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A bstract We deploy an advanced Machine Learning (ML) environment, leveraging a multi-scale cross-attention encoder for event classification, towards the identification of the gg → H → hh → b b ¯ b b ¯ process at the High Luminosity Large Hadron Collider (HL-LHC), where h is the discovered Standard Model (SM)-like Higgs boson and H a heavier version of it (with m H > 2 m h ). In the ensuing boosted Higgs regime, the final state consists of two fat jets. Our multi-modal network can extract information from the jet substructure and the kinematics of the final state particles through self-attention transformer layers. The diverse learned information is subsequently integrated to improve classification performance using an additional transformer encoder with cross-attention heads. We showcase that our approach surpasses current alternative methods used to establish sensitivity to this process in performance, whether solely based on kinematic analysis or combining this with mainstream ML approaches. Then, we employ various interpretive methods to evaluate the network results, including attention map analysis and visual representation of Gradient-weighted Class Activation Mapping (Grad-CAM). Finally, we note that the proposed network is generic and can be applied to analyse any process carrying information at different scales. Our code is publicly available for generic use ( https://github.com/AHamamd150/Multi-Scale-Transformer-Encoder ).

A bstract The A → Z (*) h decay signature has been highlighted as possibly being the first testable probe of the Standard Model (SM) Higgs boson discovered in 2012 ( h ) interacting with Higgs companion states, such as those existing in a 2-Higgs Doublet Model (2HDM), chiefly, a CP-odd one ( A ). The production mechanism of the latter at the Large Hadron Collider (LHC) takes place via b b ¯ -annihilation and/or gg -fusion, depending on the 2HDM parameters, in turn dictated by the Yukawa structure of this Beyond the SM (BSM) scenario. Among the possible incarnations of the 2HDM, we test here the so-called Type-II, for a twofold reason. On the one hand, it intriguingly offers two very distinct parameter regions compliant with the SM-like Higgs measurements, i.e., where the so-called ‘SM limit’ of the 2HDM can be achieved. On the other hand, in both configurations, the AZh coupling is generally small, hence the signal is strongly polluted by backgrounds, so that the exploitation of Machine Learning (ML) techniques becomes extremely useful. In this paper, we show that the application of advanced ML implementations can be decisive in establishing such a signal. This is true for all distinctive kinematical configurations involving the A → Z (*) h decay, i.e., below threshold ( m A < m Z + m h ), at its maximum ( m Z + m h < m A < 2 m t ) and near the onset of t t ¯ pair production ( m A ≈ 2 m t ), for which we propose Benchmark Points (BPs) for future phenomenological analyses.

In this study, we focus on the bosonic decays of light charged Higgs bosons in the 2-Higgs Doublet Model (2HDM) Type-I. We quantify the Branching Ratios (BRs) of the H ± → W ± h and H ± → W ± A channels and show that they could be substantial over several areas of the parameter space of the 2HDM Type-I that are still allowed by Large Hadron Collider (LHC) and other experimental data as well as theoretical constraints. We suggest that H ± → W ± h and/or H ± → W ± A could be used as a feasible discovery channel alternative to H ± → τ ν .

A bstract We suggest an explanation for and explore the consequences of the excess around 95 GeV in the di-photon and di-tau invariant mass distributions recently reported by the CMS collaboration at the Large Hadron Collider (LHC), together with the discrepancy that has long been observed at the Large Electron-Positron (LEP) collider in the b b ¯ invariant mass. Interestingly, the most recent findings announced by the ATLAS collaboration do not contradict, or even support, these intriguing observations. Their search in the di-photon final state similarly reveals an excess of events within the same mass range, albeit with a bit lower significance, thereby corroborating and somewhat reinforcing the observations made by CMS. We demonstrate that the lightest CP-even Higgs boson in the general 2-Higgs Doublet Model (2HDM) Type-III can explain simultaneously the observed excesses at approximately 1.3 σ C.L. while satisfying up-to-date theoretical and experimental constraints. Moreover, the 2HDM Type-III predicts an excess in the pp → t t ¯ H SM production channel of the 125 GeV Higgs boson, H SM . This effect is caused by a up to 12% enhancement of the H SM tt Yukawa coupling in comparison to that predicted by the Standard Model. Such an effect can be tested at the High Luminosity LHC (HL-LHC), which can either discover or exclude the scenario we suggest. This unique characteristic of the 2HDM Type-III makes this scenario with the 95 GeV resonance very attractive for further theoretical and experimental investigations at the (HL-)LHC and future colliders.

Expanding upon our ongoing investigation of Vector-Like Quark (VLQ) phenomenology within a 2-Higgs Doublet Model (2HDM) framework, in this paper, we complement a previous one dedicated to Vector-Like Top-quarks (VLTs) by studying Vector-Like Bottom-quarks (VLBs), specifically focusing on their behavior in the alignment limit of a Type-II Yukawa structure. We examine the potential for detecting VLBs at the Large Hadron Collider (LHC) and analyze their decay signatures, encompassing both Standard Model (SM) processes and exotic decays. The objective is to differentiate among singlet, doublet, and triplet configurations of VLBs by identifying distinct decay patterns, thereby providing insights into the structure of Beyond the SM (BSM) physics.

A bstract We analyse new signals of a 3-Higgs Doublet Model (3HDM) at the Large Hadron Collider (LHC) where only one doublet acquires a Vacuum Expectation Value (VEV), preserving a Z 2 parity. The other two doublets are inert and do not develop a VEV, leading to a dark scalar sector controlled by Z 2 , with the lightest CP-even dark scalar H 1 being the Dark Matter (DM) candidate. This leads to the loop induced decay of the next-to-lightest scalar, H 2 → H 1 ℓ ℓ ¯ ℓ = e μ , mediated by both dark CP-odd neutral and charged scalars. This is a smoking-gun signal of the 3HDM since it is not allowed in the 2-Higgs Doublet Model (2HDM) with one inert doublet and is expected to be important when H 2 and H 1 are close in mass. In practice, this signature can be observed in the cascade decay of the SM-like Higgs boson, h → H 1 H 2 → H 1 H 1 ℓ ℓ ¯ into two DM particles and di-leptons or h → H 2 H 2 → H 1 H 1 ℓ ℓ ¯ ℓ ℓ ¯ into two DM particles and four-leptons, where h is produced from gluon-gluon Fusion. In order to test the feasibility of these channels at the LHC, we devise some benchmarks, compliant with collider, DM and cosmological data, for which the interplay between these production and decay modes is discussed. In particular, we show that the resulting detector signatures, or , with the invariant mass of ℓ ℓ ¯ pairs much smaller than m Z , can potentially be extracted already from Run 3 data and at the High-Luminosity phase of the LHC.

A comprehensive extension of the ordinary 2-Higgs Doublet Model (2HDM), supplemented by vector-like quarks (VLQs), in the “alignment limit” is presented. In such a scenario, we study the possibility that large hadron collider (LHC) searches for VLQs can profile their nature too, i.e., whether they belong to a singlet, doublet, or triplet representation. To achieve this, we exploit both standard model (SM) decays of VLQs with top-(anti)quark electromagnetic (EM) charge ( T ), i.e., into b ,  t quarks and W ± , Z , h bosons (which turn out to be suppressed and hence T states can escape existing limits) as well as their exotic decays, i.e., into b ,  t (and possibly B ) quarks and H ± , H , A bosons. We show that quite specific decay patterns emerge in the different VLQ representations so that, depending upon which T signals are accessed at the LHC, one may be able to ascertain the underlying beyond standard model (BSM) structure, especially if mass knowledge of the new fermionic and bosonic sectors can be inferred from (other) data.

A bstract Aiming to uncover the CP properties of spin-0 particle Dark Matter (DM), we explore a two-component DM scenario within the framework of 3-Higgs Doublet Models (3HDMs), a well-motivated set-up previously studied due to the complementarity of its collider and astrophysical probes. We devise benchmark points in which the two components of DM have same CP in one case and opposite CP in another. We then show several cross section distributions of observables at collider experiments where the two cases are clearly distinguishable.

The detection of a heavy neutral CP-even Higgs boson of the B - L Supersymmetric Standard Model (BLSSM), h ′ , with m h ′ ≃ 400 GeV , at the Large Hadron Collider (LHC) for a center-of-mass energy of s = 14 TeV , is investigated. The following production and decay channels are considered: g g → h ′ → ZZ → 4 ℓ and (with being the Missing Transverse Energy (MET)), where ℓ = e , μ , with integrated luminosity L int = 300 fb - 1 (Run 3). Furthermore, we also look into the di-Higgs channel g g → h ′ → hh → b b ¯ γ γ at the High-Luminosity LHC (HL-LHC) with an integrated luminosity of L int = 3000 fb - 1 . We demonstrate that promising signals with high signal-to-background statistical significance ( S / B ) can be obtained through the three aforementioned channels.

We present a reinterpretation study of existing results from the CMS Collaboration, specifically, searches for light Beyond the Standard Model (BSM) Higgs pairs produced in the chain decay p p → H SM → h h ( a a ) into a variety of final states, in the context of the CP-conserving 2-Higgs Doublet Model (2HDM) Type-I. Through this, we test the Large Hadron Collider (LHC) sensitivity to a possible new signature, p p → H SM → Z A → Z Z h , with Z Z → j j μ + μ - and h → b b ¯ . We perform a systematic scan over the 2HDM Type-I parameter space, by taking into account all available theoretical and experimental constraints, in order to find a region with a potentially visible signal. We investigate the significance of it through a full Monte Carlo simulation down to the parametrised detector level. We show that such a signal is an alternative promising channel to standard four-body searches for light BSM Higgs bosons at the LHC already with an integrated luminosity of L = 300 fb - 1 . For a tenfold increase of the latter, discovery should be possible over most of the allowed parameter space.