Search

Ara que el LHC ha proporcionat 120 fb-1 de dades, l'evidència d'una diferència d'energia entre el model estàndard (SM) i la nova física ha augmentat. Això fa que la teoria de camps efectiva (EFT) sigui un mètode versàtil per restringir la nova física amb una dependència mínima del model. En aquesta tesi, basada en el meu treball realitzat durant la meva candidatura a doctorat [1-4], fem ús de la tècnica EFT en diversos estudis. Comencem per estudiar l'extracció de acoblament trilineal del Higgs en els col·lisionadors actuals i futurs de leptons, utilitzant correccions de següent ordre en la producció de Higgs i producció de Higgs doble. Els nostres anàlisis minimitzen la dependència del model gràcies a l'ús de l'EFT. Argumentem que per restringir les diferents possibles desviacions al Model Estàndard, un ajust global amb la inclusió de tants observables com sigui possible és necessari. Hem trobat que la inclusió del trilineal en els processos únics d'Higgs tindrà un efecte marginal a LHC aconseguint una precisió d'ordre ú. La situació és diferent els futurs col·lisionadors de leptons, on l'alta precisió i la diferent energia de centre de masses poden donar el 50% de precisió. A continuació, ampliem l'EFT afegint un singlet escalar per estudiar les propietats del CP de la partícula que podria haver estat amagada després de l'infame excés de di-fotons a 750 GeV. Definim les asimetries sensibles al CP, tant en els canals de fusió de vectors com gluons, i estudiem el seu poder de diferenciar entre el CP imparell o fins i tot les hipòtesis. Finalment, ens movem de l'EFT i considerem un model simplificat de Higgs compost per comparar les mesures a baixa energia procedents de la mesura del dipol elèctric (EDM) de neutrons i electrons, amb les cerques al LHC. La teoria de camps efectiva no està completament absent, ja que calculem les correccions de dos loops al EDM de quarks i leptons lleugers que coincideixen amb el nostre model simplificat per als operadors de dimensions superiors i obtenim límits per al nostre model. A continuació, adaptem les cerques de l'LHC i comparem els límits actuals i futurs Hem trobat que el límit actual és competitiu amb el que proveeix la cerca directa de LHC, que és d'uns quants TeV. La futura actualització de l'experiment que permetrà mesurar el moment dipolar d'electrons ha de portar els límits al rang de 5-10 TeV., Now the LHC has provided 120 fb−1 of data, the evidence for an energy gap between the Standard Model (SM) and new physics has grown strong. This makes effective field the- ory (EFT) a versatile method to constrain new physics with minimal model dependence. In this thesis, based on work done during my PhD candidature [1–4], we make use of EFT techniques in a variety of studies. We start by exploring the prospect of extracting the Higgs trilinear self-coupling at current hadron and future lepton colliders, using both higher order corrections to the single-Higgs process and di-Higgs production. Our anal- ysis minimizes model dependence thanks to the use of EFT. We argue that in order to constrain the different possible deviations to the Standard Model, a global fit with the inclusion of as many observables as possible is needed. We found that the inclusion of the trilinear correction in single-Higgs processes has a marginal effect at the LHC and will give a bound on the trilinear of order one. The situation is different at lepton col- liders, where the high precision and different running energies can give bound of order 50%. We then extend our EFT by adding a scalar singlet to study the CP properties of the particle which could have been behind the infamous 750 GeV di-photon excess. We define the CP sensitive asymmetries, in both the vector and gluon fusion channels, and study their power to differentiate between the CP odd or even hypotheses. Finally, we move somewhat away from EFT, and use a simplified model to compare the constraints on composite Higgs models coming from low energy neutron and electron electric dipole moment (EDM) measurements and LHC searches. Effective field theory is not completely absent, since we compute the two loop corrections of the light quarks and leptons EDM to match our simplified model to the higher dimensional operators of a low energy effective Lagrangian, and obtain bounds for our model. We then recast LHC searches and compare the present and future bounds. We found that the current bounds are competitive with the one coming from the LHC direct search and are of order a few TeV. The future upgrade of the experiment measuring the electron dipole moment should bring the bounds to the 5-10 TeV range.

Journal of high energy physics 1806(06), 056 (2018). doi:10.1007/JHEP06(2018)056, We investigate CP-violating effects induced by light top partners in composite Higgs theories. We find that sizable contributions to the dipole moments of the light SM quarks and leptons are generically generated at the two-loop level through Barr-Zee-type diagrams. The present constraints on the electron and neutron electric dipole moments translate into bounds on top partner masses of order few TeV and are competitive with the reach of LHC direct searches. Interestingly, we find that CP-violation effects are sensitive to the same operators that control top partner single production. Near-future improvements in the determination of the electron dipole moment will extend the reach on top partner masses beyond the 5 - 10 TeV range., Published by Springer, Berlin

Journal of high energy physics 1709(09), 069 (2017). doi:10.1007/JHEP09(2017)069, The Higgs self-coupling is notoriously intangible at the LHC. It was recently proposed to probe the trilinear Higgs interaction through its radiative corrections to single-Higgs processes. This approach however requires to disentangle these effects from those associated to deviations of other Higgs-couplings to fermions and gauge bosons. We show that a global fit exploiting only single-Higgs inclusive data suffers from degeneracies that prevent one from extracting robust bounds on each individual coupling. We show how the inclusion of double-Higgs production via gluon fusion, and the use of differential measurements in the associated single-Higgs production channels WH, ZH and ttH, can help to overcome the deficiencies of a global Higgs-couplings fit. In particular, we bound the variations of the Higgs trilinear self-coupling relative to its SM value to the interval [0.1, 2.3] at 68% confidence level at the high-luminosity LHC, and we discuss the robustness of our results against various assumptions on the experimental uncertainties and the underlying new physics dynamics. We also study how to obtain a parametrically enhanced deviation of the Higgs self-couplings and we estimate how large this deviation can be in a self-consistent effective field theory framework., Published by Springer, Berlin

We perform a global effective-field-theory analysis to assess the precision on the determination of the Higgs trilinear self-coupling at future lepton colliders. Two main scenarios are considered, depending on whether the center-of-mass energy of the colliders is sufficient or not to access Higgs pair production processes. Low-energy machines allow for ~40% precision on the extraction of the Higgs trilinear coupling through the exploitation of next-to-leading-order effects in single Higgs measurements, provided that runs at both 240/250 GeV and 350 GeV are available with luminosities in the few attobarns range. A global fit, including possible deviations in other SM couplings, is essential in this case to obtain a robust determination of the Higgs self-coupling. High-energy machines can easily achieve a ~20% precision through Higgs pair production processes. In this case, the impact of additional coupling modifications is milder, although not completely negligible.

Journal of high energy physics 2018(2), 178 (2018). doi:10.1007/JHEP02(2018)178, We perform a global effective-field-theory analysis to assess the precision on the determination of the Higgs trilinear self-coupling at future lepton colliders. Two main scenarios are considered, depending on whether the center-of-mass energy of the colliders is sufficient or not to access Higgs pair production processes. Low-energy machines allow for ∼ 40% precision on the extraction of the Higgs trilinear coupling through the exploitation of next-to-leading-order effects in single Higgs measurements, provided that runs at both 240/250 GeV and 350 GeV are available with luminosities in the few attobarns range. A global fit, including possible deviations in other SM couplings, is essential in this case to obtain a robust determination of the Higgs self-coupling. High-energy machines can easily achieve a ∼ 20% precision through Higgs pair production processes. In this case, the impact of additional coupling modifications is milder, although not completely negligible., Published by Springer, Berlin