Hadronic Sector Research Articles

Deconfinement phase transition in compact stars: Maxwell versus Gibbs construction of the mixed phase

We study different realizations of the first-order deconfinement phase transition inside a compact star by comparing the Gibbs and Maxwell construction for the mixed phase. The hadronic sector is described within the relativistic mean field model including hyperons. The quark sector is described by the MIT bag model. We find that these two realizations lead to very different star properties, in particular, the composition of the stellar matter. We also find that for the Maxwell construction there is a sharp discontinuity in the baryon density and the electron chemical potential. We argue that a sharp jump in the electron chemical potential should lead to the redistribution of electrons and formation of strong electric fields around the discontinuity surface.

From Kadanoff-Baym dynamics to off-shell parton transport

The description of strongly interacting quantum fields is based on two-particle irreducible (2PI) approaches that allow for a consistent treatment of quantum systems out-of-equilibrium as well as in thermal equilibrium. As a theoretical test case the quantum time evolution of Φ4-field theory in 2+1 space-time dimensions is investigated numerically for out-of-equilibrium initial conditions on the basis of the Kadanoff-Baym-equations including the tadpole and sunset self energies. In particular we address the dynamics of the spectral (‘off-shell’) distributions of the excited quantum modes and the different phases in the approach to equilibrium described by Kubo-Martin-Schwinger relations for thermal equilibrium states. A detailed comparison of the full quantum dynamics to approximate schemes like that of a standard kinetic (on-shell) Boltzmann equation is performed. We find that far off-shell 1↔3 processes are responsible for chemical equilibration, which is not included in the Boltzmann limit. Furthermore, we derive generalized transport equations for the same theory in a first order gradient expansion in phase space thus explicitly retaining the off-shell dynamics as inherent in the time-dependent spectral functions. The solutions of these equations compare very well with the exact solutions of the full Kadanoff-Baym equations with respect to the occupation numbers of the individual modes, the spectral evolution as well as the chemical equilibration process. Furthermore, the proper equilibrium off-shell distribution is reached for large times contrary to the quasiparticle Boltzmann limit. We additionally present a direct comparison of the solution of the generalized transport equations in the Kadanoff-Baym (KB) and Botermans-Malfliet (BM) form; both solutions are found to agree very well with each other. The off-shell transport equation in the BM scheme allows for an explicit solution within an extended dynamical quasiparticle Ansatz. This leads to generalized equations of motion for dynamical quasiparticles that exceed the classical Hamilton equations and allow for the description of dynamical spectral functions. The dynamical quasiparticle model (DQPM) is used to extract partonic spectral functions from lattice QCD in the temperature range 0.8≤T/Tc ≤10. By consideration of time-like and space-like sectors of ‘observables’ such as number densities, energy densities etc. mean-field potentials as well as effective interactions are extracted at different temperature T and quark chemical potentials μq. The latter determine the off-shell dynamics in the Parton-Hadron-String Dynamics (PHSD) transport approach. Illustrative examples for off-shell dynamics in the hadron and parton sector are presented for e+e- production from nucleus-nucleus collisions from SIS to RHIC energies. The generalized transport approach, furthermore, qualifies for the description of hadronization without leading to the problem of entropy reduction as in conventional coalescence models.

Up- and down-quark masses from finite-energy QCD sum rules to five loops

The up- and down-quark masses are determined from an optimized QCD finite-energy sum rule involving the correlator of axial-vector divergences, to five-loop order in perturbative QCD, and including leading nonperturbative QCD and higher order quark-mass corrections. This finite-energy sum rule is designed to reduce considerably the systematic uncertainties arising from the (unmeasured) hadronic resonance sector, which in this framework contributes less than 3--4% to the quark mass. This is achieved by introducing an integration kernel in the form of a second degree polynomial, restricted to vanish at the peak of the two lowest lying resonances. The driving hadronic contribution is then the pion pole, with parameters well known from experiment. The determination is done in the framework of contour improved perturbation theory, which exhibits a very good convergence, leading to a remarkably stable result in the unusually wide window ${s}_{0}=1.0--4.0\text{ }\text{ }{\mathrm{GeV}}^{2}$, where ${s}_{0}$ is the radius of the integration contour in the complex energy (squared) plane. The results are ${m}_{u}(Q=2\text{ }\text{ }\mathrm{GeV})=2.9\ifmmode\pm\else\textpm\fi{}0.2\text{ }\text{ }\mathrm{MeV}$, ${m}_{d}(Q=2\text{ }\text{ }\mathrm{GeV})=5.3\ifmmode\pm\else\textpm\fi{}0.4\text{ }\text{ }\mathrm{MeV}$, and $({m}_{u}+{m}_{d})/2=4.1\ifmmode\pm\else\textpm\fi{}0.2\text{ }\text{ }\mathrm{MeV}$ (at a scale $Q=2\text{ }\text{ }\mathrm{GeV}$).

Light quark masses from QCD sum rules with minimal hadronic bias

The light quark masses are determined using a new QCD Finite Energy Sum Rule (FESR) in the pseudoscalar channel. This FESR involves an integration kernel designed to reduce considerably the contribution of the (unmeasured) hadronic resonance spectral functions. The QCD sector of the FESR includes perturbative QCD (PQCD) to five loop order, and the leading non-perturbative terms. In the hadronic sector the dominant contribution is from the pseudoscalar meson pole. Using Contour Improved Perturbation Theory (CIPT) the results for the quark masses at a scale of 2 GeV are m u ( Q = 2 GeV ) = 2.9 ± 0.2 MeV , m d ( Q = 2 GeV ) = 5.3 ± 0.4 MeV , and m s ( Q = 2 GeV ) = 102 ± 8 MeV , for Λ = 381 ± 16 MeV , corresponding to α s ( M τ 2 ) = 0.344 ± 0.009 . In this framework the systematic uncertainty in the quark masses from the unmeasured hadronic resonance spectral function amounts to less than 2 – 3 %. The remaining uncertainties above arise from those in Λ, the unknown six-loop PQCD contribution, and the gluon condensate, which are all potentially subject to improvement.

Strange quark mass from finite energy QCD sum rules to five loops

The strange quark mass is determined from a new QCD Finite Energy Sum Rule (FESR) optimized to reduce considerably the systematic uncertainties arising from the hadronic resonance sector. As a result, the main uncertainty in this determination is due to the value of ΛQCD. The correlator of axial-vector divergences is used in perturbative QCD to five-loop order, including quark and gluon condensate contributions, in the framework of both Fixed Order (FOPT), and Contour Improved Perturbation Theory (CIPT). The latter exhibits very good convergence, leading to a remarkably stable result in the very wide range s0 = 1.0−4.0 GeV2, where s0 is the radius of the integration contour in the complex energy (squared) plane. The value of the strange quark mass in this framework at a scale of 2 GeV is ms(2 GeV) = 95±5 (111±6) MeV for ΛQCD = 420 (330) MeV, respectively.

Probing Supersymmetric Grand Unification through Flavor Physics

Flavor Changing Neutral Current (FCNC) and CP violating processes are a powerful tool to probe the Standard Model (SM) and, hence, to constrain or obtain indirect hints of New Physics (NP) beyond it. Within Supersymmetric Grand Unified theories it is generally possible to link processes occurring in the leptonic and hadronic sectors; thus, their correlated analysis provides a very interesting low energy test for a Grand Unified theory at high energies. Similarly to the FCNC decays, we also show that the Lepton Flavor Universality tests in low-energy systems ( K l 2 and π l 2 ) offer a unique opportunity in shedding light on physics beyond the Standard Model; the smallness of NP effects is more than compensated, in terms of NP sensitivity, by the excellent experimental resolution and the good theoretical control.

Flavor Physics in SUSY Grand Unified Theories

Within Supersymmetric Grand Unified theories with soft breaking terms arising at the Planck scale, it is generally possible to link Flavor Changing Neutral Current (FCNC) and CP violating processes occurring in the leptonic and hadronic sectors. So, a correlated analysis of low-energy observables in the leptonic and hadronic sectors, can provide indications of the existence of a Grand Unified theory at high energies. We show how bounds on leptonic FCNC involving the third generation translate into constraints on FCNC B decays. Moreover, we show that, besides FCNC transitions, also lepton-flavor (LF) universality tests in M ℓ 2 decays (with M = π , K , B ), offer a unique opportunity to study the flavour structure of physics beyond the SM.

Hybrid protoneutron stars with the MIT bag model

We study the hadron-quark phase transition in the interior of protoneutron stars. For the hadronic sector, we use a microscopic equation of state involving nucleons and hyperons derived within the finite-temperature Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ the MIT bag model both with a constant and a density-dependent bag parameter. We calculate the structure of protostars with the equation of state comprising both phases and find maximum masses below 1.6 solar masses. Metastable heavy hybrid protostars are not found.

The B - TAU FCNC Connection in SUSY Unified Theories

In the context of SUSY grand unification a link is established between the hadronic and leptonic soft breaking sectors. Such relation is here exploited in particular for FCNC processes in B physics. It is shown how bounds on leptonic FCNC involving the third generation translate into constraints on FC B decays. In the second part of the contribution we show that tests of lepton universality in K and B decays can represent an interesting handle to obtain relevant information on the amount of FCNC in the second and third fermion generation.

Implications ofR-parity violating supersymmetry for atomic and hadronic electric dipole moments

We calculate the electric dipole moments (EDM) of the neutral $^{199}\mathrm{Hg}$ atom, deuteron, nucleons and neutral hyperons $\ensuremath{\Lambda}$, ${\ensuremath{\Sigma}}^{0}$ and ${\ensuremath{\Xi}}^{0}$ in the framework of a generic SUSY model without $R$-parity conservation (${\mathrm{R\ensuremath{\llap{\not\;}}}}_{p}\mathrm{SUSY}$) on the basis of the SU(3) version of chiral perturbation theory (ChPT). We consider $CP$-violation in the hadronic sector induced by the chromoelectric quark dipole moments and $CP$-violating 4-quark effective interactions. From the null experimental results on the neutron and $^{199}\mathrm{Hg}$ atom EDMs we derive limits on the imaginary parts of certain products $\mathrm{Im}({\ensuremath{\lambda}}^{\ensuremath{'}}{\ensuremath{\lambda}}^{\ensuremath{'}*})$ of the trilinear ${\mathrm{R\ensuremath{\llap{\not\;}}}}_{p}$-couplings and demonstrate that they are more stringent than those existing in the literature. Using these limits we give predictions for the EDMs of neutral hyperons. We also estimate the prospects of future storage ring experiments on the deuteron EDM and show that the expected improvement of the above limits in these experiments may reach several orders of magnitude.

The FLUKA code: an overview

FLUKA is a multipurpose MonteCarlo code which can transport a variety of particles over a wide energy range in complex geometries. The code is a joint project of INFN and CERN: part of its development is also supported by the University of Houston and NASA. FLUKA is successfully applied in several fields, including but not only, particle physics, cosmic ray physics, dosimetry, radioprotection, hadron therapy, space radiation, accelerator design and neutronics. The code is the standard tool used at CERN for dosimetry, radioprotection and beam-machine interaction studies. Here we give a glimpse into the code physics models with a particular emphasis to the hadronic and nuclear sector.

Strange star Equation of State with a modified Richardson potential

Richardson potential is an phenomenological interquark interaction taking care of two aspects of QCD, namely the asymptotic freedom and the confinement. The original potential has a scale parameter having value ∼400 MeV and is well tested in hadronic property calculations. This potential was then used in strange star calculation. Strange stars are very compact stars composed of strange quark matter, i.e. a very high density strange quark phase consisting of deconfined u, d and s quarks. Here the value of the scale parameter was taken as 100 MeV. The argument was that for a deconfined quark system like a strange star, the scale parameter may have a value quite different from that used in hadronic sector. To remove this discrepancy we introduced two scale parameters in the potential, one for the asymptotic freedom part and the other for the confining part. With suitable values of the parameters, this modified potential has been successfully used in both baryonic property and strange star calculations. The Equation of States obtained with the modified potential are also used to obtain mass–radius relations for the strange stars.

Rotating twin stars and signature of quark-hadron phase transition

The quark-hadron phase transition in a rotating compact star has been studied. The NLZ (nonlinear consistent zero point energy) model has been used for the hadronic sector and the MIT bag model has been used for the quark sector. It has been found that rotating twin star (third family) solutions are obtained up to $\ensuremath{\Omega}\ensuremath{\approx}4000\phantom{\rule{0.3em}{0ex}}{s}^{\ensuremath{-}1}$. Stars that are rotating faster than this limit do not show twin star solution. A backbending in the moment of inertia is also observed in the supermassive rest mass sequences. The braking index is found to diverge for a star having a larger region of mixed phase.

The hadron-quark phase transition in neutron stars

We study the hadron-quark phase transition in the interior of neutron stars (NS). For the hadronic sector, we use a microscopic equation of state (EOS) involving nucleons and hyperons derived within the Brueckner-Hartree-Fock approach. For the quark sector, we employ the MIT bag model, as well as the Nambu--Jona-Lasinio (NJL) and the Color Dielectric (CD) models, and find that the NS maximum masses lie in the interval between 1.5 and 1.8 solar masses.

Chemical equilibration in relativistic heavy ion collisions

In the hadronic sector of relativistic heavy ion physics, the ρ ⇆ 2 π reaction is the strongest one, strong enough to equilibrate the ρ with the pions throughout the region from chemical freezeout to thermal freezeout when free-particle interactions (with no medium-dependent effects) are employed. Above the chiral restoration temperature, only ρ's and π's are present, in that the chirally restored A 1 is equivalent to the ρ and the mesons have an SU(4) symmetry, with no dependence on isospin and negligible dependence on spin. In the same sense the σ and π are “equivalent” scalars. Thus the chirally restored ρ ⇆ 2 π exhaust the interspecies transitions. We evaluate this reaction at T c and find it to be much larger than below T c , certainly strong enough to equilibrate the chirally restored mesons just above T c . When emitted just below T c the mesons remain in the T c + ε freezeout distribution, at least in the chiral limit because of the Harada–Yamawaki “vector manifestation” that requires that mesonic coupling constants go to zero (in the chiral limit) as T goes to T c from below. Our estimates in the chiral limit give deviations in some particle ratios from the standard scenario (of equilibrium in the hadronic sector just below T c ) of about double those indicated experimentally. This may be due to the neglect of explicit chiral symmetry breaking in our estimates. We also show that the instanton molecules present above T c are the giant multipole vibrations found by Asakawa, Hatsuda and Nakahara and of Wetzorke et al. in lattice gauge calculations. Thus, the matter formed by RHIC can equivalently be called: chirally restored mesons, instanton molecules, or giant collective vibrations. It is a strongly interacting liquid.

Hybrid stars with the color dielectric and the MIT bag models

We study the hadron-quark phase transition in the interior of neutron stars (NS). For the hadronic sector, we use a microscopic equation of state (EOS) involving nucleons and hyperons derived within the Brueckner-Bethe-Goldstone many-body theory, with realistic two-body and three-body forces. For the description of quark matter, we employ both the MIT bag model with a density dependent bag constant, and the color dielectric model. We calculate the structure of NS interiors with the EOS comprising both phases, and we find that the NS maximum masses are never larger than 1.7 solar masses, no matter the model chosen for describing the pure quark phase.

ProbingCPviolation with the deuteron electric dipole moment

We present an analysis of the electric dipole moment (EDM) of the deuteron as induced by CP- violating operators of dimension 4, 5 and 6 includingQCD, the EDMs and color EDMs of quarks, four-quark interactions and the Weinberg operator. We demonstrate that the precision goal of the EDM Collaboration's proposal to search for the deuteron EDM, (1 3)×10 27 ecm, will provide an improvement in sensitivity to these sources of one-two orders of magnitude relative to the existing bounds. We consider in detail the level to which CP-odd phases can be probed within the MSSM. The most stringent constraints on flavor-diagonal CP violation in the hadronic sector arise from bounds on the EDMs of the neutron (1), mercury (2), and in certain cases thallium (3). These experiments have important implications for physics beyond the Standard Model, and its supersymmetric extensions in particular (see e.g. (4)). In what follows, we will show that a proposed measure- ment of the deuteron EDM (5), with projected sensitivity

Grand unification of quark and lepton flavor changing neutral currents.

In the context of supersymmetric grand unified theories with soft breaking terms arising at the Planck scale, it is generally possible to link flavor changing neutral current and CP violating processes occurring in the leptonic and hadronic sectors. We study the correlation between flavor changing squark and slepton mass insertions in models à la SU(5). We show that the constraints coming from lepton flavor violation exhibit a strong impact on CP-violating B decays.

Mass modification ofDmeson in hot hadronic matter

We evaluate the in-medium $D$ and $\bar D$-meson masses in hot hadronic matter induced by interactions with the light hadron sector described in a chiral SU(3) model. The effective Lagrangian approach is generalized to SU(4) to include charmed mesons. We find that the D-mass drops substantially at finite temperatures and densities, which open the channels of the decay of the charmonium states ($\Psi^\prime$, $\chi_c$, $J/\Psi$) to $D \bar D$ pairs in the thermal medium. The effects of vacuum polarisations from the baryon sector on the medium modification of the $D$-meson mass relative to those obtained in the mean field approximation are investigated. The results of the present work are compared to calculations based on the QCD sum-rule approach, the quark-meson coupling model, chiral perturbation theory, as well as to studies of quarkonium dissociation using heavy quark potential from lattice QCD.

Non-diagonal flavour observables in B and collider physics

Until now the focus within the direct search for supersymmetry has mainly been on flavour diagonal observables. Recently lepton flavour violating signals at future electron positron colliders have been studied. There is now an opportunity to analyse the relations between collider observables and low-energy observables in the hadronic sector. In a first work in this direction, we study flavour violation in the squark decays of the second and third generations taking into account results from B physics, in particular from the rare decay b → s γ. Correlations between various squark decay modes can be used to get more precise information on various flavour violating parameters. PACS: 12.60.Jv – 13.25.Hv – 14.80.Ly