Top Partners Research Articles

Constraining fine tuning in composite Higgs models with partially composite leptons

Minimal Composite Higgs Models (MCHM) have long provided a solution to the hierarchy problem of the Standard Model, yet suffer from various sources of fine tuning that are becoming increasingly problematic with the lack of new physics observations at the LHC. We develop a new fine tuning measure that accurately counts each contribution to fine tuning (single, double, triple, etc) that can occur in a theory with np parameters, that must reproduce no observables. We then use a novel scanning procedure to perform a comprehensive study of three different two-site, 4D, SO(5) → SO(4) MCHMs with all third generation fermions included, distinguished by the choice of the lepton embeddings. These are the MCHM5 − 5 − 55 − 5 − 5, MCHM14 − 14 − 105 − 5 − 5 and MCHM14 − 1 − 105 − 5 − 5, where MCHMl − τ − νq − t − b has the lepton doublet partner in representation l, tau partner in representation τ, and so on. We find that embedding at least one massive lepton in the symmetric 14 of SO(5) moderately reduces the tuning for the case of low top partner masses (in line with previous results), but that this is balanced against the increased complexity of the model when one properly accounts for all sources of fine tuning. We study both the current relative fine-tuning of each scenario, and the future prospects. Noting that the different scenarios behave differently with respect to future improvements in collider measurements, we find that the MCHM14 − 1 − 105 − 5 − 5 enjoys a relatively low increase in fine tuning even for a future lower bound on the top partner masses of 3.4 TeV (or equivalently a maximum Higgs-fermion or Higgs-gluon coupling deviation of 2%).

Production of extra quarks decaying to dark matter beyond the narrow width approximation at the LHC

This paper explores the effects of finite width in processes of pair production of an extra heavy quark with charge 2/3 (top partner) and its subsequent decay into a bosonic Dark Matter (DM) candidate -- either scalar or vector -- and SM up-type quarks at the Large Hadron Collider (LHC). This dynamics has been ignored so far in standard experimental searches of heavy quarks decaying to DM and we assess herein the regions of validity of current approaches, based on the assumption that the extra quarks have a narrow width. Further, we discuss the configurations of masses, widths and couplings where the latter breaks down.

Search for single production of vector-like top partners at the Large Hadron Electron Collider

The new vector-like top partners with charge 2/3 are a typical feature of many new physics models beyond the Standard Model (SM). We propose a search strategy for single production of top partners T focusing on both the T→Wb and T→th decay channels at the Large Hadron Electron Collider (LHeC). Our analysis is based on a simplified model in which the top partner is an SU(2) singlet, with couplings only to the third generation of SM quarks. We study the observability of the single T through the processes e+p→T(→bW+)ν¯e→bℓ++E̸Tmiss and e+p→T(→th)ν¯e→t(→jj′b)h(→bb¯)E̸Tmiss at the LHeC with the proposed 140 GeV electron beam (with 80% polarization) and 7 TeV proton beam. For three typical T-quark masses (800, 900 and 1000 GeV), the 3σ exclusion limits on the TWb coupling are respectively presented for various values of the integrated luminosity.

Search for top quark partners with charge 5/3 in proton-proton collisions at sqrt{s}=13 TeV

A search for the production of heavy partners of the top quark with charge 5/3 (X5/3) decaying into a top quark and a W boson is performed with a data sample corresponding to an integrated luminosity of 2.3 fb−1, collected in proton-proton collisions at a center-of-mass energy of 13 TeV with the CMS detector at the CERN LHC. Final states with either a pair of same-sign leptons or a single lepton, along with jets, are considered. No significant excess is observed in the data above the expected standard model background contribution and an X5/3 quark with right-handed (left-handed) couplings is excluded at 95% confidence level for masses below 1020 (990) GeV. These are the first limits based on a combination of the same-sign dilepton and the single-lepton final states, as well as the most stringent limits on the X5/3 mass to date.

Reappraisal of dark matter co-annihilating with a top or bottom partner

We revisit the calculation of relic density of dark matter particles co-annihilating with a top or bottom partner, by properly including the QCD bound-states (onia) effects of the colored partners, as well as the relevant electroweak processes which become important in the low mass region. We carefully set up the complete framework that incorporates the relevant contributions and investigate their effects on the cosmologically preferred mass spectrum, which turn out to be comparable in size to those coming from the Sommerfeld enhancement. We apply the calculation to three scenarios: bino-stop and bino-sbottom co-annihilations in supersymmetry, and a vector dark matter co-annihilating with a fermionic top partner. In addition, we confront our analysis of the relic abundance with recent direct detection experiments and collider searches at the LHC, which have important implications in the bino-stop and bino-sbottom scenarios. In particular, in the bino-stop case recent LHC limits have excluded regions of parameter with a direct detection rate that is above the neutrino floor.

Colorful Twisted Top Partners and Partnerium at the LHC

In scenarios that stabilize the electroweak scale, the top quark is typically accompanied by partner particles. In this work, we demonstrate how extended stabilizing symmetries can yield scalar or fermionic top partners that transform as ordinary color triplets but carry exotic electric charges. We refer to these scenarios as “hypertwisted” since they involve modifications to hypercharge in the top sector. As proofs of principle, we construct two hypertwisted scenarios: a supersymmetric construction with spin-0 top partners, and a composite Higgs construction with spin-1/2 top partners. In both cases, the top partners are still phenomenologically compatible with the mass range motivated by weak-scale naturalness. The phenomenology of hypertwisted scenarios is diverse, since the lifetimes and decay modes of the top partners are model dependent. The novel coupling structure opens up search channels that do not typically arise in top-partner scenarios, such as pair production of top-plus-jet resonances. Furthermore, hypertwisted top partners are typically sufficiently long lived to form “top-partnerium” bound states that decay predominantly via annihilation, motivating searches for rare narrow resonances with diboson decay modes.

Search for single production of a heavy vector-like T quark decaying to a Higgs boson and a top quark with a lepton and jets in the final state

A search for single production of vector-like top quark partners (T) decaying into a Higgs boson and a top quark is performed using data from pp collisions at a centre-of-mass energy of 13 TeV collected by the CMS experiment at the CERN LHC, corresponding to an integrated luminosity of 2.3 fb−1. The top quark decay includes an electron or a muon while the Higgs boson decays into a pair of b quarks. No significant excess over standard model backgrounds is observed. Exclusion limits on the product of the production cross section and the branching fraction are derived in the T quark mass range 700 to 1800 GeV. For a mass of 1000 GeV, values of the product of the production cross section and the branching fraction greater than 0.8 and 0.7 pb are excluded at 95% confidence level, assuming left- and right-handed coupling of the T quark to standard model particles, respectively. This is the first analysis setting exclusion limits on the cross section of singly produced vector-like T quarks at a centre-of-mass energy of 13 TeV.

Trump policies to change dynamics.

We propose the construction of the international trade network based on top trade relations (i.e., country i is linked to country j if j is i's top trade partner). The constructed network captures most important relations in international trade. The overall network displays a tree-like hierarchical structure. It is organized around global central countries (especially the US, China, and Germany) under which there are more levels of local centers. We develop a model that uses country behavior in local triadic environment to account for the formation of such network structure. The census of triads confirms the applicability of this model.

Eurasian Economic Union: a challenge for EU policy towards Kazakhstan

As a top trading partner and the foreign investor in Kazakhstan, attempting to deepen bilateral relations and review its previous policy towards Kazakhstan and the post-Soviet Central Asian region (The post-Soviet Central Asian region unites five former Soviet republics: Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan and Uzbekistan) as a whole, the European Union is facing up to a new set of internal and external conditions which affects its approach to the East. One of the crucial determinants taken into account in terms of the European Union policy towards its Kazakh partner derives from the more advanced processes of Eurasian integration created by the Russian Federation. The question is whether the EU will be able to compete or complement the consistent steps of the Russian integration project and whether the EU should move beyond a trade and investment approach and place emphasis on the other strategic areas? The main research objective concentrates on the identification and examination of the relationship between political decisions and the economic ties of Kazakhstan and its main strategic partners. Considering the current geopolitical situation in Ukraine and Central Asia, the new ‘EU-Kazakhstan Enhanced Partnership and Cooperation Agreement’ will develop more areas targeted at security and stabilization issues. However, the top-down initiatives are only the legal basis of sectorial cooperation, and the intensification of bilateral relations comes from bottom-up cooperation and people-to-people contacts.

Uzbekistan: Trade Regime and Recent Trade Developments

The trade regime currently in place in Uzbekistan supports the development of import-substituting industries and hinders the development of export-oriented industries. Consequently, primary commodities continue to dominate the country’s merchandise exports. The rapid expansion of merchandise exports in 2001-2010 was due mostly to the rise in world prices of primary commodities. The expansion of imports was to a large degree on account of increases in imports of intermediate and capital goods for import-substituting industries. Trade surpluses were achieved through high taxes on imports and rationing of foreign exchange. Significant shifts occurred in the geographic distribution of trade. The share of the EU in both exports and imports decreased, and Russia overtook the EU as Uzbekistan’s top trading partner. The share of China in both exports and imports increased considerably. The share of the Central Asian countries in exports fell significantly, while their share in imports rose modestly. Exports to Afghanistan surged, but imports from Afghanistan remained small. This suggests that there is a lot of scope for expanding economic cooperation between Uzbekistan and other Central Asian countries as well as between Uzbekistan and Afghanistan.

Search for electroweak production of a vector-like quark decaying to a top quark and a Higgs boson using boosted topologies in fully hadronic final states

A search is performed for electroweak production of a vector-like top quark partner T of charge 2/3 in association with a standard model top or bottom quark, using 2.3 fb−1 of proton-proton collision data at sqrt{s}=13 TeV collected by the CMS experiment at the CERN LHC. The search targets T quarks decaying to a top quark and a Higgs boson in fully hadronic final states. For a T quark with mass above 1 TeV the daughter top quark and Higgs boson are highly Lorentz-boosted and can each appear as a single hadronic jet. Jet substructure and b tagging techniques are used to identify the top quark and Higgs boson jets, and to suppress the standard model backgrounds. An excess of events is searched for in the T quark candidate mass distribution in the data, which is found to be consistent with the expected backgrounds. Upper limits at 95% confidence level are set on the product of the single T quark production cross sections and the branching fraction mathrm{mathcal{B}}left(mathrm{T}to mathrm{t}mathrm{H}right) , and these vary between 0.31 and 0.93 pb for T quark masses in the range 1000-1800 GeV. This is the first search for single electroweak production of a vector-like T quark in fully hadronic final states.

A flavor-safe composite explanation of RK

In these proceedings we discuss a flavor-safe explanation of the anomaly found in RK=B(B→Kμ+μ−)/B(B→Ke+e−) by LHCb, within the framework of composite Higgs models. We present a model featuring a non-negligible degree of compositeness for all three generations of right-handed leptons, which leads to a violation of lepton-flavor universality in neutral current interactions while other constraints from quark- and lepton-flavor physics are met. Moreoever, the particular embedding of the lepton sector considered in this setup provides a parametrically enhanded contribution to the Higgs mass that can weak considerably the need for ultra-light top partners.

Single production of the top partner in the T → tZ channel at the LHeC

In this paper, we study the possibility of detecting the heavy vector-like top partner T in a simplified model with the decay channel T→tZ at the Large Hadron Electron Collider (LHeC). We first investigate the single top partner production process including the intergenerational mixing and the results show that the mixing between the top partner with the first generation can largely enhance the production cross section. We further study the observability of the single top partner through the process e+p→T(→tZ)ν¯e→t(→bjj′)Z(→ℓ+ℓ−)ν¯e at the LHeC with the proposed 140 GeV electron beam and 7 TeV proton beam. For some typical heavy T quark masses, the 3σ exclusion limits as well as the 5σ discovery region are respectively presented in terms of parameter space regions.

Tadpole-induced electroweak symmetry breaking and pNGB Higgs models

We investigate induced electroweak symmetry breaking (EWSB) in models in which the Higgs is a pseudo-Nambu-Goldstone boson (pNGB). In pNGB Higgs models, Higgs properties and precision electroweak measurements imply a hierarchy between the EWSB and global symmetry-breaking scales, vH ≪ fH. When the pNGB potential is generated radiatively, this hierarchy requires fine-tuning to a degree of at least ∼ vh2/fH2. We show that if Higgs EWSB is induced by a tadpole arising from an auxiliary sector at scale fΣ ≪ vH, this tuning is significantly ameliorated or can even be removed. We present explicit examples both in Composite Higgs models based on SO(5)/SO(4) and in Twin Higgs models. For the Twin case, the result is a fully natural model with fH ∼ 1 TeV and the lightest colored top partners at 2 TeV. These models also have an appealing mechanism to generate the scales of the auxiliary sector and Higgs EWSB directly from the scale fH, with a natural hierarchy fΣ ≪ vH ≪ fH ∼ TeV. The framework predicts modified Higgs coupling as well as new Higgs and vector states at LHC13.

LHC vector resonance searches in the toverline{t}Z final state

LHC searches for BSM resonances in l+l−, jj, toverline{t} , γγ and VV final states have so far not resulted in discovery of new physics. Current results set lower limits on mass scales of new physics resonances well into the mathcal{O}(1) TeV range, assuming that the new resonance decays dominantly to a pair of Standard Model particles. While the SM pair searches are a vital probe of possible new physics, it is important to re-examine the scope of new physics scenarios probed with such final states. Scenarios where new resonances decay dominantly to final states other than SM pairs, even though well theoretically motivated, lie beyond the scope of SM pair searches. In this paper we argue that LHC searches for (vector) resonances beyond two particle final states would be useful complementary probes of new physics scenarios. As an example, we consider a class of composite Higgs models, and identify specific model parameter points where the color singlet, electrically neutral vector resonance ρ0 decays dominantly not to a pair of SM particles, but to a fermionic top partner Tf1 and a top quark, with Tf1 → tZ. We show that dominant decays of ρ0 → Tf1t in the context of Composite Higgs models are possible even when the decay channel to a pair of Tf1 is kinematically open. Our analysis deals with scenarios where both mρ and {m}_T{{}_{{}_f}}_{{}_1} are of mathcal{O}(1) TeV, leading to highly boosted toverline{t}Z final state topologies. We show that the particular composite Higgs scenario we consider is discoverable at the LHC13 with as little as 30 fb−1, while being allowed by other existing experimental constraints.

Search for single production of the heavy vectorlike T quark with T→th and h→γγ at the high-luminosity LHC

The vectorlike top partners $T$ are predicted in many extensions of the Standard Model (SM). In a simplified model including a single vectorlike $T$ quark with charge $2/3$, we investigate the process $pp \to Tj$ induced by the couplings between the top partner with the first and the third generation quarks at the LHC. We find that the mixing with the first generation can enhance the production cross section. We further study the observability of the single heavy top partner through the process $pp \to T(\to th)j\to t(\to b \ell \nu_{\ell})h( \to \gamma\gamma) j$ at the high-luminosity~(HL)-LHC~(a 14 TeV $pp$ collider with an integrated luminosity of 3 ab$^{-1}$). For three typical heavy $T$ quark masses $m_T=600,800$ and 1000 GeV, the $3\sigma$ exclusion limits, as well as the $5\sigma$ discovery reach in the parameter plane of the two variables $g^{\ast}-R_L$, are respectively obtained at the HL-LHC.

Female sociality and sexual conflict shape offspring survival in a Neotropical primate

Most mammals live in social groups in which members form differentiated social relationships. Individuals may vary in their degree of sociality, and this variation can be associated with differential fitness. In some species, for example, female sociality has a positive effect on infant survival. However, investigations of such cases are still rare, and no previous study has considered how male infanticide might constrain effects of female sociality on infant survival. Infanticide is part of the male reproductive strategy in many mammals, and it has the potential to override, or even reverse, effects of female reproductive strategies, including sociality. Therefore, we investigated the relationships between female sociality, offspring survival, and infanticide risk in wild white-faced capuchin monkeys using long-term data from Santa Rosa, Costa Rica. Female capuchins formed differentiated bonds, and bond strength was predicted by kin relationship, rank difference, and the presence of female infants. Most females formed stable bonds with their top social partners, although bond stability varied considerably. Offspring of highly social females, who were often high-ranking females, exhibited higher survivorship during stable periods compared with offspring of less social females. However, offspring of highly social females were more likely to die or disappear during periods of alpha male replacements, probably because new alpha males are central to the group, and therefore more likely to target the infants of highly social, central females. This study shows that female sociality in mammals can have negative fitness consequences that are imposed by male behavior.

Top Partner Production at e+e- Collider in the Littlest Higgs Model with T-Parity

In the framework of the littlest Higgs Model with T-parity, we discuss the top partner production at future e+e- collider. We calculate the cross sections of the top partner production processes and associated production processes of Higgs and top partner under current constraints. Then, we investigate the observability of the T-odd top partner pair production through the process e+e-→T-T¯-→tt¯AHAH in the tt¯ dilepton channel for two T-odd top partner masses mT-=603 (708) GeV at s=1.5 TeV. We analyze the signal significance depending on the integrated luminosity and find that this signal is promising at the future high energy e+e- collider.

The global Higgs as a signal for compositeness at the LHC

The radial excitation of the global symmetry-breaking vacuum in composite Higgs models, called the “global Higgs”, has been recently a focus of investigation. In this paper we study the prospects for detecting this composite scalar at the 13 TeV LHC. We compute the global Higgs production rates and estimate the discovery potential of a global Higgs decaying into top quark pairs and into Higgs and electroweak gauge bosons with subsequent hadronic decays. The global Higgs may also decay into fermion resonances such as top partners, providing a new window into compositeness. We show that top partner jets can be effectively unresolved in some regions of the parameter space. Such “boosted top partner” signatures would deserve the development of dedicated substructure analyses.

Di-boson signatures as standard candles for partial compositeness

Composite Higgs Models are often constructed including fermionic top partners with a mass around the TeV scale, with the top partners playing the role of stabilizing the Higgs potential and enforcing partial compositeness for the top quark. A class of models of this kind can be formulated in terms of fermionic strongly coupled gauge theories. A common feature they all share is the presence of specific additional scalar resonances, namely two neutral singlets and a colored octet, described by a simple effective Lagrangian. We study the phenomenology of these scalars, both in a model independent and model dependent way, including the bounds from all the available searches in the relevant channels with di-boson and di-top final states. We develop a generic framework which can be used to constrain any model containing pseudo-scalar singlets or octets. Using it, we find that such signatures provide strong bounds on the compositeness scale complementary to the traditional EWPT and Higgs couplings deviations. In many cases a relatively light scalar can be on the verge of discovery as a first sign of new physics.