strongest beyond Standard Model rescattering effects. The range of the effective theory is extended with dispersion-relation based unitarization, and compared to the alternative extension with explicit axial-vector resonances. We estimate the
Wh
and
Zh
production cross-section, where an intermediate axial-vector resonance is generated for certain values of the chiral couplings. We exemplify our analysis with a benchmark axial-vector with
M
A
= 3 TeV. Interestingly enough, these different approaches provide essentially the same prediction. Finally we discuss the sensitivity of ATLAS and CMS to such resonances.
A
bstract
We estimate production cross sections for 2-body resonances of the Electroweak Symmetry Breaking sector (in
W
L
W
L
and
Z
L
Z
L
rescattering) from
γγ
scattering. We employ unitarized Higgs ...Effective Field Theory amplitudes previously computed coupling the two photon channel to the EWSBS. We work in the Effective Photon Approximation and examine both
e
−
e
+
collisions at energies of order 1–2 TeV (as relevant for future lepton machines) and
pp
collisions at LHC energies. Dynamically generating a spin-0 resonance around 1.5 TeV (by appropriately choosing the parameters of the effective theory) we find that the differential cross section per unit
s
,
p
t
2
is of order 0.01 fbarn/TeV
4
at the LHC. Injecting a spin-2 resonance around 2 TeV we find an additional factor 100 suppression for
p
t
up to 200 GeV. The very small cross sections put these
γγ
processes, though very clean, out of reach of immediate future searches.
In this work we interpret the Einstein-Hilbert (EH) Lagrangian of gravitation as the first term of a low-energy effective theory similar to those considered in the chiral Lagrangian approach to ...low-energy hadron physics or the electroweak chiral Lagragians describing the symmetry breaking sector of the Standard Model (SM). Starting from the one-loop computation of the elastic gravitongraviton scattering amplitude by Dunbar and Norridge, we unitarize the IR regularized partial waves by using the Inverse Amplitude Method (IAM). This method enlarges the regime of applicability of the perturbative results to higher energies of the order of the Plank scale
M
P
and allows for the possibility of poles in the second Riemann which have the natural interpretation of dynamical resonances. In this work we look for these possible resonances for the +++ and −−−− helicity channels and the
J
= 0, 2 and 4 partial waves.
Abstract We define and calculate helicity partial-wave amplitudes for processes linking the Electroweak Symmetry Breaking Sector (EWSBS) to $$\gamma \gamma $$ γ γ , employing (to NLO) the Higgs-EFT ...(HEFT) extension of the Standard Model and the Equivalence Theorem, while neglecting all particle masses. The resulting amplitudes can be useful in the energy regime ( $$500~\mathrm{{GeV}}{-}3~\mathrm{{TeV}}$$ 500 GeV - 3 TeV ). We also deal with their unitarization so that resonances of the EWSBS can simultaneously be described in the $$\gamma \gamma $$ γ γ initial or final states. Our resulting amplitudes satisfy unitarity, perturbatively in $$\alpha $$ α , but for all s values. In this way we improve on the HEFT that fails as interactions become stronger with growing s and we provide a natural framework for the decay of dynamically generated resonances into WW, ZZ and $$\gamma \gamma $$ γ γ pairs.
Abstract By considering a non-linear electroweak chiral Lagrangian, including the Higgs, coupled to heavy quarks, and the equivalence theorem, we compute the one-loop scattering amplitudes ...$$W^+W^-\rightarrow t\bar{t}$$ W + W - → t t ¯ , $$ZZ\rightarrow t\bar{t}$$ Z Z → t t ¯ and $$hh\rightarrow t\bar{t}$$ h h → t t ¯ (in the regime $$M_t^2/v^2\ll \sqrt{s}M_t/v^2\ll s/v^2$$ M t 2 / v 2 ≪ s M t / v 2 ≪ s / v 2 and to NLO in the effective theory). We calculate the scalar partial-wave helicity amplitudes which allow us to check unitarity at the perturbative level in both $$M_t/v$$ M t / v and s/v. As with growing energy perturbative unitarity deteriorates, we also introduce a new unitarization method with the right analytical behavior on the complex s-plane and that can support poles on the second Riemann sheet to describe resonances in terms of the Lagrangian couplings. Thus we have achieved a consistent phenomenological description of any resonant $$t\bar{t}$$ t t ¯ production that may be enhanced by a possible strongly interacting electroweak symmetry breaking sector.
This article presents a number of technical tools and results that may be instrumental to discern the nature of the Higgs particle. In scenarios where an additional strongly interacting sector is ...present in the electroweak theory, resulting in a composite Higgs and longitudinal components of the massive gauge bosons, unitarity, analyticity and related techniques will be crucial to understand the properties of such a sector. The situation today may be reminiscent of the pre-QCD days: a strongly interacting theory governs the short-distances, but we have access only to long-distance experiment involving Nambu–Goldstone or pseudo Nambu–Goldstone bosons. Like in those days we can only rely on symmetry and general properties of field theory. Luckily, unlike in the pre-QCD days, we have now a much clearer idea of what we may be seeking.
After presenting a classification of the various types of effective theories, we establish the criteria as to under which conditions different representations are possible and their equivalence. We discuss in detail the implications of analyticity, causality and unitarity; describe various unitarization methods and establish the properties of dynamically generated resonances and form factors. The relation to effective Lagrangians with explicit resonances is explained in the context of beyond the Standard Model (BSM) physics and the Higgs effective field theory (HEFT). We discuss how various BSM models may be reduced to the HEFT as well as implications from holography and lattice studies in establishing BSM phenomenology. The methods presented are then applied to various processes relevant to disentangle the existence and nature of an extended electroweak symmetry breaking sector visible in VV fusion: two-Higgs production, vector resonances, γγ physics and top–antitop production.
A
bstract
By including the recently discovered Higgs-like scalar
φ
in the Electroweak Chiral Lagrangian, and using the Equivalence Theorem, we carry out the complete one-loop computation of the ...elastic scattering amplitude for the longitudinal components of the gauge bosons
V
=
W
,
Z
at high energy. We also compute
φφ
→
φφ
and the inelastic process
VV
→
φφ
, and identify the counterterms needed to cancel the divergences, namely the well known
a
4
and
a
5
chiral parameters plus three additional ones only superficially treated in the literature because of their dimension 8. Finally we compute all the partial waves and discuss the limitations of the one-loop computation due to only approximate unitarity.
We define and calculate helicity partial-wave amplitudes for processes linking the Electroweak Symmetry Breaking Sector (EWSBS) to
γ
γ
, employing (to NLO) the Higgs-EFT (HEFT) extension of the ...Standard Model and the Equivalence Theorem, while neglecting all particle masses. The resulting amplitudes can be useful in the energy regime (
500
GeV
-
3
TeV
). We also deal with their unitarization so that resonances of the EWSBS can simultaneously be described in the
γ
γ
initial or final states. Our resulting amplitudes satisfy unitarity, perturbatively in
α
, but for all
s
values. In this way we improve on the HEFT that fails as interactions become stronger with growing
s
and we provide a natural framework for the decay of dynamically generated resonances into
WW
,
ZZ
and
γ
γ
pairs.
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