Nuclear Theory·nucl-th

Thursday·June 4, 2015

10 papers—5 primary·5 cross-listed

01
Dibaryons in a constituent quark model
Woosung Park🇰🇷 · Aaron Park🇰🇷 · Su Houng Lee🇰🇷
We investigate the properties of dibaryons containing u and d quarks in the constituent quark model. In constructing the ground state wave function, we choose the spatial part to be fully symmetric and the remaining color, isospin and spin part to be antisymmetric so as to satisfy the the Pauli principle. By adapting the IS coupling scheme that combine the isospin basis function with the spin basis function, and subsequently coupling this to the color singlet basis function, we construct the color $\otimes$ isospin $\otimes$ spin states compatible with the physical states of the dibaryon. By using the variational method, we then calculate the mass of the dibaryon in a nonrelativistic potential model, involving Coulomb, color confinement and color-spin hyperfine interaction. In particular, to asses the stability for different types of the confinement potential, we introduce one that is linearly proportional to the interquark distance and another to its square root. For all cases considered, we find that there are no compact bound states against the strong decay.
nucl-thhep-phPRD(2015)·65 citations
02
Comment on "Lattice determination of $Σ$ - $Λ$ mixing"
Avraham Gal🇮🇱
A recent lattice QCD (LQCD) calculation of $Σ$ - $Λ$ mixing by the QCDSF-UKQCD Collaboration [Phys. Rev. D 91, 074512 (2015)] finds a mixing angle about half of that found from the Dalitz-von Hippel (DvH) flavor SU(3) mass formula which relates the $Σ$ - $Λ$ mixing matrix element to known octet baryon mass differences and which has been used widely to evaluate charge symmetry breaking effects in $Λ$ hypernuclei. We show that the LQCD-calculated $Σ$ - $Λ$ mixing matrix element and octet baryon masses satisfy the DvH mass formula, concluding thereby that a good LQCD evaluation of $Σ$ - $Λ$ mixing requires an equally good reproduction of octet baryon mass differences which is yet to be demonstrated.
nucl-thhep-lathep-phnucl-exPRD(2015)·13 citations
03
A systematic study of longitudinal and transverse helicity amplidutes in the hypercentral Constituent Quark Model
E. Santopinto🇮🇹 · M.M. Giannini🇮🇹
We report in a systematic way the predictions of the non-relativistic hypercentral Constituent Quark model for the electromagnetic excitations of baryon resonances. The longitudinal and transverse helicity amplitudes are calculated with no free parameters for fourteen resonances, both for proton and neutron. The calculations lead to an overall fair description of data, specially in the medium $Q^{2}$ range, where quark degrees of freedom are expected to dominate.
nucl-thhep-phPRC(2012)·86 citations
04
Cancellation of the sigma meson in thermal models
Wojciech Broniowski🇵🇱 · Francesco Giacosa🇵🇱 · Viktor Begun🇵🇱
The by now well-established scalar-isoscalar resonance $f_{0} (500)$ (the $σ$ meson) seems potentially relevant in the evaluation of thermodynamic quantities of a hadronic gas, since its mass is low. However, we recall that its contribution to isospin-averaged observables is, to a surprising accuracy, canceled by the repulsion from the pion-pion scalar-isotensor channel. As a result, in practice one should not incorporate $f_{0} (500)$ in standard hadronic resonance-gas models for studies of isospin averaged quantities. In our analysis we use the formalism of the virial expansion, which allows one to calculate the thermal properties of an interacting hadron gas in terms of derivatives of the scattering phase shifts, hence in a model-independent way directly from experimentally accessible quantities. A similar cancellation mechanism occurs for the scalar kaonic interactions between the $I = 1/2$ channel (containing the alleged $K_{0}^{*} (800)$ or the $κ$ meson) and the $I = 3/2$ channel.
nucl-thhep-phnucl-exPRC(2015)·85 citations
05
Quantifying truncation errors in effective field theory
R. J. Furnstahl🇺🇸 · N. Klco🇺🇸 · D. R. Phillips🇺🇸 · S. Wesolowski🇺🇸
Bayesian procedures designed to quantify truncation errors in perturbative calculations of quantum chromodynamics observables are adapted to expansions in effective field theory (EFT). In the Bayesian approach, such truncation errors are derived from degree-of-belief (DOB) intervals for EFT predictions. Computation of these intervals requires specification of prior probability distributions ("priors") for the expansion coefficients. By encoding expectations about the naturalness of these coefficients, this framework provides a statistical interpretation of the standard EFT procedure where truncation errors are estimated using the order-by-order convergence of the expansion. It also permits exploration of the ways in which such error bars are, and are not, sensitive to assumptions about EFT-coefficient naturalness. We first demonstrate the calculation of Bayesian probability distributions for the EFT truncation error in some representative examples, and then focus on the application of chiral EFT to neutron-proton scattering. Epelbaum, Krebs, and Meißner recently articulated explicit rules for estimating truncation errors in such EFT calculations of few-nucleon-system properties. We find that their basic procedure emerges generically from one class of naturalness priors considered, and that all such priors result in consistent quantitative predictions for 68% DOB intervals. We then explore several methods by which the convergence properties of the EFT for a set of observables may be used to check the statistical consistency of the EFT expansion parameter.
nucl-thhep-phnucl-exphysics.data-anPRC(2015)·319 citations
06
High x Structure Function of the Virtually Free Neutron
Wim Cosyn🇧🇪 · Misak M. Sargsian🇺🇸
The pole extrapolation method is applied to the semi-inclusive inelastic electron scattering off the deuteron with tagged spectator protons to extract the high-x structure function of the neutron. This approach is based on the extrapolation of the measured cross sections at different momenta of the spectator proton to the non-physical pole of the bound neutron in the deuteron. The advantage of the method is in the possibility of suppression of the nuclear effects in a maximally model-independent way. The neutron structure functions obtained in this way demonstrate a surprising x dependence at $x \geq 0.6$ and $1.6 \leq Q^{2} \leq 3.38$ GeV $^{2}$ , indicating a possible rise of the neutron to proton structure function ratio. If the observed rise is valid in the true deep inelastic region then it may indicate new dynamics in the generation of high-x quarks in the nucleon. One such mechanism we discuss is the possible dominance of short-range isosinglet quark-quark correlations that can enhance the d-quark distribution in the proton.
↳ hep-phnucl-exnucl-thPRC(2016)·7 citations
07
Role of the $Λ_{c}^{+} (2940)$ in the $π^{-} p \to D^{-} D^{0} p$ reaction close to threshold
Ju-Jun Xie🇨🇳 · Yu-Bing Dong🇨🇳 · Xu Cao🇨🇳
We report on a theoretical study of the $π^{-} p \to D^{-} D^{0} p$ reaction near threshold within an effective Lagrangian approach. The production process is described by $t$ channel $D^{* 0}$ meson exchange, $s$ -channel nucleon pole, and $u$ channel $Σ_{c}^{++}$ exchange. In our work, the final $D^{0} p$ results from the ground $Λ_{c}^{+} (2286)$ state and also dominantly from the excited $Λ_{c}^{+} (2940)$ state which is assumed as a $D^{* 0} p$ molecular state with spin parity $J^{P} = \frac{1}{2}^{+}$ or $\frac{1}{2}^{-}$ . We calculate the total cross section of the $π^{-} p \to D^{-} D^{0} p$ reaction. It is shown that the spin parity assignment of $\frac{1}{2}^{-}$ for $Λ_{c}^{+} (2940)$ gives a sizable enhancement for the total cross section in comparison with a choice of $J^{p} = \frac{1}{2}^{+}$ . However, our theoretical result of the total cross section is sensitive to the value of the cutoff parameter involved in the form factor of the exchanged off-shell particles. Moreover, we also calculate the second order differential cross section and find it can be used to determine the parity of the $Λ_{c}^{+} (2940)$ . It is expected that our model calculations can be tested by future experiments at J-PARC in Japan.
↳ hep-phhep-exnucl-exnucl-thPRD(2015)·45 citations
08
Collective modes of p-wave superfluid Fermi gases in BEC phase
Francesco Matera · Matthias F. Wagner
The low-energy modes of a superfluid atomic Fermi gas at zero temperature are investigated. The Bose-Einstein-condensate (BEC) side of the superfluid phase is studied in detail. The atoms are assumed to be in only one internal state, so that for a sufficiently diluted gas the pairing of fermions can be considered effective in the l=1 channel only. In agreement with previous works on p-wave superfluidity in Fermi systems, it is found that the $p_{x} + i p_{y}$ phase represents the lowest energy state in both the Bardeen-Cooper-Schrieffer (BCS) and BEC sides. Our calculations show that at low energy three branches of collective modes can emerge, with different species of dispersion relations: a phonon-like mode, a single-particle-like mode and a gapped mode. A comparison with the Bogoliubov excitations of the corresponding spinor Bose condensate is made. They reproduce the dispersion relations of the excitation modes of the p-wave superfluid Fermi gas to a high accuracy.
↳ cond-mat.quant-gasnucl-thEur.Phys.J.D(2015)·1 citation
09
A covariant model for the nucleon spin structure
G. Ramalho🇧🇷
We present the results of the covariant spectator quark model applied to the nucleon structure function $f (x)$ measured in unpolarized deep inelastic scattering, and the structure functions $g_{1} (x)$ and $g_{2} (x)$ measured in deep inelastic scattering using polarized beams and targets ( $x$ is the Bjorken scaling variable). The nucleon is modeled by a valence quark-diquark structure with $S, P$ and $D$ components. The shape of the wave functions and the relative strength of each component are fixed by making fits to the deep inelastic scattering data for the structure functions $f (x)$ and $g_{1} (x)$ . The model is then used to make predictions on the function $g_{2} (x)$ for the proton and neutron.
↳ hep-phhep-exnucl-exnucl-thProceedings of New Trends in High-Energy …·0 citations
10
Thermodynamics and CP-odd transport in Holographic QCD with Finite Magnetic Field
Tara Drwenski🇳🇱 · Umut Gursoy🇳🇱 · Ioannis Iatrakis🇺🇸
We consider a bottom-up holographic model of QCD at finite temperature T and magnetic field B, and study dependence of thermodynamics and CP-odd transport on these variables. As the magnetic field couples to the flavor sector only, one should take the Veneziano limit where the number of flavors and colors are large while their ratio is kept fixed. We investigate the corresponding holographic background in the approximation where the ratio of flavors to colors is finite but small. We demonstrate that B-dependence of the entropy of QCD is in qualitative agreement with the recent lattice studies. Finally we study the CP-odd transport properties of this system. In particular, we determine the Chern-Simons decay rate at finite B and T, that is an important ingredient in the Chiral Magnetic Effect.
↳ hep-thhep-phnucl-thJHEP(2016)·28 citations

Affiliations

first authorsco-authorsvia INSPIRE