Nuclear Theory·nucl-th

Wednesday·October 2, 2019

5 papers—3 primary·2 cross-listed

04
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 $χ_{m}$ .
↳ hep-phhep-thnucl-thPoS(2018)·0 citations
05
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.
↳ hep-phnucl-thEPJC(2019)·5 citations

Affiliations

first authorsco-authorsvia INSPIRE

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