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An empirical Equation of State for nuclear physics and astrophysics

• Debarati Chatterjee (LPC/ENSICAEN)

In order to describe astrophysical phenomena such as glitches, X-ray bursts or oscillations in neutron stars, it is essential to understand the properties of its crust and core as well as their interface. In order to achieve this, it is crucial to develop a unified and consistent scheme to describe both the finite nuclei in the crust and homogeneous matter in the core within the same framework. We employ a recently developed metamodel, based on the density functional theory, in which the Equation-of-State (EoS) of homogeneous matter is described in terms of empirical parameters measured in nuclear experiments. The metamodel is extended to describe non-homogeneous matter in the crust and tested against nuclear observables. This empirical EoS is then employed to study the liquid-phase phase transition that determines the crust-core interface of neutron stars.

QCD probes at LHC

• Gustavo Gil Da Silveira (Universidade do Estado do Rio de Janeiro (BR))

The talk will cover results from all LHC experiments on measurements of particle production in pPb and PbPb, multiplicity dependence of particle production, collectivity studies, elliptic flow, and jet quenching.

Critical parameters of consistent relativistic mean-field models

• Mariana Dutra da Rosa Lourenço (Instituto Tecnológico de Aeronáutica)

The critical parameters related to the liquid-gas phase transition are calculated for 34 relativistic mean-field models, which were shown to satisfy nuclear matter constraints in a comprehensive study involving 263 models. The compressibility factor was calculated and compared with the van der Waals equation of state. The critical temperatures were compared with experimental data and just two classes of models can reach values close to them. A correlation between the critical parameters and the incompressibility was obtained.

Implications of hadronic interactions in the Cosmic Ray and Neutrino Physics

• Victor Gonçalves (Universidade Federal de Pelotas)

A comprehensive study of the heavy quark production in ultra high energy cosmic ray interactions in the atmosphere is presented considering that the primary cosmic ray can be either a photon, neutrino or a proton. We show that the contribution of heavy quarks for cosmic ray interactions is in general non-negligible and can be dominant depending of the process considered. Moreover, we present a detailed mapping of the dominant kinematical domains contributing to the prompt atmospheric neutrino flux at high neutrino energies by studying its sensitivity to the cuts on several kinematical variables crucial for charm production in cosmic ray scattering in the atmosphere. We demonstrate that the production of neutrinos with energies larger than $E_{\nu}> 10^7$ GeV is particularly sensitive to the center-of-mass energies larger than the ones at the LHC and to the longitudinal momentum fractions in the projectile $10^{-8} < x < 10^{-5}$, which are not currently under theoretical control. Our results indicate that the precision data on the prompt atmospheric neutrino flux can efficiently constrain the mechanism of heavy quark production and underlying QCD dynamics in kinematical ranges beyond the reach of the current collider measurements.

An effective holographic approach to QCD

• Alfonso Ballon Bayona

I will describe a holographic approach to QCD where conformal symmetry is broken explicitly in the UV by a relevant operator O. This operator maps to a five dimensional scalar field, the dilaton, with a massive term. Implementing also the IR constraint found by Gursoy, Kiritsis and Nitti, an approximate linear glueball spectrum is obtained which is consistent with lattice data. Finally, I will describe the evolution of the model parameters with the conformal dimension of O. This will suggest a map between the QCD anomaly and the trace anomaly of deformed Conformal Field Theories.

Probing soft QCD with exclusive reactions

• Roman Pasechnik (Lund university)

Exclusive diffractive reactions enable us to efficiently probe soft QCD dynamics in hadronic and nuclear collisions. The color dipole approach provides universal means to evaluate both the inclusive and diffractive particle production observables beyond the concept of QCD factorisation. I will overview the most recent developments in this research field, along with current theoretical and experimental studies.

Effects of strong magnetic fields on quark matter and neutral meson properties within nonlocal chiral quark models

• Daniel Gomez Dumm (CONICET - University of La Plata, Argentina)

We study the behavior of strongly interacting matter under a strong external magnetic field in the context of chiral quark models that include nonlocal interactions. In particular, we analyze the influence of a constant magnetic field on the chiral quark condensates at zero and finite temperature, studying the deconfinement and chiral restoration critical temperatures and discussing the observed "magnetic catalysis" and "inverse magnetic catalysis" effects. In addition, we analyze in this framework the effect of the magnetic field on the properties of $\pi^0$ and $\sigma$ mesons. The predictions of nonlocal chiral quark models are compared with results obtained in lattice QCD.

BCS Pairing Gap in the Infrared Limit of the Similarity Renormalization Group

• Sergio Szpigel (Universidade Presbiteriana Mackenzie)

Effective interactions have been used to compute the pairing gap for nuclear and neutron matter in several schemes. Most often the BCS approach is based on having the scattering phase-shift as the basic input of the calculation. On the other hand, there is an arbitrariness in this procedure, as there are infinitely many interactions leading to the identical phase-shift. In this work we analyze the impact of phase-shift equivalent interactions within the BCS theory on the $^1S_0$-channel pairing gap for a translational invariant many-fermion system such as nuclear and neutron matter. We solve the BCS pairing gap equation on a finite momentum grid for a toy model separable Gaussian potential in the $^1S_0$-channel explicitly evolved through the Similarity Renormalization Group (SRG) transformation and show that in the on-shell and continuum limits the pairing gap vanishes. For finite size systems the momentum is quantized and the on-shell limit is realized for SRG cutoffs comparable to the momentum resolution. In this case the pairing gap can be computed directly from the scattering phase-shifts by an energy-shift formula $$ \Delta_{nn} (p_F) = \Delta \epsilon_F \delta^{^1S_0}_{nn}(p_F) /\pi \; , $$ where $p_F$ is the Fermi momentum and $\Delta \epsilon_F$ is the level spacing at the Fermi energy. While the momentum grid is usually used as an auxiliary way of solving the BCS pairing gap equation, we show that it actually encodes some relevant physical information, suggesting that in fact finite grids may represent the finite size of the system. For the harmonic oscillator shell model the level spacing at the Fermi energy becomes $\Delta \epsilon_F= \hbar \omega \sim 41 ~ A^{-1/3}~{\rm MeV}$ such that $\Delta_{nn} (p_F) \sim 4 ~ A^{-1/3}~{\rm MeV}$. The comparison with double differences from binding energies of stable nuclei is satisfactory and the discrepancy with the large scale analysis may be attributed to three-body forces.

Dynamics of inhomogeneous chiral condensates

• Gastao Krein (Instituto de Fisica Teorica, UNESP)

We present results of a study of the dynamics of the formation of inhomogeneous phases of the chiral transition transition in QCD. The possibility of the formation of a spatially modulated chiral condensate in the final stages of a heavy-ion collision is investigated assuming a Ginzburg-Landau-Langevin time evolution, using model-motivated free energy functionals. Time scales for the formation of inhomogeneous condensates are contrasted with the expansion rate of the medium, modelled by one-dimensional Bjorken flow.

Integral representation and Minkowski space bound state problems

• Tobias Frederico (Instituto Tecnologico de Aeronautica)

The bound state Bethe-Salpeter amplitude described by a Nakanishi two-dimensional integral representation has a smooth weight function g, which carries the detailed dynamical information. The Light-front wave function can be derived and is given by a one-dimensional, integral representation with the same weight function g. By using the generalized Stieltjes transform, g can be written in terms of the Light-Front wave function in the complex plane of its arguments. Also a new integral equation for g is derived for a bound state case. We found a prescription for obtaining the kernel N starting with the kernel K of the Bethe-Salpeter equation, and the method is valid for any kernel given by an irreducible Feynman amplitude. We briefly discuss a possible application in hadronic physics, where from the Light-front wave function one obtains the Nakanishi weight function and the associated Bethe-Salpeter amplitude.

Compact stars as a test for modified gravity theories

• Manuel Malheiro (ITA)

We investigate the equilibrium configurations of neutron stars, quark stars and white dwarfs in a modified gravity theory, namely, $f(R,T)$ gravity, for which $R$ and $T$ stand for the Ricci scalar and trace of the energy-momentum tensor, respectively. Considering the functional form $f(R,T)=R+2\lambda T$, with $\lambda$ being a constant, we obtain the hydrostatic equilibrium equation for the theory. Some physical properties of compact stars, such as: mass, radius, pressure and energy density, as well as their dependence on the parameter $\lambda$ are derived.

Precision QCD with tau decays

• Diogo Boito (Universidade de São Paulo)

Hadronic tau decays remain an excellent laboratory for the study of many aspects of QCD. The inclusive decays have been used as a source of precise information about $\alpha_s$ for the past 20 years. In the search for higher precision, partially triggered by the LHC, several aspects of this determination have been scrutinised in the recent past. The issues that arise are often of a fundamental nature. We will discuss problems pertaining to perturbative and non-perturbative QCD, with emphasis on renormalon singularities, scheme variations, and a novel approach to the violations of quark-hadron duality. The present status of $\alpha_s$ from tau decays and perspectives for the future will be summarised.

Celebration session - 30th anniversary of the International Workshop on Hadron Physics

• Erasmo Ferreira (Universidade Federal do Rio de Janeiro)
• Takeshi Kodama (Universidade Federal do Rio de Janeiro)

LHC measurements of QCD

• Arthur Moraes (CBPF - Brazilian Center for Physics Research (BR))

The talk will cover results from all LHC experiments (CMS, ATLAS and LHCb) on Z, photon and jet production in pPb and PbPb ion collisions, Heavy quark production Jet substructure and fragmentation, Double parton scattering.

A quasi-particle equation of state with a phenomenological critical point for heavy-ion nuclear collisions

• Wei-Liang Qian (University of Sao Paulo)

In this work, we propose a quasi-particle equation of state with a phenomenological critical point. The QGP phase of the model is determined by a quasi-particle model fitting to the Lattice QCD data. At zero baryon density, the model is smoothly connected to the hadronic resonance model. A phenomenological critical point is implemented in such a way when the baryon density increases and passes a critical value, the phase transition turns from a crossover into a first order phase transition. We apply the model to the study of relativistic heavy-ion collisions numerically by using a hydrodynamic model. The impact of the existence of the phenomenological critical point is addressed.

A first survey of the ghost-gluon vertex in the Gribov-Zwanziger framework

• Bruno Mintz

In order to have a proper definition of a quantum nonabelian gauge theory, such as QCD, one needs to have a well-defined generating functional. In the perturbative regime at high energies, this can be achieved through the well-known Faddeev-Popov quantization procedure. For energy scales in which the coupling of the strong force becomes sufficiently high, the perturbative approach may display some inconsistencies. One such problem is the so-called Gribov problem: in a gauge fixed theory, the ghost fields acquire a pole at finite (euclidean) momentum. Equivalently, the determinant of the Faddeev-Popov operator vanishes and the generating functional of the theory becomes void. In order to correct this problem (at least partially), Gribov suggested to restrict the functional integration of gauge fields to a subset of the field space, which is now called the Gribov region. As this restriction of the gauge fields to the Gribov region is taken into account, it turns out that the resulting gauge field propagators display a nontrivial infrared behavior, being very close to the ones observed in lattice gauge field theory simulations. In this work, we explore for the first time a higher correlation function in the presence of the Gribov horizon: the ghost-anti-ghost-gluon interaction vertex, at one-loop level. Our analytical results (within the so-called Refined Gribov Zwanziger theory) are fairly compatible with lattice YM simulations, as well as with solutions from the Schwinger-Dyson equations. This is an indication that the RGZ framework can provide a reasonable description in the infrared not only of gauge field propagators, but also of higher correlation functions, such as interaction vertices.

Quark mass generation with Schwinger-Dyson equations

• Arlene Cristina Aguilar

In this talk, I will present some the current efforts to understand the phenomenon of chiral symmetry breaking and the generation of a dynamical quark mass. To do that, we will use the framework of the Schwinger-Dyson equations. We will solve the coupled system of integral equations formed by the quark propagator and the complete non-transverse structure of the quark-gluon vertex, which is formed by four independent form factors. Particular attention is dedicated to guarantee the correct renormalization group behaviour of the quark dynamical mass and in the extraction of the phenomenological parameters such as pion constant decay.

Poster Prizes & General Assembly

Confinement and deconfinement from lattice simulations

• Tereza Mendes

We review methods and results for the study of color confinement in Yang-Mills theories using numerical simulations of infrared propagators in the lattice formulation. We discuss recent progress in considering finite-volume effects, different gauges and the finite-temperature case.

Polarised Drell-Yan results from COMPASS

• Celso Franco (LIP)

The COMPASS experiment at CERN is one of the leading experiments studying the nucleon spin structure. Until 2012 the Parton Distribution Functions and the Transverse Momentum Dependent Parton Distribution Functions (TMDs) were extensively studied at COMPASS using Semi-Inclusive Deep Inelastic Scattering measurements. In 2015, the Drell-Yan measurements with a negative pion beam interacting with a transversely polarized ammonia target have started and will be continued through 2018. The goal is to access the TMDs of both pions and protons without any prior knowledge about fragmentation functions. Since the Drell-Yan data cover the same kinematic region of the semi-inclusive data, COMPASS has the unique opportunity to test the sign change of the Sivers TMD as predicted by QCD. In this talk the first measurement of spin dependent azimuthal asymmetries in the pion induced Drell-Yan process will be presented. These asymmetries, which are related to the convolution of pion and nucleon TMDs, are extracted from pairs of oppositely charged muons with invariant masses between 4.3 GeV$c^2$ and 8.5 GeV$c^2$