arXiv subjects

Rajnandini Mukherjee

Publications and source records attributed to Rajnandini Mukherjee.

8 recordsLinked to original sources

arXiv2026

$D \to (K π)_{\mathbf{27}}$ at the SU(3)-flavour-symmetric point I: Methodology and strong phase determination

We present part one of an SU(3)-flavour-symmetric lattice QCD calculation of the amplitude for a $D$-meson decaying to a $Kπ$ final state in the 27-dimensional irreducible representation of the flavour symmetry group, denoted $(Kπ)_{\mathbf{27}}$. The Wilson--clover gauge ensembles used in this work, generated by the OpenLat collaboration, are tuned such that $M_π= M_K \approx 410\,\mathrm{MeV}$. Using the distillation framework, we construct a matrix of Euclidean correlation functions from pairs of single-hadron operators projected to definite spatial momentum. Solving a generalised eigenvalue problem yields the finite-volume energy spectrum that is used to determine the scattering phase shift from threshold up to $4 M_π\approx 1640 \,\mathrm{MeV}$, which sits below but plausibly within reach of $M_D^{\rm SU(3)} \simeq 1900\,\mathrm{MeV}$. The calculation is performed across three lattice spacings, and we apply two strategies in which the continuum limit is taken at different stages of the computation: (i) on the extracted scattering parameters and (ii) on the finite-volume energies at fixed physical volume before extracting the scattering parameters. We find consistent results across these methods for the scattering phase shift as a function of the centre-of-mass energy, $δ_{\mathbf{27}}(E_{\sf cm})$. Taking a scattering-length-only parametrisation, we infer a value for the strong phase of the weak decay, $δ_{\mathbf{27}}(M_D^{\rm SU(3)})=-38.4(2.4)^\circ$. We further describe the methodology for using the same operator basis to compute three-point correlation functions to extract $\langle (Kπ)_{\mathbf{27}}| H_W| D\rangle$, for the tree-level effective weak Hamiltonian $H_W$, and for relating such finite-volume matrix elements to the full decay amplitude. The complete analysis leading to the latter will be presented in a forthcoming manuscript.

hep-lat↗

arXiv2026

Lattice Calculation of Short-Range Contributions to Neutrinoless Double-Beta Decay $π^-\toπ^+ ee$ at Physical Pion Mass

Neutrinoless double-beta ($0νββ$) decays provide an excellent probe for determining whether neutrinos are Dirac or Majorana fermions. The short-range matrix elements associated with the $π^- \to π^+ ee$ process contribute at leading order in the $0νββ$ decay channel $nn \to ppee$ through pion exchange between nucleons. However, current lattice calculations show notable discrepancies in predicting these short-range contributions. To address this issue, we perform a lattice QCD calculation of the $π^- \to π^+ ee$ matrix elements using domain wall fermion ensembles at the physical pion mass generated by the RBC and UKQCD Collaborations. To mitigate contamination from around-the-world effects, we develop a new method to reconstruct and subtract them directly from lattice data. We then perform a nonperturbative renormalization using the RI/SMOM scheme. Compared with previous studies, this work reduces the uncertainties in the matrix elements and provides an independent cross-check that helps to reconcile the discrepancies among previous lattice calculations.

hep-lat↗

arXiv2026

Towards four-pion effects in multi-hadron decays

The rigorous treatment of four-particle intermediate and final states poses a major challenge for lattice calculations of scattering and decay amplitudes, as well as long-distance matrix elements. As a step towards addressing these challenges, we present a new formalism that perturbatively relates two- and four-particle finite-volume energies and matrix elements to the couplings of the infinite-volume theory. Our method works at leading order in the two-to-two, four-to-four, and two-to-four couplings of the theory, while also capturing the leading finite-volume effects associated with two-to-two subprocess scattering in the four-particle sector. The result takes the form of a quantization condition which we implement numerically to produce a plot of volume-dependent energies for center-of-mass energies up to the six-particle threshold. The solutions exhibit a clear signature of two- and four-particle-like states and the avoided level crossings between them, which are particularly sensitive to the two-to-four coupling. We further discuss the implications of this formalism for quantifying the four-particle contributions in decay and transition amplitudes (e.g. for hadronic $D$ decays).

hep-lat↗

arXiv2026

$K π$ scattering as a step towards $B \to K^* \ell^+ \ell^-$ from Lattice QCD

Rare $b\to s\ell^+\ell^-$ decays provide some of the most sensitive tests of the Standard Model and require precise and systematically improvable hadronic input from lattice QCD. For the phenomenologically important channel $B\to K^*\ell^+\ell^-$ this entails a first-principles treatment of a resonant $Kπ$ final state together with controlled heavy-quark dynamics. We present the status of a new exploratory lattice calculation that combines a variational determination of finite-volume $Kπ$ states with the $1+J\to2$ finite-volume formalism to access the relevant matrix elements. The computation is carried out on an RBC/UKQCD domain-wall fermion ensemble with $a^{-1} \approx 2.7\,\mathrm{GeV}$ and employs a dual heavy-quark strategy, using both a relativistic heavy-quark action tuned to the physical $b$ mass and domain-wall heavy masses extrapolating from charm. All correlation functions are computed using (stochastic) distillation, providing a versatile setup that supports a broad range of heavy-to-light transitions into resonant final states. We show first two-point results for the $K^*\leftrightarrow Kπ$ system and discuss the accessible kinematic region, which allows for a controlled study at high $q^2$. The outlook for extending the calculation to lower $q^2$ and for incorporating effects from charmonium resonances is outlined.

hep-lat↗

arXiv2024

Absorbing discretisation effects with a massive renormalization scheme: the charm-quark mass

We present the first numerical implementation of the massive SMOM (mSMOM) renormalization scheme and use it to calculate the charm quark mass. Based on ensembles with three flavours of dynamical domain wall fermions with lattice spacings in the range 0.11 -- 0.08 fm, we demonstrate that the mass scale which defines the mSMOM scheme can be chosen such that the extrapolation has significantly smaller discretisation effects than the SMOM scheme. Converting our results to the $\overline{\mathrm{MS}}$ scheme we obtain $\overline{m}_c(3\,\mathrm{GeV}) = 1.008(13)\,\mathrm{GeV}$ and $\overline{m}_c(\overline{m}_c) = 1.292(12)\,\mathrm{GeV}$.

hep-lat↗

arXiv2024

Kaon mixing beyond the standard model with physical masses

We present non-perturbative results for beyond the standard model kaon mixing matrix elements in the isospin symmetric limit ($m_u=m_d$) of QCD, including a complete estimate of all dominant sources of systematic error. Our results are obtained from numerical simulations of lattice QCD with $N_f = 2+1$ flavours of dynamical domain wall fermions. For the first time, these quantities are simulated directly at the physical pion mass $m_π$~$\sim$~$139\,\mathrm{MeV}$ for two different lattice spacings. We include data at three lattice spacings in the range $a = 0.11 $ - $ 0.07\,\mathrm{fm}$ and with pion masses ranging from the physical value up to 450$\,\mathrm{MeV}$. Compared to our earlier work, we have added both direct calculations at physical quark masses and a third lattice spacing making the removal of discretisation effects significantly more precise and eliminating the need for any significant mass extrapolation beyond the range of simulated data. We renormalise the lattice operators non-perturbatively using RI-SMOM off-shell schemes. These schemes eliminate the need to model and subtract non-perturbative pion poles that arises in the RI-MOM scheme and, since the calculations are performed with domain wall fermions, the unphysical mixing between chirality sectors is suppressed. Our results for the bag parameters in the $\overline{\mathrm{MS}}$ scheme at $3\,\mathrm{GeV}$ are $B_K~\equiv~\mathcal{B}_1 = 0.5240(17)(54)$, $\mathcal{B}_2 = 0.4794(25)(35)$, $\mathcal{B}_3 = 0.746(13)(17)$, $\mathcal{B}_4 = 0.897(02)(10)$ and $\mathcal{B}_5 = 0.6882(78)(94)$, where the first error is from lattice uncertainties and the second is the uncertainty due to the perturbative matching to $\overline{\mathrm{MS}}$.

hep-lat↗

arXiv2023

Charm quark mass using a massive nonperturbative renormalisation scheme

We present a first numerical implementation of a massive nonperturbative renormalisation scheme, RI/mSMOM, in the study of heavy quarks using the domain-wall fermion action. In particular, we calculate renormalisation constants for fermion bilinears at non-vanishing heavy-quark masses and compare the approach to the continuum of the renormalised charm-quark mass with that from a mass-independent scheme.

hep-lat↗

arXiv2023

The $I$ = 1/2 and 3/2 $K-π$ scattering length with domain wall fermions at physical pion mass with all-to-all propagators

We present our calculations for the $I$ = 1/2 and 3/2 $K-π$ s-wave scattering length with physical quark masses, extracted from the interaction energy of Euclidean two-point functions. We use the domain wall fermion action with physical quark masses at a single lattice spacing. We are specifically interested in the systematic effects due to around-the-world terms on the overall determination of the scattering length. We present our progress and discuss the various systematic effects in our preliminary results.

hep-lat↗