Publications

Order by: publication date number of citations

• Implications of new physics in $\Lambda_b \to \Lambda_c \ell \nu_{\ell}$ decay processes

  Aishwarya Bhatta, Rukmani Mohanta

  SciPost Phys. Proc. 16, 012 (2025) · published 14 July 2025 | Toggle abstract · pdf

  Several indications of lepton non universality ratios, $R{(D^*)}$, $R{(J/\Psi)}$ and the measurements on hadronic and $\tau$ longitudinal polarizations in $b \to c \ell \bar{\nu_{\tau}}$ processes have attracted a lot of attentions. By considering the most general effective Lagrangian, we carry out a model independent analysis of the semileptonic $\Lambda_b$ decays, to inspect the nature of new physics. We constraint the new physics parameter space by using the chi square fitting. We study the implications of constrained new couplings on the observable such as branching fractions, forward-backward asymmetries, lepton non universality parameter and $\Lambda_c$ and lepton longitudinal polarization fractions of the decay modes.

• Probing lepton flavor violation via $e\tau$ production in an effective framework at a future electron-positron circular coll

  Seyed Mohsen Etesami, Reza Jafari, Mojtaba Mohammadi Najafabadi, Seddigheh Tizchang

  SciPost Phys. Proc. 16, 016 (2025) · published 14 July 2025 | Toggle abstract · pdf

  In the Standard Model framework, lepton flavor is conserved in interactions. However, it can be violated in certain scenarios beyond the Standard Model. In this study, we consider $(e^{±}\tau^{\mp})$ production through a four-Fermi lepton flavor violation interaction at the future electron-positron circular collider (FCC-ee). To constrain the Wilson coefficients at four center-of-mass energies $157.5, 162.5, 240$, and $365$ GeV that have been proposed for the FCC-ee, a Standard Model Effective Field Theory (SMEFT) is used. The main sources of background are accounted for, and the study incorporates realistic detector effects. To enhance the results, we combine the individual constraints obtained at each center-of-mass energy. We show that the combined limits improve the sensitivity to lepton flavor violation couplings by a factor of approximately three compared to the individual results and are competitive with the Belle II prospects.

• Search for lepton-flavor-violating decays of the tau lepton at a future muon collider

  Gholamhossein Haghighat, Mojtaba Mohammadi Najafabadi

  SciPost Phys. Proc. 16, 017 (2025) · published 14 July 2025 | Toggle abstract · pdf

  Tau leptons can have lepton-flavor-violating (LFV) couplings to a muon or an electron and an Axion-Like Particle (ALP). ALPs are pseudo Nambu-Goldstone bosons associated with spontaneously broken global U(1) symmetries. LFV ALPs have been of a great interest in the last several decades as they can address some of the SM long-lasting problems. Assuming a future muon collider proposed by the Muon Accelerator Program (MAP), we search for LFV decays $\tau\rightarrow\ell a$ ($\ell=e,\mu$) of one of the tau leptons produced in the muon-anti muon annihilation. The ALP mass is assumed to be in the range 100 eV to 1 MeV and three different chiral structures are considered for the LFV coupling. Using a multivariate technique and performing a parameterized simulation based on the ideal target performance, we obtain expected 95$\%$ confidence level upper limits on the LFV couplings tau-electron-ALP and tau-muon-ALP. Limits are computed assuming the center-of-mass energies of 126, 350 and 1500 GeV which the future muon collider is supposed to operate at. We study the two cases of unpolarized and polarized muon beams and show that taking advantage of tau polarization-induced effects, the main background $\tau\rightarrow e/\mu + \nu\bar{\nu}$ can be significantly reduced. Results indicate that current limits on the LFV couplings can be improved by roughly one order of magnitude using the present analysis.

• Feasibility of tau g-2 measurements in ultra-peripheral collisions of heavy ions

  Nazar Burmasov, Evgeny Kryshen, Paul Buehler, Roman Lavicka

  SciPost Phys. Proc. 16, 022 (2025) · published 15 July 2025 | Toggle abstract · pdf

  The anomalous magnetic moment of the tau lepton, $a_\tau=(g_\tau - 2)/2$, is a sensitive probe of new physics but is extremely difficult to measure precisely in contrast to electron and muon moments. The best experimental limits were set by the DELPHI collaboration more than 15 years ago in studies of the ditau production in the $ee\to ee\tau\tau$ process. Ultra-peripheral collisions (UPCs) of heavy ions at the LHC may provide a unique opportunity to improve the $a_\tau$ constraints in the studies of ${\rm Pb + Pb}\to {\rm Pb + Pb}+\tau\tau$ process. We review recent proposals to study ditau production via semi-leptonic tau decays in Pb-Pb UPC with the available ATLAS and CMS data and discuss the feasibility to explore this process down to low transverse momenta of decay leptons with the ALICE and LHCb experiments.

• Exploring neutrino masses and mixing in the seesaw model with $L_e-L_\tau$ gauged symmetry

  Papia Panda, Mitesh Kumar Behera, Priya Mishra, Shivaramakrishna Singirala, Rukmani Mohanta

  SciPost Phys. Proc. 16, 024 (2025) · published 15 July 2025 | Toggle abstract · pdf

  We investigate neutrino phenomenology in the $U(1)_{L_e-L_\tau}$ gauge extension of the Standard Model with symmetry following the framework of type-(I+II) seesaw mechanism. For this, we have added three right handed neutrinos, one singlet and one scalar triplet in our model. We show that the model can successfully accommodate the observed neutrino oscillation data and consistent with the results from lepton flavor violation and neutrinoless double beta decay process.

• Probing $\delta_{CP}$ phase and charged lepton flavour violation with $A_4$ flavor symmetry and deviations to tri-bi-maximal mixing via $z_2 \times z_2$ invariant perturbation in the neutrino sector

  Gayatri Ghosh

  SciPost Phys. Proc. 16, 025 (2025) · published 15 July 2025 | Toggle abstract · pdf

  In this work, a flavour theory of a neutrino mass model based on $A_{4}$ symmetry is considered to explain the phenomenology of CP violation phase and charged lepton flavour violation. The spontaneous symmetry breaking of $A_{4}$ symmetry in this model leads to tribimaximal mixing in the neutrino sector at a leading order. $\mathrm{A} z_{2} × z_{2}$ invariant perturbations in this model is introduced in the neutrino sector which leads to testable predictions of $\theta_{13}$ and $\mathbf{C P}$ violation. We consider an effective theory with an $A_{4} × z_{2} × z_{2}$ symmetry, which after spontaneous symmetry breaking at high scale which is much higher than the electroweak scale leads to charged lepton flavour violation processes once the heavy Majorana neutrino mass degeneracy is lifted either by renormalization group effects or by a soft breaking of the $A_{4}$ symmetry.

• T-violating effect in $\nu_\tau (\bar{\nu}_\tau)-$nucleon quasielastic scattering

  A. Fatima, M. Sajjad Athar and, S. K. Singh

  SciPost Phys. Proc. 16, 026 (2025) · published 15 July 2025 | Toggle abstract · pdf

  The production cross sections and polarization observables of the $\tau$ leptons produced in the $|\Delta S| = 0$ and $1$ induced $\nu_{\tau}(\bar{\nu}_{\tau})-N$ quasielastic scattering have been studied. The effect of T violation, in the case of $\Delta S=0$ and 1 processes, and the SU(3) symmetry breaking effects, in the case of $\Delta S=1$ processes, on the total scattering cross sections as well polarization observables are explored. Experimentally, it would be possible to observe these effects in the forthcoming (anti)neutrino experiments like DUNE, SHiP and DsTau.

• Probing new physics with the leptonic g-2

  Paride Paradisi

  SciPost Phys. Proc. 16, 030 (2025) · published 15 July 2025 | Toggle abstract · pdf

  We present a concise review of the new physics sensitivity of leptonic dipole moments and their interrelationship. In particular, focusing on the current muon g-2 anomaly, we analyse both high-energy and low-energy tests to confirm or to falsify it.

• A continuum determination of the strong isospin-breaking contribution to the muon anomalous magnetic moment

  Kim Maltman, Christopher James, Randy Lewis

  SciPost Phys. Proc. 16, 031 (2025) · published 15 July 2025 | Toggle abstract · pdf

  First-principles lattice determinations of the Standard Model expectation for the leading order hadronic vacuum polarization contribution to the anomalous magnetic moment of the muon have become sufficiently precise that further improvement requires including strong and electromagnetic isospin-breaking effects. We provide a continuum estimate of the strong isospin-breaking contribution, $a_\mu^{SIB}$, using $SU(3)$ chiral perturbation theory. The result is shown to be dominated by resonance-region contributions encoded in a single low-energy constant whose value is known from flavor-breaking hadronic $\tau$ decay sum rules. Implications of the form of the result for lattice determinations of $a_\mu^{SIB}$ are also discussed.

• New $\tau$-based evaluation of the hadronic vacuum polarization contribution to the muon anomalous magnetic moment

  Jesús Alejandro Miranda Hernández, Pablo Roig Garcés

  SciPost Phys. Proc. 16, 032 (2025) · published 15 July 2025 | Toggle abstract · pdf

  We revisit the radiative corrections to the $\tau^-\to\pi^-\pi^0\nu_\tau(\gamma)$ decays using Resonance Chiral Theory for the structure-dependent part. This channel is the most important one to understand the hadronic vacuum polarization piece of the muon g-2, which dominates the uncertainty of its data-driven prediction in the Standard Model. Using our results, the discrepancy between theory and experiment for this observable is reduced to $\sim2.2\sigma$.