99 research outputs found
Multiple Z' -> t-tbar signals in a 4D Composite Higgs Model
We study the production of top-antitop pairs at the Large Hadron Collider as
a testbed for discovering heavy Z' bosons belonging to a composite Higgs model,
as, in this scenario, such new gauge interaction states are sizeably coupled to
the third generation quarks of the Standard Model. We study their possible
appearance in cross section as well as (charge and spin) asymmetry
distributions. Our calculations are performed in the minimal four-dimensional
formulation of such a scenario, namely the 4-Dimensional Composite Higgs Model
(4DCHM), which embeds five new s. We pay particular attention to the case
of nearly degenerate resonances, highlighting the conditions under which these
are separable in the aforementioned observables. We also discuss the impact of
the intrinsic width of the new resonances onto the event rates and various
distributions. We confirm that the 14 TeV stage of the LHC will enable one to
detect two such states, assuming standard detector performance and machine
luminosity. A mapping of the discovery potential of the LHC of these new gauge
bosons is given. Finally, from the latter, several benchmarks are extracted
which are amenable to experimental investigation.Comment: 30 pages, 3 figures. Text and figures updated to match published
versio
Echoes of the electroweak phase transition: discovering a second Higgs doublet through A0 → ZH0
The existence of a second Higgs doublet in nature could lead to a cosmological first-order electroweak
phase transition and explain the origin of the matter-antimatter asymmetry in the Universe. We obtain the
spectrum and properties of the new scalars H0, A0, and H� that signal such a phase transition and show that
the observation of the decay A0 → ZH0 at LHC would be a “smoking gun” signature of these scenarios. We
analyze the LHC search prospects for this decay in the llbb¯ and llWþW− final states, arguing that current
data may be sensitive to this signature in the former channel as well as there being great potential for a
discovery in either channel at the very early stages of the 14 TeV run
as a discovery tool for bosons at the LHC
The Forward-Backward Asymmetry (AFB) in physics is commonly only
perceived as the observable which possibly allows one to interpret a
signal by distinguishing different models of such (heavy) spin-1 bosons. In
this article, we examine the potential of AFB in setting bounds on or even
discovering a at the Large Hadron Collider (LHC) and show that it
might be a powerful tool for this purpose. We analyze two different scenarios:
s with a narrow and wide width, respectively. We find that in both
cases AFB can complement the cross section in accessing signals.Comment: arXiv admin note: substantial text overlap with arXiv:1503.0267
Non-exotic signals in , and final states at the LHC
In the attempt to fully profile a boson accessible at the Large Hadron
Collider (LHC), we study the sensitivity of di-lepton (for the electron, muon
and tauon cases) and di-quark (for the case of the heavy flavours, and,
possibly, ) samples to the nature of the new gauge state, for a
one-dimensional class of non-exotic bosons. Assuming realistic final state
reconstruction efficiencies and error estimates, we find that, depending on the
CERN collider energy and luminosity, the best chances of extracting the
quantum numbers occur when two or more of these channels are simultaneously
explored, as none of them separately enables one to fully probe the parameter
spaces of the aforementioned models. Effects of Standard Model (SM) background
as well interferences between this and the various signals have been
accounted for. A complete study of cross sections and asymmetries (both spatial
and spin ones) makes clear the need for complementarity, especially for their
disentanglement over the full parameter space.Comment: 23 pages, 10 figures. Main revision of scopes; added section 2.4.3 to
describe strategy to fit couplings and table 3 to compare significances.
Updated/added references. Results unchange
Positivity and the electroweak hierarchy
We point out that an unnatural hierarchy between certain higher-dimensional operator coefficients in a low-energy effective field theory (EFT) would automatically imply that the Higgs' vacuum expectation value is hierarchically smaller than the EFT cutoff, assuming the EFT emerged from a unitary, causal and local UV completion. Future colliders may have the sensitivity to infer such a pattern of coefficients for a little hierarchy with an EFT cutoff up to O(10) TeV
Hierarchical versus degenerate 2HDM: the LHC run 1 legacy at the onset of run 2
Current discussions of the allowed two-Higgs-doublet model parameter space after LHC run 1 and the prospects for run 2 are commonly phrased in the context of a quasidegenerate spectrum for the new scalars. Here, we discuss the generic situation of a two-Higgs-doublet model with a nondegenerate spectrum for the new scalars. This is highly motivated from a cosmological perspective since it naturally leads to a strongly first-order electroweak phase transition that could explain the matter-antimatter asymmetry in the Universe. While constraints from measurements of Higgs signal strengths do not change, those from searches of new scalar states get modified dramatically once a nondegenerate spectrum is considered
Non-linear Higgs portal to Dark Matter
The Higgs portal to scalar Dark Matter is considered in the context of non-linearly realised electroweak symmetry breaking. We determine the dominant interactions of gauge bosons and the physical Higgs particle h to a scalar singlet Dark Matter candidate. Phenomenological consequences are also studied in detail, including the possibility of distinguishing this scenario from the standard Higgs portal in which the electroweak symmetry breaking is linearly realised. Two features of significant impact are: i) the connection between the electroweak scale v and the Higgs particle departs from the (v + h) functional dependence, as the Higgs field is not necessarily an exact electroweak doublet; ii) the presence of specific couplings that arise at different order in the non-linear and in the linear expansions. These facts deeply affect the Dark Matter relic abundance, as well as the expected signals in direct and indirect searches and collider phenomenology, where Dark Matter production rates are enhanced with respect to the standard portal
Truncation, validity, uncertainties
The truncation of the standard-model effective field theory, its validity andthe associated uncertainties have been discussed in meetings of the LHC EFT WG.Proposals were made by participants to address these issues. No consensus wasreached and no formal recommendation is therefore put forward at this time.None of the proposals has been approved or validated and further work is neededto establish a prescription. This note aims at summarizing the proposals andpoints of debate.<br
Truncation, validity, uncertainties
The truncation of the standard-model effective field theory, its validity andthe associated uncertainties have been discussed in meetings of the LHC EFT WG.Proposals were made by participants to address these issues. No consensus wasreached and no formal recommendation is therefore put forward at this time.None of the proposals has been approved or validated and further work is neededto establish a prescription. This note aims at summarizing the proposals andpoints of debate.<br
- …