arXiv subjects
Publications and source records attributed to Archana Radhakrishnan.
We present a lattice QCD study of heavy baryons containing charm and bottom quarks, with particular emphasis on the relativistic treatment of all valence quarks. We use $N_f=2+1+1$ HISQ ensembles at the physical point to compute ground-state energies of spin-$3/2^+$ baryons, including singly-, doubly-, and triply-heavy charmed and bottom baryons. This work represents the first investigation of heavy baryons using fully relativistic bottom quarks.
We present the most precise determination to date of the ground-state masses of the triply charmed baryons with both parities, obtained by continuum extrapolation and fully addressing the systematic uncertainties. The calculations are performed on six $N_f=2+1+1$ HISQ ensembles, generated by the MILC collaboration, with two complementary setups for the valence charm action, one using the HISQ action and the other using the overlap fermion action. Our prediction for the mass of the lowest two triply charmed spin-3/2 baryons are: $M_{\Omega_{ccc}} (3/2^{+}) = 4793 (5) \left(^{+11}_{-8}\right)$ MeV, and $M_{\Omega_{ccc}} (3/2^{-}) = 5094 (12) \left(^{+19}_{-17}\right)$ MeV.
We present an efficient method for extracting energy levels from lattice QCD correlation functions by computing the eigenvalues of the transfer matrix associated with the lattice QCD Hamiltonian. While mathematically and numerically equivalent to the recently introduced Lanczos procedure, our approach introduces a novel prescription for removing spurious eigenvalues using a kernel density estimator (KDE) and Gaussian-convoluted histogram method. This strategy yields a robust and stable estimate of the energy spectrum, outperforming the Cullum-Willoughby filtering technique in efficiency. In addition, we detail how this method can be applied to extract overlap factors from two-point correlation functions, as well as matrix elements from three-point functions with a current insertion. Furthermore, we extend the methodology to accommodate correlation matrices constructed from a variational basis of operators, with its Block formulation. We demonstrate the efficacy of this framework by computing the two lowest energy levels for a broad range of hadrons, including several nuclei. Although the signal-to-noise ratio is not significantly improved, the extracted energy levels are found to be more reliable than those obtained with conventional techniques. Within a given statistical ensemble, the proposed method effectively captures both statistical uncertainties and systematic errors, including those arising from the choice of fitting window, making it a robust and practical tool for lattice QCD analysis.
We present the most precise results for the ground state mass of the triply-charmed spin-$3/2$ baryon using lattice quantum chromodynamics. The calculations are performed on six $N_f=2+1+1$ Highly Improved Staggered Quark (HISQ) lattice ensembles generated by the MILC collaboration. Two different lattice setups are employed: in the first one, a fully dynamical calculation with HISQ action is performed, while in the second calculation, an overlap action is utilized for the valence charm quark dynamics. Following the continuum extrapolation of our results, obtained at five different lattice spacings, two different volumes, and two different actions, our prediction for the mass of the lowest triply charmed spin-3/2 baryon, $\Omega_{ccc} (3/2^{+})$, is $4793 (5) \left(^{+11}_{-8}\right)$ MeV. This is the most precise determination to date, fully addressing the systematic uncertainties. We also predict the $\Omega_{ccc} (3/2^{-})$ mass to be $5094 (12) \left(^{+19}_{-17}\right)$ MeV.
We report a lattice QCD study of the heavy-light meson-meson interactions with an explicitly exotic flavor content $bc\bar u\bar d$, isospin $I\!=\!0$, and axialvector $J^P=1^+$ quantum numbers in search of possible tetraquark bound states. The calculation is performed at four values of lattice spacing, ranging $\sim$0.058 to $\sim$0.12 fm, and at five different values of valence light quark mass $m_{u/d}$, corresponding to pseudoscalar meson mass $M_{ps}$ of about 0.5, 0.6, 0.7, 1.0, and 3.0 GeV. The energy eigenvalues in the finite-volume are determined through a variational procedure applied to correlation matrices built out of two-meson interpolating operators as well as diquark-antidiquark operators. The continuum limit estimates for $D\bar B^*$ elastic $S$-wave scattering amplitude are extracted from the lowest finite-volume eigenenergies, corresponding to the ground states, using amplitude parametrizations supplemented by a lattice spacing dependence. Light quark mass $m_{u/d}$ dependence of the $D\bar B^*$ scattering length ($a_0$) suggests that at the physical pion mass $a_0^{phys} = +0.57(^{+4}_{-5})(17)$ fm, which clearly points to an attractive interaction between the $D$ and $\bar B^*$ mesons that is strong enough to host a real bound state $T_{bc}$, with a binding energy of $-43(_{-7}^{+6})(_{-24}^{+14})$ MeV with respect to the $D\bar B^*$ threshold. We also find that the strength of the binding decreases with increasing $m_{u/d}$ and the system becomes unbound at a critical light quark mass $m^{*}_{u/d}$ corresponding to $M^{*}_{ps} = 2.73(21)(19)$ GeV.
We present a lattice QCD study of the elastic $S$-wave $D\bar{B}$ scattering in search of tetraquark candidates with explicitly exotic flavor content $bc\bar u\bar d$ in the isospin $I\!=\!0$ and $J^P=0^+$ channel. We use four lattice QCD ensembles with dynamical $u/d$, $s$, and $c$ quark fields generated by the MILC Collaboration. A non-relativistic QCD Hamiltonian, including improvement coefficients up to $\mathcal{O}(\alpha_sv^4)$, is utilized for the bottom quarks. For the rest of the valence quarks we employ a relativistic overlap action. Five different valence quark masses are utilized to study the light quark mass dependence of the $D\bar{B}$ scattering amplitude. The finite volume energy spectra are extracted following a variational approach. The elastic $D\bar{B}$ scattering amplitudes are extracted employing L\"{u}scher's prescription. The light quark mass dependence of the continuum extrapolated amplitudes suggests an attractive interaction between the $\bar B$ and $D$ mesons. At the physical pseudoscalar meson mass ($M_{ps}=M_{\pi}$) the $D\bar{B}$ scattering amplitude has a sub-threshold pole corresponding to a binding energy of $-39(^{+4}_{-6})(^{~+8}_{-18}) \mbox{~MeV}$ with respect to the $D\bar{B}$ threshold. The critical $M_{ps}$ at which the $D\bar{B}$ scattering length diverges and the system becomes unbound corresponds to $M^*_{ps}=2.94(15)(5) \mbox{~GeV}$. This result can hold significant experimental relevance in the search for a bound scalar $T_{bc}$ tetraquark, which could well be the next "doubly heavy" bound tetraquark to be discovered with only weak decay modes.
We present the first calculation in lattice QCD of the process $γK \to Kπ$ in which the narrow $K^*$ vector resonance appears. Using a lattice on which the pion has a mass of 284 MeV, we determine the transition amplitude at 128 points in the $(Q^2, E_{Kπ})$ plane, and find suitable resonant scattering descriptions. We demonstrate the need to account for $S$--wave $Kπ$ elastic scattering when converting the finite-volume matrix elements computed in lattice QCD to the physically relevant infinite-volume matrix elements, even when we are primarily interested in the $P$--wave amplitude. Analytically continuing parameterizations of the $γK \to Kπ$ amplitude to the $K^*$ resonance pole, we obtain the $K^{*+} \to K^+ γ$ transition form-factor, and compare the $Q^2=0$ value to the corresponding value extracted from the experimental partial-decay width.