Nuclear Theory·nucl-th

Tuesday·June 16, 2015

15 papers—7 primary·8 cross-listed

08
High-precision determination of the pion-nucleon $σ$ -term from Roy-Steiner equations
Martin Hoferichter🇩🇪 · Jacobo Ruiz de Elvira🇩🇪 · Bastian Kubis🇩🇪 · Ulf-G. Meißner🇩🇪
We present a determination of the pion-nucleon ( $π N$ ) $σ$ -term $σ_{π N}$ based on the Cheng-Dashen low-energy theorem (LET), taking advantage of the recent high-precision data from pionic atoms to pin down the $π N$ scattering lengths as well as of constraints from analyticity, unitarity, and crossing symmetry in the form of Roy-Steiner equations to perform the extrapolation to the Cheng-Dashen point in a reliable manner. With isospin-violating corrections included both in the scattering lengths and the LET, we obtain $σ_{π N} = (59.1 \pm 1.9 \pm 3.0)$ MeV $= (59.1 \pm 3.5)$ MeV, where the first error refers to uncertainties in the $π N$ amplitude and the second to the LET. Consequences for the scalar nucleon couplings relevant for the direct detection of dark matter are discussed.
↳ hep-phastro-ph.COhep-latnucl-thPRL(2015)·341 citations
09
Electromagnetic $N - Δ (1232)$ transitions within the point-form of relativistic quantum mechanics
Yubing Dong🇨🇳 · Mauro Giannini🇮🇹 · Elena Santopinto🇮🇹 · Andrea Vassallo🇮🇹
The electromagnetic $N - Δ (1232)$ transition amplitudes are calculated using the point-form of relativistic quantum mechanics. The relativistic effects incorporated in the electromagnetic matrix elements give a good description of the transition amplitudes to the $Δ (1232)$ resonance, reproducing well the $Q^{2}$ behaviour of the data, apart from the low $Q^{2}$ one.
↳ hep-phnucl-thFew Body Syst.(2014)·5 citations
10
Compositeness of the strange, charm and beauty odd parity $Λ$ states
C. Garcia-Recio🇪🇸 · C. Hidalgo-Duque🇪🇸 · J. Nieves🇪🇸 · L.L. Salcedo🇪🇸 · L. Tolos🇪🇸
We study the dependence on the quark mass of the compositeness of the lowest-lying odd parity hyperon states. Thus, we pay attention to $Λ -$ like states in the strange, charm and beauty, sectors which are dynamically generated using a unitarized meson-baryon model. In the strange sector we use an SU(6) extension of the Weinberg-Tomozawa meson-baryon interaction, and we further implement the heavy-quark spin symmetry to construct the meson-baryon interaction when charmed or beauty hadrons are involved. In the three examined flavor sectors, we obtain two $J^{P} = 1/ 2^{-}$ and one $J^{P} = 3/ 2^{-}$ $Λ$ states. We find that the $Λ$ states which are bound states (the three $Λ_{b}$ ) or narrow resonances (one $Λ (1405)$ and one $Λ_{c} (2595)$ ) are well described as molecular states composed of $s$ -wave meson-baryon pairs. The $\frac{1}{2}^{-}$ wide $Λ (1405)$ and $Λ_{c} (2595)$ as well as the $\frac{3}{2}^{-}$ $Λ (1520)$ and $Λ_{c} (2625)$ states display smaller compositeness and so they would require new mechanisms, such as $d$ -wave interactions.
↳ hep-phnucl-exnucl-thPRD(2015)·46 citations
11
Relativistic quark-diquark model of baryons. Non strange spectrum and nucleon electromagnetic form factors
M. De Sanctis🇨🇴 · J. Ferretti🇲🇽 · E. Santopinto🇮🇹 · A. Vassallo🇮🇹
We briefly describe our relativistic quark-diquark model, developed within the framework of point form dynamics, which is the relativistic extension of the interacting quark-diquark model. In order to do that we have to show the main properties and quantum numbers of the effective degree of freedom of constituent diquark. Our results for the nonstrange baryon spectrum and for the nucleon electromagnetic form factors are discussed.
↳ hep-phnucl-thAIP Conf.Proc.(2012)·2 citations
12
On the sensitivity of extracting the astrophysical cross section factor of the 12C(a,g) reaction from existing data [Comment on Schuermann et al. Phys. Lett. B711(2012)35]
Moshe Gai (U Connecticut)
We address a conflicting report on the value and uncertainty of the astrophysical cross section factor of the 12C(a,g) reaction extracted from existing data. In sharp contrast to previously reported ambiguities (by up to a factor 8), Schuermann et al. suggest an accuracy of 12%. We demonstrate that the so claimed "rigorous data selection criteria" used by Schuermann et al. relies on the s-factors extracted by Assuncao et al. But these results were shown in a later analysis (by this author) to have large error bars (considerably larger than claimed by Assuncao em et al.) which render these data not appropriate for a rigorous analysis. When their "rigorous data selection" is adjusted to remove the results of Assuncao et al. the astrophysical cross section factor cannot be extracted with 12% accuracy, or even close to it. Such data on the S_E2 values at low energies deviate by up to a factor two from their fit and exhibit a sharper slope rising toward low energies, leading to strong doubt on their extrapolated S_E2(300) value and the quoted small error bar. Contrary to their claim the small value of S_E1(300) ~10 keVb cannot be ruled out by current data including the most modern gamma-ray data. As previously observed by several authors current data reveal ambiguities in the value of S_E1(300) ~10 keVb or ~80 keVb, and the new ambiguity that was recently revealed (by this author) of S_E2(300) ~60 keVb or ~154 keVb, appear to be a more reasonable evaluation the status of current data.
↳ nucl-exastro-ph.SRnucl-thComment on Schuermann et al. Phys. Lett. …·2 citations
13
R-mode constraints from neutron star equation of state
M. C. Papazoglou🇬🇷 · C. C. Moustakidis🇬🇷
The gravitational radiation has been proposed a long time before, as an explanation for the observed relatively low spin frequencies of young neutron stars and of accreting neutron stars in low-mass X-ray binaries as well. In the present work we studied the effects of the neutron star equation of state on the r-mode instability window of rotating neutron stars. Firstly, we employed a set of analytical solution of the Tolman-Oppemheimer-Volkoff equations with special emphasis on the Tolman VII solution. In particular, we tried to clarify the effects of the bulk neutron star properties (mass, radius, density distribution, crust size and elasticity) on the r-mode instability window. We found that the critical angular velocity $Ω_{c}$ depends mainly on the neutron star radius. The effects of the gravitational mass and the mass distribution are almost negligible. Secondly, we studied the effect of the elasticity of the crust, via to the slippage factor $S$ and also the effect of the nuclear equation of state, via the slope parameter $L$ , on the instability window. We found that the crust effects are more pronounced, compared to those originated from the equation of state. Moreover, we proposed simple analytical expressions which relate the macroscopic quantity $Ω_{c}$ to the radius, the parameter $L$ and the factor $S$ . We also investigated the possibility to measure the radius of a neutron star and the factor $S$ with the help of accurate measures of $Ω_{c}$ and the neutron star temperature. Finally, we studied the effects of the mutual friction on the instability window and discussed the results in comparison with previous similar studies.
↳ astro-ph.SRnucl-thAstrophys.Space Sci.(2016)·16 citations
14
Dissipative properties of hot and dense hadronic matter in excluded volume hadron resonance gas model
Guru Prakash Kadam🇮🇳 · Hiranmaya Mishra🇮🇳
We estimate dissipative properties viz: shear and bulk viscosities of hadronic matter using relativistic Boltzmann equation in relaxation time approximation within ambit of excluded volume hadron resonance gas (EHRG) model. We find that at zero baryon chemical potential the shear viscosity to entropy ratio ( $η / s$ ) decreases with temperature while at finite baryon chemical potential this ratio shows same behavior as a function of temperature but reaches close to Kovtun-Son-Starinets (KSS) bound. Further along chemical freezout curve, ratio $η / s$ is almost constant apart from small initial monotonic rise. This observation may have some relevance to the experimental finding that the differential elliptic flow of charged hadrons does not change considerably at lower center of mass energy. We further find that bulk viscosity to entropy density ( $ζ / s$ ) decreases with temperature while this ratio has higher value at finite baryon chemical potential at higher temperature. Along freezout curve $ζ / s$ decreases monotonically at lower center of mass energy and then saturates.
↳ hep-phnucl-thPRC(2015)·97 citations
15
Strangeness production in heavy-ion collisions
Alessia Palmese🇩🇪 · Giuseppe Pagliara🇮🇹 · Alessandro Drago🇮🇹 · Olena Linnyk🇩🇪 · Wolfgang Cassing🇩🇪
A study of the "horn" in the particle ratio $K^{+} / π^{+}$ for central heavy-ion collisions as a function of the collision energy $s$ is presented. We analyse two different interpretations: the onset of deconfinement and the transition from a baryon- to a meson-dominated hadron gas. We use a realistic equation of state (EOS), which includes both hadron and quark degrees-of-freedom. The Taub-adiabate procedure is followed to determine the system at the early stage. Our results do not support an explanation of the horn as due to the onset of deconfinement. Using only hadronic EOS we reproduced the energy dependence of the $K^{+} / π^{+}$ and $Λ/ π^{-}$ ratios employing an experimental parametrisation of the freeze-out curve. We observe a transition between a baryon- and a meson-dominated regime; however, the reproduction of the $K^{+} / π^{+}$ and $Λ/ π^{-}$ ratios as a function of $s$ is not completely satisfying. We finally propose a new idea for the interpretation of the data, the roll-over scheme, in which the scalar meson field $σ$ has not reached the thermal equilibrium at freeze-out. The rool-over scheme for the equilibration of the $σ$ -field is based on the inflation mechanism. The non-equilibrium evolution of the scalar field influences the particle production, e.g. $K^{+} / π^{+}$ , however, the fixing of the free parameters in this model is still an open issue.
↳ hep-phnucl-thPoS(2015)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE