arXiv subjects

Stefano Moretti

Publications and source records attributed to Stefano Moretti.

At least 91 records · Page 5Linked to original sources

arXiv2023

Electroweak Multi-Higgs Production: A Smoking Gun for the Type-I Two-Higgs-Doublet Model

Extending the Higgs sector of the Standard Model (SM) by just one additional Higgs doublet field leads to the two-Higgs-doublet model (2HDM). In the Type-I $Z_2$-symmetric limit of the 2HDM, all the five new physical Higgs states can be fairly light, $\mathcal{O}(100)$\,GeV or less, without being in conflict with current data from the direct Higgs boson searches and the $B$-physics measurements. In this article, we establish that the new neutral as well as the charged Higgs bosons in this model can all be simultaneously observable in the multi-$b$ final state. The statistical significance of the signature for each of these Higgs states, resulting from the electro-weak (EW) production of their pairs, can exceed 5$σ$ at the 13\,TeV High-Luminosity Large Hadron Collider (HL-LHC). Since the parameter space configurations where this is achievable are precluded in the other, more extensively pursued, 2HDM Types, an experimental validation of our findings would be a clear indication that the true underlying Higgs sector in nature is the Type-I 2HDM.

hep-ph↗

arXiv2023

A Fermionic Portal to Vector Dark Matter from a New Gauge Sector

We present a new class of Dark Matter (DM) models wherein the Standard Model (SM) is extended with a new $SU(2)_D$ dark gauge sector. In this framework the stability of DM is provided by the conservation of a $U(1)$ global symmetry, which upon appropriate charge assignments for the $SU(2)_D$ multiplets, effectively leads to a $\mathbb{Z}_2$ symmetry subgroup. The origin of the global $U(1)$ symmetry which ensures the stability of DM can be justified in the form of a dark EW sector or through an underlying composite structure. The key ingredient of the model is a Vector-Like (VL) fermion doublet of $SU(2)_D$ , the members of which are singlets of the SM Electro-Weak (EW) gauge group, which mediate the interactions between the dark sector and the SM, via new Yukawa interactions. This class of models, labelled as Fermion Portal Vector DM (FPVDM), allows multiple realisations, depending on the properties of the the VL partner and the scalar potential. After spontaneous breaking of the $SU(2)_D$ symmetry via a new scalar doublet, the ensuing massive vector bosons with non-zero dark-isospin are DM candidates. The new class of FPVDM models suggested here has numerous phenomenological implications for collider and non-collider studies. As a practical example, we discuss here in detail a realisation involving a VL top partner assuming no mixing between the two physical scalars of the theory, the SM Higgs boson and its counterpart in the dark sector. We thus provide bounds on this setup from both collider and astroparticle observables.

hep-ph↗

arXiv2023

Flavon Signatures at the HL-LHC

The detection of a single Higgs boson at the Large Hadron Collider (LHC) has allowed one to probe some properties of it, including the Yukawa and gauge couplings. However, in order to probe the Higgs potential, one has to rely on new production mechanisms, such as Higgs pair production. In this paper, we show that such a channel is also sensitive to the production and decay of a so-called `Flavon' field ($H_F$), a new scalar state that arises in models that attempt to explain the hierarchy of the Standard Model (SM) fermion masses. Our analysis also focuses on the other decay channels involving the Flavon particle, specifically the decay of the Flavon to a pair of $Z$ bosons ($H_F \to Z Z$) and the concurrent production of a top quark and charm quark ($H_F\to tc$), having one or more leptons in the final states. In particular, we show that, with 3000 fb$^{-1}$ of accumulated data at 14 TeV (the Run 3 stage) of the LHC an heavy Flavon $H_F$ with mass $M_{H_F} \simeq 2m_t $ can be explored with $3σ-5σ$ significance through these channels.

hep-ph↗

arXiv2023

Exploring high scale seesaw models through a supersymmetric portal

The seesaw scale is a priori unknown. If the seesaw scale is low, one may directly look for the new particles predicted by seesaw models. If the seesaw scale is high, such an approach is unfeasible. We show that in some supersymmetric seesaw models the large Yukawa couplings of high scale seesaw models leave their fingerprints to Higgs-slepton couplings and that this can result in decays of the type $\tildeν_{2}\rightarrow \tildeν_{1}h$ in Type-I and Type-III seesaw models and $\tilde{\ell}^{\pm}_{2}\rightarrow \tilde{\ell}^{\pm}_{1}h$ in the latter. Unfortunately the current exclusion bounds make it impossible to see a significant signal even at the High-Luminosity phase of the LHC. In this paper, we highlight that the High-Energy phase of the LHC (with $\sqrt{s}=27$~TeV) could afford one with some sensitivity to those in the single lepton channel.

hep-ph↗

arXiv2023

Deconstructing squark contributions to di-Higgs production at the LHC

We present a novel approach to the study of di-Higgs production via gluon-gluon fusion at the LHC. The relevant Feynman diagrams involving two Standard Model-like Higgs bosons $hh$ are computed within a simplified model approach that enables one to interpret possible signals of new physics in a model-independent way as well as to map these onto specific theories. This is possible thanks to a decomposition of such a signal process into all its squared amplitudes and their relative interferences, each of which has a well-defined coupling structure. We illustrate the power of this procedure for the case of both a minimal and next-to-minimal representation of Supersymmetry, for which the new physics effects are due to top squarks entering the loops of $gg\to hh$. The squarks yield both a change of the integrated cross section and peculiar kinematic features in its differential distributions with respect to the Standard Model. These effects can in turn be traced back to the relevant diagrammatic and coupling structures and allow for a detailed analysis of the process. In order to do so, we perform systematic scans of the parameter spaces of such new physics scenarios and identify benchmark points which exhibit potentially observable features during the current and upcoming runs of the LHC.

hep-ph↗

arXiv2023

Fat $b$-Jet Analyses Using Old and New Clustering Algorithms in New Higgs Boson Searches at the LHC

We compare different jet-clustering algorithms in establishing fully hadronic final states stemming from the chain decay of a heavy Higgs state into a pair of the 125 GeV Higgs boson that decays into bottom-antibottom quark pairs. Such 4$b$ events typically give rise to boosted topologies, wherein bottom-antibottom quark pairs emerging from each 125 GeV Higgs boson tend to merge into a single, fat $b$-jet. Assuming Large Hadron Collider (LHC) settings, we illustrate how both the efficiency of selecting the multi-jet final state and the ability to reconstruct from it the masses of all Higgs bosons depend on the choice of jet-clustering algorithm and its parameter settings. We indicate the optimal choice of clustering method for the purpose of establishing such a ubiquitous Beyond the SM (BSM) signal, illustrated via a Type-II 2-Higgs Doublet Model (2HDM).

hep-ph↗

arXiv2023

TeV-scale leptoquark searches at the LHC and their E$_6$SSM Interpretation

We perform a model-independent search for leptoquarks (LQs) at the Large Hadron Collider through their pair-production and subsequent decay into $t\bar t ττ$ intermediate states. We show that, assuming full luminosity of the Run 2, a fully hadronic signal emerging from this intermediate state can surpass in sensitivity the established searches relying on leptons in the final state. Our conclusion is supported by a thorough Monte-Carlo analysis, and we advocate the deployment of our proposed search channel in the proper experimental setting of the Run 3. Furthermore, in order to highlight the full scope of this approach for constraining LQ theories, we interpret our results in the context of the string-inspired Exceptional Supersymmetric Standard Model, which naturally predicts the $S_1-$type scalar LQ states that we analyse here.

hep-ph↗

arXiv2023

Exploring SM-like Higgs Boson Production in Association with Single-Top at the LHC Within a 2HDM

We investigate the possibility of detectable 2-Higgs Doublet Model (2HDM) type-II cross-sections at the High-Luminosity phase of the Large Hadron Collider (HL-LHC) for the production of the Standard Model (SM)-like Higgs boson ($h$) in association with a single top (anti)quark over the parameter space region corresponding to the so-called `wrong-sign solution' of the bottom (anti)quark Yukawa coupling. We isolate the latter by using the toolbox Magellan, which performs Markov Chain Monte Carlo (MCMC) scans in the presence of all current theoretical and experimental constraints, which relevance is accounted for accurately by using built-in Bayesian statistical methods. It is found that the allowed points in the 2HDM type-II parameter space of the aforementioned kind would not only provide inclusive rates considerably above those of the equivalent SM process but also distributions in several kinematical observables that are very different from the SM, both of which can help disentangle the SM from the 2HDM hypothesis. This difference is a consequence of the bottom-gluon fusion sub-process, which in the 2HDM becomes dominant over all others, with the latter remaining very close to the SM yields. We prove that this phenomenology would be observable at the HL-LHC for the illustrative example of $h$ to bottom-antibottom quark decays.

hep-ph↗

arXiv2023

Light $Z'$ Signatures at the LHC

In this work, we discuss a distinctive $pp\to {\rm Higgs}\to Z'Z'\to 4l$ ($l=e,μ$) signal at the Large Hadron Collider (LHC), where the `Higgs' label refers to the SM-like Higgs state discovered in 2012 or a lighter one in the framework of a theoretical model embedding a spontaneously broken $U(1)'$ symmetry in addition to the Standard Model (SM) gauge group. The additional $U(1)'$ symmetry generates a very light $Z'$ state, with both vector and axial (non-universal) couplings to fermions, which are able to explain the so-called Atomki anomaly, compliant with current measurements of the Anomalous Magnetic Moments (AMMs) of electron and muon as well as beam dump experiments. We show that the cross section for this process should be sufficiently large to afford one with significant sensitivity during Run 3 of the LHC.

hep-ph↗

arXiv2023

The decay $A^0\to h^0 Z^{(*)}$ in the inverted hierarchy scenario and its detection prospects at the Large Hadron Collider

Searches are being carried out at the Large Hadron Collider (LHC) for the decay of the CP-odd scalar ($A^0$) in Two-Higgs-Doublet Models (2HDMs) with Natural Flavour Conservation (NFC) in the channel $A^0\to h^0 Z$ (with $m_{h^0}=125$ GeV and $Z$ on-shell). In the absence of any signal, limits on the parameter space of $[\tanβ, \cos(β-α), m_{A^0}]$ in each 2HDM are derived for $m_{A^0} > 225$ GeV. In this work we consider the scenario of inverted hierarchy with $m_{h^0}<125$ GeV and $m_{H^0}=125$ GeV in which the decay $A^0\to h^0 Z^{(*)}$ (i.e. including the case of an off-shell $Z$) can have a large branching ratio in the 2HDM (Type I) for $m_{A^0}<225$ GeV. We calculate the signal cross section $σ(gg\to A^0)\times {\rm BR}(A^0\to h^0Z^{(*)})\times {\rm BR}(h^0\to b\overline b)$ in the 2HDM (Type I) with NFC and compare its magnitude with the cross section for the case of normal hierarchy ($m_{h^0}=125$ GeV) that is currently being searched for at the LHC. For the experimentally unexplored region $m_{A^0} < 225$ GeV it is shown that the above cross section for signal events in the scenario of inverted hierarchy can be of the order of a few picobarns. Such sizeable cross sections are several orders of magnitude larger than the cross sections for the case of normal hierarchy, thus motivating an extension of the ongoing searches for $A^0\to h^0 Z^{(*)}$ to probe the scenario of inverted hierarchy.

hep-ph↗

arXiv2022

Explaining the ${\mathcal{R}}(D)$ and ${\mathcal{R}}(D^{\ast})$ Anomalies in the $B-L$ Supersymmetric Standard Model with Inverse Seesaw

We investigate the ${\mathcal{R}}(D)$ and ${\mathcal{R}}(D^{\ast})$ anomalies in the context of the $B-L$ extension of the Minimal Supersymmetric Standard Model with Inverse Seesaw. We demonstrate that the lepton penguin $W^{\pm}l \barν_l $ ($l=e,μ,τ$) mediated by CP-even/odd right-handed sneutrinos, charginos and neutralinos can account for these anomalies simultaneously.

hep-ph↗

arXiv2022

Lexicographic Ranking based on Minimal Winning Coalitions

In this paper, we consider the consistency of the desirability relation with the ranking of the players in a simple game provided by some well-known solutions, in particular the Public Good Index [14] and the criticality-based ranking [1]. We define a new ranking solution, the Lexicographic Ranking based on Minimal winning coalitions (LRM), strongly related to the Public Good Index being rooted in the minimal winning coalitions of the simple game, proving that it is monotonic with respect to the desirability relation [17], when it holds. A suitable characterization of the LRM solution is provided. Finally, we investigate the relation among the LRM solution and the criticality-based ranking, referring to the dual game.

cs.GT↗

arXiv2022

Re-evaluating Jet Reconstruction Techniques for New Higgs Boson Searches

The ultimate motivation of our study is to look for signs of physics beyond the Standard Model (BSM). We investigate whether different jet clustering techniques might be more or less suited to the particular final states of interest. In particular, we are interested in fully hadronic final states emerging from the decay chain of the Standard Model like Higgs boson into pairs of light Higgs states, the latter in turn decaying into bottom-anti bottom pairs. We show that, the ability of selecting the multi-jet final state and to reconstruct invariant masses of the Higgs bosons from it depend strongly on the choice of acceptance cuts, resolution parameters and reconstruction algorithm as well as its settings. Hence, we indicate the optimal choice of the latter for the purpose of establishing such a benchmark as a BSM signal. We then repeat the exercise for a heavy Higgs boson cascading into two SM-like Higgs states, obtaining similar results.

hep-ph↗

arXiv2022

Measuring neutrino dynamics in NMSSM with a right-handed sneutrino LSP at the ILC

We study the possibility of measuring neutrino Yukawa couplings in the Next-to-Minimal Supersymmetric Standard Model with right-handed neutrinos (NMSSMr) when the lightest Supersymmetric partner (a right-handed sneutrino) is the Dark Matter (DM) candidate, by exploiting a `dijet + dilepton + Missing Transverse Energy' (MET) signature. We show that, unlike the miminal realisation of Supersymmetry (SUSY), i.e., the MSSM, for which the DM candidate is a much heavier (fermionic) state (a neutralino), this non-minimal SUSY model offers one with a much lighter (bosonic) state (a sneutrino) as DM, which can be produced at future $e^+e^-$ colliders with energies up to about 500 GeV. The emerging signal, from chargino pair production and subsequent decay, is extremely pure so it allows for the possibility of extracting the Yukawa parameters of the (s)neutrino sector. These results should then motivate searches for light DM signals at such accelerators, where a DM candidate with mass at the Electro-Weak (EW) scale can then be accessed.

hep-ph↗

arXiv2022

Probing a 96 GeV Higgs Boson in the Di-Photon Channel at the LHC

Recently the CMS collaboration reported a $\sim 3 σ$ local excess in the di-photon spectrum at 96 GeV. The same mass range concurs with a $\sim2 σ$ local excess in the $b\bar{b}$ invariant mass spectrum in four-jet events collected at LEP. In this contribution we show that at 1$σ$ level the 2HDM type-III can perfectly fit both excesses simultaneously, while satisfying all experimental and theoretical constraints.

hep-ph↗

arXiv2022

Explaining the 96 GeV Di-photon Anomaly in a Generic 2HDM Type-III

Motivated by results recently reported by the CMS Collaboration about an excess in the di-photon spectrum at about 96 GeV, especially when combined with another long-standing anomaly at the same value in the $b\bar b$ invariant mass spectrum in four-jet events collected at LEP, we show that a possible explanation to both phenomena can be found at 1$σ$ level in a generic 2-Higgs Doublet Model (2HDM) of Type-III in presence of a specific Yukawa texture, wherein Lepton Flavour Violating (LFV) (neutral) currents are induced at tree level. Bounds from Higgs data play a major role in limiting the parameter space of this scenario, yet we find solutions with $m_H = 125$ GeV and $m_h = 96$ GeV consistent with current theoretical and experimental bounds.

hep-ph↗

arXiv2022

Multilepton Signatures from Dark Matter at the LHC

Leptonic signatures of Dark Matter (DM) are one of the cleanest ways to discover such a secluded form of matter at high energy colliders. We explore the full parameter space relevant to multi-lepton (2- and 3-lepton) signatures at the Large Hadron Collider (LHC) from representative minimal consistent models with scalar and fermion DM. In our analysis, we suggest a new parametrisation of the model parameter spaces in terms of the DM mass and mass differences between DM and its multiplet partners. This parametrisation allows us to explore properties of DM models in their whole parameter space. This approach is generic and quite model-independent since the mass differences are related to the couplings of the DM to the Standard Model (SM) sector. We establish the most up-to-date LHC limits on the inert 2-Higgs Doublet Model (i2HDM) and Minimal Fermion DM (MFDM) model parameter spaces, by using the complementary information stemming from 2- and 3-lepton signatures. We provide a map of LHC efficiencies and cross-section limits for such 2- and 3-lepton signatures allowing one to easily make model-independent reinterpretations of LHC results for analogous classes of models. We also present combined constraints from the LHC, DM relic density and direct search experiments indicating the current status of the i2HDM and MFDM model.

hep-ph↗

arXiv2022

Revisiting Jet Clustering Algorithms for New Higgs Boson Searches in Hadronic Final States

We assess the performance of different jet-clustering algorithms, in the presence of different resolution parameters and reconstruction procedures, in resolving fully hadronic final states emerging from the chain decay of the discovered Higgs boson into pairs of new identical Higgs states, the latter in turn decaying into bottom-antibottom quark pairs. We show that, at the Large Hadron Collider (LHC), both the efficiency of selecting the multi-jet final state and the ability to reconstruct from it the masses of the Higgs bosons (potentially) present in an event sample depend strongly on the choice of acceptance cuts, jet-clustering algorithm as well as its settings. Hence, we indicate the optimal choice of the latter for the purpose of establishing such a benchmark Beyond the SM (BSM) signal.

hep-ph↗