arXiv subjects

Bhubanjyoti Bhattacharya

Publications and source records attributed to Bhubanjyoti Bhattacharya.

At least 19 recordsLinked to original sources

arXiv2026

A massive right-handed sterile neutrino in three-body ${\bar B}\to D^*\ell^-{\bar N}_R$ decays - a Monte Carlo simulation study

We investigate the differential decay distributions of $\bar{B}\to D^*\ell^-{\bar N}_R $, where $N_R$ is a heavy right-handed neutrino (RHN) and $\ell = e, μ$. We employ a newly developed Monte Carlo event generator based on the EvtGen framework that can simulate beyond-the-Standard-Model processes. We validate the implementation of the model by comparing the Monte-Carlo results with analytical results for several kinematic variables such as $q^2$ and missing mass, as well as signatures in the angular distributions such as $A_{FB}$, $S_{3}$, $S_{5}$, etc. This MC Generator will enable new experimental searches for RHNs. We discuss the sensitivity of various observables to the presence of an RHN and the feasibility of an experimental analysis at Belle II.

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arXiv2026

Flavor Violations in $B$-Mesons within Non-Minimal SU(5)

Recent anomalies in $B$-meson decays, such as deviations in $R_{D^{(*)}}$ and $B\to Kν{\barν}$, suggest possible lepton flavor universality violation and new exotic interactions. In this work, we explore these anomalies within a non-minimal SU(5) grand unified theory (GUT) framework, which introduces a 45-dimensional Higgs representation predicting exotic scalar particles, including the leptoquark $R_2$ and diquark $S_6$. The $R_2$ leptoquark addresses charged current anomalies in $b\to cτν$ transitions, the $S_6$ diquark contributes to nonleptonic neutral current processes, such as $B\to Kπ$, while at the loop level, diagrams involving the exchanges of the leptoquark, diquark, and the Standard Model particles contribute to $B\to Kν{\barν}$, offering solutions to longstanding puzzles.

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arXiv2026

Axion-like particles and sterile neutrinos solve the $B\to Kν\barν$ and $B\to πK$ puzzles

The recent measurement of the branching ratio of $B^+ \to K^+ + \mathrm{inv}$ (where ``inv'' denotes invisible states) by the Belle II collaboration is enhanced relative to the standard model expectation by 2.7$σ$. An older puzzle persists in measurements of the branching ratios and CP asymmetries of $B \to πK $ decays. We address these two anomalies in flavor-changing neutral current $B$ decays, with a short-lived axion-like particle (ALP) with mass close to that of the $π^0$. In the model with the minimum number of new couplings, the ALP has couplings to the photon, top quark and a heavy sterile neutrino. The ALP contributes to the $B \to π^0 K $ decays by mixing with the $π^0$. It contributes to $B^+ \to K^+ + \mathrm{inv}$ by its off-shell coupling to sterile neutrino pairs. The model can explain the excess in the total rate, but not the observed distribution of signal events. We make predictions for all $B \to K^{(*)} + \mathrm{inv}$ modes and for the rare kaon decays, $K^+ \to π^+ + \mathrm{inv}$ and $K_L \to π^0 + \mathrm{inv}$. We find an appreciable contribution to the magnetic moment of the muon, and negligible contributions to the magnetic moment of the electron and $b \to s e^+ e^-$.

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arXiv2026

Anomalies in Hadronic $B \to VV$ Decays

Recently, a fit of charmless $B\to PP$ decays ($B \in \{B^0, B^+, B_s^0\}$, $P \in \{ π, K, η, η' \}$) to the latest data was performed under the assumption of flavour SU(3) symmetry [SU(3)$_F$]. It was found that there is a $4.1σ$ disagreement with the SU(3)$_F$ limit of the Standard Model [$\rm SM_{SU(3)_F}$]. In this paper, we extend this analysis to charmless $B \to VV$ decays ($V \in \{ρ, K^*, ϕ, ω\}$). The fit examining $B \to ρK^*$ decays, assuming only isospin symmetry, is found to be acceptable. When we fit to $B \to VV$ decays with $V \in \{ ρ, K^* \}$ within SU(3)$_F$, we find a $5.2σ$ discrepancy with SM$_{SU(3)_F}$. Finally, when $B \to VV$ decays with $V \in \{ ρ, K^*, ϕ, ω\}$ are considered, the discrepancy grows to $>7σ$. The theoretical input in this analysis is modest, so our results are quite rigorous, group theoretically, and hold almost exactly in the SU(3)$_F$ limit. Although it seems unlikely that the introduction of $\sim 30$% SU(3)$_F$-breaking effects can account for this discrepancy, this must be verified.

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arXiv2026

Comment on "QCD-factorization amplitudes from flavour symmetries: beyond the $SU(3)$ symmetric case''

Recently, a fit to $B \to PP$ decays ($P \in \{π, K, η, η'\}$) was performed (arXiv:2604.19612, "QCD-factorization amplitudes from flavour symmetries: beyond the $SU(3)$ symmetric case''}) using a formalism that combines topological diagrams with QCD factorization, and a good fit was found. We also recently performed such a fit, under the assumption that the $B \to PP$ amplitudes are related by flavour SU(3) symmetry, but we found a very poor fit. The two results therefore disagree with one another. The source of this disagreement is that we applied EWP-tree relations (ETRs). These were derived $\sim 30$ years ago, and relate different topological diagrams or reduced matrix elements, thus reducing the number of unknown parameters in the fit. In their paper, it is asserted that ETRs are invalid, so that analyses that use them are unreliable. We are writing this Comment to explain why this assertion is incorrect. The key point is that ETRs are mathematically rigorous, group theoretically. If SU(3) is unbroken, and the small Wilson coefficients $c_{7,8}$ in the weak effective Hamiltonian are neglected, ETRs follow automatically and are exact. That is, this is a group theory result -- no hadronic calculations are involved. In this Comment, we also point out several weaknesses of their formalism.

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arXiv2026

Isospin-based EWP-tree Relations

In 1998, it was shown that, if flavor SU(3) symmetry [SU(3)$_F$] is assumed in charmless $B \to PP$ decays ($P$ is a light pseudoscalar meson), some reduced matrix elements involving electroweak penguin (EWP) operators are related to those involving tree operators. Similarly, EWP diagrams are related to tree diagrams. These SU(3)$_F$ EWP-tree relations were recently used in global analyses of $B \to PP$ decays. They have also been used over the years in analyses of the $B \to πK$ puzzle, even though the $B \to πK$ amplitudes are related by isospin symmetry [SU(2)$_I$], and not the full SU(3)$_F$. In this paper, we show that, even if only SU(2)$_I$ is assumed, there are still EWP-tree relations. In $ΔS=0$ decays, these relations are similar to those of SU(3)$_F$, and can be used to take into account the EWP contributions in the extraction of the CP phase $α$ from $B \to ππ$ decays. In $ΔS=1$ decays, the SU(2)$_I$ EWP-tree relations are quite different from those of SU(3)$_F$; when these are used to analyze the $B \to πK$ puzzle, one now finds a 4-5$σ$ discrepancy with the Standard Model, much larger than what was previously found. We argue that, if one analyzes a set of hadronic $B$ decays whose amplitudes are related by isospin, one must use the SU(2)$_I$ EWP-tree relations for that set of decays in the analysis.

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arXiv2026

New physics searches via angular distributions of $ \bar{B} \to D^* (\to D π) τ(\to \ell ν_τ\barν_\ell) \barν_τ$ decays

The study of $\bar{B} \to D^* τ{\barν}_τ$ angular distribution can be used to obtain information about new physics (or beyond the Standard Model) couplings, which are motivated by various $B$ anomalies. However, the inability to measure precisely the three-momentum of the $τ$ lepton hinders such measurements, as the tau decay contains one or more undetected neutrinos. Here, we present a measurable angular distribution of $\bar{B} \to D^* τ{\barν}_τ$ by considering the additional decay $τ\to \ell ν_τ\barν_\ell$, where $\ell \in \{ e , μ\}$. The full process used is $\bar{B} \to D^* (\to D π) τ(\to \ell ν_τ\barν_\ell) \barν_τ$, in which only the $\ell$ and $D^*$ are reconstructed. A fit to the experimental angular distribution of this process can be used to extract information on new physics parameters. To demonstrate the feasibility of this approach, we generate simulated data for this process and perform a sensitivity study to obtain the expected statistical errors on new physics parameters from experiments in the near future. We obtain a sensitivity of the order of 5% for the right-handed current and around 6% for the tensor current. In addition, we use the recent lattice QCD data on $B \to D^*$ form factors and obtain correlations between form factors and new physics parameters.

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arXiv2026

The Deconstruction of Flavor in the Privately Democratic Higgs Sector

The Standard Model (SM) of particle physics fails to explain the observed hierarchy in fermion masses or the origin of fermion-flavor structure. We construct a model to explain these observations in the quark sector. We introduce a spectrum of new particles consisting of six of each -- massive singlet vector-like quarks (VLQs), singlet scalars, and SU(2)-doublet scalars. SM quark masses are generated when the neutral components of the SU(2)-doublet scalars acquire non-zero vacuum expectation values (VEVs). We impose global symmetries to ensure that Yukawa couplings stay roughly flavor diagonal and democratic (of the same order), as well as to suppress tree-level flavor-changing neutral currents. Quark-mass hierarchy then follows from a hierarchy in scalar VEVs. The singlet scalars also acquire weak-scale VEVs. Together with the VLQs, they act as messengers between different generations of quarks in the SM. These messenger particles are responsible for generating the elements of the Cabibbo-Kobayashi-Masakawa (CKM) matrix which depend on the ratios of the singlet VEVs and VLQ masses. Constructed this way, the CKM matrix is found to be \emph{independent} of the SM fermion masses. Using the measured values of the CKM matrix elements and assuming order-one couplings, we derive constraints on the masses of the VLQs and discuss prospects for probing our model in the near future.

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arXiv2025

Anomalies in Hadronic $B$ Decays: an Update

Recently, $B\to PP$ decays ($B = \{B^0, B^+, B_s^0\}$, $P = \{ π, K \}$) were analyzed under the assumption of flavor SU(3) symmetry (SU(3)$_F$). Although the individual fits to $ΔS=0$ or $ΔS=1$ decays are good, it was found that the combined fit is very poor: there is a $3.6σ$ disagreement with the SU(3)$_F$ limit of the standard model (SM$_{\rm{SU(3)}_F}$). One can remove this discrepancy by adding SU(3)$_F$-breaking effects, but 1000\% SU(3)$_F$ breaking is required. In this paper, we extend this analysis to include decays in which there is an $η$ and/or $η'$ meson in the final state. We now find that the combined fit exhibits a $4.1σ$ discrepancy with the SM$_{\rm{SU(3)}_F}$, and 1000\% SU(3)$_F$-breaking effects are still required to explain the data. These results are rigorous, group-theoretically -- no theoretical assumptions have been made. But when one adds some theoretical input motivated by QCD factorization, the discrepancy with the SM$_{\rm{SU(3)}_F}$ grows to $4.9σ$.

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arXiv2025

Quasielastic Lepton-Nucleus Scattering and the Correlated Fermi Gas Model

The neutrino research program in the coming decades will require improved precision. A major source of uncertainty is the interaction of neutrinos with nuclei that serve as targets for such experiments. Broadly speaking, this interaction often depends, e.g., for charge-current quasi-elastic scattering, on the combination of ``nucleon physics", expressed by form factors, and ``nuclear physics", expressed by a nuclear model. It is important to get a good handle on both. We present a fully analytic implementation of the Correlated Fermi Gas Model for electron-nucleus and charge-current quasi-elastic neutrino-nucleus scattering. The implementation is used to compare separately form factors and nuclear model effects for both electron-carbon and neutrino-carbon scattering data.

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arXiv2025

Neutrino Nonstandard Interactions and Lepton Flavor Universality violation at SND@LHC via charm production

In this work, we explore the effect of neutrino nonstandard interactions (NSI) involving the charm quark at SND@LHC. Using an effective description of new physics in terms of four-fermion operators involving a charm quark, we constrain the Wilson coefficients of the effective interaction from two and three-body charmed meson decays. In our fit, we include charmed meson decays not only to pseudoscalar final states but also to vector final states and include decays to the $η$ and $η^\prime$ final states. We also consider constraints from charmed baryon decays. We then study the effect of new physics in neutrino scattering processes, involving charm production at SND@LHC, for various benchmark new physics couplings obtained from the low energy fits. Finally, we also study the effects of lepton universality violation (LUV) assuming that the new physics coupling is not lepton universal.

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arXiv2024

Anomalies in Hadronic $B$ Decays

In this paper, we perform fits to $B \to PP$ decays, where $B = \{B^0, B^+, B_s^0\}$ and the pseudoscalar $P = \{π, K\}$, under the assumption of flavor SU(3) symmetry [SU(3)$_F$]. Although the fits to $ΔS=0$ or $ΔS=1$ decays individually are good, the combined fit is very poor: there is a $3.6σ$ disagreement with the SU(3)$_F$ limit of the standard model (SM$_{\rm{SU(3)}_F}$). One can remove this discrepancy by adding SU(3)$_F$-breaking effects, but 1000% SU(3)$_F$ breaking is required. The above results are rigorous, group-theoretically - no dynamical assumptions have been made. When one adds an assumption motivated by QCD factorization, the discrepancy with the SM$_{\rm{SU(3)}_F}$ grows to $4.4σ$.

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arXiv2024

Charmless $B\to PPP$ Decays: the Fully-Antisymmetric Final State

Under flavor $SU(3)$ symmetry (SU(3)$_F$), the final-state particles in $B\to PPP$ decays ($P$ is a pseudoscalar meson) are treated as identical, and the $PPP$ must be in a fully-symmetric (FS) state, a fully-antisymmetric (FA) state, or in one of four mixed states. In this paper, we present the formalism for the FA states. We write the amplitudes for the 22 $B\to PPP$ decays that can be in an FA state in terms of both SU(3)$_F$ reduced matrix elements and diagrams. This shows the equivalence of diagrams and SU(3)$_F$. We also give 15 relations among the amplitudes in the SU(3)$_F$ limit, as well as the additional four that appear when the diagrams $E$/$A$/$PA$ are neglected. We present sets of $B \to PPP$ decays that can be used to extract $γ$ using the FA amplitudes. The value(s) of $γ$ found in this way can be compared with the value(s) found using the FS states.

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arXiv2023

A U-spin Puzzle in $B$ Decays

We impose U spin symmetry ($SU(2)_{\rm Uspin}$) on the Hamiltonian for $B$ decays. As expected, we find the equality of amplitudes related by the exchange $d \leftrightarrow s$. We also find that the amplitudes for the $ΔS=0$ processes $B^0 \to π^+π^-$, $B_s^0\toπ^+ K^-$ and $B^0\to K^+ K^-$ form a U-spin triangle relation. The amplitudes for $B_s^0\to K^+ K^-$, $B^0\toπ^- K^+$ and $B_s^0\toπ^+π^-$ form a similar $ΔS=1$ triangle relation. And these two triangles are related to one another by $d \leftrightarrow s$. We perform fits to the observables for these six decays. If perfect U spin is assumed, the fit is very poor. If U-spin-breaking contributions are added, we find many scenarios that can explain the data. However, in all cases, 100\% U-spin breaking is required, considerably larger than the naive expectation of $\sim 20\%$. This is the U-spin puzzle; it may be strongly hinting at the presence of new physics.

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arXiv2022

Implications for the $ΔA_{FB}$ anomaly in ${\bar B}^0\to D^{*+}\ell^- {\barν}$ using a new Monte Carlo Event Generator

Recent experimental results in $B$ physics from Belle, BaBar and LHCb suggest new physics (NP) in the weak $b\to c$ charged-current and the $b\to s$ neutral-current processes. Here we focus on the charged-current case and specifically on the decay modes $\bar{B}^0\to D^{*+}\ell^- \barν$ with $\ell = e$ and $μ$. The world averages of the ratios $R_D$ and $R_D^{*}$ currently differ from the Standard Model (SM) predictions by $3.4σ$ while recently a new anomaly has been observed in the forward-backward asymmetry measurement, $A_{FB}$, in $ \bar{B}^0\to D^{*+}μ^- \barν$ decay. It is found that $ΔA_{FB} = A_{FB}(B\to D^{*} μν) - A_{FB} (B\to D^{*} e ν)$ is around $4.1σ$ away from the SM prediction in an analysis of 2019 Belle data. In this work we explore possible solutions to the $ΔA_{FB}$ anomaly and point out correlated NP signals in other angular observables. These correlations between angular observables must be present in the case of beyond the Standard Model physics. We stress the importance of $Δ$ type observables that are obtained by taking the difference of the observable for the muon and the electron mode. These quantities cancel form factor uncertainties in the SM and allow for clean tests of NP. These intriguing results also suggest an urgent need for improved simulation and analysis techniques in $\bar{B}^0\to D^{*+}\ell^- \barν$ decays. Here we also describe a new Monte Carlo Event-generator tool based on EVTGEN that we developed to allow simulation of the NP signatures in $\bar{B}^0\to D^{*+}\ell^- ν$, which arise due to the interference between the SM and NP amplitudes. We then discuss prospects for improved observables sensitive to NP couplings with 1, 5, 50, and 250 ab$^{-1}$ of Belle II data, which seem to be ideally suited for this class of measurements.

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arXiv2022

A new tool to search for physics beyond the Standard Model in ${\bar B}\to D^{*+}\ell^- {\barν}$

Recent experimental results in $B$ physics from Belle, BaBar and LHCb suggest new physics (NP) in the weak $b\to c$ charged-current and the $b\to s$ neutral-current processes. Here we focus on the charged-current case and specifically on the decay modes $B\to D^{*+}\ell^- \barν$ with $\ell = e, μ,$ and $τ$. The world averages of the ratios $R_D$ and $R_D^{*}$ currently differ from the Standard Model (SM) by $3.4σ$ while $ΔA_{FB} = A_{FB}(B\to D^{*} μν) - A_{FB} (B\to D^{*} e ν)$ is found to be $4.1σ$ away from the SM prediction in an analysis of 2019 Belle data. These intriguing results suggest an urgent need for improved simulation and analysis techniques in $B\to D^{*+}\ell^- \barν$ decays. Here we describe a Monte Carlo Event-generator tool based on EVTGEN developed to allow simulation of the NP signatures in $B\to D^*\ell^- ν$, which arise due to the interference between the SM and NP amplitudes. As a demonstration of the proposed approach, we exhibit some examples of NP couplings that are consistent with current data and could explain the $ΔA_{FB}$ anomaly in $B\to D^*\ell^- ν$ while remaining consistent with other constraints. We show that the $Δ$-type observables such as $ΔA_{FB}$ and $ΔS_5$ eliminate most QCD uncertainties from form factors and allow for clean measurements of NP. We introduce correlated observables that improve the sensitivity to NP. We discuss prospects for improved observables sensitive to NP couplings with the expected 50 ab$^{-1}$ of Belle II data, which seems to be ideally suited for this class of measurements.

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arXiv2022

Enhancing HEP research in predominantly undergraduate institutions and community colleges

The long-term success of HEP lies in expanding inclusiveness beyond national labs and academic research institutions to a vast community of predominantly undergraduate institutions (PUI) and community colleges (CC). Institutions such as PUIs and CCs offer an early starting point in the pipeline that can mitigate issues of lack of diversity and underrepresented participation of different groups in HEP. However, there are many underlying systemic, structural, and cultural challenges that need to be addressed collectively. Experimental collaborations are largely populated by national labs and research-focused academic institutions (non-PUIs). The faculty at PUIs and CCs have a high teaching load that is detrimental to their research participation. In addition, there is a lack of guidance, access, and tough competition for securing research funding. The students also suffer from a lack of research infrastructure and technical equipment that can only be found at national labs and larger universities. There are existing successful efforts to enhance the HEP research experience of students and faculty members. This paper discusses ways to leverage these to provide more research opportunities and establish a sustainable national program targeting specifically the issues faced by communities at PUIs and CCs. The need for research mentoring and skill building for faculty members is also laid out. The changes discussed in this paper would make a direct impact on the current spectrum of challenges.

physics.ed-ph↗

arXiv2021

Flavor $SU(3)$ in Cabibbo-favored $D$-meson decays

Model-independent description of nonleptonic decays of charmed mesons is a challenging task due to large nonperturbative effects of strong interactions on the transition amplitudes. We discuss the equivalence of two different flavor-$SU(3)$-based descriptions of Cabibbo-favored non-leptonic decays of charmed mesons to two-pseudoscalars final states including the $η$ and $η^\prime$ mesons.

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