Nuclear Theory·nucl-th

Tuesday·April 28, 2015

8 papers—7 primary·1 cross-listed

01
The dual quark condensate in local and nonlocal NJL models: an order parameter for deconfinement?
Federico Marquez🇨🇱 · Aftab Ahmad🇲🇽 · Michael Buballa🇩🇪 · Alfredo Raya🇨🇱
We study the beahviour of the dual quark condensate $Σ_{1}$ in the Nambu-Jona-Lasinio (NJL) model and its nonlocal variant. In quantum chromodynamics $Σ_{1}$ can be realted to the breaking of the center symmetry and is therefore an (approximate) order parameter of confinement. The deconfinement transition is then signaled by a strong rise of $Σ_{1}$ as a function of temperature. However, a similar behaviour is also seen in the NJL model, which is known to have no confinement. Indeed, it was shown that in this model the rise of $Σ_{1}$ is triggered by the chiral phase transition. In order to shed more light on this issue, we calculate $Σ_{1}$ for several variants of the NJL model, some of which have been suggested to be confining. Switching between "confining" and "non-confining" models and parametrizations we find no qualitative difference in the behaviour of $Σ_{1}$ , namely, it always rises in the region of the chiral phase transition. We conclude that without having established a relation to the center symmetry in a given model, $Σ_{1}$ should not blindly be regarded as an order parameter of confinement.
nucl-thhep-phPLB(2015)·21 citations
02
Neutron Resonance Widths and the Porter-Thomas Distribution
Alexander Volya · Hans A. Weidenmüller · Vladimir Zelevinsky
Experimental evidence has recently put the validity of the Porter-Thomas distribution (PTD) for partial neutron widths into question. We identify two terms in the effective Hamiltonian that violate orthogonal invariance (the basis for the PTD). Both are due to the coupling to the decay channels. We show that realistic estimates for the coupling to the neutron channel and for non-statistical gamma decays yield significant modifications of the PTD.
nucl-thPRL(2015)·20 citations
03
Hydrodynamics with chiral anomaly and charge separation in relativistic heavy ion collisions
Yi Yin🇺🇸 · Jinfeng Liao🇺🇸
Matter with chiral fermions is microscopically described by theory with quantum anomaly and macroscopically described (at low energy) by anomalous hydrodynamics. For such systems in the presence of external magnetic field and chirality imbalance, a charge current is generated along the magnetic field direction --- a phenomenon known as the Chiral Magnetic Effect (CME). The quark-gluon plasma created in relativistic heavy ion collisions provides an (approximate) example, for which the CME predicts a charge separation perpendicular to the collisional reaction plane. Charge correlation measurements designed for the search of such signal have been done at RHIC and the LHC for which the interpretations, however, remain unclear due to contamination by background effects that are collective flow driven, theoretically poorly constrained, and experimentally hard to separate. Using anomalous (and viscous) hydrodynamic simulations, we make a first attempt at quantifying contributions to observed charge correlations from both CME and background effects in one and same framework. The implications for the search of CME are discussed.
nucl-thhep-phhep-thnucl-exPLB(2016)·50 citations
04
Nonperturbative numerical calculation of the fine and hyperfine structure of muonic hydrogen by Breit potential including the effects from the proton size
Hou-Rong Pang · Hai-Qing Zhou
By solving the two-body Schordinger equation in a very high precise nonperturbative numerical (NPnum) way, we reexamine the contributions of fine, hyperfine structure splittings of muonic hydrogen based on the Breit potential. The comparison of our results with those by the first order perturbative theory ( $^{1 s t}$ PT) in the literature shows, when the structure of proton is considered, the differences between the results by the $^{1 s t}$ PT and NPnum methods are small for the fine and hyperfine splitting of $2 P$ state, while are about $- 0.009$ meV and $0.08$ meV for the $F = 1$ and total hyperfine splitting of $2 S$ state of muonic hydrogen, respectively. These differences are larger than the current experimental precision and would be significant to be considered in the theoretical calculation.
nucl-thphysics.atom-ph1 citation
05
Test of time-reversal symmetry in the proton-deuteron scattering
Yu.N. Uzikov🇷🇺 · A.A. Temerbayev🇰🇿
The integrated cross section $σ$ for a special type of double polarized proton-deuteron scattering constitutes a null test forvtime-invariance violating but P-parity conserving effects. Using the Glauber theory for the $p d$ elastic scattering and different types of phenomenological T-odd P-even NN-interactions we show that the contribution of the lowest mass meson exchange, i.e. the $ρ$ -meson, to the null-test signal $σ$ vanishes. Variation of the cross section $σ$ due to strong hadronic and Coulomb interaction is studied and its energy dependence is calculated in the GeV region.
nucl-thInt.J.Mod.Phys.Conf.Ser.(2016)·4 citations
06
Constraints on the Neutron Skin and the Symmetry Energy from the Anti-analog Giant Dipole Resonance in 208Pb
L.G. Cao · X. Roca-Maza · G. Colo' · H. Sagawa
We investigate the impact of the neutron-skin thickness Delta(R) on the energy difference between the anti-analog giant dipole resonance (AGDR), E(AGDR), and the isobaric analog state (IAS), E(IAS), in a heavy nucleus such as 208Pb. For guidance, we first develop a simple and analytic, yet physical, approach based on the Droplet Model that linearly connects the energy difference E(AGDR)-E(IAS) with Delta(R). To test this correlation on more fundamental grounds, we employ a family of systematically varied Skyrme energy density functionals where variations on the value of the symmetry energy at saturation density J are explored. The calculations have been performed within the fully self consistent Hartree-Fock (HF) plus charge-exchange random phase approximation (RPA) framework. We confirm the linear correlation within our microscopic apporach and, by comparing our results with available experimental data in 208Pb, we find that our analysis is consistent with Delta(R) = 0.204 \pm 0.009 fm, J = 31.4 \pm 0.5 MeV and a slope parameter of the symmetry energy at saturation of L = 76.4 \pm 5.4 MeV - the attached errors correspond to a lower-limit estimate of the systematic plus experimental uncertainties. These results are in agreement with those extracted from different experimental data albeit, L and Delta(R) are somewhat large when compared to previous estimations based on giant resonance studies.
nucl-thPRC(2015)·27 citations
07
A Tale of Tails: Photon Rates and Flow in Ultra-Relativistic Heavy Ion Collisions
Larry McLerran🇺🇸 · Bjoern Schenke🇺🇸
We consider the possibility that quark and gluon distributions in the medium created in high energy heavy ion collisions may be modified by a power law tail at energies much higher than the temperature. We parametrize such a tail by Tsallis distributions with an exponent motivated by phenomenology. These distributions are characterized by an effective temperature scale that we assume to evolve in time like the temperature for thermal distributions. We find that including such a tail increases the rates for photon production and significantly delays the emission times for photons of a fixed energy. We argue that these effects are sufficiently large that they should be able to account for photon yields and flow patterns seen in LHC and RHIC experiments.
nucl-thNPA(2016)·36 citations
08
Gaussian Anisotropy In Strange Quark Stars
H. Panahi🇮🇷 · R. Monadi🇮🇷 · I. Eghdami🇮🇷
In this paper for studying the anisotropic strange quark stars, we assume that the radial pressure inside the anisotropic star is a superposition of pressure in an isotropic case plus a Gaussian perturbation term. Considering a proportionality between electric charge density and the density of matter, we solve the TOV equation for different cases numerically. Our results indicate that anisotropy increases the maximum mass $M_{ma x}$ and also its corresponding radius $R$ for a typical strange quark star. According to our calculations, an anisotropy amplitude of $A = 3 \times 1 0^{33} N m^{- 2}$ with a standard deviation of $σ = 3 \times 1 0^{3} m$ leads to a neutron star of 1.97 $M_{⊙}$ . Furthermore, electric charge not only increases the maximum mass and its corresponding radius, but also raises up the anisotropy factor. We can see that the tangential pressure $p_{t}$ and anisotropy factor $Δ$ unlike the radial pressure $p_{r}$ have a maximum on the surface and this maximum increases by adding electric charge effect. However, we show that anisotropy can be more effective than electric charge in rasing maximum mass of strange quark stars.
↳ astro-ph.SRnucl-thChin.Phys.Lett.(2016)·20 citations

Affiliations

first authorsco-authorsvia INSPIRE