Nuclear Theory·nucl-th

Tuesday·August 1, 2017

9 papers—3 primary·6 cross-listed

04
Proton and neutron electromagnetic form factors and uncertainties
Zhihong Ye🇺🇸 · John Arrington🇺🇸 · Richard J. Hill🇺🇸 · Gabriel Lee🇮🇱
We determine the nucleon electromagnetic form factors and their uncertainties from world electron scattering data. The analysis incorporates two-photon exchange corrections, constraints on the low-Q2 and high-Q2 behavior, and additional uncertainties to account for tensions between different data sets and uncertainties in radiative corrections.
↳ nucl-exhep-phnucl-thPLB(2018)·182 citations
05
Surface Magnetic Catalysis
Hao-Lei Chen🇨🇳 · Kenji Fukushima🇯🇵 · Xu-Guang Huang🇨🇳 · Kazuya Mameda🇯🇵
We study fermions in a magnetic field in a finite size cylinder. With the boundary condition for the fermion flux, we show that the energy spectra and the wave-functions are modified by the finite size effect; the boundary makes the degenerate Landau levels appear only partially for states with small angular momenta, while the boundary effect becomes stronger for states with large angular momenta. We find that mode accumulation at the boundary occurs for large angular momenta and the magnetic effect is enhanced on the boundary surface. Using a simple fermionic model, we quantify the magnetic catalysis, i.e. the magnetic enhancement of the fermion pair condensation, in a finite size cylinder. We confirm that the magnetic catalysis is strongly amplified at the boundary due to the mode accumulation.
↳ hep-phcond-mat.mes-hallhep-thnucl-thPRD(2017)·33 citations
06
The Born-Oppenheimer approximation in an effective field theory language
Nora Brambilla🇩🇪 · Gastão Krein🇧🇷 · Jaume Tarrús Castellà🇩🇪 · Antonio Vairo🇩🇪
The Born--Oppenheimer approximation is the standard tool for the study of molecular systems. It is founded on the observation that the energy scale of the electron dynamics in a molecule is larger than that of the nuclei. A very similar physical picture can be used to describe QCD states containing heavy quarks as well as light-quarks or gluonic excitations. In this work, we derive the Born--Oppenheimer approximation for QED molecular systems in an effective field theory framework by sequentially integrating out degrees of freedom living at energies above the typical energy scale where the dynamics of the heavy degrees of freedom occurs. In particular, we compute the matching coefficients of the effective field theory for the case of the $H_{2}^{+}$ diatomic molecule that are relevant to compute its spectrum up to $O (m α^{5})$ . Ultrasoft photon loops contribute at this order, being ultimately responsible for the molecular Lamb shift. In the effective field theory the scaling of all the operators is homogeneous, which facilitates the determination of all the relevant contributions, an observation that may become useful for high-precision calculations. Using the above case as a guidance, we construct under some conditions an effective field theory for QCD states formed by a color-octet heavy quark-antiquark pair bound with a color-octet light-quark pair or excited gluonic state, highlighting the similarities and differences between the QED and QCD systems. Assuming that the multipole expansion is applicable, we construct the heavy-quark potential up to next-to-leading order in the multipole expansion in terms of nonperturbative matching coefficients to be obtained from lattice QCD.
↳ hep-phnucl-thphysics.atom-phPRD(2018)·100 citations
07
Chiral Lagrangians with $Δ (1232)$ to one loop
Shao-Zhou Jiang🇨🇳 · Yan-Rui Liu🇨🇳 · Hong-Qian Wang
We construct the Lorentz-invariant chiral Lagrangians up to the order $O (p^{4})$ by including $Δ (1232)$ as an explicit degree of freedom. A full one-loop investigation on processes involving $Δ (1232)$ can be performed with them. For the $π ΔΔ$ Lagrangian, one obtains 38 independent terms at the order $O (p^{3})$ and 318 independent terms at the order $O (p^{4})$ . For the $π N Δ$ Lagrangian, we get 33 independent terms at the order $O (p^{3})$ and 218 independent terms at the order $O (p^{4})$ . The heavy baryon projection is also briefly discussed.
↳ hep-phhep-latnucl-thPRD(2018)·13 citations
08
Lattice Quantum Monte Carlo Study of Chiral Magnetic Effect in Dirac Semimetals
D.L. Boyda🇷🇺 · V.V. Braguta🇷🇺 · M.I. Katsnelson🇳🇱 · A.Yu. Kotov🇷🇺
In this paper Chiral Magnetic Effect (CME) in Dirac semimetals is studied by means of lattice Monte Carlo simulation. We measure conductivity of Dirac semimetals as a function of external magnetic field in parallel $σ_{∥}$ and perpendicular $σ_{⊥}$ to the external field directions. The simulations are carried out in three regimes: semimetal phase, onset of the insulator phase and deep in the insulator phase. In the semimetal phase $σ_{∥}$ grows whereas $σ_{⊥}$ drops with magnetic field. Similar behaviour was observed in the onset of the insulator phase but conductivity is smaller and its dependence on magnetic field is weaker. Finally in the insulator phase conductivities $σ_{∥, ⊥}$ are close to zero and do not depend on magnetic field. In other words, we observe manifestation of the CME current in the semimetal phase, weaker manifestation of the CME in the onset of the insulator phase. We do not observe signatures of CME in the insulator phase. We believe that the suppression of the CME current in the insulator phase is connected to chiral symmetry breaking and generation of dynamical fermion mass which take place in this phase.
↳ cond-mat.str-elhep-lathep-phhep-th+1Annals Phys.(2018)·10 citations
09
On the radiation beaming of bright X-ray pulsars and constraints on neutron star mass-radius relation
Alexander A. Mushtukov · Patrick A. Verhagen · Sergey S. Tsygankov · Michiel van der Klis · Alexander A. Lutovinov · Tatiana I. Larchenkova
The luminosity of accreting magnetised neutron stars can largely exceed the Eddington value due to appearance of accretion columns. The height of the columns can be comparable to the neutron star radius. The columns produce the X-rays detected by the observer directly and illuminate the stellar surface, which reprocesses the X-rays and causes additional component of the observed flux. The geometry of the column and the illuminated part of the surface determines the radiation beaming. Curved space-time affects the angular flux distribution. We construct a simple model of the beam patterns formed by direct and reflected flux from the column. We take into account the possibility of appearance of accretion columns, whose height is comparable to the neutron star radius. We argue that depending on the compactness of the star the flux from the column can be either strongly amplified due to gravitational lensing, or significantly reduced due to column eclipse by the star. The eclipses of high accretion columns result in specific features in pulse profiles. Their detection can put constraints on the neutron star radius. We speculate that column eclipses are observed in X-ray pulsar V 0332+53, leading us to the conclusion of large neutron star radius in this system ( $\sim 15 km$ if $M \sim 1.4 M_{⊙}$ ). We point out that the beam pattern can be strongly affected by scattering in the accretion channel at high luminosity, which has to be taken into account in the models reproducing the pulse profiles.
↳ astro-ph.HEnucl-thMNRAS(2018)·46 citations

Affiliations

first authorsco-authorsvia INSPIRE

Proton and neutron electromagnetic form factors and uncertainties

Surface Magnetic Catalysis

The Born-Oppenheimer approximation in an effective field theory language

Chiral Lagrangians with Δ(1232) to one loop

Lattice Quantum Monte Carlo Study of Chiral Magnetic Effect in Dirac Semimetals

On the radiation beaming of bright X-ray pulsars and constraints on neutron star mass-radius relation

Affiliations

Chiral Lagrangians with $Δ (1232)$ to one loop