arXiv subjects

Dhiren Panda

Publications and source records attributed to Dhiren Panda.

8 recordsLinked to original sources

arXiv2026

Role of heavy neutral lepton in lepton number violating $B$ meson decays

We study the phenomenology of heavy neutral leptons (HNLs) in $B$-meson decays as probes of physics beyond the Standard Model. Focusing on the leptonic channels $B \to \mu N$ and $B \to \tau N$, we constrain the allowed regions in the $M_N$--$|U_{\ell N}|^2$ plane using current experimental data. Using these constraints, we investigate lepton-number violating ($\Delta L=2$) processes mediated by on-shell HNLs, including $B_{(c)}^- \to \pi^+ \mu^- \mu^-$ and $B_c^- \to J/\psi\, \pi^+ \mu^- \mu^-$. For benchmark values $|U_{\mu N}|^2 = 10^{-6}$ and $M_N = 2$-- $3\,\mathrm{GeV}$, the predicted branching ratios lie in the range $\mathcal{O}(10^{-13})$--$\mathcal{O}(10^{-8})$. Among the channels, $B_c^- \to \pi^+ \mu^- \mu^-$ shows the largest enhancement, while $B_c^- \to J/\psi\, \pi^+ \mu^- \mu^-$ is strongly suppressed. These results indicate a clear channel dependence, with $B_c$ modes providing enhanced sensitivity to HNL effects and offering promising avenues for future searches of lepton number violation.

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arXiv2025

Quantum decoherence signatures in charmless non-leptonic $B$ decays

Quantum coherence plays a crucial role in the dynamics of neutral meson systems, aiding in the extraction of various Standard Model parameters. However, real physical systems always interact with their surroundings, which causes decoherence. In case of time dependent analysis of non-leptonic neutral $B$ meson decays, this decoherence can be modeled using a single parameter, $\lambda$. Since decoherence can affect the observed dynamics of flavor oscillations and CP violation, it becomes essential to revisit the key SM parameters such as the CKM angles $(\alpha, \beta, \gamma)$ and the mass differences of neutral $B$ mesons ($\Delta m_{d,s}$). In this work, we study the CKM phase $\beta$ as well as the penguin contributions in the $B_d^0 \to J/\psi K_S$ decay mode in the presence of decoherence. We employ the pseudo-experiment (Toy Monte-Carlo) technique and perform an $SU(3)_F$ analysis using the $B_d^0 \to J/\psi \pi^0$ process. Furthermore, we investigate the $B_d^0 \to \pi^+ \pi^-$ decay mode to understand how the decoherence influences the CP violating observables. Our findings reveal that the presence of decoherence can affect crucially the measured values of the observables.

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arXiv2025

Unraveling New Physics Effects in $b \rightarrow s \ell_1 \ell_2$ Transitions with a Model-Independent Perspective

Motivated by recent anomalies in observables associated with flavor-changing neutral current (FCNC) transitions, specifically $b \rightarrow s \ell^+ \ell^-$ processes, we present a comprehensive analysis of lepton flavor-violating (LFV) decay modes mediated by $b \rightarrow s \ell_1 \ell_2$ transitions with $\ell_1 \neq \ell_2$. While such LFV processes are forbidden within the Standard Model (SM), they naturally arise in several of its extensions, including models featuring additional vector-like fermions and extra $Z'$ bosons. Employing the most general effective Hamiltonian for $b \rightarrow s \ell_1 \ell_2$ transitions, we derive the angular distributions of the relevant decay modes. Adopting a model-independent framework, we systematically study the LFV decays $B \rightarrow K^* \ell_1 \ell_2$, $B_s \rightarrow \phi \ell_1 \ell_2$, $B \rightarrow K_2^* \ell_1 \ell_2$, and $\Lambda_b \rightarrow \Lambda \ell_1 \ell_2$. Although LFV mesonic decays have been widely explored, the corresponding baryonic decays remain comparatively under-investigated. We provide bounds on branching ratio ($\mathcal{B}$), forward-backward asymmetry ($\mathcal{A}_{FB}$), and longitudinal lepton polarization fraction ($\mathcal{F}_L$). Furthermore, considering the projected sensitivities of the LHCb upgrade and Belle II experiments, we estimate upper limits for these observables, offering promising avenues for probing new physics in these LFV channels.

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arXiv2024

Analysis of $b \to c \ell \nu $ baryonic decay modes in SMEFT approach

The flavor-changing neutral current decays of heavy bottom quark, alongside the flavor-changing charged current processes mediated by $b \to (c, u)$ in semileptonic $B$ decays are emerged as powerful tools for exploring physics beyond the Standard Model. In this work, we focus on the feasibility of interpreting the processes mediated by $b \to c \tau \nu$ transitions, in particular, the semileptonic $b$-baryonic decay modes $\Sigma_b \to \Sigma_c^{(*)} \tau^-\bar{\nu}_\tau$ and $\Xi_b \to \Xi_c \tau^-\bar{\nu}_\tau$ in the context of SMEFT approach. We perform a detailed analysis of the sensitivity of new physics operators on various observables such as branching ratio, forward-backward asymmetry parameter, lepton non-universal observable and the longitudinal polarization fraction of the $b$-baryonic decay channels.

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arXiv2024

Correlative study of flavor anomalies and dark matter in the light of scalar leptoquark

We explore $U(1)_{L_e-L_\mu}$ gauge extension of the Standard Model with particle content enlarged by three neutral fermions, of which the lightest one contributes to dark matter content of the Universe. The scalar sector is enriched with a $\tilde{R}_2$ scalar leptoquark doublet to investigate flavor anomalies in $B$-meson sector, an additional inert scalar doublet to realize neutrino mass at one loop and a scalar singlet to spontaneously break the new $U(1)$. We discuss dark matter relic density and direct detection cross section in scalar and gauge portals. New physics contribution for $b \to s$ transition comes from penguin diagrams with $Z^\prime$, leptquark and new fermions. We analyze the constraints on the model parameters from the established observables of $B \to K^{(*)} \mu^+ \mu^-$ and $B_s\to \phi \mu^+ \mu^-$ decay channels. Utilizing the permissible parameter space consistent with both flavor and dark sectors, we discuss the impact on various observables such as branching ratio, forward-backward asymmetry, longitudinal polarisation asymmetry, and also lepton non-universality of $\Lambda_b \to \Lambda ^* (1520) (\to pK) \ell ^+\ell ^-$ decay channel.

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arXiv2024

Exploring the lepton flavor violating decay modes $b \to s \mu ^{\pm} \tau ^{\mp}$ in SMEFT approach

We perform an analysis of the consequences of various new physics operators on the lepton flavor violating (LFV) decay modes mediated through $b \to s \ell _1 \ell _2$ transitions. We scrutinize the imprints of the (pseudo)scalar and axial(vector) operators on the exclusive LFV decay channels $ B_{(s)} \rightarrow (\phi, K^{*}, K_{2}^{*})\ell_{1}\ell_{2}$ and $\Lambda_{b}\rightarrow \Lambda \ell_{1}\ell_{2}$, where $\ell_{1}, \ell_{2}$ represent $\mu$ or $\tau$. The new physics parameters are constrained by using the upper limits of the branching fractions of the $B \to \tau \mu$ and $B \to K \tau \mu$ processes, assuming the new physics couplings to be real. We then explore the key observables such as the branching fraction, the forward-backward asymmetry, and the longitudinal polarisation fraction of the $B \to (K^*, \phi, K_2^*) \tau ^{\pm} \mu ^{\mp}$ decays. In addition, we also investigate the impact of the new physics couplings on the baryonic $\Lambda _b \to \Lambda \tau ^{\pm} \mu ^{\mp}$ decay channels mediated by the $b \to s$ quark level transition. With the experimental prospects at LHCb upgrade and Belle II, we also predict the upper limits of the above-discussed observables, which could intrigue the new physics search in these channels.

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arXiv2024

Imprints of new physics operators in the semileptonic $B \to a_1 (1260) \ell^- \bar{\nu}_\ell$ process in SMEFT approach

At present, there are several measurements of $B$ decays that exhibit discrepancies with the predictions of the Standard Model, and suggest the presence of new physics in $b\to s$ and $b \to c(u)$ quark level transitions. Motivated by the prospects of the ongoing high-luminosity $B$ factories, we study the exclusive $B \to a_1 (1260) \ell^- \bar{\nu}_\ell$ process within the Standard Model Effective Field Theory (SMEFT) formalism, to understand the sensitivity of new physics. The new physics parameters are constrained by using the experimental branching fractions of the (semi)leptonic $B \to \ell \bar{\nu}$ and $B \to (\pi, \rho, \omega) \ell \bar{\nu}$ processes (where $\ell = e, \mu, \tau$) which undergo $b \to u \ell \bar{\nu}$ quark level transitions. We then perform a comprehensive angular analysis of the exclusive $B \to a_1 (1260) \ell^- \bar{\nu}_\ell$ process in the Standard Model and in the presence of various new physics operators. We also provide the predictions and comment on various observables, such as branching ratio, forward-backward asymmetry, and the test of lepton flavor non universality of the $B \to a_1 (1260) \ell^- \bar{\nu}_\ell$ channel.

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arXiv2023

Investigating $ Υ(ns) \to τ^+ τ^- $ decay in the Leptoquark scenario

Several measurements on $R_D, R_{D^*}$, and $R_{J/ ψ}$ by the BaBar, Belle, and LHCb experiments show significant deviations from their Standard Model (SM) predictions, which illustrate the fact that the concept of lepton flavor universality (LFU) is violated in semileptonic $B$ meson as well as leptonic $Υ(ns)(n=1,2,3)$ decays. Recently BaBar experiment announced that at $1.8σ$ level, $R_Υ(3s)= {\rm Br}(Υ(3s) \to τ\barτ)/{\rm Br}(Υ(3s) \to μ\barμ)$ shows an acceptance with the SM. These fascinating findings point towards the possible implication of new physics in the $b \to c τ\barν$ transitions, which in turn, creates a new direction to look for new physics in $b \bar{b} \to τ\barτ $ process. Thereby, the new physics contributions to the $b \to c τ\barν$ process would inevitably alter the $b \bar{b} \to τ\barτ $ transitions. Here we conduct a $χ^{2}$ fit to constraining the new parameters by using the measured values of $ R_D$, $R{_D*}$, $ R_{J/ ψ}$, $ R_{X_C}$, $F_L (D^*)$ and $P_τ (D^*)$. In this context, we investigate the effect of constrained new physics couplings on the branching ratios and LFU parameters $R_{Υ(ns)}$ through leptoquark models such as $S_3, \tilde{S_1}, \tilde{R_2}, U_1, U_3 $ and $ V_2$.

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