Abstract: Heavy-ion collisions, such as Pb-Pb or p-Pb, produce extreme conditions in temperature and density that make the hadronic matter transition to a new state, called quark-gluon plasma (QGP). Simulations of heavy-ion collisions provide a way to improve our understanding of the QGP's properties. These simulations are composed of a hybrid description that results in final observables in agreement with accelerators like LHC and RHIC. However, recent works pointed out that these hydrodynamic simulations can display acausal behavior during the evolution in certain regions, indicating a deviation from a faithful representation of the underlying QCD dynamics. To pursue a better understanding of this problem and its consequences, this work simulated two different collision systems, Pb-Pb and p-Pb at root sNN = 5.02 TeV. In this context, our results show that causality violation, even though always present, typically occurs on a small part of the system, quantified by the total energy fraction residing in the acausal region. In addition, the acausal behavior can be reduced with changes in the prehydrodynamic factors and the definition of the bulk-viscous relaxation time. Since these aspects are fairly arbitrary in current simulation models, without solid guidance from the underlying theory, it is reasonable to use the disturbing presence of acausal behavior in current simulations to guide improvements towards more realistic modeling. While this work does not solve the acausality problem, it sheds more light on this issue and also proposes a way to solve this problem in simulations of heavy-ion collisions.

Abstract: We perform a theoretical study of the J/psi -> omega (Phi)K* K + c.c. -> omega(Phi)K-0 pi+ K- reactions with the assumption that the f1(1285) is dynamically generated from a single channel K*K + c.c interaction in the chiral unitary approach. Two peaks in the K-0 pi+ K- invariant mass distribution are observed, one clear peak locates at the f(1)(1285) nominal mass, the other peak locates at around 1420MeV with about 70MeV width. We conclude that the former peak is associated with the f(1)(1285) and the latter peak is not a genuine resonance but a manifestation of the kinematic effect in the higher energy region caused by the K* K + c.c. decay mode of the f(1)(1285).

Abstract: The production of eta and eta' mesons is studied in proton -proton and proton -lead collisions collected with the LHCb detector. Proton -proton collisions are studied at center -of -mass energies of 5.02 and 13 TeV and proton -lead collisions are studied at a center -of -mass energy per nucleon of 8.16 TeV. The studies are performed in center -of -mass (c.m.) rapidity regions 2.5 < y(c.m.) < 3.5 (forward rapidity) and -4.0 < y(c.m.) < -3.0 (backward rapidity) defined relative to the proton beam direction. The eta and eta' production cross sections are measured differentially as a function of transverse momentum for 1.5 < p(T) < 10 GeV and 3 < p(T) < 10 GeV, respectively. The differential cross sections are used to calculate nuclear modification factors. The nuclear modification factors for eta and eta' mesons agree at both forward and backward rapidity, showing no significant evidence of mass dependence. The differential cross sections of eta mesons are also used to calculate eta/pi 0 cross-section ratios, which show evidence of a deviation from the world average. These studies offer new constraints on mass -dependent nuclear effects in heavy -ion collisions, as well as eta and eta' meson fragmentation.

Abstract: The N*(1535) can be dynamically generated in the chiral unitary approach with the coupled channels, K0E+; K+E0; K+A, and eta p. In this work, we evaluate the correlation functions for every channel and face the inverse problem. Assuming the correlation functions to correspond to real measurements, we conduct a fit to the data within a general framework in order to extract the information contained in these correlation functions. The bootstrap method is used to determine the uncertainties of the different observables, and we find that, assuming errors of the same order than in present measurements of correlation functions, one can determine the scattering length and effective range of all channels with a very good accuracy. Most remarkable is the fact that the method predicts the existence of a bound state of isospin 12 nature around the mass of the N*(1535) with an accuracy of 6 MeV. These results should encourage the actual measurement of these correlation functions (only the K+A one is measured so far), which can shed valuable light on the relationship of the N*(1535) state to these coupled channels, a subject of continuous debate.

Abstract: We analyze the adiabatic regularization scheme to renormalize Proca fields in a four-dimensional Friedmann-Lemaitre-Robertson-Walker spacetime. The adiabatic method is well established for scalar and spin-1/2 fields, but is not yet fully understood for spin-1 fields. We give the details of the construction and show that, in the massless limit, the renormalized stress-energy tensor of the Proca field is closely related to that of a minimally coupled scalar field. Our result is in full agreement with other approaches, based on the effective action, which also show a discontinuity in the massless limit. The scalar field can be naturally regarded as a Stueckelberg-type field. We also test the consistency of our results in de Sitter space.