Nuclear Theory·nucl-th

Wednesday·October 2, 2019

5 papers—3 primary·2 cross-listed

01
[Submitted on 30 Sept 2019]
Adiabatic hydrodynamization in rapidly-expanding quark-gluon plasma
Jasmine Brewer🇺🇸 · Li Yan🇨🇳 · Yi Yin🇺🇸
We propose a new scenario characterizing the transition of the quark-gluon plasma (QGP) produced in heavy-ion collisions from a highly non-equilibrium state at early times toward a fluid described by hydrodynamics at late times. We develop an analogy to the evolution of a quantum mechanical system that is governed by the instantaneous ground states. In the simplest case, these slow modes are "pre-hydrodynamic" in the sense that they are initially distinct from, but evolve continuously into, hydrodynamic modes. For a class of collision integrals, the pre-hydrodynamic mode represents the angular distribution (in momentum space) of those gluons that carry most of the energy. We illustrate this scenario using a kinetic description of weakly-coupled Bjorken expanding plasma. Rapid longitudinal expansion drives a reduction in the degrees of freedom at early times. In the relaxation time approximation for the collision integral, we show quantitatively that the full kinetic theory evolution is dominated by the pre-hydrodynamic mode. We elaborate on the criterion for the dominance of pre-hydrodynamic slow modes and speculate that adiabatic hydrodynamization may describe the pre-equilibrium behavior of the QGP produced in heavy-ion collisions.
Comments:
7 pages, 1 figure. Added appendix and updates to match published version
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Theory (hep-th); Fluid Dynamics (physics.flu-dyn)
arXiv:
1910.00021 [pdf]
PLB(2021)·66 citations
02
[Submitted on 1 Oct 2019]
Conversion between the formal and observed parameters in $R$ -matrix theory
M. Katsuma
The conversion between the formal and observed parameters is obtained from the phase equivalence between the $R$ -matrix and Breit-Wigner formula, and it is applied to a study of the low-energy $E$ 1 $S$ -factor of $^{12}$ C( $α$ , $γ_{0}$ ) $^{16}$ O. As an example, weak interference between 1 $^{-}$ states in $^{16}$ O is discussed. As well as the ordinary $R$ -matrix method, the present method calculates the $S$ -matrix and cross sections, independent of the boundary condition. Therefore, the $E$ 1 $S$ -factor at $E_{c . m .} = 300$ keV is found to be reduced from the current evaluation.
Comments:
4 pages, 2 figures; to appear in JPS Conference Proceedings, 15th International Symposium on Origin of Matter and Evolution of Galaxies (OMEG15), Kyoto Japan, July 2-5, 2019
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1910.00158 [pdf]
JPS Conf.Proc.(2020)·2 citations
03
[Submitted on 1 Oct 2019]
Reaction Theory and Advanced CDCC
A.M. Moro🇪🇸 · J. Casal🇮🇹 · Jin Lei🇺🇸 · M. Gómez-Ramos🇪🇸
The Continuum-Discretized Coupled-Channels (CDCC) has been successfully employed to describe elastic and breakup of nuclear reactions induced by weakly bound projectiles. In this contribution, we review some other, less widespread applications of the CDCC wavefunction, some of them in combination with other reaction formalisms, which are being currently employed in the analysis of reactions involving three or more fragments in the initial or final state.
Comments:
Invited contribution to INPC 2019 (Glasgow, UK, July 2019)
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1910.00307 [pdf]
J.Phys.Conf.Ser.(2020)·0 citations
04
[Submitted on 1 Oct 2019] (cross-list from hep-ph)
Proper time evolution of magnetic susceptibility in a magnetized quark-gluon plasma
S.M.A. Tabatabaee🇮🇷 · N. Sadooghi🇮🇷
In ultrarelativistic heavy-ion collisions, enormous magnetic fields are generated because of fast-moving charged particles. In the presence of these magnetic fields, the spin of particles is aligned either in the parallel or in the antiparallel direction with respect to the direction of the magnetic field. A finite magnetization is thus produced. It is known that a finite magnetic susceptibility, $χ_{m}$ , changes the evolution of the energy density of the quark-gluon plasma (QGP), which is believed to be created in these collisions. Depending on whether the system under consideration is a paramagnetic ( $χ_{m} > 0$ ) or diamagnetic ( $χ_{m} < 0$ ) fluid, it slows down or speeds up the decay of the energy density, and affects other thermodynamic quantities. In general, one expects that the magnetic susceptibility depends on the magnetic field and temperature. Bearing in mind that these parameters evolve with the evolution of the fluid, a nonuniform magnetic susceptibility in this system is thus expected. In this work, we first determine $χ_{m}$ by using a certain analogy to the standard anisotropic kinetic theory, where the one-particle distribution function is replaced by the corresponding anisotropic distribution function. We then determine the proper time dependence of the magnetic susceptibility in the framework of the ideal transverse magnetohydrodynamics. We also study the effect of dissipation on the evolution of $χ_{m}$ .
Comments:
8 pages, 4 figures, XIII Quark Confinement and the Hadron Spectrum - Confinement2018, 31 July - 6 August 2018, Maynooth University, Ireland
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1910.00226 [pdf]
PoS(2018)·0 citations
05
[Submitted on 1 Oct 2019] (cross-list from hep-ph)
A new angle on an old problem: Helicity approach to neutron beta decay in the Standard Model
Stefan Groote🇪🇪 · Jürgen G. Körner🇩🇪 · Blaženka Melić🇭🇷
We elaborate on the dichotomy between the description of the semileptonic decays of heavy hadrons on the one hand and the semileptonic decays of light hadrons such as neutron $β$ decays on the other hand. For example, almost without exception the semileptonic decays of heavy baryons are described in cascade fashion as a sequence of two two-body decays $B_{1} \to B_{2} + W_{off - shell}$ and $W_{off - shell} \to ℓ + ν_{ℓ}$ whereas neutron $β$ decays are analyzed as true three-body decays $n \to p + e^{-} + ν ˉ_{e}$ . Within the cascade approach it is possible to define a set of seven angular observables for polarized neutron $β$ decays as well as the longitudinal, transverse and normal polarization of the decay electron. We determine the dependence of the observables on the usual vector and axial vector form factors. In order to be able to assess the importance of recoil corrections we expand the rate and the $q^{2}$ averages of the observables up to NLO and NNLO in the recoil parameter $δ = (M_{n} - M_{p}) / (M_{n} + M_{p}) = 0.689 \cdot 1 0^{- 3}$ . Remarkably, we find that the rate and three of the four parity conserving polarization observables that we analyze are protected from NLO recoil corrections when the second class current contributions are set to zero.
Comments:
22 pages, 5 figures and 2 tables
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1910.00283 [pdf]
EPJC(2019)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE

Adiabatic hydrodynamization in rapidly-expanding quark-gluon plasma

Conversion between the formal and observed parameters in R-matrix theory

Reaction Theory and Advanced CDCC

Proper time evolution of magnetic susceptibility in a magnetized quark-gluon plasma

A new angle on an old problem: Helicity approach to neutron beta decay in the Standard Model

Affiliations

Conversion between the formal and observed parameters in $R$ -matrix theory