WIMP and FIMP Dark Matter in Singlet-Triplet Fermionic Model

• Abhishek Roy (Institute Of Physics, Bhubaneswar, India)

We present an extension of the SM involving three triplet fermions, one triplet scalar and one singlet fermion, which can explain both neutrino masses and dark matter. One triplet of fermions and the singlet are odd under a $Z_2$ symmetry thus the model features two possible dark matter candidates. The two remaining $Z_2$-even triplet fermions can reproduce the neutrino masses and oscillation parameters consistent with observations. We consider the case where the singlet has feeble couplings while the triplet is weakly interacting and investigate the different possibilities for reproducing the observed dark matter relic density. This includes production of the triplet WIMP from freeze-out and from decay of the singlet as well as freeze-in production of the singlet from decay of particles that belong to the thermal bath or are thermally decoupled. While freeze-in production is usually dominated by decay processes, we also show cases where the annihilation of bath particles give substantial contribution to the final relic density. This occurs when the new scalars are below the TeV scale, thus in the reach of the LHC. The next-to-lightest odd particle can be long-lived and can alter the successful BBN predictions for the abundance of light elements, these constraints are relevant in both the scenarios where the singlet or the triplet are the long-lived particle.In the case where the triplet is the DM, the model is subject to constraints from ongoing direct, indirect and collider experiments. When the singlet is the DM, the triplet which is the next-to-lightest odd particle can be long-lived and can be probed at the proposed MATHUSLA detector. Finally we also address the detection prospects of triplet fermions and scalars at the LHC.

New features in the Z2×Z2 3HDM two component DM model.

• Rafael Filipe Teixeira Boto (Instituto Superior Técnico)

We discuss the constraints and phenomenology of the Z2×Z2 three Higgs doublet model (3HDM) with two inert scalars, originating two dark matter (DM) particles. We elucidate the competing vacua and we submit the model to all theoretical, collider and astrophysical constraints. We find unexplored regions of parameter space and investigate their experimental signatures. In particular, we find regions where the two DM particles contribute equally to the relic DM density. The whole mass range for a given component can be populated for the model, even for intermediate mass regions that require the other component to dominate the relic density calculation.

Probing the invisible at the LHC

• Maria Gonçalves (CFTC-UL)

Considering the Higgs as a mediator between the Standard Model (SM) and the Dark Sector has been extensively studied in the literature. The simplest case is to assume that Dark Matter (DM) is a real singlet scalar (RSS) particle. However, the experimental data largely constrain this model, and only masses at the TeV scale or at the Higgs resonance are allowed. We extended the one RSS case to two different RSS DM particles, invariant under two independent Z2 symmetries. This opens up a new mass window for the lighter DM particle, which is within reach of the Large Hadron Collider (LHC). In fact, searches such as monojet and mono-Z, in association with large missing transverse momentum, can be used to probe the model. Furthermore, extending the model to include three RSS DM particles can also be promising and may still lead to signatures at the LHC.

Dark Coloured Scalars Impact on Single and Di-Higgs Production at the LHC

• Daniel Neacsu (CFTC-UL)

One of the simplest ways to address the Dark Matter problem is to enlarge the scalar sector of the Standard Model (SM) by including a dark sector with a discrete symmetry. At the LHC, the search for a stable DM candidate can then be conducted through missing energy detection in processes which include DM production. However, other new physics scenarios may also necessitate the inclusion of coloured scalars in this sector. These would contribute via loop processes to the Higgs production signals. Some of these models do not have a limit on the number of coloured scalars they can include. In this work we take this number as a parameter and examine the contributions to single Higgs and double Higgs production, considering current experimental data and future prospects. While we cannot constraint this number without fixing the masses and couplings, we can determine for which number of scalars these processes can become relevant in constraining the parameters. We also discuss the complementarity between the two. Finally, we look at the case where the coloured scalars are part of an SU(2) multiplet, for which we find that the electroweak observable T parameter imposes significant restrictions on the difference of the heavy coloured scalar masses.

Interference effects in resonant di-Higgs production at the LHC

• Daniel Winterbottom

In this talk, I will present an investigation into finite width and interference effects in di-Higgs production at the LHC, with a particular focus on the real Higgs singlet extension of the Standard Model. This extension enhances di-Higgs production through the resonant decays of an additional heavy scalar into two SM-like Higgs bosons. The study examines the impact of interference between non-resonant and resonant diagrams, revealing that this interference has a significant effect on the cross-sections and differential distributions at the LHC. Additionally, I will introduce a new tool that employs a matrix-element reweighting method, enabling the efficient modeling of interference effects in computational simulations.

Higgs Pair Production in a Composite 2HDM

• Felix Egle

In composite Higgs models the scalar particles in the Higgs sector are not elementary particles, but of composite nature, arising as pseudo Nambu-Goldstone bosons from new broken symmetries. In a composite 2-Higgs-Doublet Model (2HDM) thus a 2HDM-like structure is generated, but with couplings already predetermined by the composite nature of the model. In this talk we present Higgs Pair production in a composite 2HDM realization via gluon fusion. We give a brief introduction into the model and an overview over the calculation, highlighting the new couplings and diagrams contributing to di-Higgs production. We apply current experimental limits on our results and study differential distributions for specific benchmark scenarios.

Impact of new experimental data on the C2HDM

• Duarte Fontes

The complex two-Higgs doublet model (C2HDM) is one of the simplest extensions of the SM with a source of CP-violation in the scalar sector. It has a Z2 symmetry, softly broken by a complex coefficient. There are four ways to implement this symmetry in the fermion sector, leading to models known as Type-I, Type-II, LS and Flipped. In the latter three models, there is a priori the surprising possibility that the 125GeV Higgs boson couples mostly as a scalar to top quarks, while it couples mostly as a pseudoscalar to bottom quarks. This “maximal” scenario was still possible with the data available in 2017. Since then, there have been more data on the 125GeV Higgs boson, direct searches for CP-violation in angular correlations of τ-leptons produced in Higgs boson decays, new results on the electron EDM, new constraints from LHC searches for additional Higgs bosons and new results on b →sγ transitions. Highlighting the crucial importance of the LHC’s Run 2, I combine all these experiments and show that the “maximal” scenario is now excluded in all models. Still, one can have a pseudoscalar component in hτ¯τ couplings in the LS model as large as 87% of the scalar component.

Possible large pseudoscalar Yukawa couplings in the complex 3HDM

• Jorge Romao (Instituto Superior Tecnico)

As LHC's Run3 unfolds, we peer deeper into the couplings of the 125GeV Higgs (h125​) and also test for extra scalars. Even before such extra scalars are found, one can probe them by using the fact that theories with multiple Higgs doublets allow for substantial deviations of the couplings of h125 from their SM values. Indeed, the observed couplings already place stringent limits on such theories. We investigate the curious possibility that h125 couples to the top quark mostly as a scalar, while it couples to the bottom quark mostly as a pseudoscalar. This possibility was allowed by 2017 data for the so-called C2HDM; a two Higgs doublet model with a single source of explicit CP violation. It was shown recently that this possibility disappears when using the full experimental data of 2024. Here we discuss a three Higgs doublet with explicit CP violation (C3HDM), and show that the curious CP-even/CP-odd tt/bb possibility is partly resuscitated, prompting further experimental exploration of this prospect.

New scalars and Z' bosons

• Zoltán Péli (Eotvos Lorand University (HU))

Anomaly free U(1) extensions of the standard model (SM) predict a new neutral gauge boson Z'. When the Z' obtains its mass from the spontaneous breaking of the new U(1) symmetry by a new complex scalar field. The model also predicts a second real scalar s and the searches for the new scalar and the new gauge boson become intertwined. We present the computation of benchmark points for production and decay of such a scalar s for models with a light Z' boson, when the decay h -> Z' Z' may have a sizeable branching ratio. We show how Higgs signal strength measurement in this channel can provide stricter exclusion bounds on the parameters of the model than those obtained from the total signal strength for Higgs boson production.

Signatures of new neutral scalars in multi-Higgs models

• João Pedro Pino Gonçalves (University of Aveiro)

We propose a new collider signature for heavy neutral scalars typically found in various classes of multi-Higgs models. This signature is particularly relevant in the context of Large Hadron Collider (LHC) measurements and is based on a topology involving two charged leptons and four jets originating from first and second generation quarks. We discuss how the kinematics of the scalar fields can be leveraged to effectively distinguish the signal from dominant backgrounds and explore the discovery potential of these new heavy scalars in upcoming LHC runs. The proposed method can be applied to analyze the statistical significance of heavy scalar production at the LHC and future colliders in any multi-Higgs model. This work was published in Phys. Rev. D 107, 095041.

Multi-scale cross-attention Transformer encoder for event classification

• Ahmed Hammad

In this talk I will emphasize the significance of employing attention-based Transformer models for analyzing particle clouds. Specifically, I will delve into the utilization of a multi-modal transformer model equipped with both self-attention and cross-attention mechanisms to effectively analyze various scales of inputs for the process of di-Higgs production. In the ensuing boosted Higgs regime, the final state consists of two fat jets. The input clouds include the intricate local substructures of jets as well as the broader, high-level reconstructed kinematics. Additionally, I will introduce interpretation techniques such as attention maps and Grad-CAM to provide insights into the network's outcomes.

Probing the early Universe with BSMPT v3: CP in the Dark, a test case

• João Viana (CFTC-UL)

BSMPT v3 is a c++ program capable of computing the spectrum of primordial gravitational waves (GW) produced in a strong first-order phase transition for any scalar extension of the Standard Model. The GW spectrum can then be compared with the LISA experiment measurements, which are expected in ~15 years, and further constraint the model parameters. As a test case, we looked into the CP in the Dark model and computed the SNR in LISA. The model can be tested in the triple Z anomalous vertex at the LHC.

Phase transition, Gravitational waves and baryon asymmetry in the 2HDM

• AJAY Kaladharan

The knowledge of the Higgs potential is crucial for understanding the origin of mass and the thermal history of our Universe. In this talk, we demonstrate how collider measurements and observations of stochastic gravitational wave signals can complement each other to explore the multifaceted scalar potential in the 2HDM framework. In 2HDM, we examine key ingredients triggering first-order phase transition by looking at the shape of the Higgs potential. I will also discuss the complementarity with colliders and gravitational wave detectors in the 2HDM. Furthermore, using the complex 2HDM, we will discuss the impact of the tunneling profile in the calculation of the baryon asymmetry associated with electroweak baryogenesis.

Intermediate Charge-Breaking Phases in the 2HDM

• Christoph Borschensky (Karlsruhe Institute of Technology)

The evolution of the early Universe around the electroweak epoch is an ideal testbed for physics beyond the Standard Model and in particular extended scalar sectors. The universe may have experienced a sequence of phases of exotic nature, one of these being an intermediate phase where the electromagnetic charge is not conserved. In my talk, intermediate $U(1)_\mathrm{em}$ charge-breaking (CB) phases in the CP-conserving 2-Higgs Doublet Model will be investigated. While previously studied only in the approximation of high temperatures, the possibility for their existence in the one-loop effective potential including thermal corrections is confirmed. I will discuss the relation of CB phases with the (non-)restoration of the electroweak $SU(2)\times U(1)$ symmetry at high temperatures, and the consistency with current collider data. For certain selected benchmark scenarios, the features of a CB phase in the evolution of the vacuum will be examined, such as the occurrence of a first-order phase transition to the CB phase from the neutral one.

Effective 2HDM Yukawa Interactions and a Strong First-Order Electroweak Phase Transition

• Anisha . (Karlsruhe Institute of Technology)

The top quark as the heaviest particle in the SM defines an important mass scale for Higgs physics and the electroweak scale itself. It is therefore a well-motivated degree of freedom which could reveal the presence of new interactions beyond the SM. In this talk, I will discuss the modifications of the top-Higgs interactions in the 2HDM using the effective field theory deformations of these interactions from the point of view of a strong first-order electroweak phase transition (SFOEWPT). We show that such modifications are compatible with current Higgs data and that an SFOEWPT can be tantamount to a current overestimate of exotic Higgs searches' sensitivity at the LHC in $t\bar t$ and four top quark final states. We argue that these searches remain robust from the point of accidental signal-background interference so that the current experimental strategy might well lead to 2HDM-like discoveries in the near future.

Searching for HWW anomalous couplings with simulation-based inference

• Marta Silva (LIP)

The sensitivity to the dimension-6 CP-odd operator, $o_{H\tilde{W}}$ is explored, using simulation-based inference methods. These methods leverage simulator information to train neural networks that estimate likelihood ratios, capturing correlations between observables and avoiding sub-optimal steps from traditional methods (e.g. histogram-based analyses). ALICES, a cross-entropy estimator of the likelihood ratio, is benchmarked against SALLY, a detector-level optimal observable, and against traditional histograms of kinematic and angular observables. The ALICES and SALLY methods yielded tighter constraints than a 1D histogram of $Q_{\ell} \cos \delta^+$, but SALLY's results closely matched those from a 2D histogram of $p_T^W$ and $Q_{\ell} \cos \delta^+$. However, SALLY remains promising, given its potential for simultaneous probing of several couplings. Although ALICES sometimes struggled to capture the minima and likelihood shapes accurately, further refinement could enhance its sensitivity beyond both SALLY and 2D histograms. These results underscore the value of further exploring these methods with Run 3 data to potentially improve current ATLAS and CMS results."

Revisiting the decoupling limit of the Georgi-Machacek model with a scalar singlet

• Rojalin Padhan

We study the connection between collider and dark matter phenomenology in the singlet extension of the Georgi-Machacek model. In this framework, the singlet scalar serves as a suitable thermal dark matter (DM) candidate. Our focus lies on the region $v_{\chi}<1$ GeV, where $v_{\chi}$ is the common vacuum expectation value of the neutral components of the scalar triplets of the model. Setting bounds on the model parameters from theoretical, electroweak precision and LHC experimental constraints, we find that the BSM Higgs sector is highly constrained. Allowed values for the masses of the custodial fiveplets, triplets and singlet are restricted to the range $140~ {\rm GeV }< M_{H_5^0} < 350~ {\rm GeV }$, $150~ {\rm GeV }< M_{H_3^0} < 270 ~{\rm GeV }$ and $145~ {\rm GeV }< M_{H} < 300~ {\rm GeV }$. The extended scalar sector provides new channels for DM annihilation into BSM scalars that allow to satisfy the observed relic density constraint while being consistent with direct DM detection limits. The allowed region of the parameter space of the model can be explored in the upcoming DM detection experiments, both direct and indirect. In particular, the possible high values of BR$(H^0_5\to\gamma\gamma)$ can lead to an indirect DM signal within the reach of CTA. The same feature also provides the possibility of exploring the model at the High-Luminosity run of the LHC. In a simple cut-based analysis, we find that a signal of about $4\sigma$ significance can be achieved in final states with at least two photons for one of our benchmark points.

A Smoking Gun signature of the 3HDM

• Atri Dey

We analyze 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 Z2 parity. The other two doublets are inert and do not develop a VEV, leading to a dark scalar sector controlled by Z2, with the lightest CP-even dark scalar H1 being the Dark Matter (DM) candidate. This leads to the loop-induced decay of the next-to-lightest scalar, H2→H1ℓℓ(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 H2 and H1 are close in mass. In practice, this signature can be observed in the cascade decay of the SM-like Higgs boson, ℎ→H1 H2→H1 H1ℓℓ into two DM particles and di-leptons or ℎ→H2 H2→H1 H1ℓℓℓℓ 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, [inline-graphic not available: see fulltext] or [inline-graphic not available: see fulltext], with the invariant mass of ℓℓ pairs much smaller than mZ, can potentially be extracted already from Run 3 data and at the High-Luminosity phase of the LHC.

Searching for resonant flavor-changing charged Higgs production at the LHC

• Mohamed Krab

We suggest a resonant cb̄ → H+ production search, followed by bosonic H+ → W+H weak decay at the Large Hadron Collider (LHC). In the general two Higgs doublet model (G2HDM) that has flavor-changing neutral Higgs couplings, H+ is resonantly produced via the top-charm ρtcVtb coupling at tree level, while H+ → W+H weak decay occurs within the exotic second doublet, leading eventually to same sign dilepton signals. We perform a signal-to-background analysis at the 14 TeV LHC and show that discovery seems possible with LHC Run 2 data already at hand.

Searching for light Higgs bosons in the 2HDM at the LHC

• SOUAD SEMLALI (School of Physics and Astronomy, University of Southampton)

In the framework of the Two Higgs Doublet Model (2HDM), we investigate the scope of the LHC in accessing the processes H to hh to 2b2tau, 2b2gamma and pp to Z* to hA to 4tau by performing a Monte Carlo (MC) analysis aimed at extracting these signals from the Standard Model (SM) backgrounds, in the presence of a dedicated trigger choice and kinematical selection. We prove that some sensitivity to such channels exists already at Run 3 of the LHC, whilst the High-Luminosity LHC (HL-LHC) will either confirm or disprove these theoretical scenarios over sizable regions of the 2HDM parameter space.