Nuclear Theory·nucl-th

Thursday·December 19, 2019

12 papers—4 primary·8 cross-listed

05
Effective charge from lattice QCD
Zhu-Fang Cui🇨🇳 · Jin-Li Zhang🇨🇳 · Daniele Binosi🇮🇹 · Feliciano De Soto🇪🇸 · Cédric Mezrag🇫🇷 · Joannis Papavassiliou🇪🇸 · Craig D. Roberts🇨🇳 · Jose Rodríguez-Quintero🇪🇸 · Jorge Segovia🇪🇸 · Savvas Zafeiropoulos🇫🇷
Using lattice configurations for quantum chromodynamics (QCD) generated with three domain-wall fermions at a physical pion mass, we obtain a parameter-free prediction of QCD's renormalisation-group-invariant process-independent effective charge, $α^(k^{2})$ . Owing to the dynamical breaking of scale invariance, evident in the emergence of a gluon mass-scale, this coupling saturates at infrared momenta: $α^(0) / π = 0.97 (4)$ . Amongst other things: $α^(k^{2})$ is almost identical to the process-dependent (PD) effective charge defined via the Bjorken sum rule; and also that PD charge which, employed in the one-loop evolution equations, delivers agreement between pion parton distribution functions computed at the hadronic scale and experiment. The diversity of unifying roles played by $α^(k^{2})$ suggests that it is a strong candidate for that object which represents the interaction strength in QCD at any given momentum scale; and its properties support a conclusion that QCD is a mathematically well-defined quantum field theory in four dimensions.
↳ hep-phhep-exhep-latnucl-ex+1CPC(2020)·144 citations
06
Lattice QCD Determination of $g_{A}$
André Walker-Loud🇺🇸 · Evan Berkowitz🇺🇸 · David A. Brantley🇺🇸 · Arjun Gambhir🇺🇸 · Pavlos Vranas🇺🇸 · Chris Bouchard🇬🇧 · Chia Cheng Chang🇯🇵 · M. A. Clark🇺🇸 · Nicolas Garron🇬🇧 · Bálint Joó🇺🇸 · Thorsten Kurth🇺🇸 · Henry Monge-Camacho🇺🇸 and 4 other authors
The nucleon axial coupling, $g_{A}$ , is a fundamental property of protons and neutrons, dictating the strength with which the weak axial current of the Standard Model couples to nucleons, and hence, the lifetime of a free neutron. The prominence of $g_{A}$ in nuclear physics has made it a benchmark quantity with which to calibrate lattice QCD calculations of nucleon structure and more complex calculations of electroweak matrix elements in one and few nucleon systems. There were a number of significant challenges in determining $g_{A}$ , notably the notorious exponentially-bad signal-to-noise problem and the requirement for hundreds of thousands of stochastic samples, that rendered this goal more difficult to obtain than originally thought. I will describe the use of an unconventional computation method, coupled with "ludicrously'" fast GPU code, access to publicly available lattice QCD configurations from MILC and access to leadership computing that have allowed these challenges to be overcome resulting in a determination of $g_{A}$ with 1% precision and all sources of systematic uncertainty controlled. I will discuss the implications of these results for the convergence of $S U (2)$ Chiral Perturbation theory for nucleons, as well as prospects for further improvements to $g_{A}$ (sub-percent precision, for which we have preliminary results) which is part of a more comprehensive application of lattice QCD to nuclear physics. This is particularly exciting in light of the new CORAL supercomputers coming online, Sierra and Summit, for which our lattice QCD codes achieve a machine-to-machine speed up over Titan of an order of magnitude.
↳ hep-lathep-phnucl-exnucl-thPoS(2020)·41 citations
07
123-321 Models of Classical Novae
Jordi Jose (1,2) · Steven N. Shore (3) · Jordi Casanova (2) ((1) UPC Barcelona, (2) IEEC Barcelona, (3) U Pisa)
High-resolution spectroscopy has revealed large concentrations of CNO and sometimes other intermediate-mass elements in the shells ejected during nova outbursts, suggesting that the solar composition material transferred from the secondary mixes with the outermost layers of the underlying white dwarf during the thermonuclear runaway. Multidimensional simulations have shown that Kelvin-Helmholtz instabilities provide self-enrichment of the accreted envelope with material from the outermost layers of the white dwarf, at levels that agree with observations. However, the Eulerian and time-explicit nature of most multidimensional codes used to date and the overwhelming computational load have limited their applicability, and no multidimensional simulation has been conducted for a full nova cycle. This paper explores a new methodology that combines 1-D and 3-D simulations. The early stages of the explosion (i.e., mass-accretion and initiation of the runaway) have been computed with the 1-D hydrodynamic code SHIVA. When convection extends throughout the entire envelope, the structures for each model were mapped into 3-D Cartesian grids and were subsequently followed with the multidimensional code FLASH. Two key physical quantities were extracted from the 3-D simulations and subsequently implemented into SHIVA, which was used to complete the simulation through the late expansion and ejection stages: the time-dependent amount of mass dredged-up from the outer white dwarf layers, and the time-dependent convective velocity profile throughout the envelope. More massive envelopes than those reported from previous models with pre-enrichment have been found. This results in more violent outbursts, characterized by higher peak temperatures and greater ejected masses, with metallicity enhancements in agreement with observations.
↳ astro-ph.SRastro-ph.HEnucl-exnucl-thAstron.Astrophys.(2020)·36 citations
08
$ΛΛ$ and N $Ξ$ interactions from Lattice QCD near the physical point
Kenji Sasaki · Sinya Aoki · Takumi Doi · Shinya Gongyo · Tetsuo Hatsuda · Yoichi Ikeda · Takashi Inoue · Takumi Iritani · Noriyoshi Ishii · Keiko Murano · Takaya Miyamoto · (HAL QCD Collaboration)
The $S$ -wave $ΛΛ$ and $N Ξ$ interactions are studied on the basis of the (2+1)-flavor lattice QCD simulations close to the physical point ( $m_{π} ≃ 146 MeV$ and $m_{K} ≃ 525 MeV$ ). Lattice QCD potentials in four different spin-isospin channels are extracted by using the coupled-channel HAL QCD method and are parametrized by analytic functions to calculate the scattering phase shifts. The $ΛΛ$ interaction at low energies shows only a weak attraction, which does not provide a bound or resonant dihyperon. The $N Ξ$ interaction in the spin-singlet and isospin-singlet channel is most attractive and lead the $N Ξ$ system near unitarity. Relevance to the strangeness= $- 2$ hypernuclei as well as to two-baryon correlations in proton-proton, proton-nucleus and nucleus-nucleus collisions is also discussed.
↳ hep-lathep-phnucl-thNPA(2020)·174 citations
09
Charged pion condensation in dense quark matter: Nambu--Jona-Lasinio model study
T. G. Khunjua🇷🇺 · K. G. Klimenko🇷🇺 · R. N. Zhokhov🇷🇺
In this short review we tried to give an outline of investigations of charged pion condensation (PC) in dense baryonic (quark) matter in the framework of effective Nambu--Jona-Lasinio (NJL) type models. The possibility of charged PC phase in dense quark matter with isospin asymmetry is investigated. First, it is demonstrated that this phase can be realized in the framework of massless NJL model. But the existence of this phase is enormously fragile to the values of current quark mass %.Then, and we show that charged PC phase is forbidden in electrically neutral dense quark matter with $β$ -equilibrium when current quark masses are close to their physical value of 5.5 MeV. Nevertheless, then it is shown that in real physical systems there could be conditions promoting the appearance of charged PC phenomenon in dense quark matter, namely, it was shown that if one includes into consideration the fact that system can have finite size, then a dense charged PC phase can be realized there. It was also demonstrated that the possibility of inhomogeneous pion condensate might allow this phase to appear. And more recently it was revealed that there is another interesting factor that can induce a charged PC phase in dense quark matter even without isospin imbalance. It is a chiral imbalance of the system (non-zero difference between densities of left- and right-handed quarks). This results can be interesting in heavy ion collision experiments, where it is expected to get high baryon densities. It is of interest also in the context of the neutron stars, where quark matter might be realized in the core and very high baryon and isospin densities are attained.
↳ hep-phhep-thnucl-thSymmetry(2019)·27 citations
10
Smearing of causality by compositeness divides dispersive approaches into exact ones and precision-limited ones
Felipe J. Llanes-Estrada🇪🇸 · Raul Roldan-Gonzalez (Univ. Complutense of Madrid)🇪🇸
Scattering off the edge of a composite particle or finite-range interaction can precede that off its center. An effective theory treatment with pointlike particles and contact interactions must find that the scattered experimental wave is slightly advanced, in violation of causality (the fundamental underlying theory being causal). In practice, partial-wave or other projections of multivariate amplitudes exponentially grow with imaginary E, so that upper complex-plane analyticity is not sufficient to obtain a dispersion relation for them, but only for a slightly modified function (the modified relations additionally connect different J). This limits the maximum precision of certain dispersive approaches to compositeness based on Cauchy's theorem leading to partial-wave dispersion relations. This may be of interest to some dispersive tests of the Standard Model with hadrons, and to unitarization methods used to extend electroweak effective theories. Interestingly, the Inverse Amplitude Method is safe (as the inverse amplitude has the opposite, convergent behavior allowing contour closure). Generically, one-dimensional sum rules such as for the photon vacuum polarization, one-dimensional form factors or the Adler function, to name a few, are not affected by this uncertainty. Likewise, fixed-t dispersion relations were cleverly constructed to avoid it and consequences therefrom are solid.
↳ hep-phnucl-thSciPost Phys.Core(2022)·7 citations
11
Covariant multipole expansion of local currents for massive states of any spin
Sabrina Cotogno🇫🇷 · Cédric Lorcé🇫🇷 · Peter Lowdon🇫🇷 · Manuel Morales🇨🇭
We study the structure of scalar, vector, and tensor currents for on-shell massive particles of any spin. When considering higher values for the spin of the particle, the number of form factors (FFs) involved in the decomposition of the matrix elements associated with these local currents increases. We identify all the fundamental structures that give rise to the independent FFs, systematically for any spin value. These structures can be conveniently organised using an expansion in covariant multipoles, built solely from the Lorentz generators. This approach allows one to uniquely identify the terms which are universal and those that arise because of spin. We derive counting rules which relate the number of FFs to the total spin $j$ of the state, showing explicitly that these rules match all the well-known cases up to spin 2.
↳ hep-phhep-thnucl-thPRD(2020)·66 citations
12
Accretion-induced collapse to third family compact stars as trigger for eccentric orbits of millisecond pulsars in binaries
David Edwin Alvarez-Castillo · John Antoniadis · Alexander Ayriyan · David Blaschke · Victor Danchev · Hovik Grigorian · Noshad Khosravi Largani · Fridolin Weber
A numerical rotating neutron star solver is used to study the temporal evolution of accreting neutron stars using a multi-polytrope model for the nuclear equation of state named ACB5. The solver is based on a quadrupole expansion of the metric, but confirms the results of previous works, revealing the possibility of an abrupt transition of a neutron star from a purely hadronic branch to a third-family branch of stable hybrid stars, passing through an unstable intermediate branch. The accretion is described through a sequence of stationary rotating {stellar} configurations which lose angular momentum through magnetic dipole emission while, at the same time, gaining angular momentum through mass accretion. The model has several free parameters which are inferred from observations. The mass accretion scenario is studied in dependence on the effectiveness of angular momentum transfer which determines at which spin frequency the neutron star will become unstable against gravitational collapse to the corresponding hybrid star on the stable third-family branch. It is conceivable that the neutrino burst which accompanies the deconfinement transition may trigger a pulsar kick which results in the eccentric orbit. A consequence of the present model is the prediction of a correlation between the spin frequency of the millisecond pulsar in the eccentric orbit and its mass at birth.
↳ astro-ph.HEnucl-thAstron.Nachr.(2019)·12 citations

Affiliations

first authorsco-authorsvia INSPIRE