arXiv subjects

Abdelhak Djouadi

Publications and source records attributed to Abdelhak Djouadi.

At least 19 recordsLinked to original sources

arXiv2026

A possible interpretation of the LUX-ZEPLIN recoil event in the 2HD+a scenario

It is tantalizing to consider the recent observation of the LUX-ZEPLIN (LZ) experiment of a high energy nuclear recoil candidate at $E_{\rm Recoil} \simeq 248$ keV as the long-awaited signal of a weakly interacting massive Dark Matter (DM) particle. Although this signal is still weak and needs to be confirmed by further data and inspection, we attempt to interpret it in the context of the 2HD+a model in which a two-Higgs doublet model (2HDM) is supplemented by a light pseudoscalar Higgs boson $a$ and an isosinglet fermionic DM particle $χ$. The model has the virtue of reproducing the correct cosmological density and evading the previous limits from direct and indirect detection of DM particles, while passing all constraints from colliders searches and high-precision measurements in the Higgs, electroweak boson and heavy-flavor sectors. We indeed find regions of the parameter space of the model, with a rather heavy 2HDM spectrum but a very light pseudoscalar $a$ boson, $m_a \approx 1-10$ GeV, as well as a DM fermion with a mass of a few hundred GeV, which are compatible with the LZ recoil event. The related extensive investigation of the parameter space of the 2HD+a model with fermionic DM, including the wide range of complementary constraints from both DM phenomenology and collider searches as well as precision measurements are presented.

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arXiv2026

Charting Dark Matter down to the neutrino floor/fog in the 2HD+a scenario

Next-generation direct detection experiments will probe dark matter (DM) scattering cross-sections deep into the neutrino fog, the regime where coherent neutrino scattering becomes an irreducible background. We investigate whether thermally produced weakly interacting massive particles (WIMPs) can naturally populate this regime while satisfying relic density and indirect detection constraints. Adopting as a case study the 2HD+a model, we have performed comprehensive parameter scans over the Type-I and Type-II Yukawa configurations. We have included the limit of strongly suppressed singlet--doublet {\it A-a} mixing sin$θ\! \to \! 0$ and we show that annihilation into {\it ha} and ${\it Ha}$ final states sustains the correct relic density while loop-induced direct detection cross-sections naturally land inside the neutrino fog; in the same limit the light pseudoscalar boson becomes long-lived, featuring displaced-vertex signatures when produced at colliders. Finally, in the case of zero mixing, we have considered a new possibility for DM phenomenology as the $a$ state becomes cosmologically stable and, consequently, an additional DM component. We map all the viable parameter space against current LZ and FERMI-LAT bounds and projected XLZD and CTA sensitivities. We find that the single component setup lies naturally below the neutrino floor for DM masses above 100 GeV while, on the contrary, most of the parameter space of the two component DM scenario is strongly disfavored already considering present limit. The parameter space of both single and two component DM scenario can be nevertheless broadened by considering specific relations among the model parameters to suppress the coupling between the 125 GeV bosons and two $a$ states. Our results represent in any case a motivation to fully exploit future tonne-scale detectors.

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arXiv2025

Interpreting the current Higgs excesses at the LHC in the 2HD+a framework

There are several excesses of events in current LHC data, yet not exceeding the level of significance which would make them to be considered as firm. They point to the possibility of the presence of a new Higgs particle in the spectrum, in addition to the already observed 125 GeV state. In particular, there are excesses involving a diphoton resonance at invariant masses of about 95 GeV, 152 GeV and 650 GeV and an extra scalar might accompany the recent observation of a toponium at a mass of about 350 GeV. Several interpretations of these excesses have been attempted in extensions of the Standard Model. In this paper, we aim to explain them in the framework of a two Higgs doublet model supplemented by a relatively light pseudoscalar Higgs boson $a$ which would correspond to the putative resonance in most cases. This realistic 2HD+a scenario is attractive as it is has the virtue to pass all experimental constraints from high-precision experiments and collider searches and, at the same time, to allow for a viable explanation of the dark matter in the universe. We first update the present constraints on the model, in particular taking into account the latest results on dark matter and Higgs searches, as well the high-precision measurements, including those from Higgs and flavor physics. We then show that the additional Higgs states with the proper mass spectrum and adjusted couplings to fermions, would explain all the LHC excesses (but individually) while passing the former experimental constraints as well as the theoretical ones.

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arXiv2025

Contrasting Pseudoscalar Higgs and Toponium States at the LHC and Beyond

We discuss ways to discriminate at hadron colliders between a quasi-bound toponium state and a pseudoscalar Higgs boson A, as predicted in many extensions of the Standard Model. We apply the discussion to the excess of t tbar threshold events recently observed at the LHC by the CMS collaboration \cite{CMS}, which could in principle be due to either possibility. Working in an effective theory in which only an additional pseudoscalar A boson is present in the spectrum, with a mass above the 2 m_t threshold and a significant coupling to top quarks, we discuss the interference between A production in the dominant gluon-fusion process gg \to A with subsequent A\to t tbar decays, and the QCD continuum background, gg\to t tbar. While this interference is absent in the case of toponium, it is essential for evaluating A production. It is difficult to resolve the peak/dip structure that it generates because of the experimental smearing of the t tbar invariant mass spectrum. However, by comparing the total A production rates for different integration domains of the t tbar invariant mass or, eventually, at different center of mass energies, one may be able to observe its effects. We then discuss additional mechanisms for A production in pp collisions, including loop-induced production in association with the lighter h boson, gg \to hA, and production in association with top-quark pairs, gg/q\bar q \to t tbar. A These mechanisms have small cross sections at the LHC, and their observation will necessitate higher luminosities or collider energies.

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arXiv2025

A complete effective field theory for dark matter

We present an effective field theory describing the relevant interactions of the Standard Model with an electrically neutral particle that can account for the dark matter in the Universe. The possible mediators of these interactions are assumed to be heavy. The dark matter candidates that we consider have spin 0, 1/2 or 1, belong to an electroweak multiplet with arbitrary isospin and hypercharge and their stability at cosmological scales is guaranteed by imposing a $\mathbb{Z}_2$ symmetry. We present the most general framework for describing the interaction of the dark matter with standard particles, and construct a general non-redundant basis of the gauge-invariant operators up to dimension six. The basis includes multiplets with non-vanishing hypercharge, which can also be viable DM candidates. We give two examples illustrating the phenomenological use of such a general effective framework. First, we consider the case of a scalar singlet, provide convenient semi-analytical expressions for the relevant dark matter observables, use present experimental data to set constraints on the Wilson coefficients of the operators, and show how the interplay of different operators can open new allowed windows in the parameter space of the model. Then we study the case of a lepton isodoublet, which involves co-annihilation processes, and we discuss the impact of the operators on the particle mass splitting and direct detection cross sections. These examples highlight the importance of the contribution of the various non-renormalizable operators, which can even dominate over the gauge interactions in certain cases.

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arXiv2024

Steven Weinberg and Higgs Physics

As a tribute to Steven Weinberg, we summarize the immense impact that he had on the understanding of the mechanism of spontaneous symmetry breaking and on the physics of the Higgs boson. In particular, four landmark contributions to this field are highlighted. A first one is his early work with Goldstone and Salam on spontaneously broken continuous symmetries that paved the way to the Higgs mechanism. A second towering breakthrough is his model of leptons which later became the Standard Model of particle physics and for which he was awarded the Nobel prize with Glashow and Salam. A third seminal work is the so-called Weinberg-Linde lower bound on the Higgs boson mass that was derived from the requirement of the stability of the electroweak vacuum. Finally, we will summarize his important contributions in model-building of new physics with extended Higgs sectors and their possible impact in flavor physics and CP-violation. The historical aspects as well as the contemporary way of viewing these four major topics are summarized and their impact on today Higgs physics, and more generally particle physics, is highlighted.

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arXiv2024

Interference Effects in $\mathbf{gg \to H \to Z γ}$ Beyond Leading Order

The ATLAS and CMS collaborations at the LHC have recently announced evidence for the rare Higgs boson decay into a $Z$ boson and a photon. We analyze the interference between the process $gg\! \to \! H \! \to \! Z γ$ induced by loops of heavy particles, which is by far the dominant contribution to the signal, and the continuum $gg \to Z γ$ QCD background process mediated by light quark loops. This interference modifies the event yield, the resonance line-shape and the apparent mass of the Higgs boson. We calculate the radiative corrections to this interference beyond the leading-order approximation in perturbative QCD and find that, while differing numerically from the corresponding effects on the more studied $gg \! \to \! γγ$ signal, they are generally rather small. As such, they do not impact significantly the interpretation of the present measurements of the $H \to Z γ$ decay mode.

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arXiv2023

Iteration on the Higgs-portal for vector Dark Matter and its effective field theory description

We reanalyze the effective field theory (EFT) approach for the scenario in which the particles that account for the dark matter (DM) in the universe are vector states that interact only through the Standard Model-like Higgs boson. These DM particles are searched for in direct and indirect detection in astrophysical experiments and in invisible Higgs decays at the LHC. The constraints obtained in these two search types are complementary and correlated. In recent years, it has been advocated that the EFT approach is problematic for small DM mass and that it does not capture all the aspects of vector DM; one should thus rather interpret the searches in ultraviolet complete theories that are more realistic. In this note, we show that a more appropriate definition of the EFT with the introduction of an effective New Physics scale parameter, can encompass such issues. We illustrate this by matching the EFT to two examples of ultraviolet completions for it: the U(1) model with a dark photon and a model that was recently adopted by the LHC experiments in which vector-like fermions generate an effective interaction between the Higgs and the DM states at the one-loop level. Additionally, we find that the region of parameter space that is relevant for DM phenomenology is well inside the range of validity of the EFT. It thus provides a general parametrization of the effects of any ultraviolet model in the regime under exploration, making it the ideal framework for model-independent analyses of the vector DM Higgs-portal.

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arXiv2023

SuSpect3: A C++ Code for the Supersymmetric and Higgs Particle Spectrum of the MSSM

We present the program SuSpect3 that calculates the masses and couplings of the Higgs and supersymmetric particles predicted by the Minimal Supersymmetric Standard Model (MSSM). The model is implemented in both its non-constrained version, the MSSM, and its constrained versions, such as the minimal supergravity and the gauge or anomaly mediated supersymmetry breaking models, in which the soft supersymmetry-breaking parameters obey certain universal boundary conditions at the high energy scale. The low energy parameters are then obtained using renormalization group equations and electroweak symmetry breaking, and all the dominant radiative corrections have been consistently implemented. SuSpect3 is a major rewrite, in C++ object oriented programming, of the FORTRAN code SuSpect. It includes all the features of the earlier code in an improved and updated manner, and involves new options such as compressed SUSY scenarios, an MSSM-inflation model and the possibility of using the observed Higgs mass as an input. The main features and the use of the program are explained.

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arXiv2023

The hMSSM with a Light Gaugino/Higgsino Sector: Implications for Collider and Astroparticle Physics

The hMSSM is a special parameterization of the minimal supersymmetric extension of the Standard Model (MSSM) in which the mass of the lightest Higgs boson is automatically set to the LHC measured value, $M_h\!\!=\!\! 125$\,GeV, by adjusting the supersymmetric particle spectrum such that it provides the required amount of radiative corrections to the Higgs boson masses.\ The latter spectrum was in general assumed to be very heavy, as indicated by the present exclusion limits of the LHC, not to affect the phenomenology of the Higgs sector.\ In this work, we investigate the impact on the hMSSM by a light gaugino and higgsino sector, that is allowed by the present LHC data.\ In particular, we discuss the radiative corrections due to charginos and neutralinos to the Higgs boson masses and couplings and show that an hMSSM can still be realized in this context.\ We first describe how this scenario is implemented in the package SuSpect that generates the MSSM Higgs and supersymmetric spectra.\ We then analyze the possible impact of Higgs boson decays into these new states, as well as the reverse cascade channels with Higgs bosons in the final states, for the constraints on the MSSM Higgs sector at the LHC.\ We further explore the cosmological constraints on the hMSSM with a light gaugino--higgsino spectrum.\ We analyze the relic abundance of the lightest neutralino as a candidate of the dark matter in the Universe and the constraints on its mass and couplings by the present and future astroparticle physics experiments.

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arXiv2023

Non-supersymmetric SO(10) models with Gauge and Yukawa coupling unification

We study a non-supersymmetric SO(10) Grand Unification Theory with a very high energy intermediate symmetry breaking scale in which not only gauge but also Yukawa coupling unification are enforced via suitable threshold corrections and matching conditions. For gauge unification, we focus on a few symmetry breaking patterns with the intermediate gauge groups ${\rm SU(4)_C \times SU(2)_L \times SU(2)_R}$ (Pati-Salam) and ${\rm SU(3)_C \times SU(2)_L \times SU(2)_R\times U(1)_{B-L}}$ (minimal left-right symmetry) assuming an additional global U(1) Peccei--Quinn symmetry, and having the Standard Model supplemented by a second Higgs doublet field at the electroweak scale. We derive the conditions as well as the approximate analytical solutions for the unification of the gauge coupling constants at the two-loop level and discuss the constraints from proton decay on the resulting high scale. Specializing to the case of the Pati-Salam intermediate breaking pattern, we then impose also the unification of the Yukawa couplings of third generation fermions at the high scale, again at the two-loop level. In the considered context, Yukawa unification implies a relation between the fermion couplings to the 10- and 126-dimensional scalar representations of the SO(10) group. We consider one such possible relation which is obtainable in an ${\rm E_6}$ model where the previous two scalar fields are part of a single multiplet. Taking into account some phenomenological features such as the absence of flavor changing neutral currents at tree-level, we derive constraints on the parameters of the low energy model, in particular on the ratio of the two Higgs doublets vacuum expectation values $\tanβ$.

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arXiv2023

The 2HD+a model: collider, dark matter and gravitational wave signals

We perform a comprehensive study of a model in which the Higgs sector is extended to contain two Higgs doublet fields, with the four types of possibilities to couple to standard fermions, as well as an additional light pseudoscalar Higgs boson which mixes with the one of the two doublets. This 2HD+a model includes also a stable isosinglet massive fermion that has the correct thermal relic abundance to account for the dark matter in the Universe. We summarize the theoretical constraints to which the model is subject and then perform a detailed study of the phenomenological constraints. In particular, we discuss the bounds from the LHC in the search for light and heavy scalar resonances and invisible states and those from high precision measurements in the Higgs, electroweak and flavor sectors, addressing the possibility of explaining the deviation from the standard expectation of the anomalous magnetic moment of the muon and the $W$-boson mass recently observed at Fermilab. We also summarize the astrophysical constraints from direct and indirect detection dark matter experiments. We finally conduct a thorough analysis of the cosmic phase transitions and the gravitational wave spectrum that are implied by the model and identify the parameter space in which the electroweak vacuum is reached after single and multiple phase transitions. We then discuss the prospects for observing the signal of such gravitational waves in near future experiments such as LISA, BBO or DECIGO.

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arXiv2023

A model for fermionic dark matter addressing both the CDF $\mathbf{M_W}$ and the $\mathbf{(g-2)_μ}$ anomalies

We explore a simple and renormalizable model which incorporates a new stable fermion that accounts for the dark matter in the universe and which, at the same time, provides an interpretation of two recent measurements that deviate from the expectation in the Standard Model: the muon anomalous magnetic moment and the mass of the W-boson recently performed by the CDF collaboration. The model has a fermionic sector that involves a singlet and a doublet fields and in which the lightest state is the DM and interacts mainly through the Higgs portal. Two realizations of such a possibility are considered: one in which the Higgs sector is minimal and another in which it is extended to contain two doublet fields.

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arXiv2022

Yukawa coupling unification in non-supersymmetric SO(10) models with an intermediate scale

We discuss the possibility of unifying in a simple and economical manner the Yukawa couplings of third generation fermions in a non-supersymmetric SO(10) model with an intermediate symmetry breaking, focusing on two possible patterns with intermediate Pati-Salam and minimal left-right groups. assume a minimal Yukawa sector at high energy, starting with two Higgs bi-doublets at the intermediate scale which then simply reduce to a two Higgs doublet model at the electroweak scale. We first enforce gauge coupling unification at the two-loop level by including the threshold corrections in the renormalisation group running which are generated by the heavy fields that appear at the intermediate symmetry breaking scale. We then study the running of the Yukawa couplings of the top quark, bottom quark and tau lepton at two-loops in these two breaking schemes, when the appropriate matching conditions are imposed. We find that the unification of the third family Yukawa couplings can be achieved while retaining a viable spectrum, provided that the ratio of the vacuum expectation values of the two Higgs doublet fields is large, $\tanβ\approx 60$.

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arXiv2022

The 2HD+a model for a combined explanation of the possible excesses in the CDF $\mathbf{M_W}$ measurement and $\mathbf{(g-2)_μ}$ with Dark Matter

The new measurement of the $W$ boson mass performed by the CDF experiment at the Tevatron shows a significant deviation not only with the expectation in the Standard Model but also with other precision measurements performed at LEP, the Tevatron and the LHC. We nevertheless take this new measurement at face value and interpret it as an effect of new physics. We particularly try to link it with other possible anomalies such as the recent muon $g-2$ and consider a scenario that addresses some shortcomings of the Standard Model. We show that a model with two doublets and a light pseudoscalar Higgs fields, supplemented by a stable isosinglet fermion, can simultaneously explain the possible $M_W$ and $(g-2)_μ$ anomalies and accounts for the weakly interacting massive particle that could be responsible of the dark matter in the universe.

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arXiv2021

Models with two Higgs doublets and a light pseudoscalar:a portal to dark matter and the possible $\mathbf{(g-2)_μ}$ excess

In the context of a two-Higgs doublet model, supplemented by an additional light pseudoscalar Higgs boson and a stable isosinglet fermion, we consider the possibility of addressing simultaneously the discrepancy from the standard expectation of the anomalous magnetic moment of the muon recently measured at Fermilab and the longstanding problem of the dark matter in the universe which can be accounted for by a thermal weakly interacting massive particle. We show that it is indeed possible, for a range of masses and couplings of the new light pseudoscalar and the fermionic states, to explain at the same time the two features while satisfying all other constraints from astroparticle physics and collider searches, including the constraints from flavor physics.

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arXiv2021

An effective field theory of the Delta-resonance

We present an effective field theory of the $Δ$-resonance as an interacting Weinberg's $(3/2,0)\oplus (0,3/2)$ field in the multi-spinor formalism. We derive its interactions with nucleons $N$, pions $π$ and photons $γ$, and compute the $Δ$-resonance cross-sections in pion-nucleon scattering and pion photo-production. The theory contains only the physical spin-3/2 degrees of freedom. Thus, it is intrinsically consistent at the Hamiltonian level and, unlike the commonly used Rarita-Schwinger framework, does not require any additional ad hoc manipulation of couplings or propagators. The symmetries of hadronic physics select a unique operator for each coupling $NπΔ$ and $γπΔ$. The proposed framework can be extended to also describe other higher-spin hadronic resonances.

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arXiv2021

Higher-spin particles at high-energy colliders

Using an effective field theory approach for higher-spin fields, we derive the interactions of colour singlet and electrically neutral particles with a spin higher than unity, concentrating on the spin-3/2, spin-2, spin-5/2 and spin-3 cases. We compute the decay rates and production cross sections in the main channels for spin-3/2 and spin-2 states at both electron-positron and hadron colliders, and identify the most promising novel experimental signatures for discovering such particles at the LHC. The discussion is qualitatively extended to the spin-5/2 and spin-3 cases. Higher-spin particles exhibit a rich phenomenology and have signatures that often resemble the ones of supersymmetric and extra-dimensional theories. To enable further studies of higher-spin particles at collider and beyond, we collect the relevant Feynman rules and other technical details.

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