Leticia F. Palhares

Deconfinement in the presence of a strong magnetic background: An exercise within the MIT bag model

We study the effect of a very strong homogeneous magnetic field B on the thermal deconfinement transition within the simplest phenomenological approach: the MIT bag pressure for the quark- gluon plasma and a gas of pions for the hadronic sector. Even though the model is known to be crude in numerical precision and misses the correct nature of the (crossover) transition, it provides a simple setup for the discussion of some subtleties of vacuum and thermal contributions in each phase, and should provide a reasonable qualitative description of the critical temperature in the presence of B. We find that the critical temperature decreases, saturating for very large fields.

Large

We investigate the effect of a homogeneous magnetic field on the thermal deconfinement transition of QCD in the large Nc limit. First we discuss how the critical temperature decreases due to the inclusion of Nf≪Nc flavors of massless quarks in comparison to the pure glue case. Then we study the equivalent correction in the presence of an external Abelian magnetic field. To leading order in Nf/Nc, the deconfinement critical temperature decreases with the magnetic field if the flavor contribution to the pressure behaves paramagnetically, with a sufficiently large magnetization as to overcome any possible magnetic effects in the string tension. Finally, we discuss the effects from a finite quark mass and its competition with magnetic effects.

N_c

We investigate finite-size effects on the chiral phase diagram of strong interactions within the linear sigma model coupled to quarks. We estimate the modification of the pseudocritical transition line and isentropic trajectories for sizes that are representative of the systems created in relativistic heavy-ion collision experiments. The corrections are clearly non-negligible and might significantly affect signatures of the chiral critical endpoint based on estimates for an infinite system. We argue that a finite-size scaling analysis should be tested in the process of data analysis of the Beam Energy Scan program at RHIC and in future experiments at FAIR-GSI, through the use of full scaling plots and a chi-squared method as tools for searching the critical endpoint.

Deconfinement Transition in the Presence of a Magnetic Field

We describe the deconfining critical temperature dependence on the pion mass and on the isospin chemical potential in remarkably good agreement with lattice data. Our framework incorporates explicit dependence on quark masses, isospin and baryonic chemical potentials for the case of two flavors through ingredients from well-known high- and low-energy theories. In the low-energy sector, the system is described by a minimal chiral perturbation theory effective action, corresponding to a hot gas of pion quasiparticles and heavy nucleons. For the high-temperature sector we adopt a simple extension of the fuzzy bag model. We also briefly discuss the effects of mass asymmetry and baryon chemical potential.

Chiral transition in a finite system and possible use of finite-size scaling in relativistic heavy ion collisions

We discuss finite-size effects on the phase diagram of strong interactions and consequences for the experimental search of the critical endpoint in high-energy heavy-ion collisions. We point out that a finite-size scaling analysis may be crucial in the process of data analysis in the Beam Energy Scan program at RHIC and in future experiments at FAIR-GSI.

Quark mass and isospin dependence of the deconfining critical temperature

In-medium Yukawa theory is part of the thermodynamics of the standard model of particle physics and is one of the main building blocks of most effective field theories of fermionic systems. By computing its pressure we investigate the nonperturbative thermodynamics at finite temperature and density using the optimized perturbation theory framework. Our calculations are valid for arbitrary fermion and scalar masses, temperature, chemical potential, and not restricted to weak coupling. The model is considered in the presence as well as in the absence of condensates. Comparison with nonperturbative results shows that second-order perturbation theory fails in the first case but performs rather well when condensates are absent, even at high-temperature regimes.

Finite-size effects and signatures of the QCD critical endpoint

Yukawa theory at vanishing temperature provides (one of the ingredients for) an effective description of the thermodynamics of a variety of cold and dense fermionic systems. We study the role of masses and the renormalization group flow in the calculation of the equation of state up to two loops within the MS scheme. Two-loop integrals are computed analytically for arbitrary fermion and scalar masses, and expressed in terms of well-known special functions. The dependence of the renormalization group flow on the number of fermion flavors is also discussed.

Nonperturbative Yukawa theory at finite density and temperature

We investigate the effects of dissipation in the deconfining transition for a pure SU (2) gauge theory. Using an effective model for the order parameter, we study its Langevin evolution numerically, and compare results from local additive noise dynamics to those obtained considering an exponential non-local kernel for early times.

Perturbative Yukawa theory at finite density: The role of masses and renormalization group flow at two loops

Recent results for the two-loop thermodynamic potential of QCD at finite density have shown that nonzero quark mass corrections to the pressure are relevant and can dramatically affect the structure of compact stars. Motivated by these findings, we consider a simple toy model - cold and dense Yukawa theory - to study the effects of finite fermion masses on the pressure. The role of renormalization group running of the coupling and mass is also discussed. Results within this simple model might be useful in the description of condensates in the core of neutron stars.

Dissipation and memory effects in pure glue deconfinement

Taking into account the finiteness of the system created in heavy ion collisions, we show sizable results for the modifications of the chiral phase diagram at volume scales typically encountered in current experiments and demonstrate the applicability of finite-size scaling as a tool in the experimental search for the critical endpoint. Using data from RHIC and SPS and assuming finite-size scaling, we find that RHIC data from 200 GeV down to 19.6 GeV is only consistent with a critical point at \mu \gtrsim 510 MeV. We also present predictions for the fluctuations at lower energies currently being investigated in the Beam Energy Scan program.