Interpolating 't Hooft model between instant and front forms

TL;DR

This paper introduces an interpolating framework between instant and light-front forms of dynamics in the 't Hooft model, deriving mass gap and bound-state equations that unify and extend previous results, with implications for chiral symmetry and parton distributions.

Contribution

It formulates an interpolating mass gap and bound-state equations in the 't Hooft model, bridging instant and light-front dynamics and exploring their implications for meson spectra and parton distributions.

Findings

Mass spectra are independent of the interpolation angle for equal mass quark-antiquark states.

The Gell-Mann–Oakes–Renner relation holds across the interpolation, confirming chiral symmetry breaking.

Wave functions exhibit reference frame dependence, useful for quasi parton distribution calculations.

Abstract

The 't Hooft model, i.e. the two-dimensional quantum chromodynamics in the limit of infinite number of colors, is interpolated by an angle parameter $\delta$ between $\delta=0$ for the instant form dynamics (IFD) and $\delta=\pi/4$ for the light-front dynamics (LFD). With this parameter $\delta$, we formulate the interpolating mass gap equation which takes into account the non-trivial vacuum effect on the bare fermion mass to find the dressed fermion mass. Our interpolating mass gap solutions link the IFD and LFD results with the $\delta$ parameter. We find the interpolation angle independent characteristic energy function which satisfies the energy-momentum dispersion relation of the dressed fermion, identifying the renormalized fermion mass function and the wave function renormalization factor. Using the dressed fermion propagator interpolating between IFD and LFD, we derive the corresponding quark-antiquark bound-state equation in the interpolating formulation. The mass spectra of mesons bearing the feature of the Regge trajectories are found independent of the $\delta$-parameter for the equal mass quark and antiquark bound-states. The Gell-Mann - Oakes - Renner relation for the pionic ground-state in the zero fermion mass limit is confirmed indicating that the spontaneous breaking of the chiral symmetry occurs regardless of the quantization for $0 \le \delta \le \pi/4$. We obtain the corresponding bound-state wave functions and discuss their reference frame dependence. Applying them for the computation of the so-called quasi parton distribution functions, we note a possibility of utilizing not only the reference frame dependence but also the interpolation angle dependence to get an alternative effective approach to the LFD-like results.