The present work aims to study an extension of the Standard Model (SM) that addresses the prominent SM shortcomings, i.e., can explain the neutrino mass, the dark matter (DM) content, and the matter-antimatter asymmetry of the Universe. The model introduces the possibility of a multicomponent DM scenario leading to distinctive signals at colliders. The SM is extended by a “dark” SU(2) gauge symmetry and new fermions and scalar doublets, charged only under SU(2) , that provide candidates for a multicomponent DM. Previously, we have considered in this model the asymmetric DM scenario, while in the present work, we explore the symmetric DM case. We focus on the parameter region where the dark fermion DM annihilates dominantly into the additional dark gauge bosons and the “inert” doublet DM annihilates to SM states via the SM Higgs resonance. This particular choice of doublet mass ensures that the heavier BSM Higgs always has one decay mode open to DM leading to the possibility of detecting such particles at the LHC, in the missing energy plus dijet ( + 2$\textit{j}$) final states. We also discuss the prospects for detecting DM through direct and indirect detection experiments and via Long-Lived-Particle searches. Finally, we show that, as typical of other WIMP models, for low DM mass, signals can be expected in future collider experiments, but for the higher mass range above 500 GeV we have to rely solely on direct detection experiments. Both types of experiments will be essential to fully cover the allowed parameter space.

Germany

Laura Covi

India

Shyamashish Dey

South Korea

Sarif Khan

Santosh Rai

Multicomponent dark matter with collider implications

The inert doublet model (IDM), a minimal extension of the Standard Model (SM), provides a scalar dark matter (DM) candidate that belongs to the additional Higgs doublet. The model faces challenges in achieving the correct relic abundance for compressed spectra and DM masses in the high-mass range. In this work we introduce a $\textit{Z}$ -odd singlet vector-like quark (VLQ) into the IDM framework that helps us alleviate these issues and provide new channels of contributions to the relic abundance. The VLQ not only enhances the DM relic abundance for masses above 550 GeV but also eases constraints from direct detection experiments by enabling smaller couplings between the inert scalars and the SM Higgs. We analyze the impact of the VLQ on DM phenomenology, including relic density, direct and indirect detection constraints. The results demonstrate that the extended IDM framework not only resolves existing limitations in the compressed spectrum but also offers exciting prospects for detection in current and future collider experiments.

Prasanta Das

Saumyen Kundu

Revisiting the inert scalar dark matter with vector-like quarks

We study the prospect of heavy singlet neutrinos as a dark matter (DM) candidate within a neutrinophilic U(1) model, where the Standard Model (SM) is extended with a U(1) gauge symmetry, and neutrino mass and oscillation parameters are explained through an inverse see-saw mechanism. The lightest of the heavy neutrinos plays the role of the DM, while the newly introduced scalars and the extra gauge boson  $$Z'$$  <math> <msup> <mi>Z</mi> <mo>′</mo> </msup> </math>   act as mediators between the dark sector and the SM sector. We show the range of model parameters where this DM candidate can be accommodated in the Weakly Interacting Massive Particle (WIMP) or Feebly Interacting Massive Particle (FIMP) scenario. The observed DM relic density (DMRD) is achieved via the new gauge boson and singlet scalar portals in the WIMP scenario, whereas within the FIMP scenario, these two particles assume a distinct yet pivotal role in generating the observed DMRD.

Egypt

Waleed Abdallah

Anjan Barik

Tousik Samui

Heavy neutrino as dark matter in a neutrinophilic U(1) model

We investigate the possibility of multi-lepton (four and six) signatures, including an exotic signature of same-sign four-lepton (SS4L) as signals of pair production of a doubly charged Higgs in the minimal left-right symmetric model, extended with two doublet scalars. The right-handed neutrino masses are generated in this model through a dimension-5 lepton-number violating operator allowing the triplet scalar interactions with leptons to become negligibly small. This leads to interesting six-lepton and SS4L signatures that can be observed at the high-luminosity phase of the Large Hadron Collider (HL-LHC) with almost no background for doubly charged Higgs with mass below 500 GeV.

Tathagata Ghosh

Rafiqul Rahaman

Search for a leptophobic doubly charged Higgs in same-sign four-lepton and six-lepton signatures in a left-right symmetric model

We perform a collider search for fatjet signals originating from boosted heavy neutral and charged leptons with masses between a few hundred GeV to a TeV. These heavy leptons originate from the decay of heavy gauge bosons with masses above 4 TeV in a left-right symmetric extension of the Standard Model (SM), which considers a universal seesaw mechanism for the generation of all the SM fermion masses. The fatjet signals arise naturally in this model due to the presence of heavy seesaw partners of the SM fermions which decay to SM gauge bosons carrying large boosts. We employ substructure based variables lepton sub-jet fraction (LSF) and lepton mass drop (LMD) together with kinematic variables of fatjets to look for fatjet signals associated with non-isolated leptons. These variables help in reducing the SM backgrounds while retaining enough statistics for signal events, which leads to a robust discovery potential at the high-luminosity Large Hadron Collider (HL-LHC).

Atri Dey

Fatjet signatures of heavy neutrinos and heavy leptons in a left-right model with universal seesaw at the HL-LHC

We consider a fermionic dark matter (DM) in the left–right symmetric framework by introducing a pair of vector-like (VL) doublets in the particle spectrum. The stability of the DM is ensured through an unbroken  $$\mathcal {Z}_2$$  <math> <msub> <mi>Z</mi> <mn>2</mn> </msub> </math>   symmetry. We explore the parameter space of the model compatible with the observed relic density and direct and indirect detection cross sections. The presence of charged dark fermions opens up an interesting possibility for the doubly charged Higgs signal at LHC and ILC. The signal for the doubly charged scalar decaying into the dark sector is analyzed in multilepton final states for a few representative parameter choices consistent with DM observations.

Purusottam Ghosh

Confronting dark fermion with a doubly charged Higgs in the left–right symmetric model

In this work, we explore the signals of an  $$S_3$$  <math> <msub> <mi>S</mi> <mn>3</mn> </msub> </math>  -symmetric two Higgs doublet model with two generations of vector-like leptons (VLLs) at the proposed International Linear Collider (ILC). The lightest neutral component of the VLL in this model provides a viable dark matter (DM) candidate satisfying the current relic density data as well as circumventing all direct and indirect DM search constraints. Some representative benchmark points have been selected with low, medium and high DM masses, satisfying all theoretical and experimental constraints of the model and constraints coming from the DM sector. The VLLs (both neutral and charged) will be produced in pair leading to multi-lepton and multi-jet final states. We show that the ILC will prove to be a much more efficient and useful machine to hunt for such signals compared to LHC. Using traditional cut-based analysis as well as sophisticated multivariate analysis, we perform a detailed analysis of some promising channels containing mono-lepton plus di-jet, di-lepton, four-lepton and four jets along with missing transverse energy in the final state at 1 TeV ILC.

Indrani Chakraborty

Dilip Ghosh

Nivedita Ghosh

Signals for vector-like leptons in an  $$S_3$$  <math> <msub> <mi>S</mi> <mn>3</mn> </msub> </math>  -symmetric 2HDM at ILC

We study the  $$S_3$$  <math> <msub> <mi>S</mi> <mn>3</mn> </msub> </math>  -symmetric two Higgs doublet model by adding two generations of vector like leptons (VLL) which are odd under a discrete  $$Z_2$$  <math> <msub> <mi>Z</mi> <mn>2</mn> </msub> </math>  -symmetry. The lightest neutral component of the VLL acts as a dark matter (DM) whereas the full VLL set belongs to a dark sector with no mixings allowed with the standard model fermions. We analyse the model in light of dark matter and collider searches. We show that the DM is compatible with the current relic density data as well as satisfying all direct and indirect dark matter search constraints. We choose some representative points in the model parameter space allowed by all aforementioned dark matter constraints and present a detailed collider analysis of multi-lepton signals viz. the mono-lepton, di-lepton, tri-lepton and four-lepton along with missing transverse energy in the final state using both the cut-based analysis and multivariate analysis respectively at the high luminosity 14 TeV LHC run.

Dark Matter and Collider Searches in  $$S_3$$  <math> <msub> <mi>S</mi> <mn>3</mn> </msub> </math>  -Symmetric 2HDM with Vector Like Lepton

The search for new physics at high energy accelerators has been at the crossroads with very little hint of signals suggesting otherwise. The challenges at a hadronic machine such as the LHC is compounded by the fact that final states are swamped with jets which one needs to understand and unravel. A positive step in this direction would be to separate the jets in terms of their gluonic and quark identities, much in a similar spirit of distinguishing heavy quark jets from light quark jets that has helped in improving searches for both neutral and charged Higgs bosons at the LHC. In this work, we utilise this information using the jet substructure techniques to comment on possible improvements in sensitivity as well as discrimination of new resonances in the all hadronic mode that would be crucial in pinning down new physics signals at HL-LHC, HE-LHC and any future 100 TeV hadron collider.

Aruna Nayak

Improving heavy dijet resonance searches using jet substructure at the LHC

Search for compressed supersymmetry at multi-TeV scale, in the presence of a light gravitino dark matter, can get sizable uplift while looking into the associated fat- jets with missing transverse momenta as a signature of the boson produced in the decay process of much heavier next-to-lightest sparticle. We focus on the hadronic decay of the ensuing Higgs and/or Z boson giving rise to at least two fat-jets and    in the final state. We perform a detailed background study adopting a multivariate analysis using a boosted decision tree to provide a robust investigation to explore the discovery potential for such signal at 14 TeV LHC considering different benchmark points satisfying all the theoretical and experimental constraints. This channel provides the best discovery prospects with most of the benchmarks discoverable within an integrated luminosity of   <math> <mi>ℒ</mi> </math>  $$ \mathrm{\mathcal{L}} $$  = 200 fb −1. Kinematic observables are investigated in order to distinguish between compressed and uncompressed spectra having similar event yields.