J. L. Diaz-Cruz

Lepton Flavour Violating Heavy Higgs Decays Within the nuMSSM and Their Detection at the LHC

Abstract Within the ν MSSM , a Minimal Supersymmetric neutrino See-saw Model, Lepton Flavour Violating Higgs couplings are strongly enhanced at large tan β (≳30), which can lead to BR ( H 0 / A 0 → τ μ ) ≃ O ( 10 − 4 ) , for M H 0 / A 0 ≳ 160 GeV . Enhancements on the production of Higgs bosons, through the gluon fusion mechanism, g g → H 0 / A 0 , and the associated production channel g g , q q ¯ → b b ¯ H 0 / A 0 , whose rates grow with tan β , as well as the mass degeneracy that occurs between the H 0 and A 0 states in this regime, also contribute to further the possibilities to detect a heavy Higgs signal into τμ pairs. We show that the separation of τμ Higgs events from the background at the upcoming CERN Large Hadron Collider could be done for Higgs masses up to about 600 GeV for 300 fb−1 of luminosity, for large tan β values. However, even with as little as 10 fb−1 one can probe H 0 / A 0 masses up to 400 GeV or so, if tan β = 60 . Altogether, these processes then provide a new Higgs discovery mode as well as an independent test of flavour physics.

Yukawa textures and charged Higgs boson phenomenology in the type-III two-Higgs-doublet model

We discuss the implications of assuming a four-zero Yukawa texture for the properties of the charged Higgs boson within the context of the general two-Higgs-doublet model of type III. We begin by presenting a detailed analysis of the charged Higgs boson couplings with heavy quarks and the resulting pattern for its decays. The production of charged Higgs bosons is also sensitive to the modifications of its couplings, so that we also evaluate the resulting effects on the top decay t?bH+ as well as on “direct” cb? ?H++c.c. and “indirect” qq? ,gg?t? bH++c.c. production. A significant scope exists at the Large Hadron Collider for several H± production and decay channels combined to enable one to distinguish between such a model and alternative two-Higgs-doublet scenarios.

Mass matrix ansatz and lepton flavor violation in the two-Higgs doublet model-III

Predictive Higgs-fermion couplings can be obtained when a specific texture for the fermion mass matrices is included in the general two-Higgs doublet model. We derive the form of these couplings in the charged lepton sector using a Hermitian mass matrix Ansatz with four-texture zeros. The presence of unconstrained phases in the vertices phi-li-lj modifies the pattern of flavor-violating Higgs interactions. Bounds on the model parameters are obtained from present limits on rare lepton flavor violating processes, which could be extended further by the search for the decay tau -> mu mu mu and mu-e conversion at future experiments. The signal from Higgs boson decays phi -> tau mu could be searched at the large hadron collider (LHC), while e-mu transitions could produce a detectable signal at a future e mu-collider, through the reaction e mu -> h0 -> tau tau.

Testing flavor-changing neutral currents in the rare top quark decayst→cViVj

We discuss the Flavor-Changing Neutral Current (FCNC) decays of the top quark t -> c Vi Vj (Vi=gamma, Z, g) in the framework of the Standard Model (SM) and in a two-higgs doublet model (2HDM) with tree-level FCNC couplings. While in the SM the expected branching ratios are extremelly small, in the 2HDM they may be sizable, of order 10^(-5) - 10^(-5), and thus accesible at the CERN LHC. We conclude with the interesting observation that the FCNC decay modes may not be equally suppressed as their corresponding decays t ->c Vi in this 2HDM.

An effective Lagrangian description of charged Higgs decays H+→W+γ, W+Z and W+h0

Abstract Charged Higgs decays are discussed within an effective Lagrangian extension of the two-Higgs doublet model, assuming new physics appearing in the Higgs sector of this model. Low-energy constraints are used to imposse bounds on certain dimension-six operators that describe the modified charged Higgs interactions. These bounds are used then to study the decays H + → W + γ , W + Z and W + h 0 , which can have branching ratios (BR) of order 10 −5 , 10 −1 and O (1), respectively; these modes are thus sensitive probes of the symmetries of the Higgs sector that could be tested at future colliders.

Has a Higgs-flavon with a 750 GeV mass been detected at the LHC13?

Abstract Higgs-flavon fields appear as a part of the Froggatt–Nielsen (FN) mechanism, which attempts to explain the hierarchy of Yukawa couplings. We explore the possibility that the 750 GeV diphoton resonance recently reported at the LHC13 could be identified with a low-scale Higgs-flavon field H F and find the region of the parameter space consistent with CMS and ATLAS data. It is found that the extra vector-like fermions of the ultraviolet completion of the FN mechanism are necessary in order to reproduce the observed signal. We consider a standard model (SM) extension that contains two Higgs doublets (a standard one and an inert one) and one complex FN singlet. The inert doublet includes a stable neutral boson, which provides a viable dark matter candidate, while the mixing of the standard doublet and the FN singlet induces flavor violation in the Higgs sector at the tree-level. Constraints on the parameters of the model are derived from the LHC Higgs data, which include the search for the lepton flavor violating decay of the SM Higgs boson h → μ ¯ τ . It is also found that in some region of the parameter space the model may give rise to a large branching ratio for the H F → h h decay, of the order of 0.1, which could be searched for at the LHC.

Exact formulae for Higgs production through eγ → eH in the non-linear Rξ--gauge

Abstract We study the production of the SM Higgs boson ( H 0 ) at future eγ colliders, through the reaction eγ → eH 0 . The amplitude is evaluated using the non-linear R ξ-gauge, which greatly simplifies the calculation. Complete analytical expressions for the amplitudes are presented, which include the contributions from 1-loop triangles γγ * H 0 and γZ * H 0 as well as the W - and Z -boxes with their related eeH 0 triangle graphs. The resulting cross section for this mechanism indicates that it could be used to detect the Higgs signal and to test its properties.

Anomalies, beta functions, and supersymmetric unification with multidimensional Higgs representations

In the framework of supersymmetric grand unified theories, the minimal Higgs sector is often extended by introducing multidimensional Higgs representations in order to obtain realistic models. However these constructions should remain anomaly-free, which significantly constrains their structure. We review the necessary conditions for the cancellation of anomalies in general and discuss in detail the different possibilities for supersymmetric SU(5) models. Alternative anomaly-free combinations of Higgs representations, beyond the usual vectorlike choice, are identified, and it is shown that their corresponding {beta} functions are not equivalent. Although the unification of gauge couplings is not affected, the introduction of multidimensional representations leads to different scenarios for the perturbative validity of the theory up to the Planck scale.

ELECTROWEAK–HIGGS UNIFICATION AND THE HIGGS BOSON MASS

We propose an alternative unification scenario where the Higgs self-coupling (λ) is determined by imposing its unification with the electroweak gauge couplings. An attractive feature of models within this scenario is the possibility to determine the Higgs boson mass by evolving λ from the electroweak–Higgs unification scale MGH down to the electroweak scale. The unification condition for the gauge (g1, g2) and Higgs couplings is written as g1 = g2 = f(λ), where being the normalization constant. Two variants for the unification condition are discussed; scenario I is defined through the linear relation: g1 = g2 = kHλ(MGH), while scenario II assumes a quadratic relation: . Fixing kH = O(1) and the standard normalization (kY = 5/3), we obtain a Higgs boson mass value mH ≃ 190 GeV, with similar results for other normalizations such as kY = 7/4 and 3/2. However, the unification scale MGH depends on the value of kY, going from 1.8 ×1012GeV up to 4.9 ×1014GeV for 7/4 > kY > 3/2. Possible tests of this idea at a future linear collider and its application for determining the Higgs spectrum in the two-Higgs doublet model are also discussed. We also elaborate on these unification scenarios within the context of a six-dimensional SU(3)c×SU(3)w Gauge–Higgs unified model, where the Higgs boson arises as the extra-dimensional components of the 6D gauge fields.

Tests of Higgs and top effective interactions

Abstract We study the possibility to detect heavy physics effects in the interactions of Higgs bosons and the top quark at future colliders using the effective Lagrangian approach, where the SM Lagrangian is modified by non-renormalizable operators that are invariant under the full strong and electroweak group. The modification of the interactions may enhance the production of Higgs bosons at hadron colliders through the mechanisms of gluon fusion and associated production with a W boson or t t pairs. The most promising signature is through the decay of the Higgs boson into two photons, whose branching ratio is also enhanced in this approach. As a consequence of our analysis we get a bound on the chromomagnetic dipole moment of the top quark.