arXiv subjects

Poulose Poulose

Publications and source records attributed to Poulose Poulose.

At least 19 recordsLinked to original sources

arXiv2026

The Alternative Left-Right Scenario: Unitarity, Vacuum Stability and RG Evolution

We study the theoretical constraints on the scalar sector of the Alternative Left-Right Model (ALRM), an $E_6$-motivated extension of the Standard Model based on the gauge group $\mathrm{SU}(3)_c \otimes \mathrm{SU}(2)_L \otimes \mathrm{SU}(2)_{R'} \otimes \mathrm{U}(1)_{B-L}$, supplemented by a global $\mathrm{U}(1)_S$ symmetry. We derive the complete set of tree-level perturbative unitarity constraints on the model, resulting in 14 independent conditions on the quartic scalar couplings. When combined with the boundedness-from-below conditions and the requirement of positive-definite scalar mass-squared eigenvalues, these constraints are found to be complementary, with their simultaneous imposition yielding significantly more stringent restrictions on the parameter space than either set alone. We then perform a one loop renormalization group analysis, evolving the model parameters from the electroweak scale up to a high energy cut-off scale, and requiring that the vacuum stability, the unitarity, and the perturbativity conditions are preserved throughout. The renormalisation group evolution is found to restrict the allowed parameter space considerably beyond the tree-level bounds, with the constraints on the quartic couplings becoming more stringent as the cut off scale is raised. Consequently, the physical scalar masses in the model acquire upper bounds. For the right-hand symmetry breaking scale, $v_R = 10$ TeV and requiring theoretical consistency up to $10^{16}$ GeV, we obtain $m_{H_1^\pm} \lesssim 6.5$ TeV, $m_{H_2^\pm} \lesssim 1.5$ TeV, and $m_{H_1^0} \simeq m_{A_1} \lesssim 1.3$ TeV, with all bounds scaling with $v_R$. These findings offer a predictive and falsifiable framework for searches of the extended Higgs sector of the ALRM at the current and future collider experiments.

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arXiv2026

Disappearing Track Signals from a Light Charged Higgs in the Alternative Left-Right Model

We study the phenomenology of a light charged Higgs boson in the framework of the Alternative Left--Right Symmetric Model (ALRM). In this model, stringent flavor constraints are evaded due to a non-conventional fermion spectrum in which the right-handed up-type quarks are paired with the exotic down-type quarks rather than the Standard Model down-type quarks, leading to the absence of tree-level flavor-changing neutral currents. Furthermore, a specific assignment of the global $U(1)_S$ symmetry and the resulting emergent $R$-parity prevent mixing between the right- and left-handed charged gauge bosons, $W_R$ and $W_L$, providing additional suppression of flavor-violating effects. The ALRM accommodates potentially viable dark matter candidates, both fermionic and scalar ones. In this context, an associated charged Higgs state, $H_2^\pm$, belonging to the dark sector can naturally acquire a sub-TeV to TeV-scale mass without conflicting with any experimental constraints. We focus on scenarios in which $H_2^\pm$ behaves as a long-lived particle due to a sub-GeV mass splitting with the dark matter candidate. We identify regions of parameter space consistent with the observed dark matter relic density and other experimental constraints. A detailed analysis of disappearing track signatures is performed, including realistic tracklet reconstruction efficiencies, and the existing ATLAS search are recast to assess the current limits and future sensitivities. We find that the HL-LHC has limited sensitivity to TeV-scale charged Higgs bosons in this scenario, while the 27 TeV HE-LHC can effectively probe the relevant parameter space, with a 100 TeV collider offering substantially enhanced discovery potential.

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arXiv2025

Dark Matter-Driven Low-Scale Leptogenesis via Neutrino Portal

We propose a novel framework for low-scale leptogenesis within an extension of the Standard Model (SM) that includes three SU(2) singlet right-handed neutrinos, a singlet charged neutral fermion, and a real scalar field. In this setup, the CP asymmetry arises through a rich interplay of mechanisms, including two-body decays of the lightest right-handed neutrino into leptons and Higgs or into dark-sector particles, as well as multiple 2 -> 2 scattering processes involving visible and dark states. Crucially, the CP-violating phases originate not only from conventional vertex and self-energy corrections but also from novel interference effects mediated by the dark sector, which significantly enrich the sources of asymmetry. A distinctive feature of our model is the direct connection between the dark sector and leptogenesis, providing a unified explanation for both the matter-antimatter asymmetry and DM abundance. This connection leads to enhanced CP violation in neutrino interactions and predicts new dark-sector particles accessible at the LHC.

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arXiv2025

Leptonic probes of Alternative Left-Right Symmetric Models

We explore constraints on the parameter space of the alternative left-right model originating from the leptonic sector. Our analyses focuses on both lepton-flavour-conserving observables, particularly the anomalous magnetic moment of the muon, and lepton-flavour-violating processes like $μ\to e γ$ decay and $μ-e$ conversions in nuclei. While contributions to the anomalous magnetic moment fall below the measured values at 2$σ$, current and future experimental sensitivities to flavour-violating branching rations of the Standard Model leptons are expected to impose lower bounds on the mass of the peculiar $SU(2)_R$ gauge boson of the model. This provides complementary constraints relative to existing limits, which are indirect and derived from collider bounds on the mass of the associated neutral gauge boson $Z^\prime$.

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arXiv2024

Flavour-changing top quark decays in the alternative left-right model

We examine flavour-changing neutral-current decays of the top quark, $t\to q γ$, $t \to qZ$, $t \to q H$, and $ t\to q g$ (with $q=u, c$), in the Alternative Left-Right Model, a left right-symmetric model featuring exotic quarks and light bosons. These decays have a very small probability of occurring within the Standard Model, but they can be enhanced in this model through the presence of the exotic states. While associated signals may be detected directly at the LHC, rare decays have the advantage of offering means to probe new particles indirectly, through loop-contributions. We perform a comprehensive analysis of the model's parameter space to demonstrate the possible existence of enhancements in the corresponding branching ratios, of $10^6$ for the branching ratios $\mathcal{B}(t\to uZ)$ and $\mathcal{B}(t \to uH)$, and in the range of $10^{2} - 10^{4}$ for the other decays, relative to the Standard Model. We subsequently determine the preferred parameter space regions of the model in terms of potential of being reached in the near future.

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arXiv2024

Collider Signatures of $W_R$ boson in the Alternative Left-Right Model

Alternative Left-Right Models offer an attractive option to left-right models. Emerging from $E_6$ grand unification, these models are consistent with light scalars which do not induce flavour-changing neutral currents due to the presence of exotic quarks. Here we investigate the signature at the LHC collider of the charged $W_R$ boson, which can be lighter than in left-right models. We include constraints from collider data and show that $W_R$ can be produced in pairs, or in conjunction with a light charged Higgs boson. The final decay products involve leptons or jets. We explore all production and decay possibilities and indicate which ones are most promising to be observed at the colliders. Our analysis shows that signals of $W_R$ bosons can be observed at the LHC at 27 TeV, some for lower luminosity, and under most favourable conditions, even at 13 TeV.

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arXiv2022

Dark Matter in the Alternative Left Right Model

The Alternative Left-Right Model is an attractive variation of the usual Left-Right Symmetric Model because it avoids flavour-changing neutral currents, thus allowing the additional Higgs bosons in the model to be light. We show here that the model predicts several dark matter candidates naturally, through introduction of an $R$-parity similar to the one in supersymmetry, under which some of the new particles are odd, while all the SM particles are even. Dark matter candidates can be fermionic or bosonic. We present a comprehensive investigation of all possibilities. We analyze and restrict the parameter space where relic density, direct and indirect detection bounds are satisfied, and investigate the possibility of observing fermionic and bosonic dark matter signals at the LHC. Both the bosonic and fermionic candidates provide promising signals, the first in LHC at 300 fb$^{-1}$, the second at higher luminosity, 3000 fb$^{-1}$. Signals from bosonic candidates are indicative of the presence of exotic $d^\prime$ quarks, while fermionic candidates imply the existence of charged Higgs bosons, all with masses in the TeV region.

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arXiv2022

Vacuum Structure of Alternative Left-Right Model

We investigate an Alternative Left-Right Model (ALRM) with $SU(2)_L$ as well as $SU(2)_R$ gauge groups, but unlike the traditional left-right symmetric models (LRSM) is not symmetric under the exchange of the fermion content. Interestingly, it can be embedded in $E_6$, while its low energy Higgs structure resembles the LRSM, involving Higgs doublets $χ_{L,R}$ and one Higgs bidoublet $Φ$. We analyze the scalar potential and the vacuum structure of the theory analytically to ensure the stability of scalar potential via bounded from below (BFB) and copositivity criteria, accompanied by a numerical study. We establish the necessary criteria for electric charge preserving vacua, yielding constraints on various coupling parameters of the theory. Finally we obtain constraints on the parameters of the model from collider data on the masses of the Higgs scalars.

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arXiv2022

Leptogenesis from a feebly interacting dark matter sector

We perform an analysis of leptogenesis in the context of a simple extension of the Standard Model by two fermions; one charged ($χ$) and one neutral ($ψ$), in addition to three right-handed neutrinos, $N_i$, interacting through a charged gauge singlet scalar $S$. The dark sector ($χ$, $ψ$ and $S$) interacts feebly and produces a relic density consistent with measurements. The decay of right-handed neutrinos into the charged scalar $S$ and lepton provides an additional source of CP asymmetry, along with contributing through the virtual exchange of $S$ in the standard decay channel. With this the out-of-equilibrium decay of right-handed neutrinos, combined with lepton number changing scattering processes can generate the required baryon asymmetry of the universe even for right-handed neutrino masses in 10 TeV region, without requiring neutrinos to have degenerate masses.

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arXiv2021

Quantum interference effects in Higgs boson pair-production beyond the Standard Model

New physics frameworks like the Next-to-Minimal Supersymmetric Standard Model and the Next-to-2-Higgs-doublet Model contain three neutral CP-even Higgs bosons. It is possible for the heavier two of these states to have masses identical to each other, which can result in a sizeable quantum interference between their propagators in processes they mediate. For both these models, we study the impact of such interference on the pair-production of the lightest of the three scalars, which we identify with the observed 125 GeV Higgs boson, in the gluon-fusion channel at the Large Hadron Collider (LHC). We find that the inclusion of these effects can substantially alter the cross section, compared to its value when they are ignored, for this process. Our results illustrate the importance of taking possible quantum interference effects into account not only when investigating the phenomenology of extended Higgs sectors at the future Run(s) of the LHC, but also when imposing its current exclusion bounds on the parameter spaces of these models.

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arXiv2020

Tracing the anomalous $tqg$ and $tqγ$ flavor changing interactions at the FCC-he

We investigate the possible presence of Flavor Changing Neutral Current (FCNC) couplings of the top quark with gluon and photon through $e^-p\to e^-tj$ process at the Future Circular Collider in the proton-electron mode (FCC-he). Focusing on disentangling the effects of different couplings that could be present, we exploit the presence of the scattered electron, the angular distribution of which is sensitive to the type of coupling involved. Top quark polarisation accessed through the angular distribution of the decay lepton provides additional handle in identifying the nature of the couplings. Further, we demonstrate the potential of electron beam polarisation in distinguishing the left-handed and right-handed couplings of both gluon and photon separately. Considering an $e^-p$ collider of beam energies of $E_{e(p)} = 60~(50000)$~GeV at 2~ab$^{-1}$ integrated luminosity, couplings can be probed at the level of $10^{-2}$ with the corresponding branching fractions of ${\rm BR}(t\to uγ)\le 4 - 7 \times 10^{-6}$ and ${\rm BR}(t\to cγ) \le 1-2 \times 10^{-5}$, depending on if the coupling is right-handed or left-handed. The corresponding limits on the gluon couplings lead to ${\rm BR}(t\to ug)\le 1.7 \times 10^{-5}$ and ${\rm BR}(t\to cg) \le 3-4 \times 10^{-5}$.

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arXiv2020

Freeze-in and Freeze-out of Dark Matter with Charged Long-lived Partners

We present a novel framework capable of addressing the dark matter problem through freeze-in and freeze-out mechanisms, separately or together, depending on the region of the parameter space considered. In the dark matter dynamics, the model features an interplay of thermal production along with sizeable contribution through feeble decay of associated dark fermionic partner, which finally freezes out to the right relic density for a wide range of masses and couplings. Apart from the fermionic dark matter candidate, the model introduces two charged partners, one fermionic and another scalar, which often have delayed decays leading to distinct characteristics of such long-lived particles (LLP) in the colliders like the LHC. Our analysis shows that within the present scenario, LLP of decay length that could be probed at the LHC experiments are compatible with dark matter masses ranging from a few GeV to close to a TeV, as opposed to the requirement of keV-MeV dark matter in simple FIMP scenarios with LLP. In addition, the model presents hitherto unexplored interesting possibilities in the LLP searches, like (i) LLP to LLP to SM cascade decays, which could be searched for within the LHC detectors and (ii) heavy neutral particle decaying within MATHUSLA with two jets and large missing energy. A supplementary aspect of the model is the presence of a heavy neutrino facilitating Type-I seesaw mechanism without disturbing the dark matter side.

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arXiv2019

Fingerprinting the Top quark FCNC via anomalous $Ztq$ couplings at the LHeC

A study of the top quark \emph{Flavour Changing Neutral Current} (FCNC) through $Z$-boson has been performed in the proposed future $e^-p$ collider for the energy, $E_{e(p)} = 60~(7000)$~GeV. We considered an effective theory where the anomalous FCNC couplings are of vector and tensor nature. The effect of these couplings is probed in the single top production along with the scattered electron. The polar angle $θ$ of the electrons coming out of the primary vertex in association with the top quark polarization asymmetries constructed from the angular distribution of the secondary lepton arising from the top decay, allow to distinguish the Lorentz structure of the coupling. From a multi-parameter analysis, we obtain a reach of ${\cal O} (10^{-2})$ in the case of $Ztu$ and $Ztc$ couplings at an integrated luminosity of 2~ab$^{-1}$ at 95\% C.L.

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arXiv2019

Interplay of Scalar and Fermionic Components in a Multi-component Dark Matter Scenario

We explore the multi-component dark matter (DM) scenario considered in a simple extension of the standard model with an inert scalar doublet and a singlet fermionic field providing the two DM candidates. The DM states are made stable under the unbroken $Z_2\times Z_2'$ discrete symmetry. An additional gauge singlet scalar field is introduced to facilitate the interaction of the dark fermion with the visible sector. Presence of a charged fermionic field having the same $Z_2$ charge as that of the inert scalar field allows exploring the dark matter mass regions otherwise disallowed, like in the standard Inert Doublet Model (IDM) scenarios. With these arrangements, it is shown that the light DM scenario and the desert region in the intermediate mass range of DM in the standard IDM case can be made compatible with the relic density bounds and direct detection limits. Further, detailed parameter space study is carried out keeping the coexistence of both the scalar and fermionic components in focus, showing that sizable parameter space regions are available for the entire mass range of $10\ \rm GeV \le M_{DM}\le 2000$ GeV.

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arXiv2019

Measuring Higgs self couplings in the presence of VVH and VVHH at the ILC

The recent discovery of a Higgs boson at the LHC, while establishing the Higgs mechanism as the way of electroweak symmetry breaking, started an era of precision measurements involving the Higgs boson. In an effective Lagrangian framework, we consider the $e^+e^-\rightarrow ZHH$ process at the ILC running at a centre of mass energy of 500 GeV to investigate the effect of the $ZZH$ and $ZZHH$ couplings on the sensitivity of $HHH$ coupling in this process. Our results show that the sensitivity of the trilinear Higgs self couplings on this process has somewhat strong dependence on the Higgs-gauge boson couplings. Single and two parameter reach of the ILC with an integrated luminosity of 1000 fb$^{-1}$ are obtained on all the effective couplings indicating how these limits are affected by the presence of anomalous $ZZH$ and $ZZHH$ couplings. The kinematic distributions studied to understand the effect of the anomalous couplings, again, show a strong influence of $Z$-$H$ couplings on the dependence of these distributions on $HHH$ coupling. Similar results are indicated in the case of the process, $e^+e^-\rightarrow ν\bar νHH$, considered at a centre of mass energy of 2 TeV, where the cross section is large enough. The effect of $WWH$ and $WWHH$ couplings on the sensitivity of $HHH$ coupling is clearly established through our analyses in this process.

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arXiv2018

Relaxing LHC constraints on the $W_R$ mass

We study mass bounds of the $W_R$ gauge boson in generic left-right symmetric models. Assuming that the gauge bosons couple universally to quarks and leptons, we allow different gauge couplings $g_R \ne g_L$ and mass mixing, $V_{CKM}^L \ne V_{CKM}^R$ in the left and right sectors. Imposing constraints from collider experiments and $K^0$, $B_d$, $B_s$ physics, we investigate scenarios where $W_R$ is lighter, or heavier than the right handed neutrino $ν_R$. In these scenarios, $W_R$ mass bounds can be considerably relaxed, while $Z_R$ mass bounds are much more stringent. In the case where $M_{W_R} \le M_{ν_R}$, the experimental constraints come from $W_R \to tb $ and $W_R \to jj$ channels, while if $M_{W_R} \ge M_{ν_R}$, the dominant constraints come from $W_R \to \ell \ell jj $. The observed (expected) limits in the two-dimensional ($M_{W_R}$, $M_{ν_R}$) mass plane excluded at 95\% confidence level extend to approximately $M_{W_R}$= 3.1 (3.3) TeV in the $ee$ channel and 3.3 (3.4) TeV in the ($μμ$) channel, for a large range of right-handed neutrino masses up to $M_{ν_R}$= 2.1 (2.1) TeV in the $ee$ channel and 2.6 (2.5) in the ($μμ$) channel, representing a significant relaxation of the mass bounds.

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arXiv2018

Quantum interference among heavy NMSSM Higgs bosons

In the Next-to-Minimal Supersymmetric Standard Model (NMSSM), it is possible to have strong mass degeneracies between the new singlet-like scalar and the heavy doublet-like scalar, as well as between the singlet-like and doublet-like pseudoscalar Higgs states. When the difference in the masses of such states is comparable with the sum of their widths, the quantum mechanical interference between their propagators can become significant. We study these effects by taking into account the full Higgs boson propagator matrix in the calculation of the production process of $τ^+τ^-$ pairs in gluon fusion at the Large Hadron Collider (LHC). We find that, while these interference effects are sizeable, they are not resolvable in terms of the distributions of differential cross sections, owing to the poor detector resolution of the $τ^+τ^-$ invariant mass. They are, however, identifiable via the inclusive cross sections, which are subject to significant variations with respect to the standard approaches, wherein the propagating Higgs bosons are treated independently from one another. We quantify these effects for several representative benchmark points, extracted from a large set of points, obtained by numerical scanning of the NMSSM parameter space, that satisfy the most important experimental constraints currently available.

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arXiv2017

Two Higgs bosons near 125 GeV in the NMSSM: beyond the narrow width approximation

In the next-to-minimal supersymmetric (NMS) Standard Model (SM), it is possible for either one of the additional singlet-like scalar and pseudoscalar Higgs bosons to be almost degenerate in mass with the ~125 GeV SM-like Higgs state. In the real NMSSM (rNMSSM), when the mass difference between two scalar states is comparable to their individual total decay widths, the quantum mechanical interference, due to the relevant diagonal as well as off-diagonal terms in the propagator matrix, between them can become sizable. This possibility invalidates usage of the narrow width approximation (NWA) to compute the cross section for the production of a di-photon pair with a given invariant mass via resonant Higgs boson(s) in the gluon fusion process at the Large Hadron Collider (LHC). When, motivated by the baryon asymmetry of the universe, CP-violating (CPV) phases are explicitly invoked in the Higgs sector of the NMSSM, all the interaction eigenstates mix to give five CP-indefinite physical Higgs bosons. In this scenario, the interference effects due the off-diagonal terms in the Higgs mass matrix that mix the pseudoscalar-like state with the SM-like one can also become significant, when these two are sufficiently mass-degenerate. We perform a detailed analysis, in both the real and complex NMSSM, of these interference effects, when the full propagator matrix is taken into account, in the production of a photon pair with an invariant mass near 125 GeV through gluon fusion. We find that these effects can account for up to ~40% of the total cross section for certain model parameter configurations. We also investigate how such mutually interfering states contributing to the ~125 GeV signal observed at the LHC can be distinguished from a single resonance.

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