Marina Nielsen

Bio: Marina Nielsen is an academic researcher from University of São Paulo. The author has contributed to research in topics: Meson & QCD sum rules. The author has an hindex of 41, co-authored 262 publications receiving 6876 citations. Previous affiliations of Marina Nielsen include University of Maryland, College Park & Stanford University.

Heavy quarkonium: progress, puzzles, and opportunities

Abstract: A golden age for heavy-quarkonium physics dawned a decade ago, initiated by the confluence of exciting advances in quantum chromodynamics (QCD) and an explosion of related experimental activity. The early years of this period were chronicled in the Quarkonium Working Group (QWG) CERN Yellow Report (YR) in 2004, which presented a comprehensive review of the status of the field at that time and provided specific recommendations for further progress. However, the broad spectrum of subsequent breakthroughs, surprises, and continuing puzzles could only be partially anticipated. Since the release of the YR, the BESII program concluded only to give birth to BESIII; the B-factories and CLEO-c flourished; quarkonium production and polarization measurements at HERA and the Tevatron matured; and heavy-ion collisions at RHIC have opened a window on the deconfinement regime. All these experiments leave legacies of quality, precision, and unsolved mysteries for quarkonium physics, and therefore beg for continuing investigations at BESIII, the LHC, RHIC, FAIR, the Super Flavor and/or Tau-Charm factories, JLab, the ILC, and beyond. The list of newly found conventional states expanded to include h(c)(1P), chi(c2)(2P), B-c(+), and eta(b)(1S). In addition, the unexpected and still-fascinating X(3872) has been joined by more than a dozen other charmonium- and bottomonium-like "XYZ" states that appear to lie outside the quark model. Many of these still need experimental confirmation. The plethora of new states unleashed a flood of theoretical investigations into new forms of matter such as quark-gluon hybrids, mesonic molecules, and tetraquarks. Measurements of the spectroscopy, decays, production, and in-medium behavior of c (c) over bar, b (b) over bar, and b (c) over bar bound states have been shown to validate some theoretical approaches to QCD and highlight lack of quantitative success for others. Lattice QCD has grown from a tool with computational possibilities to an industrial-strength effort now dependent more on insight and innovation than pure computational power. New effective field theories for the description of quarkonium in different regimes have been developed and brought to a high degree of sophistication, thus enabling precise and solid theoretical predictions. Many expected decays and transitions have either been measured with precision or for the first time, but the confusing patterns of decays, both above and below open-flavor thresholds, endure and have deepened. The intriguing details of quarkonium suppression in heavy-ion collisions that have emerged from RHIC have elevated the importance of separating hot- and cold-nuclear-matter effects in quark-gluon plasma studies. This review systematically addresses all these matters and concludes by prioritizing directions for ongoing and future efforts.

Optimized δ expansion for relativistic nuclear models

Abstract: The optimized δ-expansion is a nonperturbative approach for field theoretic models which combines the techniques of perturbation theory and the variational principle This technique is discussed in the λφ4 model and then implemented in the Walecka model for the equation of state of nuclear matter The results obtained with the δ expansion are compared with those obtained with the traditional mean field, relativistic Hartree and Hartree-Fock approximations

Can the X ( 3872 ) be a 1 ++ four-quark state?

Abstract: We use QCD spectral sum rules to test the nature of the meson X(3872), assumed to be an exotic four-quark (ccqq) state with J{sup PC}=1{sup ++}. For definiteness, we work with the diquark-antidiquark current proposed recently, at leading order in {alpha}{sub s}, consider the contributions of higher dimension condensates and keep terms which are linear in the light quark mass m{sub q}. We find M{sub X}=(3925{+-}127) MeV which is compatible, within the errors, with the experimental candidate X(3872), while the SU(3) breaking-terms lead to an unusual mass-splitting M{sub X{sup s}}-M{sub X}=-(61{+-}30) MeV. The mass-difference between the neutral states due to isospin violation is about (2.6{approx}3.9) MeV. For the b-quark, we predict M{sub X{sub b}}=(10144{+-}106) MeV for the X{sub b}(bbqq), which is much below the BB* threshold, and for the X{sub b}{sup s}(bbss), a mass-splitting M{sub X{sub b}{sup s}}-M{sub X{sub b}}=-(121{+-}182) MeV. Our analysis also indicates that the mass-splitting between the ground state and the radial excitation of about (225{approx}250) MeV is much smaller than in the case of ordinary mesons and is (within the errors) flavor-independent. We also extract the decay constants, analogous to f{sub {pi}}, of such mesons, which are useful for further studies of their leptonic and hadronicmore » decay widths. The uncertainties of our estimates are mainly due to the ones from the c and b quark masses.« less

Quantum mechanical continuum solvation models.

Abstract: 6.2.2. Definition of Effective Properties 3064 6.3. Response Properties to Magnetic Fields 3066 6.3.1. Nuclear Shielding 3066 6.3.2. Indirect Spin−Spin Coupling 3067 6.3.3. EPR Parameters 3068 6.4. Properties of Chiral Systems 3069 6.4.1. Electronic Circular Dichroism (ECD) 3069 6.4.2. Optical Rotation (OR) 3069 6.4.3. VCD and VROA 3070 7. Continuum and Discrete Models 3071 7.1. Continuum Methods within MD and MC Simulations 3072