Z-peaked excess from heavy gluon decays to vector-like quarks

A 3 sigma excess has been recently announced by ATLAS in events with Z-peaked dilepton pairs, jets, and large transverse missing energy. We interpret this finding in the context of composite Higgs / RS theories. We find that composite Higgs theories with custodial symmetry protection to the $Zb\bar{b}$ coupling predict a significant contribution to $ZZbb$ (and to $hhbb$) final states coming from heavy gluon decays to pairs of bottom-partner vector-like quarks. The heavy gluon to vector-like quarks signal is largely accepted by the ATLAS selection if one of the $Z$ boson in the $ZZbb$ final state decays leptonically and the other to neutrinos. For a bottom partner of $\sim$900 GeV, we find that the ATLAS excess can be reproduced by composite Higgs models, in an experimentally allowed parameter space, for heavy gluon masses roughly in a range 1.87 - 2.15 TeV and for heavy gluon couplings to light quarks within $\sim(0.3-0.65) g_S$. We briefly discuss the implication of this result for future experimental tests.Comment: 23 pp. v2: minor changes, references adde

Early discovery of top partners and test of the Higgs nature

Top partners from a new strong sector can be discovered soon, at the 8 TeV LHC, by analyzing their single production, which exhibits a large enhancement in the cross section compared to the analogous productions of bottom partners and exotic quarks. We analyze the subsequent decay of the top partners into a 125 GeV Higgs. This channel proves to be very promising for both the discovery of top partners and a test of the Higgs sector. For a reference value $\lambda_{\tilde{T}}=3$ of the Higgs coupling to the top partner, we could have a discovery (observation) at the 8 TeV LHC, with 30 fb$^{-1}$, for top partner masses up to 760 (890) GeV. If the LHC and Tevatron excesses near 125 GeV are really due to a composite Higgs, naturalness arguments demand top partners below $\sim 1$ TeV. Our results highlight thus that the 8 TeV LHC already has a large sensitivity on probing the composite Higgs hypothesis. The LHC reach is even wider at $\sqrt{s}=14$ TeV. With $\lambda_{\tilde{T}}=3$ the LHC with 100 fb$^{-1}$ can observe (at 5$\sigma$) a Higgs from a top partner decay for masses of this latter up to $\simeq 1450$ GeV. In the case the top partner was as light as $\simeq 500$ GeV, the 14 TeV LHC would be sensitive to the measure of the $\lambda_{\tilde{T}}$ coupling in basically the full range $\lambda_{\tilde{T}}>1$ predicted by the theory.Comment: 9 pp. Minor changes. Version to appear in PRD. arXiv admin note: substantial text overlap with arXiv:1204.046

A New Strategy to Discover Heavy Colored Vectors at the Early LHC

We perform a study of the LHC discovery reach on a heavy gluon (G*) and heavy fermions (top and bottom excitations), coming from a new composite sector. We find that heavy fermion resonances have a great impact on the composite gluon phenomenology. If the composite gluon is heavier than composite fermions, as flavor observables seem to suggest, the search in the channel where G* decays into a heavy fermion plus its Standard Model partner is very promising, with the possibility for both the G* and heavy fermions to be discovered at the early stage of the LHC. The channel offers also the possibility to extract important information on model parameters, such as the top degree of compositeness.Comment: Presented at IFAE 2011, Incontri di Fisica delle Alte Energie, Perugia, Italy, 27-29 April. 4 pages, 3 figures. References adde

New W-prime signals at the LHC

We study the $W^{'}$ phenomenology in composite Higgs/ warped extra dimensional models focusing on the effect of fermionic resonances at $\sim$1 TeV. After deriving the existing bounds from the current LHC-8 analyses, we highlight the most promising signatures for $W^{'}$ discovery at the 14 TeV LHC. We find in particular very promising the study of $W^{'}$ decay modes into vector-like top partners, specifically the decay into a doublet of custodian heavy fermions, $T_{5/3} T_{2/3}$, and the decay into a heavy fermion plus a Standard Model quark. We perform a detailed parton level analysis of the channel $W^{'}\to T_{5/3} T_{2/3}$ in the same-sign dilepton final state, finding that it is a very promising signature to test the region at high $W^{'}$ mass, $m_{W^{'}}\gtrsim 2$ TeV, and of the $W^{'}\to Tb$ mode, that is one of the best channels to test the intermediate $W^{'}$ mass region and that, already with the LHC-8 data, could extend the present exclusion bounds.Comment: 25 pp. v2: minor changes, references added, version to appear in Phys. Rev.

Diphoton Resonances at the LHC

We review the current status of searches for new physics beyond the Standard Model in the diphoton channel at the LHC and estimate the reach with future collected data. We perform a model independent analysis based on an effective field theory approach and different production mechanisms. As an illustrative example, we apply our results to a scenario of minimal composite dynamics.Comment: 13 pages, 3 figures; invited review for MPLA; journal versio

Charged resonances and MDM bound states at a multi-TeV muon collider

A multi-TeV muon collider proves to be very efficient not only for the search for new heavy neutral particles, but also for the discovery of charged bosons of the $W^\prime$ type. We find that, by analyzing the associated production with a Standard Model W, charged resonances can be probed directly up to multi-TeV mass values close to the collision energy, and for very small couplings with the SM fermions, of the order of $10^{-3}-10^{-4}$ times the SM weak coupling. Additionally, charged bound states of WIMP Minimal Dark Matter, specifically a Majorana fermionic 5-plet, can be discovered with low statistics by running above the kinematic threshold, at a center-of-mass energy just slightly above the mass of the MDM bound state. This opens up a very interesting possibility for the discovery of WIMPs, complementary to the search for the resonant production of the neutral MDM bound state component, which relies on an on-peak search. For 5-plet MDM, indeed, the proposed search strategy is more efficient than the WIMP searches based on mono-X, missing-mass and disappearing tracks signatures.Comment: v2: several improvements and additions, ref.s added. 10 pages, 6 figures, 1 tabl

ΔF=1\Delta F=1 constraints on composite Higgs models with LR parity

We analyze the bounds on the spectrum of composite Higgs models (CHM) that come from flavor observables, by means of simple two-site effective Lagrangians, which incorporate a custodial symmetry and a Left-Right parity and which could also be adopted in further phenomenological studies on CHM. We derive, in particular, an important constraint on the masses of the $(t_L, b_L)$ partners, which does not depend on the flavor structure of the sector beyond the SM. This bound is obtained from the "infrared" contribution to $b \to s\gamma$ induced by the flavor-conserving effective vertex $Wt_Rb_R$. We find that the presence of a custodial symmetry can play a role in protecting this effective coupling and, as a consequence, in attenuating the constraint, which, however, remains of the order of 1 TeV. In addition to this bound, we calculate the constraints from the "ultraviolet" contribution to $b \to s \gamma$, induced by loops of heavy fermions, and to $\epsilon^{'}/\epsilon_K$.Comment: 35 pp. Version to appear in PR

Phenomenology of heavy fermion and vector resonances in composite Higgs models

In this project we study the phenomenology of models where the Higgs is a bound state of a strongly interacting dynamics at the TeV scale and we assess the LHC potential to discover new heavy colored states. In the first part of the thesis we analyze the bounds on the spectrum of Composite Higgs Models (CHM) that come from flavor observables. In the second part we propose a novel strategy to discover a heavy gluon ($G^*$) and heavy fermions at the LHC. We do so by means of simple two-site effective Lagrangians, which could also be used in further phenomenological studies on CHM. From the analysis of the bounds on the CHM spectrum, we derive an important constraint on the masses of the heavy fermions which does not depend on the flavor structure of the sector beyond the SM. This bound is obtained from the infrared contribution to $b \to s\gamma$ induced by the flavor-conserving effective vertex $Wt_Rb_R$. We find that the presence of a custodial symmetry can play a role in protecting this effective coupling. Studying the heavy colored vectors phenomenology, we find that heavy composite fermions have a great impact on the phenomenology of heavy composite gluon at the LHC. If the composite gluon is heavier than the composite fermions, as flavor observables seem to suggest, the search in the channels where $G^*$ decays into one heavy fermion plus its Standard Model partner is very promising, with the possibility for both the $G^*$ and heavy fermions to be discovered at the early stage of the LHC. These channels offer also the possibility to extract important information on model's parameters, such as the top degree of compositeness.Comment: Ph.D. Thesis (Advisor: Roberto Contino). Dec 2011. 110 pp. Graduation date added. References adde