We consider a scalar field model with a gφ 4 4 interaction and compute the mass correction at next-to-leading order in a large-N expansion to study the summability of the perturbative series. It is already known that at zero temperature this model has a singularity in the Borel plane (a "renormalon"). We find that a small increase in temperature adds two countable sets both with an infinite number of renormalons. For one of the sets the position of the poles is thermal independent and the residue is thermal dependent. In the other one both the position of poles and the residues are thermal dependent. If we consider the model at extremely high temperatures, however, one observes that all the renormalons disappear and the model becomes Borel summable.R 3 × S 1 [20] and the CP N −1 non-linear sigma model on arXiv:1804.10708v2 [hep-th]

We investigate the process of dimensional reduction of one spatial dimension in a thermal scalar field model defined in D dimensions (inverse temperature and D − 1 spatial dimensions). We obtain that a thermal model in D dimensions with one of the spatial dimensions having a finite size L is related to the finite temperature model with just D − 1 spatial dimensions and no finite size. Our results are obtained for one-loop calculations and for any dimension D. For example, in D = 4 we have a relationship between a thin film with thickness L at finite temperature and a surface at finite temperature. We show that, although a strict dimensional reduction is not allowed, it is possible to define a valid prescription for this procedure. * erich@cbpf.br †

Hidden charm mesons continue playing an essential role as relevant probes to understand the evolution of partonic matter. It is expected that the charmonia that survived the quark-gluon plasma phase suffer collisions with other particles composing the hadronic matter. In this work, we intend to contribute on this subject by presenting an updated study about the interactions of J/ψ with surrounding hadronic medium. The meson-meson interactions are described with a SU (4) effective Lagrangian, and within the framework of unitarized coupled channel amplitudes projected onto s-wave. The symmetry is explicitly broken to SU (3) by suppression of the interactions driven by charmed mesons. We calculate the cross sections for J/ψ scattering by light pseudoscalar mesons (π, K, η) and vector mesons (ρ, K * , ω), as well as their inverse processes. Keeping the validity of this present approach in the low CM energy range, the most relevant channels are evaluated and a comparison of the findings with existing literature is performed.

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Boundary conditions effects are explored for size-dependent models in thermal equilibrium. Scalar and fermionic models are used for D = 1 + 3 (films), D = 1 + 2 (hollow cylinder) and D = 1 + 1 (ring). For all models a minimal length is found, below which no thermally-induced phase transition occurs. Using quasiperiodic boundary condition controlled by a contour parameter θ (θ = 0 is a periodic boundary condition and θ = 1 is an antiperiodic condition) it results that the minimal length depends directly on the value of θ. It is also argued that this parameter can be associated to an Aharonov-Bohm phase.