arXiv subjects

Lipika Kolay

Publications and source records attributed to Lipika Kolay.

9 recordsLinked to original sources

arXiv2026

Anomalous Dimensions, Matching, and Phenomenology of Dirac Fermionic Dark Matter Effective Interactions

We explore a fermionic dark matter (DM) extension of the Standard Model Effective Field Theory (SMEFT) and establish a complete renormalisation-group framework for its phenomenological investigation. We derive the anomalous-dimension matrix of all relevant dimension-five and dimension-six operators involving Standard Model (SM) and DM fields, enabling the consistent evolution of the associated Wilson coefficients (WCs) across energy scales. By combining renormalisation-group running with matching at the relevant thresholds, we construct a robust bridge between high-scale new physics and experimental observables. We then perform a comprehensive phenomenological analysis, evaluating the contributions of these operators to observables spanning a wide range of energies and deriving constraints on the WCs from current data. We obtain stringent and complementary bounds on the DM effective field theory (DMEFT) WCs from electroweak precision observables, flavour processes, lepton-flavour-violating decays, top-quark flavour-changing neutral-current decays, and invisible meson decays. Interpreted in terms of the effective scale of new physics, the resulting limits demonstrate that current precision measurements probe energy scales ranging from the TeV regime to several tens or even hundreds of TeV, highlighting the remarkable sensitivity of indirect searches to dark-sector interactions.

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arXiv2026

Complex Scalar Dark Matter with a Vector-Like Quark and Lepton: Precision, Flavor, and HL-LHC

We investigate a minimal extension of the SM consisting of a $\mathbb{Z}_3$-stabilized complex scalar dark matter (CSDM) candidate, a down-type vector-like quark (VLQ), and a charged vector-like lepton (VLL). The additional vector-like fermions not only enable the CSDM to reproduce the observed relic abundance beyond the Higgs-resonance region through semi-annihilation and co-annihilation processes, but also induce correlated signatures across flavor, electroweak precision, dark matter, and collider observables. We perform a comprehensive one-loop analysis of neutral meson mixing, rare meson decays, charged lepton flavor violation, anomalous magnetic moments of charged leptons, and $Z$-pole observables. We find that neutral meson mixing and rare meson decays provide the dominant constraints on the VLQ sector, while charged lepton flavor-violating processes strongly restrict the VLL Yukawa couplings. Current direct-detection limits require Higgs-DM coupling $\lambda_{\Phi H} \lesssim5\times10^{-3}$ and the VLQ Yukawa coupling $\mathtt{y}_d \lesssim 0.05$ for TeV-scale VLQ masses, whereas present indirect-detection searches impose no additional constraints. Combining all flavor, electroweak precision, dark matter, and collider constraints, we identify viable parameter regions with CSDM masses above approximately $1.0~\rm TeV$ and VLQ masses above about $1.5~\rm TeV$. We also find that the LHC can exclude VLQs (VLLs) with masses up to approximately $1.6~(0.38)$ TeV, depending on the CSDM mass, at the $2\sigma$ confidence level. The HL-LHC can further probe an extended region of the parameter space, with discovery prospects at the $3\sigma$ level. Finally, we demonstrate the complementarity of flavor, dark matter, and collider searches in probing this framework.

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arXiv2026

Probing Invisible Fermions in $B \to D^{*}\ell X_{\text{inv}}$ via Angular Observables

Semileptonic decays $B \to D^{*} \ell X_{\text{inv}}$ provide a sensitive probe of light invisible particles, such as sterile neutrinos or dark-sector fermions. Within a general weak effective theory framework, we show that a massive invisible fermion induces distinctive modifications in the angular distributions. We identify observables with enhanced sensitivity to the invisible particle mass, allowing a clear discrimination of such scenarios, and highlight angular structures that differentiate left- and right-handed lepton-dark-sector currents.

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arXiv2026

Probing Light Dark Fermions in $B \to D^{(*)}\ell X_{\rm inv}$ via Rate Distributions

Experimental analyses of the semileptonic decays $ B \to D^{(*)} \ell \bar{\nu}$ typically rely on the assumption that the missing energy originates from a massless neutrino, as predicted by the Standard Model. However, this assumption may not hold in scenarios where the invisible final-state particle is instead massive, such as a sterile neutrino or a dark-sector fermion. In this work, we explore how the presence of a massive dark sector fermion modifies the kinematic and angular distributions of these decays. Our analysis is carried out within the framework of a general weak effective theory, and we also discuss effective and simplified models in which these interactions may arise. In addition, we study the implications of these effects for the extraction of the CKM matrix element $ |V_{cb}|$. Overall, our results show that relaxing the standard assumption of a massless neutrino can lead to observable effects and provide a framework for systematically investigating their impact on semileptonic $B$- decay distributions.

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arXiv2025

Constraining anomalous $W tb$ and related SMEFT couplings using low-energy and electroweak precision observables

We investigate constraints on couplings of Standard Model effective field theory (SMEFT) operators contributing to $Wtb$ effective vertex at tree level. We study the one-loop level impact of these couplings on the low-energy flavour changing charged and neutral current processes and on the electroweak precision observables. We use the available data on these relevant processes to constrain the associated SMEFT/$Wtb$ couplings. Solving the renormalisation group equations, we connect the SMEFT couplings at different scales and use the bounds at low energy to obtain the relevant bounds at the large scale $Λ$. Our findings indicate significantly improved constraints on the couplings compared to existing constraints on $Wtb$ couplings by ATLAS and CMS. Additionally, we predict branching ratios for various top-FCNC processes, which exceed SM expectations by several orders of magnitude but remain within the reach of future colliders. These SMEFT couplings, or anomalous couplings of the effective $Wtb$ vertex, can further constrain different UV-complete and simplified models that generate such interactions at the tree or loop level.

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arXiv2025

Up-type FCNC in presence of Dark Matter

Dark Matter (DM) is a known unknown. Apart, current experimental constraints on flavor-changing neutral current (FCNC) processes involving up-type quarks also provide scope to explore physics beyond the Standard Model (SM). In this article, we establish a connection between the flavor sector and the DM sector with minimal extension of the SM. Here a singlet complex scalar field, stable under $\mathbb{Z}_3$ symmetry, acts as DM and couples to SM up-type quarks through a heavy Dirac vector-like quark (VLQ), which shares the same $\mathbb{Z}_3$ charge as of the DM. The model thus addresses the observed $D^0-\bar{D^0}$ mixing, top-FCNC interactions, and $D^0$ meson decays, together with DM relic density, while evading the direct and indirect DM search bounds. The model can be probed at the future high-energy muon collider, through distinctive signatures of VLQ production, where the VLQ decays into DM and SM particles, abiding by the existing bounds.

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arXiv2025

Flavour and Electroweak Precision Constraints on a Simplified Dark Matter Model with a Light Spin-0 Mediator

This work investigates the allowed parameter spaces of a simplified dark matter (DM) model characterized by a spin-0 mediator with masses in the low to intermediate range ($ < $ 10 GeV). We systematically divide the parameter space into various mass regions of the mediator and constrain the model parameters using a diverse set of observables, including flavour-changing charged and neutral current processes such as rare and semi-leptonic decays of pseudoscalar mesons (B and K), electroweak precision observables, alongside data from fixed-target experiments. Additionally, we explore the model's capability to explain recent Belle-II data on invisible B-meson decays. Our study includes a detailed examination of DM properties and the constraints from Big Bang nucleosynthesis. We present bounds on model parameters through individual and simultaneous analyses of the available inputs and highlight their implications for understanding DM phenomenology. Furthermore, we obtain bounds on the couplings of the possible gauge-invariant dimension-5 operators, leading to the possible interactions between the spin-0 mediator and the SM gauge bosons and fermions. This study comprehensively investigates the constraints and theoretical implications associated with low-mass spin-0 mediator DM models.

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arXiv2024

Exploring Constraints on Simplified Dark Matter Model Through Flavour and Electroweak Observables

This study focuses on a combined analysis of various available inputs to constrain the parameter spaces of a simplified dark matter (SDM) model featuring a spin-0 mediator and fermionic dark matter (DM). The spin-0 mediator interacts with standard model (SM) fermions, SM gauge bosons, and DM. We constrain the parameter spaces of different relevant couplings, DM mass, and the mediator mass, using the data from flavour-changing charged and neutral current processes, CKM matrices, $W$ and $Z$-pole observables, DM relic density, direct and indirect detection bounds. We have calculated bounds on the couplings from both separate and simultaneous analyses of the mentioned processes. We identify correlated parameter spaces for all the relevant parameters which include the couplings and the masses. For the DM and mediator masses, we have scanned the region between 100 GeV and 1000 GeV. Using our results, we have obtained bounds on the couplings of possible higher dimensional operators from which we can formulate our SDM.

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arXiv2024

Multiparticle scalar dark matter with $\mathbb{Z}_N$ symmetry

More than one dark sector particle transforming under the same symmetry provides one stable dark matter (DM) component which undergoes co-annihilation with the heavier particle(s) decaying to DM. Specific assumptions on the kinematics and on the coupling parameters may render the heavier component(s) stable and contribute as DM. The choices of the charges of the dark sector fields under transformation play a crucial role in the resultant phenomenology. In this paper, we systematically address the possibility of obtaining two scalar DM components under $\mathbb{Z}_N$ symmetry. We consider both the possibilities of DM being weakly interacting massive particle (WIMP) or pseudofeebly interacting massive particle (pFIMP). We elaborate upon $\mathbb{Z}_3$ symmetric model, confronting the relic density allowed parameter space with recent most direct and indirect search bounds and prospects. We also highlight the possible distinction of the allowed parameter space in single component and two component cases, as well as between WIMP-WIMP and WIMP-pFIMP scenarios.

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