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Perturbative unitarity bounds for effective composite models

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 Added by Orlando Panella
 Publication date 2019
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and research's language is English




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In this paper we present the partial wave unitarity bound in the parameter space of dimension-5 and dimension-6 effective operators that arise in a compositeness scenario. These are routinely used in experimental searches at the LHC to constraint contact and gauge interactions between ordinary Standard Model fermions and excited (composite) states of mass $M$. After deducing the unitarity bound for the production process of a composite neutrino, we implement such bound and compare it with the recent experimental exclusion curves for Run 2, the High-Luminosity and High-Energy configurations of the LHC. Our results also applies to the searches where a generic single excited state is produced via contact interactions. We find that the unitarity bound, so far overlooked, is quite complelling and significant portions of the parameter space ($M,Lambda$) become excluded in addition to the standard request $M le Lambda$.



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The perturbative unitarity bound is studied in the monojet process at LHC. The production of the dark matter is described by the low-energy effective theory. The analysis of the dark matter signal is not validated, if the unitarity condition is violated. It is shown that the current LHC analysis the effective theory breaks down, at least, when the dark matter is lighter than O(100) GeV. Future prospects for $sqrt{s}$ = 14 TeV are also discussed. The result is independent of physics in high energy scales.
105 - Yasuhiro Yamamoto 2014
We study the compatibility of the unitarity bound and the 8TeV LHC on the effective theory of the scalar dark matter. In several signals of effective interactions, mono-jet with missing energy events are studied. We found that, at least, if the dark matter mass is about 800GeV or heavier, contributions of events violating the unitarity are not negligible. The unitarity conditions in the 14TeV LHC are also calculated.
We study the perturbative unitarity bound given by dimension six derivative interactions consisting of Higgs doublets. These operators emerge from kinetic terms of composite Higgs models or integrating out heavy particles that interact with Higgs doublets. They lead to new phenomena beyond the Standard Model. One of characteristic contributions by derivative interactions appear in vector boson scattering processes. Longitudinal modes of massive vector bosons can be regarded as Nambu Goldstone bosons eaten by each vector field with the equivalence theorem. Since their effects become larger and larger as the collision energy of vector bosons increases, vector boson scattering processes become important in a high energy region around the TeV scale. On the other hand, in such a high energy region, we have to take the unitarity of amplitudes into account. We have obtained the unitarity condition in terms of the parameter included in the effective Lagrangian for one Higgs doublet models. Applying it to some of models, we have found that contributions of derivative interactions are not so large enough to clearly discriminate them from the Standard Model ones. We also study it in two Higgs doublet models. Because they are too complex to obtain the bound in the general effective Lagrangian, we have calculated it in explicit models. These analyses tell us highly model dependence of the perturbative unitarity bounds.
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