Adrian Carmona

Neutrino masses from an A4 symmetry in holographic composite Higgs models

We show that holographic composite Higgs Models with a discrete A4 symmetry can be built, which naturally predict hierarchical charged lepton masses and an approximate tri-bimaximal lepton mixing with the correct scale of neutrino masses and a characteristic phenomenology. They also satisfy current constraints from electroweak precision tests, lepton flavor violation and lepton mixing in a large region of parameter space. Two features arise in our model phenomenologically relevant. First, an extra suppression on the lepton Yukawa couplings makes the τ lepton more composite than naively expected from its mass. As a consequence new light leptonic resonances, with masses as low as few hundreds of GeV, large couplings to τ and a very characteristic collider phenomenology, are quite likely. Second, the discrete symmetry A4 together with the model structure provide a double-layer of flavor protection that allows to keep tree-level mediated processes below present experimental limits. One-loop processes violating lepton flavor, like μ → eγ, may be however observable at future experiments.

Stealth gluons at hadron colliders

Abstract We find that a heavy gluon G of mass 800–900 GeV with small, mostly axial-vector couplings to the light quarks and relatively large vector and axial-vector couplings to the top quark can explain the t t ¯ forward–backward asymmetry observed at the Tevatron with no conflict with other top-quark or dijet data. The key ingredient is a complete treatment of energy-dependent width effects and a new decay mode G → q Q , where q is a standard quark and Q a vector-like quark of mass 400–600 GeV. We show that this new decay channel makes the heavy gluon invisible in the t t ¯ invariant mass distribution and discuss its implications at the Tevatron and the LHC.

Lepton Flavor and Nonuniversality from Minimal Composite Higgs Setups

We present a new class of models of lepton flavor in the composite Higgs framework. Following the concept of minimality, they lead to a rich phenomenology in good agreement with the current experimental picture. Because of a unification of the right-handed leptons, our scenario is very predictive and can naturally lead to a violation of lepton-flavor universality in neutral current interactions. We will show that, in particular, the anomaly in R_{K}=B(B→Kμ^{+}μ^{-})/B(B→Ke^{+}e^{-}), found by LHCb, can be addressed, while other constraints from quark- and lepton-flavor physics are met. In fact, the minimal structure of the setup allows for the implementation of a very powerful flavor protection, which avoids the appearance of new sources of flavor-changing neutral currents to very good approximation. Finally, the new lepton sector provides a parametrically enhanced correction to the Higgs mass, such that the need for ultralight top partners is weakened considerably, linking the mass of the latter with the size of the neutrino masses.

Single vectorlike quark production at the LHC

Abstract A gluon resonance G of mass below 1 TeV could be the origin of the t t ¯ forward–backward asymmetry observed at the Tevatron provided that new decay modes G → q Q ¯ , with q a standard quark and Q its massive excitation, make G broad enough. We consider all the different cases, with q the top, the bottom or a light quark and dominant decay modes Q → W q ′ or Q → Z q . We show that current experimental searches are unable to probe the model, but that minimal departures from these analyses can explore a large region of its parameter space for the current LHC luminosity. This includes the challenging case with the new quarks decaying mostly into light quark flavors. In some channels not only the heavy quark but also the massive gluon can be reconstructed, which would stablish the origin of the t t ¯ asymmetry. Similar analyses can be applied to more general models with new massive gluons and vectorlike quarks.

Phenomenology of non-custodial warped models

We study the effect of bulk fermions on electroweak precision observables in a recently proposed model with warped extra dimensions and no custodial symmetry. We find that the top-quark mass, together with the corrections to the

Physical constraints on a class of two-Higgs doublet models with FCNC at tree level

Z{b_L}{\bar{b}_L}

A naturally light Higgs without light top partners

vertex and the one-loop contribution to the T parameter, which is finite, impose important constraints that single out a well defined region of parameter space. New massive vector bosons can be as light as ~ 1.5TeV and have large couplings to the tR quark, and suppressed couplings to the tL, bL and lighter quarks. We discuss the implications for searches of models with warped extra dimensions at the LHC.

Diboson resonant production in non-custodial composite Higgs models

A bstractWe analyse the constraints and some of the phenomenological implications of a class of two Higgs doublet models where there are flavour-changing neutral currents (FCNC) at tree level but the potentially dangerous FCNC couplings are suppressed by small entries of the CKM matrix V. This class of models have the remarkable feature that, as a result of a discrete symmetry of the Lagrangian, the FCNC couplings are entirely fixed in the quark sector by V and the ratio v2/v1 of the vevs of the neutral Higgs. The discrete symmetry is extended to the leptonic sector, so that there are FCNC in the leptonic sector with their flavour structure fixed by the leptonic mixing matrix. We analyse a large number of processes, including decays mediated by charged Higgs at tree level, processes involving FCNC at tree level, as well as loop induced processes. We show that in this class of models one has new physical scalars beyond the standard Higgs boson, with masses reachable at the next round of experiments.

New Higgs Production Mechanism in Composite Higgs Models

A bstractWe demonstrate that the inclusion of a realistic lepton sector can relax significantly the upper bound on top partner masses in minimal composite Higgs models, induced by the lightness of the Higgs boson. To that extend, we present a comprehensive survey of the impact of different realizations of the fermion sectors on the Higgs potential, with a special emphasis on the role of the leptons. The non-negligible compositeness of the τR in a general class of models that address the flavor structure of the lepton sector and the smallness of the corresponding FCNCs, can have a significant effect on the potential. We find that, with the τR in the symmetric representation of SO(5), an increase in the maximally allowed mass of the lightest top partner of ≳ 1 TeV is possible for minimal quark setups like the MCHM5,10, without increasing the tuning. A light Higgs boson mH ∼ (100−200) GeV is a natural prediction of such models, which thus provide a new setup that can evade ultralight top partners without ad-hoc tuning in the Higgs mass. Moreover, we advocate a more minimal realization of the lepton sector than generally used in the literature, which still can avoid light partners due to its contributions to the Higgs mass in a different and very natural way, triggered by the seesaw mechanism. This allows to construct the most economical SO(5)/SO(4) composite Higgs models possible. Using both a transparent 4D approach, as well as presenting numerical results in the 5D holographic description, we demonstrate that, including leptons, minimality and naturalness do not imply light partners. Leptonic effects, not considered before, could hence be crucial for the viability of composite models.

Tau Custodian searches at the LHC

A bstractWe show that the recently reported excess in resonant diboson production can be explained in the context of non-custodial composite Higgs models. Dibosons are generated via the s-channel exchange of massive vector bosons present in these models. We discuss the compatibility of the signal excess with other diboson experimental searches. We also discuss the tension between diboson production and other experimental tests of the model that include electroweak precision data, dilepton, dijet and top pair production and show that there is a region of parameter space in which they are all compatible with the excess.