Nuclear Theory·nucl-th

Monday·November 11, 2019

11 papers—5 primary·6 cross-listed

06
Electromagnetic contribution to $Σ$ - $Λ$ mixing using lattice QCD+QED
Z.R. Kordov🇦🇺 · R. Horsley🇬🇧 · Y. Nakamura🇯🇵 · H. Perlt🇩🇪 · P.E.L. Rakow🇬🇧 · G. Schierholz🇩🇪 · H. Stüben🇩🇪 · R.D. Young🇦🇺 · J.M. Zanotti🇦🇺
Mixing in the $Σ^{0}$ - $Λ^{0}$ system is a direct consequence of broken isospin symmetry and is a measure of both isospin-symmetry breaking as well as general SU(3)-flavour symmetry breaking. In this work we present a new scheme for calculating the extent of $Σ^{0}$ - $Λ^{0}$ mixing using simulations in lattice QCD+QED and perform several extrapolations that compare well with various past determinations. Our scheme allows us to easily contrast the QCD-only mixing case with the full QCD+QED mixing.
↳ hep-lathep-phnucl-thPRD(2020)·15 citations
07
Pions in hot dense matter and their astrophysical implications
Bryce Fore🇺🇸 · Sanjay Reddy🇺🇸
We study the role of pions in hot dense matter encountered in astrophysics. We find that strong interactions enhance the number density of negatively charged pions and that this enhancement can be calculated reliably for a relevant range of density and temperature using the virial expansion. We assess the influence of pions and muons on the equation of state (EOS) and weak interaction rates in hot dense matter. We find that thermal pions increase the proton fraction and soften the EOS. We also find that charged current weak reactions involving pions and muons $ν ˉ_{μ} + μ^{-} \to π$ and $ν_{μ} + π^{-} \to μ^{-}$ make an important contribution to the opacity of muon neutrinos. This could influence the dynamics of core-collapse supernovae and neutron star mergers. Finally, we note that pion-nucleon reactions can alter the evolution of the proton fraction when weak interactions are not in equilibrium.
↳ astro-ph.HEnucl-thPRC(2020)·100 citations
08
Roper State from Overlap Fermions
Mingyang Sun🇺🇸 · Ying Chen🇨🇳 · Gen Wang🇺🇸 · Andrei Alexandru🇺🇸 · Shao-Jing Dong🇺🇸 · Terrence Draper🇺🇸 · Jacob Fallica🇺🇸 · Ming Gong🇨🇳 · Frank X. Lee🇺🇸 · Anyi Li🇺🇸 · Jian Liang🇺🇸 · Keh-Fei Liu🇺🇸 · Nilmani Mathur🇮🇳 · Yi-Bo Yang🇨🇳
The Roper state is extracted with valence overlap fermions on a $2 + 1$ -flavor domain-wall fermion lattice (spacing $a = 0.114$ fm and $m_{π} = 330$ MeV) using both the Sequential Empirical Bayes (SEB) method and the variational method. The results are consistent, provided that a large smearing-size interpolation operator is included in the variational calculation to have better overlap with the lowest radial excitation. Similar calculations carried out for an anisotropic clover lattice with similar parameters find the Roper $\approx 280$ MeV higher than that of the overlap fermion. The fact that the prediction of the Roper state by overlap fermions is consistently lower than those of clover fermions, chirally improved fermions, and twisted-mass fermions over a wide range of pion masses has been dubbed a "Roper puzzle." To understand the origin of this difference, we study the hairpin $Z$ -diagram in the isovector scalar meson ( $a_{0}$ ) correlator in the quenched approximation. Comparing the $a_{0}$ correlators for clover and overlap fermions, at a pion mass of 290 MeV, we find that the spectral weight of the ghost state with clover fermions is smaller than that of the overlap at $a = 0.12$ fm and $0.09$ fm, whereas the whole $a_{0}$ correlators of clover and overlap at $a = 0.06$ fm coincide within errors. This suggests that chiral symmetry is restored for clover at $a \leq 0.06$ fm and that the Roper should come down at and below this $a$ . We conclude that this work supports a resolution of the "Roper puzzle" due to $Z$ -graph type chiral dynamics. This entails coupling to higher components in the Fock space (e.g. $N π$ , $N π π$ states) to induce the effective flavor-spin interaction between quarks as prescribed in the chiral quark model, resulting in the parity-reversal pattern as observed in the experimental excited states of $N, Δ$ and $Λ$ .
↳ hep-phhep-latnucl-thPRD(2020)·18 citations
09
From Parton Saturation to Proton Spin: the Impact of BFKL Equation and Reggeon Evolution
Yuri V. Kovchegov🇺🇸
Lev Lipatov was a giant in the field of strong interactions and a dominant force in high-energy QCD for many decades. His work deeply influenced both how we think about QCD and how we perform calculations in the theory. Below we describe the work in two related research directions: the physics of parton saturation and proton spin at small $x$ . Both developments would have been impossible without Lipatov's groundbreaking work. Saturation physics would not have happened without the Balitsky-Fadin-Kuraev-Lipatov (BFKL) equation. The recent progress in our theoretical understanding of the proton spin contribution coming from small- $x$ partons started with the seminal paper by Kirschner and Lipatov resumming double logarithms of energy in the Reggeon evolution.
↳ hep-phnucl-exnucl-th0 citations
10
Anisotropic Compact Stars in Rastall-Rainbow Gravity
Clésio E. Mota🇧🇷 · Luis C. N. Santos🇧🇷 · Franciele M. da Silva🇧🇷 · Cesar V. Flores🇧🇷 · Tiago J. N. da Silva🇧🇷 · Débora P. Menezes🇧🇷
In this work, we have investigated anisotropic neutron stars in the framework of Rastall-Rainbow gravity. All our calculations were computed using the IU-FSU realistic equation of state (EoS), in which was considered two cases: standard nucleonic composition and the one with the eight lightest baryons. From the neutron star masses and radii obtained we conclude that anisotropic pressure has significant consequences on the structure of stellar objects. In particular, when anisotropy is considered within the general relativity framework, it significantly modifies the maximum stellar mass. On the other hand, when Rastall-Rainbow gravity and anisotropy are simultaneously considered, they provide the best results for mass and radius values, including important astrophysical objects such as the LMXB NGC 6397 and the extremely massive pulsar millisecond MSP J0740 + 6620. Although the expected inclusion of hyperons in the nuclear model reproduces stellar masses smaller than those produced by standard nucleonic matter, we shown that the hyperon puzzle problem can be solved by including anisotropic effects on compact stars in the context of the Rastall-Rainbow gravity.
↳ astro-ph.HEgr-qcnucl-th9 citations
11
Binomial acceptance corrections for particle number distributions in high-energy reactions
Oleh Savchuk🇺🇦 · Roman V. Poberezhnyuk🇺🇦 · Volodymyr Vovchenko🇩🇪 · Mark I. Gorenstein🇺🇦
The binomial acceptance correction procedure is studied for particle number distributions detected in high energy reactions in finite regions of the momentum space. We present acceptance correction formulas for scaled variance, skewness, and kurtosis. Our considerations include various specific types of particles - positively or negatively charged, baryons and antibaryons - as well as conserved charges, namely, the net baryon number and electric charge. A simple model with effects of exact charge conservation, namely the Bessel distribution, is studied in some detail where effects of multi-particle correlations are present. The accuracy of the binomial filter is studied with UrQMD model simulations of inelastic proton-proton reactions. Binomial acceptance correction procedure works well when used inside a small region of phase space as well as for certain efficiency corrections, in particular for constructing net proton fluctuation from net baryon ones. Its performance is less accurate when applied to obtain UrQMD fluctuations in a finite rapidity window from fluctuations in the full $4 π$ space.
↳ hep-phhep-exnucl-thPRC(2020)·29 citations

Affiliations

first authorsco-authorsvia INSPIRE

Electromagnetic contribution to Σ-Λ mixing using lattice QCD+QED

Pions in hot dense matter and their astrophysical implications

Roper State from Overlap Fermions

From Parton Saturation to Proton Spin: the Impact of BFKL Equation and Reggeon Evolution

Anisotropic Compact Stars in Rastall-Rainbow Gravity

Binomial acceptance corrections for particle number distributions in high-energy reactions

Affiliations

Electromagnetic contribution to $Σ$ - $Λ$ mixing using lattice QCD+QED