@inproceedings{bib_Vect_2025, AUTHOR = {Diganta Das, Soumyadip Kundu, Anirudhan A. Madathil, Tanumoy Mandal, Subhadip Mitra}, TITLE = {Vector leptoquark contributions to lepton dipole moments}, BOOKTITLE = {Physical Review D}. YEAR = {2025}}

Leptoquarks (LQs) can contribute to the magnetic and electric dipole moments of charged leptons, which the current experiments have measured with good accuracy. We revisit the parameter spaces of TeV-scale vector LQs that contribute to these observables and study how these models fare against the LHC bounds. We show that significant portions of the parameter space are excluded when the current LHC data is utilized effectively. We find that only U1and V2 can explain the observed positive shift in (aμexp-aμSM) through a lepton chirality-flipping contribution with O(1) LQ-quark-lepton coupling. We also see how these two LQs can fit the electron dipole moment and atomic parity violation measurements. We find that the current electric dipole moment measurements of the muon cannot restrain the LQ-quark-lepton couplings within perturbative regions.

@inproceedings{bib_Λb__2023, AUTHOR = {Diganta Das, Jaydeb Das, Girish Kumar, Niladribihari Sahoo}, TITLE = {Λb → Λð→ pπ − Þl+l− as probe of CP-violating new physics}, BOOKTITLE = {Physical Review D}. YEAR = {2023}}

We investigate the possible sizes of all the CP-violating asymmetries offered by the angular distribution of rare decay Λb → Λð→ pπ−Þlþl− in the Standard Model and new physics scenarios motivated by the recent b → slþl− anomalies. We work in a model-independent effective theory framework and discuss the sensitivity of CP asymmetries to new O9;10 operators and their chirality flipped counterparts. We find that the size of many of the CP asymmetries can be at the level of a few percent in new physics scenarios consistent with current b → slþl− data at a level of 1σ. We emphasize that measurements of these CP asymmetries can be used to discriminate different new physics scenarios in b → slþl−.

@inproceedings{bib_Soft_2023, AUTHOR = {Debajyoti Choudhury, Diganta Das, Jaydeb Das}, TITLE = {Soft photon corrections in B → K(∗)ℓ+ℓ− and→ Λ(∗)ℓ+ℓ − decays}, BOOKTITLE = {Technical Report}. YEAR = {2023}}

Abstract: We calculate QED corrections to the semileptonic decays H1 → H2ℓ +ℓ − where ℓ = e, µ and H1,2 are hadrons. The soft and/or collinear divergences are regulated in a gauge-invariant manner and demonstrably cancel, leaving behind a finite residue that depends on the (infrared) momentum cutoff below which a photon is considered to be indistinguishable. On resuming, the said sensitivity reduces drastically, i.e., for the NLL result as compared to the NLO one. The overall correction is negative and its magnitude is larger for a lighter lepton. For B → K(∗) decays, the corrections improve the agreement for the differential distributions, while the behavior is more complicated for Λb → Λ (∗) decays. Rather intriguingly, the corrections serve to regenerate the tension for the lepton flavor universality observables RK and RK∗ .

@inproceedings{bib_Ster_2022, AUTHOR = {Diganta Das, Jaydeb Das}, TITLE = {Sterile neutrinos in Λb0 → (Λc+,p+) ℓ1- ℓ2- ℓ3+ ν decays}, BOOKTITLE = {Physical Review D}. YEAR = {2022}}

We study lepton number violating and lepton number conserving semileptonic decays of heavy baryons Λ0 b to three charged leptons and a neutrino. The decays occur through two intermediate quasidegenerate GeV-scale sterile neutrinos of either Majorana or Dirac type that can be on-shell. Interference between the intermediate heavy neutrinos leads to CP violation in the final states. Effect of neutrino oscillations between the heavy states are also considered in observables of interests, i.e., branching ratio, and the CP-asymmetry. Given the present constraints on the heavy-to-light mixing elements jVeNj and jVμNj, CP-averaged branching ratio of Λ0 b → ðΛc; pÞμμeν with intermediate Majorana neutrinos is almost two orders of magnitude larger than for the same with Dirac neutrinos, whereas, CP-averaged branching ratio of Λ0 b → ðΛc; pÞeeμν is of the same order of magnitude for both Majorana and Dirac neutrino induced decays. CP-violation is found to be appreciable when the neutrino mass difference is comparable with the average decay widths.

@inproceedings{bib_Λb__2022, AUTHOR = {Diganta Das, Jaydeb Das, Girish Kumar, Niladribihari Sahoo}, TITLE = {Λb → Λ(→ pπ−)` +` − as probe of CP-violating New Physics}, BOOKTITLE = {Physical Review D}. YEAR = {2022}}

We investigate the possible sizes of all the CP-violating asymmetries offered by the angular distribution of rare decay Λb → Λ(→ pπ−)` +` − in the Standard Model and new physics scenarios motivated by the recent b → s`+` − anomalies. We work in a model-independent effective theory framework and discuss the sensitivity of CP asymmetries to new O9,10 operators and their chirality flipped counterparts. We find that the size of many of the CP asymmetries can be at the level of few percent in new physics scenarios consistent with current b → s`+` − data at level of 1σ. We emphasize that measurements of these CP asymmetries can be used to discriminate different new physics scenarios in b → s`+` −.

@inproceedings{bib_Reno_2022, AUTHOR = {B. Ananthanarayan, Diganta Das, Mohd Siddique Akbar Alam Khan}, TITLE = {Renormalization group improved ms and |Vus| determination from hadronic tau decays}, BOOKTITLE = {Physical Review D}. YEAR = {2022}}

We determine the strange quark mass ( � � ) and quark mixing element | � � � | , and their joint determination from the Cabibbo suppressed hadronic � decays in various perturbative schemes. We improve this analysis compared to the previous analysis based on the optimal renormalization or the renormalization group summed perturbation theory (RGSPT) scheme by replacing the theoretical longitudinal contributions with phenomenological parametrization; the RGSPT coefficients are used for the dimension-4 Adler functions. The improved analysis results in the extraction of � � ( 2     GeV ) = 98 ± 19   MeV and | � � � | = 0.2191 ± 0.0043 from the RGSPT scheme

@inproceedings{bib_Pros_2022, AUTHOR = {G. Colangelo, M. Davier, A. X. El-Khadra, M. Hoferichter, C. Lehner, L. Lellouch, T. Mibe, B. L. Roberts, Diganta Das}, TITLE = {Prospects for precise predictions of aµ in the Standard Model}, BOOKTITLE = {Technical Report}. YEAR = {2022}}

We discuss the prospects for improving the precision on the hadronic corrections to the anomalous magnetic moment of the muon, and the plans of the Muon g −2 Theory Initiative to update the Standard Model prediction.

@inproceedings{bib_Prec_2021, AUTHOR = {Arvind Bhaskar, Diganta Das, Tanumoy Mandal, Subhadip Mitra, Cyrin Neeraj}, TITLE = {Precise LHC limits on the U1 leptoquark parameter space}, BOOKTITLE = {European Physical Society Conference on High Energy Physics}. YEAR = {2021}}

A TeV scale leptoquark (LQ) is one of the promising explanations of the recent anomalies in the semileptonic decays of 퐵 mesons. Among the various LQs, the vector U1 is capable of explaining the anomalies in both 푅퐷(∗) and 푅퐾 (∗) observables. We use the current LHC data to put bounds on the parameter space of U1 relevant for the anomalies. Precise bounds are drawn by recasting the latest 휏휏 and 휇휇 searches by the ATLAS and CMS collaborations. We find that it is imperative to include the resonant production modes for obtaining limits in the low mass regions. For higher mass points, the non-resonant production modes play a dominant role.

@inproceedings{bib_Pola_2021, AUTHOR = {Diganta Das, Ria Sain}, TITLE = {Polarized Λb baryon decay to pπ and a dilepton pair}, BOOKTITLE = {Physical Review D}. YEAR = {2021}}

The recent anomalies in b → slþl− transitions could originate from some new physics beyond the Standard Model. Either to confirm or to rule out this assumption, more tests of b → slþl− transition are needed. Polarized Λb decay to a Λ and a dilepton pair offers a plethora of observables that are suitable to discriminate new physics from the Standard Model. In this paper, we present a full angular analysis of a polarized Λb decay to a Λð→ pπÞlþl− final state. The study is performed in a set of the operator where the Standard Model operator basis is supplemented with its chirality flipped counterparts, and new scalar and pseudoscalar operators. The full angular distribution is calculated by retaining the mass of the final state leptons. At the low hadronic recoil, we use the heavy quark effective theory framework to relate the hadronic form factors which lead to simplified expression of the angular observables where short- and longdistance physics factorize. Using the factorized expressions of the observables, we construct a number of test of short- and long-distance physics including null tests of the Standard Model and its chirality flipped counterparts that can be carried out using experimental data.

@inproceedings{bib_CP_v_2021, AUTHOR = {Diganta Das, Jaydeb Das}, TITLE = {CP violation with a GeV-scale Majorana neutrino in Λb → (Λ+c ; p +) π + μ − μ − decays}, BOOKTITLE = {Physical Review D}. YEAR = {2021}}

We explore the possibility of CP violation in baryonic Λb → ðΛþ c ; pþÞπþμ−μ− decays which are mediated by two Majorana sterile neutrinos and are jΔLj ¼ 2 lepton-number-violating processes. Appreciable CP asymmetry can be obtained if there are two on-shell Majorana neutrinos that are quasidegenerate in mass with the mass difference of the order of average decay widths. We find that, given the present constraints on the heavy to light mixing element jVμNj, the Λb → pþπþμ−μ− and Λb → Λþ c πþμ−μ− decay rates are suppressed but could be within the experimental reach at the LHC. If searches of the modes are performed, then experimental limits on the rates can be translated to constraints on the Majorana neutrino mass mN and heavy to light mixing element squared jVμNj 2. We show that the constraints on the ðmN; jVμNj 2Þ parameter space coming from the jΔLj ¼ 2 baryonic decays are complementary to the bounds coming from other processes.