arXiv subjects

M. J. Herrero

Publications and source records attributed to M. J. Herrero.

At least 19 recordsLinked to original sources

arXiv2024

Exploring correlations between HEFT Higgs couplings $κ_V$ and $κ_{2V}$ via HH production at $e^+e^-$ colliders

In this work we explore the phenomenological implications at future $e^+e^-$ colliders of assuming anomalous couplings of the Higgs boson to gauge bosons $HVV$ and $HHVV$ ($V=W,Z$) given by the $κ$-modifiers with respect to the Standard Model couplings, $κ_V$ and $κ_{2V}$, respectively. For this study we use the Higgs Effective Field Theory (HEFT) where these two $κ$ parameters are identified with the two most relevant effective couplings at leading order, concretely $a=κ_V$ and $b=κ_{2V}$. Our focus is put on these two couplings and their potential correlations which we believe carry interesting information on the underlying ultraviolet theory. The particular studied process is $e^+e^- \to HH ν\bar ν$, where the vector boson scattering subprocess $WW \to HH$ plays a central role, specially at the largest planned energy colliders. Our detailed study of this process as a function of the energy and the angular variables indicates that the produced Higgs bosons in the BSM scenarios will have in general a high transversality as compared to the SM case if $κ_V^2 \neq κ_{2V}$. In order to enhance the sensitivity to these HEFT parameters $κ_V$ and $κ_{2V}$ and their potential correlations we propose here some selected differential cross sections for the $e^+e^- \to HH ν\barν$ process where different kinematic properties of the BSM case with respect to the SM are manifested. Finally, we will focus on the dominant Higgs decays to $b \bar b$ pairs leading to final events with 4 $b$-jets and missing transverse energy from the undetected neutrinos and will provide the expected accessibility to the $(κ_V,κ_{2V})$ effective couplings and their potential correlations. In our study we will consider the three projected energies for $e^+e^-$ colliders of 500 GeV, 1000 GeV and 3000 GeV.

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arXiv2024

One-loop corrections for WW to HH in HEFT with the electroweak chiral Lagrangian

In this work we present the computation of the one-loop electroweak radiative corrections to the scattering process $WW\to HH$ within the context of the Higgs Effective Field Theory (HEFT). We assume that the fermionic interactions are like in the Standard Model, whereas the Beyond Standard Model interactions in the bosonic sector are given by the Electroweak Chiral Lagrangian. The computation of the one-loop amplitude and the renormalization program is performed in terms of the involved one-particle-irreducible functions (1PI) and using $R_ξ$ covariant gauges. The renormalization of 1PI functions at arbitrary external momenta is a more ambitious program than just renormalizing the amplitude with on-shell external legs and it has the advantage that they can be used in several scattering amplitudes. In fact, we use here some of the 1PI functions already computed in our previous work (devoted to $WZ \to WZ$). We will complement them here with the computation of the new 1PI functions required for $WW \to HH$. From this renormalization procedure we will also derive the full set of renormalized coefficients of the EChL that are relevant for this scattering process. In the last part, we will present the numerical results for the EChL predictions of the one-loop level cross section, $σ(WW \to HH)|_{\rm 1-loop}$, as a function of the center of mass energy, showing the relative size of the one-loop radiative corrections respect to the tree level prediction in terms of the EChL coefficients. The results of the one-loop corrections to $WW \to HH$ for the SM case will be also presented, for comparison with the EChL case, following the same computational method, i.e., by means of the renormalization of 1PI functions.

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arXiv2023

Role of $λ_{hH^+H^-}$ in Higgs boson decays $h$ to $bs$ in the 2HDM

Within the Two Higgs Doublet Model (2HDM) with $\mathcal{CP}$ conservation and a softly broken $Z_2$ symmetry, we analyze the flavor changing Higgs decays $h\to bs$ ($bs$ refers jointly to the two decay channels $b\bar s$ and $\bar b s$), where $h$ is identified with the SM-like Higgs boson discovered at the LHC. We provide a comprehensive study of the decay width $Γ(h \to bs)$ with particular focus on the most relevant effects from the triple Higgs coupling $λ_{hH^+H^-}$. Furthermore, we consider all the relevant theoretical and experimental constraints to determine which predictions for the $\mathrm{BR}\left(h\to bs\right)$ are still allowed by the current data. We find that the predictions for $\mathrm{BR}\left(h\to bs\right)$ in types II and III can be several orders of magnitude smaller compared to the SM value. In contrast, in type I and IV we find that the predicted enhancements in the decay rates with respect to the SM of up to about 70% and 50%, respectively, are still allowed. We discuss how these deviations from the SM are caused by interference effects controlled by the coupling $λ_{hH^+H^-}$ which can be large for very heavy $H^\pm$. To better understand the role of $λ_{hH^+H^-}$ in the $h \to bs$ decay we derive and analyze here the analytical results for the $hbs$ one-loop effective vertex that is generated by integrating out the heavy $H^\pm$.

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arXiv2023

Non-decoupling effects from heavy Higgs bosons by matching 2HDM to HEFT amplitudes

In this work we explore the low energy effects induced from the integration of the heavy Higgs boson modes, $H$, $A$ and $H^\pm$, within the Two Higgs Doublet Model (2HDM) by assuming that the lightest Higgs boson $h$ is the one observed experimentally at $m_h \sim 125$ GeV. We work within the context of Effective Field Theories, focusing on the Higgs Effective Field Theory (HEFT), although some comparisons with the Standard Model Effective Field Theory (SMEFT) case are also discussed through this work. Our main focus is placed in the computation of the non-decoupling effects from the heavy Higgs bosons and the capture of such effects by means of the HEFT coefficients which are expressed in terms of the input parameters of the 2HDM. Our approach to solve this issue is by matching the amplitudes of the 2HDM and the HEFT for physical processes involving the light Higgs boson $h$ in the external legs, instead of the most frequently used matching procedure at the Lagrangian level. More concretely, we perform the matching at the amplitudes level for the following physical processes, including scattering and decays: $h\to WW^*\to Wf\bar{f'}$, $h\to ZZ^*\to Zf\bar{f}$, $WW \to hh$, $ZZ \to hh$, $hh \to hh$, $h \to γγ$ and $h \to γZ$. One important point of this work is that the matching is required to happen at low energies compared to the heavy Higgs boson masses, and these are heavier than the other particle masses. The proper expansion for this heavy mass limit is also defined here, which provides the results for the non-decoupling effects presented in this work. We finally discuss the implications of the resulting effective coefficients, and remark on the interesting correlations detected among them.

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arXiv2022

Sensitivity and constraints to the 2HDM soft-breaking $Z_2$ parameter $m_{12}$

In this letter we study the specific sensitivity and constraints to the soft breaking $Z_2$ parameter $m_{12}$ of the Two Higgs Doublet Model (2HDM). $m_{12}$ is considered here as an input parameter of the model together with the masses of the Higgs bosons, $m_h$, $m_H$, $m_A$, $m_{H^\pm}$, the ratio of the two Higgs vacuum expectation values, $\tan β$, and $\cos(β-α)$, with $α$ and $β$ the mixing angles of the $\mathcal{CP}$-even and $\mathcal{CP}$-odd Higgs sector, respectively. We explore in particular the sensitivity to $m_{12}$ in the decays of the lightest Higgs boson $h$ to two photons, assuming: 1) that $h$ is the state observed at the LHC at $\sim 125 \ \mathrm{GeV}$, and 2) the $h$ couplings to the SM particles are SM-like, by going to the alignment limit, $\cos(β-α) = 0$. The aim of this work is to demonstrate possible constraints on $m_{12}$ from the present measurement of the di-photon signal strength, $μ_{γγ}$. These constraints are relevant in the region of the 2HDM parameter space that is allowed by all the other constraints, specifically, theoretical constraints as well as experimental constraints from LHC Higgs rate measurements, Higgs boson searches, flavor physics and precision observables. The exploration is performed in the four different Yukawa types of 2HDM, where the allowed region by all the other constraints depends on the model type. We also analyze the case that the Higgs-boson mass spectrum accommodates a possible new world average of $m_W$ including the recent CDF measurement.

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arXiv2022

Double Higgs production at TeV $e^+e^-$ colliders with Effective Field Theories: sensitivity to BSM Higgs couplings

In this work we study the production of two Higgs bosons at the two planned electron positron colliders with energies at the TeV domain, CLIC and ILC, within the context of Effective Field Theories (EFTs) to describe beyond the Standard Model Higgs Physics. We focus first on the case of the Higgs Effective Field Theory (HEFT) and next we compare with the case of the Standard Model Effective Field Theory (SMEFT). The predictions for double Higgs production in both EFTs are first presented for the most relevant subprocess participating in the total process of our interest, $e^+e^- \to HH ν\bar ν$, which is the scattering of two gauge bosons, $WW \to HH$, also called $WW$ fusion. The predictions for the cross section $ σ(W_X W_Y\to HH)$ as a function of the subprocess energy are analyzed in full detail for the two EFTs, for all the polarization channels with longitudinal and transverse modes $XY=LL, TT,LT,TL$, and for the most relevant effective operators in both cases. We will demonstrate that in the HEFT case, the total cross section can be fully understood in terms of the $LL$ contribution and this in turn is dominated at these TeV energies mainly by two HEFT coefficients. By doing the matching between the two EFTs at the level of the scattering amplitude for the subprocess, we will be able to find the correspondence of the leading coefficients in the HEFT and the SMEFT. In the final part of this work we will then explore the sensitivity to these two most relevant HEFT coefficients, at CLIC (3 TeV, 5 ab$^{-1}$) and ILC (1 TeV, 8 ab$^{-1}$). We will then conclude on the accessible region of these two parameters by studying the predicted rates at these two $e^+e^-$ colliders for the final state $b \bar b b \bar b ν\bar ν$ leading to characteristic signals with 4 bottom jets and missing energy.

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arXiv2022

Triple Higgs Couplings in the 2HDM: The Complete Picture

The measurement of the triple Higgs coupling is one of the main tasks of the (HL-)LHC and future lepton colliders. Similarly, triple Higgs couplings involving BSM Higgs bosons are of high interest. Within the framework of Two Higgs Doublet Models (2HDM) we investigate the allowed ranges for all triple Higgs couplings involving at least one light, SM-like Higgs boson. We present newly the allowed ranges for 2HDM type III and IV and update the results within the type I and II. We take into account theoretical constraints from unitarity and stability, experimental constraints from direct BSM Higgs-boson searches, measurements of the rates of the SM-like Higgs-boson at the LHC, as well as flavor observables and electroweak precision data. For the SM-type triple Higgs coupling w.r.t. its SM value, $λ_{hhh}/λ_{hhh}^\mathrm{SM}$, we find allowed intervals of $\sim [-0.5,1.3]$ in type~I and $\sim [0.5,1.0]$ in the other Yukawa types. These allowed ranges have important implications for the experimental determination of this coupling at future collider experiments. We find the coupling $λ_{hhH}$ between $\sim -1.5$ and $\sim +1.5$ in the four Yukawa types. For the triple Higgs couplings involving two heavy neutral Higgs bosons, $λ_{hHH}$ and $λ_{hAA}$ we find values between $\sim -0.5$ and $\sim 16$, and between $\sim -1$ and $\sim 32$ for $λ_{hH^+H^-}$. These potentially large values could lead to strongly enhanced production of two Higgs-bosons at the HL-LHC or high-energy lepton colliders.

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arXiv2021

Large triple Higgs couplings in the 2HDM at $e^+e^-$ colliders

Within the framework of the $\cal CP$ conserving Two Higgs Doublet Models (2HDM) type I and II we investigate the di-Higgs production at future $e^+e^-$ colliders in order to find effects coming from triple Higgs couplings. We define and explore some benchmark planes that show large values of these couplings, still in agreement with all the relevant theoretical and experimental constraints. Within those planes two production channels are considered: $e^+e^-\to h_ih_jZ$ and $e^+e^-\to h_ih_jν\barν$, with $h_ih_j=hh,\ HH\ \mathrm{and}\ AA$. We discuss on the sensitivity to $κ_λ:=λ_{hhh}/λ_{hhh}^\mathrm{SM}$ and $λ_{hhH}$ in the $hhν\barν$ production and to $λ_{hHH}$ ($λ_{hAA}$) in the $HHν\barν$ ($AAν\barν$) production at CLIC 3 TeV via the cross section distribution on the invariant mass of the final-state Higgs-pair.

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arXiv2021

Sensitivity to Triple Higgs Couplings via Di-Higgs Production in the 2HDM at e+e- Colliders

An important task at future colliders is the investigation of the Higgs-boson sector. Here the measurement of the triple Higgs coupling(s) plays a special role. Based on previous analyses, within the framework of Two Higgs Doublet Models (2HDM) type~I and~II, we define and analyze several two-dimensional benchmark planes, that are over large parts in agreement with all theoretical and experimental constraints. For these planes we evaluate di-Higgs production cross sections at future high-energy $e^+e^-$ colliders, such as ILC or CLIC. We consider two different channels for the neutral di-Higgs pairs $h_i h_j=hh,hH,HH,AA$: $e^+e^- \to h_i h_j Z$ and $e^+e^- \to h_i h_j ν\bar ν$. In both channels the various triple Higgs-boson couplings contribute substantially. We find regions with a strong enhancement of the production channel of two SM-like light Higgs bosons and/or with very large production cross sections involving one light and one heavy or two heavy 2HDM Higgs bosons, offering interesting prospects for the ILC or CLIC. The mechanisms leading to these enhanced production cross sections are analyzed in detail. We propose the use of cross section distributions with the invariant mass of the two final Higgs bosons where the contributions from intermediate resonant and non-resonant BSM Higgs bosons play a crucial role. We outline which process at which center-of-mass energy would be best suited to probe the corresponding triple Higgs-boson couplings.

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arXiv2021

Sizable triple Higgs couplings in the 2HDM: Prospects for future $e^+e^-$ colliders

In the framework of the $\mathcal{CP}$ conserving Two Higgs Doublet Model (2HDM), type I and II, we study the triple Higgs couplings with at least one light $h$ Higgs boson that is identified by the 125 GeV Higgs boson. We define benchmark planes that exhibit large values of triple Higgs couplings, while being in agreement with all experimental and theoretical constraints. Finally, we analyze the impact of the triple Higgs couplings on the production cross section of two neutral Higgs bosons in two channels, $σ(e^+e^-\to h_i h_j Z)$ and $σ(e^+e^- \to h_i h_j ν\barν)$ with $h_i h_j = hh, hH, HH, AA$. We show that the triple Higgs couplings have an important impact on these $e^+e^-$ production cross sections.

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arXiv2020

Exploring sizable triple Higgs couplings in the 2HDM

An important task at future colliders is the measurement of the triple Higgs coupling. Depending on its size relative to the Standard Model (SM) value, certain collider options result in a higher experimental accuracy. Within the framework of Two Higgs Doublet Models (2HDM) type I and II we investigate the allowed ranges for all triple Higgs couplings involving at least one light, SM-like Higgs boson. We take into account theoretical constraints (unitarity, stability), experimental constraints from direct Higgs-boson searches, measurements of the SM-like Higgs-boson properties, flavor observables and electroweak precision data. We find that the SM-type triple Higgs coupling w.r.t. its SM value, $λ_{hhh}/λ_{\rm SM}$, can range between $\sim -0.5$ and $\sim 1.5$. Depending on which value is realized, the HL-LHC can compete with, or is clearly inferior to the ILC. We find the coupling $λ_{hhH}$ between $\sim -1.5$ and $\sim 1.5$. Triple Higgs couplings involving two heavy Higgs bosons, $λ_{hHH}$, $λ_{hAA}$ and $λ_{hH^+H^-}$ can reach values up to ${\cal O}(10)$, roughly independent of the 2HDM type. This can lead to potentially strongly enhanced production of two Higgs-bosons at the HL-LHC or high-energy $e^+e^-$ colliders.

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arXiv2019

Unitarization effects in EFT predictions of WZ scattering at the LHC

Effective field theories are an incredibly powerful tool in order to study and understand the true nature of the symmetry breaking sector dynamics of the Standard Model. However, they can suffer from some theoretical problems such as that of unitarity violation. Nevertheless, in order to interpret experimental data correctly a fully unitary prescription is needed. To this purpose, unitarization methods are addressed, but each of them leads to a different (unitary) prediction. Because of this, there is an inherent theoretical uncertainty in the determination of the effective field theory parameters due to the choice of one unitarization scheme. In this work, we quantify this uncertainty assuming a strongly interacting electroweak symmetry breaking sector, described by the effective electroweak chiral Lagrangian. We focus on the bosonic part of this effective Lagrangian and choose in particular the WZ scattering as our main VBS channel to study the sensitivity to new physics at the LHC. We study the different predictions of various well known unitarization methods, considering the full coupled system of helicity amplitudes, and construct the 95\% confidence level exclusion regions for the most relevant electroweak chiral Lagrangian parameters, given by the two anomalous quartic gauge couplings $a_4$ and $a_5$. This provides a consistent analysis of the different constraints on EChL parameters that can be achieved by using different unitarization methods in a combined way.

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arXiv2019

Dynamical vector resonances from the EChL in VBS at the LHC: the WW case

In this work we study the phenomenology of the process $pp\to W^+W^-jj$ at the LHC, in the scenario of the resonant vector boson scattering subprocess $W^+W^-\to W^+W^-$ which we describe within the effective field theory framework of the Electroweak Chiral Lagrangian. We assume a strongly interacting electroweak symmetry breaking sector in which dynamically generated resonances with masses in the TeV scale appear as poles in the Electroweak Chiral Lagrangian amplitudes unitarized with the Inverse Amplitude Method. The relevant resonance here, $V_0$, is the neutral component of the triplet of vector resonances which are known to emerge dynamically at the TeV scale for specific values of the Electroweak Chiral Lagrangian parameters. With the aim of studying the production and possible observation of $V^0$ at the LHC, via the resonant $W^+W^-\to W^+W^-$ scattering, a MadGraph~5 UFO model has been developed employing a phenomenological Proca Lagrangian as a practical tool to mimic the correct $V^0$ properties that are predicted with the Inverse Amplitude Method. We choose to study the fully hadronic decay channel of the final gauge bosons $W W\to J(jj)J(jj)$ since it leads to larger event rates and because in the alternative leptonic decay channels the presence of neutrinos complicates the reconstruction of the resonance properties. In this context, the 2 boosted jets from the $W$ hadronic decays, $jj$, are detected as a single fat jet, $J$, due to their extreme collinearity. We perform a dedicated analysis of the sensitivity to these vector resonances $V^0$ with masses between 1.5 and 2.5 TeV at the LHC with $\sqrt{s}=13$ TeV and the planned high luminosity of 3000 ${\rm fb}^{-1}$, paying special attention to the study of efficient cuts to extract the resonant vector boson fusion signal from the QCD background, which clearly represents the main challenge of this search.

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arXiv2019

Probing the Higgs self-coupling through double Higgs production in vector boson scattering at the LHC

In this work we explore the sensitivity to the Higgs self-coupling $λ$ in the production of two Higgs bosons via vector boson scattering at the LHC. Although these production channels, concretely $W^+W^- \to HH$ and $ ZZ \to HH$, have lower rates than gluon-gluon fusion, they benefit from being tree level processes, being independent of top physics and having very distinctive kinematics that allow to obtain very clean experimental signatures. This makes them competitive channels concerning the sensitivity to the Higgs self-coupling. In order to give predictions for the sensitivity to this coupling, we first study the role of $λ$ at the subprocess level, both in and beyond the Standard Model, to move afterwards to the LHC scenario. We characterize the $pp\to HHjj$ case first and then provide quantitative results for the values of $λ$ that can be probed at the LHC in vector boson scattering processes after considering the Higgs boson decays. We focus mainly in $pp\to b\bar{b}b\bar{b}jj$, since it has the largest signal rates, and also comment on the potential of other channels, such as $pp\to b\bar{b}γγjj$, as they lead to cleaner, although smaller, signals. Our whole study is performed for a center of mass energy of $\sqrt{s}=14$ TeV and for various future expected LHC luminosities.

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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

One-loop effective LFV $Zl_kl_m$ vertex from heavy neutrinos within the Mass Insertion Approximation

In this paper we study the effective lepton flavor violating vertex of an electroweak $Z$ gauge boson and two charged leptons with different flavor, $l_k$ and $l_m$, that is generated to one-loop in low scale seesaw models with right handed neutrinos whose masses are heavier than the electroweak scale. We first compute the form factor describing this vertex by using the mass insertion approximation, where the flavor non-diagonal entries of the neutrino Yukawa coupling matrix are the unique origin, to one-loop level, of lepton flavor changing processes with charged leptons in the external legs. Then, by considering the proper large right handed neutrino mass expansion of the form factor, we derive a formula for the $Z l_k l_m$ effective vertex which is very simple and useful for fast phenomenological estimates. In the last part of this work we focus on the phenomenological applications of this vertex for simple and accurate estimates of the $Z \to l_k {\bar l}_m$ decay rates. Concretely, this vertex will allow us to conclude easily on the maximum allowed decay rates by present data in the inverse seesaw model. The found rates are promising, at the reach of future lepton colliders.

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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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