A rotating string model versus baryon spectra

TL;DR

This paper models baryons as rotating strings with a quark and diquark endpoints, fitting baryon spectra and comparing different string configurations, with results consistent across meson and baryon data and implications for holographic models.

Contribution

It introduces a single-string baryon model with a quark and diquark, favoring it over Y-shaped models, and connects it to holographic string theory, fitting baryon trajectories with endpoint masses.

Findings

Single-string model fits baryon Regge trajectories well.

Universal slope of 0.95 GeV^-2 for baryons, consistent with meson data.

No clear evidence for a non-zero baryonic vertex mass.

Abstract

We continue our program of describing hadrons as rotating strings with massive endpoints. In this paper we propose models of baryons and confront them with the baryon Regge trajectories. We show that these are best fitted by a model of a single string with a quark at one endpoint and a diquark at the other. This model is preferred over the Y-shaped string model with a quark at each endpoint. We show how the model follows from a stringy model of the holographic baryon which includes a baryonic vertex connected with N_c strings to flavor probe branes. From fitting to baryonic data we find that there is no clear evidence for a non-zero baryonic vertex mass, but if there is such a mass it should be located at one of the string endpoints. The available baryon trajectories in the angular momentum plane (J,M^2), involving light, strange, and charmed baryons, are rather well fitted when adding masses to the string endpoints, with a single universal slope of 0.95 GeV^-2. Most of the results for the quark masses are then found to be consistent with the results extracted from the meson spectra in a preceding paper, where the value of the slope emerging from the meson fits was found to be 0.90 GeV^-2. In the plane of quantum radial excitations, (n,M^2), we also find a good agreement between the meson and baryon slopes. The flavor structure of the diquark is examined, where our interest lies in particular on baryons composed of more than one quark heavier than the u and d quarks. For these baryons we present a method of checking the holographic interpretation of our results.