Understanding the subnuclear physics using Lattice Quantum ChromoDynamics

Strong interaction is the key to the existence of the nucleon and more than 90% of the mass in the visible universe. Quantum ChromoDynamics (QCD), with quarks and gluons as the fundamental degrees of freedom, is the widely accepted theory for the strong interactions. Nucleon is the most stable member of the family of strongly interacting particles, known as hadrons, which are believed to be compounds of gluons and different flavors of quarks at low energies. Even so, to this date, all theoretical interpretations of the hadron spectrum and its properties are based on QCD-inspired phenomenological models that approximate the strong interactions in the hadronic regime. This is because there are no ab-initio methods to rigorously determine the hadron spectrum and their properties from the QCD Lagrangian. The only exception to this is by numerically studying the theory defined on a discretized space-time, dubbed as lattice QCD, which at least till the early 2000s was considered limited in scope based on computational as well as theoretical grounds. With the advent of advanced particle colliders and detectors such as LHCb, BESIII, an assortment of hadrons (particularly those containing charm and bottom quark flavors) has been discovered over the past two decades. It is getting increasingly accepted that there is no single phenomenological model that can describe all the observed hadrons collectively. At the same time, the recent advancements in both computational and theoretical fronts have made lattice QCD computations more practical and powerful tool to perform first-principles investigations in hadron physics.

In this talk, I will take you through various hadron spectroscopic calculations from the past decade, using lattice QCD, with special emphasis on those addressing hadrons with charm and bottom quark flavors. Predictions and postdictions of the energy spectrum, insights into the nature of hadronic excitations based on these investigations, and its implications on the experimental and phenomenological fronts will be discussed. Following this, I will briefly outline various ongoing and planned efforts in spectroscopy, hadron structure determinations and finite temperature investigations and their possible implications in high energy physics.