arXiv subjects

Gilbert Moultaka

Publications and source records attributed to Gilbert Moultaka.

At least 19 recordsLinked to original sources

arXiv2024

Resonances all over the place?

We provide a possible interpretation of excesses reported by ATLAS and CMS at around 95GeV, 650GeV and possibly 320GeV, in terms of CP-even scalars. In particular, the combined {\sl global} statistical significances of independent indications for a 650GeV object reach the $4\sigma$ level! While this seems sufficient incentive for a further investigation, this object cannot be fitted in tradional singlet or doublet extensions of the Standard Model. It requires by itself a larger extension with doubly-charged scalars, that naturally fits the two other excesses on top of the SM-like 125~GeV Higgs. We describe the minimal model and give some numerical illustrations.

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arXiv2024

Scalar sector of Type 2 Seesaw model explorations with multi-lepton final states

Originally motivated for the generation of (Majorana) neutrino masses, the Type 2 Seesaw Model has also a rich extended Higgs sector with, if accessible at the LHC, a distinctive phenomenology of neutral, charged and doubly-charged states. The goal of the work is to present an exhaustive phenomenological study of the most promising production and decay channels of pair or associated scalars, decaying directly or in cascades to Standard Model particles at the LHC. The study is complementary to the literature in that it highlights a previously unnoticed important sensitivity to a mixing angle. The ensuing uncertainty calls for a comprehensive experimental search strategy for the various processes. These processes can be studied within LHC energies reach, by comparing cutflow results for different final states. We carried out prospective search analyses with multi-lepton, jets and missing energy configurations, assuming an ATLAS-like detector at LHC and HL-LHC, for charged, doubly-charged, and for the first time neutral scalar productions. The work is a collaboration between ATLAS experimentalists and theoreticians in continuation of an endeavor that lead to previous published ATLAS analyses for the search of (doubly)charged Higgs bosons, aiming at proposals for future experimental searches.

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arXiv2024

Indications for new scalar resonances at the LHC and a possible interpretation

Over the last few years, the CMS and ATLAS collaborations at the Large Hadron Collider (LHC) have reported excesses that could hint at several new scalar resonances. Although none of them has touched the discovery level, at least two of them, at about 95 GeV and 650 GeV, have been indicated by more than one experiments, and have reached statistical significance worthy of a serious investigation. Conservatively using only the numbers given by the experimental collaborations, we find combined global significances around 3$\sigma$ and 4$\sigma$ respectively for the 95~GeV and 650~GeV putative resonances. There are some more, like the one at 320 GeV, which have also been hinted at. We show that the data on only the 650 GeV resonance, assuming they stand the test of time, predict the existence of a doubly-charged scalar, and make the more common extensions of the scalar sector like those by gauge singlet scalars, the 2-Higgs doublet models or the Georgi-Machacek model, highly disfavored. We provide the readers with a minimalistic model that may possibly explain all the indications. Such a model can also accommodate the hints of a singly charged scalar at about 375 GeV, and a doubly charged scalar at about 450 GeV, as found by both the major LHC Collaborations, the combined global significance for each of them being above $2.5\sigma$. We show that even the scant data, with large error bars, have the potential to strongly constrain our model containing four scalar multiplets, which makes the model easily testable and falsifiable. Our analysis comes with the obvious caveat that the allowed parameter space that we find depends on the available data on all the new resonances, and may change in future. One may also note that this is an exploratory exercise that illustrates the difficulties when it comes to fitting several resonances simultaneously, even for next-to-minimal extensions of the SM.

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arXiv2024

Type-II Seesaw Higgs triplet productions and decays at the LHC

The Type-II Seesaw Model provides an attractive scenario to account for Majorana-neutrino masses. Its extended Higgs sector, if sufficiently light, can have a rich and distinctive phenomenology at the LHC while yielding automatically an essentially Standard-Model-Higgs-like state. Several phenomenological studies have been devoted to the scalar sector of this model, as well as experimental searches focusing mostly on the (doubly-)charged states. In this paper we present an exhaustive study of the main production and decay channels of all the non-standard scalar states originating from the $SU(2)_L$ doublet and a complex triplet of the model. We stick to scenarios where lepton-number-violating decays are suppressed, for which present experimental limits are still weak, highlighting theoretical parameter sensitivities that were not previously emphasized in the literature and the uncertainties they can induce for the experimental searches at the LHC. A comprehensive classification of the various cascade decays and corresponding Standard Model particle multiplicities is provided. As an illustration, a detailed prospective search study at the LHC with an ATLAS-like detector is carried out on some benchmark points, for charged, doubly-charged, and, for the first time, neutral state productions

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arXiv2023

MSSM-inflation revisited: Towards a coherent description of high-energy physics and cosmology

The aim of this paper is to highlight the challenges and potential gains surrounding a coherent description of physics from the high-energy scales of inflation down to the lower energy scales probed in particle-physics experiments. As an example, we revisit the way inflation can be realised within an effective Minimal Supersymmetric Standard Model (eMSSM), in which the $LLe$ and $udd$ flat directions are lifted by the combined effect of soft-supersymmetric-breaking masses already present in the MSSM, together with the addition of effective non-renormalizable operators. We clarify some features of the model and address the question of the one-loop Renormalization Group improvement of the inflationary potential, discussing its impact on the fine-tuning of the model. We also compare the parameter space that is compatible with current observations (in particular the amplitude, $A_{\scriptscriptstyle{\mathrm{S}}}$, and the spectral index, $n_{\scriptscriptstyle{\mathrm{S}}}$, of the primordial cosmological fluctuations) at tree level and at one loop, and discuss the role of reheating. Finally we perform combined fits of particle and cosmological observables (mainly $A_{\scriptscriptstyle{\mathrm{S}}}$, $n_{\scriptscriptstyle{\mathrm{S}}}$, the Higgs mass, and the cold-dark-matter energy density) with the one-loop inflationary potential applied to some examples of dark-matter annihilation channels (Higgs-funnel, Higgsinos and A-funnel), and discuss the status of the ensuing MSSM spectra with respect to the LHC searches.

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arXiv2022

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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arXiv2022

The Higgs Boson Mass as Fundamental Parameter of the Minimal Supersymmetric Standard Model

In the Minimal Supersymmetric Standard Model (MSSM) the mass of the lightest neutral Higgs boson is determined by the supersymmetric parameters. In the $m_h$MSSM the precisely measured Higgs boson replaces the trilinear coupling $A_t$ as input parameter. Expressions are derived to extract $A_t$ in a semi-analytical form as a function of the light Higgs boson (pole) mass. An algorithm is developed and implemented at two--loop precision, generalizable to higher orders, to perform this inversion consistently. The result of the algorithm, implemented in the SuSpect spectrum calculator, is illustrated on a parameter set compatible with LHC measurements.

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arXiv2020

Vacuum Stability Conditions for Higgs Potentials with $SU(2)_L$ Triplets

Tree-level dynamical stability of scalar field potentials in renormalizable theories can in principle be expressed in terms of positivity conditions on quartic polynomial structures. However, these conditions cannot always be cast in a fully analytical resolved form, involving only the couplings and being valid for all field directions. In this paper we consider such forms in three physically motivated models involving $SU(2)$ triplet scalar fields: the Type-II seesaw model, the Georgi-Machacek model, and a generalized two-triplet model. A detailed analysis of the latter model allows to establish the full set of necessary and sufficient boundedness from below conditions. These can serve as a guide, together with unitarity and vacuum structure constraints, for consistent phenomenological (tree-level) studies. They also provide a seed for improved loop-level conditions, and encompass in particular the leading ones for the more specific Georgi-Machacek case. Incidentally, we present complete proofs of various properties and also derive general positivity conditions on quartic polynomials that are equivalent but much simpler than the ones used in the literature.

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arXiv2017

Stashing the stops in multijet events at the LHC

While the presence of a light stop is increasingly disfavored by the experimental limits set on R-parity conserving scenarios, the naturalness of supersymmetry could still be safely concealed in the more challenging final states predicted by the existence of non-null R-parity violating couplings. Although R-parity violating signatures are extensively looked for at the Large Hadron Collider, these searches always assume 100\% branching ratios for the direct decays of supersymmetric particles into Standard Model ones. In this paper we scrutinize the implications of relaxing this assumption by focusing on one motivated scenario where the lightest stop is heavier than a chargino and a neutralino. Considering a class of R-parity baryon number violating couplings, we show on general grounds that while the direct decay of the stop into Standard Model particles is dominant for large values of these couplings, smaller values give rise, instead, to the dominance of a plethora of longer decay chains and richer final states that have not yet been analyzed at the LHC, thus weakening the impact of the present experimental stop mass limits. We characterize the case for R-parity baryon number violating couplings in the $10^{-7} - 10^{-1}$ range, in two different benchmark points scenarios within the model-independent setting of the low-energy phenomenological Minimal Supersymmetric Standard Model. We identify the different relevant experimental signatures, estimate the corresponding proton--proton cross sections at $\sqrt{s}=14$ TeV and discuss signal versus background issues.

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arXiv2016

Low Energy Supergravity Revisited (I)

General forms of the K\"ahler and superpotenials that lead to consistent low energy broken Supersymmetry originating from $N=1$ Supergravity have been classified and used for model building since more than three decades. We point out the incompleteness of this classification when hidden sector vacuum expectation values are of the order of the Planck mass. Focusing in this paper mainly on the case of minimal K\"ahler potential, we adopt a rigorous approach that retrieves on the one hand the known forms, and demonstrate on the other hand the existence of a whole set of new forms for the superpotential of which we give a complete classification. The latter forms involve a new type of chiral superfields having the unusual property of belonging neither to the hidden sector nor to the conventional observable sector. Comparing the obtained forms with the conventional ones, we argue how new possibilities for model building can arise, and discuss the gravity mediation of soft as well as additional hard (but parametrically small) Supersymmetry breaking, in the presence of the new type of chiral superfields. In the simplest case, we study the vacuum structure, characterize the masses and couplings of the scalar components to the hidden and observable sectors and discuss briefly the physical role they could play. In the generic case, we estimate the magnitude and possible consequences of the hard breaking of Supersymmetry in terms of the interplay between hidden and visible sectors mass scales.

hep-th↗

arXiv2014

Type II Seesaw Higgsology and LEP/LHC constraints

In the {\sl type II seesaw} model, if spontaneous violation of the lepton number conservation prevails over that of explicit violation, a rich Higgs sector phenomenology is expected to arise with light scalar states having mixed charged-fermiophobic/neutrinophilic properties. We study the constraints on these light CP-even ($h^0$) and CP-odd ($A^0$) states from LEP exclusion limits, combined with the so far established limits and properties of the $125-126$~GeV ${\cal H}$ boson discovered at the LHC. We show that, apart from a fine-tuned region of the parameter space, masses in the $\sim 44$ to $80$ GeV range escape from the LEP limits if the vacuum expectation value of the Higgs triplet is $\lesssim {\cal O}(10^{-3})$GeV, that is comfortably in the region for 'natural' generation of Majorana neutrino masses within this model. In the lower part of the scalar mass spectrum the decay channels ${\cal H} \to h^0 h^0, A^0 A^0$ lead predominantly to heavy flavor plus missing energy or to totally invisible Higgs decays, mimicking dark matter signatures without a dark matter candidate. Exclusion limits at the percent level of these (semi-)invisible decay channels would be needed, together with stringent bounds on the (doubly-)charged states, to constrain significantly this scenario. We also revisit complementary constraints from ${\cal H} \to γγ$ and ${\cal H} \to Z γ$ channels on the (doubly)charged scalar sector of the model, pinpointing non-sensitivity regions, and carry out a likeliness study for the theoretically allowed couplings in the scalar potential.

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arXiv2011

Revisiting No-Scale Supergravity Inspired Scenarios

We consider no-scale supergravity inspired scenarios, emphasizing the possible dynamical determination of the soft supersymmetry-breaking parameters as triggered by the radiative corrections that lift an essentially flat tree-level potential in the hidden sector. We (re)emphasize the important role played by the scale-dependent vacuum energy contribution to the effective potential for the occurrence of consistent no-scale minima. The most relevant input parameters are introduced as $B_0$ (the soft breaking mixing Higgs parameter) and $η_0$ (the cosmological constant value at high energy) instead of $\mhalf$ and $\tan β$, the latter being determined through a (generalized) potential minimization at electroweak scales. We examine the theoretical and phenomenological viability of such a mechanism when confronted with up-to-date calculations of the low energy sparticle spectrum and with present constraints from the LHC and other observables. The tight dark matter relic density constraint for a neutralino LSP scenario can be considerably relaxed for a gravitino LSP scenario possible in this framework.

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arXiv2011

Revisiting No-Scale Supergravity Inspired Scenarios: Updated Theoretical and Phenomenological Constraints

We consider no-scale inspired supergravity scenarios, where the gravitino mass and related soft supersymmetry-breaking parameters are determined dynamically by radiative corrections to an essentially flat tree-level potential in the supersymmetry breaking hidden sector. We examine the theoretical and phenomenological viability of such a mechanism, when including up-to-date calculations of the low energy sparticle spectrum and taking into account the latest LHC results and other experimental constraints. We (re)emphasize the role of the scale-dependent vacuum energy contribution to the effective potential, in obtaining realistic no-scale electroweak minima, examining carefully the impact of boundary conditions and of variants of the minimization procedure. We also discuss and implement the B_0 (soft breaking Higgs mixing parameter) input boundary condition at high scale, therefore fixing tan beta(B_0) at low scales. For general high scale boundary conditions with non-vanishing B_0, m_0..., our analysis provides theoretical correlations among the supersymmetric, soft and vacuum energy parameters and related phenomenological consequences at the LHC. For instance, a zero vacuum energy at the GUT scale would lead to a decoupled supersymmetric spectrum, together with a light standard model-like Higgs boson at the electroweak scale. Given the experimental exclusion limits, a substantial class of the boundary conditions, and in particular the strict no-scale with m_0=A_0=B_0=0, are only compatible with a stau being the lightest MSSM particle. Then an enlarged allowed parameter space emerges when assuming a gravitino LSP to account for the observed dark matter relic density.

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arXiv2009

Gravitino Dark Matter and the Cosmic Lithium Abundances

Supersymmetric extensions of the standard model of particle physics assuming the gravitino to be the lightest supersymmetric particle (LSP), and with the next-to-LSP decaying to the gravitino during Big Bang nucleosynthesis, are analyzed. Particular emphasis is laid on their potential to solve the "Li7 problem", an apparent factor 2-4 overproduction of Li7 in standard Big Bang nucleosynthesis (BBN), their production of cosmologically important amounts of Li6, as well as the resulting gravitino dark matter densities in these models. The study includes several improvements compared to prior studies. Heavy gravitinos in the constrained minimal supersymmetric standard model (CMMSM) are reanalyzed, whereas light gravitinos in gauge-mediated supersymmetry breaking scenarios (GMSB) are studied for the first time. It is confirmed that decays of NLSP staus to heavy gravitinos, while producing all the dark matter, may at the same time resolve the Li7 problem. For NLSP decay times ~ 1000 sec, such scenarios also lead to cosmologically important Li6 (and possibly Be9) abundances. However, as such scenarios require heavy > 1 TeV staus they are likely not testable at the LHC. It is found that decays of NLSP staus to light gravitinos may lead to significant Li6 (and Be9) abundances, whereas NLSP neutralinos decaying into light gravitinos may solve the Li7 problem. Though both scenarios are testable at the LHC they may not lead to the production of the bulk of the dark matter. A section of the paper outlines particle properties required to significantly reduce the Li7 abundance, and/or enhance the Li6 (and possibly Be9) abundances, by the decay of an arbitrary relic particle.

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arXiv2007

The dark matter as a light gravitino

We address the question of gravitino dark matter in the context of gauge mediated supersymmetry breaking models. A special emphasis is put on the role played by the MSSM singlet messenger in the case of SO(10) grand unification.

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arXiv2006

Very Light Gravitino Dark Matter

We address the question of dark matter in the context of gauge mediated supersymmetry breaking models. In contrast with mSUGRA scenarios, the messenger of the susy breaking to the visible sector can play an important role allowing a relic gravitino in the $\sim {keV}$ to $10 {MeV}$ mass range to account for the cold dark matter in the Universe.

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arXiv2006

Natural gravitino dark matter in SO(10) gauge mediated supersymmetry breaking

It is shown that gravitinos with mass m_{3/2} ~ 0.1-1 MeV may provide suitable cold dark matter candidates in scenarios of gauge mediated supersymmetry breaking (GMSB) under SO(10) grand unification coupled to supergravity, which accommodate a messenger sector of mass scale M_X ~ 10^6 GeV. This is due to the combined effects of renormalizable loop-suppressed operators and generic non-renormalizable ones governing the dilution of a pre-existing equilibrium gravitino abundance via messenger decay. The above range of gravitino and messenger masses can be accommodated in indirect GMSB scenarios. The gravitino abundance does not depend on the post-inflationary reheat temperature and it is shown that leptogenesis can generate successfully the baryon asymmetry.

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arXiv2006

Gravitino, Axino, Kaluza-Klein Graviton Warm and Mixed Dark Matter and Reionisation

Stable particle dark matter may well originate during the decay of long-lived relic particles, as recently extensively examined in the cases of the axino, gravitino, and higher-dimensional Kaluza-Klein (KK) graviton. It is shown that in much of the viable parameter space such dark matter emerges naturally warm/hot or mixed. In particular, decay produced gravitinos (KK-gravitons) may only be considered cold for the mass of the decaying particle in the several TeV range, unless the decaying particle and the dark matter particle are almost degenerate. Such dark matter candidates are thus subject to a host of cosmological constraints on warm and mixed dark matter, such as limits from a proper reionisation of the Universe, the Lyman-alpha forest, and the abundance of clusters of galaxies.. It is shown that constraints from an early reionsation epoch, such as indicated by recent observations, may potentially limit such warm/hot components to contribute only a very small fraction to the dark matter.

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