Search

Abstract We investigate the pair-production of Right-Handed Neutrinos (RHNs) via a $$B-L$$ B - L $$Z'$$ Z ′ boson and present the sensitivity studies of the active-sterile neutrino mixing ( $$|V_{\mu N}|$$ | V μ N | ) at the High-Luminosity run of the LHC (HL-LHC) and a future pp collider (FCC-hh). We focus on RHN states with a mass of $$10-70$$ 10 - 70 GeV which naturally results in displaced vertices for small $$|V_{\mu N}|$$ | V μ N | . Being produced through a mass resonance with $$M_{Z'} \ge 1$$ M Z ′ ≥ 1 TeV, the RHNs are heavily boosted, leading to collimated decay products that give rise to fat-jets. We investigate the detection prospect of dedicated signatures in the inner detector and the muon spectrometer, namely a pair of displaced fat-jets and the associated tracks, respectively. We find that both the HL-LHC and FCC-hh can be sensitive to $$|V_{\mu N}| > 10^{-6}$$ | V μ N | > 10 - 6 and $$|V_{\mu N}| > 10^{-7}$$ | V μ N | > 10 - 7 with the number of events reaching $${\mathcal {O}}(10)$$ O ( 10 ) and $${\mathcal {O}}(10^3)$$ O ( 10 3 ) , respectively. This allows probing the generation of light neutrino masses through the Seesaw mechanism.

Abstract Extending the Standard Model with right-handed neutrinos (RHNs) is well motivated by the observation of neutrino oscillations. In the type-I seesaw model, the RHNs interact with the SM particles via tiny mixings with the active neutrinos, which makes their discovery in the laboratory, and in particular at collider experiments in general challenging. In this work we instead consider an extension of the seesaw model with RHNs with the addition of a leptoquark (LQ), and employ a non-minimal production mechanism of the RHN via LQ decay, which is unsuppressed by neutrino mixing. We focus on relatively light RHN with mass O $$ \mathcal{O} $$ (10) GeV and LQ with mass 1.0 TeV, and explore the discovery prospect of the RHN at the proposed Large Hadron electron Collider. In the considered mass range and with the given interaction strength, the RHN is long lived and, due to it stemming from the LQ decay, it is also heavily boosted, resulting in collimated decay products. The unique signature under investigation is thus a displaced fat jet. We use kinematic variables to separate signal from background, and demonstrate that the ratio variables with respect to energy/number of displaced and prompt tracks are useful handles in the identification of displaced decays of the RHN. We also show that employing a positron beam provides order of magnitude enhancement in the detection prospect of this signature.

Abstract We consider the gauged B − L model which is extended with a secluded dark sector, comprising of two dark sector particles. In this framework the lightest Z $$ \mathcal{Z} $$ 2-odd particle is the dark matter candidate, having a feeble interaction with all other SM and BSM states. The next-to-lightest Z $$ \mathcal{Z} $$ 2-odd particle in the dark sector is a super-wimp, with large interaction strength with the SM and BSM states. We analyse all the relevant production processes that contribute to the dark matter relic abundance, and broadly classify them in two different scenarios, a) dark matter is primarily produced via the non-thermal production process, b) dark matter is produced mostly from the late decay of the next-to-lightest Z $$ \mathcal{Z} $$ 2-odd particle. We discuss the dependency of the relic abundance of the dark matter on various model parameters. Furthermore, we also analyse the discovery prospect of the BSM Higgs via invisible Higgs decay searches.

Abstract 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 χ < 1 GeV, where v χ 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 GeV < M H 5 0 $$ {M}_{H_5^0} $$ < 350 GeV, 150 GeV < M H 3 0 $$ {M}_{H_3^0} $$ < 270 GeV and 145 GeV < M H < 300 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 5 0 $$ {H}_5^0 $$ → γγ) 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 4σ significance can be achieved in final states with at least two photons for one of our benchmark points.

Abstract We study the phenomenology of leptophilic Z′ gauge bosons at the future high-energy e + e − and μ + μ − colliders, as well as at the gravitational wave observatories. The leptophilic Z′ model, although well-motivated, remains largely unconstrained from current low-energy and collider searches for Z′ masses above O $$ \mathcal{O} $$ (100 GeV), thus providing a unique opportunity for future lepton colliders. Taking U 1 L α − L β $$ \textrm{U}{(1)}_{L_{\alpha }-{L}_{\beta }} $$ (α, β = e, μ, τ) models as concrete examples, we show that future e + e − and μ + μ − colliders with multi-TeV center-of-mass energies provide unprecedented sensitivity to heavy leptophilic Z′ bosons. Moreover, if these U(1) models are classically scale-invariant, the phase transition at the U(1) symmetry-breaking scale tends to be strongly first-order with ultra-supercooling, and leads to observable stochastic gravitational wave signatures. We find that the future sensitivity of gravitational wave observatories, such as advanced LIGO-VIRGO and Cosmic Explorer, can be complementary to the collider experiments, probing higher Z′ masses up to O $$ \mathcal{O} $$ (104 TeV), while being consistent with naturalness and perturbativity considerations.