arXiv subjects

J. Portoles

Publications and source records attributed to J. Portoles.

At least 19 recordsLinked to original sources

arXiv2016

Lepton Flavour Violation in Hadron Decays of the Tau Lepton in the Simplest Little Higgs Model

We study Lepton Flavour Violating hadron decays of the tau lepton within the Simplest Little Higgs model. Namely we consider $τ\rightarrow μ(P, V, PP)$ where $P$ and $V$ are short for a pseudoscalar and a vector meson. We find that, in the most positive scenarios, branching ratios for these processes are predicted to be, at least, four orders of magnitude smaller than present experimental bounds.

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arXiv2015

Instanton-mediated baryon number violation in non-universal gauge extended models

Instanton solutions of non-abelian Yang-Mills theories generate an effective action that may induce lepton and baryon number violations, namely $ΔB = ΔL = n_f$, being $n_f$ the number of families coupled to the gauge group. In this article we study instanton mediated processes in a $SU(2)_{\ell} \otimes SU(2)_h \otimes U(1)$ extension of the Standard Model that breaks universality by singularizing the third family. In the construction of the instanton Green functions we account systematically for the inter-family mixing. This allows us to use the experimental bounds on proton decay in order to constrain the gauge coupling of $SU(2)_h$. Tau lepton non-leptonic and radiative decays with $ΔB = ΔL = 1$ are also analysed.

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arXiv2013

Three pseudoscalar meson production in $e^+ e^-$ annihilation

We study, at leading order in the large number of colours expansion and within the Resonance Chiral Theory framework, the odd-intrinsic-parity $e^+ e^- \rightarrow π^+ π^- (π^0, η)$ cross-sections in the energy regime populated by hadron resonances, namely $3 \, m_π \lsim E \lsim 2 \, \mbox{GeV}$. In addition we implement our results in the Monte Carlo generator PHOKHARA 7.0 and we simulate hadron production through the radiative return method.

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arXiv2013

Zeros of the $W_L Z_L \rightarrow W_L Z_L$ amplitude: With or without a light Higgs

The existence of a new strong interacting sector around E ~ 1 TeV is a common feature of Higgsless electroweak theories but also of theories with a light Higgs, for instance, when this is not elementary. In those schemes, this new interaction could be at the origin of an extended spectra with, in particular, spin-1 resonances that could be hinted in elastic gauge boson scattering. Information on those resonances, if they exist, must be contained in the low-energy couplings of the electroweak chiral effective theory. Using the facts that: i) the scattering of longitudinal gauge bosons, W_L, Z_L, can be well described in the high-energy region (E >> M_W) by the scattering of the corresponding Goldstone bosons (equivalence theorem) and that ii) the zeros of the scattering amplitude carry the information on the heavier spectrum that has been integrated out; we employ the O(p^4) electroweak chiral Lagrangian, with or without a light Higgs state to identify the parameter space region of the low-energy couplings where vector resonances may arise.

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arXiv2012

Kaon Decays in the Standard Model

A comprehensive overview of kaon decays is presented. The Standard Model predictions are discussed in detail, covering both the underlying short-distance electroweak dynamics and the important interplay of QCD at long distances. Chiral perturbation theory provides a universal framework for treating leptonic, semileptonic and nonleptonic decays including rare and radiative modes. All allowed decay modes with branching ratios of at least 10^(-11) are analyzed. Some decays with even smaller rates are also included. Decays that are strictly forbidden in the Standard Model are not considered in this review. The present experimental status and the prospects for future improvements are reviewed.

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arXiv2010

Basics of Resonance Chiral Theory

We review the main components that have to be considered, within Resonance Chiral Theory, in the study of processes whose dynamics is dominated by hadron resonances. We show its application in the study of the tau -> (3 pion) nu_tau decay.

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arXiv2010

Hadron structure in tau -> KKpi nu_tau decays

We analyse the hadronization structure of both vector and axial-vector currents leading to tau -> KKpi nu_tau decays. At leading order in the 1/Nc expansion, and considering only the contribution of the lightest resonances, we work out, within the framework of the resonance chiral Lagrangian, the structure of the local vertices involved in those processes. The couplings in the resonance theory are constrained by imposing the asymptotic behaviour of vector and axial-vector spectral functions ruled by QCD. In this way we predict the hadron spectra and conclude that, contrarily to previous assertions, the vector contribution dominates by far over the axial-vector one in all KKpi charge channels.

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arXiv2010

tau -> pi pi pi nu_tau decays and the a_1(1260) off-shell width revisited

The tau -> pi pi pi nu_tau decay is driven by the hadronization of the axial-vector current. Within the resonance chiral theory, and considering the large-Nc expansion, this process has been studied in Ref.[1]. In the light of later developments we revise here this previous work by including a new off-shell width for the lightest a_1 resonance that provides a good description of the tau -> pi pi pi nu_tau spectrum and branching ratio. We also consider the role of the rho(1450) resonance in these observables. Thus we bring in an overall description of the tau -> pi pi pi nu_tau process in excellent agreement with our present experimental knowledge.

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arXiv2009

Sensitivity to the Higgs sector of SUSY-seesaw models via LFV tau decays

Here we study and compare the sensitivity to the Higgs sector of the SUSY-seesaw models via the LFV tau decays: tau-> 3 mu, tau->K^{+}K^{-}, tau->mu eta and tau-> mu f_{0}. We emphasize that, at present, the two later channels are the most efficient ones to test indirectly the Higgs particles.

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arXiv2009

Sensitivity to the Higgs Sector of SUSY-Seesaw Models in the Lepton Flavour Violating tau-->mu f0(980) decay

In this work we study the Lepton Flavour Violating semileptonic tau --> mu f0(980) decay within the context of SUSY-Seesaw Models, where the MSSM spectrum is extended by three right handed neutrinos and their SUSY partners, and where the seesaw mechanism is used to generate the neutrino masses. We estimate its decay rate when it proceeds via the Higgs mediated channel tau --> mu H* --> mu f0(980), where H refers to the CP-even MSSM Higgs bosons h^0 and H^0, and the Lepton Flavour Violating tau mu H vertex is radiatively generated via SUSY loops. In order to describe the f0(980) meson we follow the guidelines from chiral constraints. As an implication of our computation, we explore the sensitivity to the Higgs sector in this decay and compare it with other LFV tau decay channels. The confrontation of our predictions for BR(tau --> mu f0(980)) with its very competitive present experimental bound leads us to extract some interesting restrictions on the most relevant model parameters, particularly, tanbeta and m_{H^0}.

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arXiv2008

Lepton Flavour Violation in charged leptons within SUSY-seesaw

In this paper we review our main results for Lepton Flavour Violating (LFV) semileptonic tau decays and muon-electron conversion in nuclei within the context of two Constrained SUSY-Seesaw Models, the CMSSM and the NUHM. The relevant spectrum is that of the Minimal Supersymmetric Standard Model extended by three right handed neutrinos, $ν_{R_i}$ and their corresponding SUSY partners, ${\tilde ν}_{R_i}$, ($i=1,2,3$). We use the seesaw mechanism for neutrino mass generation and choose a parameterisation of this mechanism that allows us to incorporate the neutrino data in our analysis of LFV processes. In addition to the full one-loop results for the rates of these processes, we will also review the set of simple formulas, valid at large $\tan β$, which are very useful to compare with present experimental bounds. The sensitivity to SUSY and Higgs sectors in these processes will also be discussed. This is a very short summary of the works in Refs. \cite{Arganda:2008jj} and \cite{Arganda:2007jw} to which we refer the reader for more details.

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arXiv2008

Analysis of tau -> Ks pion nu_tau Belle data in a chiral framework

The recent measurement of the tau -> Ks pion nu_tau spectrum by the Belle Collaboration provides the frame to set forth a theoretical description of the decay, which is based on the contributing vector F_+(s) and scalar F_0(s) form factors. We show that a good representation of data is obtained through the use of form factors calculated within resonance chiral theory and constrained by dispersion relations and short-distance QCD. Hence we obtain a determination of K*(892) parameters and the low-energy parameterization of F_+(s).

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arXiv2008

LFV in semileptonic $τ$ decays and $μ-e$ conversion in nuclei in SUSY-seesaw

Here we review the main results of LFV in the semileptonic tau decays $τ\to μPP$ ($PP = π^+ π^-, π^0 π^0, K^+ K^-, K^0 \bar{K}^0$), $τ\to μP$ ($P = π, η, η^{\prime}$), and $τ\to μV$ ($V = ρ, ϕ$) as well as in $μ-e$ conversion in nuclei within SUSY-seesaw scenarios, and compare our predictions with the present experimental bounds

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arXiv2008

Lepton flavour violating semileptonic tau decays in constrained MSSM-seesaw scenarios

In this work we study the Lepton Flavour Violating semileptonic $τ$ decays: 1) $τ\to μPP$ with $PP= π^+π^-, π^0π^0, K^+K^-, K^0 {\bar K}^0$; 2) $τ\to μP$ with $P=π^0, η, η'$ and 3) $τ\to μV$ with $V = ρ^0, ϕ$. We work within the context of two constrained MSSM scenarios: the CMSSM and NUHM. A full one-(SUSY)loop computation is presented and the importance of the various contributions, the $γ$-, $Z$-, and Higgs bosons mediated ones are analysed. The hadronization of quark bilinears is performed within the chiral framework. Some discrepancies in the predicted rates for BR($τ\to μη$), BR($τ\to μη'$) and BR($τ\to μK^+K^-$) are found with respect to previous estimates, which will be commented here. These three channels will be shown to be the most competitive ones to test simultaneously the Lepton Flavour Violation and the Higgs sector. We further present here a set of approximate formulas for all the semileptonic channels which we believe can be useful for further comparison with present and future data.

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arXiv2007

Chiral Low-Energy Constants: Status and Prospects

Chiral low-energy constants (LECs) carry the information of short-distance dynamics involving heavier degrees of freedom not present in the chiral Lagrangian. Our knowledge of the LECs is all-important at phenomenological level because their relevance in the prediction of hadronic observables at low-energies and on the other side because they provide hints on the construction of a dual theory of QCD in the low-energy regime. I review briefly the status of these important couplings.

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arXiv2007

Form Factors in the radiative pion decay

We perform an analysis of the form factors that rule the structure-dependent amplitude in the radiative pion decay. The resonance contributions to pion -> e nu_e gamma decays are computed through the proper construction of the vector and axial-vector form factors by setting the QCD driven asymptotic properties of the three-point Green functions VVP and VAP, and by demanding the smoothing of the form factors at high transfer of momentum. A comparison between theoretical and experimental determinations of the form factors is also carried out. We also consider and evaluate the role played by a non-standard tensor form factor. We conclude that, at present and due to the hadronic incertitudes, the search for New Physics in this process is not feasible.

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arXiv2007

Analytical approaches to the calculation of f+(0)

Kl3 decays constitute, at present, the golden modes to extract |Vus| from experimental data. Its incertitude is dominated by the theoretical error in the determination of the vector form factor at zero transfer of momentum. I review the most relevant analytical approaches for the calculation of this parameter.

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arXiv2007

Large-Nc estimate of the chiral low-energy constants

Chiral low-energy constants incorporate short-distance information from the dynamics involving heavier degrees of freedom not present in the chiral Lagrangian. We have studied the contribution of the lightest resonances to the chiral low-energy constants, up to O(p^6), within a systematic procedure guided by the large-Nc limit of QCD and also including short-distance asymptotic constraints.

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