New Physics Model Sidesteps Flavour Rules and Hints at Dark Matter Particles

Scientists are investigating the potential for discovering a light charged Higgs boson within the Alternative Left-Right Symmetric Model (ALRM), a theoretical framework which addresses limitations of the Standard Model. Hrishikesh Deka from the Indian Institute of Technology Guwahati, Avnish from the University of Hyderabad, and Poulose Poulose from St. Joseph’s University, alongside their colleagues, demonstrate how the ALRM evades stringent flavour constraints through a unique fermion spectrum and symmetry assignment. This research is significant because it explores scenarios where this charged Higgs boson acts as a long-lived particle linked to dark matter, potentially leaving detectable ‘disappearing track’ signatures in high-energy particle collisions. Their detailed analysis, incorporating realistic detector efficiencies and recasting existing ATLAS searches, suggests that future colliders, particularly the 27 TeV HE-LHC and a prospective 100 TeV collider, offer the best prospects for probing and ultimately discovering these elusive particles.

This model circumvents stringent flavour constraints by employing a unique fermion spectrum where right-handed up-type quarks are paired with exotic down-type quarks, effectively eliminating tree-level flavour-changing neutral currents.

Furthermore, a specific assignment of a global symmetry, coupled with an emergent R-parity, prevents mixing between the right- and left-handed charged gauge bosons, providing additional suppression of flavour-violating effects. The ALRM naturally accommodates viable dark matter candidates, both fermionic and scalar, and in this context, an associated charged Higgs state can acquire a mass ranging from sub-TeV to TeV scales without conflicting with existing experimental constraints.

Researchers are concentrating on scenarios where this charged Higgs behaves as a long-lived particle, exhibiting a sub-GeV mass splitting with the dark matter candidate. Detailed analysis has identified regions of parameter space consistent with the observed dark matter relic density and other experimental limitations, paving the way for potential discoveries.
A comprehensive analysis of disappearing track signatures has been performed, incorporating realistic tracklet reconstruction efficiencies, and existing ATLAS searches have been recast to assess current limits and future sensitivities. Results indicate that the High-Luminosity LHC possesses limited sensitivity to TeV-scale charged Higgs bosons in this scenario, however, the 27 TeV High-Energy LHC can effectively probe the relevant parameter space. Significantly, a 100 TeV collider offers substantially enhanced discovery potential, suggesting a pathway towards validating this innovative theoretical framework.

Charged Higgs boson pair and single production via proton-proton collisions at varying centre of mass energies are investigated

A detailed analysis of disappearing signatures underpinned this work, employing realistic tracklet reconstruction efficiencies and a recasting of existing ATLAS searches to assess current limits and future sensitivities. The methodology began with parton-level event generation using CalcHEP-3.9.2 coupled with SPheno-4.0.5, simulating proton-proton collisions producing charged Higgs bosons and associated particles.
Subsequent parton showering and hadronization were performed with Pythia-8.3, preparing the events for detector-level simulation. Delphes-3.5.0, configured with a default ATLAS detector card, then simulated the interaction of particles within the detector environment. The NNPDF23 lo 0130 qed parton distribution function set was employed, fixing the QCD renormalization and factorization scales to twice the charged scalar mass.

Signal processes considered included p p →H+ 2 H− 2 and p p →H+ 2 A1/H0 1, with total production cross sections calculated for 13, 14, 27, and 100 TeV centre-of-mass energies, as detailed in Table 8. To identify these events, an initial-state radiation-induced mono-jet signature, accompanied by large missing transverse momentum, was utilized, aiming to reduce the apparent missing energy.
Event pre-selection required at least one isolated tracklet, a high transverse momentum jet, and significant missing transverse momentum. This pairing eliminates tree-level flavor-changing neutral currents, offering a pathway to explore potentially viable dark matter candidates.

A specific assignment of global symmetry and the resulting emergent -parity further suppress flavor-violating effects by preventing mixing between the right- and left-charged gauge bosons, and . Detailed analysis focuses on scenarios where a charged Higgs boson, behaves as a long-lived particle due to a sub-GeV mass splitting with the dark matter candidate.
Regions of parameter space consistent with the observed dark matter relic density and other experimental constraints have been identified through detailed simulations. Disappearing signature analyses, incorporating realistic tracklet reconstruction efficiencies, were performed and existing ATLAS searches were recast to assess current limits and future sensitivities.

Results indicate limited sensitivity of the High-Luminosity LHC (HL-LHC) to TeV-scale charged Higgs bosons within this scenario. However, the 27 TeV High-Energy LHC (HE-LHC) can effectively probe the relevant parameter space. A 100 TeV collider is predicted to offer substantially enhanced discovery potential, extending the reach of the investigation.
The ALRM’s particle content is defined within the symmetry group SU(3)C ⊗SU(2)L ⊗SU(2)R′ ⊗U(1)B−L ⊗U(1)S, as detailed in Table 1. The model incorporates a U(1)S soft-breaking Majorana mass term for right-handed neutrinos, allowing for gauge singlet properties. Scalar potential analysis, respecting the symmetry structure, reveals vacuum expectation values (vev) for Φ, χL, and χR, influencing the properties of the resulting particles.

Specifically, the vev assignments lead to a residual Z2 symmetry, ensuring the stability of R-odd particles. Masses of the charged gauge bosons are determined by the coupling constants of SU(2)L and SU(2)R’ interactions, with MWL = 1/2 gL q v2u + v2 L and MWR = 1/2 gR q v2u + v2 R. The R-parity odd nature of WR prevents its mixing with WL and eliminates its contribution to low-energy observables, effectively removing flavor sector constraints on its mass. This model features a unique fermion spectrum where right-handed up-type quarks pair with exotic down-type quarks, effectively suppressing tree-level flavor-changing neutral currents.
A global symmetry assignment and resulting parity further suppress flavor-violating effects, allowing for the existence of viable dark matter candidates, both fermionic and scalar. The analysis focused on scenarios where the charged Higgs boson decays into dark matter, exhibiting a long-lived particle behavior due to a small mass difference between it and the dark matter candidate.

Detailed simulations of disappearing signatures were performed, assessing current limits from ATLAS searches and projecting future sensitivities at the High-Luminosity Large Hadron Collider, the 27 TeV High-Energy Large Hadron Collider, and a potential 100 TeV collider. Results indicate limited sensitivity at the HL-LHC, improved prospects at the 27 TeV HE-LHC, and substantially enhanced discovery potential at a 100 TeV collider.

The study acknowledges that the HL-LHC possesses limited sensitivity to TeV-scale charged Higgs bosons in this specific scenario. Future research should concentrate on exploring the parameter space with higher-energy colliders, particularly the 27 TeV and 100 TeV options, to further probe and constrain the model’s predictions.