By representing each collider event as a point cloud, we adopt the graphic convolutional network (GCN) with focal loss to reconstruct the Higgs jet in it. This method provides higher Higgs tagging efficiency and better reconstruction accuracy than the traditional methods, which use jet substructure information. The GCN, which is trained on events of the $H+\text{jets}$ process, is capable of detecting a Higgs jet in events of several different processes, even though the performance degrades when there are boosted heavy particles other than the Higgs boson in the event. We also demonstrate the signal and background discrimination capacity of the GCN by applying it to the $t\overline{t}$ process. Taking the outputs of the network as new features to complement the traditional jet substructure variables, the $t\overline{t}$ events can be separated further from the $H+\text{jets}$ events.

In many models incorporating the type-I seesaw mechanism, the right-handed neutrino ($N$) couples to heavy vector/scalar bosons and thereby has resonant pair production. It has barely received attention thus far; however, it may provide the best avenue to probe TeV scale $N$ without requiring anomalously large mixing between $N$ and the active neutrino ${\nu }_L$. In this paper we explore the discovery prospects of (mainly heavy) $N$ pair production at the 14 TeV LHC and future 100 TeV $pp$ collider, based on the three signatures: (1) trilepton from $N(\to \ell W_{\ell })N(\to \ell W_h)$ with $W_{\ell /h}$ being the leptonically/hadronically decaying $W$; (2) boosted di-Higgs boson plus ${\cancel{E}}_T$ from $N(\to {\nu }_{L}h)N(\to {\nu }_{L}h)$; (3) a single boosted Higgs boson with leptons and ${\cancel{E}}_T$ from $N(\to \ell W_{\ell })N(\to {\nu }_{L}h)$. At the 100 TeV collider, we also consider the situation when the Higgs boson is overboosted, thus losing its jet substructure. Interpreting our tentative results in the benchmark model, the local $B-L$ model, we find that the (multi-) TeV scale $N$ can be probed at the (100) 14 TeV colliders.

We consider a minimal renormalizable and gauge invariant dark matter (DM) model, in which the singlet fermion DM has only axial couplings to a new pseudoscalar mediator. The mixing between the pseudoscalar mediator and the standard model (SM) Higgs boson induces the interactions between the DM and SM particles. The DM candidate in this model can provide the correct thermal relic density and evades all direct detections, while it can produce observable signals in indirect detection experiments due to its large annihilation cross section. A comparative study for DM phenomenology at the LHC is conducted for models with scalar mediators that have either scalar or pseudoscalar couplings to SM particles and the DM. We find that the three scenarios have distinguishable features in scalar decay branching ratio, DM pair production cross section as well as the signal reaches at the LHC. The LHC searches for some visible signals related to the scalar sector are also discussed.

Some interpretations of $$ {R}_{D^{\left(\ast \right)}} $$ R D ∗ anomaly in B meson decay using leptoquark (LQ) models can also generate top quark decays through Flavor Changing Neutral Current (FCNC). In this work we focus on two LQs, i.e. scalar S ₁ and vector U ₁ which are both singlet under the SU(2) _L gauge group in the Standard Model (SM). We investigate their implications on the 3-body top FCNC decays t → cℓ _i ℓ _j at tree level and the 2-body t → cV at one-loop level, with ℓ being the SM leptons and V = γ, Z, g being the SM gauge bosons. We utilize the 2σ parameter fitting ranges of the LQ models and find that Br(t → cℓ _i ℓ _j ) at tree level can reach $$ \mathcal{O} $$ O (10⁻⁶) and Br(t → cV) at one-loop level can reach $$ \mathcal{O} $$ O (10⁻¹⁰). Some quick collider search prospects are also analyzed.