A contact interaction is used to calculate an array of pion twist-two, -three and -four generalised transverse light-front momentum dependent parton distribution functions (GTMDs). Despite the interaction’s simplicity, many of the results are physically relevant, amongst them a statement that GTMD size and shape are largely prescribed by the scale of emergent hadronic mass. Moreover, proceeding from GTMDs to generalised parton distributions, it is found that the pion’s mass distribution form factor is harder than its electromagnetic form factor, which is harder than the gravitational pressure distribution form factor; the pressure in the neighbourhood of the pion’s core is commensurate with that at the centre of a neutron star; the shear pressure is maximal when confinement forces become dominant within the pion; and the spatial distribution of transversely polarised quarks within the pion is asymmetric. Regarding transverse momentum dependent distribution functions, their magnitude and domain of material support decrease with increasing twist. The simplest Wigner distribution associated with the pion’s twist-two dressed-quark GTMD is sharply peaked on the kinematic domain associated with valence-quark dominance; has a domain of negative support; and broadens as the transverse position variable increases in magnitude.

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In this paper, we use the two-flavor Nambu–Jona-Lasinio (NJL) model to study the quantum chromodynamics (QCD) chiral phase transition. To deal with the ultraviolet (UV) issue, we adopt the popular proper time regularization (PTR), which is commonly used not only for hadron physics but also for the studies with magnetic fields. This regularization scheme can introduce the infrared (IR) cutoff to include quark confinement. We generalize the PTR to zero temperature and finite chemical potential case use a completely new method, and then study the chiral susceptibility, both in the chiral limit case and with finite current quark mass. The chiral phase transition is second-order in [Formula: see text] and [Formula: see text] and crossover at [Formula: see text] and [Formula: see text]. Three sets of parameters are used to make sure that the results do not depend on the parameter choice.

Kaon generalized parton distributions (GPDs) and the leading Fock state light-front wave functions are investigated in the framework of Nambu–Jona-Lasinio model with proper time regularization. In addition, we compared the form factors, parton distribution functions, and generalized form factors obtained from them, respectively. The first Mellin moments of GPDs result in the form factors of local currents. The second Mellin moments of vector GPDs are related to gravitational form factors, the quark mass distribution $$\theta _2$$ θ 2 and the quark pressure distribution $$\theta _1$$ θ 1 . When taking a Fourier transform of GPDs in impact parameter space, we can get the mean-squared impact parameter for the quarks of the kaon: $$\langle {\varvec{b}}_{\bot }^2\rangle _K^u=0.149$$ ⟨ b ⊥ 2 ⟩ K u = 0.149 fm$$^2$$ 2 , $$\langle {\varvec{b}}_{\bot }^2\rangle _K^s=0.088$$ ⟨ b ⊥ 2 ⟩ K s = 0.088 fm$$^2$$ 2 . This means that the kaon s quark is nearer to the center of transverse momentum than the u quark. We also give the light-cone energy radius for the quarks of the kaon from the mass distribution $$\theta _2$$ θ 2 : $$r_{E,LC}^{u,K}=0.187 $$ r E , L C u , K = 0.187 fm, $$ r_{E,LC}^{s,K}=0.167$$ r E , L C s , K = 0.167 fm, and the light-cone charge radius from quark form factors of the kaon: $$r_{c,LC}^{u,K}=0.390 $$ r c , L C u , K = 0.390 fm, $$r_{c,LC}^{s,K}=0.296 $$ r c , L C s , K = 0.296 fm, which means that the s quark has a smaller extent than the u quark. The light-front transverse-spin distributions $$\rho _u^1\left( {\varvec{b}}_{\bot },{\varvec{s}}_{\perp }\right) $$ ρ u 1 b ⊥ , s ⊥ and $$\rho _u^2\left( {\varvec{b}}_{\bot },{\varvec{s}}_{\perp }\right) $$ ρ u 2 b ⊥ , s ⊥ show distortions, the average shift are $$\langle b_{\bot }^y\rangle _1^u=0.116$$ ⟨ b ⊥ y ⟩ 1 u = 0.116 fm and $$\langle b_{\bot }^y\rangle _2^u=0.083$$ ⟨ b ⊥ y ⟩ 2 u = 0.083 fm. On the kinematic domain associated with the valence-quark dominance, the unpolarized Wigner distribution from light-front wave functions is sharply peaked. It extends as the transverse position variable increases in magnitude and has a domain of negative support. Through the comparison of distributions from the two methods, we find that they give the same multi-dimensional mapping of the kaon in the Nambu–Jona-Lasinio model.