Nuclear Theory·nucl-th

Wednesday·September 14, 2016

13 papers—5 primary·8 cross-listed

01
Collisions of Small Nuclei in the Thermal Model
J. Cleymans🇿🇦 · B. Hippolyte🇫🇷 · H. Oeschler🇩🇪 · K. Redlich🇩🇪 · N. Sharma🇮🇳
An analysis is presented of the expectations of the thermal model for particle production in collisions of small nuclei. The maxima observed in particle ratios of strange particles to pions as a function of beam energy in heavy ion collisions, are reduced when considering smaller nuclei. Of particular interest is the $Λ/ π^{+}$ ratio shows the strongest maximum which survives even in collisions of small nuclei.
nucl-thhep-phActa Phys.Polon.Supp.(2017)·0 citations
02
Phonon-particle coupling effects in single-particle energies of semi-magic nuclei
E.E. Saperstein · M. Baldo · S.S. Pankratov · S.V. Tolokonnikov
A method is presented to evaluate the particle-phonon coupling (PC) corrections to the single-particle energies (SPEs) in semi-magic nuclei. In such nuclei always there is a collective low-lying $2^{+}$ phonon, and a strong mixture of single-particle and particle-phonon states often occurs. As in magic nuclei, the so-called $g_{L}^{2}$ approximation, where $g_{L}$ is the vertex of the $L$ -phonon creation, can be used for finding the PC correction $δ Σ^{PC} (ε)$ to the initial mass operator $Σ_{0}$ . In addition to the usual pole diagram, the phonon "tadpole" diagram is also taken into account. In semi-magic nuclei, the perturbation theory in $δ Σ^{PC} (ε)$ with respect to $Σ_{0}$ is often invalid for finding the PC corrected SPEs. Instead, the Dyson equation with the mass operator $Σ (ε) = Σ_{0} + δ Σ^{PC} (ε)$ is solved directly, without any use of the perturbation theory. Results for a chain of semi-magic Pb isotopes are presented.
nucl-thJETP Lett.(2016)·8 citations
03
Light-Front spin-dependent Spectral Function and Nucleon Momentum Distributions for a Three-Body System
Alessio Del Dotto🇮🇹 · Emanuele Pace🇮🇹 · Giovanni Salmè🇮🇹 · Sergio Scopetta🇮🇹
Poincare' covariant definitions for the spin-dependent spectral function and for the momentum distributions within the light-front Hamiltonian dynamics are proposed for a three-fermion bound system, starting from the light-front wave function of the system. The adopted approach is based on the Bakamjian-Thomas construction of the Poincare' generators, that allows one to easily import the familiar and wide knowledge on the nuclear interaction into a light-front framework. The proposed formalism can find useful applications in refined nuclear calculations, like the ones needed for evaluating the EMC effect or the semi-inclusive deep inelastic cross sections with polarized nuclear targets, since remarkably the light-front unpolarized momentum distribution by definition fulfills both normalization and momentum sum rules. It is also shown a straightforward generalization of the definition of the light-front spectral function to an A-nucleon system.
nucl-thhep-phPRC(2017)·23 citations
04
Microscopic Calculations of Vortex-Nucleus Interaction in the Neutron Star Crust
Kazuyuki Sekizawa · Gabriel Wlazłowski · Piotr Magierski · Aurel Bulgac · Michael McNeil Forbes
We investigate the dynamics of a quantized vortex and a nuclear impurity immersed in a neutron superfluid within a fully microscopic time-dependent three-dimensional approach. The magnitude and even the sign of the force between the quantized vortex and the nuclear impurity have been a matter of debate for over four decades. We determine that the vortex and the impurity repel at neutron densities, 0.014 fm $^{- 3}$ and 0.031 fm $^{- 3}$ , which are relevant to the neutron star crust and the origin of glitches, while previous calculations have concluded that the force changes its sign between these two densities and predicted contradictory signs. The magnitude of the force increases with the density of neutron superfluid, while the magnitude of the pairing gap decreases in this density range.
nucl-thastro-ph.HEcond-mat.quant-gascond-mat.supr-conJPS Conf.Proc.(2017)·1 citation
05
$ϕ$ meson self-energy in nuclear matter from $ϕN$ resonant interactions
D. Cabrera🇪🇸 · A. N. Hiller Blin🇪🇸 · M. J. Vicente Vacas🇪🇸
The $ϕ$ -meson properties in cold nuclear matter are investigated by implementing resonant $ϕN$ interactions as described in effective approaches including the unitarization of scattering amplitudes. Several $N^{*}$ -like states are dynamically generated in these models around $2$ GeV, in the vicinity of the $ϕN$ threshold. We find that both these states and the non-resonant part of the amplitude contribute sizably to the $ϕ$ collisional self-energy at finite nuclear density. These contributions are of a similar strength as the widely studied medium effects from the $K ˉ K$ cloud. Depending on model details (position of the resonances and strength of the coupling to $ϕN$ ) we report a $ϕ$ broadening up to about $40$ - $50$ MeV, to be added to the $ϕ \to K ˉ K$ in-medium decay width, and an attractive optical potential at threshold up to about $35$ MeV at normal matter density. The $ϕ$ spectral function develops a double peak structure as a consequence of the mixing of resonance-hole modes with the $ϕ$ quasi-particle peak. The former results point in the direction of making up for missing absorption as reported in $ϕ$ nuclear production experiments.
nucl-thhep-phPRC(2017)·39 citations
06
Breaking the sound barrier in AdS/CFT
Carlos Hoyos🇪🇸 · Niko Jokela🇫🇮 · David Rodríguez Fernández🇪🇸 · Aleksi Vuorinen🇫🇮
It has been conjectured that the speed of sound in holographic models with UV fixed points has an upper bound set by the value of the quantity in conformal field theory. If true, this would set stringent constraints for the presence of strongly coupled quark matter in the cores of physical neutron stars, as the existence of two-solar-mass stars appears to demand a very stiff Equation of State. In this article, we present a family of counterexamples to the speed of sound conjecture, consisting of strongly coupled theories at finite density. The theories we consider include $N = 4$ super Yang-Mills at finite R-charge density and non-zero gaugino masses, while the holographic duals are Einstein-Maxwell theories with a minimally coupled scalar in a charged black hole geometry. We show that for a small breaking of conformal invariance, the speed of sound approaches the conformal value from above at large chemical potentials.
↳ hep-thastro-ph.HEhep-phnucl-thPRD(2016)·75 citations
07
Dispersive treatment of $K_{S} \to γ γ$ and $K_{S} \to γ ℓ^{+} ℓ^{-}$
Gilberto Colangelo🇨🇭 · Ramon Stucki🇨🇭 · Lewis C. Tunstall🇨🇭
We analyse the rare kaon decays $K_{S} \to γ γ$ and $K_{S} \to γ ℓ^{+} ℓ^{-}$ $(ℓ = e \mbox or μ)$ in a dispersive framework in which the weak Hamiltonian carries momentum. Our analysis extends predictions from lowest order $S U (3)_{L} \times S U (3)_{R}$ chiral perturbation theory ( $χ$ PT $_{3}$ ) to fully account for effects from final-state interactions, and is free from ambiguities associated with extrapolating the kaon off-shell. Given input from $K_{S} \to π π$ and $γ γ^{(*)} \to π π$ , we solve the once-subtracted dispersion relations numerically to predict the rates for $K_{S} \to γ γ$ and $K_{S} \to γ ℓ^{+} ℓ^{-}$ . In the leptonic modes, we find sizeable corrections to the $χ$ PT $_{3}$ predictions for the integrated rates.
↳ hep-phhep-latnucl-thEPJC(2016)·16 citations
08
Hidden Local Symmetry and Beyond
Koichi Yamawaki🇯🇵
Gerry Brown was a godfather of our hidden local symmetry (HLS) for the vector meson from the birth of the theory throughout his life. The HLS is originated from very nature of the nonlinear realization of the symmetry G based on the manifold G/H, and thus is universal to any physics based on the nonlinear realization. Here I focus on the Higgs Lagrangian of the Standard Model (SM), which is shown to be equivalent to the nonlinear sigma model based on G/H= SU(2)_L x SU(2)_R/SU(2)_V with additional symmetry, the nonlinearly realized scale symmetry. Then the SM does have a dynamical gauge boson of the SU(2)_V HLS, "SM rho meson", in addition to the Higgs as a pseudo dilaton as well as the NG bosons to be absorbed into the W and Z. Based on the recent work done with S. Matsuzaki and H. Ohki, I discuss a novel possibility that the SM rho meson acquires kinetic term by the SM dynamics itself, which then stabilizes the skyrmion dormant in the SM as a viable candidate for the dark matter, what we call "Dark SM skyrmion (DSMS)".
↳ hep-phhep-thnucl-thIJMPE(2017)·18 citations
09
Exclusive photoproduction of a $γ ρ$ pair with a large invariant mass
R. Boussarie🇫🇷 · B. Pire🇫🇷 · L. Szymanowski🇵🇱 · S. Wallon🇫🇷
Exclusive photoproduction of a $γ ρ$ pair in the kinematics where the pair has a large invariant mass and the final nucleon has a small transverse momentum is described in the collinear factorization framework. The scattering amplitude is calculated at leading order in $α_{s}$ and the differential cross sections for the process where the $ρ -$ meson is either longitudinally or transversely polarized are estimated in the kinematics of the JLab 12-GeV experiments.
↳ hep-phhep-exnucl-exnucl-thJHEP(2017)·78 citations
10
The 5 MeV bump - a nuclear whodunit mystery
Patrick Huber🇺🇸
We perform a combined analysis of recent NEOS and Daya Bay data on the reactor antineutrino spectrum. This analysis includes approximately 1.5 million antineutrino events, which is the largest neutrino event sample analyzed to date. We use a double ratio which cancels flux model dependence and related uncertainties as well as the effects of the detector response model. We find at 3-4 standard deviation significance level, that plutonium-239 and plutonium-241 are disfavored as the single source for the the so-called 5 MeV bump. This analysis method has general applicability and in particular with higher statistics data sets will be able to shed significant light on the issue of the bump. With some caveat this also should allow to improve the sensitivity for sterile neutrino searches in NEOS.
↳ hep-phhep-exnucl-exnucl-thPRL(2017)·88 citations
11
Energy loss as the origin of an universal scaling law of the elliptic flow
Carlota Andrés🇪🇸 · Mikhail Braun🇷🇺 · Carlos Pajares🇪🇸
It is shown that the excellent scaling of the elliptic flow found for all centralities, species and energies from RHIC to the LHC for $p_{T}$ less than the saturation momentum is a consequence of the energy lost by a parton interacting with the color field produced in a nucleus-nucleus collision. In particular, the deduced shape of the scaling curve describes correctly all the data. We discuss the possible extensions to higher $p_{T}$ , proton-nucleus and proton-proton collisions as well as higher harmonics.
↳ hep-phnucl-thEPJA(2017)·13 citations
12
van der Waals Interactions in Hadron Resonance Gas: From Nuclear Matter to Lattice QCD
Volodymyr Vovchenko🇩🇪 · Mark I. Gorenstein🇺🇦 · Horst Stoecker🇩🇪
An extension of the ideal hadron resonance gas (HRG) model is constructed which includes the attractive and repulsive van der Waals (VDW) interactions between baryons. This VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryon densities. The VDW parameters $a$ and $b$ are fixed by the ground state properties of nuclear matter, and the temperature dependence of various thermodynamic observables at zero chemical potential are calculated within VDW-HRG model. Compared to the ideal HRG model, the inclusion of VDW interactions between baryons leads to a qualitatively different behavior of second and higher moments of fluctuations of conserved charges, in particular in the so-called crossover region $T \sim 140 - 190$ MeV. For many observables this behavior resembles closely the results obtained from lattice QCD simulations. This hadronic model also predicts nontrivial behavior of net-baryon fluctuations in the region of phase diagram probed by heavy-ion collision experiments. These results imply that VDW interactions play a crucial role in thermodynamics of hadron gas. Thus, the commonly performed comparisons of the ideal HRG model with the lattice and heavy-ion data may lead to misconceptions and misleading conclusions.
↳ hep-phhep-latnucl-thPRL(2017)·216 citations
13
Octet Baryon Magnetic Moments from Lattice QCD: Approaching Experiment from a Three-Flavor Symmetric Point
Assumpta Parreno🇪🇸 · Martin J. Savage🇺🇸 · Brian C. Tiburzi🇺🇸 · Jonas Wilhelm🇩🇪 · Emmanuel Chang🇺🇸 · William Detmold🇺🇸 · Kostas Orginos🇺🇸
Lattice QCD calculations with background magnetic fields are used to determine the magnetic moments of the octet baryons. Computations are performed at the physical value of the strange quark mass, and two values of the light quark mass, one corresponding to the three-flavor symmetric point, where the pion mass is 800 MeV, and the other corresponding to a pion mass of 450 MeV. The moments are found to exhibit only mild pion-mass dependence when expressed in terms of appropriately chosen magneton units- the natural baryon magneton. A curious pattern is revealed among the anomalous baryon magnetic moments which is linked to the constituent quark model, however, careful scrutiny exposes additional features. Relations expected to hold in the large-Nc limit of QCD are studied; and, in one case, a clear preference for the quark model over the large-Nc prediction is found. The magnetically coupled Lambda-Sigma system is treated in detail at the three-flavor symmetric point, with the lattice QCD results comparing favorably with predictions based on SU(3)F symmetry. This analysis enables the first extraction of the isovector transition magnetic polarizability. The possibility that large magnetic fields stabilize strange matter is explored, but such a scenario is found to be unlikely.
↳ hep-lathep-phnucl-thPRD(2017)·41 citations

Affiliations

first authorsco-authorsvia INSPIRE