21 research outputs found
Model analysis of thermal UV-cutoff effects on the chiral critical surface at finite temperature and chemical potential
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Electromagnetic pion and kaon form factors in light-cone resummed perturbative QCD
Full text linkWe analyze the electromagnetic pion and kaon form factor by including radiative and higher-twist effects within the framework of resummed perturbative QCD in the spacelike region. We focus on the transition from the perturbative to nonperturbative behavior in the phenomenological intermediate-energy regime. Using a modified “kT” factorization scheme with transverse degrees of freedom, we evaluate the nonperturbative soft contributions as distinct from the hard contributions, ensuring no double counting via the Ward identity at Q2=0. The soft contributions are obtained via local quark-hadron duality, while the hard contributions rest on the well-known collinear factorization theorem using model wave functions with modified Brodsky-Huang-Lepage–type ansatz and distribution amplitudes derived from light-cone QCD sum rules. Our analysis shows that the perturbative hard part prevails for large Q2 beyond 50–100 GeV2, while for low and moderate momentum transfers below 10–16 GeV2, the soft contributions dominate over the hard part. Thus, we demonstrate the importance of including the soft contributions for explaining the experimental form-factor data
Investigation of
No full textWe study the () three-body system using low-energy effective field theory (EFT). Due to the acute inadequacy of empirical information in this sector, there exists substantial degree of ambiguity in determining various few-body observables, some of which are expected to yield vital clues to resolving longstanding contentious issues in hypernuclear physics. Moreover, in astrophysical studies, a precise determination of neutron star equation of state (EoS) of putative hyperonic cores relies on essential input from the sector. In this obscure current scenario, a pionless EFT analysis provides a systematic model-independent framework for assessing the feasibility of light three-particle-stable bound states, utilizing low-energy universality. Here we take recourse to a simplistic speculation of the three-body system by eliminating the repulsive spin-singlet sub-system, while retaining the predominantly attractive (possibly bound) spin-triplet and the virtual bound spin-singlet nn sub-systems. In particular, a qualitative leading order EFT investigation by introducing a sharp momentum ultraviolet cut-off parameter into the coupled integral equations indicates a discrete scaling behavior akin to a renormalization group limit cycle, thereby suggesting the formal existence of Efimov states in the unitary limit, as . Our subsequent non-asymptotic analysis indicates that the three-body binding energy is sensitively dependent on the cut-off without the inclusion of three-body contact interactions. Furthermore, our analysis reproduces several values of the binding energy MeV, predicted in context of existing potential models, with the regulator in the range MeV. Finally, based on these model inputs for , a ballpark estimate of the three-body scattering length in the range fm, is naively constrained by our EFT analysis. Despite approximations, the resulting Phillips line is expected to yield a robust feature of the halo-bound system. For pedagogical reasons, using a simple toy model interacting three-bosons system, we highlight in the appendices the typical universal features leading to emergence of RG limit cycle and Efimov states which are amenable to a low-energy EFT formalism
Analytical evaluation of elastic lepton-proton two-photon exchange in chiral perturbation theory
No full textWe present an exact evaluation of the two-photon exchange contribution to the elastic lepton-proton scattering process at low-energies using heavy baryon chiral perturbation theory. The evaluation is performed including next-to-leading order accuracy. This exact analytical evaluation contains all soft and hard two-photon exchanges and we identify the contributions missing in a soft-photon approximation approach. We evaluate the infrared divergent four-point box diagrams analytically using dimensional regularization. We also emphasize the differences between muon-proton and electron-proton scatterings relevant to the MUSE kinematics due to lepton mass differences
