## Ph.D defense: Two Dimensional Lattice Gauge Theory with and without Fermion Content

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Venue: | CP 220 |

### by Dibakar Sigdel, Adviser Dr. R. Narayanan

Quantum Chromo Dyamics (QCD) is a relativistic �eld theory of a non-abelian gauge fi�eld coupled to several flavors of fermions. Two dimensional (one space and one time) QCD serves as an interesting toy model that shares several features with the four dimensional physically relevant theory.The main aim of the research is to study two dimensional QCD using the lattice regularization.

Two dimensional QCD without any fermion content is solved analytically using lattice regularization. Explicit expressions for the expectation values of Wilson loops and the correlation of two Polyakov loops oriented in two different directions are obtained. Physics of the QCD vacuum is explained using these results.

The Hamlitonian formalism of lattice QCD with fermion content serves as an approach to study quark excitations out of the vacuum. The formalism is �first developed and techniques to numerically evaluate the spectrum of physical particles, namely, meson and baryons are described. The Hybrid Monte Carlo technique was used to numerically extract the lowest meson and baryon masses as a function of the quark masses. It is shown that neither the lowest meson mass nor the lowest baryon mass goes to zero as the quark mass is taken to zero. This numerically establishes the presence of a mass gap in two dimensional QCD.