arXiv subjects

Sahabub Jahedi

Publications and source records attributed to Sahabub Jahedi.

18 recordsLinked to original sources

arXiv2026

Systematic study of lepton-flavor-violating dark matter interactions via indirect detection in effective field theories

Lepton-flavor-violating (LFV) interactions involving dark matter (DM) particles remain a largely unexplored area. In this study, we systematically investigate LFV DM interactions within the framework of effective field theories by analyzing astrophysical photons and positrons produced from DM annihilation. Employing the astrophysical photon and positron data collected by Fermi-LAT, INTEGRAL, XMM-Newton, and AMS-02, we place meaningful constraints on all leading-order effective operators involving a DM pair and a flavor-violating charged lepton pair. Our analysis covers the three well-known DM candidates: a scalar, a fermion, and a vector particle. For the photon flux, we consider contributions from final-state radiation, radiative decay, and inverse Compton scattering and examine their respective sensitivity regions across different DM masses and photon energies. We find that, for DM masses below $\mathcal{O}(20\,\rm GeV)$, INTEGRAL provides the most stringent constraints on annihilation cross sections and effective operators in all three LFV channels, whereas AMS-02 offers the strongest constraints above $\mathcal{O}(20~\rm GeV)$.

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arXiv2026

Neutron stars as thermometers for reheating induced dipole dark matter

We investigate the electromagnetic interactions of dipole dark matter (DM) within an effective field theory framework, considering both standard and non-standard cosmological scenarios. We first study the prospects of DM production via both the freeze-out and freeze-in mechanisms within the standard radiation-domination. We then investigate how the viable DM parameter space is modified in a non-standard cosmological scenario due to entropy dilution during reheating. Existing constraints on the parameter space are discussed, and we highlight the discovery potential of future direct detection experiments to probe these scenarios. We further investigate the implications of neutron star heating for dipole DM. Due to the momentum-dependent nature of the interaction, dipole DM is captured efficiently by neutron stars, thereby making neutron star heating a sensitive probe of the dipole DM parameter space.

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arXiv2026

Electroweak phase transition in SMEFT: Gravitational wave and collider complementarity

We study the first-order electroweak phase transition (FO-EWPT) within the Standard Model Effective Field Theory (SMEFT) framework induced by dimension-6 operators. Such phenomena can be probed independently via \textit{di}-Higgs production at the collider experiments as well as via the detection of gravitational waves (GW). There are three (one) dimension-6 SMEFT operators that simultaneously modify the Higgs potential at tree (1-loop) level and contribute to the \textit{di}-Higgs production at the hadron colliders. With \textit{di}-Higgs production being suppressed at current LHC runs, we aim to probe this production at high luminosity (HL) and high energy (HE) runs of the LHC to achieve better sensitivity of dimension-6 SMEFT operators. The correlations among these operators are analyzed in the context of probing FO-EWPT, emphasizing the complementarity between future GW observations and upgraded LHC searches.

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arXiv2026

Probing ALP-portal fermionic dark matter at the $e^+e^-$ colliders

Axion-like particles (ALPs) are promising candidates for mediating interactions between a dark sector and the Standard Model (SM). In this work, considering the effective interactions of ALPs with the SM gauge bosons and a fermion dark matter (DM), we explore the DM relic satisfied parameter space and assess its testability through indirect searches. The effect of early kinetic decoupling is also discussed in the resonant regime. The potential of probing such ALP-portal fermionic DM at the electron-positron colliders is investigated with the mono-photon plus missing energy final states. We show that a spectacular distinction between the signal and SM background is possible via the missing energy variable, the seed of which lies in the ALP-photon interaction, which also governs the relic density of DM. We further discuss the sensitivity of ALP-photon coupling using the $χ^2$ analysis at the future electron-positron collider specifications.

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arXiv2026

Charged lepton flavor violating decays with a pair of light dark matter and muonium invisible decay

In this paper, we initiate the study of lepton flavor violating (LFV) dark matter (DM) interactions, expanding our focus beyond the flavor-conserving DM interactions typically considered in conventional direct and indirect detections. We work in an effective field theory (EFT) framework, focusing on the leading-order local operators of the form, $\bar \ell_j Γ\ell_i\,{\tt DM}^2$, where $(ij)=(eμ, eτ, μτ)$ and the DM includes the three well-known scenarios: a scalar, a fermion, and a vector. We derive the invariant-mass distribution for the three-body decay $\ell_i \to \ell_j +{\tt DM+DM}$ and demonstrate that it can be used to distinguish between different operator structures and to determine the DM mass. By utilizing current experimental bounds on the charged muon LFV decay involving neutrinos and the ratio of tau leptonic decay widths, we establish stringent limits on the effective scale associated with each operator. Additionally, for the $eμ$ flavor combination, we investigate the muon four-body radiative decay ($μ\to e +{\tt DM+DM}+γ$) to complement our probe of such interactions. Finally, we examine muonium invisible decays based on the derived bounds on the effective operators and find that the branching ratios can be significantly enhanced compared to the predictions of the standard model. In particular, any future observation of the para-muonium invisible decay serves as a compelling signature for these flavored DM interactions.

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arXiv2025

Multi-messenger FIMP

We propose a multi-messenger frontier probe of non-thermal or freeze-in massive particle (FIMP) dark matter (DM) by considering an effective field theory (EFT) setup. Assuming leptophilic operators connecting DM with the standard model (SM) bath, we consider DM mass ($m_{\rm DM}$) and the reheat temperature of the Universe ($T_{\rm rh}$) in a regime which prevents DM-SM thermalisation. Low $T_{\rm rh}$ allows sizeable DM-SM interactions even for non-thermal DM allowing the latter to be probed at direct, indirect detection frontiers as well as future electron-positron and muon colliders. An extended reheating period governed by monomial inflaton potential after its slow-roll phase not only generates the required abundance of non-thermal DM via ultraviolet (UV) freeze-in but also brings the scale-invariant primordial gravitational waves (GW) within reach of near future experiments across a wide range of frequencies. While particle physics experiments can probe $T_{\rm rh} \sim O(10)$ GeV and FIMP DM with mass $m_{\rm DM} \sim O(1)$ TeV, future GW detectors are sensitive to a much wider parameter space.

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arXiv2025

Lepton collider as a window to reheating via freezing in dark matter detection. Part I

We propose a methodology to infer the reheat temperature ($T_{\rm RH}$) of the Universe from the collider signal of freezing in dark matter (DM). We demonstrate it for the mono-$γ$ signal at the electron-positron colliders, which indicates to a low-scale $T_{\rm RH}$, after addressing observed DM abundance, BBN, and other relevant constraints. The method can be used to correlate different reheating dynamics, DM models, and collider signals.

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arXiv2025

Optimal sensitivity of anomalous charged triple gauge couplings through $W$ boson helicity at the $e^+e^-$ colliders

We study the estimation of anomalous charged triple gauge couplings (cTGCs) parameterized in a model-independent Standard Model effective field theory (SMEFT) framework via $WW$ production followed by semi-leptonic decay at the $e^+e^-$ colliders. The anomalous $(WWV~(V=γ,Z))$ couplings are given in terms of Wilson coefficients of three CP-conserving and two CP-violating dimension-6 operators in the HISZ basis. We adopt the optimal observable technique (OOT) to extract the sensitivity of these anomalous couplings and compare it with the latest experimental limits on anomalous couplings studied at the LHC. The limits on the anomalous couplings obtained via OOT are significantly tighter than the ones obtained using standard $χ^2$ analysis. The impact of different helicity combinations of the $W$ boson pair in determining optimal sensitivity is analyzed. The constraints on CP-violating operators from the electron electric dipole moment (EDM) are also discussed.

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arXiv2025

Lepton collider as a window to reheating via freezing in dark matter detection. Part II

Dark matter (DM) genesis via Ultraviolet (UV) freeze-in embeds the seed of reheating temperature and dynamics in its relic density. Thus, discovery of such a DM candidate can possibly open the window for post-inflationary dynamics. However, there are several challenges in this exercise, as freezing-in DM possesses feeble interaction with the visible sector and therefore very low production cross-section at the collider. We show that mono-photon (and dilepton) signal at the ILC, arising from DM effective operators connected to the SM field strength tensors, can still warrant a signal discovery. We study both the scalar and fermionic DM production during reheating via UV freeze-in, when the inflaton oscillates at the bottom of a general monomial potential. Interestingly, we see, right DM abundance can be achieved only in the case of bosonic reheating scenario, satisfying bounds from big bang nucleosynthesis (BBN). This provides a unique correlation between collider signal and the post-inflationary dynamics of the Universe within single-field inflationary models.

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arXiv2025

Optimal New Physics estimation in presence of Standard Model backgrounds

In this work, we develop a numerical technique for the optimal estimation of the new physics (NP) couplings applicable to any collider process without any simplifying assumptions. This approach also provides a way to measure the quality of the NP estimates derived using standard $χ^2$ analysis and can be used to gauge the advantages of various modalities of collider design. We illustrate the techniques and arguments by considering the pair production of heavy charged fermions at an $e^+e^-$ collider.

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arXiv2024

Collider and CMB complementarity of leptophilic dark matter with light Dirac neutrinos

We study the discovery prospects of leptophilic dark matter (DM) in future lepton colliders by considering the light neutrinos to be of Dirac type. Adopting an effective field theory (EFT) approach, we write down dimension six operators connecting the standard model (SM) fields, light Dirac neutrinos and DM. Considering DM relic to be generated via the thermal freeze-out, we check the discovery prospects at future lepton colliders via mono-photon plus missing energy searches. The right chiral parts of light Dirac neutrinos get thermalised due to their interactions with the bath as well as leptophilic DM, leading to enhanced effective relativistic degrees of freedom $N_{\rm eff}$ within reach of future cosmic microwave background (CMB) experiments. The interplay of existing bounds from cosmological observations related to DM relic and $N_{\rm eff}$, direct and indirect detection of DM, astrophysics and collider observations leave promising discovery prospects at future electron and muon colliders along with complementary signatures at future CMB experiments.

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arXiv2024

Exploring Optimal Sensitivity of Lepton Flavor Violating Effective Couplings at the $e^+e^-$ Colliders

We analyze lepton flavor violation (LFV) using the Standard Model Effective Field Theory (SMEFT) framework at the future lepton colliders. Our focus is on the associated production of tau lepton with electron/muon at the electron-positron ($e^+e^-$) colliders, related to four-Fermi SMEFT effective operators. In accordance with the upper limits on effective couplings from lepton flavor violating tau decays, we conduct a cut-based analysis to achieve sufficient signal significance. We utilize the optimal observable technique (OOT) to estimate the optimal sensitivity of the effective couplings. The impact of electron beam polarization and the interplay of signal and background in enhancing the optimal sensitivity of the effective couplings are discussed in detail. We find that the sensitivity of flavor-violating effective couplings is enhanced by order of one for 3 TeV center-of-mass (CM) energy and 1000 $\rm{fb}^{-1}$ integrated luminosity at the $e^+e^-$ colliders.

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arXiv2024

Probing flavor constrained SMEFT operators through $tc$ production at the Muon collider

We investigate flavour violating four Fermi Standard Model Effective Field Theory (SMEFT) operators of dimension-six that can be probed via $tc ~(\bar{t}c+t\bar{c})$ production at the multi-TeV muon collider. We study different FCNC and FCCC processes related to $B$, $B_s$, $K$ and $D$ decays and mixings, sensitive to these operators and constrain the corresponding couplings. The tensor operator turns out to be most tightly bound. We perform event simulation of the final state signal from $tc$ production together with the SM background to show that operators after flavour constraint can reach the discovery limit at 10 TeV muon collider. We further adopt the optimal observable technique (OOT) to determine the optimal statistical sensitivity of the Wilson coefficients and compare them with the flavour constraints. We use the limits to predict the observational sensitivities of the rare processes like $K_L \to π_0 \ell \ell$, $D_0 \to μμ$, $t \to c\ell\ell$.

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arXiv2023

Optimal estimation of Dimension-8 Neutral Triple Gauge Couplings at $e^+ e^-$ Colliders

We investigate the measurement of non-standard ZZV (V = γ, Z) couplings through Z-boson pair production at the $e^+ e^-$ colliders. We adopt Standard Model Effective Field Theory (SMEFT) approach to study these anomalous neutral triple gauge couplings. There are one CP-conserving and three CP-violating dim-8 SMEFT operators that contribute to ZZV couplings. Using optimal observable technique, the sensitivity of these NP couplings has been estimated and then we compare it with the latest experimental limits on dim-8 couplings at CERN LHC. Effect of beam polarization and correlations among CP-violating ZZV couplings are discussed. Comparison of statistical limits of new physics couplings between optimal observable technique and contemporary cut-based analysis has also been studied in detail.

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arXiv2023

Optimal determination of New Physics couplings: A comparative study

We study the determination of new physics (NP) parameters using the optimal observable technique (OOT) in situations where the standard model (SM) dominates over the NP effects, and when the NP dominates over the SM contribution, using the 2-Higgs doublet model as an illustrative example; for the case of SM domination we extend our results using an effective theory parameterization of NP effects. For the case of SM dominance we concentrate on $t \bar{t}$ production in an $e^+e^-$ collider, while for the case of NP dominance we consider both $t \bar{t}$ production and pair production of charged scalars, also in an $e^+e^-$ collider. We discuss the effects of the efficiency of background reduction, luminosity and beam polarization, and provide a comparison of the optimal uncertainties with those obtained using a standard $χ^2$ analysis of (Monte Carlo generated) collider data.

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arXiv2023

Probing anomalous $Z\,Z\,γ$ and $Z\,γ\,γ$ Couplings at the $e^+\,e^-$ Colliders using Optimal Observable Technique

We study the anomalous $ZZγ$ and $Zγγ$ couplings that can be probed via $Zγ$ production at the $e^+ \, e^-$ colliders. We take Standard Model Effective Field Theory (SMEFT) approach to examine these anomalous neutral triple gauge couplings in a model independent way. There are four independent dimension-8 operators that generate these gauge interactions, one of them is CP-conserving and rest three are CP-violating. We adopt optimal observable technique to extract the sensitivity at which these anomalous couplings can be probed at future $e^+e^-$ colliders and then compare the results with the latest experimental limit obtained at the LHC. We also study the impact and advantage of beam polarization in these precision measurements. Statistical limit (95\% C.L.) on individual anomalous couplings as well as the correlation between various couplings have been discussed in detail.

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arXiv2022

Probing heavy charged fermions at $e^+e^-$ collider using the Optimal Observable Technique

In this work we study the production of color-neutral and singly-charged heavy leptons at the proposed International Linear Collider. We use the optimal observable technique to determine the statistical accuracy to which the coupling of such fermions to the $Z$ gauge boson (vector, axial or chiral) can be measured. We also consider a UV-complete model that contains these particles as well as a dark matter candidate, and consider some observable effects involving both; the correspondence to chargino production in supersymmetric models with heavy sleptons is briefly discussed.

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arXiv2022

Effective Leptophilic WIMPs at the $e^+e^-$ collider

We consider higher-dimensional effective (EFT) operators consisting of fermion dark matter (DM) connecting to Standard Model (SM) leptons upto dimension six. Considering all operators together and assuming the DM to undergo thermal freeze-out, we find out relic density allowed parameter space in terms of DM mass ($m_χ$) and New Physics (NP) scale ($Λ$) with one loop direct search constraints from XENON1T experiment. Allowed parameter space of the model is probed at the proposed International Linear Collider (ILC) via monophoton signal for both Dirac and Majorana cases, limited by the centre-of-mass energy $\sqrt s=$1 TeV, where DM mass can be probed within $m_χ<\frac{\sqrt{s}}{2}$ for the pair production to occur and $Λ>\sqrt s$ for the validity of EFT framework.

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