arXiv subjects

A. E. Cárcamo Hernández

Publications and source records attributed to A. E. Cárcamo Hernández.

104 records · Page 6Linked to original sources

arXiv2015

Composite Resonances effects on EWPT and Higgs diphoton decay rate

In scenarios of strongly coupled electroweak symmetry breaking, heavy composite particles of different spin and parity may arise and cause observable effects on signals that appear at loop levels. The recently observed process of Higgs to $γγ$ at the LHC is one of such signals. We study the new constraints that are imposed on composite models from $H\to γγ$, together with the existing constraints from the high precision electroweak tests. We use an effective chiral Lagrangian to describe the effective theory that contains the Standard Model spectrum and the extra composites below the electroweak scale. Considering the effective theory cutoff at $Λ= 4πv \sim 3 $ TeV, consistency with the $T$ and $S$ parameters and the newly observed $H\to γγ$ can be found for a rather restricted range of masses of vector and axial-vector composites from $1.5$ TeV to $1.7$ TeV and $1.8$ TeV to $1.9$ TeV, respectively, and only provided a non-standard kinetic mixing between the $W^{3}$ and $B^{0}$ fields is included.

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arXiv2015

Higgs boson coupling to a new strongly interacting sector

In the framework of strongly interacting dynamics for electroweak symmetry breaking, heavy composite particles may arise and cause observable effects, as they should couple strongly to the resulting Higgs boson and affect the signals that appear at one loop level. Here we study this expected behavior, contrasting it with current experimental knowledge. We work in a simple and generic scenario where the lowest lying composite states are the Higgs scalar doublet and a massive vector triplet. We use an effective chiral Lagrangian to describe the theory below the compositeness scale $Λ$, assumed to be $4πv \simeq~3$ TeV. The effective theory contains the Standard Model spectrum and the extra composites. We determine the constraints on this scenario imposed by our current knowledge of the $Zb\bar{b}$ vertex, the $T$ and $S$ oblique parameters, and the recently measured Higgs mass and its diphoton decay rate. We found that the $T$ and $S$ parameters as well as the Higgs diphoton decay do not provide important constraints on the model. In contrast, the constraints arising from the $Zb\bar{b}$ vertex and from the Higgs mass at $126$ GeV are fulfilled only if the heavy vector resonances do not couple strongly with quarks, and at the same time the Higgs boson has a moderate but not too strong coupling to the heavy composite resonances.

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arXiv2015

Higgs $\rightarrow$ $μτ$ as an indication for $S_4$ flavor symmetry

Lepton flavor violating Higgs decays can arise in flavor symmetry models where the Higgs sector is responsible for both the electroweak and the flavor symmetry breaking. Here we advocate an $S_4$ three-Higgs-doublet model where tightly constrained flavor changing neutral currents are suppressed by a remnant $Z_3$ symmetry. A small breaking of this $Z_3$ symmetry can explain the $2.4\,σ$ excess of Higgs decay final states with a $μτ$ topology reported recently by CMS if the new neutral scalars are light. The model also predicts sizable rates for lepton flavor violating Higgs decays in the $eτ$ and $e μ$ channels because of the unifying $S_4$ flavor symmetry.

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arXiv2015

Precision measurements constraints on the number of Higgs doublets

We consider an extension of the Standard Model with an arbitrary number $N$ of Higgs doublets (NHDM), and calculate their contribution to the oblique parameters $S$ and $T$. We examine the possible limitations on $N$ from precision measurements of these parameters. In view of the complexity of the general case of NHDM, we analyze several benchmark scenarios for the Higgs mass spectrum, identifying the lightest CP-even Higgs with the Higgs-like particle recently observed at the LHC with the mass of $\sim 125$ GeV. The rest of the Higgses are put above the mass scale of $\sim 600$ GeV, below which the LHC experiments do not detect any Higgs-like signals except for the former famous one. We show that, in a scenario, with all the heavy Higgses degenerate at any scale, there are no limitations on the number $N$ of the Higgs doublets. However, upper limits appear for certain not completely degenerate configurations of the heavy Higgses.

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arXiv2015

Viable textures for the fermion sector

We consider a modification of the Fukuyama-Nishiura texture and compare it to the precision quark flavour data, finding that it fits the data very well but at the cost of accidental cancelations between parameters. We then propose different viable textures for quarks, where only the Cabibbo mixing arises from the down sector, and extend to the charged leptons while constructing a complementary neutrino structure that leads to viable lepton masses and mixing.

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arXiv2015

$S_3$ discrete group as a source of the quark mass and mixing pattern in $331$ models

We propose a model based on the $SU(3)_{C}\otimes SU(3)_{L}\otimes U(1)_{X}$ gauge symmetry with an extra $S_{3}\otimes Z_{2}\otimes Z_{4}\otimes Z_{12}$ discrete group, which successfully accounts for the SM quark mass and mixing pattern. The observed hierarchy of the SM quark masses and quark mixing matrix elements arises from the $Z_{4}$ and $Z_{12}$ symmetries, which are broken at very high scale by the $SU(3)_{L}$ scalar singlets ($σ$,$ζ$) and $τ$, charged under these symmetries, respectively. The Cabbibo mixing arises from the down type quark sector whereas the up quark sector generates the remaining quark mixing angles. The obtained magnitudes of the CKM matrix elements, the CP violating phase and the Jarlskog invariant are in agreement with the experimental data.

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arXiv2014

An SU(5) grand unified model with discrete flavour symmetries

We propose a model based on the $SU(5)$ grand unification with an extra $Z_{2}\otimes Z_{2}^{\prime}\otimes Z_{2}^{\prime \prime}\otimes Z_{4}\otimes Z_{12}$ flavor symmetry, which successfully describes the observed SM fermion mass and mixing pattern. The observed quark mass and mixing pattern is caused by the $Z_{4}$ and $Z_{12}$ symmetries, which are broken at very high scale by the $SU(5)$ scalar singlets $σ$ and $χ$, charged respectively under these symmetries and which acquire VEVs at the GUT scale. The light neutrino masses are generated via a type I seesaw mechanism with three heavy Majorana neutrinos. The model has in total 17 effective free parameters, from which 2 are fixed and 15 are fitted to reproduce the experimental values of the 18 physical parameters in the quark and lepton sectors. The model predictions for both quark and lepton sectors are in excellent agreement with the experimental data.

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arXiv2014

Lepton masses and mixing in $SU(3)_{C}\otimes SU(3)_{L}\otimes U(1)_{X}$ models with a $S_3$ flavor symmetry

We propose a model based on the gauge group $SU(3)_{C}\otimes SU(3)_{L}\otimes U(1)_{X}$ with an extra $S_{3}$ flavor symmetry, which accounts for the lepton masses and mixing. The small active neutrino masses are generated via a double seesaw mechanism. In this scenario, the spectrum of neutrinos presents very light, light and very heavy masses. The model predicts a quasidegenerate normal hierarchy active neutrino mass spectrum and the relation $Δm_{21}^{2}\ll Δm_{31}^{2}$ arises from effective six-dimensional operators. The obtained neutrino mixing parameters are in agreement with the neutrino oscillation experimental data. We find CP violation in neutrino oscillations with a Jarlskog invariant of about $10^{-2}$.

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arXiv2014

Fermion masses and mixings in an $SU(5)$ grand unified model with an extra flavor symmetry

We propose a model based on the $SU(5)$ grand unification with an extra $A_{4}\otimes Z_{2}\otimes Z_{2}^{\prime }\otimes Z_{2}^{\prime \prime}\otimes U\left( 1\right) _{f}$ flavor symmetry, which accounts for the pattern of the SM fermion masses and mixings. The observed hierarchy of charged fermion masses and quark mixing matrix elements arises from a generalized Froggatt-Nielsen mechanism triggered by a scalar $\mathbf{24}$ representation of $SU(5)$ charged under the global $U(1)_{f}$ and acquiring a VEV at the GUT scale. The light neutrino masses are generated via a radiative seesaw mechanism with a single heavy Majorana neutrino and neutral scalars running in the loops. The model predictions for both quark and lepton sectors are in good agreement with the experimental data. The model predicts an effective Majorana neutrino mass, relevant for neutrinoless double beta decay, with values $m_{ββ}=$ 4 and 50 meV for the normal and the inverted neutrino spectrum, respectively. The model also features a suppression of CP violation in neutrino oscillations, a low scale for the heavy Majorana neutrino (few TeV) and, due to the unbroken $Z_{2}$ symmetry, a natural dark matter candidate.

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arXiv2014

The Effect of Composite Resonances on Higgs decay into two photons

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arXiv2013

Lepton masses and mixings in a $A_{4}$ multi-Higgs model with radiative seesaw mechanism

We propose a renormalizable multi-Higgs model with $A_{4}\otimes Z_{2}\otimes Z^{\prime}_{2}$ symmetry, accounting for the experimental deviation from the tribimaximal mixing pattern of the neutrino mixing matrix. In this framework we study the charged lepton and neutrino masses and mixings. The light neutrino masses are generated via a radiative seesaw mechanism, which involves a single heavy Majorana neutrino and neutral scalars running in the loops. The obtained neutrino mixings and mass squared splittings are in good agreement with the neutrino oscillation experimental data for both normal and inverted hierarchy. The model predicts an effective Majorana neutrino mass $m_{ββ}=$ 4 meV and 50 meV for the normal and the inverted neutrino spectrum, respectively. The model also features a suppression of CP violation in neutrino oscillations, a low scale for the heavy Majorana neutrino (few TeV) and, due to the unbroken $Z_2$ symmetry, a natural dark matter candidate.

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arXiv2013

Radiative seesaw-type mechanism of quark masses in SU(3\)_{C}\otimes SU(3\)_{L}\otimes U$1$_{X}$

We take up again the study of the mass spectrum of the quark sector in a model with gauge symmetry $SU(3)_{c}\otimes SU(3)_{L}\otimes U(1)_{X}$ (331). In a special type II-like 331 model, we obtain specific zero-texture mass matrices for the quarks which predict four massless quarks ($u,c,d,s$) and two massive quarks ($b,t$) at the electroweak scale ($\sim $ GeV). By considering the mixing between the SM quarks and new exotic quarks at large scales predicted by the model, we find that a third quark (associated to the charm quark) acquires a mass. The remaining light quarks ($u,d,s$) get small masses ($\sim$ MeV) via radiative corrections.

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arXiv2012

Top quark effects in composite vector pair production at the LHC

In the context of a strongly coupled Electroweak Symmetry Breaking, composite light scalar singlet and composite triplet of heavy vectors may arise from an unspecified strong dynamics and the interactions among themselves and with the Standard Model gauge bosons and fermions can be described by a $SU(2)_L\times SU(2)_R/SU(2)_{L+R}$ Effective Chiral Lagrangian. In this framework, the production of the $V^{+}V^{-}$ and $V^{0}V^{0}$ final states at the LHC by gluon fusion mechanism is studied in the region of parameter space consistent with the unitarity constraints in the elastic channel of longitudinal gauge boson scattering and in the inelastic scattering of two longitudinal Standard Model gauge bosons into Standard Model fermions pairs. The expected rates of same-sign di-lepton and tri-lepton events from the decay of the $V^{0}V^{0}$ final state are computed and their corresponding backgrounds are estimated. It is of remarkable relevance that the $V^{0}V^{0}$ final state can only be produced at the LHC via gluon fusion mechanism since this state is absent in the Drell-Yan process. It is also found that the $V^{+}V^{-}$ final state production cross section via gluon fusion mechanism is comparable with the $V^{+}V^{-}$ Drell-Yan production cross section. The comparison of the $V^{0}V^{0}$ and $V^{+}V^{-}$ total cross sections will be crucial for distinguishing the different models since the vector pair production is sensitive to many couplings. This will also be useful to determine if the heavy vectors are only composite vectors or are gauge vectors of a spontaneously broken gauge symmetry.

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arXiv2011

Composite Vectors and Scalars in Theories of Electroweak Symmetry Breaking

In the context of a strongly coupled Electroweak Symmetry Breaking, composite triplet of heavy vectors belonging to the $SU(2)_{L+R}$ adjoint representation and a composite scalar singlet under $SU(2)_{L+R}$ may arise from a new strong interaction invariant under the global $SU(2)_L\times SU(2)_R$ symmetry, which is spontaneously broken down to $SU(2)_{L+R}$. This thesis consists of two parts. The first part is devoted to the study of the heavy composite vector pair production at the LHC via Vector Boson Fusion and Drell-Yan annihilation under the assumption that the interactions among these heavy vector states and with the Standard Model gauge bosons are described by a $SU(2)_L\times SU(2)_R/SU(2)_{L+R}$ Effective Chiral Lagrangian. The expected rates of multi-lepton events from the decay of the composite vectors are also given. The second part studies the associated production at the LHC of a composite vector with a composite scalar by Vector Boson Fusion and Drell-Yan annihilation in the framework of a $SU(2)_{L}\times SU(2)_{R}/SU(2)_{L+R}$ Effective Chiral Lagrangian with massive spin one fields and one singlet light scalar. The expected rates of same sign di-lepton and tri-lepton events from the decay of the composite vector and composite scalar final state are computed. The connection of the Effective Chiral Lagrangians with suitable gauge models is elucidated.

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