arXiv subjects

Jorge de Blas

Publications and source records attributed to Jorge de Blas.

33 records · Page 2Linked to original sources

arXiv2021

$B$ anomalies under the lens of electroweak precision

The measurements carried out at LEP and SLC projected us into the precision era of electroweak physics. This has also been relevant in the theoretical interpretation of LHCb and Belle measurements of rare $B$ semileptonic decays, paving the road for new physics with the inference of lepton universality violation in $R_{K^{(*)}}$ ratios. The simplest explanation of these flavour anomalies -- sizeable one-loop contributions respecting Minimal Flavour Violation -- is currently disfavoured by electroweak precision data. In this work, we discuss how to completely relieve the present tension between electroweak constraints and one-loop minimal flavour violating solutions to $R_{K^{(*)}}$. We determine the correlations in the Standard Model Effective Field Theory that highlight the existence of such a possibility. Then, we consider minimal extensions of the Standard Model where our effective-field-theory picture can be realized. We discuss how these solutions to $b \to s \ell \ell$ anomalies, respecting electroweak precision and without any new source of flavour violation, may point to the existence of a $Z^{\prime}$ boson at around the TeV scale, within the discovery potential of LHC, or to leptoquark scenarios.

hep-ph↗

arXiv2020

On the future of Higgs, electroweak and diboson measurements at lepton colliders

LEP precision on electroweak measurements was sufficient not to hamper the extraction of Higgs couplings at the LHC. But the foreseen permille-level Higgs measurements at future lepton colliders might suffer from parametric electroweak uncertainties in the absence of a dedicated electroweak program. We perform a joint, complete and consistent effective-field-theory analysis of Higgs and electroweak processes. The full electroweak-sector dependence of the $e^+e^- \to WW$ production process is notably accounted for, using statistically optimal observables. Up-to-date HL-LHC projections are combined with CEPC, FCC-ee, ILC and CLIC ones. For circular colliders, our results demonstrate the importance of a new $Z$-pole program for the robust extraction of Higgs couplings. At linear colliders, we show how exploiting multiple polarizations and centre-of-mass energies is crucial to mitigate contaminations from electroweak parameter uncertainties on the Higgs physics program. We also investigate the potential of alternative electroweak measurements to compensate for the lack of direct $Z$-pole run, considering for instance radiative return to these energies. Conversely, we find that Higgs measurements at linear colliders could improve our knowledge of the $Z$ couplings to electrons.

hep-ph↗

arXiv2020

CLIC Higgs coupling prospects with a longer first energy stage

One of the most attractive features of a linear collider is the ability to extend its energy reach in stages, and to adapt the running plan flexibly in terms of maximum centre-of-mass energy and time spent at each stage. The baseline luminosity staging scenario for CLIC is well-established, and has been used to obtain sensitivity projections for Standard Model measurements and Beyond Standard Model scenarios. Here, as an exercise to illustrate what could be obtained from an alternative running scenario, Higgs coupling sensitivities are presented for the case where more data is collected at the initial stage $\sqrt{s}=380$ GeV, before proceeding to the higher energy stages of $\sqrt{s}=1.5$ and 3 TeV. This could be achieved through running for longer, or operating the collider at an increased repetition rate of 100 Hz at the initial stage, or a combination of both.

hep-ex↗

arXiv2019

Proposal for the validation of Monte Carlo implementations of the standard model effective field theory

We propose a procedure to cross-validate Monte Carlo implementations of the standard model effective field theory. It is based on the numerical comparison of squared amplitudes computed at specific phase-space and parameter points in pairs of implementations. Interactions are fully linearised in the effective field theory expansion. The squares of linear effective field theory amplitudes and their interference with standard-model contributions are compared separately. Such pairwise comparisons are primarily performed at tree level and a possible extension to the one-loop level is also briefly considered. We list the current standard model effective field theory implementations and the comparisons performed to date.

hep-ph↗

arXiv2018

Current and future constraints on Higgs couplings in the nonlinear Effective Theory

We perform a Bayesian statistical analysis of the constraints on the nonlinear Effective Theory given by the Higgs electroweak chiral Lagrangian. We obtain bounds on the effective coefficients entering in Higgs observables at the leading order, using all available Higgs-boson signal strengths from the LHC runs 1 and 2. Using a prior dependence study of the solutions, we discuss the results within the context of natural-sized Wilson coefficients. We further study the expected sensitivities to the different Wilson coefficients at various possible future colliders. Finally, we interpret our results in terms of some minimal composite Higgs models.

hep-ph↗

arXiv2017

The Global Electroweak and Higgs Fits in the LHC era

We update the global fit to electroweak precision observables, including the effect of the latest measurements at hadron colliders of the $W$ and top-quark masses and the effective leptonic weak mixing angle. We comment on the impact of these measurements in terms of constraints on new physics. We also update the bounds derived from the fit to the Higgs-boson signal strengths, including the observables measured at the LHC Run 2, and compare the improvements with respect to the 7 and 8 TeV results.

hep-ph↗

arXiv2017

Electroweak precision constraints at present and future colliders

We revisit the global fit to electroweak precision observables in the Standard Model and present model-independent bounds on several general new physics scenarios. We present a projection of the fit based on the expected experimental improvements at future $e^+ e^-$ colliders, and compare the constraining power of some of the different experiments that have been proposed. All results have been obtained with the HEPfit code.

hep-ph↗

arXiv2016

New vector bosons and the diphoton excess

We consider the possibility that the recently observed diphoton excess at $\sim 750$ GeV can be explained by the decay of a scalar particle ($φ$) to photons. If the scalar is the remnant of a symmetry-breaking sector of some new gauge symmetry, its coupling to photons can be generated by loops of the charged massive vectors of the broken symmetry. If these new $W^\prime$ vector bosons carry color, they can also generate an effective coupling to gluons. In this case the diphoton excess could be entirely explained in a simplified model containing just $φ$ and $W^\prime$. On the other hand if $W^{\prime}$ does not carry color, we show that, provided additional colored particles exist to generate the required $φ$ to gluon coupling, the diphoton excess could be explained by the same $W^{\prime}$ commonly invoked to explain the diboson excess at $\sim 2$ TeV. We also explore possible connections between the diphoton and diboson excesses with the anomalous $t\bar{t}$ forward-backward asymmetry.

hep-ph↗

arXiv2015

Renormalization Group Constraints on New Top Interactions from Electroweak Precision Data

Anomalous interactions involving the top quark contribute to some of the most difficult observables to directly access experimentally. They can give however a sizeable correction to very precisely measured observables at the loop level. Using a model-independent effective Lagrangian approach, we present the leading indirect constraints on dimension-six effective operators involving the top quark from electroweak precision data. They represent the most stringent constraints on these interactions, some of which may be directly testable in future colliders.

hep-ph↗

arXiv2015

Observable Effects of General New Scalar Particles

We classify all possible new scalar particles that can have renormalizable linear couplings to Standard Model fields and therefore be singly produced at colliders. We show that this classification exhausts the list of heavy scalar particles that contribute at the tree level to the Standard Model effective Lagrangian to dimension six. We compute this effective Lagrangian for a general scenario with an arbitrary number of new scalar particles and obtain flavor-preserving constraints on their couplings and masses. This completes the tree-level matching of the coefficients of dimension five and six operators in the effective Lagrangian to arbitrary extensions of the Standard Model.

hep-ph↗

arXiv2015

Global Bayesian Analysis of the Higgs-boson Couplings

We present preliminary results of a bayesian fit to the Wilson coefficients of the Standard Model gauge invariant dimension-6 operators involving one or more Higgs fields, using data on electroweak precision observables and Higgs boson signal strengths.

hep-ph↗

arXiv2012

LHC Signals of Non-Custodial Warped 5D Models

We study the implications at the LHC for a recent class of non-custodial warped extra-dimensional models where the AdS_5 metric is modified near the infrared brane. Such models allow for TeV Kaluza-Klein excitations without conflict with electroweak precision tests. We discuss both the production of electroweak and strong Kaluza-Klein gauge bosons. As we will show, only signals involving the third generation of quarks seem to be feasible in order to probe this scenario.

hep-ph↗

arXiv2010

New neutrino interactions at large colliders

We update present bounds on the helicity of the neutrinos produced in muon decay, including e+ e- -> fbar f LEP 2 data. These significantly reduce the limits derived from all the other electroweak precision data. In Standard Model extensions designed to maximize the RH neutrino production in such a decay the neutrino deficit eventually observable in a near detector at a neutrino factory can be of the order of 5 %. Motivated by the current LHC run at 7 TeV, we also update previous work providing discovery limits on see-saw mediators at this centre of mass energy. Lepton triplets with 200 GeV could be discovered with luminosities of 1 - 1.5 fb^-1. Scalar triplets of the same mass might be seen with 0.75 - 3 fb^-1. What makes their search also attractive in the first LHC analyses.

hep-ph↗

arXiv2010

Combining Anomaly and Z' Mediation of Supersymmetry Breaking

We propose a scenario in which the supersymmetry breaking effect mediated by an additional U(1)' is comparable with that of anomaly mediation. We argue that such a scenario can be naturally realized in a large class of models. Combining anomaly with Z' mediation allows us to solve the tachyonic slepton problem of the former and avoid significant fine tuning in the latter. We focus on an NMSSM-like scenario where U(1)' gauge invariance is used to forbid a tree-level mu term, and present concrete models, which admit successful dynamical electroweak symmetry breaking. Gaugino masses are somewhat lighter than the scalar masses, and the third generation squarks are lighter than the first two. In the specific class of models under consideration, the gluino is light since it only receives a contribution from 2-loop anomaly mediation, and it decays dominantly into third generation quarks. Gluino production leads to distinct LHC signals and prospects of early discovery. In addition, there is a relatively light Z', with mass in the range of several TeV. Discovering and studying its properties can reveal important clues about the underlying model.

hep-ph↗

arXiv2006

Tools for Deconstructing Gauge Theories in AdS5

We employ analytical methods to study deconstruction of 5D gauge theories in the AdS5 background. We demonstrate that using the so-called q-Bessel functions allows a quantitative analysis of the deconstructed setup. Our study clarifies the relation of deconstruction with 5D warped theories.

hep-th↗