arXiv subjects

A. Dobado

Publications and source records attributed to A. Dobado.

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.

hep-ph↗

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 $pp \to JJjj$.

hep-ph↗

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.

hep-ph↗

arXiv2017

Handbook of LHC Higgs Cross Sections: 4. Deciphering the Nature of the Higgs Sector

This Report summarizes the results of the activities of the LHC Higgs Cross Section Working Group in the period 2014-2016. The main goal of the working group was to present the state-of-the-art of Higgs physics at the LHC, integrating all new results that have appeared in the last few years. The first part compiles the most up-to-date predictions of Higgs boson production cross sections and decay branching ratios, parton distribution functions, and off-shell Higgs boson production and interference effects. The second part discusses the recent progress in Higgs effective field theory predictions, followed by the third part on pseudo-observables, simplified template cross section and fiducial cross section measurements, which give the baseline framework for Higgs boson property measurements. The fourth part deals with the beyond the Standard Model predictions of various benchmark scenarios of Minimal Supersymmetric Standard Model, extended scalar sector, Next-to-Minimal Supersymmetric Standard Model and exotic Higgs boson decays. This report follows three previous working-group reports: Handbook of LHC Higgs Cross Sections: 1. Inclusive Observables (CERN-2011-002), Handbook of LHC Higgs Cross Sections: 2. Differential Distributions (CERN-2012-002), and Handbook of LHC Higgs Cross Sections: 3. Higgs properties (CERN-2013-004). The current report serves as the baseline reference for Higgs physics in LHC Run 2 and beyond.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

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.

hep-ph↗

arXiv2014

The Raychaudhuri equation in homogeneous cosmologies

In this work we address the issue of studying the conditions required to guarantee the Focusing Theorem for both null and timelike geodesic congruences by using the Raychaudhuri equation. In particular we study the case of Friedmann-Robertson-Walker as well as more general Bianchi Type I spacetimes. The fulfillment of the Focusing Theorem is mandatory in small scales since it accounts for the attractive character of gravity. However, the Focusing Theorem is not satisfied at cosmological scales due to the measured negative deceleration parameter. The study of the conditions needed for congruences convergence is not only relevant at the fundamental level but also to derive the viability conditions to be imposed on extended theories of gravity describing the different expansion regimes of the universe. We illustrate this idea for f(R) gravity theories.

gr-qc↗

arXiv2013

On the non-attractive character of gravity in f(R) theories

In General Relativity without a cosmological constant a non-positive contribution from the space-time geometry to Raychaudhuri equation is found provided that particular energy conditions are assumed and regardless the considered solution of the Einstein's equations. This fact is usually interpreted as a manifestation of the attractive character of gravity. Nevertheless, a positive contribution to Raychaudhuri equation from space-time geometry should occur since this is the case in an accelerated expanding Robertson-Walker model for congruences followed by fundamental observers. Modified gravity theories provide the possibility of a positive contribution although the standard energy conditions are assumed. We address this important issue in the context of f(R) theories, deriving explicit upper bounds for the contribution of space-time geometry to the Raychaudhuri equation. Then, we examine the parameter constraints for some paradigmatic f(R) models in order to ensure a positive contribution to this equation. Furthermore, we consider the implications of these upper bounds in the equivalent formulation of f(R) theories as a Brans-Dicke model.

gr-qc↗

arXiv2010

Photon spectra from quark generation by WIMPs

In this work we provide the fitting formula valid for the simulated photon spectra from WIMP annihilation into light quark-anti quark (qq-) channels in a wide range of WIMP masses. We illustrate our results for the cc- channel.

hep-ph↗

arXiv2010

Photon spectra from WIMP annihilation

If the present dark matter in the Universe annihilates into Standard Model particles, it must contribute to the fluxes of cosmic rays that are detected on the Earth, and in particular, to the observed gamma ray fluxes. The magnitude of such contribution depends on the particular dark matter candidate, but certain features of the produced photon spectra may be analyzed in a rather model-independent fashion. In this work we provide the complete photon spectra coming from WIMP annihilation into Standard Model particle-antiparticle pairs obtained by extensive Monte Carlo simulations. We present results for each individual annihilation channel and provide analytical fitting formulae for the different spectra for a wide range of WIMP masses.

hep-ph↗

arXiv2009

Black Holes in f(R) theories

In the context of $f(R)$ theories of gravity, we address the problem of finding static and spherically symmetric black hole solutions. Several aspects of constant curvature solutions with and without electric charge are discussed. We also study the general case (without imposing constant curvature). Following a perturbative approach around the Einstein-Hilbert action, it is found that only solutions of the Schwarzschild-(anti) de Sitter type are present up to second order in perturbations. Explicit expressions for the effective cosmological constant are obtained in terms of the $f(R)$ function. Finally, we have considered the thermodynamics of black holes in anti-de Sitter space-time and found that this kind of solutions can only exist provided the theory satisfies $R_0+f(R_0)<0$. Interestingly, this expression is related to the condition which guarantees the positivity of the effective Newton's constant in this type of theories. In addition, it also ensures that the thermodynamical properties in $f(R)$ gravities are qualitatively similar to those of standard General Relativity.

gr-qc↗

arXiv2009

Comment on "Viable singularity-free f(R) gravity without a cosmological constant" [arXiv:0905.1941]

A modified f(R) gravity model has been recently proposed in Phys. Rev. Lett. 102, 221101 (2009) [arXiv:0905.1941] whose cosmological behaviour is clearly distinguishable from LCDM. Contrary to previous opinions which consider that self-consistent f(R) gravity models distinct from LCDM are almost ruled out, the authors claim that the proposed model is cosmologically viable. Here we show that although the model satisfies some consistency conditions, precisely because of its departure from LCDM behaviour, it does not satisfy local gravity constraints and, in addition, the predicted matter power spectrum conflicts with SDSS data.

astro-ph.CO↗

arXiv2008

Cosmological density perturbations in modified gravity theories

In the context of f(R) theories of gravity, we study the cosmological evolution of scalar perturbations by using a completely general procedure. We find that the exact fourth-order differential equation for the matter density perturbations in the longitudinal gauge, reduces to a second-order equation for sub-Hubble modes. This simplification is compared with the standard (quasi-static) equation used in the literature. We show that for general f(R) functions the quasi-static approximation is not justified. However for those f(R) adequately describing the present phase of accelerated expansion and satisfying local gravity tests, it does give a correct description for the evolution of perturbations.

astro-ph↗

arXiv2008

Is the CMB cold spot a gate to extra dimensions?

One of the most striking features found in the cosmic microwave background data is the presence of an anomalous Cold Spot (CS) in the temperature maps made by the Wilkinson Microwave Anisotropy Probe (WMAP). This CS has been interpreted as the result of the presence of a collapsing texture, perhaps coming from some early universe Grand Unified Theory (GUT) phase transition. In this work we propose an alternative explanation based on a completely different kind of texture which appears in a natural way in a broad class of brane-world models. This type of textures known as brane-skyrmions can be understood as holes in the brane which make possible to pass through them along the extra-dimensional space. The typical scales needed for the proposed brane-skyrmions to correctly describe the observed CS can be as low as the electroweak scale.

astro-ph↗

arXiv2008

On the evolution of density perturbations in f(R) theories of gravity

In the context of $f(R)$ theories of gravity, we study the evolution of scalar cosmological perturbations in the metric formalism. Using a completely general procedure, we find the exact fourth-order differential equation for the matter density perturbations in the longitudinal gauge. In the case of sub-Hubble modes, the expression reduces to a second-order equation which is compared with the standard (quasi-static) equation used in the literature. We show that for general $f(R)$ functions the quasi-static approximation is not justified. However, for those functions adequately describing the present phase of accelerated expansion and satisfying local gravity tests, it provides a correct description for the evolution of perturbations.

astro-ph↗

arXiv2006

Catching photons from extra dimensions

In extra-dimensional brane-world models with low tension, brane excitations provide a natural WIMP candidate for dark matter. Taking into account the various constraints coming from colliders, precision observables and direct search, we explore the possibilities for indirect search of the galactic halo branons through their photon producing annihilations in experiments such as EGRET, HESS or AMS2.

astro-ph↗

arXiv2006

Some model-independent phenomenological consequences of flexible brane worlds

In this work we will review the main properties of brane-world models with low tension. Starting from very general principles, it is possible to obtain an effective action for the relevant degrees of freedom at low energies (branons). Using the cross sections for high-energy processes involving branons, we set bounds on the different parameters appearing in these models. We also show that branons provide a WIMP candidate for dark matter in a natural way. We consider cosmological constraints on its thermal and non-thermal relic abundances. We derive direct detection limits and compare those limits with the preferred parameter region in the case in which the EGRET excess in the diffuse galactic gamma rays is due to dark matter annihilation. Finally we will discuss the constraints coming from the precision tests of the Standard Model and the muon anomalous magnetic moment.

hep-ph↗