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J. J. Sanz-Cillero

Publications and source records attributed to J. J. Sanz-Cillero.

At least 19 recordsLinked to original sources
arXiv2018

Collider phenomenology of vector resonances in WZ scattering processes

We study the production of vector resonances at the LHC via $WZ$ scattering processes and explore the sensitivities to these resonances for the expected future LHC luminosities. The electroweak chiral Lagrangian and the Inverse Amplitude Method (IAM) are used for analyzing a dynamically generated vector resonance, whose origin would be the (hypothetically strong) self interactions of the longitudinal gauge bosons, $W_L$ and $Z_L$. We implement the unitarized scattering amplitudes into a single model, the IAM-MC, that has been adapted to MadGraph~5. It is written in terms of the electroweak chiral Lagrangian and an additional effective Proca Lagrangian for the vector resonances, so that it reproduces the resonant behavior of the IAM and allows us to perform a realistic study of signal versus background at the LHC. We focus on the $pp\to WZjj$ channel, discussing first on the potential of the hadronic and semileptonic channels of the final $WZ$, and next exploring in more detail the clearest signals. These are provided by the leptonic decays of the gauge bosons, leading to a final state with $l^+_1l^-_1l^+_2νjj$, $l=e,μ$, having a very distinctive signature, and showing clearly the emergence of the resonances with masses in the range of $1.5$-$2.5\,{\rm TeV}$, which we have explored.

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arXiv2018

Pseudoscalar pole light-by-light contributions to the muon $(g-2)$ in Resonance Chiral Theory

We have studied the $P\toγ^\starγ^\star$ transition form-factors ($P=π^0,η,η'$) within a chiral invariant framework that allows us to relate the three form-factors and evaluate the corresponding contributions to the muon anomalous magnetic moment $a_μ$, through pseudoscalar pole contributions. We use a chiral invariant Lagrangian to describe the interactions between the pseudo-Goldstones from the spontaneous chiral symmetry breaking and the massive meson resonances. We will consider just the lightest vector and pseudoscalar resonance multiplets. Photon interactions and flavor breaking effects are accounted for in this covariant framework. This article studies the most general corrections of order $m_P^2$ within this setting. Requiring short-distance constraints fixes most of the parameters entering the form-factors, consistent with previous determinations. The remaining ones are obtained from a fit of these form-factors to experimental measurements in the space-like ($q^2\le0$) region of photon momenta. The combination of data, chiral symmetry relations between form-factors and high-energy constraints allows us to determine with improved precision the on-shell $P$-pole contribution to the Hadronic Light-by-Light scattering of the muon anomalous magnetic moment: we obtain $a_μ^{P,HLbL}=(8.47\pm 0.16)\cdot10^{-10}$ for our best fit. This result was obtained excluding BaBar $π^0$ data, which our analysis finds in conflict with the remaining experimental inputs. This study also allows us to determine the parameters describing the $η-η'$ system in the two-mixing angle scheme and their correlations. Finally, a preliminary rough estimate of the impact of loop corrections ($1/N_C$) and higher vector multiplets (asym) enlarges the uncertainty up to $a_μ^{P,HLbL} = (8.47\pm 0.16_{\rm sta}\pm0.09_{1/N_C}{}^{+0.5}_{-0.0}{}_{\rm asym})\cdot 10^{-10}$.

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arXiv2018

Resonant $pp\to W^+ Zjj$ events at the LHC from a unitarized study of the EChL

We present a study of the production of vector resonances at the LHC via $W^+Z$ vector boson scattering and explore the sensitivities to these resonances for expected LHC luminosities. We work in the framework of the electroweak chiral Lagrangian, where these resonances can be generated dynamically by unitarizing the scattering amplitudes. We implement all these features into a model adapted for MonteCarlo, the IAM-MC, that allows us to give predictions for the sensitivity to these resonances and to the relevant parameters involved for $pp \to W^+Zjj$, $pp\to \ell_1^+\ell_1^-\ell_2^+νjj$, and $pp \to JJjj$.

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arXiv2017

Production of vector resonances at the LHC via WZ-scattering: a unitarized EChL analysis

In the present work we study the production of vector resonances at the LHC by means of the vector boson scattering $WZ \to WZ$ and explore the sensitivities to these resonances for the expected future LHC luminosities. We are assuming that these vector resonances are generated dynamically from the self interactions of the longitudinal gauge bosons, $W_L$ and $Z_L$, and work under the framework of the electroweak chiral Lagrangian to describe in a model independent way the supposedly strong dynamics of these modes. The properties of the vector resonances, mass, width and couplings to the $W$ and $Z$ gauge bosons are derived from the inverse amplitude method approach. We implement all these features into a single model, the IAM-MC, adapted for MonteCarlo, built in a Lagrangian language in terms of the electroweak chiral Lagrangian and a chiral Lagrangian for the vector resonances, which mimics the resonant behavior of the IAM and provides unitary amplitudes. The model has been implemented in MadGraph, allowing us to perform a realistic study of the signal versus background events at the LHC. In particular, we have focused our study on the $pp\to WZjj$ type of events, discussing first on the potential of the hadronic and semileptonic channels of the final $WZ$, and next exploring in more detail the clearest signals. These are provided by the leptonic decays of the gauge bosons, leading to a final state with $\ell_1^+\ell_1^-\ell_2^+νjj$, $\ell=e,μ$, having a very distinctive signature, and showing clearly the emergence of the resonances with masses in the range of 1.5-2.5 TeV, which we have explored.

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arXiv2017

Resonances and loops: scale interplay in the Higgs effective field theory

As there seems to be a large mass gap between the SM and new physics particles, the EFT framework emerges as the natural approach for the analysis and interpretation of collider data. However, this large gap and the fact that (so far) all the measured interactions look pretty much SM-like does not imply that the linear Higgs representation as a complex doublet $ϕ$ in the SMEFT is always appropriate. Although there is a wide class of SM extensions that accept this linear description, this realization does not always provide a good perturbative expansion. The HEFT and its organization according to a chiral expansion cures these issues. Path integral functional methods allow one to compute the corrections to the NLO effective action: at tree level, the heavy resonances only contribute to the $O(p^4)$ low-energy couplings (or higher) according to a pattern that depends on their quantum numbers and is suppressed by their masses; at the one-loop level, all the new-physics corrections go to the $O(p^4)$ effective action (or higher) and are suppressed by an intrinsic scale of the LO HEFT Lagrangian, which has been related in recent times with the curvature of the manifold of scalar fields (being the SM its flat limit and having the HEFT effective action an expansion in the curvature). This two suppression scales (resonance masses and non-linearity/curvature) compete at NLO and may, in principle, be very different/similar depending on the particular BSM scenario and the observable at hand. Likewise, experiments do not tell us yet whether $O(p^4)$ loops are essentially negligible or not, as it is shown with a couple of examples. In summary, the HEFT extends the range of applicability of the SMEFT, which, although justified for a pretty wide class of BSM scenarios, introduces a bias in the data analyses and does not provide the most general EFT framework.

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arXiv2017

A broad 750 GeV diphoton resonance? Not alone

The hint for a possible resonance in the diphoton channel with mass of 750~GeV disappeared in the data presented at ICHEP'16 by ATLAS and CMS. However, the diphoton final state remains as one of the golden channels for new physics discoveries at the TeV scale in the LHC experiments. This motivates us to analyze model-independently the implications of an O(TeV) bump in the $γγ$ final state. By means of forward sum-rules for $γγ$ scattering, we show that a spin-0 resonance with mass of the order of the TeV and a sizable $γγ$ partial width -of the order of a few GeV- must be accompanied by higher spin resonances with $J_R\geq 2$ with similar properties, as expected in strongly coupled extensions of the Standard Model or, alternatively, in higher dimensional deconstructed duals. Furthermore, independently of whether the putative O(TeV) candidate is a scalar or a tensor, the large contribution to the forward sum-rules in the referred scenario implies the presence of states in the spectrum with $J_R\geq 2$, these high spin particles being a manifestation of new extra-dimensions or composite states of a new strong sector.

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arXiv2017

Sum-rule constraints on possible diphoton resonances at LHC

The study of the forward scattering amplitude $V(k,λ) V(k'λ')\to V(k,λ) V(k',λ')$ of real massless gauge bosons $V$, e.g. photons or gluons, leads to a sum-rule that can be used to investigate beyond the Standard Model signals at LHC in the $γγ$ channel. The sum-rule only relies on general properties such as analyticity, unitarity and crossing. We use the now buried 750 GeV diphoton resonance as a case of study to exemplify the constraints that the forward sum-rule requires to any new physics candidate. In the case of a large $γγ$ or $gg$ partial width, of the order of 10 GeV in our 750 GeV analysis, one finds that an infinite tower of states with spin $J_R=2$ and higher must be ultimately incorporated to the beyond Standard Model theory in order to fulfill the sum-rule. We expect these techniques may be useful in next diphoton searches at LHC and future colliders.

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arXiv2016

Study of the lowest tensor and scalar resonances in the $τ\to πππν_τ$ decay

In this note we present a new parametrization of the hadronic current for the decay $τ\to πππν_τ$ derived from the chiral lagrangian with explicit inclusion of resonances. We have included both scalar, vector and axial-vector resonances. For the first time, the lowest tensor resonance ($f_2(1270)$) is included as well. Both single and double-resonance contributions to the hadronic form factors are taken into account. To satisfy the correct high energy behaviour of the hadronic form factors, constraints on numerical values of the vertex constants are obtained.

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arXiv2015

Composite resonances and their impact on the EW chiral Lagrangian

In this talk we study the low-energy effective couplings generated by strongly-coupled electroweak models that contain heavy composite resonances. Invariance under $SU(2)_L\times SU(2)_R$ is a key ingredient in the construction of the resonance action. For simplicity, in these proceedings we focus our attention on the impact of a heavy colourless vector V, which transforms as a triplet under the custodial group. More precisely, we study the couplings that are relevant for the vector form-factors of the L+R current into two electroweak Goldstones and into two Standard Model fermions, which contribute to the oblique parameters S and T and the anomalous $Z\to f\bar{f}$ couplings, respectively. Our predictions are compatible with bounds from direct and indirect searches for Mv > 1.5 TeV. Finally, although we consider an antisymmetric tensor formalism to describe the vector resonance, we derive the equivalent action in the Proca four-vector representation and show that the predictions for low-energy couplings and form-factors are identical, as expected.

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arXiv2015

Electroweak chiral Lagrangian with a light Higgs

In this talk we discuss the structure of electroweak low-energy effective theories where the Higgs is non-linearly realized, typically in scenarios where the Higgs is a pseudo Nambu-Goldstone boson of some beyond Standard Model symmetry. The organization of the perturbative counting and the relevance of the various next-to-leading order contributions is studied. We discuss some new results on the structure of the one-loop ultraviolet divergences and the contribution from tree-level heavy resonance exchanges to the low-energy effective theory, which are applied to a couple of explicit examples in order to show how, in the non-linear effective theory -the electroweak chiral Lagrangian with a light Higgs (ECLh)-, one-loop corrections can be as important as the contribution from higher dimension operators.

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arXiv2014

Electroweak chiral Lagrangian with a light Higgs and $γγ\to Z_L Z_L, W_L^+ W_L^-$ scattering at one loop

In these proceedings we provide a brief summary of the findings of a previous article where we have studied the photon-photon scattering into longitudinal weak bosons within the context of the electroweak chiral Lagrangian with a light Higgs, a low-energy effective field theory including a Higgs-like scalar singlet and where the electroweak would-be Goldstone bosons are non-linearly realized. We consider the relevant Lagrangian up to next-to-leading order in the chiral counting, which is explained in some detail here. We find that these amplitudes are ultraviolet finite and the relevant combinations of next-to-leading parameters ($c_γ$ and $a_1-a_2+a_3$) do not get renormalized. We propose the joined analysis of $γγ$-scattering and other photon related observables ($Γ(h\toγγ)$, $S$--parameter and the $γ^*\to W^+_LW^-_L$ and $γ^*\to hγ$ electromagnetic form-factors) in order to separate and determine each chiral parameter. Moreover, the correlations between observables provided by the NLO computations would lead to more stringent bounds on the new physics that is parametrized by means of this effective Lagrangian. We also show an explicit computation of the $γγ$--scattering up to next-to-leading order in the $SO(5)/SO(4)$ minimally composite Higgs model.

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arXiv2014

Electroweak chiral Lagrangians and the Higgs properties at the one-loop level

In these proceedings we explore the use of (non-linear) electroweak chiral Lagrangians for the description of possible beyond the Standard Model strong dynamics in the electroweak sector. Experimentally one observes an approximate electroweak symmetry breaking pattern $SU(2)_L\times SU(2)_R/SU(2)_{L+R}$. Quantum Chromodynamics shows a similar chiral structure and, in spite of the differences (in the electroweak theory $SU(2)_L\times U(1)_Y$ is gauged), it has served for years as a guide for this type of studies. Examples of one-loop computations in the low-energy effective theory and the theory including the first vector and axial-vector resonances are provided, yielding, respectively, predictions for $γγ\to Z_LZ_L,W^+_LW^-_L$ and the oblique parameters $S$ and $T$.

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arXiv2014

Electroweak Chiral Lagrangians and $γγ\to Z_L Z_L,\, W_L^+ W_L^-$ at One Loop

In these proceedings we discuss our recent work on $γγ\to W^+_L W^-_L$ and $γγ\to Z_L Z_L$ within the framework of Electroweak Chiral Lagrangians with a light Higgs. These observables are good candidates to provide indications of physics beyond the Standard Model and can complement other analyses and global fits. Making use of the equivalence theorem, we have performed the computation up to the next-to-leading order in the chiral expansion, i.e., including one-loop corrections and the full set of possible counterterms allowed at that order in the low-energy effective field theory. The one-loop amplitudes turn out to have a extremely simple structure and they are ultraviolet finite. Thus, the relevant combinations of higher order chiral couplings $c_γ^r$ and $(a_1^r-a_2^r+a_3^r)$ do not run. We also identify an additional set of observables that depend on these same parameters, which can be use to complement the $γγ$ analysis through a global fit.

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arXiv2014

One-loop $γγ\to W^+_L W^-_L$ and $γγ\to Z_L Z_L$ from the Electroweak Chiral Lagrangian with a light Higgs-like scalar

In this work we study the $γγ\to W^+_L W^-_L$ and $γγ\to Z_L Z_L$ scattering processes within the effective chiral Lagrangian approach, including a light Higgs-like scalar as a dynamical field together with the would-be-Goldstone bosons $w^\pm$ and $z$ associated to the electroweak symmetry breaking. This approach is inspired by the possibility that the Higgs-like boson be a composite particle behaving as another Goldstone boson, and assumes the existence of a mass gap between $m_h$, $m_W$, $m_Z$ and the potential new emergent resonances, setting an intermediate energy region (above $m_{h,W,Z}$ and below the resonance masses) where the use of these effective chiral Lagrangians are the most appropriate tools to compute the relevant observables. We analyse in detail the proper chiral counting rules for the present case of photon-photon scattering and provide the computation of the one-loop $γγ\to W^+_L W^-_L$ and $γγ\to Z_L Z_L$ scattering amplitudes within this Effective Chiral Lagrangian approach and the Equivalence Theorem, including a discussion on the involved renormalization procedure. We also propose here a joint analysis of our results for the two-photon scattering amplitudes together with other photonic processes and electroweak (EW) precision observables for a future comparison with data. This could help to disentangle the nature of the light Higgs-like particle.

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arXiv2014

Assessing the accuracy of the Brodsky-Lepage prediction

We show that a consistent set of short-distance conditions on the odd-intrinsic parity resonance chiral Lagrangian couplings can be derived in the large-$N_C$ limit and the single resonance approximation. These constraints are satisfied both by the VVP Green function and all its associated form-factors. Moreover, they are in agreement with earlier results found in the normal parity sector, which further supports the overall consistency of the approach. Here we take a new perspective and examine the consequences of these high-energy relations on the precise coefficient of the $1/Q^2$-term of meson form-factors, which rules their asymptotic behavior. In particular, we show that the coefficient derived using our consistent set of short-distance constraints is in remarkable accordance with the Brodsky-Lepage prediction, being alternative results for these coefficients disfavored.

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arXiv2013

Padé Approximants and Resonance Poles

Based on the mathematically well defined Padé Theory, a theoretically safe new procedure for the extraction of the pole mass and width of a resonance is proposed. In particular, thanks to the Montessus de Ballore theorem we are able to unfold the Second Riemann Sheet of an amplitude to search for the position of the resonant pole in the complex plane. The method is systematic and provides a model-independent treatment of the prediction and the corresponding errors of the approximation.

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arXiv2012

Relations between anomalous and even-parity sectors in AdS/QCD

We derive the O(p6) Chiral Perturbation Theory Lagrangian in the massless quark limit for a class of gravity dual models of Quantum Chromodynamics with the chiral symmetry broken through boundary conditions. The odd O(p6) couplings are related to the O(p4) low-energy constants (LEC's) in the even-parity sector. Some combinations of even O(p6) couplings are found to be universal and independent of the peculiarities of the model. These relations turn out to be the manifestation at low energies of a broader relation between anomalous and even-parity amplitudes.

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