Next-to-leading order effects on the lightest scalar tetraquark mass estimates using QCD Laplace sum-rules

Multiquark states have been of great interest among hadronic physicists, and despite the big breakthrough that came in 2003 with the discovery of the charmonium-like tetraquark candidate X(3872), their structure and masses are still eclipsed by theoretical uncertainties in the precision of the calculations. The study of tetraquarks can give us another insight to understand strong interactions at the elementary level and at different energy scales. The goal of this research is to explore light-quark tetraquark structures and estimate their masses using the QCD sum-rules approach. The specific focus is on the controversial light scalar tetraquark σ (denoted as f0(500) in the Particle Data Group classification scheme), and the contributions from next-to-leading order (NLO) diagrams to the spectral functions are incorporated in the process of finding a Borel window for a reliable sum-rule analysis. After a deep examination, this thesis includes analyses in terms of a single and a double resonance models, where the heavier state (980 MeV) used is the scalar f0(980). The results showed that the NLO terms play a significant role in the spectral function picture with contributions of up to 74% with respect to the leading-order (LO) perturbative terms, but their effects are suppressed in ratios used within the Laplace sum-rules scheme. Moreover, the key improvement is that NLO corrections benefit substantially the methodology by locating a suitable physical Borel window where the mass prediction range is reliable and result in the σ mass prediction around 0.52 GeV < mσ < 0.69 GeV. It was also found that the relative strength of the f0(980) coupling to the current is approximately three to four times stronger than the σ, such results are in agreement with chiral Lagrangian determinations, hence in accordance with the tetraquark scheme